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

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FXUS64 KEWX 171737
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1237 PM CDT Tue Oct 17 2017

.AVIATION...
Mostly clear skies and VFR conditions will continue at the Central
Texas terminals through the period. This afternoon light northerly
flow will continue, with light and variable winds overnight.
Southerly flow returns tomorrow with southeast winds between 5 and 10
knots for Wednesday afternoon and evening.

&&

.PREV DISCUSSION... /ISSUED 626 AM CDT Tue Oct 17 2017/

AVIATION...
/12Z TAFS/
VFR conditions are expected across area terminals through the period.
North to northeast winds around 5-6 knots across the I-35 sites
through late afternoon. KDRT should have a light northerly flow
for next several hours and then wind shift to the southeast 5 to 10
knots late this morning into the afternoon hours. Light and variable
winds expected this evening and overnight.

PREV DISCUSSION... /ISSUED 414 AM CDT Tue Oct 17 2017/

SHORT TERM (Today through Wednesday)...

Well below normal low temperatures are ongoing this morning as a perfect
radiational cooling set-up is in place. Readings are nearly 10F
degrees below normal for this time of year. A nice rebound into the
70s are expected this afternoon. A near repeat of today`s weather is
expected again Wednesday with a slightly higher temperature range
shift. No hazards and plenty of sun are expected.

This morning will be the first morning both Austin and (likely San
Antonio) have dropped below 50 degrees since 24th of April earlier
this year (nearly 6 months ago). Dewpoints in the mid to low 40s and
near calm winds with clear skies are allowing for long-wave radiation
to escape efficiently. Conversely, when the sun rises, expect quick
rebound of temperatures with 6-9 degree hourly temperature jumps in
the mid- to late-morning hours as the region rebounds into the mid
to upper 70s.

A near repeat of weather conditions will occur Wednesday with a warm
temperature shift occurring by 2-4F degrees over today`s readings on
the lows and highs, respectively. East and then southerly flow will
resume as moisture increases slowly with broad low-level ridging
across the northern Gulf of Mexico.

LONG TERM (Wednesday Night through Monday)...

A more active pattern is expected this upcoming weekend as rain and
thunderstorm chances increase with the passage of a stronger cold
front. The associated system appears to preliminarily show modest
dynamic jet stream and thermodynamic support to support the
possibility of strong storms for portions of the area. Will leave
this hazard risk out of the Hazardous Weather Outlook for now but
evolution and timing will need to monitored closely. See below for
more details.

By late-week, low-level wind flow will be southeast and south with
mid-level southwest winds as a weak short-wave trough pivots across
Texas in the southern jet stream branch. Dewpoints will return to
the low- to mid-60s by Thursday but instability will remain weak as
a strong capping inversion looks to be in place. A few coastal plain
and sea-breeze induced showers could occur Thursday afternoon but
coverage should be minimal. By Friday, capping inversion looks to
weaken but the initial short-wave exits north and east of the region
with no strong forcing mechanisms across south-central Texas. Weak
instability of 1000-1500 J/Kg Friday should support isolated to
scattered showers/storms along and east of US 281. Cap appears too
strong farther west on Friday for rain activity.

The main timeframe to focus on will be the weekend as both the GFS
and EC advertise a sharpening long-wave trough axis over Texas and
the central plains. The first short-wave Thursday and Friday will
act to prime the area with ample moisture /surface dewpoints in mid-
upper 60s/ for the weekend. This will mean widespread low clouds
Saturday that eventually mix out to partly cloudy skies in the
afternoon. A decent capping inversion looks to be present Saturday
afternoon and should keep most rain/storms at bay. However, by
Saturday night and into Sunday morning, the greatest dynamic and
convergent forcing will occur as a front moves through the region.
Timing of the front will be critical juxtaposed to available diurnal
CAPE evolution and dynamic forcing. Both GFS and EC bring the front
late Saturday night (GFS slightly faster) and timing is not optimal
for generating the theoretical strongest storms for this system.
However, deep layer shear of 40 knots and possible ML CAPE near
2000-2500 J/Kg could pose risk for a semi-broken line of storms along
the front as it moves through the region from NW to SE. The most
likely area to be affected of the stronger storm activity will be
farther north and east where greater height falls and upper level
divergence will exist. CIPS analogs also suggest this to be the case
looking at the top 15 matches to this pattern. It is too early to
speculate on hazard type. Stay tuned as area, hazard type, and storm
evolution confidence are refined through the week.

The front should be mostly through the region by Sunday afternoon
with clearing and cooler conditions behind it starting early next
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              80  49  82  59  82 /   0   0   0   0  10
Austin Bergstrom Intl Airport  79  47  81  59  81 /   0   0   0   0  10
New Braunfels Muni Airport     78  49  82  59  81 /   0   0   0   0  10
Burnet Muni Airport            76  46  80  56  79 /   0   0   0   0  10
Del Rio Intl Airport           78  50  81  59  81 /   0   0   0   0  -
Georgetown Muni Airport        78  48  81  57  81 /   0   0   0   0  10
Hondo Muni Airport             80  49  83  59  84 /   0   0   0   0  -
San Marcos Muni Airport        79  48  82  58  82 /   0   0   0   0  10
La Grange - Fayette Regional   80  49  83  59  84 /   0   0   0  -   20
San Antonio Intl Airport       79  50  82  60  81 /   0   0   0   0  10
Stinson Muni Airport           80  51  81  60  81 /   0   0   0   0  10

&&

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

$$

Mesoscale/Aviation...Treadway
Synoptic/Grids...04
Public Service/Data Collection...Treadway



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