Weekly Severe Weather Discussion

Severe Weather Discussion for April 26 – May 2, 2010.
Valid: 04/25/2010.

Highlights:

– Severe thunderstorms are possible Thursday – Saturday, although
confidence regarding mode and significance is low.

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

Probabilities:

– Severe Thunderstorms in Oklahoma: 50%
– Storm Chase: 40%

Discussion:

Weather looks quiet Monday as a northern stream shortwave trof passes
by to the north and pushes a cold front through the region. Tuesday
and Wednesday also look dry with neutral motion in the atmosphere and
low surface moisture.

GFS/ECMWF were in great agreement yesterday and provided confidence
regarding a potential medium-end event on Thursday. However, with the
18z GFS yesterday that agreement ceased and there is great variability
now beyond 84 hours. Today's 12z ECMWF is relatively consistent with
prior runs in developing a western U.S. longwave trof and lifting the
initial closed low slowly along the Canada/U.S. border. The GFS in
contrast rapidly progressive the lead low eastward and leaves trofing
in the southwest U.S. This causes a cold front to progress rapidly
across Oklahoma as the lead wave moves into the Great Lakes area.
Today's 18z GFS has shifted westward from prior solutions noted above.
It now follows the ECMWF's lead with the closed low remaining north
of Montana and trofing in the southwest. A shortwave trof does eject
eastward on Thursday into the region. Moisture return looks probable,
but not a guarantee. 18z NAM/GFS are similar with moisture return at
84 hrs, following the GFS to 102 hrs yields 60-65F dewpoints in
Oklahoma with CAPE values near 2000 J/Kg. Wind fields are nothing
short of impressive. So, the primary considerations are, ultimate
evolution of the upper system and subsequent surface features/moisture
return. There is decent confidence of a medium-end event and
probabilities are set for such.

Storm chances continue into the weekend with model agreement rapidly
going south. While the GFS is used for Thursday, the evolution Friday
and beyond is progressive like the prior runs. This is in contrast to
the ECMWF such that forecast confidence again lowers for the end of
the week. Even though the GFS pushes Gulf moisture well south, the
ECMWF must get the nod here and I'll keep storm chances in for Friday
and Saturday. Special discussions will be needed tomorrow, so
forecast changes will be handle with them.

Didn't make any substantial changes to temperatures this week, but
bust potential could be high Friday/Saturday if the GFS verifies.

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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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