Weekly Severe Weather Discussion

Severe Weather Discussion for September 10 – 16, 2007.
Valid: 09/10/2007.

Highlights:

– Temperatures below normal today and Tuesday, near normal Wednesday – Friday and below normal Saturday/Sunday.

– Thunderstorms are possible on Friday.

– Oklahoma City received 6.28 inches of rain this morning in 6 hours. OKC is around 51 inches of rain for the year, about 4.5 inches for the record yearly max.

– Tropical storm season peaks today, with current conditions seasonable.

Probabilities:

– Severe Thunderstorms in Oklahoma: 15%
– Storm Chase: < 5%
– Winter Precip: < 5%

Discussion:

Polar jet is rather active across the lower 48 as fall is near. The pattern today and much of the week is for a ridge off the west coast, extending north to Alaska with a closed low over Hudson Bay. This pattern will allow two strong shortwave trofs to progress through the flow into the north-central U.S. and on into the northeast sections. The net result will be two cold fronts this week.

The first cold front is moving into northwest Oklahoma early this afternoon per the Oklahoma Mesonet. Current dewpoints in OKC are 70F with far northwest OK in the upper 50s. This change in airmass will progress rapidly south today with the front expected to push to the Gulf Coast by Wednesday. Models indicate the front will washout as the next shortwave trof dives into the north-central U.S. and a surface low develops in Colorado. Return flow gets setup by late Thursday with 60F dewpoints advecting north. Next cold front moves into the state on Friday and its location will determine the best chance for thunderstorms. The 12z GFS has the front in central Oklahoma Friday afternoon. Given time of year, I can go with this forecast, but the front may be a little slower than currently progged. With temperatures in the upper 70 to mid 80s and dewpoints in the 60s, thunderstorms are possible. I'm going with a low chance on the severe scale as the mid-level flow looks to be weak.
I'm not sure how organized the storms will be.

Ample sun angle and warm ground means that we'll warm up between cold front blasts. As such, Wednesday and Thursday will be near normal (86F in OKC) with Friday – Sunday below normal. The lack of moisture will make conditions feel rather nice, especially after Saturday's 73F dewpoint.

The tropics are pretty much seasonable with today marking the peak in tropical storm season. There is a system near the Cape Verde area that is being watched. Gabrielle really wasn't of interest since it was weak and initially subtropical.


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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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