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

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FXUS64 KFWD 190341
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
941 PM CST Wed Jan 18 2017

.UPDATE...
Extensive moisture in the lowest 5000 ft of the atmosphere will
remain in place overnight until dry air surges in from the west
Thursday in the wake of the departing low pressure system.
Therefore, North and Central Texas will remain cloudy overnight.
Areas of fog are also expected with near saturated surface
conditions and light winds. Although some areas may see some brief
dense fog, before sunrise, most visibilities will remain above
1/2 mile. Therefore, we will not issue a dense fog advisory at
this time. If any areas do see dense fog, it will most likely be
west of the Interstate 35 corridor where higher clouds will clear
first. We will be watching trends closely overnight.

The only major change to this forecast will be to remove pops. A
few sprinkles or drizzle is still possible, but measurable
rainfall seems unlikely.

79

&&

.AVIATION...
/ISSUED 538 PM CST Wed Jan 18 2017/
An upper low is currently moving east across the TX/NM border. The
deep moisture fetch and associated precipitation east of the
system is also shifting east, and is currently crossing the TX/LA
border. All TAF sites are expected to be free of any convection
through the forecast period.

The main issue will be the redevelopment of IFR conditions this
evening and possibility of LIFR overnight. All short term & hi-res
guidance indicates a lowering of cigs and visibilities after
sunset. Shallow moisture, cool conditions and light winds means
that patchy dense fog will be a possibility. At this time, we will
indicate IFR CIGs developing between 00Z and 06Z with LIFR CIGs
06-09Z at all locations. TAFs will not include dense fog at this
time, with the expectation that low cigs will hopefully preclude
dense fog development. However, we will need to monitor trends
later this evening and overnight.

Low level winds will begin to veer after 19/12Z as the upper low
swings east through the Southern Plains. Drier air and increasing
southerly flow will scour out fog and low cigs, with a return to
VFR expected late Thursday morning.

30


&&




.SYNOPSIS...
Areas of rain will continue to exit southeastern portions of
North and Central TX today as the best ascent shifts towards east.
Relatively dry, breezy and mild conditions are expected through
at least the remainder of the work week with additional storm
chances this weekend ahead of a Pacific front. Thereafter, mild
conditions will generally prevail with generally mild conditions
next week. A slightly longer duration cool period is expected
towards the middle of next week in the wake of another cold front.

&&

.SHORT TERM (Tonight through Friday)...
Surface analysis this afternoon showed a frontal boundary draped
across the upper TX coast just to the north of the Houston area
which likely explains some of the heavy rainfall across that part
of TX. A little further north across our southeastern zones,
isentropic ascent along the 290-300K theta surfaces has resulted
in rain. This conveyor of ascent appears to be shifting towards
the east pretty quickly and I`ll go ahead and decrease PoPs a bit
further with just chance to slight chances for rain across far
southeastern zones. I won`t remove PoPs completely as the upper
jet strengthens a bit more aloft, but instability should remain
low enough to preclude any appreciable threat for thunder. With
low level moisture not being completely scoured out, I`ll maintain
some low end rain chances, mainly for areas near and east of the
I-35 corridor. The remnant low level moisture will also remain in
place for some areas of fog west of the Highway 281 corridor with
patchy fog elsewhere. The one caveat to widespread dense fog may
be the dense canopy of mid/upper level moisture streaming in from
the Pacific. That being said, I won`t completely rule out dense
fog across areas west of I-35. Elsewhere, patchy fog is expected.
Overnight low temperatures shouldn`t tumble too far with tonight
due to the remnant low level moisture as well.

For Thursday---Morning fog should dissipate from west to east as
southwesterly flow overspreads much of North and Central TX.
Shortwave ridging should ensure that nearly all of North and
Central TX remain precipitation-free and so I`ve hedged towards a
dry forecast with little to no upward synoptic scale ascent.
There may be a few weak showers out across eastern zones, but even
the chance for this appears low. Fog should dissipate from west
to east as dry air aloft begins to overspread the area as the
925-700mb trough slides eastward. Low level 925mb flow does
strengthen to about 30-35 knots, so this could support some breezy
west winds. The recent rainfall should ensure that fire weather
concerns remain low, but 1 hour fuels may start to cure a little
in response as adiabatic compression allows temperatures to climb
above normal values for this time of year. While these southwest
winds normally support going well above guidance, I`ll keep a
slightly more conservative Max T forecast for Thursday given the
wet soils and resultant evapotranspiration which may act to curb
the diurnal temperature trend.

Thursday Night into Friday Morning temperatures remain tricky as
there will be a gradual gradient in low level moisture across the
forecast area. Western zones look to be on the drier side of the
airmass and should experience conditions more favorable for better
radiational cooling while eastern zones will remain slightly
milder with the higher low level moisture content. As a result,
I`ll have a west to east gradient with cooler conditions across
far western zones with slightly milder overnight readings across
the eastern sections of the forecast area.

For Friday---Temperatures on Friday should be above normal yet
again as southwest winds continue across North and Central TX.
Most areas will climb into the 70s as low level flow from the
southwest continues to promote downsloping. There may be a few
passing mid and upper level clouds, but a majority of North and
Central TX will be mostly sunny. Similar to Thursday, shortwave
ridging should ensure that precipitation chances remain at a
minimal. There may be some patchy drizzle/fog again on Friday
morning, but overall the potential appears to be pretty low.
Overnight temperatures will be on the milder side as low level
moisture does stream northward late Friday into Saturday. With
the moisture streaming northward, I`ll keep a mention of low rain
chances across far southeastern and eastern zones with a low
chance for an isolated storm or two. It`s possible that these rain
chances may be removed as there remains some capping across the
region which may mitigate precipitation chances all together
Friday night into Saturday. We will have a closer look at this in
later forecasts as additional model output becomes available.

&&

.LONG TERM (Saturday through Tuesday)...
For Saturday---The active weather pattern continues on Saturday
as low level moisture continues to stream northward. A Pacific
cold front will start to sharpen and will slide eastward towards
the I-35 corridor. Mid and upper level moisture will be on the
increase ahead of a stout upper trough forecast to slide in from
the west. Most models project that a 130 knot upper level jet will
overspread the Big Country with very strong mid-level flow
present as well. This should allow low level moisture to return
fairly quickly to the north. The biggest question will be the
quality of this moisture and right now, models suggest that it`ll
be quite shallow. That in mind, models do place a good portion of
North and Central TX within the left exit region of the
aformentioned upper level jet and with 40 to 50 meter height falls
overspreading the area coupled with an uncapped airmass, there
should be some precipitation that develops, especially east of
I-35. The combination of adequate wind shear and instability
should support some strong to perhaps severe storms, if storms
develop. At this time, the best chances will be along and east of
the Pacific front which should slice eastward through the day. In
the wake of the front, southwest winds coupled with dry air at the
surface will foster warm conditions. In addition, very deep
mixing (up to 800 mb perhaps) for this time of year suggest that
Saturday will be a breezy day.

For late Saturday into Sunday evening---Rain chances will linger
across eastern and northeastern zones as the upper and surface
lows begin to fill and slide eastward. While winds will turn to
the north and northwest in the wake of FROPA, there should be
enough of a westerly wind component to foster downsloping and I`ve
nudged temperatures upward from the previous forecast/closer to
ECMWF guidance. The big story on Sunday will likely be the very
breezy conditions advertised. GFS output, though the GFS may be a
little overzealous in its` mixing of the PBL, suggests that
sustained winds of 25-28 knots will be possible. The ECMWF,
however, isn`t too terribly far behind with advertising strong
winds on Sunday. If models converge, it`s probable that a Wind
Advisory may be necessary, especially for western and southwestern
zones. Sunday afternoon should be a mostly dry day and it`s
likely that some minor fire weather concerns could crop up as 1
hour fuels cure.

For Monday and beyond---warm conditions will continue on Monday
as northwest winds turn more towards the west. Models have trended
warmer with Max T values for next week, with the ECMWF being very
aggressive as it advertises mid 70s across a good portion of
North and Central TX. For now, I`ll go with 60s to low 70s given
the uncertainty in the magnitude of downsloping. Tuesday promises
to be another warm and breezy day with continued west winds. A
cold front is expected to slide southward through North and
Central TX during the middle of next week. The north winds should
usher in a slightly more prolonged period of colder conditions.
At this time, precipitation chances appear low with the limited
moisture, so for now, I`ll keep rain chances below 10% next week.

24-Bain

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    47  73  50  74  50 /  10  10   0  10  10
Waco                45  73  45  74  50 /  10  10   0  10  10
Paris               48  68  50  70  50 /  10  10   5  10  10
Denton              44  71  43  73  48 /  10  10   0  10  10
McKinney            46  70  46  72  49 /  10  10   0  10  10
Dallas              47  72  51  75  51 /  10  10   0  10  10
Terrell             47  71  50  73  51 /  10  10   0  10  10
Corsicana           49  72  51  75  52 /  10  10   0  10  20
Temple              46  74  46  75  52 /  10  10   0  10  10
Mineral Wells       44  74  42  73  46 /  10  10   0  10  10

&&

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

$$

30/79



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