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Area Forecast Discussion (AFD)

Issued by Fort Worth/Dallas, TX (FWD)

                            
000
FXUS64 KFWD 230914
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
414 AM CDT Mon Sep 23 2019


.SHORT TERM...

/Today Through Tuesday/

Rain and isolated thunderstorm chances will continue today 
and tomorrow (Tuesday) mainly for parts of North Texas. The
highest rain chances are during the afternoon hours, and there is
no guarantee that all locations will experience rain/storms. High
temperatures will remain above normal values, except for those 
areas that experience showers/storms near peak heating today and 
Tuesday. 

Surface analysis this morning revealed that a diffuse front was
draped across the Low Rolling Plains and extended back to the 
northeast across western and central Texoma. This front will be 
the impetus for rain/storm chances over the next couple of days. 
Subtle isentropic upglide along the 305K theta surface was likely
resulting in a slight uptick in isolated to widely scattered 
showers this morning. RAP isentropic progs suggest that this 
upglide will persist through the morning hours, roughly near and 
north of a Breckenridge to Denton to Paris line. Given the moist 
regime, I'll advertise 30-50 PoPs through noon today across these 
regions. Slight chance PoPs exist south of this line to about the 
I-20 corridor. Lightning activity has been largely absent this 
morning and I'll leave most activity as showers, except across 
extreme northeastern parts of the forecast area near Bonham and 
Paris where instability may be a little larger. 

Thunderstorms will become increasingly more probable this 
afternoon as daytime heating helps to bolster instability values 
to near 1500 J/kg. Forecast soundings for areas near and north of
I-20 are characterized by a hot and well-mixed bounday layer
(exhibiting an inverted-V type profile). While severe weather 
doesn't appear likely at this time owing to the paltry deep layer 
wind shear (about 20-25 knots), the aformentioned sounding 
profile could support a gusty outflow wind potential. There's also
a threat for pockets of heavy rain this afternoon as most of 
North Texas will be within a zone of PWATs near or just above 2" 
per GOES PWAT product (which is about 175% of normal). The exact 
coverage of showers and thunderstorms is the tricky part to this
forecast. Given the moist regime, my first inclination is to 
believe that the probability for large cold pool development---and
thus the potential for slightly more organized/widespread
storms---is on the low side. This would support a more 
conservative PoP forecast. If deep bounday layer mixing is able to
transpire before convective initiation, it's conceivable that the
areal coverage of convection will be much greater and would 
warrant a more aggressive PoP than currently forecast. For now, 
I'll keep PoPs capped at around 50 percent for locations near and 
north of I-20 this afternoon/early evening and will defer to the 
day shift to make adjustments based on radar trends and 12 UTC hi-
res guidance. Otherwise, the first day of astronomical fall won't
feel like it for many locales across the area (especially Central
Texas), except for maybe those locations that experience 
showers/storms at peak heating. If convection can form a decent 
cold pool, it may reinforce the front southward some, spelling at 
least a temporary cool down for some locales. 

Showers and storms should wane some this evening, though if the
coverage is greater, it's possible that activity may persist well
into the night. I've advertised slight chance to chance PoPs in 
the hopes of capturing this potential with best rain and isolated 
thunderstorm chances remaining near and north of I-20. Overnight 
low temperatures are expected to fall into the 70s across the 
entire area. The urban areas will likely remain in the mid 70s. 
Low level southerly flow will likely push the diffuse frontal 
boundary northward. There could be a low end fog/mist potential as
this boundary sloshes northward, but the potential looks too low 
to include in the forecast. 

From a synoptic meteorology standpoint, Tuesday appears quite
similar to Monday with a weak frontal boundary draped across parts
of North Texas. The one addition to the picture will be the 
presence of a mid-level vorticity max---possibly convectively 
induced. While there's likely to be the addition of residual 
outflow boundaries from Monday, I'll paint the highest PoPs based 
on the expected placement of the surface frontal boundary (likely 
near the US HWY 380 corridor) and track of the mid-level vorticity
max. With this feature (the vort max) lifting northward during 
the mid to late morning hours, coupled with the increase in 
instability, there should be another round of showers and 
thunderstorms. Where rain/storms actually develop will be 
dependent on the development and track of the vort max as well as 
the placement of the surface frontal boundary and residual 
convective outflow. As a result, I'll keep PoPs at or below 50 
percent given this uncertainty. At this time, however, it appears 
that areas near and north of US HWY 380 will stand the best chance
for rain/storms on Tuesday.

Bain

&&

.LONG TERM...

/Wednesday Through Early Next Week/

By the middle of the week, Texas will be sandwiched between a 
deepening cut-off low in the Desert Southwest and a subtropical
ridge over the Gulf of Mexico. This relative weakness in the mid-
level flow will maintain some low rain chances Wednesday and
Thursday, but it still appears the midweek showers and
thunderstorms will be primarily confined to the more vigorous
westerly flow through the Texas Panhandle and Oklahoma. Although
the core of the ridge will be displaced to our east, mid-level
heights will above North and Central will still be anomalously
high for late September. As a result, abundant sunshine will push
afternoon temperatures into the low to mid 90s regionwide. Normal
high temperatures on September 25 range from the lower 80s along
the Red River to the upper 80s in Central Texas. While Wednesday's
highs may be as much as 10 degrees above normal, this is far from
unprecedented. Our forecast high of 93F at DFW Airport has been
matched (or bettered) more than 20 times historically on that
calendar date, thus occurring more frequently than once every 6 
years. The record values at DFW (102F in 2005) and Waco (106F in
2011) won't be challenged. Although Wednesday may be the hottest
day of the bunch, the heat will persist; but breezy south winds 
and increased cloud cover on Thursday will shave a degree or two
off high temperatures.

The cut-off low is now projected to slip well south of the U.S./
Mexico border, settling over Baja California on Tuesday and
Wednesday. Further separated from the polar flow, its ejection
will be delayed. Despite the changes from previous outlooks,
extended guidance appears to be using the same playbook, and the
feature is expected to swing through the Texas Panhandle as a
shearing open wave Friday night. Even with the slower evolution,
its track will still be too far from North and Central Texas to
provide much of a bump in PoPs. But with the onset of turbulent 
southwest flow above a moist and unstable boundary layer, Friday
may still be the most favorable time period within the extended
forecast for appreciable rainfall.

As this system is absorbed into the polar flow this weekend,
ridging will attempt to retrograde back into the Lone Star State,
but the tropical conveyor on its western periphery may maintain
some low shower/storm chances. The ridge will eventually take hold
early next week, maintaining the unseasonably warm temperatures
through the end of the month but also helping to reduce the influx
of Gulf moisture. While not as mild as normal, the lower humidity
will be a welcome change.

25

&&

.CLIMATE...

September Superlatives for Dallas/Fort Worth

There have been 17 days this month with at least 95F at DFW
Airport. This is just 4 days shy of the September record of 21
days, set in 2005. While forecast highs are in the 90s the
remainder of the month, this may be a tough record to match.

For Dallas/Fort Worth, there has never been a September without 
temperatures in the 60s. DFW has so far remained above 70F the 
entire month, and all of the low temperatures we have in our
forecast for the rest of the month are in the 70s.

Through the 22nd, our current month is the 2nd warmest on record.
The warm end to the month may challenge September 1939 as the
warmest September on record.

There has been no measurable rainfall at DFW Airport this month.
The driest September on record occurred during the multi-year
drought in the early part of this decade: September 2014 tallied
only 0.06" of rainfall. The last calendar month with no 
measurable precipitation at DFW Airport was August 2000 (0.00").


.AVIATION... /Issued 1133 PM CDT Sun Sep 22 2019/
/06z TAFs/

A weak upper shortwave continues to support light showers across 
North Texas this evening, although activity is generally on a 
downward trend as of 430z. Any lingering rain overnight is 
expected to remain north of the DFW airports, and VFR conditions 
should prevail at all TAF sites through the morning. There is a 
low-end potential for brief MVFR cigs at Waco around daybreak, but
the higher potential will remain off to the east with a weak and 
veered low level jet in place. 

New convective development should occur throughout the day in
response to weak upper troughing in the presence of a quasi-
stationary surface front. This activity will be scattered in 
nature, but could begin impacting TAF sites during the early to 
mid afternoon. Will continue to advertise a few hours of VCTS at 
the Metroplex airports during this time which will last into the 
early evening. Waco should remain well south of convective
activity through the period. While south winds around 10 kts will
prevail, convective outflows could cause short-lived wind shifts 
during the afternoon or evening hours around the DFW area.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    90  75  88  75  93 /  50  20  30   5  20 
Waco                94  73  94  72  95 /  10   5  10   5   5 
Paris               84  71  86  71  87 /  50  30  50  10  20 
Denton              89  73  87  74  93 /  50  20  40  10  20 
McKinney            89  72  86  74  92 /  50  20  40  10  20 
Dallas              91  75  88  76  94 /  50  20  30   5  20 
Terrell             91  73  88  73  94 /  40  20  20   5  10 
Corsicana           93  73  92  72  93 /  10   5  10   0   5 
Temple              93  73  94  72  93 /   5   5  10   0   5 
Mineral Wells       88  72  90  72  93 /  50  20  40  10  10 

&&

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

$$

24/25