Alert archive / Minnesota / Severe Thunderstorm Watches in 2021

Severe Thunderstorm Watch 387

July 23, 202118 counties in Minnesota

The Storm Prediction Center issued this severe thunderstorm watch at Jul 23, 2021, 4:48 PM CDT for 18 counties in Minnesota. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: Jul 23, 2021, 4:48 PM CDT (21:48 UTC)
Expired: Jul 23, 2021, 11:26 PM CDT
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

Counties Aitkin County, MN, Becker County, MN, Beltrami County, MN, Carlton County, MN, Cass County, MN, Clearwater County, MN, Cook County, MN, Hubbard County, MN, Itasca County, MN, Koochiching County, MN, Lake County, MN, Lake of the Woods County, MN, Mahnomen County, MN, Norman County, MN, Pennington County, MN, Polk County, MN, Red Lake County, MN, Saint Louis County, MN

The radar

The Duluth radar (KDLH), 176 km from the middle of the area, began a volume at 21:50 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: 5%
One or more EF2 to EF5 tornadoes: 2%
Ten or more severe wind reports: 40%
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: 30%
Six or more combined severe hail and wind reports: 70%

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
Jul 23, 4:50 PM CDT	Severe Thunderstorm Warning	DLH	Koochiching	22 min
Jul 23, 4:59 PM CDT	Severe Thunderstorm Warning	DLH	Itasca, Koochiching	38 min
Jul 23, 5:34 PM CDT	Severe Thunderstorm Warning	DLH	Itasca	45 min
Jul 23, 6:22 PM CDT	Severe Thunderstorm Warning	FGF	Beltrami, Hubbard	27 min
Jul 23, 6:28 PM CDT	Severe Thunderstorm Warning	DLH	Cook, Lake, Saint Louis	62 min
Jul 23, 7:30 PM CDT	Severe Thunderstorm Warning	DLH	Cook, Lake, Saint Louis	37 min
Jul 23, 8:02 PM CDT	Severe Thunderstorm Warning	DLH	Aitkin, Cass, Itasca	43 min
Jul 23, 8:39 PM CDT	Severe Thunderstorm Warning	DLH	Saint Louis	36 min
Jul 23, 8:56 PM CDT	Severe Thunderstorm Warning	DLH	Saint Louis	34 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

International Fa, MN (KINL), launched 12:00Z, 9.8 hours before the alert went out and 110 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: 470 J/kg
Mixed-layer CIN: -131 J/kg
Mixed-layer LCL: 725 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 112 m²/s²
0-3 km storm-relative helicity: 115 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

309 
WWUS20 KWNS 232145
SEL7  
SPC WW 232145
MNZ000-LSZ000-240600-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 387
NWS Storm Prediction Center Norman OK
445 PM CDT Fri Jul 23 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Northern Minnesota including the Arrowhead
  Lake Superior

* Effective this Friday afternoon and Saturday morning from 445
  PM until 100 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...Isolated strong-severe thunderstorms are already present
over parts of the region and adjoining portions of ON.  Through the
evening, this activity is expected to increase in coverage, from
northwestern MN to the Boundary Waters and Lake Superior North
Shore, with storms moving eastward to southeastward.  Damaging gusts
and large hail both are expected.

The severe thunderstorm watch area is approximately along and 55
statute miles north and south of a line from 50 miles south
southwest of Thief River Falls MN to 65 miles northeast of Silver
Bay MN. 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.

&&

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.

...Edwards

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 23, 1:25 PM CDT	Mesoscale Discussion	SPC	Beltrami, Clearwater, Hubbard, Mahnomen, Marshall, Norman and 4 more	2 hr

Nearby

Severe Thunderstorm Watches in Minnesota, 2021 Every 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.