Freeze Warning 1, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1102 PM CST Fri Dec 31 2021

.UPDATE...
Please see the 06Z aviation forecast discussion below.

&&

.AVIATION...
Overall, no significant changes have been made to the latest
aviation forecasts. Low end MVFR/upper end IFR cigs are expected
along I-35 overnight with conditions gradually improving back to VFR
late tomorrow morning as winds shift from the south to southwest. Fog
formation continues to appear unfavorable with elevated winds
overnight. Winds continue to trend more westerly along I-35 during
the early to mid afternoon hours as a Pac front/dryline move in from
the west. For DRT, we will keep the forecast VFR with northwest winds
through the current forecast period.

&&

.PREV DISCUSSION... /ISSUED 256 PM CST Fri Dec 31 2021/

SHORT TERM (Tonight through Saturday Night)...

A look at the upper air pattern across the lower 48 shows a long
wave trough over the west coast with strong short waves over
northern Baja and a digging s/w going through the Pacific NW. There
is an upper ridge over the eastern Gulf and western Caribbean which
is helping to keep the east coast in a W to SW upper air flow
pattern. At the surface the main weather feature for us is a strong
cold front currently over the Central Plains which will eventually
push through our area in about 36 hours. Temperatures over the
northern Plains are currently below zero.

The abundant low clouds and fog from this morning are slowly
thinning and by late afternoon most areas should at least be partly
cloudy. Our area remains in the very soupy airmass with dewpoints in
the 60s on the east side of a surface trough/dryline out in West
Central Texas...and will remain that way for about another 18 hours
or so before the Baja wave passes over TX. Look for more low clouds
and some light fog to develop by late evening and continue all the
way through Saturday morning. Looks like too much wind, especially
in the lowest few 1000 feet, to get really dense fog.  Cant rule out
some local dense fog areas based on the smoke likely generated by
fireworks...have had this issue in the past over AUS and SAT. Models
have backed off a bit on the small pops that we have been carrying
over the northern cwa as the upper energy passes over the state
tonight. We are carrying a very small sliver of 20 pop over Llano
and Burnet Counties.  Half the CAMS show nothing, others like the TT
WRF do show some showers overnight across the northern CWA.

A significant dry slot will come through tomorrow behind the wave,
dropping dewpoints and shifting winds to westerly by afternoon. See
the fire discussion below. Downsloping will occur with warm Max
temps Saturday...near 90 over the south, low to mid 80s I-35, and
upper 70s Hill Country. Some daily records could fall. Then we will
wait for the northerly winds and cold front to slam through the area
by late evening. A wind Advisory is possible Sat night into Sunday.
An advection freeze will occur for about the northern half the cwa
tomorrow night, some additional freeze warnings for our eastern
counties may be needed.  Wind chills could get as low as the single
digits in the Hill Country by early Sun AM...teens and 20s
windchills elsewhere. This cold start to January will be vastly
different than the record warm December we are just ending.

LONG TERM (Sunday through Friday)...

The aforementioned cold front should pass through the region from
north to south early Sunday morning. Strong consensus among the
global models brings the boundary into our Hill Country counties by
03Z Sunday, and show it departing for the Coastal Plains around 12Z.
Gusty northwesterly surface winds will usher in the coldest air of
the season thus far behind the front. Those living in the Hill
Country and southern Edwards Plateau will wake up to sub-freezing
temperatures Sunday morning, with regions to the south remaining
slightly above the freezing mark. Gusty 20-25 MPH northerly winds
will make it a struggle for most locations to escape the forties
Sunday afternoon. The one exception may be across our southwestern
counties, where a positively-tilted ridge axis building in the wake
of the departing long wave trough will be approaching. This could
relax the surface pressure gradient, and thus the surface wind field,
sufficiently enough to allow a scattering of 50-plus degree high
temperatures to be reached Sunday afternoon.

Said pressure ridge will settle in to the remainder of the area
overnight Sunday into Monday morning. Resultant subsidence in the
column, clear skies, and light-calm surface winds should work to
maximize radiational cooling Sunday night. Alongside the polar air
mass in place behind the cold front, this will spell a widespread
freeze across the region, likely warranting the issuance of a freeze
warning as the period draws closer. Trends will continue to be
monitored to fine tune the precise counties that will be included
over the next 24-36 hours.

In welcome news, this shot of winter should be brief as the ridge
vacates and south to southwesterly flow returns by Tuesday morning.
Moderation of daytime highs will follow on Tuesday and Wednesday,
before another sharp cold front arrives during the day on Thursday.
Model trends will need to be monitored further, but it's possible
that our daytime highs could occur predawn Thursday morning as cold
advection drops temperatures through the remainder of the day. It
appears that this cold shot will also be brief, as temperatures climb
back to normal through the remainder of the forecast period.

FIRE WEATHER...

Elevated fire weather conditions are anticipated across the region
Sunday behind the cold front, as sustained 20-25 MPH winds, and RH
values below 30 percent will be in place across the area. Further RH
reductions to near 20 percent will likely occur in spots west of San
Antonio, although the approaching surface ridge may relax winds to
lighter values. Nevertheless, near-critical fire weather conditions
could result across this area later Sunday afternoon.

Another localized area of elevated fire weather, particularly across
Edwards, Real, and Val Verde counties, will be possible Monday
afternoon as RH values once again drop to near and possibly below the
20 percent level. Trends will continue to be monitored should
amendments to this forecast become necessary.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              70  81  29  46  25 /  10  -   -    0   0
Austin Bergstrom Intl Airport  69  82  27  47  22 /  -   -   -    0   0
New Braunfels Muni Airport     69  84  30  49  23 /  -   -    0   0   0
Burnet Muni Airport            64  79  23  44  21 /  10  -    0   0   0
Del Rio Intl Airport           62  85  36  55  28 /  -    0   0   0   0
Georgetown Muni Airport        68  80  24  45  22 /  10  -    0   0   0
Hondo Muni Airport             65  85  32  53  22 /  -    0   0   0   0
San Marcos Muni Airport        68  84  27  48  21 /  -   -    0   0   0
La Grange - Fayette Regional   72  84  30  46  23 /  -   -   -    0   0
San Antonio Intl Airport       68  83  32  49  25 /  -   -    0   0   0
Stinson Muni Airport           69  87  36  53  27 /  -   -    0   0   0

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

Short-Term/Aviation...Platt
Long-Term...Oaks

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
1059 AM CST Fri Dec 31 2021

TXZ171>173-183>194-202>209-217>225-228-011700-
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-
1059 AM CST Fri Dec 31 2021

This Hazardous Weather Outlook is for South-Central Texas..

.DAY ONE...Today And Tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Elevated fire weather conditions are possible Saturday through
Monday due to low humidity and gusty winds.

A strong cold front will move through the area Saturday night.
Freezing temperatures are forecast Sunday morning across the Hill
Country and Austin metro area along with wind chill values in the
teens. A widespread freeze is forecast Sunday night into Monday
morning. Low temperatures in the upper teens to low 20s are
forecast across the Hill Country and mid 20s to upper 20s
elsewhere.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.