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

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FXUS64 KFWD 131751

Area Forecast Discussion
National Weather Service Fort Worth TX
1151 AM CST Tue Nov 13 2018

/18Z TAFs/

Concerns...Ongoing MVFR cigs, but improving to VFR this afternoon
for the rest of the forecast period.

The anticipated drier airmass has finally arrived into our area,
starting to clear out some of the post-frontal low cloud deck.
Although this has been slower than previosly anticipated, the MVFR
ceilings will scatter out early this afternoon. VFR conditions
are expected for all the TAF sites through the rest of the
forecast period and beyond. There may be some lingering moisture
late tonight into tomorrow morning as the upper level system
continues to move east, but this should stay east of the DFW
Metroplex and Waco aiports. Winds will continue to be in the 10-20
kt range through the afternoon, but will diminish to near or
around 10 kt after 00Z.



.UPDATE... /Issued 943 AM CST Tue Nov 13 2018/

The back edge of the expansive stratocumulus cloud deck continues
to move southward through the northern counties of Texas at mid
morning. The clearing trend is running a tad slower than
previously expected, however, and we`ve updated the grids for
today to reflect this delay. Trimmed the daytime temps down just a
degree or two to correspond to this delayed clearing, in addition
to the continued weak/moderate cold advection. Also removed the
low PoPs for the southeastern counties, as this light
precipitation has slipped out of our area.



.SHORT TERM... /Issued 332 AM CST Tue Nov 13 2018/
/Through Tonight/

Main focus through the short term is the potential for some very
light and inconsequential wintry precip across our southern zones
this morning.

It`s a brisk start to the day with continued cold/dry advection
ongoing beneath the cold frontal inversion. As of 330 AM, almost
all of the forecast area has fallen below freezing with the
exception of our southeastern zones which are hovering in the mid
30s. The entire area remains under a Freeze Warning through 9 AM,
and it is likely that remaining areas will reach the 32 degree
mark by daybreak. Otherwise, meager moisture trapped within the
inversion layer has resulted in widespread stratus encompassing
the entire forecast area. However, the arrival of drier air will
mean the gradual demise of this cloud shield throughout the day,
with clearing occurring from north to south. Winds have remained
gusty overnight with momentum from a 20-30 kt low-level jet being
mixed down to the surface. Breezy conditions will continue
throughout the morning hours and contribute to wind chills in the
teens and low 20s area-wide.

Aside from the low-level post-frontal airmass, our other feature
of concern is a sharp positively-tilted trough axis just upstream
which is contributing to large-scale mid-level ascent over the
eastern half of Texas. Indications of this lift can be identified
by relatively cooler cloud tops via morning satellite imagery, as
well as weak radar echoes overspreading the Texas Hill Country.
Most of this lift is occurring within the 600-400mb layer, which
has saturated at temperatures of minus 10-20C. This is likely
contributing to dendrite growth, as well as some ice crystals
within the mid-level cloud layer. As this precipitation falls, it
will encounter very dry air around 700mb, which should result in
sublimation of most hydrometeors, at least initially. It`s
conceivable that enough wet-bulbing may occur to result in
sufficient saturation through the low and mid-levels for some
precipitation to survive the trip to the surface, resulting in
brief light flurries or a few ice pellets as this area of ascent
overspreads our Central Texas counties by daybreak or shortly
after. If more moisture was available, there would be a better
shot for some meaningful wintry precip, but such dry low-level
air will mean very sparse occurrences of any snowflakes or ice
pellets this morning. This paragraph has essentially been a long-
winded way of saying that I can`t rule out a few insignificant
snow flurries this morning in Central Texas. A 20% chance of
flurries/sleet has been maintained in the forecast through the
morning hours roughly south of a Hamilton to Canton line.

Otherwise, high temperatures today will be held in the upper 30s
and low 40s due to the persistent cold advection. Wind chills
during the afternoon hours will likely still be in the 20s or low
30s thanks to breezy NNW winds at 15-25 mph. Winds will finally
decrease this evening as the surface pressure gradient relaxes as
the high pressure center drifts closer to the area. Most cloud
cover will be exiting the area by sunset, so the lighter winds,
clearing skies, and low dewpoints will set the stage for
impeccable radiational cooling conditions tonight. The one
exception may be our eastern zones where wrap-around moisture near
the low-level low pressure circulation may result in periodically
cloudy skies overnight. Regardless, everyone in the forecast area
should see lows in the 20s, with even some teens possible across
the north or northwest. We`ll let the following shifts determine
if another Freeze Warning is necessary tonight for any of our
southeastern zones that only briefly touched 32 this morning. With
the absence of stronger winds, wind chill values will essentially
be identical to the ambient temperatures through early Wednesday
morning. There may be some instances of patchy frost, although
fairly large temperature/dewpoint spreads should limit
development and have not included a mention in the worded forecast
at this time. It`s worth noting that record lows are 21 for DFW
and 23 for Waco on Nov 14th. These temperatures are probably a
bit out of reach for Wednesday morning, although both sites could
certainly come within a few degrees of these values.



.LONG TERM... /Issued 332 AM CST Tue Nov 13 2018/
/Wednesday Through Next Monday/

The period from Wednesday through Thursday continues to remain on
cold side with freezing morning temperatures to start each day
under clear skies. Unidirectional, low level northwest flow
underneath the residual and deep frontal inversion should mix down
and maintain brisk conditions with wind speeds 10 to 15 mph on
Wednesday, though not near as windy as today. Despite the abundant
sunshine Wednesday, the deep cold core mid-level low will be slow
to move out and with low temperature thickness values both in the
low and mid levels. The very dry continental airmass in place
will help temperatures warm slowly into the 40s by afternoon with
the assist of insolation, but modest northwest breezes will
continue to make it feel a bit chilly outside. The amplified
cyclonic flow overhead on Wednesday is expected to dampen quickly
in wake of the departing deep mid level low on Thursday. The broad
surface ridge will continue sliding southeast across the Texas/
Louisiana coastlines and the Northwest Gulf of Mexico. Low level
warm advection within the 925mb-850mb layer will commence and
combine with continued abundant sunshine to help temperatures
recover into 50s, to even lower 60s west of U.S. 281. Winds will
back around to the west-southwest at 5 to 10 mph.

A warm up to near climatological temperatures(mid-upper 60s) is
expected Friday and Saturday, as mid-level flow aloft becomes
zonal overhead. This will induce increasing lee side pressure
falls with the return of south-southwest winds near 10 mph each
day. Low temperatures Friday morning won`t be as cold, but still
on the cool side in the mid-upper 30s. Low level surface dew point
temperatures will be slow to recover with the Western Gulf of
Mexico having been scoured by all the recent cold fronts.
Increasing south breezes and slightly higher surface dew points
across the area Friday night will hold low temperatures Saturday
morning in the the 40s, though a few readings in the upper 30s
could occur within typical protected rural areas. An increase of
mid to high level cloudiness is expected as we progress through
the day Saturday with the passing of progressive mid-level energy
aloft moving readily east across the Southern Plains. The airmass
in the lower-mid levels will be slow to recover and remain too dry
to support any precipitation, though certainly I cannot rule a
few areas of virga by later in the day Saturday west of I-35.

Changes to sensible weather begin occurring by Sunday and
continuing into early next week, as split, low-amplitude mid-
level flow sets up across the Central CONUS. North and Central
Texas will be underneath more of the southern branch of the split
flow with a strong shortwave trough moving southeast across the
Mid Mississippi Valley by Sunday Night. This will support a cold
front, though not as deep and cold into the area Sunday. Medium
range deterministic models and their ensemble members are actually
in decent agreement both with surface features and the split
flow, longwave pattern aloft. However, as is usually the case this
far out in time, is the tracking of shortwave energy within the
fast mid-level flow and availability with the Gulf of Mexico
having little if any recovery time for adequate moisture recovery
for rainfall. After collaboration with neighboring offices, it was
agreed upon to remain conservative and only introduce very low
rain chances until these trickier variables can be better resolved
with future sampling of the atmosphere.

Otherwise, the increasing cloud cover and anticipated low-level
cold advection Sunday will result in highs in the 40s across the
northwest half of the region and in the 50s from DFW south and
east. High temperatures next Monday will only recover into the 50s
areawide, as cloud cover and surface high pressure settling
across the area keep low level warming suppressed until warm
advection commences moving into next Tuesday.



Dallas-Ft. Worth    39  24  46  29  58 /   0   0  10   5   5
Waco                40  24  48  27  59 /   0   0   5   5   0
Paris               37  26  43  28  52 /   0   0  20  10  10
Denton              39  22  46  28  58 /   0   0  10   5   5
McKinney            38  23  44  28  55 /   0   0  10   5   5
Dallas              39  26  46  31  57 /   0   0  10   5   5
Terrell             38  23  46  28  56 /   0   0  10   5   5
Corsicana           38  25  45  30  55 /   0   0  10   5   5
Temple              40  25  49  28  59 /   0   0   5   0   0
Mineral Wells       40  21  47  28  61 /   0   0   5   0   5




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