Winter Weather Discussion for December 8 – 11, 2007.
– Freezing rain advisory for the I-44 corridor north/west through Sunday morning.
– Winter Storm Watch for much of Oklahoma, except the southeast 1/5th, Sunday night through Tuesday morning.
12z models are in somewhat better agreement on the evolution of this event, however the temperature issues continue. 12z NAM is the cooler model and has been for a few runs now. The GFS is much warmer and I don't think it should be ignored.
12z NAM shows a huge warm layer throughout the event. This warm layer should grow late Monday into Tuesday as WAA really gets going. This warm layer is about 8C and 125mb thick. Since precipitation will initiate in this layer, there will not be any wet-bulb cooling to bring the sounding below 0C. As such, at least through Tuesday, no snow is expected in the area. The situation will likely be different in the Texas/Oklahoma panhandles where the sounding should all be below 0C.
Currently temperatures are upper 20s to upper 70s across the state. The frontal boundary is located from Durant to Stillwell. This boundary should not move much more until Sunday evening as the shortwave trof moving over KS/NE gets east of the region. Temperatures are rather cool across KS/NE with upper teens/low 20s common. How much, if any advects into Oklahoma the next few days given lack of reinforcing cool surges and snow pack remains to be seen. If any, the nocturnal cycle will probably have the greatest impact on temperatures going below freezing. Another issue, there isn't much dry air with the cold air. As such, there should be little to no wet-bulbing. The only ways to cool the area will be CAA or nocturnal cooling.
For Saturday night through early Sunday it appears that there is a decent chance for freezing drizzle across much of the area. This is in response to the shortwave trof passing north of the region. As this system gets east, the cold air in Kansas should have a southward push on it and the precip will stop for a period of time. Since it only takes a little bit of freezing rain/drizzle to cause problems, I do expect some issues for much of the I-44 north/west areas on Sunday.
Attention then turns to the big low over the southwest U.S. as it starts to move east towards the region. Models are in decent agreement with this system and the associated widespread precipitation on Monday into early Tuesday. Some serious WAA will occur across the region and eventually it should make it to the surface. As such, the freezing rain will turn to a cold rain at some point Monday for parts of the area. It is the precip before this change over that is the concern. With expected activity on Sunday, any on Monday will make things a lot worse. Much of this forecast has been with the colder NAM, with the 12z GFS much warmer. If the GFS is correct, there will be very little time for freezing rain. No reason to pick one over the other right now, but it is something to watch.
I'm still not seeing this event as a big deal, but have to admit it only takes a little freezing rain to cause big problems. And, the hardest part is knowing where it will all occur. I do think northwest Oklahoma to be the hardest hit area with 0.50 inches of freezing rain from near Weatherford to Enid to Ponca City. Outside of that area, generally 0.25 inches or less will be expected. Areas south of OKC, if they get any at all, should be 0.25 inches or less. An ice storm warning is likely for parts of westby ern through north-central OK by this evening, although the NWS may do the entire area. An updated discussion will likely be needed this evening.
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