May 23, 1996 Last Chance, Colorado Chase By Bill Reid

From: "William T. Reid" <73551.2512@CompuServe.COM>


The following is my chase account of May 23, 1996, which was highlighted by the
gorgeous low-precipitation supercell near Last Chance, Colorado.

The previous day, May 22, was a great chase day for my chase friends and myself,
thanks to the tornadic Benkelman, Nebraska, supercell.  The weather pattern
continued very favorable for severe weather on the High Plains on Thursday, the
23rd, as the trough over the Great Basin was forecast to send more upper-level
energy and vorticity into Colorado, Kansas, and Nebraska.  I awoke in Oberlin,
Kansas, and headed to the National Weather Service in Goodland for some weather
information.

My idea wasn't very original, as the office parking lot was full late that
morning!   At least eight other chase teams, including Roger Edwards, the
Verkaiks, Tim Samaras and Dean Cosgrove were there, as was a "Nightline" TV news
crew to document the chase exploits of Daphne and Richard Thompson.  The Storm
Prediction Center had northern Kansas, southern Nebraska, and extreme eastern
Colorado in a moderate risk area for severe weather.  Helicities and capes were
more than sufficient for supercells and tornadoes.  A frontal boundary was
oriented about east-west near the KS/NE border and extended westward into
Colorado.  Convergence was excellent along the front, so the only question was:
"Where along this boundary should we hang out?"

I felt that the first storms to go up would likely be near the front range in
Colorado, so we left Goodland and headed west on Interstate 70.  Skies were
mostly clear as we entered Colorado early in the afternoon, and I was a little
concerned that we might be too far south of the boundary.  We headed north on
385 at Burlington.  It turned out that we were closer than I thought, as we
found ourselves under a dense stratus overcast before reaching the next paved
road, U.S. 36.  We stopped in Cope for gas and a little food, and then found a
hill west of town where we were able to pull in NOAA Weather Radio.  By this
time, about 3 p.m. MDT, a tornado watch had already been issued for much of
northeastern Colorado, and the low clouds were breaking up a little and moving
in quickly from the east.  With no warnings yet and with visibility limited by
the low clouds, I had to get back into the clear skies.

We tried the dirt road network south of Anton and breezed through Thurman and
Shaw.  Finally we were able to see what we were looking for, and it was a good
one!  A large and isolated thunderstorm tower was taking shape directly to our
west as we drove the dusty Road 3X through northern Lincoln County.  At 5 p.m.
we had made it to pavement again, Highway 71, and a tornado warning was issued
for the rotating tower about 15 miles to our west.  The cell was northwest of
Limon, so that put it along Interstate 70 near Agate.  It was moving northeast,
towards Last Chance.  We were in an excellent spot to watch the storm approach
and strengthen.

The storm's base was rather low to the ground, by Colorado standards, and we
could see beneath it.  We did not observe any circulations near the ground, but
everything else was rotating!  The storm's updraft base took on a beautiful and
sculpted laminar appearance, with a smooth inflow tail sticking way out to its
northeast.  The mid and upper levels of the tower were rock hard and showed
obvious rotation, but were not smooth and laminar-looking.  The updraft was
powerful and magnificent, with a strong and hard back-sheared anvil and wild,
inverted cumulus bulging downward infront of it up top.  This storm is the most
beautifu low-precipitation supercell I have ever seen.  

We  watched the storm drift over an area with no roads to our northwest from
Highway 71, near the Lincoln and Washington county line.  We had inflow winds of
about 20 knots, and the eastern edge of the base was encroaching.  Lightning
started to shoot down out of the anvil to our north, and precipitation began to
increase from the storm's base.  At about 5:45 p.m. another tornado warning was
issued, this time for southwest Washington County, and the NWS put the storm 27
miles north of Limon, just to our north.  We did not see any tornado, though the
area of precipitation was increasing and a rain-wrapped tornado could not be
ruled out.  Our road options were not good---we could flirt with the core and
try our luck with dirt roads south and southeast of Last Chance.  (It was
obvious that Last Chance and U.S. 36 were a little too far north, and were
probably getting the (hail) shaft.  This storm was no longer an LP.)  Our other
option was to head back south about 5 miles to Road 3X, and then go east to keep
up with the storm.  We played it safe and retreated southward.  There was some
new development to the south-southwest, so we thought that it might be a good
idea to keep an eye on that, too.

We stopped and chatted with Bobby Prentice at Road 3X and Highway 71, about
halfway between Limon and Last Chance.  Our supercell, now to our
north-northeast, still looked good up top --- but the lower levels were
beginning to lose all definition.  It was disappointing to watch such a gorgeous
storm get so sloppy looking, as haze and precipitation increased dramatically.
Our chase day was coming to an untimely end.  We drove south to Limon, but the
activity towards our south was not strengthening.  Soon we found ourselves in
fog and very cool northeasterly winds.  We couldn't see a storm, or a tornado,
if it was a wheat field away!  There was still an hour of daylight left, but we
had gloom and doom conditions as we headed back towards Goodland on Interstate
70.  Moist air north of the frontal boundary, in combination with outflow from
the storm, really put the "slop" into "upslope" this evening!  

This was one of the strangest chases I've ever had.  It was about an hour's
worth of watching and worshipping from Highway 71, and then it was over!