Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX
FXUS64 KEWX 171152
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
552 AM CST Tue Jan 17 2017
.AVIATION... /00Z TAFS/
Isentropic lift pattern can be seen lifting north from the Coastal
Bend toward the I-35 Corridor TAF sites, with some of the more
convective parts of the activity on track to impact SAT/SSF first,
then potentially AUS later in the morning. Most of the rainfall rates
in this area should be light to moderate. A separate and similar area
of showers is expanding around DRT. Ceilings from the showers around
DRT/AUS should trend downward toward IFR later this morning while
hovering mainly at IFR for SAT/SSF. This evening, continued
saturation from the rains should bring a few more areas into lifr
cigs with slightly better vsbys. There should be an evening to late
night period where storms and heavier rainfall rates could drop vsbys
below 1 mile along I-35, but the timing is not well pinned down by
the finer res models to support a TEMPO or prevailing group at this
time. Some slight improvements are expected late tonight at DRT as
some of the energy aloft lifts NE, but increasing stability and
possible end to rain chances could send cigs/vsbys the other
direction as well.
.PREV DISCUSSION... /ISSUED 346 AM CST Tue Jan 17 2017/
SHORT TERM (Today through Wednesday)...
The cold front early this morning was located across the far
southeast CWA, from Lavaca through Karnes counties. A weak secondary
surge will push the front just south of the CWA later this morning.
Meanwhile the upper level low near Baja California will lift
northeast into Arizona and New Mexico today and broaden into Kansas,
the Panhandle, and far West Texas Wednesday. East of the low an
energetic and moist sub-tropical Pacific flow will continue. As the
low moves east isentropic ascent will increase across South-Central
Texas today and tonight. This will lead to showers and isolated
thunderstorms developing farther west into the CWA this afternoon.
The forcing peaks late tonight and into Wednesday morning across
central and eastern counties, with coverage of showers expected to
become widespread along with scattered thunderstorms.
Mid level lapse rate do marginally increase and there is some modest
elevated CAPE. Can`t rule out the possibility of an isolated storm
or two producing hail. In addition, with the exception of the Rio
Grande some locations could pick up 1-2 inches of rainfall through
Wednesday morning. When combined with some saturated locations from
Sunday night`s rainfall, this could lead to minor flooding concerns.
The forcing moves into far eastern counties and southeast Texas
Wednesday afternoon, with a reduction in precipitation expected into
the central CWA.
Temperatures today may not climb much, and in fact fall through noon
in many locations with the weak secondary surge. Highs in the low to
mid 50s northern areas and upper 50s to low 60s south.
LONG TERM (Wednesday Night through Monday)...
The upper level low eventually kicks out into the central Plains
Wednesday night into Thursday. The 00Z ECMWF maintains a little more
energy and moisture in the base of the trough Wednesday night across
the eastern CWA, with QPF shown along and east of I-35. The 00Z GFS
is farther east with the QPF Wednesday night, along the coast. We
have kept low POPs in the forecast for Wednesday night to account for
Drier, warmer, and sunny Thursday as the area is between systems.
A longwave trough deepens through the western CONUS and into the
Southwest U.S. and Texas Friday. A shortwave will cut off into a
potent 535 dm low through North Texas and Oklahoma Saturday into
Sunday morning. Looks like the bulk of the precip with this system
may stay north of the area.
The bigger issue for our CWA is going to be the wind that will
develop Sunday, on the southwest side of the departing low. Deep
northwest flow will develop over the CWA on Sunday. Strong SFC-700
mb wind speeds are shown to develop right through the CWA, with both
the ECMWF and GFS showing 45-55 kts of 925-700 mb flow. Dry
adiabatic forecast soundings up through 800 mb should promote good
vertical mixing of the higher momentum aloft to the surface. This,
combined with a 10 mb surface pressure gradient across the CWA,
should result in a windy day. GFS and ECMWF MOS guidance has been
indicating sustained surface winds exceeding 30 kts across many
locations Sunday, and given the mixing should see even high gusts.
A Wind Advisory will be almost certain if models verify. Despite the
recent rains, these type of wind speeds combined with forecasted low
RH values Sunday should result in at least elevated fire weather
concern for any of the finer, cured winter fuels. The winds should
gradually diminish around and after sunset Sunday.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 55 48 58 48 73 / 80 90 70 30 10
Austin Bergstrom Intl Airport 56 48 58 47 72 / 80 90 80 40 10
New Braunfels Muni Airport 57 49 59 48 73 / 80 90 80 30 10
Burnet Muni Airport 52 44 57 43 71 / 80 90 50 20 -
Del Rio Intl Airport 58 48 63 45 74 / 70 40 10 - 0
Georgetown Muni Airport 54 46 57 46 72 / 80 90 60 30 10
Hondo Muni Airport 60 50 62 47 74 / 80 80 50 20 10
San Marcos Muni Airport 57 49 59 48 72 / 80 90 80 30 10
La Grange - Fayette Regional 61 52 60 51 71 / 70 90 90 50 30
San Antonio Intl Airport 58 49 61 48 74 / 80 90 70 30 10
Stinson Muni Airport 60 52 62 49 74 / 80 90 70 30 10