Weekly Severe Weather Discussion

Severe Weather Discussion for April 6 – 12, 2009.
Valid: 04/05/2009.

Highlights:

– Showers and thunderstorms are expected Saturday afternoon into
Sunday. Severe weather potential looks to be on the low-end with
large hail the primary threat in Oklahoma. A more robust event may be
in store for Texas.

– Significant early spring freeze is likely in Oklahoma with
temperatures Tuesday morning in the upper teens to mid 20s.

– Wildfire threat will be very high Wednesday and Thursday.

– Monday temperature will be near 50F, Tuesday low 60s, Wednesday –
Thursday upper 70s, Friday mid 60s, Saturday – Sunday upper 60s.

Probabilities:

– Severe thunderstorms in Oklahoma: 10%
– Storm Chase: 5%
– Winter Precip: 5%

Discussion:

Powerful eastern U.S. longwave trof will translate east the next few
days and should be off the east coast by late Wednesday. In its wake
a Canadian cold front moved across Oklahoma early Sunday. Said front
will move southeast and whack the Gulf. 30F dewpoints will be pushed
offshore in an odd early April cold push. 12z models are in good
agreement through the forecast period with some differences relative
to next weekend.

Upper ridge is progged to develop across the region by mid-week with a
southern stream shortwave trof under cutting the ridge late Wednesday
into Thursday. 12z ECMWF/GFS timing is accepted for this time period.
Gulf will be recovering at this point and I doubt that sufficient
moisture will make it into Oklahoma for precipitation with this
system. More than likely it will be like the past few where a dryline
races across the state during the day. Current progs would indicate a
slight chance of thunderstorms across the eastern 1/4 of Oklahoma on
Thursday, but I'm leaving that out of the forecast. Greater threat
will be wildfires on Wednesday and Thursday as surface winds and
temperatures increase across the state.

Upper system moves east of the region late Thursday and pushes Gulf
moisture to the coastline. Models agree that a strong trof will
approach the region late Saturday into Sunday. GFS and ECMWF have
amazingly similar progs at this time period and given recent trends
believe the timing, and strength of the system. Gulf recovery will
continue and better moisture should be able to return for this system.
As such, precipitation chances are introduced for Saturday afternoon
into Sunday. SPC Day 7-8 looks good and I do agree on the general
idea of severe chances for the weekend. However, the upper system
looks to take the southern route and Oklahoma may end up on the north
side of the warm front. If anything, a double warm front structure
may develop with a boundary in Texas representing tropical moisture.
GFS progs copious amounts of precip in Texas and this would likely
interfere with overall moisture return into Oklahoma and reduce the
severe threat. There is certainly plenty of time to monitor this
system for a medium-end event in Oklahoma. At this point the likely
significant severe threat would be in Texas.

18z NAM temperatures are used through Wednesday with little
modification. 12z GFS is issued Thursday and Friday, then modified
Saturday and Sunday. I brought Sat/Sun temperatures down some in
anticipation of isentropic lift and clouds. If I'm wrong, then a
medium-end event would certainly be possible also in Oklahoma.

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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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