Severe Weather Discussion 2007-3-2

Severe Weather Discussion for February 23 – 24, 2007.
Valid: 02/21/2007.

*Active Severe Weather Expected Friday and Saturday*

Highlights:

– Severe thunderstorms are possible Friday afternoon across western TX/OK/KS. Primary threats are large hail and strong winds. However, if enough moisture returns, tornadoes will be a concern.

– Significant severe weather event is possible late Friday through Saturday across all of the region. Primary threats are isolated tornadoes, hail to quarter size, and damaging winds.

– This is a potentially dangerous severe weather event, covering a large part of Texas/Oklahoma/Kansas.

Discussion:

Complex evolution to our first severe weather event for 2007. 00z models are in decent agreement and the 12z NAM-WRF is close, although it did speed the system up a few hours.

Prior forecast reasoning remains the same. Powerful longwave trof will move into the western U.S. late Thursday and rapidly move eastward into the region early Saturday. At the surface a strong surface low is progged to develop late Thursday and intensify during the day Friday. This will result in southerly flow across the region. Moisture should be pooled near the Gulf Coast late Thursday and readily return during the day on Friday. Current models agree that 55-60F dewpoints will return to much of western/central Oklahoma on Friday. Deep layer moisture return will continue in earnest during the evening, but do not expect much more than 62-63F as it is still late February.

Wind speeds aloft will increase dramatically on Friday leading to a strongly sheared environment across the region. 12 NAM-WRF soundings from FSI 00z Sat yields impressive shear but rather weak instability. Tough call if the lower instability is correct, but it is still early in the season and sun angle isn’t that great. Some of the instability issues may be the NAM mixing out moisture at 850mb, probably not going to happen but we’ll see. Friday is a day to watch as a few sneaker thunderstorms may develop. If any activity develops it will likely become an LP supercell given strong shear and decent moisture. Storms should remain very isolated and may not survive much past dark.

SPC Day 3 has a 10% hatched area over western OK and a 30% area of part of western OK/central OK; these also extend into adjacent parts of Texas/Kansas. SPC Day 4-8 continues previous trend of highlighting much of the region for severe weather. The issue here is the time break on the outlooks. By policy the outlooks break at 12z, meaning that the Day 1 from the prior day ends at 11:59z and the new Day 1 takes over at 12:00z. Since activity should start near or before 12z, part of the Day 3 may be taking this into consideration. Either way, an active severe event is expected from Friday afternoon through late Saturday across much of the region.

Saturday’s event is expected to be a squall line from central Texas into Kansas during the early morning hours. The primary threats will be isolated tornadoes, large hail (nickels/quarters), and damaging winds. The wind threat may be the real issue here and is what will get the enhanced risk (moderate/high) areas issued.

Persons across Texas into Kansas are urged to monitor the weather forecasts for Friday and Saturday.

Probabilities:

Risk area for any part of OK/TX (valid: 02/22 Day 2, Day 3):

Slight: 100%, 100%
Moderate: 100%, N/A
High: N/A, N/A

Chase Status:

Level 2 – Watching Friday, but not convinced.

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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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