Dense fog with visibilities of 1/4 mile or less formed over sections of Southwest Wisconsin during the early morning hours of April 30th. The fog formed with light winds and a very moist near-surface atmosphere following rain showers the previous afternoon and evening.
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 MKX wrote it up.
Dense fog with visibilities of 1/4 mile or less formed over sections of Southwest Wisconsin during the early morning hours of April 30th. The fog formed with light winds and a very moist near-surface atmosphere following rain showers the previous afternoon and evening.
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 Apr 29, 9:46 PM CST, 4 hours 49 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 1046 PM CDT SUN APR 29 2012 .UPDATE...RAIN IS DECREASING IN COVERAGE FROM SOUTH TO NORTH AS DRY SLOT AND AXIS OF SHORTWAVE TROUGH MOVE INTO THE REGION. DO EXPECT AT LEAST LGT SCT SHOWERS TO CONTINUE THROUGHOUT THE NIGHT DUE TO 925-700 MB WARM ADVECTION AND ANOTHER PASSAGE OF A WEAK SHORTWAVE TROUGH THAT IS CURRENTLY OVER WRN IA. AT THE SFC...AN INVERTED SFC TROUGH WILL MOVE ACROSS THE CWA BTWN 08Z AND 15Z. THE LIGHT WINDS WITH THE TROUGH PASSAGE AND MOIST LOW LEVELS WILL LEAD TO AREAS OF FOG. && .AVIATION/06Z TAFS/...SCT SHOWERS WILL CONTINUE THROUGH THE OVERNIGHT DUE TO WARM ADVECTION AHEAD OF AN INVERTED SFC TROUGH. THE INVERTED SFC TROUGH WILL PASS FROM WEST TO EAST ACROSS SRN WI FROM 08Z-15Z. THE CIGS WILL LOWER TO 400-500FT WITH VSBYS FALLING TO 1-2 MILES. STRATUS CLOUDS WILL LINGER THROUGH MONDAY DUE TO WEAK FLOW IN THE WAKE OF THE TROUGH PASSAGE. THE STRATUS WILL LIFT TO MVFR CIGS BY THE MIDDLE OF THE DAY AND POSSIBLY BECOME VFR CIGS AROUND 3.5 KFT BY LATE AFTERNOON. && .PREV DISCUSSION... /ISSUED 935 PM CDT SUN APR 29 2012/ UPDATE...RAIN IS DECREASING IN COVERAGE FROM SOUTH TO NORTH AS DRY SLOT AND AXIS OF SHORTWAVE TROUGH MOVE INTO THE REGION. DO EXPECT AT LEAST LGT SCT SHOWERS TO CONTINUE THROUGHOUT THE NIGHT DUE TO 925-700 MB WARM ADVECTION AND ANOTHER PASSAGE OF A WEAK SHORTWAVE TROUGH THAT IS CURRENTLY OVER WRN IA. AT THE SFC...AN INVERTED SFC TROUGH WILL MOVE ACROSS THE CWA BTWN 09Z AND 15Z. THE LIGHT WINDS WITH THE TROUGH PASSAGE AND MOIST LOW LEVELS WILL LEAD TO AREAS OF FOG. PREV DISCUSSION... /ISSUED 334 PM CDT SUN APR 29 2012/ VERY SHORT TERM...TONIGHT AND MONDAY...FORECAST CONFIDENCE IS HIGH. THE LARGER SYNOPTIC FEATURE LIFTING OUT OF THE CENTRAL PLAINS LOOKS A WHOLE LOT MORE IMPRESSIVE ON SATELLITE VS THE CORRESPONDING 500MB CHARTS EARLY THIS AFTERNOON. THIS IS CLEARLY A NICE SYNOPTIC SYSTEM COMING AT US AND SHOULD BRING THE ENTIRE AREA SOME RAIN TONIGHT GIVEN THE UNDERLYING. THERE IS FAIRLY DEEP AND RATHER VIGOROUS UPWARD VERTICAL MOTION MOVING IN THIS EVENING WITH THE UPPER JET SUGGESTING SOME COUPLING OF ENTRANCE/EXIT REGIONS OF TWO JET SEGMENTS. THE 850MB JET AT THE SAME TIME INCREASES TO 30 TO 40 KNOTS...NOSING INTO SOUTHERN WISCONSIN AND TRIGGERING A VERY IMPRESSIVE SURGE OF MOISTURE. MIXING RATIOS AT 800MB GO FROM 2.5G/KG AT MID DAY SUNDAY TO 8.5G/KG AT MIDNIGHT. THE 850MB LOW AND WARM FRONT TRACK RIGHT THROUGH THE FORECAST AREA OVERNIGHT. THE SFC LOW AND WARM FRONT SHOULD PASS JUST TO OUR SOUTH. EVERY MODEL HAS OUR ENTIRE FORECAST AREA GETTING HIT WITH 1/4 TO 1/2 INCH OF RAIN TONIGHT. A FEW ARE FOCUSING THE HEAVIEST PRECIP FROM MADISON ON WEST...CLOSER TO THE BEST CONVERGENCE WITH THE 850MB JET. OTHERS ARE MORE EQUAL OPPORTUNITY FOR THE AREA. INSTABILITY IS RATHER WEAK...BUT THE SOUNDINGS STILL SHOW SOME SKINNY REGIONS...GOOD FOR A SLIGHT CHANCE OF THUNDER...ESPECIALLY GIVEN THE MOISTURE SURGE COMING AT US. THE LOW PUSHES OFF TO THE EAST MONDAY MORNING. THERE MAY STILL BE SOME SHOWERS IN THE FAR SOUTHEAST BETWEEN 12-15Z...OTHERWISE LOOK FOR CLOUDS IN THE MORNING WITH SOME BREAKS POSSIBLE IN THE AFTERNOON. NOT BAD TEMP WISE AS WINDS TURN WESTERLY AND 925MB TEMPS DON/T REALLY TANK. SHORT TERM...MONDAY NIGHT THROUGH WEDNESDAY NIGHT. MONDAY NIGHT...FORECAST CONFIDENCE MEDIUM TO HIGH. VERY WEAK RIDGING BETWEEN SHORT WAVE TROUGHS MONDAY NIGHT. 12Z NAM FASTEST WITH 700 MB WAA BUT FORECAST SOUNDINGS SHOW MOISTENING LIMITED TO 700-600 MB LAYER...WITH WEAK 850-700MB FRONTOGENESIS... AND VERY DRY BELOW WITH DRY FLOW AROUND RETREATING SURFACE HIGH KEEPING BETTER LOW-LEVEL MOISTURE RETURN TO THE WEST. FOCUS OF 850MB THERMAL/MOISTURE ADVECTION ALSO WELL WEST. WILL LEAVE DRY...BUT WITH INCREASING MID CLOUDS IN THE SOUTHWEST. LOW TEMPERATURES WILL BE REACHED AROUND 06Z..THEN STEADY OUT ALONG THE LAKE WHILE SLOWLY RISING INLAND. TUESDAY...FORECAST CONFIDENCE MEDIUM. PERSISTENT BUT WEAK WARM AIR ADVECTION DURING THE DAY...WITH FOCUS OF STRONGEST LOW LEVEL FLOW STAYING TO THE WEST OVER THE ERN DAKOTAS AND MN. THERE IS A WEAK SHORT WAVE MOVING ACROSS ILLINOIS DURING THE AFTERNOON WITH 1000-850MB THETA E ADVECTION INCREASING AHEAD OF THIS WEAK WAVE. CAPE BUILDS CLOSE TO 800-1000 J/KG IN THE FAR WEST AND SOUTH...THEN DROPS OFF MARKEDLY TO THE NORTH. BLENDED POPS REFLECT THIS WELL LIMITING CHANCE POPS TO THE SOUTH. LEANED TOWARDS COOLER SIDE OF GUIDANCE NUMBERS SINCE CLOUDS AND EXPECTED PRECIPITATING WILL TEMPER THE WARMER 925 MB TEMPERATURES. TUESDAY NIGHT...FORECAST CONFIDENCE MEDIUM. FOCUS OF LOW-LEVEL JET SHIFTS TOWARD STATE...THOUGH IT WEAKENS AS INITIAL WAVE LIFTS NORTHWARD FROM NRN MN INTO CANADA. STRONGER 850 MB WINDS WILL BE FARTHER SOUTH...TIED TO LEE CYCLOGENESIS IN THE CENTRAL PLAINS. BETTER CHANCE FOR PRECIPITATION LOOKS TO BE BETWEEN 06Z AND 12Z WEDNESDAY BASED ON TIMING OF WEAK ISENTROPIC LIFT AND LAYER Q-VECTOR CONVERGENCE. WILL HOLD POPS TO CHANCE CATEGORY FOR NOW. WARM OVERNIGHT LOWS INLAND IN THE UPPER 50S TO LOW 60S WHILE FAR EAST COOLS INTO THE MID 50S WITH SOUTHEAST WINDS BEFORE WINDS SHIFT SOUTH AFTER MIDNIGHT. WEDNESDAY AND WEDNESDAY NIGHT...FORECAST CONFIDENCE LOW TO MEDIUM. HIGH CONFIDENCE OF PRECIPITATION...BUT LOW CONFIDENCE CONCERNING TIMING AND RESULTANT SEVERE POTENTIAL. DIFFERING PLACEMENT... STRENGTH AND TIMING OF SHORT WAVE ENERGY AMONG THE MODELS LEADS TO DIFFERENCES IN PLACEMENT OF STRONGER LOW-LEVEL WINDS AND BEST THERMAL ADVECTION/FORCING. A CONSENSUS BLEND FAVORS SLOWER GFS/ECMWF...WITH LIKELY POPS FOR THE NORTHWEST CWA...MAINLY FOR THE AFTERNOON...THEN LIKELY EVERYWHERE FOR WEDNESDAY NIGHT...FAVORING THE EVENING. HIGH TEMPERATURES IN THE MID TO UPPER 70S EVERYWHERE ON SOUTHWEST WINDS AND STEEP MID LEVEL LAPSE RATES HELPING TO PRODUCE SURFACE-BASED CAPE VALUES AROUND 2000 J/KG BY WEDNESDAY EVENING...WITH 0-6KM BULK SHEAR OF 30-35 KNOTS. LIMITING FACTORS INCLUDE REDUCED HEATING DUE TO CONVECTIVE DEBRIS FROM UPSTREAM CONVECTION REDUCING INSTABILITY. WILL KEEP MENTION OF SEVERE IN THE HWO. ALL SOLUTIONS KEEP SURFACE TROUGH NORTHWEST OF CWA THROUGH 12Z THURSDAY...SO OVERNIGHT LOWS IN THE 60S EVERYWHERE. LONG TERM....LONG TERM...THURSDAY THROUGH SUNDAY. FORECAST CONFIDENCE LOW. IN SPITE OF MODEL DIFFERENCES...THEY GENERALLY AGREE IN KEEPING SOUTHERN WISCONSIN CLOSE TO...OR JUST ON THE WARM SIDE OF THE 850 MB BAROCLINIC ZONE RUNNING PARALLEL TO WEST-SOUTHWEST UPPER FLOW INTO FRIDAY. CHANCES OF SHOWERS AND/OR THUNDERSTORMS AS WEAK WAVES MOVE THROUGH THE FLOW...BUT LITTLE AGREEMENT TO TIMING. BLENDED SOLUTION BRINGS HIGHS IN THE 70S THURSDAY AND FRIDAY...THOUGH COOLER IN THE FAR EAST FRIDAY AS LIGHT GRADIENT WINDS TURN NORTHEAST TO EAST IN THE AFTERNOON. GFS AND ECMWF TO AGREE THAT COOLER AIR WILL SETTLE INTO SOUTHERN WISCONSIN BY SUNDAY...BUT ONLY TO SEASONAL NORMS...WITH ANOTHER WAVE APPROACHING FROM THE ROCKIES THAT WILL DETERMINE OUR EARLY WEEK WEATHER NEXT WEEK. AVIATION/00Z TAFS/... LOOK FOR GRADUALLY DETERIORATING CONDITIONS THROUGH THE OVERNIGHT HOURS...CULMINATING IN IFR CIGS DEVELOPING BETWEEN 09-12Z TONIGHT. THE EVENING STARTS OUT WITH MID LEVEL CLOUDS...BUT WILL LOWER QUICKLY AS RAIN PUSHES IN WITH THE APPROACH OF A LOW PRESSURE SYSTEM LIFTING OUT OF THE CENTRAL PLAINS. RAIN SHOULD HIT KMSN BY 00-01Z AND THE SOUTHEAST TAF SITES ABOUT 02-03Z. RAIN SHOULD CONTINUE IN A PRETTY STEADY FASHION THROUGH ABOUT 10-11Z WHEN IT TAPERS TO SOME SHOWERS BEFORE ENDING ENTIRELY BY OR SHORTLY AFTER 12Z. LOOK FOR THE IFR CIGS TO RISE TO MVFR DURING MONDAY MORNING AND VFR MONDAY AFTERNOON. WINDS WILL BE EASTERLY THROUGH MIDNIGHT...THEN LOOK FOR A WIND SHIFT TO THE WEST BEFORE SUNRISE AS A TROF PASSES THROUGH. MARINE... EAK LOW PRESSURE PASSING TO THE SOUTH OF LAKE MI TONIGHT AND MONDAY WILL RESULT IN A TIGHTENING PRESSURE GRADIENT. SURFACE WINDS ARE EXPECTED TO REMAIN ONSHORE RESULTING IN LOW LEVEL INVERSION. LATEST MODIS IMAGERY AND MID LAKE BUOY CONTINUE TO SHOW SRN LAKE MI SFC TEMPS IN THE LOW TO MID 40S. EXPECT INVERSION TO PREVENT STRONGER WINDS FROM REACHING LAKE SURFACE TNGT. HOWEVER...WIND GUSTS EXCEEDING 20KTS MAY BE FELT AT SGNW3 AND KNSW3 WHERE ANEMOMETER HEIGHTS ARE 60FT ABV LAKE SFC. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && UPDATE...GEHRING TONIGHT/MONDAY AND AVIATION/MARINE...DAVIS MONDAY NIGHT THROUGH SUNDAY...REM
HAZARDOUS WEATHER OUTLOOK...UPDATE NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 732 PM CDT SUN APR 29 2012 WIZ046-047-051-052-056>060-062>072-302100- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 732 PM CDT SUN APR 29 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SUNDAY SEVERAL ROUNDS OF THUNDERSTORMS ARE EXPECTED FROM TUESDAY NIGHT INTO FRIDAY AS WARMER...MORE HUMID AIR SETTLES OVER SOUTHERN WISCONSIN. SEVERAL LOW PRESSURE SYSTEMS MOVING NORTHEAST ALONG A BOUNDARY THAT WILL BE DRAPED ACROSS WISCONSIN INTO THE CENTRAL PLAINS WILL BE RESPONSIBLE FOR THE THUNDERSTORMS. THERE IS A POTENTIAL FOR SEVERE THUNDERSTORMS TUESDAY NIGHT AND WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE REQUIRED LATER THIS WEEK. LMZ643>646-302100- 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- 732 PM CDT SUN APR 29 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SUNDAY SEVERAL ROUNDS OF THUNDERSTORMS ARE EXPECTED FROM TUESDAY NIGHT INTO FRIDAY AS WARMER...MORE HUMID AIR SETTLES OVER THE WESTERN GREAT LAKES. SEVERAL LOW PRESSURE SYSTEMS MOVING NORTHEAST ALONG A BOUNDARY THAT WILL BE DRAPED ACROSS WISCONSIN INTO THE CENTRAL PLAINS WILL BE RESPONSIBLE FOR THE THUNDERSTORMS. THERE IS A POTENTIAL FOR SEVERE THUNDERSTORMS TUESDAY NIGHT AND WEDNESDAY. GEHRING WWW.WEATHER.GOV/MKX
The national radar mosaic for the moment the first event began.
1 dense fog. Local standard time, as filed.
The AWOS at Monroe airport (KEFT) reported visibilities of 1/4 mile or less during the early morning hours of April 30th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2012Every state in 2012This day in weather historyWarnings in Wisconsin, April 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: 377921.