Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX
FXUS64 KEWX 042345
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
545 PM CST Sun Dec 4 2016
Rain will continue off and on overnight and into Monday afternoon.
CIGs are MVFR at all airports and will stay that way until later
this evening when they will drop to IFR in Austin and San Antonio.
Should see improvement to MVFR and then VFR by late afternoon
.PREV DISCUSSION... /ISSUED 408 PM CST Sun Dec 4 2016/
SHORT TERM (Tonight through Monday Night)...
The deep mid-to-upper level trough over Mexico that helped cause
our persistent rainfall pattern over the past 36-48 hours is
finally beginning to eject to the northeast towards Big Bend.
Although we are having a relative lull in the action with only
scattered light showers over most of the region now, IR satellite
imagery shows convective activity is increasing over southwestern
Coahuila in response to PVA and height falls ahead of the trough.
In response to these height falls and cooling from 700-850 mb,
several hi-res models continue to show a brief increase in
elevated CAPE values to around 300-400 J/kg this evening into the
early morning hours. This elevated instability combined with
strengthening ESE-WNW oriented isentropic ascent overspreading
the region will allow for widespread showers and a few embedded
thunderstorms through Monday morning. Rainfall intensities should
steadily fall throughout the morning hours with clearing skies and
all activity exiting the region from SW to NE by mid-afternoon.
Hi-res and global model trends continue to trend downwards in the
intensity of showers and coverage of thunderstorm activity
tonight. Therefore, model QPF values have come down as well, so
there is higher confidence that rain rates should generally remain
below one inch an hour with rainfall totals of 1-2 expected across
the region. However, a few locally heavier downpours are still
possible, and if these fell over the Hondo to San Antonio to
Bastrop corridor that has already received widespread 3 to 5 inch
rain totals, flash flooding would be possible. Therefore, we have
continued the Flash Flood Watch for those counties due to their
saturated soils and standing water from antecedent rainfall
conditions until 6 AM Monday. However, we have cancelled the watch
for Fayette, Lavaca, and Lee Counties that should be able to
handle the expected rainfall totals given their flatter terrain
and lower rainfall amounts of 1 to 3 inches relative to those
counties left in the watch.
LONG TERM (Tuesday through Sunday)...
Our most pleasant weather over the next week is expected Monday
evening through Wednesday afternoon as clear skies and light
northerly winds combine with near normal highs in the 60s and lows
in the 40s. Some spots in the Rio Grande Plains may warm up into
the lower 70s as W-SW aloft mixes down, but northerly winds may
move in by the afternoon to help dampen some of this warming.
Global models have delayed the timing of the much advertised
strong cold front for the second set of consecutive model runs,
but regardless of its exact timing, much cooler temperatures will
overspread South Central Texas by Wednesday evening. A light
freeze may be possible Thursday morning in the Hill Country
counties, but strong northerly winds should preclude a widespread
freeze elsewhere even though wind chill values will be in the 20s.
Northerly 15-20 mph winds with gusts over 25 mph expected behind the
front on Thursday will make for a blustery day with wind chill
values in the 30s before winds begin to relax some for the evening
to allow for a widespread freeze across the entire CWA. Low
temperatures Friday morning should range from the mid 20s to lower
30s with wind chill values in the teens and 20s. Another light
freeze is possible on Saturday morning before temperatures begin
to warm back up to near seasonal normals for the weekend.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 48 57 47 67 46 / 90 80 - 0 0
Austin Bergstrom Intl Airport 48 56 44 67 44 / 90 80 - 0 0
New Braunfels Muni Airport 48 59 46 70 46 / 90 80 - 0 0
Burnet Muni Airport 46 53 44 63 43 / 90 90 - 0 0
Del Rio Intl Airport 48 61 45 70 47 / 90 50 0 0 0
Georgetown Muni Airport 47 54 45 64 44 / 90 90 - 0 0
Hondo Muni Airport 49 61 44 72 46 / 90 60 0 0 0
San Marcos Muni Airport 49 59 45 69 45 / 90 80 - 0 0
La Grange - Fayette Regional 50 57 46 71 47 / 90 80 - 0 0
San Antonio Intl Airport 48 59 48 71 46 / 90 60 0 0 0
Stinson Muni Airport 49 60 46 72 48 / 90 60 0 0 0
Flash Flood Watch through late tonight for the following counties:
Public Service/Data Collection...Williams