Severe Thunderstorm Warning 201, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
320 PM CDT MON SEP 4 2006

.DISCUSSION...
320 PM CDT

H5 LOW CONITNUES ON TRACK THIS AFTERNOON. DIRUNRAL HEATING HAS
ENHANCED DEVELOPMENT OF SEVERAL THUNDERSTORMS IN NORTHWEST PORTION
OF FORECAST AREA. SMALL HAIL AND HEAVY RAIN APPEAR TO BE THE MAIN
TRHEAT FROM THESE STORMS AT THIS TIME.

CENTER OF UPPER LOW WILL MOVE ACROSS FORECASTS AREA TUESDAY WITH
SHOWERS LIKELY. EXPECT SYSTEM TO BE FAR ENOUGH EAST BY END OF DAY
THAT PRECIP SHOULD END BETWEEN 00Z AND 06Z. UPPER FLOW THEN BEGINS
TO BACK ALLOWS TEMPS TO WARM THE UPPER 70S BEFORE NEXT SYSTEM DROPS
SOUTHEAST OUT OF CANADA LATE IN THE WEEK. FRONTAL SYSTEM WILL
DEVELOP WITH UPPER TROUGH AND MOVE ACROSS FORECAST AREA LATE FRIDAY
AND SATURDAY.

&&

.AVIATION DISCUSSION FOR 18Z TAFS...
1230 PM CDT

THE UPPER LOW OVER ERN IOWA WILL MOVE VERY SLOWLY EWD OVER THE NEXT
SEVERAL HOURS.  SKIES HAVE GONE BKN OVER NCNTRL IL...ALLOWING SOME
SFC INSOLATION AND INCREASING LOW-LVL INSTABILITY. SCT SHRA AND ISOL
TS HAVE ALREADY DVLPD JUST WEST OF RFD AND SHOULD CONTINUE TO DVLP
EWD DURG THE AFTN HOURS.  FOR THE REMAINDER OF THE AFTERNOON AND
EARLY EVENING HOURS...TS AS WELL AS CIGS WILL BE PROBLEMATIC.  GIVEN
THE SLOW EWD PROGRESSION OF THE UPR LOW...FEEL THAT TS ARE LIKELY TO
AFFECT THE TAF SITES...BUT INDIVIDUAL CELLS SHUD BE SCT AND WL BE
MOVING NWD AT ARND 20KT.  SO...WILL GO WITH A TEMPO GROUP FOR TS TO
TAKE INTO CONSIDERATION THE SPEED AND SCT NATURE OF THE CELLS.
AFTER SUNSET...TS LIKELYHOOD SHOULD DECREASE AS THE MAIN SOURCE OF
INSTABILITY IS THE COLD POOL ALOFT ASSOCIATED WITH THE UPPER LOW.
WITH SFC COOLING AFTER SUNSET...THE DEEP LAYER INSTABILITY SHOULD
DECREASE.  TWD MORNING...VSBY WILL BECOME THE AREA OF CONCERN.  WITH
THE RAIN THAT OCCURRED LAST NIGHT AND ANY ADDITIONAL RAINFALL LATER
TODAY...THE LOW LEVELS WILL REMAIN QUITE MOIST.  WINDS ARE EXPECTED
TO REMAIN VERY LIGHT DUE TO THE VERY WEAK PRESSURE GRADEINT AT THE
SFC.  SO AT THE VERY LEAST...MVFR VIS IS EXPECTED WITH FURTHER
REDUCTIONS TO IFR POSSIBLE.  BY LATE MORNING...FCST RH TIMESECTIONS
ARE INDICATING THAT SKIES SHOULD GO SCT.  THE REGION WILL SHIFT TO A
MORE COLD ADVECTIVE PATTERN UNDER NLY WINDS AROUND THE BACK SIDE OF
THE UPPER FLOW.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LM...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
430 PM CDT MON SEP 4 2006

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-050930-
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DU PAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
430 PM CDT MON SEP 4 2006

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL
AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA.

.DAY ONE... TONIGHT

SEVERE THUNDERSTORMS ARE EXPECTED TO CONTINUE ACROSS NORTH CENTRAL
AND NORTHEASTERN ILLINOIS THROUGH AROUND 700 PM CDT.  THE STORMS
WILL GENERALLY REMAIN NORTH OF INTERSTATE 80...HOWEVER ISOLATED
SEVERE THUNDERSTORMS ARE POSSIBLE SOUTH OF INTERSTATE 80 NEAR THE
ILLINOIS RIVER.  THE GREATEST THREAT FROM THESE STORMS IS LARGE HAIL
UP TO GOLF BALL SIZE...HOWEVER...FUNNEL CLOUDS HAVE BEEN OBSERVED
THIS AFTERNOON AND ISOLATED TORNADOES ARE POSSIBLE.

THUNDERSTORMS ARE EXPECTED TO MOVE INTO FAR NORTHWESTERN INDIANA BY
AROUND 700 PM CDT.  THE STORMS SHOULD CONTINUE THROUGH AROUND 1000
PM CDT.  SOME OF THESE THUNDERSTORMS MAY BE SEVERE PRODUCING LARGE
HAIL.

.DAYS TWO THROUGH SEVEN... TUESDAY THROUGH SUNDAY

THERE IS A CHANCE OF THUNDERSTORMS FRIDAY AND FRIDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE NECESSARY THROUGH EARLY TONIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)

LMZ740>745-766-050930-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
430 PM CDT MON SEP 4 2006

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS
AND INDIANA WATERS OF LAKE MICHIGAN.

.DAY ONE... TONIGHT

THUNDERSTORMS ARE EXPECTED TO MOVE OVER SOUTHERN LAKE MICHIGAN BY
AROUND 700 PM CDT THIS EVENING. THERE IS A SLIGHT RISK THAT SOME OF
THE THUNDERSTORMS MAY BE SEVERE. THE PRIMARY THREAT IS HAIL...
FREQUENT LIGHTNING AND WIND GUSTS TO 30 KNOTS.

ISOLATED WATERSPOUTS ON THE SOUTHERN HALF OF LAKE MICHIGAN TONIGHT.

.DAYS TWO THROUGH SEVEN... TUESDAY THROUGH SUNDAY

ISOLATED WATERSPOUTS ON THE SOUTHERN HALF OF LAKE MICHIGAN THROUGH
TUESDAY AFTERNOON.

THERE IS A CHANCE OF THUNDERSTORMS FRIDAY AND FRIDAY NIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
338 PM CDT MON SEP 04 2006

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

0326 PM     HAIL             ROCKFORD                42.27N 89.06W
09/04/2006  U0.88 INCH       WINNEBAGO          IL   TRAINED SPOTTER

            QUARTER INCH ACCUMULATION OF NICKEL SIZED HAIL ON THE
            NORTHEAST SIDE OF ROCKFORD

&&

CGITRO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 PM CDT MON SEP 04 2006

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

0335 PM     HAIL             ROCKFORD                42.27N 89.06W
09/04/2006  E0.75 INCH       WINNEBAGO          IL   TRAINED SPOTTER

            3/4 INCH HAIL ON THE NORTHEAST SIDE OF ROCKFORD

&&

CGITRO