388 
FXUS64 KFWD 271228 CCA 
AFDFWD

Area Forecast Discussion...CORRECTED
National Weather Service Fort Worth TX
628 AM CST Wed Feb 27 2019


.AVIATION...
/12z TAFs/

Certainly a pretty nasty morning for flying with widespread LIFR
and even VLIFR conditions across the North and Central Texas
terminals. The current thinking is that we'll hold on to the very
poor vsbys and cigs through the mid-morning hours, after which
point some gradual improvements should take place. Anticipate that
the Metroplex sites will remain essentially IFR into the afternoon
before an arctic boundary slides through during the 20-22z
timeframe. A modest northeast windshift may occur towards 19z, but
the winds will begin to pick up more noticeably after 21z as the
frontal inversion starts to deepen. Most guidance supports low-
MVFR cigs in the post-frontal airmass, but a period of -DZ BR may
materialize after 28/04z as the saturated depth increases a bit
and winds increase out of the southwest above 2 kft. While winds
will turn pretty sharply from the north at the surface to the west
or southwest aloft, the potential for LLWS may be tempered by
generally modest 25-30 kt winds aloft and the directional change
occurring above about 3 kft. Expect breezy north winds to persist
through much of the TAF period, although some abatement will occur
in the DFW extended. 

Regarding any wintry weather potential across the Metroplex TAF
sites: the latest indications are that the surface freezing line 
may encroach upon the Metroplex very late tonight, likely after 
4-5 AM. The latest thinking, however, is that air temperatures 
will remain right around 33-36 through the immediate Metro, 
precluding any notable impacts from light drizzle. However, if 
this freezing line makes a stronger push southward, then a brief 
period of -FZDZ could be possible between about 28/10z-28/15z or 
so before temperatures warm above 32 F. The primary sites we'd be 
concerned about would be AFW and perhaps DFW-DAL. We'll keep a 
close eye on observation and model trends today for this 
potential. 

Waco stands a bit of a better chance of breaking out to MVFR or
even VFR briefly this afternoon as 925 mb flow begins to veer. Any
reprieve will be short-lived, however, as the aformentioned front
surges through sometime around 28/00z. The multi-model consensus
at this point indicates the frontal inversion will have deepened 
to about 1200 feet or more by the time it arrives in Waco, so will
refrain from mentioning IFR at this time. 

Carlaw

&&


.SHORT TERM... /Issued 346 AM CST Wed Feb 27 2019/
/Today through Thursday/

Quite the weather potpourri in the short term portion of the
forecast with numerous forecast challenges and subtle features to
pay attention to, including an increasing threat for winter
weather impacts north and west of the Metroplex. The main issues
are as follows:

/1/ Areal and temporal extent of dense fog/drizzle this morning
/2/ Timing a sharp arctic front into the forecast area with a 
large north-south temperature gradient anticipated today 
/3/ Potential for re-development of drizzle this evening and
overnight with sub-freezing temperatures and an associated threat
for freezing drizzle near the Red River.

Baroclinicity is the word of the night here across the Southern 
Great Plains in association with a remarkable arctic cold front. 3
AM surface analysis places the leading edge of this feature from
near a Vernon, TX to Pauls Valley and Tulsa, OK line. Temperatures
fall sharply from the mid 50s to the south and east of this line
into the upper 20s and lower 30s to the north and west. Single
digit readings are commonplace across parts of southwestern
Kansas. The 00z Norman, Oklahoma upper-air sounding revealed the 
hallmark feature of an arctic front with an exceptionally shallow 
frontal inversion just 600-700 feet off the deck. This boundary 
will play a key role in our forecast today for high temperatures, 
and tonight for a wintry precipitation potential. More on this in 
a bit. 

/1/ First, widespread fog and drizzle is ongoing early this 
morning across pretty much all of North and Central Texas as 
moisture is being squeezed out in the lowest 1500 feet or so. A 
Dense Fog Advisory remains in effect for most of the CWA through 
10 AM and the current configuration looks good. Latest guidance 
suggests we may need to extend eastern portions of the advisory 
potentially through noon, but this will be addressed a bit later 
this morning.

/2/ Once this fog lifts, most of the forecast area will remain
shrouded in low clouds into the afternoon hours. The one exception
may be locales roughly south of I-20 and also west of US-281 where
veering flow may allow drier air to scour out the pesky stratus
for a time. The aformentioned cold front is expected to begin a
more concerted southward push this morning, perhaps aided by a
passing mid-level perturbation across Oklahoma. It seems pretty
unlikely that diurnal mixing will be able to chew away at the 
widespread stratus today, giving this feature the go-ahead to 
move a bit quicker than we'd typically expect during the daylight 
hours. We've essentially tossed out all of the stronger-mixing 
guidance from the temperature, dewpoint, and wind forecast for 
today, instead relying on a mixture of the NAM, HREF, and SREF for
hourly trends. This results in the boundary sagging south of the 
Red River through the mid-late morning, into the Metroplex in the 
3-6 PM timeframe, and through our Central Texas counties before 
midnight. As a result, temperatures will fall through the day into
the 30s and 40s across our northwest, while highs in the upper 
70s will be possible in parts of Central Texas. 

/3/ The main concern is this evening and overnight as the 
potential for some wintry precipitation seems to be increasing for
parts of the region. The old adage "The trend is your 
friend...until it ends" seems applicable here, as the last five 
runs of the SREF have consistently indicated colder surface 
temperatures behind the front. With this evening's HREF and TT-WRF
guidance supporting the latest iterations of the SREF/NAM, we've 
dragged some upper 20 degree readings into our far northwest after
midnight, with the freeze line laying up somewhere near to just 
west and north of the Metroplex before daybreak on Thursday.

This normally wouldn't be much of an issue, but coarse and hi-
resolution guidance alike indicates a marked increase in the 
900-800 mb flow this evening, possibly in response to a passing 
jet streak. This southwesterly/westerly flow will overtop the 
shallow and cold arctic boundary, and could result in the 
development of drizzle with the saturated layer sufficiently deep 
up to about 3500-4000 feet. While any QPF in the sub-freezing 
airmass is expected to remain light, freezing drizzle (as opposed 
to freezing rain) can be a problem since ice-to-liquid ratios are
actually maximized for light precipitation rates. Combine this 
with almost ideal wetbulb temperatures around 27-29 degrees F, a 
northerly breeze around 10-15 mph and persistent cold advection, 
there is some concern for a light icing potential for locales 
north and west of an Eastland to Weatherford to Denton to Bonham 
line with the main window of concern roughly during the 3-10 AM 
timeframe. If you believe some of the most aggressive guidance, 
some outlying locales in northwest and western Tarrant county may 
flirt with the 30-31 degree mark as well. Again, amounts would 
only be a few hundredths of an inch, but this is enough to 
potentially cause problems on elevated surfaces, even with 
antecedent warm road temperatures given the breezy north winds 
behind the front. 

With that laid out, our confidence in winter-related impacts 
wasn't quite high enough to warrant the issuance of a Winter
Weather Advisory for our north and west counties, but this is
something we may need to consider later today as trends in the
cold front's progression and post-frontal upglide are elucidated. 

The rest of Thursday looks cold and dreary. With the moist-layer
still some 2000+ feet thick, any hope of mixing low stratus out
seems far-fetched, and we'll side once again with the coldest
guidance and indicate highs in the 40s north and low 50s south. 

Carlaw

&&

.LONG TERM... /Issued 346 AM CST Wed Feb 27 2019/
/Thursday Night into Next Week/

Several challenges remain with the extended forecast period,
including high temperatures on Friday, timing of a strong cold
front Saturday into Saturday night, and any potential winter
weather thereafter.

Initially on Thursday evening, North and Central Texas should be
solidly under the influence of a very shallow, cold surface air
mass, following prior intrusion of a front that currently sits 
just to our northwest. Despite the passage of at least one 
shortwave trough late Thursday into Friday, any surface mass 
response may be significantly muted by the stable, dense nature of
this cold air. In turn, continued to trend Friday's highs colder 
generally along/east of the US-281 corridor, especially given 
potential for persistent warm advection aloft to maintain low 
clouds and some areas of drizzle. Where winds are able to veer to 
the south/southwest and deeper mixing can occur, temperatures 
could rise dramatically into the upper 60s and 70s. A large 
gradient will likely exist to the west of I-35 so further 
refinements to the temperature forecast should be expected.

Forecast uncertainty increases even more by Saturday, as
significant timing differences exist regarding the passage of the
second, long-advertised cold front. The 00Z GFS is quicker in 
pushing this front southward across North and Central Texas
through the day, while the 00Z ECMWF is much slower, delaying the
frontal passage until primarily Saturday night. The 00Z Canadian
meanwhile pushes the front into North Texas Saturday morning, but
then stalls it in a manner similar to the ECMWF, before again 
moving it south overnight. Analysis of large-scale fields in 
medium-range guidance suggests these timing differences are 
sensitive to the evolution and progression of an upstream 
mid/upper jet streak and related vorticity maximum crossing the 
Desert Southwest through Saturday. The ECMWF/Canadian solutions 
display a more robust system, which induces a stronger mass 
response along the low-level baroclinic zone Saturday. In turn, 
strengthening southerly flow ahead of the system delays the 
southward push of this cold air mass until late Saturday into the 
overnight hours, once surface cyclogenesis occurs near the 
Arklatex and points northeast.

The ECMWF/Canadian evolution described above seems within reason,
but large uncertainty still exists in exactly where the 
baroclinic boundary initially establishes prior to the influence 
of the upstream impulse. As such, did not try to lean too heavily 
one way or another with temperatures Saturday, showing 60s in 
Central Texas and 40s/50s near the Red River, along with a 
standard diurnal curve. This curve will need to be cast aside like
a dirty towel if the GFS solution verifies, though.

As for precipitation chances, spatiotemporal details are still
questionable, given uncertainty with timing of the front and
subsequent development along its leading edge. Additionally, the
zone of maximized warm-air advection aloft remains vague due to
questions regarding the positioning of the baroclinic zone. 
Regardless, precipitation chances will be on the increase Saturday
into early Sunday across the region. 

Most of this precipitation is expected to fall as rain, but
temperatures across the Rolling Plains and Red River are currently
forecast to fall below freezing overnight Saturday. If sufficient
precipitation can linger behind the low-level cyclone into Sunday
morning, some mixture of rain, freezing rain, and sleet will be 
possible. However, the delayed nature of the front and lack of a 
more amplified mid/upper system suggest that most isentropic and
mid-level frontogenetic ascent will be focused ahead of the 
cyclone, yielding primarily downglide once temperatures are cold 
enough to support freezing/frozen precipitation. Therefore, the 
winter-weather potential still seems marginal at this time 
considering that most deep precipitation processes could end prior
to enough surface cooling. However, large uncertainty in the 
expected evolution of this system warrants maintaining some
freezing rain/sleet mention across northern/western areas.

Taper PoPs to 20s everywhere Sunday night, although this could be
overdone. Still, any passing weak/sheared impulses may be
sufficient for a band of light rain or snow. Would expect any such
amounts to be light. The same could be said for any systems early
next week, but low predictability/potential in this cyclonic flow
regime and the dry nature of the antecedent air mass preclude PoPs
Monday and onward. With that said, there is high confidence in 
cold conditions, and most folks will likely wake to temperatures 
in the 20s (and perhaps teens!) Monday morning. For March 4th, 
these temperatures will be upwards of 20 degrees below normal. 
Expect only a slow modification of this air mass through mid-week,
with a continuation of cold/cool conditions.

Picca

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    63  34  47  38  60 /  10  30  30   5  10 
Waco                71  38  52  42  63 /  10  20  30  10  10 
Paris               59  33  47  38  54 /  20  30  30  10  10 
Denton              62  32  47  34  58 /  20  30  30   5  10 
McKinney            61  33  46  35  58 /  20  30  30   5  10 
Dallas              65  35  48  41  60 /  20  30  30   5  10 
Terrell             65  35  47  40  60 /  20  30  30  10  10 
Corsicana           66  37  49  42  60 /  20  20  30  10  10 
Temple              76  40  54  43  67 /   5  20  30  10  10 
Mineral Wells       65  32  48  36  64 /  10  30  20   5  10 

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST this morning for TXZ091>095-
101>107-116>123-130>135-143>148-156>162-174-175.

&&

$$

90/11