Severe Weather Discussion 2007-4-2

Severe Weather Discussion for February 28, 2007.
Valid: 02/25/2007.

Highlights:

– Severe thunderstorms are possible from central Texas into central Oklahoma, and point east on Wednesday. Primary threat is large hail.

Discussion:

Powerful closed low heading east this morning across the northeast U.S. Lots of interesting weather with it and even some damage in parts of the region. At the surface a cold front has pushed moisture well off the Gulf Coast as the surface ridge settles across Texas.

12z models in decent agreement on the evolution of the next progressive longwave trof. There are differences between the GFS and NAM, which has implications on this forecast. For now, I'm going with the NAM, since the differences aren't worth messing with right now.

Models are little more robust with moisture return for Wednesday as the Gulf opens up and modified air heads north on Tuesday. Moisture will be slow to increase across Oklahoma, as is common this time of year. However, by Wednesday afternoon dewpoints around 55F are expected across the state. As with the last system, this one will be quite dynamic resulting in 850mb/700mb winds of 40-50kts. This could again be an issue if instability fails to develop. Currently the NAM has CAPE up to 1500 J/Kg across central Oklahoma Wednesday afternoon with LIs around -4. It has a very narrow instability axis, so not sure if anything can get going. The NAM has an odd temperature sink to the east and would assume this is cloud cover. Given last Friday and time of year, this may be an accurate prog. However, as noted in the panhandle last Friday, it doesn't take much.

GFS is much lower on instability for the same amount of moisture. It looks like the model is developing a double barrel surface low and this is noted by how it handles the 500mb longwave trof. I'm not convinced of this solution and for now will just keep it in mind.

Current thinking is that the dryline will move into central Oklahoma/Texas Wednesday afternoon with storm initiation by 4pm. This is backed up by the NAM's UVV fields and the location of a 70-75kt 500mb jet in SW OK. Storms will then move into eastern Oklahoma. NAM does show some significant cooling at 700mb by 6pm, so a squall line may develop after the initial storms. As with the prior event, instability will be the governor. I still think this is a high-end slight risk for the region and see nothing to warrant a moderate. That may change if daytime temperatures warm, like what happened in the panhandle on Friday. I'm going to wait another day before introducing the tornado threat, but one obviously exists with discrete storms.

Probabilities:

Risk area for any part of OK/TX (valid: 02/26, Day 3):

Slight: 100%
Moderate: 0%
High: N/A

Chase Status:

Level 1 – Normal – Wednesday does have my interest.

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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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