An early-morning MCS left a boundary over northern TX,
extending southwestward to the Abilene area and the west to
south of Lubbock. A dryline was forecast to move into West
Texas during the day.
Warm, moist low-level air was leading to large amounts of
CAPE near the old outflow boundary in N TX, but upper flow
was weakening rapidly in that region. VORTEX targeted the
dryline and local terrain features in west Texas for storm
initiation. CAPE was rather small, but forecasted to
increase throughout the day, as backing and increasing
low-level flow brought higher-CAPE air northwestward into the
region.
The dryline became quite sharp and retreated slowly late in
the afternoon over the Caprock area. Cumulus was observed on
the dryline for several hours, and a good initiation
experiment was conducted with the NOAA P-3 and NCAR Electra,
as well as mobile CLASS and mobile mesonet teams. The
dryline failed to initiate convection. Our best guess for
the reason is that the sounding was moist-neutral through the
lowest 250 mB, and then CAPE increased above that level. We
are guessing that the clouds which formed along the dryline
entrained too much dry air between the LCL and the more
favorably stratified air above 600 mB.
Events so far during VORTEX make it obvious that we have
little or no useful knowledge about the processes of storm
initiation and the processes that suppress initiation. The
best we can do at this point is to make sure the environment
would support supercells, guess whether or not the "lid" can
be "broken", identify a boundary along which we expect
convergence, and hope for the best. When in the field, we
realize that the initiation of storms is a much more
complicated process, depending to a large degree on events
that occur on scales we don't routinely observe, on subtle
features in the low-level stratification and shear structure,
and for which we don't have routine, dependable numerical
guidance.
Erik Rasmussen
Jerry Straka