Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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FXUS64 KEWX 252029
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
329 PM CDT Mon Sep 25 2017

.SHORT TERM (Tonight through Tuesday Night)...
The effects of Tropical Depression Pilar will provide initially much
needed rain over our western counties, then a flash flood threat for
some areas as early as this evening. Streamer showers continue to
affect areas generally along and just east of the Hwy 281 corridor
with brief heavy downpours of 0.5 to 1 inch. Most of this activity
will be diurnally driven, starting in the predawn hours and wrapping
up by sundown. West of Hwy 281, rain chances will be around the
clock, and the Watch issued early this afternoon for areas west of a
Kerrville to Dilley line kicks in at 00Z this evening. Moderate to
occasional heavy rain has targeted the Del Rio and Brackettville
areas early today but only slow accumulations to around 2.5 inches
have been noted so far.

Mesoscale features ejecting off the higher terrain of Mexico will
make specific focal points for convection difficult to define in
terms of timing and amounts. Based on some patterns shown by many of
the non-gfs runs, the heaviest rains are expected to fall between
06Z and 18Z over the next two nights/mornings. The mcv that moved
into the Brackettville this morning and weakened still brings a focal
point for afternoon convection over the Rio Grande Plains. Pwat
values near the Rio Grande remain around 2-2.1 inches according to
the SPC mesoanalysis, but the NAM suggest values in excess of 2.5
inches possible by early Tuesday morning. The fact that the mcv`s
are tracking almost due east would suggest the heavy rain focal point
could shift east with time and erode the ridging aloft that has
models limiting higher rainfall total east of I-35 for now.
Localized 4 to 6 inch rains will be possible each morning period
with more common amounts of 0.5 to 1.5 inches expected closer to Hwy
281.

&&

.LONG TERM (Wednesday through Monday)...
A cold front is expected to slip into the area during the day
Wednesday although gradually shifting winds may make it difficult to
notice a fropa. The front will be initially shallow as well, so
continued heavy rain will become more broad covering for late
Wednesday into Wednesday night. Pwat values are suggested to be at or
above 2.5 inches through Wednesday night, with lowering values
expected by daytime Thursday. Rainfall rates are expected to decrease
by this time, but the continuing feed of heavy rain will likely mean
continuing flash flooding possible through Thursday afternoon, and
river flooding for another day or two beyond that.

Storm total qpf amounts still are well shy of the synoptic models
that suggest all the rain will pile up in the same areas west of Hwy
83, but due to the presence of Ewd moving mcv`s, expect more areas
east of Hwy 83 to see a heavy rain threat that will hopefully be
handled better in later model runs. Storm total rains from this
afternoon through Thursday afternoon remain fairly conservative with
widespread 4 to 6 inch storm total amounts in the watch area with
isolated amounts around 1 foot through midday Thursday. Afterwards,
rains should be more spotty and light as the frontal layer deepens
and the amount of perturbations coming out of Mexico dwindle. Storm
total rains over the more populated areas of Austin/San Antonio are
currently expected to be more in the 1-2 inch range with less than 1
inch expected over our far eastern counties.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              73  88  73  85  72 /  20  50  40  40  30
Austin Bergstrom Intl Airport  72  88  72  86  71 /  20  50  40  30  30
New Braunfels Muni Airport     73  85  73  86  70 /  30  70  50  40  30
Burnet Muni Airport            71  83  70  81  67 /  20  50  50  50  30
Del Rio Intl Airport           73  83  72  82  70 /  90  90 100  80  80
Georgetown Muni Airport        71  87  72  84  70 /  20  40  40  40  30
Hondo Muni Airport             74  88  73  86  70 /  60  80  80  70  60
San Marcos Muni Airport        72  86  72  86  70 /  20  60  40  40  30
La Grange - Fayette Regional   72  89  73  88  72 /  20  30  20  20  20
San Antonio Intl Airport       74  85  74  85  72 /  40  70  60  50  40
Stinson Muni Airport           75  86  74  84  72 /  40  70  60  50  40

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 7 PM CDT this evening through Thursday
evening for the following counties: Bandera...Dimmit...Edwards...
Frio...Kerr...Kinney...Maverick...Medina...Real...Uvalde...Val
Verde...Zavala.

&&

$$

Mesoscale/Aviation...Allen
Synoptic/Grids...Oaks
Public Service/Data Collection...Williams



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