Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
826 PM EDT Thu Apr 18 2024
Day 2
Valid 12Z Fri Apr 19 2024 - 12Z Sat Apr 20 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE TEXAS BIG BEND AND WEST TEXAS UP THROUGH THE RED RIVER...

...20Z Update...

A small break in the convective potential will ensue on Friday with
a return mainly occurring Friday evening through the end of the
period. A cold front will continue to motion south through TX
Friday before stalling over the south-central portion of the
state later in the afternoon. Out west, a shortwave trough will
propagate eastward off the Pacific with increased large scale
forcing occurring downstream over the Desert Southwest, eventually
into TX by early Saturday morning. The combination of favorable
upper forcing and cooler air advecting behind the cold front will
enable a deepening isentropic environment in-of the southern plains
from the Red River down through north TX. A secondary area of
interest will be over the TX Big Bend where a weak shortwave
impulse moving out of Mexico could spur a round of convection off
the Serranias del Burro with southwestern steering flow taking it
towards the Rio Grande by nightfall.

There's a split in the potential within guidance with some
sneaking the convective cluster over the border with locally heavy
rainfall focused over the Rio Grande and southern Edwards Plateau.
Others maintain a quiet outlook with the convection dissipating
before crossing the border. This was reflected well within the HREF
EAS probabilities remaining low into the 10-15% range with only a
few guidance promoting the potential. Despite the low
probabilities, moisture rich environment and higher end QPF within
the upper quartile of outcomes allows for a maintenance of the
MRGL risk area encompassing the Big Bend into the Edwards Plateau.

Further north, the output from deterministic is very split with a
50/50 distribution on low end QPF development between 00-12z
Saturday and much more favorable QPF for MRGL concerns to arise
over the western rolling plains up through north TX and the Red
River Valley. Considering the GFS/ECMWF ML output for the time
frame being fairly similar and leaning towards the higher end of
the QPF distribution, decided to maintain the MRGL from previous
forecast and link the two areas together with some adjustments on
the edges based on ensemble bias corrected data and HREF blended
mean QPF footprint.

Kleebauer