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

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FXUS64 KFWD 241754

Area Forecast Discussion
National Weather Service Fort Worth TX
1254 PM CDT TUE MAY 24 2016

Main forecast challenge is the low potential for thunderstorms
early this evening developing near or over the TRACON. While there
is no low level focus for storms to initiate near the I-35
corridor, all models show erosion of the cap due to forcing
reaching the region late this afternoon ahead of a shortwave
trough...and some models indicate that warm advection showers
will develop and possibly grow into storms in the very unstable
environment. Again, due to limited surface focus it is possible
nothing will develop, but there is enough concern to watch this
potential very closely. The cap will strengthen again after
3z/10pm when the shortwave trough moves past the region which
would end any threat for storms. For now have indicated VCSH from
0-2z or 7-9pm CDT for DAL/DFW as the models that do convect seem
to keep it just west of these sites. For the other Metroplex sites
have indicated VCTS during that same 2 hour window due to ever so
slightly higher probabilities there.

Otherwise southerly flow will continue at 10-15kt through the
period. Generally VFR CIGs will prevail this afternoon and this
evening. MVFR CIGs will return overnight and have used similar
timing/trends as what occurred yesterday and last night. Given
the slightly stronger southerly flow and warmer temps tonight feel
comfortable keeping CIGs just above IFR even though MOS does
indicate that this will occur.



The complex of overnight/early morning showers and thunderstorms
which moved along the Red River has decayed. In its wake, skies
briefly cleared across our far northwestern zones, but persistent
deep southerly flow has brought widespread stratus back across the
entire region. Given the deep surface moisture in place (mean
mixing ratio of the 12Z FWD sounding came in at just north of 15
g/kg) and continued warm advection...we`ve seen a few showers pop
up this morning. As a result...made a few updates to the
inherited forecast to add low shower chances to the grids.

The forecast for the afternoon remains tricky. Models indicate a
subtle shortwave will move out of the Trans-Pecos region this
morning and into the Texas Panhandle this afternoon. Given the
presence of very steep mid level lapse rates on the order of 8 to
9 C/km, it won`t take much lift to encourage the development of
isolated showers and thunderstorms which would pose a risk for
localized hail and wind damage given the amount of buoyancy
present. At this time, feel the Texas Tech WRF has a decent handle
on the convective evolution today, and will show only 20% POPS
across the CWA this afternoon.



Morning water vapor imagery depicted broad large-scale ascent
overspreading much of West Texas with a diffluent flow pattern
aloft. Weak ascent near the dryline was once again able to
initiate numerous storms Monday evening and only a lone small complex
near Wichita Falls remains as of 4AM. It`s possible that this
activity may skirt our northwestern areas including Bowie or
Gainesville before dissipating this morning, but its associated
outflow as well as a strengthening cap should cause a rapid
decrease in it intensity as it approaches.

The next 48 hours are the most challenging portion of the forecast
as we remain in a regime of weak dynamic forcing yet very
favorable thermodynamics for the development and maintenance of
thunderstorms. Most areas across North and Central TX may remain
mostly cloudy for the majority of today, but this will not hinder
the amount of instability we achieve this afternoon. While a
capping inversion is expected to remain in place, it won`t mean an
end to our precipitation chances today. Steep lapse rates in the
700-500mb layer imply that even the smallest amount of lift will
be capable of generating isolated elevated showers or thunderstorms
this afternoon. In addition, sprinkles or light showers will also
be capable of developing below the cap in a persistent deck of
stratus clouds that should hold into the afternoon hours. Low-
level warm advection will be the strongest across our eastern
areas today, roughly east of a line from Sherman to Hearne, and
would not be surprised to see isolated to scattered showers and
storms develop by late morning or early afternoon.

The next concern will be late Tuesday and early Wednesday morning
with some guidance suggesting another complex of storms from
northern OK and southern KS possibly impacting our northern zones
around midnight Wednesday morning. All models have been very
inconsistent with this potential, but the latest ECMWF supports
this solution along with the 00Z NAM and previous run of the TT
WRF. At this point, an MCS reaching our area seems unlikely with
most of the steering flow being primarily towards the east, but
have maintained low PoPs to account for the potential.

A similar setup to Tuesday is expected on Wednesday afternoon.
Very warm temperatures (approaching or even exceeding 90F for
some locations) combined with surface dewpoints in the low 70s
will yield 4000-5000J/kg of SBCAPE on Wednesday afternoon. Once
again, the absent ingredient is forcing for ascent, which means
that the cap should hold strong on Wednesday afternoon. However,
with such a large amount of instability in place, it will not take
much to generate an isolated thunderstorm or two on Wednesday
afternoon, which of course would have the potential to become
severe with such ample CAPE. The potential for seeing any storms
could increase if an outflow boundary is present anywhere in our
CWA from possible convection overnight Tuesday night. This is
another case where the occurrence of any storms is highly
dependent on convection from the previous day.

Stronger lift will finally reach the area on Thursday in the form
of a potent upper trough. A lead shortwave should be capable of
generating a round of storms on Thursday afternoon. Limited shear
may help to mitigate the severe threat on Thursday, but strong
instability in place means that there will be at least a low-end
severe threat during this time. There will also be flood concerns
beginning on Thursday and lasting into Friday with PW values
around 2SD above normal. At this time, the highest potential for
the heaviest rainfall seems to be located across portions of
Central TX. As the main trough axis swings through on Friday,
additional rounds of storms are possible, some of which may be
severe. It`s still too early to pin down details with this system,
but Thursday and Friday will feature the highest chances for
widespread rain and thunderstorms in this forecast period, much
more so than the isolated to scattered activity that has plagued
us for the past week.

The Memorial Day weekend forecast is still very unclear at this
point, but after the main trough axis swings through on Friday, we
should be largely subsident for most of Saturday. However, we will
still remain in a weak warm advection regime with ample moisture
and abundant instability in place which means that low chances for
showers and storms seem possible virtually any day over the
weekend. Saturday through Monday will by no means be a washout,
but have introduced some low PoPs with chances for isolated
showers and storms as mid-level lapse rates will be too steep to
disregard the potential for elevated activity each day. Strong
forcing will be lacking once again during this time frame, but any
weak disturbance rotating through the broad troughiness in place
over the western CONUS seems it would be capable of initiating
isolated storms. More rain and storm chances will continue next
week as another broad upper trough takes shape and abundant
moisture remains in place.



Dallas-Ft. Worth    85  74  90  76  84 /  20  20  10  10  60
Waco                86  74  90  75  84 /  20  20  10  20  60
Paris               83  70  87  71  82 /  20  40  10  10  40
Denton              83  72  88  72  84 /  20  20  10  10  60
McKinney            84  72  87  73  82 /  20  30  10  10  50
Dallas              85  74  90  77  84 /  20  20  10  10  50
Terrell             84  73  88  73  82 /  20  30  10  10  50
Corsicana           86  74  89  74  84 /  20  20  10  10  50
Temple              86  74  88  74  83 /  20  10  10  20  60
Mineral Wells       83  72  89  72  85 /  20  20  10  10  60


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