Alert archive / South Dakota / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 533

July 27, 201210 counties in South Dakota

The Storm Prediction Center issued this severe thunderstorm watch at Jul 27, 2012, 4:24 PM MDT for 10 counties in South Dakota. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Jul 27, 2012, 4:24 PM MDT (22:24 UTC)
Expired: Jul 27, 2012, 8:50 PM MDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

Counties Bennett County, SD, Butte County, SD, Custer County, SD, Fall River County, SD, Haakon County, SD, Jackson County, SD, Lawrence County, SD, Meade County, SD, Pennington County, SD, Ziebach County, SD

The radar

The Rapid City radar (KUDX), 32 km from the middle of the area, began a volume at 22:25 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: 20%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 30%
Ten or more severe hail reports: 30%
One or more hailstones of 2 inches or more: 20%
Six or more combined severe hail and wind reports: 70%

Warnings issued inside it

4 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Jul 27, 4:46 PM MDT	Severe Thunderstorm Warning	UNR	Lawrence, Meade	59 min
Jul 27, 5:29 PM MDT	Severe Thunderstorm Warning	UNR	Pennington	61 min
Jul 27, 5:59 PM MDT	Severe Thunderstorm Warning	UNR	Custer, Haakon, Jackson, Meade, Pennington	61 min
Jul 27, 6:55 PM MDT	Severe Thunderstorm Warning	UNR	Haakon, Jackson, Mellette, Pennington	72 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

Rapid City, SD (KUNR), launched 12:00Z, 10.4 hours before the alert went out and 39 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1749 m above ground
0-6 km bulk shear: 54 kt
0-1 km storm-relative helicity: 115 m²/s²
0-3 km storm-relative helicity: 214 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

522 
WWUS20 KWNS 272223
SEL3
SPC WW 272223
SDZ000-280600-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 533
NWS STORM PREDICTION CENTER NORMAN OK
425 PM MDT FRI JUL 27 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

       WESTERN SOUTH DAKOTA

EFFECTIVE THIS FRIDAY AFTERNOON FROM 425 PM UNTIL MIDNIGHT MDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65
STATUTE MILES EAST AND WEST OF A LINE FROM 90 MILES NORTH
NORTHEAST OF RAPID CITY SOUTH DAKOTA TO 70 MILES SOUTH SOUTHEAST
OF RAPID CITY SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE
WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 531...WW 532...

DISCUSSION...WIDELY SCATTERED TSTMS ARE ANTICIPATED TO DEVELOP
ACROSS THE WATCH AREA THIS EVENING IN ADVANCE OF A WEAK MIDLEVEL
IMPULSE CRESTING MEAN RIDGE AXIS.  AIR MASS IS CHARACTERIZED BY
STEEP LOW TO MIDLEVEL LAPSE RATES AND A DEEPLY MIXED BOUNDARY LAYER.
 WHEN COUPLED WITH AROUND 40 KT OF DEEP-LAYER SHEAR...SETUP WILL
PROMOTE HIGH-BASED SUPERCELLS WHICH MAY TRANSITION TO A SMALL MCS
THIS EVENING WITH THE PRIMARY HAZARDS BEING DAMAGING WINDS AND SOME
HAIL.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 27025.


...MEAD

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 27, 2:27 PM MDT	Mesoscale Discussion	SPC	Butte, Custer, Fall River, Lawrence, Pennington	3 hr

Nearby

Severe Thunderstorm Watches in South Dakota, 2012 Every severe thunderstorm watch in 2012

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.