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May 30
May
30,1998 C. Iowa and S. Minnesota Severe Weather
We left North Platte Ne
early in the morning on I-80, and planned to chase in or
around Iowa later in the day. Pat McMahon was chasing with me today, and we were
hoping to hook up with Brian Stertz later. He was driving to Iowa from near St.Louis and
was heading towards the Waterloo Ia area. We were all in general
agreement that the area between Waterloo and Des Moines would be the target area for storm
chasing by afternoon. The Storm Prediction Center outlooked the
northeast quarter of Iowa for a moderate risk of severe storms, while the rest of
Iowa was outlooked with a slight risk. A surface low was expected to track from
SC Nebraska into S. Minnesota by evening. The accompanying warm front was
forecasted to lift from C. Iowa into S. Minnesota by evening. This was expected to
be the focus for severe storms and tornadoes by afternoon. Very unstable air and
backed surface winds would enhance tornado potential later, especially over the
northeast section of Iowa. South of the warm front, a very strong cap was forecast-
ed to build into the southern half of Iowa. By late in the morning, strong and a few
severe storms were moving into NW Iowa from extreme NE Nebraska and from
SE South Dakota. The general trend of this convection was a slight decrease as
the storms moved southeastward into Iowa.
Brian arrived in Waterloo
late in the morning, and we were now approaching the
Omaha Ne area on I-80. Brian was closely watching the storms over NW Iowa on
radar, but he was not overly impressed. A few severe t-storm warnings were in
effect for the counties between Spencer and Sioux City Iowa late in the morning.
Quarter sized hail and wind gusts of 60 mph were mentioned in the bulletins. No
big deal yet!! We were not too concerned since this time of the day typically does
not favor tornadic storms. Brian called us and let us know that the storms were
not supercells as of yet. We continued east on I-80 crossing into Iowa at noon. We
needed to get northeast, so we turned off of I-80 and headed north on U.S. 59 to
the town of Harlan Ia.
Since time was on our
side, we decided to stop for lunch at Pizza Hut in Harlan.
Brian was continuing to monitor the storms to the west of Waterloo, and decided
to head west towards I-35 for a closer look. One thing which interested him the
most was that the storms started to move right of the mid-level flow (340 degrees
instead of the 320 degree movement earlier). The storms were also indicating a
dramatic increase in intensity as they approached Fort Dodge Ia. Shortly before
1pm, the storms organized into a single supercell structure southwest of the city
of Fort Dodge Ia. Hail reports ranging from dime sized to up to tennis ball sized
were soon reported in S.Calhoun and SW Webster counties. Brian tried to reach
us but was unable to get through to inform us of this supercell. Unfortunately we
were unaware of the new developments until about 15 minutes later. We heard a
report on the local radio that a tornado warning was issued. We did not make out
which county was warned, so we waited for the announcement to air again. The
tornado warning was for Greene Co., and this was only 2 counties to the ne of the
town of Harlan. That was all we needed to hear!! We grabbed our pizza to go
and quickly headed out the door. I know for fact this scenario has played out for
other chasers in the past . Chasers dining at Pizza Hut, meanwhile tornadoes
were in the area but unknown to the chaser. I guess from now on, this will be
named the Pizza Hut Effect!!
We were now in warp
factor chase mode, and Brian reached us later letting us
know that he was heading south on I-35. He planned to intercept the storm near
Ames IA. We unfortunately now were forced to play catch-up!! The first tornado
reports were observed in Greene and Boone counties to the northwest of Ames.
Hail reports also increased in number as the supercell tracked southeast. As the
storm approached the town of Boone Ia, hail was reported in excess of 5 inches
in diameter! Tornado warnings were soon extended into Story Co. It was now
very apparent that we were dealing with a full-fledged monster supercell. We
were still 20 miles to the west when the tornado warning was issued, but Brian
was in prime position to view the large HP supercell heading for the city of Ames.
Brian finally reached the east side of Ames on I-35, just as the storm was moving
across the city. Hail up to softball sized and funnel cloud reports were broadcast
on WHO radio (Des Moines) from the Ames area. Brian watched the enormous
supercell pound the area with softball sized hail and then shot about 5 minutes
of video of the strongly rotating HP supercell. He also got video of a brief tornado
northwest of Ames. Unfortunately, he had to abandon his video position as the
ominous hail core was tracking down U.S. Highway 30 right towards him!!
We figured to intercept
the the storm about 5-10 miles east of Ames as the storm
moved more easterly with time. Tornado warnings were extended into Marshall
Co. to the east of Ames ,and the storm was expected to track towards the towns
of Colo and Marshalltown. We finally caught up to the storm near Colo Ia. The
storm rotation was still very evident, but the circulation was becoming more rain-
wrapped with time as it moved east, just south of U.S. 30. The circulation just
missed striking the town of Melbourne Ia to the north as we watched the storm
near the town of State Center. We tracked the storm through Marshall Co., but
could not see a defined wall cloud. Tornado warnings continued for Marshall Co.
and were even extended into Tama Co. as strong circulation was noted on radar.
The storm looked to us like that it was on the down-side at this time. The overall
size of the storm decreased significantly as it moved east to the La Grand Ia area.
The cap was working into the area big time, so now we had to decide our next option. There
was still lots of daylight chasing available!!
Brian left the storm near
Marshalltown, and was finally able to reach us by cell-
phone to see what we were planning to do now. We were in La Grand when we
decided to end our pursuit of this storm. Brian waited for us to back-track to I-35,
and did some damage surveying near Melbourne while he waited for us to meet
up with him. We missed connections around Colo, but eventually hooked up on
I-35 north of Ames. Now it was time to decide what to chase next!!
The cap was intensifying
dramatically over Iowa, so we shifted our chase
attention to the north in Minnesota. One area which we failed to notice was the
Sioux Falls South Dakota area. Later this would haunt us!! Anyway, we figured
that since the cap was very strong over Iowa, most of the focus and low-level
forcing would be directed into S.Minnesota. The surface low was expected in this
area by evening. Our data was very limited at this time, so we decided to head
for the Minneapolis area to continue our chase. We were not aware of three very
critical factors. One, a double surface low situation was setting up. The primary
surface low was remaining anchored over extreme NE Nebraska, in response to
the approaching shortwave. The surface low tracking towards Minnesota was a
weaker frontal wave type. The second factor, and most important one, was that
the moisture was flooding into the E.South Dakota area, and the airmass there
was destabilizing rapidly. The third factor we overlooked, was the fairly strong
shortwave working southeastward into W. South Dakota late in the afternoon. All
of these factors were coming together over E. South Dakota!!!
We had already made up
our minds to head to Minnesota,and we moved across
the Minnesota border just before 6 pm. Unfortunately, we were still without data
at this time. The Storm Prediction Center issued a tornado watch for much C. and
S. Minnesota so our optimism was now on the increase once again. The cap was
starting to expand northward progressively into S. Minnesota, so we planned the
best area for supercells would be west and northwest of Minneapolis, as this area
would be in advance of the northeastward moving surface low. Severe storms
soon fired in this area, and a few storms developed circulations on radar. We
focused on one of the rotating storms which was moving towards the St. Cloud
Mn area. This storm was producing golfball sized hail and had the best rotation
signature on radar. We noticed pronounced laminar banding in the low-level
clouds as we headed northwest from Minneapolis. This was indicating to us that
there was good low level inflow into the storms, as well as, significant low-level
forcing. Unknown to us, the start of the E. South Dakota tornado outbreak was in
the early stages of development 250 miles to our west-southwest at this time too!!
We watched the storms eventually line out into a squall line as the surface low
passed to our north. The cold front then started to focus the squall line and other
severe storm development from near St.Cloud to near Marshall Mn. Also at this
time, pva from the approaching shortwave was spreading into W. Minnesota.
This was aiding in the all out explosion of storms in Central and SW Minnesota.
It was now appearing as though a mean squall line situation was developing, so
we decided to pull over on the NW side of Minneapolis for dinner at Applebee's.
While we waited for our food, we finally found out for the first time that tornadic
supercells had developed northwest and west of Sioux Falls. We did not hear of
the Spencer tornado at this time, but this did tend to spoil our dinner!!
We were now facing a bust chase as a raging squall line was underway from
east of St.Cloud to the west of Minneapolis and southwest to the Worthington Mn
area. We were hoping to catch "tail-end charlie" somewhere south of Minneapolis.
Two factors would hinder our pursuit. The first was that we would have to cross
through the heart of the storms aligned north-south on the squall line. The second
factor was that darkness was now upon us so visual inspection of the storm would
be very difficult. Since we had to head back to Ames anyway to retrieve Brian's
car, we decided to go for the gusto!! Finding the gusto was not too hard this night.
Severe t-storm warnings were issued two counties in advance as the nasty squall
line approached Minneapolis at 50 mph. Wind gusts of over 80 mph and large
hail was reported with the stronger cells embedded in the squall line. We were
near Apple Valley Mn when we found the leading edge of the squall line. Winds
of over 70 mph and intense rainfall blasted us as we headed south on I-35. We
definitely could verify this warning! The further south we went on I-35, the more
intense the wind gusts became. Radar indicated a very strong bow echo close
to our location near the Scott/Dakota county line. Hail soon mixed in with the rain
and wind gusts were now well over 80 mph. Just northwest of Lakeville Mn, we
encountered gusts approaching 90 mph. Power flashes filled the sky with eerie
bursts of blue-green colors as power poles were brought down by the howling
winds. Highway signs also gave way under the incredible winds. We continued
cautiously south and came up on stopped vehicles on the interstate as well as
some debris. A very scary situation!! As we headed further south, numerous cars
were blown off the road and emergency crews were attempting to reach the
scene through the blinding rainfall. The hardest hit area was definitely in Scott,
Dakota, and N. Rice counties. Wind gusts (estimated by us on I-35) were over
85 mph at times, while sustained winds roared at over 60 mph!! This area was
well matched with the apex of the bow echo on radar.
Radio reports indicated
that extreme wind damage was done through the area
between Chanhassen and Fairbault. Some early reports indicated that winds in
excess of 110 mph were reported in Scott Co. We managed to work our way past
the chaos on I-35, and found a break in the line south of Fairbault. The break was
short-lived however. We could see the arcus gust front approaching us quickly
from the west. Soon wind gusts over 70 mph and very intense rains blasted our
vehicle again. This storm did not appear to be as severe as the storm encounter-
ed 15 minutes earlier in the northern part of the county though. Radar showed the
rapid eastward movement of the north section of the line, but a slower progress
with southern end of the line. Tail- end charlie was indicated near Albert Lea Mn
so we picked up the pace and made it through the last of the cores near the town
of Owatonna Mn. Unfortunately for us, no rotation was indicated with the storm at
Albert Lea. Normally tail-end charlie storms provide for exciting times , especially
when the area south of the storm is capped. Tonight's show would not provide us
that excitement however!!
We continued south on
I-35 into Iowa and then heard of a rapidly developing
storm near Mason City. We could see the lightning with the storm to our south but
we were not too optimistic. The storm quickly intensified as it moved into Mason
City, and a severe t-storm warning was issued. Hail up to golfball sized and wind
gusts of 70 mph were expected with this storm. The only problem was that it too
was racing of to the east at 50 mph. This would be our last storm seen that night
as the storms raced into Wisconsin in a derecho structure. The Mason City storm
did remain isolated long enough to develop rotation, and did produce a tornado
in Howard Co. Iowa later. Little did we know that we witnessed the start of a major
wind event which would cross the country, and cause massive damage in New
York, Pennsylvania, and other states later.
We decided to call it a
day, and headed back to Ames to drop Brian off at his car
and then to find a hotel in Ames. As we pulled into the hotel, Brian ran over to our
minivan with a surprised look on his face. Brian was listening to ABC Radio's
national news segment and heard that a violent tornado had hit the small town
of Spencer SD. Fatalities were reported and the town was virtually destroyed the
story went on to indicate. We scrambled for a South Dakota map to see exactly
where this town was. We were shocked to see that the town was only about 40
miles west of Sioux Falls. We then realized that we had busted! The rest of the
evening was spent researching earlier weather data to see the cause of this bad
tornado. When we got further in our research, the situation was very evident and
classic in set-up. If only we had seen the data just 6 hours earlier!!
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