June 27, 1999   Nebraska Panhandle Supercell....again !!

After the mammoth supercell we witnessed yesterday at Sidney NE, we knew it
would be hard to duplicate this again!! The town of Sidney was thrashed by the
awesome power of the supercell...busted out windows, downed tree limbs/power
lines, and flooded streets were common across the Sidney area on Saturday evening. We slept hard and woke up to sounds of squeaky floors above us. We
were in a basement room and there was large number of people staying in the
family style room above us. By the time we got the sand out of our eyes (literally),
it was already 10:30 am. We did a quick review of the weather data before going
out for some breakfast. The SPC outlooked much of the Nebraska Panhandle, NE
Colorado, and E. Wyoming for a moderate risk of severe storms. Oddly enough,
tornadic supercells were again mentioned for much the same area, but a little
further west. A weak surface low was expected to form near Cheyenne WY, and a
fairly strong dry line was expected to firm up from near Laramie to near Denver.
The more important feature though was going to be the outflow boundary that
was pushed well south into E.Colorado overnight. The tail-end of this outflow
boundary was actually pushed up into the Foothill areas and looked as though
it might intersect the dry line somewhere west or northwest of Cheyenne. This
was where we targeted the initial development for today.

We packed up the vehicle and headed back to the Country Kitchen for breakfast.
On the way, we noticed considerable property damage in town, and saw lots of
resident's surveying the aftermath and inspecting the large holes in the windows
left by the very large hail and 70 mph+ winds in town. Many vehicles also were
dented with broken windshields and side mirrors. The worst damage we saw
was closer to I-80 where we hid out during the storm. Lots of sign and window
damage was seen here. We expected this with the 85 mph blast of wind that
roared into this area. The Country Kitchen sign was nearly completely ripped off
of the pole. The Holiday Inn and U.S. flags were also torn from the flagpole- a
good testament to the strength of the winds and hail. Getting back to the weather
situation today....One thing Brian and I noticed right away was the "feel" of the
air in Sidney. The air felt cool and stable, and the clouds above us were of the
"soft"/ worked over airmass variety. We had a hard time believing that this was an
airmass that supercells would thrive in. However, we were on the High Plains so
anything goes-especially this time of year!! We had a good breakfast and made
the decision to head west on I-80.

Over the next 3 hours, the airmass transformed impressively over SE Wyoming
as we headed into Cheyenne. The upslope/low cloudiness broke up and the
sun warmed temperatures from the upper 60's to the lower 80's by the time we
reached Cheyenne. Dew points also improved at this time. Earlier in the morning,
dew points were in the upper 40's, but climbed into the mid 50's as the moisture
pooled along the boundary. A weak swirl was forming immediately west of the
Cheyenne area on the streamline plot. Also at this time, the dry line was firming
up in the Laramie area. West winds were gusting to 35 mph in Laramie. Further
to the east, moderate east to southeast winds prevailed. We had to run some
errands in Cheyenne and got those out of the way. To the north of Cheyenne, an
area of clustered towering cumulus developed along the Laramie Range to the
west of Wheatland WY. Several other clusters of towering cu also bubbled to the
east and northeast of Cheyenne. The airmass looked to be recovering in good
shape here, but satellite was indicating that an area of subsidence was moving
into SE Wyoming from Colorado. This was seen as a rapid erosion of all clouds
in this area. The surface plot showed that the dry line was mixing east and the
surface low was becoming more established. The area of northeast winds was
concentrated to the north of Cheyenne, so this was the likely area for supercell
development, especially with the increasing cap. Brian and I monitored the
weather data while Kathryn completed her camcorder sortie.

By mid afternoon, the SPC issued a tornado watch for much of E.Wyoming and
the Nebraska Panhandle. The cluster of towering cumulus near Wheatland was
now consolidating into a single supercell. We tried to call up Cheyenne NEXRAD
but were unable to get any images for some reason. We would have to rely on satellite and surface data, and our own eyes for the developing supercell. Our
initial attention was focused on the developing storm that was moving east at a
very fast clip from the Hillsdale WY area. This storm very quickly fuzzed and was
just a patch of cirrus by the time we set off for chasing. Further to our north though,
the supercell continued to intensify and increase in size. We made the critical
decision to go after this storm after we saw an overshooting dome explode above
the anvil to our north about 50 miles. The chase was now on. Brian was driving
and we raced north on WY-213 from Burns. Fortunately, my first radar image in
3 hours came in from the Cheyenne radar site. The supercell to the north was the
real deal !! A major hook echo was seen on radar and baseball sized hail was
also indicated on radar. The storm had a severe t-storm warning on it, and the
location was listed as 5 miles west of Wheatland. We were initially concerned as
the storm motion was listed as northeast at 35 mph. Later though, the diffluent
flow took over and the supercell tracked east-southeast. We now had quite a bit
of distance to close on the supercell.

I continued to watch the storm circulation increase dramatically as it tracked on to
the southeast, and we blasted north on U.S. 85 for the Yoder/Hawk Springs area.
The further we traveled, the more impressed we became with respect to the storm
structure visually and on radar. The radar velocity display was indicating that the
circulation was tightening up and a tornado looked to be likely soon northwest of
town of Slater WY. We made excellent time closing in on the supercell, and the
visibility under the updraft was surprisingly good. We were still 30 miles away
and could see a bowl shaped lowering/wall cloud hanging down from the flat
rain free base. As we approaced Hawk Springs, we could now see that the wall
cloud was starting to take on a conical funnel shape. We crossed a ridge top and
were stunned by what we saw. A well developed tornado was on the ground !!
We wanted to make absolutely sure before we hit the red alert button and called
the report in. Another ridge was in the way so we continued north and reached
yet another ridge crest. The tornado was now larger and looked to be a mature
vortex now. The tornado was fairly wide for Wyoming standards (estimated at
200 yards wide) and was tracking very slowly to the southeast. The tornado
intensity appeared to be F-1 from our vantage point and was picking up large
amounts of dirt/debris. I called this in now and the 911dispatcher advised me
that a Wyoming state trooper was also watching this tornado from I-25. She seemed startled that we could see this from so far away- we were probably 20 miles from the tornado. Brian plotted the position as 3-4 miles north of Slater.
This was the same position the trooper reported. After we reported this, we
were surprised a tornado warning was not issued later by the Cheyenne NWS. Granted the tornado was over open country, but one would have thought that a warning would be issued with 2 confirmed reports!! Anyway, there was no road options we could take to get closer to the tornado. We pulled over and watched it slowly dissipate to our northwest.

Radar indicated the occlusion of the original tornadic circulation, and the rapid
formation of a new circulation closer to us on the tail-end of the gust front from
the original circulation. We watched a fresh storm tower/updraft explode on the
southeast flank of the supercell, and 10-15 miles to our northwest. The supercell
appeared to split into 2 separate cells at this time on radar. Cell# 1 was weaker
and it headed east. Cell#2 was becoming the "big daddy" supercell and it was
tracking southeast from 300-310 degrees. We realized that this was going to be
the main show. There was absolutely no storms or organized cumulus to the
south of this storm. It was on the edge of the cap. Cell#2 updraft region showed
a large WER (weak echo region) on radar and we could see a strong westerly
RFD working into the backside of the storm now. We could also see that the huge
hailcore was also sagging down from the north. We watched the circulation increase as the FFD(forward flank downdraft) increased convergence into the updraft. Eventually the cold/wet FFD blasted us with cool gusty northeast winds.
This and the advancing hailcore signaled a time to move. We knew what sized
hail this storm was capable of and could see the solid wall of the hailcore that
was dropping straight south for us. We back tracked and headed east on WY-161
for the town of Huntley. The circulation was tracking directly for this town.

Tornado warnings were quickly posted on the storm for S.Goshen Co., and a
developing tornado was indicated near Yoder. We were right there and we kept
a close watch on the area. A major outflow episode soon followed as an intense
surge of rain/hail cooled air blasted to the southeast. This storm looked to be a
major outflow dominated supercell. The circulation continued to develop on the
southeast leading edge of the supercell as it closed in on the state line. We did
not want to be "caught" in the large hailcore so we headed into Nebraska ahead
of the circulation. We pulled over several times to watch this incresing rotation,
but our stops were very brief. We plotted a storm track and the circulation was
now heading right for the Scottsbluff/Gering NE area. A tornado warning was very
quickly posted for Scotts Bluff Co. as the circulation was indicated 4 miles nw of
Lyman NE. We watched the circulation continue to intensify, but outflow remained
a major problem still. The wall cloud would organize quickly, and then blast out
and dissipate very quickly. This process happened time after time since the onset
of the circulation back in Platte Co. Wyoming. We were concerned that there was
just too much cold air from the huge hailcore to sustain a good warm inflow for
tornado development.

We passed through Lyman and local resident's were scrambling for shelter, and
the tornado sirens were adding to the chaaotic scene. Several residents actually
were "bugging" out and left town in a hurry, while several other went out to spot.
By now, the number of chasers nearly tripled as the highway was lined with many
cars and chasers with video cameras. We headed south and then east on NE-92
to the town of Stegall. When we reached this town, the circulation actually showed
some promise as it firmed up into a tighter area of rotation. Inflow was quite a bit
stronger here to so we knew there was still hope. The swirling rotation headed
directly for the Scotts Bluff National Monument, and would actually pass directly
over the town of Gering. Scottsbluff would eventually be nailed by the huge hail
core that was immediately north of the circulation. A large group of chasers, law
enforcement, and other spotters/residents pulled over on the incline of the "bluff"
and watched the rotation approach quickly. I recognized Al Moller who was solo
chasing from Fort Worth as well as several other chase teams. We wanted to get
ahead of the wall cloud that was forming as well as the probable storm chasing caravan that was about to move on. We headed into Gering and planned to get
east of town to watch this incredible circulation sweep over Scotts Bluff. When
we pulled over, we were amazed on how much different the airmass looked. A
multitude of inflow bands were racing to the west and southwest overhead, and
our winds were now blowing hard out of the northeast. The sky had the classic
pre-tornado look, very hazy and dark.

The wall cloud crossed the bluff and descended down on Gering. First, the main
rotation center passed over town, then the strong RFD and blast of hail hit town.
We watched this from about 3 miles east of town, and it was an incredible sight!!
Brian and I have seen this once before in April 1996, when a large wall cloud
went over the Arbuckle Mountains and the wall cloud descended right down on
the town of Davis OK. This was slightly more impressive because of the scenic
quality of Scotts Bluff. The major wall cloud swirled violently as it moved to the
southeast from Gering. Horizontal vorticity tubes writhed overhead, and we could
see very intense cloud motions that were very nearly tornadic. We watched for
dust swirls under this area, but saw just blowing dust with the strong RFD. The
thump of occasional quarter sized hail was a warning sign to get moving!! We
continued on to the southeast on NE-92 towards the Bayard/Mc Grew area. The
radar signatures were all pointing to the development of a tornado very soon!!
A strong inbound/outbound couplet was forming just to our northwest and was
intensifying rapidly. We could see Chimney Rock ( a major landmark for early
settlers) to our southeast, and it looked on radar as if the circulation was going to
track right for this landmark. Kathryn was watching the wall cloud to our west get
better organized and yelled for us to stop. She saw the first signs that a tornado
was forming!! We pulled over just north of Chimney Rock on NE-92. Tornado #2
for the day was about to happen!!

A small conical lowering poked down from the flat wall cloud base and was with
out a doubt very close to producing a tornado. Very quickly, a dust bowl started
to appear right under this feature that was about 2 miles west of Chimney Rock.
For the first 2-3 minutes, only a dust bowl was swirling on the ground under the
elevated cone. However, a pronounced condensation funnel appeared just as
the rotation above became more violent. The tornado was probably on the order
of a weak F1 or F0  intensity. The width of the tornado increased to nearly 100
yards as it moved right for Chimney Rock. We had a great vantage point of both
the tornado and Chimney Rock, and were starting to think we might see history
happen right before our eyes with our video cameras rolling!! The tornado was
fairly strong for about 5 minutes before it roped out. The tornado moved almost
due south as the outflow pushed it miraculously away from Chimney Rock. We
wanted to capture video as it crossed over the rock formations south of Chimney
Rock so we headed south on the park access road. The tornado continued to
beautifully rope out as we approached it from the north. We were so transfixed on
this sight that we failed to recognize the huge hailcore that was heading right for
us from the north. After the tornado gusted out, we turned around and saw the
core advancing quickly down the access road. We were about to get pounded!!

Unfortunately, we had to head back into the hailcore to get back to the paved
road. We had no choice but to drive north into the hailcore. The further north we
drove, the larger the hail (now up to golfball sized) and the stronger the winds were. The north winds were driving large amounts of hail into the vehicle and I
was fairly concerned we were going to lose the windshield. We made it back to
NE-92 and now the hail was blasting the left side with quarter-golfball sized hail.
We continued on east on NE-92 and knew we were close to breaking out from the nasty hailcore. The circulation continued on to the southeast, although we lost
sight of this feature through the rain/hail. Tornado warnings remained in effect for
Morrill Co. as the radar indicated tornado was near Bridgeport. We needed badly
to get ahead of this huge hailcore so we could watch the area of concern without
getting pounded by hail and our view obscured by rain curtains. We actually did
find the edge of the hailcore just northwest of Bridgeport. Tornado sirens were
going off in town, and is usually the case, major chaos was the rule as residents
scrambled for shelter. We had a critical decision to make at this point. We had to
decide if we risk getting caught again in the hailcore or risk the chance of being
unable to find gas further down the line. We were a notch above empty at this
time. Radio reports were indicating that BASEBALL sized hail was now reported
on the west and northwest sides of Bridgeport. This report pretty much made the
decision for us. Other chasers did stop for gas and we assumed they probably
were unaware of this report. Al Moller and a group of other chasers raced east out
of Bridgeport as the hailcore was spreading over the city. Intermittent quarter to
golfball sized hail fell on us as we were the last vehicle in the chaser caravan to
leave town on U.S. 385.

We could see the area where the circulation was located, but rain curtains hid the
wall cloud features from our view. The large and threatening hailcore loomed to
our immediate northwest and was very green in color, almost with hints of aqua.
Unfortunately, we reached the critical stage for gas. We needed to find a station
fast. The closest sizeable town was Dalton, and the next closest town was Sidney.
We branched off on U.S. 385 and headed for Dalton, not a real big town but big
enough to have at least one or two gas stations. One thing that worked against
our plan to get gas there was that it was after 6 pm on a Sunday. Sure enough,
by the time we reached Dalton, the town was rolled up for the night-everything
was closed. Time for plan B. We needed to go all the way to Sidney on I-80 for
gas. We basically ran on fumes as we had to go another 20 miles to Sidney. We
cut off the air and Brian dropped his speed down to 60. Plan B was unfortunately
our last resort. The storm was about 25 miles to our north now and moving to the
southeast heading into Garden Co.. This would mean we would probably have
to go east on I-80 and then north for Oshkosh or Lewellen. We filled up and had
a quick food grab in Sidney. Radar still indicated a strong circulation with the
supercell, although it was looking more linear on reflectivity. From the distance,
the supercell looked like it was re-organizing because of the multiple updraft
appearance now on the south side. The main updraft area was about 30 miles to
our northeast, and radar indicated this was near Oshkosh (Garden Co.).

Our best bet for intercepting the supercell again was to go over to Big Springs
and then north to Lewellen. The supercell was tracking southeast right for the
town of Lewellen and then Lake Mc Conaughy. We had a very good chance
again to intercept the circulation again!! We raced east on I-80 and made it to
Big Springs just as the main circulation passed just to the south of Lewellen.
As we headed north on Day Rd in rural Deuel Co., we could see the large flat
rain free base to our north. We could see the wall cloud now about 10-12 miles
to our northwest. One thing that struck both Brian and I as odd, the supercell had an LP structure now. The core was nowhere to be found, although there were
rain curtains swirling under the wall cloud. We could see the hint of a core well
to our north, but the core was translucent in appearance-we could see storm
towers distant north through the core. Radar indicated the storm had weakened
some, but still had large hail in it. Where was a good question!! We watched the
circulation attempt to wrap up from about a mile away, but this circulation looked
much weaker now. Circulation was broad and the RFD looked to be too strong
to allow the inflow to balance the overall rotation. Dust swirls kicked up by the
RFD were incorrectly called in as a tornado, as we were just 1/2 mile away from
these dusty and very brief spin ups. These were more gustnado in nature than
actual tornado, especially since this spin up was not directly under the main rotation center.

Our overall opinion of the supercell was that it was that it was on the decline. The
circulation was weakening and the storm structure was appearing more linear on
radar. We needed to get back to I-80, so we slowly progressed southeast on U.S.
Highway 26 towards Ogallala. The supercell abruptly cycled again and now was
again appearing as though it was possibly going to produce a tornado. Just to
the northwest of Ogallala, we pulled over and watched the now menacing looking
supercell approach us. The storm appeared as though it was now dropping to
the south-southeast. We were right in front of the organizing circulation/wall cloud
again. The broad circulation tightened up considerably as it approached U.S. 26,
and the sky turned a weird shade of green and darkened. Quickly, very large raindrops and occasional dime sized hail started to fall. We could hear a loud
roar approaching us from the north. The roar was not a tornado, but the sound of
very large hail falling from the supercell/hailcore. Needless to say, it was time to move, and move fast!! We reached the west edge of Ogallala and quarter to
golfball sized hail started to fall. Local radio was reporting that baseball sized
hail was now reported 2 miles west and northwest of town pretty much in the area we were stopped along U.S. 26 just 5 minutes earlier!! It was now appearing yet
another Nebraska town was going to be nailed by horrendous hailstorm. Even
though the largest hail was still west of town, we were far from out of the woods!!

Golfball sized hail picked up in intensity, and we were getting pounded as we
drove through Ogallala to get to I-80. More hail welts were picked up here!! The
core was now over the city and we had to drive 2 more miles to get to I-80. Hail
made for a deafening roar in the vehicle as we plotted our way out of this noisy
and potentially damaging situation. Brian said to go east on I-80 to avoid the
largest hail- the supercell was now producing 5 inch diameter hail on the west
side of Ogallala. This huge hailstone area was going to track south-southeast so
we darned sure did not want to go south on NE-61. The interesting thing about
our decision was that we ended up driving through nearly 10 minutes of quarter
sized hail on I-80 as we headed east from Ogallala. Other severe storms were
popping along what looked to be an east-west outflow boundary or cold front.
We passed through several small cores before reaching the road to McCook. We
certainly needed to start back for Tulsa now as the sun had set!!

We prepared for the marathon drive back to Tulsa, and split the driving into shifts
as we had to go about 800 miles. We reached Tulsa around 6am, just in time for
sunrise over Oklahoma. We now realized that summer had set in across Tulsa
as the overnight low in Tulsa was 82 degrees, a very muggy 82 degrees!! The
only hope from here on out was isolated supercells in the High Plains or a long
distance chase to N.Dakota or Minnesota. The forecast models were indicating
that something might happen later today when northwest flow interacted with a
weak boundary across the Texas/Oklahoma Panhandles. We'll see !!