Severe Weather Discussion 2007-5-4

Severe Weather Discussion for March 21 – 25, 2007.
Valid: 03/20/2007.

Highlights:

– Isolated severe thunderstorms are possible Wednesday evening across western Oklahoma and the Texas panhandle northward into Nebraska. Primary threat in the Oklahoma part is large hail.

– Severe thunderstorms are possible Thursday across northern Oklahoma into Kansas. Primary threat is large hail.

– Severe thunderstorms are possible Friday – Sunday across parts of the region. Difficult to pin down the area at this point.

– Models may not have a good handle on heavy rain potential in the region, this will be monitored.

Discussion:

Finally getting a handle on what this system will do. 12z models remain in good agreement on the evolution of this system and the fact that it will spend a few days in Mexico. This has completely changed my outlook for severe weather across the region. SPC outlooks are good reference. Contrary to earlier thinking, it appears the cold front as a result of a northern stream shortwave trof will be the main player the next few days. The dryline may be a player Wednesday afternoon, but should be less important Thursday and Friday. Upper system is progged to eject Saturday into Sunday, which will bring the dryline back into the mix.

Overnight convection and activity this morning was not handled very well by the models, especially the 3-5 inch rain totals in northern Oklahoma. This activity may linger part of today as the cold front remains anchored in Oklahoma.

Wednesday was once looking like a decent day and has not turned to more of a subtle day. The main reason is the much slower movement of the upper system in the southwest U.S. The 500mb and higher jet streaks do not reach the area as earlier thought. This would lead to multi-cell development. Also, the dryline will not have much convergence and SPC has indicated shortwave ridging across the region. These issues necessitate lowering the chase level back to normal. The most likely activity will be in Kansas/Nebraska along the synoptic cold front moving south in wake of the northern stream shortwave trof. Isolated activity may occur in western Oklahoma into the panhandles during the late afternoon/early evening hours.

More likely convection will occur Thursday as the cold front moves into the state and interacts with deep layer moisture. Not sure the models are handling any part of the rainfall forecast very well. For now, isolated severe thunderstorms are possible during the day, with large hail the primary threat. SPC has the panhandles in their Day 4 outlook and that is a big we'll see. Mid-level winds remain < 30kts and the dryline diffuse. However, there maybe enough upslope flow to generate convection in New Mexico, not something you see often in March.

I'm not going to touch Friday – Sunday at this point, other than to note Saturday and Sunday have the best severe potential right now. The upper system is progged to slowly eject northeast on Saturday, placing the panhandles and western Oklahoma in favorable parameters. Main issue, as always, will be rain cooled air and cloud cover. Much time to talk about those days. As it stands significant severe weather is not expected through Friday. I've kept the slight risk chances high since severe thunderstorms are expected.

Probabilities:

Risk area for any part of OK/TX (valid: 03/21 Day 1, Day 2, Day 3):

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