An upper disturbance moving through a moist and unstable air mass produced isolated severe storms with large hail over portions of Menominee and Keweenaw counties on the evening of the 7th.
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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.
An upper disturbance moving through a moist and unstable air mass produced isolated severe storms with large hail over portions of Menominee and Keweenaw counties on the evening of the 7th.
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 7, 2:29 PM EST, 1 hour 56 minutes earlier.
Area Forecast Discussion National Weather Service Marquette MI 329 PM EDT Mon Aug 7 2017 .SHORT TERM...(This evening through Tuesday) Issued at 322 PM EDT MON AUG 7 2017 Tonight: Fairly quiet weather pattern expected tonight across the U.P. Diurnal cu this evening will quickly dissipate with loss of daytime heating. Lake breeze boundaries along with close proximity to a weak shortwave exiting the area late this afternoon, may allow some isolated showers and thunderstorms to develop over south central portions of the U.P., quickly diminishing this evening. There is a weak trough that will slide across northern portions of the area late this afternoon into this evening; however, forcing will be weak and moisture is very limited, so the main impact will be a few extra clouds and maybe a some isolated showers and thunderstorms over the Keweenaw Peninsula and near Isle Royale into this evening. Otherwise, the rest of the area will see mostly clear skies with light winds. This will lead to temperatures dropping into the mid 40s over the inland west portions of the U.P. and upper 40s to low 50s elsewhere. Tuesday: Quiet conditions are expected through much of the day ahead of the next approaching weak cold front. The cold front, draped from west to east across Ontario, will sag slowly southward into the far northern portions of the U.P. by 21Z/08. The main impact will be increasing clouds in the afternoon hours, with only scattered rain showers expected over the north half of the Keweenaw Peninsula by late afternoon. In addition, there may be a few showers that develop along Lake Michigan lake breeze boundaries; however, moisture is fairly limited, so coverage should be marginal. High temperatures are expected to be near normal with highs in the low 80s across most of the Upper Peninsula. .LONG TERM...(Tuesday night through Monday) Issued at 323 PM EDT MON AUG 7 2017 No significant high impact weather expected in the long term. Rain chances ramp up as the week goes on with greatest chances centered on Thu as low pressure system tracks over the the Upper Great Lakes. Next weekend continues to trend drier than it looked last couple days. Temps and winds: Upper level troughing persists across the Great Lakes through next weekend. Temps should mostly be at or slightly below normal through the period. Warmest day would be Wed with highs mainly in the 70s. Stronger shortwave troughing and potential for sfc low tracking just south of Upper Michigan would result in cooler temps in the 60s to lower 70s prevailing Thu and especially on Fri as stronger winds north develop as the low begins to depart to the east. Once the low moves far enough to the east, high temps will gradually warm toward normal late in the weekend into early next week. Min temps may drop into the 40s interior late this week into next weekend as high pressure settles overhead. Otherwise, min temps should stay in the 50s. Despite up and down temperature swings through the period, pressure gradients remain pretty weak so no strong winds are expected. Possible exception would be late Thu into Fri as the low pressure system moves through but with MSLP only around 1010-1012mb and weak cold air advection, should not see the type of winds that affected Upper Michigan late last week. Winds could be strong enough to result in small craft conditions on both Lk Superior and Lk Michigan. Rain and thunderstorms: As it looked like yesterday, there will be frequent chances for rain most of the week, but due to only marginal instability and overall weaker effective shear, chances of severe storms are on the lower side. Outside chance of a lake breeze aided shower or thunderstorm late Tue aftn then there could be some elevated weak convection Tue night as sfc trough drops through the area. With the trough in the vcnty on Wed and additional convergence added by lake breezes, could see some thunderstorms form Wed afternoon into Wed evening, especially scntrl and east where there is less cooling/stabilizing influence from notherly winds shifting off Lk Superior. MLcapes up to 1000j/kg could lead to isolated stronger storms during peak heating on Wed, but with the weaker shear should not see any severe storms. Greatest chances for showers and thunderstorms will be on Thu/Thu night as the sfc low crosses just south of Upper Michigan, placing the area in the more dynamic cyclonic flow side of the low. Chances of thunderstorms on Thu with MLcapes up to 1000j/kg over eastern sections. Like Wed though the shear of 25 kts or less is probably going to be too low to support severe storms. Rain chances probably remain high into Fri too as even though sfc low will be heading out of the area, the upper level trough/cool temps aloft should promote some convection developing through the day with any daytime heating. Small chances for rain still there for the weekend and into early next week. Stabilizing north flow off of Lk Superior due to the approaching high pressure and eventually overall drying with the high should keep any chances very low. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 132 PM EDT MON AUG 7 2017 VFR conditions expected through the TAF period at each site. There is a small chance of a stray shower near CMX this afternoon as a weak trough passes through; however, very dry air is in place, so any chance is very marginal and have opted to not include in the TAF. The next chance of showers and thunderstorms for any of the TAF sites would be Tuesday afternoon, toward the end or after the end of this TAF period. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 322 PM EDT MON AUG 7 2017 Under a continued fairly weak pressure gradient, winds are expected to remain below 20 knots through the entire forecast period. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && SHORT TERM...KEC LONG TERM...JLA AVIATION...KEC MARINE...KEC
Hazardous Weather Outlook National Weather Service Marquette MI 419 PM EDT Mon Aug 7 2017 MIZ001>007-009>014-084-085-081200- Keweenaw-Ontonagon-Northern Houghton-Baraga-Marquette-Alger-Luce- Gogebic-Iron-Dickinson-Menominee-Delta-Southern Schoolcraft- Southern Houghton-Northern Schoolcraft- 419 PM EDT Mon Aug 7 2017 /319 PM CDT Mon Aug 7 2017/ This Hazardous Weather Outlook is for portions of western Upper Michigan and central Upper Michigan. .DAY ONE...Tonight Thunderstorms are possible early this evening over the Keweenaw and south central. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Thunderstorms are possible Wednesday through Friday, mainly during the afternoon and evening hours. .SPOTTER INFORMATION STATEMENT... The need for weather spotter reports is not anticipated at this time. LSZ162-240>251-263>267-081200- 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- 419 PM EDT Mon Aug 7 2017 /319 PM CDT Mon Aug 7 2017/ This Hazardous Weather Outlook is for portions of Eastern Lake Superior...Central Lake Superior and Western Lake Superior. .DAY ONE...Tonight Thunderstorms are possible early this evening over western and central Lake Superior, mainly from Isle Royale to the Keweenaw Peninsula. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday There is a slight chance of thunderstorms Tuesday afternoon into Tuesday evening and Wednesday afternoon into Wednesday evening, mainly over western Lake Superior. More thunderstorms are possible Thursday afternoon through Friday. .SPOTTER INFORMATION STATEMENT... The need for weather spotter reports is not anticipated at this time. LMZ221-248-250-081200- 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- 419 PM EDT Mon Aug 7 2017 This Hazardous Weather Outlook is for portions of Northern Lake Michigan. .DAY ONE...Tonight Thunderstorms are possible early this evening. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Thunderstorms are possible Wednesday afternoon into Wednesday evening, then again Thursday night and Friday. .SPOTTER INFORMATION STATEMENT... The need for weather spotter reports is not anticipated at this time. JLA
Special Weather Statement
National Weather Service Marquette MI
444 PM EDT MON AUG 7 2017
MIZ001-072145-
Keweenaw MI-
444 PM EDT MON AUG 7 2017
...SPECIAL WEATHER STATEMENT FOR ISLE ROYALE...
At 443 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from 41 miles northeast of Thunder Bay Ontario to
Mott Island Park Headquarters on Isle Royale. Movement was south at
15 mph.
Half inch hail and winds in excess of 30 mph will be possible with
these storms.
Locations impacted include...
On Isle Royale, Mott Island Park Headquarters, Siskiwit Lake and
Rock Harbor.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Persons in
campgrounds should consider seeking sturdy shelter until these
storms pass.
&&
LAT...LON 4819 8835 4811 8835 4789 8869 4787 8874
4788 8881 4815 8880 4819 8870
TIME...MOT...LOC 2043Z 340DEG 12KT 4879 8856 4811 8854
RolfsonThe Marquette radar (KMQT), 193 km away, was scanning. The volume nearest the first event began at 21:23 UTC.
3 hail. Local standard time, as filed.
A delayed report from the park ranger at Isle Royale National Park reported gusty winds and hail the size of quarters.
A report via social media of nickel sized hail near Gourley.
There was a delayed report of significant amounts of dime to nickel sized hail with a few stones up to quarter size. Hail drifts of six inches were observed with some hail on the ground the next morning.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Michigan in 2017Every state in 2017This day in weather historyWarnings in Michigan, August 2017
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: 713921, 713923, 713926.