Severe Weather Discussion – 2008-10-2

Severe Weather Discussion for May 1, 2008.
Valid: 04/29/2008.

Highlights:

– Active severe weather day is possible on Thursday for much of
central/eastern Oklahoma north-northeast into Iowa.

Discussion:

Little change to yesterday's forecast or reasoning. Models are in
general agreement regarding the evolution of this event. There are
subtle differences that will affect the outcome, some of which are
noted in SPC Day 3.

12z NAM/GFS both create a double barrel 925/850mb low with the initial
low lifting northward during the day as the secondary low develops
during the afternoon hours on Thursday. This creates a weakness in
the winds across north-central Oklahoma. This is not an unreasonable
solution, but I'd rather wait another model run at 00z before
incorporating this change. The difference would seem to have some
impact on the severe weather threat for Oklahoma. However, at this
juncture it still appears that an active day is likely for points east
of I-35 and south of I-44.

Models remain consistent on 65F surface dewpoints with 850mb values
around 12-14C. While not great for early May, it will have to do.
The atmosphere remains in a rather energetic state as a 6-wave pattern
continues across the Northern Hemisphere. Again, this appears to be
the issue with storm season as medium wavelength trofs are the norm
and unable to dig southward into the SW U.S. This has implications
for Oklahoma on Thursday as the closed low wraps up over northeastern
Colorado/western Nebraska.

Long story short, confidence in Thursday's event remains low. There
appears to be decent confidence of a mesoscale medium-impact event in
the area noted above for Thursday afternoon into the night time hours.
Winds will marginally favor supercells, but may be assisted by
thermodynamic parameters.

I agree with SPC Day 3 and Edwards did a real good job. My problem
with going with a moderate for Thursday is the displacement of the
threat area from the best upper level winds. With the dryline mixing
to I-35, which appears likely, even though I thought we'd see a
slowing trend (I'm not giving up just yet) and the best upper level
winds in western Oklahoma, the timing does not appear that great.

We'll see, lots of time left to go.

Probabilities:

Risk area for any part of OK/TX (valid: 04/30 Day 2):

Slight: 100%
Moderate: 70%
High: 0%

Chase Status:

Level 1 – Normal, going to hold here another day.

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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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