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

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FXUS64 KEWX 270505

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1105 PM CST Sun Jan 26 2020

Model trends have continued to shy away on low clouds and fog
formning over Central Texas, but still expect an episode of LIFR
conditions around AUS, and maybe some brief ground fog around
SAT/SSF. DRT will remain vfr through the period unless a storm forms
overhead in late evening Monday. Low cloud return along I-35 tomorrow
night may be earlier than advertised, but wanted to highlight the
more impactful IFR conditions as rain chances increase closer to
daybreak Tuesday.


.PREV DISCUSSION... /ISSUED 243 PM CST Sun Jan 26 2020/

SHORT TERM (Tonight through Monday Night)...
Surface analysis this afternoon shows a remnant frontal boundary or
surface trough bisecting Central Texas. Clear skies have allowed for
temperatures to rise into the 70s as of 2 PM. The dry northwest flow
aloft producing these clear conditions remains overnight and allow
for clear skies to continue, but will flatten Monday ahead of a
shortwave trough diving towards the state from the Pacific
Northwest. Surface ridging spreading into the region overnight
combined with clear skies will result in good conditions for
radiational cooling, allowing temperatures to fall 5-10 degrees
cooler than this morning into the mid 40s to low 50s.

Recent rainfall within the past week will provide for another round
of fog development overnight, but near surface drying that occurred
today will complicate how expansive the fog deck is overnight. This
is because in environments where humidity decreases as height above
ground increases (as is what happens when drier air moves in above
the surface), moisture at the ground mixes upward and transports
drier air to the surface. This helps inhibit fog development. Based
on surface observations this afternoon and the decreasing dew point
trend across the Hill Country, Edwards Plateau, and Rio Grande
Plains, not expecting any kind of fog development in these areas
overnight. Closer to and east of Interstate 35, however, trends have
been more steady and fog potential will be higher. High resolution
guidance shows greatest potential for fog (and dense fog)
development near the Austin metro and east towards the Brazos
Valley, with a secondary area spreading into the Coastal Plains.
Expect short-term updates overnight to better account for this fog
potential depending on how much additional drying occurs this

Otherwise, southerly flow resumes during the day Monday as height
falls ahead of the Pacific Northwest shortwave trough induce a
surface low over Northwest Texas. Dry conditions will continue
through the day as temperatures climb into the 70s to low 80s, but
rain chances increase late Monday night as strong forcing from the
shortwave arrives. Showers and a few thunderstorms are expected to
develop across the Edwards Plateau and spread east as a thunderstorm
complex towards the Austin and San Antonio metros during the pre-
dawn hours Tuesday. Strong mid-level lapse rates in excess of 8 C/km
may support some small hail development within thunderstorms.

LONG TERM (Tuesday through Sunday)...
The Pacific front should be moving along the I-35 corridor during the
morning commute hours based on latest guidance. The frontal passage
will quickly exit the area by Tuesday afternoon. Some HiRes models
suggest two convective lines, one ahead and the other one along the
front/wind shift as the system moves over the Hill Country. Once the
front gets closer to the I-35 corridor, these convective lines break
apart and the one that dominates is the one pushing across the
southeastern portion of South Central Texas. Rainfall accumulations
associated with this system could range from one tenth to one quarter
inch with a few spots possibly getting up to one half inch.

Breezy northwest conditions are expected on Tuesday morning into the
afternoon period as 15 to 20 mph winds with gusts of 25 to 30 mph are
possible in the wake of the front. The wind relaxes a bit Tuesday
night into Wednesday.

Dry and cool weather is expected on Wednesday with highs in the 60s
before another round of showers and thunderstorms arrive on Thursday.

A Pacific Northwest system is forecast to push across the four
corners region and then into the Southern Plains on Thursday. An
associated Pacific front is also forecast to move across the
area early Friday morning while a coastal low pressure system
develops and moves to the upper Texas coast. The combination of
these features will bring chances for rain mainly on Thursday
afternoon into the evening and continuing through Friday morning.

The GFS and Canadian weather model solutions still faster and less
aggressive than ECMWF. Opted for the faster solution and put an end
to rain chances by Friday afternoon. Rainfall amounts for this second
round could range from one tenth to one quarter inch.

The upcoming weekend looks good with ridging aloft and surface winds
out of the west to southwest. This represent a warmer trend with
highs upper 60s to lower 70s on Saturday and lower to mid 70s on


Austin Camp Mabry              50  72  53  69  42 /   0   0  30  30  -
Austin Bergstrom Intl Airport  43  73  51  70  41 /   0   0  30  40  10
New Braunfels Muni Airport     46  74  52  70  42 /   0   0  30  30  -
Burnet Muni Airport            45  71  51  65  38 /   0   0  30  30  -
Del Rio Intl Airport           48  79  51  70  41 /   0   0  20   0   0
Georgetown Muni Airport        44  71  52  67  40 /   0   0  30  30  10
Hondo Muni Airport             46  77  52  72  41 /   0   0  30  20   0
San Marcos Muni Airport        46  74  52  70  41 /   0   0  30  40  -
La Grange - Fayette Regional   47  73  55  71  43 /   0   0  30  50  10
San Antonio Intl Airport       49  74  54  71  43 /   0   0  30  30  -
Stinson Muni Airport           48  76  54  72  44 /   0   0  30  30  -




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