549 
FXUS64 KFWD 061004
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
404 AM CST Tue Feb 6 2018


.SHORT TERM...
/Today and Tonight/

While there are a plethora of concerns through the first 24 hours
of the forecast, the primary challenge is the potential for some
wintry weather across our north/northwest zones this afternoon and
evening and the associated temperature forecast. As a result, a 
small Winter Weather Advisory has been issued for a few of our 
north and northwest counties, as discussed below. Lesser, but 
noteworthy concerns consist of the potential for some strong or 
borderline severe storms (hail threat) this afternoon across the 
eastern half of the forecast area and a chance for some locally 
heavy rain. 

First, the temperatures:
A reinforcing cold front is making southward progress through
Oklahoma and parts of North Texas this morning. Temperatures are
falling primarily into the low to mid 20s in its wake. To the
south, widespread low clouds with patchy fog and drizzle currently
reside across much of Central Texas. This cloud bank should expand
northward through the morning hours as isentropic ascent increases
above the shallow arctic airmass. The challenge today lies
primarily with the surface temperature forecast as this will
determine whether (or where) precipitation falls as rain or
freezing rain (snow is out of the question and sleet is also quite
unlikely). At the moment, the concern lies with areas roughly
north of a Graham to Sherman line where temperatures could hold in
the mid to upper 20s through most of the day. If light
rain/drizzle occurs is this environment, it will be more than
capable of freezing upon contact and causing issues on sidewalks
and some roadways. Unfortunately, one can find a model that shows
surface temperatures anywhere between 20 and 40 degrees during
this time, so plenty of uncertainty remains. Given what should be
ample cloud cover and strong cold advection fueled by northerly
winds at 10-20 mph, the colder side of guidance makes sense here
which would suggest temperatures around 28-31 degrees within our
area of concern through the afternoon and evening. There are a
couple factors working in our favor in terms of preventing
widespread freezing rain issues. The first is the fact that rain
will be falling from a cloud layer that is nearly +13C (about 55F)
and substantial energy will need to be spent to cool these drops
to freezing at the surface. In addition, latent heat release from
any freezing that may occur could help to nudge the temperatures
up a degree or two once precipitation would begin freezing. How
these factors will hold up against any wet-bulbing remains to be
seen. If surface temperatures can stay closer to 31-32F,
significantly fewer impacts can be expected versus 28-29F. We'll
have to keep a close eye on temperature trends both inside and 
outside of the Advisory throughout the day and potentially 
expand/shift the counties included.

Next, the lift and lapse rates:
Plenty of isentropic ascent will occur above the shallow arctic
airmass in place ahead of an approaching shortwave trough. While
dynamic lift from the shortwave itself isn't terribly strong, this
overrunning combined with steepening mid-level lapse rates of 7-8
C/km will be perfectly capable of supporting precipitation really
at any location across the forecast area today. As lapse rates
steepen with the approaching shortwave, there will actually be
1000-1500 J/kg of MUCAPE available rooted around 800-850mb, with
the highest values the farther south and east your location. As a
result, thunderstorms will certainly be possible despite surface
temperatures in the 30s and low 40s area-wide. With decent
instability and 40-50 kts of shear through the lowest 6 km, some
hail (no, not sleet) will be possible which could approach severe
limits if stronger storms are able to get going. In terms of other
storm threats, the tornado threat is 0 with the wind threat not
much higher since storms will not be surface based whatsoever.
There will be the potential for some fairly heavy rain however,
and it's possible some of our far eastern areas could pick up 1-2"
by the time precipitation ends tonight. Where temperatures are
below freezing, some brief thunder-freezing rain can't be ruled
out either with many high-res models suggesting some convective
elements could be present even west of I-35.

Finally, the timing:
Light precipitation will be capable of beginning across parts of
North Texas by late morning or early afternoon, but the primary
concern for potential light freezing rain will begin around
mid/late afternoon into the evening. Numerous showers and
thunderstorms should also be developing throughout the afternoon
time period especially along and east of I-35. Locally heavy rain
and a marginal hail threat will begin as early as mid afternoon
and linger into the evening hours. This will all occur with
surface temperatures in the 30s or low 40s for most of the
forecast area. Precipitation should be quickly exiting to the
southeast between midnight and 6am. While we should remain socked
in with low clouds through the overnight hours, continued cold
advection should still allow temperatures to fall into the 20s 
and low 30s area- wide. Any lingering moisture on roads or 
sidewalks with have the potential to freeze overnight. 

-Stalley

&&


.AVIATION... /Issued 1154 PM CST Mon Feb 5 2018/
The westward extent of the MVFR ceilings extended just east of a 
KLZZ-KINJ-KDAL-KF00 line as of 05z. Expect the stratus spread 
back across the rest of the TAF sites 09-10z. Expect lower end 
MVFR for most of the day but some IFR conditions are possible 
during the afternoon. As an upper level disturbance approaches, 
scattered showers and thunderstorms are expected to develop by 21z
Tuesday. The precipitation should end at the Metroplex TAF sites 
after 03z...which should be before temperatures fall below
freezing.


A cold front is expected to move through the Metroplex by 22z
Tuesday and through Waco around 01z. Northeast winds around 5 
knots at TAF issuance time will become northerly at 10 to 15 knots
with the frontal passage. 

58

&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    37  30  45  31  55 /  70  80   5   0   5 
Waco                43  33  44  31  56 /  80  70  20  10  10 
Paris               41  29  45  30  53 /  80  90   0   0   0 
Denton              36  26  46  26  56 /  60  70   5   0   0 
McKinney            39  28  44  26  53 /  70  80   5   0   5 
Dallas              39  30  45  32  55 /  70  80   5   0   5 
Terrell             44  31  44  30  55 /  80  90   5   5   5 
Corsicana           46  32  43  32  54 /  90  90  20  10  10 
Temple              44  32  44  33  56 /  70  60  40  10  10 
Mineral Wells       35  26  47  27  57 /  40  50   5   0   0 

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 PM this afternoon to midnight CST 
tonight for TXZ091>093-101-102.

&&

$$

26/82