Severe Thunderstorm Warning 330, NWS Norman, OK

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
1226 PM CDT Thu May 18 2017

.AVIATION...18/18Z TAF Issuance...
Very complicated aviation forecast today. Confidence is high that
thunderstorms will develop during the period, but there remains
much uncertainty in the timing and location of the initial
development in western Oklahoma and western north Texas.
Therefore, tried to keep the TAFs simple, using TEMPOs for TSRA at
all sites, with prevailing -TSRA during stretches where
confidence is highest. Ceilings and visibilities will likely vary
between MVFR and IFR at sites impacted by thunderstorms during
the period.

Kurtz

&&

.PREV DISCUSSION... /issued 1025 AM CDT Thu May 18 2017/

UPDATE...
Here is a mesoscale update.

DISCUSSION...
Determining exactly when and where storms occur today remains a
challenge. Latest guidance overall has been suggesting an earlier
start for storm initiation with first storms forming across
southwestern Oklahoma and western north Texas around noon.

Overall, based on latest model guidance (particularly the
HRRR/RAP) and incoming data from a special 15 UTC KOUN sounding,
confidence is growing that storms will form earlier and somewhere
over southwestern Oklahoma or western north Texas around noon
today. The 15 UTC KOUN sounding depicted that the base of the low
level inversion has lifted about 40 mb (from around 900 mb to 860
mb) and low level moisture deepening below the inversion. Based on
latest HRRR/RAP guidance, this lifting is expected to continue in
the next few hours, which would allow for storms to form earlier
than previously expected once surface temperatures reach the
lower to mid 80s near or just east of the dryline across
southwestern Oklahoma and western north Texas. A weak mid level
disturbance may be causing the lift, though the exact cause for
the lift remains uncertain.

If these storms form around noon in southwestern Oklahoma and
western north Texas, they may at first be slighlty elevated with
giant hail as the main hazard. However, these storms would likely
become surface-based due to daytime heating no later than 3 pm as
they move northeast. This could increase the tornado potential
across western north Texas, southwestern and central Oklahoma this
afternoon and evening while slightly decrease the tornado
potential in northwestern Oklahoma. Again, the exact details
remain uncertain today.

The bottom line is that the combination of shear, instability,
and moisture support significant severe storms with giant hail
and tornadoes this afternoon and evening somewhere over the
western two thirds of Oklahoma and western north Texas.

MBS

PREV DISCUSSION... /issued 639 AM CDT Thu May 18 2017/

DISCUSSION...
The 12Z aviation discussion follows....

AVIATION...
A large, powerful storm system will move through the southern
Plains today and tomorrow. A jagged deck of stratus will cover
much of central and eastern Oklahoma (also the Wichita Falls area
in Texas) this morning, then break up toward 18Z. Intense/severe
thunderstorms are forecast to develop quickly during the early
afternoon, probably between 19Z and 20Z, across western Oklahoma
and adjacent parts of Texas. The initial storms will mainly affect
KLAW, KCSM, KHBR, and KSPS, then spread/move east/northeast with
time. Then, a cold front will enter northern Oklahoma around
sunrise on Friday, bringing a minor wind shift and possibly some
very low stratus to far northern Oklahoma. At the same time, a
renewed deck of stratus will be advancing north across the Red
River.

CmS

PREV DISCUSSION... /issued 342 AM CDT Thu May 18 2017/

DISCUSSION...
The second shortwave trough in this week's series is rounding the
base of the longwave trough, and is now centered near Salt Lake
City, Utah. At the same time, a surge in low-level moisture is
advancing quickly north across Oklahoma. High dewpoint
temperatures have extended to Ponca City, Oklahoma City, and
Lawton, and this humidification will extend across most of the
remainder of Oklahoma (and western north Texas) by this
afternoon.

The HRRRX model has been fairly consistent in breaking out the
initial convection early this afternoon over Texas, in the general
vicinity of Abilene, then spreading/expanding this area rapidly
north through the afternoon. In a general sense, this is probably
what will happen. Supercell thunderstorms are likely within the
expected environment, and the SPC has issued a "High Risk" of
severe storms for today for much of the northwest quadrant of
Oklahoma, with lesser risk areas covering the remainder of our
forecast area.

A cold front will move into northern Oklahoma on Friday, and by
evening, it should be near I-44. This will limit the risk of
severe storms to the north, but along and south of the front,
there will again be a risk of severe storms. There is more
question about what will happen tomorrow, since lingering early-
morning convection will alter the environment in unpredictable
ways.

Rainfall tomorrow may be quite heavy near the front. There is
still some uncertainty where the heaviest rain may fall, and
whether it will be enough to cause more than localized flooding,
so there is not yet justification for a flood watch. Nevertheless,
some urban and small stream flooding seems likely, if the expected
scenario is correct.

The front will continue its advance on Saturday and Sunday, as
rain/storm chances slowly diminish from the northwest. This will
bring a relatively quiet period for most of the weekend and into
early next week. Another wave sweeping south across the Plains
will, however, bring another chance of showers and thunderstorms
(with a lower risk of severe storms) for Tuesday and parts of
surrounding days.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  66  78  58  70 /  60  80  90  20
Hobart OK         65  82  55  71 /  50  70  70  20
Wichita Falls TX  69  84  61  73 /  40  70  80  40
Gage OK           57  79  48  70 /  60  40  30  10
Ponca City OK     65  78  56  70 /  70  70  80  30
Durant OK         69  83  66  76 /  40  40  70  60

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch from 7 PM CDT this evening through Saturday morning
     for OKZ005>048-050>052.

TX...Flood Watch from 7 PM CDT this evening through Saturday morning
     for TXZ083>090.

&&

17/25/04

Hazardous Weather Outlook...UPDATED
National Weather Service Norman OK
1158 AM CDT Thu May 18 2017

OKZ004>048-050>052-TXZ083>090-191100-
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-
1158 AM CDT Thu May 18 2017

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

.DAY ONE...This afternoon and tonight...

.Thunderstorms...
There is a high risk for severe thunderstorms this afternoon and
evening in parts of Oklahoma.

Location...
The high risk is over much of northwest Oklahoma, east of a
Buffalo to Leedey line and north of a Leedey to Kingfisher to
Blackwell line. Locations in the high risk area include
Woodward...Alva...Watonga...Enid...Medford...and Cherokee.
Moderate to enhanced risk areas surround the high risk area
across the rest of Oklahoma into western north Texas.

Timing...
Mainly 1 PM until 10 PM.

Impacts...
Tornadoes...possibly strong and long-tracked...
Hail up to softball size...
Damaging winds 70 to 80 mph...

Discussion...
A warm and very unstable airmass is in place across most of
Oklahoma, east of a dryline. As heating continues and an upper
level storm slowly approaches, severe storms are expected to
develop by early afternoon. Several models indicate the first
storms will form across southwest Oklahoma and western north
Texas.

Instability and deep layer shear will support supercell
thunderstorms which will have the potential to produce very large
hail, damaging winds, and some tornadoes. Storms may organize into
lines or clusters by late afternoon or this evening as they track
northeast. Storms should begin to weaken by late evening.

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

.Heavy Rainfall...
Locally heavy rainfall and flooding may occur with storms this
afternoon and tonight.

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

.Thunderstorms...
There is an enhanced risk for severe thunderstorms Friday when
tornadoes, large hail, and damaging winds are all possible.
Mainly dry weather is expected Sunday and Monday. Thunderstorm
chances will increase around Tuesday of next week.

.Heavy Rainfall...
There is a potential for excessive rainfall Friday until Saturday
morning, particularly over portions of central into southwest
Oklahoma and adjacent parts of western north Texas. If you live in
an area that is prone to flash flooding, pay attention to the
forecasts and warnings later this week.

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

MBS/BT

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE Norman OK
113 PM CDT THU MAY 18 2017

OKZ033-034-036-TXZ083-181845-
Harmon OK-Greer OK-Jackson OK-Hardeman TX-
113 PM CDT THU MAY 18 2017

...SIGNIFICANT WEATHER ADVISORY FOR southeastern Harmon...south
central Greer...western Jackson and northwestern Hardeman Counties
Until 145 PM CDT...

AT 111 PM CDT, a strong thunderstorm was located 7 miles west of
Eldorado, moving northeast at 40 MPH.

HAZARDS INCLUDE...
Hail up to the size of nickels...
Wind gusts to 50 MPH...

Locations impacted include...
Altus, Eldorado, Gould, Duke and McQueen.

LAT...LON 3437 9977 3445 9996 3477 9972 3476 9946
      3463 9930
TIME...MOT...LOC 1811Z 222DEG 36KT 3448 9977

KURTZ

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE Norman OK
125 PM CDT THU MAY 18 2017

TXZ084-087-181915-
Foard TX-Knox TX-
125 PM CDT THU MAY 18 2017

...SIGNIFICANT WEATHER ADVISORY FOR western Foard and northwestern
Knox Counties Until 215 PM CDT...

AT 121 PM CDT, a strong thunderstorm was located near Guthrie,
moving northeast at 35 MPH. This storm will approach rural areas of
northwestern Knox and western Foard counties in the next 30 to 45
minutes. This storm may become severe.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

&&

LAT...LON 3419 10005 3424 10004 3390 9965 3366 9999
      3383 10000 3384 10005
TIME...MOT...LOC 1821Z 210DEG 30KT 3364 10030

KURTZ

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