Weekly Severe Weather Discussion

Severe Weather Discussion for April 16 – 22, 2007.
Valid: 04/16/2007.

Highlights:

– Near normal temperatures all week, with a slight dip on Tuesday.

– Severe Thunderstorms are possible on Tuesday across southern Oklahoma into Texas.

– Active severe weather day is possible Saturday across western Oklahoma and the Texas panhandle.

Probabilities:

– Severe Thunderstorms in Oklahoma: 60%
– Storm Chase: 40%
– Winter Precip: < 5%

Discussion:

Active weather pattern will continue this week with one noticeable difference, it will be much warmer outside than the past two weeks. Hopefully we can put the jackets away!

Weakening southern stream closed low will move over Texas on Tuesday and open up by late in the day. There is the potential for severe weather given moisture return and favorable speed and directional shear. However, models are low on instability given expected precipitation and cloud cover early in the day. Any areas that can break-out into sunlight will have a better chance at severe weather. Currently the primary threats look to be large hail and damaging winds, but isolated tornadoes cannot be ruled out in central Texas.

Shortwave trof will then progress eastward into confluent flow and be absorbed by larger eastern northern stream closed low. A longwave ridge develops across the central U.S. by Wednesday and this deflects the next system northward into the northern U.S. A weak Pacific cold front will make a run at the region, but little southward progress is expected given the northward movement of the northern stream shortwave trof.

A longwave trof develops out west as the next system moves into the lower 48. This one has the potential to be a weather maker across the region and is currently slated for a Saturday arrival. 12z GFS from 04/15 delayed this system until Sunday but the reliable ECMWF and later runs of the GFS have settled on a Saturday afternoon arrival. Gulf was seriously whacked last week by the large eastern U.S. closed low, but recovery has already begun and I expect at least 60F dewpoints into Texas for tomorrow's system. This moisture will be pushed south by the weakening system tomorrow with some shortwave surface ridging along the Gulf Coast. This will restrict moisture return on Wednesday and Thursday.

On Friday a surface low should develop across Colorado, initiating moisture return across the region. The Gulf should still be recovering at that time, so high octane moisture may not be available. However, deep layer moisture of at least 10C up to 850mb will be. Surface moisture quality should be 60-65F dewpoints through western Oklahoma into Kansas. GFS CAPE values reveal 2000-2500 J/Kg across this region by Saturday afternoon. Models are likely under playing temperatures and resultant thermodynamics on Saturday. This, like last Friday, looks prototypical to an outbreak.

The severe thunderstorm potential is set for tomorrow, which is on the low-end of the scale and especially for Saturday which looks to be a medium to high-end event. Chase potential is set a little higher than climo given this is a Day 6 forecast. Discussions will likely be needed starting Wednesday.

For more information, weather news, weather blog, and chase summaries go to http://www.hook-echo.com.

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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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