Flash Flood Warning 24, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
700 PM CDT WED JUL 18 2007

.DISCUSSION...220PM
COMPLEX AND POTENTIALLY POTENT SITN CONTINUING WITH ASSORTED THREATS
DURING THE NOCTURAL HRS. LAST NIGHTS RAIN FROM OGLE AND LEE COUNTIES
SEWD INTO LASALLE AND LIVINGSTON COUNTIES MAKE THESE AREAS VERY
VULNERABLE TO ADDITIONAL RAIN AND SUBSEQUENT FLOODING TNGT AND
THURSDAY.

UPPER TROUGH WHICH HAS SUPPORTED SEWD MOVING MCS SYSTEMS PAST 2 DAYS
WILL BE BUCKLING LATER TONIGHT AND THURSDAY WITH SHORT WAVE PIVOTING
SWD FROM MANITOBA THROUGH THE MIDWEST DRAGGING COOLER AIR INTO
REGION LATER THURSDAY.  SECOND IMPULSE IS MOVING OUT OF THE WESTERN
DAKS THIS AFTN AND WILL SLIDE ESE AHEAD OF HIGHER AMPLITUDE DEVELMT.
THIS LATTER SYSTEM IS NOW BEGINNING TO INTERACT WITH BAROCLINIC ZONE
STRETCHING FROM SE SDAK ACROSS NRN IOWA INTO SRN WISC.  VERY MOSIT
AIR SOUTH OF THIS BOUNDARY WILL BE THE FUEL FOR TSTMS/MCS EXPECTED
TO FORM OVER WRN IOWA OR SW MINN DURING THE LATE AFTN.  WHOLE FLOW
PATTERN IS NOW MORE E-W SO EXPECT ANY ORGANIZED CONVECTION TO MOVE
TWD NRN ILL DURING THE NIGHT.  AVAILABLE ACARS SOUNDINGS AND MODEL
SOUNDINGS FROM ORD WESTWARD ACROSS IOWA SHOW A CONTINUED VERY DEEP
NEARLY ADIABATIC LAPSE RATE IN AN ELEVATED ZONE ABOVE 850MB.
POCKETS OF DRY AIR ALSO SEEN IN THESE WHICH SUGGESTS BOTH STRONG
BUOYANCY AS WELL AS WIND POTENTIAL.

AT THIS POINT EXPECT CONVECTION SHOULD ORGANIZE ALONG THE IOWA/MINN
BORDER MORE OR LESS..AND TRACK EAST OR ESE INTO NRN ILLINOIS DURING
THE LATE EVENING OR AFTER MIDNIGHT. CANNOT IGNORE SLOW APPROACH OF
MAIN CANADIAN FRONT INTO NRN WISC WHICH MAY INITIATE ITS OWN ZONE OF
CONVECTION BUT AT THIS POINT THE SHORT WAVE ENHANCED CONVECTION FROM
THE WEST IS OF MORE CONCERN.

FLOODING...SOUTH AND WESTERN PORTIONS OF CWA SATURATED. DIFFERENCE
IN TONIGHTS SITUATION IS A BETTER INFLOW EXPECTED ACROSS IOWA AND
NRN MISSOURI. 925MB AND 850MB MODEL WINDS ARE WELL ORGANIZED DURING
THE NIGHT WITH UP TO 35KTS SEEN ON THE NAM80. THUS LOW LEVEL FORCING
OF MOIST AIR INTO CONVECTIVE CLUSTERS MAY IMPROVE RAIN PRODUCTION.
WILL LEAVE FFA AS IS FOR NOW IT BOTH TIME...12Z THUR...AND AREA.
PRECIP WILL FADE OFF TO THE SE THUSDAY AFTERNOON.

FROM FRIDAY ONWARD ALL GUIDANCE SUGGESTS A LARGE SLOW MOVING
ANTICYCLONE WILL PARK OVER THE MIDWEST WITH SLOW MODIFICATION OF
TEMPS AFTER SUNDAY. NO READON TO ARGUE AS UPPER AIR PATTERN FEATURES
A HIGH AMPLITUDE RIDGE FROM THE PLAINS INTO THE MIDWEST.  KML

&&

.AVIATION...

00Z TAFS...AREA OF THUNDERSTORMS DEVELOPING ACROSS FAR NORTHERN IL
ACROSS THE PAST HR AND CONINTUING TO EXPAND TO THE SE. HAVE CARRIED
TEMPO TS FOR THE FIRST FEW HRS WITH THE EXPECTATION THAT THIS
ACTIVITY WOULD BE PUSHING EAST OF THE TERMINALS. BUT DEVELOPMENT
CONTINUES ACROSS NW IL/SW WI SO THIS WILL LIKELY NEED TO BE ADJUSTED
AS THE EVENING GOES ON. SECOND TEMPO TS WAS FOR THE MAIN LINE OF TS
ACROSS IA WHICH...NOW APPEARS LIKE IT WILL PUSH SOUTHEAST...MAINLY
SOUTH OF THE TAFS DURING THE LATE EVENING AND EARLY MORNING HRS BUT
RAIN WITH EMBEDDED TS STILL LOOKS REASONABLE. PRECIP CHANCES AROUND
SUNRISE QUESTIONABLE AND WILL NEED TO BE LOOKED AT WITH NEXT SET OF
TAFS. FRONT MOVES THRU THE AREA LATE THURSDAY MORNING SHIFTING WINDS
NORTH...THEN SPEEDS INCREASE IN THE AFTERNOON WITH GUSTS 20-25KTS.
CMS

&&

.MARINE DISCUSSION...

245 PM CDT

A WEAK AND DIFFUSE FRONTAL TROUGH FROM SOUTHERN
MINNESOTA...SOUTHEASTWARD ACROSS SOUTHERN LAKE
MICHIGAN WILL REMAIN STATIONARY THROUGH THIS EVENING. MEANWHILE...A
LOW PRESSURE CENTER OVER NEBRASKA WILL MOVE EASTWARD ACROSS THE
UPPER MIDWEST TONIGHT...TO A POSITION NEAR DETROIT BY THURSDAY
MORNING.  AS THIS LOW MOVES EAST OF THE LAKE TONIGHT...A
TRAILING COLD FRONT WILL SURGE SOUTHWARD ACROSS LAKE
MICHIGAN...CLEARING THE SOUTH END OF THE LAKE EARLY THURSDAY
MORNING. IN THE WAKE OF THIS FRONT...A HIGH PRESSURE CENTER WILL
BUILD ACROSS MINNESOTA AND INTO THE WESTERN GREAT LAKES THURSDAY AND
FRIDAY. THIS WILL CREATE HAZARDOUS CONDITIONS FOR SMALL CRAFT ACROSS
SOUTHERN LAKE MICHIGAN FROM THURSDAY AFTERNOON THROUGH FRIDAY DUE TO
NORTH WINDS IN EXCESS OF 20 KNOTS AND WAVES IN EXCESS OF 5 FEET
THROUGH THE PERIOD.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FLOOD WATCH UNTIL 12Z THURSDAY FOR OGLE...LEE...LA SALLE...
GRUNDY...LIVINGSTON...IROQUOIS AND FORD.
IN...FLOOD WATCH UNTIL 12Z THURSDAY FOR BENTON.
LM...SMALL CRAFT ADVISORY 15Z THURSDAY THROUGH 03Z SATURDAY.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
400 PM CDT WED JUL 18 2007

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
190930-
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-
400 PM CDT WED JUL 18 2007

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

.DAY ONE...TONIGHT.

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS TONIGHT ACROSS MOST
OF NORTHERN ILLINOIS AND A SMALL PORTION OF NORTHWEST INDIANA.
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ELSEWHERE.

THE MODERATE RISK AREA IS ALONG AND SOUTH OF A LINE FROM
ROCKFORD...TO DOWNTOWN CHICAGO...TO PORTAGE INDIANA.

ISOLATED THUNDERSTORMS DURING THE LATE AFTERNOON AND EARLY EVENING
WILL GIVE WAY TO MORE ORGANIZED STORMS MOVING IN FROM THE WEST
TOWARD AND AFTER MIDNIGHT.

THESE STORMS MAY EVOLVE INTO A LINEAR CLUSTER CAPABLE OF PRODUCING
DAMAGING WINDS AS IT MOVES EAST SOUTHEASTWARD INTO NORTHERN ILLINOIS
LATER THIS EVENING.

FLOODING...
HEAVY RAINFALL RESULTING FROM LAST NIGHTS THUNDERSTORMS HAS CAUSED
FLOODING FROM LEE COUNTY ILLINOIS...SOUTHEASTWARD THROUGH THE
PONTIAC AREA.  OVER 5 INCHES OF RAIN WAS REPORTED THROUGH EARLY
THIS MORNING IN THESE AREAS.

DUE TO THE POTENTIAL FOR ADDITIONAL THUNDERSTORM DEVELOPMENT THIS
AFTERNOON AND TONIGHT...THE FLASH FLOOD WATCH FOR SOUTHERN AND
WESTERN PORTIONS OF THE OUTLOOK AREA HAS BEEN EXTENDED UNTIL 7AM
THURSDAY.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

THUNDERSTORMS WILL LIKELY BE ONGOING SOUTH OF THE KANKAKEE AND
ILLINOIS RIVERS THURSDAY MORNING...WITH A CHANCE OF MORNING
THUNDERSTORMS NORTH.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT. MEASUREMENTS OF HEAVY
RAINFALL OR REPORTS OF FLOODING WOULD BE APPRECIATED.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO
WEBPAGE: WEATHER.GOV/CHICAGO

LMZ740>745-766-190930-
WINTHROP HARBOR TO WILMETTE HARBOR IL-
WILMETTE HARBOR TO NORTHERLY ISLAND IL-
NORTHERLY ISLAND TO CALUMET HARBOR IL-
CALUMET HARBOR IL TO GARY IN-
GARY INDIANA TO BURNS HARBOR-
BURNS HARBOR TO MICHIGAN CITY-
LAKE MICHIGAN OPEN WATERS FROM WINTHROP HARBOR IL EASTWARD TO THE
MID POINT OF THE LAKE AND SOUTHWARD TO MICHIGAN CITY MI BEYOND 5 NM
OFFSHORE-
400 PM CDT WED JUL 18 2007

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

.DAY ONE...TONIGHT.

THUNDERSTORMS ARE LIKELY TONIGHT.  SOME OF THESE STORMS MAY BE
SEVERE WITH WIND GUSTS IN EXCESS OF 34 KNOTS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

HAZARDOUS WINDS AND WAVES FOR SMALL CRAFT ARE EXPECTED TO DEVELOP BY
THURSDAY AFTERNOON...AND CONTINUE INTO FRIDAY.  NORTH WINDS
SUSTAINED AROUND 25 KNOTS WILL LIKELY RESULT IN WAVES IN EXCESS OF 6
FEET AND AN INCREASED THREAT OF RIP CURRENTS ALONG THE INDIANA
SHORELINE.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO
WEBPAGE: WEATHER.GOV/CHICAGO

KL

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