Alert archive / Minnesota / Mesoscale Discussions in 2021

Mesoscale Discussion 1566

August 20, 202110 counties in Minnesota; 9 counties in North Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 20, 2021, 1:41 PM CDT for 10 counties in Minnesota; 9 counties in North Dakota. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Aug 20, 2021, 1:41 PM CDT (18:41 UTC)
Expired: Aug 20, 2021, 4:15 PM CDT
In force: 3 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 60%

Counties Clay County, MN, Kittson County, MN, Marshall County, MN, Norman County, MN, Pennington County, MN, Polk County, MN, Red Lake County, MN, Roseau County, MN, Traverse County, MN, Wilkin County, MN, Cass County, ND, Grand Forks County, ND, Pembina County, ND, Ransom County, ND, Richland County, ND, Sargent County, ND, Steele County, ND, Traill County, ND, Walsh County, ND

The radar

The Fargo/Grand Forks radar (KMVX), 80 km from the middle of the area, began a volume at 18:45 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.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

The nearest sounding before it

Aberdeen, SD (KABR), launched 12:00Z, 6.7 hours before the alert went out and 248 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: 1019 J/kg
Mixed-layer CIN: -14 J/kg
Mixed-layer LCL: 682 m above ground
0-6 km bulk shear: 40 kt
0-1 km storm-relative helicity: 45 m²/s²
0-3 km storm-relative helicity: 73 m²/s²
Significant tornado parameter: 0.3
Supercell composite: 2.2

Open this sounding in Storm Lab

The text

As transmitted.

228 
ACUS11 KWNS 201841
SWOMCD
SPC MCD 201841 
MNZ000-SDZ000-NDZ000-202115-

Mesoscale Discussion 1566
NWS Storm Prediction Center Norman OK
0141 PM CDT Fri Aug 20 2021

Areas affected...eastern North Dakota into northwest Minnesota...far
northeast South Dakota

Concerning...Severe potential...Watch possible 

Valid 201841Z - 202115Z

Probability of Watch Issuance...60 percent

SUMMARY...Storms are likely to increase in coverage after 20Z, with
a few becoming severe.

DISCUSSION...Surface analysis shows a low deepening over eastern ND,
with a trough extending into northeast SD. A cold front extending
south from the low continues to push eastward, with midlevel cooling
pivoting northeastward across the central Dakotas. A warm front
continues to develop northward ahead of the low, from southeast ND
into northwest MN, where scattered storms have cooled temperatures
locally.

Heating continues over portions of the area, which will lead to
further destabilization ahead of the cold front. As large-scale
ascent increases, storms are expected to form near the low, and
along the warm advection zone where small storms are currently
forming. While low-level shear is not particularly strong, objective
analysis as well as VWPs indicate sufficient 0-1 SRH (near 100
m2/s2) for a minor tornado threat for storms that remain discrete.
Otherwise, congealing storms are possible into the evening, with a
few damaging gusts possible.

..Jewell/Guyer.. 08/20/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FGF...ABR...BIS...

LAT...LON   45659645 45649689 45739751 46059804 46619814 47259800
            49059759 49029582 48399576 47369585 46079620 45659645

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 20, 2:24 PM CDT	Severe Thunderstorm Watch	SPC	Becker, Beltrami, Cass, Clay, Clearwater, Crow Wing and 16 more	8 hr
Aug 20, 3:58 PM CDT	Severe Thunderstorm Watch	SPC	Big Stone, Blue Earth, Brown, Chippewa, Cottonwood, Douglas and 26 more	6 hr
Aug 20, 5:51 PM CDT	Mesoscale Discussion	SPC	Becker, Beltrami, Cass, Chippewa, Clearwater, Douglas and 20 more	84 min

Nearby

Mesoscale Discussions in Minnesota, 2021 Mesoscale Discussions in North Dakota, 2021 Every mesoscale discussion 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.