Weekly Severe Weather Discussion

Severe Weather Discussion for September 24 – 30, 2007.
Valid: 09/24/2007.

Highlights:

– Temperatures well above normal today, leveling out to near and slightly above normal the remainder of the week.

– Fall started yesterday, not that it feels like it.

– Tropics are very active.

– Thunderstorms are possible late Monday into Tuesday for much of Oklahoma, severe weather risk is low.

– Severe thunderstorms are possible on Saturday across mainly northwest Oklahoma.

Probabilities:

– Severe Thunderstorms in Oklahoma: 20%
– Storm Chase: 5%
– Winter Precip: < 5%

Discussion:

500mb flow will be progressive this week with several systems to affect the region. The flow does not change much this week, which makes the forecast a little easier. First system is approaching the region this morning and is located in Utah per water vapor imagery. This shortwave trof will translate slowly eastward the next 48 hours and weaken as the longwave ridge over the southeast U.S. holds firm. A cold front will move into the region on Tuesday and into Texas by late Tuesday. 00z NAM/GFS are in reasonable agreement with the front in southern Oklahoma by 7pm Tuesday. This front will reach the Gulf Coast and allow cooler/drier into the region. Showers and thunderstorms are likely along the front given the current moist environment. Mid-level winds are around 10-15 kts and this should preclude a severe weather threat. Isolated severe thunderstorms are possible, as would be expected in Oklahoma. Another shortwave trof moves rapidly eastward just behind the first, no
affect is expected from this system. There could be a windshift move into Kansas, but I'd doubt it would get very far south. Temperatures will cool down nicely behind the cold front on Tuesday, setting up a pleasant fall like week.

Another system moves into the western U.S. on Friday and progresses eastward into the region by Saturday. As seems to be the case in this part of the world, a critical ingredient is missing for a severe weather event. Prior cold front and associated surface high will be just east of the Gulf by Saturday with the 1016mb line at Houston. Model surface and 850mb dewpoints are not that impressive, except in a narrow return area across western Oklahoma/Texas panhandle northward into Nebraska. SPC has highlighted this area in their Day 6 outlook and I certainly agree. LIs look to reach -6 and CAPE values 1500-2500 J/Kg. Unfortunately this does not look to be a widespread event for Oklahoma, but mainly confined to the northwest sections. Either way, potential for an organized severe weather event is enough to raise the probabilities for this week. Better moisture return would increase the areal and significance of the severe weather threat. Another complicating factor is the
tropical system models advertise in the Bay of Campeche. This will be monitored and special discussions issued if necessary.

This system will drag a cold front into the region on Sunday, but this front may not get very far south. Either way, after today temperatures should be near or above normal through the remainder of the week. Current normal high for OKC is 81F. I think we'll be in the low/mid 80s, after today, per what NWS OUN has in their zones.

The tropics have gotten rather active the past few days with several areas of interest. Jerry is way east and is not a concern. TD10 was a decent rain maker for areas that really needed it. There is a system, as noted above, in the Bay of Campeche that needs to be monitored. NAM is a little excited about it, while the GFS doesn't seem to care. Another system is located near the Leeward Islands with a final one just west of Cape Verde. Anything of interest will be covered with special discussions.

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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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