Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 050521
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1221 AM CDT THU MAY 5 2016

.UPDATE...
843 PM CDT

ONLY MINOR CHANGES MADE TO THE FORECAST THROUGH THURSDAY MORNING.
A SHARPLY DEFINED COMMA-HEAD SIGNATURE ASSOCIATED WITH AN UPPER
LOW IS OVER NORTHERN INDIANA/SOUTHERN MICHIGAN THIS EVENING.
FORCING FOR ASCENT WITH THIS HAS RETROGRADED WESTWARD INTO THE
FORECAST AREA BUT WILL BEGIN TO SHIFT MORE SOUTHWARD THE REST OF
TONIGHT. SOME LIGHT RAIN SHOWERS MAY REACH AS FAR EAST AS NEAR
I-57...BUT FOR THE MOST PART SHOULD ONLY BE IN NORTHWEST INDIANA.
THE PRESSURE GRADIENT TIGHTENING AROUND THE SYSTEM WILL LEAD TO AN
INCREASE IN BLUSTERY CONDITIONS THE REST OF TONIGHT IN FAR
NORTHEAST ILLINOIS AND FAR NORTHWEST INDIANA. HAVE BUMPED UP
CLOUD FORECAST FOR EASTERN AREAS EARLY THURSDAY BUT STILL
EXPECTING CLEARING BY LATE MORNING. THE TEMPERATURE FORECAST LOOKS
ON TRACK.

MTF

&&

.SHORT TERM...
213 PM CDT

THROUGH THURSDAY...

THE REMAINDER OF THE AFTERNOON WILL CONTINUE TO BE GLOOMY AND
BLUSTERY WITH CLOUDY SKIES AND GUSTY NORTH-NORTHWEST WINDS.  HI-RES
GUIDANCE CONTINUES TO BACK OFF ON SHOWER ACTIVITY THIS AFTERNOON.
SURFACE DEWPOINT DEPRESSIONS ARE ALSO A BIT HIGHER THAN I WOULD LIKE
TO SEE...BUT DECIDED TO KEEP ISOLATED LIGHT RAIN SHOWERS IN THE
FORECAST THIS AFTERNOON AS A FEW SPRINKLES ARE POSSIBLE. NOT
EXPECTING MUCH PRECIP AT ALL...AND THINKING THE VAST MAJORITY OF THE
REGION WILL SEE DRY CONDITIONS THROUGH TONIGHT.  KEPT A CHANCE OF
SHOWERS OVER NORTHWEST INDIANA LATE THIS EVENING AS GUIDANCE
INDICATES THAT THE BAND OF SHOWERS OVER MICHIGAN WILL ROTATE
SOUTHWEST THIS EVENING.

HIGH PRESSURE THEN SPREADS OVER THE REGION THURSDAY. CLOUDS SCATTER
OUT THROUGH THE MORNING AND WINDS LIGHTEN. EXPECTING A LAKE BREEZE
TO FORM IN THE AFTERNOON. HIGH TEMPS WILL BE IN THE 60S AWAY FROM
THE LAKE AND IN THE 50S ALONG THE LAKE SHORE.

JEE

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

237 PM...FORECAST CONCERNS INCLUDE VERY WARM TEMPS FRIDAY...
CHANCE OF THUNDERSTORMS LATE FRIDAY NIGHT INTO SATURDAY AHEAD OF
A COLD FRONT AND THEN AN UNSETTLED PATTERN NEXT WEEK.

A RIDGE OF HIGH PRESSURE WILL BE MOVING ACROSS THE AREA THURSDAY
NIGHT. AS WARM AIR ADVECTION BEGINS TO SPREAD ACROSS THE REGION...
THERE WILL BE AN INCREASE IN MID LEVEL MOISTURE/CLOUDS AND THERE
IS A SMALL POTENTIAL FOR A FEW LIGHT SHOWERS OR SPRINKLES FRIDAY
MORNING BUT MAINTAINED A DRY FORECAST FROM THIS DISTANCE. THE REST
OF FRIDAY IS SHAPING UP TO BE VERY WARM WITH HIGHS INTO THE LOWER
80S MOST AREAS IN ILLINOIS AND MID/UPPER 70S IN NORTHWEST INDIANA.
LOW LEVEL WINDS AROUND/JUST UNDER 10KTS FRIDAY AFTERNOON WOULD
SUGGEST A LAKE BREEZE PROBABLY WILL FORM ALONG THE IL SHORE BUT
PERHAPS NOT MOVE TOO FAR INLAND BUT CONFIDENCE IS LOW GIVEN HOW
COLD THE LAKE REMAINS AND HOW WARM INLAND TEMPS WILL BE. POSSIBLE
THAT THE LAKE BREEZE COULD MOVE FURTHER INLAND THEN CURRENTLY
EXPECTED...ESPECIALLY BY LATE AFTERNOON/EARLY EVENING.

A COLD FRONT WILL MOVE SOUTH ACROSS LAKE MICHIGAN FRIDAY NIGHT
ARRIVING INTO NORTHERN IL JUST AFTER DAYBREAK SATURDAY MORNING
AND THEN CONTINUING SOUTH ACROSS THE AREA DURING THE MORNING.
SHOWERS AND A FEW THUNDERSTORMS WILL BE POSSIBLE FROM EARLY
SATURDAY MORNING THROUGH MID SATURDAY AFTERNOON...ENDING NORTH TO
SOUTH. TEMPS WILL BE TRICKY SATURDAY...LIKELY REMAINING STEADY
NEAR THE LAKE...PERHAPS ONLY IN THE 50S. THEN RISING SOUTH OF THE
FRONT IN THE MORNING THEN RISING NORTH OF THE FRONT...AWAY FROM
THE LAKE IN THE AFTERNOON AS SKIES CLEAR. BUT FOR MUCH OF THE AREA
NORTH OF THE KANKAKEE/ILLINOIS RIVERS...SATURDAY WILL BE MUCH
COOLER. THE FRONT SHOULD MOVE FAR ENOUGH SOUTH OF THE AREA TO END
PRECIP CHANCES EVERYWHERE SATURDAY EVENING...BUT CLOSE ENOUGH TO
MAINTAIN LOW CHANCE POPS ACROSS THE FAR SOUTH.

WEAK HIGH PRESSURE WILL BUILD ACROSS THE GREAT LAKES REGION
SUNDAY AND SUNDAY NIGHT...AS THE COLD FRONT BEGINS TO MOVE BACK
NORTH AS A WARM FRONT MONDAY AHEAD OF LOW PRESSURE WHICH WILL MOVE
ACROSS THE AREA TUESDAY OR WEDNESDAY. THERE REMAINS SOME LARGE
TIMING DIFFERENCES BETWEEN THE GFS AND ECMWF SO CONFIDENCE
REGARDING TIMING IS LOW BUT CHANCE POPS WARRANTED FROM SUNDAY
NIGHT THROUGH WEDNESDAY...THOUGH THERE WILL LIKELY BE PROLONGED
DRY PERIODS. WITH THE CURRENT EXPECTED LOW TRACK SOUTH OF THE
LAKE...THAT WILL LIKELY MEAN EASTERLY FLOW AND COOLER ONSHORE
FLOW...FOR PERHAPS SEVERAL DAYS. CMS

&&

.AVIATION...
FOR THE 06Z TAFS...

HIGH PRESSURE STRETCHES FROM LAKE SUPERIOR INTO THE CENTRAL PLAINS
AND WILL INCH TOWARDS NORTHERN ILLINOIS OVERNIGHT AND THROUGH THE
DAY THURSDAY. A MODEST NORTHERLY GRADIENT PERSISTS ACROSS NORTHERN
ILLINOIS LATE THIS EVENING AHEAD OF THE RIDGE AXIS...WHICH WILL
ALLOW A NORTHERLY BREEZE WITH GUSTS TO AROUND 20 KT AT TIMES TO
CONTINUE THROUGH MUCH OF THE OVERNIGHT HOURS. IN ADDITION...AN UPPER
LOW OVER INDIANA LATE THIS EVENING WILL CONTINUE TO RESULT IN SOME
SHOWERS ACROSS NORTHERN INDIANA AND LAKE MICHIGAN. GYY SHOULD BE THE
ONLY TERMINAL THAT SEES PRECIP...THOUGH MDW IN PARTICULAR MAY BE
CLOSE AND CANNOT RULE OUT A FEW SPRINKLES AND/OR SOME MVFR CIGS
SNEAKING THAT FAR WEST...WITH FEW018 ALREADY SHOWING UP IN THE
MDW OB.

VFR CONDITIONS AND MODEST NORTH WINDS WILL CONTINUE THROUGH THE DAY
THURSDAY...THOUGH SHOULD SEE GUSTS TAPERING THROUGH THE DAY AS THE
RIDGE GETS CLOSER AND THE GRADIENT TO RELAXES. ANTICIPATE A LAKE
BREEZE WILL FORM DURING THE AFTERNOON TURNING WINDS TO THE
NORTHEAST. AROUND SUNSET THURSDAY EVENING...WINDS ARE EXPECTED TO
BECOME LIGHT AND VARIABLE AS THE HIGH MOVES OVERHEAD...THEN
EVENTUALLY BECOME WESTERLY BY EARLY FRIDAY AS THE RIDGE SINKS TO
OUR SOUTH.

BMD

&&

.MARINE...
213 PM CDT

HEADLINES...WILL CONTINUE THE GALE WARNING AND SMALL CRAFT AS
PLANNED.

WINDS AND WAVES SUBSIDE AS HIGH PRESSURE BUILDS OVERHEAD TONIGHT.
WINDS BECOME SOUTH TO SOUTHWEST BY FRIDAY MORNING AND INCREASE
THROUGH THE DAY AHEAD OF THE NEXT LOW PRESSURE SYSTEM THAT PASSES
OVER ONTARIO. THE LOWS COLD FRONT SHIFTS DOWN THE LAKE FRIDAY NIGHT
INTO SATURDAY MORNING WITH WINDS BECOMING NORTH TO 30 KT BEHIND IT.
A SMALL CRAFT ADVISORY MAY BE NEEDED FOR HIGH WAVES SATURDAY.
ANOTHER HIGH PRESSURE SYSTEM MOVES OVER THE LAKE SUNDAY BEFORE
QUICKLY SHIFTING EAST OVER THE EAST COAST EARLY MONDAY MORNING.
WHILE GUIDANCE DIFFERS ON THE PATH OF THE LOW MID NEXT WEEK...BOTH
AGREE THAT A LOW MAY IMPACT THE MIDWEST REGION IN THE MIDDLE PART OF
NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ743-LMZ744-LMZ745-LMZ777-LMZ779 UNTIL 4 AM
     THURSDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 AM THURSDAY TO 7
     PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 AM THURSDAY.

&&

$$

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