Winter Weather Discussion – 2006-12-1

Winter Weather Discussion for November 28 – November 30, 2006.
Valid: 11/26/2006.

Highlights:

– Isolated thunderstorms are possible Monday and Tuesday across much of Oklahoma.

– Severe Thunderstorms are likely across southeast Oklahoma and much of eastern Texas on Wednesday.

– Significant cold front will move through the area on Wednesday, resulting in temperatures much below normal Thursday through Sunday.

– Frozen precipitation is possible late Wednesday through Thursday across much of Oklahoma and parts of north Texas.

Discussion:

Lots going on, so lets get to it.

Deep layer moisture return underway as longwave trof develops in the western U.S. While time of year negates rich moisture, decent moisture is returning with surface dewpoints AOA 50F in Oklahoma. 850mb dewpoints are AOA 12C. Persistent cloud cover has limited instability in the warm sector and lack of deep layer lift should limit convective potential through early Monday.

Clouds should be another issue on Monday as deep layer moisture continues to move into the region. Going forecast of upper 60s for high temperatures looks good right now. Limited instability is progged across parts of Oklahoma with mainly elevated instability around 700J/Kg. This should be enough for thunder if storms can develop. A weak shortwave trof should move across the region on Monday with showers possible. Strong shortwave trof should eject east from the mean longwave position Monday evening with a 20 unit vortmax showing up on the 12z GFS. Widespread showers and thunderstorms should occur in advance of this wave. Tuesday should see clearing skies and much warmer temperatures behind initial wave on Monday. Little in the way of upper support on Tuesday, so little expected precip wise.

Wednesday starts the big event as a large part of the longwave trof ejects northeast into Canada. This will give the Arctic air to our a north a solid push, resulting in decreasing temperatures during the day Wednesday. A dramatic change is in the offering as temperatures will start out in the upper 50s, warming into the 60s before the front moves through. Afternoon temperatures should be in the in the 40s with a strong north wind, resulting in wind chills in the teens. Thunderstorms are likely along the front from central Oklahoma on southeast. Severe thunderstorms are possible in Oklahoma, but more likely in areas farther south. Deep layer lift along the front should yield a squall line, with limited tornado potential. Strong winds and large hail are the primary threats.

The exciting part of this forecast is potential for winter weather late Wednesday into Thursday. Earlier model runs ejected the longwave trof east on Wednesday with the main upper support east of the region as the cold front move through the region. Recent model runs and observations indicate the upper system is stronger than progged with 500mb winds of 120kt – 130kts on the west side of the trof. This should yield a slower and deeper system. So, with a slower system, expected around Thursday with the Arctic cold front south of the region and subfreezing surface temperatures; frozen precip becomes an issue. Here is where the models disagree on the forecast. Upper system should move through the region on Thursday with deep layer lift given strong PVA gradient and a 28 unit vortmax. GFS is much colder at 850mb than other models and this may be causing it to forecast lower QPF. Tough call but there seems decent potential for a winter mix across the state late Wednesday into
Thursday. If the 12z GFS and DGEX verify, we could have some problems in southeast Oklahoma late Thursday.

Stay tuned!

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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of Hook-Echo.com. For his day job, Putnam works in emergency management for information technology.
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