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

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FXUS64 KEWX 192335 AAA

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
635 PM CDT Sat Aug 19 2017

VFR conditions are expected throughout the majority of this forecast
period. KSAT and KSSF may see a brief period with a BKN layer. Due to
the small period of time just went with a tempo group. Winds will be
S/SE 8-15 knots through 05Z-06Z then decrease to 4-8 knots. After 16z
Sunday southerly winds increase to 8-12 knots. KDRT likely will
remain easterly near 10 knots overnight and through 16Z then SE at
10-15 knots with some gusts to near 20 knots. Isolated convection
should remain out of the vicinity of the terminals.


.PREV DISCUSSION... /ISSUED 325 PM CDT Sat Aug 19 2017/

SHORT TERM (Tonight through Sunday Night)...
A mid-to-upper level ridge of high pressure remains over South
Central Texas today, leading to hot and dry conditions with high
temperatures headed for the upper 90s and lower 100s. Relatively dry
surface dew points in the mid to upper 60s should keep heat index
values in the 100-105 degree for most spots this afternoon, with some
isolated higher values mainly east of I-35 in the Coastal Plains. The
relatively dry atmospheric profile with weak subsidence inversions
aloft should also prevent convection from developing this afternoon
over the region, with convection generally remaining north and west
of the region. Tonight should be similar to last night as mostly
clear skies will allow temperatures to fall into the mid 70s before
scattered to broken low clouds form along the Escarpment by sunrise.

A weak upper level easterly disturbance moving in from the Gulf and a
slow-moving trough over the western United States will help weaken
the ridge of high pressure slightly tomorrow. This weakening ridge
coupled with a slight increase in surface moisture ahead of the Gulf
disturbance may allow for a slight decrease in temperatures and
slight increase in humidity tomorrow. Considering model guidance has
been running 1-2 degrees cooler than observed highs, we went ahead
and increased high temperatures slightly for tomorrow to keep them in
the upper 90s and lower 100s. If these values and the increased dew
points pan out, we should see a slight increase in heat index values
tomorrow more in the 103-108 degree range outside of the Hill Country
where values will be below 100. However, we should still be below
Heat Advisory criteria tomorrow, so our ongoing SPS on elevated heat
indices should suffice. Moisture levels will not recover enough
tomorrow to overcome subsidence inversions aloft, so the region
should remain dry tomorrow as well.

LONG TERM (Monday through Saturday)...
The weak upper level disturbance in the Gulf (or TUTT low) will
continue to approach the upper Texas Gulf Coast for Monday and
Tuesday as the ridge continues to gradually erode. This should allow
for a gradual increase in cloud cover and humidity over most of the
region with isolated showers and thunderstorms in the Coastal Plains.
Temperatures should degrease a few degrees to keep most spots in the
upper 90s, but heat index values should still remain elevated in the
103-107 degree range for most spots due to the increase in humidity.
Confidence is increasing in the prospect of a weak front approaching
or moving into the region late Wednesday into Thursday as a strong
trough moves through the Midwest with the ridge weakened considerably
over South Central Texas by the inverted trough. This should trigger
isolated to scattered showers and thunderstorms over at least
northern portions of the region for Wednesday with outflows helping
push the weak front further south for Thursday to bring rain chances
and slightly cooler temperatures to the entire region. There may be a
locally heavy rainfall threat along the front during these periods,
but there is also a chance that the subtropical ridge briefly
rebuilds from the west to keep the front north of our area.

The forecast past the middle of next week is even more uncertain as
what occurs during with the front during the middle of the week will
affect the strength of the ridge over the region for the later part
of next week. In addition, the remnants of Harvey should move into
the Bay of Campeche on Thursday and Friday and begin to move
northwest into Mexico for Saturday. Model ensembles keep the remnants
south of the Rio Grande, but the increased moisture should at least
give south Texas and possibly the southern half of our CWA continued
rain chances into next weekend. Thus, there is at least a decent
possibility of a continued wet period and shift away from hot and
dry weather in the extended forecast.


Austin Camp Mabry              77 101  76 100  76 /   0   0  -   10  -
Austin Bergstrom Intl Airport  76 100  75  99  74 /   0   0  -   10  -
New Braunfels Muni Airport     75  99  75  98  75 /   0   0  -   10  -
Burnet Muni Airport            73  97  73  95  73 /  -    0  -   10  -
Del Rio Intl Airport           78 102  78 100  78 /   0  -   -   -   -
Georgetown Muni Airport        75  98  75  97  75 /  -    0  -   10  -
Hondo Muni Airport             74 100  74  99  74 /   0   0  -   -   -
San Marcos Muni Airport        75 100  75  99  75 /   0   0  -   10  -
La Grange - Fayette Regional   77  99  76  99  75 /  -   -   -   20  -
San Antonio Intl Airport       76  99  76  97  76 /   0   0  -   10  -
Stinson Muni Airport           75 100  76  99  76 /   0   0  -   10  -




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