May 11, 1999     NE Oklahoma Chase

While most chase days are able to be targeted well in advance, today was the
classic example of elements coming together at the last minute!! The forecast
models were indicating that severe storms would develop by early evening in
or around the Tulsa area. A slight risk for severe storms was outlooked for much
of NE Oklahoma for the late afternoon and evening hours. The cap was expected
to hold convection down until then. A weak dry line/surface trough was located
over C.Oklahoma by early afternoon, but was anticipated to move steadily to the
east towards Tulsa. I knew that this was going to be a later show so I really did
not pay much attention to the weather until around 4pm. Satellite imagery showed
a line of towering cumulus bubbling on the convergence line nw-sw of Tulsa. A
few of the tcu were starting to glaciate(anvil out), but the cap held these cells in
check. Further to the east, several areas of clusted cumulus development were
organizing near Claremore and Okmulgee Co.. These 2 clusters eventually would
become the supercells later. Brian Stertz got off work at 4pm, and he too started
to notice the 2 clusters of cumulus development. He was already planning to chase so he drove over and we got things ready.

Originally, we started to head for the cluster of towering cumulus over Okmulgee
Co. and extreme S.Tulsa Co.. We also paid attention to the cluster forming to the
immediate east of Tulsa. Brian was driving so I started to pull up radar data to
monitor these 2 areas. We started to notice something that would change plans
considerably. The winds started to veer across Tulsa, and the developing cell
over Okmulgee Co. fell apart. Meanwhile, the cell near the Tulsa/Rogers Co. line
started to explode!! The convergence line had met the unstable air!! We raced back up to I-44 and continued east on U.S. 412. The storm was now becoming a
supercell just to the south of Claremore. Radar indicated that very large hail was
pounding S.Rogers Co. between Claremore and Inola. We could see the updraft
base already so we were in great shape to intercept. The closer we got to the
storm, the larger the hook echo on radar grew. We watched the base closely for any appendages/funnels, but the storm was in the early stages of circulation.

Just east of Inola, we pulled over and watched the circulation tighten up slowly
to our north. Apparently, the circulation had already gusted out. Rain and hail
obscured our view of the storm's first circulation area that was about 3-5 miles
south of I-44. We were looking at the tail end of the gust front. Gust fronts are
usually a bad sign for storm chasers; however, the tail end of a storm circulation
gust front can also be the lead in to later exciting times. We watched the storm
rotate and continue to send out more and more outflow, enhancing the very slow
moving gust front. In classic cyclic style, the tail end of the gust front quickly held
up and a new fresh storm tower exploded along the gust front. At first, weak rain
curtains appeared under the new updraft. However, this updraft region exploded
into a substantial core with frequent cloud-ground lightning strikes to our north.

The new storm took control and was soon THE supercell, although the northern
part of the storm continued to drop large hail and had weak rotation on radar. We
followed the new supercell east towards Chouteau on U.S.412. Radar indicated
moderate rotation with the storm, but a very large hook echo was shaping up nicely to the west of Pryor and northwest of Chouteau. Initially, the updraft base
was fairly high and uniformly flat. In just a few minutes time, a wall cloud started
to lower from the flat base and numerous cloud tags/scud appeared. A tornado
warning was issued for S.Mayes Co. for the supercell. Moderate rotation was
giving way to more intense circulation as the RFD started to punch into the main
updraft tower and wall cloud area. We watched the storm wrap up in a big way
about 2 miles north of 412 or immediately northeast of Chouteau. Thick inflow
bands appeared out of nowhere and this was very interesting to us. This storm
was in hyper-spin mode now!!

The RFD blasted us with 70 mph+ winds as we tracked the storm slowly east
along 412. By now numerous spotters, law enforcement and local resident' s
lined the highway. A tornado appeared to be imminent, but the circulation soon
became obscured by rain curtains. We wanted to get away from the local circus
around Chouteau, so we headed further east on 412 towards the Cherokee Tpk.
near the town of Locust Grove. We pulled over and the Cherokee Co. Sheriff
joined us as we watched the visibly rotating storm tower approach. Prominent
inflow bands streaked back to the west into the circulation that we now feared
was rain-wrapped. The Sheriff watched the storm with us and wondered where
the tornado would come out from. The tornado warning was extended into his
county, and the developing tornado was reported along 412 to our west. Radar
was now indicating that the storm was turning right (southeast) so we plotted a
new intercept area to the northwest of Peggs near the small town of Murphy. The
Sheriff headed that way too, and we all watched the very low bowl shaped wall
cloud cross over the ridge to our west. No funnels or tornadoes were under the
wall cloud, although it did have incredible spin as it continued to track even more
to the southeast (340 degrees at 35 mph). We knew our viewing time was on the
wane so we looked for other storms which were in chaseable areas. Sunset was
coming quick so intercept would almost surely be after dark.

Radar indicated a new increasing supercell developing over S.Wagoner Co.. We
were in fair shape to intercept this supercell, but not the greatest position we
could be in. We had to take the windy road out of Peggs south in order to get
ahead of the very large core and get in front of the circulation area. We reached
Tahlequah ahead of the core (now producing baseball sized hail). We remained
focused on the circulation that was crossing Fort Gibson Lake and heading to
the east-southeast. Brian plotted an intercept and this was going to be very near
the town of Fort Gibson. We hoped that we could 1) avoid the large hail, and 2)
reach town before the wall cloud passed. The supercell continued to violently
rotate on radar as there was now a complete donut shaped circulation on radar.
A tornado had to be on the ground!! We could see long and thick inflow bands
pointing to the circulation about 5 miles to our west. We headed west on U.S.62
towrds the town of Fort Gibson. The circulation abruptly turned more to the southeast as we closed in on Fort Gibson. Tornado warnings were extended for
W.Cherokee and E.Muskogee Co. We were just east of town and we could finally
make out the outlin of the large low hanging wall cloud. Unfortuantely, with the
southeast movement of the supercell, the large core came upon us very quickly.
we headed a little more east to get out of the rain. The winds were switching
back and forth from north to northeast. The circulation passed just to our west
and south!!

Extremely heavy rains and large hail (up to golfball sized) pounded us as we moved back west into Fort Gibson. Spotters were now reporting intense rotation
and funnel clouds immediately east of Fort Gibson Lake in W.Cherokee Co. We
were now cutoff from the view of the circulation to our south. North winds raged
on as we approached the main part of the core. The hail intensity increased as well!! We were smack dab in the middle of a hurricane hailer!!! Numerous cars
pulled off as winds approached 80 mph+ and nickel-quarter sized hail blasted
the area. A few cars even ended up in the ditch as the intense core moved across
U.S. 62. By this time, a tornado was reported near the town of Braggs, or just 5
miles to our south. Our chase was over, but it was interesting to listen to the ham
radio traffic/spotters as the circulation continued on to our southeast. On the way
back to Tulsa, we passed through yet another severe core and hail larger than
quarter sized pelted us on the Muskogee Tpk. in S.Wagoner Co.. We returned
back to Tulsa around midnight, and tornado warnings continued for Cherokee
and Sequoyah Counties for the circulation we followed earlier. Not bad for a
slight risk day!!