April 3, 2008
Storm Chase
Southwest
Oklahoma/Northwest Texas
Editor: Putnam E. Reiter
Forecast/Setup -
Risk Area: Moderate Risk
Initial Target Area: Lawton, Oklahoma
A warm up event occurred on Sunday 03/30
into 03/31. On Sunday a cluster of storms developed in western Oklahoma
and moved east. These storms evolved into two supercells that moved into
central Oklahoma. As the first storm hit HWY 81, it turned left
(northeast) and accelerated, indicating that it was elevated. The storm
eventually was absorbed into the larger supercell back west. The second
supercell also turned left at HWY 81, but it did not weaken. It continued
northesat and produced a tornado in western sides of Edmond. Storms
developed on Monday in central and eastern Oklahoma. A few tornado hits
were recorded. A cold front pushed through the area and to the Texas Gulf
coast.
Models progged another southern stream
shortwave trof to move into the region on Thursday. This looked like a
very favorable setup since moisture would be in Texas and this system looked
stronger than the one on Monday. For Day 3, SPC gave the area a slight
risk with a 30%. The Day 2 went to a moderate risk with a 45%/10% hatched
area over much of Oklahoma into Texas. The Day 1 continued the moderate
risk but brought it south some, with 10% tornado, 45%/10% hatched hail, and 30%
wind.
The reason for some of the changes was due
to model indications that the upper system will shear out as it moved into
confluent flow across the region. Additionally, there were indications
that a lead shortwave trof would lift northeast across the region early in the
morning. This would serve to veer surface winds and push a cold front into
Oklahoma. It also caused the 850mb and 925mb lows to lift out with it,
causing somewhat unidirectional flow and a weakness in the flow.
Even though we had some concerns about the
eventual evolution of this event, there seemed enough parameters to warrant a
chase. Thermodynamics were progged to be quite impressive across with
region given temperatures in the upper 70s and dewpoints in the mid 60s.
These did develop and the models had a pretty tough time, especially with
moisture. The NAM had a real tough time with moisture and the warm front.
The warm front moved farther north than the NAM progged. The GFS did a
pretty good job with the warm front and associated thermodynamic fields. A
key indicator was that OKC hit 80F today and was only progged to hit 69F.
Storms fired about three hours ahead of
prediction. Initial activity occurred in northwest Texas with storms
remaining discrete. More cluster activity developed in Oklahoma. One
main storm in northwest Texas produced the most high-impact weather across
Archer City and points east. The storm continued east and started to
weaken as it moved near Marietta. Other storms developed near it and one
back in northwest Texas. Around 18:00 CDT a northward moving outflow
boundary in southwest to central Oklahoma developed convection. This
activity lined out but a few discrete storms developed around 21:00. A few
discrete storms moved along the Red River into McCurtain County.
The only tornado warning in Oklahoma was in
McCurtain County. Overall this event was not what we forecasted, but those
happen. There were storms, so that's a win. Looking back at the
thermodynamic data there was a CAPE min just south of the northwest Texas
activity. This explains why the storm was very intense until it got near
Nocoma, Texas, where it seems the storm started to ingest lower CAPE air.
Storms managed to develop farther east along I-35, where CAPE values were
higher. Farther north in Oklahoma, storms had more CAPE to work with but
the surface - 850mb flow was rather weak. I think these factors
contributed to a reduction in this event.
SPC Products:
SWO
Day 1
Graphics:
Risk Area
-
Tornado
Prob -
Damaging Wind Prob -
Hail Prob -
Storm Plot
- LSRs
- MCD's
Misc Products:
Area Weather Updates
Sounding:
OUN and FWD
GFS 00z Initialization:
Surface Pressure
- Dewpoints -
CAPE
- CIN -
Surface Temperature
- 850mb
Temperatures -
850mb Dewpoints
- 850mb Wind -
850mb Relative Humidity
- 700mb Wind
- 700mb
Temperatures -
700mb Relative Humidity
- 500mb Temperature
- 500mb Wind
-
500mb Relative Humidify
- 500mb Vorticity
-
400mb Wind -
300mb Wind -
250mb Wind
- 250mb Relative
Humidity -
200mb Wind
Hook-Echo Discussions
- see the blog, sequence number is 2008-7-X
SPC Case Review
The Chase -
Team 1 - Brett
LaBare, David
Underwood, Rob Ferguson, and Putnam Reiter
Miles Driven - 300
Departure Time - 14:00 CDT
Return Time - 19:30 CDT
We left Oklahoma City and headed south on I-44 towards Lawton,
our original target. We picked this due to the expected retreat of the
dryine during the afternoon. It would fit the best spot for storms given
instability and some speed/directional shear. Before we could leave,
storms started to develop in northwest Texas. This prompted a weather
watch from SPC.
As we headed south we got radar data and saw two storms of
interest. The first storm was near I-35 and the second one approaching
Waurika. I toyed with going through Duncan, but we ended up staying on
I-44. This is one issue I've really been trying to work on, ie not
modifying our chase target unless necessary. As we got close to Lawton,
another storm had developed southeast of Archer City. This storm
immediately seemed different and a better target. We kept on going south,
intending to intercept this storm. Getting into Texas the storm was quite
impressive and had a mesocyclone. We stopped for fuel and resumed our trek
south.
This is where things got tough. TxDOT had closed the 281
exit from I-44 in Wichita Falls. So, we had to exit to the old HWY through
downtown. This was made worse due to a wreck. I decided to navigate
us to Kemp Road and then south to Southwest Parkway on back to HWY 281. To
say the least, this really set us back. The storm was moving 45mph and did
not slow down. It seems the storm could not get rooted in the boundary
layer. I really expected it to happen, but given the instability min to
the south, not a shocker.
Since the storm had taken off to the northeast, we had to lay
catch up. We took 1954 east from HWY 281 and drooped out on HWY 287 just
northwest of Henrietta. We headed southeast on HWY 287 and exited at 287B
to turn north into Henrietta. We linked up with HWY 82 and went east.
The storm had impressive VILs much of this time, but as we got east I started to
know the storm was losing some structure. We continued east through
Ringgold. About 5-6 miles east we finally saw some hail on the ground.
We had been looking for it given the numerous reports of baseball and softball
hail. Additionally, RADAR kept suggesting some pretty impressive hail
sizes also.
At this point we noted the storm had really lost its structure
and a new severe thunderstorm warning had it heading east at 55mph. There
was no way we'd catch it and wasn't worth the effort. The weather service
had been on the radio concerned about the storms developing in central and
southwest Oklahoma. We decided to go look into this, so we headed back
west and at Ringgold turned north on HWY 81. The time was about 17:15 and
there was plenty of sunlight left. We watched the towering CU to our north
develop into thunderstorms. RADAR showed a different view in the sense
that a line was forming. We watched it as we headed north and the
organization hadn't improved by the time we reached it at 18:50. Since it
was obvious this day was done, we decided to jump on I-44 at Chickasha and head
home.
Storms did continue along the outflow boundaries in this area
until the cold front undercut them. They did try to become discrete, with
a few managing to produce some nice hail. However, that was the extent of
their impacts.
Lessons
Learned -
- Forecasting: I really can't complain here,
it happens. A lot other chasers were out and we did get storms.
- Traffic: Wichita Falls was horrible and I think we handled
this pretty well. If I had thought a little ahead of the storm, we
might have spent more time on it.
Multimedia
-
Backedge of Archer City storm, looking south from Wichita
Falls - 1
Rob having fun - 1
Squall line in Oklahoma as view from HWY 81, looking north -
1
Fredrick, OK - RADAR Loop
- 1.2MB
Webcam - 10MB
Encounters
-
Engaged
Storm: Belcherville, Texas
Tornado: No
Funnel: No
Hail (larger than 0.75 inches): Yes - on the side of the road
Wall Cloud: No
Wind (above 57.4 mph): No
Engaged Storm: Ninnekah - Squall line
Tornado: No
Funnel: No
Hail (larger than 0.75 inches): No
Wall Cloud: No
Wind (above 57.4 mph): No
