Photo Gallery - Page 3

April 15

April 15, 1998 Eastern Missouri and Southern Illinois Chase

The forecast for severe weather was highly optimistic and promising for the
St.Louis Mo. area. A high risk of severe storms was outlooked by the Storm
Prediction Center for much of Eastern Mo and S.Illinois. A strong upper level
jet stream max was forecasted to cross over the 850 mb jet axis just to the
east of St.Louis by early evening. An intensifying surface low was to track from
SW Mo to C Illinois causing strong convergence and surface pressure falls
in the outlooked area. Early morning t-storms created a pronounced outflow
boundary east-west across Mo from near Nevada to just north of Rolla to near
Mt.Vernon Illinois. This outflow boundary was expected to provide the focus
for severe weather, including strong tornadoes, across the area.

I left Tulsa on a Southwest Airline flight to St.Louis at 10:30 am anticipating
severe storm development late in the afternoon. On the flight to St.Louis,
I noticed a lone storm organizing over W.Missouri (with an over-shooting top)
and thought that this might be the start of the severe weather day. Little did I
know that this would be one of the few storms to fire in Missouri this day. The
storm pulsed several times before I reached St.Louis and became severe at
times producing nickel to quarter sized hail between Nevada and Camdenton
Mo. I met up with St.Louis residents Brian Stertz and Rich Thies at Brian's apt.
shortly before noon. The storm over W.Missouri continued to pulse to severe
levels and it showed signs of supercell structure as it moved towards the Lake
of Ozarks area in C. Missouri. We analyzed weather data exhaustively to pick
out our chase target area. Severe parameters were much more favorable in
S.Illinois, but we could not disregard this long lived storm tracking towards
us from the west- especially since it has produced up to golfball sized hail in
the Camdenton area.

The airmass in St.Louis remained fairly cool much of the afternoon, but tried to
recover by late afternoon; the recovery was sure to be more rapid to the south
of St.Louis. We targeted the Festus Mo area and headed south to avoid rush-
hour traffic on I-270. On a local scale, the outflow boundary held firm for much
of the afternoon with a very slight drift to the north. The storm over the Lake of
Ozarks area was now a bonafide supercell with increasing circulation on radar.
Temperatures south of the boundary rose well into the 80's, while temperatures
held in the upper 60's to lower 70's north of the boundary. An explosive and
favorable condition indeed!! The limiting factor to severe weather this day was
the cap (warm air aloft) and the instability needed to break this cap. Everyday
there is a limiting factor, and this happened to be today's forecasting challenge.

Our initial thoughts were that the storms would fire east/west along the outflow
boundary once the cap gave way. We did not expect that a storm which formed
in W.Mo would be the only significant supercell to develop on the Missouri side
of the Mississippi River. We waited patiently in Festus for other storms to pop,
but grew ever more concerned with the storm passing nw of Rolla. Tornado
warnings had been continually issued for this storm as it tracked east at 30 mph.
The cap held tight over Mo and we decided to head for the storm now in Maries
county Mo (which was under a newly issued tornado warning). Around 4pm, the
tornado warning was extended into Gasconade and Franklin counties-this was
just 30 miles to our northwest. We picked up the pace and headed through the
windy back roads to reach our new target city-St.Clair (Franklin Co.). A tornado
report(unconfirmed) was placing the circulation between Owensville and our
target city St.Clair.

wallcdmo41598.jpg (18034 bytes)

More Info & Pictures