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

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FXUS64 KEWX 232342

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
542 PM CST Mon Nov 23 2020

Skies have cleared and lifted to VFR across most of the area this
evening, although are few spots are still seeing MVFR ceilings hang
around. With southeasterly winds becoming more southerly overnight
the return of surface moisture will mean another round of MVFR and
IFR ceilings across South Central Texas. MVFR cigs will set in
between 05z-08z, with IFR following for most of the morning. Ceilings
will finally begin to improve between 15z-20z on Tuesday. In
addition to the ceilings fog and light rain will be possible,
especially across the San Antonio terminals. Winds by late morning on
Tuesday will begin to pick up and be gusty out of the south for the
afternoon hours.


.PREV DISCUSSION... /ISSUED 302 PM CST Mon Nov 23 2020/

SHORT TERM (Tonight through Tuesday Night)...
The upper levels this afternoon consist of a trough-ridge-trough
pattern that will slightly amplify through the short term as the
western CONUS trough slides to the Plains by the end of the period.
At the surface, lee cyclogenesis is ongoing over CO as the sfc high
over the mid-Mississippi Valley continues to exit to the east. In
response, increasingly southeasterly low level flow will gradually
strengthen overnight tonight and become due southerly during the day

The influx of warmth and moisture will mean another night of low
clouds and patchy fog, although it is not expected to become dense
and should mainly be relegated to the Hill Country and San Antonio
Metro. Model soundings indicate a warm cloud depth nearing 5kft
which should be plenty deep enough to squeeze out some isolated
shower activity across central and eastern portions of the area late
tonight through about midday Tuesday with some modest isentropic
lift depicted on the 300K surface. No thunder expected during this
period given a sharp warm nose above the saturated layer. Clouds
will take a couple extra hours to scatter out compared to the last
several days, but will clear from SW to NE through the late morning
and afternoon. Well above average highs should reach the mid 70s to
mid 80s though will fall short of record values, and it will feel
pretty sticky by the afternoon across the east half with dew points
in the mid to upper 60s.

As the trough and sfc low shift eastward/northeastward respectively
Tuesday night, an attendant cold front will move into south-central
TX. Should begin to move in around midnight and by 12Z Wednesday is
likely to have moved through about two thirds of the area with only
the Coastal Plains left in the warm sector. Some showers and perhaps
even a thunderstorm or two will be possible along the front, but
only for areas northeast of San Antonio.

LONG TERM (Wednesday through Monday)...
A cold front initially located over the coastal plains Wednesday
morning will continue to move southward toward deep south Texas
during the afternoon hours. There will be a low chance for some
showers along the front in the far eastern portion of Fayette county.
The remainder of the region will remain dry on Wednesday. Some
cooler air will filter in from the north, resulting in daytime highs
in the lower 70s to lower 80s. Overnight lows will drop into the
lower 40s to lower 50s as we expect clear skies and light winds to be
in place. Southerly winds make a quick return on Thursday,
Thanksgiving Day and this should boost highs into the mid 70s to
lower 80s. We should stay dry during the daylight hours. However, as
some weak upper disturbances embedded in the southwest flow aloft
move into the region, we will keep a low chance for rain along the
Highway 77 corridor during the evening, then spread rain chances back
west to near the I-35 corridor after midnight.

The flow aloft continues to become increasingly active on Friday and
with the warm air advection pattern strengthening in the low-levels,
we will see plenty of cloud cover, warm temperatures and a continued
chance of rain for most areas. The exception will be out west along
the Rio Grande where moisture levels will be lower. We do expect a
cold front to move in during the afternoon, but there are some timing
differences noted among the medium range models.

An active pattern is expected as we head into the upcoming weekend as
an upper level system moves across north Texas. We continue to see
some disagreement among the models in handling this feature. However,
we have seen a fairly consistent pattern in the models showing some
decent chances for badly needed rainfall across the area. The
operational ECMWF has higher precipitation amounts when compared to
the GFS and this will need to be monitored in future model runs. The
good news is that we are seeing a steady or increasing trend in the
GEFS ensemble and ECMWF ensemble precipitation amounts. For now, it
appears rain chances will be favored late Friday into early Saturday
as the frontal boundary moves in from the north.

The forecast for Sunday and Monday remains in question, with the
operational GFS trending drier vs. the ECMWF showing the upper system
lagging to our west, resulting in a wetter pattern. For now, we will
trend toward the drier solution as there does seem to be some support
from the Canadian model. We will show a decreasing chance for
precipitation on Sunday from west to east. We will also keep
temperatures below normal Sunday and Monday as the pattern favors
another surge of cooler air moving in from the north late Sunday or
early Monday.


Austin Camp Mabry              69  59  79  58  73 /   0  20  20  30   0
Austin Bergstrom Intl Airport  71  59  80  58  74 /   0  20  20  30  -
New Braunfels Muni Airport     72  62  83  61  79 /   0  20  20  10   0
Burnet Muni Airport            66  59  78  52  71 /   0  20  20  30   0
Del Rio Intl Airport           76  63  85  55  79 /  10  -   -    0   0
Georgetown Muni Airport        68  57  78  53  71 /   0  20  20  30   0
Hondo Muni Airport             74  60  83  57  81 /  10  20  20  -    0
San Marcos Muni Airport        72  59  81  59  76 /   0  20  20  20   0
La Grange - Fayette Regional   73  60  82  63  73 /   0  10  20  20  10
San Antonio Intl Airport       72  62  81  61  78 /   0  20  20  10   0
Stinson Muni Airport           74  62  82  61  79 /   0  20  20  -    0




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