773 
FXUS64 KFWD 051739
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1139 AM CST Tue Dec 5 2017


.UPDATE...
The brisk winds of change are upon us as last night's strong cold
front continues to plow southward towards the Gulf Coast. Breezy
north winds will persist today, but will gradually diminish later
this evening and overnight as the pressure gradient relaxes.
Interestingly, lower-level cold advection isn't all that
pronounced across the region in the wake of the front, with the
core of the strongest CAA displaced to our north and east. Still,
the stout north winds and dense cloud cover will help hold the
diurnal temperature range in check across our northern and western
counties. Bumped temperatures up a few degrees into the upper 50s
across our Central Texas counties based on latest temperature
trends. We'll leave a very low mention of a shower across the
south and east where weak isentropic upglide will persist. 

This evening and overnight, isentropic upglide focused near 
305-310 K will increase as a disturbance currently dropping 
through the Great Basin approaches the region. As this lift 
encounters moisture above 700 mb, light precipitation is expected 
to develop. Very dry air below this level will create an 
environment conducive for cooling due to diabatic effects as 
initial precipitation evaporates. While temperatures everywhere 
are expected to remain above to well above freezing tonight and 
into Wednesday, wet bulb zero heights are expected to fall to 
under 2 kft or so, and this could support a potential for some 
very light sleet mixing in with rain as far north as the I-20 
corridor based on this morning's model guidance. This mention of 
very light sleet has been added to the forecast after midnight 
tonight west of I-45 and south of a Graham to Rockwall line. We'll
stress again, however, that above-freezing temperatures mean
any impacts from wintry precipitation will remain extremely
minimal. Updated products have been sent. 

Carlaw

&&


.AVIATION... /Issued 600 AM CST Tue Dec 5 2017/
12 UTC TAF Cycle

Concerns---Potential for rain showers at all TAF sites. Potential
for turbulence beneath showers.

Light rain showers will continue at Waco over the next couple of 
hours before dry air overspreads from the north. Farther north at 
the Metroplex TAFs, the threat for showers this morning will be 
low, but non-zero. Mid-level clouds between FL070 and FL120 will 
continue to overspread the area. Northerly winds of around 10 to 
15 knots will continue. There is a risk that wind gusts may 
approach 25 knots later this afternoon. Winds will subside around 
and after 00 UTC Wednesday. Stronger lift will overspread from the
southwest this evening and into early Wednesday increasing rain 
chances. There will be a potential for turbulence beneath rain 
showers at all TAF sites. With better low level moisture across 
Central TX, I've added a mention of VCSH during the mid-evening 
hours with -SHRA from midnight through 12 UTC at Waco. There's a 
potential for -RASN at Waco, but for now, the better risk for this
appears just outside of the 12 UTC TAF cycle. For the Metroplex 
TAF sites, low levels will be slightly drier and warmer and rain 
showers should be more scattered in nature. Showers across D10 
should diminish in areal coverage after 12 UTC for the D/FW 
extended TAF.

24-Bain

&&

.SHORT TERM... /Issued 349 AM CST Tue Dec 5 2017/
/Today and Tonight/

A cold front continues to slice southward through Central and 
East TX as of 3 AM. This feature will likely continue to generate 
showers (though a rumble of thunder or two cannot be completely 
ruled out) across the aformentioned geographical area through at 
least noon today. There could be a few light rain showers or 
sprinkles farther back to the northwest, but widespread rain isn't
expected today near the I-20 corridor. From mid-morning through 
noon, it appears that large scale lift shuts off for much of the 
afternoon hours which only supports a low chance for light rain 
showers across Central and East TX. 

After a day of record warmth for some areas, conditions will be 
noticeably cooler today! Mid-level cloud cover in tandem with 
northerly winds should keep most highs across most areas in the 
50s. A few spots across western and northern zones may only climb 
into the upper 40s for high temperatures.

For tonight, isentropic lift along the 310K theta surface should 
overspread from the west and southwest. While the lift is 
respectable in magnitude, low levels will remain parched, at least
initially. This should mean that much of what falls should be in 
the form of virga early in the evening. As the low levels slowly 
saturate through the late evening and into the nighttime hours, 
the chances for more widespread measurable precipitation 
increases. I've reflected this thinking in the grids and at this 
time it appears as if areas south of I-20 will have the better 
probability of measurable rain. Forecast soundings, particularly 
for locations near and west of highway 281, do suggest that a few 
snowflakes or sleet pellets could mix in with the light rain as 
evaporative effects help to cool the column sufficiently. 
Currently, no impacts are expected due to recent warmth and 
surface temperatures remaining in the mid to upper 30s.

24-Bain

&&

.LONG TERM... /Issued 349 AM CST Tue Dec 5 2017/
/Wednesday through Tuesday/

Wednesday is likely to be the coldest day this week across North 
and Central Texas and could feature some mixed wintry 
precipitation across parts of Central Texas through the afternoon.
The cold front that came through last night will be well south of
the area at the start of the day, but extensive cloud cover will 
be present with temperatures generally in the mid to upper 30s to 
start the day. A broad area of moderate to strong mid level 
isentropic ascent will be ongoing from deep south Texas well into 
North Texas Wednesday morning. This will result in extensive 
northward moisture transport atop the cool air already in place. A
large area of light to moderate precipitation is expected to be 
ongoing or in the process of rapidly developing around 12Z 
Wednesday across much of Central Texas. Precipitation should 
eventually become focused along and east-west oriented band of 
strong 700mb frontogenesis by midday. The coarser resolution 
models have this band set up generally from Lampasas to 
Temple/Killeen and eastward with most of the precipitation 
extending from the Waco area southward into Central Texas. The 
higher resolution guidance is a little farther north with the 
precipitation, however, it is a safe bet that most of the 
precipitation will be focused across our southern counties.

As we go through the day Wednesday, an upstream shortwave will 
dig through the Central Plains amplifying an already large trough 
over all of the eastern CONUS. As it does, a broad area of 
stronger forcing for ascent will spread into Central Texas. This 
area will also be in a favorable quadrant of an 130 kt upper jet 
located across north and northeast Texas. Through the day, thermal
profiles will continue to cool. Initial precipitation during the 
morning hours may initially fall into relatively dry air below 
800mb but this is expected to saturate fairly quickly by mid to 
late morning. Forecast soundings from the Waco area southward 
through Bell county and westward to Lampasas and Mills counties 
become cold enough by midday to support snowfall production with a
deep saturated layer above 900mb. Surface temperatures are 
expected to remain above freezing through the day across the 
entire region, and there are some questions as to how cold the 
lowest 100mb or so above the surface get, but overall it looks 
like a good bet that some areas will see at least a little snow or
sleet mix in with light rain during the day Wednesday. This 
favored area would again be from Goldthwaite to Waco and south to 
Temple/Killeen and Lampasas.

As far as impacts are concerned...temperatures at the surface are
expected to remain in the mid/upper 30s which will support 
melting of any frozen precipitation. At this time, it appears that
no significant impacts would be expected other than some minor 
accumulations on grassy surfaces in the coldest areas. 
Temperatures are expected to remain in the mid/upper 30s across 
our southwest counties on Wednesday and will warm into the 40s and
lower 50s farther north. Areas near the Red River may be the 
warmest, especially if the clouds clear faster than currently 
forecast.

Temperatures Thursday through the upcoming weekend will be near 
or slightly below climatological normals as a large trough remains
in place across much of the central and eastern U.S. Clouds are 
expected to clear Wednesday night and it should remain clear 
through the end of the week.

Dunn

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    55  40  49  35  53 /   5  30  10   0   0 
Waco                59  36  37  33  51 /  40  40  60  30  10 
Paris               50  37  52  33  47 /  10  10   5   0   0 
Denton              52  36  47  32  49 /   5  20   5   0   0 
McKinney            52  36  51  33  50 /   5  20   5   0   0 
Dallas              55  41  51  35  51 /   5  30  10   0   0 
Terrell             54  38  49  34  53 /  10  30  10   5   0 
Corsicana           57  40  40  34  54 /  50  40  40  20   5 
Temple              58  39  39  34  52 /  40  40  80  40  20 
Mineral Wells       51  36  44  30  48 /   5  30  20   5   0 

&&

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

$$

90/82