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000
FXUS63 KLOT 181940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
240 PM CDT TUE JUN 18 2013

.DISCUSSION...
239 PM CDT

STRATUS LAYER THAT WAS ANCHORED OVER FAR NORTHEAST IL/NORTHWEST IN
THIS MORNING HAS ERODED WITH THE WARM AIR HEATING THE SFC. VISIBLE
IMAGERY INDICATES A FEW AREAS OF CUMULUS CLOUDS THAT HAVE DEVELOPED
THIS AFTERNOON ACROSS NORTHERN IL. IN ADDITION SOME BUILDING CUMULUS
CLOUDS WERE NOTED ALONG A PONTIAC TO KANKAKEE LINE...IN AN AREA OF A
STRONGER THERMAL DIFFERENTIAL. HOWEVER THE LIFT MECHANISM IN THIS
AREA IS MINIMAL...AND SO A FEW ISOLATED SHOWERS/THUNDERSTORMS MAY
DEVELOP BUT QUICKLY DISSIPATE. ALL PRECIPITATION OVER THE CWFA WILL
BE DIURNALLY DRIVEN...THUS BY SUNSET OR IMMEDIATELY AFTER SUNSET
PRECIP WILL COME TO AN END. FURTHER SOUTH STRONGER INSTABILITY WAS
POSITIONED ACROSS CENTRAL IL STRETCHING WEST THROUGH NORTHERN
MISSOURI. MID-LVL WAVE CONTINUES TO PIVOT EAST ACROSS FAR NORTHWEST
IL THIS AFTERNOON...AND WILL MAINTAIN THE NORTHEAST FLOW ACROSS MUCH
OF THE CWFA. AS A RESULT COOL TEMPS WILL PERSIST THIS EVENING...WITH
MINIMAL CLOUD COVER FROM THE DIFFLUENT FLOW ALOFT. SKIES WILL BECOME
MOSTLY CLEAR TONIGHT...WITH THE LLVL FLOW WEAKENING. THIS SHOULD
PROVIDE DECENT RADIATIONAL COOLING WITH TEMPS OVERNIGHT EXPECTED TO
BE IN THE MID 50S SOUTH OF I-80. FURTHER NORTH TEMPS WILL BE MUCH
COOLER TO ARND 50...POSSIBLY THE UPR 40S FOR AREAS ALONG AND NORTH
OF A ROCKFORD...AURORA...WAUKEGAN LINE.

CONFIDENCE...HIGH.

WEDNESDAY THROUGH THURSDAY...

500MB TROUGH AXIS SLOWLY PIVOTS TO THE EASTERN GREAT LAKES WED...AND
WILL CONTINUE TO PUSH EAST THUR. THE SFC RIDGE WILL ALSO BEGIN TO
PUSH EAST...HOWEVER AN ONSHORE OR NORTHEAST TO EAST FLOW WILL
PERSIST INTO WED FOR MUCH OF NORTHERN IL. THE DIFFERENCE FOR WED
WILL BE THAT THE 850MB THERMAL TROUGH WILL LINGER OVERHEAD. WITH
ABUNDANT SUNSHINE AND SFC HEATING...TEMPS SHUD WARM INTO THE MID/UPR
70S OR POSSIBLY THE LOW 80S FROM LASALLE TO IROQUOIS COUNTY.

FOR THUR 500MB HEIGHTS WILL BEGIN TO RISE WITH FLOW BEGINNING TO
TURN TO THE SOUTHEAST IN THE LLVLS. A WEAK LAKE BREEZE MAY DEVELOP
AND PUSH INTO LAKE COUNTY IL...WHICH WOULD MOST LIKELY PROVIDE A
COOLING TREND IN THE AFTN HOURS. 850MB TEMPS WILL STEADILY WARM FOR
THUR TO ARND 14 TO 16 DEG C...WITH CONTINUED THIN CLOUD COVER. THIS
WILL ALLOW TEMPS TO WARM INTO THE LOW/MID 80S. THE CAVEAT WILL BE
AREAS OF LAKE COUNTY IL POST FRONTAL PASSAGE THAT WILL ALLOW TEMPS
TO FALL INTO THE 60S IN THE AFTN.

IT DOES APPEAR THAT ENOUGH DRY AIR WILL LINGER THRU THUR
AFTN/EVE...THUS HAVE HELD ONTO A DRY FORECAST IN THIS TIMEFRAME.
THIS PATTERN WILL BE CHANGING AS WE MIGRATE INTO THE EXTENDED
PERIODS.

CONFIDENCE IN TEMPERATURE FORECAST...HIGH.
CONFIDENCE IN DRY WEATHER THROUGH THUR...MEDIUM/HIGH.

FRIDAY THROUGH MONDAY...
MINIMAL CHANGES FROM PREVIOUS FORECAST IN REGARDS TO THE EXTENDED
PERIODS. POSSIBLY THE FIRST STRETCH OF 90 DEG DAYS IS UPON US FOR
SUN/MON/TUE.

GUIDANCE HAS A WARM FRONTAL BOUNDARY LIFTING OVERHEAD FRI WITH
SOUTHERLY FLOW USHERING IN ADDTL LLVL MOISTURE. IT DOES APPEAR A
WAVE WILL ALSO PUSH OVER THE CWFA FRI...WITH POTENTIAL FOR
SHOWERS/THUNDERSTORMS. TEMPS WILL BE SLIGHTLY WARM FOR FRI INTO THE
UPR 80S...WITH A FEW 90 DEGREE POINTS ACROSS THE CWFA.

ENSEMBLES FOR SEVERAL DAYS HAVE CONTINUED TO INDICATE THAT A 500MB
RIDGE ACROSS THE CENTRAL CONUS WILL ADVECT EAST AND BECOME ANCHORED
ACROSS THE EASTERN HALF OF THE CONUS BY THE WEEKEND AND POSSIBLY
PERSIST THROUGH EARLY NEXT WEEK. ADDITIONALLY...GUIDANCE HAS PROGGED
850MB TEMPS TO RISE TO ARND 20-22 DEG C FOR THE WEEKEND THRU EARLY
NEXT WEEK. CONSISTENCY FROM PREVIOUS RUNS SUGGESTS HIGH CONFIDENCE
IN THIS WARM STRETCH ARRIVING. THEN SUN/MON/TUE APPEAR TO BE NEAR
CARBON COPIES WITH TEMPS EASILY WARMING TO 90 DEGREES...POSSIBLY THE
LOW 90S. CLIMATOLOGY BASED ON THE 850MB TEMPS PROGGED AND TIME OF
YEAR WOULD SUGGEST TEMPS TO BE WARMER AS FORECASTED. A COUPLE
LIMITING FACTORS MIGHT BE THE POTENTIAL FOR A SERIES OF WAVES
BRINGING INSTABILITY AND THUNDERSTORM POTENTIAL EACH DAY OF THE
EXTENDED...ALONG WITH DEW PTS PROGGED TO BE ARND 70 DEG.
THIS COULD POTENTIALLY KEEP TEMPS IN CHECK IN THE MID/UPR 80S.

CONFIDENCE IN TEMPERATURE FORECAST...HIGH.
CONFIDENCE IN PRECIP/CONVECTIVE FORECAST...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY NORTHEAST WINDS INTO THIS EVENING. CMS

//DISCUSSION...UPDATED 18Z...

IFR/LIFR CIGS STILL PERSISTING SOUTH OF MDW FROM IGQ TO GYY EAST
ALONG THE INDIANA SHORELINE. CLEARING FROM THE EAST ALONG WITH
EROSION FROM THE SOUTHWEST SEEMS TO HAVE SLOWED IN THE PAST HR OR
SO. WHILE VFR CONDITIONS ARE NOW EXPECTED AT ORD/MDW...WILL NEED
TO MONITOR TRENDS FOR GYY THROUGH THE AFTERNOON. SOME CU ALONG
WITH MID CLOUDS POSSIBLE THROUGH EARLY EVENING...THEN SKC EXPECTED
FOR THE REMAINDER OF THE PERIOD.

NORTHEAST WINDS WILL REMAIN IN THE 10-15KT RANGE WITH GUSTS IN THE
16-20KT RANGE INTO THIS EVENING WITH WINDS DIMINISHING UNDER 10KTS
BY MID/LATE EVENING THEN TURNING MORE EASTERLY WEDNESDAY MORNING.

AS A WEAK WAVE MOVES SOUTH OF THE TERMINALS THIS AFTERNOON...THERE
COULD BE SOME SHOWERS AND POSSIBLY AN ISOLATED TSRA BUT ANY
ACTIVITY THAT DEVELOPS IS EXPECTED TO REMAIN SOUTH OF ALL THE
TERMINALS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE REGARDING WIND SPEEDS/GUSTS THROUGH THE
  PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...VFR.
FRIDAY THROUGH MONDAY...PERIODIC CHANCES FOR THUNDERSTORMS...ELSE VFR.

BMD

&&

.MARINE...
137 PM CDT

A SURFACE RIDGE OF HIGH PRESSURE ACROSS THE UPPER GREAT LAKES
REGION...WILL SHIFT EASTWARD TOWARDS NEW ENGLAND BY WEDNESDAY
EVENING. MEANWHILE...LOW PRESSURE IS EXPECTED TO TAKE SHAPE ACROSS
THE PLAINS STATES. THIS PRESSURE PATTERN WILL REMAIN IN PLACE FOR A
FEW DAYS INTO THE WEEKEND. OVERALL...THIS WILL RESULT IN A PROLONGED
PERIOD OF SOUTHERLY WINDS ACROSS THE LAKE. WIND MAGNITUDES GENERALLY
LOOK TO BE IN THE 10 TO 20 KT RANGE...WITH A FEW PERIODS OF 15 TO 25
KT SOUTHERLY WINDS...ESPECIALLY LATER IN THE PERIOD.

THERE WILL ALSO BE INCREASING CHANCES FOR A FEW PERIODS OF
THUNDERSTORM ACTIVITY FRIDAY AND INTO THE WEEKEND OVER THE LAKE. A
FAIRLY ACTIVE WEATHER PATTERN LOOKS TO SETUP UP ACROSS THE GREAT
THE NORTHERN CONUS AND GREAT LAKES REGION.

IN THE SHORTER TERM...I HAVE EXTENDED THE SMALL CRAFT ADVISORY INTO
THIS EVENING FOR THE ILLINOIS SHORES AND MAINTAINED THE ADVISORY
THROUGH LATE TONIGHT FOR THE INDIANA SHORES. LOCAL BUOY OBS INDICATE
WAVES AROUND 4 FT...AND WITH THE ONSHORE FLOW CONTINUING TO BE IN THE
15 TO 20 KT RANGE AHEAD OF THE SURFACE HIGH...I DO NOT SEE ANY
IMPROVEMENT IN THE WAVE CONDITIONS FOR SEVERAL MORE HOURS.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 4 AM WEDNESDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 4 AM WEDNESDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS UNTIL 10 PM TUESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE NORTHERLY IS TO MICHIGAN CITY IN UNTIL 4 AM
     WEDNESDAY.

&&

$$

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