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

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304
FXUS64 KFWD 070528
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1128 PM CST Tue Dec 6 2016

.AVIATION...
Light north to northeast winds overnight will veer to light
southeasterly during the morning hours Wednesday in advance of an
Arctic front. Moisture return will be meager at best as return
flow will be weak, probably just enough to maintain the lingering
low clouds currently in place. These clouds will likely preclude
fog development in the Waco area (where the higher dewpoints are),
though some minor visibility reductions cannot be ruled out due to
the low dewpoint depressions across Central TX. The DFW area
resides on the edge of a low cloud deck, so things may clear out
periodically during the night. Fortunately the cloud bases are
around 3500 feet so BKN vs SCT shouldn`t make too big of a
difference.

The front will surge south through the Plains overnight, likely
making it into the Metroplex Wednesday afternoon. Hi-res guidance
indicates some light precip with and behind the boundary, but
most of this will have difficulty reaching the ground. Even if it
does, temperatures should remain above freezing for most of the
overnight hours. Slightly better moisture will be in place at
KACT, but feel that it will just not be cold enough at the surface
for any freezing rain or freezing drizzle. That said, we will
still need to keep an eye on trends tomorrow in case future model
runs indicate a colder than expected airmass, or more available
post-frontal moisture.

Either way, strong north winds are expected at all locations
during the overnight hours Wednesday night into the morning hours
Thursday.

30

&&




.SYNOPSIS...
Cold and winter-like conditions will dominate the weather regime
across North and Central TX for the short term portion of the
forecast. This does include a low chance for some light wintry
precipitation mainly across the Big Country and parts of Central
TX. Thereafter, quiet conditions should prevail through the
remainder of the work week with a slight warm up for part of the
weekend. Low rain chances and another shot of cooler air are both
forecast on Sunday with dry conditions thereafter.

&&

.SHORT TERM (Tonight through Thursday)...
Surface analysis this afternoon revealed that the cold front
responsible for the extensive cloud cover, drizzle and fog has
cleared all of our Central TX counties. In its wake north winds
have ushered in lower temperatures with most areas in the upper
40s and 50s at this hour. Across the northern High Plains,
temperatures in the single digits and teens are being observed
even at 3 PM in the afternoon. This airmass is expected to slide
southward over the next 12 to 24 hours. Zonal flow across the
Central Rocky Mountains will help to induce some weak lee-side
pressure falls. In response, the winds across our area should turn
more easterly and eventually southeasterly through Wednesday. We
will have to keep an eye on these trends upstream as they may
serve to briefly disrupt the southward advance of cold air. That
being said, the return flow is expected to be pretty modest. With
wet grounds still in place and cool conditions, we could see some
patchy fog develop, mainly south of I-20.

Wednesday should be a little warmer than today as CAA is shut off
by the increasing southerly flow. Low level cloud cover, however,
will remain and should keep most areas in the 50s to low 60s. A
weak shortwave embedded in the strong zonal flow is expected to
cross the Central and Southern Plains through the day on
Wednesday. As this occurs, a shallow, but strong front will plunge
towards the Red River as cold, dense air crashes southward. There
is some weak synoptic scale ascent via the RRQ of a 100-115 knot
upper level jet that may prove sufficient at generating some
scattered convection, mainly east of a Sherman/Denison to Dallas
to Temple line. Right now, it looks like instability will be too
meager to support thunder, so for now I`ll just carry a mention of
showers. With regards to FROPA---most NWP tends to struggle with
propagation of these shallow airmasses. While there does appear to
be a loose consensus with FROPA, climatology supports going with
a more aggressive timeframe for FROPA. The strongest cold air
advection is expected to occur across the Big Country as cold air
damming induces a weak barrier jet across western zones. With this
in mind, I expect that the cold front will likely near the Red
River by Wednesday afternoon before reaching the I-20 corridor by
sunset. By early morning Thursday, the cold front should be near
the Waco and Killeen metro areas and clear most of our Central TX
counties by sunrise Thursday. Strong north winds will occur as
mixing and the pressure gradient tightens in the wake of the cold
front.

For late Wednesday into Thursday---Broad troughing should be
enough to assist any weak frontogenetical forcing to produce some
very light precipitation late Wednesday into Thursday. Both GFS
and ECMWF models output a fair amount of QPF just south of the
I-20 corridor and down through Central TX. While there is good
agreement in both of these models, the overall forcing appears
pretty subtle and as a result, I`ll trend on the lower side for my
PoP/QPF. If forcing becomes stronger/more apparent---it`s
possible that PoP/QPF will need to be adjusted in magnitude and
space. P-type forecast is difficult due to the uncertainty
revolving around the amount of lift juxtaposed with the best
moisture and cold air. As mentioned above, most NWP appears to be
too warm with regards to their hourly temperature output. In
addition, it`s likely that if precipitation is falling, more cooling
of the lower troposphere will likely continue. After closely
examining model soundings and discussion with surrounding offices,
I`ve added some wintry precipitation, mainly along and southwest
of an area bounded by an Eastland to Waxahachie to Waco to
Temple/Killeen line. Initial precipitation in the wake of the
front will start out as light rain/drizzle before transitioning to
light freezing/rain/drizzle. As the depth of the colder air
increases and secondary ice processes (seeder-feeder) begin to
dominate, a transition to light snow will be possible for the
aformentioned areas.

With regards to wintry precipitation impacts---they are expected
to be LOW and should NOT be widespread. Soil temperature
observations here at NWS Fort Worth indicate that ground
temperatures are still in the mid to upper 50s (and this is likely
representative for areas further south and west). Wind speeds will
also be strong around 20 to 22 knots (and possible near Wind
Advisory criteria) and this should help to quickly whisk away any
residual water on road surfaces. However, trace amounts of ice
and/or snow will be possible, mainly on elevated surfaces as
temperatures will fall into the mid 20s for a few hours. These
strong winds will also result in wind chills in the teens and
twenties as well on Thursday morning! Again, impacts due to
wintry precipitation are expected to be LOW and at this time, it
does not appear that this warrants a Winter Weather Advisory.
Nevertheless, we will continue to monitor trends in temperature
and PoP/QPF as there has been a slow trend of greater
precipitation chances further towards the north near the I-20
corridor.

Dry air should overspread from north to south through the day on
Thursday which should effectively shut off widespread
precipitation, though enough low level moisture may remain to
produce some periods of drizzle. Otherwise, it`ll be a very raw
day with temperatures in the upper 30s and 40s. North winds will
make it feel even colder.

&&

.LONG TERM (Friday through Monday)...
Late Thursday into Friday---Late Thursday and Friday should
remain precipitation free as dry air overspreads North and Central
TX. The real story will be the bitterly cold conditions on Friday
morning. High pressure should settle in across the region and with
light winds, clear skies, a very good radiational night Thursday
night into Friday morning should set up. Temperatures during this
time frame are forecast to fall into the teens and twenties across
a good portion of North and Central TX. We will have to monitor
trends in model output across southern/southeast zones where 925mb
flow does appear to be a bit stronger. This may help to keep the
boundary layer coupled a bit more to the free atmosphere and may
serve to keep temperatures up by a few degrees and I`ve raised
overnight lows on Friday morning by a few degrees here. Wind
chills will remain low, but the light winds should make them a bit
more tolerable on Friday morning.

Saturday and Beyond---A warm up will be in store as zonal flow
continues to the north. A longer period of southerly flow may
allow sufficient low level moisture to stream northward ahead of a
broad trough that is expected to approach from the north. Models
generate a fair amount of QPF late Saturday into Sunday, but
examination of forecast soundings show that the depth of moisture
remains quite shallow. As a result, I`ll keep thunder out of the
package right now and will keep rain chances below long term
models. A weak boundary should slide southward through the region
late Saturday into Sunday. The cooler air behind this front isn`t
expected to be nearly as pronounced as Thursday and temperatures
may only fall by just a few degrees in its wake.

24-Bain

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    41  55  29  37  20 /   5   5  10  10   0
Waco                41  59  31  39  20 /   5   5  40  20   5
Paris               39  50  26  37  19 /   5  10  20  10   0
Denton              37  53  26  37  16 /   0   5  10  10   0
McKinney            39  53  28  37  17 /   5  10  20  10   0
Dallas              42  55  30  37  21 /   5   5  20  10   0
Terrell             41  55  30  37  19 /   5  10  20  10   0
Corsicana           44  57  34  38  20 /   5   5  30  20   5
Temple              43  59  32  39  23 /   5  10  40  20   5
Mineral Wells       35  54  27  37  17 /   0   5  10  10   0

&&

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

$$

30/58



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