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

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FXUS64 KEWX 201731 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1231 PM CDT Sun Aug 20 2017

.AVIATION.../18Z TAF CYCLE/

VFR conditions prevail across the region with a FEW/SCT040 cumulus
deck across the Texas coastal plains to nearly SKC across Rio Grande
Valley. Winds will increase this afternoon to near 10-13 knots with
periodic gusts to the mid- to upper-teens. Winds will subside
overnight to 10 knots or less from the south to southeast. Periodic
MVFR and even IFR ceilings will again be possible Monday morning for
KSAT/KSSF from 11-14Z. KAUS may experience brief MVFR conditions for
an hour or so but have not included a MVFR ceiling just yet.
Subsequent TAF cycles may need to include a short time-frame or
TEMPO MVFR deck for AUS 11-13Z. KDRT may also come close to MVFR but
low-levels may just be dry enough for only FEW/SCT clouds near 015.
All sites will jump back to VFR by 13-15Z Monday with continued south
winds.

&&

PREV DISCUSSION... /ISSUED 430 AM CDT Sun Aug 20 2017/

SHORT TERM (Today through Monday)...
The subtropical ridge axis is currently centered over south central
Texas according to 20/00Z upper air observations as well as recent
water vapor satellite imagery. Satellite data also shows an axis of
higher moisture across the central Gulf, with precipitable water
values around 2".

The above mentioned ridge axis will remain intact today, bringing
another round of above normal temperatures and dry weather to the
region. Afternoon heat index values for the Rio Grande plains and
along and east of I-35 should top out in the 102-107 degree range
today. In addition, a few locations east of I-35 may briefly reach
108 degrees. We will mention elevated heat index values in a Special
Weather Statement and encourage heat safety given the continued
above normal temperatures.

On Monday, an axis of higher moisture will begin to spread across
south Texas in advance of a TUTT low. The increased moisture and
daytime heating should be enough to generate mainly isolated
convection during the late afternoon and early evening hours. Most of
the convection is expected to remain east of the I-35 corridor.
However, some of the hi-res models do show the possibility a few
cells could reach the I-35 corridor. For now, we will keep rain
chances east of I-35 and continue to monitor model trends. The
increase in moisture will also keep elevated heat index values over
the region on Monday.

LONG TERM (Monday Night through Saturday)...
The main feature of interest for the early portion of the work week
will be an approaching TUTT low. The short range models generally
agree in weakening this low as it encounters a stout subtropical
ridge axis. For now, we will keep rain chances confined to the
coastal plains on Tuesday and go with a dry forecast elsewhere. The
weather pattern appears to become a little more active as we head
into the middle and latter portion of this week. The medium range
models agree in showing a slightly more active northerly flow aloft
in the mid and upper levels, but differ on rain chances across the
region. It does appear the northerly flow aloft will aid in a weak
cold front moving into north Texas early Thursday. The southward
progression of this front remains in question and will likely be
dominated by how much convection develops along and behind the
boundary. The ECMWF continues to show a better chance for
precipitation, while the GFS is not as optimistic. While we do expect
an uptick in precipitation, suspect the ECMWF MOS guidance numbers
are too high. We will generally keep rain chances in the 20-40% range
for Wednesday through Saturday and adjust as needed. In addition to
rain chances, we should see a gradual easing of high temperatures
closer to climatological normals beginning Thursday. Finally, the
remnants of Harvey are expected to emerge over the Bay of Campeche
on Thursday and will add to the forecast difficulty for late this
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              77  98  76  99  76 /   0  10  10  10  -
Austin Bergstrom Intl Airport  75  97  75  98  76 /   0  10  10  10  -
New Braunfels Muni Airport     75  97  75  98  75 /   0  10  10  10  -
Burnet Muni Airport            73  95  73  95  74 /   0  10  -   10  -
Del Rio Intl Airport           77 100  78 100  78 /   0  -    0  10  -
Georgetown Muni Airport        75  96  75  97  76 /   0  10  10  10  -
Hondo Muni Airport             74  98  74  99  74 /   0  -   -   10  -
San Marcos Muni Airport        75  98  75  99  75 /   0  10  10  10  -
La Grange - Fayette Regional   76  98  76  98  75 /  -   20  10  20  -
San Antonio Intl Airport       76  96  76  97  76 /   0  10  -   10  -
Stinson Muni Airport           76  97  76  98  76 /   0  10  -   10  -

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Mesoscale/Aviation...Allen
Synoptic/Grids...17
Public Service/Data Collection...YB



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