June 26, 1999     Nebraska Panhandle Tornadic Supercell

As can be expected this time of the year, storm chasing involves quite a bit more driving than usual. The focus area for supercells typically shifts to the High Plains and the N.Plains states; in order to chase from Tulsa, very long drives to get into
position are the rule. Since an extended period of severe weather was forecast for the weekend of June 26 and 27, I prepared to chase the High Plains. Brian and Kathryn also were planning to chase with me this weekend which was good considering the amount of driving involved. We prepared to leave Tulsa early on
Saturday morning and our initial target zone was either NE Colorado or possibly (hopefully) NW Kansas. This area was setting up nicely for a significant upslope severe weather event. A surface low was expected to deepen during the day on
Saturday over WC/SW Kansas. This would result in a very large area of upsloping east to northeast winds across much of E. Colorado, NW Kansas, W. Nebraska, and E.Wyoming. Unseasonably strong mid level southwest winds would result in
very deep layers of shear in these areas. Supercells were likely and tornadoes were also a very real threat. An area of strong diffluence at mid levels was also located over NE Colorado and W.Nebraska so the potential for the famous right moving High Plains tornadic supercell was very high today. The SPC (Storm
Prediction Center) outlooked much of the High Plains ofColorado, Nebraska, E.Wyoming and NW Kansas with a moderate risk of severe storms and tornadoes.Very unstable air (for the High Plains) was expected to combine with deep layer of shear to produce a regional outbreak of tornadic supercells. We left Tulsa at 7am and departed for original target zone- Yuma and Washington Co. in the northeast corner of Colorado. These counties have a notorious history this time ofyear that you just cannot ignore!!!

We drove through much of Kansas under the dominance of a strong cap, but alsounder a fairly strong low level jet. Low level clouds were ripping north at 40-50 mph across S.Kansas, and were heading northwest from C.Kansas. The 850 lowmust have been firming up a litlle further north than the forecast models indicated last night. The morning upper air data indicated the 850 low was developing over NE Wyoming rather than SE Wyoming. This might alter our chase plans later, but we were not sure about this. One thing that was really apparent was that a cold front was sagging south through C/E Nebraska, but was hanging up over SW/WC Nebraska. Also, satellite images revealed that moisture was wrapping back to the west into the Nebraska Panhandle and E. Wyoming. After the episodes in early June, both Brian and I knew what that meant for later!! Deep moisture wrapping
under the jet is almost a sure guarantee of supercells anywhere/anytime! As we cruised west on I-70, we recognized that the cap was increasing, particularly to the south of I-70. Low clouds were disappearing the further west we traveled, and
it looked as if a mid level wave had just passed and subsidence was moving in. On our long storm chasing adventure earlier in June, both Brian and I learned a great deal about chasing the High Plains and where we needed to chase when the cap was an increasing factor. We learned that when cap was strong and increasing, the only hope for supercell development was where there was a fetch of northeast winds. This wind direction seemed to be the magical factor for tornadoes. Surface data was showing that E. Wyoming and Nebraska Panhandle were where there was a large area of northeast winds by late morning.

We continued on to Colby on I-70 arriving there shortly after 1 pm. The new SPC outlook continued to point at NE Colorado, W.Nebraska,SE Wyoming, and extreme NW Kansas for a moderate risk including tornadic supercells. We hoped for a "quick" lunch in Colby but there was restaurant convergence for locals and vacationers alike on I-70 today. The anticipated 15 minute pit stop was stretched into an hour stop, so we lost some valuable time there. The cap was now very strong along and south of I-70. This was good and bad. Good because it would focus the building up atmospheric energy into our target zone. Bad because it was appearing that the cap was working into NE Colorado and NW Kansas as well. Our drive was now going to be longer it was appearing. We kept heading west through Goodland and Burlington on I-70. The only hint that storms were
about ready to develop was an cluster of cumulus along the Laramie Range in E.Wyoming. Other cumulus was bubbling, but appeared to be severely capped as there was little in the way of sustained growth. We headed north from Seibert CO and headed for the Fort Morgan area. We pulled over near the town of Last
Chance; today was still young so we were not down to our last chance!! The winds were due east and were becoming gusty, usually a good thing this time of year in E.Colorado for tornadoes. The cap was just too strong and we began to recognize our need to get north and quick. The southwest flow was drivingvery dry air down the lee side of the Rockies into the Plains. Denver's dew point plummeted by late afternoon to the upper 30's, and it was appearing that much of the deeper moisture was scouring out from the extreme cap.

We watched several towers attempt to break the cap without success. Radar was showing that several weak storms attempted to grow in the foothills, but the only real development continued to the north of Cheyenne. Everywhere else, the cap was in control. We could actually see the cluster of storms in Wyoming to the very distant north from Last Chance. We knew that we needed to get closer to this area so we blasted north for the Nebraska Panhandle. Initially, this cluster of storms
was multi-cellular, but it eventually congealed into separate cells. The movement of the cells was originally to the east, but the diffluence turned them more to the southeast with time. We raced north from Brush CO and now could see that a well developed supercell was forming to our north. Radar was indicating a large hook echo near the town of Chugwater WY. We plotted the storm's path over the next hour and it was heading for the Kimball NE area. Actually, there were now two separate supercells. One tracking for Kimball and another tracking towards the
Scottsbluff NE area. The southern storm appeared to be the more dominant and established supercell. We traversed Weld Co. in no time at all, and the supercell was just approaching the Wyoming/Nebraska border. A severe t-storm warning
for this storm was quickly upgraded to a tornado warning for S.Goshen Co. in E. Wyoming. The circulation was anchored near the town of Lagrange WY, but the supercell was literally exploding in size. The supercell had finally reached the
60 degree dew points. Both Brian and I were wondering (out loud) what would happen when the storm moved into the 65 -70 dew points!!

The supercell continued to grow larger on radar with time and the main rotation was also increasing. We crossed the Nebraska border at nearly the same time the supercell did to our northwest. The circulation continued to track very slowly to the southeast; meanwhile, the parent storm tracked more east-southeast. The
diffluence was very evident now. Radar indicated that the circulation was going to pass north of Kimball. We filled up with gas in Kimball and we could see a wall cloud to our northwest. The storm's speed picked up significantly at this time. After our pit stop, we had to decide if we were going to go west on I-80 and then north, or just go straight north on NE-71. For a brief moment we started west on I-80, but once we saw the size and position of the wall cloud, we turned around and headed back for NE-71. The circulation was actually going to track across S.Banner and N.Kimball Counties. One advantage we had, the High Plains made visibility very good so we were able to watch the wall cloud from a great distance. Radar was now indicating baseball sized hail near Harrisburg NE to our north. The circulation had moved into SW Banner Co., and a tornado warning was now
issued for S.Banner and N.Kimball Counties. The developing tornado was over open country 14 miles southwest of Harrisburg. This was where we could see the wall cloud. No funnels, but numerous cloud tags were swirling about the wall cloud to our northwest about 15 miles. Unfortunately, we had to take dirt roads to get to the wall cloud. Open country in the Nebraska Panhandle truly means wide open rangeland!!

We got behind a local farmer kicking up dust and blotting out our view of the wallcloud for several minutes. We pulled over and let this car move on. The wall cloud was looking as though it was becoming rain wrapped. The contrast of the wall cloud against the core/rain curtains was reduced dramatically. Radar confirmed
the core was staring to surround the circulation. We certainly did not expect this on the High Plains!! We were at the intersection of County Rds 17 and 48 where we watched the circulation pass to our north about 3 miles. Radar was indicating that there were now 2 circulations(common for diffluent situations). The stronger
circulation was the one that passed to our north and was embedded in rain and hail. The second circulation developed about 5 miles to our w-sw apparently on the tail end of circulation#1 gust front. We headed east on CR-48 and kept ahead of circulation#1. Numerous dust swirls were appearing in open fields around us,but the main circulation was still to our north. Eventually, vigorous rotation worked towards the ground under the main circulation. A dusty tornado was now under-way about 2 miles to our n-ne( or about 5 miles south of Harrisburg-Banner Co.).
We watched this tornado for about 2-3 minutes before the advancing core andgust front made us move on quickly.

We made it back to NE-71 as circulation#2 was approaching quickly from the west. Several other chasers/spotters were watching from the highway. We did not want to get nailed by the huge hail core that was approaching from the northwest so we headed south on NE-71. This was a good decision because the
circulation was going to cross south of the intersection of CR-48 and NE-71. We could see very strong rotation in the clouds as the circulation spun directly for us.The RFD was punching southeast and we could see the main rotation area inthe rain curtains not more than a mile to our northwest. Unfortunately, the RFD
blasted us with dust as winds kicked up to 70 mph from the west. The dust cutoff our view of the circulation eventually. Radar continued to show the dual storm circulations as it headed across NE Kimball Co.. We wanted to get ahead of the storm using PAVED roads this time. Rain was falling out ahead of the circulations and was making for slick roads on the unimproved county roads. We passed back through Kimball and reached I-80. On radar, the supercell tripled in size asit headed southeast for S.Morrill and N.Cheyenne Co.. Two very strong areas of
circulation on radar were now showing up. The northern circulation appeared to be deeply embedded in the core. The southern circulation(#2 from earlier) was more removed from the core and had a better tornado potential for this reason.
It was tracking just to the northwest of Potter NE.

With the circulation to our northwest, we continued east on I-80 stopping every now and then to watch the supercell, that was becoming more HP with time. We watched radar closely to see if the circulations were going to isolate themselves from the core a little more so we could intercept. As expected, the supercell was
now gusting out from all the cold air generated by the huge hailcore. Right over I-80, a new storm updraft formed rapidly just to our east. Fortunately, we passed under the updraft before the huge hail formed. We only got huge raindrops and dime/quarter sized hail. We knew that golfballs were soon to appear though!!
This updraft formed a circulation almost as fast as it developed from just a small towering cumulus. The circulation was forming right over I-80 near Potter and we noticed something right away that was missing earlier. Low level clouds were ripping to the west- we were now in the 850 jet. Time for action!!

We continued to head east on I-80 and the circulation tracked more or less right behind us for much of the way. We were at the Brownson exit when we realized that this was the real deal. Surface winds were east-northeast at 40-50 mph and
low level clouds were screaming in at unbelievable speeds. A tornado was sure to be imminent now!! Radar was indicating amazing circulation that was heading right for the town of Sidney as were we. We could see a very dark/low hanging
wall cloud to our west, but we could also see a very menacing hailcore sagging our direction. We pulled over at the main Sidney exit and we could not decide which was going to nail us first- the baseball sized hailcore or the developing tornado to the west of town!! Inflow into this circulation was extreme as we had
blowing dust/gravel at our location just south of Sidney. We could see the large scale rotation to our west about 3 miles. The front side of the circulation was racing north at an incredible rate and the backside was diving south at speeds that both Brian and I estimated at 100 mph. Surely a tornado would appear for
video before we would have to seek shelter from the huge hailcore!!

The sky was now a very dark/ominous shade of forest green. We were on the edge of something bad and something even worse!! Radio indicated that a tornado was now confirmed on the ground to our west about 2 miles tracking southeast. Exteremely large hail was also moving into the west side of Sidney with winds of over 80 mph. Now it was decision time!! Do we risk having the
vehicle/windshield smashed by baseballs or do we get south ahead of the tornado to our southwest. Rain curtains blocked our view of the tornado that was still reported on the ground. Road options made our decision for us. Dirt roadswere all that were available to us to get ahead of the tornado, and we were not
ready to deal with the potential of slick roads and huge hail. We did the sanething to do and pulled under the canopy of the Holiday Inn Express. We knew what was about to nail us!! A few of the guests were looking out for the stormat the front door. The clock was now ticking when the huge hail and extreme
outflow winds would hit our location. Several of the guests were more concerned about the tornado(that was now 5 miles to our south) than they were of the huge hailcore that was bearing down on us. We told them what was about to happen and I went into the hotel to advise everybody to get away from the windows.
Baseball sized hail and 90 mph winds are not a time when you want to look out the window!!

The leading edge of the hailcore was ushered in by a dramatic blast of 90 mph winds. Very large hail (mostly golfball, but a few hailstones up to baseball sized)pounded down with incredible intensity. At first, the strong winds suspended the large hail and rolled the larger hailstones bowling ball style. Brian went to the
sw corner of the hotel and was watching from behind the protective west wall ofthe hotel. The wall shielded him from the wind driven hail and he had a very unique view of the incredible hailstorm. Glass was heard breaking from the hail from time to time, and large objects/debris were thrown into the air by the 70-80 mph winds now. The full fury of the enormous supercell was now upon us. For the next 30-40 minutes, a continuous pounding of quarter to golfball sized hail impacted the vehicles and buildings around us. Brian held his position at the corner of the Holiday Inn Express, meanwhile Kathryn and I watched from under the canopy of the hotel. An incredible amount of hail fell for the 30+ minutes, and the temperatures dropped into the lower 60's and actually created a wind chill of much lower than that!! Once the hail subsided, Brian joined us under the canopy and had an amazed look on his face when he returned. This was the first time he had ever been outside and actually felt the hail hit the ground!! The supercell moved off to the south and southeast into Colorado and tornado warnings were issued for Logan and W.Sedgwick Counties. Thankfully we headed under shelter
before this monster hit, otherwise we might have lost the windshield as many cars in the lot had. A few renegade hailstones did blow under the canopy and left some welts on the vehicle. It was hard to believe that we were actually not in the meanest part of the storm either!! Softball sized hail and 85 mph+ winds
blasted the areas immediately west and south of Sidney. I guess you could say we "escaped" the supercell....

After the wrath of the supercell was over, we were forced to scramble for lodging and a place to eat. Power was knocked out to most of the restaurants and hotels along I-80, and numerous motorists were forced off the highway by the massive supercell. This made hotel rooms a PREMIUM in Sidney. We were fortunate to find a basement room(how fitting) at an old-style motel in Sidney. Once we got our motel room, the next big task was finding a restaurant open at 10pm. Most of the restaurants had closed early because of the storm and we worked through
the flooded town to find a place to eat. Fortunately, Dude's Steakhouse was open but was in process of closing. We pleaded with the restaurant manager and she served us. Special thanks to the employees for that consideration. Dinner was very good and we were very thankful the restaurant served us. Otherwise, we
may have had to resort to convenience store food(no thanks). Numerous stories and rumors abounded about devastated homes and extreme property damage west and south of town. The restaurant manager told us that this was the first time
in 30 years of business that patrons and employees had to seek shelter in the cooler!! We closed out our check and headed to get some beer- there was lots of data to review and look over!! After an hour or so of intense data absorption, we called it a night. Tomorrow was looking to be a repeat performance, but we were
still uncertain of a specific target area. Overnight convection and too many outflow boundaries precluded any decision of a target area for tomorrow's chase. The RUC model was showing that the action might initiate a little further west Sunday.