Sunday, March 29, 2015

From snow to storms - spring returns to the Mid-South

Snow and 40+ degrees??

Wasn't yesterday's snow weird?? I drove through a pretty steady graupel shower around 2:45 yesterday afternoon in Bartlett with temps in the low 40s. Some of you reported sleet or snow shaped like "round balls" yesterday - that was graupel, or "dippin dots" as we are known to call it. The reason for this phenomena with temps above 40 was because the air quickly dropped below freezing by about 1000-1500' up. Thus precip fell as snow with partial melting in the lowest layer of the atmosphere, forming the unique precip type that mixed with sprinkles and snowflakes.

Graupel in Oxford, MS at about 3:30 Saturday. Photo courtesy @larryh921on Twitter.

But now that that is over, it's time to welcome spring back to the Mid-South! And we'll welcome it back, less than 36 hours later, with thunderstorms.

The overall pattern

You will probably be familiar with the sound of thunder by week's end, as it looks like there may be multiple rounds of thunderstorms. The overall pattern will put us in the "warm sector" with low pressure in the Plains and southerly flow across the region for much of the week, starting Tuesday. Impulses in the atmosphere could spark a few rounds of storms, mainly Wednesday through Friday, before a decent cold front finally moves through right before we head into Easter weekend, clearing out in time for a pretty decent weekend it appears.

The pattern this week will mean a few things: 1) much warmer air this week - we're talking lots of 70s! 2) southerly wind that brings more humidity (you probably won't need the lotion as much this week), and 3) those scattered t'storms, a few of which could at times be strong. It's too early to time out these impulses that might bring a few strong storms, but this is just an early heads up.

Tonight's thunderstorms

As for the first round that starts off the week, that happens tonight. A cold front will move through the area just after midnight, which will prompt storms to form, likely right over the metro. The Memphis metro is in a MARGINAL risk of severe storms, or category 1 out of 5. The marginal risk is driven by a 5% probability of hail larger than 1" within 25 miles of any point in the metro. Given that the probability of severe hail within 25 miles of the a point in the metro on April 1st is roughly 1%, this means that our risk of severe hail is about 5 times normal for this time of year.

A reminder of the "new" severe weather outlook classification system. We have a Marginal Risk of hail storms tonight.

A Marginal Risk of severe storms exists ahead of a cold front tonight from the Mid-South (star) to north TX.

The aforementioned cold front that arrives overnight won't run into sufficient warm, moist Gulf air until it gets pretty close to the metro, as most of the ingredients for storms (moisture, instability, and some wind shear) will exist along and south of the I-40 corridor. Thus, the front may be dry, or perhaps just bring a few showers, as it approaches our area. Once it gets close, I expect scattered storms to fire with the necessary lift that the front provides. The most likely area to see storms capable of producing hail will be in north MS, though a few can't be ruled out north of the TN/MS state line. The best timing for storms appears to be between 10pm-4am, though by 1am or so, the threat exits west TN and Crittenden Co. and is confined to north MS.

Instability, a necessary ingredient for storms, is measured here by CAPE, which will be present at 10pm basically along and south of I-40. North MS and southern AR has the highest available energy to fuel storms. With no CAPE to our north, there is little chance of thunderstorms as the front approaches, until it gets to the metro. Graphic courtesy WxBell.

Simulated radar from the HRRR high-res model valid at midnight, showing a broken line of storms from central AR along the TN/MS state line. The cold front will be where the lighter rain (greens) are just to our north. Graphic courtesy WxBell.

This week

Once the front clears the area, clouds depart with it and tomorrow looks to be a perfectly beautiful spring day - sunny and 70! Tuesday may also stay mostly dry, and if it does, we'll look for highs to get into the mid 70s. By Tuesday night or Wednesday, Gulf moisture-laden air is back in place and warm temps will combine with passing impulses to bring the possibility of scattered storms each day until another front moves through late week. For those looking ahead to Easter Sunday, conditions at this time appear dry and cool, but not cold like this morning. Being a week out, that could surely change. Stay tuned!

Erik Proseus
MWN Meteorologist

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Friday, March 27, 2015

Wait, I thought winter was over! The four-letter 'S' word returns...

I'm reminded of an elementary school song (that has always annoyed me as a parent) that goes like this: "This is the song that never ends, yes it goes on and on my friends...", etc. The worst part is that the lyrics are such that it repeats ad nauseum. Despite some recent bouts of spring weather, it seems a slight tweak to those words could apply. "This is the winter that never ends, yes it goes on and on my friends..."

Cold temperatures

Many of us woke up to frost this morning as temps fell into the mid to upper 30s. Now a Freeze Warning is in effect for areas northeast of Shelby County (including Tipton and Fayette Counties) and a Frost Advisory for the rest of the area Saturday morning. A repeat of these cold conditions can be expected Sunday morning until finally a bit of a pattern shift will mean some warmer temps return.

Freeze Warning tonight for the counties in light blue. Frost Advisory for the darker blue counties including Memphis and Shelby County.

But that's not all...

However, cold is not all we're dealing with unfortunately. Yes, we're putting a chance of snow in the forecast for tomorrow - March 28th.  I've been looking at the possibility all week actually, and doing my best to ignore it like a middle school pimple, in the hopes that it goes away. Alas, it hasn't. Kudos to the GFS model for not budging all week on the upper-level disturbance that brings the precip chance tomorrow.

Our favorite response in Facebook comments to this story... :-)

Atmospheric setup

The setup looks like this: the pattern that brought brutally cold air and rounds of ice and snow to the eastern U.S. over the past couple of months has re-appeared. It features a large trough of low pressure in the upper and mid-levels east of the Mississippi River and a ridge of high pressure over the western states. The Mid-South happens to be positioned in the "sweet spot" - northwest flow between the ridge and trough where the jet stream is setup and upper-level disturbances track like trains on an atmospheric train track (one such disturbance is responsible for our showers today in nearly the same setup).

At 500mb (18,000') a large ridge (and warmer air) is to our west, while a trough (and cooler air) covers the Midwest and Northeast. The Mid-South is in "northwest flow" with wind blowing from the northwest. Graphic courtesy WxBell.

At 30,000' (300mb), the huge dip in the jet stream over the eastern U.S./Canada is evident with the Mid-South on the western periphery of that trough. The let stream overhead is the "train track" for upper level disturbances to move along.
As we head into tomorrow, we'll start off a few degrees colder than today, and with increased cloud cover and a bit better chance of precip, surface temperatures won't climb quite as quickly tomorrow. In addition, temperatures at 5000' (a measuring stick of sorts for winter weather) are well below freezing, meaning that precip that falls through that level is snow.

Precipitation forecast by the GFS model between 7am-1pm Saturday, along with 5000' temperatures in the red/blue lines. The 5000' freezing line is sold blue and southwest of the metro. Temps at this level over Memphis are about -4°C (28°F). Precip at this level is snow, and falling into slightly warmer air. 

The flies in the ointment

There are two main model discrepancies to consider: 1) the height of the freezing level above ground and 2) the exact track of the main axis of precip. In the colder solutions that promote a better chance of snow, the freezing level is closer to 500-1000' (low enough to get snow at the surface), while in the warmer models, it's closer to 2000' (more of a chance of the snow melting before reaching the ground). The exact track of the narrow band of precip that is expected is also hard to determine, but appears to be from northeast AR across the metro into north-central MS.

The track of the precip on the GFS model is in the previous graphic. This one shows the NAM model track with "simulated radar" valid at 1pm. It is a little warmer and indicates more rain than snow possibilities.  It also has the precip slightly southwest of the GFS track.

Bottom line

So how do we think this plays out? The most likely scenario sees a light rain/snow mix beginning after 8am with temperatures in the mid 30s. As temps slowly rise to near 40, precip should change over to just rain by noon or so. Because rain is mixed with snow, precip is light, and temperatures are above freezing, no accumulation is expected, especially on roads. A low probability exists for a dusting on grass/mulch beds, etc. but this would mainly be to the northwest of the metro in northeast AR. Tomorrow afternoon sees a chance of rain showers continuing until about mid-afternoon with temperatures remaining in the 40s. It'll be a cold day.

Another word on near or below freezing temps

Besides the snow, for those who have tender vegetation already in the ground, frost (or a light freeze east of the Bluff City) is possible tonight and again Sunday morning. Make plans to cover those plants. By Sunday afternoon, we should be back in the 60s and hopefully FINALLY putting winter in the rearview mirror! By the way, the average last freeze at Memphis International Airport is March 19, but it's March 28 (tomorrow) at the Agricenter, which is also representative of most of the suburbs. The latest snow ever recorded in Memphis is April 25, so this is not unprecedented by any means. I personally am looking forward to 70s again next week!

Erik Proseus
MWN Meteorologist

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Monday, March 23, 2015

Spring thunderstorms precede a weekend "blackberry winter"

9:45am Tuesday - SPC graphics updated for enhanced severe weather risk to our west.

Signs of spring have taken hold in the Mid-South, such as blooming dogwoods and daffodils and the smell of fresh mulch. It has been an unusually quiet severe weather season nationwide featuring no severe weather watches or tornadoes so far this month. That could change in the next couple days as a large-scale upper level trough and associated cold front march through the Plains into the Mississippi Valley through Thursday. The Storm Prediction Center has placed Enhanced Risk (category 3 of 5) areas in the Ozarks Tuesday and over the southern Plains Wednesday, while a Slight Risk (category 2 of 5) extends east to areas just north of the Mid-South.

Tuesday's severe weather risk areas as posted by the Storm Prediction Center

Wednesday's severe weather risk areas as posted by the Storm Prediction Center

Mid-South Impacts

The system responsible for the possible severe weather will move into the Mid-South late Wednesday night into Thursday morning. The ingredients for severe storms will diminish some as the cold front approaches early Thursday morning, thus severe weather is not expected in the Mid-South. However, there will be a decent chance of thunder overnight Wednesday. Behind the cold front, rain will be likely on Thursday, tapering by afternoon. Temperatures well into the 70s ahead of the front will remain in the 50s on Thursday, some 20° cooler than Wednesday.

Once the frontal system clears, the large trough will settle over the eastern U.S., not unlike a good part of the winter. This will mean very cool temperatures for late March with highs again in the 50s Friday and near 50 ° on Saturday. Mornings will also be unseasonably cool Saturday and Sunday in particular with lows well into the 30s expected! Some would call this a "blackberry winter" (not the troubled Blackberry that you use for work e-mail, the fruit...) or a "dogwood winter," referencing the flowers in bloom when the cold snap hits. We'll just call it too cold!

Frost is probable especially outside the city and a few hours of sub-freezing conditions are possible in the coldest outlying areas. We would suggest holding off another week if you haven't already planted plants susceptible to frost. Fortunately, it appears the cold streak will be quick-hitting. We should be back into the 60s to start next week. (By the way, the average last freeze in Memphis is March 22 and the latest 32° reading ever recorded was April 16. These dates are later outside the city and in rural areas - for instance at the Agricenter the average is March 28 - so this weekend's cold snap is not totally outside the norm, especially with a late winter this year.)

Side note on crap apps

A couple of people have mentioned seeing a snowflake in the extended forecast on their iPhone weather app today. This is why we recommend using human-powered weather instead of an app driven by a computer model. YES, one of the computer models dropped some light snow over us on Saturday on one of its four runs today. It was gone with the next set of data. We're not fickle enough to put that in the forecast then take it right back out and HIGHLY DOUBT we'll see any snowflakes this weekend. We recommend you...

Erik Proseus
MWN Meteorologist

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Changes to severe weather products coming, including Impact-Based Warnings

There are several recent and upcoming changes to severe weather products issued by both SPC and local National Weather Service (NWS) offices, including Memphis, that you need to be aware of.

SPC Convective Outlooks (effective date: October 2014)

We've talked about the changes made last October to SPC's Day 1-3 convective outlooks in a previous blog. To recap, the three-tier system of Slight, Moderate, and High risk categories has become a five-tier system, adding Marginal and Enhanced categories on either side of a Slight risk. We invite you to read the linked blog above for details on these changes. We'll pair the 5-point numerical value of the forecast category when discussing the risk for the Memphis metro to help eliminate confusion associated with the new names.

In addition to the Day 1-3 outlooks, the Day 4-8 experimental outlooks issued by SPC previously only displayed areas with a 30% probability of severe weather during this period. In December 2014, these outlooks were also modified to display areas under either a 15% or 30% risk of severe storms, which provides meteorologists and the public with a heads up to lower risk severe weather areas in the day 4-8 period that weren't previously highlighted.

Impact-Based Warnings (IBW) (effective date for Memphis: April 1, 2015)

While SPC is responsible for nationwide issuance of Tornado and Severe Thunderstorm Watches, local NWS offices issue the warnings for their area of responsibility. Starting April 1, the Memphis office of the NWS will join many other offices across the nation in an experimental change to the format of Tornado and Severe Thunderstorm Warnings that began a couple of years ago with a handful of offices in the central U.S.

Areas where impact-based warnings will be used in 2015

Called "impact-based warnings," the format change was made in response to the findings of a service assessment done after the Joplin, MO tornado in May 2011. That assessment found that "credible, extraordinary risk signals prompt people to take protective actions." One of the intended outcomes of IBW is to motivate proper public response to warnings by distinguishing between low and high impact events. In addition, it allows the warning system to be optimized within the existing infrastructure, realigning the message in terms of societal impacts, thereby communicating recommended actions more concisely.

The changes will have no effect on the mechanics of warning polygons, but will provide more detailed hazard and action information within Tornado and Severe Thunderstorm Warnings. That detail will include the impacts the severe storm could cause, which will be reflected in the updated format of the warning bulletins. The changes include the addition of "event tags" at the bottom of each Tornado and Severe Thunderstorm Warning. These tags include "Tornado" and "Tornado Damage Threat," which are described below. In addition to those tags, Severe Thunderstorm Warnings will carry maximum hail size and wind speed tags. Tornado Warnings will also carry a maximum hail size tag.

The Tornado tag will have three possible options:

  • "Possible" - Reserved for Severe Thunderstorm Warnings, indicating that the storm has some potential to produce a tornado, but forecaster confidence is not high enough to issue a Tornado Warning.
  • ""Radar Indicated" - Evidence on radar and near storm environment is supportive of a tornado, but there is no confirmation.
  • "Observed" - A tornado is confirmed by spotters, law enforcement, etc.
The Tornado Damage Threat tag will also have three options:
  • No tag - Used most of the time when tornado damage is possible, but the tornado is expected to be short-lived.
  • Considerable - Used rarely, when there is credible evidence of an ongoing or imminent tornado capable of producing considerable damage. Tornado is expected to be long-lived.
  • Catastrophic - Used exceedingly rarely, when a severe threat to human life and catastrophic damage is occurring. Only used when reliable sources confirm a violent long-lived tornado. This tag will trigger the "Tornado Emergency" warning.
The example below summarizes the possible tag options and also shows the Impact bullet in the warning that describes the threat to life and property.

Some additional examples of warnings using the new tags are shown below (changes are highlighted in red).

Severe Thunderstorm Warning with new tags.

Tornado Warning for radar indicated tornado.

Tornado Warning for an observed tornado producing considerable damage

Tornado Emergency for an observed tornado producing catastrophic damage.

More information from the NWS on the 2015 IBW Demonstration is contained within the YouTube video below created by NWS-Memphis and on this website.

Severe weather watches add "Summary" section (effective date: April 14, 2015)

Finally, beginning April 14, all Tornado and Severe Thunderstorm Watches issued by SPC will contain a "Summary" section. According to SPC, the summary will provide a "general 1-2 sentence statement of the severe weather expected in and close to the watch area. This new section facilitates consistent, forecaster-driven, concise communication for public consumption." For more information on this change, please see this page from the SPC.

Erik Proseus
MWN Meteorologist

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Wednesday, March 18, 2015

MWN Lightning Round: A trio of astronomical events on Friday!

The MWN Lightning Round returns! This Friday, March 20, will feature not one... not two... but THREE astronomical events!

Vernal Equinox - SPRING!

The official first day of spring is Friday, March 20. Specifically in Memphis, the equinox occurs at 5:45pm CDT, when the sun crosses the equator from south to north. For the next 6 months, the sun will remain north of the equator, resulting in the usual hot, sultry summer in the Mid-South!

The orientation of the sun to the earth on the vernal equinox

In an odd technicality, while equinox means "equal parts day and night," the length of the day in most places is not actually a precise 12 hours on March 20. In Memphis, our 12-hour day was on March 17, when the sun rose and set at 7:09 (am and pm respectively). The reason for this is because the earth's atmosphere refracts, or bends,  sunlight, such that we can actually see the sun rising (and setting) a little before (after) it technically occurs. For more details, we invite you to check out this article from

The Missing Supermoon

A supermoon occurs on Friday! But don't get too excited... A supermoon, or perigee moon, occurs when a full or new moon makes its closest approach to Earth, thus making it look larger than usual. By a looser definition, it occurs "with the moon at or near (within 90% of) its closest approach to Earth in a given orbit." By this definition, there are 6 supermoons in 2015. However, this month's supermoon, which also coincides with the equinox and an eclipse (see below) is a NEW moon, meaning it is 100% obscured by the Earth's shadow. Thus, the "missing supermoon!"

Total (solar) eclipse of the heart

The third in our astronomical trilogy will require an expensive plane ticket to be able to see in person, as it won't be visible in the Americas either. (Basically, we realized we're telling you about a bunch of stuff you won't be able to experience firsthand...) A total solar eclipse will occur in the wee hours of the morning Friday with best viewing over northern Europe and into Greenland.

A solar eclipse occurs when the Earth, moon, and sun all line up in such a way that the moon blocks the sun for viewers on Earth, either partially or totally (thus the type of eclipse). The next eclipses visible in Memphis will be a partial lunar eclipse in the early morning hours on April 4 and a total lunar eclipse on September 27. The next solar eclipse viewable locally occurs August 21, 2017 - a near total eclipse! (We'll be sure to remind you...)

Cool astronomy stuff like these events (at least the supermoon and eclipses) can be watched live, or later, on the internet if you can't shuck out the cash to fly to where they are visible. There are several good sites, but we especially like

So there you are - 3 astronomical events all occurring on the same day!

Erik Proseus
MWN Meteorologist

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Monday, March 16, 2015

The Results Show: Reviewing our 2014-2015 Winter Outlook

Now that it is mid-March with highs in the mid 70s, we can probably safely safe winter 2014-'15 is over for the Mid-South. That doesn't mean we won't see temps drop below freezing for a couple of hours some morning or frost on the ground. In fact, on average the last freeze date is still about a week away (March 22 at Memphis International Airport, later in outlying areas), but we don't see it getting that cold this week!

Methodology behind this year's outlook

So, in the name of full transparency (and perhaps curiosity more than anything), I thought it would be educational to re-visit the winter outlook I prepared early last November. As I said then, "if I got paid for accurate long-range outlooks, my family would be hungry!" As a reminder, my outlook was based on a few key pieces of data:
  • 10 analog years with weak El Nino conditions (1952, 1953, 1954, 1959, 1970, 1977, 1978, 1988, 2005, 2007)
  • Recent research by NWS-Memphis on El Nino impacts in the Mid-South
  • Research and 2014-'15 winter outlooks composed by WeatherBell, WeatherTrends360, and NOAA
Going into this winter, there was a better than 50/50 chance we'd see weak El Nino conditions before the season was over. As it turns out, NOAA declared just this month that El Nino had officially arrived. So while it didn't start until March, it actually takes a few months of above average Pacific sea surface temps to make it official. We were basically dealing with weak El Nino conditions in the Pacific for at least part of the winter.

The MWN Winter Outlook

Here's the outlook I made November 10, 2014 for the upcoming winter:
  1. Temps slightly below to below average (possibly as cold as 2013-'14)
  2. Precipitation near average
  3. Snowfall near to above average (average is about 4")
  4. Periods of large temperature swings and possible severe weather
For the sake of this discussion, since we had some of the earliest measurable snowfall on record last November and the biggest snow/ice events into the first week of March, I'm calling "MWN Winter" the period from Nov 10-Mar 10. I'll also look at the period meteorologists define as winter, which is Dec 1-Feb 28.

The Results... drum roll please

Let's look at each point in succession:
  1. "Temps slightly below to below average" - CORRECT - The most recent 30-year average temperature for Nov 10-Mar 10 is 45.6°.  This year's average was 42.0°, which is more than 3.5° below normal, but not quite as cold as last year (41.3°), which will be remembered for a January that was colder than any since the mid 1980s. This year, February was #7 coldest on record. In 141 years of record-keeping, this period ranked #26 coldest, or in the top 20%. For meteorological winter, this year's average was 41.1°, which was 2.7° below the most recent 30-year average of 43.8°. 
  2. "Precipitation near average" - INCORRECT - Total precipitation for the Nov 10-Mar 10 period was 13.22", which was 6.28" below the latest 30-year average. In fact, parts of the metro were classified as being in "severe drought" during this winter. For meteorological winter, precipitation totaled 8.25", or 5.63" below normal.
  3. "Snowfall near to above average" - CORRECT - Snowfall (which includes sleet, but not freezing rain) averages 3.8" a year in Memphis based on the 30-year climatological record used by the NWS. For the entire winter (our Nov 10-Mar 10 window), total snowfall was 6.1". Since some of that was outside the traditional "meteorological winter" period, the total is higher for MWN winter than meteorological winter (2.3", or 1.1" below average). We firmly believe that the 3.1" in March in 0.2" in November (which was some of the earliest on record) should count though!
  4. "Periods of large temperature swings and possible severe weather" - PARTIALLY CORRECT  - Starting with the second point, there were no severe convective storms this winter, which was what we were alluding to in this outlook. However the series of ice and snow storms that affected the Mid-South from mid-February to early March arguably had a wider impact on the entire metro than a round or two of severe thunderstorms would have. I believe these were "severe" for winter, but will only take half-credit for them! As to the point of large temperature swings, I think I nailed this one. Looking strictly at daily average temperatures (which averages the high and low for a day) between Nov 10-Mar 10, there were a total of 30 instances in which the daily average temperature varied by more than 10°F on consecutive days (many of them were much more than 10°). This is not a swing of 10° between one day's high (or low) and the next day's high (or low), it is the average daily temp moving by that much, which is harder to accomplish. All in all, despite the general cold weather pattern, we saw frequent large temperature swings over the course of the winter, from warm to cold, or from cold to colder!
In sum, 3 of the 4 points made in this year's winter outlook were correct, which surprised even me when I went back and re-visited the winter numbers. I can't guarantee that kind of accuracy on winter outlooks going forward, but this year I seemed to be on the right track!

What were your overall impressions of this past winter? Comment below or drop us a Facebook comment or tweet! We'd love to hear from you!

Erik Proseus
MWN Meteorologist

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Thursday, March 12, 2015

Winter's over - time for spring weather!

Now that we've successfully navigated through three weeks of winter weather, but perhaps not the potholes left behind (info on potholes from TDOT), it's time to turn our attention to spring! Spring weather means two things in the Mid-South: warmer temperatures and chances of thunderstorms.

Gulf low brings unsettled weather

This morning, low pressure is located over the northwestern Gulf of Mexico and will move slowly north into the western Mid-South by Friday. If it were a few months later, we'd be looking more closely at a system like this for subtropical or tropical characteristics

This low will mean a chance of showers today and increasing rain chances heading into tonight and Friday. Thunderstorms will also be possible overnight and during the day Friday as warm, moist, unstable Gulf air rides over the area. In our area, no severe weather is expected, though some strong storms might be found to our south - across areas from Houston to New Orleans to Jackson, MS to south AL and the Florida Panhandle - today and tonight.

Surface map at noon Thursday showing the Gulf low near Houston. Showers will spread well north of the low into the Mid-South today.

By noon Friday, the low will move east of Dallas, lifting more moisture into the region with chances of thunderstorms as well. Rain will be heavy at times.

Heavy rain threat

In addition to the chance of thunderstorms, heavy rain will be possible. With periods of heavy rain, saturated ground from recent snowfall, and stream and river levels running high, some flooding will be possible. A Flood Watch has been posted from this afternoon through early Saturday morning for the metro as 1-3" of rain is expected.

Precipitable water values show the amount of available moisture in the air above us. Values of 1.5-2.0" this time of year are very high and indicate the potential for heavy rain. The image above is valid at noon Friday as low pressure sits over east TX. Graphic courtesy WxBell Analytics.

Weekend outlook

As the low pressure system lingers over the Mid-South and weakens Saturday, it will remain cloudy with a few lingering showers during the day. The entire system moves out by Sunday, resulting in high pressure taking over and more sunshine. The good news in all this is that temperatures will remain warm - mainly in the 50s and 60s.

Long-range outlook

By the start of next week, when many of your kids will be on spring break, the weather looks great! We'll see lots of sunshine, spring-like high temps (60s) and cool mornings (40s), and no freezing. The next weather-maker looks to hold off until late next week once we get through the next few days. Click here for the complete MWN Forecast or check it out on our mobile app.

Erik Proseus
MWN Meteorologist

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Tuesday, March 10, 2015

February 2015 Climate Data and Forecast Accuracy

February Recap

Temperatures were the big story in February, with the month ending as the 7th coldest on record. In fact, the second half of the month was the coldest comparable period in recorded history, breaking the previous record by over 5 degrees. The previous three months were very dry with severe drought in some parts of the metro, though near normal precipitation in February relieved some of the drought conditions. The 3-month severe weather drought continued through February, though wintry precipitation visited the metro multiple times in the second half of the month.

National temperature anomaly (departure from normal) for February shows the eastern 2/3 of the nation well below normal for the month. Graphic courtesy WxBell Analytics.

For the three-month period defined as "meteorological winter" (December-February), Memphis International Airport had an average temperature of 41.1 degrees (2.3 degrees below normal), 8.25" of precipitation (5.86" below normal), and 2.3" in snow (1.1" below normal).

Memphis International Airport, Memphis, TN

Average temperature: 36.2 degrees (9.3 degrees below average)
Average high temperature: 45.0 degrees (9.7 degrees above average)
Average low temperature: 27.4 degrees (8.9 degrees below average)
Warmest temperature: 66 degrees (14th)
Coolest temperature: 13 degrees (19th)
Records set or tied: The second half of February (15th-28th) was the coldest on record and the average temperature for the month was the 7th coldest on record. The high on the 23rd (28 degrees) tied a record (1889) for the lowest maximum temperature on record for the date.
Comments: Three days had high temps below freezing and 21 days had lows below freezing (11.5 days above average).

Monthly total: 4.35" (0.04" below average)
Days with measurable precipitation: 7
Wettest 24-hour period: 2.29" (20th-21st)
Total Snowfall: 2.3" (1.0" below average)
Records set or tied: None
Comments: Four days had precipitation above 0.50". There was no thunder reported at the airport for the third straight month. There were four days with snow reported, four days with freezing rain reported and two days with sleet.

Peak wind: South/41 mph (21st)
Average wind: 9.8 mph
Average relative humidity: 59%
Average sky cover: 70%

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

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 34.8 degrees
Average high temperature: 45.1 degrees
Average low temperature: 25.8 degrees
Warmest temperature: 65.0 degrees (14th)
Coolest temperature: 11.0 degrees (19th)
Comments: None

Monthly total: 4.58" (automated rain gauge), 4.64" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 7
Wettest date: 2.13" (21st) (via automated gauge)
Total Snowfall: 1.6"
Comments: Winter precip occurred on 4 days (16th, 17th, 20th, 22nd) totaling 1.35" of freezing rain and sleet and 1/4" of snow.

Peak wind: Northwest/26 mph (1st)
Average relative humidity: 71%

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

MWN Forecast Accuracy

MWN average temperature error: 2.41 degrees
MWN forecast temperatures within 2 degrees of actual: 67%
MWN average dewpoint error: 3.05 degrees
MWN forecast dewpoints within 2 degrees of actual: 48%

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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Friday, March 6, 2015

Recap of the March 4-5, 2015 #MemSnow Winter Storm

A major late season winter storm, the last in a long string of winter weather events that started in mid-February, dropped significant amounts of sleet Wednesday evening before changing to snow Wednesday night. By the time most folks woke up Thursday morning, the Mid-South had become a winter wonderland with 2-6" of snow on top of about 1/2"-1" of sleet.

In it's wake, #StupidCold Arctic air pushed in once again. Temps remained in the 20s to near 30 Thursday, though afternoon sun started to help interstates improve. However, temperatures plummeted this morning, setting daily low temperature records and threatening all-time March cold weather readings. Primary roads should improve this afternoon as the mercury climbs above freezing with abundant sun. Secondary roads and side streets, as well as shaded roads, will take another couple days to fully melt. Spring is just around the corner though, as temperatures recover into the 40s Saturday, 50s Sunday, and 60s next week with no hints of any frozen precipitation in the forecast! Hallelujah!

A few graphics that sum up the event:

Coldest temps ever recorded in Memphis in March.  This morning's official low of 15 will tie for #4.

Top 10 single day snowfalls in March. Memphis officially recorded 3.1" on Thursday, putting it at #8.

Preliminary graphic from NWS Memphis with snow/sleet totals across the Mid-South. Memphis Int'l ended up at 3.6" total, the Agricenter had 4.1", and MWN in Bartlett received 4.0".

With the widespread heavy snow, the snow counter, which counts days since last 1" snow reading, it officially retired!

Snow cover can be easily seen in this morning's visible satellite image. The only clouds are in the bottom right of the image, while the rest of the "white" is snow. It's neat to be able to pick out rivers/tributaries in the midst of the snow!

U.S. snow cover as of this morning. A huge swath of snow blankets many southern states as meteorological spring begins!
WMC-TV put together a nice recap of pics and social media posts on the storm shown below. Check out some of the cool snowmen! You can also scroll our timeline on Facebook and Twitter for lots of pics and facts.

Here's to the REAL start of spring!

Erik Proseus
MWN Meteorologist

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Tuesday, March 3, 2015

Tuesday night update on Wednesday night's winter storm [video blog]

15 minute video blog embedded below with details on the Wednesday night winter storm as we see them as of 7pm Tuesday night.

Details continue to come together, though some model solutions still seem to be a little questionable. Despite that, impacts are expected to be significant Wednesday night and Thursday. The main change from previous updates is a delayed onset of winter precipitation and slightly enhanced precipitation amounts.

And for those that want the bottom line, a few graphics:

Approximate position of the freezing line indicated by black dashes, indicating roughly when precipitation changes from rain to freezing rain, followed a few hours later by sleet, then snow after midnight.

Bitterly cold temperatures will end the week, followed by a steady warming trend. Roads should improve markedly (especially primary roads and interstates) on Friday with March sun and some traffic.

More updates Wednesday and throughout the event... follow us on social media and

Erik Proseus
MWN Meteorologist

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Monday, March 2, 2015

Monday night details on Wednesday's winter storm [video blog]

15 minute video blog embedded below with details as we see them as of 9pm Monday night. TIMING, PRECIPITATION TYPES, AND AMOUNTS SUBJECT TO CHANGE. The general pattern seems to be coming together though.

And for those that want the bottom line, first a graphic from the NWS and then our call on this storm and potential impacts:

More updates Tuesday and throughout the event... follow us on social media and

Erik Proseus
MWN Meteorologist

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Sunday, March 1, 2015

March comes in like a lion, or maybe a snow leopard

Welcome to the first day of meteorological spring! We in the weather business compile seasonal weather and climate stats according to "meteorological seasons." March-May is considered "spring." Unfortunately, the first week of March looks more like a continuation of winter (with a one day exception) than spring.

Fe"brrrr"-ary recap

First, a brief recap of the month since the groundhog poked his head out of the burrow. February seemed to be when winter STARTED this year, particularly the last 2 weeks. The tables below showed that the month was preliminarily the coldest since 1978 and the 7th coldest since 1875 in Memphis. That was driven mainly by the last two weeks of the month (when normal highs are in the upper half of the 50s), which was the coldest last half of February on record, and it wasn't even close, shattering the previous coldest by nearly 5.5°F!

So I know we all want winter to end after the last two weeks. Unfortunately, except Tuesday, the first week of March looks to continue the recent cold. The month will be coming in like a lion (or maybe a snow leopard) this year!

Early this week

An inclement few days is ahead as a frontal system wavers through the area to start the week. Showers will occur today as a cold front draws near. That front moves through tonight with rain expected. Fortunately, temperatures  should stay just above freezing tonight so no icing is expected in the metro, but wind chills will be in the 20s Monday morning. A few showers will also occur Monday with a north wind  holding temperatures in the mid 40s (normal is near 60).

As low pressure develops in the central U.S., the front will pull back north overnight Monday night with temperatures rising and more showers expected. By Tuesday morning, we'll be above 50 with a south wind kicking up. Tuesday, although wet, will be the warmest day of the week with highs well into the 60s. Thunderstorms will be likely though Tuesday night as yet another cold front (this one with Arctic air behind it) moves through the region. (At this point, they do not look severe.) The Arctic reinforcement arrives Wednesday morning.

The NWS indicates a cold front moves through the region Tuesday night, followed by a reinforcing Arctic front Wednesday morning as shown above.

Wednesday - too early to call for sure

Wednesday's high will occur at midnight and temps are expected to fall all day. We should see the mercury in the 40s Wednesday morning as we wake up, but look for temps to fall to freezing sometime during the day Wednesday, with precipitation continuing.

(Yeah I've used that animated GIF in the past couple weeks already, but is there a more appropriate one?)

So this is where it gets tricky! It's too far out to know exactly when that happens, how fast the low to mid levels cool down (which is critical in precipitation type forecasting), as well as how much precipitation falls into cold air and when it ends. There are model opinions that literally run the gamut, from cold rain to Snowmaggedon (hey, why hide the truth). But these models literally change multiple times a day, and your national weather apps that run on them do too. We will not forecast ice and snow amounts and timing at this time - it's simply too early to know with any certainty! Whatever we would say, we'd be lying.

What we should ALL prepare for, though, is the possibility, perhaps even the likelihood, that another round of winter weather will affect the entire region Wednesday, maybe into Wednesday night. Snow and/or sleet/ice accumulation COULD be significant, but we won't make a call on that yet. In this situation, it's a must to follow trusted sources for weather info and prepare accordingly. Check them regularly. A forecast from Sunday or Monday will most certainly not be right come Wednesday, but trends are important.

End of the week

Looking beyond Wednesday, Arctic air pushs in once again for a few days with lows probably back in the teens and highs in the 30s to end the week. Hopefully this is Old Man Winter's LAST GASP! I know you're over it... so are we!

We'll be keeping a very close eye on it, and when we feel comfortable doing so (maybe late tomorrow) will make a first call on what to expect. Follow us on Facebook or Twitter for the latest info and you can always check our latest forecast on, our mobile apps, or mobile website.

Erik Proseus
MWN Meteorologist

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