Severe Weather Discussion 2010-4-2

Severe Weather Discussion for April 22-23, 2010.
Valid: 04/20/2010.


– Severe thunderstorms are expected Thursday afternoon and evening
across the eastern Texas panhandle and far western Oklahoma.

– Active severe weather day is possible across central/eastern
Oklahoma on Friday. Details are sketchy and depend largely on
convection Thursday night and ultimate evolution of the upper system.

– Chase Readiness is increased to Level 2.


18z models are similar to prior runs on the overall details of what to
expect Thursday and Friday. There is seemingly little need for a
long discussion as several items will remain questionable until
Thursday morning. The main question will be the development of
precipitation late Wednesday night and the ultimate impacts on the
setup. 18z NAM appears much more realistic on precip chances through
Thursday evening with round one starting Wednesday along a cold front
in northern OK. What maybe grid scale convective feedback or a very
small would-be mesoscale convective system shows up on the NAM. The
front should drift to near I-4o by early Thursday and most likely
drift northward during the day. Models continue to hint at this
outcome but as always, extensive convection on the boundary will
retard northward movement. NAM shows round 2 hitting early Thursday
near the dryline and moving eastward across Oklahoma. QPF amounts are
on the low side and seem focused along the front in northern OK. OUN
had a good point about a warm front, representing tropical moisture
being in the Lubbock to Abilene area on Thursday. If this truly
happens, then upglinde could enhance convection. These are details
that can't be determine this far out and will be part of the
situational awareness on Thursday. In general the NAM has decreased
QPF but not areal coverage, so trending this is difficult. Moisture
is expected to be good with dewpoints around 65F along with good
directional shear. Wind speeds could be better, but most likely
adequate. SPC Day 3 looks good and see no reason the slight risk
won't be continued. I doubt we'll see a moderate on the Day 2, so I'm
keeping moderate probs low.

If Thursday was complex, Friday is down right rough! All models now
agree that part of the large western U.S. closed low will eject
north-northeast on Friday. This will result in a push on the dryline
in the Texas panhandle and a substantial increase in winds across
Oklahoma. Models differ on dryline location Friday afternoon with the
GFS just east of OKC and the NAM farther west. Last time this happen,
the NAM verified but that is not enough reason by itself to pick one
over the other. As such, I'll go with OUN's HWY 81 location for now,
with the caveat that a westward shift may be in the offering on future
discussion. An active severe weather day appears possible on Friday
given the atmospheric wind profile. Thermodynamics will be a big
issue, as always, given expected convection on Thursday. These
mesoscale details will be monitored the next few days.

Preliminary chase target on Thursday is Shamrock to Wellington to
Childress. I won't rule out a westward shift to Memphis.


Risk area for any part of OK/TX (valid: 04/21 Day 2, Day 3):

Slight: 100%, 100%
Moderate: 10%, 0%
High: 0%, N/A

Chase Readiness:

Level 2 – watching Thursday.

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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of For his day job, Putnam works in emergency management for information technology.
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