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

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FXUS64 KFWD 271155

Area Forecast Discussion
National Weather Service Fort Worth TX
655 AM CDT Sat May 27 2017

/12Z TAFs/

Several challenges continue through tonight with regard to cigs
this morning, a dryline and isolated storms by early evening, then
a cold front and a possible MCS overnight into early Sunday

MVFR cigs overspread all airports across North and Central TX 2-3
hours ago. KGKY/KDAL have already risen above 2 kft, but the
others, including KACT in Central TX remain in lower MVFR. KACT
may even see a brief window of IFR through mid morning, due to a
the strong inversion being rooted lower than up around DFW.
Moisture below the inversion is deeper than yesterday and more
widespread. Despite veering 30-35 knot flow at 925mb on area
radars, expect late May heating and mixing to take place after
mid morning to help all cigs lift then eventually into VFR by
midday, then to VFR and scattering out this afternoon.

Isolated, discrete dryline storms will be possible mostly north
of I-20 very late this afternoon and early evening. A "dryline
bulge" is expected to occur WNW of DFW which would enhance lift in
combination of hot temperatures around 100 degrees. Upper support
however will be lacking and morning upper air analysis still
indicates a strong capping inversion rooted at 890mb here at FWD.
As such, and with models struggling on whether to convect or not
late today, have left any mention of VCTS out of the DFW Metroplex
TAFs. However, as an MCS or QLCS develops on a cold front across
southern OK later this evening, I did insert VCTS after 08Z with
the approach of the cold front. As noted in the public discussion,
any cluster should be forward propagating and move more into the
Ark-La-Tex versus straight south into North TX. That said, the
high instability in place does have me concerned for at least
scattered storms moving into the I-20 corridor before daybreak

Otherwise, south winds 10-15 knots will prevail through mid
morning, before increasing to 15-17 knots and becoming occasionally
gusty this afternoon and evening. Winds should veer ahead of the
cold front overnight to the southwest or possibly west with FROPA
occurring after sunrise, which is beyond this forecast.



.PREV DISCUSSION... /ISSUED 348 AM CDT Sat May 27 2017/
An active few days of weather are ahead, but the main forecast
problem lies within the first 36 hours regarding the convective
potential late this afternoon through the overnight period.
Otherwise, one more day of very hot and humid conditions is
expected and a Heat Advisory is in effect for part of North TX
this afternoon. Otherwise, an unsettled weather pattern will
persist throughout much of the upcoming week with multiple days of
scattered storms and near-normal temperatures.

A broad upper trough across the western US is resulting in lee
surface cyclogenesis near the TX Panhandle this morning. A sharp
surface dryline extends southward from this feature through West
TX and a cold front is draped to the northeast through parts of KS
and MO. These features will result in some large changes to our
sensible weather over the next 24-36 hours, including the
potential for some storms beginning late this afternoon and again
late tonight. A potent warm sector resides southeast of the
surface low with dewpoints in the mid 70s along with unseasonably
warm temperatures. These conditions will result in another hot and
humid afternoon with heat index readings at or above 100F for
most of the area.

By late afternoon, the dryline will advect toward our western
zones, although its eastward progress may be hampered by the
fairly deep moisture layer which will not be able mix out very
quickly. There is still concern over a low potential for storms to
develop along the dryline by late afternoon, although initiation
will be a challenge given there should still be a stout cap in
place with a lack of large-scale ascent. If a storm or two were
able to initiate and sustain themselves into the favorable air
east of the dryline, they would likely become severe as a
supercellular storm mode would be favored given the shear
parameters. The aformentioned warm/moist boundary layer will
result in several thousand J/kg of SBCAPE which would be
incredibly favorable for any discrete storms if they`re able to
survive in a capped environment. Very large hail would be the
primary threat with this activity, although damaging winds and an
isolated tornado would be possible too. While the thermodynamics
are certainly quite favorable for severe weather, the question
remains whether any storms will be able to initiate whatsoever.
Most CAM solutions make much more sense than yesterday morning`s
runs which had previously been igniting widespread dryline
convection within the forecast area. Most models this morning are
much more reluctant to do so and many keep us completely dry
through the evening hours. Given the cap and lack of ascent, a
dry forecast actually seems like the best bet and it seems quite
possible that the environment will squander the extreme
instability in place today, at least regarding dryline convection.
Have left low PoPs as the threat for this convection to develop
is still non-zero.

The second area of concern will be later tonight as a cluster of
convection develops in southern OK along the advancing cold front
where there actually will be sufficient forcing for storm
development. This activity should congeal into an MCS probably
around midnight or later. The forecast problem lies in where this
activity will move once it has developed. Given the ample
instability and potential for strong cold pool development, it
seems like a forward-propagating MCS should be favored in which
case Corfidi vectors would suggest this complex would be steered
more eastward toward the Arklatex. This solution seems to be
favored by the extended HRRR-X, and the GFS. However, some
guidance is suggesting a potential for more of a linear QLCS to
move southward immediately along the front into North TX as far
south as I-20. Given the instability, this scenario is possible,
but probably less likely than the previously-discussed MCS racing
off to the east while possibly skirting our northeastern
counties. The low-level flow is also quite veered which should
limit the amount of convergence immediately along the front. This
scenario of dropping an MCS southward into North TX seems to be
favored by the 3km NAM Nest and the ECMWF. Have left PoPs
overnight to account for both scenarios. If this complex does take
a southward track, it should be decaying as it moves towards I-20,
but would still be capable of a damaging wind threat.

All of the aforementioned convection (or lack thereof) will have
a substantial effect on Sunday`s setup. The cold front should be
slowing down and stalling somewhere across Central TX by midday
Sunday, as it outruns any semblance of upper forcing to drive it
farther south. Additional scattered storms will be likely along
the front beginning Sunday morning with the highest chances in the
afternoon when instability is maximized along the frontal zone.
With low confidence regarding the front`s exact position, have
left fairly low PoPs through Sunday afternoon and evening. Some of
these storms could be strong or severe, but this will be
conditional on how worked-over the environment is (if at all) from
any previous convection.

A broader swath of rain and thunderstorms is expected later
Sunday night as a secondary upper disturbance nears the region. A
plume of rich moisture will still be in place immediately along
the stalled frontal zone through Central TX and rain may become a
bit more widespread during this time. As mentioned above, the
exact location of the front and therefore the highest rain
chances remain uncertain, but chances generally increase the
farther south your location.

Shower and thunderstorm chances will linger into Monday mostly
across Central TX before the diffuse frontal zone lifts back
northward as a warm front on Tuesday. Broad troughing will persist
over the western half of the US through most of the upcoming
week. This will mean continued chances for scattered and
thunderstorms every day as multiple disturbances progress through
the southwesterly flow aloft. Have made very few changes to
previous forecast throughout this time as pinning down
times/locations for the highest rain chances in the midst of such
a diffuse pattern is not realistic at this point.



Dallas-Ft. Worth    95  75  85  66  86 /  20  40  20  20  10
Waco                92  76  87  65  84 /  10  20  30  60  30
Paris               89  71  82  62  84 /  10  60  20  20  10
Denton              95  72  84  61  86 /  20  40  20  20  10
McKinney            93  74  83  62  85 /  20  50  20  20  10
Dallas              94  76  85  67  86 /  10  40  20  30  10
Terrell             89  74  83  65  83 /  10  40  30  40  20
Corsicana           91  74  85  67  84 /  10  30  30  60  30
Temple              92  75  88  66  83 /   5  20  40  60  40
Mineral Wells       98  72  84  61  85 /  20  30  20  20  10


Heat Advisory from 2 PM this afternoon to 7 PM CDT this evening
for TXZ091-092-101>103-116>119-131>133.



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