Heat in Illinois, July 15 to 17, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1045 AM CDT SAT JUL 15 2006

.UPDATED DISCUSSION FOR MORNING GRIDS/ZONE FORECASTS...

TEMPS WARMING RAPIDLY THOUGH THE MID 80S BUT SHOULD SLOW DOWN AS
THEY APPROACH 90. ACARS DATA FROM ORD SUGGESTS LOW LEVEL ADIABATIC
LAPSE RATE WILL BE REACHED AROUND 90 SO CURRENT FCST MAX TEMPS IN
LOW-MID 90S LOOK REASONABLE FOR TODAY. AIR ABOVE IMMEDIATE SURFACE
IS QUIE DRY SO MIXING DURING THE DAY WILL DROP DEW POINTS OFF A BIT.
LAKE BREEZE ALSO PROBABLE FOR PART OR MOST OF COOK COUNTY AND OTHER
COASTAL AREAS TODAY.  MODELS AND MOS CONTINUE TO POINT TOWARD
SUN-MON AS BEING HOTTEST IN THIS SERIES. THERMAL RIDGE POKING IN
FROM CRESTING ANTICYCLONE ALOFT WILL BOOST LOW LEVEL TEMPS INTO
UPPER 90S AND HEAT INDICES PAST 100. SOME QUESTION ABOUT TUESDAY
WITH WRF AND GFS AT ODDS ON WEAK COOL FRONT SLIDING BY TO THE N.
NOT ENOUGH NEW INFO AT THIS TIME TO MAKE ANY CONCLUSIONS THOUGH.
LOOKS LIKE A BRIEF RETURN TO EXCESSIVE TEMPS ON THURSDAY BEFORE MORE
SUSTAINED COOLING CAN BE CONTAMPLATED.  NO UPDATES AT MID MORNING.
KL

PREVIOUS DISCUSSION...310 AM CDT

BROAD UPPER RIDGE TO SPREAD EASTWARD ACROSS FORECAST AREA THIS
WEEKEND...RESULTING IN HEAT WAVE WHICH LINGERS INTO NEXT WEEK. MAIN
FORECAST CONCERN WILL BE TEMPS...AS WELL AS SFC DEW POINTS TEMPS AND
RESULTING HEAT INDICIES.

WITH BUILDING UPPER RIDGE...THICKNESSES/TEMPS INCREASING TODAY AND
SUNDAY. FCST 850 HPA TEMPS IN 21-23 C DEG RANGE TODAY...AND AROUND
24 DEG C SUNDAY. FCST SOUNDINGS INDICATE WE MAY NOT MIX COMPLETELY
THROUGH 850 HPA THOUGH...SO HAVE USED A BLEND OF GFS/WRF 950 HPA
TEMPS AND MAV GUIDANCE RESULTING BASICALLY IN MID 90S FOR AFTN MAXES
TODAY. WEAK SFC PRESSURE GRADIENT DUE TO HIGH PRESSURE RIDGE AXIS
FROM MO TO WRN GRTLKS...WITH FCST 950 HPA FLOW GNRLY 4-8 KTS
SUPPORTIVE OF LAKE BREEZE DEVELOPMENT IN CHICAGO AREA...WITH TEMPS
LIMITED TO UPPER 80S CLOSE TO THE LAKE MICHIGAN SHORE. WARMER TEMPS
LOOK APPROPRIATE SUNDAY AS FCST AREA IS IN CLOSER PROXIMITY TO
THERMAL RIDGE DUE TO SHORT WAVE PASSING THROUGH ONTARIO AND NUDGING
RIDGE A BIT TO THE SOUTH. WITH SFC RIDGE SINKING INTO OH
VLY...APPEARS WILL HAVE ENOUGH SLY GRADIENT WINDS TO KEEP LAKE
BREEZE AT BAY WITH TEMPS INTO UPPER 90S ENTIRE AREA. AS DEPICTED IN
CURRENT GRIDS EXPECT EXCESSIVE HEAT WARNING CRITERIA WILL BE MET FOR
COOK COUNTY SUNDAY...MONDAY AND TUESDAY SO WILL MAINTAIN CURRENT
WATCH.

MAIN CONCERN WITH HEAT INDICIES AND HEADLINES AWAY FROM CHICAGO IS
WITH SFC DEW POINT TEMPS TODAY AND SUNDAY. SFC PARCEL TRAJECTORIES
INDICATED FROM SRN MN...AND UPSTREAM 00Z SATURDAY RAOBS AT ABR AND
MPX INDICATE QUITE A BIT OF DRY AIR ABOVE THE SURFACE. WHILE RAW
MODEL SFC DWPTS IN 70S...STATISTICAL MODEL OUTPUT REMAINS RATHER
CONSERVATIVE WITH LOW-MID 60S...AND EVEN A FEW UPPER 50S THIS AFTN
FROM GFS MAV. BASED ON DEGREE OF EXPECTED SUBSIDENCE AND DRYING
NOTED IN WATER VAPOR LOOPS AM INCLINED TO LOWER CURRENT DEW POINT
GRIDS A BIT...INTO THE UPPER 60S/AROUND 70. THIS WOULD SUGGEST
POTENTIAL FOR TAGGING 105 DEG HEAT INDEX CRITERIA SUNDAY AFTN IN A
FEW PLACES...THOUGH WOULD LIKE TO HOLD OFF ON THIRD PERIOD HEAT
ADVISORY AWAY FROM CHICAGO FOR NOW TO GET A BETTER JUDGMENT OF
MIXING OF DRIER AIR THIS AFTN. SLIGHT MODERATION OF THERMAL RIDGE ON
MONDAY EXPECTED TO RESULT IN SLIGHTLY LOWER MAXES...BUT ONLY BACK TO
THE MID 90S. OVERNIGHT MINS THROUGH PERIOD EXPECTED TO REMAIN IN
70S...AND LIKELY NOT DIPPING BELOW 80 SUNDAY NIGHT AMONGST THE STEEL
CONCRETE AND GLASS OF DOWNTOWN CHICAGO.

A COLD FRONT...TRAILING FROM SFC LOW ASSOCIATED WITH ONTARIO SHORT
WAVE...DROPS SOUTH ACROSS WI MONDAY AND APPROACHES IL/WI BORDER BY
12Z TUES. INTERESTINGLY...BOTH WRF AND GFS DVLP CONVECTION ALONG
FRONT INTO EXTRM NRN IL BY SUNRISE TUESDAY APPARENTLY FORCED BY WEAK
SHORT WAVE TROUGH AND WEAK CONVERGENCE ON NOSE OF 15 KT 850 HPA
FLOW. STEEP MID LEVEL LAPSE RATES AND POTENTIALLY UNSTABLE AIRMASS
ALOFT...THOUGH CONVECTION WILL BE FIGHTING SOUTH INTO CAPPED AIR
MASS AND AT THIS TIME HAVE LOW CONFIDENCE THAT ACTIVITY WILL
ACTUALLY MAKE IT INTO FCST AREA. PERHAPS BIGGER QUESTION IS WILL
FRONT SLIP INTO NE IL AND REDUCE TEMPS SLIGHTLY TUES. WRF ACTUALLY
DEVELOPS CONVECTIVE OUTFLOW AND MESO-HIGH WHICH SWINGS WINDS TO THE
N TUES MORNING...THOUGH GFS KEEPS FRONT JUST NORTH OF FCST AREA.
AGAIN...BASED ON LIMITED POTENTIAL FOR STORMS MOVING INTO CAP WILL
MAINTAIN CURRENT FCST OF FRONT REMAINING NORTH OF FCST AREA.

RATZER

&&

.AVIATION DISCUSSION FOR 12Z TAFS...

645 AM CDT

LITTLE CHANGE IN THINKING FROM 06Z TAFS WITH FOCUS TODAY ON WINDS
AND POTENTIAL FOR LAKE BREEZE DEVELOPMENT.

11Z MSAS ANALYSIS PLACES SURFACE ANTICYCLONE FROM SOUTHERN MISSOURI
INTO CENTRAL IOWA. MAIN UPPER LEVEL FEATURE TODAY WILL BE THE
APPROACH OF THE BROAD WESTERN CONUS UPPER RIDGE. AS THIS RIDGE
PROGRESSES EASTWARD...SURFACE HIGH WILL SLIDE EAST/SOUTHEAST INTO
WEST CENTRAL ILLINOIS THIS AFTERNOON...AND INTO EAST CENTRAL
ILLINOIS INTO CENTRAL INDIANA OVERNIGHT. LOT WSR-88D VAD WIND
PROFILE STILL INDICATING NORTHWEST WINDS BETWEEN 15-20 KNOTS AT 2K FT
DOWNSTREAM OF THIS RIDGE AXIS WHICH AGREES FAIRLY WELL WITH SOME OF
THE ACARS SOUNDINGS FROM NORTHEAST ILLINOIS THIS MORNING. THESE
WINDS SHOULD SLACKEN OFF TODAY WITH APPROACH OF THIS RIDGE WHICH
SHOULD ALLOW LAKE BREEZE TO AFFECT TERMINALS BY MID TO LATE
AFTERNOON. CURRENTLY HAVE TIMING OF LAKE BREEZE AT MDW AT 20Z...ORD
AT 21Z...AND AT DPA AROUND 22Z. SYNOPTIC GRADIENT WILL BECOMING
INCREASINGLY FAVORABLE TO A SOUTHEAST WIND TONIGHT...SO WILL
CONTINUE TREND OF MODIFYING LAKE BREEZE TO SOUTHEAST BY 00Z AND THEN
LIGHT SOUTH AFTER 03Z AS SURFACE HIGH CONTINUES TO DRIFT TO THE
SOUTHEAST. SOME CONCERN FOR FOG DEVELOPMENT TONIGHT GIVEN DEPARTING
SURFACE HIGH...WEAK SURFACE PRESSURE GRADIENT...AND CLEAR SKIES.
WILL NOT INSERT ANY FOG AT THIS TIME...BUT FUTURE SHIFTS MAY NEED TO
CONSIDER INCLUSION OF MVFR VSBYS LATE TONIGHT.  NDM

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...EXCESSIVE HEAT WATCH COOK COUNTY/CHICAGO 18Z SUN-00Z WED
.IN...NONE.
.LM...NONE.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1000 AM CDT SAT JUL 15 2006

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-160930-
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-
430 AM CDT SAT JUL 15 2006

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

.DAY ONE... TODAY AND TONIGHT

HOT AND HUMID WEATHER WILL BUILD INTO THE REGION TODAY...AND WILL
CONTINUE THROUGH THE WEEKEND AND INTO NEXT WEEK. AFTERNOON HIGH
TEMPERATURES WILL REACH THE MIDDLE 90S TODAY...WITH HEAT INDICIES
APPROACHING 100 IN SOME AREAS. HOWEVER...WINDS OFF OF LAKE MICHIGAN
WILL LIMIT HIGH TEMPERATURES TO THE UPPER 80S THIS AFTERNOON.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

HOT AND HUMID WEATHER WILL REMAIN ACROSS THE AREA THROUGH MUCH OF
NEXT WEEK. HIGH TEMPERATURES ARE EXPECTED TO REACH THE UPPER 90S
SUNDAY...AND THE MID 90S MONDAY AND TUESDAY. THE COMBINATION OF HEAT
AND HUMIDITY WILL ALLOW AFTERNOON HEAT INDICIES TO REACH 100 TO 105.
OVERNIGHT LOW TEMPERATURES WILL ONLY BE IN THE 70S. AN EXCESSIVE
HEAT WATCH IS IN EFFECT FOR CHICAGO AND COOK COUNTY FROM SUNDAY
AFTERNOON THROUGH TUESDAY EVENING. WHILE NOT QUITE AS WARM AS THE
EARLY PORTION OF THE WEEK...TEMPERATURES THROUGH FRIDAY ARE EXPECTED
TO REMAIN NEAR 90.

THE ILLINOIS ENVIRONMENTAL PROTECTION AGENCY HAS DETERMINED THAT AN
AIR POLLUTION ACTION DAY WILL BE DECLARED FOR TOMORROW, SUNDAY JULY
16, 2006 FOR THE GREATER CHICAGO METROPOLITAN AREA. THIS AREA
INCLUDES THE COUNTIES OF
COOK..DUPAGE..KANE..KENDALL..GRUNDY..LAKE..MCHENRY AND WILL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NECESSARY.

&&

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

LMZ740>745-766-160930-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
1000 AM CDT SAT JUL 15 2006

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

.DAY ONE... TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

&&

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