NWS Area Forecast Discussion

FXUS64 KFWD 182346

Area Forecast Discussion
National Weather Service Fort Worth TX
546 PM CST Mon Feb 18 2019

/00Z TAFS/

Widespread high cloud cover continues to stream in from the
southwest across much of Texas this evening. All of this is ahead
of a strong storm system that will dig into the southwest U.S. on
Tuesday. VFR conditions prevail areawide at this time but a rapid
deterioration is expected early Tuesday morning that will persist
through the end of the current TAF period. As the upper trough
gets closer later tonight, strong southerly winds above the
shallow cold airmass will transport rich Gulf moisture northward.
We should see a rapid lowering of ceilings to around 2000 ft by
sunrise with additional lowering into IFR category and areas of
rain developing through the early morning. Rain will continue into
the afternoon hours with the threat for heaviest rainfall in the
late morning to early afternoon timeframe. We`ll have a TEMPO for
2SM +RA during this time. Otherwise, the bulk of the heaviest
precipitation will move east by late afternoon, although light
northerly winds and ample moisture will result in areas of -DZ
with continued IFR cigs. Some improvement can be expected late
overnight into Wednesday morning.



.SHORT TERM... /Issued 311 PM CST Mon Feb 18 2019/

Under the influence of 100+ kt southwesterly 250mb flow, thick
upper-level cloud cover will continue to stream across much of
the region through tonight. Our 12Z observed sounding and
forecast soundings illustrate a considerably deep layer of dry air
from the surface to the mid levels that should persist through
early tonight. However, an approaching shortwave trough over the
Desert Southwest will induce intensifying isentropic ascent and
moistening across Central Texas after 06Z and North Texas after
approximately 09Z. The end result will be a rapidly lowering cloud
deck across the region, while rain chances also increase from
south to north. Initially, saturation may be too shallow for
anything more than drizzle. However, deepening saturation towards
daybreak should promote an expansion of heavier drizzle and light
rain showers, especially across Central Texas.

Temperatures will remain cool/cold, owing to initial wet-bulb
cooling and continued light east/northeast flow at the surface.
Low temps will range from the lower 30s across the Rolling Plains
to the lower 40s near the Brazos Valley. At least prior to 12Z, no
freezing precipitation is expected across our northwest counties,
given residual dry profiles to the north of the strongest low-
level ascent.



.LONG TERM... /Issued 311 PM CST Mon Feb 18 2019/
/Tuesday through Sunday/

A dreary and gloomy Tuesday is anticipated for much of North and
Central Texas with cold conditions and very good precipitation
chances. Some of that precipitation may fall in the form of light
freezing rain across the Big Country and along the Red River.
Impacts at this time are expected to be very low. A brief warm up
is expected on Wednesday, with rain and thunderstorm chances
returning to the area Thursday and into the first half of the

The first order of business is to address the winter weather
potential on Tuesday morning. It should be stressed that
significant impacts due to any accumulation of ice are NOT
expected at this time as near-surface temperatures will be quite
marginal for ice accretion. A shield of light rain should have
expanded northward from the overnight hours into early Tuesday as
isentropic ascent and richer theta-e air overspread the area.
Locations along the Red River should have fallen down to near 32
degrees preceding this precipitation. As precipitation falls into
a slightly drier airmass, evaporative cooling should be enough to
allow temperatures to tumble to or just below 32 degrees. With
850mb temperatures in the 3 to 5 Celsius range, there will be
about a 2-4 hour window for light freezing rain. Significant
impacts are NOT expected due to 1) the brief nature of the light
freezing rain, 2) due to the latent heat release associated with
freezing/transfer of slightly warmer air aloft down to the surface
via raindrops and 3) the lack of reinforcing colder air at the
surface. That being said, I cannot completely rule out some very
minor icing on elevated and exposed surfaces (trees, powerlines
and cars).

By the noontime hour on Tuesday, I expect that any winter
precipitation will be confined to areas north of the Red River.
Tuesday could really be summed up with one phrase---it will be
gross outside. Guidance is in very good agreement regarding rain
chances and I have painted 90-100% PoPs across most of the areas.
With temperatures in the 30s and low 40s, it will feel quite cold,
especially with period of light to moderate rain. Mid-level lapse
rates do steepen some nearly 70 meter height falls graze North
and Central Texas and as such I`ll advertise some isolated
thunderstorms. Severe weather is NOT expected given the very
marginal instability profiles. Brief periods of heavy rain may
result in some rises on area small streams, creeks and a few of
the faster responding rivers. Some minor flooding will be
possible, but overall parameters for substantial flooding across
the FA appear underwhelming. Rain and isolated thunderstorm
chances will dwindle very quickly during the overnight hours from
west to east as much drier air invades from the Big Country in the
wake of a Pacific front.

Wednesday will be much more pleasant temperature-wise as breezy
west to northwest winds are anticipated. High temperatures should
climb into the upper 50s to low 60s as downsloping should support
near to just above normal temperatures. There may be some
lingering mid/upper level clouds and if this cloud cover is a
little denser than currently anticipated, this may temper
afternoon highs some. It should remain rain-free Wednesday through
early Thursday. Surface to 850mb flow should turn back towards
the east and southeast which will allow for some return flow.
Depending on how far south Wednesday`s front scours out the low
level moisture will ultimately dictate when the chances for light
rain re-enter the forecast. The latest ECMWF remains the
aggressor and pulls moisture necessary for precipitation very
quickly back to the north. This seems a bit overdone and I`ll side
with the slightly slower/drier GFS. For the official forecast,
I`ll advertise low PoPs across Central Texas (particularly across
the Brazos Valley) just after daybreak Thursday. Rain chances will
spread back northwestward over the remainder of the area through
the afternoon hours on Thursday. A rumble of thunder or two cannot
be ruled out, especially across East Texas. Severe weather is
unlikely during this time.

The risk for showers and thunderstorms will persist Friday and
into the first half of the weekend as the southerly moist regime
persists. The cloud cover and rain chances should keep
temperatures generally near seasonal averages. Strong WAA is
expected to offset the cloud cover and rain on Saturday, however,
as a very potent upper trough is projected to eject eastward out
of the Pacific southwest. Deterministic GFS and ECMWF remain at
odds with the ECMWF being a bit less amplified/quicker with the
placement of the upper low. What is known is that a pretty potent
storm system will likely move into the Southern Plains next
weekend which could mean a round of strong thunderstorms. Another
known is that models tend to struggle with these digging systems
and are oftentimes too quick to lift the feature. With the current GFS
offering the solution that fits this conceptual model and due to
it exhibiting better overall run-to-run consistency, I`ll side
with this solution. This may mean a higher coverage of
thunderstorms across North and Central Texas. Current values of
shear and instability do indicate that there will be a threat for
organized convective modes, especially across East Texas and this
will be something to monitor over the next several days.



Dallas-Ft. Worth    35  39  36  62  38 /  20  90  20   0   5
Waco                38  41  36  64  37 /  30  90  30   0   5
Paris               34  37  37  58  35 /  10 100  50   0   5
Denton              34  36  34  60  35 /  10  90  20   0   5
McKinney            34  36  35  59  35 /  20 100  30   0   5
Dallas              37  40  36  62  39 /  20  90  30   0   5
Terrell             36  40  36  61  36 /  20 100  40   0   5
Corsicana           39  42  36  63  38 /  30 100  40   0  10
Temple              39  43  36  64  38 /  40  90  30   0  10
Mineral Wells       32  37  33  60  36 /  20  90  20   0   5




NWS FWD Office Area Forecast Discussion