Excessive Heat in Illinois, July 8 to 10, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
635 AM CDT SUN JUL 8 2007

.DISCUSSION REGARDING MORNING ZONES/GRIDS...

ONCE AGAIN...FORECAST THROUGH NEAR TERM REMAINS ON TRACK.  ONLY A
FEW PATCHES OF HIGH LEVEL CLOUDINESS INDICATED ON MORNING SATLT
IMAGERY DRIFTING SEWD ACROSS SRN WI.  THESE SHOULD BE OF LTL
CONSEQUENCE TDY AS EXTENSION OF WRN U.S. HOT DOME BUILDS INTO MID MS
VLY.  RISING H5 HGTS SUGGEST AIR MASS WILL RMN CAPPED TDY AND HIGH
CLOUDINESS/CONVECTIVE DEBRIS FROM NRN PLAINS AND UPR MIDWEST SHOULD
TEND TO DSIPT AS IT MOVES TOWARD AREA.

COMBINATION OF THIS MID LVL SUBSIDENCE AND INCRSG SWLY LLVL FLOW
WILL RESULT IN INCRSG TEMPS AND HUMIDITY.  TEMPS TDY EXPECTED TO BE
ARND 5 F DEG WARMER THAN YDY...WITH DEW POINTS ARND 70 ALREADY IN
PLACE.

LLVL FORCING TO CONTINUE TNGT...KEEPING SWLY SFC/BOUNDARY LYR WIND
SPEED SOMEWHAT ELEVATE OVERNIGHT.  DEW POINTS TO RMN HIGHER TNGT AS
WELL DUE TO MOISTURE POOLING LIKELY TO OCCUR AHD OF APCHG FRONT.
ADD IN MORE TSTM BLOW OFF FROM NW AND THE STAGE IS SET FOR A MUGGY
NIGHT.  EXPECT FA TO HAVE CONDS TNGT THAT ARE SIMILAR TO CURRENT WX
OVR SERN MN THIS MORNING WHERE TEMPS RMN IN 75 TO 80 DEG RANGE YET
AT THIS HR.  BASED ON THIS...BELIEVE MOS GUID FOR MINS TNGT ARE A
BIT TOO LOW SO HAVE GONE BACK TO MID 70S MINS AND MUGGY WORDING IN
FCST.

AS WEAKENING FRONTAL BOUNDARY SAGS SWD INTO FA ON MON...THINGS GET
INCREASINGLY COMPLICATED. MODELS APPEAR IN CLOSER AGREEMENT IN
HAVING THIS BOUNDARY BCM STNRY IN VCTY OF I-80 CORRIDOR BY MON
AFTN.  THUS HAVE MAINTAINED INHERITED TEMP/SKY COVER AND POP GRIDS
FOR MON-MON NGT.  GIVEN THAT SHORT WV TROF EXPECTED TO SUPPORT
INITIAL FRONTAL MOVEMENT IS POS SHEARED AND ZIPS OFF TO STLAWR VLY
BY MIDDAY MONDAY...IDEA OF STALLING BOUNDARY STILL SEEMS PLAUSIBLE.
 BASED ON THIS...EXPECT MODEST S-N TEMP GRADIENT TO SET UP
ON MON...WITH HIEST PROB OF TSTM DVLPMT ALG AND N OF BOUNDARY.
MON NGT AND TUES TIME-HEIGHT CROSS SECTIONS ALSO CONTINUE TO SHOW
DECENT AMT OF MOISTURE CONVERGENCE RIDING OVR SFC BOUNDARY...WITH
PLENTY OF INSTABILITY POOLED ALG/S OF BOUNDARY HEADING INTO MONDAY
NIGHT.  BASED ON THIS...HAVE GONE WITH HIGHEST POPS OVR NRN PORTION
OF FA...AND LOW CHC POPS TO S.

MUCH MORE SIG CHGS TO TAKE PLACE TUE-WED AS MUCH STGR WAVE DIGS SEWD
ACROSS MANITOBA...PUSHING STG SFC COLD FRONT SEWD ACROSS GRTLKS-UPR
MS VLY BY ERLY WED MRNG.  LLVL FLOW FCST TO BACK AHD OF THIS FEATURE
ON TUES...EFFECTIVELY WASHING OUT ANY REMNANTS OF FIRST
FRONTAL BOUNDARY.  THEREFORE...EXPECT SOME RETURN OF HEAT AND
HUMIDTY NWD OVR ENTR FA ON TUES-TUES NGT.  WILL KEEP CHC TSTMS IN
THRU WED MRNG DUE INTITIALLY TO OLD BOUNDARY IN AREA AND DEGREE OF
INSTABILITY PRESENT...TO BE FOLLOWED BY APCH OF WED MRNG COLD FRONT.

ONLY NOTEABLE CHG IN GUIDANCE...INCLUDING GFS/NAM/EURO...HAS BEEN TO
ACCELERATE FRONT THRU RGN EARLIER THAN IN PREVIOUS RUNS.
AGAIN...THIS TREND LOOKS REASONABLE GIVEN STRENGTH OF DIGGING UPR
SYS TO N AND DRYING/SUBSIDENCE WITH ASSD JET MAX FCST TO PUNCH
ACROSS UPR MS VLY BY 12Z WED.  ALTHOUGH GFS APPEARS TO DVLP
CONVECTIVE FEEDBACK PROBLEMS BY 84 HRS...THE FACT THAT OTHER
GUIDANCE COMES TO THE SAME END...ALBEIT BY DIFFERENT MEANS...LENDS
CREDENCE TO EARLIER FROPA.  THEREFORE HAVE TRENDED TO DRY FCST FROM
NW-SE ACROSS FA DURG WED TIME PERIOD.

SHOULD SEE SIG TURN TO COOLER/LESS HUMID CONDS WD NGT AND THURE AS
HI PRES BUILDS ACROSS UPR MS VLY AND SETTLES OVR IL BY END OF WEEK.

MERZLOCK

&&

.AVIATION...

FOR THE 1200 UTC TAFS...MODEST SW GRADIENT FLOW ASSOCIATED WITH LOW
PRESSURE NEAR LK SUPERIOR WILL SUPPORT GUSTY SW WINDS TODAY.  ACARS
FROM ORD SHOWS 30KTS WITHIN 2500FT OF SFC SO SOME G25KT LKLY DURING
HEAT OF THE DAY.  PATCHY HIGH CLOUDS FROM OLD DAKOTA CONVECTION WILL
SPREAD INTO REGION.  OVERALL SUBSIDENCE HOWEVER WILL HELP THIN THESE
AS WELL AS LIMIT ANY AFTERNOON CU. GUSTINESS IN WINDS WILL ABATE AT
SUNSET. WEAK APPROACHING COOL FRONT FROM NW LATER TONIGHT WILL
MAINTAIN LIGHT SW WINDS DURING THE NIGHT BECOMING MORE WLY TOWARD
SUNRISE MON. HOT TEMPS THIS AFTERNOON WILL MEAN HIGH DENSITY
ALTITUDE SITUATION.  KML
&&

.MARINE...
215 AM CDT
SURFACE LOW OF 29.5 INCHES MOVING INTO LAKE SUPERIOR THIS AFTERNOON
THEN EAST INTO ONTARIO MONDAY WILL DRAG A COOL FRONT SOUTHWARD
THROUGH THE LAKE LATER TODAY AND TONIGHT. SOUTHWEST WINDS TO 25KTS
AHEAD OF FRONT. FEW TATMS TO REAR.  FRONT BECOMES STALLED OVER NRN
ILLINOIS MONDAY WHILE NEXT LOW PRESSURE OF 29.6 INCHES FORMS NEAR LK
WINNEPEG EARLY TUESDAY.  THIS SYSTEM WILL TRACK ACROSS NRN LAKES WED
PUSHING A MORE VIGOROUS FRONT THROUGH LK MICH ON WEDNESDAY. NW FETCH
IS LKLY TO PERSIST INTO FRIDAY.  SCA FOR SRN LK MICH COASTAL WATERS
TODAY FOR WIND.  KML

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVSY FOR TODAY IL/IN NEARSHORE WATERS.

&&

HAZARDOUS WEATHER OUTLOOK...CORRECTION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
430 AM CDT SUN JUL 8 2007

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
082130-
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-
430 AM CDT SUN JUL 8 2007/530 AM CDT SUN JUL 8 2007

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

.DAY ONE...TODAY AND TONIGHT.

HOT AND MUGGY CONDITIONS WILL RAISE HEAT INDEX READINGS TO AT OR
JUST ABOVE 100 THIS AFTERNOON.  ALTHOUGH A HEAT ADVISORY IS NOT
ANTICIPATED...PERSONS PLANNING TO SPEND TIME OUTDOORS SHOULD BE
AWARE OF AN INCREASED LEVEL OF HEAT STRESS.

CONDITIONS ARE EXPECTED TO REMAIN QUITE MUGGY THROUGH TONIGHT AS
WELL WITH OVERNIGHT LOWS ONLY DROPPING INTO THE MIDDLE AND UPPER 70S
MOST AREAS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

THERE WILL BE A CHANCE OF THUNDERSTORMS FROM MONDAY THROUGH
WEDNESDAY MORNING.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER NORTHERN
ILLINOIS AND EXTREME NORTHWEST INDIANA ON MONDAY AND MONDAY NIGHT.
THE GREATEST LIKELIHOOD OF SEVERE STORMS IS EXPECTED TO OCCUR MONDAY
AFTERNOON AND EVENING AS A WEAK FRONTAL BOUNDARY BECOMES STATIONARY
ACROSS THE AREA...AND INSTABILITY PEAKS DURING THE HEAT OF THE DAY.

THE SLIGHT RISK AREA IS GENERALLY ALONG AND NORTH OF INTERSTATE 80.
LARGE HAIL AND BRIEF DAMAGING WIND GUSTS ARE THE MAIN THREATS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NECESSARY THROUGH TONIGHT.

&&

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

LMZ740>745-766-082130-
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, WINTHROP HARBOR IL EASTWARD TO THE MID-
POINT OF THE LAKE AND SOUTHWARD TO MICHIGAN CITY MI BEYOND 5 NM
OFFSHORE-
430 AM CDT SUN JUL 8 2007

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

.DAY ONE...TODAY AND TONIGHT.

A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE ILLINOIS AND INDIANA
NEARSHORE WATERS THROUGH TODAY.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

THERE WILL BE A CHANCE OF THUNDERSTORMS FROM MONDAY THROUGH
WEDNESDAY MORNING.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN LAKE
MICHIGAN MONDAY AND MONDAY NIGHT.  THE GREATEST LIKELIHOOD OF SEVERE
STORMS IS EXPECTED TO OCCUR MONDAY AFTERNOON AND EVENING.

BRIEF WIND GUSTS IN EXCESS OF 34 KNOTS ARE THE MAIN THREAT.

&&

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

MERZLOCK