Wednesday, January 28, 2015

On blizzards, communicating uncertainty, hype, and YOUR responsibility

The "Blizzard of 2015" has been the biggest weather story so far this winter due to multiple factors - from the promises of a "historic, epic, life-threatening, crippling" storm, to the equally stunning "forecast bust" for the media epicenter of the world, to the claims of hype, to apologies by officials. After a day or so to let the dust settle and the hotheads get it all off their chest, I figured I'd put my thoughts on the record.

The Blizzard of 2015 Forecast

First let me qualify my interest in this non-local story (we tend to stick to Memphis-centric events). My main job is as a meteorologist for a Fortune 500 company and my responsibilities include tracking and forecasting large-scale national (and some international) weather events. So I had done my own forecast for this event, even though it didn't take place locally. As my regular readers know, another great interest of mine is in communication, specifically the communication of weather information in a manner that the lay person (you) can clearly understand and take action on. Upon review and analysis, and you may be surprised by this, the repercussions of the blizzard were actually more about (perhaps poor) communication than the actual forecast.

I'll set the stage with the snow accumulation forecast (from the official government source, the National Weather Service - top image) and the results, also from NOAA/NWS (bottom image). I've focused on the NYC-Boston corridor, since that's where the majority of people affected live and work. You'll notice that, generally, the NWS did a very nice job with a high-impact, upper-end event that resulted in 30"+ in 5 separate states and several "top 10s" for single event snowfall. You'll also notice that west of a line from VT to western MA to western CT to NY/NJ excluding Long Island (or basically the blue areas on the bottom map), the forecast went awry, in some cases by a lot.

NWS forecast snowfall accumulation for this Blizzard of 2015 as of early Monday morning (5am). The event peaked from Monday evening through Tuesday morning. Widespread 18-24"+ totals were expected from NJ well north into New England.

A zoom of actual snowfall amounts from the blizzard. Eastern New England was buried in 1 1/2 to near 3 feet of snow, but there was a sharp "back edge" that extended from NYC to VT (top center of image). Graphic courtesy NOAA/WxBell.
So as far as the actual snow forecast was concerned (I'm not getting into the wind, coastal flooding, etc), the biggest issue was with the back side of the storm, where a tight gradient in snowfall totals set up. Notice in particular the disparity between Long Island, with 12-22" of snow, and far eastern NJ, with 2-5". It just so happened that the "all-or-nothing" line was just east of Manhattan. (Of course, as a Memphian, I would argue that 4-8" doesn't classify as "nothing," but I digress...) Actual totals in the NYC metro included 6.5" at Newark, NJ on the west to 11" at JFK and LaGuardia Airports on the east.

First of all, I argue that the chief complaint with this storm being a "bust" was due to where the "bust" occurred - in the most populous city with the loudest media in the world (that's not said as an insult to NYC or national media, but simply as fact). How many networks had positioned cameras 50 miles east on Long Island where 18" was common exactly as forecast? If that "back edge" had set up in the middle of the Dakotas and some cattle ranchers or oil workers got 8" less than predicted, it would have been a non-event and the Weather Service would never have been dragged through the mud and felt it necessary to send their chief to "do some 'splainin'."

However, given how it worked out, there is some good that can come from this event once the weather community is allowed to stop defending themselves and can get to analyzing the actual event and their messaging.

Computer models present a dilemma

You hear about weather models all the time. You know that there are several, that they all provide different forecasts of the environment, and that, like siblings, they sometimes agree well, but most of the time have their differences of opinion. Sometimes they just plain old duke it out. You also know that usually, as an event gets closer in time, they tend to arrive at a common solution, even if the details are slightly different.

In this case, all of the models had their version of how the blizzard would play out. They were similar in the areas where the forecast and actual conditions matched well (eastern MA to Long Island). They were not so similar on the western side of the system, which happened to include NYC. The European model (Euro), which everyone knows was the darling after Hurricane Sandy, and the North American model (NAM), which tends to do very well at short-term forecasts, had a fairly common solution that the NWS (and subsequently most of the private forecasting companies) latched onto. It was one that produced 15-25" of snow in NYC.

Then there was the newly-upgraded American stalwart, the Global Forecast System (GFS), which had a long track record of good forecasts until it was updated earlier this month. It's still a great model, but the weather community as a whole hasn't seen it perform in these conditions in its "upgraded state." It was forecasting around 8-12" for NYC. As you can see, the GFS beat the pants off the Euro/NAM solution in one area where it mattered most (metro NYC). The NWS (and many others) picked the wrong model.

How we (the weather community) can, and must, do better

So what should the weather community do with a high-impact, high-visibility forecast in which the range of possible solutions are far apart? Pick one and cross their collective fingers? (I'm oversimplifying a great deal here, by the way. That's not exactly what the NWS did, but they definitely leaned in that direction.)  The better method (and this is not a new idea, it's been discussed many times over the past 24 hours from the head of NWS on down) is to communicate something other than a specific total, or even range, for a location.

There was a measure of uncertainty in the forecast. The uncertainty was inherently much higher in the NYC area than the Boston area because the available data being used as input had a wider spread. So why not COMMUNICATE THE UNCERTAINTY? Use the range of model options available and your expertise and training to say "is the most likely outcome, but there is a chance we could see and a lesser chance we could see Z."

Every forecast we create has a measure of uncertainty or confidence associated with it. This can be expressed in probabilities or using words. However, especially with winter forecasts, continuing to call for Y inches will only reduce the public's confidence in the forecast because the chances are better you'll be wrong than right, even if it's by an inch or two. To their credit, a couple of NWS offices in the northeast are already doing this in an experimental state, providing a "most likely" outcome and probabilities of other outcomes. These products must be expanded and made more visible. (I didn't know about it until after the storm had ended and would've been very helpful in my forecasting efforts.)

An experimental "snow accumulation potential" forecast issued by the Philly NWS office.

In addition, in this world of soundbites and headlines and 140-character tweets, hype drives clicks and viewers. I'm not insinuating that the NWS, or any other forecast agency, hyped the event. But in the media-driven culture of NYC, it's very easy to take the "high end" forecast and run with it. "TWO FEET OF SNOW ON BROADWAY" draws eyeballs. No matter that that forecast had a very low probability of actually verifying. (That also leads into an entirely separate topic of amateurs with access to model data proliferating the worst case scenarios on social media and making the weather community as a whole look bad... but again, I digress...)

Should forecasters apologize for their mistakes?

There was also some discussion of whether those who issued the forecasts had the responsibility, or felt pressured in some way, to publicly apologize, which a few did. Personally, I don't mind the NWS Director holding a press conference to help educate others what goes on in the decision-making and forecast-creation process. It's insightful and, I believe, lends confidence in and credence to the process, building trust along the way. However, I don't necessarily find it mandatory to be remorseful for the errant forecast produced, especially when the event is over-forecast. Again, while explaining oneself can be educational and build trust, we provide the best forecast we can with the information, knowledge, and experience we have accumulated. It's a forecast and we're human. Sometimes we'll be wrong! 

I truly believe that providing a confidence factor or probability forecast instead of a cut-and-dry "this is what it'll do" can be extremely useful in these situations. Some may see it as waffling, but smart consumers will use the information to make informed decisions depending on their risk or tolerance level. After all, that's what we do every day with our rain forecasts right? If there's a 20% chance, you may leave the umbrella at home and take your chance. But if you or the event you are involved in can't tolerate a stray shower overhead for whatever reason, you'll take precautions. This same probability forecasting is now being done with severe weather, why can't it also apply to winter weather scenarios?

The weather consumer's responsibility

My last comment will be regarding the consumer's (i.e., YOUR) responsibility. As an example, too often someone will read a forecast that indicates a very low likelihood of rain in two days. Then they get busy, don't pay any attention to the forecast, and are shocked when it rains on that day that "was supposed to be dry." The meteorologist was wrong again! I say bull.

I honestly believe that meteorologists have gotten so GOOD that the public is surprised when we're wrong! And so the myth is perpetuated that we missed it *again.* In actuality, the weather pattern changed a bit, we updated our forecasts the day before (or the morning of) that rain, you didn't see the change, and then blame the weather guy/gal. While we have many new ways of providing our information on demand (social media, apps, etc.) compared to 10-20 years ago, when you had to wait until noon, 5pm or 10pm to "watch the weather," it is NOT our responsibility to hand deliver it to you. I believe that as long as we make it available and keep it current, it's your responsibility to keep up with it. If you don't, it's on you.

Closing argument

I'll close with this. For the vast majority of us in the weather enterprise, we pride ourselves on being accurate. We spend HOURS pouring over data, considering all potential solutions, and using our previous experiences to provide the most likely solution to our customers.

Could we communicate the information more effectively? You better believe it.

Are we learning as we go? Absolutely.

Do we tire of hearing how great a job we have because "we get paid even if we're wrong"? Would you? :-)

But we also KNOW when we botch a forecast. Because we tend to be, well, anal, and pride ourselves on hitting the high temp to the degree or timing the rain to the hour, we are harder on ourselves than anyone else and their criticism. So we've gotten good at brushing off the haters, learning from the experience, and applying it to the next event! :-) After all, we're only as good as our last forecast right?

Thanks for reading, and feel free to let me know what you think in the comments or hit MWN up on social media!

Erik Proseus
MWN Meteorologist

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Thursday, January 22, 2015

9:50pm update on snow potential for Friday - as challenging as it gets

Will keep this brief, as it's getting late, but after earlier today backing off the potential for snow during the day on Friday and calling for just a chance of a rain/snow mix as precip ends Friday evening, models (and the atmosphere) are again leaning a bit more towards a potentially cooler solution for the early morning hours Friday.

Any snow that can mix in will likely be caused by an atmospheric process called "dynamic cooling," which is too complicated to explain here but is basically a lowering of air pressure due to rising motion. The lower pressure causes temps (above the surface) to cool. Even 1-2 degrees could be enough to mix snow with rain in the early to mid-morning hours, even though we'll be in the mid 30s at the surface. The challenge is that this process is very difficult to forecast until it occurs.  We can see that the potential is there, but we don't know if it will be enough to push us over the edge for snow.  What we do know is that 1000' up, precipitation will be mostly snow! Whether it melts prior to reaching the surface is the big question.

We also know this - even if some snow mixes with rain during rush hour through mid-morning, the ground and air temperatures will be ABOVE freezing. Any accumulation (should there be enough snow to cause it) would be on grassy surfaces or bare ground and would be minimal and quickly washed off by rain. Roads are expected to be wet, not icy.

We'll see what we wake up to. In the meantime, plan on schools being in session, roads being wet, and temperatures being cold! Get the latest official MWN forecast on our website or apps, linked below.

Erik Proseus
MWN Meteorologist

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Update on Friday's snow threat - the news isn't good

This blog post has been superceded

A more recent update to expected conditions can be found here.

Original post: 11:20am Thursday

After raising the flag yesterday on the possibility of a rain/snow mix Friday, unfortunately it appears we're going to have to lower it to half mast, in remembrance of years gone by when, according to all of you, big snow happened multiple times every year.

While I'm not ruling out ALL snow tomorrow, the latest data has trended a tad warmer during the day. As mentioned in yesterday's blog post, a couple degrees either way could make a big difference. In this case, the couple degrees was on the warm end, starting with morning lows closer to 37-38 rather than 35. Though temps won't rise more than a couple of degrees Friday with rain falling, there is a big difference between 40 and 36 when it comes to snow. So go ahead... I know you want to...


If you're still reading, it's probably because I said "not ruling out ALL snow." Colder air does move in after dark Friday and some lingering precip could still be around. Therefore, I've kept a slight chance of light snow in the evening forecast. Don't get your hopes up and don't change plans. Roads will be fine due to previous warmth. Just look forward to another decent weekend with highs back to 50+. The solace comes in the fact that our "biggest snows" - by official records, not people's selective memories - tend to come in the last half of winter and very early spring. Winter's not over!

Erik Proseus
MWN Meteorologist

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Wednesday, January 21, 2015

MWN Winter Weather Discussion for Friday, January 23

Despite the Mid-South being just past the coldest period of the year according to climate records, our current stretch of 55°+ days, which stands at 6 and includes a few mid 60s, is the longest such streak since Nov. 19-24. That is about to end though, as a cold dome of high pressure over the Rockies shifts east across the northern tier of the U.S. Today will be the last day in the 50s  for several days.

South of the high pressure that moves by to our north, a low pressure system over south Texas will get its act together and also move east along the Gulf coast. The Mid-South ends up in a squeeze play with cold air from the north moving in as moisture wraps around the low to our south. This is one of our classic winter weather patterns, but it always depends on the details, which are never the same from one storm to the next. How cold will it get and how much moisture will be present. As usual, the intersection of the "just cold enough" air and available moisture will be right over the region. There is still disagreement in the models on the amount of precipitation and degree of cold air. Yesterday, most models were still in the "no precip" camp, but they are coming around.

NWS forecast position of the low pressure responsible for potential Mid-South snow. The "Gulf low" track is a favorable one for the production of snow in the winter in Memphis.
Light rain looks to move into the area during the day Thursday, though most precipitation will remain over MS, so only light amounts are expected with temperatures in the 40s. By Thursday night, air temperatures cool into the mid 30s as light rain becomes more likely with the low over coastal Louisiana. Temperatures will probably fall to the mid 30s by dawn Friday morning. It is from this point on that we consider the potential for a rain/snow mix - through the day Friday as the low moves along the northeast Gulf coast and a trailing upper level trough moves through the region. Temperatures at the surface will likely stay in the mid 30s all day Friday with precipitation falling, then fall to near 30 for a low Saturday morning with precip ending Friday evening.

So, tell us straight - how much are we talking and schools be cancelled?
A big factor on any snow accumulation is the fact that we have been warm recently, so streets and even the ground have warmed up a bit from our early January deep freeze. For now, my early expectation is that some areas in the metro might see up to in inch of snow, mainly on grassy or exposed surfaces. Most major and secondary roads would be fine in this scenario, though slick spots could develop in those areas that get slick first - bridges and overpasses. (Note that brine pre-treatment, if applied, will wash off prior to any snow falling. It won't do any good.)

I have NO IDEA about schools, and they aren't making a decision this early anyway. The scenario could completely change by Friday morning. A couple of degrees either way could result in snow amounts ranging from nothing to a few inches based on the amount of precipitation expected. For now, plan ahead for all possibilities and let those paid to make those decisions Friday morning do their job, which always involves the safety of the children over anyone's convenience.

From the NOAA/NWS Weather Prediction Center - probability of 1" or more snow on Friday.
A low chance of 1" doesn't mean no snow however.
Finally, a word about content you might see on social media. The graphic from NWS-Norman (Oklahoma City) below sums it up very well. "Beware the Share" - don't share stuff that doesn't pass the eye test or is from a source you don't know and trust. Anyone can draw a map of the worst case scenario and post it as gospel.

We'll update again as new information arrives or our opinion changes, but no later than Thursday afternoon. Any intermediate updates will be posted on our Facebook and Twitter feeds.

Erik Proseus
MWN Meteorologist

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Friday, January 16, 2015

A reprieve from the January cold!

We've had our share of cold weather to start 2015 with an average temperature for the first half of the month that is over 6 degrees below normal! That will make the next 5 days or so even more enjoyable as warmer air overtakes the region producing multiple days with highs in the 50s and lows above freezing.

Even though this past week was climatologically the coldest week of the year, the Mid-South has been in "outperform" mode. Through January 15, the average high temp has been just under 43 degrees, which is 7 degrees below normal. The average low of 27.2 is nearly 5.5 degrees below normal.
Temperature so far this month (blue bars) have generally been well below normal (brown bands). We'll have more blue bars in the red area (above normal) by this time next week!
It's also been fairly dry to start the year with precipitation about an inch below normal already. The dry spell continues, but now with more pleasant temperatures that should result in more folks outside this weekend, soaking in some welcome sunshine and shedding the winter coats! Even a weak cool front Saturday night will do little to suppress temps as highs both Saturday and Sunday reach the upper 50s. No rain is expected with this front as dry air throughout the atmosphere will mean just a few clouds Saturday night and a brief wind shift.

Output from the "new" GFS model (see below) for Saturday night as a weak cold front moves through. The closest precip looks to stay along and north of the Ohio River as dry air won't support rain this far south.
Monday will see highs approach 60 and Tuesday would be the same except for a few more clouds with another cold front that is also expected to pass throughout precipitation. We're forecasting another day of highs in the upper 50s. (Our normal high this time of year is near 50.)

The tide appears to turn as we head into the end of next week as cooler air seeps in behind Tuesday's front with a general downward trend in temperatures. In addition, a "southern stream" weather system, which rides the subtropical jet stream positioned in the northern Gulf of Mexico, will throw abundant cloud cover over the area late next week. Being a week out, precipitation forecasts could change significantly, but for now most of the precip looks to stay just to our south. However, with colder air back in place, we'll have to monitor this system closely for the potential of a wintry mix. Too soon to make any calls on that though!

Output from the "new" GFS model (see below) for next Thursday night as low pressure moves through the northern Gulf in the "southern stream." Temps will be cold; the question is where the northern edge of the precipitation will be. Graphic courtesy WeatherBell Analytics.
For now, enjoy the beautiful January weekend that continues into early next week! These are what we call "bonus days" in a typically cold, often cloudy, time of year.

Side note - for weather geeks

For you weather weenies out there, we have referenced and posted graphics on this blog in the past few months from a "parallel" or "upgraded" GFS computer model that was being tested alongside the operational GFS. The GFS is the American workhorse model - with global output and long-range capabilities. As of Wednesday morning, January 14, that "upgrade" became the "new" operational GFS. There are several improvements within the model, but perhaps the biggest is an increase in horizontal resolution by nearly four-fold in the ten day forecast and more than three-fold out to 16 days.

An increase in horizontal and vertical resolution was also accomplished on the ensemble modelling system that the GFS is a part of (the GEFS). This increase in resolution was enabled by a recent tripling in capacity of the supercomputers NOAA runs the models on, mostly funded by the Hurricane Sandy supplement that directed tens of millions of federal dollars into a lagging NWS computing infrastructure.

NOAA supercomputers "Tide" and "Gyer" process NWS model data used globally for atmospheric prediction.
Other valuable improvements in various computer models are forthcoming this year, but this month's upgrade was certainly welcome and follows other recent upgrades, including the operational launch of the HRRR high-resolution rapid refresh model nowcasters rely heavily on and the upgrade of the high-resolution hurricane model, known as HWRF. All of the model upgrades, collectively, will only help to improve the accuracy of forecasts provided by your local weather folks. As you know - garbage in, garbage out.

Erik Proseus
MWN Meteorologist

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Friday, January 9, 2015

2014 Memphis Annual Climate Recap - A Cool and Wet Year

2014 Annual Recap

Overall, 2014 can be characterized as cool and wet in the Memphis metro, marked by a few specific events or periods that give rise to that characterization. As outlined below in the statistical summary, two very heavy rain days provided nearly one-fifth of the total rainfall for the year - without those two days the 2014 rainfall would've been over 6" below normal,  while a "Garden of Eden" summer (particularly a wet June and cool July) and very cold late fall (November) contributed to below normal temperatures. Despite the cool than normal temperatures, Memphis touched 100 degrees once late in the summer (August 24, which also tied a record high for the date) when conditions turned hot as children returned to school. That was offset by a cold January that featured two days with lows in the single digits.

Severe weather was infrequent in 2014. There was one tornado in the Memphis metro, an EF-0 (75-80 mph wind) that occurred early in the morning on April 28 in the Bolton community of northeast Shelby County. (That was also the day of the Tupelo, MS EF-3 tornado that made headlines.) NWS-Memphis issued 18 Tornado Warnings during 2014 that touched some part of the 8-county domain (Memphis metro area). Strong thunderstorms and very heavy rain were much more common than rotating supercells or tornadic spin-up's in squall lines across the Mid-South.

Memphis International Airport, Memphis, TN

Average temperature: 61.3 degrees (1.8 degrees below average)
Average high temperature: 70.7 degrees (1.8 degrees below average)
Average low temperature: 51.9 degrees (1.7 degrees below average)
Warmest temperature: 100 degrees (August 24)
Coolest temperature: 8 degrees (January 7)

Heating degree days: 3397 (432 above average)
Cooling degree days: 2161 (97 below average)
Days above 90 degrees: 55 (9.3 days below average)
Days below 32 degrees: 60 (17.2 days above average)
Last freeze/first freeze: March 24-November 12 (233 day growing season)

Records set or tied: Record low on May 16 (46), record low maximums on July 18 (69) and July 19 (79), record low on July 29 (64), tied record high on August 24 (100), tied record warm minimum on August 25 (79), record warm minimum on November 30 (61).
Comments: July 2014 was the 6th coolest on record (78.0 degrees). 2014 was the coolest year in Memphis since 1997 and 15th coolest on record.

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: 57.63" (3.95" above average)
Days with measurable precipitation: 113 (5.3 days above average)
Days with 1"+ precipitation: 17 (0.4 days below average)
Wettest day: 5.87" (June 29)

Total Snowfall: 1.0" (2.8" below average)
Days with a trace or more snowfall: 15
Greatest snow depth: 1" (March 4)

Records set or tied: February 4 (2.88"), March 2 (2.39"), March 28 (3.14"), June 29 (5.87"), September 11 (4.45").
Comments: Two heavy rain/flash flood events accounted for 18% of the year's rainfall - June 29 (7th wettest day on record) and September 11, both also daily records. June 2014 was the 2nd wettest June and 8th wettest month on record (13.40").

Precipitation accumulation for 2014 is plotted as the dark green line, compared with a normal year in brown. Precipitation stayed fairly close to normal until June when it jumped well above normal before narrowing the gap over the last quarter of the year.

Peak wind: South/61 mph (October 2)
Average wind: 7.8 mph
Average relative humidity: 65%
Average sky cover: 60%

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

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 59.9 degrees
Average high temperature: 70.8 degrees
Average low temperature: 49.5 degrees
Warmest temperature: 100.0 degrees (August 28)
Coolest temperature: 6.2 degrees (January 7)

Heating degree days: 3897
Cooling degree days: 2099

Monthly total: 58.99" (automated rain gauge), 60.47" (manual CoCoRaHS rain gauge)
Wettest date: 7.62" (September 11)

Total Snowfall: 2.0"
Days with a trace or more snowfall: 15
Greatest snow depth: 1.0" (March 3-5)

Peak wind: West/32 mph (January 18)
Average relative humidity: 76%
Average barometric pressure: 30.07" Hg

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

MWN Forecast Accuracy

Number of forecasts produced and rated in 2014: 554
MWN average temperature error: 2.17 degrees
MWN forecast temperatures within 2 degrees of actual: 67.7%
MWN average dewpoint error: 2.52 degrees
MWN forecast dewpoints within 2 degrees of actual: 62.4%

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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December 2014 Climate Data and Forecast Accuracy

December Recap

Dry conditions continued from November into December, although temperatures swung from well below normal in November to above average this month. Despite a cloudy month (80% average cloud cover), precipitation was more than 3" below the average of 5.74". The clouds didn't hinder temperatures from ending more than 2.5 degrees above normal. In fact, wintertime cloud cover directly contributes to warmer overnight lows. In December, low temperatures averaged 4.5 degrees above normal. Daytime highs were less than a degree above average. As in November, there was no severe weather during December. the last severe weather warnings issued by NWS-Memphis for 2014 came on October 13.

Memphis International Airport, Memphis, TN

Average temperature: 46.2 degrees (2.6 degrees above average)
Average high temperature: 52.8 degrees (0.7 degrees above average)
Average low temperature: 39.6 degrees (4.5 degrees above average)
Warmest temperature: 67 degrees (5th, 6th)
Coolest temperature: 27 degrees (31st)
Records set or tied: None
Comments: The average temperature departure from normal (2.6 degrees) was the warmest  monthly departure from normal of 2014.

Monthly total: 2.60" (3.14" below average)
Days with measurable precipitation: 11
Wettest 24-hour period: 1.16" (5th-6th)
Total Snowfall: 0.0" (0.2" below average)
Records set or tied: None
Comments: Only one day had precipitation above 0.35", which was the 5th (1.10"). December 2014 was the 23rd driest December in 142 years of record keeping.  There were no thunderstorms or freezing/frozen precipitation recorded at the airport.

Peak wind: West/33 mph (15th)
Average wind: 7.3 mph
Average relative humidity: 73%
Average sky cover: 80%

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

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 44.8 degrees
Average high temperature: 52.5 degrees
Average low temperature: 38.3 degrees
Warmest temperature: 66.5 degrees (5th)
Coolest temperature: 26.6 degrees (31st)
Comments: None

Monthly total: 2.24" (automated rain gauge), 2.26" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 13
Wettest date: 0.91" (5th) (via automated gauge)
Total Snowfall: 0.0"
Comments: None

Peak wind: Northwest/20 mph (6th)
Average relative humidity: 84%

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

MWN Forecast Accuracy

MWN average temperature error: 2.39 degrees
MWN forecast temperatures within 2 degrees of actual: 59%
MWN average dewpoint error: 2.55 degrees
MWN forecast dewpoints within 2 degrees of actual: 54%

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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Thursday, January 8, 2015

No-foolin' Arctic airmass takes Mid-South's collective breath away

The much anticipated Arctic airmass arrived as forecast overnight, though it's easy to forget what wind chills of zero feel like when it's been a year since their last visit! It almost just makes it hard to breath.

Temperatures plummeted into the single digits across nearly the entire metro this morning with wind chills hovering near zero. Though temperatures have "warmed" into the mid 20s this afternoon, a now-southerly wind of 10-15 mph has the same effect on wind chills as a north wind at the same speed. It still feels like the teens out.

This morning's official low of 9 degrees at Memphis International is just the 8th single digit low in the past 20 years (see list below), though it was far from the record low of -2 set in 1886. The last sub-zero readings in Memphis were on December 22nd (-4) and 23rd (-3), 1989.

Coldest Low Temperatures since 1995
  1. February 3, 1996 (4° F)
  2. February 4, 1996 (4° F)
  3. January 11, 1997 (8° F)
  4. January 7, 2014 (8° F)
  5. February 2, 1996 (9° F)
  6. January 8, 2010 (9° F)
  7. January 24, 2014 (9° F)
  8. January 8, 2015 (9° F)
Below are some images that seem to tell the story.

Temperatures across the metro from official and personal weather stations just before 6:30am when low temperatures occurred.

Regional temperature map as of 6:30am

We weren't the only place that was bitterly cold this morning...

As for where this cold air came from...

With temps that low, there are always interesting ice creations...

...even as far south as the Mississippi Delta!
As for how long the cold air will last, a reinforcing cold front will move through early Friday, ushering in another Canadian high, but this one not quite as cold. We may briefly get above freezing Friday afternoon after temperatures linger in the low to mid 20s overnight, but then it's right back into the mid teens by Saturday morning with another high near freezing. We look to get safely above freezing Sunday afternoon when the next precipitation arrives. This precip could briefly start as light ice (freezing rain or sleet) before becoming all rain. We'll be monitoring the Sunday-Wednesday period closely and update the forecast and blog as more info becomes available.

Stay warm!

Erik Proseus
MWN Meteorologist

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Tuesday, January 6, 2015

Arctic high brings prolonged sub-freezing conditions to the Mid-South

By now, most are aware that bitterly cold Arctic air will encompass the region for the latter half of the week thanks to a massive ridge of high pressure building into the region from western Canada. This will be the coldest air Memphis has experienced since last January, which featured two Arctic blasts of this magnitude - one about this time of the month that produced a low of 8 degrees, and another later in the month with a low of 9 (both recorded at Memphis International).

Wednesday night at midnight - cold high pressure dominates the center of the country with Arctic air all the way to the Gulf coast. Graphic courtesy WeatherBell Analytics.

Brutal cold temperatures and wind chills

Lows only drop into the mid 20s tonight as clouds increase due to an upper-level disturbance that fronts the Arctic air. However brisk northerly wind on Wednesday will put a halt to any daytime warming, even as skies clear by mid-day, resulting in temperatures slowly falling during the afternoon. A few flurries are also possible across the area during the morning hours but should have little to no impact.

Wednesday 6pm departure from normal temperatures per the GFS model. We'll be nearly 20 degrees below normal with portions of the midwest more than 30 degrees below normal. Notice the well above normal temps west of the Continental Divide. Graphic courtesy WeatherBell Analytics.

Thursday morning will bring the coldest temperature readings of the period across the central U.S., including the Mid-South. Not only will there be very cold temperatures, but wind that produces dangerous wind chill readings. In the metro, I expect single digit wind chills by Wednesday evening and even some negative single digit wind chills (0 to -5) early Thursday morning as lows drop into the upper single digits in the city and suburbs and possibly near 5 in outlying areas. A Wind Chill Advisory is possible for the area Wednesday night.

GFS modeled wind chills for Wednesday evening. The purple to blue-green transition represents will chills of 0. Graphic courtesy WeatherBell Analytics.

Thursday morning low temperatures from the GFS model. Red to purple transition marks the 10 degree line. Graphic courtesy WeatherBell Analytics.

Thursday 6am departure from normal temperatures per the GFS model. We'll be more than 20 degrees below normal. Graphic courtesy WeatherBell Analytics

Temperatures will remain below freezing on Thursday with highs in the upper 20s, though it won't be as cold Thursday night due to wind becoming southerly. Friday morning's lows will also be in the 20s. Finally, by Friday afternoon, we should see temperatures make it back above freezing for a few hours with highs in the mid 30s - ending a streak of 60+ hours of sub-freezing temperatures.

Near-record high pressure

In addition to the extremely cold temperatures, the strength of the high pressure system itself (as measured by sea level pressure readings) will get close to setting all-time readings as well (the highest high?). For Memphis, our all-time highest pressure reading is 30.96", or 1048 mb, set (coincidentally enough) 91 years ago yesterday (January 5, 1924). This week's high will weaken a bit as it builds south from the northern plains towards the Mid-South, but models are still forecasting a maximum pressure reading Wednesday night in Memphis near 1044 mb, just shy of our all-time record.

Surface weather map for January 5, 1924 when pressure readings set their all-time high in Memphis at 30.96". Map courtesy Joe Lauria, FOX4-TV in Kansas City.


The brutal cold temperatures are worthy of preparation on the part of Mid-Southerners as single digit temperatures don't happen often here. We preach the "4 P's" of cold weather planning: people, pets, pipes, and plants. Make sure all are accounted for.
  • Take care of any loved ones or friends who, for whatever reason, are susceptible to very cold temperatures. Bundle up the kids, drive them to the bus stop, and of course use your own warm weather gear - gloves, scarves, etc. Yes, it'll be that cold.
  • Bring your pets in or SAFELY provide them a warm space wherever they stay. Frozen bowls of water and food are not appreciated by your furry friends. 
  • Cover outdoor pipes and spigots and wrap interior pipes and/or leave water dripping in faucets on exterior walls (this is mainly for Wednesday night as we'll remain in the 20s tonight). 
  • Finally, any plants that are near cold windows should be relocated. At this point, there are probably few outdoor plants that are not cold tolerant left standing!

We'll be monitoring conditions and providing updates on social media the next few days. In addition, we'll be carefully watching the next precipitation maker expected Sunday and/or Monday as cold air will be slow to retreat. Models are all over the board, but we have included a chance of wintry precipitation in our forecast for now with more fine-tuning to come.

Erik Proseus
MWN Meteorologist

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Friday, January 2, 2015

Temperature roller coaster in town for a few days with thunder at its apex!

Miss the Zippin' Pippin? Well a roller coaster of another sort will be visiting Memphis over the next day or two, one featuring some wild swings in temperatures as a strong storm system approaches the area. Unfortunately, it also will be bringing us high chances of rain and even some thunder that will dampen any outdoor plans for the first part of the weekend.

While its been a drizzly and foggy afternoon across the metro much of the day, as temperatures hovered in the lower to mid 40s, a change can be expected as a warm front currently along the Gulf Coast moves closer to the region late tonight. Milder air will begin to take over, leading to temperatures that will actually rise through the overnight into the 50s. Though drizzle will taper initially, a good chance of showers will develop as the night progresses, and a rumble or two of thunder can't be ruled out, especially toward morning.

SPC Outlook for Saturday. While the metro is within the "Marginal Risk" category for severe storms, the threat locally appears fairly limited.
For Saturday, plan for a soaker. Rain is likely much of the day, and the rain could be heavy at times. As a low pressure area strengthens and moves just northwest of the region, southerly wind will also increase, surging temperatures into the mid 60s. A cold front across Arkansas will begin moving into the region by afternoon, leading to even more rain and thunderstorms.

With the mild air in place and some strong wind dynamics aloft, the Storm Prediction Center is monitoring parts of the Mid-South for a Marginal Risk (category 1 of 5) of a few strong storms. At this time, for the Memphis metro, the amount of instability or energy to drive storms to severe levels appears quite limited, so we do not anticipate much more than a general risk of thunder. If any stronger storm were to develop, gusty wind would be the primary threat. The main threat of severe weather should be across eastern Mississippi and western Alabama where the SPC is highlighting a Slight Risk (cat 2 of 5) zone. Through Saturday night, heavy rainfall totals around 1.0-1.5" inches will be common in the metro, though flooding is not a significant threat with this system.

By later Saturday night, as the cold front sweeps past the metro, colder air will once again filter back into the region. Temperatures by Sunday morning should be near 40, and they may only fall during the day Sunday into the 30s as strong northwesterly wind takes over.

A temperature roller coaster is forecast over the next week with a downhill plunge from Saturday night to Monday, a brief climb on Tuesday, then another plunge into the teens by Thurday morning. Shown above, the parallel GFS model courtesy WeatherBell Analytics.

Looking a bit further out, an even colder period looks to develop by Wednesday into Thursday of next week as a strong Arctic high pressure moves out of Canada, bringing some biting cold air with it. Temperatures will reach their coldest levels of the winter season so far, especially Thursday morning, with teens likely across the region. Highs may struggle to reach the freezing mark both Wednesday and Thursday.

Precipitation is not expected in this pattern, so winter weather should not be a concern. Nevertheless, it may be a good idea to make some early preparations for a period of very cold temperatures later next week, and of course continue to follow MemphisWeather.Net as we will be updating that potential and the forecast temperatures as new model guidance comes in.

Kevin Terry

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Thursday, January 1, 2015

2015 starts wet with a chance of wintry precip

Happy New Year!  

Unfortunately, we will start 2015 in a wet and cool fashion. A hint of possible sleet has put us meteorologists in front of the computer models and checking out current atmospheric conditions early! I'll mainly focus on the upcoming 8 hours, as that is when the threat of any wintry precipitation occurs.

The details ("Why")

The morning weather picture is shaping up much as anticipated, perhaps a degree or two warmer here at the earth's surface but about as expected in the lower levels of the atmosphere. The 6am sounding from Little Rock (shown below, and which is fairly similar to what we have here in Memphis) indicates temperatures are above freezing up to about 10,000' with a pocket of near-freezing temps at about 5,000'. This level is also the upper bound of the dry air with saturated conditions for several thousand feet above that.

As precipitation begins to fall this morning, it first has to moisten up the lowest 5,000' through evaporation. So initially, radar echoes will be primarily precipitation aloft that is evaporating before reaching the ground, resulting in "virga" but also setting the stage for rain this afternoon. During this process though, the temperatures in the lowest 5,000' will also cool a bit as humidity rises and the air saturates. When this happens, precipitation that is falling could encounter air that is sub-freezing (provided the cooling pushes the temperature down that far).

The evaporation and encountering of sub-freezing air could result in a bit of sleet occurring here at the surface until the low levels saturate and warm to freezing or above.  That process could take a few hours and looks to be complete by late afternoon.

12Z (6am) Little Rock atmospheric sounding showing dry air in the low levels, saturation above 5,000', and temps above freezing up to 10,000', as described above.

A closer zoom of the lowest 10,000' of the sounding above. Temps are near freezing at 5000', but generally above freezing up to 10,000'. Rain will be the predominant precip type, but some sleet could occur as the low levels moisten and some sub-freezing air is encountered by falling precip as that occurs.

The Bottom Line ("What")

Initial precipitation could be a mix of rain and light sleet through the afternoon. Fortunately, temperatures here at the ground will remain above freezing (though they will likely cool from the upper 30s by a couple of degrees this afternoon). That means any sleet that falls melts and, when mixed with rain, washes off, so no significant impacts are expected and roads (even the elevated ones) should fare well.

After today...

Looking a bit further out, mainly light rain is expected to continue off and on throughout the night (as temperatures remain steady above freezing), tomorrow (as temperatures rise just a bit into the lower 40s), and Friday night (as temps rise even more, perhaps to near 50).  On Saturday, as developing low pressure moves by to our west, the Mid-South will get into the "warm sector" of the low with southerly wind pushing temperatures well into the 50s (models think perhaps the 60s). Heavier rain and some thunderstorms will be the result, ending as a cold front moves through Saturday afternoon. Behind the front, MUCH colder air moves back in as another Arctic high pressure system builds into the region. Sunday will be cold and windy with temperatures possibly falling into the 30s during the day. Now if we can just get these cold temperatures and precipitation to line up better!

2015 starts off wet with 2" or more of rain expected through January 3.

Follow us on social media all day for any reports of sleet (feel free to send your reports) and keep an eye on your MWN mobile app for the latest conditions, radar and forecast. You can also send your precip type reports via #mSpotter in the app or the mPing app. Both are very helpful to us!

Erik Proseus
MWN Meteorologist

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