Sunday, January 13, 2013

Park the ark and prepare for possible light wintry weather Monday

Rain has ended across the metro (FINALLY!) with rainfall totals near 3" since midnight across Shelby County and higher amounts in other locations around the metro. Multiple Flash Flood Watches, Warnings, and Advisories were issued due to rising creeks and rivers and urban flooding on roadways and low-lying areas.  Thankfully now that rain has moved out, water can recede and you can turn in the keys to teh ark you rented.
Doppler  radar estimated rainfall since early Saturday morning.  Many locations saw 3-5" of rain this weekend! 

Questions remain

Our attention now turns to the cold weather and possible precipitation in the cold sector, versus thunderstorms and flooding in the warm sector!  The huge front/trough that moved through early today is still hanging out just to our east and another wave will ride along the front on Monday. However, since we're on the cold side of the front, there are two concerns: 1) how close will the precipitation get (and how much if it gets here) and 2) what will the temperature profile look like when and if it does arrive.  These questions cannot be answered definitively tonight, even though we're less than 24 hours from the precipitation event, as computer models are really struggling with this scenario.
GFS model sounding of the atmosphere at 3pm Monday. Temperature scale along the bottom, height going up, red line is temperature as one ascends above ground. The blue line is freezing. The red line is below freezing  up to about 4,000', then above freezing tot about 9,000', then below freezing again.  This indicates that precipitation that forms around 10,000' will be liquid until it gets below 4,000', then freezes, resulting in a wintry mix (freezing rain or sleet). Not all models agree with this one, thus the lower confidence in the forecast.

What to expect

Given our best educated guess and what little consensus there is in the model data, we expect to see temperatures bottom out in the upper 20s tonight then struggle to reach freezing tomorrow afternoon. (With expected north wind, look for wind chills to stay in the upper teens to lower 20s all day.)  Precipitation will be most likely just southeast of the metro, over north MS, but we expect some amount of it to reach at least a part of our coverage area.  The best chance will be over Tate/Marshall/Fayette Counties, though there will also be about a 50/50 chance of precip for the rest of the metro, including Memphis & Shelby County, DeSoto County, and Tipton County.  The most likely time for precipitation will be from noon util 6pm Monday.

As for precipitation type, surface temperatures will support multiple precipitation types, none of which are rain.  Temperatures is the lowest few thousand feet above ground will determine what type of most likely, and that is where model discrepancy comes into play.  Our best guess right now is for a mix of snow and sleet, possibly mixed with freezing rain.  All precipitation should be light and total accumulations would likely max out at a half-inch of snow/sleet and a very light glaze of freezing rain.

Probabilities of accumulating freezing rain (0.01"+) Monday. The metro is in the 40% range. MWN expects primarily light sleet and snow.

Bottom line

Overall, we are NOT expecting a significant winter weather event, but the possibility for light icing of bridges and overpasses during the afternoon and PM rush hour exists, as well as as dusting of snow on exposed surfaces.  Roadways in general should not be a real issue due to recent (very) warm temperatures.  We do NOT recommend a grocery store run for bread, milk, and eggs and please do NOT ask us about schools. :-)

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1 comment:

Anonymous said...

For a that mean schools will be open? lol jk don't kill me