May 5, 2007
Storm Chase
Western
Oklahoma
Editor: Putnam E. Reiter
Forecast/Setup -
Risk Area: Enhanced Moderate Risk
Initial Target Area: Arnett, Oklahoma
April was a quiet month for Oklahoma severe
weather wise, with much of the action going on all around us. The notable
exception was April 23rd, but even that day only produced isolated activity in
northwest Oklahoma. It stands to reason that
much of the chaser community in Oklahoma had its collective eyes on the incoming
system for today. There was much discussion about the potential activity
across the region due to a variety of forecast solution from the models.
What we did know was that deep layer
moisture was available and said moisture was of the tropical variety. This
was due to no cold front intrusions in the Gulf for over a week. Dewpoints
were expected to be in the upper 60s across the state with CAPE values above
5000 J/Kg. My first clue that something was up occurred Tuesday on a
routine look at the short-range models. The NAM had an area of 5500 J/Kg
CAPE in western Oklahoma Friday afternoon. I issued a discussion, but many
other spots didn't talk about storms. On Thursday I continued the thinking
given SPC's interest on Friday and of course the growing interest on Saturday.
Friday certainly seemed like an active day,
if storms could break the cap. The models typically under forecast the cap
and this was no exception. Originally, Saturday was contingent on Friday
activity. There are events when Day 1 (Friday) activity evolves into an
MCS or squall line and eats away at the moisture. This would reduce a
severe weather threat for Day 2. Then there is the other end of the scalle
when storms fail to form or are only isolated. Friday ended up being the
latter for Oklahoma and as many people already know didn't matter for Kansas
either. It is rather rare in the Plains when a place gets hit twice in two
days.
What made this setup so difficult was the
blocking pattern forecast to develop as the upper system moved into the Plains.
This has happened several times this year as the pattern has been very
amplified. For this event a 582dm ridge was forecast to develop across the
eastern U.S. as the longwave trof moved into the western U.S. Said trof
was progged to close off and cutoff from the main jet. However, there was
a lot of variability within the models regarding system placement and wind
speeds.
On Friday a dryline moved into western
Oklahoma and Kansas. By late afternoon storms developed along this feature
in NW Oklahoma and Kansas. These storms produced several tornadoes,
including the Greensburg, KS, wedge. No other activity occurred in the
region. The 00z NAM indicated that widespread precip would occur Saturday
morning and this was rather reminiscent of April 24th. A big difference
here was the cap, as it was progged to be much stronger. Indeed the cap
held nicely overnight and through part of the day on Saturday. During late
morning a shortwave trof brushed NW OK. A few thunderstorms developed as a
result. These storms moved north into Kansas with no other activity by
mid-afternoon. Another interesting issue was the cirrus shield across the
region.
The cirrus shield kept temperatures down
across parts of the region, but CAPE values were still 4000 J/Kg over a large
area. There was some uncertainity if storms would even develop, but by
early afternoon some activity did develop in northwest Oklahoma. After
this time dryline was quiet for several hours until about 5:00pm. Storms
rapidly developed along the dryline in northwest Oklahoma and moved north.
This activity may have initially be elevated as it moved north at 40-50mph.
Around 7pm storms develop farther south on the dryline in the eastern Texas
panhandle. These storms were surface based and moved into western
Oklahoma. The two south storms, one near Arnett and the other near
Sweatwater produced tornadoes. The Sweetwater storm was a long-track
supercell that produced a few tornadoes. By late in the evening all the
storms had moved into Kansas or dissipated.
SPC Products:
SWO
Day 1
Graphics:
Risk Area
-
Tornado
Prob -
Damaging Wind Prob -
Hail Prob -
Storm Plot
- LSRs
- MCD's - Watch
Misc Products:
Tornado Warnings
- Area Weather Updates
Sounding:
00z DDC
and OUN
NAM 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
-
250mb Wind
- 250mb Relative
Humidity
Hook-Echo Discussions for this event.
SPC Case Review
The Chase -
Team 1 - David
Underwood, Rob Ferguson, and Putnam Reiter
Miles Driven - 590
Departure Time - 13:00 CDT
Return Time - 01:20 - 05/06/2007 CDT
We left Oklahoma City and headed west on I-40. We got to
Clinton and turned north on HWY 183 and then went to HWY 33 where we turned
west. There wasn't much going on at this point, other than some activity
that developed in far northwest Oklahoma and raced northward into Kansas.
As we approached HWY 283 north of Cheyenne I really thought we
should turn south and stage at Cheyenne. There was something about this
area I thought was favorable. We decided to go to our original spot at
Arnett. Getting to Arnett, we got fuel and sat just west of town. We
noticed that the dryline was close as we watched several areas of towering
cumuulus. We saw one take off around 4:46pm CDT and watched it split.
Both died and we went back to waiting. About 5:56pm CDT we saw a storm
develop just northwest of us and decided we would follow it. There was no
activity south of this storm and we figured it would be a good one. We
followed HWY 46 north out of Arnett. As we got north of May we got
storm-scale features.
The storm had a nice rain-free base but no lowerings at this
point. It was moving north-northeast, but started to turn more northeast
as it neared Buffalo. It was about this time the storm developed a
persistent wall-cloud with differential motion. We witnessed an RFD cycle
just southwest of Buffalo with several brief funnels. As the storm passed
north of Buffalo the base started to rapidly rise. We noticed on RADAR
that the storm was weakening and then got word of development farther south.
We started back south from Buffalo on HWY 183, moving pretty
fast. We got just west of Fort Supply and took some back roads to the
west. The idea here was to get west of the storms and come around the
backside. That was a failure on our part as the storms moved around
15-20mph. Another issue was the storms were moving north-northeast.
We should have kept going south and drove in front of them. That would
have been a better chase option and probably would have allowed to see activity.
We headed southwest from Fargo on HWY 15 to Gage where we
turned south on HWY 46. As we got close to Arnett we noted a left split
coming at us real fast. Knowing that left split supercells typically
produce very large hail, we decided to get west of it. We did this on a
dirt road and barely missed getting nailed by the storm. We got within a
few miles of the Texas Panhandle as the storm passed. We then got to HWY
60 and headed east. There were two storms south of us, both of them
tornadic. Our effort continued to be getting west of these storms and at
this point we didn't have a choice. The storms had very little eastward
movement. We ended up taking an interesting trip through the Canadian
River (on a dirt road) to stay west of the activity.
Around sunset we got to Durham and saw the southern storm
getting very close to our position. We stopped just south of HWY 33 on HWY
30 and waited for the storm to pass. It was a long wait, but lots of cloud
motion and lightning. Around 9:0pm we got enough clearance to continue
south on HWY 30 and attempt to round the southwest side. We got to
Cheyenne and got some fuel. From there we headed north on HWY 283 to Roll.
We did see some tree damage midway between Reydon and Cheyenne on HWY 47.
We got to Roll and went east on HWY 47 as we got close to the storm. At
this point it was close to 10pm and there was very little lightning. We
decided to head on home through Weatherford and Kingfisher. The storm
continued to produce large hail and may have even spun up a tornado or two.
Lessons
Learned -
- Forecasting: This isn't a lesson learned,
this is how good our forecasting can be. Our two spots, Elk City/Sayre
and Arnett both were within a few miles of tornadoes. Pretty
impressive to us.
- What ultimately got us was when we left the Buffalo storm and headed
back south for the I-40 stuff. I took us on the west route, which
wasn't a good idea given the storm motion. Had we stayed east, we'd
seen a tornado. Lots of other people stayed east and got to see
action. Not a huge deal to us since we got to see some neat stuff
ourselves.
Multimedia
-
Fredrick, OK - RADAR
Loop - 1.5MB
Vance, OK - RADAR Loop - 2.5MB
Webcam - 15MB
Encounters
-
Engaged
Storm: Near May
Tornado: No
Funnel: Yes
Hail (larger than 0.75 inches): No.
Wall Cloud: Yes
Wind (above 57.4 mph): No
Engaged Storm: Roll
Tornado: No
Funnel: No
Hail (larger than 0.75 inches): No
Wall Cloud: No
Wind (above 57.4 mph): No
