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

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432
FXUS64 KFWD 221813 AAB
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
113 PM CDT MON AUG 22 2016

.AVIATION...
A complicated forecast to say the least is in store for the
remainder of the day.

For the Metroplex sites: a mixture of MVFR and VFR cigs exists,
but the overall trend has been for these to gradually increase.
It appears that cigs should continue to slowly lift towards VFR
through the early-afternoon hours (outside of showers and storms).
The activity from the Metroplex and north has had little if any
lightning with it, although we`re starting to see a bit more vigor
to the activity at this time. Given the isolated nature of the
storms so far, have elected to simply prevail VCTS through early
evening before the loss of daytime heating squelches lingering
shower or storm activity. Given the tropical nature of the
airmass, even the lighter showers will be capable of dropping
visibilities briefly under 2 SM. We will monitor convective trends
and amend as necessary through this afternoon and evening.

There are some conflicting signs regarding the potential for
overnight MVFR stratus in the Metroplex. At this time, it appears
that the best moisture profiles should remain to the south and
west, but some recent high-resolution guidance has been pretty
insistent on developing low stratus into the Metroplex sites after
23/11Z or so. For now, have elected to forgo inclusion of MVFR
cigs, but future shifts will need to evaluate this potential
further. Finally, as the low-level jet gets going overnight, some
borderline non-convective LLWS may be possible, but the greatest
potential looks to remain west of the TAF sites.

For Waco: most activity has moved north, but some additional
isolated thunderstorm development will be possible through mid-
afternoon, potentially lingering a bit longer than indicated in
the current TAF. Otherwise, VFR should be the rule before MVFR
stratus returns late tonight.

Carlaw

&&

.UPDATE...
Quick morning update to increase PoPs across the far southern
counties based on latest radar trends. Several convective clusters
continue to spread north through the Hill Country and southeast
Texas this morning aided by moderate isentropic ascent through
800mb. This should continue to spread north as suggested by the
latest RAP/HRRR guidance as southerly flow strengthens through the
morning. A little farther to the north...the remnant frontal
boundary is still lingering near the Red River. This will also
provide some support for scattered showers and storms through the
morning and will keep PoPs in the 30-40% range. No other changes
needed at this time.

Dunn

&&


.SYNOPSIS...
A deceptively tricky forecast for today with slight chance
to chance PoPs across a good portion of North and Central TX.
Generally low rain chances will continue for just about each day
this week and into the weekend.

&&

.SHORT TERM (Today through Wednesday)...
The main concern in the short term period, specifically today
will be morning fog and rain chances. 3:30 A.M. surface analysis
revealed that the old baroclinic zone responsible for the stark
difference in sensible weather across the region on Sunday had
slowly lifted northward to somewhere between the Highway 380 and
I-20 corridor. This boundary, will likely continue to lift to the
north very slowly over the next several hours, as ASOS and OK
Mesonet observations are just beginning to show some surface
pressure falls. Most locations near and north of a Graham to
Denton to Sherman/Denison line were in the mid 60s at this hour
due to a combination of light winds and much drier air at the
surface. Warm FROPA should inject near 70 degree dewpoint air into
this cooler air which should yield quick/efficient saturation and
result in the development of some fog along the Red River. Latest
runs of the operational AND experimental HRRR appear to support
this scenario and I have added a mention of patchy fog for a few
of the Red River counties down to near the Highway 380 corridor.
Patchy fog will also continue across Central TX where dewpoint
depressions remain low. Overall confidence on dense fog is low at
this time, but we will monitor observations and if visibilities
start to deteriorate rapidly, a dense fog advisory may be needed.

Otherwise, this morning should see an uptick in convection as
weak ascent atop the shallow frontal surface continues. Regional
radars are starting to indicate some light returns along the I-20
corridor as well as additional convection across the TX Coastal
Plain. The areal coverage of the convection continues to remain
challenging this morning as the CAMs and synoptic models offer
slightly varying solutions. One thing that has been consistent is
that most model guidance is VERY aggressive with regards to
PoPs/QPF. While this is a strong signal, observational data at
this time does not necessitate such aggression.

Current implications are that the already ill-defined boundary
will gradually lose its baroclinicity through the afternoon hours
near the Red River. As faster mid-level flow overspreads the
southern Rockies, deeper lee-side cyclogenesis should induce
stronger low level flow. The increasing warm/moist advection
through the afternoon may be enough to spark additional showers
and thunderstorms. Again, some model guidance continues to
advertise very high rain chances, but given the loosely defined
warm front and modest warm moist advection, I think the overall
coverage only warrants a 50% PoP (as opposed to some of the 60-70%
advertised by some guidance), with the best chances near and north
of a Goldthwaite to Waxahachie to Emory line. It`s here that the
convergence along the ill-defined front and warm air advection are
juxtaposed. Overall severe weather prospects look low, but cannot
rule out some brief periods of heavy rain. Fortunately, activity
should move swiftly to the north and this should mitigate a high-
end flash flood risk.

Rain chances will continue through the overnight hours,
especially along and north of the I-20 corridor/Red River, where
low level flow is expected to remain strong and some weak synoptic
scale ascent in the form of the entrance region of an upper jet
may be enough to keep activity going. Low rain chances on Tuesday
morning will gradually decrease as the main conveyor of winds
aloft shift towards the north. The lee trough remains fairly stout
during the day on Tuesday and Wednesday and with increasing
mid/low level heights from the southeast U.S. ridge axis, the low
level pressure gradient will tighten. Provided that sufficient
diurnal mixing occurs, breezy south to south-southwest winds can
be expected for the western 2/3rds of North and Central TX on
Tuesday and perhaps into the day on Wednesday. Tuesday and
Wednesday should see rebounding temperatures with daytime highs in
the 80s and 90s as the afternoon time periods for both days appear
dry at this time.

&&

.LONG TERM (Thursday through Saturday)...
A majority of the day on Thursday appears dry as a cold front
slides southwards through Oklahoma. With a fairly broad trough
across the western CONUS, I think it`ll be difficult for the front
to slip south of the Red River and it should lift back northward
on Thursday evening. Medium and long range model guidance
continues to indicate fairly high rain chances on Thursday. Given
the upper air pattern and low potential for the front to slide to
the south of the Red River, I will maintain just slight chance
PoPs along the Red River. In addition there will be low PoPs
across eastern zones where there is a low chance that convection
that develops along the spine of the Ozarks and across east TX
slides westward.

For Friday and beyond---low rain chances continue across just
about all of North and Central TX. Due to the lack of any forcing
as advertised by model output, will have to broad brush PoPs in
the extended. Temperatures during this time will be near seasonal
averages with afternoon highs in the 80s and 90s and overnight low
temperatures in the 70s.

24-Bain

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    87  75  91  76  93 /  50  30  10   5   5
Waco                89  75  90  75  92 /  60  20  10   5   5
Paris               81  71  90  73  92 /  50  40  10   5   5
Denton              86  73  90  74  94 /  50  30  20   5   5
McKinney            85  74  90  75  92 /  50  30  10   5   5
Dallas              87  76  91  76  93 /  50  20  10   5   5
Terrell             86  74  90  75  92 /  50  20  10   5   5
Corsicana           88  75  91  74  92 /  60  20  10   5   5
Temple              88  74  90  74  92 /  60  10  10   5   5
Mineral Wells       86  72  90  73  94 /  50  30  10   5   5

&&

.FWD Watches/Warnings/Advisories...
None.
&&

$$



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