Forecast Discussion for Dallas/Ft. Worth, Texas

000
FXUS64 KFWD 200438
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1138 PM CDT Fri Oct 19 2018


.AVIATION...
/06Z TAFs/

Challenges and concerns: Primary concerns will be cigs through
early afternoon Saturday, vsbys at especially DFW airports through
15z, and timing cold FROPA after later Saturday morning.

Currently, subsidence is slowly progressing east across the
airports with -RA/-SHRA remaining to the east of Waco Regional.
Due to lift remaining nearby, cigs continue to vary between low
MVFR BLO FL020 and IFR across DFW airports, with IFR(almost LIFR)
at Waco, but drier air is just off the doorstep.

It is very difficult to ascertain whether to prevail IFR or low
MVFR across the DFW Metro. For now, I will prevail low MVFR
before 12z with TEMPO IFR, before prevailing IFR 12z-15z just in
advance of the cold FROPA. As north winds increase behind the
cold FROPA later Saturday morning, cigs will rise through the MVFR
category, then become becoming VFR and scatter out later Saturday
afternoon as north winds increase to near 15 knots and deeper dry
air entrains into the area.

Waco will likely prevail at IFR, but may see TEMPO MVFR cigs in
the 10z-14z just ahead of the cold FROPA with subsidence
increasing. Similar to DFW area airports, look for Waco to go
quickly into VFR once cold FROPA has occurred before midday and
deeper dry air entraining into the area.

Top-down drying will likely result in areas of BR/FG mainly NW of
DFW airports where temperatures will cool more toward saturation.
Patchy BR in the MVFR category will be forecast at DFW/DAL/GKY
with possible IFR at AFW/FTW through mid morning Saturday. Waco
will see less subsidence and more of a cirrus canopy, thus vsbys
will only be advertised into the MVFR category until cold FROPA
occurs later in the morning.

05/

&&


.UPDATE... /Issued 1008 PM CDT Fri Oct 19 2018/
The shortwave disturbance aloft responsible for the widespread
rainfall earlier this afternoon and early evening will continue
exiting east of the area and toward the Lower Mississippi Valley
through Saturday morning. Though ongoing, scattered rain chances
will continue across parts of Central Texas late tonight and
Saturday, amounts are not expected to be widespread or more than
an additional quarter of an inch, thus the Flash Flood Watch has
been cancelled. Despite decreasing rain chances, ongoing flooding
on mainsteam rivers and associated tributaries will continue
through the weekend at many sites on the Trinity, Sabine, Red, and
Brazos basins.

Large-scale subsidence behind the departing shortwave disturbance
will continue to overtake much of the western and northern part of
the area overnight and Saturday morning. Occasional breaks in clouds
may allow for enough radiational cooling and saturation of the
near surface layer west of I-35 and 35W and along and north of
I-20 for the development of fog across these areas. It appears
some patchy dense fog is possible as well through mid-morning
Saturday. Confidence is too low at this point for any consideration
of a Dense Fog Advisory due to several meteorological factors in
play, however I do expect some fog formation with temperatures
cooling down to saturation by daybreak Saturday. Lows will remain
steady in the 50s.

A cold front and increasing north winds arrive later Saturday
morning and will likely put an end to the fog, as speeds increase
to between 10 and 15 mph with occasional gusts in excess of 20
mph. Despite this, low level cold advection will lag well behind
the leading edge of the front with some insolation allowing highs
Saturday afternoon to rise to between the mid 60s and lower 70s.
With at least partial clearing in advance of the true colder air
and 850mb front, look for highs to rebound to between the mid 60s
and lower 70s Saturday afternoon. Low level cold advection is
expected to arrive late Saturday night into Sunday with highs
falling back into the 60s. Still, the more abundant sunshine will
make for a welcome reprieve from the periods of rainfall seen the
past week.

05/

&&

.SHORT TERM... /Issued 315 PM CDT Fri Oct 19 2018/
/Rest of Today and Tonight/

Well...another day...with more rain. Sounds like a broken record
at this point, but the good news is that drier air is noted just
upstream, and will be gradually filtering into the region tonight
and into Saturday.

In the meantime, light to moderate rainfall continues this
afternoon across much of the forecast area, although precipitation
will be ending across our westernmost counties over the next few
hours as the main area of ascent is incrementally pivoting
eastward. Rainfall chances will remain high through the rest of
the afternoon and early-evening hours for roughly the southeastern
2/3rds of the CWA where a combination of isentropic upglide and
frontogenetic forcing will persist. In fact, most guidance
indicates a brief intensification of FGEN along the sloping
frontal surface now through about 8 PM or so, which could act to
locally enhance rainfall rates from either side of a Temple to
Waco to DFW line. Hourly rates are expected to generally remain
under one inch per hour, but any additional rainfall will carry a
flood risk as a vast majority will just immediately runoff. We`ve
elected to cancel the Flash Flood Watch for our far western
counties where the threat for heavier rainfall has ended, but will
continue it for the I-35 corridor counties up to the Metroplex
through 10 PM this evening.

Rain chances will continue to decrease late this evening, with
precipitation-free conditions expected north and west of a
Comanche to Denton to Bonham line after midnight. Light to
moderate rainfall should persist across our far southeast.

While drier air above 900 mb will swiftly progress south of the
Red River overnight, moisture will remain in copious supply in the
lowest 1000 feet or so before a reinforcing surface cold front
moves through towards daybreak on Saturday. At least briefly
clearing skies, combined with soggy soils and the high near-
surface moisture spell a potential for fog development late
tonight north and west of an Eastland to Mineral Wells to Sherman
line. Some hi-res guidance indicates the potential for dense fog,
but this threat should be fairly short-lived before breezier and
drier northerly surface winds sweep through.

Carlaw

&&

.LONG TERM... /Issued 315 PM CDT Fri Oct 19 2018/
/Saturday through Friday/

A temporary end to widespread rainfall will occur Saturday as a
shortwave exits the region to the east and a reinforcement of dry
air arrives behind a cold front. Clouds (and any lingering light
rain) will end from north to south through the day with a mostly
sunny and warmer afternoon likely for most areas. Highs Saturday
will be generally in the upper 60s and lower 70s.

Temperatures will cool fairly rapidly after sunset Saturday due to
a clear sky, dry air in place and a light northeast wind. Lows
Sunday morning will range from the mid 40s to the mid 50s. There
will be a low potential for some patchy fog due to saturated
soils, but it appears that low level advection of dry air will be
sufficient to limit fog formation.

Upper level high pressure will slowly deamplify and shift eastward
to start the work week while another upper low churns over the
West Coast. Although large scale lift will increase Sunday night
through Tuesday. Moisture will be slow to return and remain
generally across South Texas. However, there should be enough
moisture and lift across Central Texas to warrant some chance
PoPs, especially on Monday.

Large scale forcing for ascent and deeper moisture will arrive
Tuesday night/Wednesday when the West Coast upper low opens up
and translates eastward across the region. Steepening mid level
lapse rates should result in some isolated thunder as well as some
pockets of brief heavy rainfall. For now we will not highlight
the potential for flooding with this midweek system, but it goes
without saying that any additional rainfall could cause some
problems.

Overall, the second half of next week should be dry with generally
zonal flow aloft. It appears that deep moisture will be confined
to South Texas as a tropical system moves east across Mexico.
However, there is still a chance that some of this moisture may
reach the southern zones, producing additional rainfall Thursday
and Friday, but for now we will keep the forecast dry.

Temperatures Sunday through Friday will remain below normal with
highs generally in the 60s with lows in the upper 40s to the mid
50s.


79

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    57  71  50  65  49 / 100   5   0   0   5
Waco                58  71  50  67  49 /  90  20   0   0  10
Paris               55  71  47  62  45 / 100   5   0   0   0
Denton              55  69  47  64  47 /  90   5   0   0   5
McKinney            56  70  47  64  47 / 100   5   0   0   5
Dallas              58  71  51  65  50 / 100   5   0   0   5
Terrell             58  72  49  65  48 / 100  10   0   0   5
Corsicana           58  71  50  65  49 / 100  20   0   0   5
Temple              59  70  53  67  50 / 100  20   0   5  10
Mineral Wells       56  71  47  65  49 /  40   5   0   5  10

&&

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

$$

05/26

NWS FWD Office Area Forecast Discussion