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

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FXUS64 KEWX 140439

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1039 PM CST Wed Dec 13 2017

No significant changes from previous TAFs. High and some mid-level
clouds will continue to stream across the region from the southwest
for this TAF period. All airports will have high CIGs overnight.
Winds while generally 10 kts or less will shift overnight to the west
or northwest and then to the north Thursday afternoon when a weak,
dry cold front moves through the area.


.PREV DISCUSSION... /ISSUED 332 PM CST Wed Dec 13 2017/

SHORT TERM (Tonight through Thursday Night)...
High clouds associated with an active subtropical jet have kept
temperatures down in the upper 50s and lower 60s, while temperatures
in north Texas are in the lower 70s under clear skies. Aircraft
soundings out of SAT and AUS are not as saturated at 25-30 kft as
they were this morning, but the dynamics aloft are still helping to
maintain this cloud cover. This subtropical jet should continue to
remain over the region tonight to keep scattered to broken high
clouds overhead. These clouds combined with light southwest winds
will keep temperatures up in the lower to mid 40s tonight.

A fast-moving shortwave will dig south along the Rocky Mountains
tonight to help push a weak cold front through the region around
sunrise tomorrow morning. However, this will just cause winds to
become northerly as high temperatures should be similar to today due
to weak cold air advection aloft being delayed until later in the
afternoon and evening hours. This seems reasonable as temperatures
are in the 50s and 60s behind the front right now in Kansas. Rain
chances will increase tomorrow evening into the overnight hours as a
cutoff low splits off over the Gulf of California from the shortwave
disturbance that generally pushes into the eastern tier of the U.S.
PVA associated with this cutoff low combined with a subtropical jet
and very weak isentropic ascent to our south at midlevels will allow
for a slight chance of showers mainly south of the Highway 90 and
Interstate 10 corridors. Hi-res models suggest this precipitation
shield and cloud shield will be very defined as weak isentropic
descent will be over the northern half of our area, so lows tomorrow
night will range from the lower to mid 30s in the northern Hill
Country to mid 40s over our southern counties.

LONG TERM (Friday through Wednesday)...
Friday should be cool and dry across the entire area except possibly
our southern-most counties as cold air advection behind tomorrow
morning`s front should be complete and isentropic descent settles
over the region. Although the subtropical jet will continue to remain
active to continue high clouds over the region, the cutoff low should
remain over the Gulf of California to keep the best dynamics to our
west. Another shortwave moving down the Pacific Coast should finally
eject this cutoff low to the northeast over Texas on Saturday to
provide ample PVA aloft with strong divergence aloft associated with
a jet streak. These upper level dynamics combined with strong
isentropic ascent and some warm frontal dynamics should allow for
scattered to widespread showers during the afternoon, evening, and
overnight hours. Although we should not have any surface-based
instability, elevated instability aloft will support the potential
for some isolated thunderstorms embedded within the showers. In
general, rainfall totals should range between 0.25-0.50" on average
with some isolated higher totals closer to an inch further east.

Another weak front will move through the region on Sunday morning
to clear out the region from west to east with temperatures actually
increasing behind the front as cold air advection will be non-
existent with southwest flow aloft. Temperatures for the first half
of next week should be near to slightly above normal with generally
dry conditions aside from possibly isolated showers at some point as
a fast-moving shortwave passes. However, model differences are too
large at the current moment to pinpoint a specific time when these
showers may occur. Another weak front should move through the region
by the middle of next week to reinforce dry conditions, but above
normal temperatures should continue until the next weekend when a
much stronger cold front may move through South Central Texas.


Austin Camp Mabry              43  64  42  58  39 /   0   0  10  -    0
Austin Bergstrom Intl Airport  39  63  41  57  37 /   0   0  10  -    0
New Braunfels Muni Airport     42  64  43  58  38 /   0   0  10  10  -
Burnet Muni Airport            41  61  36  57  34 /   0   0  -    0   0
Del Rio Intl Airport           43  66  44  60  41 /   0   0  10  10  -
Georgetown Muni Airport        41  63  39  57  37 /   0   0  -   -    0
Hondo Muni Airport             43  67  43  60  38 /   0   0  10  10  -
San Marcos Muni Airport        42  63  43  57  38 /   0   0  10  10  -
La Grange - Fayette Regional   42  64  44  56  38 /   0   0  10  10  -
San Antonio Intl Airport       45  65  45  59  41 /   0   0  10  10  -
Stinson Muni Airport           44  67  46  59  41 /   0   0  10  10  -




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