Severe Weather Discussion 2007-7-1

Severe Weather Discussion for April 12 – 13, 2007.
Valid: 04/10/2007.

Highlights:

– Isolated severe thunderstorms are possible on Thursday across southwestern Oklahoma into northwest Texas. Primary threats are large hail and damaging winds.

– Active severe weather day is possible on Friday across the eastern half of OK/TX.

Discussion:

Fascinating weather situation developing for the end of this week and is borderline prototypical (classic) tornado outbreak. Since I gave a review of the general atmospheric pattern yesterday, I'm going to deal with the main factors leading up to Thursday and Friday.

Weak upper system will move across Texas today and is primarily responsible for the cloud cover across the region. Clearing line is near I-35 in Texas and arcs northwest to western Oklahoma. Stronger northern stream shortwave trof will move across Nebraska late today into tomorrow and push a cold front through the region.

A much stronger southern stream shortwave trof will move into the SW U.S. on Thursday. This system is progged to remain progressive and move into the central U.S. on Friday. Wind fields aloft will be favorable for organized severe thunderstorms on Thursday. However, recent passage of Pacific cold front will limit moisture in the threat area. Moisture is currently progged to be around 50-55F across this region by late afternoon. Storms that develop will likely be supercells and of the LP type. However, storm initiation is very much in question due to limited moisture.

A more robust event may occur on Friday as the upper system impinges on the region. Moisture return will continue during the night with widespread 60-65F dewpoints across Oklahoma and Texas Friday morning; with some 65-70F dewpoints making a run at eastern Texas. Wind fields will be very favorable for organized severe weather on Friday. The main question will be overnight convection from Thursday's activity or even the warm front moving north. Also, until 00z today models had been quite fast with the system speed. 00z ECMWF and 12z NAM agree on slowing the upper system and given what happened on March 28th I'm going with these progs. 12z NAM cranks out a lot of QPF in the warm sector early Friday morning, limiting daytime heating. Not sure what to think of this and for now not going to worry. This model and ECMWF have the dryline very near I-35 at 7pm, so storm initiation will likely be a little west of this location.

There are many details to review over the next few days, but it appears that parameters may come together for a significant severe weather event for eastern Texas/Oklahoma on Friday. Additionally, significant severe weather may continue on east this Saturday.

I have a 100% slight risk up for the Day 2 since SPC is all over it. I'm going with a 30% moderate on Friday to get this day on the RADAR, however I'm not sure SPC will actually do it in the Day 3. My threat area for Friday would be all of central/eastern OK/TX into eastern KS/western MO. I'd put a 30% area over central and northern Texas into southeast Oklahoma.

Probabilities:

Risk area for any part of OK/TX (valid: 04/11 Day 2, Day 3):

Slight: 100%, 100%
Moderate: 10%, 30%
High: 0%, 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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