February 23, 2007
Severe Weather Event
Oklahoma
Editor: Putnam E. Reiter
Forecast/Setup -
Risk Area: Enhanced Moderate Risk
Winter 2006-2007 has been much more active than
the prior two and probably longer. During December and January, split flow
dominated the lower 48 with plenty of winter precipitation for the southern
plains. January into February saw below normal temperatures with only a
few days above normal. Despite all the cold air, there had been limited
intrusions into the Gulf. The most significant intrusion occurred around
the 13th of February when Canadian and some Arctic air moved through the plains
into the Gulf. This pushed 50F + dewpoints to the Yucatan and Cuba.
Recovery started a few days later, but there was a long ways to go.
Models consistently progged a change to the
longwave pattern by mid/late February where the Hudson Bay low and associated
eastern U.S. longwave trof and eastern Pacific ridge were replaced by a more
progressive pattern. Model agreement was quite good, with the first longwave trof to move into the western U.S. around February 21st/22nd.
Models indicated this torf would remain progressive as it moved rapidly across
the region late on the 23rd into the 24th. While the Gulf had recovered
nicely, there was still modified air in-place with some recirculated Canadian
Polar air into the Gulf region.
Models continued in good agreement through this
event, even though there were some timing difference a few days ahead of the
event. SPC highlighted this setup in their Day 4-8 outlook and subsequent
outlooks to Day 1. For this event the Day 1 had a moderate risk across
western/central Oklahoma with 10% hatched areas for significant severe weather
on the tornado, hail, and wind graphics. For a review of their thinking,
read the links below.
My forecast went with the threat of supercells in
the Texas panhandle during the late afternoon with a significant squall line
that night, moving across Oklahoma. The panhandle activity verified as
storms developed around 5pm. SPC had a tornado watch in-place and around
four supercells developed in the eastern Texas panhandle. These storms
moved northeast into far western Oklahoma and southwest Kansas. One
tornado was reported near McLean Texas with decent video. Another tornado
is indicated in SPC's severe reports log.
This activity started to decrease in intensity as
it moved into the cooler and much more stable air across Oklahoma. This
was due to cloud cover that remained over western Oklahoma during the day,
keeping temperatures in the low 60s. In the Texas panhandle temperatures
warmed into the low 70s with dewpoints increasing to the mid 50s. This
resulted in CAPE values around 1500J/Kg and LIs to -6. In Oklahoma there
was little to no CAPE.
While the instability was a concern, it was
expected that as the trof approach storms would be able to develop due to forced
lift, cap removal, and steepening lapse rates. However, as luck would have
it, little activity developed and certainly nothing significant. The
Oklahoma storm shield worked great. The dryline progressed rapidly
eastward during the night and was in Oklahoma City at 6am on the 24th. Said
feature continued east with showers and thunderstorms along it. This
activity intensified during the late morning as thermodynamics improved across
eastern Oklahoma. Wind damage occurred in Spiro with two mobile homes
destroyed and about 20 others minor damaged. Activity then continued in to
Arkansas and Louisiana where additional damaged occurred, especially in
southeast Arkansas.
My belief as to why Oklahoma missed out on the severe stuff is
lack of instability and the very dynamic upper system. The 850mb jet was
50-60kts overnight and this most likely sheared any attempts at convection.
What I'm a little surprised at is the OUN sounding from 12z, below.
Instability was decent for this time of year and yet little to no convection
occurred. It would appear the cap might have held until the dryline
passed.
One big story from this event was
the very strong gradient winds that occurred behind the dryline and cold front
as the surface low departed. Here
is a Mesonet map of max wind gusts for Saturday, none of these were from
thunderstorms. Something else to consider is that the models will not tell
you if a precip here is severe convection, convection, or rain. Sometimes
they can't even tell you if it is winter or liquid. That is a talent
forecasters have to develop and it takes years. This event is a good
example as very limited severe weather occurred in Oklahoma despite the model
progs of 0.50 inches, however in southeast Arkansas, it was all severe.
It was certainly an interesting early season event. I
wrote a discussion on this only for historical purposes. It was certainly
a lesson learned for me.
SPC Products: SWO
Day 1
Graphics:
Risk Area
-
Tornado
Prob -
Damaging Wind Prob -
Hail Prob -
Storm Plot
-
LSRs
Sounding:
OUN - 12z
Mesoeta 00z Initialization:
Surface Pressure
-
Dewpoints -
CAPE -
0-3km Helicity
-
850mb
Temperatures -
850mb Dewpoints
-
850mb Windspeed
-
850mb Vertical
Velocity -
850mb Relative Humidity
-
700mb Wind
-
700mb
Temperatures
-
700mb Relative Humidity
-
700mb Vertical
Velocity -
500mb Vertical Velocity
-
500mb Temperature
-
500mb Wind
-
250mb Wind
-
250mb Relative
Humidity
Hook-Echo Discussions for this event.
