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

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FXUS64 KFWD 240325
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1025 PM CDT MON MAY 23 2016

.UPDATE...
Minor changes to the forecast regarding PoPs tonight and tomorrow.
Otherwise, the remainder of the forecast remains in great shape.

The 00 UTC FWD RAOB showed the presence of a stout cap across much
of North and Central TX this evening. Upstream convection across
the Low Rolling Plains isn`t nearly as widespread as it was 24
hours ago and continues to move very slowly towards the east.
While it is possible that activity may try to develop a cold pool
and move eastward, this scenario appears unlikely according to
most model guidance. Nevertheless, I will hold onto low PoPs for
areas near and north of I-20. If storms are able to persist as
they move eastward they may pose an isolated severe risk with
hail, winds and heavy rain being the main hazards.

Further south across Central TX---I feel that the probability for
storms through the overnight hours will remain very low with the
strong cap and lack of sufficient lift, though brief sprinkles may
be possible. In addition---convection across the Concho Valley and
Big Country has decayed, resulting in little chances for re-
development along convective outflow.

For the day on Tuesday...I did add a mention of storms along the
Red River and across northeastern zones as nearly all of the
guidance suggests that rain will be possible. I think that these
precipitation chances are linked to the ongoing complex of storms
across the KS/NE border. The orientation of backward propagating
Corfidi vectors do have a favorable orientation which would drag
some of this activity slowly down through eastern OK and across
portions of NE TX. The overall coverage/intensity at this point in
time remains unknown and only warrants inclusion of a 20 PoP at
this time.

The rest of the forecast remains in great shape and updated
products have been transmitted.

Bain

&&

.AVIATION...
/ISSUED 643 PM CDT MON MAY 23 2016/
The primary aviation weather concern with this forecast will be
the return of MVFR/IFR ceilings this evening/overnight. MVFR
ceilings are already in place in Waco and should lower to IFR
between 05Z and 06Z. Some LIFR ceilings are also possible in Waco
towards sunrise. The Metroplex TAF sites should remain above 1000
ft through the night/Tuesday morning. All ceilings should lift
above 3000 ft Tuesday afternoon.

The only other concern tonight will be the possibility of
thunderstorms. Storms which formed on the dryline across West
Texas this afternoon will continue moving east through the
evening. These storms should weaken as they approach North Texas
due to subsidence currently in place across the region.
Therefore...storm chances will be too low at any of the TAF sites
to mention in this forecast.

A south wind will prevail between 10 and 15 knots along with some
gusts around 25 knots...especially Tuesday afternoon.

79


&&



.PREV DISCUSSION... /ISSUED 348 PM CDT MON MAY 23 2016/
A special early afternoon sounding nicely depicted the subsidence
drying and strengthening cap that occurred in the wake of this
morning`s convective system that tracked across the northern
zones. The stronger cap will have implications on the forecast
tonight as almost all guidance indicates it should hold strong.
However this same guidance indicates some convection occurring
across either the western or northern zones this evening and
overnight. Obviously this convection will be elevated above the
cap where the atmosphere will contain sufficient instability for
thunderstorms due to extremely unstable lapse rates of almost 9
deg C per km. Since this convection will not have access to the
very unstable surface air, it will tend to temper the severe
weather threat with just marginally severe wind/hail possible over
the region. Otherwise some very light showers below the capping
inversion will occur due to unseasonably strong moisture
advection which has already been responsible for the thick cloud
cover and drizzle this afternoon west of I-35.

Water vapor loop shows a shortwave trough moving through the Big
Bend region at this time and it appears most of the model guidance
has identified this feature. As forcing for ascent occurs ahead
of this shortwave, scattered thunderstorms will fire along the dry
line across West Texas and the Texas Panhandle. This activity
should move to the east faster tonight than last night, likely
because it will become elevated above the capping inversion and
move only with regard to the mid level mean flow. While I don`t
anticipate an MCS to develop out of this activity and affect our
region, the presence of anvil precipitation seeding the unstable
mid level atmosphere with moisture out ahead of the storms will
allow scattered and mostly disorganized convection to also quickly
develop eastward. Model guidance has some wildly varying QPF
solutions, but in general the consensus has focused on the
northwestern and northern zones for the most favored area tonight
beginning around 9 pm and tracking eastward through the early
morning hours. This is the region where mid level warm advection
and lift is strongest and it makes sense to be the favored area
for scattered convection. The highest pops of 40 percent will be
featured across this area, with 30 percent down to I-20, and 20
percent across the southern half of the CWA. Since convection in
our area is highly dependent on the scope of the dry line
convection out west, there is a very real possibility that the CWA
will stay dry tonight. Therefore have kept the PoPs on the lower
side due to the lower confidence.

The departing shortwave trough Tuesday morning will ensure another
round of subsidence in its wake tomorrow. The cap will again be
strong, but due to steep mid-upper level lapse rates there is the
possibility of another round of elevated convection Tuesday night
primarily over the northern zones. A low severe wind/hail threat
will exist with this activity. Otherwise another mostly cloudy,
warm, and humid day will be the rule with lows in the low 70s and
highs in the mid 80s. The cap will intensify further on Wednesday
and therefore we will keep the forecast dry despite a very unstable
airmass developing over the region as high temps reach the low
90s west to mid 80s east. Wednesday looks to be the warmest day of
the week with the high humidity pushing the heat index into the
upper 90s.

Rain chances increase Thursday as an unseasonably strong shortwave
trough begins to move toward the region. This system will take an
unusually far southern track for late May and therefore will
provide the forcing to lift and erode the capping inversion over
the area by Thursday afternoon. The very moist and unstable
airmass in place will be allowed to utilize its potential energy
in the form of what will likely be vigorous convection. Meanwhile
shear profiles will increase ahead of this upper level system
enough to support supercell convective modes. High precipitable
water values of up to 2 inches, strong 30-40 kt low level flow,
and diffluent thickness contours all point toward an increasing
risk of widespread heavy rain and flooding. These synoptic
dynamics for rain and storms look favorable from Thursday into
Friday afternoon. While it is tempting to get into the details of
a severe weather forecast, it is a bit early to do so at this
time. There could be copious mid level moisture and elevated
convection that would limit the overall severe weather threat. In
addition there is a concern that the vigorous convection may tend
to develop more across South Central and Southeast Texas as the
ECMWF shows which would intercept the best moisture/instability
across North Texas. So while there`s forecast skill to say that a
significant severe weather and heavy rain event may be looming in
the general region by the end of the week, it is too early to say
whether this will definitely impact our CWA or not. Either way it
will be the focus of our attention over the next few days.

Otherwise height rises and diminished moisture/instability in the
wake of this system will likely ensure a dry Saturday, but low
chances of storms will creep back into the forecast Sunday and
Memorial Day as shortwave troughs continue to ripple through in
southwesterly flow aloft. Temperatures by the weekend will be
warm with temperatures in the upper 80s for highs and lows in the
low to mid 70s. Don`t worry plenty of humidity will be available
to make Memorial Day feel like summer.

TR.92



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    73  85  73  90  74 /  30  10  20  10  20
Waco                73  86  73  88  74 /  10  10  10  10  20
Paris               69  83  70  86  73 /  30  20  20  10  10
Denton              71  84  71  90  74 /  30  20  20  10  10
McKinney            71  84  71  88  74 /  30  10  20  10  10
Dallas              73  86  73  89  75 /  30  10  20  10  20
Terrell             70  86  72  89  74 /  20  10  20  10  10
Corsicana           71  86  73  87  74 /  10  10  10  10  20
Temple              73  86  73  88  75 /  10  10  10  10  20
Mineral Wells       73  84  71  90  73 /  30  20  20  10  10

&&

.FWD Watches/Warnings/Advisories...
None.
&&

$$

79/15



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