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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