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

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FXUS64 KEWX 201729

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1129 AM CST Mon Jan 20 2020

.AVIATION... /18z TAFs/
Other than some passing mid-level clouds across the Edwards Plateau
and Rio Grande Plains skies are mostly clear. VFR conditions will
continue through this TAF period. Clouds will be on the increase from
the west and northwest on Tuesday, but ceilings should remain VFR
through tomorrow evening. The approaching upper level disturbance
could spark off a few showers to the northwest of DRT tomorrow
afternoon, but any impacts to the terminals are expected just beyond
this TAF period. Winds will be out of the northeast and east today
generally around 10 knots before decreasing overnight. Tuesday winds
will become more southeasterly and pick up to between 10 and 12 knots
ahead of the approaching weather maker.


.PREV DISCUSSION... /ISSUED 548 AM CST Mon Jan 20 2020/

VFR skies will persist through the next 30 hours. Scattered mid-level
clouds are appearing this morning, and these will gradually become
more continuous in later periods. Light NE winds will prevail along
I-35 while the return of light E/SE winds has occurred at DRT.

PREV DISCUSSION... /ISSUED 359 AM CST Mon Jan 20 2020/

SHORT TERM (Today through Tuesday)...
Pockets of mid-level cloudiness will slowly increase across the area
today through Tuesday as a weak ridge axis crosses Texas Tuesday.
Falling heights aloft will enable the deepening of a moist layer in
the mid levels will clouds gradually thickening. Temperatures today
should reflect plenty of sun reaching the surface, with highs a few
degrees warmer than Sunday. Then the diurnal range begins to shrink.
Tonight`s lows will be less cool, and Tuesday`s max temps may fail
to warm to those of today. A few showers are expected to spread into
the Hill Country and Edwards Plateau Tuesday afternoon, but this
trend is shifting later in time versus earlier model projections that
had the beginning of rain chances start at daybreak and reaching the
I-35 corridor in the afternoon.

LONG TERM (Tuesday Night through Sunday)...
The wettest portion of the forecast is expected Tuesday night
through Thursday as a series of upper troughs swing across the state.
The first of these disturbances is expected to reach the Texas
Panhandle Tuesday afternoon, forcing an eastward expanding shield of
rain across West and West Central Texas. As the disturbance reaches
the Red River Tuesday evening, mid-level height falls across the
region on the order of 40-80 meters and rapid top-down moistening
will allow rain showers to spread from the Hill Country and Central
Texas towards the Coastal Bend by Wednesday morning. Lows Tuesday
night will range in the low 40s to low 50s.

While breaks in the rain will be possible on Wednesday, a second,
stronger disturbance approaches from the west by Wednesday afternoon
and results in increasing rain chances. As stronger height falls in
the 100-140 meter range arrive, a surface trough or convergence area
is expected to be induced roughly near the Highway 77 corridor based
on the 00Z suite of model guidance. This area will be the focus for
the highest rain amounts of 1 to 2 inches. This tapers off into the
0.5 to 1 inch range near the Interstate 35 corridor with less than
0.5 inches west of Interstate 35. Steepening mid-level lapse rates
with the upper trough`s passage Wednesday afternoon and night will
allow for some isolated embedded thunderstorms to also develop and
create at least a locally heavy rainfall risk east of a Kenedy to
Gonzales to La Grange line.

How far inland the surface trough is able to extend Wednesday
afternoon and evening will be very important in assessing any kind of
severe thunderstorm potential associated with this system. As of
now, any kind of warm sector (and the source for surface-based
instability) appears to remain relegated to the Texas coast... which
would keep thunderstorms elevated and any severe thunderstorm threat
low. However, backing of the surface flow in the vicinity of what
appears to be a warm front combined with increasing low level shear
(0-1 km bulk shear vectors of 25-30 knots) may mean a brief tornado
threat is possible Wednesday afternoon/evening near and east of the
Highway 77 corridor. Again, this is highly conditional on how far
inland the warm sector is able to make it and 00Z guidance does not
currently support this, but trends will need to be monitored in
future forecasts. The upper trough shifting east of the region by
early Thursday morning will result in rain and any kind of hazardous
weather moving into Southeast Texas with it, leaving the region
generally dry behind an associated cold front with highs in the low
60s to low 70s.

Dry northwest flow behind the mid-week system flattens out over the
weekend with cool mornings in the 30s to low 40s and mild afternoon
highs in the 60s Friday through the upcoming weekend.


Austin Camp Mabry              58  39  58  43  55 /   0   0   0  70  80
Austin Bergstrom Intl Airport  58  36  59  43  55 /   0   0   0  70  80
New Braunfels Muni Airport     60  38  59  46  57 /   0   0   0  70  80
Burnet Muni Airport            57  37  55  42  53 /   0   0   0  80  80
Del Rio Intl Airport           60  41  59  50  64 /   0   0  10  60  30
Georgetown Muni Airport        57  36  56  42  53 /   0   0   0  70  80
Hondo Muni Airport             61  38  61  49  60 /   0   0   0  70  80
San Marcos Muni Airport        58  37  59  44  57 /   0   0   0  70  80
La Grange - Fayette Regional   58  37  59  44  58 /   0   0   0  50  80
San Antonio Intl Airport       59  40  60  49  58 /   0   0   0  70  80
Stinson Muni Airport           60  40  62  51  59 /   0   0   0  70  80




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