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April 26
April 26,1998 C. Iowa Severe Storms
I was joined today by
Brian Stertz , who I have chased many storms with over the
past 12 years. He was visiting from St.Louis and was hoping to chase at least one
of the days he and his wife Debbie took off to visit Tulsa. We patiently waited for
a severe storm situation to gel but with no luck. We reviewed the weather data
frequently and April 26 was the only day in which severe weather could possibly
develop. That morning, we analyzed the data and the numerous forecast models
to pick out our target area. Iowa looked to be the area where all of the favorable
parameters were coming together. The limiting factor once again would be the cap. We left
Tulsa around 10am for Iowa and targeted the Des Moines area for
the best chance of tornadoes today.
The Storm Prediction
Center outlooked almost all of Iowa with a moderate risk
of severe storms based on a strong outflow boundary/ dry-line intersection over
SW Iowa and a negatively tilted shortwave expected to rotate through Iowa by
evening. The cap minimized any convection so we felt comfortable leaving Tulsa
so late in the morning. By the time we reached Des Moines, the outflow boundary
was seperating 70 degree air with near 90 degree air. Also a dryline was moving
into W.Iowa. We arrived in Des Moines just as the storms started to fire to the sw.
Interesting hourly weather observations at 5pm were reported. At Des Moines,
the temperature was 72 and the winds were 120 degrees at 18mph. At the same
time, Shenandoah (80 miles sw of Des Moines) was reporting a temp. of 98 with
winds at 250 degrees gusting to 32mph and a dewpoint of 30. Not a bad setup
usually!! Today, however, was different thanks to the cap.
Storms fired on both the
dryline to the west and along the east/west outflow
boundary over C.Iowa. We opted to chase the dryline storms since they were
more isolated and would be moving right at us! Visually the storms appeared
to be struggling as we headed west on I-80. The cap was still too strong to allow
the storms to become surface based. We continued to hope that the shortwave
would break the cap as the mid-level cooling pushed in from the west. Instead,
most of the mid-level cooling remained over NW Iowa as the vortmax lifted due
north across Nebraska into NW Iowa. Once again the cap would win! The storms
attempted to break the cap, and a few had decent hook echoes to the s and sw of Des
Moines. However, these storms could never truly become surface based
and would produce only large hail. We tracked one of the storms from near the
town of Winterset to near Knoxville. Impressive hail cores were observed but
that was about the extent of severe weather this day. Chalk this day up as a bust!
Now it was time for the long drive back to Tulsa....
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