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

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FXUS64 KEWX 250806

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
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              81  64  81  63  83 /  30  90  50  30  30
Austin Bergstrom Intl Airport  80  65  81  63  83 /  30  90  60  30  30
New Braunfels Muni Airport     82  65  81  62  84 /  30  90  40  20  20
Burnet Muni Airport            80  63  78  60  80 /  40  70  50  20  30
Del Rio Intl Airport           86  67  87  63  93 /  30  70  10  -   -
Georgetown Muni Airport        80  65  80  62  81 /  30  80  50  30  30
Hondo Muni Airport             83  65  85  62  89 /  30  90  30  20  10
San Marcos Muni Airport        82  65  82  62  84 /  30  90  50  30  20
La Grange - Fayette Regional   81  66  82  64  84 /  30  80  60  30  30
San Antonio Intl Airport       83  66  83  63  86 /  30  90  40  20  10
Stinson Muni Airport           84  66  83  65  87 /  30  90  40  20  10




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