An upper level trough of low pressure rotated through Wisconsin resulting in numerous showers and thunderstorms. Cold air aloft associated with the trough, coupled with the warm waters of Lake Michigan, provided favorable conditions for the development of waterspouts.
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The episode as NWS GRB wrote it up.
An upper level trough of low pressure rotated through Wisconsin resulting in numerous showers and thunderstorms. Cold air aloft associated with the trough, coupled with the warm waters of Lake Michigan, provided favorable conditions for the development of waterspouts.
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 Green Bay, WI wrote its last area forecast discussion before the first event at Aug 9, 11:12 AM CST, 58 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREEN BAY WI 1212 PM CDT THU AUG 9 2012 UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE .SHORT TERM...TONIGHT AND THURSDAY. UPPER TROF/LOW TO DROP THROUGH WI TODAY. CONCERNS ARE ON PCPN TRENDS/COVERAGE WITH SYSTEM. LIGHT SHOWERS CONTINUE OVER SOUTHERN THIRD OF CWA...LEFT OVER FROM SECOND SHORT WAVE NOW PASSING OFF TO THE EAST/INVERTED TROF AT THE SURFACE MOVING INTO WESTERN WI. LATEST RADAR IMAGERY SHOWING THIS AREA TO BE EXPANDING ONCE AGAIN AS DYNAMICS WITH UPPER LOW COME INTO PLAY. SECOND AREA OF SHOWERS/ISOLD THUNDER NOW OVER WESTERN LAKE SUPERIOR. DID NOT MAKE MANY CHANGES TO PREVIOUS PACKAGE...INITIALLY JUST EXPANDING CATEGORICAL POPS TO THE WEST EARLY THIS MORNING. SOME CONCERN ON TEMPS NORTH CENTRAL MAY BE A BIT TOO COOL THIS AFTERNOON IF CLEARING WORKS IN EARLIER THAN CURRENTLY DEPICTED. DRIER AIR/SFC HIGH BUILDING IN THIS EVENING TO BRING AN END TO MUCH OF PCPN...EXCEPTION ALONG LAKESHORE WHERE NORTHEAST FLOW EXPECTED TO LEAD TO SOME LAKE EFFECT/INSTABILITY SHOWERS. AFTER 06Z SURFACE WINDS SHIFT MORE NORTHERLY ALONG THE LAKESHORE...WITH MAIN SHOWER BAND EXPECTED TO PUSH JUST OFFSHORE. PULLED BACK ON FOG WORDING WITH GRADIENT EXPECTED TO REMAIN UP MOST OF NIGHT. RATHER PLEASANT DAY FRI WITH HIGH PRESSURE AT THE SURFACE. TEMPERATURES EXPECTED TO BE BELOW NORMAL. .LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY. UPPER LOW WILL CONTINUE TO SLOWLY MOVE AWAY FROM THE AREA FRIDAY NIGHT. THE MODELS ARE HINTING WINDS AT 850MB/925MB MAY BACK TO THE NORTHEAST FRIDAY EVENING AS WEAK TROUGH ROTATES AROUND THE UPPER LOW. THE WRF/CANADIAN WAS THE MOST PRONOUNCED WITH WINDS BACKING TO THE NORTHEAST COMPARED TO THE GFS. COOL AIR AT 850MB FLOWING OVER THE RELATIVELY WARM WATERS OF THE BAY AND LAKE COULD PRODUCE CLOUDS AND POTENTIAL FOR SOME LAKE/BAY EFFECT SHOWERS. FOR NOW...HAVE INCREASED CLOUD COVER TO ACCOUNT FOR THE BACKING WINDS OFF THE BAY AND LAKE. LATER SHIFTS MAY NEED TO ADD A SMALL CHANCE OF SHOWERS IF THIS SCENARIO PLAYS OUT. ON SATURDAY...MAY BE A LITTLE OPTIMISTIC WITH SKY COVER. WITH COOL AIR ALOFT FLOWING OVER THE RELATIVELY WARMER WATERS OF LAKE SUPERIOR... EXPECT SKIES BECOME PARTLY CLOUDY FOR AWHILE DURING THE MORNING BEFORE DRIER AIR MIXES OUT THE CLOUDS SATURDAY AFTERNOON. WOULD NOT BE SURPRISED IF A FEW SPOTS WENT MOSTLY CLOUDY FOR A BRIEF PERIOD SATURDAY MORNING. THE 00Z WRF/GFS BUFKIT DID SHOW THIS SCENARIO. HIGH PRESSURE WILL DOMINATE THE WEATHER PATTERN SATURDAY NIGHT. MODELS CONTINUE TO SHOW WEAK FEATURE MOVING ACROSS THE SOUTHWEST LATE SUNDAY AFTERNOON. WENT WITH A SLIGHT CHANCE OF SHOWERS SUNDAY AFTERNOON ACROSS THE FAR SOUTHWEST. THE 00Z GFS/CANADIAN NOW SHOW TWO SEPARATE FEATURES THAT WILL BRING A CHANCE OF SHOWERS AND STORMS TO THE AREA SUNDAY NIGHT AND MONDAY. 00Z GFS/CANADIAN NOW SHOW COMPLEX OF SHOWERS AND STORMS DEVELOPING ACROSS THE SOUTHERN HALF OF THE STATE SUNDAY NIGHT AND THEN MOVE EAST OF THE AREA MONDAY MORNING. A SECONDARY TROUGH DROPPING SOUTHEAST INTO NORTHERN WISCONSIN MONDAY AFTERNOON WILL BRING A CHANCE OF SHOWERS AND STORMS TO THE NORTH...THEN ACROSS THE ENTIRE AREA MONDAY NIGHT. NORTHWEST FLOW WILL DOMINATE THE WEATHER PATTERN FOR THE REMAINDER OF THE FORECAST PERIOD. BEST CHANCE FOR SHOWERS AND STORMS AFTER MONDAY NIGHT WOULD OCCUR ON WEDNESDAY WITH RETURN FLOW. AS USUAL WITH NORTHWEST FLOW PATTERNS...TIMING MAY VARY OVER THE NEXT SEVERAL MODEL RUNS. CONFIDENCE IS SOMEWHAT LOWER THAN AVERAGE BY THE MIDDLE OF NEXT WEEK ON THE TIMING OF THESE FEATURES. && .AVIATION...A COOL UPPER TROUGH WILL CONTINUE TO DROP SOUTH THROUGH WISCONSIN THIS AFTERNOON. SHOWERS AT TAF SITES ENDING FROM NORTHWEST TO SOUTHEAST THIS EVENING AND OVERNIGHT. WIDESPREAD MVFR CIGS/VSBYS IN SHOWERS EXPECTED...LOCAL IFR WITH SCT TO BKN LOW CLOUDS AROUND 800 FT EARLY THIS AFTERNOON...EXPECTED TO IMPROVE BY THIS EVENING. COOL AIR MASS AND NORTHEAST WIND FLOW TO CREATE BREEZY CONDITIONS NEAR THE LAKE ALONG WITH SCATTERED SHOWER ACTIVITY THROUGH THE NIGHTTIME HOURS. CLOUDS WILL CLEAR OUT FROM NORTHWEST TO SOUTHEAST WITH WIDESPREAD VFR CONDITIONS EXPECTED THROUGHOUT BY 06Z FRIDAY. VFR CONDITIONS WILL PREVAIL FOR FRIDAY HOWEVER GUSTY NORTH WINDS ARE EXPECTED BY FRIDAY LATE MORNING. WOLF && .MARINE...COOL AIR MASS MOVING OVER LAKE ASSOCIATED WITH UPPER LOW TO LEAD TO BREEZY/WINDY CONDITIONS OVER THE WATER TONIGHT AND FRI. INSTABILITY SHOWERS ALSO EXPECTED. STUDIES INDICATE CONDITIONS GOOD FOR WATERSPOUT FORMATION TONIGHT...INTO FRI MORNING. ALREADY IN FORECAST...SO NO CHANGES NEEDED. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GREEN BAY WI 1034 AM CDT THU AUG 9 2012 WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-101545- VILAS-ONEIDA-FOREST-FLORENCE-NORTHERN MARINETTE-LINCOLN-LANGLADE- MENOMINEE-NORTHERN OCONTO-DOOR-MARATHON-SHAWANO-WOOD-PORTAGE- WAUPACA-OUTAGAMIE-BROWN-KEWAUNEE-WAUSHARA-WINNEBAGO-CALUMET- MANITOWOC-SOUTHERN MARINETTE-SOUTHERN OCONTO- 1034 AM CDT THU AUG 9 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND NORTHEAST WISCONSIN. .DAY ONE...THIS AFTERNOON AND TONIGHT ISOLATED THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON OVER CENTRAL AND NORTHEAST WISCONSIN...THOUGH SEVERE WEATHER IS NOT EXPECTED. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY OR TONIGHT. LMZ521-522-541>543-101545- THE BAY OF GREEN BAY SOUTH OF A LINE FROM CEDAR RIVER MI TO ROCK ISLAND PASSAGE-LAKE MICHIGAN FROM WASHINGTON ISLAND TO SHEBOYGAN- 1034 AM CDT THU AUG 9 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHWEST LAKE MICHIGAN AND THE WATERS OF GREEN BAY. .DAY ONE...THIS AFTERNOON AND TONIGHT ISOLATED THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON...THOUGH SEVERE WEATHER IS NOT EXPECTED. CONDITIONS ARE EXPECTED TO BECOME FAVORABLE FOR SOME OF THE SHOWERS AND THUNDERSTORMS TO PRODUCE WATERSPOUTS LATE THIS AFTERNOON THROUGH FRIDAY MORNING. NORTHEAST WINDS ARE ALSO EXPECTED TO INCREASE TONIGHT PRODUCING HAZARDOUS CONDITIONS FOR SMALL CRAFT. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY CONTINUED STRONG AND GUSTY NORTHEAST WINDS WILL CREATE HAZARDOUS BOATING CONDITIONS. THOSE WITH MARINE INTERESTS SHOULD MONITOR LATER FORECASTS. IN ADDITION...HIGH WAVES WILL CREATE HAZARDOUS CONDITIONS FOR BEACH GOERS ALONG THE LAKE MICHIGAN SHORE...WITH STRONG CURRENTS POSSIBLE ALONG PIERS AND BREAK WATERS.
The Green Bay radar (KGRB), 51 km away, was scanning. The volume nearest the first event began at 18:12 UTC.
2 waterspout. Local standard time, as filed.
A trained spotter reported a waterspout over Lake Michigan, south of Kewaunee.
A trained spotter reported another waterspout over Lake Michigan, south of Kewanuee.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Lake Michigan in 2012Every state in 2012This 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: 399390, 399392.