3/29/98 Chase Summary by Mike Umscheid and Jay Antle


From: Mike Umscheid (mscheid@SOUND.NET):
Chase Account:  Northwestern Iowa "Dejavu Chase" -- March 29, 1998

On Sunday, dynamics were in place for a large outbreak of severe
weather across much of the midwestern states.  An intense upper low
with associated 80+ knot speed max at 500mb was setup across the
northeastern plains states and Midwest.  At 14Z, surface analysis
showed a 995mb surface low located near Akron, CO with a dryline
extending from the low through northwestern Kansas to the eastern
OK/TX Panhandles.  A tongue of moisture was advecting through
southeast NE at this time with a dewpoint of 61 at Beatrice, NE.  A
warm front was extending from the surface low ENE to just north of OMA
through just around the DSM area during the mid morning hours.  This
warm front was advecting unstable air at the surface to the IA/MN
border.  By late afternoon, the surface triple point was forecast to
be right around Norfolk, NE.  As it turned out, our forecast would be
off by a critical 100 miles or so.  My chase partner, Jay Antle, and I
analyzed the latest morning data and 15Z swody1 before we departed.
Our look at morning sounding data and ETA forecasts showed a decent
cap but one that should break with the arrival of all the intense
dynamics and surface heating.  SPC's Moderate Risk area was extended
further southwest to the NE/MO border, which led us to think even more
that the dryline should have no problem firing today after some decent
surface heating right around the triple point vicinity.  Based on our
interpretation and forecast of the surface data, soundings, and swody1
guidance, we decided an area just south of Sioux City, IA was a good
target area.  Hodos, Lifted Indices, and EHIs, were pointing to a good
chance of supercell development wherever convection went up.  Things
looked almost like a sure thing up on the warm front along the IA/MN
border but that was just a BIT too far for a one day chase out of KC
(we both had committments the next morning).  And besides, we thought
the cap would break along the dryline further south....ugh.

We set off towards our target around 9:15am heading north on I-29 out
of KC.  As we got into Iowa, we were eager to see what the surface
wind fields were doing, and we stopped at one of Iowa's DTN weather
terminals at a rest stop (Thanks, Iowa DOT!!!).  The warm front
appeared to be right around the MN/IA border as of 11am obs, and our
triple point was still on target.  We started approaching the southern
end of our target area about 1pm between Omaha and Sioux City.  We
were socked in low Stratocu for much of the morning until we got to
the Omaha area, and as we broke out, we curiously watched a decent
north to south band of semi-congestus Accus about 20-30 miles east of
us.  We were bothered by that because it looked rather suspicious, but
was well south of our target... mistake #1.  We checked out DTN radar
again when we were north of Omaha about an hour later and noticed that
our Accus Congestus was developing into some convection... and heading
into some high CAPEs.  Shortly after 1:30pm, we stopped again to take
a gander at DTN radar and find out about the 1930Z swody1.  To our
dismay, our Accus Congestus from two hours ago or so had developed
into potent severe looking cells on radar in north central IA.
However, lacking warp drive, these cells were now too far away to
chase.

Jay and I had July 1, 1997 in the back of our mind as we both
separately busted big time that day... in northern Iowa.  This was not
going to be dejavu, we thought.  Over the rest of the day that became
a bit of a mantra.  We stationed out at the DTN terminal just south of
Sioux City for about 20 minutes to get some data.  Jay tried to get a
hold of Mike Phelps for a swody1 update, but couldn't get a hold of
him.  So as a resort, I called my regular chase partner, Jon Smith, to
find the latest.  1930Z outlook was pretty much the same story, and we
had an MCD issued for our target area.  Things were looking up.  Just
before we left, shortly before 2pm, Jon gives us information of a PDS
red box for much of northern IA right on the eastern end of our
target.  As we left, we saw towers going up about 50 miles to our
north-northeast.  The motion on these storms was very quick... about
35-45 knots in some cases.  We took another quick look at the radar
and saw storms firing in extreme southeastern SD.  We decided to go
after that.

We approached Sioux City around 3pm.  We decided to continue
north-northwest on I-29 north of SUX into southeastern SD in hopes of
some tail-end-charlie action... mistake #2.  We were quickly
approaching the dryline and we decided, whoa, we are way too far west.
 We needed some data.  Jay gave Phelps another call to see what was
up, and if our dryline was showing signs of breaking.  Things still
looked hopeful, however the cap still remained strong south of the MN
border.  We headed back south briefly towards SUX and continued
northeast on US-75 which was the best NE option open to us, time was
4pm.

Time to hope for a tail-end-charlie.  We encountered a broken line of
towering cu along the dryling as we exited SUX.  Off to the NE we
could see that some of these were putting out soft fuzzy anvils.  We
monitored very interesting lowerings (the kind you only find
interesting on your first real chase of the season) from elongated
bases of the flanking towers.  Shortly after 4:30pm, 6 S of Orange
City, some of the flanking towers appeared to be growing into Cb's and
under the main flanking tower we continued to watch suspicious wall
cloud features.  We decided to hang out and monitor the flanking line
between the towns of Hospers and Alton along SR-60.  We were looking
at the main flanking tower, now producing some rain shafts, and what
appeared to be hail shafts also with the white, milky, appearance to
the precip shaft.  We now had a persistent wall cloud (no rotation)
feature fairly evident on our main flanking tower.  We could see the
TCU for miles to the southwest along the dryline, which was now
beginning to blend in with the cold front.

At around 5:20, we headed east along US-18 to get east of the main
flanking tower.  The storm never got its act together and fizzled
apart.  At the same time, the towers to the south and west were
getting quite a bit better organized.  About 5:35, we went south along
US-59.  At 5:45, we stopped to monitor the situation south of
Primghar.  We were observing a lot of motion underneath the ragged
bases of some of the towers as they were approaching us from the west.
 Nothing was organized, which caused quite a bit of frustration as we
were running out of daylight quickly.  We were watching in hopes of
something to break this cap open, but to no avail.  We continued south
along a county at the town of Paulina.  At this time, we noticed some
nice congestus tops, but no bases.  Talk about confusion and
frustration.  We had some awesome backlit cauliflower congestus, but
with no bases!  Jay called it "a convective freak show."  The thoughts
of horror:  July 1, 1997 High Risk bust.  It was all too familiar.
Who would have thought we would have a cap suppressing convection in
northern Iowa and not even being April yet!

Well, the daylight bust was upon us.  The sun was setting, and time to
go home pretty much empty handed.  But wait...  these caps usually
bust right at sunset, and we were still along the dryline.  Sure
enough it happened, after we ran out of light.  We got to the town of
Quimby and headed home southwest along SR-31.  As the sun was setting,
congestus was now flying to our southwest, into nice Cb structures.
Lightning was now visible, and now we noticed a nice anvil trying to
form with some backshearing.  We were approaching the town of
Smithland around 7:30pm with frequently vivid lightning.  The
lightning was incredible inside the Cb.  Between 7:20 and 7:45 before
we entered the core of the storm, we witnessed incredible continuous
cloud to cloud lightning.  We were in the middle of nowhere and we had
no escape from this storm which was coming NE at us.  We traversed
slowly into the rain core, and started getting heavy hail, no larger
than peas in size.  This was a little too much, so we headed back
north to escape the heavy core.  There was a SVR issued for the storm,
but with such high EHI's in the area, we didn't dare risk getting
caught in a bear's cage situation.  We got north of the storm finally,
and continued our trek towards I-29.

We never though this chase day would end as there was more development
around the OMA area after around 9pm, with lightning visible to our
northwest as we continued home on I-29.  We narrowly escaped having to
punch more core as we crossed the Missouri line as there were SVR's
going out for the far northeastern counties of KS into SE Nebraska.
The lightning at this time was illuminating some of the bases, which
looked quite interesting.  We even saw what seemed to be an impressive
shelf cloud on one dying cell which was west of Nebraska City.  This
all came to an end, and our chase day finally came to an end as we got
home to Kansas City shortly after 12:30am.  Oh well, we got to see two
severe storms go up in Iowa and have an even greater respect for warm
fronts in strong dynamic situations as well as ACCUS.  And hell, it IS
March.

Mike Umscheid, mscheid@sound.net
Jay Antle, Astrosfan1@aol.com

* Video still are found at www.sound.net/~mscheid/chase98/mar29


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