Severe Weather Discussion 2007-5-5

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

Highlights:

– Isolated severe thunderstorms are possible today – Saturday across the region. Primary threat is large hail.

– Severe thunderstorms are possible on Sunday across parts of the region.

Discussion:

Glad to know this forecast can get even more complex. Models continue to delay the ejection of our friend in the southwest. This creates problems regarding expected sensible weather and timing of severe thunderstorms…if any.

SPC products look good for the next several days and form the basis for this discussion. Today, a narrow slight risk covers parts of western OK into the panhandles. Convergence along the dryline may be sufficient to initiate isolated storms. Any storms that do develop will have the potential to produce severe weather given CAPE values around 1800 J/Kg and LIs to -7.

Thursday may be the best day for widespread activity, with isolated severe thunderstorms, as a synoptic cold front moves into the region. Conditions should be very similar to today as the upper system remains anchored in the southwest U.S. SPC Day 2 has a slight risk for northern Oklahoma into southeast Kansas.

Friday and Saturday are very tough at this point as conditions look to be rather subtle around the region. On Friday the synoptic cold front may move north out of the state, removing the focus for thunderstorms. Additionally, cloud cover from overnight precipitation should hold down temperatures. Farther west, the dryline should be the main focus along with upslope flow. SPC Day 3 has a slight risk for this area and certainly agree with that product. Saturday may see more of the same out west as the cap should hold in this area and there are no obvious features to breach it. Model QPF progs are not reliable and I'm going with persistence at this point.

Normally I would not continue discussions, but enough uncertainty exists to keep things going for a few more days.

Sunday may be the best chance at severe thunderstorms for the region. A blend of the 12z GFS/00z ECMWF was used to derive system trajectory late Saturday into Sunday. Upper low will be weakening and lifting north-northeast on Saturday. This will result in very little push on the dryline. On Sunday the upper system should start moving more eastward across Kansas, however the dryline should not move too far east given lacking mid-level dynamics. GFS has decent wind fields in-place and favorable dryline location for activity. Issue will be day-time heating as the GFS keeps CAPE/LI values in the limited range. It also has lots of QPF in Texas and I'm not biting on to that right now. Sunday will be monitored for chase potential.

12z GFS/00z ECMWF and SPC Day 4-8 all note that another western U.S. trof should move onshore early next week. This may prove interesting as moisture should remain very close and above normal for this time of year.

Probabilities:

Risk area for any part of OK/TX (valid: 03/22 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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