Friday, February 12, 2016

A blast of cold, then Valentine's Day precip - but what type?

A very cold start to the week gave way to slightly warmer temperatures to end it, but another Arctic blast is diving south today and will reach the Mid-South tonight. No precipitation is forecast with this Arctic front, but you'll definitely notice it tomorrow as the "feels like" temperatures will be some 30° colder at mid-day than they were today (low 50s vs. low 20s)!


Morning lows will be in the lower 20s with brisk north wind producing wind chills in the lower half of the teens. If you are getting up for an early run... let's just say you won't see me passing you! That's  certainly cold for here, but check out these wind chills to our north at 6am tomorrow:

Wind chill values from the GFS (American) model at 6am CST Saturday. Graphic courtesy WxBell.
Despite sun, temperatures will remain in the mid 30s tomorrow afternoon with wind chills getting no higher than the 20s. That sets the stage for a cold night Saturday night with lows again in the 20s, although the approach of our next weather-maker will throw clouds over the area, acting like a blanket and keeping the mercury from completely bottoming out. This will be key in the forecast for Sunday. That weather-maker will bring precipitation into the region on Valentines's Day. You can already see where this has the potential to go...


You guessed it, we're looking closely at temperatures and timing of precipitation on Sunday. It appears the earliest precipitation will fall across northeast AR and west TN and that it could arrive during the morning hours, when it's still pretty cold.



Points to consider


  1. Precip during the day Sunday will be light, in fact very light in the morning.
  2. There is lots of dry air to overcome near the surface thanks to the very cold high pressure that will be over us prior to the precip arriving. This will serve to evaporate the initial precip as it falls.
  3. Temperatures a few thousand feet up will be warmer than they are at the surface - in fact, above freezing most likely over the metro. That means no snow. The concern is light icing.
  4. Southerly wind will help to push temperatures up in the morning ,despite cloud cover and evaporating precip. The key is, how quickly do they get above freezing?
Here are a couple of models we look at to show you just how close they think the transition from rain to ice will be to the metro during the morning. The red line is the 32° line and the blue line is 35°, both valid at noon. First the mid-day (18Z) GFS model:


Precipitation forecast Sunday morning and noon temperatures from the GFS model. Graphic courtesy WxBell.

And here's the mid-day NAM model, which specializes in short-term forecasts:

Precipitation forecast Sunday morning and noon temperatures from the NAM model. Graphic courtesy WxBell
Too close to call!

What we expect

*IF* we get any icing in the metro, it'll be more likely north (Tipton County) than south (DeSoto County), it will be very light (but it doesn't take much to foul up a flyover), and it will most likely be freezing rain, which produces a light glaze on exposed surfaces. Our official forecast calls for a slight chance of freezing rain or rain Sunday morning. By late morning, temperatures are expected to be warm enough for rain.

Sunday evening into the overnight will be wet. Could be some frog-stranglers and gully-washers out there. Rain will likely continue on President's Day before moving out Monday night. Find some indoor activities for the children. Here are the totals expected from this system over the next 5 days from the NWS Weather Prediction Center:


After moderate temperatures early next week, the good news is that strong southerly flow re-establishes itself and the pattern favors well above normal temperatures to return by mid-week and last at least a few days. Does that mean winter is over? Did it snow on March 5th last year? I'm not calling it just yet...



Erik Proseus
MWN Meteorologist

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Sunday, February 7, 2016

Eastern U.S. trough is bringin' winter back (yeah)

A SUPER day in the weather department today as temperatures push towards the 60° mark thanks to a warm southwest breeze and a good deal of sunshine. A big shift in the upper level pattern takes place this week though, transitioning overnight tonight as an Arctic cold front moves through the Mid-South. Yep, it's bringin' sexy winter back!


On Monday morning, you'll likely notice the difference immediately, even though temperatures won't be any colder than the past few mornings (mid 30s). A strong northwest wind will be in place and keep temperatures from climbing much at all Monday as clouds circulate around a large trough of low pressure that builds south at the upper levels of the atmosphere.

A large upper level trough is depicted in blues in the map above valid at 6pm Monday. Air over the Mid-South will have origins in Canada, meaning a very cold pattern. Under the trough, upper level disturbances will rotate around the low bringing scattered snow showers. The Mid-South will be on the edge of these systems with borderline temperatures to support light snow. Graphic courtesy Pivotal Weather.
Under the trough, scattered snow showers are expected for much of the Midwest, Ohio and Tennessee Valleys, and northeast U.S. The Mid-South will be on the periphery of the coldest air, which in this case is both good and bad. Areas under the deeper cold air will have the best chances of light, but accumulating, snow, but they'll also be bitterly cold, while we'll only be "coat-and-gloves" cold.

Simulated radar from the NAM model valid at 6pm Monday shows the potential for very light precipitation. With temperatures falling to the mid 30s by this time, sprinkles or flurries could result. The blue narrow line is the forecast freezing line. Graphic courtesy Pivotal Weather.

Upper level flow around the main low over the Great Lakes will drive pieces of energy around it like spokes on a wheel. For us, northwest flow will mean fairly dry, cold air, but also low precip chances late Monday into early Tuesday. Most snowfall will occur to our northeast closer to the main low. Graphic courtesy Pivotal Weather.
A forecast sounding (conditions aloft over Memphis) at 3pm Monday shows the temperature (red line) falling below the freezing level (blue line) at about 1200' above the ground with a surface temperatures in the lower 40s. This means that precip would fall from the clouds as snow but would likely melt in the lowest 1000' to rain. Once the surface temperature drops into the mid 30s by sunset, there is a better chance the snow survives the lowest several hundred feet without completely melting.
The trough will hang around for the first half of the week, keeping colder than normal conditions around through that period.

Average surface temperatures from Monday night through Saturday night will be well below normal across the eastern half of the country and well above normal out west, reflecting the upper level pattern of a large trough of low pressure in the east and ridge of high pressure in the west. Graphic courtesy WeatherBell.
Once the trough moves east, upper level ridging will move in, bringing temperatures back to near or above normal by the end of the week into next weekend. Other than the Monday to early Tuesday threat of very light precipitation, the pattern supports a dry forecast until late next weekend.

Trends indicate a warming trend back to near or slightly above normal temperatures by next weekend, according to the American Ensemble model system. Graphic courtesy WeatherBell.
Erik Proseus
MWN Meteorologist

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Saturday, February 6, 2016

January 2016 Climate Data and Forecast Accuracy

January Recap

After a very warm end to 2015, the pattern shifted to start the new year and January temperatures ended up almost exactly "average" for the month. However, by daily averages, a relatively cold month was actually offset by about a week's worth of well above average days spread throughout the month. Precipitation was well below normal with one significant winter threat on the 22nd that ended up producing a coating of snow and freezing rain across the southern metro and up to 3" in the far northern metro. Thunderstorms rumbled through the metro on the 9th, which was the wettest day of the month and produced a couple of small hail and high wind reports, and on the 21st.

Graphic produced by NWS-Memphis showing approximate snowfall amounts on January 22.

Memphis International Airport, Memphis, TN

Temperature
Average temperature: 41.1 degrees (0.1 degrees below average)
Average high temperature: 50.4 degrees (0.6 degrees above average)
Average low temperature: 31.8 degrees (0.8 degrees below average)
Warmest temperature: 73 degrees (31st)
Coolest temperature: 18 degrees (11th)
Records set or tied: Tied record warm minimum temperature: 61 degrees (January 31).
Comments: None.


Precipitation
Monthly total: 2.27" (1.71" below average)
Days with measurable precipitation: 7 (2.5 days below normal)
Wettest 24-hour period: 1.31" (9th)
Total Snowfall: 0.3"
Records set or tied: None
Comments: Despite only 0.3" of snow at the airport, surrounding areas, especially in Tipton County, received nearly 3" of snow on the 22nd.


Miscellaneous
Peak wind: Southwest/40 mph (31st)
Average wind: 8.8 mph
Average relative humidity: 64%
Average sky cover: 50%

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature
Average temperature: 39.8 degrees
Average high temperature: 49.7 degrees
Average low temperature: 29.8 degrees
Warmest temperature: 72.0 degrees (31st)
Coolest temperature: 17.4 degrees (11th)
Comments: None.

Precipitation
Monthly total: 2.58" (automated rain gauge), 2.73" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 7
Wettest date: 1.24" (9th) (via automated gauge)
Total Snowfall: 0.9" (22nd)
Comments: None

Miscellaneous
Peak wind: South/30 mph (31st)
Average relative humidity: 76%

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

MWN Forecast Accuracy

MWN average temperature error: 2.82 degrees
MWN forecast temperatures within 2 degrees of actual: 58%
MWN average dewpoint error: 2.32 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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Friday, February 5, 2016

National Weatherperson's Day: Not just a day to thank your meteorologist

Today is National Weatherperson's Day. Yes, it really is a recognized day, and no, Hallmark has nothing to do with it (have you ever seen a Happy National Weatherperson's Day card??). I hear that broadcast meteorologists around the nation got free food from McDonalds. I wasn't so lucky, but I'm not holding a grudge. :-)

National Weatherperson's Day occurs on the birthday of John Jeffries, one of America's first weather observers in the late 18th century, and recognizes the mostly behind-the-scenes efforts of thousands of forecasters who work to make sure that you are informed on both a routine basis, but mostly in those times that really matter. While the most visible work is done by broadcasters who appear on your televisions each day, an even bigger force of nature is working out of the limelight to produce the data that is used, the models that are our guide, and the watches and warnings that get relayed to the you, the public, to keep you safe. The U.S. is fortunate to have the best weather forecasts and warnings, that are also the most widely available, in the world. Kudos to all who share a similar passion and dedication to their craft as I! (For more on the role of the National Weather Service in the weather enterprise, see this Weatherperson's Day article.)

Super Tuesday Outbreak Anniversary

February 5th is more than just National Weatherperson's Day though. It is also the anniversary of one of the largest tornado outbreaks on record. On Super Tuesday, 2008, and into the wee hours of February 6th, 87 tornadoes touched down from the Mid-South into the Ohio Valley, killing 56 and injuring hundreds. At the time, it was the deadliest U.S. tornado outbreak since 1985, rivaling the 1974 Super Outbreak and, later, the 2011 Super Outbreak.

Storm reports from Super Tuesday 2008. Red dots are tornadoes. Graphic courtesy SPC.
Locally, an EF-2 tornado touched down in Southaven, MS and traveled northeast into the city of Memphis in the Hickory Hill area, causing heavy damage to the Hickory Ridge Mall and the surrounding area, all while being captured on live TV by a skycam operated by WREG-TV. Further northeast, Jackson, TN will never forget the EF-4 that struck Union University, rendering 80% of the residential living accommodations uninhabitable, but taking no lives despite the dormitories being full of students.

Doppler Radar returns (precip left, wind velocity right) from the DeSoto/Shelby Co. tornado as it crosses the state line. The inverted green triangle shows the approximate position of the strongest radar-detected rotation.

Cirrus Weather Solutions' Birthday

Two years later (2010), on this very day, I officially opened a new business in the state of Tennessee, Cirrus Weather Solutions. It seemed an appropriate day to officially commence operation of a business devoted to keeping Mid-Southerners informed on weather regimes that affect the region and safe during severe weather events. Since then, Cirrus Weather Solutions has served as the umbrella organization for MemphisWeather.net, JacksonWeather.net, and StormWatch+, a mobile service that pushes precise, and fully customizable, severe weather notifications to the public and which was a natural by-product of Cirrus' mission to protect, inform, and educate.

Thank you all for making MemphisWeather.net one of your trusted weather sources! Your feedback (positive and "constructive") allows MWN to bring you the best weather information available for Memphis and the Mid-South. Social media provides an outlet for instant feedback so that we can refine our processes, even during severe weather events, and our mobile apps are one more way we can reach as many as possible when inclement weather threatens. I can't thank you enough for following along, downloading the apps, and keeping me motivated!

Erik Proseus
MWN Meteorologist

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