In a near perfect reversal of the wild pattern experienced in early May, the large-scale flow regime was characterized by a powerful longwave trough over the eastern U.S. and western U.S. ridge. Between these two height anomalies, a weak northwesterly flow persisted over the Plains for most of the period. This led to sporadic, very isolated severe thunderstorm setups that were difficult to forecast and made all the more precious by their paucity. The pattern was especially disappointing for storm chasers given the fact this is the time of year when veteran chasers schedule their annual trips to the Plains. Nonetheless, the tour ended on a positive note with the intercept of several very photogenic storms.

Chase Days: May 23-June 1
Group leader: David Gold
Drivers: David Gold and Terry Hill
Days on which noteworthy storms were observed: May 25, May 30, May 31, June 1

Day 3 - May 25: Large outflow dominant severe thunderstorm over southeastern New Mexico.

Day 8 - May 30: Classic supercell over northeastern Colorado; several wall clouds and funnels observed.

Day 9 - May 31: Classic evening supercell over the northwestern Nebraska Panhandle.

Day 10 - June 1:  Strong squall line with photogenic shelf cloud and gustnadoes over western Kansas.

The data this day suggested that the convective event would be quite well-focused and fairly easy to intercept. As it turned out, getting the right storm wasn't so easy and it was a bit further north and east than many expected. Nonetheless, it turns out that the intercept was about as successful as it could have been. A classic high-plains beast of a supercell that formed in the late evening hours provided our group a real treat!

Meteorology:

After days of "Death Ridge 2003" (remind me to add this weather module to my future storm chasing video game ;), the pattern was finally de-amplifying enough to bring flow at mid and upper-tropospheric levels back over the high plains and we couldn't be happier to see the days of lame flow and little to no instability pass into history. The setup this day featured a west to west-northwesterly current aloft that intensified with increasing latitude so the name of the game was "Go North, Young Man!". The farther north a potentially unstable low-level parcel could advect and rise, the stronger the deep-layer shear and therefore the higher the potential for rotating updrafts. For the following discussion, please refer to the crude composite/surface analysis presented in Fig. 1. By mid-afternoon, a persistent surface mesoscale circulation became clearly evident (see the "L" stamped at this location) as moist low-level air (for those elevations) flowed into the dryline convergence zone over the Wyoming/Nebraska border region near Torrington. Aloft, mid-tropospheric winds were clearly stronger over Wyoming/South Dakota/western Nebraska (35-40 kts at 500 mb; purple wind barbs) than farther south over Colorado (25 kts at DEN). The convective forecast took into account not only this basic meteorological setup but also the propensity of specific topographic features to enhance mechanical lifting of moist low-level air. In particular, I was most interested in the Laramie Range west and northwest of Cheyenne, WY and the Cheyenne Ridge, a topographic ridge oriented roughly east to west along the Colorado/Wyoming/Nebraska state line with peak elevations of 5400-5600 feet above mean sea level. Thus, we set up shop in Pine Bluffs, Wyoming (the first exit on I-80 in extreme southeastern Wyoming) where I fired up the satellite internet dish and proceeded to download data for hours, all the while scanning the skies to the southwest through northwest for signs of convective development along the two orographic features mentioned above.

The Chase:

With time, it became clear that the atmosphere was simply too capped to support sustained thunderstorm development along the Cheyenne Ridge and we committed to the area further north near Torrington. By 5:30pm CDT, a large thunderstorm developed rapidly along Hwy 85 between Lusk and Torrington but then it became visually soft and unimpressive. All additional thunderstorm initiation attempts ended in failure except for a large multicellular complex that developed near Chadron. At Scottsbluff, we first went up Hwy 71 with the intent of just watching this severe storm move off to the east-southeast. However, soon after taking off this updraft became soft and mushy like all its predecessors so we stopped for a bathroom break. Emerging from the convenience store, another glance at this distant storm revealed that it had re-intensified and was taking on impressive supercell characteristics. Moreover, I began to fear that if we were to see any storms this day it would have to be this one since no new development was evident further west. We took off east on Hwy 26, watching as this storm became more and more impressive by the minute. It had a huge columnar updraft pounding upwards through a rapidly backshearing anvil with a large dome-shaped overshooting top. My main meteorological concern was that by the time we intercepted it, it would have moved into cooler, less unstable air over the lower terrain to the northeast of Alliance. Again, at the time it was the only show in town. By the time we had reached the junction of 26 and 385, Bill Gargan (who was kindly nowcasting for us from Lubbock) informed me of a new explosive thunderstorm development that had just occurred over extreme northwestern Nebraska. Damn! I cursed my earlier impatience with the atmosphere and the impulsive grab for the storm we were currently chasing (which, incidently, was now doing just what I had feared; going downhill in intensity. Fast.) We raced northward to Alliance, re-fueling there and then heading northwest on Hwy 2, intending to try to get in position to see the storm in the waning daylight and at least see the kind of impressive lightning show that an isolated high-plains supercell is capable of producing. Making surprisingly fast time (spurred on by reports of a confirmed tornado), we got to the Hwy 2/71 intersection southwest of Marsland, NE by 9:20 pm CDT and by this time we were being treated to a widening view of the supercell's updraft base, mid-level collar cloud and hail core. Horizontally-arcing lightning bolts flared across the lower portion of the updraft. As we got closer, we were able to take in more of the whole storm structure, which included multiple low-level occlusions, wall clouds, low-level striations, mid-level banding and more. I must admit that I was a bit disappointed to have missed a glimpse of the tornado produced by this storm but I later learned that (a) the tornado was best seen from the northwest (b) there were several chasers parked south of the updraft the whole time on Hwy 71 (our original north option out of Scottsbluff) that missed the tornado due to brevity/obscuring by a rain shaft and (c) we got the best of the structure that this storm allowed chasers to see; it took a while for the storm to get close enough to the only viable road to enjoy the entire milieu. The video stills are below. Note that I did not attempt to take any lightning video, although this was an absolutely incredible show! Hopefully, some SLT participants got some useable shots that they would be willing to share here at a later date.

We wound up viewing a fairly photogenic shelf cloud as we got chased across Kansas by a severe squall line that, at times, became haboob-like in its ferocity.

Meteorology:

For now, I'll just leave it at this: the models lied to me. The ETA model promised that a mid-tropospheric wind maximum would translate southeastward into the high plains of Colorado/Kansas in phase with the diurnal peak in insolation. In reality, mid-level winds were really lame, resulting in shear profiles that were too weak to support supercells. Weak convective inhibition and a fairly well-mixed boundary layer resulted in too many storms that (after briefly producing weak landspouts near Arapahoe, CO) generated a big cold pool that subsequently forced a fast-moving squall line. We were able to punch eastward and get ahead of the line at Syracuse, letting it chase us all the way to Dodge City, KS.