Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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FXUS64 KFWD 131150 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
550 AM CST Mon Feb 13 2017

.AVIATION...
/12Z TAFs/

Early challenges to be timing of veering surface winds and cig
categories through this evening. Additional challenges include
timing increasing rain and isolated convective chances, with cigs
lowering once again overnight tonight with the an approach of a
strong upper low and increasing rainfall.

The entire region was within a warm advection regime with broad
stratus field at different levels (MVFR at Waco, low VFR at DFW
airports). Waco will lower to below 2000 feet the next few hours,
while DFW airports lower into high MVFR above 2000 feet as low
level warm advection continues strengthening. In addition, some
spotty light showers or sprinkles will continue until mixing
commences later this morning into early afternoon with a brief
period of VFR cigs area-wide by mid afternoon. Increasing
isentropic ascent and residual boundary layer cooling will allow
cigs to fall back into the MVFR category by late evening, with
possible IFR during the pre-dawn hours with widespread SHRA with
MVFR VSBYS. Have added a VCTS group to Waco after midnight in a
regime of slightly higher values of instability.

N/NE winds around 10 knots will initially veer E/NE 10 to 15 mph
with mixing by this afternoon, as an inverted surface trough over
the Rio Grande Plains of S TX slides eastward. As this surface
trough moves east across Central/S-Central TX tonight, eventually
winds will back around to the N/NE less than 10 knots, then N 10
to 15 knots in the 24-30 hour TAF period. For now, have left the
extra period off of the DFW TAF, seeing all the transitions we`ll
be experiencing the first 24 hours.

05/

&&

.SYNOPSIS...
Slightly cooler conditions can be anticipated over the next
several days as rain chances slowly increase. Periods of moderate
to at times heavy rain will be possible across parts of North and
Central TX with rainfall amounts in the 1 to 3 inch range. With
most of the rain falling over the course of a couple of days,
widespread flash flooding still appears unlikely. Drier weather is
expected for the latter half of the work week with a chance for
rain next Sunday.

&&

.SHORT TERM (Today and Tuesday)... Surface and satellite analysis
this morning showed that the front that moved through the area on
Sunday has stalled down across the Rio Grande River Valley. High
pressure across the Central Plains continues to slide eastward
which will bottle up a majority of the colder air to the north,
leaving fairly mild conditions across North and Central TX. Water
vapor imagery revealed that the large upper low, that will be the
main impetus for rain over the next few days, continued to dig
down across the Gulf of California.

For Today---I`ve made some alterations to the inherited forecast
based on current observations/expectations. Radar this morning
indicated some lightning-free convection developing across
portions of the northern Hill Country, likely in response to the
isentropic upglide ongoing along the 295 K theta surface. The 00
UTC FWD RAOB indicated a narrow strip of moisture just above 850mb
with relatively dry atmosphere elsewhere. For that reason, most
of the activity likely won`t produce widespread measurable rain,
at least initially. That being said, I`ve painted a 20 PoP across
mainly western and southern zones, where a slightly higher
quantity of moisture is expected to be juxtaposed with better
isentropic ascent along the 295 and 300 K theta surfaces.
Elsewhere, I`ll go with a mention of sprinkles. Rain amounts today
should be on the light side, with most locations experiencing
less than a tenth of an inch of rain. Despite considerable
cloudiness, warm air advection in response to the approach of the
upper trough to the west and surface high pressure sliding to the
east will likely support milder conditions than initially
anticipated and as a result, I`ll increase temperatures upward in
line with most numerical model guidance.

The sprinkle or light rain activity for areas east of highway 281
should decrease in areal coverage through the day as the stronger
isentropic ascent subsides temporarily. West of highway 281,
however, low level flow will likely strengthen as the upper trough
nudges eastward out of the Pacific Southwest. Strong cyclogenesis
is expected to occur across the Rio Grande River Valley with a
plume of high theta-e air being transported northward across
southwestern and western zones. There will likely be a sharp
gradient in PoPs out west, but have slowly nudged these values
upward with the thinking that the better rain chances will likely
be closer to the later afternoon and early evening hours. Tonight
into Tuesday morning should feature mild conditions as the spine
of an inverted surface trough becomes oriented across North and
Central TX. This implies good warm air advection at the surface
and just aloft. The best precipitation chances should occur
near/and west of this trough and I`ve oriented PoPs accordingly.

The exception to the mild conditions may be across
northwestern/western zones where the greatest coverage of rain is
expected. Taking a look at model derived wet-bulb forecast, the
potential looks pretty low to cool too drastically given the
increasing low level moisture and I`ll keep forecast min
temperatures into Tuesday morning near and just above than these
values across the west and northwest. Models track the surface low
eastward pretty quickly and if this occurs sooner than currently
thought, slightly cooler conditions may be experienced Tuesday
morning as stronger CAA would occur across northwest zones.

For Tuesday---Tuesday is expected to be a cool and raw day across
much of North and Central TX with widespread rain likely. The
area that may remain somewhat mild will be across southern and
southeastern zones---I`ll explain this later below. An upper jet
is forecast to be positioned such that a majority of North and
Central TX will be in the left exit region of said jet. This implies
good synoptic scale ascent. With a favorable synoptic regime coupled
with output from several convective allowing models, rain seems a
sure bet across nearly all of North and Central TX. Some of the rain
could be heavy at times given PWATs will climb in the 150 to 200
percent of normal range. While these values are high, we still feel
that the threat for widespread flash flooding remains low for a
couple of reasons. 1). The recent dry spell has resulted in fairy
high flash flood guidance and we feel confident that these values
will likely not be approached. 2). Some convective allowing models
suggest a loosely organized (and likely weakly electrified) complex
will move quickly from west to east on Tuesday and this is likely
when the heaviest rainfall will occur. 3). Storm total precipitation
totals in the 1 to 3 inches of rain will likely occur of the course
of 12 to 24 hours which should allow rain to ease into the ground.
That being said, I can`t rule out some minor flooding in flood prone
or low lying areas. If the convective band (reason #2) moves slower
than currently thought, we could see some heftier rainfall rates
which would increase the flash flood potential.

Temperatures on Tuesday across the forecast area will vary
considerably and will ultimately depend on the location of the
surface low. Most models project that the surface low will travel
across our Central TX counties. Strong WAA should occur to the
south of this feature and will likely pull up warmer and slightly
more unstable air northward. The stronger WAA warrants bumping
temperatures upward on Tuesday. At this time, it looks like the
most likely area for this to occur will be along and southeast of
a Temple/Killeen to Palestine line where temperatures may climb
into the upper 50s and low 60s. Elsewhere, temperatures in the mid
40s to near 50 are expected. With there being some semblance of
instability across southern zones, I have kept in the mention of
thunder, but think that the coverage only warrants isolated
wording at this time. Furthermore, there may be a low end
potential for some gusty winds with some precipitation
drag/momentum transfer across areas that find themselves in the
warm sector. Overall, severe weather appears unlikely at this
time, however. Rain chances should dwindle from west to east late
Tuesday into Wednesday.

&&

.LONG TERM (Wednesday through Sunday)...
For Wednesday---Rain chances will diminish late Tuesday and into
the pre-dawn hours on Wednesday. Previous concerns about a
potential rain-snow mix across northwest zones also continue to
dwindle as it appears that drier air will establish itself around
the western periphery of the upper low quickly on Wednesday before
deeper and colder air arrives. In fact, with the upper trough
translating pretty quickly to the east, it`s probable that much of
Wednesday will remain dry and cool after sunrise and I`ve
continued with a dry forecast. North winds should usher in cooler
and drier conditions and temperatures on Wednesday morning should
fall into the upper 30s along the northwest to low to mid 40s
elsewhere. The cooler air may not reach far southeastern zones
until after 12 UTC on Wednesday, so a few readings near 50 degrees
may be possible. Daytime temperatures should climb into the mid
to upper 50s with even a few low 60s possible.

For Thursday and Friday---Thursday and Friday should be mostly
quiet in terms of precipitation chances. With clear skies, light
winds, and likely damp soils a good setup for widespread radiation
fog will be possible on Thursday morning. For now, will go with
patchy fog, but we will keep tabs on this as there should be a
decent potential for dense fog if rain amounts are to verify and
a good radiational cooling night sets up. Temperatures on
Thursday morning will be noticeably lower than those experienced
the previous nights. Thursday and Friday, daytime conditions
should moderate with above normal temperatures expected. I`ve gone
with a blend of some of the warmer guidance as the atmosphere
should be dry and allow for a steep diurnal curve. With wet soils,
however, there`s a risk that evapotranspiration could help keep
things a little cooler (under quiescent conditions) than numbers
advertised by some of the MOS guidance. Both days look dry, with
regards to precipitation chances.

For Saturday and Sunday---Even warmer conditions are expected as
our mild winter continues across North and Central TX. A couple
of upper troughs should slide eastward which will help induce lee-
side cyclogenesis this weekend. This should allow moisture to be
drawn northward into the area, resulting in low rain chances late
Saturday and into Sunday. There may be a chance for some organized
convection on Sunday as the wind field at mid and upper levels
intensifies and low level moisture/instability will be in place.
For now, we will monitor the potential for any type of turbulent
weather in the extended.

24-Bain

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    60  47  50  42  57 /  20 100  90  30  10
Waco                64  52  53  44  59 /  20 100 100  10   5
Paris               53  45  49  42  56 /  10  90 100  60  10
Denton              57  42  48  41  57 /  20 100  90  30   5
McKinney            57  46  50  42  56 /  20 100  90  40  10
Dallas              60  49  50  43  57 /  20 100  90  30  10
Terrell             60  49  52  43  57 /  20 100 100  30  10
Corsicana           64  53  54  45  58 /  20  90 100  20  10
Temple              65  57  57  44  59 /  20  90 100  10   5
Mineral Wells       58  44  46  40  57 /  30 100  90  10   5

&&

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

$$

05/24



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