Thunderstorms developed in the afternoon under an upper level low pressure system that moved across northern Wisconsin. Some of the storms produced wind gusts over 35 mph and pea size hail.
Every event with a place to put it. 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 GRB wrote it up.
Thunderstorms developed in the afternoon under an upper level low pressure system that moved across northern Wisconsin. Some of the storms produced wind gusts over 35 mph and pea size hail. A storm in southern Portage County downed several trees and a flag pole in Almond.
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 20, 2:02 PM CST, 39 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREEN BAY WI 302 PM CDT THU AUG 20 2009 .SYNOPSIS...LARGE SCALE PATTERN ACRS THE CONUS WL BE SLOWLY PROGRESSIVE FOR AT LEAST THE FIRST PART OF THE FCST PERIOD. PATTERN WAS HIGHLY AMPLIFIED...BUT WL LOSE AMPLITUDE AS DEEP UPR TROF SLOWLY PULLS OFF TO THE EAST. BY THE MIDDLE OF NEXT WK...MAIN BAND OF WESTERLIES EXPECTED TO RECEDE NWD INTO CANADA WHILE UPR RIDGE RE-ESTABLISHES ITSELF FM THE PLAINS TO THE PRAIRIE PROVINCES OF CANADA. THAT WL LEAVE WNWLY UPR FLOW ACRS THE AREA FCST AREA. EXPECT BLO NORMAL TEMPS AND SCT PCPN AS UPR TROF WORKS ACRS THE RGN EARLY IN THE PERIOD. THEN A PERIOD OF DRY WX WITH MODERATING TEMPS EXPECTED FOR THE WEEKEND AND INTO EARLY NEXT WK. TEMPS SHOULD REACH ABV NORMAL LEVELS BY NEXT WK. && .SHORT TERM...TNGT/FRI. ENOUGH SUNSHINE ACRS C/E-C WI TO ALLOW SFC-BASED INSTABILITY TO DEVELOP THIS AFTN. SCT TSRA HAVE DEVELOPED...AND STEEP LOW-LEVEL LAPSE RATES WL BE FAVORABLE FOR GUSTY WINDS. DON/T EXPECT WIDESPREAD SVR WX...BUT MAY NEED TO ISSUE A COUPLE WARNINGS ON THE STRONGEST STORMS. REMNANTS OF COMMA HEAD WL PIVOT BACK INTO THE N LATER THIS EVENING...SO WILL GO WITH CATEGORICAL POPS THERE. WL TAPER BACK TO SCT OVER THE SE PART OF THE AREA. USED BLEND OF GUID MIN TEMPS. EXPECT PLENTY OF CLDS AGAIN TOMORROW. LOWER DWPTS WL LIMIT INSTABILITY...SO LEFT THUNDER OUT OF THE FCST FOR NOW. CONSENSUS OF GUID WAS TO LOWER MAX TEMPS FOR TOMORROW. BUT LOOKING AT CURRENT TEMPS IN THE MID 60S TO ARND 70 IN NW MN AND THE DAKOTAS...DIDN/T WANT TO OVER DO IT. MOVED TOWARD CONSENSUS OF THE GUID...BUT STILL HEDGED A LITTLE TOWARD PREV FCST. .LONG TERM...FRIDAY NIGHT THROUGH THURSDAY. UPPER LOW CONTINUES TO PULL AWAY FROM THE AREA FRIDAY NIGHT. THE SHOWERS WILL END FRIDAY EVENING...THEN CLOUDS WILL BE ON THE DECREASE FROM WEST TO EAST. HIGH PRESSURE WILL BUILD INTO THE REGION FOR SATURDAY. LATEST MODEL RUNS INDICATED MORE LOW LEVEL MOISTURE AROUND 850MB. WILL ADD MORE CLOUDS FOR THE MORNING AND EARLY AFTERNOON HOURS. CLOUDS SHOULD RAPIDLY DIMINISH LATE SATURDAY AFTERNOON. DUE TO MORE CLOUD COVER...WILL LOWER MAXIMUM TEMPERATURES A FEW DEGREES ON SATURDAY. HIGH PRESSURE WILL DOMINATE THE REGION SATURDAY NIGHT...BRINGING CLEAR AND COOL CONDITIONS TO THE REGION. HIGH PRESSURE WILL REMAIN IN CONTROL OF THE WEATHER SUNDAY AND INTO MONDAY. NEXT SYSTEM WILL AFFECT THE REGION LATER MONDAY NIGHT ACROSS THE NORTH AND OVER THE ENTIRE REGION ON TUESDAY. CONFIDENCE IS A LITTLE HIGH AND HAVE INCREASED RAIN CHANCES ON TUESDAY. MAXIMUM TEMPERATURES ON TUESDAY COULD BE WARMER THAN ADVERTISED IF PRECIPITATION HOLDS OFF AND THERE IS LESS CLOUDS. COLD FRONT IS EXPECTED TO BE ACROSS THE AREA ON TUESDAY...MAKING HIGH TEMPERATURES DIFFICULT AND DEPENDENT ON THE ABOVE MENTIONED PARAMETERS. THE COLD FRONT GRADUALLY SHIFTS SOUTHWARD TUESDAY NIGHT. WILL CONTINUE THE SMALL CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHEAST PORTION OF THE FORECAST AREA. MODELS DIVERGE ON THE SOLUTION AS THE GFS IS QUICKER WITH THE FRONT. PLENTY OF TIME TO MAKE NECESSARY ADJUSTMENTS AS NEEDED DEPENDING ON MODEL TRENDS. WEST COAST RIDGE BUILDS AGAIN LATER NEXT WEEK. SURFACE HIGH WILL DOMINATE THE REGION NEXT THURSDAY. && .AVIATION...EXPECT IFR CONDITIONS TO SPREAD SEWD ACRS THE AREA DURING THE NGT AS UPR SYSTEM STARTS TO EDGE EWD. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && SKOWRONSKI/ECKBERG
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GREEN BAY WI 242 PM CDT THU AUG 20 2009 WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-211100- 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- 242 PM CDT THU AUG 20 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL AND NORTHEAST WISCONSIN. .DAY ONE...THIS AFTERNOON AND TONIGHT SCATTERED THUNDERSTORMS ARE EXPECTED DURING THE MIDDLE TO LATE AFTERNOON...ESPECIALLY OVER CENTRAL AND EAST-CENTRAL WISCONSIN. THE STRONGEST STORMS COULD APPROACH SEVERE CRITERIA...AND PRODUCE BRIEF TORRENTIAL RAINS...AND WIND GUSTS AROUND 50 MPH. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY THUNDERSTORMS ARE POSSIBLE AGAIN NEXT TUESDAY AND WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED TO BE NECESSARY THIS AFTERNOON OR TONIGHT. LMZ521-522-541>543-211100- THE BAY OF GREEN BAY SOUTH OF A LINE FROM CEDAR RIVER MI TO ROCK ISLAND PASSAGE-LAKE MICHIGAN FROM WASHINGTON ISLAND TO SHEBOYGAN- 242 PM CDT THU AUG 20 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHWEST LAKE MICHIGAN AND THE WATERS OF GREEN BAY. .DAY ONE...THIS AFTERNOON AND TONIGHT SCATTERED THUNDERSTORMS ARE EXPECTED DURING THE MIDDLE TO LATE AFTERNOON...ESPECIALLY SOUTH OF STURGEON BAY. THE STRONGEST STORMS COULD APPROACH SEVERE CRITERIA...AND PRODUCE BRIEF TORRENTIAL RAINS...AND WIND GUSTS TO AROUND 45 KNOTS. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY THUNDERSTORMS ARE POSSIBLE AGAIN NEXT TUESDAY AND WEDNESDAY. JS
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE GREEN BAY WI 159 PM CDT THU AUG 20 2009 WIZ045-201945- WAUSHARA- 159 PM CDT THU AUG 20 2009 ...STRONG THUNDERSTORMS EXPECTED IN EASTERN WAUSHARA COUNTY... AT 157 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR REDGRANITE...OR 7 MILES SOUTHEAST OF WAUTOMA...MOVING NORTHEAST AT 25 MPH. TORRENTIAL RAINS...WIND GUSTS TO 45 MPH...AND SMALL ARE HAIL ARE POSSIBLE WITH THIS STORM. THIS STORM WILL BE NEAR... AURORAVILLE BY 200 PM POY SIPPI BY 205 PM BORTH BY 210 PM THE TOWNS OF SPRING LAKE...LOHRVILLE...AURORAVILLE...PINE RIVER...POY SIPPI...BORTH AND TUSTIN ARE ALSO IN THE PATH OF THIS STORM. ECKBERG
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE GREEN BAY WI 218 PM CDT THU AUG 20 2009 WIZ048-202000- WINNEBAGO- 218 PM CDT THU AUG 20 2009 ...STRONG THUNDERSTORMS EXPECTED IN NORTHWESTERN WINNEBAGO COUNTY... AT 215 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR LAKE POYGAN...OR 9 MILES NORTH OF BERLIN... MOVING NORTHEAST AT 35 MPH. BRIEF HEAVY RAIN...GUSTY WINDS TO 50 MPH AND SMALL HAIL ARE POSSIBLE WITH THIS STORM. THE STORM WILL BE NEAR WINNECONNE BY 225 PM...WINCHESTER AND LARSEN BY 235 PM.. THIS STORM WILL AFFECT MAINLY RURAL AREAS OF NORTHWESTERN WINNEBAGO COUNTY...INCLUDING THE TOWNS OF LAKE POYGAN...ZITTAU AND ALLENVILLE. ECKBERG
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE GREEN BAY WI 228 PM CDT THU AUG 20 2009 WIZ031-037>039-074-202015- BROWN-OUTAGAMIE-SHAWANO-SOUTHERN OCONTO COUNTY-WAUPACA- 228 PM CDT THU AUG 20 2009 ...STRONG THUNDERSTORMS EXPECTED IN EASTERN WAUPACA...NORTHWESTERN BROWN...OUTAGAMIE...SHAWANO AND SOUTHERN OCONTO COUNTIES... AT 225 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 5 MILES SOUTHWEST OF CLINTONVILLE TO NEW LONDON TO 10 MILES SOUTHEAST OF NEW LONDON...MOVING NORTHEAST AT 30 MPH. WINDS UP TO 40 MPH AND SMALL HAIL ARE EXPECTED WITH THESE STORMS. THESE STORMS WILL BE NEAR... CLINTONVILLE BY 235 PM CDT. BLACK CREEK BY 250 PM CDT. BLACK CREEK BY 255 PM CDT. PULASKI BY 315 PM CDT. THE TOWNS OF MEDINA...SUGAR BUSH...DALE...SYMCO...READFIELD... HORTONVILLE...BEAR CREEK...STEPHENSVILLE...SHIOCTON AND GREENVILLE ARE ALSO IN THE PATH OF THESE STORMS. EB
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE GREEN BAY WI 308 PM CDT THU AUG 20 2009 WIZ039-202045- BROWN- 308 PM CDT THU AUG 20 2009 ...STRONG THUNDERSTORMS WITH GUSTY WINDS EXPECTED IN BROWN COUNTY... AT 306 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A LINE OF STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 8 MILES SOUTH OF PULASKI TO 11 MILES SOUTHWEST OF GREEN BAY TO 6 MILES SOUTHEAST OF KAUKAUNA...MOVING EAST AT 30 MPH. WINDS AROUND 40 MPH ARE EXPECTED WITH THESE STORMS. THESE STORMS WILL BE NEAR... GREEN BAY BY 330 PM CDT. DENMARK BY 340 PM CDT. THE TOWNS OF WRIGHTSTOWN...HOLLAND...ASKEATON...GREENLEAF...KUNESH... ASHWAUBENON...ANSTON...DE PERE...MORRISON AND SHIRLEY ARE ALSO IN THE PATH OF THESE STORMS. BERSCH
The Green Bay radar (KGRB), 106 km away, was scanning. The volume nearest the first event began at 20:42 UTC.
1 thunderstorm wind. Local standard time, as filed.
A thunderstorm produced wind gusts estimated to near 70 mph near Almond. The storm downed several trees, including a large section of a willow. The tree fell onto a 28' diameter swimming pool, severely damaging the pool. A flag pole was also damaged.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2009Every state in 2009This day in weather historyWarnings in Wisconsin, August 2009
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: 184643.