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

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FXUS64 KEWX 211430
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
830 AM CST Sat Jan 21 2017

.UPDATE...
Dense fog has extended well into the Rio Grande Plains and parts of
the Edwards Plateau based on several observations, so we have
extended the Dense Fog Advisory until 10 AM for Real, Edwards, Val
Verde, Kinney, and Maverick Counties. The dense fog is more patchy
elsewhere aside from some areas along the I-35 corridor where it is a
bit more widespread, so we may need to drop those areas from the
advisory before it expires. High temperatures were increased 1-2
degrees and winds were increased slightly over parts of the western
Hill Country. Aside from retrending grids based on observations, no
other changes have been made to the forecast. A Wind Advisory is
still in effect for Val Verde, Edwards, and Kinney Counties beginning
at Noon and ending at 6 PM as westerly 25-30 mph winds gusting to 40
mph are expected behind a pre-frontal trough.


&&

.PREV DISCUSSION... /ISSUED 644 AM CST Sat Jan 21 2017/

UPDATE...
Please see the 12Z aviation forecast discussion below.

AVIATION...
Areas of fog continue across south central Texas, with IFR and LIFR
conditions firmly in place along the I-35 corridor. Fog and low
clouds will begin to lift and dissipate between 15Z-16Z, with VFR
conditions expected after 17Z. At DRT, satellite and obs show the
edge of the fog and low clouds is just over the terminal and this
will result in a tempo group for LIFR conditions through 14Z.
conditions should improve quickly back to VFR after 16Z as the
shallow moisture mixes out. Gusty west winds are then anticipated
over DRT this afternoon.

Westerly winds are then set to increase across all areas beginning
late tonight into early Sunday morning. All terminals can expect
gusty west to northwest winds through the daytime hours on Sunday.

PREV DISCUSSION... /ISSUED 350 AM CST Sat Jan 21 2017/

SHORT TERM (Today through Sunday)...
The short term period focus was on the nuances of the well advertised
upcoming non-convective wind event this weekend. All signs continue
to point to a windy weekend, beginning as early as this afternoon for
parts of our west and northwest, and persisting through the day
Sunday.

For this afternoon...the surface low responsible for the tight
pressure gradient draped across Texas this weekend will strengthen
quickly off the lee of the Southern Rockies and move into the Texas
Panhandle. This will kick winds up this afternoon for areas in West
Central and possibly as far south as the Rio Grande/Big Bend area.
The tricky variable is wind magnitude as there continues to be some
disagreement among statistical guidance and deterministic model
output. The most gung ho wind producer is the GFS/MAV advertising
locations such as Del Rio seeing 30+ kt sustained winds this
afternoon and again overnight tonight. However, the MET/ECS
counterparts are quite a bit less vigorous this afternoon and instead
hold off on the strongest winds until Sunday. Through collaboration
with neighbors, it was agreed upon that the less aggressive models
are likely a bit underdone due to the intensity of the progged
surface gradient. Thus opted to populate winds with a GFS leaning
blend of the statistical guidance. This resulted in forecast winds in
excess of the 26 mph sustained Wind Advisory threshold this afternoon
for Val Verde, Kinney, and Edwards counties.

Additionally...near critical fire weather conditions should develop
along the Rio Grande River where Min RH values are expected to drop
to right around 20 percent. Some locations including Eagle Pass could
briefly reach critical values in the afternoon but will be highly
dependent on wind potential to push farther south than as indicated
in the current model suite.

For this evening and overnight...a brief period of sub advisory level
winds are expected between 00Z-06Z due to a passing weak surface
ridge but the gradient will quickly recover after 06Z and intensify
wind fields moving into the early morning hours Sunday and also
spreading east encompassing the entirety of the CWA. Thus another
wind advisory will likely be needed for much if not all of Sunday.

Again very low RH values and these widespread wind values will result
in this time likely critical values along the Rio Grande River.
Therefore a Fire Weather Watch has been issued for these counties
along the Rio Grande River for the afternoon hours on Sunday.

LONG TERM (Sunday Night through Friday)...
The long term period is comparatively less interesting as the
aforementioned surface low moves well east Sunday night and the winds
begin to subside. We then will be left under a brief ridging period
Monday and Tuesday which will continue well above average
temperatures for late January.

The next cold front expected looks to arrive Tuesday night
effectively cooling temperatures Wednesday to only slightly above
average and on Thursday more seasonal (upper 50s and 60s). Lows will
cool substantially on Thursday and Friday falling into the 30s in the
northern half of the CWA and 40s elsewhere.

Otherwise no significant PoPs or hazards in the forecast expected for
the week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              77  51  68  45  73 /  20  10   0   0   0
Austin Bergstrom Intl Airport  77  50  69  43  72 /  10  10   0   0   0
New Braunfels Muni Airport     77  50  69  43  73 /  10  -    0   0   0
Burnet Muni Airport            74  47  64  41  71 /  20  10   0   0   0
Del Rio Intl Airport           78  50  70  41  76 /  10   0   0   0   0
Georgetown Muni Airport        77  49  66  42  71 /  20  10   0   0   0
Hondo Muni Airport             79  48  71  40  76 /  10   0   0   0   0
San Marcos Muni Airport        77  50  69  43  72 /  10  10   0   0   0
La Grange - Fayette Regional   77  51  68  44  70 /  10  20   0   0   0
San Antonio Intl Airport       78  51  70  44  74 /  10  -    0   0   0
Stinson Muni Airport           80  50  71  44  74 /  10   0   0   0   0

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST this morning for the following
counties: Atascosa...Bastrop...Bexar...Caldwell...Comal...De Witt...
Dimmit...Edwards...Fayette...Frio...Gonzales...Guadalupe...Hays...
Karnes...Kinney...Lavaca...Lee...Maverick...Medina...Real...
Travis...Uvalde...Val Verde...Williamson...Wilson...Zavala.

Wind Advisory from noon today to 6 PM CST this evening for the
following counties: Edwards...Kinney...Val Verde.

&&

$$

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


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