Severe Thunderstorm Warning 142, NWS Norman, OK

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
709 AM CDT Wed Apr 22 2020

...New UPDATE...

.UPDATE...
Issued at 709 AM CDT Wed Apr 22 2020

Isentropic ascent beneath steep midlevel lapse rates across
northern Oklahoma has led to an extensive area of elevated
convection. MUCAPE of at least 2,500 J/kg and effective shear of
40-50 knots, as well as long hodographs (strong winds at anvil
level) all support large hail potential. Complex storm
interactions may temper the significant hail sizes to some degree
though. The largest hail would likely be in semi-isolated
convective cores.

Additionally, sufficient moisture through a deep layer and
potential for multiple heavy rain cores at a given location raise
the risk for flooding and possibly flash flooding, especially in
urban areas. For this reason, we have issued a Flood Watch and
extended it through 03z, though the greatest threat should be
early.

As far as the evolution of convection further south, a first look
at the 12z sounding shows a saturated layer near 700-mb that is
relatively uncapped. Thus, additional elevated convection may
increase this morning across central Oklahoma extending southwest
into western north Texas as large scale ascent from the
approaching trough increases. This complicates afternoon storm
development/evolution and mesoscale details will be important to
monitor today to assess convective timing and threats. The best
chance of surface-based convection will be within a narrow band of
moisture and enhanced instability just ahead of the Pacific
front/dryline. This moisture along with low-level shear
contributes to a concerning parameter space, but storm
mode/evolution is a little uncertain. Shear vectors are orthogonal
enough to be concerned about discrete storms, though deep frontal
forcing will be present. A clearer picture should evolve later
this morning.

BRB

&&

.SHORT TERM...
(Today and tonight)
Issued at 106 AM CDT Wed Apr 22 2020

Initial diurnal thunderstorm development late afternoon in the
Texas Panhandle moved east-southeast, with more development than
previously expected further east along diffuse warm front within
warm/moist advection regime. As low level jet and theta-e
advection strengthened, a cluster of very large hail-producing
supercells evolved and continued east-southeastward through
southern Oklahoma. Until stronger large scale ascent arrives, a
relatively quiet period is expected the next few hours. Toward
dawn, an increase in storm coverage is expected across western and
northern Oklahoma.

Specific details with regards to convective timing and hazards
will depend on mesoscale details and how storms initiate and
evolve. Current thinking is that more widespread convection with
perhaps a marginal hail threat will mainly be focused across
northern Oklahoma. Further south, convective development during
the mid-late morning is expected to occur along and ahead of the
Pacific front/dryline merger. Surface based storms should become
more common with all hazards possible across primarily south-
central into southeast Oklahoma.

Behind the dryline/front, gradient winds and momentum transfer
could lead to strong wind gusts up to 40 mph across western north
Texas and southwest Oklahoma.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 106 AM CDT Wed Apr 22 2020

We transition to northwest flow aloft late this week through next
week. One shortwave trough and associated southeastward moving
surface low could result in more thunderstorms Thursday night
through Friday. This will be followed by a dry period and slightly
cooler temperatures into the weekend, but still not far from
climatology.

&&

.AVIATION...
(12Z TAFS)
Issued at 630 AM CDT Wed Apr 22 2020

Bottom line, changing conditions at all TAF sites throughout the
day with many impactful weather elements, including storms,
gradient winds, wind shifts, and low stratus. Widespread
thunderstorms over northern Oklahoma this morning will likely
impact WWR and PNC. This is the highest confidence scenario for
thunderstorms impacting TAF sites today, with uncertainty in
convective evolution growing through the afternoon. Current
thinking is that storms will gradually increase southwest Oklahoma
and shift into central Oklahoma by midday, with severe storms
containing hail and wind possible. Showers on the west side of
evolving/eastward moving surface low could impact TAF sites even
after thunderstorms move east. Ceiling heights will likely be
variable through the day and amendments will be likely. A return
to VFR conditions should occur this evening at the latest.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  71  53  79  57 /  90  20   0  30
Hobart OK         74  51  81  55 /  80   0   0  20
Wichita Falls TX  82  54  82  59 /  70   0   0  10
Gage OK           67  47  81  51 /  90   0   0  40
Ponca City OK     67  52  78  54 / 100  60   0  40
Durant OK         76  56  79  59 /  90  30   0  10

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch through this evening for OKZ006>008-011>013-020.

TX...None.
&&

SHORT TERM...12
LONG TERM....12
AVIATION...12

Hazardous Weather Outlook
National Weather Service Norman OK
459 AM CDT Wed Apr 22 2020

OKZ004>048-050>052-TXZ083>090-231000-
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-
459 AM CDT Wed Apr 22 2020

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

.DAY ONE...Today and Tonight...

.Thunderstorms...
Early this morning, strong to severe thunderstorms with a threat
of large hail up to golf ball size will occur in northwest
Oklahoma. Additional storm development along with a greater threat
for storms to be severe is expected by late morning or midday
further south into portions of central and southern Oklahoma and
western north Texas.

The most intense storms of the day are expected from midday
through the afternoon across south-central and southeast Oklahoma,
including Ardmore, Ada, Durant, Shawnee and surrounding areas.
Across this area, large hail up to baseball size and damaging
winds could accompany the storms and a few tornadoes are
possible. Severe storms will move out of the area by early
evening.

Storm movement today is expected to be northeastward at 30 to 40
mph.

.Heavy Rainfall and Flooding...
Localized flooding is possible in areas where multiple storms
occur. This is most likely across northern Oklahoma through the
afternoon.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday...

.Thunderstorms...
Thunderstorms will be possible Thursday night into Friday. The
chance of severe storms is low.

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

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