A surge of warm, moist, unstable air ahead of an approaching cold front resulted in rounds of numerous thunderstorms across southern WI. A few thunderstorms became severe with damaging wind gusts.
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 MKX wrote it up.
A surge of warm, moist, unstable air ahead of an approaching cold front resulted in rounds of numerous thunderstorms across southern WI. A few thunderstorms became severe with damaging wind gusts. Heavy rainfall also occurred across the area.
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 Sep 17, 10:17 AM CST, 3 hours 8 minutes earlier.
AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 1117 AM CDT THU SEP 17 2015 .UPDATE... SCATTERED SHOWERS AND THUNDERSTORMS ARE SPREADING INTO WESTERN WISCONSIN LATE THIS MORNING IN RESPONSE TO WEAK 925-700MB WARM AIR ADVECTION AND STEADY MOISTURE TRANSPORT. THE LATEST 14Z HRRR MODEL SHOWS THIS CONVECTION TRACKING EAST THROUGH SOUTHERN WI THROUGH EARLY AFTERNOON. THIS MAY PAN OUT GRADUALLY OVER TIME... BUT THE CONVECTION IS GETTING EATEN BY DRY AIR AS IT WORKS EAST LATE THIS MORNING. THE INSTABILITY AND MOISTURE WILL NEED TIME TO SPREAD EAST TODAY TO SUPPORT CONVECTION. CAPE VALUES ARE BETWEEN 500 AND 1000 J/KG IN WESTERN/SOUTH CENTRAL WI. LOW LEVEL SHEAR IS DECENT BUT BULK SHEAR IS WEAK SO NOT EXPECTING SEVERE WITH THESE BRIEF THUNDERSTORMS. THE MAIN EVENT WILL ARRIVE THIS EVENING AS A LINE OF CONVECTION IS EXPECTED TO SLIDE SOUTHEAST THROUGH WI WITH A COLD FRONT. THERE IS A SLIGHT RISK FOR SEVERE WEATHER NORTHWEST OF MADISON AND A MARGINAL RISK ELSEWHERE. && .AVIATION/18Z TAFS/... GUSTY SOUTH WINDS AGAIN TODAY WITH GUSTS TO 20-25 KNOTS. SHOWERS AND THUNDERSTORMS TRACKING INTO SOUTH CENTRAL WI ARE DISSIPATING AS THEY HEAD EAST OF MADISON DUE TO DRY AIR. THE ENVIRONMENT WILL GET BETTER FOR SUPPORTING CONVECTION FARTHER EAST LATER IN THE AFTERNOON. EXPECT CHANCE OF SHOWERS AND THUNDERSTORMS FOR MUCH OF THE DAY. THUNDERSTORM CHANCES INCREASE LATE THIS AFTERNOON AND EVENING WITH THE APPROACH OF SURFACE COLD FRONT. EXPECT MVFR VSBYS IN THE STORMS...WITH SOME STRONG WIND GUSTS AND HAIL POSSIBLE OVER MAINLY SOUTH CENTRAL WISCONSIN LATE THIS AFTERNOON AND EVENING. WILL SEE MVFR CIGS FRIDAY MORNING BEHIND PCPN WITH THE COLD AIR ADVECTION BEHIND THE FRONT. && .PREV DISCUSSION... /ISSUED 657 AM CDT THU SEP 17 2015/ TODAY...FORECAST CONFIDENCE MEDIUM TWO AREAS OF CONVECTION ONGOING...THE FIRST NARROW BAND OF SHOWERS AND THUNDERSTORMS IN ERN MN/WRN WI DRIVEN BY 850-700 MB WARM AIR ADVECTION/MOISTURE TRANSPORT AS WELL AS CVA WITH LEAD SHORT WAVE UNDER INCREASING 250 MB UPPER LEVEL DIVERGENCE. SECOND AREA IN THE DAKOTAS IS WITH FORCING ASSOCIATED WITH MAIN SHORT WAVE TROUGH AND SURFACE LOW. UPPER LEVEL DIVERGENCE/DIFFLUENCE INCREASES THIS AFTERNOON AS IT SHIFTS EAST AHEAD OF APPROACHING UPPER TROUGH...WITH A LEAD SHORT WAVE REACHING LAKE MICHIGAN BY 00Z. HOWEVER 700 MB OMEGA WEAKENS AROUND 18Z IN AREA OF 850 MB DIVERGENCE AS STRONGEST 850 MB WINDS SPLIT... WITH ONE MAX LIFTING OFF TO THE NORTH OVER THE U.P. AND LAKE SUPERIOR AND A SECOND MAX APPROACHES FROM MISSOURI AHEAD OF THE MAIN TROUGH. NAM ACTUALLY SHOWING SUBSIDENCE OVER SRN WI DURING THE AFTERNOON...WHICH EXPLAINS THE LACK OF QPF OVER THE FORECAST AREA. WILL FOLLOW CONSENSUS BLEND WHICH BRINGS INITIAL WAA PCPN INTO SOUTH CENTRAL WI THIS MORNING THEN LIFTS IT NORTH...WITH REDEVELOPMENT TO THE SOUTHWEST AHEAD OF NEXT WARM...MOIST SURGE THIS AFTERNOON... KEEPING MOST OF SOUTHEAST WISCONSIN DRY. CLOUDS...AND THIS FIRST ROUND OF PCPN WILL KEEP HIGH TEMPS A BIT LOWER IN THE WEST THAN THAT PAST FEW DAYS BUT WILL STILL REACH 80 MOST LOCATIONS WITH THE WARMEST TEMPS IN THE SOUTHEAST. THOUGH 850 MB WINDS LOWER...WILL STILL MIX UP TO AROUND 900 MB AND 20-25 KT WINDS SO IT WILL BE BREEZY AGAIN THIS AFTERNOON. TONIGHT...FORECAST CONFIDENCE MEDIUM. SHOWERS AND THUNDERSTORMS WILL REDEVELOP TONIGHT AS COLD FRONT/SURFACE TROUGH MOVES INTO THE REGION. PRECIPITABLE WATER VALUES REACH 1.8 TO 1.9 INCHES FOR TONIGHT WITH MOISTURE TRANSPORT RIDING IN ON 30-40KT LOW LEVEL JET AHEAD OF APPROACHING .WITH MOST-UNSTABLE CAPE VALUES OF 1000-1300 J/KG. COULD SEE SOME HEAVY RAIN TONIGHT...WITH SOUTH CENTRAL POSSIBLY SEEING 3/4 INCH TO 1 INCH AND THE SOUTHEAST WIDESPREAD 1/2 INCH AMOUNTS BY FRIDAY MORNING...WITH LOCALLY HIGHER AMOUNTS POSSIBLE. FORTUNATELY FLASH FLOOD GUIDANCE IS HIGH WITH 1-HOURLY THRESHOLDS AROUND 2 INCHES AND 3 TO 6-HOURLY BETWEEN 2.5 AND 3 INCHES. DEEP LAYER SHEAR DOES RISE TO 25-30 KNOTS SO POTENTIAL IS THERE FOR ROTATING CELLS THAT COULD PRODUCE HAIL AND STRONG WIND GUSTS. SPC HAS MOST OF SOUTH CENTRAL IN A SLIGHT RISK...MAINLY DURING PERIOD OF MAXIMUM INSTABILITY FOR LATE THIS AFTERNOON AND EVENING...AND THE REST OF SOUTHERN WISCONSIN IN A MARGINAL RISK FOR SEVERE. FRIDAY AND SATURDAY...FORECAST CONFIDENCE...MEDIUM THE COLD FRONT IS EXPECTED TO STALL FRIDAY IN THE VICINITY OF THE WI/IL BORDER. MEANWHILE...ANOTHER SURFACE LOW WILL TAKE AIM AT THE AREA...MOVING THROUGH THE STALLED FRONTAL ZONE FRIDAY NIGHT AHEAD OF A STRONG SHORTWAVE. THINK THAT THERE MAY BE A FEW LINGERING SHOWERS/STORMS EARLY FRIDAY FROM THE FRONTAL PASSAGE...WITH IT POSSIBLY TURNING DRY FOR A TIME MID MORNING INTO EARLY AFTERNOON. MAY SEE A FEW MID/LATE AFTERNOON STORMS AS INSTABILITY INCREASES...THOUGH BULK OF FORCING NOT SET TO ARRIVE UNTIL THE EVENING AND OVERNIGHT HOURS. MODELS STILL STRUGGLING WITH THE PATH/SPEED OF THE STRONG SURFACE LOW FRIDAY NIGHT. THE GFS HAS IT OVER THE SOUTHERN TIP OF LAKE MICHIGAN AT DAYBREAK SATURDAY...WITH THE NAM PUTTING THE CENTER OF THE LOW OVER THE WESTERN FORECAST AREA. MEANWHILE...THE ECMWF AND CANADIAN HAVE THE LOW OVER EASTERN LOWER MICHIGAN. FOR NOW...STUCK CLOSE TO THE ECMWF/CANADIAN SOLUTIONS...WHICH HAVE BEEN PRETTY CONSISTENT THE LAST COUPLE DAYS. EITHER WAY...LOOKS LIKE A WET EVENING AND NIGHT WITH WIDESPREAD RAINFALL EXPECTED. BEST CHANCE FOR CONVECTION IN THE SOUTHEAST FORECAST AREA...AS THE WARM SECTOR AND BETTER INSTABILITY TRY TO SNEAK IN. MODELS STILL GENERALLY PAINTING OUT 0.5 TO 1.O INCH OF RAIN OVERNIGHT. HAVE POPS LINGERING INTO SATURDAY MORNING...MAINLY IGNORING NAM FOR NOW...WHICH WOULD LINGER RAIN MUCH OF THE DAY. SHOULD BE DRY BY LATE MORNING OR EARLY AFTERNOON AS HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST. THOUGH THE SURFACE FRONT IS PROGGED TO BE MAINLY SOUTH OF MUCH OF THE FORECAST AREA BY LATE MORNING FRIDAY...MODELS STILL SHOWING PRETTY MILD TEMPS AT 925 MB. KEPT HIGHS CLOSER TO MODEL 2M TEMPS THOUGH...AS IT WILL PROBABLY BE HARD TO TAP THOSE WARMER TEMPS GIVEN THE POSITION OF THE FRONT...ALONG WITH CLOUDS AND PRECIP CHANCES. WILL BE COOLER THEN SATURDAY IN THE WAKE OF THE DEPARTING LOW. SUNDAY THROUGH WEDNESDAY...FORECAST CONFIDENCE...HIGH MODELS IN PRETTY GOOD AGREEMENT THAT HIGH PRESSURE WILL BE OVERHEAD FOR SUNDAY THROUGH WEDNESDAY. LOOKS LIKE PLENTY OF SUNSHINE WITH HIGH TEMPS WARMING BACK TO AROUND OR A LITTLE ABOVE AVERAGE VALUES FOR THE LAST COUPLE DAYS OF SUMMER. AVIATION/12Z TAFS... NARROW BAND OF SHOWERS AND THUNDERSTORMS OVER FAR WESTERN WISCONSIN EARLY THIS MORNING IS DIMINISHING AS LOW-LEVEL JET MOVES TO THE NORTH. WILL WATCH SHOWERS AND STORMS IN IOWA APPROACHING WITH A WEAK WAVE...BUT EXPECT VFR CONDITIONS THROUGH THE MORNING AND EARLY AFTERNOON. GUSTY SOUTH WINDS AGAIN TODAY WITH GUSTS TO 20-25 KNOTS. SHOWER AND STORM CHANCES INCREASE LATE THIS AFTERNOON AND EVENING WITH THE APPROACH OF SURFACE COLD FRONT. EXPECT MVFR VSBYS IN THE STORMS...WITH SOME STRONG WIND GUSTS AND HAIL POSSIBLE OVER MAINLY SOUTH CENTRAL WISCONSIN LATE THIS AFTERNOON AND EVENING. WILL SEE MVFR CIGS FRIDAY MORNING BEHIND PCPN WITH THE COLD AIR ADVECTION BEHIND THE FRONT. MARINE... SOUTH WINDS AGAIN INCREASE TO 10 TO 20 KNOTS BY LATE MORNING....WITH GUSTS TO 25 KNOTS FREQUENT ENOUGH FROM PORT WASHINGTON NORTH TO KEEP SMALL CRAFT ADVISORY AS IS. WINDS AND WAVES MARGINAL SOUTH OF PORT WASHINGTON. LOOKING FOR THUNDERSTORMS TO REACH THE NEARSHORE WATERS BY EARLY EVENING AHEAD OF A COLD FRONT. SOME STORMS COULD PRODUCE STRONG WIND GUSTS AND HAIL. BEACHES... WITH SOUTH WINDS OF 15 TO 25 KNOTS AND WAVES OF 3 TO 5 FEET HAVE ISSUED A BEACH HAZARD STATEMENT FOR THE BEACHES OF SHEBOYGAN COUNTY TO LINE UP WITH THE SMALL CRAFT ADVISORY. HAZARDOUS CONDITIONS WILL LINGER INTO THE EVENING BEFORE WINDS AND WAVES LOWER. A MODERATE SWIM RISK WILL EXIST AT THE LAKE MICHIGAN BEACHES FROM OZAUKEE COUNTY SOUTH THROUGH KENOSHA COUNTY FROM MID MORNING THROUGH EARLY EVENING. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...BEACH HAZARDS STATEMENT UNTIL 10 PM CDT THIS EVENING FOR WIZ052. LM...SMALL CRAFT ADVISORY UNTIL 10 PM CDT THIS EVENING FOR LMZ643. && UPDATE...MRC TODAY/TONIGHT AND AVIATION/MARINE...REM FRIDAY THROUGH WEDNESDAY...DDV
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 409 AM CDT THU SEP 17 2015 WIZ046-047-051-052-056>060-062>072-180915- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 409 AM CDT THU SEP 17 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS WILL BECOME LIKELY LATE THIS AFTERNOON NORTHWEST OF MADISON...AND OVERSPREAD SOUTHERN WISCONSIN TONIGHT AS A WEAK COLD FRONT APPROACHES. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS...GENERALLY ALONG AND WEST OF A RIPON...MADISON TO MONROE LINE WITH A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE REST OF SOUTHERN WISCONSIN DURING THIS TIME. A BEACH HAZARD STATEMENT IS IN EFFECT FOR SHEBOYGAN COUNTY FROM MID-MORNING THROUGH EARLY EVENING FOR A HIGH SWIM RISK. A MODERATE SWIM RISK EXISTS AT THE LAKE MICHIGAN BEACHES FROM OZAUKEE COUNTY SOUTH THROUGH KENOSHA COUNTY. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY SHOWERS AND THUNDERSTORMS MOVE BACK INTO SOUTHERN WISCONSIN FRIDAY AFTERNOON AND FRIDAY NIGHT AS LOW PRESSURE MOVES NORTHEAST ACROSS NORTHERN ILLINOIS AND SOUTHEAST WISCONSIN. HEAVY RAINFALL WILL BE POSSIBLE. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS DURING THIS TIME THAT COVERS ALL BUT THE FAR NORTHWEST SECTIONS OF SOUTHERN WISCONSIN. MODERATE TO HIGH SWIM RISKS ARE EXPECTED AT TIMES FROM FRIDAY THROUGH SATURDAY AT LAKE MICHIGAN BEACHES FROM SHEBOYGAN COUNTY SOUTH TO KENOSHA COUNTY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING...AND AGAIN FRIDAY EVENING. LMZ643>646-180915- 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- 409 AM CDT THU SEP 17 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...TODAY AND TONIGHT A SMALL CRAFT ADVISORY IS IN EFFECT NORTH OF PORT WASHINGTON FROM MID-MORNING THROUGH EARLY EVENING FOR BREEZY SOUTH WINDS AND HIGH WAVES. SHOWERS AND THUNDERSTORMS WILL REACH THE NEARSHORE WATERS THIS EVENING AS A WEAK COLD FRONT APPROACHES. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY THERE IS A CHANCE FOR SHOWERS AND THUNDERSTORMS FRIDAY AFTERNOON ...BECOMING LIKELY FRIDAY NIGHT AS LOW PRESSURE MOVES NORTHEAST ACROSS NORTHERN ILLINOIS AND SOUTHEAST WISCONSIN. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS DURING THIS TIME. REM WWW.WEATHER.GOV/MKX
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
109 PM CDT THU SEP 17 2015
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1243 PM NON-TSTM WND GST BELMONT 42.74N 90.33W
09/17/2015 M50 MPH LAFAYETTE WI TRAINED SPOTTER
DOWNTOWN BELMONT
&&
RSCHAARSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
158 PM CDT THU SEP 17 2015
WIZ062-063-067>069-171930-
ROCK-LAFAYETTE-IOWA-GREEN-DANE-
158 PM CDT THU SEP 17 2015
...GUSTY SOUTHERLY WINDS BEHIND A LINE OF THUNDERSTORMS WILL AFFECT
SOUTHERN IOWA...SOUTHERN DANE...LAFAYETTE... ROCK AND GREEN
COUNTIES...
AT 154 PM CDT...THE THUNDERSTORMS WERE LOCATED NEAR JANESVILLE...
MOVING EAST AT 20 MPH.
WIND GUSTS UP TO 50 MPH ARE POSSIBLE BEHIND THESE STORMS.
LOCATIONS IMPACTED INCLUDE...
WESTERN MADISON...JANESVILLE...BELOIT...FITCHBURG...STOUGHTON...
MONROE...VERONA...OREGON...MCFARLAND...MOUNT HOREB...MILTON...
EDGERTON...EVANSVILLE...DODGEVILLE...BRODHEAD...MINERAL POINT...
DARLINGTON...BELLEVILLE...NEW GLARUS AND CLINTON.
LAT...LON 4251 9042 4304 9043 4301 8901 4285 8901
4284 8877 4249 8878
TIME...MOT...LOC 1854Z 252DEG 16KT 4270 8914
BSHSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
224 PM CDT THU SEP 17 2015
WIZ062>064-067>070-172045-
JEFFERSON-ROCK-LAFAYETTE-IOWA-GREEN-DANE-WALWORTH-
224 PM CDT THU SEP 17 2015
...STRONG SOUTHERLY WINDS BEHIND A LINE OF THUNDERSTORMS WILL AFFECT
SOUTHERN IOWA...SOUTHERN JEFFERSON...WALWORTH...SOUTHERN
DANE...LAFAYETTE...ROCK AND GREEN COUNTIES...
AT 222 PM CDT...A LINE OF THUNDERSTORMS WAS ALONG A LINE EXTENDING
FROM NEAR WHITEWATER TO NEAR MOUNT MORRIS...AND MOVING EAST AT 25
MPH. THE STRONGEST WINDS WILL BE TO THE WEST OF THESE STORMS.
WIND GUSTS UP TO 50 MPH ARE POSSIBLE WITH THESE SHOWERS.
LOCATIONS IMPACTED INCLUDE...
JANESVILLE...BELOIT...FITCHBURG...WHITEWATER...STOUGHTON...FORT
ATKINSON...MONROE...ELKHORN...OREGON...LAKE GENEVA...MILTON...
EDGERTON...EVANSVILLE...DODGEVILLE...EAST TROY...BRODHEAD...WILLIAMS
BAY...MINERAL POINT...DARLINGTON AND DELAVAN LAKE.
LAT...LON 4251 9042 4296 9043 4296 8854 4284 8854
4284 8831 4250 8831
TIME...MOT...LOC 1922Z 275DEG 21KT 4284 8881 4199 8947
BSHThe Milwaukee radar (KMKX), 52 km away, was scanning. The volume nearest the first event began at 19:25 UTC.
2 thunderstorm wind, 1 heavy rain. Local standard time, as filed.
A swath of wind damage with numerous branches and trees down including one large uprooted tree. Trees and branches down on cars and one house. Power poles and powerlines down. Street signs blown down.
One large tree uprooted and some shingles removed from the roof of a home.
Urban and rural street flooding occurred across the county due to 3 to 4 inches of rainfall over several hours. No road closures were needed and the water did subside during the early morning hours.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2015Every state in 2015This day in weather historyWarnings in Wisconsin, September 2015
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: 599287, 599288, 599289.