Increasing moisture and instability ahead of cold front approaching from the Northern Plains aided the development of strong thunderstorms over portions of Lake Superior on the evening of the 9th.
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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 MQT wrote it up.
Increasing moisture and instability ahead of cold front approaching from the Northern Plains aided the development of strong thunderstorms over portions of Lake Superior on the evening of the 9th.
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 Marquette, MI wrote its last area forecast discussion before the first event at Aug 9, 6:35 PM EST, 5 minutes earlier.
Area Forecast Discussion National Weather Service Marquette MI 735 PM EDT Sun Aug 9 2020 .SHORT TERM...(This evening through Monday) Issued at 240 PM EDT SUN AUG 9 2020 Upper air pattern consists of a 500 mb trough across the northern Rockies and northern plains with a MCV in MN this morning. The upper trough will continue to move east into the upper Great Lakes tonight into Mon. Some deeper moisture and 850-500 mb q-vector convergence moves through tonight and moves out of the eastern cwa Mon afternoon. Tough forecast for this period as there are numerous mcv's off to the west of the area and also a lot of old outflow boundaries around the area as well. Thinking is that there will be a line that moves in late this afternoon across the far west, then this gradually moves eastward with time tonight and then exits slowly out of the cwa with the passage of the cold front across the area on Mon. Followed close to the conshort for pops for this time period as this model seemed to have the best handle on the ongoing convection off to the west and was the slowest to bring in pops into the far west late this afternoon. Could be some severe weather with this line with large hail and damaging wind gusts the primary threat. There could also be some heavy rain with the high dew points in the area as well. Confidence is low with this forecast however, especially later in the time period as it all hinges on the evolution of the convection this evening. .LONG TERM...(Monday night through Sunday) Issued at 342 PM EDT SUN AUG 9 2020 With the cold front clear through the UP and any remaining thunderstorms exiting over the far eastern CWA, Monday night begins a long period of tranquil weather over our area. By Tuesday, models show a closed upper low over Hudson Bay and a second short wave moving into the Canadian Rockies. The northern tier of the CONUS remains in low-amplitude quasi-zonal mid-level flow. A packet of mid- level dry air on Tuesday will keep skies completely clear but could lead to deep mixing and drying out of the PBL. This could drop afternoon RH to around 20-25% which, in combination with a breezy SW gradient wind gusting to 20-25 mph at times, may lead to a concern for fire weather. However most of the area having seen copious rainfall over the weekend into early Monday should limit the fire weather potential overall. Ridging builds in for Wednesday through at least Friday leading to continued warm and rain-free weather. GEFS mean 850 mb temps continue hover right around 16-17 C each of those three days, pretty much in line with what the deterministic EC and UKMET, among other guidance. Light synoptic/background flow will allow Lake Superior lakebreezes to develop on Wednesday keeping those shorelines cooler in the upper 70s, but elsewhere highs should easily reach the mid 80s. Thursday and Friday look equally as warm, with less relief along the Lake Superior shoreline as strengthening SSE flow will keep the lakebreeze mostly offshore those days. Given the run-to-run and model-to-model consistency in 850 mb temps, and given that the NBM seems to be running a bit cool, added about a couple degrees to afternoon highs each of these three days, except along the Lake Superior shoreline on Wednesday. By the weekend the pattern becomes more unsettled again. The GFS and EC both show a strong short wave digging into the Northern Plains late Friday and then lifting northeastward through northern Ontario Saturday into Sunday. As the ridge overhead begins to break down and shift east, there may be one or two ridge-roller type MCSs Friday night or Saturday, depending on the exact strength and orientation of the height gradient. Then the system's cold front moves through around Saturday or Sunday leading to additional thunderstorm chances. Given the agreement in the models, could have gone higher with POPs, but for now was content to just keep the NBM's broad chance POPs through much of the weekend until the fine scale details come into focus. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 733 PM EDT SUN AUG 9 2020 IFR and LIFR conditions possible with thunderstorms across the area tonight into Monday morning. A complex of thunderstorms will push from NW WI and the western U.P into the central portion of the U.P this evening. Expect IFR and LIFR as the storms pass through IWD and CMX. Less certainty exists with the evolution of these storms at SAW so kept things VFR for now. Another round thunderstorms is expected in the morning hours as a cold front pushes through the area from W to E bringing another period of lower CIGS/VIS. Have conditions improving to VFR between the rounds of storms but wouldn't be surprised if IFR CIGS hang on at CMX and IWD. Expect VFR conditions by mid to late morning Monday as dry air filters in behind the cold front. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 240 PM EDT SUN AUG 9 2020 The winds will shift from the E/SE to W/SW at 10 to 20 knots as a cold front moves through tonight. Thunderstorms could briefly produce much stronger winds, as well as possibly some hail overnight. Once the cold front clears the lake on Monday, winds look to remain 10-20 knots with gusts up to 25 knots, particularly in the western lake between Isle Royale and the Keweenaw Peninsula due to funneling. Winds will subside slightly Monday night before picking back up again in western Superior between Isle Royale and the Keweenaw Peninsula; look for winds to pick up to 15-20 knots with gusts up to 25 knots again due to the funneling of the winds in this area. Winds will decrease to around or less than 20 knots Tuesday night and should remain that way through the rest of the mid-week. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && SHORT TERM...07 LONG TERM...RJC AVIATION...NL MARINE...TAP
Hazardous Weather Outlook National Weather Service Marquette MI 357 PM EDT Sun Aug 9 2020 MIZ001>007-009>014-084-085-102000- Keweenaw-Ontonagon-Northern Houghton-Baraga-Marquette-Alger-Luce- Gogebic-Iron-Dickinson-Menominee-Delta-Southern Schoolcraft- Southern Houghton-Northern Schoolcraft- 357 PM EDT Sun Aug 9 2020 /257 PM CDT Sun Aug 9 2020/ This Hazardous Weather Outlook is for portions of western Upper Michigan and central Upper Michigan. .DAY ONE...Tonight Thunderstorms are likely through the overnight hours. Some of the storms could produce large hail, damaging winds, and heavy rain. .DAYS TWO THROUGH SEVEN...Monday through Saturday Thunderstorms are possible again on Monday, mainly over south- central and eastern Upper Michigan. There is a moderate swim risk for the Lake Michigan beaches of Schoolcraft County on Monday. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report any observed hail or wind damage from thunderstorms to the National Weather Service in Marquette. The public may also submit reports to the National Weather Service via phone, on our website, or through Facebook or Twitter using #906wx. LSZ162-240>251-263>267-102000- Lake Superior west of a line from Saxon Harbor WI to Grand Portage MN beyond 5NM-Saxon Harbor WI to Black River MI- Black River to Ontonagon MI- Ontonagon to Upper Entrance of Portage Canal MI- Upper Entrance of Portage Canal to Eagle River MI- Eagle River to Manitou Island MI- Manitou Island to Point Isabelle MI- Point Isabelle to Lower Entrance of Portage Canal MI- Lower Entrance of Portage Canal To Huron Islands MI Including Keweenaw and Huron Bays-Huron Islands to Marquette MI- Marquette to Munising MI-Munising to Grand Marais MI- Grand Marais to Whitefish Point MI- Lake Superior from Saxon Harbor WI to Upper Entrance to Portage Canal MI 5NM off shore to the US/Canadian border including Isle Royale National Park- Lake Superior from Upper Entrance to Portage Canal to Manitou Island MI 5NM off shore to the US/Canadian Border- Lake Superior West of Line from Manitou Island to Marquette MI Beyond 5NM from shore- Lake Superior East of a line from Manitou Island to Marquette MI and West of a line from Grand Marais MI to the US/Canadian Border Beyond 5NM from shore- Lake Superior from Grand Marais MI to Whitefish Point MI 5NM off shore to the US/Canadian border- 357 PM EDT Sun Aug 9 2020 /257 PM CDT Sun Aug 9 2020/ This Hazardous Weather Outlook is for portions of Eastern Lake Superior...Central Lake Superior and Western Lake Superior. .DAY ONE...Tonight Areas of dense fog will remain possible today and tonight. Thunderstorms are likely through the overnight hours. Some of the storms could produce large hail, damaging winds, and heavy rain. Areas of fog are expected tonight and could be locally dense. .DAYS TWO THROUGH SEVEN...Monday through Saturday Thunderstorms are possible again on Monday, mainly over far eastern Lake Superior. Areas of fog are expected on Monday and could be locally dense. .SPOTTER INFORMATION STATEMENT... The need for weather spotter reports is not anticipated at this time. LMZ221-248-250-102000- Green Bay North of line from Cedar River MI to Rock Island Passage-Seul Choix Point to Point Detour MI- 5NM East of a line from Fairport MI to Rock Island Passage- 357 PM EDT Sun Aug 9 2020 This Hazardous Weather Outlook is for portions of Northern Lake Michigan. .DAY ONE...Tonight Thunderstorms are likely tonight. Some of the storms could produce large hail, damaging winds, and heavy rain. .DAYS TWO THROUGH SEVEN...Monday through Saturday Thunderstorms are possible again on Monday. .SPOTTER INFORMATION STATEMENT... The need for weather spotter reports is not anticipated at this time. RJC
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MARQUETTE MI
210 PM EDT SUN AUG 9 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0900 AM HEAVY RAIN 1 SE MENOMINEE 45.11N 87.61W
08/09/2020 M1.00 INCH MENOMINEE MI CO-OP OBSERVER
CO-OP OBSERVER STATION MENM4 MENOMINEE.
&&
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</html>The Marquette radar (KMQT), 117 km away, was scanning. The volume nearest the first event began at 23:41 UTC.
3 marine thunderstorm wind. Local standard time, as filed.
The spotter at Freda measured a peak thunderstorm wind gust of 40 mph.
The Marquette Coast Guard station measured a peak thunderstorm wind gust of 56 mph.
The Marquette Coast Guard station measured a peak thunderstorm wind gust of 56 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Lake Superior in 2020Every state in 2020This day in weather history
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: 915482, 915483, 915484.