The May 16, 2001 Southern Nebraska supercell
This day was marked by a degree of uncertainty regarding how "organized" the day's thunderstorms would be. The weather map below is a "composite map", so called because it combines onto one chart information from various altitudes within the troposphere. This particular map is somewhat limited in scope, intending to point out the key factor expected to limit the severity of the day's storms: weak mid-tropospheric winds (the large blue wind barbs at North Platte, Nebraska and Dodge City, Kansas). Note the northwestern edge of deep low-level moisture (here, denoted as the 65 degree dewpoint isoline), another key variable necessary for significant severe weather, present across southern Nebraska. This moist airmass is poised to move north underneath the stronger mid-level winds present generally along and north of the I-80 corridor. Also, note the "convergence boundary" present from northwestern Kansas northeastward across Nebraska. Not liking the anemic mid-level windspeeds farther south in Kansas (note the 5 kt northeasterly wind present at Dodge City, Kansas) we decided to target the boundary farther north across southern Nebraska, thinking that the deeper moisture would continue to become established along the boundary there during the day. This happened, and the storm shown below (and marked on the map as a red dot) was the result. For another version of the summary click here.
The incipient storm billows upward with strongest development on the western flank (side), or on the right side of the cloud mass shown above. Cloud masses like this almost always quickly develop into full-fledged severe storms. |
The cloud top becomes flatter and partially glaciated. We decide to move from our video position (2 miles south of York, Nebraska on Highway 81) and go south and east to get ahead of this thing. |
Once we get to Highway 6 we go east towards Friend. Note the vertical wall on the back edge of the updraft and the thick, billowy anvil. |
We stop briefly to marvel at the knife-edged anvil on the storm's western side. This well-defined anvil often indicates that the storm is quite intense. We are very anxious to get south ahead of the updraft. |
Finally getting ahead of the storm, we stop to check out the updraft base several times. Here, we are looking north at the underside of the severe storm (we are at the intersection of Hwy 15 and 4 near Western, NE). The hail core is clearly visible in the background. At times, the base would begin rotating pretty strongly. |
Winding our way to the south and east we finally watch as the storm updraft tightens, attaining a fairly spiral look with stubby flanking inflow cloud features curving in from the south and wrapping around a tight little mid-level mesocyclone (click on picture for features pointed out). |
And so, with such obvious visual signs of storm-scale rotation, we weren't really all that surprised when a narrow but laminar funnel emerged from the precipitation cascade within the dryslot. |
Another shot of this pretty little funnel cloud. |
The storm updraft continues to shrivel and weaken, leaving a healthy precipitation core. |
Within 15 minutes, all that is left of our storm is a very skinny updraft tower at low-levels with a fatter top portion - an atmospheric mushroom!
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As we drive south to our Salina, Kansas hotel, we enjoy a sunset-enhanced view of a distant CB (cumulonimbus) to our west! |