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907 
FXUS64 KFWD 220925
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
425 AM CDT Sun Sep 22 2019

.SHORT TERM...
/Today and Monday/

The main concern in the short term forecast period will be the
risk for showers and thunderstorms across parts of the area.
Widespread severe weather is not expected, but heavy rain may
result in some flood issues near and north of US HWY 380 over the
next 24 to 36 hours.

A conveyor of rich moisture associated with T.S. Lorena continues
to stream northward ahead of a trough now positioned across the
Four Corners region. This moisture plume has resulted in multiple
waves of showers/storms across West Texas---some of which may 
skim portions of our Big Country and western Texoma counties this 
morning. Associated with the Four Corners trough is a cold front 
that is steadily oozing southward into the Central and Southern 
Plains. These three weather features will result in rain/storm 
chances for North Texas and parts of the Big Country. Current 
indications are that the cold front will progress southward 
through the day today with occasional quicker surges southward as
portions of the boundary are reinforced by convective cold pools.
The aformentioned trough has been progged by the general model 
consensus over the last several days to translate eastward across 
the Panhandles. As this front slows near the Red River, forcing 
from the ageostrophic response beneath the entrance region of a 90
knot upper level jet streak around the base of the trough, in 
tandem with low level moisture convergence along the front, 
should result in an eruption of convection across southwestern 
Oklahoma and adjacent portions of North Texas.

Most HREF members agree that convective initiation is probable by
2100 UTC today. The coverage, unfortunately, is a little 
uncertain, but given the aformentioned synoptic background, it 
appears that scattered to numerous showers and storms are a good 
possibility across the region this afternoon/evening. I've nudged
PoPs upward into the likely category for this timeframe across 
areas west and north of the D/FW Metroplex given the decent 
agreement among many HREF members. PoPs generally taper downward 
toward 20 percent closer to I-20. Rain/storm chances across the 
Brazos Valley and Central Texas today are associated with streamer
showers penetrating the underbelly of the mid-level ridge this 
morning, then afternoon convection associated with the reinforced
sea-breeze front expected to drift northward.

The potential for severe weather will be limited across North 
Texas as deep layer shear is expected to remain paltry further 
away from the core of the stronger mid/upper level flow. Deep 
layer shear vectors are largely parallel to the slow moving cold 
front, and with PWAT values forecast to be 175% of normal, there 
will be a heavy rain and subsequent flood risk. The moist regime 
may also promote some precipitation loading and a gusty downburst 
risk in the afternoon hours, but the flood threat appears more 
appreciable. 48 hour MRMS rainfall data appear to line up well 
with automated gauges and indicate that some areas along the Red 
River received between 2 and 4 inches of rain on Friday. With the 
potential for training convective cells over some of these areas, 
there will be a heightened risk for flooding. Confidence in the 
exact placement of the heaviest rain this afternoon/evening 
precludes the issuance of a Flood Watch for any of our counties at
this time. Moreover, I expect that most of the flood issues can 
be handled with advisories. Otherwise, temperatures today will 
climb into the upper 80s (across the Red River) to mid 90s (across
Central Texas). 

Extended reaches of hi-res guidance hint at another potential for
showers and storms on Monday. Initially, convection may fire near/
west of US HWY 281 where modest flow atop the stalled frontal 
boundary/residual outflow may be sufficient to lift parcels upward
to their LFC. Confidence in exactly where the boundary stalls is 
a little on the low side, but the scenario advertised by model 
guidance seems reasonable. For now, I'll paint a large area of 
30-40 PoPs with the greatest rain/storm chances across the Big 
Country. Cooler conditions are forecast on Monday given the 
potential for rain/clouds. Unfortunately, a good portion of the 
area will remain in the 90s...except along the Red River and
across parts of the Big Country where highs may remain in the 80s.

Bain

&&

.LONG TERM...
/Tuesday Through Next Weekend/

A full-latitude trough will make landfall on the West Coast today.
Despite spending a considerable amount of time over the relative
data void of the North Pacific, guidance has been in lockstep 
with its evolution over the western U.S. early this week. It will
become a closed low near Las Vegas on Monday, digging even more
equatorward on Tuesday. It is at that point that an upstream jet 
streak emerging from the Pacific will pinch off the low, which
will spend the middle of the week stranded in the Desert
Southwest.

Despite the calendar's transition to astronomical autumn, 
subtropical ridging will attempt to maintain power. But the
proximity of the cut-off low upstream will keep a mid-level
weakness in place, beneath which an onshore fetch will sustain a 
supply of unseasonably rich tropical moisture. Although the
ridge's position will limit the extent of convection (while 
pushing afternoon temperatures into the 90s each day), the weather
will remain a bit unsettled. The bulk of the convective activity
Tuesday through Thursday will be within the more vigorous westerly
flow through the Panhandles and Oklahoma, but some of this
activity may be inclined to slip south of the Red River. This
would apply to both nocturnal convection into the daylight portion
of the mornings and the peak heating of the afternoons. More
scattered (primarily diurnally driven) showers/storms will be
possible elsewhere.

Forecasters often bemoan the unpredictability of cut-off lows, but
this particular version is remarkably well behaved with no more
model spread than any other feature would have at day 5. Latest
runs continue to project a northeastward ejection through the
Texas Panhandle with the time more narrowly focused on Friday. Far
removed from the forcing, North and Central Texas may miss out on
the associated precipitation entirely. Ridging will attempt to 
retrograde back into Texas next weekend, but the tropical conveyor
on its western periphery may keep the unsettled weather in place.

25

&&

.AVIATION... /Issued 1122 PM CDT Sat Sep 21 2019/
/06z TAFs/

While VFR conditions currently prevail at the TAF sites, another
round of MVFR stratus is expected overnight. The onset of low cigs
should occur around 09-10z at Waco and closer to 11-12z across 
the DFW area. Stratus is likely to be less widespread than the 
previous couple of nights, although at least some intermittent 
cigs will be possible through mid to late morning at any of the 
TAF sites. Cig heights will predominantly be at or above 2 kft, 
although some may briefly fall into the 1-2 kft range. Conditions 
should improve to VFR at all airports by late Sunday morning. 
Scattered afternoon convection is expected across parts of North 
Texas and southern Oklahoma, but at this time, am expecting all 
activity to remain north and west of the TAF sites. Will maintain 
rain-free TAFs for the time being, but northern 
arrivals/departures may be affected. South winds are expected to 
prevail, although outflow boundaries from any convection could 
result in temporary wind shifts late Sunday afternoon or evening. 

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    95  75  92  75  92 /  10  40  30  20  30 
Waco                94  73  95  73  94 /  10  10  10  10  20 
Paris               89  72  86  72  86 /  10  30  60  40  50 
Denton              92  74  88  74  91 /  10  60  40  30  40 
McKinney            93  74  89  74  91 /  10  40  40  30  40 
Dallas              95  76  92  76  93 /  10  40  30  20  30 
Terrell             93  74  94  74  93 /  10  20  30  20  30 
Corsicana           95  72  93  72  91 /  10  10  20  10  20 
Temple              94  72  94  72  91 /  10  10  10  10  20 
Mineral Wells       92  71  89  72  91 /  20  50  40  20  30 

&&

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

$$

25/24