Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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000
FXUS64 KFWD 090535
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1135 PM CST Sun Dec 8 2019


.AVIATION...
A 40 kt low level jet will continue to pull Gulf moisture
northward tonight, however, all stratus overnight/Monday morning
should remain south and east of the TAF sites. High clouds will
remain over the entire region overnight and Monday as an
approaching upper low draws in Pacific moisture. Ceilings will
gradually lower through the day, but remain VFR through 06Z
Tuesday.

Breezy southerly winds tonight will veer to the southwest Monday
morning ahead of a cold front. The front will move across the
Metroplex TAF sites around 20Z and Waco between 21 and 22Z.
A north to northwest wind is expected behind the front through
Monday night. Wind speeds overnight through Monday evening will
range from 12 to 16 knots along with some gusts around 25 knots.

Most of the TAF cycle should be precipitation free, however, some
post-frontal light rain will develop at all TAF sites late Monday
evening/overnight.

79

&&


.LONG TERM... /Issued 313 PM CST Sun Dec 8 2019/
/Monday Night Onward/

The main focus through the extended portion of the forecast
is the chance for some snow to mix with rain on Tuesday morning.
Due to warm surface temperatures, little/no accumulations or
impacts are expected, thus no winter weather headlines are
planned.

Cold advection through the low levels will persist through Monday
night following the strong cold frontal passage earlier in the day.
Meanwhile, a potent upper trough will be digging through New
Mexico and West Texas, overspreading our CWA with vigorous dynamic
lift. Strong DCVA coupled with our positioning within the right
entrance region of an intensifying upper jet streak will result in
broad large-scale ascent through the mid levels. The attendant
steeply-sloped frontogenesis towards the colder air will result
in a large frontogenetical band of precipitation developing to our
west (initially as virga) before it spreads eastward into North
Texas while top-down saturation occurs simultaneously. As a
result, a fairly widespread cold rainfall should be ongoing by
~3am Tuesday morning.

At the onset of precipitation Monday evening, the column
will still be relatively warm. However, over the next several
hours, forced ascent will act to cool the mid levels, while CAA
and evaporative cooling work simultaneously to send low-level
thermal profiles towards their wet bulb temperatures. By early
Tuesday morning, these mechanisms should allow the column to cool
sufficiently to allow for some snow to begin mixing with rain
across parts of North Texas. The majority of model soundings
indicate anomalously high Pacific moisture content through the mid
and upper levels, which will allow for profiles to be saturated
all the way to -20C or -30C, more than sufficient to saturate the
dendritic growth zone. The bit of uncertainty that remains is
regarding the low-level thermal profiles, particularly in the
lowest 1km, where a warm nose of +2C to +4C may still reside
through the morning hours. Despite its shallow nature, a warm nose
of +4C would likely be enough to melt most snow on its journey to
the surface. However, just a degree or two cooler and snow will
likely be able to survive the trip. Given trends towards colder
solutions in recent model runs, particularly last night`s 00z and
this morning`s 12z suites, there is a greater likelihood that
some portions of North Texas will observe a bit of snow on Tuesday
morning. In fact, it`s worth noting that all 20 GEFS members and
all 50(!) EPS members are now producing at least a small amount of
snow in some portion of our northwestern CWA during this time
period. This has increased confidence such that the mention of a
chance of snow has been expanded across North Texas (including
parts of the DFW Metroplex) with this forecast issuance.

In the "unlikely but not impossible" category: While I do not
have sleet mentioned in the worded forecast, it is possible that a
precipitation transition could consist of a brief mix of
rain/sleet before snow is observed, but rain and snow should be
the predominant 2 precipitation types. Since surface temperatures
are expected to be at or above freezing within the forecast area,
no mention of freezing rain has been included either, but there
is an outside chance that one of our far northwestern zones could
briefly dip to 31F or 30F while rain is still falling. Model-
derived precipitation types struggle mightily in these types of
scenarios with such subtleties in thermal profiles, and they have
largely been disregarded in this forecast in lieu of top-down
sounding analysis.

The bit of good news with this type of setup is that extremely
cold air is difficult to come by at the surface, and most surface
temperatures are expected to be above freezing while any snow (or
rain for that matter) would fall. This will inhibit accumulations
on roadways, especially given the fact that temperatures will
have been in the upper 60s and 70s just 12-18 hours previously.
Should a complete transition to snowfall occur and persist for a
couple of hours at any given location, then some minor
accumulations would be possible on surfaces like grass,
vehicles, and rooftops. At most, a slick spot on a bridge or two
could be a possibility, but overall, impacts from any wintry
weather should be little to none.

By midday, much drier air will begin advecting into the low
levels, acting to shut down precipitation from northwest to
southeast during the day. Clearing will actually occur across
North Texas by the afternoon, which should allow temperatures to
actually warm into the low or even mid 40s. All precipitation is
expected to exit the forecast area by Tuesday evening, with a cold
night in store area-wide. Most areas will fall to near or below
freezing by Wednesday morning.

The remainder of the extended forecast is on the quiet side, with
little rain chances through the day 4-7 time period. Another
strong upper trough will sweep through the Southern Plains on
Thursday/Friday, but moisture will be completely scoured from our
area, keeping all the associated rain chances well to our east.
Slightly warmer temperatures (closer to normal) should prevail
through the rest of the week with highs in the 50s to near 60 and
lows in the 30s and 40s. Another strong cold front may arrive late
next weekend or early next week, but the precipitation potential
appears low with that system at this time due to limited moisture
recovery.

-Stalley

&&

.SHORT TERM... /Issued 1256 PM CST Sun Dec 8 2019/
/Today and Tomorrow/

The area remains under a blanket of upper level clouds brought in
from a healthy stream of Pacific Moisture. Stout westerly flow
overtop of the southern Rockies has induced rather strong pressure
falls over the TX/OK Panhandles this morning and will continue to
do so through the afternoon. This has tightened the pressure
gradient across the region, increasing the wind speeds to between
15-20 mph with gusts approaching 30 mph. The winds will gradually
veer to become out of the southwest by the late afternoon as the
surface low pulls eastward. This will deflect the more sub-tropical
air east, however, a noticeably more humid airmass will advect into
the region over the next 12 hours. The wind speeds should remain
gusty through the early evening hours as the boundary layer
struggles to decouple completely.

A prefrontal dryline feature should move through North and Central
Texas tomorrow morning, further veering the winds to become out
of the west by around noon. A deepening trough over the western
CONUS will kick out the parent surface low and drive its attendant
cold front south tomorrow afternoon. The current timing of the
front looks to be around noon for the Red River counties, around
3 PM for the Metroplex, and around 6/7 PM for Waco/Killeen. Areas
across Central Texas can expect a rather warm day tomorrow with
compressional warming and dry westerly flow helping to warm
temperatures roughly 15-20 degrees above climatology.

Frontal passage will bring a sharp drop in temperatures and gusty
winds out of the north. A dry pre frontal boundary layer will
prevent the development of precip along/behind the leading edge of
the front despite strong forced ascent. This will begin to change
as another wave of mid level pacific moisture advects into the
area behind the front late tomorrow afternoon. This will allow for
widespread mid level cloudiness and virga to develop west of
I-35, creating top-down moistening of the column. The virga will
gradually moisten the lower levels with measurable precipitation
eventually reaching the ground by the early evening hours. This
precip is expected to gradually overspread across the entire
region overnight. Additional details regarding the evolution of
the precipitation tomorrow night and Tuesday can be read in the
Long Term portion of the forecast.

Bonnette


&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    60  71  37  43  31 /   0  10  90  70   5
Waco                59  81  38  43  29 /   0   5  90  90  10
Paris               57  67  36  42  28 /   0  20  90  70   5
Denton              59  68  35  45  27 /   0  20  80  50   5
McKinney            58  69  35  43  27 /   0  10  90  70   5
Dallas              60  72  37  45  32 /   0  10  90  70   5
Terrell             60  75  37  45  28 /   0   5  90  90   5
Corsicana           60  78  39  42  31 /   0   5  90  90  10
Temple              59  82  40  43  30 /   0   0  80  90   5
Mineral Wells       56  69  33  43  26 /   0  20  90  50   5

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

79


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