NWS Area Forecast Discussion

FXUS64 KFWD 201804

Area Forecast Discussion
National Weather Service Fort Worth TX
104 PM CDT Fri Oct 20 2017

Predominantly MVFR conditions are expected throughout the TAF
period aside from a window of VFR conditions through portions of
this afternoon. Moisture continues to move northward through North
and Central TX which is leading to isolated showers embedded within
a deck of BKN stratus. This is the extent of precipitation
expected through the current TAF period with limited lift and a
capping inversion in place; a mention of VCSH will suffice through
the rest of the afternoon. Otherwise, the continued arrival of
deep moisture through the boundary layer will lead to prevailing
MVFR cigs at all TAF sites beginning this evening and lasting into
Saturday. While brief IFR cigs as low as 600 ft will be possible
tonight, have only included a Tempo mention at Waco where
confidence is a bit higher in occurrence. The slightly stronger
winds expected at DFW Metroplex sites may cause enough turbulent
mixing to hold cigs at or above 1000 ft overnight, however,
ceiling trends will need to monitored closely during the
overnight hours.



.UPDATE... /Issued 1017 AM CDT Fri Oct 20 2017/
Quick update this morning to lower PoPs a bit through the
afternoon hours. Scattered showers continue to develop and
dissipate just as quickly within a fairly thin layer of moisture
beneath a capping inversion. Without much ascent present, this
should be the extent of convection throughout the rest of the
afternoon with showers unable to harness the better instability
rooted above the cap. Otherwise, clouds will continue to be on
the increase as low stratus pushes north and additional mid-level
clouds arrive from the west associated with a weak approaching

Products for this update have already been transmitted.



.SHORT TERM... /Issued 400 AM CDT Fri Oct 20 2017/
/Today and Tonight/

After quiet weather for much of this past week, changes are
already occurring across parts of the region this morning. Upper
level troughing is now established across the region, and the
main shortwave within the trough is coming onshore in the Pacific
Northwest. However, several weaker disturbances are embedded in
the trough ahead of the main shortwave and will cross the region
today and tonight. Low and mid level moisture is already
increasing from the south and will continue to do so through

With the moisture advection occurring early this morning, showers
have been moving north across our southeastern counties. Hi-res
model guidance and operational models are in very good agreement
that convection will continue to move across the region today,
mainly along and east of the Interstate 35 corridor. Instability,
lapse rates, and shear values from soundings continue to support
a mention of thunderstorms. We still cannot rule out the potential
for a strong or marginally severe thunderstorm, but this
potential may be hampered by a weak cap and/or weakening lapse
rates during the afternoon hours as indicated on forecast
soundings. More widespread strong/severe storms are not expected

Rain chances decrease this evening as the best moisture advection
shifts north of the region. However, we will keep low shower and
isolated storm chances in the forecast overnight as troughing
continues overhead and the low level jet increases to 30-40 kts,
providing some warm air advection/isentropic lift. Rainfall totals
for today will range from zero in most of our western counties to
over a half inch in some areas in our eastern counties.

Otherwise, expect mostly cloudy skies today and tonight with winds
of 10-15 mph for much of the period. Tempered highs under guidance
in our eastern counties today due to rain and cloud cover, but
just about all locations will experience highs in the 70s. A few
locations in the west and south could reach 80 degrees. Overnight
lows will be noticeably warmer in the 60s and lower 70s.



.LONG TERM... /Issued 400 AM CDT Fri Oct 20 2017/
Rich Gulf moisture will be in place across the region on Saturday.
A thick blanket of clouds will begin the day, and showers beneath
a capping inversion may be ongoing across our eastern zones.
Additional low-level moist advection will delay the erosion of the
low clouds. Our western zones will have the best chance of seeing
adequate sunshine, with the low clouds likely persisting in areas
east of the I-35 corridor.

A jet streak emerging from the Rockies will veer the mid-level
flow, encouraging the development and eastward advancement of a
West Texas dryline. Although the dryline will encounter MLCAPE
values approaching or even exceeding 2000J/kg to our west,
westerly capping flow may keep the boundary quiet throughout the
afternoon hours. Even though the dryline is unlikely to reach our
CWA, there should be enough afternoon sun deeper into the humid
air to sufficiently destabilize the boundary layer. The inhibition
will be the limiting reactant, and guidance is uninclined to
allow convective initiation across North and Central Texas
Saturday afternoon. Any cells that are able to realize the
extraordinary instability could quickly become severe with
favorable shear for maintenance.

As a cold front dives into northwestern Oklahoma late in the day,
it will encounter an environment of increasing instability and
steadily eroding CIN. Western Oklahoma will likely be the focus
for the most vigorous convective initiation late Saturday
afternoon and into the evening hours. The window for supercells
may be small. As the front races southeastward into an endless
supply of fuel, the convective elements will likely congeal into a
linear complex before entering North Texas. This line may unzip
southward along the front as it overtakes the dryline, charging
into our western zones late Saturday evening. This complex will
pose primarily a wind threat, but favorable 0-1km shear (enhanced
by the frontal boundary or associated outflow) may support
embedded tornadoes. Any cells that remain discrete may also pose a
hail threat with deep-layer shear supportive of long-lived
updrafts. It still appears the better shear and dynamics will be
along and north of the I-20 corridor, and with veering inflow
ahead of it, the linear MCS should diminish in intensity as it
enters our southern and eastern zones early Sunday morning.

The convective complex will exit the region on Sunday, and gusty
north winds will follow in its wake. With abundant sunshine,
afternoon temperatures should reach the 70s regionwide, but the
winds will make it feel cooler than that.

After a cool start to the day on Monday, downslope winds will aid
in a quick warm up. This warming trend will be short-lived with
another front arriving Monday night. Deep northwest flow will
maintain mild daytime temperatures Tuesday and Wednesday. As the
flow becomes more zonal on Thursday, some locations may reach 80F,
but the parade of autumn fronts will continue with another
arriving Thursday night.



Dallas-Ft. Worth    77  70  84  61  74 /  30  20  30  90  20
Waco                77  71  86  62  76 /  30  20  30  90  20
Paris               77  65  80  60  71 /  30  20  40  90  30
Denton              77  68  83  58  74 /  30  20  30  90  10
McKinney            77  67  83  60  73 /  30  20  30  90  20
Dallas              77  70  84  61  74 /  30  20  30  90  20
Terrell             75  68  85  61  74 /  40  20  30  90  30
Corsicana           75  69  84  63  73 /  40  20  40  90  40
Temple              79  71  86  63  77 /  30  20  30  90  30
Mineral Wells       77  67  86  56  74 /  20  20  30  80   5





NWS FWD Office Area Forecast Discussion