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

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FXUS64 KEWX 211820
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1220 PM CST Sat Jan 21 2017

.UPDATE.../EASTWARD EXPANSION OF WIND ADVISORY FOR TODAY/
The pre-frontal trough is currently in west Texas and extends
through Dryden just to the west of Val Verde County where they
currently have sustained winds above 30 mph and gusts above 40 mph.
Hi-res models continue to forecast higher wind speeds and gusts
further east than previously thought as the surface feature is moving
through a bit faster than expected. In addition, higher momentum air
aloft at 850-925 mb should mix out pretty efficiently with clear
skies over most of the region allowing for highs in the upper 70s to
lower 80s. Therefore, the Wind Advisory has been extended for another
row counties to the east where confidence is increasing that they
will see westerly winds sustained at 25-30 mph gusting to 40 mph or
above. We will continue to monitor trends to see if the Wind Advisory
needs additional expansion this afternoon along with monitoring near
critical fire weather conditions in the Rio Grande Plains as
relative humidity values may dip below 20 percent before winds relax
briefly for the evening hours before picking up again overnight.



&&

.PREV DISCUSSION... /ISSUED 1201 PM CST Sat Jan 21 2017/

AVIATION.../18Z TAF CYCLE/

After low clouds and areas of dense fog earlier this morning, all
TAF sites and the region have recovered to VFR. Main aviation
highlight today will be the strong west winds near KDRT with lower
winds at KAUS/KSAT/KSSF. KDRT winds will increase to near 25 knots
with 35 knot gusts possible 19Z-00Z. A wind advisory is in effect
till 00Z for Rio Grande Plains and the Hill Country. For
KAUS/KSAT/KSSF, winds will be lighter than KDRT but will still reach
upwards of 20-25 knots at times from the west. KDRT could also be
closer to lower clouds moving late this afternoon and evening as a
brisk weather disturbance moves across the area. Any SHRA should stay
north of KDRT but some intermittent MVFR to VFR clouds could skirt
near KDRT. Confidence is low on the lower cloud ceilings but have
trended with a SCT035 this afternoon/evening.

Winds will decrease through the early to mid-evening but will then
increase again and become quite strong overnight and through Sunday
morning across the entire region as a front moves through. No rain
is expected with the frontal passage but strong NW winds of 20-30
knots with gusts to 40-45 knots will be likely across much of the
region. Main timeframe will be from 06Z-18Z Sunday. Low-level
turbulence and wind shear will be likely during this time-frame.

PREV DISCUSSION... /ISSUED 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 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              78  51  68  45  73 /  10  20   0   0   0
Austin Bergstrom Intl Airport  77  50  69  43  72 /  10  20   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
Georgetown Muni Airport        77  49  66  42  71 /  20  20   0   0   0
Hondo Muni Airport             79  48  71  40  76 /  10  -    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

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM CST this evening for the following
counties: Bandera...Edwards...Gillespie...Kerr...Kinney...Llano...
Maverick...Real...Uvalde...Val Verde...Zavala.

&&

$$

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



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