Alert archive / Minnesota / Severe Thunderstorm Watches in 2016

Severe Thunderstorm Watch 486

September 20, 201612 counties in Iowa; 19 counties in Minnesota; 9 counties in Wisconsin

The Storm Prediction Center issued this severe thunderstorm watch at Sep 20, 2016, 9:34 PM CDT for 12 counties in Iowa; 19 counties in Minnesota; 9 counties in Wisconsin. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued
Sep 20, 2016, 9:34 PM CDT (02:34 UTC)
Expired
Sep 21, 2016, 3:00 AM CDT
In force
5 hr
Issued by
the Storm Prediction Center
Largest hail expected
2 in
Strongest gust expected
60 kt
All 40 counties

Allamakee County, IA, Cerro Gordo County, IA, Chickasaw County, IA, Clayton County, IA, Fayette County, IA, Floyd County, IA, Hancock County, IA, Howard County, IA, Mitchell County, IA, Winnebago County, IA, Winneshiek County, IA, Worth County, IA, Blue Earth County, MN, Brown County, MN, Dodge County, MN, Faribault County, MN, Fillmore County, MN, Freeborn County, MN, Goodhue County, MN, Houston County, MN, Le Sueur County, MN, Martin County, MN, Mower County, MN, Nicollet County, MN, Olmsted County, MN, Rice County, MN, Steele County, MN, Wabasha County, MN, Waseca County, MN, Watonwan County, MN, Winona County, MN, Buffalo County, WI, Crawford County, WI, Grant County, WI, Jackson County, WI, La Crosse County, WI, Monroe County, WI, Richland County, WI, Trempealeau County, WI, Vernon County, WI

The radar

The Minneapolis radar (KMPX), 113 km from the middle of the area, began a volume at 02:35 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
10%
One or more EF2 to EF5 tornadoes
2%
Ten or more severe wind reports
50%
One or more gusts of 65 knots or more
10%
Ten or more severe hail reports
50%
One or more hailstones of 2 inches or more
30%
Six or more combined severe hail and wind reports
70%

Warnings issued inside it

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

IssuedProductOfficeCountiesLasted
Sep 20, 10:23 PM CDTSevere Thunderstorm WarningMPXBlue Earth, Waseca37 min
Sep 20, 10:32 PM CDTSevere Thunderstorm WarningMPXBlue Earth, Brown, Le Sueur, Nicollet, Sibley33 min
Sep 20, 10:49 PM CDTSevere Thunderstorm WarningMPXBlue Earth, Waseca41 min
Sep 20, 11:59 PM CDTFlash Flood WarningMPXSteele, Waseca3 hr
Sep 21, 12:06 AM CDTSevere Thunderstorm WarningMPXSteele, Waseca24 min
Sep 21, 12:21 AM CDTSevere Thunderstorm WarningARXJackson, Trempealeau41 min
Sep 21, 12:25 AM CDTSevere Thunderstorm WarningMPXFreeborn, Steele, Waseca35 min
Sep 21, 12:30 AM CDTSevere Thunderstorm WarningARXWabasha32 min
Sep 21, 12:51 AM CDTSevere Thunderstorm WarningARXDodge, Olmsted54 min
Sep 21, 1:00 AM CDTSevere Thunderstorm WarningMPXSteele30 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

Minneapolis, MN (KMPX), launched 00:00Z, 2.6 hours before the alert went out and 115 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-pSkew-T log-p diagram, Minneapolis, MN at 00:00Z on 2016-09-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Minneapolis, MN at 00:00Z on 2016-09-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 230 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
1882 m above ground
0-6 km bulk shear
52 kt
0-1 km storm-relative helicity
230 m²/s²
0-3 km storm-relative helicity
662 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.5

Open this sounding in Storm Lab

The text

As transmitted.

574 
WWUS20 KWNS 210232
SEL6  
SPC WW 210232
IAZ000-MNZ000-WIZ000-210800-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 486
NWS STORM PREDICTION CENTER NORMAN OK
935 PM CDT TUE SEP 20 2016

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF 
  NORTHEAST IOWA
  SOUTHERN MINNESOTA
  SOUTHWEST WISCONSIN

* EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 935 PM
  UNTIL 300 AM CDT.

* PRIMARY THREATS INCLUDE...
  SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 2
    INCHES IN DIAMETER POSSIBLE
  SCATTERED DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

SUMMARY...THUNDERSTORMS ARE BEGINNING TO FORM OVER SOUTH-CENTRAL
MN...AND WILL LIKELY TRACK EAST-SOUTHEASTWARD ACROSS THE WATCH AREA.
 INITIAL STORMS MAY POSE A THREAT OF LARGE HAIL...WITH AN INCREASING
RISK OF DAMAGING WINDS AFTER MIDNIGHT.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 50
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES NORTH
NORTHWEST OF FAIRMONT MINNESOTA TO 55 MILES EAST SOUTHEAST OF LA
CROSSE WISCONSIN.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

&&

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 29030.


...HART

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 20, 8:01 PM CDTMesoscale DiscussionSPCAllamakee, Howard, Mitchell, Winneshiek, Worth119 min
Sep 20, 11:26 PM CDTMesoscale DiscussionSPCAllamakee, Clayton, Howard, Winneshiek2 hr
Sep 21, 1:33 AM CDTMesoscale DiscussionSPCAllamakee, Howard, Winneshiek117 min
Sep 21, 2:00 PM CDTMesoscale DiscussionSPCAllamakee, Benton, Black Hawk, Boone, Bremer, Buchanan and 56 more2 hr
Sep 21, 6:01 PM CDTMesoscale DiscussionSPCAllamakee, Bremer, Butler, Cerro Gordo, Chickasaw, Clayton and 10 more2 hr
Sep 21, 2:31 PM CDTMesoscale DiscussionSPCAnoka, Carver, Chippewa, Chisago, Dakota, Goodhue and 15 more89 min

Nearby

Severe Thunderstorm Watches in Minnesota, 2016Severe Thunderstorm Watches in Iowa, 2016Severe Thunderstorm Watches in Wisconsin, 2016Every severe thunderstorm watch in 2016

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.