Sunday, January 31, 2016

10 Questions: Sunday afternoon update on Groundhog Day storms

A windy and unseasonably warm day is concluding across the metro. Temperatures climbed to 70 degrees with wind gusts measured as high as 40 mph thanks to the sun poking through between the clouds, mixing strong wind at a few thousand feet down to the surface. A cold front will move into the area tonight, stalling just to our south and resulting in weakening wind and a shift to the northeast for Monday. Scattered showers will dot the area overnight near the front but precip amounts remain light overall. Temperatures remain mild.

At midnight tonight, a cold front will be draped across the area with scattered showers the result. As the low pressure in the southern Rockies moves east, it will begin to pull that front back north Tuesday night. Graphic courtesy NWS.
On Monday, despite cloudy skies and northeast wind, temperatures will still likely make it to the mid 60s as cold air remain positioned well to our north and the front hangs around the area. By Monday night, the cold front becomes a warm front as it retreats north back through the metro in response to a deepening (strengthening) low pressure system that will move across the Plains. Temperatures will remain mild as southerly wind re-establishes itself across the area, setting the stage for a potentially stormy Groundhog Day.

By Tuesday morning, the Mid-South will be firmly entrenched in the warm sector of the approaching storm with a warm front to the north and southerly wind escorting Gulf moisture and warmth north. Graphic courtesy NWS.
Regarding Tuesday, additional model data is available now that we are within 3 days of the event, including the North American Model (NAM), which offers a little greater insight into the details of the atmosphere than the Global Forecast System (GFS) and European models do. There are many similarities between the various models, but still some fairly important differences, especially with regards to the storm mode - squall line versus discrete (single cell) storms. How the storm mode plays out will ultimately determine a few important factors, including whether everyone in the metro sees storms (the coverage), how strong they may be, and perhaps just as important, the tornado threat.

Here are answers to 10 questions you might be asking:
  1. What time are we looking at for storms to affect the metro? Models are narrowing their focus on the afternoon hours. Ultimately the storm mode could determine this as well.
  2. So are we talking squall line or individual supercells? And why does it matter? That's the million dollar question. There are factors that support both and differences of opinion that are based on good evidence both ways. Based on the consistency of the NAM model over the past day, which tends to have a little better handle on the mesoscale (local scale) details, I'm starting to give as much credence to the supercell scenario as the squall line scenario. However, there is still a good amount of evidence that supports a squall line forming rather quickly in far eastern AR by mid-day and moving across the metro.
  3. Why does it matter what the storm mode is? Squall lines tend to result in more of a high wind threat (50-60 mph+) with isolated weak "spin-up" tornadoes given enough low level shear, while supercells are more likely to produce larger, strong tornadoes that stay on the ground longer since they don't have to complete with neighboring cells for energy. 
  4. Is there any good news on the supercell front? Yes. If supercells are the result, they are more likely to form further east than the squall line, according to the NAM model data. The key factor here is a "cap," or atmospheric lid, between about 5-10,000'. A stronger lid keeps the storms from forming until the bubbling airmass below (measured by instability) is strong enough to blow the lid off. Storms form and can start rotating fairly quickly given the atmospheric shear we'll be dealing with. The NAM model favors supercells, but doesn't form them until the late afternoon when they would likely be east of the metro (barely) given the current timing of the approaching front. If this were to happen, it's conceivable that most of the metro escapes with no storms.
  5. The NAM modeled CAPE values (an indicator of instability) approach 1000 J/kg mid-afternoon Tuesday. Values this high are more than sufficient to produce severe thunderstorms in early February, when instability is typically the main factor that is missing to produce strong storms. Graphic courtesy WxBell.
  6. How bad will it be in my neighborhood? You know I can't answer that. :-) As described, there are multiple scenarios with outcomes that range from nothing happening to a squall line to a supercell that moves over your house. As always, we root for you, not the storms.
  7. Should I change plans? Not yet. Hopefully we'll know better at this time tomorrow what the storm mode will be and the likely initiation area (west or east of the metro), which can then guide that decision making. Most likely, we'll either get a squall line, which you would want to be cognizant of and ready to shelter if very strong wind occurs, or supercells, which could form to our east but could fire over the metro. Stay tuned.
  8. Could we completely miss out on all storms? See #5. Yes, it is possible. That's why we will have rain chances that aren't 100%. It's not a done deal that everyone gets storms at this point.
  9. What factors are still uncertain that would contribute to a higher confidence forecast? A few key ones, namely the amount of instability and the strength of the cap. In addition, there are indications that surface wind could veer to the southwest in the afternoon, which would reduce low level shear and result in a lower tornado threat even if storms do form. The real wild card appears to be instability and low-level moisture - dictated by how warm we get during the day ahead of the other factors coming together to promote storms. Morning showers could limit instability and thus storm strength, but models are still indicating more than sufficient instability for severe storms despite some morning rain. Breaks in the clouds during the afternoon would also allow additional warming in the low levels, which would cause more instability to be realized. These are the type of factors that simply aren't well known 48 hours in advance. One factor the models do show fairly uniformly is abundant low level moisture. Dewpoints in the mid 60s are forecast, which is more than sufficient to fuel strong to severe storms this time of year.
  10. The GFS (American) model depicts dewpoints in the mid 60s as far north as Memphis by Tuesday mid-day, providing the fuel for storms to feed on. Notice how quickly the dewpoints drop off behind the front in central AR as much drier air moves in quickly. Graphic courtesy WxBell.
  11. Could this storm be remembered years from now as the Groundhog Day Storm of 2016? That might be a little dramatic, but if supercells form and drop tornadoes, there's a decent chance, given the favorable dynamics in play, that they could be strong. Again, we root against severe weather. However, the setup is similar to previous events that have produced severe weather, including January 19, 1988, which produced multiple significant tornadoes in west TN and north MS. 
  12. What do I do now? First of all, stay tuned. The details that really matter have yet to be determined. You should also start preparing for the possibility of severe weather Tuesday afternoon and early evening. Where will you be and what will you do if a warning is issued? Review your safety plan. Know how you'll get warning information. I highly recommend our app with the StormWatch+ upgrade that customizes watches and warnings the way you want them, and only delivers them to you if you are in the path of the storm. See the links below. Some additional tips are also shown below. Be prepared, not scared!
Here's your graphical takeaway:

Once the severe storm threat ends early Tuesday evening, much drier and cooler air infiltrates the region. A dry forecast is anticipated for the rest of the week with seasonal temperatures. On a side note, this same system will be dropping a significant amount of snow from the Front Range of the Rockies across the central Plains and into the Upper Midwest Monday through Wednesday. If you're traveling that direction, keep an eye on forecasts for the areas you'll be heading to.

Erik Proseus
MWN Meteorologist

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Saturday, January 30, 2016

MWN Video Blog: Details on weekend warmth, then Tuesday storms

A very warm weekend is in progress, but the crystal ball has a good chance of strong to severe storms in it for Tuesday. We break down the weather for this weekend and an early look at what we might expect on Tuesday afternoon in today's video blog shown below.

We are monitoring the potential for severe weather on Tuesday, mainly in the afternoon Currently, there is a 30% risk of severe weather within 25 miles of Memphis. Graphic courtesy SPC.
Monitor our social channels listed below, this blog, and our website and mobile apps for the latest updates and dust off the severe weather action plan you had ready back on December 23rd when severe weather was expected.

Erik Proseus
MWN Meteorologist

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Friday, January 22, 2016

On "busted" forecasts, building trust, and expectations

Have you ever tried to predict the final score of a sports game - basketball, football, or even low-scoring games like soccer - before it began? Probably not, though you may have put money, or maybe just a handshake, on the final score - either an over/under or against the spread.

How hard is it, for example, to predict the total number of points that will be scored in a basketball game before the game begins? I'll even give you a buffer of 5-10 points for a "right" answer. Even right before the game, you don't know how individual players will perform, how external factors will be involved, how the game will be called by the referees, let alone a freak injury to the star player.

And if you have money or your reputation on the line? The stakes grow higher.

It's similar for your local meteorologist trying to predict the amount of snow your backyard will receive. Sure, we have pretty good stats on the factors (players) involved, the predictability can generally be quantified, and we can use history as a guide. But sometimes the key player (an upper level low for instance) suffers a broken face ala Mike Conley. Or more likely, the key player under-performs versus what you would expect for any of a number of reasons, as the "deformation zone" did this morning.

And like the gambler, the stakes are high if you have enough people that rely on your opinion to make decisions that are important to them.

This is not a commentary of excuses. It's not even really a commentary of "reasons." It's more to get a few things off my chest, which maybe I should keep to myself but here they are anyway.

Before I get too far though, I will start by apologizing. I know, I don't have to. But I need to, if for no other reason than to clear my conscience. You don't have to accept it. It doesn't both me one way or the other. It's your problem if you want to hold a grudge, not mine. But I still feel like I owe you an apology because you made plans that either were or weren't necessary, you had hopes and expectations that were dashed, or you had trust in a stated outcome, even if that outcome was caveated (which it was).

If there's one thing I strive to do more than accurately predict the weather, it's to earn and keep your trust. I teach my kids that trust is hard to gain, but easy to lose. I spend hours poring over computer model data, reading and learning to refine my skills, studying social media trends and technique, and diligently answering your questions and comments or anticipating them so I can answer them in a blog before you ask.  Trust is as big a deal to me as nailing a forecast. I work very hard at both. Part of maintaining that trust, in my opinion, is admitting when you are wrong. I was wrong (at least partially considering the entire area I was forecasting for, but maybe for your backyard, completely).

My dilemma, or maybe it's not actually mine, is that some of you have expectations that, honestly, can't be met. Just like you can't predict the final score of a basketball game before it tips, I can't tell you how much snow you'll get in your backyard! It's that simple. No amount of money poured into technology or brilliance of atmospheric scientists with PhD's will produce a computer model that can do that anytime in the near future! (Side note: Though the ultimate position of the axis of heaviest snow didn't quite extend into the metro as far as I predicted, nor did it produce quite as much snow as expected, there were 3" snow reports on the Shelby/Tipton border, which is literally just several miles from those of you who claimed to get "nothing." Higher totals weren't much farther north than that. That means the forecast wasn't actually as bad as your perception of it. But that's not my point here.)

There are also those that seem to not be happy unless the worst happens. In predicting and communicating the weather, we as a weather industry will almost always err on the side of caution. Not to the extent that we're crying wolf intentionally or "hyping," but making sure that the array of possible outcomes we communicate reasonably include some of the credible outliers. There are those who get mad because they didn't get the snow on the highest end of the range or insist that because "it didn't happen at my house" it shouldn't be discussed. I have 3 words: "bless your heart."

Providing all reasonable outcomes allows decision makers (including each of you) to prepare for that outcome. We would rather over-warn than under-warn, because under-warning has much more dire consequences. It's the nature of the business. (Side note on "hype": we don't hype on MWN. Hype requires that I am overstating because there is something in it for me. The services we provide, by and large, are free. I gain nothing, but stand to lose a lot of that trust I talked about above, by overstating intentionally.)

Finally, the other problem that is not mine, but that I have to deal with in this business, is the preponderance of comments that are shared electronically that most human beings would never share to another person's face. We feel like we can hide behind an online "persona" or type whatever we're thinking without filter. I understand it and occasionally have been guilty of it myself, but I try hard to make sure that I don't "share" something in print that I wouldn't say if the person were standing in front of me. Asking kindly for an explanation as to what went wrong with a forecast is one thing, but passive-aggressive statements and outright blame for something I have ZERO control over is uncalled for. Again, "bless your heart."

Some will say, "Well you chose your field and chose to make yourself 'available' to the public by getting on Twitter and Facebook, that's what you get when you screw up!" No, I CHOSE my field because I had a passion for it long before Twitter had been invented. I CHOSE to be on social media because I felt like I had something valuable to offer and it was a means to offer that service. I didn't choose to be thrown under a bus. But, I realize, sometimes that comes with the territory. Meteorologists that have been in the field for any length of time gain a thick skin. We know when we're wrong before you do most of the time because, as a whole, we are as passionate about what we do as any career out there. We judge ourselves before you judge us. Ask just about any meteorologist why they do what they do and it's because they LOVE their job and couldn't imagine doing anything else. When things don't work out, we work to figure out why so we can do better next time.

One last comment: to those who have taken the time to write a note of appreciation or encouragement today, or any other day, THANK YOU. It's why I do this. Together, we'll shake off the haters. :-)

Thanks for reading and for placing your TRUST in My team and I work hard to provide the very best service possible, but there are definitely times we mess up, and I can guarantee you there will be more! In this business, they are called "opportunities to learn and grow." Someone much more powerful than me is in control, I just try to predict the outcome!

Be safe and enjoy the snow day,

Erik Proseus
MWN Meteorologist

Thursday, January 21, 2016

Thursday afternoon update on Friday's winter storm

It's the day before a major winter storm and it's been chaotic. But enough about Kroger...
Here's the latest information you need to know.

Overview - what you need to know

Watches/Warnings/Advisories: Winter Storm Warnings are now in effect for tonight through Friday.
What/when: Rain changing to sleet or freezing rain after 4am, then snow by 8am and lasting into the afternoon. Strong wind and bitter wind chills Friday and Friday night.
Where: The entire Memphis metropolitan area
How much: Minor ice accumulation (less than 1/4") as rain transitions to snow, then periods of heavy snow possible into early afternoon. Widespread 3-6" snow amounts.
Possible Impacts: Significant. Possibly heavy snow coupled with north wind gusts to 30-40 mph and temperatures near 30° on Friday could result in areas with power outages and near-whiteout conditions, resulting in hazardous to impossible travel conditions. Wind chills in the teens Friday and Friday night.
Confidence: High. Snow amounts will differ from point to point depending on mesoscale banding features and possible convection (thunder) that may occur, either of which would enhance snow amounts. However, confidence in a significant winter storm occurring is high.
NWS-Memphis snowfall projections as of early Thursday afternoon. We are in agreement with these totals.
Models continue to have slight variations that produce differing snow and ice amounts, but that is the nature of the south - forecasting a winter storm is never straight forward. As always, we encourage you to pay most attention to the IMPACTS of the storm and not the exact snow totals, though we have provided the most likely outcome above.  Impacts from this storm will require preparation, so below you'll find out winter weather preparedness tips, which include tips to prepare for power outages, which are possible due to heavy snow and high wind.

MWN Winter Weather Tips. Click for larger image.
As with yesterday's blog post and thinking, the setup location and intensity of the deformation zone will be the biggest driver of heavy snow. We also have a trailing upper level low pressure system that will move just to the south of the city which will also have an effect on snow totals, as mentioned on last night's video chat. Atmospheric lift associated with the upper low could drive totals to the higher end of our guidance, especially if we get some thundersnow, which is not impossible.

We'll have more details in another video chat tonight, scheduled for 9pm, as well as on our social media channels. In the meantime, tonight is the time to wrap up all preparations for yourself, those you care for including pets, and alternate plans for tomorrow should (perhaps when) they need to be enacted.

Links to watch tonight's video chat
MWN Hangout page with chat:

Erik Proseus
MWN Meteorologist

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Wednesday, January 20, 2016

Significant winter storm likely on Friday - initial details

With the relatively minor (for most) winter event this morning now in the rearview mirror, we turn our attention to the next one, which has the potential to pack a punch and be much more of an impact to the Mid-South. As we did yesterday here on the blog, we'll start with the overview and then get into the nitty-gritty details.

Map of current watches/warnings/advisories in effect for the Mid-South.

Overview - what you need to know

Watches/Warnings/Advisories: Winter Storm Watch from midnight to 6pm Friday.
What: Some sleet to start, mostly snow; strong wind and bitter wind chills
Where: The entire Memphis metropolitan area
When: Starting around dawn Friday morning and ending late Friday afternoon
How much: Minor sleet accumulation (1/4") as rain transitions to snow, then periods of heavy snow possible through early afternoon. Exact snow amounts uncertain, but as much as 2-6" is likely somewhere close to the metro.
Possible Impacts: Significant. Possibly heavy snow coupled with north wind gusts to 30-40 mph and temperatures falling into the 20s on Friday could result in areas with power outages and treacherous travel. Wind chills will drop as low as 10-15° on Friday.
Confidence: Moderate-High. Details on exactly where heavy snow will set up is the biggest question mark, but it is likely that the entire metro will have significant impacts nonetheless.

Computer model data has begun to coalesce around a common solution as far as the big picture for Friday with minor details still to be hammered out. There is enough consensus, however, to have moderate to high confidence in an impactful event affecting the entire metro starting early Friday and continuing through the day. The main concerns are snow accumulation and strong wind, which will likely produce hazardous to treacherous travel conditions, possible power outages, and very cold wind chills.

NWS-Memphis briefing graphic with their thoughts on the storm. Click for larger image.

Detailed discussion - the details behind the forecast

Low pressure will develop over southern AR Thursday, strengthening rapidly as it moves across north MS overnight. Computer models now have decent agreement on the track and strength of the low, with minor variances. Rain will occur on Thursday with temperatures above freezing, but perhaps not much above 40°. Rain continues Thursday night with temperatures falling through the 30s and wind increasing as the low moves across north MS.

By early Friday morning (4-8am most likely), temperatures will be cold enough for rain to transition, perhaps briefly to sleet, then to snow. Periods of heavy snow are possible Friday morning as the low moves into north AL. Strong northerly wind on the backside of the departing low will result in temperatures continuing to slowly fall into the upper 20s by mid-day. Wind gusts of 30-40 mph are conceivable due to the strength of the low, which will move east to become a Nor'Easter (that the national media is quickly catching onto) and will produce up to a couple of feet of snow in portions of the Northeast U.S.

The key to knowing where the heaviest snow will fall lies in where the deformation zone behind the departing low pressure develops. A deformation zone is basically an area around the north to northwest side of a mature low pressure system where warm, moist air that rises and wraps around the low in a counter-clockwise fashion meets cold air being drawn into the system from the north. Deformation zones produce an area of heavy snow and there tends to be a sharp cut-off to snowfall amounts on the edge of this zone. The prediction of exactly where that deformation zone sets up and where the snow cut-off lies is nearly impossible more than a day in advance of the event. However, I have fairly high confidence that at least parts of the metro will receive heavy snow on Friday and that there will be enough snow for all to result in significant impacts (we are in the south after all).

The deformation zone is the area on the back side (left) of the low pressure area ("L" in upper left) where warm moist air wraps around into the cold air zone around the low, producing an axis of heavy snowfall. Graphic courtesy COMET.
Is there bust potential? Yes, but missing out on any snow is not likely. The confidence in snow actually occurring is almost certain. The forecast will be refined and changed over the next 36 hours. Nothing is certain until it happens, but we expect it will be the details that change, not the fact that the event will be significant for the Memphis area and result in major challenges to travel and commerce on Friday.

What should we do now? First, stay in touch. We'll provide the latest information as we get it and address any changes to the forecast. Read and follow the tips below, since power outages are possible. If you have travel planned in the region Friday, postpone or cancel it if possible.

Winter Weather Preparedness Tips. Click for larger image.
 Looking ahead, a dry weekend is in store, but it will continue to be cold Saturday (probably in the 30s) with a warming trend as we head into Sunday and Monday.

Tune in TONIGHT at 9pm as we host a Google+ Hangout video discussion of this event, streamed live on YouTube. You'll be able to watch via the MWN website here or here on YouTube,

Erik Proseus
MWN Meteorologist

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Tuesday, January 19, 2016

Tonight is worth monitoring - Winter Weather Advisory posted

** UPDATED at 3:35pm for southward extension of the Winter Weather Advisory, adjustments to the overview section, and red text in the discussion **

Yesterday I discussed the risk of reading much into medium-range snowfall forecasts, especially in terms of amounts, in the context of potential Mid-South snowfall this Friday. Today, we take a closer look at tonight's system, which now looks to bring some potentially impactful weather to northern portions of the metro. First the overview, then I'll get into the weeds:

Overview - what you need to know

Watches/Warnings/Advisories:  Winter Weather Advisory for Tipton County, 9pm tonight til noon Wednesday. Winter Weather Advisory for Crittenden, Shelby, & Fayette Counties, 9pm tonight til 9am Wednesday.
What: Freezing rain / Sleet
Where: North of I-40, with the highest confidence in impacts over Tipton County
When: As early as midnight tonight, most likely between 3-9am Wednesday
How much: Light (0.10") icing in north Shelby/Crittenden/Fayette Co's; up to 1/4" of ice in Tipton County with additional minor sleet accumulation
Possible Impacts: Minor icing mainly on bridges/overpasses in north Shelby County. A glaze on all surfaces with minor sleet accumulation in Tipton County, resulting in hazardous travel before noon Wednesday.
Confidence: Moderate-High in Tipton County, Moderate for the rest of the metro

After careful review of all available data this morning, confidence has increased in the potential for a freezing rain /sleet event for areas north of the Bluff City. In our metro counties, Tipton is our chief concern. Areas from Crittenden County east through Shelby and Fayette County are of some concern for light icing as well. North Mississippi is not expected to see freezing precipitation of impact at this time.

Detailed discussion - the details behind the forecast

Precipitation will move across the region overnight tonight through mid-morning Wednesday as weak low pressure moves into the area and southerly wind increases overnight. Temperatures during the day today likely won't reach earlier forecasted highs due to cloud cover and easterly wind (which doesn't bring warm air), probably only reaching the mid 30s. This sets the stage for air to be near or below freezing north of I-40 tonight when precipitation arrives.

As the night progresses, very slow warming is expected as southerly wind increases aloft, but the freezing line will likely be very near the Shelby/Tipton border as precipitation falls most steadily in the 3-9am time frame. For northern Shelby and southern Tipton County, warm air above the surface means the surface temperature will determine whether the rain that falls freezes on contact (freezing rain, which glazes cold exposed surfaces) or not (at 33° or above). Further north in Tipton County, there appears to be some colder air trapped in the lowest couple thousand feet, which introduces the possibility of freezing rain mixing with sleet. A very small amount of precipitation is possible late this evening and early overnight as mid-level moisture moves over the region. However, due to very dry air in the low levels (today's dewpoint below 15° is Exhibit A), most of that initial precipitation should evaporate as it falls. It will serve to moisten up the low levels though, prepping the atmosphere for the steadier rain later in the night.

From the NWS, the probability of one tenth of an inch of freezing rain (enough for minor impacts, including hazardous roads) through 6am Wednesday.

Potential impacts

Temperatures could be near or just below freezing in Shelby/Fayette/Crittenden Counties during this early period, but any rain should be so light as to not cause much in the way of impacts. If you'll be traveling on overpasses or bridges overnight though (say for instance, the new mega-flyovers in east Memphis), you'll want to exercise caution.

The main impacts will be felt in Tipton County, where total ice accumulation from this event could reach 1/4" with minor sleet accumulation as well, especially near Covington. This will be enough to make roads slick (especially since the temperatures ahead of this system are cold and there is no sunshine to warm the roads) and glaze over trees, power lines, and other exposed surfaces. Widespread power outages are not expected though due to the relatively light amount of precip and, with temperatures warming above freezing during the day Wednesday, ice should melt as the day goes on. Caution is advised for those traveling after midnight and before about noon Wednesday in Tipton County and points north, or if you're heading east towards Nashville on I-40 during the morning.

Early afternoon winter weather graphic from NWS-Memphis. Click for larger image.
Given model trends, if there is a change to the forecast, it would most likely be the introduction of more slightly greater amounts of freezing rain over northern Shelby County. Everyone in west TN and east AR needs to monitor the situation carefully, but those from north of West Memphis to the northern suburbs of Memphis should be prepared for the possibility of light freezing rain that could impact travel early Wednesday morning. **UPDATE: This potential scenario is now covered by the expansion of the Winter Weather Advisory to include the counties bordering MS, including Shelby County. **

Looking ahead, rain is expected Thursday and Thursday night before likely changing to light snow early Friday. This system also has the potential for some winter weather impact on Friday. We'll tackle that one once we get through the first one!

We'll have the latest info on our social media channels listed below. Also be sure to download the mobile app for current conditions from around the metro, our latest MWN Forecast, current watch/warning/advisory map, as well as our Twitter feed. StormWatch+, when activated, will let you know of any changes to the Winter Weather Advisories via push notification.

Erik Proseus
MWN Meteorologist

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Monday, January 18, 2016

A Warm 2015 Memphis, TN Annual Climate Recap

2015 Annual Recap

Overall, 2015 was a warm year with lengthy dry periods that were offset by wet streaks that resulted in near normal precipitation for the year. January continued the dry weather that ended 2014 with moderate to severe drought in place by the end of the month. The month started cold but ended near average. February turned very cold, as the second half of the month was the coldest such period on record (by over 5 degrees). A little over 2" of snow was recorded from multiple events. March will best be known for the significant snowfall on the 4th-5th (3.6" at the airport, but up to 6" outside the city) and record cold temperatures following.

There was no thunder in 2015 until well into April, which is very unusual. Speaking of April, the weather turned warm and dry and severe weather was well below normal and this pattern continued into May. With the exception of a chilly Memphis in May Barbecue Fest weekend, May was warm and severe weather remained minimal. June and July continued the warm and dry trend until a deluge of rain fell late in June, which began a week of below normal temperatures that included the July 4th weekend, which also recorded a flash flood event due to heavy rainfall. Scattered wind and hail reports were observed on a few June days, but the main severe weather event was a storm complex with widespread 50-60 mph wind on July 14th that resulted in 30,000 MLGW customers without power.

Severe weather and flash flooding struck again on August 5th and set the tone for a cooler than average month (despite high of 98 degrees on the 3rd and 4th which were offset by a cool end to the month) with drier than average conditions for the remainder of the month. Summer was slow to depart in September with well above normal temperatures and very dry conditions interrupted by one wet day that produced 85% of the month's total rainfall. Warmth continued into October, which delayed the start of the cool fall season, and dry weather continued until the last week of the month.

November and December ended the year very warm, each ending in the top 5 warmest months on record. November was very wet (8th wettest on record with over 10" of precipitation) with a few minor severe weather reports and some flash flooding on the 17th. Precipitation slowed in December, ending below average, but the most notable severe weather of the year occurred just before Christmas with multiple long-track violent tornadoes occurring in north MS on the 23rd, including EF-3 damage in Holly Springs (Marshall Co.) Multiple warm weather records were set during Christmas week as the mercury touched 80 degrees the day after Christmas for the only the 2nd time in December on record. It was also the first time on record that no sub-freezing temperatures were recorded in the month of December at Memphis International Airport.

All severe and winter weather reports in the metro area received by NWS-Memphis in 2015. Click for larger image.

All tornado tracks for 2015 in the Memphis warning area. Click for larger image. Graphic courtesy NWS-Memphis.

Memphis International Airport, Memphis, TN

Average temperature: 64.3 degrees (1.2 degrees above average)
Average high temperature: 73.4 degrees (0.9 degrees above average)
Average low temperature: 54.9 degrees (1.3 degrees above average)
Warmest temperature: 99 degrees (July 20, July 29)
Coolest temperature: 9 degrees (January 8)

Heating degree days: 2650 (315 below average)
Cooling degree days: 2479 (221 above average)
Days at or above 90 degrees: 77 (12.7 days above average)
Days at or below 32 degrees: 41 (1.8 days below average)
Last freeze/first freeze: March 24-November 12 (233 day growing season)

Records set or tied: February 23 (28° - tied coolest high), March 6 (15° - record low), July 20 (81° - tied warmest low), July 29 (82° - warmest low), October 3 (59° - coolest high), October 15 (93° - record high), October 23 (69° - tied warmest low), November 4 (67° - warmest low), November 5 (66° - tied warmest low), November 27 (63° - tied warmest low), December 11 (77° - tied record high), December 12 (76° - record high, 67° - warmest low), December 22 (70° - tied record high), December 23 (73° - tied record high, 63° - warmest low), December 24 (76° - tied record high), December 26 (80° - record high/2nd warmest December high), and December 27 (77° - tied record high).
Comments: 2015 was the 10th warmest year on record (64.3°), December was the 2nd warmest on record (54.1°), November was the 4th warmest on record (57.8°), and February was the 7th coolest on record (36.2°).

Temperatures for the year (lows/highs) are plotted in dark blue against the normals (brown), record highs (red) and record lows (light blue).  Where the dark blue extends above or below the brown indicates temperatures above or below normal, respectively.

Monthly total: 52.66" (1.02" below average)
Days with measurable precipitation: 114 (16.3 days above average)
Days with 1"+ precipitation: 16 (1.4 days below average)
Wettest day: 3.40" (July 3)

Total Snowfall: 5.9" (2.1" above average)
Days with a trace or more snowfall: 8
Greatest snow depth: 4" (March 5)

Records set or tied: Only one daily record rainfall amount occurred in 2015 - July 3 (3.40").
Comments: November was the 8th wettest on record (10.16") and January was the 9th driest on record (1.30").

Precipitation accumulation for 2015 is plotted as the dark green line, compared with a normal year in brown. With a few exceptions, precipitation remained below normal for much of the year, making a little headway in late winter and the summer and then nearly getting back to average the last 6 weeks of the year.

Precipitation totals for the NWS-Memphis area of responsibility with individual totals plotted. Graphic courtesy NWS-Memphis.

Peak wind: North/48 mph (July 14)
Average wind: 7.4 mph

Click here for monthly/daily statistical recaps for Memphis International Airport.

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 61.5 degrees
Average high temperature: 73.3 degrees
Average low temperature: 52.0 degrees
Warmest temperature: 99.0 degrees (July 29)
Coolest temperature: 7.9 degrees (January 8)

Heating degree days: 3482
Cooling degree days: 2211

Annual total: 55.33" (automated rain gauge), 57.19" (manual CoCoRaHS rain gauge)
Wettest date: 3.59" (November 17)

Total Snowfall: 5.5"
Days with a trace or more snowfall: 11
Greatest snow depth: 4.0" (March 5)

Peak wind: West/35 mph (July 14)
Average relative humidity: 77%
Average barometric pressure: 30.08" Hg

Click here for monthly/daily statistical recaps for Bartlett, TN.

MWN Forecast Accuracy

Number of forecasts produced and rated in 2015: 556
MWN average temperature error: 2.30 degrees
MWN forecast temperatures within 2 degrees of actual: 64.7%
MWN average dewpoint error: 2.25 degrees
MWN forecast dewpoints within 2 degrees of actual: 67.4%

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours) and the numbers above represent the error/accuracy of the entire 2.5 day period. Historical accuracy statistics can be found here.

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Regarding medium-range snowfall forecasts and this week's chances

From a weather perspective, most attention nationally is focused on potential impacts from a Nor'Easter early this weekend in the media capital of the world. But here in the Mid-South, we'll be dealing with the backside of the same low pressure system that becomes the Nor'Easter late Thursday night/Friday morning. As the low pulls away, cold air will dive south, potentially changing lingering rain into snow.

This post serves as a reminder of how best to consume "#snOMG forecasts" (snow-OMG, or models showing crazy, excessive, or improbable snow totals beyond a couple of days in advance). I'll also lump in any snowfall graphic that doesn't clearly describe the source and include some context on the confidence or probability of the depicted scenario occurring. In a nutshell, take any of those types of forecasts with a grain of salt! I'm not saying that the #snOMG scenario can't, or won't, happen, just as I'm not saying you won't win the lottery if you buy a ticket!

Looking past the early Wednesday event, which I have high confidence will be a cold rain in the metro, the next potential winter event is early Friday. I've seen several people sharing graphics from the "born-in-the-USA" GFS model this morning with little to no context. In fact I'll share this morning's hype-cast model run, with you too...

So those who would like you to believe (or maybe just want to believe themselves and also happen to have a public voice on Facebook or Twitter) that we will get accumulating snow will post something like the above, only without the caveats I added.

Let me add some responsible context to the above graphic - not because I hate snow (I actually love snow), but because it's the responsible thing to do. I don't shy away from discussing snow chances, I just do it in a responsible fashion.

1. The same GFS model has an "ensemble" system in which the model is run 21 additional times with very slightly different parameters as input in an attempt to address the uncertainty factor and provide a range of possible options. Of the 22 total members, only 7 have 2" of snow. This means that there is roughly a 32% chance that 2" or more of snow falls, according to the same model that everyone is sharing that says we'll get 3-5". Here is the snowfall forecast from all 22 GFS ensemble members:

All 22 members of the GFS ensemble forecast from this morning, showing the possible snowfall totals by Friday evening. Graphic courtesy of the awesome weather model site WeatherBell Analytics.

2. The morning run of the European (ECMWF) model that so many people like to hang their hat on for medium-range forecasting (especially when it is convenient to do so), indicates we could see a dusting to 1/2" of snow. (Graphic not shown due to sharing restrictions by the provider and European modeling center, so you'll have to trust me on this one.)

3. Like the GFS, the European model also has an ensemble, only its made up of 51 members rather than 21. A check of the precip totals from last night's European ensemble forecasts (this morning's run was not complete as of this writing) showed that only 9 of them forecast 1" or more of precipitation. So that means the Europeans, which are so darn good at medium-range forecasting, give us less than a 20% chance of 1" of snow.

4. I also looked at the Canadian, Japanese, UK, and Navy models - basically everything I could get my hands on - and none of them showed the amount of snow the GFS is showing. Finally, let's go to the official government source of forecasts for the U.S., the National Weather Service. Their 4-day winter weather outlook depicts just a 10% chance of receiving 0.25" of liquid equivalent (melted) snow/sleet. Since snow typically has about a 10:1 snow/rain ratio, that equates to about 2.5" of snow. Thus, a 10% chance of 2.5" of snow. Not out of the realm to see this much, but not likely by any means.

The NWS 4-day winter weather outlook shows a 10% chance of seeing roughly 2.5" of snow, based on .25" liquid equivalent. 
So, the best snowfall forecast beyond a couple of days is not a single model run from your favorite model, but simply...

For more on how to handle these long-range "hype-casts" and our goals at MWN with respect to these types of forecasts, see this write-up we posted a couple of weeks ago.

As always, we'll watch the models and evolving patterns and let you know what we expect when we have the confidence to say so, or if we have low confidence, we'll let you know that too! Please don't take the four-day forecast of 5" you saw on Facebook, disregard updates from your trusted sources between now and then, and wonder why "they got it wrong again" when you wake up to a dusting Friday morning!

More updates as we go through the week, including that low confidence Wednesday morning event. See our social media feeds or forecast in the MWN app.

Erik Proseus
MWN Meteorologist

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Sunday, January 17, 2016

On Arctic cold and multiple winter weather chances

Cold weather has come to stay for a while and while it's not as cold as places to our north...

Sunday noon wind chill values. Graphic courtesy WeatherBell.'s still cold by southern standards! The cold air in place will mean there will be a few time periods I'll be watching for the potential for wintry weather. In addition, the coldest of the Arctic air will drop into the metro tomorrow.

A reinforcing cold front arrives tonight, which drops our mid 40s of today below the freezing mark for tomorrow. The front will mainly bring clouds and an increase in the north wind, but it will also try and "wring out" what little moisture is in the air. With temps falling below freezing, snow flurries will be possible this evening, mainly to our west. However, I'm not optimistic.  Here's what the mid-day high-res model thinks might be happening at midnight:

Very light snow/flurries is depicted over the metro by the HRRR model at midnight tonight. Graphic courtesy WeatherBell.
Most likely a non-event as far as precip is concerned. HOWEVER, it's a good thing the baby chicks aren't out at the bus stops in the morning! Here's what the high-resolution NAM model predicts for 8am Monday wind chills:

8am wind chills will be in the lower teens Monday morning if you have to go to work. Graphic courtesy WeatherBell.
Yep, lower teens! Actual air temperatures will drop to near 20° to start the MLK holiday with afternoon highs struggling to reach freezing. If you will be out tomorrow for work, or maybe to catch the Grizzlies annual MLK Day basketball game at the Forum, layer up! It'll be teeth-chattering weather!

Another cold morning is expected Tuesday as the kiddos head back to school with lows again near 20° but afternoon highs rebound a bit back into the lower 40s as clouds increase ahead of the next weather-maker. (It's also worth mentioning to make sure your pets are taken care of as far as a warm place to stay and water that won't freeze, especially from tonight through Tuesday morning.)

Speaking of the next system, the round of precipitation I'm most keeping my eye on arrives early Wednesday morning. It's won't be nearly as cold as previous mornings as wind shifts to the south, but we might still see temperatures bottom out in the mid 30s overnight Tuesday into early Wednesday morning. Depending on when exactly the precipitation arrives, a light wintry mix is possible during that time frame. I feel the best chances for anything freezing or frozen will be north of the metro as it will take a little longer for the cold to retreat north of that area. However, as Jim Carrey would say:

Well, I suppose! The NWS has highlighted the area they think will have the "best" chance (below), but you'll notice the confidence factor is still pretty low on that event. We'll keep our eyes on it!

Rain is expected through at least mid-day Wednesday as low pressure and a front moves through the region. A lull in the precip occurs Wednesday PM before another low pressure system tracks through the region Thursday bringing more rain chances. Both medium range models I look at routinely (the American GFS and European ECMWF) keep lingering very light precipitation in the area Thursday night and early Friday as more Arctic cold air spills south. This would be time period #3 to monitor for the potential for winter weather.

In sum, winter cold has invaded the U.S. with periods of sub-freezing air dropping into the Mid-South. With a storm track that also favors a weather system moving through every few days, we'll need to keep a close eye on the timing of these to gauge the respective winter weather chances with each. We'll keep you updated via this blog, our social media feeds (links below), and the MWN Forecast, which you can find on the web, mobile web, and our app (links also below).

And for those who wondered whether winter would ever arrive during our balmy December... it's here! :-)

Erik Proseus
MWN Meteorologist

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Thursday, January 14, 2016

Holiday weekend outlook - another Arctic infiltration

The Mid-South has enjoyed pleasant weather for the past couple of days as temperatures have been some 10-15° above normal. A "southern stream" system, meaning that the storm rides along the subtropical jet stream versus the polar jet stream, will affect our weather tomorrow with showers expected starting early Friday morning and ending, for the most part, by lunchtime.

GFS model rainfall forecast from midnight through noon Friday showing light amounts of rain are expected over the metro with heavier amounts well southeast. 

Earlier this week there was a bit of concern over a strong thunderstorm or two. However, it now appears that the best instability will be confined to areas closer to the Gulf Coast and, though a rumble of thunder is possible as the front approaches late morning to early afternoon. Temperatures will remain mild overnight (lower 50s) due to warm southerly wind continuing. We'll rebound to 60° again tomorrow before the front arrives.

Noontime temperatures on Friday as forecast by the GFS model. Relatively warm air cover the Mid-South, but much colder air over the  Midwest is poised to drop south, indicating that the weekend will be much colder.

Behind the front, we cool off substantially, as one would expect in January. Mostly cloudy skies are expected Saturday with temperatures about 20° cooler (lower 40s for highs) as another system moves by well to our south. We had been watching this one with some interest as various computer models had the low pressure center tracking either along the Gulf Coast or further south into the Gulf. The further north, the more likely that some light precip might fall into Arctic air in place over the area.

Southeastern U.S. surface map and forecast precip for Saturday evening from the GFS model. Low pressure will be far enough to our south that we'll see clouds but dry conditions. Note the freezing line in blue over the metro.

It now appears that we will remain dry, with odds of a trace amount of a wintry mix just slightly better than the odds you had of winning the Powerball jackpot lat night. (In other words, Munford could get a foot of snow.)

For Sunday, cold dry air will be in place with lows in the 20s and highs in the 40s. A reinforcing shot of cold air arrives for Monday when some areas may struggle to get above freezing. (Another Monday, another Arctic blast! Happy MLK Day.) The next system to keep an eye on arrives Tuesday/Wednesday with sufficiently cold temperatures overnight and perhaps just enough warmth during the day to warrant monitoring the potential precip type. It is a fairly weak system though, so timing, temperatures, and precip potential are highly uncertain as of this writing. The next best chance for precip after tomorrow will be late next week.

Find the complete MWN Forecast on our mobile apps or here and stay tuned to our social media posts for the latest information.

Erik Proseus
MWN Meteorologist

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Friday, January 8, 2016

MWN Lightning Round: River crests, Saturday storms, then a cold blast!

Today we present another edition of the "MWN Lightning Round" with brief thoughts on a few topics. We'll start with water...

Mississippi River Flooding

It's good news when, just like a severe weather event not panning out, the river crests below predicted levels during a flood. A week ago, the Mississippi River forecast called for a maximum stage at Memphis of 43.5 feet (almost 10 feet above flood stage), which would have caused a fair number of issues in various parts of the city and surrounding area. As it turns out, the forecast crest was lowered during the week and we ended up with the river topping out at 39.59 feet on the Memphis gauge at 5:00am this morning. The river will slowly recede for several days before falling faster as we head further into January, so snap your pictures now if you want to see the highest January crest on record in Memphis.

These are the best pictures available that capture the full extent of the flooding, near crest, at Memphis. The volume...
Posted by US National Weather Service Memphis Tennessee on Thursday, January 7, 2016

Thunderstorms usher in next cold front

We're back to 60° today after a cold start to the New Year, a pattern change we promised as y'all were sweating through an 80° day just after Christmas. While the overall pattern has given us a short reprieve to end the week, another Arctic blast is set to move into the northern half of the U.S. this weekend with the Mid-South getting "modified Arctic" air on its southern edge. That means no record temperatures, but a return to cold air by Sunday. In the meantime, low pressure will develop and move through the Mid-South on Saturday. Rain begins before dawn but the best chance of thunder will be around mid-day into the early afternoon as the low passes just to our west.

A Marginal (category 1 of 6) Risk of severe weather exists Saturday afternoon, primarily for the threat of large hail, but also an isolated tornado due to plenty of shear and cold air aloft.
A Marginal Risk of severe weather is forecast Saturday afternoon if we can get a little unstable air in place. Upper level jet dynamics, which creates wind shear, and cold air aloft will be sufficient to sustain strong storms capable mainly of producing some hail, though an isolated tornado risk will need to be monitored as well. Monitor our Facebook and Twitter feeds for the latest details. By late afternoon, a cold front will move through the metro, ending the storm risk and leading us to item #3 in the Lightning Round...

Arctic air strafes the region

Behind Saturday afternoon's front and the departing low pressure system, temperatures fall quickly on northwest wind Saturday night. We'll be down to 30° by Sunday morning with wind chills in the upper teens. It now appears moisture will be gone by then, so the very small chance of s--w that was mentioned earlier in the week appears to not happen.

Plan on staying warm Sunday though as temperatures remain in the 30s all day (and wind chills in the 20s) despite a mostly sunny day. It won't be nearly as cold as up north though! The NFL playoff game in Minneapolis on Sunday will see wind chills well below zero and temperatures in the single digits! Our cold lasts through the first half of next week with lows in the 20s and highs in the 40s as a reinforcing front arrives via a clipper system on Tuesday. Light snow will be possible well to our north with that system, but we'll likely only see an increase in clouds on Tuesday. It appears we'll be back near 50 in a week or so.

The overall pattern doesn't change a great deal though, so we'll need to keep an eye on most precipitation-producing systems for a while for any threat of something other than liquid. Nothing worth mentioning at this point though!

Erik Proseus
MWN Meteorologist

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December 2015 Climate Data and Forecast Accuracy

December Recap

Above average temperatures continued in December for the fourth straight month. In fact, after the 4th warmest November on record, this month ended as the 2nd warmest December on record. Precipitation was about an inch below normal.

Severe weather marked the last week of the month, particularly on the eve of Christmas Eve (December 23rd) as a Moderate Risk severe weather outlook area included the Memphis metro. The outlook proved to be accurate as multiple supercells tracked across the region, including one that dropped hail in Bartlett and another that produced two long-lived violent tornadoes that traversed north MS, including producing devastating damage in the Holly Springs area in the far southeast metro. See graphic below for high level overview and our previous post for more detail.

For the year 2015, the average temperature at Memphis International Airport was 64.1°, which is 1.0 degree above normal and ended as the 10th warmest year on record. Precipitation for 2015 ended at 52.66", which was 1.02" below normal.

Memphis International Airport, Memphis, TN

Average temperature: 54.1 degrees (10.5 degrees above average)
Average high temperature: 63.1 degrees (11.0 degrees above average)
Average low temperature: 45.1 degrees (10.0 degrees above average)
Warmest temperature: 80 degrees (26th)
Coolest temperature: 32 degrees (18th)
Records set or tied: Maximum temperature records were set on the 12th (76 degrees) and 26th (80 degrees) and tied on the 11th (77 degrees), 22nd (70 degrees), 23rd (73 degrees), 24th (76 degrees), and 27th (77 degrees). The high of 80 degrees on the 26th was only the 2nd time a high of 80 degrees had been reached in the month of December on record and was, therefore, the 2nd highest temperature recorded in the month of December on record (81 degrees, 12/2/1982). Record maximum low temperatures were set on the 12th (67 degrees) and 23rd (63 degrees).
Comments: December 2015 was the 2nd warmest December on record, trailing only 1889 (60.2 degrees). Only 3 daily average temperatures were below normal. 16 days were at least 10 degrees above average. Ten days had high temperatures at or above 70 degrees and it was the first December on record that recorded no sub-freezing temperatures.

Monthly total: 4.77" (0.97" below average)
Days with measurable precipitation: 10 (0.3 days above normal)
Wettest 24-hour period: 1.61" (25th)
Total Snowfall: None
Records set or tied: None
Comments: None

Peak wind: Southeast/35 mph (13th)
Average wind: 8.3 mph
Average relative humidity: 70%
Average sky cover: 70%

Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 52.2 degrees
Average high temperature: 62.7 degrees
Average low temperature: 41.8 degrees
Warmest temperature: 78.6 degrees (26th)
Coolest temperature: 25.7 degrees (4th)
Comments: None.

Monthly total: 5.57" (automated rain gauge), 5.65" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 9
Wettest date: 1.82" (25th) (via automated gauge)
Total Snowfall: None
Comments: None

Peak wind: South/31 mph (28th)
Average relative humidity: 81%

Click here for a daily statistical recap for Bartlett, TN.

MWN Forecast Accuracy

MWN average temperature error: 2.40 degrees
MWN forecast temperatures within 2 degrees of actual: 60%
MWN average dewpoint error: 2.56 degrees
MWN forecast dewpoints within 2 degrees of actual: 63%

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours). Historical accuracy statistics can be found here.

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