Overview
On August 20th, a strong upper wave moving through the area prompted strong and severe thunderstorms throughout the area. Heavy rain and sporadic wind gusts occurred through the afternoon and evening. Mini supercells developed as well, producing numerous wall clouds, funnel clouds, and one EF-0 tornado. The heavy rain was much needed after experiencing drought for the majority of the summer.Tornadoes:
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Tornado - 4 E Erie
Track Map  
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The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:
| EF0 Weak 65-85 mph |
EF1 Moderate 86-110 mph |
EF2 Significant 111-135 mph |
EF3 Severe 136-165 mph |
EF4 Extreme 166-200 mph |
EF5 Catastrophic 200+ mph |
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Photos & Video
Photos and video of the mini supercells that prompted the tornado warnings
Extremely low wall cloud with occasional funnel-esque features along it, 3 miles west of Enderlin, ND #ndwx @NWSGrandForks @NWSBismarck pic.twitter.com/CO54sBnhvP
— Weather Unrated (@WxUnrated) August 20, 2021
Near Amenia. #VNLFirstAlert #ndwx pic.twitter.com/Obfyi9zOlY
— Eric Whitehill (@torchaser) August 20, 2021
Wow. @NWSGrandForks nw of casselton pic.twitter.com/TMteXh2kwz
— The Rear Flank 🎬 (@charliemizza) August 20, 2021
Hunter nd @NWSGrandForks @WDAYnews pic.twitter.com/MR3S8DRUsK
— The Rear Flank 🎬 (@charliemizza) August 20, 2021
Another attempt about to happen on top of norcross MN. evident rotation @NWSAberdeen pic.twitter.com/QsyTSgEWXu
— Chris_Wicklund (@Wicky_dubs_WX) August 20, 2021
Radar
This event had three tornado warnings and 5 severe thunderstorm warnings issued in the afternoon and early evening hours of August 20th.
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| The line that prompted severe thunderstorm warnings in Minnesota. | Reflectivity and Velocity of the tornado warned storm in Barnes, Griggs, and Steele counties | Reflectivity and Velocity of the tornado warned storm in Cass and Barnes counties |
Storm Reports
PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE GRAND FORKS ND
312 PM CDT WED AUG 25 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0116 PM TSTM WND DMG 4 E HAZEL 48.02N 96.03W
08/20/2021 Pennington MN PUBLIC
FAUL ASK AND PINE TREES BROKEN DOWN IN A SHELTER BELT.
PHOTO AND REPORT POSTED VIA SOCIAL MEDIA. TIME ESTIMATED
BASED ON RADAR
0155 PM TSTM WND DMG 5 ESE HIGH LANDING 48.02N 95.71W
08/20/2021 Pennington MN PUBLIC
TIN ROOF PANEL BLOWN OFF A SHED.
0234 PM FUNNEL CLOUD 6 WNW ENDERLIN 46.66N 97.72W
08/20/2021 Barnes ND TRAINED SPOTTER
PERSISTENT AND LOW WALL CLOUD WITH POSSIBLE FUNNEL. PHOTO
AND REPORT POSTED VIA SOCIAL MEDIA.
0325 PM TSTM WND GST 1 NW BAUDETTE 48.72N 94.60W
08/20/2021 M52.00 MPH Lake Of The Woods MN ASOS
PEAK WIND MEASURED AT THE BAUDETTE INTERNATIONAL AIRPORT
/KBDE/.
0418 PM TORNADO 4 E ERIE 47.11N 97.30W
08/20/2021 F0 Cass ND TRAINED SPOTTER
A FUNNEL WITH BRIEF TOUCHDOWN. REPORT POSTED VIA SOCIAL
MEDIA. SOME TREE BRANCHES AND CORN STALKS WERE SEEN
SWIRLING IN THE DEBRIS. PEAK WINDS ESTIMATED TO 70 MPH.
MAXIMUM WIDTH TO 40 YARDS. TRACK LENGTH OF LESS THAN ONE
QUARTER MILE TO THE EAST-NORTHEAST BY 419 PM CDT.
0432 PM FUNNEL CLOUD 6 NNW LUVERNE 47.33N 97.98W
08/20/2021 Steele ND TRAINED SPOTTER
PERSISTENT WALL CLOUD WITH BRIEF FUNNEL.
0505 PM TSTM WND GST 1 W CUMMINGS 47.51N 97.10W
08/20/2021 E70.00 MPH Traill ND TRAINED SPOTTER
0525 PM TSTM WND DMG 2 N ALMORA 46.28N 95.37W
08/20/2021 Otter Tail MN PUBLIC
LARGE TREE BLOWN DOWN. TIME ESTIMATED BASED ON RADAR.
0530 PM TSTM WND DMG 5 W ELDRED 47.68N 96.89W
08/20/2021 Polk MN PUBLIC
LARGE ASH AND COTTONWOOD BRANCHES BLOWN DOWN IN A SHELTER
BELT. TIME ESTIMATED BASED ON RADAR.
0645 PM NON-TSTM WND GST 2 N MADDOCK 47.99N 99.53W
08/20/2021 M60.00 MPH Benson ND MESONET
PEAK WIND MEASURED AT AN NDAWN STATION MEASURED AT 10
METERS.
0723 PM NON-TSTM WND GST 6 ESE LEEDS 48.26N 99.32W
08/20/2021 M63.00 MPH Benson ND MESONET
PEAK WIND MEASURED AT THE NDAWN STATIONS NILES 3SE AT 10
METERS.
0816 PM NON-TSTM WND GST 4 SSW DEVILS LAKE 48.06N 98.91W
08/20/2021 M55.00 MPH Ramsey ND MESONET
SUSTAINED AT 45 GUSTING TO 55 MPH AT THE RWIS STATION ON
HIGHWAY 20 AT MP98.
&&
$$
Rain Reports
Public Information Statement National Weather Service Grand Forks ND 1122 AM CDT Sat Aug 21 2021 ...PRECIPITATION REPORTS... Location Amount Time/Date Provider Pelican Rapids 4.88 in 0810 AM 08/21 Public 3 NNW Huntersville 3.80 in 0953 AM 08/21 Public Roseau 3.45 in 0810 AM 08/21 Public Wadena 3.25 in 0955 AM 08/21 Public Thief River Falls 2.90 in 0935 AM 08/21 Public Wadena 2.88 in 1100 PM 08/20 Public Park Rapids 2.75 in 0200 AM 08/21 Public Park Rapids AP MN 2.73 in 0553 AM 08/21 ASOS Roseau MN 2 E 2.73 in 0408 AM 08/21 RAWS Fertile MN 0.6 E 2.71 in 0300 AM 08/21 COCORAHS Badoura MN 2 E 2.53 in 0406 AM 08/21 RAWS 2 SE Menahga 2.50 in 0748 PM 08/20 Public Glacial Ridge Portable 2.49 in 0532 AM 08/21 RAWS Grand Forks ND 2.5 SE 2.40 in 0200 PM 08/20 COCORAHS Roseau MN 2.40 in 0530 AM 08/21 HADS Thorhult MN 2.40 in 0500 PM 08/20 COOP Holt MN 6 E 2.26 in 0530 AM 08/21 HADS Badoura MN 1 SE 2.25 in 0530 AM 08/21 HADS Baudette MN 3 S 2.13 in 0406 AM 08/21 RAWS 2 WSW Fergus Falls 2.00 in 0756 PM 08/20 Public 3 WSW Holmes 2.00 in 0136 PM 08/20 Trained Spotter Baudette AP MN 1.93 in 0553 AM 08/21 ASOS Fertile MN 3 WSW 1.90 in 0545 AM 08/21 HADS Baudette MN 12 S 1.83 in 0515 AM 08/21 HADS 2 ESE Bygland 1.83 in 0100 AM 08/21 Public Buxton ND 4 ENE 1.80 in 0600 AM 08/21 AWS Bemidji 1.69 in 0805 AM 08/21 Public Moorhead 1.66 in 0124 AM 08/21 Broadcast Media Fergus Falls MN 3 W 1.65 in 0545 AM 08/21 HADS Elizabeth MN 2 NNE 1.63 in 0600 AM 08/21 CWOP Alvarado MN 5 NNE 1.62 in 0600 AM 08/21 AWS Fargo ND 7 SW 1.61 in 0552 AM 08/21 CWOP West Fargo 1.60 in 0824 PM 08/20 Public Fergus Falls MN 1.57 in 0559 AM 08/21 CWOP Hope ND 5.4 WNW 1.54 in 0945 PM 08/20 COCORAHS Walhalla ND 3 NNE 1.54 in 0600 AM 08/21 AWS Bemidji MN 8 N 1.51 in 0600 AM 08/21 CWOP Fargo ND 3.6 NNE 1.43 in 0720 PM 08/20 COCORAHS Moorhead MN 1 NE 1.42 in 0555 AM 08/21 CWOP Holt MN 15 E 1.41 in 0520 AM 08/21 RAWS Lake Park MN 7.9 S 1.40 in 0630 PM 08/20 COCORAHS 2 S Oberon 1.40 in 1047 AM 08/20 Public Grand Forks ND 7 SW 1.32 in 0600 AM 08/21 CWOP Fargo 1.2 ESE 1.30 in 0700 PM 08/20 COCORAHS Fargo AP ND 1.29 in 0553 AM 08/21 ASOS Florian MN 1 S 1.28 in 0545 AM 08/21 HADS Mentor MN 2 SW 1.28 in 0558 AM 08/21 CWOP Arygle MN 12 WNW 1.23 in 0600 AM 08/21 CWOP Fort Totten ND 5 ENE 1.21 in 0551 AM 08/21 RAWS Hatton ND 2 S 1.21 in 0600 AM 08/21 AWS Highlanding MN 20 E 1.21 in 0530 AM 08/21 HADS Thief River Falls MN 2 W 1.20 in 0600 AM 08/21 AWS Grand Forks AP ND 1.19 in 0553 AM 08/21 ASOS Northcote MN 2 ENE 1.19 in 0545 AM 08/21 HADS Hallock AP MN 1.17 in 0555 AM 08/21 AWOS Hampden ND 3 SE 1.17 in 0458 AM 08/21 RAWS Glyndon MN 2 NW 1.14 in 0545 AM 08/21 HADS Grygla MN 6 WNW 1.13 in 0530 AM 08/21 HADS Frazee MN 3 E 1.12 in 0555 AM 08/21 CWOP Bemidji MN 5 N 1.10 in 0605 AM 08/21 AWS Osage MN 5 NW 1.08 in 0530 AM 08/21 HADS Cooperstown ND 5 E 1.05 in 0500 AM 08/21 HADS Bemidji MN 2 WNW 1.04 in 0406 AM 08/21 RAWS Malung MN 1 NW 1.03 in 0530 AM 08/21 HADS Glyndon MN 2 N 0.99 in 0545 AM 08/21 HADS Alvarado MN 1 N 0.98 in 0530 AM 08/21 HADS Cormorant MN 5 NW 0.97 in 0600 AM 08/21 AWS Rlnm5 0.96 in 0409 AM 08/21 RAWS Gonvick MN 0.93 in 0555 AM 08/21 CWOP Detroit Lakes MN 1 N 0.92 in 0520 AM 08/21 RAWS Webster ND 0.92 in 0600 AM 08/21 AWS Mahnomen 1 SE MN 0.91 in 0545 AM 08/21 HADS Detroit Lakes MN 5.7 N 0.90 in 0430 AM 08/21 COCORAHS Harwood ND 0.89 in 0545 AM 08/21 CWOP Lake Itasca MN 2 SE 0.86 in 0407 AM 08/21 RAWS Bagley MN 0.84 in 0605 AM 08/21 AWS Warroad MN 0.81 in 0530 AM 08/21 HADS Walhalla ND 3.6 SSE 0.76 in 0600 AM 08/21 COCORAHS Bemidji AP MN 0.75 in 0555 AM 08/21 AWOS Brooks MN 3 WNW 0.74 in 0545 AM 08/21 HADS Grand Forks ND AFB 0.74 in 0556 AM 08/21 ASOS Devils Lake ND 0.69 in 0559 AM 08/21 CWOP Leeds ND 4 SE 0.69 in 0515 AM 08/21 HADS Thief River Falls AP MN 0.69 in 0556 AM 08/21 AWOS Staples AP MN 0.68 in 0555 AM 08/21 AWOS Michigan ND 0.67 in 0500 AM 08/21 COOP Norcross MN 1 NW 0.67 in 0500 AM 08/21 HADS Lisbon ND 18 E 0.66 in 0549 AM 08/21 RAWS Bagley MN 5 N 0.65 in 0555 AM 08/21 CWOP Brooks MN 0.63 in 0605 PM 08/20 AWS Dakota Junction MN 1 WSW 0.62 in 0605 PM 08/20 AWS Mentor MN 9 W 0.62 in 0600 AM 08/21 HADS Felton MN 8 NE 0.61 in 0545 AM 08/21 HADS Karlstad MN 0.61 in 0406 AM 08/21 RAWS Red Lake Falls MN 0.60 in 0530 AM 08/21 HADS Warren MN 3 ENE 0.60 in 0545 AM 08/21 HADS Clemenston MN 0.59 in 0500 AM 08/21 HADS Campbell MN 0.51 in 0530 AM 08/21 HADS Observations are collected from a variety of sources with varying equipment and exposures. We thank all volunteer weather observers for their dedication. Not all data listed are considered official. $$
Storm Total QPF across the area
Environment
Synoptic environment:
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| 300mb analysis | Potential Vorticity | 18Z Sounding from ABR |
Near-storm environment:
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| Surface-Based CAPE | Effective Bulk Shear | Supercell Composite Parameter |
Additional environmental data:
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| WPC Surface Analysis from 12Z August 20th through 00Z August 21st |
Issued at 103 PM CDT Fri Aug 20 2021 Storms continue to track northeastward, with the bulk of the activity pushing past the international border as expected. Primary concern in the near term is the line of storms in northwest Minnesota exhibiting some QLCS-like qualities. With 0-3km shear vectors pointed perpendicular to portions of the line, this region may be an area to watch over the next few hours for brief tornadoes. Looking at surface analysis, the surface low has begun to deepen and appears to be centered over central North Dakota with the cold front draping southward just east of Bismarck, with a warm front/theta-e gradient stretching across the central Red River Valley and turning northward. An area of clearing clouds has begun to enter North Dakota, destabilizing the air-mass beneath. Within this area of clearing, a plume of modest MLCAPE (around 1500-2000 J/kg in the south Red River Valley) has begun to filter in. Areas of cumulus are already being seen on satellite within the south Valley with a few showers cropping up. Notably, within the south RRV and into NE South Dakota, showers have begun to form along what appears to be a boundary of differential diabatic heating, fueling near surface destabilization and creating what appears to be some sort of boundary. Moderate effective bulk shear (35-40 knots) exists across the area, favoring some storm organization this afternoon. Looking at model derived soundings, hodographs appear favorable for some tornado potential this afternoon. While not the textbook hook hodographs typical for tornadoes, there is a low level area of veering within the warm sector that could provide an environment for tornado development this afternoon. On top of that, with the cold front upstream creating pre-existing vorticity, the potential is still on track for tornadoes. Hail and damaging winds remain a concern as well from the strongest storms this afternoon. Observational trends will have to be monitored to be more specific on threat areas, but at this time most areas still remain under the threat for severe weather this afternoon. && |
Issued at 332 PM CDT Fri Aug 20 2021 Current concerns over the next few hours will be the potential for mini supercells in the south valley south of the warm front and near the pressure trough, and convection along the cold front to the west. Increased convective coverage is expected as the bulk of forcing pushes northeastward. Line of storms continues to advect northeastward in northwest Minnesota crossing out of the CWA within the next hour or two. Concern now shifts towards southeast North Dakota where what appears to be a pre-frontal trough has begun to take shape over the area and is well within the vicinity of the warm front. As of 20z, a mini supercell has developed northwest of Enderlin. Surface analysis continues to show broad cyclonic circulation centered in southeast North Dakota. Attached to it remains the cold front stretching southward into South Dakota, with a warm front that stretches across the RRV before jutting northward into Canada. A pressure trough was also noted, with 1001-1002mb being reported in NE SD. In this area, moderate instability exists with 2000+ J/kg of MLCAPE and effective bulk shear values approaching 40+ knots, supporting the development of mid level mesocyclones. There is a concern with these individual storms that have developed across the south valley to potentially become mini-supercells, as there is likely an area of enhanced cyclonic flow and vorticity within this region and the close proximity to the warm front facilitating localized increases in SRH. Effective layer STP values are also starting to filter in above one across the region. Putting all of this together, there is the potential for mini supercell development with the threat for tornadoes. Gazing back further west, the cold front continues to push east- northeastward, and is already providing a focused area of convection to our west. The expectation is for this threat along the cold front to continue, as meaningful instability remains well in place within the warm sector, and there isn't any expectation at this time for the mini-supercells to scour that out. Finally, as the bulk of the forcing continues northeastward, the expectation is for convective coverage to increase in the valley. All hazards remain possible at this time, including tornadoes. Trends will continue to be monitored for potential more development in the central valley over the next few hours as well as monitoring of the convection near the cold front. && |
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