Weekly Severe Weather Discussion

Severe Weather Discussion for May 12 – 18, 2008.
Valid: 05/11/2008.

Highlights:

– Severe thunderstorms are possible on Tuesday across much of Oklahoma.

– Severe thunderstorms are likely in Texas Wednesday and Thursday.

– Thunderstorms and isolated severe are possible in Oklahoma Wednesday
and Thursday.

– Temperatures will be in the upper 70s Monday – Wednesday, cooling
off Thursday and warming back up into the 80s for the weekend.

Probabilities:

– Severe Thunderstorms in Oklahoma: 40%
– Storm Chase: 25%
– Winter Precip: < 5%

Discussion:

Unseasonably strong cold front moved through the region this morning
with low temperatures in the 40s across much of Oklahoma. Associated
surface high will push Gulf moisture south of the coastline, resulting
in Monday being a dry day. Temperatures should recover as winds turn
southerly on the west side of the high.

On Tuesday a western U.S. shortwave trof develops and assists in
moisture return to the area. Models indicate that seasonable moisture
should return to the region ahead of a southward advancing cold front
in Oklahoma. 12z NAM/GFS continue at odds regarding the location of
this boundary at peak heating. GFS is much faster than the NAM. I
tend to favor the NAM due to time of year and that the upper system
will split in two. Piece one will go across the U.S./Canadian border
with piece two settling into New Mexico. The cold front will be
oriented parallel to the mean flow and this should slow its movement.
We shall see on that one. Either way instability and
speed/directional shear should be sufficient for severe thunderstorms.
SPC Day 3 is a good product, although my forecast rules don't allow
for forecasting two big events in one week. I do consider Tuesday a
possible chase day, but will continue to monitor. At this point I see
a high-end slight risk to a possible medium-end event. 2008 has not
been prototypical in any sense, other than yesterday for eastern
Oklahoma. Even that wasn't well forecast as the tornado that killed
almost 20 people wasn't in SPC's moderate risk.

The cold front may move south of the state on Wednesday and
overrunning severe thunderstorms are possible. This would keep the
primary threat to large hail. Storms may occur on Thursday as the
longwave trof over the central U.S. reloads late Wednesday into
Thursday. Trof clears the region on Friday as a longwave ridge
develops over the western U.S. This will place Oklahoma in strong
northerly flow aloft and limit chances for severe weather. Thursday
should be cool as the cold front gets south of the area with a warm up
through the weekend as the surface high moves east.

Pattern appears to deamplify late in the weekend as another western
U.S. trof approaches. Model reliability beyond 5-6 days is poor, so
will not attempt to forecast any develops beyond the normal forecast
period. I'm ready for some global warming at this point.

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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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