Thursday, February 19, 2009

First call on Saturday's potential winter weather

A few more models runs have passed and two of the primary runs - the morning NAM and GFS - are in good agreement for the next 48-60 hours. Both indicate precipitation holding off until Saturday morning after dawn and starting as rain with temps in the 40s and warm air aloft. The cold front will pass through around noon time, allowing much colder air to filter into the region. Both models also keep the precip over the area through the afternoon hours, ending it by dusk. I also think that the surface temps the models are showing Saturday (50-52 for highs and mid 40s Saturday afternoon) are too warm, maybe by 5 degrees. I can't see 10 degrees of warming from AM lows during the few hours prior to cold frontal passage with extensive cloud cover and rain, even with a southwest wind during the AM.

The timing of that cold air (temps will be falling from morning highs down into the 30s in the afternoon) and the precip shutting off will be critical, as usual for our Mid-South location. It appears as though there is a potential for 1/10" of liquid equivalent (precipitation) between noon and about 5 pm. If that were to all fall as snow, we'd see somewhere around an inch (given a standard 10:1 snow to liquid water ratio). However, I think that air cold enough to support snow will be delayed a couple of hours behind the front.

My best guess at precip amount and timing at this point then is this: rain changing to snow by mid-afternoon with a dusting on elevated, grassy, or exposed surfaces, ending by 5 pm. No accumulation on streets and right now I don't expect to see any ice. Locations well east of Memphis (say closer to the TN River) will have the best chance of seeing an inch or more. I'll update again as conditions warrant.

Anyone care to comment? Remember my poll from ~3 weeks ago? 6-in-7 of you said we weren't yet done with the snow - you may be the best prognosticators in the business!

1 comment:

Adam said...

well i live in lawrenceburg and i dont think it will get to 55 degrees and i think the rain will change to snow wat about you