Weekly Severe Weather Discussion

Severe Weather Discussion for April 30 – May 6, 2007.
Valid: 04/30/2007.


– Several chances for rainfall through Thursday. Isolated severe thunderstorms are possible, primary threats are hail to quarter size and damaging winds.

– Organized severe thunderstorms are possible Saturday and Sunday.

– Temperatures will be above normal all week.


– Severe Thunderstorms in Oklahoma: 50%
– Storm Chase: 30%
– Winter Precip: < 5%


Low confidence forecast this week with high-impact weather in the Day 6-7 time periods. As such, the probabilities are set to climatology.

Zonal flow is in progress across the region today with a small sub-tropical closed low moving across the area. This system is not much of a weather maker but when combined with the current moist environment is enough lift to result in isolated severe thunderstorms. Said low will lumber around the region for a few days before it is kicked eastward by another system. About the same time the northern jet stream will buckle as a longwave trof develops across the western U.S. The second sub-tropical system will move through the region by late Thursday as the western U.S. longwave trof takes shape. This trof is progged to move into the central U.S. and stall as a 584dm ridge develops in the eastern U.S. This is a familiar pattern and resembles that of late March.

The weather pattern for the next few days will favor low-end severe weather. Friday and Saturday appears to be quiet at this point, but cannot rule out severe thunderstorms as southwest flow aloft develops. Lack of cold front intrusions into the region means that deep layer tropical moisture will be in-place across the region. Resultant instability looks to be at least 2500 J/Kg on any given day. With southwest flow aloft, the cap should be increasing and surface boundaries will be outside of favorable winds aloft. As such, do not expect medium or high-end events during this time period. SPC has the area outlooked for Fri and Sat but for now just going to monitor it.

More interesting weather appears to develop on Sunday. This does look like a medium-end event as deep layer tropical moisture continues to flow north across the region. 12z ECMWF/GFS models continue to prog the upper system over the 4-corners area Sunday morning with the 500mb jet streak in NM/CO. Given the presence of the strong eastern U.S. ridge and model variability this far out, not sure where the strongest winds will end up on Sunday afternoon. 18z GFS suggests that the area will sit out with this system. As such, this exemplifies the low-confidence aspect of this forecast. The upper pattern lends some credibility to the 18z GFS. I will update any changes with special discussions during the week.

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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