#2350 Postby weatherdude1108 » Mon Feb 03, 2020 5:15 pm
000
FXUS64 KEWX 032111
AFDEWX
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
311 PM CST Mon Feb 3 2020
.SHORT TERM (Tonight through Tuesday Night)...
Broad areas of elevated light rain showers are drifting NE across
South-Central Texas this afternoon with rain gauges mainly reporting
only a trace or 0.01 inch. South winds of 15 to 25 mph have
contributed to a deeper layer of low level moisture and the evening
forecast period still looks to have enough moisture and instability
to support a few thunderstorms forming mainly west of I-35. The
rapid refresh models continue to suggest this deeper convection, but
have backed off of what was a more robust output for storms from the
early morning updates. With the canopy of mid clouds curbing daytime
heating potential, expect most of the activity to be showers with
only some short lived storms. Rainfall amounts are expected to be
mostly below 1/4 inch, as cell movement should be at least 30 knots.
Rain chances should taper off after midnight, with a mostly cloudy
morning keeping min temps in the 50s and lower 60s. Tuesday continues
to look like the warmest day of the week, although model confidence
is gaining on a faster FROPA late in the afternoon into the Hill
Country as forecast by the NAM model.
The model consensus continues to show rapid cooling overnight with a
potential for freezing temperatures along our northern county
warning area border by 12Z Wednesday. Scattered to numerous showers
are expected to overrun the front, and model soundings from the NAM
suggest a cold layer sufficient to generate a few sleet pellets with
light freezing rain between 9Z and 12Z north of the Rocksprings and
Llano areas. With inherited warm ground temperatures prior to the
front, no ice accumulations are anticipated in the short-term
through Tuesday night. Post-frontal rainfall amounts should be
mainly in the 1/10-1/4 inch range through Tuesday night.
&&
.LONG TERM (Wednesday through Monday)...
Strong north winds and much colder temperatures will prevail through
the day on Wednesday behind the cold front. We have trended the high
temperature forecast colder, weighted closer to the NAM12 and NAM
MOS guidance, which tends to do better with shallow, cold airmasses.
This will result in high temperatures Wednesday only in the 30s
across the Hill Country and 40s elsewhere. Wind chill values will be
in the upper teens to low 20s through the Hill Country Wednesday
morning and upper 20s to upper 30s elsewhere.
Forcing along the 850mb front, combined with upper level forcing in
the southwest flow aloft, will generate the best chances for
precipitation during the day on Wednesday across the Hill Country
into Central Texas. Using a top-down forecast approach, soundings
indicate mostly liquid falling during the day on Wednesday. However,
there may be enough cold air advection in the lowest 750 meters to
allow for some freezing into ice pellets across portions of the
northern Hill Country. Also, some locations across the northern Hill
Country may see surface air temperatures reach freezing Wednesday
morning and struggle to rise back above freezing during the day.
Ground temperatures are warm across the region, however can`t rule
out some isolated spots through the northern Hill Country where
bridges and overpasses see some very light freezing rain and sleet
accumulations on Wednesday. The remainder of the precipitation
across the area during the day on Wednesday should remain liquid
The big question, and lower confidence portions of the forecast,
continues to be Wednesday night into Thursday morning as the core
of the dynamical forcing in the base of the trough moves across the
region. The GFS and NAM12 continue to trend drier, as the 850mb
front clears the area and also an increasingly dry layer beneath
700mb is indicated on forecast soundings. GEFS plumes as well as
SREF plumes point to lower probabilities of precipitation across the
region, at less than 20%. The 12Z ECMWF and Canadian are still
indicating more QPF than the GFS and NAM12, across the eastern Hill
Country and along and east of I-35. We have trended PoPs into the
slight chance category for Wednesday night. With that said, and again
using a top- down approach, precipitation that does develop in the
base of the upper level trough does have the potential to fall as a
rain/freezing rain/sleet mix along and north of U.S. 90. There is a
lesser probability of flurries/light snow on the back side of any
precipitation axis ending west to east, across portions of the Hill
Country and Central Texas, as temperatures in the the ice crystal
initiation region of the cloud cool to sufficient levels. Again, this
is assuming any precipitation does develop and were to make it all
the way to the ground without evaporation or sublimation occurring.
At the current time impacts appear very minimal, given both the low
confidence of precipitation occurring and precip amounts remaining
light.
It is urged to pay close attention to the forecast over the next
24-36 hours as additional fluctuations are likely to the Wednesday
through Wednesday night time frame.
A hard freeze is forecast Wednesday night into Thursday morning
across the Hill Country, with a light freeze across portions of the
I-35 corridor. Clearing and warmer during the day on Thursday with
highs forecast to rebound into the mid 50s to mid 60s. The warming
trend continues into Friday, with highs back into the upper 60s to
mid 70s. A weak cold front is forecast to move through the area
Saturday with dry conditions over the weekend.
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