Flash Flood and Hail in Illinois, June 7 to 8, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
715 PM CDT THU JUN 7 2007

.SEVERE WEATHER DISCUSSION...

INITIAL DEVELOPMENT OF CONVECTION IN IOWA HAS PROPAGATED OFF THE
DRYLINE...BUT HAS FAILED TO MORPH INTO A LINE BETTER YET AN
ORGANIZED LINE. THE STRONG SHEAR HAS ALLOWED SOME OF THE DISCRETE
CELLS TO DEVELOP SUPERCELLULAR CHARACTERISTICS OVER EASTERN IOWA BUT
ON A WHOLE THE SUPERCELL STRUCTURES HAVE BEEN MORE TRANSIENT
FEATURES WHICH HAVE GENERALLY STRUGGLED TO MAINTAIN THEMSELVES.

WITH THE INITIAL CONVECTION NOW HAVING MOVED OFF THE DRYLINE THERE
DOESNT APPEAR TO BE ANY REASON FOR THE CONVECTION TO EVOLVE INTO A
LINE IN THE NEXT FEW HOURS. THE 20Z DVN SOUNDING FROM DVN ACTUALLY
SHOWS THE CAP SHARPENING UP A BIT SINCE 18Z. IN ADDITION...THE
CIRRUS CANOPY FROM UPSTREAM CONVECTION IS CUTTING BACK SOME
INSTABILITY. ALL IN ALL THE CIRRUS CANOPY...LACK OF CONVERGENCE WITH
STORMS OFF THE DRYLINE...AND STRONG CAP ALL SEEM TO BE POINTING
TOWARD THE CURRENT CONVECTION CONTINUING TO STRUGGLE IN THE NEAR
TERM.

DESPITE THE APPARENT NEGATIVES...INSTABILITY REMAINS MORE THAN
SUFFICIENT FOR SUPERCELLS GIVEN THE VERY IMPRESSIVE DEEP LAYER
SHEAR. WITH THE ENVIRONMENT PRIMED THE WAY IT IS WHILE CERTAINLY LET
THE CURRENT WATCH RIDE AS IS...BUT CONFIDENCE IN A HIGHER END A
SEVERE EVENT IS STARTING TO WANE SLIGHTLY.

IZZI

&&

.DISCUSSION...

318 PM...SVR POTENTIAL COVERED WELL IN DISCUSSION ABOVE...SPS AND
HWO SO FOCUS HERE WILL BE ON REST OF THE FORECAST...INCLUDING WIND
ADVISORY. SFC WINDS HAVE BEEN GUSTY THIS AFTERNOON BUT GENERALLY
JUST SHY OF ADVISORY CRITERIA. HOWEVER...WITH STRONGEST GRADIENT
STILL TO PASS ACROSS THE AREA THRU EARLY EVENING AND CONTINUED
MIXING...WILL LEAVE WIND ADVISORY UP THRU THE EVENING...BUT MAY
NEED TO BE DROPPED BEFORE CURRENT EXPIRATION TIME OF 05Z.

FRONT CLEARS CWA FRIDAY MORNING AND MODELS SHOW LINGERING SHOWERS
ACROSS THE SE CWA FEW A FEW HRS AFTER 12Z SO WILL MAINTAIN CHANCE
POPS FOR A FEW HRS. OTHERWISE HIGH PRESSURE BUILDS ACROSS THE REGION
FRIDAY INTO SATURDAY THEN PUSHES EAST SUNDAY SO WEEKEND SHAPING UP
TO BE DRY BUT EASTERLY FLOW TO KEEP THE LAKESHORE A FEW DEGREES
COOLER.

WARM FRONT BEGINS TO LIFT NORTH ACROSS THE AREA MONDAY NIGHT INTO
TUESDAY WITH CHANCES OF PRECIP INCREASING DURING THIS TIME.
RELUCTANT TO INCLUDE SEVERAL PERIODS OF LOW CHANCE POPS BUT HAVE
INCLUDED CHANCE POPS ACROSS IL DURING THE DAY TUESDAY AS WARM FRONT
LIFTS NORTH. HIGHS CLIMB BACK INTO THE LOWER/MID 80S FOR HIGHS NEXT
WEEK WITH A CHANCE OF PRECIP BUT NOT ENOUGH CONFIDENCE TO INCLUDE
BEYOND TUESDAY. CMS

&&

.AVIATION DISCUSSION FOR 00Z TAFS...

MAIN FORECAST CONCERNS CONTINUE TO BE ON THUNDERSTORM POTENTIAL AND
WINDS.

MAIN UPPER LEVEL TROUGH CONTINUES TO LIFT THROUGH THE NORTHERN
PLAINS WITH COLD FRONT EXTENDING SOUTHWARD ACROSS FAR WESTERN IOWA.
DRY LINE HAS PUSHED OUT AHEAD OF THE COLD FRONT ACROSS SOUTHEAST
MINNESOTA INTO EASTERN IOWA. MAIN AREAS OF CONVECTION HAVE DEVELOPED
TO THE EAST OF THIS DRY LINE IN ASSOCIATION WITH A WEAK PRE-FRONTAL
TROUGH. AT THIS TIME...SCATTERED SHOWERS AND THUNDERSTORMS ARE
MAINLY CONFINED TO FAR EASTERN IOWA/NORTHWEST ILLINOIS/SOUTHERN
WISCONSIN WITH THESE STORMS EXPECTED TO EXIT NORTHWEST ILLINOIS OVER
THE NEXT FEW HOURS. ACARS SOUNDINGS SHOWING VERY STRONG CONVECTIVE
INHIBITION ACROSS NORTHEAST ILLINOIS. CONVECTIIVE INHIBITION SHOULD
GRADUALLY DIMINISH OVER THE NEXT FEW HOURS AS UPPER SYSTEM SLOWLY
TRACKS OFF TO THE EAST. UPPER JET STREAK ALSO LIFTING THROUGH
DOWNSTREAM PORTION OF THIS UPPER TROUGH MAY ALSO PROVIDE ENHANCED
LIFT IN THE ENTRANCE REGION OF THIS UPPER JET STREAK...BUT THIS
LOOKS TO BE MUCH LATER THIS EVENING TOWARD MIDNIGHT. WILL CONTINUE
TO CARRY MENTION OF TSRA...ESPECIALLY IN THE 04Z-08Z TIME FRAME BUT
CONVECTIVE COVERAGE MAY NOT BE AS EXTENSIVE AS PREVIOUSLY THOUGHT.

WINDS WILL CONTINUE TO GUST IN THE 25-30 KNOT RANGE THIS EVENING AND
WILL LOW LEVEL REMAINING WELL MIXED THIS EVENING WILL KEEP WINDS IN
THIS GENERALY NEIGHBORHOOD THROUGH THE EVENING. WIND GUSTS SHOULD
DIMINISH LATER TONIGHT WITH APPROACH OF THE COLD FRONT. CURRENT
THINKING IS THAT WIND SHIFT WITH THE COLD FRONT WILL BE THROUGH RFD
AROUND THE 09Z-10Z TIME FRAME AND FOR THE REMAINDER OF THE TERMINALS
SHORTLY AFTER 12Z. WINDS WILL THEN SHIFT TO THE NORTHWEST TOMORROW
MORNING BEHIND THE FRONT. EXPECTING JUST SOME VFR CU TOMORROW
DEVELOPING BY LATE MORNING BUT SYNOPTIC SUBSIDENCE AND DRIER LOW
LEVEL AIR SHOULD PREVENT ANY CIGS.

MARSILI

&&

.MARINE...

235 PM...UNSEASONABLY STRONG LOW PRESSURE OF 28.95 INCHES OVER
NORTHERN MINNESOTA THIS AFTERNOON WILL MOVE RAPIDLY NORTHEAST TO
HUDSON BAY BY FRIDAY AFTERNOON. VERY TIGHT PRESSURE GRADIENT
PRODUCING STRONG SOUTH WINDS ACROSS THE LAKE INTO THIS EVENING. WARM
AIR MOVING OVER COLD WATER HAS MODERATED THE AMOUNT OF WIND REACHING
THE LAKE SURFACE...HOWEVER HAD ONE SHIP REPORT OF 32 KNOTS THIS
MORNING AND NORTH BUOY GUSTING TO 30 KNOTS WITH 8 TO 9 FOOT WAVES.
MANY LAND STATIONS ALONG SHORE REPORTING GALE FORCE WINDS/GUSTS.
WILL CONTINUE GALE WARNING THROUGH THIS EVENING. A STRONG COLD FRONT
WILL SWEEP ACROSS LAKE MICHIGAN LATE TONIGHT AND EARLY FRIDAY
MORNING. THE FRONT WILL BE ACCOMPANIED BY A LINE OF STRONG TO SEVERE
THUNDRSTORMS. LOCALIZED WIND GUSTS OVER 50 KNOTS WITH SEVERE STORMS
ARE POSSIBLE.

HIGH PRESSURE OF 30.05 INCHES WILL BUILD INTO THE MID MISSISSIPPI
VALLEY LATE FRIDAY AND INTO THE GREAT LAKES SATURDAY AND SUNDAY.
FAIRLY TRANQUIL PATTERN EXPECTED INTO EARLY NEXT WEEK.

ALLSOPP

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LM...GALE WARNING OPEN WATERS THROUGH 03Z TONIGHT.
      GALE WARNING NEARSHORE THROUGH 05Z TONIGHT.
      SMALL CRAFT NEARSHORE WATERS 05Z TONIGHT THROUGH FRIDAY
      MORNING.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
720 PM CDT THU JUN 7 2007

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-080930-
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-
720 PM CDT THU JUN 7 2007

...SEVERE THUNDERSTORMS POSSIBLE THIS EVENING...

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

.DAY ONE... TONIGHT

SEVERE THUNDERSTORMS HAVE MOVED INTO NORTHWEST ILLINOIS AND SOUTHERN
WISCONSIN FROM EASTERN IOWA. MORE STORMS ARE DEVELOPING IN NORTHERN
MISSOURI AND ARE MOVING RAPIDLY EAST NORTHEASTWARD TOWARD WESTERN
ILLINOIS. THESE STORMS COULDA WORK THEIR WAY INTO NORTHERN ILLINOIS
LATER THIS EVENING AND CONTINUE INTO NORTHWEST INDIANA IN THE EARLY
MORNING HOURS.

WINDS THROUGHOUT THE ATMOSPHERE ARE QUITE STRONG...AND GIVEN THE
DEGREE OF INSTABILITY PRESENT...THE POTENTIAL REMAINS STRONG FOR
SEVERE THUNDERSTORMS. THE PRIMARY SEVERE WEATHER THREAT IS EXPECTED
TO BE DAMAGING STRAIGHT LINE WINDS...POSSIBLY IN EXCESS OF 60 MPH
WITH THE MORE INTENSE STORMS. IN ADDITION TO THE RATHER SUBSTANTIAL
RISK OF DAMAGING WINDS...THERE IS ALSO POTENTIAL FOR LARGE HAIL AND
POSSIBLY EVEN ISOLATED TORNADOES.

PRESENT INDICATIONS ARE THAT THE SEVERE THUNDERSTORMS COULD MOVE
INTO PORTIONS OF NORTH CENTRAL ILLINOIS BETWEEN 10 PM AND
MIDNIGHT...THE CHICAGO METROPOLITAN AREA SOUTHWEST TO PONTIAC AND
LA SALLE BETWEEN MIDNIGHT AND 2 AM...AND INTO NORTHWEST INDIANA
SOUTHWEST INTO FAR SOUTHERN PORTIONS OF THE OUTLOOK AREA IN THE
EARLY MORNING HOURS.

.DAYS TWO THROUGH SEVEN... FRIDAY THROUGH WEDNESDAY

THERE IS A LINGERING CHANCE OF THUNDERSTORMS THROUGH NOON ON
FRIDAY...FOR PORTIONS OF THE OUTLOOK AREA SOUTHEAST OF A LINE
FROM GARY TO KANKAKEE TO GIBSON CITY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE NEEDED ACROSS NORTH CENTRAL ILLINOIS
LATER THIS EVENING...AND ACROSS THE REMAINDER OF THE OUTLOOK AREA
FROM AFTER MIDNIGHT.

&&

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

LMZ740>745-766-080930-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
720 PM CDT THU JUN 7 2007

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

.DAY ONE... TONIGHT

A GALE WARNING IS IN EFFECT FOR THE OPEN AND NEARSHORE WATERS
EARLY TONIGHT. A SMALL CRAFT ADVISORY WILL BE IN EFFECT FOR THE
NEARSHORE WATERS THROUGH FRIDAY MORNING.

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS EVENING AND
OVERNIGHT. THE MAIN SEVERE WEATHER THREAT WILL BE DAMAGING
WINDS...BUT LARGE HAIL AND FREQUENT LIGHTNING ARE LIKELY AS WELL.

.DAYS TWO THROUGH SEVEN... FRIDAY THROUGH WEDNESDAY

A SMALL CRAFT ADVISORY WILL BE IN EFFECT FOR BOTH THE ILLINOIS AND
INDIANA NEARSHORE WATERS THROUGH FRIDAY MORNING.

&&

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