Severe Thunderstorm Warning 33, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
322 PM CDT FRI MAY 30 2008

.DISCUSSION...
320 PM CDT

IN THE NEAR TERM...MAIN FOCUS WILL BE ON SEVERE WEATHER POTENTIAL
THROUGH THIS EVENING. TWO DISTINCT AREAS OF CONCERN WILL NEED TO
BE MONITORED OVER THE NEXT SEVERAL HOURS. THE FIRST OF THESE AREAS
IS ACROSS FAR SOUTHERN PORTIONS OF THE CWA WHERE SURFACE BASED
CONVECTION WILL BECOME INCREASINGLY LIKELY. PLEASE SEE BELOW
MESOSCALE DISCUSSION FOR FURTHER DETAILS REGARDING CONVECTIVE
SCENARIO FOR THIS EVENING. THE FIRST AREA IS ACROSS SOUTHERN
PORTIONS OF THE FORECAST AREA CURRENTLY UNDER A TORNADO WATCH
WHERE POTENTIAL FOR SURFACE BASED CONVECTION IS INCREASING. STILL
CONCERN FOR POTENTIAL REDEVELOPMENT FURTHER BACK TO THE WEST AS
THE UPPER TROUGH ACROSS THE NORTHERN PLAINS MOVES INTO THE UPPER
MS RIVER VALLEY. FOR FURTHER DETAIL CONCERNING SHORT TERM
CONVECTIVE POTENTIAL PLEASE SEE CONVECTIVE DISCUSSION BELOW.

HAVE NOT MADE SIGNIFICANT CHANGES TO THE FORECAST TODAY...WITH NEW
12Z MODELS IN GENERAL SUPPORT OF GOING FORECAST. FORECAST
SOUNDINGS ON SATURADY STILL APPEAR TO ONLY ADVERTISE VERY MARGINAL
INSTABILITY WITH LITTLE IN THE WAY OF FORCING FOR VERTICAL MOTION
AS MID/UPPER LEVEL TROUGH AXIS MOVES OFF TO THE EAST. LAKE COOLING
TOMORROW IS EXPECTED MAINLY FOR NORTHWEST INDIANA COUNTIES WITH
NORTHWEST WINDS BEHIND SURFACE TROUGH PASSAGE. OTHERWISE...AWAY
FROM THE LAKE...TEMPERATURES SHOULD RANGE FROM UPPER 70S NORTH TO
LOWER 80S SOUTH. NEXT CHANCE OF PRECIP EXPECTED BY LATER MONDAY AS
WEST EAST BOUNDARY DEVELOPS ACROSS THE MID MS RIVER VALLEY. MODELS
DEVIATE QUITE A BIT IN REGARDS TO EVOLUTION OF A PACIFIC UPPER
LEVEL TROUGH FOR MID WEEK. GFS TAKES THIS UPPER TROUGH WITH MORE
AMPLITUDE INTO THE PLAINS TUESDAY NIGHT WHILE ECMWF TAKES THE
UPPER TROUGH MUCH FURTHER NORTH. WITH WEST EAST BOUNADRY LIKELY IN
THE VICINITY THROUGH MUCH OF THE MIDDLE AND END OF NEXT
WEEK...WILL MAINTAIN INHERITED POPS BUT HOLD OFF ON ANY ADDITIONAL
POPS FOR DAY 7 UNTIL MORE CONFIDENCE CAN BE ESTABLISHED.

MARSILI

&&

MESOSCALE CONVECTIVE UPDATE...
220 PM CDT

VERY COMPLEX CONVECTIVE SCENARIO UNFOLDING THIS AFTERNOON.

FIRST...AMPLE INSOLATION AND DESTABILIZATION HAS TAKEN PLACE
SOUTH OF THE TRACK OF THIS MORNINGS DECAYING MCS. IN THIS
AREA...INCLUDING OUR FAR SOUTHERN CWA...ATMOSPHERE IS NOW PRIMED
FOR SFC BASED CONVECTION AND SURFACED BASED STORMS HAVE BEGUN TO
DEVELOP. MODERATE INSTABILITY AND STRONG...THOUGH MOSTLY
UNIDIRECTIONAL...SHEAR WILL SUPPORT ORGANIZED SEVERE THUNDERSTORMS
THIS AFTERNOON. CONVECTIVE MODE SHOULD EVOLVE TO MORE SHORT
LINES/LEWPS WITH TIME...THOUGH SOME SUPERCELLULAR STRUCTURES ARE
CERTAINLY POSSIBLE FOR A TIME. EVEN IF SUPERCELLS DEVELOP...LCL
HEIGHTS ARE SOMEWHAT HIGH AND LOW LEVEL SHEAR PRETTY WEAK FOR ANY
SUBSTANTIAL TORNADO THREAT. THE PRIMARY THREAT WITH THIS SURFACE
BASED CONVECTION SHOULD BE LARGE HAIL/DAMAGING WINDS.

SECOND AREA OF CONCERN IS BAND OF ELEVATED CONVECTION DEVELOPING
FROM WC ILLINOIS ENE INTO NORTHWEST INDIANA. NOT TOO SURE WHY THIS
CONVECTION HAS BEEN STEADILY INCREASING...BUT GIVEN STRONG
STABILITY OF SURFACE BASED PARCELS NEAR THIS CONVECTION AND THE
FACT ITS DEVELOPING OVERTOP A STRATUS DECK...IT IS LIKELY
ELEVATED AND THE ONLY POSSIBLE SVR THREAT ITD POSE IS A MARGINAL
HAIL THREAT UNLESS IT MOVES INTO AN AREA MORE PRIMED FOR BOUNDARY
LAYER BASED CONVECTION AND UPDRAFTS BECOME ROOTED IN BOUNDARY LAYER.

THIRD AREA OF CONCERN IS WITH GROWING AREA OF TOWERING CU OVER
NORTHWEST ILLINOIS INTO EASTERN IOWA AHEAD OF WHAT APPEARS TO BE
A PRE-FRONTAL TROUGH/CONVERGENCE ZONE. AIRMASS APPEARS TO BE
RECOVERING QUICKLY FROM EARLY MORNING CONVECTION WITH MODIFIED
ACARS SOUNDINGS SUGGESTING UPWARDS OF 1500 J/KG OF SB CAPE WITH
LITTLE INHIBITION. STRONG SHEAR AND MODERATE INSTABILITY WOULD
AGAIN SUPPORT LARGE HAIL/DAMAGING WIND THREAT SHOULD CONVECTIVE
INITIATION OCCUR IN THIS AREA OR ALONG THE OTHER AREA OF
DEVELOPING SFC BASED CU OVER NORTHERN IOWA. WHILE INSTABILITY HAS
BEEN SLOWER TO DEVELOP IN THIS AREA...THE ARRIVAL OF ADDED FORCING
FROM SHORTWAVE APPROACHING FROM THE NORTHWEST MAY ENHANCE ASCENT
AND CREATE A MORE CONVECTIVE-FRIENDLY ENVIRONMENT IN THIS REGION
LATER THIS AFTERNOON INTO THIS EVENING.

IZZI

&&

.AVIATION...

1800 UTC TAFS...
WAKE LOW INDUCED WINDS DIMINISHING PAST 30-60 MINUTES WITH RFD
BELOW 20 KTS FOR SOME TIME AND ORD NOW ONLY G23 KTS. MDW G29 KTS
AND WAUKEGAN HARBOR STATION GUSTING 46 KTS AT 1640Z DOWN TO 12KTS
AT 1740Z. SEVERAL REPORTS OF TREE DAMAGE AND OVERTURNED SEMI ON
I-90/U.S. 20 WITH EARLIER NON CONVECTIVE WINDS ASSOCIATED WITH
WAKE LOW ENHANCED BY ISALOBARIC COMPONENT WITH STRONG PRESSURE
FALLS ALONG THE IL/WI BORDER NORTHEASTWARD.

ONGOING CONVECTION WILL CONTINUE TO DECAY THIS AFTERNOON EXCEPT
FOR EXPECTED RE-INTENSIFICATION TO THE SOUTHEAST WHERE SURFACE
BASED INSTABILITY HAS BEEN INCREASING AND LOW LEVEL MOISTURE
POOLING WITH DEW PTS CLIMBING INTO THE MID 60S. FOR NORTHERN IL
AIRPORTS ONGOING PRECIP WILL SLIDE OFF TO THE EAST AND SOUTH FOR A
BREAK LATER THIS AFTERNOON AS LOW-MID CLOUDS SCATTER OUT IN
ADVANCE OF COLD FRONT STILL BACK OVER CENTRAL IOWA.

EXPECT THUNDERSTORMS TO RE-FIRE LATER IN THE HEAT OF THE AFTERNOON
ALONG AND AHEAD OF THE COLD FRONT AND MOVE EAST INTO NORTH CENTRAL
AND NORTHEAST ILLINOIS THIS EVENING... GENERALLY BETWEEN 00Z AND
06Z. SEVERE THREAT EXISTS WITH THESE STORMS WITH HAIL UP TO THE
SIZE OF QUARTERS AND WIND GUSTS TO 60KTS.

ED F

&&

.MARINE...
224 AM CDT

MAIN CONCERN OVER THE WATERS OF LAKE MICHIGAN WILL BE MAINLY TODAY
AS A LOW PRESSURE SYSTEM TRACKS ACROSS THE CENTRAL PLAINS AND ON
UP INTO NORTHERN WISCONSIN. THUNDERSTORMS ARE EXPECTED TO DEVELOP
OUT TO THE EAST OF THIS SYSTEM...WHICH AT TIMES COULD PRODUCE SOME
LOCALLY STRONG WINDS ACROSS THE LAKE. RAIN AND STORMS HAVE ALREADY
DEVELOPED FROM WISCONSIN TRACING BACK ALL THE WAY INTO NEBRASKA.
THESE OFF AND ON STORMS ARE EXPECTED TO CONTINUE UNTIL FRIDAY
EVENING...MORESO ACROSS THE SOUTHERN HALF OF THE LAKE. OFFSHORE
WINDS WILL LIKELY BE GUSTING TO AROUND 20-25 KNOTS WITH SOME
HIGHER GUSTS POSSIBLE...PARTICULARLY WITH ANY STORMS THAT RUMBLE
THROUGH. WILL LIKELY BE GOING WITH A SMALL CRAFT ADVISORY TODAY
FOR THESE GUSTY WINDS.

HALBACH

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 6 PM CDT THIS AFTERNOON FOR LMZ740-
     LMZ741-LMZ742-LMZ743-LMZ744-LMZ745.

&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 PM CDT FRI MAY 30 2008

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1145 AM     NON-TSTM WND DMG WAUKEGAN                42.37N 87.87W
05/30/2008                   LAKE               IL   AMATEUR RADIO

            ESTIMATED WIND GUSTS OF 55 MPH WITH TREES AND LARGE
            BRANCHES DOWN NEAR LEWIS AVENUE.

&&

RODRIGUEZ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
214 PM CDT FRI MAY 30 2008

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1015 AM     NON-TSTM WND DMG 3 E ROCKFORD            42.27N 89.00W
05/30/2008                   WINNEBAGO          IL   TRAINED SPOTTER

            LARGE TREE DOWN ACROSS WOODLAND DRIVE.

&&

RODRIGUEZ

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
227 PM CDT FRI MAY 30 2008

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1015 AM     NON-TSTM WND DMG 3 E ROCKFORD            42.27N 89.00W
05/30/2008                   WINNEBAGO          IL   TRAINED SPOTTER

            LARGE TREE DOWN ACROSS WOODLAND DRIVE.

1015 AM     NON-TSTM WND DMG ROCKFORD                42.27N 89.06W
05/30/2008                   WINNEBAGO          IL   EMERGENCY MNGR

            ROOF BLOWN OFF A BUILDING AT ROCKFORD AIRPORT.

1015 AM     NON-TSTM WND GST ROCKFORD AIRPORT        42.20N 89.10W
05/30/2008  M63.00 MPH       WINNEBAGO          IL   ASOS

            MEASURED WINDS HAVE BEEN CONTINUOUSLY BETWEEN 45 AND 55
            KNOTS FOR OVER 15 MINUTES NOW. EVENT CONTINUES AS OF 1033
            AM CDT.

1045 AM     NON-TSTM WND DMG 2 SE MCHENRY            42.32N 88.26W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            WIND GUSTS UP TO AROUND 40 MPH WITH TREE LIMBS AND POWER
            LINES DOWN.

1050 AM     NON-TSTM WND GST ISLAND LAKE             42.28N 88.20W
05/30/2008  M64.00 MPH       MCHENRY            IL   MESONET

1055 AM     NON-TSTM WND DMG ROCKFORD                42.27N 89.06W
05/30/2008                   WINNEBAGO          IL   TRAINED SPOTTER

            SMALL LIMBS DOWN NEAR INTERSECTION OF I90 AND BUSINESS
            US-20.

1055 AM     NON-TSTM WND DMG WOODSTOCK               42.31N 88.44W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            MEASURED WIND GUST OF 57 MPH WITH 4 FOOT IN DIAMETER TREE
            DOWN AND MULTIPLE POWER LINES DOWN.

1100 AM     NON-TSTM WND GST 6 SSE BEACH PARK        42.35N 87.81W
05/30/2008  M58.00 MPH       LMZ740             IL   C-MAN STATION

1100 AM     NON-TSTM WND DMG WOODSTOCK               42.31N 88.44W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            TREE ON HOUSE NEAR BIRCH AND JULIE STREET. INJURIES
            REPORTED.

1100 AM     NON-TSTM WND DMG WOODSTOCK               42.31N 88.44W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            UNKNOWN AMOUNT OF INJURIES ASSOCIATED WITH FALLING DEBRIS
            NEAR INTERSECTION OF KISHWAUKEE VALLEY AND ROSE FARM
            STREET.

1100 AM     NON-TSTM WND DMG WOODSTOCK               42.31N 88.44W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            LIGHTPOLE IN INTERSECTION OF RT. 47 AND RT. 120.

1100 AM     NON-TSTM WND DMG WOODSTOCK               42.31N 88.44W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            TREE ON HOUSE NEAR BIRCH AND JULIE STREET.

1102 AM     NON-TSTM WND GST MUNDELEIN               42.27N 88.00W
05/30/2008  M51.00 MPH       LAKE               IL   EMERGENCY MNGR

1110 AM     NON-TSTM WND DMG LIBERTYVILLE            42.28N 87.97W
05/30/2008                   LAKE               IL   TRAINED SPOTTER

            TREE DOWN ON ELLIS AVENUE AT WINCHESTER RD.

1110 AM     NON-TSTM WND DMG MARENGO                 42.25N 88.60W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            LARGE TREE DOWN NEAR FOREST ST. AND HWY 23.

1132 AM     NON-TSTM WND DMG MARENGO                 42.25N 88.60W
05/30/2008                   MCHENRY            IL   TRAINED SPOTTER

            OVERTURNED SEMI ON RT. 20 AND I90.

1136 AM     NON-TSTM WND GST ROCHELLE                41.92N 89.06W
05/30/2008  M53.00 MPH       OGLE               IL   AWOS

            REPORT FROM ROCHELLE AIRPORT.

1145 AM     NON-TSTM WND DMG WAUKEGAN                42.37N 87.87W
05/30/2008                   LAKE               IL   AMATEUR RADIO

            ESTIMATED WIND GUSTS OF 55 MPH WITH TREES AND LARGE
            BRANCHES DOWN NEAR LEWIS AVENUE.

1145 AM     NON-TSTM WND GST GURNEE                  42.38N 87.94W
05/30/2008  M61.00 MPH       LAKE               IL   MESONET

            MEASURED AT SCHOOL MESONET.

1153 AM     NON-TSTM WND DMG MALTA                   41.93N 88.86W
05/30/2008                   DE KALB            IL   LAW ENFORCEMENT

            TREES DOWN.

1155 AM     NON-TSTM WND GST DE KALB                 41.93N 88.75W
05/30/2008  M52.00 MPH       DE KALB            IL   AWOS

            MEASURED AT DE KALB AIRPORT.

1200 PM     NON-TSTM WND DMG STREAMWOOD              42.02N 88.17W
05/30/2008                   COOK               IL   TRAINED SPOTTER

            ESTIMATED 55 MPH GUSTS WITH SMALL TREE LIMBS DOWN.

1200 PM     NON-TSTM WND GST 2 E CHICAGO             41.88N 87.59W
05/30/2008  M58.00 MPH       LMZ741             IL   C-MAN STATION

            MEASURED AT HARRISON-DEVER CRIB.

&&
EVENT IS ONGOING AND REPORTS MAY BE ADDED LATER AS THEY ARE RECEIVED.

RODRIGUEZ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
246 PM CDT FRI MAY 30 2008

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1130 AM     NON-TSTM WND DMG LIBERTYVILLE            42.28N 87.97W
05/30/2008                   LAKE               IL   AMATEUR RADIO

            ESTIMATED WIND GUST 55MPH. 30 FOOT TREE DOWN ACROSS POWER
            LINES NEAR RT. 137 AND DES PLAINES RIVER.

&&

WOJTOWICZ