Light winds, clear skies and a humid air mass over the region led to the formation of dense fog over most of South Central and Southeast Wisconsin. Many areas saw dense fog mainly between the hours of 2 am and 9 am CDT on August 1st, though Sheboygan County saw visibilities drop to 1/4 mile or less around 11 pm CDT on July 31st.
Every event with a place to put it; 7 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 MKX wrote it up.
Light winds, clear skies and a humid air mass over the region led to the formation of dense fog over most of South Central and Southeast Wisconsin. Many areas saw dense fog mainly between the hours of 2 am and 9 am CDT on August 1st, though Sheboygan County saw visibilities drop to 1/4 mile or less around 11 pm CDT on July 31st.
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 Milwaukee, WI wrote its last area forecast discussion before the first event at Jul 31, 2:30 PM CST, 9 hours 30 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 330 PM CDT SAT JUL 31 2010 .SHORT TERM...MEDIUM FCST CONFIDENCE THROUGH TUE NT. N-S WIND SHIFT LINE SEEN ON RADAR IN FAR ERN WI IS MOVING TOWARD LAKE MI AND THE LAKE BREEZE. ISOLD SHOWERS WILL REMAIN POSSIBLE ALONG THIS CONVERGENT ZONE FOR THE NEXT COUPLE HOURS. CLOUD COVER IS BECOMING MORE SCT WITH SOME HEATING AND MIXING OCCURRING. HIGH PRESSURE AND CALM WINDS TO SETTLE OVER THE REGION TNT. THE COMBINATION OF LGT NLY WINDS LOWERING DEWPOINTS A LITTLE...AND WARM SOIL TEMPS ARE FACTORS THAT WILL INHIBIT WIDESPREAD DENSE FOG WHILE CLEAR SKIES AND RADIATIONAL COOLING WITHIN MOIST SFC CONDITIONS SUPPORTS IT. WILL MENTION AREAS OF DENSE FOG FOR NOW AND HOLD OFF ON DENSE FOG ADVISORY. FOG TO LINGER INTO SUN AM WITH HIGH PRESSURE TO MOVE EAST LATE IN THE DAY. SSWLY WINDS WILL PREVAIL INTO MON WITH WARM TEMPS AND INCREASING HUMIDITY WHILE A FLAT RIDGE WILL DEVELOP OVER THE NRN CENTRAL USA INTO EARLY NEXT WEEK. SLIGHT CHANCE POPS REMAIN FOR AREAS WEST OF KMSN FOR MON AFT WHILE CHANCE POPS ARE FCST MON NT THROUGH TUE NT. A LLJ AND WARM FRONT WILL SET UP OVER IA WITH BEST INSTABILITY AND LIFT TO REMAIN SOUTH...THUS CHANCE POPS VERSUS SOMETHING HIGHER. .LONG TERM...WEAK HIGH PRESSURE TO SETTLE OVER THE AREA WED INTO EARLY FRI WITH STNRY FRONT REMAINING TO THE SOUTH. A PRESSURE TROUGH AND SHORTWAVE MOVING ACROSS THE PLAINS WILL THEN BRING THE FRONT BACK NWD AS A WARM FRONT WITH CHANCES OF TSTORMS ON SAT. ABOVE NORMAL TEMPS TO CONTINUE. && .AVIATION...AFTERNOON CUMULUS ACROSS THE WEST WILL DECREASE WITH THE LOSS OF HEATING THIS EVENING. ADDITIONALLY...EXPECTING STRATUS TO THE WEST TO DECREASE AS WAVE CONTINUES TO PULL AWAY AND HIGH PRESSURE BUILDS IN. WITH SKIES BECOMING MOSTLY CLEAR AND WINDS LIGHT TO CALM...EXPECTING AREAS OF FOG TO DEVELOP AFTER MIDNIGHT. MAIN CONCERN AT THIS MOMENT IS HOW LONG CLOUDS TAKE TO CLEAR IN THE EAST...AS LATER CLEARING WOULD INHIBIT THE FOG POTENTIAL. OVERALL...IFR VSBYS SEEM LIKE A GOOD BET...WITH A CHANCE FOR SOME LOCATIONS TO GO EVEN LOWER. HESITANT TO BE TOO AGGRESSIVE IN THE TAFS YET...UNTIL CLEARING SEEMS MORE CERTAIN IN THE EAST. WILL HAVE TO WATCH TRENDS THIS EVENING. FOG WILL LIFT IN THE MORNING AS THE SUN HEATS THINGS UP...WITH VFR CONDITIONS RETURNING FOR THE DAY UNDER MOSTLY SUNNY SKIES. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && SHORT/LONG TERM...20 AVIATION/MARINE...07
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 310 PM CDT SAT JUL 31 2010 WIZ046-047-051-052-056>060-062>072-012015- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 310 PM CDT SAT JUL 31 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TONIGHT WIDESPREAD FOG AND AREAS OF DENSE FOG ARE EXPECTED TONIGHT...MAINLY AFTER MIDNIGHT. THE BEST CHANCE FOR DENSE FOG WILL BE IN RIVER VALLEYS SUCH AS THE WISCONSIN RIVER VALLEY AND IN LOW LYING MARSHY AREAS. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THERE IS A CHANCE OF THUNDERSTORMS MONDAY AFTERNOON THROUGH TUESDAY NIGHT AS A COLD FRONT DROPS THROUGH THE STATE. THE STRONGEST STORMS SHOULD REMAIN WEST AND SOUTH OF THE AREA. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TONIGHT. LMZ643>646-012015- SHEBOYGAN TO PORT WASHINGTON WI- PORT WASHINGTON TO NORTH POINT LIGHT WI- NORTH POINT LIGHT TO WIND POINT WI- WIND POINT WI TO WINTHROP HARBOR IL- 310 PM CDT SAT JUL 31 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...TONIGHT PATCHY FOG IS EXPECTED TONIGHT...ESPECIALLY AFTER MIDNIGHT TONIGHT. DENSE FOG IS POSSIBLE...MAINLY RIGHT ALONG THE SHORE. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THERE IS A CHANCE OF THUNDERSTORMS MONDAY NIGHT THROUGH TUESDAY NIGHT AS A COLD FRONT DROPS DOWN LAKE MICHIGAN. DDV WWW.WEATHER.GOV/MKX
The national radar mosaic for the moment the first event began.
7 dense fog. Local standard time, as filed.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Sheboygan County late in the evening of July 31st and lasting until the morning of August 1st. The Sheboygan airport ASOS reported visibilities of 1/4 mile or less during this time.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Fond Du Lac County during the early morning of August 1st. The Fond Du Lac airport ASOS reported visibilities of 1/4 mile or less during this time.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Washington County during the early morning of August 1st. The West Bend airport AWOS reported visibilities of 1/4 mile or less during this time.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Washington County during the early morning of August 1st. Law enforcement officials reported widespread visibilities of 1/4 mile or less during this time.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Rock County during the early morning of August 1st. The Janesville airport AWOS reported visibilities of 1/4 mile or less during this time.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Sauk County during the early morning of August 1st. The Wisconsin Dells airport AWOS reported visibilities of 1/4 mile or less during this time.
Light winds, clear skies and a humid air mass led to the formation of dense fog over Iowa County during the early morning of August 1st. The Mineral Point airport AWOS reported visibilities of 1/4 mile or less during this time.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2010Every state in 2010This day in weather historyWarnings in Wisconsin, August 2010
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: 258564, 258566, 258584, 258586, 258587, 258589, 258588.