Weekly Severe Weather Discussion

Severe Weather Discussion for May 5 – 11, 2008.
Valid: 05/04/2008.

Highlights:

– Isolated severe thunderstorms are possible across western Oklahoma
and the Texas panhandle Monday and Tuesday afternoons.

– Severe thunderstorms are likely Wednesday afternoon across eastern
Oklahoma/Texas into Arkansas.

– Isolated sever thunderstorms are possible on Saturday.

– Temperatures will be in the mid 70s to low 80s all week. Wednesday
is likely to be the warmest day of the week.

Probabilities:

– Severe Thunderstorms in Oklahoma: 25%
– Storm Chase: 25%
– Winter Precip: < 5%

Discussion:

I'm not impressed with any given day this regarding severe weather
potential on the medium-end of the scale. There are several
opportunities for low-end severe weather this week and the
probabilities are set for this. Wednesday may have some chase
potential, but the details are rather muddied. A cold front is
expected Wednesday evening and again late Saturday across the state.
Moisture does not get pushed to the Gulf, so rapid return is possible
from both frontal passages.

Models are in decent agreement on the pattern evolution this week.
First item of interest is the approach of the SW U.S. closed/cutoff
low. All three operational models (NAM/GFS/ECMWF) have increased the
ejection of this system on Wednesday, kind of an odd occurrence.
Before the upper system reaches the region, moisture will increase on
Monday and Tuesday under southerly surface flow. With temperatures in
the upper 70s and dewpoints in the low 60s, CAPE values may reach 1500
J/Kg on Monday with areas up to the 2500 J/Kg level on Tuesday.
Convergence along the dryline will be weak on both days and may be
tough to get storms to develop. However, it cannot be ruled out.

Current progs indicate this system will move northeast into Oklahoma
Wednesday morning and through the state by late afternoon. This is
not a favorable pattern for significant severe in Oklahoma, although
in the eastern 1/3rd of so it would seem possible. Many parameters
will be in-place for severe thunderstorms, however I think eastern
Oklahoma into Arkansas will benefit most from this event. Another
concern is the rapid progression of the dryline, with it reaching far
eastern Oklahoma by 00z Tuesday. If this occurs, storm initiation
along this boundary may be tough as the dryline would tend to push
them along, resulting in dry are ingestion. Despite this concern, any
storms that do develop will have the potential for medium-end impacts.
I just not sure how much of Oklahoma will be covered. Also, with
the upper system over Oklahoma City at 1pm and strong forcing in the
area, a squall line may develop on the dryline, so medium-end impacts
would be dependent on the ability of discrete storms to form ahead of
the dryline. GFS was primarily used for this part of the forecast,
NAM seems way overdone on precip chances Wednesday afternoon/evening.

Thursday and Friday will be dry as a cold front moves south into Texas.

Late Friday, the cold front weakens and moisture returns to the
region. For several runs the GFS showed a medium-end event around the
10th/11th, however that has since gone away. I'm not going to ignore
the potential, but the ECMWF has been much less amplified and the GFS
has trended towards this solution. It appears that another cold front
passage is likely late Saturday into Sunday.

CDC ensemble progs continue to show the Northern Hemisphere in a very
energetic pattern, preventing longwave trofs from developing. GFS
shows a rather significant pattern change around the 12-14th, so will
have to see if this actually occurs. I'm afraid I missed the best day
of the year on Thursday 05/01, but I hope not. Storm season 08
continues to be very disappointing, but we were handed a nice storm in
Oklahoma City the past Thursday.

At this time I do not anticipate special discussions for Wednesday and
this is in contrast to SPC's Day 4 outlook. However, I will continue
to monitor and initiate discussions if model signals improve on the
potential for a medium-end event.

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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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