Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 140538
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1238 AM CDT MON APR 14 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

//DISCUSSION...UPDATED 06Z...

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874 UNTIL 3 PM
     MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878 UNTIL 3
     PM MONDAY.

&&

$$

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