AWUS01 KWNH 211000
FFGMPD
TXZ000-211530-

Mesoscale Precipitation Discussion 0123
NWS Weather Prediction Center College Park MD
559 AM EDT Tue Apr 21 2026

Areas affected...Triangle of Central Texas...

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

Valid 211000Z - 211530Z

SUMMARY...Flash flooding risk possible given slow
moving/back-building warm-advective shallow but efficient showers/thunderstorms. Rates of 1-1.25"/hr are possible with
localized 2-3" totals.

DISCUSSION...A very effective dynamic environment is helping to
draw above normal moisture into a favorable ascent pattern over
the next few hours across the Triangle of central Texas. GOES-E
WV suite depicts a decaying MCV across southeast TX along the
southeast periphery of favorable mid to upper-level divergent
pattern along the northeast quadrant of a 70kt 3H west to east jet
along/north of 30N. Combined with NW to SE diffluent pattern from
500-250mb providing strong divergence for effective convective
outflow. However, it is also directing strong ageostrophic
forcing by helping to accelerate the early morning western Gulf
jet streak fluxing enhanced low level moisture northward into the
isentropic ascent plane. CIRA LPW along with VWP vectors denote
core of west Gulf jet is propagating 20-25kts in the core of .8 to
1" moisture in the surface to 850mb layer. Combine this with the
axis of 700-500 mid-level moist flow from the subtropical eastern
Pacific results in combined PW values nearing 1.5" near the best
isentropic ascent currently through the San Saba River Valley.

As such, recent 10.3um EIR and RADAR show increasing shallow
convective activity along the NW to SE oriented DPVA into the best diffluence/divergence region downstream. The only limiting factor
is the lack of higher theta-E air resulting in a broader unstable
layer. Currently, it is limited to 100-250 J/kg of MUCAPE but
only expected to increase toward 500 J/kg toward mid-morning as
the core of the western Gulf air reaches the area of concern.
Deep layer flux and ascent should allow for solid convergence and
low level precipitation development likely with smaller droplets
in warm-cloud process generation. This should allow for increased
rainfall rates, but without the greater vertical depth, is likely
to be limited to the 1.25" range at max. Convective cells are
likely to move toward the northeast, but with continued south to
southwest low level inflow, propagation vectors should be
supportive of upstream redevelopment/back-building of the shallow
cores. This should allow for increased overall duration to
potentially support highly focused/localized maximum totals of
2-3" through to afternoon.

Hydrologically, these maximum totals are at the minimum thresholds
of 1 but more likely 3 hour FFG values in the area, particularly
along the southwest edge of the area of concern. NASA SPoRT LIS
0-40cm soil conditions suggest average saturation around 45-55%
and as such, most rainfall will be beneficial, but an isolated
incident or two of flash flooding is considered possible given the
strong dynamics and setup's history.

Gallina

ATTN...WFO...EWX...FWD...SJT...

ATTN...RFC...FWR...NWC...

LAT...LON 32539720 32209657 31769628 31419629 31169645
30919666 30589712 30449755 30679836 31159887
31779894 32509834

$$

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