April 21, 2004
Storm Chase
Central Oklahoma
Editor:
Putnam E. Reiter
Forecast/Setup -
Risk Area: Moderate - 10%
hatched area on tornado graphic
Initial Target Area: Anadarko, Oklahoma
A strong Canadian cold front
moved through the region around April 12th. This surface feature went
through the Gulf with a 1035 surface high settling to near Brownsville.
While the surface high moved east and return flow started a few days later, the
high held on to the Gulf until the 20th. Early on the 20th true Gulf
moisture started northward and set the stage for a rather active weather week.
Aloft a broad longwave trof developed
across the central U.S. with periodic shortwave trofs moving through the mean
flow. A surface cold front moved to northern Oklahoma Tuesday morning.
Tuesday afternoon severe thunderstorms developed across much of eastern Oklahoma
in response to moisture return and mid-level support. While a few tornado
warnings were issued, none have been confirmed. With the strong convection
Tuesday night the cold front moved south into southern Oklahoma.
Models progged this feature to
moved rapidly north on Wednesday as the surface low reformed west into NW Texas
in response to another shortwave trof moving toward the region. The
dryline was progged to move to near central Oklahoma by late afternoon with the
warm front in far northern Oklahoma. Mid-level winds were favorable for
severe thunderstorms and supercells, however surface speeds were weaker than
Tuesday.
Initially we had a tough time
deciding our target area. SPC outlooks and other NWS data helped. We
eventually decided on Anadarko, going with the dryline. Early Wednesday
morning clouds persisted until 12:30pm across much of central Oklahoma.
The clouds put central Oklahoma a few degrees behind the rest of the state.
Despite these clouds, temperatures warmed into the mid-70s resulting in CAPE
values around 2500 J/Kg. The 18z Norman sounding revealed that the cap was
a little stronger and would hold down convection until mid-afternoon.
The cap did break, around
15:45, as two storm clusters developed. One was south of El Reno and the other
south of Chickasha. The first area developed into one storm and moved
east-northeast across Oklahoma City. The second area developed into three
individual storms as they moved east from Chickasha. Rapid convective
development continued across much of Oklahoma by 16:30 with some storms moving
due north and others moving east. This resulted in storm mergers and
inflow disruption. The only confirmed tornado was in western Oklahoma.
The Oklahoma City storm was a prolific hail producer, as noted by the pictures
below.
Severe thunderstorms develop
once again on Thursday in a similar synoptic pattern. The main difference
was that the surface boundaries remained across mainly eastern Oklahoma.
Several confirmed tornadoes occurred near Tulsa in a region that was probably
favored by a leftover mesolow that backed the surface winds and increased 0-1km
helicity. Also, CAPE values were higher this day with 3600 J/Kg noted
across southeast Oklahoma by mid-afternoon. This was due in part to
continued quality moisture return from the Gulf.
SPC Products: SWO
Day 1
Graphics:
Risk Area
-
Tornado Prob -
Damaging Wind Prob -
Hail Prob -
Storm Plot -
LSRs
- Mesoscale Discussions
- Watch
-
Misc Text -
Tornado Warnings
Surface Maps:
Temperature
- Dewpoint -
Wind Speed -
CAPE -
LI
Soundings:
18z
OUN -
ARPS
Sounding
Mesoeta 00z Initialization:
Surface Pressure -
850mb Temperatures
-
850mb Dewpoints
-
850mb Windspeed -
850mb Relative
Humidity -
850mb Vertical Velocity
- 700mb
Wind -
700mb Temperatures -
700mb Relative Humidity -
500mb Vertical Velocity -
500mb Temperature -
500mb
Vorticity -
500mb
Wind -
500mb Relative Humidity -
250mb Relative Humidity
- 250mb Wind
The Chase -
Team 1 - Andy Wallace,
David Underwood, Rob Ferguson, and Putnam Reiter
Miles Driven - 180
Departure Time - 14:30
Return Time - 19:00
We left Oklahoma City and
headed south on I-44. Our intention was to place ourselves in the middle
of our target region. We stopped at the McDonald's just north of Chickasha
on I-44. We stayed there for about 30 minutes watching the clouds.
Cumulus was the main cloud type, although two areas of enhanced CU were noted.
One area was north near Tuttle and the other one was just to our south.
The main question was which one would break the cap. We got word that the
Tuttle storm had developed a 30dbz core and appeared to have gotten through the
cap. Additionally, the chase crew noted rapid growth to the towering
cumulus to our north. We started back north on I-44 towards Oklahoma City.
We got word that the storm had a 50dbz core. This was the one, so we got
going. Approaching Oklahoma City we got radar data back and were able to
review the setup.
The storm had a 60dbz core and
a severe thunderstorm warning by this time. We noted that the storm was
north of I-40 near Yukon and was moving northeast at 15-20mph. We
continued north into Oklahoma City on I-44. As we got north of Will Rogers
Airport we got storm scale features. The storm had good structure, but no
lowerings. The time was around 16:10 CDT and rush hour was a big concern.
We drove north of I-40 to NW 10th (Fair Park). Stopping here, we monitored
the storm. A tornado warning was issued for this area based on radar
indications. Our view had little in the way of wall cloud or funnel
activity.
After fighting radar for a
while, we finally got a view. The reflectivity data showed that the
strongest part of the storm was near I-44 and Hefner Parkway.
Additionally, surface observations indicated a break between the main rain core
and closer features. Assuming a northeast movement, we decided to drift
north on I-44. As we entered I-44 Rob noted rotation to our northwest.
We kept going to NW 36th at my suggestion. Exiting here, partly due to
traffic as everyone was stopped, we sat near the exit ramp long enough to see
definite rotation almost on top of us. We evacuated east to May Ave and
then south about 1/2 mile. Stopping for a few minutes to regroup we noted
that the rotation area was still quite close to us. At this point we
realized that the storm had not only turned east, it turned a little
east-southeast. We got south to NW 23rd street (Rob's original suggestion)
and went east. The storm's structure continued to rapidly improve along
with wall cloud and funnel activity. We drove on east along NW 23rd street
during rush hour traffic, luckily the storm was moving about 20mph.
Our view was obscured by
buildings and contrast, we were west-southwest of the circulation area. We
drove past Lincoln Ave into eastern Oklahoma City. The storm rapidly
became better organized and a condensation funnel developed. Eventually
the funnel was lower than the buildings. We did not call it a tornado
since we could not see surface contact. As we got close to NE 23rd and MLK
(looking to our northeast about 2-3 miles) the four of us saw black material
wrap counter-clockwise and up into the circulation. Seeing this and hearing
another report of a tornado, we called it a tornado. The black material we
believe resulted from a brief touchdown and was debris or dirt. It was
very brief and lasted only a few seconds.
Not sure of storm motion and
knowing it was getting away from us, we drove north on MLK to NE 36th.
Turning east on NE 36th we went to I-35 and decided to turn back south. While on
NE 36th the rear-flank downdraft hit us and the storm rain-wrapped the
circulation area. We drove back south to NE 23rd (also HWY 62) and went
east. As we continued east we had no features and eventually realized that
the storm had lost much of its rotation features. Getting past Sooner Road
we noted several other chasers turning around. Looking at radar we saw a
line of supercells extending across much of the state. It appeared to us
that the storms were too close to each other for tornado potential.
Additionally information from Norman NWS and SPC further confirmed this
analysis.
We did decide to go intercept
some storms farther south. So, we turned south from Harrah onto HWY 270
(also Harrah Road).
About this time we got into some heavy rainfall and moderate hail. We
definitely got quarter sized hail and maybe some golfball. The hail wasn't
too big as we didn't lose any of our wind cups. Clearing this storm, we
drove on south to I-40 and went east to HWY 177, just west of Shawnee. We
drove south to Tecumseh and took another look at radar. While the storms
remained severe we figured that the tornado potential was pretty low. At
this point we called the chase and headed back home.
Thanks to Ray for radar
support.
Lessons Learned -
- Storm motion, storm
motion, and did I mention...storm motion! This almost got us hosed.
We know that supercells may turn right. This one did so and we go catch in
a bad spot. However, our contingency plan got us to safety.
- RADAR data are not essential once on a storm. We spent too much
time trying to get data once back in OKC.
Multimedia -
Stills:
- Oklahoma City Storm,
looking west from Fair Park (NW 10th and I-44).
Pic 1,
Pic 2.
Funnel, looking east from NW 23rd and Walker.
Pic 1.
Funnel, looking north from NW 23rd and Broadway.
Pic 1.
Funnel (tornado?), looking northeast from NE 23rd and MLK.
Pic 1,
Pic 2.
- Hail leftover from the Oklahoma City storm, pictures taken at 9:00pm,
over four hours after the storm passed.
Pic 1,
Pic 2.
- Hail from the Oklahoma City storm, about an hour after it passed.
Pic 1,
Pic 2,
Pic 3,
Pic 4.
Courtesy Ray Hardy.
Animated GIF's (continuously
loop):
-
Oklahoma City WSR-88D
(RADAR) from early afternoon until late evening.
-
Chase Cam
Encounters -
Engaged Storm: NW 10th
and I-44 in Oklahoma City
Tornado: Maybe - See Note 1
Funnel: Yes
Hail (larger than 0.75 inches): Yes - in Harrah - Golfball
Wall Cloud: Yes
Wind (above 57.4 mph): Possibly, but not measured.
