NWS Austin/San Antonio, TX wrote its last area forecast discussion before the first event at Feb 10, 10:48 PM CST, 4 hours 43 minutes earlier.
Area forecast discussion, Feb 10, 10:48 PM CST, 4 hours 43 minutes before
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1048 PM CST Wed Feb 10 2021
.AVIATION...
An overcast low cloud deck will continue to persist with flight
categories ranging from LIFR to very low end MVFR ceilings through
the TAF period. Visibilities will also be reduced. Light rain along
with drizzle activity has begun across the region and should continue
to expand and increase in coverage through Thursday. A couple of
thunderstorms may be possible as well. The activity then gradually
subsides Thursday night. Brisk northerly winds also continue. We'll
need to continue to keep a close eye on the temperatures, especially
at KAUS but perhaps even near KSAT, as light freezing rain may be
possible into Thursday morning. However, the greatest confidence for
freezing rain will be further to the west and north. As a result, we
will leave out any mention of freezing rain in this TAF suite.
&&
.PREV DISCUSSION... /ISSUED 856 PM CST Wed Feb 10 2021/
UPDATE...
Elected to expand the Winter Weather Advisory further west and along
the I-35 corridor given the latest observational trends where the
temperatures have already fallen as low as 33 to 35 degrees and 00Z
short term convective allowing model guidance. For Travis and Hays
counties, best potential for any ice accumulation will be across the
western portions of the county. For Kendall and Edwards, the best
potential for ice accumulation will be across the northern portions
of those counties. Did slightly increase the ice accumulations with
portions of Burnet, Llano, Gillespie counties seeing as much as
between a tenth to perhaps near two tenths on exposed and elevated
surfaces.
Additionally, adjusted the temperatures from tonight and through
Thursday night given the latest short term guidance. Temperatures
could struggle to reach the mid 30s across the Hill Country and
around the I-35 corridor from San Marcos to Georgetown. Have also
elected to increase QPF along and south of I-35 through the 00Z
Friday hour ranging from around 3 quarters of an inch to near an
inch and a quarter across that area.
PREV DISCUSSION... /ISSUED 534 PM CST Wed Feb 10 2021/
AVIATION...
Overcast deck with IFR ceilings across much of South-Central Texas
while some clearing occurred this afternoon along the Rio Grande
where the temperatures are trending much warmer. Expect for IFR to
very low end MVFR conditions to generally maintain through the TAF
period at the TAF sites. The only exception is VFR conditions to
start the period at KDRT. Light rain showers persist and increase
overnight with more moderate rain showers and possibly a couple of
thunderstorms throughout the day on Thursday. We'll also need to
closely monitor the temperatures, especially at KAUS, as light
freezing rain could be possible near the Austin region into and
through Thursday morning. However, the greatest confidence of
freezing rain will be further to the west and north. As a result,
will leave out any mention of freezing rain in this TAF suite.
PREV DISCUSSION... /ISSUED 216 PM CST Wed Feb 10 2021/
SHORT TERM (Tonight through Thursday Night)...
FREEZING RAIN POSSIBLE OVER PORTIONS OF THE HILL COUNTRY LATE
TONIGHT INTO THURSDAY MORNING...
At the sfc, a cold front continues to slowly encroach on our western
counties, with a wide spread in temperatures across the CWA this
afternoon. Temperatures range from the upper 30s in our northern
counties, to the 40s and 50s over the San Antonio Metro, to the 60s
out west over the Rio Grande. Aloft, a 500mb shortwave trough is
present to our west, over the Baja of California, which will dig
further south into northern Mexico overnight tonight, resulting in
divergence aloft over South-Central Texas. This will result in
increasing precipitation coverage as forcing for ascent becomes
maximized over the Hill Country and Southern Edwards Plateau
Thursday morning. Good moisture advection in the 925-850mb level
will result in increased coverage of showers and even some
thunderstorms overrunning the frontal boundary as it continues to
push further southward. At this time, strong/severe storms are not
expected.
With regard to precipitation type, hiRes guidance continues to
indicate a growing threat for freezing rain over the Hill Country,
as temperatures fall to or just below 32 degrees late tonight into
Thursday morning. Model soundings depict a very shallow arctic
airmass, with temperatures at the sfc below freezing, and warming to
above freezing just 1500 feet above the sfc, around the 925mb layer.
This type of vertical temperature profile is highly favorable for
freezing rain. Have gone ahead and issued a Winter Weather Advisory
for Williamson, Burnet, Llano, Gillespie, and Kerr Counties from 06Z-
18Z (early Thu AM-midday Thursday). A light glaze is possible,
especially on elevated surfaces, more specifically, bridges and
overpasses. Once temperatures can warm back above freezing, we will
see freezing rain transition back to liquid rain by midday. With
more convective showers across the southern half of the region, we
are expecting higher rainfall totals in those areas. In general,
rainfall totals in the 0.25-0.50 inch range can be expected across
the northern half of the area, and 0.50-1.00 inch over the southern
half of the region through Thursday night, before the precip moves
off to our east.
With regard to temperatures, it's going to get cold, as the cold
front pushes through the entire region on Thursday morning,
temperatures will struggle to rebound, with only a few spots along
the Rio Grande managing to get into the lower 50s on Thursday. The
rest of the area will remain cold, in the 30s and 40s. North winds
will increase to 10-20 mph with gusts upwards of 25 mph during the
afternoon, leading a bit of a bite to the air. Wind chills will
hover in the 30s for most of the area on Thursday, with some spots
in the Hill Country feeling wind chills in the 20s at times.
Overcast skies will continue into Friday morning, as the entire area
starts out in the lower 30s. However, it's going to get much colder
in the coming days.
LONG TERM (Friday through Wednesday)...
To start the long term period, we'll be in a relative calm as a
southern stream trough axis down in Mexico continues to push slowly
east. There is a slight chance for some lingering morning showers
over the coastal Plains but most of the activity should be well out
over the gulf. High temperatures will range from the upper 30s to
the low to mid 50s, coolest northeast and warmest southwest.
Another shortwave is anticipated to approach on Saturday. This
system will bring with it some precipitation, mainly during the day,
and for the southern Edwards Plateau and portions of the Hill
Country this could come in the form of sleet or freezing rain. At
this time, model soundings are looking too warm in the saturated
layer for snow development and GEFS postage stamps/plumes also
support better chances for FZRA/IP. Meanwhile, 12Z ECMWF remains too
warm for winter precip to be much concern at all Saturday, so it's
too early to pinpoint any accumulation potential. But at this time
QPF is anticipated to max out around 0.15", so even if the colder
end of guidance ends up verifying, impacts are expected to be
minimal.
The shortwave will exit Saturday night, and we should be mostly dry
through the day Sunday. Remaining seasonably cold, but the coldest
arctic air will still be held up to our north. Another trough
pushing in from the northwest will approach Sunday night into
Monday, and models continue to come into better agreement with the
timing of the accompanying arctic air as well as the precipitation
chances. Our confidence continues to gradually increase that we
could see both an impactful winter precipitation event and an
intrusion of the coldest airmass in several years. Current thinking
is that isolated precipitation could begin Sunday evening, but the
heavier stuff will come in after midnight and exit to the east
sometime around midday Monday, Monday evening at the latest.
All precipitation types will be possible with this system across the
entirety of our coverage area and accumulations continue to be a
threat worth watching. Ensemble probabilities for accumulating snow
continue to increase across the northern half of the area, and
several inches of accumulating snow are currently well within the
realm of possibility across our northern tier of counties. Sleet and
freezing rain will be more likely than snow south and east. Again,
there's not much more that can be said at this time about
accumulations and impacts, but we will continue to refine over the
coming days. Focus in the meantime will be on the winter precip
potential Thursday and Saturday.
Operational ECMWF has now come in much colder Monday into Tuesday,
more in line with the GFS although still a touch warmer. Although
it's associated ensemble mean is a touch warmer still, confidence is
moderate to high that a sizable chunk of the area will remain below
freezing through the daytime on Monday. Lows will likely be well
into the teens Tuesday morning north and east and single digit lows
aren't out of the question if clouds are able to clear out behind
the precipitation shield as low level ridging fills in. Worst case,
there are a few GEFs ensemble members that keep SAT below freezing
from Saturday evening to Wednesday morning. For reference, the
longest SAT has ever been below freezing was 4 days 13 hours in late
Jan-Early Feb 1951. I believe we are unlikely to eclipse that but it
could become closer than any of us want, not even this native
Wisconsinite and cold/snow lover. There are some hints in the models
that the cold could be short-lived (i.e. 12Z ECMWF brings many spots
back into the 50s by Wednesday) but currently that is unsupported by
ensemble data.
PREV DISCUSSION... /ISSUED 1138 AM CST Wed Feb 10 2021/
AVIATION (18Z TAFS)...
A bit of a tricky forecast with area terminals as on and off shower
activity picks up a bit through the afternoon. Have seen improvements
to visibility at SAT/SSF/DRT, but AUS still holding onto lower vis,
so will include tempo groups for SAT/SSF/AUS with slightly lower vis
for the next 1-3 hours. In general, expect IFR CIGs to continue
through the remainder of the day at all three I-35 sites, but I
wouldn't rule out a brief rise to MVFR CIGs for a short time this
afternoon/early evening before going back to IFR after sunset. At
this time, have opted to leave IFR through tomorrow morning. At DRT,
MVFR CIGs look like a good bet for the remainder of the afternoon,
dropping to IFR after 08Z tonight. Winds could be on the gusty side
at DRT this afternoon through early Thu AM. Winds will be from the
N/NNE at I-35 sites and from the ESE at DRT. DRT switches around to
northerly, along with all 4 sites seeing gusty winds once the
secondary frontal boundary pushes all the way through the region by
12-18Z timeframe tomorrow morning. Gusty winds are expected behind
this front, but I am expecting a return to MVFR at that time along
with light rain showers.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 33 38 34 42 34 / 60 80 40 10 -
Austin Bergstrom Intl Airport 33 38 33 42 34 / 60 80 40 10 -
New Braunfels Muni Airport 36 42 36 45 35 / 60 80 50 10 -
Burnet Muni Airport 29 36 31 39 30 / 70 80 20 10 10
Del Rio Intl Airport 44 48 40 53 40 / 70 70 20 - 10
Georgetown Muni Airport 31 37 31 41 32 / 70 80 30 10 -
Hondo Muni Airport 41 45 37 49 36 / 60 80 40 10 -
San Marcos Muni Airport 35 40 33 42 34 / 60 80 50 10 -
La Grange - Fayette Regional 38 42 36 44 36 / 50 80 60 20 10
San Antonio Intl Airport 38 42 36 46 35 / 60 80 40 20 10
Stinson Muni Airport 39 43 38 46 36 / 50 80 50 20 10
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CST Thursday for Blanco-Burnet-
Edwards-Gillespie-Hays-Kendall-Kerr-Llano-Travis-Williamson.
&&
Short-Term/Aviation...Brady
Long-Term...04
Hazardous weather outlook, Feb 10, 9:05 PM CST, 6 hours 26 minutes before
Hazardous Weather Outlook...UPDATED
National Weather Service Austin/San Antonio TX
905 PM CST Wed Feb 10 2021
TXZ171>173-183>194-202>209-217>225-228-120315-
Llano-Burnet-Williamson-Val Verde-Edwards-Real-Kerr-Bandera-
Gillespie-Kendall-Blanco-Hays-Travis-Bastrop-Lee-Kinney-Uvalde-
Medina-Bexar-Comal-Guadalupe-Caldwell-Fayette-Maverick-Zavala-
Frio-Atascosa-Wilson-Karnes-Gonzales-De Witt-Lavaca-Dimmit-
905 PM CST Wed Feb 10 2021
This Hazardous Weather Outlook is for South-Central Texas..
.DAY ONE...Tonight.
Freezing rain is possible across portions of the Hill Country and
along the I-35 corridor late tonight. A Winter Weather Advisory
is in effect for Kerr, Gillespie, Llano, Burnet, and Williamson,
Blanco, Travis, Hays, Kendall and Edwards Counties until noon on
Thursday. Total ice accumulations ranging from a light glaze up
to a tenth or two of an inch are possible, especially on exposed
and elevated surfaces. Some travel impacts could be possible,
including during the morning commute.
.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.
Freezing rain is possible across portions of the Hill Country and
along the I-35 corridor late tonight. A Winter Weather Advisory
is in effect for Kerr, Gillespie, Llano, Burnet, and Williamson,
Blanco, Travis, Hays, Kendall and Edwards Counties until noon on
Thursday. Total ice accumulations ranging from a light glaze up
to a tenth or two of an inch are possible, especially on exposed
and elevated surfaces. Some travel impacts could be possible,
including during the morning commute.
A hard freeze is possible Saturday morning across the Hill
Country and will become increasingly likely across all of South
Central Texas Sunday but especially Monday and Tuesday mornings.
Slight chance for additional sleet or freezing rain will be
possible on Saturday. Additionally, there is also a chance for
snow and freezing rain Sunday night and Monday.
.SPOTTER INFORMATION STATEMENT...
Spotter Activation is not anticipated.
Brady