Panhandle of the North

HREF UH tracks

As May carries on, poleward moisture transport is beginning to support storm chases farther north. Although it’s not completely unheard-of, it is still a bit early (climatologically speaking) to be chasing in the Nebraska panhandle on May 10th. Nonetheless, modestly favorable boundary layer moisture should coincide with more than adequate deep layer shear to produce severe thunderstorms this afternoon.

Very steep mid-level lapse rates, i.e. 8 to 9 C/km in the 700-500mb layer, near and south of I-80, suggest that large to very large hail will be the main concern. A generally west-east surface boundary is not ideal for long-lived, discrete convection, given deep layer shear vectors nearly parallel to the boundary. With this in mind, any initial discrete storms in far southeastern Wyoming and the Nebraska panhandle should tend to merge into a convective complex. This scenario would favor damaging wind and large hail, spreading from the Nebraska panhandle into western Nebraska.

Two areas of focus are in play with respect to storm chase targets…

One could favor the southern fringe of activity in the far western portion of the Nebraska pandhandle, as convection allowing model (CAM) simulations favor a relatively long-lived, intense updraft helicity (UH) track just north of I-80. Given the tendency for storm mergers and less-than-ideal shear vectors, it can be inferred that the UH track is indicative of a hail swath, rather than a low-level mesocyclone. A tornado cannot be ruled out in this area, but the expected storm mode precludes a greater tornado threat.

The second of focus is a bit more of a conditional play, but would likely feature a much higher probability of a discrete supercell. Convection may fire in far northeastern Colorado by mid to late afternoon. Here, more robust low level flow should aid in convergence, as well as enlargement of low-level hodographs toward sunset. While convective initiation is more uncertain here than points north, any cells that form in this vicinity should stay isolated. Any such activity would pose a threat for large hail, along with the potential for a tornado as convection matures, especially as the low-level jet strengthens late in the day. CAM solutions are varied with positioning, longevity and intensity of any such cell, but are in general agreement that the track would be east into southwestern Nebraska, perhaps taking a right turn into far northwestern Kansas, before fading away during the evening.

It’s a waiting game and a delicate one. While the setup is much less volatile than June 12th of last year, a parallel can be drawn with respect to convective initiation. In that event, relatively messy convection fired early in the afternoon in eastern Wyoming, but more patience was needed for convection to get going in northeastern Colorado. The southern, later target paid off, as storms were more discrete in that area. A potential issue with favoring storms farther north is that it would then take at least an hour or two to re-position back to new activity to the south.

With all of this in mind, the most reasonable option would be to wait and split the difference. Expect to start near the I-80/I-76 intersection in the afternoon and pay close attention to mesoanalysis and radar/satellite imagery. From that point, it would be fairly easily to drive west/north if necessary, while still being just a short drive away from northeastern Colorado.