Flash Flood and Hail in Illinois, June 4, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
635 AM CDT SAT JUN 4 2005

.DISCUSSION FOR MORNING ZONES/GRIDS...

ESSENTIALLY ONLY MINOR TWEAKS TO GOING FORECAST...WITH MAIN FOCUS ON
PRECIP POTENTIAL AND TIMING THROUGH THIS WEEKEND.

SATELLITE LOOPS AND PROFILER ANALYSIS INDICATING A FEW SHORT WAVE
TROUGHS OF INTEREST ROUNDING BASE OF WESTERN CONUS MEAN TROUGH.
FIRST ONE IS LIFTING NORTHEAST ACROSS PLAINS OF EASTERN KANSAS EARLY
THIS MORNING...WITH ASSOCIATED CONVECTIVE ACTIVITY WRAPPING
NORTHEAST ACROSS WESTERN MO INTO IA. VARIOUS MODELS IN GOOD
AGREEMENT IN MOVING THIS SHORT WAVE TROUGH NORTHEAST INTO UPPER
MIDWEST TODAY...WITH TAIL OF VORT SWIPING FORECAST AREA DURING THE
DAY. HAVE TRIMMED BACK POPS TO ALONG/WEST OF I-39 EARLY THIS
MORNING...AS EASTERN SECTIONS OF FORECAST AREA UNLIKELY TO SEE
EFFECTS OF THIS SYSTEM UNTIL LATER THIS MORNING. ALTHOUGH DEPENDENT
UPON AMOUNT OF SUN THROUGH DEBRIS CLOUDS FROM CONVECTION TO OUR
SOUTHWEST...AIRMASS IS FORECAST BY BOTH NAM/GFS TO BECOME SOMEWHAT
UNSTABLE THIS AFTERNOON WITH NORTHWARD DEVELOPMENT OF SURFACE
WARMFRONT...BOTH INDICATING MODEL SBCAPE VALUES INTO THE 1500 J/KG
RANGE. THUS HAVE SPREAD CHANCE POPS FOR THUNDER EASTWARD ACROSS
FORECAST AREA FROM LATE MORNING ON. 850 HPA TEMPS IN +15
RANGE...WOULD SUPPORT HIGH TEMPS REACHING MID 80S THIS AFTERNOON.

GFS/NAM BOTH INDICATE SOMEWHAT ILL-DEFINED SURFACE WARM FRONT WILL
LIFT NORTH OF THE AREA THIS EVENING...WITH AFFOREMENTIONED SHORT
WAVE TROUGH/VORT AXIS MOVING OUT OF FORECAST AREA BY 00Z. DRY
FORECAST FOR MOST OF OVERNIGHT HOURS...WITH SUMMERLIKE NIGHT IN
HUMID WARM SECTOR AND MIN TEMPS 65 TO 70. NEXT SHORT WAVE
TROUGH...CURRENTLY PUSHING ACROSS CO THIS AM...MOVES ACROSS PLAINS
TONIGHT...BRINGING NEXT CHANCE OF THUNDER TO WESTERN PORTIONS OF
FORECAST AREA TOWARD MORNING. CONVECTION AGAIN EXPECTED TO INITIATE
OVER PLAINS TO THE WEST...WITH ETA FORECAST SOUNDINGS INDICATING
SLOW EASTWARD MOVEMENT AND EVEN SOME BACKBUILDING NOTED IN CORFIDI
PROPAGATION VECTORS FROM ETA SOUNDINGS. GFS DEVELOPS SOME
SUSPICIOUSLY CONVECTIVELY INDUCED VORTICITY MAXIMA THAT WOULD
SUGGEST PRECIP THREAT EARLIER THAN ETA...THOUGH AM DISCOUNTING.

GENERAL SIGNAL FROM VARIOUS MODELS IS THAT HIGHEST CONVECTIVE THREAT
TO BE SUNDAY AFTERNOON/EVENING...IN LOW LEVEL MOISTURE CONVERGENCE
AXIS AHEAD OF COLD FRONT WITH MAIN SHORT WAVE TROUGH APPROACHING
FROM THE WEST. SPC DAY 2 SLGT RISK APPEARS WARRANTED AS SEVERAL
FACTORS SUPPORT ORGANIZED STRONG CONVECTION. MODEL FORECASTS
INDICATE WARM/MOIST MODERATELY UNSTABLE AIRMASS IN PLACE ACROSS CWA
WITH SBCAPES 2000-2500 J/KG...AND 80 KT UPPER LEVEL SPEED MAX MOVING
ACROSS FA LATER IN THE DAY INCREASING 0-6KM BULK SHEAR VALUES TO
AROUND 35 KTS. 850 HPA TEMPS PUSHING +19 WOULD SUPPORT AFTERNOON
HIGH TEMPS AROUND 90 DEG IN DEEP SOUTHERLY FLOW.

FRONT PUSHES ACROSS CWA DURING THE EVENING...WITH PRECIP POTENTIAL
DIMINISHING WITH FROPA. HAVE DRIED OUT WESTERN 3/4 OR SO OF CWA
AFTER MIDNIGHT WHILE KEEPING LOWER CHANCE POPS OVERNIGHT FOR FAR
EAST/SOUTHEAST. DRY MONDAY IN GENERALLY SUBSIDENT REGION BEHIND
FRONT AND SHORT WAVE TROUGH...THOUGH STILL FAIRLY WARM.

RATZER

&&

.AVIATION...
RE 12Z TAFS...IFR HAZE THIS MORNING BUT UNLIKE YESTERDAY MORNING,
NO LOW CLOUDS SO THINGS TO RAPDILY IMPROVE NEXT FEW HOURS. EXCPECT
BY 15-16Z TO BE 6+ VIS. WEAKENING UPPER LEVEL TROF QUICKLY SWIPES
THRU AREA MID AFTERNOON. MAY BE ENOUGH TO TRIP OFF A FEW TS BUT
CONFIDENCE LOW. LITTLE BETTER CHANCE AT RFD SO HAVE VCTS BUT
ELSEWHERE JUST SOME BKN CB CLOUDS. THIS GONE BY LATE AFTERNOON AND
THEN DRY THRU NIGHT. WINDS GO FROM LIGHT SE TO S DURING DAY. SOME
MVFR HZ AGAIN TOMORROW NIGHT. WITH MORE CI BLOWOFF THINGS MIGHT HOLD
A LITTLE BETTER FOR VIS.
AF

TRS

&&

.LOT...WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LK MI...NONE.

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1100 AM CDT SAT JUN 4 2005

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-051100-
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-
1100 AM CDT SAT JUN 4 2005

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

.DAY ONE... THIS AFTERNOON AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE ILLINOIS
PORTION OF THE OUTLOOK AREA THIS AFTERNOON AND EVENING.

A LINE OF THUNDERSTORMS OVER NORTHWEST AND WEST CENTRAL ILLINOIS HAS
UNDERGONE SOME WEAKENING DURING THE MORNING HOURS...BUT IS EXPECTED
TO REGENERATE BY EARLY AFTERNOON AS IT MOVES INTO INCREASINGLY
UNSTABLE AIR OVER NORTHERN AND CENTRAL ILLINOIS.  SOME OF THESE
STORMS MAY REACH SEVERE LIMITS...WITH HAIL AND BRIEF DAMAGING WIND
GUSTS THE MAIN THREATS.

STORMS ARE EXPECTED TO MOVE INTO THE AREA ALONG AND WEST OF
INTERSTATE 39 BY 100 PM...AND REACH THE CHICAGO...JOLIET...KANKAKEE
AND PAXTON AREAS BY 300 PM CDT.  ACTIVITY WILL THEN SPREAD INTO
NORTHWEST INDIANA LATE THIS AFTERNOON.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE ENTIRE
OUTLOOK AREA SUNDAY AND SUNDAY NIGHT. SEVERE THUNDERSTORMS WILL BE
MOST LIKELY DURING THE AFTERNOON AND EVENING HOURS...AS A COLD FRONT
MOVES INTO A VERY WARM...MOIST AND UNSTABLE ENVIRONMENT ACROSS
ILLINOIS AND INDIANA. LARGE HAIL AND DAMAGING WINDS ARE ANTICIPATED
TO BE THE MAIN SEVERE WEATHER THREATS. THUNDERSTORMS ARE EXPECTED TO
COME TO AN END FROM WEST TO EAST SUNDAY NIGHT AS THE COLD FRONT
MOVES ACROSS THE OUTLOOK AREA.

THERE IS ANOTHER CHANCE OF THUNDERSTORMS TUESDAY NIGHT INTO THURSDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON...AND AGAIN SUNDAY
AND SUNDAY EVENING.

&&

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

LMZ740>745-766-051100-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
1100 AM CDT SAT JUN 4 2005

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

.DAY ONE... THIS AFTERNOON AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE ILLINOIS
PORTION OF THE OUTLOOK AREA THIS AFTERNOON AND EVENING.

A LINE OF THUNDERSTORMS OVER NORTHWEST AND WEST CENTRAL ILLINOIS HAS
UNDERGONE SOME WEAKENING DURING THE MORNING HOURS...BUT IS EXPECTED
TO REGENERATE BY EARLY AFTERNOON AS IT MOVES INTO INCREASINGLY
UNSTABLE AIR OVER NORTHERN AND CENTRAL ILLINOIS.  SOME OF THESE
STORMS MAY CONTAIN HAIL AND BRIEF WIND GUSTS IN EXCESS OF 34 KNOTS.

STORMS ARE EXPECTED TO REACH THE ILLINOIS SHORE OF LAKE MICHIGAN
AROUND 300 PM CDT.  ACTIVITY WILL THEN SPREAD ACROSS THE REMAINDER
OF SOUTHERN LAKE MICHIGAN LATE THIS AFTERNOON.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SUNDAY AND SUNDAY
NIGHT. SEVERE THUNDERSTORMS WILL BE MOST LIKELY DURING THE LATE
AFTERNOON AND EARLY EVENING HOURS...WITH DAMAGING WINDS AND LARGE
HAIL ANTICIPATED TO BE THE MAIN SEVERE WEATHER THREATS.
THUNDERSTORMS ARE EXPECTED TO COME TO AN END FROM WEST TO EAST
SUNDAY NIGHT AS A COLD FRONT MOVES THROUGH THE AREA.

THERE IS ANOTHER CHANCE OF THUNDERSTORMS TUESDAY NIGHT INTO THURSDAY.

&&

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

MERZLOCK