Strong to severe thunderstorms moved across parts of northern Illinois during the late evening hours of July 27th. Strong winds developed behind the thunderstorms across far northeast Illinois which continued into the early morning of July 28th.
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 LOT wrote it up.
Strong to severe thunderstorms moved across parts of northern Illinois during the late evening hours of July 27th. Strong winds developed behind the thunderstorms across far northeast Illinois which continued into the early morning of July 28th. Wind gusts between 45 and 55 mph were common across much of McHenry, Lake, northern Kane, northern Dupage and north central Cook Counties. Chicago O'Hare Airport gusted to 46 mph and Waukegan Airport gusted to 55 mph. Tree limbs were reported blown down in Lindenhurst in Lake County, Palatine and Elk Grove Village in Cook County and Carol Stream in Dupage County.
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 Chicago, IL wrote its last area forecast discussion before the first event at Jul 27, 5:54 PM CST, 3 hours 11 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 654 PM CDT MON JUL 27 2009 .DISCUSSION... 224 PM CDT HAVE BASED NEAR TERM OF FCST ON CURRENT SATLT/MESOSCALE TRENDS. AFTERNOON VIS IMAGERY SHOWS MID LVL LOW NOW NEAR TWIN CITIES MOVG ESEWD INTO W CNTRL WI. ASSD TSTM CLUSTER EXPECTED TO STAY N OF FA THIS EVENING. OF GREATER CONCERN IS CU FIELD ACROSS NRN IA/SRN MN. EXPECT THIS AREA TO ERUPT WITH DEEP CONVECTION LATE THIS AFTN AS BOUNDARY TRAILING SWWD FROM LOW OVR MSP INTERACTS WITH STRONG INSTABILITY AXIS. SBCAPE IN AREA NW OF MCW HAD RISEN TO 3500 J/KG AS OF 18Z. AS STORMS DVLP ALONG THIS BOUNDARY DURG THE COURSE OF THIS EVENING...EXPECT LINEAR COMPLEX TO FORM AND MOVE SEWD. AS A RESULT...WILL MAINTAIN LIKELY POPS AS PER PREVIOUS FCST...AND MOVE THIS ZONE OF SHOWERS AND STORMS SEWD ACROSS FA TONIGHT AND TUESDAY. WIND PROFILES LOOK PRETTY WEAK THOUGH...AND GIVEN LATE NIGHT-MORNING EVENT...CONCUR WITH IDEA THAT MAIN THREAT WITH THESE STORMS WILL BE LOCALLY HEAVY RAINFALL. ONLY SIG CHG TO PREVIOUS FCST IS TO ADJUST TIMING OF PRECIP FOR QUICKER FROPA ON TUESDAY. MODELS HAVE GONE BACK TO FASTER FRONTAL MOVEMENT ADVERTIZED IN EARLIER RUNS. A COUPLE OF REASONS FOR CONCURRING WITH THIS SCENARIO INCLUDE INCREASING DOWNWARD MOMENTUM SUGGESTED BY WATER VAPOR IMAGERY...AND SUBSEQUENT RISES IN SFC PRESSURE SURE TO BECOME MORE APPARENT AFTER DIURNAL HEATING SUBSIDES. ALSO...EXPECT OUTFLOW FROM CONVECTIVE DEVELOPMENT OVERNIGHT TO PUSH/PROPAGATE EFFECTIVE COLD FRONT SWD ACROSS FA DURING TUESDAY. STILL LOOKS LIKE GREATEST COVERAGE OF SHWRS/TSTMS ACROSS AREA WILL BE IN PERIOD FROM AROUND MIDNIGHT N AND W...TO MIDDAY TUESDAY OVR SERN PORTION OF FA WHERE STORMS MAY REFIRE AFTER DIURNAL DOWN TIME ON TUESDAY. OTHER CHG IS TO CONTINUE TREND OF INCRSG POPS FOR LATE WED NGT- THURSDAY AHEAD OF NEXT SHORT WAVE. MODEL TRENDS CONTINUE TO BE TOWARD A MORE VIGOROUS WAVE WITH AN ORIENTATION MORE CONDUCIVE TO STRONGER VORTICITY ADVECTION. ASSD WIND MAX LOOKS MORE SUPPORTIVE OF PERSISTENT...ORGANIZED STORMS. AS A RESULT...HAVE BUMPED UP POPS INTO CHC MENTION. ONLY COMPLICATING FACTOR WILL BE HOW MUCH LLVL FORCING/MOISTURE CONVERGENCE WILL BE AVBL AS COLD FRONT MOVES THROUGH ON THURSDAY. EUROPEAN MODEL FOCUSES DEEPEST MOISTURE INTO OLD FRONTAL BOUNDARY FCST TO STALL FROM SRN PLAINS TO S OF LWR OH VLY. ANYWAY...LATER GUIDANCE WILL LIKELY ADJUST TIMING/INTENSITY OF THIS NEXT SYS SO BELIEVE IT PRUDENT TO JUST GO WITH CHC POPS AND TO MINIMIZE DURATION OF PRECIP MENTION. LITTLE CHG DAYS 6-7 AS PERSISTENCE WOULD SUGGEST ANOTHER SYS PASSING WELL N OF AREA OVER WEEKEND. THEREFORE...WILL KEEP POPS IN MAINLY SAT NIGHT-SUNDAY AS PER HPC GUIDANCE AND COLLABORATION WITH ADJACENT FO/S. MERZLOCK && .AVIATION... 0000 UTC TAFS...MAIN FORECAST QUESTIONS FOR 00Z TAFS CONTINUE TO REVOLVE AROUND CHANCES/TIMING OF CONVECTION LATER THIS EVENING AND AGAIN ON TUESDAY. AREA OF STRONG/SEVERE THUNDERSTORMS HAVE DEVELOPED ACROSS SOUTHERN WI LAST FEW HOURS...IN VICINITY OF WEAK LOW PRESSURE REFLECTION ASSOCIATED WITH MID LEVEL DISTURBANCE AND CONVERGENT BOUNDARIES NOTED IN AFTERNOON SFC ANALYSIS. LOW LEVEL MOISTURE POOLING FROM NORTHEAST IA TO SOUTH CENTRAL WI...WHERE SPC/RUC MESOANALYSIS INDICATES AXIS OF GREATEST INSTABILITY. FARTHER SOUTH...RECENT ACARS SOUNDINGS FROM KORD INDICATE WEAK CAPPING REMAINS IN 800-850 HPA LAYER...WHICH ALONG WITH LACK OF SIGNIFICANT LOW LEVEL CONVERGENCE AND MOISTURE POOLING IS PREVENTING DEVELOPMENT THIS FAR SOUTH/SOUTHEAST AT THIS TIME. WHILE LARGER SCALE FORCING/LOW LEVEL MOISTURE CONSIDERATIONS SHOULD BECOME SOMEWHAT MORE FAVORABLE WITH TIME ACROSS NRN IL THIS EVENING...DIURNAL DECREASE IN LOW LEVEL INSTABILITY WILL LIKELY LIMIT SOUTHEASTWARD EXTENT AND INTENSITY OF CURRENT IA/WI ACTIVITY. THUS THINKING OF PREVIOUS FORECAST REMAINS VALID...WITH IDEA OF WEAKENING LINE/AREA OF CONVECTION EVENTUALLY SAGGING SOUTHEAST LATER THIS EVENING. CONFIDENCE IN COVERAGE AND TIMING SUPPORT MAINTAINING VCTS FOR NOW AND WILL MONITOR PROGRESS OF CURRENT ACTIVITY FOR POSSIBLE UPGRADE TO TEMPO/PREVAILING MENTION IF NEEDED. COLD FRONT WHICH LAGS CURRENT CONVECTION ACROSS UPPER MIDWEST IS PROGGED TO SAG ACROSS FORECAST AREA ON TUESDAY. AGAIN SOME UNCERTAINTY EXISTS WITH COVERAGE/TIMING OF CONVECTION ON TUESDAY AND THIS WILL BE AT LEAST SOMEWHAT DEPENDANT ON EVOLUTION OF TONIGHTS STORMS. APPEARS AS THOUGH BEST INSTABILITY WILL EVENTUALLY MOVE SOUTH OF TERMINALS BY MID/LATE AFTERNOON HOURS SO FOR NOW HAVE AGAIN MAINTAINED IDEA OF PREVIOUS TAFS WHICH APPEARS TO HAVE THIS WELL IN HAND. WINDS FROM SOUTHWEST TO DIMINISH AOB 10 KTS THIS EVENING...THEN BECOME WEST/NORTHWEST AROUND 10 KNOTS DURING TUESDAY AFTERNOON. OF COURSE CONVECTIVE OUTFLOW MAY MAKE DIRECTION MORE VARIABLE. RATZER && .MARINE... 212 PM CDT A COLD FRONT EXTENDING SOUTH AND SOUTHWEST FROM LOW PRESSURE IN ONTARIO WILL MOVE ACROSS NORTHERN LAKE MICHIGAN OVERNIGHT AND THE SOUTHERN PART DURING TUESDAY. SOUTH AND SOUTHWEST WINDS WILL CONTINUE TO PICK UP TO 10 TO 20 KT DURING THE REST OF THIS AFTERNOON AND TONIGHT AS THE FRONT APPROACHES. HIGH PRESSURE GRADUALLY MOVES ACROSS THE MIDWEST TUESDAY NIGHT AND WEDNESDAY. LOW PRESSURE WILL MOVE UP THE OHIO VALLEY THURSDAY NIGHT AND FRIDAY. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 336 PM CDT MON JUL 27 2009 ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 282045- WINNEBAGO-BOONE-MCHENRY-LAKE ILLINOIS-OGLE-LEE-DE KALB-KANE- DUPAGE-COOK-LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON- IROQUOIS-FORD-LAKE INDIANA-PORTER-NEWTON-JASPER-BENTON- 336 PM CDT MON JUL 27 2009 /436 PM EDT MON JUL 27 2009/ THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS... NORTHEAST ILLINOIS AND NORTHWEST INDIANA. .DAY ONE...TONIGHT. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT...MAINLY ALONG AND WEST OF INTERSTATE 39. DISCUSSION: THUNDERSTORMS ARE EXPECTED TO ERUPT LATE THIS AFTERNOON AND EARLY THIS EVENING OVER IOWA AND SOUTHERN MINNESOTA AHEAD OF AN APPROACHING COLD FRONT. THESE SHOWERS AND STORMS ARE THEN FORECAST TO MOVE SOUTHEASTWARD ACROSS NORTHERN ILLINOIS OVERNIGHT...AND ACROSS NORTHWEST INDIANA AND EAST CENTRAL ILLINOIS ON TUESDAY. GIVEN THE TIMING OF THESE THUNDERSTORMS...AND RATHER WEAK FORCING...THE THREAT OF WIDESPREAD SEVERE WEATHER APPEARS MINIMAL AT THIS TIME. HOWEVER...A FEW OF THE STORMS MAY BE STILL BE SEVERE LATER EVENING AS THEY ENTER NORTHWEST AND NORTH CENTRAL ILLINOIS. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY. THUNDERSTORMS WILL LIKELY BE ONGOING ALONG THE FRONT OVER NORTHERN ILLINOIS AND NORTHWEST INDIANA TUESDAY MORNING. STORMS MAY RE INTENSIFY TUESDAY AFTERNOON AND EVENING OVER SOUTHERN PORTIONS OF THE OUTLOOK AREA. THUNDERSTORMS ARE ALSO POSSIBLE THURSDAY INTO THURSDAY NIGHT...AND AGAIN SATURDAY INTO EARLY SUNDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NECESSARY THROUGH TONIGHT. && COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO LMZ740>745-282045- WINTHROP HARBOR TO WILMETTE HARBOR- WILMETTE HARBOR TO NORTHERLY ISLAND- NORTHERLY ISLAND TO CALUMET HARBOR-CALUMET HARBOR TO GARY- GARY TO BURNS HARBOR-BURNS HARBOR TO MICHIGAN CITY- 336 PM CDT MON JUL 27 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS NEARSHORE WATERS OF LAKE MICHIGAN AND THE INDIANA NEARSHORE WATERS OF LAKE MICHIGAN. .DAY ONE...TONIGHT. THUNDERSTORMS ARE LIKELY TONIGHT...ESPECIALLY AFTER MIDNIGHT. SOME STORMS MAY PRODUCE WIND GUSTS TO 35 KNOTS. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY. THUNDERSTORMS ARE LIKELY TUESDAY MORNING. THERE IS ALSO A CHANCE OF THUNDERSTORMS THURSDAY...AND AGAIN SATURDAY INTO EARLY SUNDAY. && COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868- 870-872-874-876-878-282045- LAKE MICHIGAN FROM MICHIGAN CITY IN TO ST. JOSEPH MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM SEUL CHOIX POINT TO ROCK ISLAND PASSAGE 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN SOUTH OF A LINE FROM SEUL CHOIX POINT TO THE MACKINAC BRIDGE AND NORTH OF A LINE FROM CHARLEVOIX MI TO SOUTH FOX ISLAND 5 NM OFFSHORE- LAKE MICHIGAN FROM CHARLEVOIX TO POINT BETSIE MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM POINT BETSIE TO MANISTEE MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM ROCK ISLAND PASSAGE TO STURGEON BAY WI- LAKE MICHIGAN FROM STURGEON BAY TO TWO RIVERS WI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM TOW RIVERS TO SHEBOYGAN WI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM SHEBOYGAN TO PORT WASHINGTON WI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM PORT WASHINGTON TO NORTH POINT LIGHT WI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM NORTH POINT LIGHT TO WIND POINT WI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM WIND POINT WI TO WINTHROP HARBOR IL 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM WINTHROP HARBOR TO WILMETTE HARBOR IL 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM WILMETTE HARBOR IL TO MICHIGAN CITY IN 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM PENTWATER TO MANISTEE MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM WHITEHALL TO PENTWATER MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM GRAND HAVEN TO WHITEHALL MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM HOLLAND TO GRAND HAVEN MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM SOUTH HAVEN TO HOLLAND MI 5 NM OFFSHORE TO MID LAKE- LAKE MICHIGAN FROM ST. JOSEPH TO SOUTH HAVEN MI 5 NM OFFSHORE TO MID LAKE- 336 PM CDT MON JUL 27 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE OPEN WATERS OF LAKE MICHIGAN. .DAY ONE...TONIGHT. THUNDERSTORMS ARE LIKELY TONIGHT. SOME STORMS MAY PRODUCE WIND GUSTS IN EXCESS OF 35 KNOTS. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY. THUNDERSTORMS ARE LIKELY TUESDAY. THERE IS ALSO A CHANCE OF THUNDERSTORMS THURSDAY INTO THURSDAY NIGHT...AND AGAIN SATURDAY AND SATURDAY NIGHT. && COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO MERZLOCK
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
957 PM CDT MON JUL 27 2009
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0949 PM HAIL 5 NW POLO 42.04N 89.65W
07/27/2009 E0.50 INCH OGLE IL CO-OP OBSERVER
DIME SIZE HAIL. VERY HEAVY RAINFALL. ESTIMATED WINDS AT
40 TO 45 MPH.
&&
BNThe Quad Cities radar (KDVN), 113 km away, was scanning. The volume nearest the first event began at 03:04 UTC.
1 thunderstorm wind, 1 high wind. Local standard time, as filed.
An eight inch diameter tree limb was blown down onto a house on 4th Street causing minor damage. Live power lines were blown down on 2nd Street.
A wind gust to 58 mph was measured 2 miles west southwest of Elgin.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2009Every state in 2009This day in weather historyWarnings in Illinois, July 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: 186334, 186336.