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

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FXUS64 KEWX 251759

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1259 PM CDT Mon May 25 2020

The large MCV over North Central TX is generating a partial frontal
push into Central TX and is likely aiding in the elevated forcing
process to promote the persistent band of convection training ESE and
approaching the AUS vcnty. Will expect to see this convective feature
to wane later in the afternoon as upstream forcing from the parent
upper low begins to generate storms over West TX and Mexico. This may
bend the southerly winds to more easterly over SAT/SSF and begin
drawing in more areas of MVFR cigs along I-35. Mesoscale models
continue to show a complex that could affect all Terminal sites late
tonight, but am beginning to believe impacts will be more minimal
around AUS and stronger at DRT. By 12Z, expect to see the primary
convective focus to shift southeast of I-35 and leaving an improving
VFR sky to finish out the 30-hr TAF period at SAT while a MVFR cig
holds on at AUS.


.PREV DISCUSSION... /ISSUED 1127 AM CDT Mon May 25 2020/

Udated to trend the higher PoPs to around I-10 over the Hill Country
for the afternoon. Slightly more north winds are trending into
Central TX and this could lower the rain potential over the eastern
periphery of our CWA border.

PREV DISCUSSION... /ISSUED 621 AM CDT Mon May 25 2020/


A few thundershowers have developed near and west of SAT/SSF and
could briefly impact the terminals over the next couple of hours.
Mainly VFR conditions are expected this morning except at DRT where
MVFR ceilings will soon build in, and brief MVFR cigs are also
possible at the I-35 sites though shouldn`t last long. Can`t rule out
an isolated afternoon thunderstorm today but our attention is on the
next complex of strong to severe storms that is expected to develop
to our north and west this evening and move through tonight, which
could bring strong wind gusts to all sites. Behind those storms,
ceilings will return to MVFR at AUS and possibly IFR for a few hours
at SAT/SSF. For the 30 hour sites, a return to VFR will come quickly,
likely around or just after sunrise Tuesday.

PREV DISCUSSION... /ISSUED 306 AM CDT Mon May 25 2020/

SHORT TERM (Today through Tuesday)...
Things are quieting down early this morning after an active evening.
An area of stratiform rain continues over our eastern counties, with
evidence of yet another wake low behind the MCS as winds have gusted
to 30 mph in a few locations. Expecting any lingering minor flooding
issues to continue to clear up overnight and all warnings have been
allowed to expire.

However, another round of strong to severe thunderstorms is in the
cards this evening and tonight, and as a result our entire forecast
area is under an SPC slight risk as well as a slight risk of
excessive rainfall in the outlook from WPC. A slow moving trough
axis will move in from the west later today with a mid-level wind
maxima at its base helping to provide slightly better deep layer
shear than the event that just concluded, closer to 40 or even 45
knots over western portions of the CWA. With plenty of moisture
return during the day today, dew points right back into the upper
60s and lower 70s are expected. In addition, steep mid-level lapse
rates near 8 C/km will mean ample instability once again, in the
1500-4000 J/kg range, highest south and west. In addition an
approaching cold front will provide strong low level forcing. Initial
development will have the potential to be supercellular in nature
over the southern Edwards Plateau in the late afternoon/early
evening hours, with large to very large hail and even a tornado or
two possible. Once again storms will likely grow upscale into a
large MCS with all severe weather hazards possible, although the
hail and tornado threat should wane as storms move southeastward.

Precipitable water values are forecast to reach the 1.7-2.0" range
yet again, and with freezing levels of 12-14,000 feet and ample low
level forcing, warm rain processes could dominate at times leading
to impressive rainfall rates. Given the heavy rain that just fell,
additional flooding impacts are of concern. Yet again, 1-3" of rain
are forecast for many locations, and isolated higher totals again as
high as 5 inches are within the realm of possibility. Similar to
yesterday where some storms developed and dumped heavy rain (and
large hail!) over the Austin metro well ahead of the primary MCS,
several high resolution models indicate this is a possibility once
again. Model depictions of convection are messy, making it difficult
to determine when and where this may occur, however the SREF does
indicate a mean QPF maxima almost directly along the escarpment/I-35
corridor this afternoon which is particularly concerning.

In terms of timing of the main event, at this time it appears to be
displaced a little later than yesterday and there is more spread
among the models making it difficult to give much certainty. Storms
should exit for the most part before sunrise Tuesday, with some wrap
around showers possible through the daytime mainly east of I-10/I-
37. Cooler temperatures are expected with highs in the upper 70s
over the Hill Country and mid to perhaps upper 80s south and west.

LONG TERM (Tuesday Night through Sunday)...
The upper level low drifts over northeastern Texas to the ARKLATEX
Wednesday into Thursday. This allows South Central Texas to dry out
with chances of showers and thunderstorms mainly over our Central
Texas to US highway 77 corridor areas in closer proximity to the
upper low.

Where there was once good agreement, there is now disagreement for
Friday through next weekend. The GFS remains consistent in taking the
upper level low slowly southwest to over Central Texas next weekend.
Meanwhile, ECMWF and GEM trends show an upper level trough over the
Great Lakes deepening over the eastern states that picks up the low
and weakening it into a shear axis over the lower Mississippi Valley
on Friday to the Gulf Coast by Sunday as the Subtropical Ridge builds
over the Plains states. ECMWF and GEM result in lower rain chances
and amounts while the GFS increases rain chances with higher amounts.
Have remained with the blended guidances and their chance POPs most
areas for Friday through next weekend. However, expect POPs will
gradually be reduced for that time period as even the GFS has trended
slightly drier.


Austin Camp Mabry              64  80  63  84  65 /  80  60  10  20  10
Austin Bergstrom Intl Airport  62  80  62  84  64 /  80  60  10  20  10
New Braunfels Muni Airport     64  80  62  87  64 /  80  50  10  10  10
Burnet Muni Airport            62  76  60  82  62 /  80  50  10  20  20
Del Rio Intl Airport           66  88  63  95  68 /  70  10   0  -   -
Georgetown Muni Airport        63  78  61  83  63 /  70  60  10  20  20
Hondo Muni Airport             66  85  61  91  65 /  80  30  -   -   -
San Marcos Muni Airport        64  80  61  87  63 /  80  50  10  10  10
La Grange - Fayette Regional   66  80  63  84  65 /  70  70  20  20  20
San Antonio Intl Airport       65  82  63  89  66 /  90  50  -   10  -
Stinson Muni Airport           66  83  64  89  67 /  90  50  -   -   -




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