Severe Weather Discussion – 2008-7-4

Severe Weather Discussion for April 2 – 3, 2008.
Valid: 04/01/2008.

Highlights:

– Isolated severe thunderstorms are possible Wednesday afternoon and
evening. Primary threats are large hail.

– Active severe weather day is possible on Thursday.

– Chase Status is increased to Level 2 for Thursday.

Discussion:

This discussion will focus on Thursday, but first I will touch on Wednesday.

Monday's cold front has stalled about 100 miles from the Gulf Coast,
as expected. The surface high responsible for said front is expected
to shift east across the northern U.S. during the night. By Wednesday
evening winds should return southerly across the region. Rapid
moisture return will occur as the front surges northward as a warm
front. Recent NAM runs are likely too slow with the front, however
this solution will need to be monitored. Models are rather quiet for
storms Wednesday night, but would certainly expect isolated severe
thunderstorm development as the warm front moves north. I agree with
Greg on supercell potential but in this case the cap may be warmer
than Sunday night. This would seem to limit convective development,
but I'm not ready to bet the farm yet. SPC Day 2 has a slight risk up
covering the warm front and I agree with their most recent product.

Attention then turns to Thursday, which has some serious potential for
severe weather. 12z NAM and especially the 18z NAM finally caught up
with the other models on system timing. As such, the GFS/NAM/ECMWF
all agree on the system impinging on the region Thursday afternoon.
As this happens, warm and moist air is expected to be in-place across
much of Oklahoma and Texas. Models are most likely not handling
dewpoints well and again are underdoing moisture advection. NAM is
likely too far south with the warm front, although the GFS is probably
too far north. I think an area just north of I-40, attached to a
surface low between Shamrock and Childress is the most likely setup.
A dryline will likely just be in the western row of counties in
Oklahoma. I believe the models are overdoing dryline mixing on
Thursday given 850mb dewpoints of 12-14C and the upper system still
approaching. I'll be surprised if the dryline clears Altus. The NAM
creates one heck of a dryline bulge in Texas Thursday afternoon. I
also believe the models are underdoing the cap given the warm
temperatures in west Texas today. Tough call, but these trends will
need to be monitored. Very impressive wind speeds will be in-place
across the region, along with associated veering with height.
Helicity values are indicated in the 300-400 m^s/s^2 on the 12z/18z
runs per Bufkit data.

As always, overnight convection is a concern and the NAM is very
robust with convection and keeping surface temps cool. These are
issues that will need to be monitored. However, like Monday, we'll be
starting off warm and it won't take much heating. Current indications
are that Thursday could be a significant severe weather day.

My moderate risk placement for Day 2 is Abilene to Enid. I know they
won't do a high risk, but it should allude how serious I think this
day is.

Probabilities:

Risk area for any part of OK/TX (valid: 04/02 Day 1, Day 2):

Slight: 100%, 100%
Moderate: 0%, 100%
High: 0%, 10%

Chase Status:

Level 2 – Monitoring Thursday

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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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