8/14/97 Chase by Gilbert Sebenste



From: "Gilbert L. Sebenste" (sebenste@geog.niu.edu):
Subject: Chase BUST, 8/14: analyze before you go!

On Wednesday, August 13th, while visiting some pals over at the College of
DuPage, I had a few hours to look at maps. I'd been too busy to even look
at them the past week or so. A meteorologist too busy too look at maps?
Top that! :-)

Anyway, what I did see was interesting. By Thursday afternoon, the lee
side trough east of the Rockies would move eastward to the longitude of
Omaha by 0Z Friday. A 50 knot plus 500 MB westerly jet streak would
approach central IA. An 850 jet of 40 knots from the southwest over
central IA, and a south-southeast wind at 20 knots would ensure storm
rotation with the 1,500-2,500 CAPEs expected. Convergence would be
strong along the trough, and mid level drying was expected to move in to
IA enhancing instability by late afternoon. LI's were expected to be
around -7. Now, where should I go?

Well, I had two choices. The first would be northeastern IA, where an
approaching mid-level shortwave...along a surface warm front...would
really kick up stuff along the front. The storm-relative helicity would
be fantastic. Southeastern MN/northeastern IA is where everything would
come together by evening, and it looked like they were sitting ducks.
OR...

I could play southwest IA with higher CAPEs, but the shear would be good,
not excellent as it would be up north. Going for the closer of the two, I
picked Mason City eastward as my call. 

I talked to Jeff Mila at the lab and he said he could blow off work today,
and work longer tomorrow. That would be great, and I told him to be in
DeKalb by 8AM. The only concern I had was an MCS messing things up,
delaying the arrival of the warm front or causing convergence somewhere
else. Time would tell. I would get up at 6:58AM with my radio cranked to
do a one hour analysis before I left to see if my forecast was still a
"go".

At 6:58AM Thursday, I hit the alarm. And I immediately fell back to sleep.

I am awakened at 8:30AM by a loud knock on my door. It's Jeff, who is
profusely apologizing for being late. With only one eye fully open, I
mumble "don't worry about it". Eek! Well, I wake up quickly after that,
eating a quick breakfast and getting everything ready. But I don't have
time for the computer---just The Weather Channel. Their severe forecast
puts northern IA in ground zero, although Iowa is literally dead center in
the outlook area. I assume everything is kosher, and to get there in time,
we leave a few minutes after 9AM. Big mistake. Always do an in-depth
analysis before you leave! We take State Road 38 west to I-39 south, I-39
to I-88 west to avoid one trollboth. Er, tollbooth.

By 10:45AM we hit I-80, and we take that west into Iowa. At 11:45AM we
hit I-380 north to Cedar Rapids. But by now, I am very concerned. I do
like the strong southeast winds buffeting my car. I do NOT like the lack
of sunshine. Just a peek or two under otherwise overcast skies. I call the
College of DuPage (COD) weather lab and talk to chaser guru Paul Sirvatka
for an update.

It is what I suspect. This is the last place I want to be. No sunshine, no
heating, no CAPE. Forget it. If I want anything, southwest IA, in the
right rear quadrant of the approaching jet max will do. And it's coming
through fast, and it will be in southern WI by 0Z. I'm not chasing MN.
Furthermore, the approaching 500 MB vortmax is further south--forecast to
move through  central NE and be over Omaha at 0Z. And, it's sunny
in southwest IA...from Des Moines To Omaha southward to KS. Hmmm.

OK, change of plans. Thank goodness it's still relatively early. We turn
around and go south, hitting I-80 west once again. This lunch will have to
be on the road, and we chow down as we leave. At 2PM we fly through Des
Moines and make the loop around the city taking I-35 south at 2:15PM.

But by 2:20PM, I'm getting nervous. There's a problem Houston, and that
is...no sun! In fact, it is now *raining* in West Des Moines. That does
it. The next rest stop we look at the DTN weather center and then call in
to COD to find out what's happening.

Well, we hit the next rest stop at 2:45PM at the Creston, IA (US 34) exit.
We quickly run to the DTN machine and see the one lone shower that hit us
over West Des Moines. Otherwise, the radar across IA is...free of echoes. 
And they stopped showing satellite pictures. Arrrrrgh. Time for another
call to COD.

This time Matt Powers answers the phone. I'm WHERE?!? Yes, I'm halfway
inbetween DSM and 30I (Lamoni) at I-35 and US 34. It was sunny out here,
right? Yes it *was*, but in a 1 hour time frame all of southwestern IA
clouded over with low stratus. The low level jet met isentropic lift at
the warm front across IA and made a marriage I now wish ended in divorce.
Huge amounts of low level moisture were being lifted over a MUCH broader
than expected baroclinic zone. Now, all of IA was cloudy,
drizzly...day 1 outlook still has us in a slight risk for severe storms
with isolated supercells, but it's questionable where we are.

Furthermore, the north/south trough of low pressure in NE wasn't moving
anymore. Where there were once decent pressure falls in western IA, now
there were none. Surface moisture and wind convergence dwindled to
near zero levels along the trough. In fact, strong moisture *divergence*
was noted throughout most of IA. Matt had two words for me: go home! SPC
may be down and the Air Force is issuing convective outlooks. That to me
means one of two things: armageddon is about to hit causing the '74
outbreak to look like a bunch of dust devils, or this chase is going to be
my lousiest ever.

However, partly because we were already out there and in our target area,
and partly because sometimes I'm stubborn as a mule, I decided to wait it
out. If anything was going to happen, it would have to be western IA.
So I decided to take U.S. 34 west to Creston. From there, I could go
anywhere, including home...quickly, if I needed to.

At 3:45PM we arrive in Creston at the Texaco station on the west side of
town. To cloudy skies and drizzle. I haven't even seen a towering CU
today so far. I mutter something under my breath about what I didn't do
this morning. And, we got out of there so quick, we forgot to put on the
old Rain-X. Well, let's take care of that now. Fine. Now what? Well, Jeff
is starting to get hungry, so we'll see what this place has to offer. I
forget to lock my car door and I head back to do so. I enter the station's
store and Jeff is beaming, pointing to a flickering monitor and saying
"Look!".

A complete DTN weather center? You gotta be kidding me! Here? At a gas
station? In the middle of nowhere? Jeff is already playing with it, but as
he leaves it momentarily to pay for his snack, the cashier
asks..."you wouldn't happen to be chasers now?" "Yes we are, from
Chicago!" Jeff replies. Well, she was from Chicago and I know a yackfest
has now ensued. That gives me ample opportunity to find out if these two
chasers are going to see anything but fog, drizzle, haze and fat cows in
these endless fields of corn (no, I don't mean the cashier!). 

I look at the radar composite for IA. One heavy shower, in Des Moines.
Otherwise nothing, except for one very light shower we hit heading into
town. Satellite shows clear skies over western IA, HUH?!?!? DTN needs a
better color table for it's sat pix, it's not picking up this stratus!
Well, the current surface maps and Iowa mesonet say it all. We're socked
in tight with low clouds. We do, however, have a 79/70 reading down the
road at the airport from the AWOS site. Is that good enough? Well, after
Jeff and the cashier stop talking, we decide it would be best to just hang
around. We spring for some of their pizza (quite good, I must admit) and
we wait.

And wait.

And wait. By 5:45PM, the wind suddenly shifts southwest. Something just
came through. Warm front? Yep. Skies are now clearing! But it's too late.
The damage is done. One strong storm in northern NE...and that's it.
And that's it for us. At 6PM, we cut our losses, and headed back home from
the same route we came.

We did stop off at a few rest stops on the way home just to see what would
happen. That strong storm in northern NE put out quite a hook echo for
awhile around 7PM. At 10PM, we are close to home, and all of a sudden
a bright flash fills the car. What was that?!? An isolated storm up by 
Rockford has just produced it's first lightning flash. Thank God we saw
*something*. Then we get home at 10:30PM in DeKalb, flip on The
Weather Channel, just in time to hear Dave Schwartz gasp and wow over an
impressive looking tornado near Minneapolis. No, that wasn't a bomb you
heard go off right around then. You probably just heard the sound of a
remote control flying at a high rate of speed into and through an active
electromagnetic particle exciter.

Well, this was a setup for disaster. I probably would have caught the
danger signs if I had just done an analysis this morning. Worse, TWC has
strong storms over us Saturday. Worse still, the day 2 from AGFWC and from
the morning SPC outlook says supercells in my backyard tomorrow.

I am humbled *and* heartened. This also happened to me April 18, 1996. 
Read my chase summary for April 19th to see what happened. It can happen
again!

And this time, yours truly...and my analyzed maps...will be ready.

Gilbert

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Gilbert Sebenste                                                     ********
Internet: sebenste@geog.niu.edu    (My opinions only!)                 *****
Owner of the Storm Chaser Homepage/SCH Canada                           ***
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