Severe Weather Discussion – 2006-8-2

Severe Weather Discussion for September 15 – 17, 2006.
Valid: 09/13/2006.

Highlights:

– Isolated severe thunderstorms are possible in the TX/OK panhandles into far western OK and northward into Kansas. Primary threats are large hail and strong winds.

– Active severe weather day is expected on Saturday from Kansas northward to South Dakota, severe thunderstorms are possible across northern Oklahoma.

– Severe thunderstorms are possible across much of Oklahoma on northeast, this accounts for early morning activity.

Discussion:

12z GFS and 00z ECMWF agree on the timing and general placement of the progged western U.S. longwave trof. The 12z NAM-WRF progresses said trof rapidly east, with it on the North Dakota/Minnesota border by 00z Sun. This solution seems way too fast and is ignored for now.

12z GFS/00z ECMWF continue to be my pick for this setup. I will monitor the NAM-WRF, but don’t feel good about its solution right now. No change to forecast reasoning for Friday. Weak southern stream shortwave trof still expected to traverse parts of the Texas/OK panhandles late Friday. This should combine with moisture return to produce a few severe thunderstorms. GFS develops some QPF in northern OK/southern KS. Good enough for me to stick with a low-end slight risk.

Attention then turns to Saturday, which continues to be a potent severe weather setup. The downer about Saturday is model trends to take the majority of lift into KS/NE. I tend to agree with this prog, but still think severe thunderstorms are possible in Oklahoma. I’m not sure how good of a chase it could be, but not giving up either.

Current progs indicate the upper system will move into the central U.S. as a closed low late Saturday. As this happens, very strong directional shear will overspread deepening moisture at the surface. This environment should be present from Oklahoma northward into Nebraska. The best 500mb – 200mb wind speeds will remain north in KS/NE along with the best lift. Decent 850/700mb winds will be present over Oklahoma and may be enough to generate deep layer lift. GFS does have UVV at 700mb across Oklahoma, near the dryline. Models remain bearish on QPF across KS/OK on Saturday into Sunday, which I find odd. Despite frontal timing, a function of system timing; the cold front should initiate convection as it moves into the deep moisture across the region. Unfortunately there is more uncertainity today than I had hoped, but such is the weather.

Sunday’s severe weather threat is a big placement issue and one that can’t be decided due to model differences. Current thinking remains eastern Oklahoma on east and north.

Still too early to comment on chasing this Saturday, I’m low on it right now given location of the best severe threat.

Probabilities:

Risk area for any part of OK/TX (valid: 09/14 Day 2, Day3):

Slight: 50%, 100%
Moderate: 0%, 10%
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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