Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX
FXUS64 KEWX 040932
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
332 AM CST Sun Dec 4 2016
.SHORT TERM (Today through Monday)...
Seeing somewhat of a lull in activity overnight with one batch of
rain south of San Antonio and light rain in the northwest CWA. The
1.5 inch plus precipitable water values from yesterday have
shifted east and much of the CWA is now in the 1.3 to 1.5 inch
range which should equate to lighter rainfall amounts today. In
addition, isentropic lift is weaker which is also helping keeping
rainfall coverage and amounts down currently compared to
yesterday. For today, with continued weak lift, should see areas
of light rain move across the region. PoPs will remain high as
most of the area will see rainfall, but amounts through this
afternoon should mostly remain less than 3/4 of an inch with most
of the area seeing less than 1/4 of an inch of rain through the
The upper low responsible for the continued rainfall across the
region is still located over northern Mexico. This deep low
pressure is strong, proven by the snowfall observed in northern
Mexico under the core of the low. This low will finally begin to
weaken and eject east this afternoon and will bring one more round
of widespread rainfall to the region beginning late this afternoon
across the western counties. The showers and isolated
thunderstorms will then spread east tonight. The high-res guidance
is in fairly good agreement that 1-2 inches of rain will fall
across a large portion of the CWA as the deep lift associated with
the eastward moving trough moves overhead.
Decided to make no changes to the Flash Flood Watch with this
forecast package. Although not expecting rainfall heavy enough for
additional impacts today kept the watch going due to the threat of
the possible 1-2 inch rainfall tonight. For most events 1-2 inches
of rain should not be enough to cause any flash flooding concerns,
but with the large swath of 2-5 inches where the current Flash
Flood Watch is in place it will not take much for additional
flooding to occur. This is evident by over 80 low water crossings
currently closed in Bexar, Hays, Caldwell, and Bastrop Counties
alone. The current Flash Flood Watch expires at 12z Monday and
this still seems reasonable and any possible extensions would come
at later shifts into Monday.
The forecast for Monday will continue to have chance to likely
PoPs for the area with the higher coverage in the eastern zones.
The best forcing associated with the upper low will be located in
the eastern zones and will push out of the region by the late
afternoon hours, which will finally end rainfall chances for the
High temperatures today will top out in the 50s areawide or only
about 3-7 degrees warmer than the low temperatures for most
locations. Cloud cover and continued rain chances are leading to
the small diurnal temperature range. Low temperatures tonight will
fall back the 5 degrees and we should see more of a warm up by
Monday afternoon as the rain ends. Highs Monday will be back in
the 60s for areas mainly south of Highway 90.
.LONG TERM (Monday Night through Saturday)...
Tuesday should be a transition day across the region with strong
westerly flow in place in the upper levels. The next storm system
will be building in the northwestern CONUS with cold air beginning
to spill out of Canada into the northern plains. This upper low
will move into the Central Plains by Wednesday morning allowing
the cold air to spill south and into the CWA Wednesday or Wednesday
night depending on which model you look at. There will remain a
20 to 30 percent chance of showers for the eastern counties with
the passage of the cold front. Temperatures will likely not get
out of the 40s on Thursday with wind chills in the teens and 20s
possible. Most of the area should see a freeze on Friday morning
with a hard freeze possible for the Hill Country.
The GFS is warming things back up much faster than previous runs
with the raw model output showing 40s for lows Saturday morning.
The ECMWF on the other hand is progging another area-wide freeze.
Will continue with a forecast closer to the ECMWF unless the new
warmer solution of the GFS is consistently shown. As southerly
flow does return by Saturday afternoon there could be a shower or
two in the warm air advection regime in the eastern counties.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 54 48 57 46 66 / 80 90 70 - 0
Austin Bergstrom Intl Airport 54 48 57 44 67 / 80 90 70 - 0
New Braunfels Muni Airport 54 48 59 45 70 / 80 90 50 0 0
Burnet Muni Airport 52 46 53 43 62 / 60 90 70 - 0
Del Rio Intl Airport 53 49 62 44 69 / 70 90 30 0 0
Georgetown Muni Airport 54 47 54 44 64 / 60 90 80 - 0
Hondo Muni Airport 56 48 61 43 72 / 80 90 40 0 0
San Marcos Muni Airport 54 48 58 44 69 / 80 90 60 - 0
La Grange - Fayette Regional 55 50 58 46 69 / 80 90 70 - 0
San Antonio Intl Airport 55 48 59 47 71 / 80 90 50 0 0
Stinson Muni Airport 55 49 60 45 72 / 80 90 40 0 0
Flash Flood Watch through late tonight for the following counties: