Severe Thunderstorm Warning 826, NWS Norman, OK

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
1109 PM CDT Thu Aug 17 2017

.AVIATION...
18/06Z TAFs. VFR conditions will be forecast for much of the
period although MVFR cigs appear possible by daybreak across
central and southern Oklahoma, which could affect OKC/OUN
terminals. TSRA will be included across northern terminals for
ongoing activity that will move eastward and also at KPNC late in
forecast period with proximity to frontal boundary.

&&

.PREV DISCUSSION... /issued 850 PM CDT Thu Aug 17 2017/

UPDATE...
Increased rain chances slightly tonight mainly in northwestern
Oklahoma. Added patchy fog mention late tonight into Friday
morning east of a Marietta to Pauls Valley to Purcell to
Stillwater line.

DISCUSSION...
Some thunderstorms may impact northwestern and northern Oklahoma
after 10 pm tonight. Fog may form across parts of central,
southern, and southeastern Oklahoma late tonight into Friday
morning.

Latest radars indicated scattered strong to severe thunderstorms
across the Panhandles near Guymon, Oklahoma south to Stinnett,
Texas as of 845 pm CDT. These storms were moving eastward. Think
this activity will move into northwestern Oklahoma towards Gage
and Woodward 10 pm to midnight, though may weaken as the storms
encounter a more stable airmass with higher amounts of CIN.
Regardless, brief gusty winds, probably sub-severe winds mainly
under 50 mph, small hail, along with heavy downpours could impact
northwestern Oklahoma later tonight.

After midnight tonight, not sure if storms will continue as they
move farther east and southeast due to stronger capping and
higher amounts of CIN. However, a low level jet will bring a
slight increase in moisture and instability to the area, which may
maintain some storms mainly over the northern half of Oklahoma. A
low level cold pool may be deep enough to help sustain
convection. If storms occur, severe potential remains low due to
MUCAPE values generally under 2000 J/kg and 0-6 km shear generally
below 30 kt (closer to 20 kt). Kept rain chances generally 20-40%
anywhere north of a Crowell, Texas to Ada line with the highest
chances northwest of a Hollis to Weatherford to Ponca City line.

Added fog mention to some locations mainly east of I-35 and
southeast of I-44 based on latest HRRR runs and as there will be
an increase in low level dewpoints (rising into the mid 70s) which
would allow for supersaturation near the ground. Doubt this fog
will become too dense due to the lack of rainfall during the day
today and as ground temperatures are rather warm (generally in
the lower to mid 80s). Regardless, visiblities may be under 1 mile
in some locations near Durant, Atoka, Ada, Ardmore, Seminole,
Shawnee, and Chandler between 1 am tonight and 10 am Friday
morning.

Products will be updated shortly.

MBS

PREV DISCUSSION... /issued 637 PM CDT Thu Aug 17 2017/

AVIATION...
18/00Z TAFs. VFR conditions will be forecast through period
outside of potential restrictions with TSRA in the 6-12Z timeframe
across northern Oklahoma terminals. Additional TSRA possible late
tomorrow but confidence too low for placement attm.

PREV DISCUSSION... /issued 338 PM CDT Thu Aug 17 2017/

DISCUSSION...
Subsidence behind eastward moving shortwave trough over the Great
Lakes and in the wake of MCS has resulted in mostly clear skies
across the area this afternoon. Some diurnal cumulus development
has been noted where low level moisture remains highest, mainly
across south-central and southeast Oklahoma. More extensive
vertical growth of cumulus and convective development should be
confined to just south of our forecast area.

Strengthening moist southerly flow over the High Plains should
support some diurnal surface based convective development later
today where 0-2 km stream lines are slightly convergent and near
the Raton Mesa. This would then move eastward with mean flow and
possibly grow up scale slightly potentially reaching our northwest
counties late this evening and progressing eastward in a weakened
state overnight. Models show a thin layer of enhanced mid-level
moisture on the 315k surface. Models can sometimes struggle with
depicting the details of moisture in these scenarios and this is
the main source of uncertainty in the overnight forecast. If mid-
level moisture is as extensive or more extensive than short term
guidance suggests, this would contribute to at least weak MUCAPE
and support elevated convection through tomorrow morning,
primarily over the northern half of the forecast area.

Current thinking is that overnight and early morning convection
shouldn't be as deleterious to later afternoon potential as some
of the recent more intense MCSs. Later in the afternoon, moderate
to strong instability should develop near a weak cold front across
northwest Oklahoma. Mid-level height rises may work against
convective development, but given the degree of diabatic
heating/destabilization, isolated to scattered thunderstorm should
form within this zone of convergence. Deep layer shear should be
marginally supportive of storm organization and some wind/hail
potential. Some consolidation and increase in coverage may occur
through late evening as storms move eastward potentially lasting
into the night.

A drier pattern should develop this weekend into next week as mean
ridging builds slightly. We'll need to watch boundary layer
moisture characteristics. If models are under forecasting low
level moisture slightly, isolated diurnal convective development
may become more likely. Otherwise, there may be a period of weak
synoptic scale forcing to aid in convective development late
Tuesday and Tuesday night.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  70  91  73  94 /  20  30  40  10
Hobart OK         72  95  74  96 /  30  20  30  10
Wichita Falls TX  73  94  74  96 /  10  10  20  10
Gage OK           68  93  69  94 /  40  40  40  10
Ponca City OK     69  91  70  92 /  30  30  40  10
Durant OK         73  92  74  95 /  10  20  30  20

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

17/11/11

Hazardous Weather Outlook...UPDATED
National Weather Service Norman OK
910 PM CDT Thu Aug 17 2017

OKZ004>048-050>052-TXZ083>090-190215-
Harper-Woods-Alfalfa-Grant-Kay-Ellis-Woodward-Major-Garfield-
Noble-Roger Mills-Dewey-Custer-Blaine-Kingfisher-Logan-Payne-
Beckham-Washita-Caddo-Canadian-Oklahoma-Lincoln-Grady-McClain-
Cleveland-Pottawatomie-Seminole-Hughes-Harmon-Greer-Kiowa-Jackson-
Tillman-Comanche-Stephens-Garvin-Murray-Pontotoc-Coal-Cotton-
Jefferson-Carter-Johnston-Atoka-Love-Marshall-Bryan-Hardeman-
Foard-Wilbarger-Wichita-Knox-Baylor-Archer-Clay-
910 PM CDT Thu Aug 17 2017

This hazardous weather outlook is for portions of northern...
western...central...and southern Oklahoma...and western
north Texas.

.DAY ONE...Tonight...

.Thunderstorms...
Scattered thunderstorms are expected to move eastward into
western and northern portions of Oklahoma after 10 pm tonight. A
few of these could be strong to severe with wind gusts around
60 mph, brief downpours, and frequent lightning as the
main concerns.

.Fog...
Patchy fog may reduce visibilities to less than 1 mile after 1 am
tonight across parts of central, southern, and southeastern
Oklahoma, mainly east of a Stillwater to Purcell to Marietta line.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday...

.Thunderstorms...
Thunderstorms will be possible each day across at least a small
part of the region through next Wednesday. Severe thunderstorms
appear possible on Friday, primarily across northern into central
Oklahoma during the late afternoon and evening hours. Damaging
winds, large hail, and flooding rainfall will be possible with the
strongest storms Friday afternoon and evening.

.Fog...
Patchy fog may reduce visibilities to less than 1 mile Friday
morning across parts of central, southern, and southeastern
Oklahoma, mainly east of a Stillwater to Purcell to Marietta line.

Get graphics and more details at weather.gov/norman...and follow
our weather forecast office on Twitter and Facebook.

MBS

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