4/7/98 Chase Summary by Scott Olthoff

From: Scott Olthoff (olthoff@atmos.uiuc.edu):
Subject: Successful IL Chase

Hi all,

I just thought I would give everyone a recap of last night's chase in
central IL.  Adam Houston and I left the Department (Urbana) around 5pm
yesterday and headed on I-72 towards Decatur to intercept two supercells
that were already producing tornadoes.  Tim Shy kept us up to date with
what was going on with the storm on our way to Decatur.

Once we were in Decatur, we were instructed to head on Rte 121 southeast
out of Decatur, because a tornado was on the ground in 1 mile west of a
little town called Mowequa about 7 or 8 miles south of Decatur. The storms
were forecast to move northeast at about 40 miles an hour.   The storm then
began to make a hard right and start moving almost due east. In between the
towns of Sullivan and Bethany on Rte 121 two storms merged almost right on
top of us.  As Adam an I were watching the updraft, 1" diameter hail
started coming out of the updraft.  We took off southeast towards Sullivan.
 Once we were in Sullivan we had to make the decision either head due east
out of  town on 121 for a few miles, or head south on Rte 32.  We started
to head east, and then thought twice as the storm was catching up too us,
so we turned around to head south of town to make sure we would be at a
safe distance. As we headed out of town the Rear Flank Downdraft hit with
50+ mile an hour winds and 1" to golf-ball size hail.  We drove out of the
hail about 1 or 2 miles south of town and then headed 3 to four miles south
to a road called Bruce, which is just south of Lake Shelbyville.  The road
is also called 8.00 N in Moultrie county and 1000 N in Coles county.  We
headed east on Bruce until we reached Rte 45 and headed north towards the
town of Humboldt. About 2 miles south of Humboldt we noticed another
Mesocyclone forming near Humboldt and since it was at sunset we pulled off
the road to watch.  The new meso headed east-northeast, at the same time we
watched a new wall cloud form 3 or 4 miles to our northwest just southeast
of Arthur (that meso was way back in back part of the storm, very similar
to what chaser's experienced with the tornadoes on Apr 19, 1996).   The
wall-cloud was about 1/4 to 1/2 mile wide and it set on the ground.  We did
notice some weak rotation from where we were.  It was at that time that the
tornado was on the ground, doing damage to several houses three to four
miles southeast of Arthur.  We did not have a video camera, but I was able
to take a couple of stills.  It was rather dark so I don't know how they
will turn out yet.  We weren't able to confirm it was a tornado until after
hearing damage reports from Arthur.

After watching the wall cloud/tornado dissipate we let the storm move away
from Arcola and then we headed into Arcola.  On our way into Arcola we
could see a new wall-cloud forming a few miles east of Arcola, being
back-lit by lightning once in awhile.  By this time it was dark and we
considered it too dangerous to continue chasing.  We pulled off onto the
I-57 bridge and watched the best we could what was happening to our east.
When the lightning back-lit the storm we were able to see a wall cloud and
some very interesting storm structure.  A tornado was reported on the
ground about 5 to 6 miles east of where we were, and just as the tornado
was being reported, the lights went out on the east side of Arcola, with no
lightning strikes. That will make your hair stand on end. 

In hindsight it was a good chase, but we just ran out of daylight. Also, We
might have been alright if we would have continued east in Sullivan, but
then again with softball size hail reported, I'm glad we didn't.   Adam and
I would like to thank Tim Shy for his excellent nowcasting and getting is
in position to see a great Illinois Supercell.  It was mine and Adam's
first Illinois tornado.

If you have any further questions just let me know.  If the pictures turn
out I will post them on the web.

Scott Olthoff

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