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

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FXUS64 KEWX 260501 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1101 PM CST Wed Nov 25 2020

.AVIATION...
/06Z TAFS/
As previously discussed, VFR conditions are forecast to prevail
through sunrise or short after on Thursday morning. Winds will be
light and variable through the overnight period. Low cigs are
expected to develop overnight across the Coastal Plains and push to
the north into the Interstate 35 and KDRT later on. If this scenario
pans out, can`t rule out a few hours of MVFR from 13Z to 16Z
Thursday at KSAT, KSSF and KDRT. At this time, we are showing cigs at
SCT018 to show the possibility of lower cigs while confident in MVFR
still low. VFR conditions will prevail from 17Z through late Thursday
evening. A cold front is forecast to push across the northern Hill
Country around the 12Z Friday time frame bringing low cigs and
visibility in the IFR/LIFR across the area sites. Increasing shower
and thunderstorm activity is expected for Friday afternoon.

&&

.PREV DISCUSSION... /ISSUED 553 PM CST Wed Nov 25 2020/

AVIATION...
/00Z TAFS/
VFR conditions are expected across area sites for most of the
forecast period. Winds are forecast to be out of the northeast and
east across the I-35 terminals and out of the southeast and east
around 6 knots or less and even becoming light and variable
overnight. Latest guidance suggest for MVFR cigs to develop late across
the Coastal Plains and slowly pushing to the north by sunrise
Thursday morning. Can`t rule out few hours of MVFR over the San
Antonio area and KDRT sites from 13Z to 16Z. VFR conditions are
expected after 16Z/17Z with winds out of the southeast areawide.

PREV DISCUSSION... /ISSUED 229 PM CST Wed Nov 25 2020/

SHORT TERM (Tonight through Thursday Night)...

Last night`s cold front is already well out over the GoMex, with
light northerly flow across south-central TX early this afternoon.
Temperatures range from the low 60s northeast to the upper 70s far
southwest as of 18Z and will top out in the 68-82 degree range today
under clear skies.

Tonight should provide an opportunity for efficient radiational
cooling as dry air over our northern counties (pwats 0.2-0.5")
combines with a decoupled boundary layer to allow lows to drop into
the 40s over most of the area. A few spots south may bottom out in
the low 50s while some of the usual cool spots north like Bergstrom
and portions of the Hill Country could potentially reach the upper
30s.

Despite a cool start to Thanksgiving Day, the surface high shifting
eastward will allow for light southerly flow once again, and with
ample sunshine temperatures will quickly recover and top out in the
70s to low 80s once again. Humidity will increase as well and dew
points over the Coastal Plains will be back into the 60s by the
evening. It`ll be a great day to spend some time outdoors
regardless!

Overnight and into early Friday, moisture will continue to increase
at low levels. Patchy fog appears possible after midnight. A few
scattered showers and potentially some embedded thunder will begin
to develop for areas along and east of I-35 after midnight as well
as some shortwave energy moves in. This is ahead of the main system
that will bring some much, much needed rain to the region Friday and
Saturday. See long term discussion for more details on that.

LONG TERM (Friday through Wednesday)...

Embedded shortwave energy within the southwest mid-level flow coming
out of Mexico and the advancement of a cold front into the region on
Friday will support increasing rain and thunderstorm potential that
spreads from east to west. Isolated strong to severe thunderstorm
activity may be possible as SPC has highlighted a marginal risk for
much of the CWA on Friday. The greatest potential for any stronger
organized convection will exist during the day over the southern
extent of the CWA with any surface based convection along or ahead
of the frontal boundary. The convective environment with 1000 to
1500 J/kg of MUCAPE, lapse rates of 6 to 7 C/km and 0-6 km bulk
shear of 40 to 60 kts will support a main threat of isolated hail
and some gusty winds. As the front advances southward, organized
surface rooted convection will become elevated as the boundary
undercuts the storms. As this occurs, this will likely reduce the
severe potential on those cells, but small hail still could not be
ruled out.

Additional embedded shortwaves advancing out of Mexico ahead of an
upper low over the Desert Southwest and isentropic lift behind the
frontal boundary with the arrival of much cooler air with northerly
winds from Friday night through Saturday, will lead to periods of
stratiform rain and elevated convection across the region. Overall,
beneficial rainfall is expected with a continued signal for 1 to 3
inches around the I-35 corridor with slightly higher amounts across
the eastern and southern coastal plains and lower amounts closer to
the Rio Grande. Despite high flash flood guidance numbers due to the
recent dry antecedent conditions, localized flooding cannot be
completely rule out with any training heavier rainfall. As a result,
the WPC has placed the region south and east of the Balcones
Escarpment in the marginal on the Day 3 Excessive Rainfall Outlook.

Rain chances will then taper off from west to east through Sunday
morning as the upper low that progressed from the Desert Southwest
over north Texas advances to the east, allowing for drier air to
infiltrate the region. With the drier air and a continued northerly
wind with surface high pressure establishing over the region, the
cooler, below average, temperatures will remain around into the
early to middle half of next week. Coldest conditions occur early
next week as light overnight winds and clear skies will promote
strong radiational cooling. Freeze products could be needed at
times, especially late Monday night into Tuesday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              45  78  60  67  53 /   0   0  30  70  70
Austin Bergstrom Intl Airport  40  78  60  69  53 /   0   0  30  70  70
New Braunfels Muni Airport     46  77  62  73  56 /   0   0  20  70  70
Burnet Muni Airport            44  76  54  62  49 /   0   0  20  50  60
Del Rio Intl Airport           49  79  57  72  52 /   0   0   0  30  60
Georgetown Muni Airport        43  77  57  65  51 /   0   0  20  60  60
Hondo Muni Airport             46  77  59  75  54 /   0   0  10  60  70
San Marcos Muni Airport        43  78  60  70  54 /   0   0  30  70  70
La Grange - Fayette Regional   45  80  64  73  59 /   0   0  40  70  80
San Antonio Intl Airport       49  77  62  72  56 /   0   0  20  70  70
Stinson Muni Airport           49  77  62  73  57 /   0   0  20  70  70

&&

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

$$

Short-Term/Aviation...17
Long-Term...Hampshire


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