Severe Weather Discussion 2008-6-3

Severe Weather Discussion for March 17 – 18, 2008.
Valid: 03/16/2008.

Highlights:

– Isolated severe thunderstorms are possible across the Texas/Oklahoma Panhandles and far western Oklahoma tonight. Primary threat is large hail.

– Active severe weather day is expected for parts of Texas, generally along and west of I-35 on Monday. Primary threats are tornadoes, large hail, and damaging winds.

– Isolated severe thunderstorms are possible across Oklahoma on Monday. Primary threat is large hail, but an isolated tornado may occur with discrete storms in southern Oklahoma. Excessive rainfall is likely in the southeast 1/4 of Oklahoma and a flash flood watch is posted for this potential.

– Severe thunderstorms are possible across eastern Texas into Louisiana on Tuesday.

Discussion:

Broad area of surface low pressure developing in New Mexico as large southern stream system moves into the southwest U.S. Afternoon surface analysis indicates that 60F dewpoints are inland about 100 miles with continued northward advancement expected the next 24 hours. By Monday afternoon 60F dewpoints should be common east of the dryline located on the TX/OK border. In Texas dewpoints should be at least 65F.

As dewpoints in increase tonight in west Texas and the panhandles, isolated thunderstorms may develop after midnight. This activity will have a large hail threat.

Tomorrow has the ingredients of a significant severe weather event for Texas. Oklahoma could get in on the action, but this is currently not expected due to limited instability. SPC Day 2 has a slight risk posted with a 10% hatched area and 30% for much of Texas near and west of I-35. By Monday morning a shortwave trof will be moving northeast across CO/NM away from the mean low position in old Mexico. Very strong winds aloft, 200mb 125kts, 500mb 80kts, and 850mb 50kts will be in-place across Texas and Oklahoma tonight into Monday. Presence of the initial shortwave trof should weaken and overcome the EML across Oklahoma by Monday morning. Widespread showers are expected with thunderstorms also possible. Large hail will be the primary threat with this activity. Later in the day, heating may occur across western Oklahoma, just east of a sharpening dryline. In Texas stronger surface heating is expected with CAPE values around 1500-2000 J/Kg. Deep layer convergence along the
dryline should be sufficient to overcome the cap in Texas with discrete storms likely. Tornadoes will be possible with this activity during the late afternoon hours into the evening. In Oklahoma, discrete storms may occur in Oklahoma with attendant tornado threat. Currently the highest impact weather for this event will be in Texas.

Surface front will sag south in Oklahoma late Monday and develop a focus area later in the night into Tuesday for heavy rain across southeast Oklahoma. NWS offices have issued flash flood watches for this area. Models indicate over 2 inches of rain in this area. Pretty impressive for a mid-March event.

Upper system will traverse east into Texas on Tuesday and should set off a squall line. Models differ a little on how fast the system will move east with the GFS the quickest. Despite which model verifies, there is sufficient confidence of another medium impact event on Tuesday for eastern Texas into Louisiana. SPC has a slight risk up on the Day 3 product and this looks good. If the GFS is correct, primary threats appear to be large hail and damaging winds, particularly on the wind threat. I'm going to go with the quicker movement of the GFS for now.

Probabilities:

Risk area for any part of OK/TX (valid: 03/17 Day 1, Day 2):

Slight: 100%, 100%
Moderate: 60%, 40%
High: 0%, 0%

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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