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

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FXUS64 KEWX 240557
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1257 AM CDT Sun Sep 24 2017

.AVIATION...
/06Z TAFS/
Low clouds are forming and expanding across part of the Hill Country
and along the western portion of Interstate 35. Expect these low
clouds with MVFR and IFR bases to prevail across the area terminals
including KDRT out west across the Rio Grande through mid Sunday
morning. HiRes models indicate some light shower activity later
tonight and around dawn for KAUS and KSAT and have added VCSH for
that period. Winds are expected to be out of the southeast and south
5 to 10 knots along the I-35 sites and 10 to 15 knots and gusts up
to 25 knots over KDRT through Sunday. VFR conditions return by 17Z
Sunday and prevail that way through late Sunday evening.


&&

.PREV DISCUSSION... /ISSUED 626 PM CDT Sat Sep 23 2017/

AVIATION.../00Z TAFS/
VFR conditions will prevail for the start of this forecast period and
again at the end of the forecast period. Will continue to see the
chance for convection from 17Z-02Z across the region. Will likely see
an increase to the coverage for Sunday. At this time the locations
and timing of any convection is difficult to pinpoint and thus have
not mentioned in the current forecast. Low clouds are expected to
develop this evening between 06Z-08Z. Will initially see MVFR cigs,
but cigs fall to IFR from 09Z-10Z and continue through 15Z-16Z before
becoming MVFR then back to VFR 17Z-18Z. Winds will be southeasterly
08-12 knots then decrease after 06Z to 5-8 knots. After 16Z winds
become SE again at 10-15 knots. With tighter gradient KDRT will see
E-SE winds 12-15 knots with gust to near 25 knots through the
forecast period. Currently not expecting to see visibilities as low
due to fog, but still areas of 5 miles at the I-35 terminals.

PREV DISCUSSION... /ISSUED 312 PM CDT Sat Sep 23 2017/

SHORT TERM (Tonight through Sunday Night)...
Sfc to H7 onshore flow will maintain pwat values at or above 1.5
inches through the weekend. Intermittent tropical showers and a few
storms will continue to stream over the area, but maintain poor
coverage due to mid level ridging in place. Sunday night, moisture
tapped from the Pacific tropics increases over the Southern Edwards
Plateau and brings an additional boost in rain chances. Temperatures
will continue a gradual trend "cooler" as the humidity increases and
keeps the summer humidity and mid-upper 90s heat indices intact over
much of the area Sunday.

LONG TERM (Monday through Saturday)...
Rain chances continue to ramp up Monday with a couple models even
generating some locally heavy rain possible early Monday. With
tropical cyclone development expected in the latest Ern Pac outlook
from NHC soon, deterministic models are converging on higher
rainfall totals in advance of an approaching weak front that is
expected to be near the area late Wednesday or early Thursday.
Convective clusters should impact the inflow to become more due
easterly by Wednesday and possibly Nely by Wednesday night. Am
expecting a slightly early frontal arrival in backdoor fashion for
Wednesday night with temperatures moderating for daytime Thursday.

Given that most model projections show the tropical disturbance in a
limit development period while offshore, would expect the threat for
heavy rains to diminish in the wake of the front, but would continue
to expect high PoPs into at least Thursday and probably into Friday.
Favor the ECM/CMC solutions that have shown more definition with the
pattern, while the GFS has a hesitance to develop and keep the
tropical low offshore while also keeping high rain chances into next
Saturday in a weak upper level flow pattern well beyond the frontal
passage. While the model trends do show the front bringing an end to
the high heat indices, there still appears to be plenty of humidity
in store for late next weekend, even if the rain chances decrease as
forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              90  72  89  73  89 /  20  10  30  30  40
Austin Bergstrom Intl Airport  90  71  89  72  89 /  20  10  30  30  40
New Braunfels Muni Airport     91  72  88  73  89 /  30  20  40  30  60
Burnet Muni Airport            88  70  87  70  85 /  20  10  20  30  40
Del Rio Intl Airport           90  75  88  72  85 /  30  50  60  70  70
Georgetown Muni Airport        89  71  88  71  87 /  20  10  20  20  40
Hondo Muni Airport             92  73  91  73  88 /  30  20  40  50  70
San Marcos Muni Airport        89  71  89  72  88 /  30  10  40  30  50
La Grange - Fayette Regional   91  72  89  73  89 /  20  10  30  20  40
San Antonio Intl Airport       91  73  88  74  88 /  40  20  40  40  70
Stinson Muni Airport           92  74  89  74  89 /  40  20  40  40  70

&&

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

$$

Mesoscale/Aviation...17
Synoptic/Grids...24



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