Severe Weather Discussion 2007-9-1

Severe Weather Discussion for May 4 – 8, 2007.
Valid: 05/01/2007.

Highlights:

– Severe Thunderstorms are possible across parts of western Oklahoma into Kansas on Friday.

– Severe Thunderstorms are possible across the Texas/Oklahoma panhandles northward into CO/KS on Saturday.

– Isolated severe thunderstorms are possible across Texas/Oklahoma panhandles northward into Nebraska on Sunday and Monday.

Discussion:

Active and low-confidence weather situation appears to be developing for parts of the region later this week. The activity appears to be confined mainly to the western part of the region. However, combination of high instability values and upper system to the west yields potential for at least one medium-end event.

Models continue to be at odds on how this will evolve, but I'm seeing better agreement on the general features. Friday is the first day on this set-up and is rather subtle. I have to wonder if I'm grasping here given the lack of interest by NWS offices on anything this day. 12z NAM/GFS create a rather large warm sector across KS/OK/TX on Friday. The dryline looks to be in western Oklahoma during the afternoon, this location also fits with the 00z ECMWF. Low/mid level winds will be on the weak side but will turn with height. And, progged instability would seemingly be sufficient for organized severe thunderstorms. Issue then becomes, can storms develop. GFS develops one storm near Enid while the NAM is dry. Given GFS CIN values around 30 J/Kg at peak heating in central/southern Oklahoma this would make sense. For now it is something to monitor. I'm not crazy enough to jump on the NAM's 5500 J/Kg CAPE prog…I'm going to put that in the "we'll see" drawer.

Saturday looks quite interesting for the Texas/Oklahoma panhandles, assuming the models don't shift things again. Dryline should surge west late Friday into Saturday as a surface low redevelops in Colorado. Tropical moisture should spread west to the I-27 area during the day. Models differ on QPF with the GFS near the Caprock. Not sure about that prog, especially given model dryline bias issues. However, CAPE values should be around 3000 J/Kg with LIs to -8. Wind fields are starting to back at 850/700mb during this time period as western U.S. closed low cuts off from the northern jet and settles in over the SW U.S. 0-1km shear looks weak but 0-3km and 0-6km shear look decent. Mesoscale events can compensate for these issues. It is certainly something to watch.

By Sunday the winds are strongly backed and unidirectional across this area. While I can't rule anything out, would not expect much more than low-end type severe weather.

12z GFS is at odds with the 00z ECMWF on when the SW U.S. cutoff low will eject northeast. If the 12z GFS verifies, then the severe threat will translate east on Monday, otherwise Monday will be more like Sunday for western areas.

I'm still not sure what to think about Friday, so I'll throw a token 50% in for a slight risk.

Probabilities:

Risk area for any part of OK/TX (valid: 05/02 Day 3):

– Slight: 50%
– Moderate: 0%
– High: N/A

Chase Status:

Level 1 – Normal

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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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