When you're
in an area of storm potential, that's not expected to break out till mid to late
afternoon, we opt to go sightseeing....and western Nebraska you can drive through the
weird sand dune country (near 4,000' ASL), go shopping in Alliance, visit the extensive
railway yards for those who prefer to gunzel (railfanning....wait for the 'Trains' page
coming soon), visit Chimney Rock (where we didn't pay $20 for a cap!!!) or visit Carhenge,
north of Alliance. All the time though, we were keeping an eye on any cumulus
developments...and by late morning, scrappy multicells were already breaking out to our
southwest between Wyoming and northeastern Colorado. We tag onto a cumulus alignment south of Alliance, which kept popping up pathetic
turkeys that glaciated. The synoptic setup today, as we have found on other occasions in
central USA, is rather complex. The surface cold front dribbles south through western NE,
and we suspect also a prefrontal trough. An upper thermal trough is expected to enter the
west of the state during the afternoon dropping mid and upper level temperatures. The
dewpoints are relatively low, somewhere between 10 and 12C, but there is sufficient
forcing from atmospheric considerations and surface temperatures are expected to reach the
mid to high 80's (26-30C). Shear is not too bad either, and we note some of the weaker
developments in the early afternoon are getting their tops blown off towards the
northeast.
A persistent and enlarging multicell complex has
managed to get itself together southwest of Alliance and slides northeast. Again its
difficult to comprehend that you are sitting near 4,000' in parts of western Nebraska, and
these storms are high based (10-14,000'). The multicell, as it approached Alliance, was
very lightning active, but we note the absence of ground strikes, with most lightning
intracloud. Cascades of falling precipitation fall form the high bases, developing a
bulbous shape as they approach the ground. The persistent nature of this multicell takes
our interest, as it did for the Vortex2 team we encountered trying to surround the
storm...
We leave Alliance eastbound on Rte 2 with the
specific aim of getting to the east side of the storm. Most of the precipitation appears
to be falling on the west side of what appeared to be a linear updraft alignment.
Occasionally we stop to photograph the magnificent precipitation shafts that cascade from
the high bases. We note the storm is struggling to maintain organisation with rainshafts
appearing all over the dark base area. Finally we move east of the rainband and find
ourselves under a clear dark base extending towards the south. The patterned arrangement
of the undulating dark bases is typical of high based storms.
We do this for about half an hour and continuously
watch outflow overrun the updraft region of the storm complex. Eventually after about an
hour, the storm steps up to a different phase and appears to be bordering on supercell
status. Lightning frequency increases markedly, then we notice a clear notch of rain free
base extending to the south and separating itself from the main precipitation core. The
embedded cells appear to be moving in a more northeasterly direction but the main updraft
core and rain free base appears to be moving in a more easterly direction (a weak right
mover on this marginally outflow dominated storm). For a brief few minutes, we video a
small funnel near the centre of the main updraft core but soon even this area is overrun
by outflow and precipitation. After another 20 minutes or so, the storm moves into top
gear and for a while appears inflow dominated, producing a large wall cloud and a
multitiered updraft. Lightning flickers constantly within the cloud structure. This is
where the storm becomes rather odd and we suspect that it might have had an anticyclonic
signature (hopefully to be confirmed).
For the next half hour we note chaser convergence
in the area and we video and photograph almost to the point of exhaustion. As late evening
approaches and the light becomes poor, we find ourselves at Thedford, unaware that we've
travelled almost 100 miles to the east of our chase start. The supercell collapses and we
are engulfed eventually in a whiteout of hail and torrential rain and a microburst that
slides our car partially off the road. Time for bed.....
Report: Clyve Herbert
Photography: Jane ONeill / Clyve Herbert |