Alert archive / Minnesota / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 397
The Storm Prediction Center issued this severe thunderstorm watch at Jul 27, 2021, 8:03 PM CDT for 13 counties in Iowa; 14 counties in Minnesota; 9 counties in Wisconsin. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Jul 27, 2021, 8:03 PM CDT (01:03 UTC)
- Expired
- Jul 28, 2021, 2:00 AM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 3 in
- Strongest gust expected
- 65 kt
All 36 counties
Allamakee County, IA, Bremer County, IA, Buchanan County, IA, Chickasaw County, IA, Clayton County, IA, Delaware County, IA, Dubuque County, IA, Fayette County, IA, Floyd County, IA, Howard County, IA, Mitchell County, IA, Winneshiek County, IA, Worth County, IA, Dakota County, MN, Dodge County, MN, Fillmore County, MN, Freeborn County, MN, Goodhue County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Ramsey County, MN, Rice County, MN, Steele County, MN, Wabasha County, MN, Washington County, MN, Winona County, MN, Buffalo County, WI, Crawford County, WI, Grant County, WI, La Crosse County, WI, Pepin County, WI, Pierce County, WI, Richland County, WI, Trempealeau County, WI, Vernon County, WI
The radar
The La Crosse radar (KARX), 57 km from the middle of the area, began a volume at 01:04 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
- 40%
- One or more gusts of 65 knots or more
- 40%
- Ten or more severe hail reports
- 60%
- One or more hailstones of 2 inches or more
- 60%
- Six or more combined severe hail and wind reports
- 90%
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, 8:30 PM CDT | Severe Thunderstorm Warning | ARX | Olmsted, Wabasha, Winona | 45 min |
| Jul 27, 9:16 PM CDT | Severe Thunderstorm Warning | ARX | Fillmore, Olmsted, Winona | 44 min |
| Jul 27, 9:48 PM CDT | Severe Thunderstorm Warning | ARX | Fillmore, Olmsted | 42 min |
| Jul 28, 12:50 AM CDT | Severe Thunderstorm Warning | DVN | Buchanan, Delaware | 40 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, 1.1 hours before the alert went out and 180 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
- 4029 J/kg
- Mixed-layer CIN
- -9 J/kg
- Mixed-layer LCL
- 1142 m above ground
- 0-6 km bulk shear
- 35 kt
- 0-1 km storm-relative helicity
- 5 m²/s²
- 0-3 km storm-relative helicity
- 65 m²/s²
- Significant tornado parameter
- 0.7
- Supercell composite
- 6.6
The text
As transmitted.
608
WWUS20 KWNS 280100
SEL7
SPC WW 280100
IAZ000-MNZ000-WIZ000-280700-
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 397
NWS Storm Prediction Center Norman OK
805 PM CDT Tue Jul 27 2021
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northeast Iowa
Southeast Minnesota
Southwest Wisconsin
* Effective this Tuesday night and Wednesday morning from 805 PM
until 200 AM CDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 3
inches in diameter likely
Scattered damaging winds and isolated significant gusts to 75
mph possible
A tornado or two possible
SUMMARY...A few supercells should become established across a
portion of the Upper Mississippi Valley before developing into a
southward-moving cluster this evening.
The severe thunderstorm watch area is approximately along and 50
statute miles east and west of a line from 55 miles north of
Rochester MN to 40 miles west of Dubuque IA. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU7).
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.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 396...
AVIATION...A few severe thunderstorms with hail surface and aloft to
3 inches. Extreme turbulence and surface wind gusts to 65 knots. A
few cumulonimbi with maximum tops to 600. Mean storm motion vector
33020.
...GramsSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 27, 7:33 PM CDT | Mesoscale Discussion | SPC | Allamakee, Black Hawk, Bremer, Buchanan, Butler, Cerro Gordo and 11 more | 87 min |
| Jul 27, 10:35 PM CDT | Mesoscale Discussion | SPC | Allamakee, Bremer, Buchanan, Chickasaw, Clayton, Delaware and 5 more | 55 min |
| Jul 28, 12:50 AM CDT | Mesoscale Discussion | SPC | Benton, Buchanan, Clayton, Delaware, Dubuque, Jackson and 2 more | 55 min |
| Jul 28, 2:48 AM CDT | Mesoscale Discussion | SPC | Big Stone, Chippewa, Douglas, Grant, Kandiyohi, Lac qui Parle and 12 more | 2 hr |
| Jul 28, 10:28 AM CDT | Mesoscale Discussion | SPC | Aitkin, Beltrami, Cass, Clearwater, Hubbard, Itasca | 2 hr |
| Jul 28, 12:59 PM CDT | Mesoscale Discussion | SPC | Koochiching, Lake, Lake of the Woods, Saint Louis | 2 hr |
| Jul 28, 3:32 PM CDT | Mesoscale Discussion | SPC | Beltrami, Clearwater, Lake of the Woods, Mahnomen, Red Lake | 118 min |
| Jul 28, 5:09 PM CDT | Mesoscale Discussion | SPC | Aitkin, Anoka, Benton, Carlton, Chisago, Crow Wing and 7 more | 2 hr |
Nearby
Severe Thunderstorm Watches in Minnesota, 2021Severe Thunderstorm Watches in Iowa, 2021Severe Thunderstorm Watches in Wisconsin, 2021Every severe thunderstorm watch in 2021
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.