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

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FXUS64 KEWX 140026
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
626 PM CST Tue Feb 13 2018

.UPDATE...
Widespread areas of fog blanket the region along and east of the
Interstate 35 corridor, with patchy fog further west into the Hill
Country and portions of the Rio Grande Plains. Therefore, we have
added fog to the weather grids for most of the region this evening
except for the Edwards Plateau and locations closer to the Rio Grande
where the mention of fog remains delayed until after Midnight. None
of our sites are currently experiencing dense fog which makes sense
considering this fog is of a more advective nature, but we will
monitor visibilities over the next few hours and issue a Dense Fog
Advisory if needed later tonight. Hi-res models also indicate that
shower activity tonight will be very limited until closer to sunrise,
so we have decreased rain chances to 20 POPs or less except for our
far southern and eastern counties. Aside from decreasing temperatures
and dew points slightly for tonight based on model and observational
trends, no significant changes were made to the current forecast.

&&

.PREV DISCUSSION... /ISSUED 619 PM CST Tue Feb 13 2018/

AVIATION...
/00Z TAFS/
IFR and even lower categories are expected across the I-35 sites this
evening into late Wednesday morning. Light northerly wind flow along
the I-35 terminals is expected to shift to the southeast overnight
continuing through Wednesday. -DZ is expected to prevail for much of
the forecast period with areas of dense fog developing late this
evening or by midnight tonight into the overnight hours. LIFR
conditions are expected along the I-35 sites during day-break
through early Wednesday afternoon. According to HiRes models and
forecast soundings, the Austin area airports may see VLIFR conditions
overnight through 14Z or so. Some other guidance do not show these
types of conditions. That said, this is a difficult forecast package
and therefore expect amendment through the period.

Across KDRT, flight conditions will range from MVFR to IFR for much
of the forecast period. There is a window for LIFR around day-break,
however, back up to MVFR by 19Z and even VFR short after. Moderate
southeasterly winds of 10 to 15 knots expected.

PREV DISCUSSION... /ISSUED 316 PM CST Tue Feb 13 2018/

SHORT TERM (Tonight through Wednesday Night)...

Main weather highlight through Wednesday will be the continued foggy
and drizzly conditions as increased moisture aids in slowly warming
temperatures.

Low clouds, fog, and the near end of the residual cold airmass
across the region has lead to another well-below normal temperature
day for South-Central Texas. Readings remain in the low to upper 40s
across much of the region with some low to mid 50s in the Rio Grande
Plains. Temperatures will remain near steady through the evening and
slightly warm overnight as vertical column positive moisture flux
occurs on veering southerly surface flow. Wednesday lows will likely
be the temperature at or near midnight tonight.

Clouds, scattered drizzle, and fog will occur again Wednesday morning
with limited recovery similar to today. Given the warmer start,
afternoon temperatures should make it into the mid 60s to near 70.
METMOS guidance remains much cooler (lower 60s) then the MAVMOS
(upper 60s/low 70s) and given the trends over the past two days and
the likely saturated conditions Wednesday, think MAVMOS might be too
warm. None-the-less, a milder day is expected with near normal
temperatures.

LONG TERM (Thursday through Tuesday)...

Temperatures will continue to increase Thursday as even greater
moisture transitions into south Texas from the Gulf of Mexico. A
cold front will move through on Friday brining north winds and much
cooler temperatures with widespread rain showers into Saturday. A
warming trend will quickly return late Sunday and into early next
week ahead of a stronger front and weather system. Strong thunderstorms
with pockets of heavy rain could be a possibility based on mid-range
projections next Tuesday. Stay tuned for future updates on this
evolution.

By Thursday, continued H5 southwest flow overtop 60-65F dewpoint
laden southeast fetch winds will aid in PWATS increasing to 1.4-1.6".
Lows Thursday morning will in the upper 50s to low 60s with highs
reaching into the mid to upper 70s despite cloud cover.
Coincidentally, a stronger longwave trough over the Central Plains
and stronger high pressure system will pivot a cold front through the
region mid-day Friday. Highs Friday will be highly depending on
location and frontal timing with cooling temperatures occurring in
the afternoon.

While there will be some showers along the convergence induced lift
with the frontal passage, the best dynamic forcing will remain north
in the dampened, low amplitude pattern. Greater rain coverage is
actually expected Saturday as a developing jet streak aids in deeper
lift farther south then any lifting mechanism on Friday. Despite
widespread showers, overall lift will not lead to convective rates
given limited instability and rainfall totals will be less than inch
through the weekend.

Return flow will commence quickly on Sunday as moisture returns on
southeast flow. A more spring-time pattern will set-up Monday and
especially Tuesday as instability increases. Monday looks too capped
for storms but a stronger shortwave on Tuesday with supportive
instability and shear could support some organized thunderstorms that
could be strong. Pockets of heavy rainfall could also be possible. Will
need to watch this evolution through the week and weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              46  68  59  76  59 /  20  20  30  20  10
Austin Bergstrom Intl Airport  45  68  59  75  59 /  20  20  30  20  10
New Braunfels Muni Airport     46  69  57  76  58 /  20  20  30  20  10
Burnet Muni Airport            45  71  59  76  56 /  20  20  20  10  10
Del Rio Intl Airport           51  71  56  77  57 /  10  10  10  10  10
Georgetown Muni Airport        46  69  60  76  58 /  20  20  20  20  10
Hondo Muni Airport             51  70  57  77  57 /  20  20  30  10  10
San Marcos Muni Airport        45  68  58  75  58 /  20  20  30  20  10
La Grange - Fayette Regional   48  70  62  77  61 /  30  30  30  20  10
San Antonio Intl Airport       47  68  58  76  59 /  20  20  30  20  10
Stinson Muni Airport           49  69  59  77  59 /  20  20  30  20  10

&&

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

$$

Mesoscale/Aviation...17
Synoptic/Grids...LH



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