Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291737
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1237 PM CDT MON SEP 29 2014

.DISCUSSION...
344 AM CDT

HIGH PRESSURE SPANNING THE REGION THIS MORNING PROVIDING ANOTHER
RELATIVELY QUIET START TO THE FORECAST PERIOD...AS TEMPS HAVE
FALLEN TO THE LOW TO MID 50S UNDER CLEAR SKIES. PATCHY FOG HAS
ONCE AGAIN DEVELOP OVER THE ENTIRE CWA EARLY THIS MORNING AND
SIMILAR TO YESTERDAY MORNING...SOME AREAS ARE OCCASIONALLY
OBSERVING VIS FALL UNDER A MILE AT TIMES. WIDESPREAD DENSE FOG
WILL ONCE AGAIN NOT BE OBSERVED THIS MORNING BUT WITH VISIBILITY
LIKELY VARYING OVER SHORT DISTANCES AND AT TIMES UNDER ONE
MILE...DID GO AHEAD AND ISSUE AN SPS THROUGH AROUND SUNRISE.
UPSTREAM TROUGH OF LOW PRESSURE AND COLD FRONT CURRENTLY MOVING
INTO FAR NORTHERN LAKE MICHIGAN THIS MORNING AS VORT MAX OBSERVED
DROPPING INTO THE UPPER MIDWEST. THESE FEATURES WILL DROP SOUTH
TOWARDS THE CWA TODAY BUT BEFORE THEY DO...ANOTHER WARM AND
PLEASANT DAY WILL OCCUR. MADE LITTLE CHANGES TO GOING MAX TEMPS
TODAY AND EXPECT A GOOD PORTION OF THE CWA TO OBSERVE LOWER 80S
TODAY UNDER MOSTLY SUNNY CONDITIONS. ALTHOUGH THERE WILL BE SOME
LAKE COOLING TODAY...DONT ANTICIPATE IT TO BE TOO MUCH NOT LET
AREAS NEAR THE LAKE OBSERVE SLIGHTLY WARMER CONDITIONS THAN HAS
BEEN OBSERVED OVER THE LAST COUPLE DAYS. THIS WILL BE DUE TO
WESTERLY WINDS KEEPING THE LAKE BREEZE RIGHT ALONG THE SHORE...AND
HAVE INCREASED TEMPS TO MID TO UPPER 70S IN THESE AREAS.

EXPECT RAPIDLY CHANGING CONDITIONS LATER TODAY WITH THE APPROACH
OF THE FRONT TO THE NORTH...WITH IT APPEARING TO HAVE A FASTER
ARRIVAL TIME. THIS FRONT ALONG WITH CLOUDIER AND COLDER CONDITIONS
SHOULD REACH THE FAR NORTHERN TIER OF COUNTIES BY THE 23-00Z TIME
FRAME....LIKELY SENDING THE WARMER TEMPS INTO THE 50S BY THE
EVENING. PREVIOUS TRENDS OF PRECIP POSSIBLY REACHING THE
NORTH/NORTHEAST PORTION OF THE CWA WITH THE APPROACH OF THIS
FRONT/VORT MAX HAVE CONTINUED...AND HAVE EXPANDED PRECIP MENTION
TO AREAS IN NORTH/NORTHEAST ILLINOIS LATE THIS AFTERNOON INTO THE
EVENING. ONLY HAVE SLIGHT CHANCE WORDING AS AM NOT OVERLY
CONFIDENT WITH OVERALL COVERAGE AND INTENSITY WITH WHATEVER
APPROACHING PRECIP LIKELY OBSERVING A DIMINISHING TREND WITH THE
DEPARTURE OF THE BEST FORCING TO THE EAST. CLOUDY AND COOL
CONDITIONS WILL THEN BE OBSERVED TONIGHT WITH THE ARRIVAL OF THIS
COLDER AIRMASS...AS TEMPS IN THE LOW/MID 40S LIKELY OVER NORTHERN
ILLINOIS AND LOW 50S ELSEWHERE.

WITH LINGERING CLOUD COVER AND THIS COLDER AIRMASS IN PLACE...ALSO
LOWERED TEMPS ON TUESDAY WITH SOME LOCATIONS POSSIBLY NOT MAKING
IT OUT OF THE 50S. TUESDAY WILL BE DRY THOUGH AS VORT MAX WILL BE
WELL EAST OF THE REGION AND A PERIOD OF RIDGING OCCURS OVER THE
MIDWEST AND GREAT LAKES REGION. LONGWAVE TROUGH WILL BE PUSHING
THROUGH WESTERN AND CENTRAL CONUS DURING THIS TIME...WITH A FAIRLY
VIGOROUS VORT MAX LIFTING NORTH THROUGH THE CENTRAL AND NORTHERN
PLAINS INTO TUESDAY NIGHT. BACKING WINDS ALOFT OUT AHEAD OF THIS
SYSTEM WILL HELP TEMPS REBOUND ON WEDNESDAY AS A PERIOD WAA
OCCURS...WITH 70 DEGREE WEATHER TRYING TO RETURN. VORT MAX WILL
QUICKLY LIFT NORTH INTO CANADA WEDNESDAY AS ANOTHER TROUGH DIGS
INTO THE CENTRAL PLAINS. THIS WILL SHIFT THE LONGWAVE TROUGH
TOWARDS THE CWA BY EARLY THURSDAY...AS ATTENDANT SURFACE
TROUGH/LOW MOVE THROUGH THE MID MISSISSIPPI VALLEY. GUIDANCE
VARIES WITH REGARDS TO EVOLUTION OF SURFACE FEATURES DURING THIS
TIME BUT SHORTWAVE ENERGY RIDING OUT AHEAD OF THIS TROUGH AS WELL
AS INCREASING MOISTURE WILL ALLOW FOR PRECIP TO WORK ITS WAY INTO
THE CWA...LIKELY REACHING THE WESTERN CWA EARLY THURSDAY. BEST
CHANCES CWA WIDE WILL BE DURING THE DAY ON THURSDAY...WITH THE
BEST CHANCES FOR THUNDER ALSO OCCURRING DURING THIS TIME.
CONFIDENCE IS LOW WITH REGARDS TO THE EXTENT OF INSTABILITY
PRESENT BUT WITH INCREASING MOISTURE AND BETTER FORCING MOVING
OVERHEAD...ENOUGH INSTABILITY SHOULD BE PRESENT FOR THUNDERSTORM
DEVELOPMENT ACROSS THE CWA.

RODRIGUEZ

&&

.AVIATION...

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

* COLD FRONT SHIFTING WINDS TO THE NORTHEAST EARLY THIS EVENING.
* MVFR AND POSSIBLY IFR CIGS OVERSPREADING TERMINALS BEHIND THE
  FRONT...WITH A WINDOW OF LIGHT RAIN AND DRIZZLE EXPECTED.

BMD

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

A COLD FRONT CONTINUES TO SLIP SOUTH ACROSS WISCONSIN AND LAKE
MICHIGAN THIS AFTERNOON BUT IN THE MEANTIME...VFR CONDITIONS AND
LIGHT WESTERLY FLOW WILL PREVAIL AT THE TERMINALS. THE FRONT WILL
ARRIVE BY EARLY THIS EVENING TURNING WINDS SHARPLY TO THE NORTHEAST
WITH GUSTS UP TO AROUND 20 KT AT TIMES BEHIND THE FRONT. LOWER CIGS
ARE ALSO EXPECTED TO OVERSPREAD THE TERMINALS BEHIND THE
FRONT...WITH HIGH CONFIDENCE IN LOWER END MVFR CIGS AND A DECENT
SHOT AT IFR CIGS. MOISTURE BEHIND THE FRONT IS SOMEWHAT SHALLOW BUT
THERE IS MODEST POST FRONTAL FORCING THAT COULD HELP SQUEEZE OUT
SOME LIGHT RAIN OR DRIZZLE THIS EVENING INTO THE OVERNIGHT HOURS. BY
THE PREDAWN HOURS TUESDAY FORCING DISSIPATES WHILE LOWER MOISTURE
LINGERS. THERE IS EXPECTED TO BE A SLIGHT DIURNAL LIFT OF THE CLOUD
BASES DURING THE DAY TUESDAY...HOWEVER MVFR CIGS ARE EXPECTED TO
LINGER THROUGH THE DAY.

BMD


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

* HIGH CONFIDENCE IN TIMING WIND SHIFT TO WITHIN AN HOUR.
* HIGH CONFIDENCE IN MVFR CIGS...LOW-MEDIUM CONFIDENCE IN A WINDOW
  OF IFR CIGS AND LIGHT RAIN/DRIZZLE.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR. EAST WINDS.

WEDNESDAY...VFR. SOUTHEAST WINDS.

THURSDAY...TSRA LIKELY...MVFR POSSIBLE. SOUTH WINDS TURNING
SOUTHWEST LATE.

FRIDAY...SLIGHT CHANCE SHRA...MVFR POSSIBLE. BREEZY WEST WINDS.

SATURDAY...SLIGHT CHANCE SHRA. VFR. WEST WINDS.

SUNDAY...VFR. SOUTHWEST WINDS.

MDB

&&

.MARINE...
257 AM CDT

A STRONG COLD FRONT WILL MOVE SOUTHWARD DOWN LAKE MICHIGAN TODAY
BRINGING A SHIFT TO NORTH AND NORTHEAST WINDS WITH A SHARP INCREASE
IN SPEEDS. HIGH PRESSURE WHICH HAS BEEN ACROSS THE REGION FOR
SEVERAL DAYS IS WEAKENING AND PUSHING SOUTHWARD ACROSS THE OHIO
VALLEY AND SOUTHEAST U.S. WEAK SURFACE LOW PRESSURE HAS DEVELOPED
AND IS MOVING EASTWARD ACROSS NORTHERN LAKE MICHIGAN EARLY THIS
MORNING DRAGGING THE COLD FRONT WITH IT. STRONG HIGH PRESSURE IS
CENTERED OVER NORTHERN ONTARIO AND WILL MOVE SOUTHWARD BUT WEAKEN AS
IT DOES SO. THE FRONT WILL REACH THE NORTHERN SHORE OF THE LAKE
TOWARD OR SOON AFTER DAYBREAK AND PUSH SOUTHWARD REACHING THE
SOUTHERN TIP EARLY THIS EVENING. SPEEDS WILL INCREASE INTO THE 20-25
KT RANGE WITH GUSTS PUSHING 30 KT BEHIND THE FRONT...ESPECIALLY
ACROSS NORTHERN SECTIONS OF THE LAKE. STRONGER GUSTS HAVE OCCURRED
ACROSS LAKE SUPERIOR EARLY THIS MORNING BUT THE PRESSURE GRADIENT
WILL LIKELY NOT BE QUITE AS STRONG AS IT MOVES ACROSS LAKE MICHIGAN.
CANNOT RULE OUT A SHORT PERIOD OF GUSTS TOPPING 30 KT NORTH THIS
MORNING HOWEVER. EXPECT THE 25-30 KT GUSTS TO SPREAD ACROSS THE
SOUTH END OF THE LAKE THIS AFTERNOON AS WELL AND WILL HOIST A SMALL
CRAFT ADVISORY FOR THE IL/IN NEARSHORE WATERS FROM FIRST THING THIS
EVENING CONTINUING UNTIL LATE TUESDAY AFTERNOON. WINDS WILL STEADILY
DIMINISH TUESDAY AS HIGH PRESSURE RIDGING BUILDS IN BUT WAVES WILL
REMAIN ELEVATED THANKS TO THE LONG FETCH DOWN THE LAKE.

THE RIDGE WILL SHIFT EAST INTO WEDNESDAY TURNING WINDS
SOUTHEASTERLY. LOW PRESSURE WILL TRACK ACROSS THE NORTHERN PLAINS
INTO MANITOBA WEDNESDAY AND WEDNESDAY NIGHT SO THE PRESSURE GRADIENT
WILL BE TIGHTENING SO A BREEZY SOUTH TO SOUTHEAST WIND WILL DEVELOP.
AN UPPER TROUGH WILL BE MOVING EASTWARD ACROSS THE CENTRAL U.S.
SPAWNING ANOTHER SURFACE LOW ACROSS THE SOUTHERN HIGH PLAINS WHICH
WILL THEN TRACK NORTHEASTWARD. GUIDANCE HAS BEEN MORE CONSISTENT
TAKING THE LOW ACROSS THE LAKE LATER THURSDAY INTO FRIDAY BUT IS
HAVING DIFFICULTY LATCHING ONTO THE STRENGTH. THERE WILL LIKELY BE
FURTHER FLUCTUATIONS WITH STRENGTH AND THEREFORE THE INTENSITY OF
WIND SPEEDS. WILL CONTINUE TO MONITOR THE POTENTIAL FOR A PERIOD OF
STRONG WINDS WITH THIS LOW THOUGH LATEST GUIDANCE HAS BACKED OFF
SIGNIFICANTLY ON THE STRENGTH.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...5 PM MONDAY TO 4
     PM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...8 PM MONDAY TO 4
     PM TUESDAY.

&&

$$

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