A cold front moving through the region generated strong to severe thunderstorms over portions of west and central Upper Michigan on the afternoon of the 20th.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
A cold front moving through the region generated strong to severe thunderstorms over portions of west and central Upper Michigan on the afternoon of the 20th.
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 May 20, 6:30 AM EST, 4 hours 30 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MARQUETTE MI 730 AM EDT SUN MAY 20 2012 .SHORT TERM...(TODAY THROUGH MONDAY) ISSUED AT 452 AM EDT SUN MAY 20 2012 THE 500MB AND ASSOCIATED SFC TROUGH SET UP TO OUR WEST WILL CONTINUE TO EDGE EASTWARD. WHILE THE ENTIRE 500MB TROUGH WILL BE INFLUENCING OUR WEATHER...IT WILL REALLY BE THE SOUTHERN TROUGH ACROSS FAR SW MN EARLY THIS MORNING THAT WILL PLAY THE BIGGEST ROLE THROUGH MONDAY. THE SLOW MOVING PATTERN WILL RESULT IN THIS SOUTHERN 500MB TROUGH TO PUSH INTO N AND CENTRAL MN BY EARLY EVENING...BEFORE SLIDING ACROSS UPPER MI/LAKE SUPERIOR MONDAY. THE SFC TROUGH SET UP FROM N QUEBEC THROUGH IWD...AND DOWN THROUGH IA AT DAYBREAK THIS MORNING WILL SLOWLY PROGRESS EASTWARD...MAKING IT ACROSS CENTRAL UPPER MI BY EARLY EVENING...AND FAR EASTERN UPPER MI SUNDAY NIGHT. AS FOR WX SPECIFICS...WE HAVE SEEN MUCH BETTER RH RECOVERY OVER THE WESTERN COUNTIES THIS MORNING /60 TO 80 PERCENT/...AFTER RECOVERIES NEAR 45 PERCENT SATURDAY MORNING OVER PORTIONS OF THE CWA. THE MQT 88-D RADAR CONTINUES TO PICK UP 20-30DBZ REFLECTIVITY OVER THE AREA. HOWEVER...MUCH OF THAT IS OVER 9KFT...AND LIKELY NOT REACHING THE SFC. THE PLACE WHERE IT MAY BE REACHING THE GROUND IS ACROSS CENTRAL AND NORTHERN LAKE SUPERIOR. THIS IS BASICALLY SAME LOCATION OF THE ORIGIN OF A TS THAT DEVELOPED OVER AFTER 05Z AND PUSHED NE OF LAKE SUPERIOR AFTER 06Z/. WITH MIXING HEIGHTS POTENTIALLY JUMPING TO NEAR 800MB AGAIN THIS AFTERNOON OVER CENTRAL UPPER MI...WE COULD TAP INTO SOME STRONGER WINDS ONCE AGAIN /ESPECIALLY WITH ANY STRONGER SHOWERS TS THAT DEVELOP/...WITH A FEW GUSTS NEARING 30-35KTS AHEAD OF THE NEARING LOW/COLD FRONT. WILL LOOK FOR THE POTENTIAL FOR A FEW STRONGER STORMS TO DEVELOP...MAINLY SOUTH OF THE WI BORDER THIS AFTERNOON. MORE SPECIFICALLY FOR IMT /BASED OFF NAM FCST SOUNDINGS/ SBCAPE VALUES TOP OUT NEAR 2.5K J/KG...WITH A FREEZING LEVEL AROUND 12.6KFT. A BOWING TS WILL NOT BE OUT OF THE QUESTION...WITH NEARLY UNIDIRECTIONAL MID LEVEL WINDS /850-500MB/ AND DRY AIR ALOFT WITH A DEWPOINT DEPRESSION NEAR 10C AT 700MB AND 8C AT 500MB. TO ADD SOME MODERATION TO THE STORM POTENTIAL...THE MORE REASONABLE GFS TOPS OUT SBCAPE VALUES NEARLY 1K J/KG LESS THAN THE NAM...AND IS NOT AS IMPRESSIVE WITH THE MID LEVEL DRY AIR EITHER. WE STILL LOOK TO GET A CWA AVERAGE OF 0.25IN OF RAIN THROUGH THIS EVENING. SPECIFIC AMOUNTS FOR ANY ONE LOCATION VARY SIGNIFICANTLY. FOR EXAMPLE...THE 21/06Z NAM IS SPITTING OUT LITTLE OVER A TRACE OF RAIN AT P53...WHILE OTHER MODELS RANGE FROM 0.5 TO 1.5IN. THE BEST BET FOR RAIN REMAINS THE WEST HALF AS THIS SYSTEM EVOLVES...WITH THE BEST FORCING SLIDING OVER N OF LAKE SUPERIOR LATE THIS AFTERNOON. EXPECT STRONGER HIGH PRESSURE...CURRENTLY LOCATED ACROSS S SASKATCHEWAN THROUGH THE W DAKOTAS AND CENTRAL PLAINS TO INVADE BEHIND THE COLD FRONT FOR SUNDAY NIGHT INTO MONDAY. THIS SHOULD HELP TO PUT AN END TO ANY LINGERING SHOWER ACTIVITY EAST. DEWPOINTS MIXING OUT INTO THE LOW TO MID 20S...WITH SFC TEMPS IN THE 60S WOULD RESULT IN RH VALUES OF 17 TO 25 PERCENT WEST OF A LINE FROM IMT TO ISHPEMING. THE STRONGEST WINDS WILL BE CENTRAL AND EAST ALONG LAKE SUPERIOR...WITH GUSTS IN THE LOW TO MID 20MPH RANGE ACROSS MOST OF THE CWA THROUGH THE DAY MONDAY. .LONG TERM...(MONDAY NIGHT THROUGH SATURDAY) ISSUED AT 452 AM EDT SUN MAY 20 2012 MON NGT...WITH DRY SFC HI PRES CROSSING THE UPR GRT LKS...EXPECT A MOCLR OVERNGT. CONSIDERING EXPECTED LGT WINDS/PWAT UNDER 0.50 INCH...TENDED TOWARD THE LO END OF GUIDANCE FOR MIN TEMPS OVER THE INTERIOR...ESPECIALLY THE WCENTRAL WHERE WINDS LOOK TO BE LIGHTEST THRU THE NGT. ADDED A MENTION OF FROST AT SOME OF THE COLDER LOCATIONS...WHERE TEMPS ARE LIKELY TO FALL NEAR 32. A RETURN SW FLOW OVER THE W LATER MAY HOLD TEMPS UP A BIT FM IWD THRU THE KEWEENAW. TUE...AS THE SFC HI PRES RDG SLIDES SLOWLY TO THE E AND TO A LINE FM THE SAULT TO NEAR DETROIT BY LATE IN THE DAY UNDER BLDG UPR RDG...A STRONGER S WIND WL DVLP OVER THE W UNDER TIGHTENING PRES GRADIENT BTWN THE RDG AND FALLING PRES IN THE PLAINS. ALTHOUGH THERE COULD BE SOME MID CLDS ASSOCIATED WITH THE RETURNING WARM AIR...GFS FCST SDNGS INDICATE THE LLVLS WL BE TOO DRY WITH ADVECTION OF LOWER H85 DEWPTS FOR ANY PCPN EVEN FM IWD-CMX. DID INCLUDE SOME LO CHCS POPS OVER NW LK SUP WHERE THE GFS/ECMWF GENERATE SOME PCPN NEAR FCST WARM FNT. TUE NGT...WITH DEEPENING TROF OVER THE NRN ROCKIES...RDG WL BUILD OVER THE GRT LKS. ALTHOUGH THE ECMWF/GFS SHOW WARM FNT SHIFTING NWD INTO ONTARIO/NW LK SUP...THESE MODELS GENERATE SOME LGT PCPN OVER PORTIONS OF MAINLY THE NW CWA. CONSIDERING FOCUS FOR H85 MSTR RETURN REMAINING TO THE W AND POSITION OF WARM FNT TO THE NW AS INDICATED BY TIGHTER PRES GRADIENT SHOWN ON THE GFS 300K ISENTROPIC SFC...OPTED TO KEEP THE LAND AREAS DRY AND MAINTAIN LO CHC POPS OVER W AND NCNTRL LK SUP. EXTENDED...THE 00Z GFS IS THE MOST PROGRESSIVE WITH THE MOVEMENT OF A LO PRES TROF ATTENDANT TO A SHRTWV/SFC LO MOVING OUT OF THE ROCKIES TROF INTO NW ONTARIO AT MID WEEK AND THE ACCOMPANYING PCPN SHIELD. CONSIDERING THE MEAN RIDGE OVER THE ERN CONUS...SUSPECT THE SLOWER 00Z ECMWF/CNDN MODELS ARE ON THE RIGHT TRACK SHOWING THE PASSAGE OF THIS DISTURBANCE THU/THU NGT. BUT FOLLOWED THE MODEL CONSENSUS GIVEN FCST UNCERTAINTY. EXPECT ABV NORMAL TEMPS AT MID WEEK IN THE SLY FLOW AHEAD OF THIS COLD FNT TO GRDLY FALL CLOSER TO NORMAL FOLLOWING THE FROPA AND IN THE NE FLOW TO THE S OF HI PRES MOVING ACROSS ONTARIO. DEPENDING ON HOW FAR S THE FNT MOVES WITH PERSISTENT MEAN RDG OVER THE SE CONUS...MORE SHRA ARE PSBL THRU SAT WHEN THIS BNDRY RETURNS N AS A WARM FNT. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING) ISSUED AT 729 AM EDT SUN MAY 20 2012 A COLD FNT WL CROSS UPR MI W-E TODAY...WITH MOST OF THE ADVERSE WX OCCURRING FOLLOWING THE FROPA AT THE 3 TAF SITES AS A STRONG UPR DISTURBANCE MOVES NEWD INTO THE UPR GRT LKS THRU TNGT. THE FNT IS OVER IWD RIGHT NOW...AND INCLUDED A MENTION OF TS EARLY WITH THE APRCH OF SOME SCT TS NOW MOVING NEWD THRU NW WI. OBS BEHIND THE FNT INDICATE CIGS DROP TO IFR...SO FOLLOWED A SIMILAR TREND IN THE TAFS. BEST CHC FOR HEAVIER SHRA/TS WL BE AT SAW LATER TODAY AS DEEPER MSTR MAY ARRIVE AT TIME OF PEAK HEATING DURING AFTN FROPA AT THAT SITE. THE ARRIVAL OF DRIER AIR IN THE LLVLS BEHIND THE FNT WL BRING A RETURN OF VFR CONDITIONS TNGT. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 452 AM EDT SUN MAY 20 2012 ALTHOUGH THERE ARE SOME STRONGER S WINDS AT THE HIER PLATFORMS OVER THE E HALF OF LK SUP LIKE STANNARD ROCK EARLY THIS MRNG UNDER A SHARPER PRES GRADIENT BETWEEN A COLD FRONT OVER FAR WESTERN LK SUP AND HI PRES TO THE E...VERY STABLE MARINE LAYER SHOULD LIMIT 10M WIND SPEEDS TO NO MORE THAN 15 TO 25 KTS. EXPECT A WIND SHIFT TO THE NW/SOME FOG IN THE WAKE OF THE COLD FRONTAL PASSAGE TONIGHT...BUT THE NW WIND SHOULD NOT EXCEED 20-25 KTS. THEN HI PRES WILL BRING LIGHT WINDS INTO WED BEFORE A STRONGER S WIND UP TO 25 KTS DEVELOPS ON WED INTO THU UNDER THE SHARPER PRES GRADIENT BETWEEN THE HI DEPARTING TO THE E AND A LO PRES TROF MOVING E FROM THE PLAINS. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && SHORT TERM...KF LONG TERM...KC AVIATION...KC MARINE...KC
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MARQUETTE MI 411 AM EDT SUN MAY 20 2012 MIZ001>007-009>014-084-085-211200- KEWEENAW-ONTONAGON-NORTHERN HOUGHTON-BARAGA-MARQUETTE-ALGER-LUCE- GOGEBIC-IRON-DICKINSON-MENOMINEE-DELTA-SOUTHERN SCHOOLCRAFT- SOUTHERN HOUGHTON-NORTHERN SCHOOLCRAFT- 411 AM EDT SUN MAY 20 2012 /311 AM CDT SUN MAY 20 2012/ THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WESTERN UPPER MICHIGAN AND CENTRAL UPPER MICHIGAN. .DAY ONE...TODAY AND TONIGHT SCATTERED THUNDERSTORMS ARE POSSIBLE OVER THE WEST HALF OF UPPER MICHIGAN THIS MORNING...AND ACROSS THE ENTIRE AREA THIS AFTERNOON. THUNDERSTORMS WILL END WEST TO EAST TONIGHT. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY AREAS OF FROST WILL BE POSSIBLE ACROSS THE INTERIOR WESTERN HALF OF UPPER MICHIGAN MONDAY NIGHT. THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY AFTERNOON OVER WESTERN UPPER MICHIGAN...AND ACROSS THE ENTIRE AREA WEDNESDAY NIGHT THROUGH SATURDAY. .SPOTTER INFORMATION STATEMENT... THE NEED FOR WEATHER SPOTTER REPORTS IS NOT ANTICIPATED AT THIS TIME. LSZ162-240>251-263>267-211200- 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- 411 AM EDT SUN MAY 20 2012 /311 AM CDT SUN MAY 20 2012/ THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN LAKE SUPERIOR...CENTRAL LAKE SUPERIOR AND WESTERN LAKE SUPERIOR. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS ARE POSSIBLE ACROSS MAINLY WESTERN LAKE SUPERIOR THIS MORNING...AND THEN OVER EASTERN LAKE SUPERIOR THIS AFTERNOON THROUGH TONIGHT. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY AFTERNOON THROUGH SATURDAY ACROSS ALL OF LAKE SUPERIOR. .SPOTTER INFORMATION STATEMENT... THE NEED FOR WEATHER SPOTTER REPORTS IS NOT ANTICIPATED AT THIS TIME. LMZ221-248-250-211200- 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- 411 AM EDT SUN MAY 20 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHERN LAKE MICHIGAN. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON THROUGH THIS EVENING. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY NIGHT THROUGH FRIDAY NIGHT. .SPOTTER INFORMATION STATEMENT... THE NEED FOR WEATHER SPOTTER REPORTS IS NOT ANTICIPATED AT THIS TIME. KF
The Marquette radar (KMQT), 124 km away, was scanning. The volume nearest the first event began at 15:57 UTC.
12 hail, 4 thunderstorm wind, 2 lightning, 1 heavy rain, 1 strong wind. Local standard time, as filed.
The observer ten miles east of Ontonagon measured 1.75 inches of total rainfall. A small creek on the residence was reported over its banks. The observer at Rockland measured 2.80 inches of storm total rainfall.
Hail lasted five minutes.
Gusts up to 40 mph were reported with the storm.
Winds estimated at 60 mph knocked over a 24-inch diameter white pine tree six miles south of Witch Lake.
Strong south winds ahead of a cold front caused downed power lines and knocked out power to more than 1200 customers in Munising.
Trees were knocked down across Highway M-95 along the Marquette/Dickinson County line.
Very strong winds knocked down small tree limbs and blew patio furniture across the yard.
Several trees were knocked down along County Road 581.
Lightning and high wind from thunderstorms caused more than 200 customers to lose power in Ishpeming.
A lightning strike from thunderstorms caused a house fire in Iron Mountain on the evening of the 20th. The home sustained damage in numerous areas, but firefighters were able to keep the damage contained to the second floor and attic. The Iron Mountain Police Department, Beacon Ambulance and Wisconsin Electric were also at the scene of the fire to assist.
Hail was reported near the Sawyer Airport.
Hail was reported near Shot Point along Highway M-28.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Michigan in 2012Every state in 2012This day in weather historyWarnings in Michigan, May 2012
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: 376544, 376517, 376518, 376519, 376520, 379138, 376521, 376523, 376524, 376529, 379196, 376531, 376535, 379153, 379185, 376538, 376539, 379184, 376541, 376543.