Alert archive / Oklahoma / Tornado Watches in 2011
Tornado Watch 320
The Storm Prediction Center issued this tornado watch at May 21, 2011, 7:08 PM CDT for 20 counties in Oklahoma. It was in force for 3 hr.
The area
The outline as issued.
The facts
- Issued
- May 21, 2011, 7:08 PM CDT (00:08 UTC)
- Expired
- May 21, 2011, 9:59 PM CDT
- In force
- 3 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 3 in
- Strongest gust expected
- 60 kt
Counties Atoka County, OK, Bryan County, OK, Carter County, OK, Choctaw County, OK, Coal County, OK, Creek County, OK, Garvin County, OK, Hughes County, OK, Johnston County, OK, Love County, OK, Marshall County, OK, McIntosh County, OK, Murray County, OK, Okfuskee County, OK, Okmulgee County, OK, Pittsburg County, OK, Pontotoc County, OK, Pottawatomie County, OK, Pushmataha County, OK, Seminole County, OK
The radar
The Norman radar (KTLX), 93 km from the middle of the area, began a volume at 00:10 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 40%
- One or more EF2 to EF5 tornadoes
- 20%
- Ten or more severe wind reports
- 10%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 40%
- One or more hailstones of 2 inches or more
- 50%
- Six or more combined severe hail and wind reports
- 60%
Warnings issued inside it
9 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 21, 7:38 PM CDT | Severe Thunderstorm Warning | OUN | Garvin, McClain, Pontotoc, Pottawatomie, Seminole | 52 min |
| May 21, 7:40 PM CDT | Tornado Warning | OUN | Johnston, Murray, Pontotoc | 31 min |
| May 21, 7:49 PM CDT | Tornado Warning | OUN | Garvin, McClain, Pontotoc | 41 min |
| May 21, 7:54 PM CDT | Severe Thunderstorm Warning | TSA | Creek | 22 min |
| May 21, 8:04 PM CDT | Tornado Warning | OUN | Pontotoc | 19 min |
| May 21, 8:24 PM CDT | Tornado Warning | OUN | Pontotoc | 51 min |
| May 21, 8:36 PM CDT | Severe Thunderstorm Warning | TSA | Creek, Okmulgee, Tulsa | 39 min |
| May 21, 9:07 PM CDT | Tornado Warning | OUN | Pontotoc, Seminole | 23 min |
| May 21, 9:29 PM CDT | Severe Thunderstorm Warning | OUN | Hughes, Pontotoc, Seminole | 11 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Norman, OK (KOUN), launched 00:00Z, 0.1 hours before the alert went out and 95 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 1388 J/kg
- Mixed-layer CIN
- -20 J/kg
- Mixed-layer LCL
- 2020 m above ground
- 0-6 km bulk shear
- 43 kt
- 0-1 km storm-relative helicity
- 144 m²/s²
- 0-3 km storm-relative helicity
- 205 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 7.5
The text
As transmitted, in the capitals the NWS used until 2016.
140
WWUS20 KWNS 220008
SEL0
SPC WW 220008
OKZ000-220500-
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 320
NWS STORM PREDICTION CENTER NORMAN OK
710 PM CDT SAT MAY 21 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
PARTS OF SOUTH CENTRAL AND SOUTHEAST OKLAHOMA
EFFECTIVE THIS SATURDAY NIGHT FROM 710 PM UNTIL MIDNIGHT CDT.
TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 55 STATUTE
MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH NORTHWEST OF
MCALESTER OKLAHOMA TO 15 MILES SOUTHWEST OF DURANT OKLAHOMA. FOR
A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU0).
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.
OTHER WATCH INFORMATION...CONTINUE...WW 316...WW 317...WW
318...WW 319...
DISCUSSION...AN ISOLATED STORM FORMED EARLIER ON THE DRYLINE IN S
CENTRAL OK...WHILE VISIBLE IMAGERY NOW SHOWS MORE DEEPENING
CONVECTION FARTHER TO THE N. EVEN THOUGH THE BOUNDARY LAYER HAS
REMAINED RELATIVELY COOL FARTHER TO THE E ACROSS SE OK TODAY...THE
COMBINATION OF STEEP MIDLEVEL LAPSE RATES AND DEWPOINTS NEAR 70 F
WILL MAINTAIN MLCAPE AOA 2500 J/KG FOR THE NEXT SEVERAL HOURS.
SINCE IT APPEARS THAT ONE OR TWO STORMS WILL BECOME SUSTAINED...THE
ENVIRONMENT IS SUPPORTIVE OF SUPERCELLS WITH VERY LARGE HAIL AND A
COUPLE OF TORNADOES.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
550. MEAN STORM MOTION VECTOR 27025.
...THOMPSONSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 21, 8:31 PM CDT | Mesoscale Discussion | SPC | LeFlore | 89 min |
| May 22, 12:42 PM CDT | Mesoscale Discussion | SPC | Carter, Garvin, Jefferson, Johnston, Love, Marshall and 2 more | 2 hr |
| May 22, 1:06 PM CDT | Mesoscale Discussion | SPC | Craig, Delaware, Mayes, Nowata, Osage, Ottawa and 3 more | 114 min |
| May 22, 1:27 PM CDT | Tornado Watch | SPC | Adair, Cherokee, Choctaw, Craig, Creek, Delaware and 19 more | 8 hr |
| May 22, 1:47 PM CDT | Tornado Watch | SPC | Atoka, Bryan, Carter, Coal, Garvin, Hughes and 10 more | 7 hr |
| May 22, 3:47 PM CDT | Mesoscale Discussion | SPC | Carter, Coal, Hughes, Johnston, Love, McIntosh and 5 more | 58 min |
| May 22, 3:48 PM CDT | Mesoscale Discussion | SPC | Adair, Cherokee, Craig, Delaware, Haskell, McIntosh and 9 more | 117 min |
| May 22, 6:10 PM CDT | Mesoscale Discussion | SPC | Adair, Cherokee, Craig, Delaware, Haskell, McIntosh and 9 more | 65 min |
| May 22, 6:34 PM CDT | Mesoscale Discussion | SPC | Atoka, Bryan, Carter, Coal, Garvin, Hughes and 10 more | 56 min |
Nearby
Tornado Watches in Oklahoma, 2011Every tornado watch in 2011
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.