Mesoscale Precipitation Discussion 0088
NWS Weather Prediction Center College Park MD
1020 AM EDT Thu Mar 27 2025

Areas affected...Lower Rio Grande Valley

Concerning...Heavy rainfall...Flash flooding possible

Valid 271420Z - 271900Z

SUMMARY...Some expansion of heavy showers and thunderstorms are
expected through this morning and into the early afternoon hours.
Heavy rainfall rates and locally slow cell-motions will foster a
threat for additional flash flooding concerns.

DISCUSSION...A mid-level trough continues to gradually advance
east across the southern High Plains and adjacent areas of
northern mainland Mexico with multiple embedded vort centers seen
in GOES-E IR/WV satellite imagery ejecting out of the base of it
toward the lower Rio Grande Valley.

Radar imagery shows one band of convection that has slowly
progressed through Deep South Texas over the last few hours, with
the core of this activity now situated over far northeast Mexico.
However, there is redevelopment seen farther northwest to the
southeast of Laredo involving Zapata, Jim Hogg, and Starr
Counties. This convection is generally forming along a weak
instability gradient that is also aligned along an inverted
surface trough which is gradually attaining sufficient
baroclinicity to be classified as a weak stationary front.

Despite rather modest instability parameters with MLCAPE values of
500 to 1000 J/kg, there will likely be some gradual recovering of
instability with time across Deep South Texas to the southeast of
this weak frontal zone which will strengthen the overall
instability gradient. This coupled with ejecting vort energy and
the left-exit region of an upper-level jet streak from northern
Mexico across the lower Rio Grande Valley will likely tend to
support and sustain the redeveloping areas of convective activity
with some gradual expansion off to the northeast expected with
time.

PWs are generally in the 1.5 to 1.7 inch range across the area,
and this coupled with the instability should be capable of
favoring convection with 1 to 2 inch/hour rainfall rates going
through the morning and early afternoon hours. The latest hires
CAM guidance is handling the ongoing activity very poorly, so
confidence is generally quite low, but given the latest convective
trends, some additional rainfall totals going through early
afternoon may reach 2 to 4 inches with isolated heavier amounts
not out of the question given slow cell-motions.

Given some of the heavier rainfall from overnight and early this
morning, and thus the moistening up of the soil conditions, these
additional rains over the next several hours may result in some
additional flash flooding concerns.

Orrison

ATTN...WFO...BRO...CRP...

ATTN...RFC...WGRFC...NWC...

LAT...LON   27619834 26959776 26359713 25829719 25959804
            26459909 27159953 27609918