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

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FXUS64 KEWX 142137

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
337 PM CST Thu Dec 14 2017

.SHORT TERM (Tonight through Friday Night)...
High clouds associated with an active subtropical jet continue to
increase across South Central Texas as a weak cold front moving
through the region advects drier air near the surface into the area.
Temperatures this afternoon are very similar to where they were this
time yesterday in the lower to mid 60s as the more significant cold
air advection is lagging well behind to the north. Elevated shower
activity is currently developing to our south between Laredo and
Corpus Christi where the upper level divergence in the right entrance
region of the jet is likely greatest at the current moment. These
showers should increase in coverage tonight and expand northward to
some extent as weak PVA increases as the shortwave passes to our
north. However, the northward extent of midlevel isentropic ascent
appears to stay to our south and dry air should make it difficult
for much precipitation to reach the surface. Therefore, we have
decreased the northern extent of 20-40 POPs to mainly along and south
of Highway 90 and Interstate 10. Northerly winds will increase to
10-15 mph with gusts to 20 mph tonight as the surface pressure
gradient increases, allowing temperatures to stay up in the upper
30s to mid 40s under broken to overcast skies.

High temperatures tomorrow will be about 5-10 degrees cooler than
today as cold air advection behind the front will be complete and
cloud cover should remain over most of the region. Jet dynamics will
be a little weaker tomorrow than they have been over the past few
days, so there may be a brief period of clearing over our northern
counties during the afternoon. A cutoff low over the Gulf of
California that will split off from the shortwave that passes to our
north tonight will begin to eject to the northeast tomorrow night as
a kicker shortwave digs southwards along the Pacific Coast. This will
ensure that cloud cover returns to the entire region tomorrow night
to help keep the entire region above freezing, albeit at least a few
degrees cooler than tonight. Isolated showers may also begin in the
Rio Grande Plains just prior to sunrise Saturday morning.


.LONG TERM (Saturday through Thursday)...
Increasing PVA at midlevels associated with the aforementioned upper
level trough, a strong jet streak at upper levels and increasing
isentropic ascent and moisture advection at lower levels will cause
rain chances to increase from west to east on Saturday. Widespread
showers will most likely occur across most of the region during the
afternoon and evening hours on Saturday as the shortwave passes
through before rain chances end from west to east overnight and clear
the region by sunrise Sunday morning. Although model soundings are
trending towards lower amounts of elevated instability, increased
lapse rates due to cooling from the passage of the shortwave may
still support at least a few elevated thunderstorms. Average
rainfall values of half an inch to an inch are expected along and
east of the Interstate 35 corridor with rainfall values generally
remaining below a half an inch further west.

A coastal surface low that develops overnight on Saturday into Sunday
will move northeast towards the Ark-La-Tex region with high pressure
quickly settling in behind. This combined with southwest flow aloft
and weak warm air advection will allow for a nice Sunday with partly
cloudy skies and temperatures warming up into the upper 60s. A pair
of weak fronts should move through the region sometime on Monday and
the middle of next week to help keep temperatures closer to normal
for the first half of the week. Although slight rain chances may be
possible with the passage of a few shortwaves, model agreement on the
timing of these waves and confidence in adequate moisture was too
low to increase POPs in any particular time period for the first half
of next week. Temperatures should warm up above average by Thursday
as southerly flow increases ahead of a strong cold front that should
move through the region towards the end of next week or the weekend.
Precipitation appears to be fairly likely with this front, but it is
too early to speculate on any timing or impacts this far out.


Austin Camp Mabry              44  58  40  53  45 /  10  10   0  50  70
Austin Bergstrom Intl Airport  43  57  38  53  44 /  10  10   0  60  70
New Braunfels Muni Airport     45  57  40  53  43 /  10  10   0  60  60
Burnet Muni Airport            41  56  36  53  43 /  10  10   0  40  60
Del Rio Intl Airport           45  59  42  52  42 /  10  10  -   40  20
Georgetown Muni Airport        41  57  38  54  44 /  -   10   0  50  70
Hondo Muni Airport             45  60  40  54  41 /  10  10  -   50  50
San Marcos Muni Airport        44  57  39  53  44 /  10  10   0  60  70
La Grange - Fayette Regional   44  56  40  54  46 /  10  10   0  50  70
San Antonio Intl Airport       45  58  42  53  45 /  10  10  -   60  60
Stinson Muni Airport           47  58  42  52  44 /  20  10  -   70  60




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