Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 172015
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

TO BE ISSUED SHORTLY.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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