Roger Edward's April 19, 1996 Chase


===== 19 Apr 96 Central IL Tornadic Supercell =====
      by Roger Edwards

NOTE:  Because I keep detailed logs, my written chase accounts
       tend to get very long.  If you have no interest in a blow-by-blow 
       of the early tornadic stages of the Springfield/Decatur/Urbana 
       storm, stop here.  

CHASE FORECAST:

Rich Thompson and I had been anticipating supercell potential in west-
Central IL for several days, helped by a very consistent ETA model
which had trended in all the "right" directions from run to run.
In particular, with instability not expected to be a problem, ETA
storm-relative wind forecasts at low, middle, and upper levels for
the evening of 19 Apr stayed within tornadic supercell guidelines
(Thompson 1996, SLSC paper) over the eventual target area.

Also, the "nose" of the low and mid level dry intrusions was aiming
the same way.  All the favorable parameters were so well overlaid in
the forecast atmosphere over west-central to central IL that each new  
model run was a virtual neon sign flashing, "TORNADOES HERE."  The 
only negative factor was the fact that I could take the day off;
which had always been the most reliable chase-bust predictor before!

I'd seen too many "near-certain" outbreak situations go awry to get 
too excited; but we planned strategy well in advance just in case.
We decided the evening before to leave Kansas City late the next morning, 
drive to the area between Quincy and Springfield, and get 40-60 miles 
ahead of expected eastern MO convective initiation.  This "bullfighter" 
strategy would allow us to 

1) get good visuals from the relatively open country in that part of IL,
2) pick a target storm from east of the Mississippi, and avoid dealing 
   the river at crunch time,
3) get far enough ahead of the fast-moving (35-40 kt) storms so that they
   would have time to organize into tornadic phases by the time they
   reached us.

The late evening (19/00Z) and chase morning (19/12Z) model runs kept
flashing the same sign even brighter.  The whole situation was so
well-defined it was almost scary.  "Something HAS to go wrong today;
Rich and I are both off and can chase in an outbreak scenario!"

[I should have looked harder at the maps; towns in that area include
Prentice, Burgess, Curran, and Kellerville!]

THE CHASE (Open your road atlas to IL):

After a leisurely 7-hour drive from Kansas City in the MEATWAGON, we 
parked at 1615 CDT just east of Pittsfield IL (W of Springfield). After
5-10 minutes, we saw anvils erupting to our NW, WSW, and distant S.
The one to the WSW was closest, moving right at us, and showed
explosive development judging from the anvil evolution.  Although
the boundary layer haze still kept the base out of view, we decided
to head farther east and allow time for the storm to evolve.  We heard
a SVR warning for Ralls County MO -- the same storm.  As we were 
jockeying for ideal vantage between Florence and Winchester (1710 CDT),
we heard a tornado warning for this cell on the IL side.  

We found a great vantage on the E side of the Illinois River valley,
5 WSW Winchester.  We become a red cape for the charging bull, which
would almost gore us.  By 1728, the rear flank rain-free base had risen
off the horizon; with the S edge of the core due W and approaching fast.  
Anvil rain had been falling on us for nearly 30 minutes.  From 1735- 
1740, a rapidly rotating wall cloud formed due W and was moving our 
way at 40 mph; and hail to .75 inch in diameter fell.  Scud S of the 
wall cloud began to rise fast and surge toward us:  a powerful RFD
was wrapping around the S side of the meso, the E edge of which by 1742 
was less than a mile W.  We repositioned to face S, in case we had 
to bail out in a hurry.  

At 1744, a dust whirl showed up in a field roughly 300 yards WSW, right 
under the interface between the RFD and the S rim of the mesocyclone,
and started cruising right at us.  We bolted S about 200 yards to let
it cross the road behind us.  While Rich filmed, I got out of the car 
just long enough to glance up and see the scud and cloud base spinning 
extremely fast:  this was the real deal!  The tornado quickly became 
enshrouded in dust and rain; and was no longer evident after 1746.

We had to go S, E, then NE to catch up; the N option was cut off.
In the meantime, we got caught in a heavy and very annoying shower
near Glasgow that slowed us down and killed our view for a few minutes.
Then, going N through Woodson toward I-72, we got stuck in a 10-car
backup behind a pickup moving 25-30 mph (in a 55 zone).  Sound familiar?

We decided to head east on I-72 to make up time; but the supercell had
a little surprise:  Going up the entrance ramp at 1818, a sunlit cone  
tornado appeared to our NE, about 4 ENE of South Jacksonville IL.  We 
closed in on I-72, exiting onto a local road that runs parallel to 
and about a mile S of the Interstate.  With the tornado about 2 miles
to our ENE, suction vortices briefly appeared.  It appeared to cross 
I-72 about the same time.

As we got to within 1/2 to 1/3 mile SSW of the tornado at 1824, it 
destroyed a small non-residential structure, sending big chunks of 
glittering, corrugated, gray sheet metal swirling up the base of the 
vortex.  Afterwards, the tornado became a diffuse circulation with no 
condensation funnel -- but occasional bursts of debris.  We finally 
found a stopping place S of the tornado, which was by now located about 
4 WNW Alexander.  The parent wall cloud had narrowed into a yellow,
sunlit barrel, rotating very fast and almost indistinguishable in 
spatial extent from the tornadic circulation.  Meanwhile, 40-45 knot
dry westerlies were blasting past us in RFD.

The tornado and wall cloud vanished quickly, as a new flank formed 
to our ENE-SE.  2 E Alexander, we saw utility poles down and wet
stubble strewn across the road.  At 1845, a slender cone tornado
(also sunlit) appeared to our ENE and roped out within 2-3 minutes.
We estimated its location at 3 N Curran.  Although the parent wall
cloud remained visible as we got back on I-72 between Curran and 
Springfield, that was our last tornado.  The storm got a few more
miles ahead of us as we circumnavigated Springfield.  We decided
not to take I-72 ENE out of Springfield since the tornadic meso 
could be right on the interstate.  Tulsa (24 Apr 93) taught me 
that lesson!  [Later that night, we saw an image from Decatur's
Ch. 20 weathercast showing the hook echo when it was right over 
I-72 near Illiopolis.  We made the right decision!]

The only other option was IL-29 SE from Springfield, which let the
storm get away but gave us magnificent views of the rock-hard
supercell racing off to the ENE in the light of the setting sun.
We were shooting stills of a large, dome-like overshoot followed by
a backshear ring, during the time (about 1735-1745) of the Decatur
tornado.  The supercell later spawned the Urbana night tornado
shown on TWC, followed by a killer tornado at Ogden.

SUMMARY:  4 severe reports (all called into WFO ILX):  3 tornadoes 
          and one hail.  Classic, cyclic supercell.
Because of the fast movement of the storm and the controlled hurry to
keep up with it; video and still photo opportunities generally stunk
during the "heat of battle."  No tripodded stuff (no time), but we shot 
some video of each hose and attempted to reel off a few stills now and 
then.  All told, a hectic but rewarding chase:  the rarity where the
forecast, intercept strategy, and atmosphere all cooperated fairly well.

Of course, I'm extremely interested in any other observations of this storm.  
Chasers coming  down from northern IL should have had a great approach  
opportunity on this beast.

                                ----------
*** No disclaimer necessary; employer not named at their request ***
"Just the angular momentum has         ===== Roger Edwards =====
 to @$#%& do it!  Come on!!!"              (   ) Forecaster
- former NSSL chase partner              former NHC Forecaster
:::::::::: http://www.nssl.uoknor.edu/~edwards/ ::::::::::
 "I FEAST ON THE SMORGASBORD OF ATMOSPHERIC VIOLENCE."