253 
FXUS64 KFWD 080433
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1033 PM CST Thu Feb 7 2019


.UPDATE...
/Rest of Tonight/
No major changes are needed to tonight's forecast. Cold and breezy
conditions will persist as lows are expected to drop into the 20s
across North and Central Texas. Northerly winds will yield wind 
chill values in the teens by sunrise. Cirrus clouds will continue
to stream across Central Texas through the night. Low level clouds
will creep northward from the Hill Country around sunrise as
additional moisture returns to the region.

Hernandez

&&


.AVIATION... /Issued 623 PM CST Thu Feb 7 2019/
/00Z TAFs/

Post-frontal low clouds have moved off to the south and east of
the region as drier air makes its way from the north. Breezy 
northerly winds will continue through the remainder of the night 
before a gradual veering begins Friday afternoon. Although VFR is 
expected through 00Z Saturday, ceilings will begin a slow 
decreasing trend beginning mid-day Friday as moisture makes a 
return to the area. Upper level southwesterly flow will keep a 
consistent stream of cirrus through the remainder of this cycle. 

Although the extended portion of the KDFW forecast remains dry, we
will continue to monitor the possibility of frozen precipitation 
in the afternoon and evening. Confidence in frozen precipitation
coverage remains low, therefore, will hold off on adding it at
this point. 

Hernandez

&&

.SHORT TERM... /Issued 401 PM CST Thu Feb 7 2019/
/Through Tonight/

Unseasonably rich boundary layer moisture contributed to the
intensity of the thunderstorms accompanying the early morning
frontal passage. Once lifted by the advancing boundary, this
moisture became the postfrontal cloud bank that has been difficult
to erode. Guidance tends to struggle with anomalies of this sort,
but the extent of today's cloud cover was only one of the 
shortcomings. Model output often downplays the intensity of cold 
advection within an arctic air mass, and today was a stark 
example, the warm bias further accentuated by the underestimated 
cloud cover. As a result, our forecast temperatures through the 
evening hours are a handful of degrees below guidance.

With additional dry advection, a deepening postfrontal boundary
layer is steadily losing its low clouds. Sun filtering through an
icy cirrostratus veil has allowed afternoon temperatures to warm 
a few degrees after their midday minimums. But with the falling 
sun angle, the cold advection will soon win out, and temperatures 
will rapidly fall this evening. The high clouds will do little to 
stem the temperature drop, and although dew points will plunge 
into the teens and even single digits, the diminishing but steady 
north winds will prevent Friday morning's low from reaching their 
full radiational cooling potential. Nevertheless, daybreak 
readings will be around 10 degrees below early February normals,
ranging from near 20F in the north and northwest to around
freezing along our southeastern boundary.

25

&&

.LONG TERM... /Issued 401 PM CST Thu Feb 7 2019/
/Friday and Beyond/

The primary concerns in the long-term portion of the forecast will
be the potential for wintry precipitation on Friday and Friday
night, and widespread rainfall Saturday night through Monday 
morning.

A potent shortwave trough, presently off the Baja Coast, will move
quickly along the International Border and into West Texas by 
late Friday. Increasing large-scale ascent in the form of an 
upper-level potential vorticity anomaly will lead to increasing 
cloud cover from southwest to northeast across Central and North 
Texas. While the sub-cloud layer will be dry initially, profiles 
will moisten throughout the day as isentropic ascent transports 
Pacific moisture into the region. These moistening profiles 
concurrent with aforementioned synoptic-scale ascent will lead to 
the development of patchy areas of light precipitation by Friday 
afternoon, initially over the Hill Country, and spreading 
northeast into the evening hours. One of the bigger challenges 
with Friday's forecast was high temperatures. Model guidance has 
struggled with today's (Thursday's) temperatures behind the strong
arctic cold front that passed this morning, with most guidance 
being some 5-10 degrees too warm. Following morning lows in the 
20s across most of the county warning area (CWA) Friday morning, 
temperatures will likely only climb into the upper 30s (perhaps 
the very low 40s) for most areas as modest cold air advection 
continues in the form of northeast winds at around 10 knots. 
Increasing cloud cover will also limit the amount of heating from 
insolation, though this cloud cover will likely arrive later in 
the day for areas north of Interstate 20. Should cloud cover move 
farther north faster than anticipated, the forecast highs for 
Friday could be too high (the official forecast lows are already a
little below guidance).

The precipitation type forecast for Friday is also tricky. NAM
forecast soundings reveal that in the morning, high cloud bases at
around 16,000 feet will be present above a deep and dry sub- 
cloud layer. This will result in most hydrometeors evaporating or
sublimating before reaching the ground. As profiles moisten late 
in the day however, precipitation should be able to reach the 
ground. Two precipitation regimes are expected to be present 
across our CWA. (1) Over roughly the northern half of our CWA 
(including the Dallas/Fort Worth Metropolitan Area), profiles 
should be saturated from about 2,000 feet AGL to above the 
dendritic growth zone (the layer where temperatures are in the 
range of -10 C to -20 C, wherein conditions are most favorable 
for ice crystal formation). This means any precipitation would 
fall as snow. A slight warm nose is forecast to exist at around 
800 mb, so some sleet pellets may occur as well. (2) Over the 
southern half of our CWA (including Waco, Killeen, Temple, and 
Palestine), a saturated dendritic growth zone should be present, 
but a significant warm nose should develop and sharpen with time 
at around 700 mb. This means any frozen precipitation in this 
region would reach the ground as sleet.

In terms of amounts, the limited amount of moisture and modest
upper-level support should keep the precipitation rates very 
light. Furthermore, a recent warm spell has allowed ground 
temperatures to warm substantially, and with temperatures forecast
to be above freezing for much of the day Friday, little to no 
accumulation is expected. That being said, the potential will 
exist for short "bursts" of moderate sleet and/or snow, which 
could lead to localized light accumulations and reductions in 
visibility, which would lead to minor travel impacts. The greatest
probability of experiencing one of these bursts likely exists 
roughly within a corridor from Hillsboro to Athens to Tyler, 
including some of the very southern fringes of the Dallas/Fort 
Worth area. The best timing would be during the evening and 
overnight hours Friday. It should be stressed however that 
pinpointing the exact location of a heavier band of wintry 
precipitation is extremely challenging. Most locations will likely
not see any accumulating wintry precipitation at all, but it is 
always safe to be prepared just in case, since the chance for 
accumulation, while low, does exist.

Precipitation should come to a brief end Saturday morning as the
upper-level potential vorticity anomaly moves off to the east.
Another upper-level disturbance will move into the area Saturday
evening however, setting off another round of precipitation.
Temperatures should be warmer however, and wintry precipitation is
not expected with this event. The main focus for rainfall on
Sunday will be a warm front (actually a retreating cold front)
which will move northeast to near our southeastern and eastern 
CWA boundary. Rainfall rates will not be particularly heavy, but a
steady rain is expected for most of the day, which will bring
event total QPF to around half an inch for most areas along and
east of Interstate 35, with a few spots in our northeastern
counties potentially seeing over one inch. The low rain rates
should minimize the threat for flooding. With regards to
temperatures on Sunday, forecast highs are well below guidance,
which has been trending colder (but remains well above freezing),
and to account for the widespread cloud cover and precipitation.

Rain chances should end by Monday afternoon and evening for most
locations. Towards the middle of next week, temperatures should
moderate to near seasonal normals as zonal flow (to slight
ridging) sets up across the southern CONUS.

Godwin

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    25  39  32  43  38 /   0  10  30  10  60 
Waco                27  39  35  42  38 /   0  20  50  20  50 
Paris               22  40  31  43  36 /   0  10  20   5  60 
Denton              23  39  30  43  36 /   0  10  20   5  50 
McKinney            22  40  31  42  37 /   0  10  20   5  60 
Dallas              25  40  33  43  38 /   0  10  30  10  60 
Terrell             24  39  33  43  37 /   0  10  40   5  60 
Corsicana           25  41  34  41  38 /   0  20  50  10  50 
Temple              26  39  35  42  39 /   0  40  50  30  50 
Mineral Wells       22  38  30  41  35 /   0  10  20  10  40 

&&

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

$$

08