Our primary
target today was Pratt, southern Kansas. After experiencing the rapid expansion of severe
storms along a cold front on Wednesday, 13th May which included tornadic supercells, we
were given a second chance to study a similar cold front dipping southeast from Nebraska
and Colorado into Kansas, northern Oklahoma and the Texas Panhandle today. We note a
feature of these cold fronts is that they are a strongly diurnal process of storm
development. Today's trip from Childress to
Pratt from early morning to midday, featured strong southerlies and southwesterlies with
dewpoints near 20C (68F). Even as we head through Canadian to Perryton and up onto the
high Oklahoma Panhandle (800m+ / 2,500'), temperatures remain in the high 20'sC (mid 80's
F). Cloud is sparse apart from patchy glaciating thin altocumulus. The synoptic prognosis
is for the front to dip into central KS by late morning with its SW alignment reaching
into the OK Panhandle and Texas Panhandle.
After arriving at Pratt around 1pm, with only
patchy low cumulus but a strong S/SW wind, temperatures are n the high 20's(C) / high
80's(F), the DP holding near 20C. We check the satellite image and note that the frontal
boundary to the NW of Pratt is showing up a rope signature. Northwest of the cold front,
most low level cumulus had disappeared while a broader cumulus field exists ahead of the
front. We ventured about 10 miles north of Pratt with the front clearly visible to the NW
as a very narrow alignment of enhanced cumulus. As the alignment approached, cumulus cloud
structure showed sudden deepening with darker bases extending towards the SW. An area of
congesting cumulus just to our north rapidly intensified.The cap today is moderately
strong and as temperatures are sustained in the high 80's (near 30C), the cold front
is now coming to life. In the upper levels, a moderately strong 500 - 300hPa jet is
present. The orientation appears to be from approx 260deg.
Within less than half an hour we are located near
the frontal boundary northeast of Pratt and watch the explosive development of storms.
Huge towers are growing rapidly and the alignment along the frontal boundary of dark bases
is now merged in a broadening development. Even as we watch backshearing anvils, rain has
not yet reached the ground in our vicinity. Increasingly more frequent thunder becomes
merged into a continuous rumble. The wind swings strongly to the northwest. We will now be
following this frontal boundary for the next 5 hours as it grows from this modest line of
storms to a massive squall line.
A heavy precipitation shaft appears to our
northeast, and we note the rain free base area starting to curve. Already at this early
stage, the massive thunderstorms are affecting the frontal boondy alignment. We move south
to keep ahead of the frontal alignment, and the storms continue to expand along the front.
Within the next hour, the frontal boundary erupts into massive storms through its entire
length through Kansas, into northwest OK and the northern TX Panhandle. As we race south
to near Medicine Lodge, the massive cell to our NE becomes tornado warned. We note the
pronounced scalloping of the frontal boundary, as downdrafts expand southeast from
collapsing storms and inflow notches appear on their southwestern flanks. As we approach
Alva, we watch an inflow notch feeding into the severe storm to our northeast and start to
rotate. We watch alignments of dust feeding from the north and separate alignments of dust
feeding from the south into what appears to be a localised meso circulation. The rain free
base rotates rapidly and perhaps, will this be a precursor to a tornadic event?The
rotating base then subsides only to reappear several miles to the southwest along the
inflow line. This pattern persists for about 10 minutes, then is obscured by precipitation
shafts as the cell collapses.
Another problem today is the cold frontal boundary
continuously overrunning and cutting off sustained uniform inflow. We move quickly south
to escape being inundated by rain and hail and try and clear the now strongly developing
gustfront, however for a short distance the road bends back into the precipitation shaft
and we are pounded by 2.5cm / 1" hail, and then escape as the road winds back towards
the south. Not only are we surfing the cold front, we are now leapfrogging the
gustfronts.....
As we move further southeast, we note the
pronounced scalloping of the frontal boundary remains but on a larger scale. We continue
east, heading for the I-35 and encounter the deployment of Vortex2 equipment along the
way. The squall line was now gaining strength and was producing numerous gustnado
developments, some of which were spectacular. We can barely outrun the squall line as we
consistently stop to photograph and continue to race east. We encounter on one stop a
Vortex2 Doppler radar truck and lots and lots and lots of chasers. The backdrop of the
squall line becomes stupendous, and we gather spectacular photographic opportunities.
As we approach Ponca City, the squall line finally
overtakes us and we turn north along 177 and head for the Kansas border. Another day is
done, and we've depleted our adrenaline again....what a brilliant study of an Oklahoma
squall line!!
Report: Clyve Herbert
Photography: Jane ONeill / Clyve Herbert |