Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Austin/San Antonio Texas
1051 am CDT Monday Sep 22 2014
MO major changes are needed to the forecast. The north winds have
made it through much of the County Warning Area...but the actual differentiating
airmass remains north of the area. Dewpoints remain in the upper
60s for south central Texas...but begin to fall north of Waco.
This dry air is expected to continue to move south. In the mean
time...isolated showers and thunderstorms will be possible for
much of the area this afternoon.
Previous discussion... /issued 627 am CDT Monday Sep 22 2014/
only concern this forecast period will be the front. This weak
cold front will move south across the region today into this
evening. Isolated showers or thunderstorms are possible this
afternoon into the evening. Due to the uncertainties with timing
and location...plus low probabilities have not included in any
rain showers/thunderstorms and rain in the terminal forecast at this time. Will monitor the
trends throughout the morning and make updates as necessary. After
some MVFR ceilings at kdrt this morning...VFR conditions are
expected for the remainder of the forecast. Winds will be east/NE at
5-10 knots. Krdt will have east-southeast winds 5-10 knots.
Previous discussion... /issued 317 am CDT Monday Sep 22 2014/
Short term (today through tuesday)...
light showers have developed over the Rio Grande plains early this
morning...but these are now mostly across the border in Mexico.
Meanwhile...the weak cold front has made it as far south as
Hillsboro...with convection popping up about 100 miles behind
frontal passage. The primary forecast issue today is the Prospect for
convection behind the front. Blended tpw imagery shows pooling of
precipitable water immediately behind the surface frontal passage...but only to 1.5 inches.
Otherwise...it/S dry ahead of the front with precipitable water in the 1-1.25 inch
range across our area. The convection-allowing mesoscale models
are in good agreement and depict deep moist convection firing
behind the front around 21-22z in our area. The best chances for
rain will be in a band 50 miles either side of I-10...but we
decided to include a generic 20 percent pop for the entire area to
allow for timing uncertainty. Low probability of precipitation will be kept through 06z
for the coastal and Rio Grande plains...but otherwise dry air will
push into the area.
Long term (tuesday night through sunday)...
high pressure will maintain low humidity with cool nights and mild
afternoons Tuesday through Thursday. We shaved a degree or two off
model consensus lows and added a degree or two to highs to account
for the dry atmosphere...which should promote a large diurnal
The global models are in fair to poor agreement in the medium
range...with the GFS and Canadian similar...and the GFS most
consistent run-to-run...while the European model (ecmwf) is unsettled. The model/S
depiction of a cut-off low range from centered over Texas to centered
over the northwest Gulf. Despite the differences...there is good
agreement Gulf return flow only gets weakly re-established. The
best combination of moist air and lift will be late Thursday night
into Friday...so low probability of precipitation were included for those periods. Otherwise...
expect a slow return to near normal temperatures and humidity.
Preliminary point temps/pops...
Austin Camp Mabry 90 64 85 64 86 / 20 10 - - -
Austin Bergstrom international Airport 90 64 85 61 85 / 20 10 - - -
New Braunfels Muni Airport 92 67 88 64 89 / 20 10 - - -
Burnet Muni Airport 89 64 86 62 86 / 20 10 - - -
del Rio International Airport 89 70 87 69 85 / 20 20 - - -
Georgetown Muni Airport 90 63 85 63 86 / 20 10 - - -
Hondo Muni Airport 94 69 91 67 91 / 20 10 - - -
San Marcos Muni Airport 90 65 86 63 86 / 20 10 - - -
La Grange - Fayette regional 92 67 86 64 88 / 20 10 - - -
San Antonio International Airport 93 70 89 67 88 / 20 10 - - -
Stinson Muni Airport 94 70 89 67 88 / 20 10 - - -
public service/data collection...12