HIGH Risk
Chasers: Don

Forecast: I placed my initial target area on the Mississippi between
St Louis and Cape Girardeau based on these parameters from the 24hr
414 ETA and hand analysis: 995mb surface low SW of STL backing winds
to the east and southeast, temps 70-75F, dewpoints aoa 65F, and maximum
surface heating yeilding CAPE values between 2000-2500 j/kg. LIs were
progged aoa -6dC. The area was just north of the core of 140kt 250mb
winds and the area of strongest cyclonic shear. A jet of 60kt 500mb
winds were approaching from the west--the ETA and RUC differed on the
location of this jet, but a hand analysis of the soundings suggested
the ETA had the better handle on this feature. This area would also be
under the nose of a 40kt 850mb LLJ. Most importantly, convection in the
morning would likely leave an outflow boundary roughly between SGF
and EVV, and forecast soundings and hodographs progged strong
deep-layer shear in this area. Target city: Chester, Illinois.

The biggest problem with this chase was the location. Southeast
Missouri and far southern Illinois are not good places to chase which
left only a narrow window of opportunity east of the river and north
of a Carbondale line. I left Wisconsin at 7am, stopping in Bloomington
for a quick peak at the latest satellite image which showed the expected
outflow boundary stretching across southeast Missouri and far southern
Illinois--too far south! I was determined to stick out my forecast
regardless so I continued down I-55, hoping the boundary would drift
north. A red box was issued to the north. Turn back? No, stick to the
forecast. I left the interstate and continued south on IL 4. Low-level
clouds had increased so I knew I was approaching the boundary. The
surface conditions: T was 68F, Td was 58F.

Just south of Sparta (aoa 3pm), the clouds quickly broke revealing
a hazy but glorious blue sky. T was now 74F, Td was 65F! I was south
of the boundary and still in chasable territory (but not by much). I
stopped and downloaded windbarbs, dewpoints, and 2hr pressure
tendencies. The surface low was just west of STL, with the strongest
pressure falls extending from STL to the southwest. I drove through
Chester and parked for over an hour--did the windows, readied the
cameras, and waited. The boundary seemed to be drifting north and
the atmosphere was destablizing rapidly evidenced by bands of tall
building ACs overhead. Finally, red box issued at 4:30.

Severe reports started coming in west of STL, tracking east at 25 mph.
Very chasable! I drove up IL 3 to Red Bud, and then west for 5 miles.
The sky was very dark to the northwest, but other than the curved edge
of the anvil to the west, no structure was evident. Tornado warning
issued aoa 5:15. Thunder to the north, a black imposing core, and then
I saw the RFD approaching, led by a churning shelf cloud. Lots of large
pendulous scud, looked like multiple wallclouds but only the area to
the north was rotating...and occluding. I went south to avoid Red Bud
because traffic had been heavy earlier so missed that touchdown. I drove
through Baldwin, Marisa, Oakdale, Ashley, Irvington, to Dix, where I
turned south because it was almost dark and stopped for a coffee in
Mt Vernon. (My chase log was lost this day so I cannot be more specific).

The HP storm seemed to have achieved a steady state for hours as it
propagated along the boundary with new low-level mesos developing along
the forward-flank downdraft which were then overrun and occluded by the
RFD. There was lots of impressive shelf cloud action, huge areas of dark
scud, several mangy wallclouds and funnels, and one cone-shaped tornado
which I captured on a new role of film. This tornado developed rapidly along
the interface of the forward/rear flank downdrafts as a lowering and then
a needle-shaped tornado which quickly evolved into the larger tornado.
That was then swallowed between the downdrafts as the RFD surged
forward. Elapsed time: 2 to 3 minutes. All the other film I took was
ruined later. (One water-damaged tornado pic)
 
After waiting for the storm to clear I-57. I drove north with the idea
of stopping in Effingham for the night. I encountered another storm in
Marion County and actually pulled off the road for a few minutes to let
the worst of it pass. Almost to Effingham, the van suddenly slid to the
right into the guardrail, bounced across the road into the opposite
guardrail, across the road again and down a steep embankment into a
grove of trees. Up to this point, I had not hydroplaned at all or felt
any indication that I was close to breaking traction. The front tires
were virtually new aqua-treads. It felt more as if I had been pushed
into the guardrail.

I went back to the scene the following day to try and figure out what
happened. The road there crosses the Little Wabash, sloping downhill
and pitched slightly as it makes a gentle curve to the left. There was
nowhere water could have ponded on the road even in a heavy rain. It
seems more likely that a wind gust was channeled through this valley
and hit the van as I reached the bridge. The first impact with the
guardrail blew the right front tire and after that, I had no control
over the van. Fortunately, I was alone and wearing a seat belt. The
air bags deployed and likely saved me from serious injury. All in all,
I felt pretty lucky afterwards, more so when I found all the equipment
in the van had survived pretty much intact.

Chase distance about 1000 miles.