774 
FXUS64 KFWD 022236
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
436 PM CST Wed Jan 2 2019


.DISCUSSION...

...Winter Weather Event Rundown...
The main concern with the forecast package is the potential for 
continuing winter weather across the Big Country and parts of 
North Texas. Light freezing rain and/or freezing drizzle will
continue tonight mainly near and west of the US HWY 281 corridor.
A gradual transition to a sleet/snow mix is anticipated early
Thursday, mainly west of US HWY 81 and north of US HWY 380 towards
sunrise Thursday. Some of this snow may be heavy, with snowfall
totals in the 3" to 5" range and thus a Winter Storm Warning has 
been issued for Young, Jack and Montague counties from much of 
Thursday and into early Friday. 

For areas northwest of a Comanche to Denton to Sherman/Denison
line...snowfall amounts will average between 1" and 3". South of
this line, a dusting of snow/sleet will be possible. All winter 
weather should come to an end by early Friday.


...Impacts... 
The greatest impacts to travel will be for areas 
generally north of US HWY 380 and west of US HWY 81. Winter 
weather may result in snow covered roads resulting in slick and 
hazardous conditions. Travel will be hampered significantly across
this area, if not impossible. For areas north of I-20 and west of
the I-35/35W corridor (not including the heart of the D/FW 
Metroplex), slick road conditions are possible, especially on 
elevated surfaces. Areas southeast of a Comanche to Denton to 
Sherman/Denison line should only see very minor impacts with 
perhaps a few slick bridges and overpasses.

In addition to winter weather, pockets of flooding are likely to 
continue this afternoon and into the evening hours. While rain 
rates have remained below 1"/hr, the very cold soils and dormant 
vegetation have proven to result in efficient runoff rates and 
we've already fielded reports of road closures of mainly secondary
and tertiary thoroughfares. It's probable that additional flood 
issues will occur through the night.

...Forecast Uncertainty...
The forecast hinges on the track of the upper low to the west as
well as surface temperatures. At this time, confidence in the
track of the upper low is moderate given the decent model
agreement. Confidence in the temperature forecast is OK, but will
be something to monitor. If the tropospheric column is cooler or
warmer, some alterations to the snow/ice accumulation forecast
will need to be made. There also remains a risk for slightly more
convective elements which could help to bolster snow/ice amounts.
At this time, feel that there is a decent chance for some of these
elements across the Winter Storm Warning. If these elements are
more expansive in areal coverage, there could be some heftier
snowfall amounts outside of the Winter Storm Warning area. 

...Meteorological Reasoning...
A very challenging forecast from a meteorological standpoint
exists across North Texas. A very potent upper low continues to 
churn and nose eastward into the Pacific southwest. Slight 
warming has commenced across much of the area as northerly winds
have weakened, shutting down the CAA. With sunset, temperatures
will likely hold steady or even fall slightly and it's probable
that there won't be much in the way of change temperature-wise 
tonight. The exception would be for locations that experience 
heavier bursts of frozen precipitation which may help to cool the
column some.

For tonight, the strong isentropic ascent that resulted in the
large rain shield should subside across East and Central Texas
resulting in it shrinking in areal coverage across our area. I've
lowered PoPs some after midnight across East and Central Texas. 
During the overnight hours, the highest PoPs were confined to 
areas west of I-35 as isentropic ascent ramps up quickly. 
Steepening 700-500mb lapse rates ahead of the very deep PV anomaly
(1.5 PVU surface down to 590mb) should foster some convective 
elements. The presence of convection would be two-fold for
sensible weather...1) quick accumulations of winter precipitation
(provided that it is cold enough) and 2) further cooling of the 
column. At this time, it appears that this potential is greatest 
west of the US HWY 281 corridor. For now, I'll advertise freezing 
rain until just after midnight, with a transition to snow/sleet. 
If the convection is very deep (produces lightning), this 
transition may occur a little sooner than advertised in the 
forecast. Farther east of this line, it appears that temperatures 
will be high enough such that only a cold rain falls, though we 
will need to watch areas just east of the Sherman/Denison area for
any lingering freezing drizzle/light freezing rain. 

As we near daybreak Thursday, it appears that the rain/freezing 
rain and snow/sleet line will inch closer to the HWY 281 
corridor. Forecast soundings show a decent isothermal layer just
above 0 C around ABI...SEP and SPS. This coupled with decent 
omega (likely due to strong low-mid level frontogenesis) in the 
dendritic growth zone should favor some heavy snowfall. It's 
possible that if NAM FGEN progs are to verify, a band of heavy 
snow may extend to the south of the current Winter Storm Warning. 
Some of the HREF members support heavier snowfall south of I-20
with snowfall output showing a potential for 2-5". For now, we 
are comfortable with letting the Winter Weather Advisory handle 
areas outside of the Winter Storm Warning, but we will need to
monitor this closely for travel along I-20. 

Towards noon on Thursday, the upper low should scoot eastward, 
cooling the column sufficiently such that a rain/snow mix is the 
most likely p-type for a good portion of North Texas. Heavy snow 
is still expected for areas along northwestern North Texas and 
northern Big Country, but things should start to wind down here. 
Closer towards the I-35 corridor, there could be some accumulating
snows, mainly north of HWY 380. South of this line, a dusting of 
snow will be possible, mainly on grassy surfaces and elevated 
surfaces. Once we get towards Thursday evening and into midnight 
Friday, lingering wrap around precipitation may persist, 
especially along the Red River. Additional accumulation will be 
possible here, but for now I'll keep new snowfall amounts around 
1/2". 

For the remainder of the forecast, generally above normal warmth
is anticipated as northwest flow should promote some downsloping.
The exception to this will be Friday as lingering snowpack and the
dense cold airmass both remain in place. This weekend and into 
early next week should be nice. The next chance for rain will be 
next week, though limited moisture should preclude any flood 
concerns. Temperatures above normal should also preclude any 
threat for winter weather as it stands right now.

Bain

&&


.AVIATION... /Issued 1219 PM CST Wed Jan 2 2019/
/18z TAFs/

Widespread forcing for ascent continues across most of North
Texas, well ahead of the primary upper level storm system over the
Southwest U.S. A fairly large shield of light to moderate rain
will continue to drift eastward across the region this afternoon,
affecting all TAFs sites prior to sunset. However, the back edge
of this initial precipitation area should begin to clear the
Metroplex airports in the 23z-02z timeframe, followed by a brief
mostly rain-free window prior to 10z. This timeline will be 
mirrored at Waco, but delayed by approximately an hour. Surface 
temps have now climbed above freezing at all TAF sites, and have 
omitted any FZRA references for today/tonight. 

As the upper low enters West Texas late tonight, lift will 
 and lapse rates aloft will begin to increase. This will lead to 
the development of a new batch of showery precipitation which will
build into the Metroplex TAF sites and Waco in the 10z-12z time 
period. For the most part, lower level temperatures will remain 
sufficiently warm to maintain all rain precipitation types prior 
to 15z Thursday. However, there is a good chance that the column 
will cool enough to produce a rain/snow mixture, or perhaps even a
total changeover to all snow after 18z Thurs. At this point, have
refrained from including any mention of -SN at KDFW after 18z, 
but later forecasts will need to assess this potential closely and
include as necessary. 

Have generally maintained IFR ceiling trends through the period,
though some variability and brief improvement to MVFR is possible
this afternoon and this evening. Visibilities should remain in the
MVFR range through 02z, owing mainly to the continued
light/moderate rain and patchy fog. Should see improvements on
this front after 00-02z, but reductions will reoccur after 10z as
the next round of precipitation moves into the area tomorrow
morning.

The easiest dimension of the forecast will is the winds - they'll
be continuously from the north at speeds averaging 8-12 knots
through tonight and Thursday.  

Bradshaw

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    35  36  33  53  37 /  90  90  40   0   0 
Waco                36  39  32  55  37 /  90  90   5   0   0 
Paris               38  38  34  53  34 /  60  90  80  20   0 
Denton              33  35  30  52  34 /  90  90  40   0   0 
McKinney            34  36  32  52  35 /  90  90  50   5   0 
Dallas              35  37  33  54  37 /  90  90  40   0   0 
Terrell             38  38  34  54  36 /  80  90  40   0   0 
Corsicana           40  40  34  54  37 / 100  90  20   0   0 
Temple              35  41  32  56  37 /  90  80   0   0   0 
Mineral Wells       30  35  28  54  33 /  90  90  20   0   0 

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST Friday for TXZ092-093-102-
103-115>117.

Winter Weather Advisory until noon CST Thursday for TXZ129>132-
141>143.

Winter Storm Warning from 3 AM Thursday to 6 AM CST Friday for 
TXZ091-100-101.

&&

$$

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