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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