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

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FXUS64 KFWD 131204 AAB
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
704 AM CDT Fri Apr 13 2018

.AVIATION...
/12Z TAFs/

Concerns: MVFR cigs this morning, strong and gusty south winds
becoming west and then northwest, and chances for SHRA and TSRA.

DFW Airports: Spotty showers and isolated thunderstorms will move
west to east across North Texas this morning. If a strong storm
develops, small hail may be possible. Otherwise this morning,
strong south winds sustained 15-25 kts with gusts of 25-35 kts
will continue. MVFR cigs between 2-3 kft will prevail until the
16-17Z hour, and then VFR is expected. Guidance is suggesting a
few thunderstorms may form east of KDAL around 17-18Z, and the
next set of TAFs may need to include VCTS for KDAL and KDFW as
these storms could be within the 15-25SM range.

A dryline will move across the region today, but will slow down
as it approaches the Metroplex, making timing the arrival of west
winds difficult. At KAFW and KFTW, the west winds could arrive
around 20-21Z, but then take a few more hours for the dryline to
push past KGKY, KDFW, and KDAL. Along the dryline, thunderstorms
will likely at least try to develop and are more likely to impact
KDFW and KDAL. Have placed a VCTS out to 25SM from 19-23Z, but if
any thunderstorm affect the airport, it will likely occur within a
1-2 hour time frame. There`s a potential these storms could be
severe with a threat for hail and damaging winds. As a cold front
moves through the region this evening, the winds will become
northwesterly.

Waco Airport: MVFR cigs and gusty south winds are expected to
prevail until about 17Z. The chance for thunderstorms in Central
Texas this afternoon is less certain than to the north and have
opted to leave a precipitation mention out of the TAFs for now. IF
storms develop in the Waco area, the best timing is in the evening
hours, and there`s a chance these storms could be severe. The
winds are expected to veer to the southwest late this afternoon,
and then will gradually turn westerly as a dryline and cold front
sweep through the area. Northwest winds are expected overnight.

JLDunn

&&


.SHORT TERM... /Issued 436 AM CDT Fri Apr 13 2018/
/Today and Tonight/

Several various weather elements plague the short term portion of
the forecast including morning rain, windy conditions, a dryline
that brings fire weather concerns and a severe storm threat, very
warm temperatures, and a cold front. For more details on today`s
fire weather concerns, please see the added section below.

This morning`s surface features that we will be tracking today
include 1) a dryline that currently lies across western Oklahoma
and West Texas, 2) an upper level trough that currently stretches
meridionally just west of the Rockies, with the base of the trough
moving east across New Mexico, and 3) a strong surface low
currently in western Kansas.

The wind is one of the main highlights this morning, and we have
decided to expand the Advisory south to Waco, and extend the time
through 10 am. Regardless if locations are technically in/out or
meeting Wind Advisory criteria this morning, breezy conditions
will persist not only this morning, but into the afternoon hours
ahead of the dryline. Behind the dryline, a new Wind Advisory has
been issued from Noon until 7 pm for west winds of 25-30 mph with
gusts approaching 40-45 mph in some of our far western counties.
The strongest winds this afternoon are expected across nearly the
same area where a Red Flag Warning has been issued.

Also this morning, we expect to see a blossom of scattered to
widespread precipitation on radar as warm air advection increases
above the cap layer. Most of this development will likely be
based above ~650 mb, and the rain will be falling into a pretty
dry layer just below. Initially, very little to no rain may reach
the surface, but with steep lapse rates above the cap, any
thunderstorms this morning should be able to generate better
amounts of precipitation that can reach the ground, and maybe even
some small hail. However, as the rain shifts east with the
shifting low level jet late this morning into the early afternoon
hours, better moistening of the lower levels in our eastern
counties will likely allow for more rain to reach the ground. Thus
have kept higher rain chances east of Interstate 45 and Highway
75. The forecast soundings still indicate this area may recover
for storms later in the day, but it could be a negating factor for
a severe weather threat across the eastern half of the CWA.

With the upper level trough progressing east this morning, and the
surface low also tracking east, the dryline should also steadily
progress east this morning, and will likely be crossing our
western border around 10-11 AM. I expect it will continue to move
east, but slow down or stall in the mid afternoon hours. This is
a slower progression than the previous forecast, and my reasoning
is 1) forecast models stall the surface low over western Kansas in
the afternoon and 2) the speed of the 850-700 mb winds actually
decrease behind the dryline as it moves across our the western
half of the CWA. The HRRR and RAP are both showing this slow down
as the dryline approaches the I-35 corridor, but their locations
vary by 1-2 counties with the HRRR slightly farther east. For
this forecast, have sided with the RAP and slow the front along a
line from Sherman to DFW to Killeen. The location of the dryline
will be critical to where storms may develop this afternoon.

Model guidance tonight has been hesitant to develop too many
storms along the dryline later today, and there are a few factors
that will need to be monitored that may inhibit storm development
and/or severe storm development. Notably, the strongest low level
winds shift east of the region in the mid afternoon hours, before
the best forcing arrives, and surface-925 mb winds ahead of the
dryline are expected to veer more towards a south-southwest
direction that could limit convergence along the dryline. However,
this is a strong trough arriving that may be able to overcome
these limitations, resulting in strong, rapid updrafts.

There does appear to be a similar signal in the model fields that
initiation will be in the 19-21Z time frame along and north of
Interstate 20. Depending on the location of the dryline, this will
likely include at least the eastern portions of the DFW Metroplex.
These initial storms are expected to move northeast. With MUCAPE
values over 2000 J/kg, shear values nearing 50 kts, and decent
lapse rates in the mid levels, these storms could be severe with
a threat for large hail and damaging winds. Although not zero, the
tornado threat appears low due to the veered southwest winds
ahead of the dryline.

None of the models are unzipping storms along the dryline north of
I-20, but 1-2 CAM models that developing isolated storms and then
a line of storms in the late afternoon and/or early evening hours
across parts of Central Texas. This development is a little
quizzical as this area appears to be farther removed from the
better upper level forcing. Still, it`s hard to ignore this signal
in the models and have maintained rain chances and a mention of
severe storms along and east of I-35 and south of I-20 through the
evening hours.

The cold front will quickly sweep across the region this evening
and overnight, overtaking the dryline, and pushing any storms
associated with the dryline out of North and Central Texas. Have
maintained some low rain chances across our southeastern counties
overnight as some light rain may develop in this area when the
upper level trough arrives.

JLDunn

&&

.FIRE WEATHER... /Issued 436 AM CDT Fri Apr 13 2018/
/Today/

Critical and elevated fire weather conditions are expected this
afternoon across our western counties behind a dryline. Along
and west of I-35, humidity values will fall into the teens and 20s
with strong west winds of 25-35 mph and gusts between 30-45 mph.
Temperatures will warm into the mid and upper 80s, and ERC values
are only near or slightly above normal. Discussions with our fire
weather partners on Thursday revealed a decent green-up has
occurring across our western counties from earlier rains. This
green-up will likely prevent any fire starts from quickly
spreading, but given the concerning fire weather conditions, we
decided to issue a Red Flag Warning where conditions will be most
critical with the strongest winds and lowest RHs. This is along
and west of a line from Montague to Erath to Mills County where
sustained winds of 25-30 mph and gusts up to 45 mph will combine
with RH values between 10-15 percent. East of this area, to the
I-35 corridor, near-critical fire weather conditions will still
exist but fuel moisture and green-up is better. However, even
though the Red Flag Warning does not extend to I-35, burning is
still not recommended anywhere west of the Interstate.

JLDunn

&&

.LONG TERM... /Issued 436 AM CDT Fri Apr 13 2018/
/Saturday through the end of next week/

A Pacific cold front and associated convection will extend from
the Texas coastal waters northeastward through the Mississippi
Valley early Saturday. Northwest winds will bring a cooler and
drier airmass across North and Central Texas behind the front.
Wind speeds of 20 to 30 MPH will coincide with minimum RH values
in the 20 to 25 percent range to produce elevated to near-critical
fire weather conditions once again across the western-most
counties Saturday afternoon. The mitigating factor will be
temperatures, which should be 10 to 15 degrees below normal for
April, so a Fire Weather watch is not planned at this time.

After a cool weekend, a warm-up will begin on Monday as south
winds return and an upper level ridge develops overhead. The ridge
will weaken late Tuesday and Wednesday as a shortwave trough
moves quickly eastward through the Central Plains. This will send
a weak cold front through North Texas on Wednesday. Little in the
way of a cool-down is expected behind the Wednesday front due to a
re-strengthening of the upper ridge.

Model guidance is consistent in showing a deep upper low
transitioning across the Southern Plains late next week and the
following weekend. Chances for showers and thunderstorms will
return by next Friday and continue into Saturday. Though still a
ways out, the time of year and strength of the upper level system
will likely bring at least a low-end potential of severe weather
to the area around day 8.

30

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    87  49  62  39  64 /  40  20   5   5   5
Waco                86  49  65  38  65 /  40  20  10   5   0
Paris               81  46  57  35  57 /  50  40  10  10   5
Denton              84  46  61  35  63 /  40  10   5   5   5
McKinney            85  46  59  36  61 /  40  20   5  10   5
Dallas              87  50  62  40  64 /  40  20   5   5   5
Terrell             84  48  62  36  62 /  40  30  10  10   5
Corsicana           83  50  61  37  62 /  40  30  10  10   0
Temple              85  52  65  39  67 /  40  20  10   0   0
Mineral Wells       87  44  62  34  65 /  30   5   0   0   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 10 PM CDT this evening for
TXZ091-100-101-115-116-129-130-141-142.

Wind Advisory from noon today to 7 PM CDT this evening for
TXZ091-100>102-115>117-129>132-141>143.

Wind Advisory until 10 AM CDT this morning for TXZ092>094-103-
104-118>120-133-134-145-159.

&&

$$

82/30



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