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

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FXUS64 KFWD 221516 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1016 AM CDT Fri Mar 22 2019


.UPDATE...
Forecast for today is on track, with few changes made in the
morning update. Morning surface analysis reveals a ridge of high
pressure anchored across the central United States. This ridge
axis should shift east as the day progresses. Combined with
surface cyclogenesis along the lee of the Sangre de Cristo
Mountains, increasing southeasterly flow should allow temperatures
to rise into the mid 70s across most of our county warning area,
despite the presence of some high clouds.

Rain and thunderstorm chances will increase late tonight as an
upper-level shortwave trough makes its way into the Central Great
Plains. The severe weather threat should be low with this early to
late morning round of thunderstorms.

Godwin

&&


.SHORT TERM... /Issued 356 AM CDT Fri Mar 22 2019/
/Today and Tonight/

A broad surface ridge, along with its` counterpart -- a shortwave
ridge aloft will remain over East Texas through this morning,
before moving slowly east toward the Lower Mississippi Valley
through Saturday evening. Our shortwave ridge aloft will gradually
give way to increasing southwest flow aloft in advance of a
strong mid level disturbance moving across Arizona/New Mexico
today. Our previous evening`s FWD sounding continue to show a
stout warm and dry elevated mixed layer(or cap aloft) based around
765mb. Though this capping inversion may rise and weaken late in
the day, dry and warm mid-level air being drawn up from the tops
of the Sierra Madre Mountain Range in Northeast Mexico will
maintain an atmospheric lid across North and Central Texas. Sans
periodic mid-high clouds from a mid level shortwave riding over
the top of our departing ridge, the area will remain dry. Partial
sunshine, especially across central and eastern parts of the CWA
will combine with a dry low-level airmass and gradually
increasing temperatures in the 925mb-850mb layer for another warm
day with highs in the 70s. Today will be breezier, as our surface
pressure gradient tightens in response to increasing mid- level
height falls just to the west of the area.

As one might expect with vigorous mid-level energy/associated
height falls lifting out the Desert Southwest and out over the
Southern High Plains, the capping inversion will "gradually"(and I
stress this) lift, moisten, and weaken across our far
west/northwest counties this evening. With the national blend PoPs
being coarser and generally in a 6-12 hour configuration, they
look to be too high for the majority of the tonight period with
regard to my recent comments on the environment. I will introduce
increasing convective chances primarily north of I-20 and west of
I-35W as we approach midnight, with stronger west to east large-
scale ascent likely occurring across areas along and north
I-20/I-30 corridor during the pre- dawn hours Saturday. The reason
for the delay in better convective coverage is due to the semi-
northerly track of our primary shortwave disturbance lifting east
across the Panhandles and toward Oklahoma/Kansas through sunrise
Saturday. This track is fairly well agreed upon amongst all the
CAMs and even the GFS with our northern tier counties seeing the
stronger ascent and faster erosion of the cap aloft. Meanwhile,
Central Texas will see a slower progression of these processes
being further south from the system track.

Kinematically, this system will have deep layer shear through 6km
30-40kts, but the Effective Bulk Wind Difference(or EBWD...a nice
indicator for supercell structures) is forecast to be fairly weak
and 20 knots or less, even along the Red River Valley. Throw in
surface dew point temperatures remaining the 40s with convective
activity likely being elevated, it doesn`t appear any storms would
reach severe limits. Thermodynamically -- or as some prefer,
"environmentally", I can`t rule out some small hail with more
vigorous updrafts toward daybreak Saturday. MUCAPE on the order
of 400-700 J/KG and steepening mid level lapse rates near 7 deg
C/km may be enough to support this potential. However, in the
overall spectrum of evolution it appears the majority of activity
late tonight will be of the "general" variety and agree with SPC`s
outlook for tonight. Otherwise, continued south breezes and
plentiful cloud cover will low temperatures late tonight well into
the 50s across much of the area.

05/

&&

.LONG TERM... /Issued 356 AM CDT Fri Mar 22 2019/
/Saturday through Thursday/

The main focus in the long term forecast period will be the
potential for strong to possibly severe convection this weekend.
Thereafter, quiet conditions are anticipated until the end of
next week when rain/storm chances return. Afternoon high
temperatures won`t be too far removed from seasonal averages with
highs in the upper 60s 70s for most days. Some locations west of
I-35 may climb into the low 80s.

This Weekend---A conveyor of slightly richer theta-e air will
spread northward from the Hill Country and up through the Big
Country during the pre-dawn hours on Saturday. Coincident with
this will be the approach of a shortwave trough with an attendant
belt of 40 to 50 knot winds around 500mb. The implied low level
WAA, weak mid-level cyclonic vorticity advection and jet entrance
forcing should be enough to spark showers and thunderstorms. The
aformentioned synoptic features all appear to overlap spatially
near and north of I-20 and west of I-35 on Saturday morning and
I`ve painted the highest PoPs across this region. The initial runs
of higher resolution model guidance have started to hone in on
this area which yields greater confidence. With the surface layer
still remaining capped, it`s probable that initial activity will
be rooted above 850mb. While MUCAPE values are modest, around
800-1000 J/kg, deep layer shear values of 40 to 50 knots will
support some organized modes. Mid-level lapse rates near 7 C/km
are projected across the aformentioned geographic region and given
that convection should be elevated, the primary hazard will be
hail. Given the deep layer shear, it wouldn`t surprise me to see a
severe hail report or two later Saturday morning.

Through the afternoon hours on Saturday, both the plume of best
theta-e and forcing for ascent /mid-level height falls/ should
shift eastward. I have reoriented PoPs in a northeast to southwest
fashion with the best chances for rain/storms being across
northeast TX down into parts of East and Central Texas. While
forcing for ascent will increase to the east as the shortwave
trough ejects into the Central Kansas, instability will actually
decrease with eastward extent. As a result, I`m not expecting too
much in the way of a strong to severe storm threat where I have
the highest PoPs (60%-70%). The better strong to severe potential
will be for any storms that can develop farther west in the an
environment characterized by MLCAPE near 1000 J/kg with deep layer
shear still around 50 knots. Despite the more more favorable
thermodynamic profile, this region will be on the backside of the
diffuse trough axis which should equate to large scale subsidence.
Nevertheless, if a convective tower is able to overcome this
subsidence---perhaps through mesoscale ascent along remnant
convective outflows---there will be a risk for organized
convective modes and thus a severe weather threat west of I-35. As
the trough axis skirts eastward Saturday night into Sunday, most
precipitation should come to an end spelling a quiet overnight
period into Sunday with mild conditions.

Sunday presents a challenge as it pertains to convective
initiation during the afternoon hours. Whether or not convection
develops will be dependent on cloud cover and the removal of a
capping inversion. Forecast soundings indicate that 850mb temps
may climb as high as 14.5 C which may be too much to overcome.
That in mind, there are a couple of features that we will be
monitoring closely over the next day or so that could compromise
the integrity of the cap. The first is the position of a dryline.
Model guidance varies some with the ECMWF and NAM being the most
aggressive. These models push the 60 degree isodrosotherm closer
to the I-35 corridor in the 18-21 UTC time frame on Sunday
afternoon. The GFS, however, arcs the dryline from near a St. Jo
to Stephenville to Comanche line late Sunday afternoon. At this
time, I wouldn`t be surprised if the GFS solution is closer to
reality given that model guidance over the past several years has
been too aggressive with mixing the dryline too far to the east.
The other feature of interest will be another belt of 50 knot mid-
level flow. In addition to large scale ascent, a surface low
should develop somewhere across the left exit region of this
feature and give birth to a pseudo-triple point as a cold front
bisects the surface low and attendant dryline. At this time, it
appears that there will likely be some pseudo-triple point
somewhere across the CWA (likely north of I-20 and near or west of
I-35) and this may be a region to monitor as small scale ascent
may assist in some erosion of the cap.

Sunday`s upper air pattern isn`t quite as amplified as Saturday`s
and with uncertainties surrounding capping issues, I`ll keep PoPs
lower (30-40%) during the afternoon hours. Should convection
develop, it`ll more than likely be north of I-20 and east of US
HWY 281. A severe threat may accompany convection given that CAPE
values will climb to near 1500 J/kg with deep layer shear values
close to 50 knots. The best threat for showers and storms will
come during the evening hours on Sunday, where convergence along
a southward moving cold front should be enough to sustain any
ongoing convection and/or initiate new convection. The most likely
area for showers and storms during the early evening hours will
be north of I-30 and near and east of I-35. Given that convection
should take on more of a linear structure, the main hazard will be
strong winds, though severe caliber hail cannot be ruled out
given the +40 knots of deep layer shear. Rain/storm chances will
then expand for areas south of I-30 and east of US HWY 281 through
the overnight hours.

Next Week---Through the morning hours on Monday, the cold front
should continue to sweep through the Brazos Valley. While
convergence along the front will continue, the boundary itself will
be departing the area of greatest large scale ascent. I`ve
coordinated with surrounding offices and diminishing PoPs as the
front (and storms) moves southward seems plausible at this time.

Despite the passage of a cold front, conditions will remain quite
mild across North and Central Texas on Monday with highs in the
70s, as clearing skies and daytime heating may hamper CAA some.
Tuesday may end up being cooler than Monday as CAA is reinforced
by building high pressure across the Ozarks. Temperatures across
most of the area may remain in the 60s on Tuesday, with a few
locales out west climbing into the 70s. Wednesday should see the
start of a warming trend through the end of the workweek as
return flow quickly sets up. Moisture will stream northward, but
the breadth is unknown at this time. For now, I`ll ride with the
blends which advertise just slight chance to chance PoPs as
another upper system arrives from the west and a dryline takes
shape across the Big Country.

Bain

&&

.AVIATION... /Issued 1145 PM CDT Thu Mar 21 2019/
/6Z TAFS/

VFR conditions prevail across the region tonight with some passing
high clouds and generally light winds. A passing ridge axis will
keep things quite across North Texas through most of Friday,
although an upstream disturbance will result in scattered
thunderstorms across far West Texas tomorrow afternoon and
evening. As this system moves east tomorrow night, moisture will
increase along with an increasing threat for showers and storms
into Saturday morning. We`ll keep any precipitation out of the
current TAFs, but rain/storm chances will increase during the day
Saturday. Light winds will become southeasterly on Friday with
increasing cloud cover Friday night.

Dunn

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    75  55  68  61  76 /   0  40  60  20  40
Waco                76  54  71  61  79 /   0  20  50  20  20
Paris               71  49  62  55  71 /   0  40  70  40  40
Denton              74  54  67  60  76 /   0  40  70  20  40
McKinney            72  53  65  59  73 /   0  40  60  30  40
Dallas              76  56  67  61  75 /   0  40  60  20  40
Terrell             75  52  66  59  73 /   0  30  70  30  40
Corsicana           76  53  69  60  77 /   0  30  60  30  30
Temple              76  54  72  61  79 /   0  20  50  20  20
Mineral Wells       75  55  71  59  82 /   5  40  60  10  20

&&

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

$$

37/08



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