Area Forecast Discussion
Issued by NWS Chicago, IL

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286
FXUS63 KLOT 040911
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
411 AM CDT WED MAY 4 2016

.SHORT TERM...
326 AM CDT

TODAY THROUGH THURSDAY NIGHT...

NEAR TERM FOCUS IS ON BLUSTERY...COOLER AND SHOWERY WEATHER
CONDITIONS TODAY.

A STRONG MID-LEVEL SHORT WAVE WAS DIGGING SOUTHEAST ACROSS THE
AREA EARLY THIS MORNING...AND WILL CONTINUE TO CARVE OUT A CLOSED
UPPER LOW OVER THE MIDWEST AND OHIO VALLEY THROUGH THIS EVENING AS
ADDITIONAL SHORT WAVE ENERGY WRAPS IN TO THE DEEPENING TROUGH FROM
THE NORTH. COINCIDENT WITH THE INITIAL VORT IS THE PASSAGE OF A
STRONG COLD FRONT...WHICH WILL BRING SHARPLY COOLER TEMPERATURES
AS WELL AS BLUSTERY NORTH WINDS TO THE REGION TODAY. CYCLONIC FLOW
AND COOL AIR ALOFT WILL SUPPORT WEAK INSTABILITY AND RESULT IN
EXTENSIVE STRATOCU AND SCATTERED SHOWERS FROM LATER THIS MORNING
THROUGH THIS AFTERNOON. STEEPEST LAPSE RATES WILL LIKELY BE OVER
THE ILLINOIS PORTION OF THE FORECAST AREA...WHILE NORTH FLOW OFF
COOL LAKE MICHIGAN WATERS WILL KEEP THE BOUNDARY LAYER MORE STABLE
ACROSS NORTHWEST INDIANA. BASED ON MODEL LOW LEVEL THERMAL
FIELDS...TEMPS MAY STRUGGLE TO BREAK THE 50 DEGREE MARK NEAR THE
LAKE IN NORTHWEST INDIANA...WHILE APPROACHING THE 60 DEGREE MARK
ACROSS THE WESTERN PARTS OF THE CWA. NORTH WIND GUSTS OF 25 TO 30
MPH WILL MAKE IT FEEL EVEN CHILLIER. A FEW SHOWERS WILL LIKELY
LINGER INTO THIS EVENING ESPECIALLY ACROSS THE SOUTHEASTERN CWA
WITH SECONDARY VORT PASSING OVERHEAD...BEFORE COMBINATION OF DRIER
AIR...SUBSIDENCE AND LOSS OF WEAK DIURNAL COMPONENT SHUTS OFF
PRECIP POTENTIAL. UNSEASONABLY CHILLY CONDITIONS CONTINUE TONIGHT
WITH READINGS EXPECTED TO FALL INTO THE MID-UPPER 30S ACROSS MANY
NORTHERN IL LOCATIONS. NORTH WINDS WILL LIKELY STAY STRONG ENOUGH
OVERNIGHT TO PREVENT ANY APPRECIABLE FROST THREAT.

STRONG HEIGHT RISES DEVELOP LATE TONIGHT AND THURSDAY AS THE DEEP
EASTERN TROUGH DRIFTS AWAY FROM THE REGION...AND UPPER RIDGING
OVER THE CENTRAL CONUS BEGINS TO SPREAD IN FROM THE WEST. SURFACE
HIGH PRESSURE RIDGE SLOWLY EDGES INTO THE FORECAST AREA LATER IN
THE DAY. DECREASING NORTH WINDS WILL LIKELY RESULT IN A
NORTHEASTERLY LAKE BREEZE DEVELOPING BY THURSDAY
AFTERNOON...THOUGH MOSTLY SUNNY SKIES AND MODERATING TEMPS WILL
MAKE FOR A BETTER DAY. TEMPS LOOK TO RECOVER INTO THE MID-UPPER
50S AWAY FROM THE IMMEDIATE LAKE SHORE IN THE EAST AND INTO THE
MID 60S FARTHER WEST ACROSS NORTH CENTRAL IL. TEMPS WILL COOL
QUICKLY THURSDAY EVENING WITH LIGHT WINDS AND MAINLY CLEAR
SKIES...THOUGH DEVELOPMENT OF WARM ADVECTION ALOFT WILL HELP KEEP
OVERNIGHT LOWS IN CHECK IN THE 40S.

RATZER

&&

.LONG TERM...
326 AM CDT

FRIDAY THROUGH TUESDAY...

FRIDAY WILL BRING A BIG WARM-UP TO THE REGION AS THE UPPER RIDGE
BUILDS IN FROM THE WEST. WEST-SOUTHWEST SURFACE WINDS DEVELOP AND
STRENGTHEN JUST ENOUGH TO PREVENT MUCH INLAND PUSH TO THE LAKE
BREEZE BOUNDARY OVER NORTHEAST ILLINOIS FRIDAY AFTERNOON...WITH
MOSTLY SUNNY SKIES HELPING TO WARM TEMPS NEARLY 20 DEGREES OVER
THURSDAYS NUMBERS. LOW LEVEL THERMAL PROGS SUPPORT HIGHS FROM THE
MID-UPPER 70S EAST TO THE LOW-MID 80S FARTHER WEST.

UNFORTUNATELY...GUIDANCE REMAINS IN GOOD AGREEMENT IN BRINGING A
FAIRLY STRONG SHORT WAVE ACROSS THE TOP OF THE RIDGE OVER THE
NORTHERN LAKES FRIDAY NIGHT THROUGH SATURDAY...WITH A SURFACE COLD
FRONT SAGGING INTO THE AREA EARLY SATURDAY. WINDS SHIFT NORTH-
NORTHEAST BEHIND THE FRONT WHICH WILL BRING AN END TO THE BRIEF
WARM-UP FOR AREAS NEAR LAKE MICHIGAN. TEMPS MAY REACH THE 60S
BEFORE THE COOL ADVECTION PUSH BEHIND THE BACK DOOR FRONT
CAUSES TEMPS TO FALL DURING THE AFTERNOON NEAR THE LAKE. EVEN WELL
INLAND TEMPS WILL LIKELY FALL FROM THE 70S INTO THE 60S BY LATE
AFTERNOON AS NORTH-NORTHEAST WINDS PICK UP. AS MODELS HAVE
CONTINUED TO TREND EARLIER WITH THE COLD FRONT SATURDAY...THE
GREATEST CHANCE OF THUNDERSTORMS WILL LARGELY BE ACROSS THE
SOUTHERN HALF OF THE CWA. THE FRONT THEN SAGS ALL THE WAY TO THE
OHIO VALLEY SATURDAY NIGHT... FOCUSING PRECIP POTENTIAL MAINLY
SOUTH OF THE CWA UNTIL THE FRONT RETURNS AS A WARM FRONT MONDAY-
TUESDAY. WHILE IT WILL BE COOLER WITH THE FRONT TO OUR SOUTH
THROUGH THE END OF THE EXTENDED PERIOD...IT WILL BE MILDER THAN
THE VERY NEAR TERM. TEMPS LOOK TO RANGE FROM THE 50S/60S RIGHT
ALONG THE LAKE TO THE 70S OVER SOUTHERN AND WESTERN PARTS OF THE
FORECAST AREA.

RATZER

&&

.AVIATION...
UPDATE FOR 09Z TAFS...
STABLE CONDITIONS BEHIND THE DEPARTING LINE OF SHOWERS HAS SLOWED
THE ARRIVAL OF GUSTIER NORTHERLY WINDS TO THE TERMINALS THIS
MORNING...HOWEVER ANTICIPATE WINDS TO VEER BACK TO THE NORTH AND
INCREASE OVER THE NEXT HOUR OR TWO. MEANWHILE...MVFR/IFR CIGS ARE
NOW NOTED IN OBS OVER SOUTHEAST WI AND INTO FAR NE IL AND ALSO
EXPECT THOSE TO OVERSPREAD THE CHICAGO AREA TERMINALS OVER THE
NEXT COUPLE HOURS...THEN GRADUALLY LIFT DIURNALLY AFTER DAYBREAK.
CONFIDENCE IN HOW FAR WEST THESE WILL SPREAD IS LOW HOWEVER...SO
HAVE BACKED OFF ON LOWEST CIGS AT RFD...AND MAY HAVE TO FOLLOW
SUIT AT DPA.

PREVIOUS DISCUSSION FOR THE 06Z TAFS...
LINE OF SHOWERS AND THUNDERSTORMS IS DROPPING INTO NORTHERN
ILLINOIS LATE THIS EVENING AND SHOULD BE CLEAR OF THE TERMINALS BY
AROUND 7-8Z. MOST LIGHTNING ACTIVITY THUS FAR HAS BEEN FOCUSED
OVER NORTH CENTRAL ILLINOIS WITH ONLY ISOLATED ACTIVITY FARTHER
EAST...SO WILL ONLY BRING THUNDERSTORMS ON STATION AT RFD...AND
WILL JUST KEEP A VCTS MENTION FOR THE CHICAGO AREA TERMINALS. A
GUST FRONT HAS SURGED OUT AHEAD OF THE MAIN LINE OF SHOWERS AND
WILL BRING STRONG GUSTY NORTHERLY WINDS...THEN BEHIND THE INITIAL
LINE OF SHOWERS AND THUNDERSTORMS THERE MAY BE SOME VARIABILITY OR
LIGHTER WINDS BEFORE THE SYNOPTIC FRONT PUSHES THROUGH A FEW HOURS
LATER WITH GUSTY WINDS PICKING UP AGAIN OUT OF THE NORTH.
CONFIDENCE IS HIGH IN THE GUSTY NORTH WINDS WITH THE GUST
FRONT...HOWEVER CONFIDENCE IN WIND DIRECTION IS LOW FOR THE FEW
HOURS FOLLOWING THE LINE OF PRECIP. HAVE BACKED OFF ON THE IFR
CIGS BEHIND THE FRONT THIS EVENING AS THEY ARE NOT SHOWING UP YET
IN UPSTREAM OBS AND MODELS SEEM TO HAVE BETTER CONSENSUS ON MVFR
OR BETTER CONDITIONS. STRONG GUSTY NORTHERLY WINDS ARE EXPECTED TO
CONTINUE THROUGH THE DAY WEDNESDAY WITH SOME SCATTERED DIURNAL
LIGHT SHOWERS POSSIBLE MAINLY DURING THE AFTERNOON.

BMD

&&

.MARINE...
244 AM CDT

A COLD FRONT IS SWEEPING SOUTH ACROSS LAKE MICHIGAN EARLY THIS
MORNING WITH NORTHERLY WINDS INCREASING IN ITS WAKE. THE GRADIENT
WILL BE STRONGEST TODAY AND TONIGHT ACROSS THE SOUTH HALF OF
LAKE MICHIGAN SUPPORTING GALE FORCE WIND GUSTS THROUGH THAT TIME
FRAME. A GALE WARNING IS IN EFFECT FOR THE OPEN WATERS OF LAKE
MICHIGAN SOUTH OF MANISTEE...AND FOR THE INDIANA/ILLINOIS
NEARSHORE WATERS. HIGH PRESSURE WILL BEGIN BUILD ACROSS NORTHERN
LAKE MICHIGAN THURSDAY ALLOWING WINDS TO DIMINISH. THE HIGH WILL
MOVE SOUTH OF THE LAKE LATE THURSDAY INTO FRIDAY AS LOW PRESSURE
MOVES ACROSS MANITOBA INTO ONTARIO WITH A FRESH SOUTHWESTERLY
BREEZE DEVELOPING...THEN A TRAILING COLD FRONT WILL MOVE SOUTH
ACROSS LAKE MICHIGAN ON SATURDAY WITH NORTHERLY WINDS TO 30 KT
EXPECTED BEHIND THE FRONT.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...ILLINOIS NEARSHORE WATERS UNTIL 3 PM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...3 PM WEDNESDAY TO
     10 AM THURSDAY.

     GALE WARNING...LMZ743-LMZ744-LMZ745-LMZ777-LMZ779 UNTIL 4 AM
     THURSDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 AM THURSDAY TO 3
     PM THURSDAY.

&&

$$

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