Weekly Severe Weather Discussion

Severe Weather Discussion for May 19 – 25, 2008.
Valid: 05/18/2008.


– Much above normal temperatures all week with highs in the upper 80s/low 90s.

– Slight chance of thunderstorms Friday and Saturday but mainly in far
western Oklahoma.

– Thunderstorms chances may improve on Sunday.


Severe Thunderstorms in Oklahoma: 20%
Storm Chase: 5%
Winter Precip: < 5%


Mother Nature gave us the big middle finger this week in what appears
to be granting our collective wishes for a western U.S. trof. We did
get said trof, but along with it an odd event for late May, an Omega
Block. The current and resulting pattern will mean well above normal
temperatures this week with highs in the upper 80s to low 90s for
Oklahoma City with western areas near 100F.

Current pattern is characterized by an eastern U.S. longwvae trof and
a western U.S. longwave ridge will give way to an even more amplified
pattern by Wednesday. This rather significant pattern shift would
seemingly be favorable for multiple runs of severe weather and
potentially a high-end event. However, western OK/TX can't seem to
get any organized activity this year and this setup continues that

First, as the intense longwave trof develops in the western U.S. and
the southern stream closes off, the ridge over the central U.S. will
intensify into Canada while the eastern U.S. low/longwave trof remains
just off shore. This is a classic Omega Blocking pattern with the
central U.S. left high and dry. Available guidance is tightly
clustered through six days and is generally accepted.

The best opportunity for convection will be Friday – Sunday as
tropical Gulf moisture moves into the region and is overlaid by
dynamic flow aloft. There are a variety of issues that keep this from
being a prototypical plains outbreak. First, given the intense
system, winds 700-200mb will be unidirectional. There is some
directional shear noted from the surface to 700mb, but none above that
level. The north/south orientation of flow at 300-200mb will likely
lead to anvil seeding. To me, this looks to be more of a heavy rain
threat for the panhandles and maybe far western Oklahoma through
Saturday. As repeated storm motion occurs over a given area. SPC Day
7 looks good and I do agree with this product. The presence of a
500mb shortwave trof on Saturday may do more to assist organized
convection given iffy directional shear. Friday/Saturday have some
distinct similarities to March 27, 2007, which was a Texas/OK/western
KS outbreak. However, big difference here is flow from 180 degrees at
700mb and above. On March 27, the winds veered strongly at the
400mb-200mb levels to 220 degrees. While there may be severe
thunderstorms, I'd think storm interactions along the dryline will
serve to limit the overall threat. In Kansas, as noted above and in
Day 7, the presence of the shortwave trof will probably assist
convective elements.

Sunday is a real iffy day and confidence is low on sensible weather.
I cannot ignore the presence of the system to our west and as such
will need to monitor for severe chances. At this point I'm going
below climatology on probabilities and if I happen to error, will
issue special discussions.

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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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