494 
FXUS64 KFWD 171207
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
607 AM CST Thu Jan 17 2019


.AVIATION...
/12Z TAFs/

A cold front is currently on the doorstep of the Metroplex, 
having just moved into the KLUD area and should enter the DFW area
in an hour or so. The front will be accompanied by northwest 
winds and another stratus deck. Bases may initially be below FL010
but should fairly quickly rise into the FL010-015 range, so the 
forecasts will simply indicate MVFR conditions coinciding with 
FROPA. The front should reach KACT a few hours later, and will 
similarly be accompanied by the MVFR cloud deck. Cigs will erode 
this afternoon as dry air mixes in from the northwest, with VFR 
conditions expected this afternoon and evening.

The front will stall and eventually return north overnight. There
is a slim possibility that patchy fog may result from the clear
skies and light return flow, but will hold off including any
visibility reductions unless future guidance suggests otherwise.
A few showers will be possible Friday, but mainly after the 18Z
hour.

30

&&


.SHORT TERM... /Issued 355 AM CST Thu Jan 17 2019/
/Today and Tonight/

Low clouds lingering along and east of the Interstate 35 corridor
are gradually shifting east as low level winds veer ahead of a
cold front. The front is currently encroaching on the northwest
corner of the CWA, and should barrel across the I-20 corridor
between sunrise and 8 AM before clearing the southeastern zones by
late morning. The boundary is accompanied by a second batch of 
stratus, so where skies are currently clear, another round of 
overcast conditions can be expected this morning as the front 
pushes through. Clouds will scatter, giving way to mostly sunny
conditions at all locations this afternoon as dry air mixes 
within the boundary layer. Cool air advection behind the front 
will keep high temperatures in the upper 50s along the Red River 
with mainly 60s elsewhere.

The front will stall just southeast of the area before lifting 
quickly back to the north overnight as the next shortwave crosses 
the Rockies and a lee cyclone intensifies. Winds will become light
and variable this evening, with light southeast winds developing 
after midnight. Mostly clear skies and weak return flow sets the
stage for patchy fog development, and have added this to the
grids for the overnight hours. Otherwise, temperatures should
remain above normal with lows ranging from the low 40s along the 
Red River to the low 50s across the far south.

30

&&

.LONG TERM... /Issued 355 AM CST Thu Jan 17 2019/
/Friday Through Wednesday/

Low level warm advection will be ongoing Friday morning with 
breezy south winds expected by 18z Friday. A lead shortwave will 
be lifting east across the Central and Southern High Plains and 
deepen the Eastern Colorado lee-side surface low. Model soundings 
continue to show a warm elevated mixed layer(or capping inversion)
maintaining at least through the early afternoon hours. This 
should mainly result in scattered sprinkles or a few rogue showers
underneath the slow-lifting cap aloft early on in the day.

This lead mid-level shortwave will quickly shunt to the northeast
of North and Central Texas through mid-afternoon. Meanwhile, the 
main mid-level energy will be moving readily through the Southern 
Rockies and moving east over the Texas/Oklahoma Panhandles after 
midday. Better large-scale ascent, pressure advection, and 30-40 
knot southwesterly upglide on the 290-305K theta surfaces increase
quickly late Friday afternoon/evening. There are some 
uncertainties to exactly where the pre-frontal trough sets up 
across the area by 00z Saturday. It appears the main mid-level 
ascent and left-exit region of a 160 knot+ upper jet max will 
coincide somewhere near or just west of I-35 late Friday per the 
GFS/SREF. However, the NAM12 looks to be 3-6 hours faster with 
surface features which could play a big role on where better 
moisture and resultant instability set up before the 
aforementioned upper jet max arrives. 

With the NAM12 being the outlier, I have opted to lean toward the
slower WRF/SREF/GFS solutions on surface features. Regardless, I 
feel the cap will hold relatively strong within the southwest flow
aloft until at least 21z or slightly later, before moistening and
lifting of the cap occur quickly early Friday evening. I have 
adjusted highest convective chances across the northeast counties 
early in the evening, before better scattered storms zipper down 
the surface trough and southward down across our eastern counties.
The arctic cold front should start overtaking the surface trough 
from northwest to southeast quickly by late evening and after. As 
in the previous few nights, I feel the current Marginal Risk from 
SPC looks overall reasonable with any brief 3-6 hour window late 
Friday across areas along/east of I-35/35W. Deep layer westerly 
shear, SBCAPE near a 1000 J/KG across Central Texas, and 
steepening lapse rates to near 7 deg/C certainly validate this 
concern. Main concern is large hail, though where richer surface 
dew point temperatures in the low-mid 60s surge into Central 
Texas, a localized damaging wind threat is certainly possible. Low
level 0-1km shear is strong as well, but relatively veered and 
combined with marginal LCL levels Friday evening, the tornado 
threat will be very low, though not zero across our southeast 
counties. Lastly, it appears the heaviest rainfall in excess of an
inch should be confined across the far eastern counties, where 
some run off and minor flooding is certainly possible Friday 
night. We are not expected widespread flash flooding, however, 
some minor rises on parts of the Sabine and maybe the Trinity 
River Basins are likely. 

Any convective strong-severe threat will come to abrupt end 
across our far eastern and Central Texas counties after midnight, 
as the upper disturbance passes across and drives an arctic front 
quickly through our region before daybreak Saturday morning. High 
temperatures will likely occur at this time, followed by slow-
falling or at best, steady temperatures in the upper 30s and 40s 
on Saturday. In addition, a very strong pressure gradient will 
combine with strong low level cold advection to drive north- 
northwest winds 20-30 mph with gusts at times to between 35-40 
mph. By Saturday afternoon, wind chill values in the 20s north and
30s south will become common. 

Now for what everyone is wanting to know regarding chances for 
wintry weather north of I-20 on Saturday. Some wrap around 
moisture is expected in wake of our departing mid-level 
disturbance and arctic front on Saturday. Sans the European model,
all other models draw in top-drying into the region quickly with 
40-50 knot downglide. As such, I will keep only slight chances for
a brief bout very light snow or snow flurries north of I-20. We 
do not expect snow to be widespread enough to result in any 
accumulations along the immediate Red River Valley due to the 
aforementioned strong downglide and dry air advection by Saturday 
afternoon. 

Brisk north winds and clearing skies will occur Saturday evening 
with wind speeds settling down Sunday morning. The dry and dense 
arctic air will likely result in most areas falling well into the 
20s. As such, wind chill values don't appear as brutal as 
previously thought, but values in teens and lower 20s by sunrise 
Sunday will still make for a frigid morning. I did remain on the 
cold side of guidance Sunday, despite the return of light south 
winds 10 mph or less across the western half of the area by 
afternoon. Despite the plentiful sunshine expected, I have highs 
only creeping into the 40s, which is still not as cold as
previously thought yesterday. You just really never know how 
quickly shallow arctic airmasses modify. 

Sunday night will be brisk and still chilly, as south winds
increase to between 10-15 mph with lows in the 30s. Breezy and 
warmer conditions return for the early work week with highs Monday
warming well back into the mid 50s to lower 60s, before another 
cold front arrives Tuesday with support from yet another strong, 
but progressive mid-level shortwave. Highs will fall back into 
the upper 40s to 50s across Central Texas. Plenty of uncertainty 
regarding moisture in advance of this front and timing of the mid 
level system, so have stayed very conservative with low PoP across
mainly our far eastern counties and Central Texas next week. 

05/

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    61  46  69  38  41 /   0   0  20  50  10 
Waco                65  48  70  40  45 /   0   0  20  40   0 
Paris               60  42  63  38  39 /  10   0  40  70  20 
Denton              60  44  69  36  40 /   0   0  20  40  10 
McKinney            60  44  67  36  39 /   0   0  30  50  10 
Dallas              62  46  68  39  41 /   0   0  20  50  10 
Terrell             63  45  68  38  41 /   5   0  30  60  10 
Corsicana           64  47  67  39  43 /   5   0  30  60   5 
Temple              68  50  70  41  46 /   5   0  20  40   0 
Mineral Wells       61  45  71  35  42 /   0   0  30  30  10 

&&

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

$$

30/05