River Flood Warning 169, NWS Fort Worth, TX

Area Forecast Discussion
National Weather Service Fort Worth TX
135 PM CST Wed Dec 26 2018

.SHORT TERM...
/Through Tonight/

Scattered thunderstorms are increasing in coverage this afternoon
along and west of the I-35 corridor, in response to a
strengthening low-level jet and warm-air advection regime
centered near the Big Country. General thinking is most of this
convection should remain rooted above a surface stable layer
for another hour or two. Still, will continue to monitor these
cells for any more notable surface-based characteristics, which
would suggest a quicker increase in the threat. Regardless, as
forcing for ascent with the primary shortwave trough (very evident
in satellite imagery over the Permian Basin) approaches North and
Central Texas, a line of storms is then expected to intensify as
it moves into our western counties around 6-8pm.

Ahead of this line, the strengthening low-level jet and
south/southeasterly surface flow will draw dew points in the lower
to possibly mid 60s northwestward through Central Texas towards
the Big Country. This should bring sufficient low-level and
mixed-layer CAPE (e.g., upwards of 1000-1500 J/kg of MLCAPE)
to primarily areas south of I-20 and west of I-35 to support the
development of surface based updrafts through the evening hours.
In turn, a threat of a few damaging wind gusts, marginally severe
hail, and a few tornadoes is expected with this line, especially
given rather stout low-level flow. Farther north (generally I-20
and points northward), decreasing surface theta-e should limit the
severe threat more. Still, a few isolated damaging gusts will be
possible and a couple of brief tornadoes cannot be ruled out
either during the late evening hours.

Storms should cross the I-35 corridor through about 8pm to
midnight, before reaching East Texas around 4am. The severe threat
should then come to an abrupt end with the departure of the line
to the east.

Picca

&&

.LONG TERM...
/Thursday through Wednesday/
With the passage of the upper trough overnight, drier westerly
flow will prevail behind the Pacific front Thursday. Temperatures
will be near or even a little warmer than today compliments of
the downslope flow and sunny skies. Winds by the evening hours
will become more northwesterly as a surface high builds down in
through the Plains. This will begin a modest but persistent cold
advection regime over the region. Temperatures will gradually fall
and it will bring a few days of chilly weather. Friday's highs
will be in the mid 40s in the northwest zones to the mid 50s
southeast, and lows Friday night will range from the upper 20s
northwest to the upper 30s southeast.

By Saturday clouds and rain chances will increase as isentropic
lift sets up over the area in response to energy translating
through the Panhandles within a stationary positive tilt upper
level trough axis. Moisture will be a bit limited with this first
round of lift so the best rain chances, while still low, will be
across the southeastern half of the area. Another shortwave will
track through Texas in southwesterly flow aloft late Sunday and
we'll see more numerous showers, especially Sunday night. Again
the best chances of rain will be over the southeast half of the
CWA where moisture is greatest and PoPs will range from likely
there to slight chance in the northwest. Daytime temperatures will
be held down by the clouds and sporadic rainfall with 30s and 40s
for highs this weekend. Likewise the cloud cover will keep low
temperatures from cooling appreciably, so believe the threat for
any freezing rain is too low to mention. While one might normally
be concerned that we could see wet bulb cooling to force temps
below freezing, by this time wind speeds are nearly calm and
therefore it would be a situation where evaporative cooling is
minimal and warm raindrops are effectively transporting heat from
the cloud layer to the ground.

This round of rain will end during the day Monday from west to
east with the passage of the shortwave trough. Clearing skies and
drier weather will prevail through the end of the week.
Temperatures will continue to be near or slightly below normal.
New Years Eve and Day festivities look seasonably chilly, but
pleasant.

TR.92

&&

.AVIATION... /Issued 1142 AM CST Wed Dec 26 2018/
/18Z TAFs/

Biggest challenge is timing of thunderstorms through TAF sites.
Current thinking is that an initial round of occasional
thunderstorms will pass through sites this afternoon so show TEMPO
groups for 20-00Z. There is some potential for Metroplex sites to
experience TS around 19-20Z, though, based on current trends. Will
continue to monitor. IFR VSBY/CIGs expected in TS cores, but
generally expecting VFR VSBY and MVFR CIGs outside of cores.

A second, more potent, line of storms is forecast to push through
TAF sites around 01-03Z this evening. Some potential for this line
to be delayed (closer to 03-05Z), but higher confidence in an
earlier passage at this time. Timing could very well be changed in
future amendments by 1-2 hours, though. Winds will change
direction from southeasterly to west/southwesterly with the
passage of the line. Gusts of around 30-40 kt would be expected,
but an isolated gust could reach 45 kt or so as storms cross TAF
sites. Otherwise, expect winds to continue to be gusty from the
southeast through this afternoon, before switching to the
west/southwest behind the line after 06Z.

VFR conditions should return by around 06-10Z as well.

Picca

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    53  64  37  51  34 /  90   0   0   0   0
Waco                51  67  39  55  36 /  90   0   0   0   0
Paris               53  66  36  50  33 /  90  10   0   0   5
Denton              50  63  34  48  32 /  90   0   0   0   0
McKinney            52  65  35  49  33 /  90   0   0   0   0
Dallas              53  66  37  51  35 /  90   0   0   0   0
Terrell             54  66  37  52  35 /  90   0   0   0   0
Corsicana           54  66  38  54  36 /  90   5   0   0   5
Temple              52  68  39  56  37 /  90   0   0   0   0
Mineral Wells       48  61  32  48  29 /  90   0   0   0   0

&&

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

11/92

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