Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/10/21
Area Forecast Discussion
National Weather Service Fort Worth TX
641 PM CST Sat Jan 9 2021
...New Short Term, Aviation...
.SHORT TERM... /NEW/
Update:
The main update with this forecast package was to remove the rain
portion of precip from Sunday afternoon onward, for areas roughly
along and west of the I-35 corridor. Thermal profiles indicate a
sub-freezing column in that area from the top to just above the
surface, with surface temperatures in the mid 30s, which should
lead to a complete transition to snow by afternoon. With near
saturated conditions in the dendritic growth zone and weak
convective elements possibly added to the equation, brief periods
of heavy snow are still expected. The watch, warning and advisory
will remain unchanged for now and will let the night shift apply
any adjustments to this and overall snow totals as necessary. For
additional details, see the below discussion from this afternoon.
30
Previous Discussion:
/This afternoon through Monday Morning/
Summary...A strong winter storm will bring accumulating snow to
portions of North and Central Texas. At this time, the greatest
potential for greater than 4 inches of snow resides in areas west
of I-35 and south of the U.S. HWY 380 corridor This includes areas
such as Cleburne...Stephenville...Comanche...Hamilton...Gatesville
and parts of Waco. There also remains a potential that parts of
East Texas and the Brazos Valley could see in excess of 3-4" of
snow (east of an Athens to Centerville line) in spots.
Impacts...Snowfall accumulation is expected mainly on grassy and
elevated surfaces. Roads may become snow-packed in the event that
1) temperatures fall below 32 degrees and/or 2) snowfall rates
exceed 1"/hr (which is possible in some areas). Heavy snowfall may
result in poor visibility and dangerous driving conditions for
motorists. In general, most roads may remain wet/slushy as opposed
to completely snow-packed.
Timing...Most of the area will remain precipitation-free through
midnight Sunday. Winter weather impacts are anticipated to begin
between 6am and 8am for locations near and west of the U.S. HWY
281 corridor...closer to 8am-10 am for areas near the I-35
corridor and then between 10am and noon for areas of East Texas.
Winter precipitation should come to an end for most areas by 10pm,
though a second round of light snow is possible during the pre-
dawn hours on Monday for locations north of I-20.
Temperatures...Sunday temps will generally be in the mid 30s,
except where precipitation falls. Heavy precipitation may push
temperatures down to near or just below 32 degrees. Sunday night,
most areas should dip down to or below 32.
Meteorological Discussion...Our well advertised upper low
continues to churn out across the 4-corners region this afternoon.
It continues to dig a bit more to the south, but by the time it
arrives over southeastern New Mexico, it`ll likely slide eastward.
This is expected to happen during the overnight hours. While lift
will slowly begin to impinge on West Texas and parts of the Big
Country, I anticipate that most areas will remain precipitation-
free tonight.
During the pre-dawn hours on Sunday, strong forcing for the ascent
in the form of 40 to 50 meter height falls will start to
overspread the area. The lift associated with this will start a
moistening from the top of the troposphere down toward the
boundary layer. With some dry air still in place, I anticipate
that any initial precipitation will remain light. As surface
cyclogenesis takes place across West Texas, our surface winds here
will become slightly more east/northeasterly. This isn`t super
favorable for massive cold air advection and thus I think
surface temperatures will likely remain in the mid 30s.
Temperatures aloft and just above the surface will start to lower
as precipitation falls thanks to evaporative cooling. The rate at
which the column "wet-bulbs" will ultimately dictate just how fast
precipitation transitions and thus impact total accumulations.
With jet exit region forcing and strong low level thermal
advection both being the strongest across the Big Country and
western Central Texas, this area seems prime for cooling of the
column via both adiabatic ascent and diabatic effects. In
addition, the strongest frontogenetical forcing is expected here,
so I really anticipate this area being the first to transition
over readily to a mostly high density (or wet) snow. Forecast
soundings for areas from near Eastland down to near Waco indicate
very impressive omega (lift) in the dendritic growth zone.
Forecast CAPE progs even indicate the potential for some elevated
instability and when you factor in the strongly sheared deep
layer, the potential for banded precipitation structures greatest
here. Areas bounded by a Cisco to Granbury to Lampasas line are
where I anticipate that we could see over 6" of snowfall. Snowfall
rates of up to 1-2"/hr seem likely in this area. Both 00Z and 12Z
HREF 12 hour Ensemble Probability Match Means (PMM) as well as
probability of >4-6" inches of snow align with where the strongest
synoptic signals for lift are and this yields high confidence in
significant snowfall across this area. As hinted at above, most of
the snow accumulation will be on grassy surfaces, outside of
where these more intense areas of snowfall develop. With
temperatures right at 32 degrees, I really anticipate that road
issues will only develop if its colder than forecast and for these
locations beneath heavy snow bands.
While the exact areal extent of these snowbands remains somewhat
in question, there are some signals that have allowed us to hone
in on areas in which we are confident will see higher snow totals.
Most of the convective allowing models indicate that a large
precipitation shield will across nearly most of forecast area by
early afternoon Sunday. Given the strong synoptic scale lift and
the tropospheric thermal profile, I feel confident that we`ll
achieve Winter Storm Warning criteria for a good portion of the
area. Along the northern periphery of the previous Winter Storm
Watch, however, there`s a little bit more uncertainty. At present
time, I felt comfortable upgrading these areas to an Advisory as the
signals for widespread banded precipitation structures for areas
near and north of a Graham to D/FW to Canton line don`t appear as
obvious. I want to stress there is certainly time for that to
change (especially if the upper low wobbles a little farther to
the north or one of the snow bands extends more to the north/west).
For now, I`ll advertise snow totals in the 1-3" range with isolated
totals of 4" (maybe higher) not being out of the question. Similar
to the above thinking, accumulation should be largely confined to
grassy surfaces, but colder conditions and heftier snow rates may
result in travel impacts on an intermittent basis.
For our Brazos Valley and East Texas counties, it`ll likely be
later in the day and into the evening hours on Sunday before the
main show arrives here. While snow bands are anticipated to
develop and eventually decay west of I-35...renewed banded
precipitation structures appear probable as surface cyclogenesis
occurs on the land/sea interface across the Texas/Louisiana
coastlines. Most of the ensemble guidance is likely underdone here
and I`ve nudged snow amounts upward above blended/WPC guidance.
For now, I`ll leave extreme eastern portions of the Brazos Valley
in a watch after coordination with surrounding offices, but if
signals for heavier snows begin to appear in even the ensemble
guidance, these locations may need to be upgraded.
But wait...there`s more. A secondary band of precipitation could
develop due to the release of weak conditional symmetric
instability along the backside of the upper low during the pre-
dawn hours on Monday morning. Regions north of I-20 and near/west
of I-35 would be the recipient of the upper lows last gasp to
produce winter precipitation. Some modest mid-level frontogenesis
thanks to a diffuse TROWAL may be sufficient to generate some
precipitation. Negative saturated equivalent potential vorticity
values suggest some weak CSI. The latest HRRR, TTU WRF and NAM
nest do indicate this potential and I`ve nudged PoPs into the
20-30 percent range across North Texas and the northern part of
the Big Country. While winter weather products are currently set
to all expire at 6am Monday, it`s possible some extension may be
necessary here.
Bain
&&
.LONG TERM... /Issued 331 PM CST Sat Jan 9 2021/
/Monday Onward/
The deep upper trough responsible for the impending winter
weather will continue to linger in the area through the middle of
the week, but with a lack of appreciable moisture, precipitation-
free conditions will persist through the end of the week.
With early Monday morning temperatures dipping below freezing,
expect to see a gradual warm up into the lower 30s where the
highest snowfall occurs by the afternoon. Locations that see less
snow, high temperatures will likely climb into the lower to mid
40s. A cold night is expected once again Tuesday morning, with
much of the region dipping down into the 20s. With saturated
soils, mostly clear skies and calm winds, we`ll need to monitor
the potential for freezing fog as it may have some impacts for the
Tuesday morning commute. Confidence in this occurring is low at
this time, therefore, it will not be mentioned in the official
forecast at this time. If confidence increases, later forecast
packages may opt to include it.
The warming trend will continue through Thursday as upper level
heights gradually increase on the western side of the well
amplified trough. Breezy southwesterly winds will push
temperatures up to around 12 degrees above normal for this time of
the year across North Texas.
A precipitation-free cold front will push through the region
Thursday night, leading to high temperatures in the upper 50s to
lower 60s on Friday. The near normal temperatures will continue
into the weekend ahead of another approaching system that could
increase rain chances next Sunday.
Hernandez
&&
.AVIATION... /NEW/
/00Z TAFs/
An upper low now crossing through New Mexico will move east into
West Texas tonight and North/Central Texas on Sunday.
Precipitation associated with the system should start out as rain
or rain/snow mix Sunday morning, then primarily to snow across
both the DFW Metroplex and Waco areas by afternoon. Snow may
become moderate to heavy at times, especially across Central
Texas including KACT. Current forecast totals range from 1 to 3
inches across the Metroplex, with DFW somewhere in the middle. For
Central Texas (including KACT) higher totals of 3-4 inches appear
more likely through Sunday evening. There is still some
uncertainty regarding the exact track of the system, which could
lead to upward or downward adjustments to these totals in future
forecasts as new model data arrives. The main impact will be poor
visibility in the heavier snow along with the accumulations on
runways and aircraft during the late morning/afternoon hours.
Most precipitation will come to an end around Sunset Sunday
evening, but there will still be periods of light snow through
the overnight hours due to wrap-around moisture on the rear flank
of the system. Otherwise, surface winds will remain out of the
northeast at 5-10 kt through Sunday morning, then shift to the
north around 10 kt during the day Sunday, then to the northwest
Sunday night.
30
&&
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 33 36 32 44 30 / 20 90 30 5 0
Waco 34 34 26 41 25 / 30 100 40 5 0
Paris 30 38 31 44 28 / 0 40 40 10 0
Denton 30 36 33 45 26 / 20 80 30 10 0
McKinney 30 37 33 44 27 / 5 70 30 10 0
Dallas 35 37 31 44 31 / 10 90 40 10 0
Terrell 31 36 30 43 28 / 5 90 50 10 0
Corsicana 35 35 30 42 27 / 10 100 50 10 0
Temple 33 33 26 41 25 / 40 100 40 5 0
Mineral Wells 31 35 26 42 25 / 30 90 30 5 0
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 6 AM Sunday to 6 AM CST Monday for
TXZ115>117-129>133-141>147-156>162-174-175.
Winter Weather Advisory from 6 AM Sunday to 6 AM CST Monday for
TXZ100>103-118>121-134.
Winter Storm Watch from Sunday morning through late Sunday night
for TXZ135-148.
&&
$$
Area Forecast Discussion
National Weather Service Lubbock TX
513 PM CST Sat Jan 9 2021
.AVIATION...
Conditions will continue to bounce between IFR and MVFR this
evening at all TAF sites. An approaching upper level storm system
has begun to draw moisture into the area creating dense fog near
KLBB. This same system will bring snowfall to all TAF sites
beginning late tonight or early Sunday morning. The heaviest snow
and lowest flight conditions will likely be within 10Z through 16Z
at KLBB and KPVW. Aircraft icing will also be an issue for the
duration of the storm.
&&
.PREV DISCUSSION... /issued 416 PM CST Sat Jan 9 2021/
UPDATE...
Quick update to the forecast to include dense freezing fog for
portions of the southern South Plains and portions of the central
and southern Rolling Plains. As moisture ahead of our impending
winter storm is being pulled into the region ceilings and
visibilities have begun to fall. A freezing fog advisory has been
issued until 6 AM CST.
&&
.LUB WATCHES/WARNINGS/ADVISORIES...
Freezing Fog Advisory until 6 AM CST Sunday for TXZ030-031-
033>037-039>043.
Winter Storm Warning until 6 PM CST Sunday for TXZ027>031-
033>044.
Winter Weather Advisory until 6 PM CST Sunday for TXZ021>026-032.
&&
$$
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