SUMMARY...At least localized patches of flash flooding appear
likely from portions of northeastern TX into eastern OK and
adjacent portions of western AR into southwestern MO and
southeastern KS. Backbuilding and training of thunderstorms will
produce 2 to 3+ in/hr rainfall.
DISCUSSION...Regional radar imagery at 14Z across the Southern
Plains showed scattered showers/thunderstorms extending from parts
of northeastern TX into eastern OK as well as portions of
northwestern AR. This activity was located within a region of
pronounced upper level diffluence and divergence, to the east of a
closed mid to upper-level low over northwestern TX. A very moist
airmass existed from the west-central Gulf Coast into eastern
OK/western AR with precipitable water values 0f 1.9 to 2.2 inches
(12Z soundings/GPS ground-based stations). Wet bulb zero heights
were 13-14 kft and MLCAPE was in the 500 to 1500 J/kg range with
little to no inhibition. There were a number of embedded mesoscale
vortices within the precipitation axis, helping to locally enhance
rather efficient rainfall rates.
With only a slow NNE motion forecast for the closed low, scattered thunderstorms will persist across northeastern TX into eastern OK
and the MOKSAROK 4-state junction. Individual thunderstorm cells
will advance north at 15-25 kt but with a southerly low level
inflow of a similar direction and magnitude (highest over
east-central OK with 850 mb winds of 25+ kt), the potential for
backbuilding and training will be high.
The placement of the upper low and corresponding zone of upper
level divergence/diffluence combined along with the region of
stronger low level flow over eastern OK seems to favor locations
north of the Red River for the greatest threat for training and
locally high rainfall over the next 3-5 hours. However, subtle
regions of low level convergence over northeastern TX may also
favor localized zones of training and high rainfall rates.
The environment will support hourly rainfall of 2 to 3+ inches at
times over isolated to widely scattered sections of TX/OK/AR with
potential for 3 to 5+ inches on a localized basis through 20Z.
These high rates are likely to lead to at least localized areas of
flash flooding into the afternoon.