Weekly Severe Weather Discussion

Severe Weather Discussion for October 1 – 7, 2007.
Valid: 10/01/2007.

Highlights:

– Severe thunderstorms are possible on Tuesday, across much of Oklahoma. Primary threats are large hail and damaging winds.

– Thunderstorms, some severe, are possible Saturday into Sunday.

– Temperatures will be in the mid-80s this week, not uncommon for early October. There is some potential for a significant cool down on Sunday, but I'm betting the farm on the ECMWF…details below.

– Tropics have calmed down a lot with little activity today. NHC is watching a system near southern Florida.

Probabilities:

– Severe Thunderstorms in Oklahoma: 35%
– Storm Chase: 10%
– Winter Precip: < 5%

Discussion:

Lots of excitement this week weather wise, with a continued active northern stream. 00z GFS/ECMWF forecast two systems to affect the region this week. System #1 will be a shortwave trof, currently located over the western U.S. This system will progressive rapidly east in the rather quick mid-level flow. While the main forcing will be north of Oklahoma, there should be enough increase in mid/lower level wind speeds to support organized severe thunderstorms. There will be some lift generated by the associated jet streaks. Progressive nature of this system places it east of Oklahoma at max heating on Tuesday. However, with the upper system lifting northeast into Michigan, the front will not have a strong push on it. Dewpoints look to be in the low/mid 60s along and south of this boundary. As SPC and OUN have indicated the main limiting factor for severe tomorrow appears to be tropical moisture from the Pacific. This may tend to limit surface heating, but either way expect a
line of thunderstorms along the front by early afternoon Tuesday. SPC has a 30% area up and I do agree. As such I've put the probabilities on the the border of a low/moderate end event.

After Tuesday the front weakens and moves back north with Oklahoma remaining in the warm sector through early Saturday. This will allow temperatures to be in the upper range of what is expected this time of year, but not unusual. Persistence from the past few weeks indicates that mid/upper 80s are common and I think we can expect more of the same through Friday.

Saturday and Sunday appear to have high bust potential. I like the 00z GFS's mid-level pattern, but am quite suspicious of the surface features. This is amplified by the 00z ECMWF being much slower than the GFS. The 06z GFS looks a lot more reasonable with the front and upper system. It advertises a shortwave trof over western Kansas at 7pm Saturday. Despite which model is correct, moisture values look to be in the mid 60s with temperatures in the 80s by Saturday afternoon. The caveat here is the potential for a tropical or subtropical system in the Gulf. This would reduce moisture return, however the NAM is a lot more excited about this system than either NHC or the GFS. There is some potential for Saturday to rise to a moderate-end event and I will monitor for now.

Normally I would worry about models slowing the system down, but I think a late Saturday maybe early Sunday passage is a good bet. This would place Sunday afternoon temperatures in the mid- 70s, which is about right for October. I'm hoping not to get beat too bad on Saturday/Sunday, but I feel it coming.

I've already talked about the one thing in the tropics of interest, so not much else to say. There are 60 days left of tropical season, but the peak part of the season has long past.

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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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