Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Austin/San Antonio Texas
113 am CDT Tue Jul 25 2017
Aviation... /06z tafs/
low clouds are forming early tonight with aus already showing a bkn
MVFR deck. GOES 16 data shows a connection of the low cloud deck
southward to around Randolph AFB, so have updated to accelerate MVFR
cig timing for all the I-35 sites. The cigs may last an extra hour
versus the previous morning, but should mix out no later than 15z. A
few showers and thunderstorms are in the current gridded forecast
over the coastal prairies, but mesoscale models paint a more stable
picture with only a shallow layer of instability at the 500 mb level.
With the forecast trending toward stability, will show a later
arrival of low cigs for Wednesday morning.
Previous discussion... /issued 924 PM CDT Mon Jul 24 2017/
convection has come to an end across the area with partly cloudy
skies expected rest of tonight. Overnight lows will generally range
from the low to mid 70s. Clouds will increase overnight mainly
east and south of Interstate 35 as dewpoints remain in the lower 70s.
The shear axis responsible for the development of storms earlier is
expected to push farther to the east of south central Texas by
Tuesday while the subtropical upper level ridge builds into the
Southern Plains. This will limit any convection to form and affect
the area on Tuesday.
Previous discussion... /issued 307 PM CDT Mon Jul 24 2017/
Short term (tonight through Tuesday night)...
scattered showers and thunderstorms have developed again across
central Texas and portions of the northern Hill Country. This
convection is being aided by interaction of a previous outflow
boundary and a mid level shear axis. These showers and storms will
continue south through the remainder of the afternoon and dissipate
around sunset. Showers and storms should impact portions of the
Austin Metro area and back west through The Hill Country. Do not
think at the moment it will reach the San Antonio Metro area, but
outflow boundaries could. Storm Prediction Center mesoanalysis indicates a mixed layer
cape pool of 2000-2500 j/kg and dcape values of 1000-1300 j/kg just
out ahead of the ongoing convection across central Texas and
stretching back through the western Hill Country. Therefore a few
stronger storms will be possible, producing small hail and wind
gusts up to 50 mph, in addition to frequent cloud to ground lightning
The mid level shear axis weakens and slides further south on Tuesday
and some mid level drying is indicated by the models. Most of the
hi resolution guidance along with the GFS and European model (ecmwf) is indicating low
chances for afternoon showers and storms across the southern and
southeast zones Tuesday afternoon, with coverage remaining isolated.
Otherwise continued warm conditions, with afternoon heat indices
ranging from 104-108 in most areas outside of The Hill Country.
Long term (wednesday through monday)...
moisture remains confined to mainly southeast zones Wednesday with
a slight chance of afternoon showers and storms. Then the ridge
builds over the area through the end of the work week with
temperatures warming further. It appears there could be some
opportunities for heat advisories Wednesday through Friday over
portions of the area.
The ridge looks to amplify over The Rockies during the weekend with
a downstream trough digging across the eastern U.S. A backdoor cold
front is indicated by the GFS to work into the area Saturday night
into Sunday and by the European model (ecmwf) Sunday. This could bring some better
chances for rainfall to the area Sunday into Monday along with
slightly cooler temps.
Preliminary point temps/pops...
Austin Camp Mabry 78 101 77 103 77 / 0 10 - 10 0
Austin Bergstrom Intl Airport 76 100 75 101 76 / - 10 - 10 0
New Braunfels Muni Airport 76 100 75 102 75 / 10 10 10 10 0
Burnet Muni Airport 75 98 75 100 75 / 0 10 10 0 0
del Rio Intl Airport 78 101 78 104 78 / 0 10 - 0 0
Georgetown Muni Airport 77 99 76 101 77 / 0 10 - 10 0
Hondo Muni Airport 76 101 75 102 75 / 10 10 10 - 0
San Marcos Muni Airport 76 100 76 101 76 / - 20 10 10 0
La Grange - Fayette regional 77 99 76 100 76 / 0 20 - 10 0
San Antonio Intl Airport 77 101 77 102 77 / 10 10 10 - 0
Stinson Muni Airport 77 101 76 102 77 / 10 10 10 10 0