Severe Thunderstorm Warning 22, NWS Norman, OK

Area Forecast Discussion
National Weather Service Norman OK
653 PM CDT Mon Mar 26 2018

.DISCUSSION...
Severe thunderstorm potential continues to decrease and mainly
confined to locations south of a Knox City to Lawton to Ardmore
line over the next 2 hours where MUCAPE remains near or just
above 1000 J/kg. Hail would be the main hazard, mainly below half
dollar size, as storms should mainly remain elevated in nature in
these areas. Think storms will continue in these areas, but
slowly weaken through the night as instability slowly decreases.

Farther north (north of a Knox City to Lawton to Ardmore line
including Oklahoma City), no severe storms are expected
for the remainder of tonight due to limited instability (MUCAPE
below 1000 J/kg).

Rain coverage will continue to increase across much of Oklahoma
and north Texas tonight, though most of it will remain fairly
light. The heaviest rainfall tonight appears to be near a Seymour,
Texas to Wichita Falls to Ada line where an additional widespread
1-3 inches of rainfall may occur. This could result in some
flooding. Flood Watch was expanded southwestward to include the
Wichita Falls, Seymour, and Walter areas where 0.50 to 2 inches of
rainfall has already occurred today.

Aviation discussion for the 00 UTC TAFs is below.

MBS

&&

.AVIATION...
Have low confidence in the TAFs due to active weather and
changing conditions.

Overall, think conditions will worsen now through 12 UTC at all
sites with widespread IFR or lower conditions developing.
Not exactly sure how quickly these lower conditions will form.

RA/-SHRA will increase in coverage now through 12 UTC.
Kept TSRA mention at KSPS where confidence of occurrence
is moderate. Exact timing of RA/SHRA/TSRA remains uncertain at
all TAF sites.

Some slowly improving conditions can be expected after 12 UTC
at many TAF sites, though IFR conditions may linger even beyond
18 UTC.

MBS

&&

.PREV DISCUSSION... /issued 229 PM CDT Mon Mar 26 2018/

DISCUSSION...
Primary forecast issue is the risk of severe weather today and the
potential for localized flooding through Tuesday.

Strong to severe thunderstorms will continue to develop across
western north Texas and southwest Oklahoma. These thunderstorms are
expected to spread northeastward through this evening. Effective
bulk shear >55 knots and MLCAPE >2500 J/kg will be more than
sufficient for supercells with the initial development. Large hail
will be primary hazard owing to the supercell storm type and
large CAPE in the hail-growth zone.

Instability is forecast to decrease toward the northeast, into
central Oklahoma, so severe weather potential should decrease with
northward extent. Also, increasing storm mergers/interactions
should mitigate the potential for higher end severe weather
farther northeast as well.

For tonight, localized flooding will become an increasing hazard.
The greatest uncertainty is this afternoon where the heaviest
rainfall will set up. Conceptually, would expect this location to
be at the nose of the low-level jet, which is where isentropic
ascent will be maximized. The 26/12Z NAM and GFS suggest the nose
of the low- level jet will be somewhere near I-44 tonight. Some of
the convective- allowing models have it just southeast of I-44,
so there could be a gradient of precipitation totals somewhere in
central Oklahoma. Isentropic ascent is expected to shift
southeastward through Tuesday, which will shift rain southeastward
through the day.

Based on the aforementioned analysis and collaboration with WFO's
Tulsa and Forth Worth, we opted to issue a Flood Watch for
locations generally southeast of I-44 and east of I-35 for the
potential for localized flooding in areas of training
thunderstorms. The RFC 3- hour Flash Flood guidance is generally
around 3 to 3.5", so widespread flash flooding is not expected.
The locations near I-44 are valid through 12Z Tuesday while
southeast Oklahoma are valid through 06Z Wednesday.

By Wednesday, as the mid/upper-level trough approaches, additional
showers and isolated thunderstorms will be possible. Rainfall
amounts should be lighter with this round of precipitation as the
higher precipitable water values should have shifted southeastward.
The greatest threat for rainfall appears to be across southern
Oklahoma and north Texas. Another shortwave trough from the
northwest may bring additional light showers on Thursday.

Forecast uncertainty begins to increase by the upcoming the
weekend. The GFS suggests a cold front will pass by on Saturday
with cooler temperatures for Sunday. The ECMWF is slower with the
cold front and has the passage during the day Sunday. For now,
have a low chance of showers on Sunday with a gradual cooling
trend into the following week. Overall, expect temperatures to
remain at or even below average through the forecast period.

Mahale

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch through Tuesday morning for OKZ025>031-039-040-044.

     Flood Watch through late Tuesday night for OKZ032-041>043-
     045>048-050>052.

TX...Flood Watch through Tuesday morning for TXZ086-088>090.

&&

10/17

Hazardous Weather Outlook...UPDATED
National Weather Service Norman OK
520 PM CDT Mon Mar 26 2018

OKZ004>048-050>052-TXZ083>090-272230-
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-
520 PM CDT Mon Mar 26 2018

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

.DAY ONE...Through Tonight...

.Thunderstorms...
There is a Slight Risk of severe thunderstorms across portions of
southern Oklahoma and western north Texas. A Marginal Risk
surrounds the Slight Risk and is primarily located across central
and southern Oklahoma and western north Texas.

Large hail up to the size of golf balls and wind gusts up to 60
mph will be the primary hazards with the strongest storms.

The risk for severe thunderstorms should continue through 9 PM.

.SPOTTER AND EMERGENCY MANAGEMENT STATEMENT...
Storm spotter groups and emergency management personnel across
western north Texas and southwest Oklahoma should prepare for
severe weather operations this evening.

.Heavy Rainfall...
Heavy rain may cause localized flooding, generally along and
southeast of I-44, this evening and overnight. A Flood Watch is in
effect.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday...

.Heavy Rainfall...
Heavy rain will continue into early Tuesday, while shifting
farther southeast, mainly affecting south central and southeast
Oklahoma on Tuesday. A Flood Watch is in effect for southeast and
south central Oklahoma through Tuesday evening.

.Thunderstorms...
There is a Marginal Risk for severe thunderstorms Tuesday in
far southeast Oklahoma.

Otherwise, there will continue to be a chance of thunderstorms
on Wednesday. Storms on Wednesday are unlikely to be severe.

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

Mahale

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE Norman OK
638 PM CDT MON MAR 26 2018

TXZ088-089-270015-
Archer TX-Baylor TX-
638 PM CDT MON MAR 26 2018

...SIGNIFICANT WEATHER ADVISORY FOR southwestern Archer and
southeastern Baylor Counties Until 715 PM CDT...

AT 637 PM CDT, a strong thunderstorm was located 4 miles north of
Elbert, moving northeast at 35 MPH.

HAZARDS INCLUDE...
Hail up to the size of nickels...

Locations impacted include...
Megargel and Westover.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Storm intensity is increasing and severe weather may develop rapidly.
Stay alert and listen for warnings.

&&

LAT...LON 3340 9907 3362 9894 3346 9861 3339 9871
TIME...MOT...LOC 2337Z 227DEG 32KT 3333 9899

BRB