** Severe Weather Possible Thursday **
** More Frosty Nights Possible **
A very interesting morning was played out with temperatures falling below freezing in parts of western Dewey County and Buffalo. Many other local valleys were down to 33 this morning. Unfortunately this may not be the last time we see these kind of temperatures. There are indications in the models of this repeating around May 6th or 7th and again around May 13th. The latest freeze ever seen in OKC was May 3rd, 1954. The latest freeze dates for much of northwest Oklahoma go into the first and second week of May, so we might be flirting with some records again. We broke a record low in OKC this morning of 35 degrees. By 9 a.m., many locations were already in the 50s as west-southwest winds kicked in.
A weak back door cold front will slide into the northern half of the state today, turning winds to the northeast. This front will have little effect and skies will remain clear. A weak wave passes over tonight with a few clouds. The front will remain hung up from west-central to south-central Oklahoma, south of OKC, for Tuesday. South of the front, temperatures will climb into the 80s with 70s north of the front. Fire danger will be high south of the front the next two days.
The front washes out and lifts northward late Tuesday. This will set the stage for a windy Wednesday with a weak moisture return. High clouds will pass over the state in association with a weak wave of energy. Gulf really opens for business Thursday. Stratus arrives Thursday morning as moisture deepens. The dry line should mix east to near US Highway 81 by afternoon. Meanwhile, a very strong upper storm will pass across Kansas, trailing into Oklahoma.
One problem with this system, as has been the case with the last many, is we keep getting upper right-lower left angled waves of energy shaped like this: /. We need them to be tilted the other direction like this: \ (negatively tilted) to get the nastiest severe weather in general. Positive upper right to lower left tilted shortwaves do not favor significant severe weather. Plus, we keep having waves that are completely rounded. I have termed this feature a "vorticity bowl."
Despite OUN's doomsday sounding forecast discussions of the past two mornings, this event is not so "classical" looking as they lead to believe. I've seen a few events produce significant severe weather without the classical negative shortwave but plenty which have favored widespread "crapvection" (garbage storms with little organization and only pulse severe capabilities). This is what happens when the cap is removed and there's no certain focusing area for storms. We will have a dry line on Thursday though so significant severe cannot be ruled out.
A front moves in behind the dry line and clears some of the moisture out Friday. Nothing seems to be normal this year. The large "vort bowl" is seen with a significant surface low near Sioux City, IA, moving up towards the Great Lakes. This in itself seems quite unusual and may hold our winds in an easterly direction to light and variable through the weekend with slightly below average temperatures. 6Z and 12Z GFS shows a wave of thunderstorms in some sort of northwest flow pattern coming down Sunday, with a high pressure bubble moving in behind it for Monday. This is a flip-flop of the 0Z run and looks much more believable. Models continue to have trouble resolving items beyond day 7 and I have been averaging the runs to come up with a decent handle on the later extended. New 12Z run has a significant shortwave coming out late Monday night into early Tuesday but the surface features do not favor significant severe weather at this time. Next week winds return to the south, favoring the continuation of a stormy pattern. The most interesting day looks to be Saturday May 10th.
OKC 73 47/75 55/82 63/83 53/72 45/71 48/69 49/62 38/68 44/74 53/79 64/83
Breezy Monday-Tuesday, Windy Wednesday-Thursday
Breezy the following week Tuesday-Wednesday, Windy Thursday-Friday (May 8th-9th)
POPS: Thursday 40%, Sunday 20%, the following Thursday 30% (questionable).
Note: May 5th-6th forecast may need some revision after seeing latest 12z run
Graphics and state forecast at www.okcfox.com
Greg
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