Weekly Severe Weather Discussion

Severe Weather Discussion for May 4 – 10, 2009.
Valid: 05/03/2009.

Highlights:

– Severe thunderstorms are possible Tuesday afternoon and evening
across far southern Oklahoma. Isolated severe thunderstorms are
possible farther north.

– Isolated thunderstorms are possible Wednesday – Friday.

– Severe thunderstorms are possible on Sunday. Agreement among the
ECMWF and GFS gives confidence to the potential for a medium-end event.

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

Probabilities:

– Severe Thunderstorms in Oklahoma: 50%
– Storm Chase: 30%
– Winter Precip: < 5%

Discussion:

Upper system moving east of the region today will not have enough dry
air to clear out the moisture currently in-place through a deep layer,
despite lower dewpoints at the surface. Another upper system will
approach the region late Monday into Tuesday. Saturday morning progs
indicated there would be something of interest with this system.
However, 00z/12z Sunday progs limit the northward return of Gulf
moisture across Oklahoma as the warm front stalls near the Red River.
The 12z ECMWF also indicates this, so the solutions look good.
Elevated thunderstorms are expected during the day Tuesday with some
chance for severe weather, mainly in southern sections.

Upper system clears the region on Wednesday, leaving moisture
in-place. Zonal flow will dominate through Saturday, some some weak
ridging, across the region. 12z GFS BUFKIT data indicates strong
instability will develop Wednesday and Thursday. While a shortwave
trof is not noted at this point, a risk of thunderstorms will be
present given time of year. A northern stream shortwave moves into
the northeast U.S. late Thursday and pushes a cold front into the
region. This front is shown to stall across Oklahoma through early
Saturday and then lift northward.

12z ECMWF/GFS indicate a southern stream shortwave trof entering the
western U.S. late Saturday. GFS is about 4-6 hours faster than the
ECMWF, which has been the case recently. No reason to pick one model
over the other. However, time of year, expected presence of moisture
and warmth beneath strengthening wind fields aloft yields potential
for a medium-end event. GFS does some strange things with the
moisture fields and for now I'm not following it.

In the dailies, I've followed the NAM through Wednesday, but modified
the Monday numbers upward. I'm not sure we'll stay cloudy all day and
any bit of clearing will allow temperatures to soar. I do agree with
the NAM temperatures Tuesday and Wednesday. GFS is followed
Thursday-Sunday with few adjustments.

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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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