Severe Thunderstorm Warning 37, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 PM CDT FRI JUN 1 2007

.DISCUSSION REGARDING AFTERNOON ZONES/GRIDS...

225 PM CDT
SPOKE OF ENERGY ROTATING AROUND MAIN UPPER VORTEX OVER THE DAKOTAS
PIVOTING THROUGH EASTERN IOWA INTO NW ILL THIS AFTERNOON. BEST SHEAR
AND VEERING PROFILE SHOULD REMAIN NEAR THE MISS RIVER AND SWING INTO
SRN WISC WHILE CLIPPING NW ILL MAINLY W OF RFD. AIRMASS REMAINS
MOIST AND INSTABILITY INCREASING ONCE SFC TEMPS REACH 80 DEG. DEW
POINTS POOLING NEAR ADVANCING WARM FRONT ALONG ILL RIVER N OF PIA
WHICH WILL AID CONVECTION THIS AFTN.  FEW CELLS ALSO FORMING IN MORE
SUNNY AREA FROM BLOOMINGTON NWD TOWARD WILL CO.  ANY THREAT FROM
THESE STORMS...ASIDE FROM WELCOME RAIN...WOULD BE HAIL OR GUSTY
WINDS.

BROADER PICTURE SHOWS UPPER LOW DRIFTING SLOWLY EAST ACROSS CENTRAL
GT LAKES SUN AND MONDAY. MODELS SHOW RETREATING JET STREAK AHEAD OF
UPPER LOW PULLING OUT THROUGH WRN WISC TONIGHT WHICH SHOULD SUPPORT
CONTINUING LKLY THREAT OF SHOWERS AND TSTMS TONIGHT. LOW LEVELS
SHOULD NOT DRY MUCH RIGHT AWAY AND SATURDAY WILL BE PRONE TO A
REPEAT OF TSTMS ALTHOUGH PROBALBY NOT WITH TORNADO POTENTIAL.
ANOTHER JET STREAK MAY SWING ALONG EASTERN PORTION OF APPROACHING
LOW SAT NIGHT FOR ANOTHER PERIOD OF LKLY TSTMS.  COOLING ALOFT WITH
MAIN VORTEX WILL THE THE CONCERN SUNDAY WITH PERIODS OF SHOWERS AND
FEW TSTMS CONTINUING. MORE STABLE CONDS SLOWLY SETTING IN DURING
FIRST PART OF NEXT WEEK AS NW TRAILING FLOW EVENTUALLY PROVIDES
STABILIZING INFLUENCE.

CURRENT SLOW MOVING PSEUDO CUTOFF LOW WILL BE REPLACED BY MORE
COHERENT PATTERN BY MIDWEEK AS RIDGING DEVELOPS OVER PLAINS IN
ADVANCE OF A HIGHER AMPLITUDE TROUGH NEAR THE WEST COAST.  THIS
LATTER SYSTEM EXPECTED TO MAKE SLOW PROGRESS EASTWARD DURING THE MID
AND LATE WEEK.

HAVE FILLED IN ALL PERIODS THROUGH THE WEEKEND WITH PRECIP THROUGH
MONDAY GIVEN THE UNCERTAINTY OF TIMING AND COVERAGE OF INSTABILITY
PRECIP. GREATEST POPS TONIGHT AND AGAIN SAT. WILL FOLLOW MV MOS
NUMBERS IN GENERAL AS AIRMASS FLUCTUATIONS NEXT FEW DAYS SHOULD BE
SMALL ONCE COOLING SETS IN SATURDAY.  KML

&&

.AVIATION...

100 PM CDT

18Z TAFS...MORNING DENSE FOG HAS DISSIPATED ACROSS THE TAF REGION
WITH JUST SOME HZ IN RFD WHERE THERE WAS DENSER FOG.  VIS SHOULD
CONTINUE TO IMPROVE THRU THE AFTERNOON.  OTHERWISE...MAIN FOCUS FOR
THIS TAF PERIOD IS ON THE WARM FRONT THAT WILL RISE UP THROUGH THE
REGION THIS AFTERNOON/EARLY EVENING.  WINDS WILL SHIFT FROM BEING
SOUTHEASTERLY TO SOUTHWESTERLY BEHIND THE FRONT.  CONVECTION WILL
LIKELY DEVELOP OUT AHEAD OF THE FRONT SO AM EXPECTING STORMS TO
DEVELOP BY 23Z ACROSS THE TAF AREA.  THERE IS ANOTHER CHANCE FOR
PRECIPITATION TOWARD THE END OF THE TAF PERIOD FOR RFD AS THE COLD
FRONT IN THE CENTRAL PLAINS MOVES INTO WESTERN ILLINOIS BY TOMORROW
AFTERNOON.

HALBACH

&&

.MARINE...

300 AM CDT

LOW PRESSURE WILL REMAIN NEARLY STATIONARY OVER THE NORTHERN PLAINS
THROUGH SATURDAY MORNING...WHILE WEAK HIGH PRESSURE DOMINATES THE
WESTERN GREAT LAKES.  THE MAIN CONCERN FOR MARINERS ON FRIDAY WILL
BE PATCHY FOG THROUGH THE MORNING HOURS FRIDAY.  DURING THE DAY
SATURDAY...THE LOW WILL MOVE INTO THE UPPER MISSISSIPPI VALLEY.
HOWEVER...OVER THE NEXT FEW DAYS...THE PRESSURE GRADIENT OVER THE
LAKE WILL REMAIN RATHER WEAK AND WINDS ARE ONLY EXPECTED TO INCREASE
INTO THE 10 TO 15KT RANGE.  THROUGH SUNDAY...WINDS WILL BE GENERALLY
SOUTHERLY...BUT OVERNIGHT SUNDAY NIGHT...THE WEAK LOW WILL CROSS THE
LAKE...CAUSING WINDS TO SHIFT NORTHWESTERLY.  PRESSURE GRADIENTS
WILL REMAIN WEAK OVER THE LAKE THROUGH THE REMAINDER OF THE FORECAST
PERIOD AND WINDS WILL REMAIN UNDER 15 KTS AND WAVES WILL REMAIN
AROUND 1 TO 2 FEET.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...TORNADO WATCH FOR NORTH CENTRAL ILLINOIS UNTIL 00Z SATURDAY
.IN...NONE.
.LM...NONE.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
320 PM CDT FRI JUN 1 2007

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-012130-
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-
320 PM CDT FRI JUN 1 2007

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

  A TORNADO WATCH IS EFFECT UNTIL 700PM FOR PORTIONS OF NORTH
  CENTRAL AND NORTHEAST ILLINOIS...GENERALLY WEST OF THE FOX AND
  ILLINOIS RIVERS.

  STRONG TO SEVERE THUNDERSTORMS WILL SPREAD EASTWARD INTO NORTH
  CENTRAL ILLINOIS THIS AFTERNOON...AND POSSIBLY CONTINUE EASTWARD
  INTO NORTHEAST ILLINOIS BY THIS EVENING. IN ADDITION HAIL UP TO
  THE SIZE OF GOLF BALLS AND DAMAGING WINDS IN EXCESS OF 60
  MPH...THE POTENTIAL EXISTS FOR AN ISOLATED TORNADO OR TWO.

  THUNDERSTORM COVERAGE IS FORECAST TO INCREASE TONIGHT...WITH THE
  POTENTIAL FOR LOCALLY HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

  THERE WILL BE A CONTINUED CHANCE OF THUNDERSTORMS THROUGH
  MONDAY...MAINLY DURING THE AFTERNOON AND EVENING HOURS.
  THE PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER WILL REMAIN LOW.

.SPOTTER INFORMATION STATEMENT...

  SPOTTER ACTIVATION IS REQUESTED THIS AFTERNOON OVER NORTH CENTRAL
  ILLINOIS AND MAY BE NEEDED ACROSS NORTHEAST ILLINOIS BY EARLY
  EVENING.

&&

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

LMZ740>745-766-012130-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
320 PM CDT FRI JUN 1 2007

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 CHANCE OF THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN
  BY LATE THIS AFTERNOON.  THUNDERSTORM COVERAGE IS EXPECTED TO
  INCREASE TONIGHT.

.DAYS TWO THROUGH SEVEN... SATURDAY THROUGH THURSDAY

  THERE WILL BE A CONTINUED CHANCE OF THUNDERSTORMS THROUGH
  MONDAY...MAINLY DURING THE AFTERNOON AND EVENING HOURS.
  THE PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER WILL REMAIN LOW.

&&

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

KML/IZZI