From Mike Powell@618:250/1 to All on Sun Apr 28 15:19:00 2024
AWUS01 KWNH 281819
FFGMPD
TXZ000-282330-
Mesoscale Precipitation Discussion 0195
NWS Weather Prediction Center College Park MD
218 PM EDT Sun Apr 28 2024
Areas affected...Texas Triangle...
Concerning...Heavy rainfall...Flash flooding possible
Valid 281820Z - 282330Z
SUMMARY...New development across areas affected this morning with
some training elements pose possible scattered flash flooding
incidents this afternoon into evening.
DISCUSSION...18z surface analysis denotes a surface low near BKD
with a well defined dry-line extending southward through the Hill
Country toward South Texas just west of Laredo. GOES-E Visible
imagery shows low level cloud streets coming off the western Gulf
increasing deep layer moisture while also advecting higher
theta-E/unstable air across areas that were fairly cloud covered
with this morning's weakening MCS. Aloft, favorable right
entrance to leaving 110kt jet streak across N OK/KS accompanied by
solid cyclonic curvature is providing weak but sufficient
divergence aloft and DPVA to back low level flow into the dry line
while ascending northward in proximity to the I-35 corridor from
San Antonio to Dallas. The sufficient ascent and increasingly
uncapped environment moving in from the south has provided
sufficient ascent for new development with strong ascent and
frequent lightning. CIRA LPW and RAP analysis suggest a slug of
remaining 700mb moisture through this axis which has increased
overall total PWATs to 1.75" in the axis and given modest 25-30kts
of low level influx, will allow for efficient rainfall production.
Rates of 1.5-1.75"/hr initially should increase with arrival of
Gulf moisture surge later this afternoon with cores capable of
2-2.5"/hr.
Deep layer flow is also a concern with respect to potential
flooding given north-northeast cell motions generally a tad east
of parallel to the dry line. This may allow for some training
cells resulting in spots of 2-4". Currently, cells are along the
axis where 1-3" fell this morning and are slowly recovering. As
such, intersections of rainfall at this rate over wet grounds
provide potential for scattered incidents of flash flooding this
afternoon.