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

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000
FXUS64 KEWX 220217 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
917 PM CDT Sat Oct 21 2017

.UPDATE...

The much talked about cold front is currently headed south and
located across a Wichita Falls to Odessa, Texas line. Along it,
strong to severe thunderstorms are ongoing across north Texas and
Oklahoma. However, as the front continues to shift south, the
stronger lift and forcing dynamics will remain north in association
to the vorticity maximum over Oklahoma. Wile SPC mesoanalysis and
suggested GFS/NAM BUFR soundings indicate upwards of 2000 J/KG of
MLCAPE over the region, a strong cap is also in place per these same
sources. Furthermore, aircraft data out of Austin and San Antonio
also indicate the presence of the capping inversion. This will keep
any pre-frontal activity at bay through the evening. The showers over
San Saba to Comanche Counties north of the area are elevated in
nature due to the overspreading of weak upper-level divergence. RAP
mass fields indicate surface convergence will weaken as the front
passes through the region while the best mid- and upper-level support
lag behind. A strong thunderstorm or two may still be possible with
the passage of the front overnight but overall trends appear to
suggest only pockets of brief heavy rain and general thunderstorms
along a Fredericksburg to Giddings line and north. Have reduced rain
chances farther west and south through the overnight. The front
should be through the entire area by late morning to near noon Sunday
with gusty north winds but clearing skies.

&&

.PREV DISCUSSION... /ISSUED 717 PM CDT Sat Oct 21 2017/

AVIATION... /00Z TAFS/
Vfr skies remain expected through the evening with some areas of
1000-2000 ft cigs expected after midnight. Lowest cigs should be
limited to the higher terrain areas. A brief dip into ifr could be
possible right as the cold front arrives and areas of convection
congregate along the front. Frontal timing appears to be consistent
among the past several runs of rapid refresh models. Regarding the
potential for TSRA, would suspect that we`ll no longer need to
consider the TSRA prevailing at SAT/SSF by the 06Z update given the
mesoscale trends in the HRRR. However, have found that the convective
handling of the HRRR runs around the 00z init time often deviate
from the broader consensus of qpf for some reason. Thus will stick
with the earlier foreast trends and modify late this evening should
the 00Z runs reflect the decreasing TSRA potential. Post-frontal sky
conditions should improve rapidly Sunday morning given the deep
layer of northerly winds behind the font.

PREV DISCUSSION... /ISSUED 252 PM CDT Sat Oct 21 2017/

SHORT TERM (Tonight through Sunday Night)...
For the rest of the afternoon, a weak embedded disturbance within the
larger shortwave has disturbed CU fields enough to produce some
showers along and just east of the I-35 corridor near Austin and
Georgetown. Proximity soundings from just about all models show the
cap holding on to prevent much in the way of anything more than a
very isolated thunder chance but included slight chc PoPs for this
area and east for the rest of the afternoon.

The bigger forecast focus is the approaching cold front overnight
tonight that will trek across Texas and reach the northern CWA likely
just before dawn. The TTU-WRF has been consistent with timing of the
front while the HRRRX continues to speed up and generate more
convection with each run. Looking at the current speed of the front,
do think the faster HRRRX is valid thus have slightly sped up the
fronts arrival in the grids but only about an hour or so.

As far shower and thunderstorm potential, the main threat will be
gusty winds and not much else for hazards. Just about every CAM
produces healthy outflow with convection firing in northern Texas,
and with the faster trends in the front as seen in the HRRRX
previously noted, this would further add confidence in gusty winds
and limit any hail potential. Still seems to be some disagreement in
the western extent of the convective line. SPCs SSEO guidance shows
enough outcomes extending into the Plateau and Hill Country to
warrant at least chance PoPs during fropa Sunday morning. Thus have
reflected as such in the grids.

The front should be clear of the CWA by 18Z, resulting in a breezy,
mild day Sunday afternoon. Did bump up gust potential to a max of 30
mph late morning and mid day as a fairly strong pressure gradient
looks to be in place post fropa. These should die down by the evening
and allow for a very favorable radiational cooling set up with high
pressure, light winds, and clear skies. Thus, lowered min T for
Monday morning to the lower end of the ECM and MEN ensemble guidance.

LONG TERM (Monday through Saturday)...
A rather benign weather pattern for much of the week as Sunday`s
front dries out the area and gradual warming occurs through mid week.
Another cold front is progged to push through the area Friday which
may be a more significant temperature changer for South Central
Texas. At current, extended guidance shows highs next weekend
struggling to exceed 70 degrees at least for the northern CWA. Still
some model disagreement in timing and strength this far out so left
this to the SuperBlend for now. However, no hazards are expected
through the extended.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              65  77  50  83  55 /  80  20   0   0   0
Austin Bergstrom Intl Airport  65  79  47  83  53 /  80  20   0   0   0
New Braunfels Muni Airport     66  81  47  82  53 /  50  30   0   0   0
Burnet Muni Airport            60  77  45  81  52 /  90  10   0   0   0
Del Rio Intl Airport           64  81  51  83  56 /  10  -    0   0   0
Georgetown Muni Airport        63  76  46  82  53 /  90  20   0   0   0
Hondo Muni Airport             67  85  46  83  52 /  20  10   0   0   0
San Marcos Muni Airport        66  81  47  83  53 /  60  30   0   0   0
La Grange - Fayette Regional   68  79  47  81  55 /  70  60   0   0   0
San Antonio Intl Airport       67  82  49  82  55 /  30  20   0   0   0
Stinson Muni Airport           68  85  50  83  55 /  30  20   0   0   0

&&

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

$$

Mesoscale/Aviation...Oaks
Synoptic/Grids...Allen


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