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Area forecast discussion
National Weather Service Fort Worth Texas
636 am CDT Fri may 26 2017

Aviation...
/12z tafs/

Challenges the next 24 hours will be sustained wind speeds and
gusts, along with timing dissipation/formation of MVFR cigs the
next 24-30 hours.

MVFR cigs developed rapidly by 09z this morning, but strong and
veering boundary layer flow around 40 knots has basically kept the
deck along and east of I-35/35e. Warming with sunrise early this
morning will push levels above 2 kft quickly as already noted at
Waco regional. With the veering low level flow in mind, have left
cigs out at Alliance/Meacham airports and only a tempo group at
dfw. Will advertise more categorical MVFR cigs at Waco, Dallas
Love Field, and Arlington. By mid-late morning, all airports
should see cigs rising and scattering to VFR with mixing and
warming of the low levels. With a "dirty" shortwave ridge above,
periods of cirrostratus will stream overhead, but with no major
effect on aviation. No precipitation was occurring or expected
today, due to a strong low level inversion and moisture being very
shallow in nature.

Occasionally gusty south winds around 15 knots today are
expected, coming down to between 10-15 knots tonight. Another
somewhat veered low level jet forms tonight, in advance of a strong
shortwave lifts northeast over the Central Plains. The capping
inversion underneath the persistent shortwave upper ridge will
keep the area dry through tonight. MVFR cigs will surge up across
all airports in the 06z-09z Saturday time frame with continued
rounds of cirrostratus above.

05/

&&



Previous discussion... /issued 345 am CDT Fri may 26 2017/
today will be the warmest day of the year thus far for many
locations with a taste of summertime heat and humidity in store.
Oppressive heat indices in the upper 90s and low 100s are expected
for much of the forecast area and even some ambient temperature
readings in the low 100s are possible across our western zones.
The increased humidity will be due to the morning surge of
moisture currently in progress as evidenced by a swath of low
stratus streaming northward through central Texas. Dewpoints will
climb into the upper 60s and 70s this morning and won't mix out to
much lower than these values this afternoon. A dryline will
advect into our western zones this afternoon with the highest
temperature readings expected to the west of this boundary in the
much drier air. No convection will result along this feature today
due to a cap practically of forged steel and a lack of ascent.
There won't be much relief from the heat after sunset as
temperatures will only fall into the mid/upper 70s overnight with
dewpoints also hovering right around this mark. While this is the
first big heat of the season, it will remain below heat advisory
criteria.

The most substantial forecast challenge at this point remains the
convective potential on Saturday. The aformentioned heat and
humidity will be similar to Friday with temperatures a few degrees
cooler and dewpoints a couple degrees higher. This will result in
extreme surface based instability values as high as 5000-6000
j/kg within the warm sector airmass ahead of a dryline. The
potential for convection rests on the strength of the capping
inversion which most guidance suggests will remain fairly strong
over most of north and central Texas. There isn't a ton a lift
available as the primary shortwave disturbance should track well
north of the area in fairly zonal, progressive flow. At the
moment, i'm a bit surprised by the amount of convection being
generated by some of the cams despite what should be a capped,
albeit potent, boundary layer airmass. I can buy a solution
similar to the 00z 3km NAM nest with a cluster of storms
developing in OK along the cold front (where the better forcing
will be located) with perhaps some isolated activity along the
dryline if sufficient surface heating/moistening is able to match
the strength of the inversion. Other models that convect the
dryline but not the cold front seem to contradict the large-scale
environment that should be in place during this time and i've
largely disregarded their solutions for now. The concern with the
cap remaining in place is that, if only a storm or two are able
to initiate along the dryline, they should quickly become
supercellular (given the 40-50 kts of shear) and will have a
wealth of high-quality warm sector air to ingest. Very large hail
would be the primary threat if this were to materialize, although
these storms would be capable of damaging winds and tornadoes as
well. We'll continue to monitor model trends with the cap and
available lift for the Saturday afternoon/evening time frame.

The next concern will be the aformentioned cluster of storms that
should develop in OK along the southward-moving cold front on
Saturday evening. This convection should grow upscale fairly
quickly into an mesoscale convective system which could potentially affect or
northeastern zones. Given the very large instability, a forward
propagating mesoscale convective system seems more likely which in theory should steer
this convection more eastward than southward. However, if cold
pool generation is not as efficient as expected, an upwind-
propagating mesoscale convective system would be possible which could sink as far south as
I-20. This complex would also have the capability to produce
severe weather, especially damaging winds, so its potential will
also be monitored over the next 48 hours.

Later Saturday night and Sunday, the cold front will slowly move
southward through north and central Texas resulting in additional
showers and thunderstorms. The potential for strong or severe
storms will hinge on the first two (potential) rounds of
convection. If dryline convection explodes Saturday evening and
the mesoscale convective system also sinks southward, our environment would be quite
worked over. However, if these this convection does not affect
the forecast area, a ripe airmass will be available to fuel
convection along the cold front throughout the day on Sunday.
While Sunday won't be a washout for Memorial Day Holiday weekend
plans, it will be the day of the highest thunderstorm potential,
so folks with outdoor activities should monitor the weather and
have contingency plans. There will be some temperature relief
behind the cold front with highs returning to near seasonal
normals (mid 80s).

The front should slow to a crawl across central Texas as it outruns
its upper support. This boundary will be capable of forcing
additional showers and storms lasting into Monday, although the
exact location of where this boundary will stall is highly
dependent on all of the aforementioned convection. Generally,
rain chances will be higher the farther south your location
through Monday night.

A cutoff upper low is expected to develop across the western US
on Tuesday which will keep much of the US in broad troughing
aloft. On Wednesday, the stalled frontal zone should lift back
northward as a diffuse warm front with a southerly flow regime
returning. For US, this will mean essentially an endless supply of
Gulf moisture throughout next week with humid conditions and high
temperatures mostly in the 80s. A few disturbances rippling
through the broad southwesterly flow will result in scattered
showers and storms throughout much of next week and possibly all
the way into next weekend. Without much of a focusing mechanism
available, it's almost impossible to pin down a more/less
favorable area for convection throughout this time and have left
generally low broad-brushed pops through the extended portion of
the forecast.

-Stalley

&&




Preliminary point temps/pops...
Dallas-ft. Worth 96 78 93 75 86 / 5 5 20 40 40
Waco 92 77 93 76 90 / 5 5 10 20 50
Paris 87 74 87 70 83 / 5 10 10 50 50
Denton 97 77 93 74 84 / 0 5 20 40 40
McKinney 93 77 90 75 84 / 5 5 20 40 40
Dallas 96 78 92 76 86 / 5 5 10 40 50
Terrell 90 76 90 74 85 / 5 5 10 40 50
Corsicana 91 76 91 75 88 / 5 5 10 30 50
Temple 92 76 92 75 88 / 5 5 10 20 50
Mineral Wells 100 76 95 74 85 / 0 5 20 30 40

&&

Forward watches/warnings/advisories...
none.

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