Weekly Severe Weather Discussion

Severe Weather Discussion for May 3 – 9, 2010.
Valid: 05/02/2010.

Highlights:

– Showers and thunderstorms are possible across Oklahoma on Thursday.

– Showers and thunderstorms are possible in northern/central Oklahoma
on Sunday.

– Temperatures will be near 80F Monday, low 80s Tuesday, mid 80s
Wednesday – Thursday, upper 60s Friday, low 70s Saturday, mid 70s
Sunday.

Probabilities:

– Severe Thunderstorms in Oklahoma: 15%
– Storm Chase: 10%

Discussion:

First part of the forecast period to be quiet as central U.S. longwave
trof, responsible for multiple high risks, shifts east and weakens.
ECMWF remains consistent in shifting a shortwave trof eastwards
towards the region on Thursday into Friday while the GFS is much
weaker with this feature. There are some substantial differences as a
result and bust potential for Thursday/Friday is high. The general
opinion of area forecasters is to side with the ECMWF and I think for
this forecast it is a good bet. The GFS has a characteristic bias of
minoring out western U.S. shortwave trofs and this may-be such a case.
As such, I have gone with warmer temperatures on Thursday than the
GFS and added slight POPs for the same. Friday will be cooler as a
relatively strong cold front moves south, aided by a northern stream
shortwave trof. ECMWF has this feature pushing said cold front to the
northern Gulf by early Sunday. This will setup a pleasant, albeit
cool Friday and Saturday. Temperatures will be below seasonable
norms, but how's that different than the rest of 2010?

The GFS, being weaker with the mid-level trof, is also weaker with the
cold front intrusion. As such, it attempts to return moisture on
Sunday with a warm front in northern Texas. This develops an
isentropic upglide potential across Oklahoma, leading to potentially
cloudy, cool, and rainy Mother's Day. I'm not high on this forecast,
which Andy and I do agree about, but I can't ignore the potential. Of
course going with the stronger ECMWF's cold front and subsequent Gulf
intrusion should negate this, but the ECMWF also show a lingering
frontal boundary along the Gulf coast. While I think my POPs for
Sunday will bust, I have gone with a slight chance. I did keep
temperatures near climo, as I see no real reason to go much lower.

Part of the reason for POPs Sunday are what looks to be a developing
southwest U.S. trof. This is noted in 12z GFS/ECMWF model progs and
there is some recent consistency. Gulf should not get hit too hard,
of course I've said that a lot this year, and decent moisture
available for return to the region. As such, more interesting weather
may be around the corner say 10-13th or so. Time of year and
available moisture would yield medium-end events if a western U.S.
trof does indeed develop. Since this splits the forecast period,
special discussions could be needed around Friday/Saturday. Once the
frontal intrusion Thu/Fri is better realized by the models, we'll have
a much better idea of impacts on the Gulf.

I followed the NAM temperature wise through Wednesday and then ECMWF
Thu/Fri, trending to climo over the weekend. I'm not completely
negative on precip chances on Thursday as time of year can provide
showers/thunderstorms along cold fronts. Probabilities are set well
below climatology for early May.

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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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