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

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FXUS64 KEWX 131125
AFDEWX

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

.AVIATION...
VFR skies will prevail today through Thursday morning with mainly
SCT-BKN decks above 10K ft. VRBl winds less than 5 KTs increase to
S to SW 7 to 15 KTs late morning into afternoon. Winds decrease to
VRBL less than 5 KTs this evening and then NW to N 7 to 12 KTs on
Thursday.

&&

.PREV DISCUSSION... /ISSUED 416 AM CST Wed Dec 13 2017/

SHORT TERM (Today through Thursday)...
Will be able to enjoy another mild day across South Central Texas as
the H5 pattern overhead undergoes a transitional period characterized
by subtle ridging and westerly winds aloft. A pre-frontal low over
the northern half of the state will enhance the PGF for the northern
half of the CWA this afternoon and likely result in some breezy
southwest winds of 15-20 mph.

After a slightly warmer morning Thursday, our next cold front will be
on approach from the north. While there is a bit of uncertainty in
the arrival time in the GFS/ECMWF, the front will serve to dry out
the low levels and seriously hinder the possibility for PoPs once it
arrives. Thus, have kept Thursday dry in the grids.

LONG TERM (Thursday Night through Tuesday)...
The long term period will begin with a cool Friday as a surface high
moves over the region. While this is occurring, H5 low pressure will
become cut off over the west coast of Mexico and tap into some
Pacific moisture, effectively channeling this moisture into South
Texas. By Saturday, another shortwave will drop down across the
Rockies originating from the Pacific Northwest and eject the Mexican
low northeast, evolving back into a negatively tilted shortwave across
the southern CONUS.

This very progressive evolution of the H5 pattern will result in
South Central Texas seeing likely a quick shot at elevated showers
and possibly some thunderstorms over the course of the day Saturday.
While dynamically, this low is quite impressive, characterized by a
100+ kt 250 mb jet streak and a saturated column above 500 mb, low
level moisture is lacking, instability is nil, and PWAT values only
slightly eclipse 1 inch. However, with 0-6 km bulk shear advertised
and plenty of dynamical lift, can`t rule out some elevated
thunderstorms as this system quickly moves through Saturday. Also,
while the bulk of the moisture and lift is aloft, QPF expectations
are rather minor, with less than a quarter inch expected.

As this system clears out Sunday, another cold front is progged to
move through, dropping temperatures again into the mid 30s on the
Plateau Monday morning. The aforementioned second shortwave will
then enter West Texas late Sunday night into Monday morning behind
the cold front and push eastward across the state. This is where
models begin to diverge as the ECMWF is significantly more
progressive with the evolution of the shortwave, and the GFS is much
slower. Thus have lower confidence in the forecast beyond Sunday.
However, next week does look warmer, likely in the mid 60s to low
70s, with the next significant cold front possibly arriving late in
the week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              68  43  64  40  57 /   0   0   0  -   -
Austin Bergstrom Intl Airport  66  39  62  40  57 /   0   0   0  -   -
New Braunfels Muni Airport     66  42  64  41  58 /   0   0   0  10  10
Burnet Muni Airport            70  40  61  37  56 /   0   0   0  -   -
Del Rio Intl Airport           65  42  66  42  60 /   0   0   0  10  10
Georgetown Muni Airport        68  40  62  38  57 /   0   0   0  -   -
Hondo Muni Airport             65  43  68  41  60 /   0   0   0  10  10
San Marcos Muni Airport        65  41  63  40  57 /   0   0   0  10  10
La Grange - Fayette Regional   66  42  64  41  59 /   0   0   0  10  10
San Antonio Intl Airport       65  45  66  43  59 /   0   0   0  10  10
Stinson Muni Airport           67  44  67  43  60 /   0   0   0  10  10

&&

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

$$

Mesoscale/Aviation...04
Synoptic/Grids...TB3



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