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

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FXUS64 KEWX 241819 AAA

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
119 PM CDT Mon Apr 24 2017

Please see the 18Z aviation forecast discussion below.


VFR conditions will continue through this evening while some high
clouds stream in from the west. Some gusty south winds are expected
through this afternoon, with gusts beginning to subside around
sunset. For the overnight hours, low clouds should manage to develop
along the I-35 corridor, with MVFR cigs expected between 09-10Z. MVFR
cigs continue through mid-morning, then lift and scatter back to VFR.
At DRT, VFR skies are expected through the period.


.PREV DISCUSSION... /ISSUED 611 AM CDT Mon Apr 24 2017/

All terminals were VFR this morning and should continue to prevail
VFR throughout much of the TAF period due to dry conditions. Winds
are expected to become breezy at KDRT this afternoon but otherwise no
impacts expected.

MVFR and possible IFR conditions are possible for the early morning
hours at the I-35 terminals Tuesday. Models indicate CIGs to develop
AOA the 1kft level but only included MVFR mention for now at the
terminals as not all models are hinting at IFR.

PREV DISCUSSION... /ISSUED 328 AM CDT Mon Apr 24 2017/

SHORT TERM (Today through Tuesday)...
Mostly clear skies are in place across the region with only some
passing high clouds in place. Temperatures remain cool behind the
Saturday cold front with values in the 40s and 50s across the
region. Southerly flow returns to the area today, and with that
temperatures this afternoon will be about 7 to 10 degrees warmer
versus yesterday. Southerly winds will be in the 8 to 20 mph range,
with the higher values across the western counties and Hill Country.
Low temperatures tonight will also be warmer, in the 60s for much of
the area.

The main story for the short-term forecast will be the continued
warm-up. Low pressure will be deepening on the lee side of the
Rockies ahead of an approaching upper level low. This will ensure
southwesterly flow at 850 mb which will promote increasing low-level
temperatures. 850 temps on Tuesday afternoon will be in the 20-27C
range with the higher values across the Rio Grande plains which are
closest to the mountainous terrain in Mexico. These 850 temps will
translate to surface high temperatures Tuesday in the upper 90s to
near 100 degrees for locations closer to the Rio Grande and upper
80s to middle 90s for the rest of South-Central Texas.

LONG TERM (Tuesday Night through Sunday)...
The previously mentioned upper level low will continue to move east
Tuesday night which will begin to shift the surface low to the east
as well. We should initially see a pre-frontal trough move through
the area Tuesday night and the actual cold frontal passage Wednesday
afternoon. Forecast soundings show a very stout CAP at 850 mb with a
shallow saturated layer underneath the inversion. Models are showing
some light QPF amounts Tuesday night across the northern CWA and
given how the forecast soundings look, this is likely overdone, and
the most we will see is some patchy drizzle Tuesday night and
Wednesday morning ahead of the front.

The cold front will have little effects on temperatures with highs
Wednesday in the 80s and 90s, but drier air will move into the
region behind the front. Afternoon humidity values will drop below 30
percent area wide with below 20 percent values likely for the Rio
Grande Plains. Winds behind the boundary Wednesday afternoon will be
in the 15 to 20 mph range and elevated to near critical fire weather
conditions are possible, especially for the western counties where
the lower humidity values are expected.

Southerly flow on the surface will quickly return by Thursday and a
return of southwest flow at 850 mb is expected with a low-level low
developing once again to our north ahead of an approaching upper
level low. This will keep high temperatures well above climatological
values for this time of the year especially on Friday and Saturday
when 850 temps are highest. The deep upper level low will approach
the region beginning Saturday, but the best forcing for ascent will
be north of South-Central Texas as the center of the low tracks well
to our north. The GFS is showing a pre-frontal trough ahead of the
cold front associated with the system moving through the area
Saturday afternoon, while the ECMWF does not have the pre-frontal
trough, just the cold front. If the GFS were to verify, some strong
to severe thunderstorms would be possible given high instability and
shear amounts. If the ECMWF were to verify severe chances would be
lower with the cold front moving through the region Saturday night
with most of the precip being post-frontal in the cold sector. Due to
much uncertainty, will not mention anything in the HWO at the present
time. Temperatures behind the front Sunday will be closer to
seasonal normals or even a few degrees below.


Austin Camp Mabry              63  90  72  88  59 /   0  -   10  10  -
Austin Bergstrom Intl Airport  61  89  72  88  57 /   0  -   10  10  -
New Braunfels Muni Airport     60  90  72  89  57 /   0  -   10  10  -
Burnet Muni Airport            59  89  66  84  54 /   0   0  10  10  -
Del Rio Intl Airport           61  98  67  91  61 /   0   0   0   0   0
Georgetown Muni Airport        62  89  71  85  56 /   0  -   10  10  -
Hondo Muni Airport             59  93  67  91  56 /   0   0   0  -    0
San Marcos Muni Airport        61  90  72  88  57 /   0  -   10  10  -
La Grange - Fayette Regional   61  88  71  88  59 /   0  -   10  20  -
San Antonio Intl Airport       63  90  72  89  59 /   0  -   10  10   0
Stinson Muni Airport           61  90  71  90  58 /   0  -   -   10   0




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