Forecast Discussion for Dallas/Ft. Worth, Texas

000
FXUS64 KFWD 191202 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
602 AM CST Wed Dec 19 2018


.UPDATE...
We issued a Dense Fog Advisory a little while ago for areas
generally along and west of the I-35/35E corridor and up to an
Eastland to Mineral Wells to Decatur line. Opted to leave McLennan
and Bell counties out of the advisory where reduced visibilities
have been more staccato in nature and hi-res guidance indicates a
slow improvement over the next hour or two. The advisory runs
through 11 AM, but we`ll likely be able to trim counties after
9-10 AM as conditions slowly improve.

Carlaw

&&

.AVIATION...
/12z TAFs/

Very poor flying conditions are expected to persist at least
through the mid-morning hours across the I-35 corridor TAF sites
due to a combination of -DZ and FG dropping vsbys to under 1 SM
at times. VLIFR/LIFR cigs will also remain in place across the
Metroplex, but a return to IFR should occur through the 15-17z
time-frame. MVFR cigs should remain rather pervasive through the
afternoon hours owing to the low sun angle and associated
insolation reductions. I have, however, indicated a brief window
where a return to VFR conditions may occur in the Metroplex ahead
of an incoming cold front, but it`s conceivable that MVFR cigs--at
least on a TEMPO basis--persist through the daylight hours today.
Shower chances will remain low across the D10 TRACON today, but
will be somewhat higher at Waco as the core of an upper-low
approaches from the west later this morning. Some guidance
indicates a low potential for a few storms to develop immediately
under the cold core, but coverage seems too sparse to warrant a
VCTS introduction at this time.

A strong cold front will move through the region this evening and
will bring with it one last chance for some precipitation before
conditions clear out after midnight. Latest guidance suggests
there may be just enough instability present to result in the
development of a few embedded storms, but confidence in this
occurring wasn`t high enough to insert a VCTS mention across the
Metroplex. Precipitation chances will be somewhat lower at Waco
this evening, and a VCSH looks to suffice for now.

Skies will clear as the front presses eastward late tonight and
into Thursday morning. Winds will gradually increase out of the
northwest and gusts of 30-40 kts are expected to develop through
the mid-late morning hours on Thursday. Winds from 330-350 degrees
should keep crosswind impacts to a minimum.

Carlaw

&&


.SHORT TERM... /Issued 335 AM CST Wed Dec 19 2018/
/Today through Thursday/

A robust mid-level shortwave is currently translating eastward
across the Concho Valley early this morning. The associated warm
conveyor is pushing east of the I-35 corridor and is taking the
initial round showers with it. We`ll carry 90-100% PoPs through
the next few hours across our far southeastern counties to cover
this area of precipitation, tapering PoPs quickly towards the
immediate Metroplex and points north to under 20%. To the west of
I-35, the mid-level dryslot has worked through, bringing an end
to the better chances for measurable precipitation. However,
plentiful moisture remains in place under 850 mb, and this is
resulting in widespread low cloud cover and the development of
light fog or drizzle. Anticipate this region of low clouds and
mist/fog to continue pushing northward this morning, with the most
pervasive visibility reductions along and west of I-35/35W.
Another area of fog is trying to sneak in across our far
northeastern counties where visibilities are fluctuating between
one quarter and two miles. At this time, it looks like most
visibilities will hang out in the one to three mile range,
although pockets of dense fog will be possible. We`ll monitor
trends this morning, but will refrain from hoisting what would be
a pretty piecemeal Dense Fog Advisory at this juncture.

For the rest of this morning, hi-res guidance indicates an
additional wave of showers/isolated storms developing along a
diffuse surface boundary which currently resides just south of our
CWA. We`ll carry the highest PoPs (60-80%) south and east of a
Canton to Mexia to Cameron line through noon as isentropic upglide
continues in this region. PWATs pushing just north of one inch
will support some locally heavy rainfall in any of the more robust
convective elements, and some minor flooding of poor-drainage
areas may result.

By later this afternoon, most of the precip associated with this
latest upper-low will have peeled east of the region as the parent
trough axis passes overhead. A cold front will follow quickly on
its heels, and a northwest wind shift will occur through the
evening hours. Moisture and instability look sufficient to warrant
bumping PoPs upwards with the frontal passage this evening into
the likely category across our far northeast, with chance PoPs
across the immediate Metroplex. Forecast soundings show a sliver
of surface-based instability will be present, so elected to
introduce some isolated thunder wording roughly north of I-45 and
east of I-35 late this evening/overnight.

Precip chances will end area-wide by late tonight/early Thursday
morning, and will be replaced by strong and gusty northwest winds.
Forecast soundings show us mixing up to around 850 mb during the
afternoon hours and tapping into an impressive unidirectional wind
field aloft. Momentum transfer of 45-50 kt flow around this level
should result in sustained winds of 20-30 mph area-wide, with
occasional gusts nearing 45 mph in spots, and this will likely
necessitate a Wind Advisory for all of North and Central Texas.
Persistent cold advection will hold high temperatures on Thursday
into the 50s.

Carlaw

&&

.LONG TERM... /Issued 335 AM CST Wed Dec 19 2018/
/Thursday Night Through Tuesday/

Strong undirectional NNW flow will be ongoing aloft in the wake
of our departing and deep latitudinal trough discussed in detail
in the short-term discussion. Drier air will continue filtering in
and it will likely be our chilliest night in the next 7 days as
the brisk NNW winds combine with temperatures dropping into the
30s for wind chills in the upper 20s north to the lower 30s
elsewhere by sunrise Friday morning. The lingering brisk winds,
particularly across the eastern half of the region will be driven
by several factors including -- a strong pressure gradient,
continued low level cold advection, and efficient momentum
transfer within the deepening frontal inversion. Friday will start
off sunny and cold, but winds will continue to diminish as both
thermal advection and the pressure gradient slacken off through
the day.

Strong insolation should help highs recover to the mid 50s East
to lower-mid 60s West. I am concerned these values could be a tad
optimistic on the model blends if the strongest warm advection
holds off longer into Friday night into Saturday. Plentiful
sunshine should combine with strong warm advection and veering low
level flow on Saturday ahead of the next surface cold front for
one of our warmer days of the extended period. It will also become
breezy as fast zonal flow aloft helps induce pressure falls to
our northwest Friday night, then shortwave ridging ensues on
Saturday. The GFS is a good 3-6 hours faster with a more shallow
surface cold front arriving by Saturday afternoon versus arriving
late Saturday afternoon or early evening on the Canadian and European
models. It tries to track a weak surface low faster across our
northern counties early Saturday as well. Not sure I`m buying this
considering support aloft somewhat lacking and and the more true
cold advection holds off until Saturday night and Sunday. I prefer
to trend with a slightly slower surface frontal passage and
warmer temperatures, especially along and south of I-20/30
Saturday afternoon. A few high temperatures could reach or
possibly exceed 70 degrees on Saturday afternoon with some
compressional warming in veered low level flow coming off the
higher terrain west of our region.

A strong shortwave in the northern stream diving southeast
Saturday night and Sunday should pull the cold front and more true
cold airmass through the area with brisk and cooler conditions on
Sunday. This system and associated surface pressure gradient do
not look to be near as intense as the cold front on Thursday with
high temperatures Sunday dropping back into the 50s to possibly
lower 60s across parts of Central Texas. Both moisture and
temperature modification occur early next week and into the
holiday period, as a longwave trough organizes over the Western
CONUS. One strong wave arrives Monday, while a stronger system
appears to arrive Wednesday. At this time, will re-introduce
convective PoPs into the forecast, but remain very conservative
and not go beyond the "chance" category per collaboration with our
neighboring WFOs with medium range models and their ensemble
members struggling with such strong mid-level energy in the
southern stream of the westerlies. Moisture and instability (at
least at this time) also do not look spectacular with the Gulf of
Mexico having been scoured by several frontal passages. Though
some holiday travel impact is possible, the extent of impacts is
very uncertain at this time. One thing is for certain, winter
weather would not be one of those impacts. We should see slightly
above normal to normal seasonal temperatures, despite experiencing
some of our shortest days of the year as we move just past the
Winter Solstice (Friday, Dec 21st).

05/

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    61  45  57  40  59 /  20  30   0   0   0
Waco                61  45  58  38  60 /  40  20   0   0   0
Paris               55  44  53  37  56 /  30  60   0   0   0
Denton              61  43  56  37  60 /  20  30   0   0   0
McKinney            58  44  55  38  58 /  20  50   0   0   0
Dallas              61  46  57  40  60 /  20  40   0   0   0
Terrell             59  45  56  38  59 /  40  50   0   0   0
Corsicana           60  45  57  39  58 /  60  30   0   0   0
Temple              63  43  58  39  62 /  40  10   0   0   0
Mineral Wells       61  42  57  35  62 /  10  10   0   0   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM CST this morning for TXZ102>104-
117>119-129>134-141>145-156-157.

&&

$$

90/05

NWS FWD Office Area Forecast Discussion