Convectively enhanced vorticity max lead to initiation of storms overnight Sunday across southern South Dakota. These initial storms grew upscale given concurrent downstream destabilization through northeast Nebraska and northwest Iowa.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS IWX wrote it up.
Convectively enhanced vorticity max lead to initiation of storms overnight Sunday across southern South Dakota. These initial storms grew upscale given concurrent downstream destabilization through northeast Nebraska and northwest Iowa. Widespread 80-100 mph winds developed through central/eastern Iowa as this derecho matured. Northern bookend and advection wing forcing led to some supercell structures across northern Illinois/southwest Wisconsin. Northern bookend turned northeast as it moved across Lake Michigan and tracked into western Michigan. As this occurred, attendant post convective wake low weakened as it crossed the lake. Thus the local area did not experience the 80 to 100 mph winds that N IL/E IA experienced. However the resultant slowing and breakup of the line as it moved across northwest Indiana/SW Michigan, yielded a LEWP and subsequent multiple small scale circulations developing along the line. These meso-vortices were associated with pockets of enhanced wind damage and brief tornado occurrences.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Northern Indiana wrote its last area forecast discussion before the first event at Aug 10, 2:18 AM EST, 3 hours 12 minutes earlier.
Area Forecast Discussion National Weather Service Northern Indiana 318 AM EDT Mon Aug 10 2020 .SYNOPSIS... Issued at 317 AM EDT Mon Aug 10 2020 Today into tonight will feature humid conditions and chances for showers and thunderstorms, especially during the late afternoon and evening. Highs today will reach the mid to upper 80s. Mainly dry conditions and seasonable temperatures are then expected for the remainder of the week. && .SHORT TERM...(Today and Tonight) Issued at 317 AM EDT Mon Aug 10 2020 A remnant mid level shortwave, and the coincident eastward fold of an upstream low level theta-e ridge, will bring chances for scattered showers and iso thunder this morning. A lull in between forcing mechanisms and weakening of the nocturnal LLJ will likely support dry conditions by late morning through mid afternoon, though will still carry a slight chc PoP as instability builds. The main focus remains on chances for a round of more widespread convection late afternoon and evening, though uncertainty lingers regarding timing/intensity. Substantial boundary layer destabilization is still expected by this afternoon (from eastern IA/srn WI east into IN/sw MI) as a Plains EML overspreads low-mid 70 sfc dewpoints. The southern fringe of height falls, and an associated cold front, will infringe on this unstable airmass upstream early-mid aftn. This should favor convective growth, with CAMS in decent agreement in bringing this activity into the area 22z- 03z. Shear/flow is limited, though any decent forward momentum of multi-cell clusters would support an isolated svr wind threat mainly west of I- 69. How quickly convection moves through into the late evening and overnight will depend on the strength of the cold pool/outflow. && .LONG TERM...(Tuesday through Sunday) Issued at 317 AM EDT Mon Aug 10 2020 Held onto a slight chance PoP into Tuesday along and southeast of US 24 as composite outflow could be slower to clear these locations. Fair wx anticipated for the mid week period otherwise as high pressure builds over the Great Lakes under confluent high zonal flow. Lingering boundary over the Mid MS/OH Valleys may then lift back north into the area late this weekend into next weekend in response to an approaching mid level trough. Retained low-mid chances during these periods as a result. && .AVIATION...(For the 06Z TAFS through 06Z Monday Night) Issued at 213 AM EDT Mon Aug 10 2020 Shortwave and associated convection over southern Lake Michigan to bring potential showers/storms to KSBN over next few hours. Downstream stability to preclude mention at KFWA with anticipatory decay. Otherwise, period of MVFR ceilings possible this morning with moistened boundary layer at KSBN. Thereafter, evolution/timing of next round of convection varies greatly per CAMS output. Side with VCTS later in evening as convection most likely tied to upstream cold front/next shortwave, currently over Northern Plains/Upper Midwest. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && SYNOPSIS...Steinwedel SHORT TERM...Steinwedel LONG TERM...Steinwedel AVIATION...Murphy Visit us at www.weather.gov/iwx Follow us on Facebook...Twitter...and YouTube at: www.facebook.com/NWSNorthernIndiana www.twitter.com/nwsiwx www.youtube.com/NWSNorthernIndiana
Hazardous Weather Outlook National Weather Service Northern Indiana 352 AM EDT Mon Aug 10 2020 INZ003>009-012>018-020-022>027-032>034-LMZ043-046-MIZ077>081-OHZ001- 002-004-005-015-016-024-025-110800- La Porte-St. Joseph IN-Elkhart-Lagrange-Steuben-Noble-De Kalb-Starke- Pulaski-Marshall-Fulton IN-Kosciusko-Whitley-Allen IN-White-Cass IN- Miami-Wabash-Huntington-Wells-Adams-Grant-Blackford-Jay- New Buffalo MI to St Joseph MI-Michigan City IN to New Buffalo MI- Berrien-Cass MI-St. Joseph MI-Branch-Hillsdale-Williams-Fulton OH- Defiance-Henry-Paulding-Putnam-Van Wert-Allen OH- 352 AM EDT Mon Aug 10 2020 /252 AM CDT Mon Aug 10 2020/ This Hazardous Weather Outlook is for northern Indiana, southwest Michigan, northwest Ohio and the nearshore waters of southeastern Lake Michigan. .DAY ONE...Today and tonight. There is a chance for thunderstorms today into tonight. A few thunderstorms could approach severe strength late this afternoon into early this evening across northern Indiana and southwest Michigan, with damaging winds the primary hazard. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. There a chances for thunderstorms Friday through Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Northern Indiana radar (KIWX), 77 km away, was scanning. The volume nearest the first event began at 10:27 UTC.
8 thunderstorm wind, 1 seiche. Local standard time, as filed.
The public reported a one to 2 foot diameter tree was blown down with several limbs up to one foot in diameter broken off along Wetherbee Rd.
The initial gust front passed the Cook Buoy (45026) near Stevensville, MI around 5:55 pm when waves were reportedly one foot. By 6:20 pm, waves had climbed to four feet and a meteotsunami was reported by an off-duty NWS employee who was at Lion’s Park Beach. Water levels rose approximately one and one half foot above the mean levels by that time, and flooding was reported along Lion’s Park Drive through the evening. Wave heights at the Cook Buoy peaked at around five feet at 8:40 pm.
According to the Berrien County EMA, there was lakeshore flooding also reported in New Buffalo, MI, which lasted into the late evening hours. A seiche could be seen at various water level gauges across Lake Michigan into the next day (Tuesday August 11th, 2020), with the most extreme fluctuations extending from shortly after the storm passed until about 5 am EDT. Lesser fluctuations of up to one foot continued through around 10 am EDT.
No specific damage amounts were noted as near record high water levels and periodic high wave action continue to cause extensive erosion.
Emergency management officials reported a tree was blown down onto a power line.
The public reported a transformer was blown down on Hollywood Rd and West Lemon Creek in Baroda township.
The public reported a large tree was blown down at Ansley and Lincoln.
The public reported half a two foot diameter tree fell onto Mars Street.
Emergency management officials reported several trees were blown down in Baroda township, Grand Beach, St. Joseph and surrounding areas.
The ASOS at the Benton Harbor airport recorded a 67 mph wind gust.
The local fire department reported large trees blown down in the Three Rivers area.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Michigan in 2020Every state in 2020This day in weather historyWarnings in Michigan, August 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 918208, 919803, 918209, 918210, 918211, 918212, 918213, 918215, 918214.