Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 212008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
308 PM CDT SUN SEP 21 2014

.DISCUSSION...
330 AM CDT...

SYNOPSIS...AN UPPER LEVEL TROUGH PASSES OVERHEAD
TODAY WITH A SLIGHT CHANCE TO CHANCE OF SHOWERS LATE THIS MORNING
INTO THIS AFTERNOON. TEMPS WILL BE COOLER WITH HIGHS IN THE 60S
TODAY...AND THEN SLOWLY RISING BACK INTO THE MID TO UPPER 70S BY
MID WEEK. ALSO LOOKING AT A DRY REST OF THE WEEK.

TODAY AND TONIGHT...
AN UPPER LEVEL TROUGH IS OVER WISCONSIN AND IT WILL ROTATE THROUGH THE
REGION THIS MORNING.  A VORTICITY STREAMER ASSOCIATED WITH THE
TROUGH WILL SLIDE SOUTH DOWN THE LAKE THIS MORNING AND EXPECTING
SHOWERS TO FORM ALONG IT.  THE FORCING AND MOISTURE WEAKEN AS THE
STREAMER MOVES OVER NORTHERN IL AND IN...BUT EXPECTING A CHANCE OF
SHOWERS NEAR THE LAKE EARLY THIS AFTERNOON.  AREAS ALONG THE WI/IL
STATE LINE WILL HAVE A SLIGHT CHANCE OF SHOWERS AROUND MIDDAY THAT
WILL SPREAD SOUTH THROUGH THE AFTERNOON. EXPECTING DRY CONDITIONS
ALONG AND SOUTH OF I-80.

COOLER AIR WILL MOVE IN WITH THE TROUGH SO HAVE HIGHS IN THE MID TO
UPPER 60S. WITH CLEAR SKIES AND LIGHT WINDS...PATCHY FOG IS POSSIBLE
OUTSIDE OF DOWNTOWN CHICAGO. LOWS WILL BE IN THE UPPER 40S ALONG THE
LAKE BUT ONLY IN THE LOW TO MID 40S IN THE OUTLYING AREAS.

MONDAY THROUGH SATURDAY...
AN UPPER LEVEL RIDGE BUILDS OVER THE REGION MONDAY NIGHT...WHILE A
SURFACE HIGH MOVES OVERHEAD MONDAY AND THE AREA REMAINS UNDER HIGH
PRESSURE THOUGH THE REST OF THE WEEK.  LOOKING AT AN EXTENDED DRY
PERIOD WITH NO RAIN EXPECTED THROUGH THE END OF THE WEEK.
TEMPERATURES SLOWLY WARM WITH HIGH TEMPS REACHING THE LOW 70S BY
TUESDAY.  FLOW WILL BE OFF OF THE LAKE FROM TUESDAY ONWARD SO AREAS
ALONG THE LAKE WILL BE A BIT COOLER.

&&

.AVIATION...

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

* GUSTY NORTH/NORTHWEST WINDS SHIFTING NORTH/NORTHEAST LATE THIS
  AFTERNOON. CMS

//DISCUSSION...UPDATED 20Z...

TWO BOUNDARIES EVIDENT ON RADAR IMAGERY EARLY THIS AFTERNOON...
ONE SOUTHEAST OF ORD TO NEAR MDW WHICH IS DRIFTING SOUTHEAST AND
THEN A LAKE ENHANCED BOUNDARY MOVING INLAND ACROSS EASTERN LAKE
AND FAR NORTHEAST COOK COUNTIES. MAINTAINED CURRENT WIND FORECAST
OF NORTH/NORTHWEST WINDS SHIFTING NORTHERLY IN THE NEXT HOUR OR
SO...AT ORD...BUT IF THIS BOUNDARY CONTINUES MOVING INLAND...A
SHIFT TO NORTH/NORTHEAST WILL BE POSSIBLE. CMS

PREVIOUS 18Z DISCUSSION...

NORTHWEST WINDS WILL CONTINUE TO TURN MORE NORTHERLY THIS
AFTERNOON AS HIGH PRESSURE SLOWLY BUILDS EAST ACROSS THE PLAINS.
THE GRADIENT SLOWLY WEAKENS AND THIS WILL ALLOW SPEEDS TO ALSO
DIMINISH SOME THROUGH THE AFTERNOON. AS THIS HAPPENS...ITS
POSSIBLE THAT WINDS COULD SHIFT TO THE NORTH/NORTHEAST LATE THIS
AFTERNOON OR EARLY EVENING. HOWEVER...CONFIDENCE REGARDING
SPECIFIC WIND DIRECTIONS AND A POSSIBLE SHIFT TO NNE IS FAIRLY
LOW AND TRENDS WILL NEED TO BE MONITORED. NORTHERLY WINDS WILL
CONTINUE INTO THIS EVENING THEN TURN BACK NORTHWESTERLY OVERNIGHT
WITH SPEEDS DIMINISHING WELL UNDER 10KTS WITH LIGHT AND VARIABLE
WINDS POSSIBLE BY MORNING IN SOME LOCATIONS.

ISOLATED SHOWERS ARE PIVOTING TO THE SOUTHEAST FROM SOUTHEAST WI
ACROSS SOUTHERN LAKE MICHIGAN. STILL POSSIBLE FOR AN ISOLATED
SHOWER ACROSS THE TERMINALS EARLY THIS AFTERNOON BUT SHOULD BE
SHORT/LIGHT WITH NO MENTION IN THIS FORECAST OTHER THAN AT GYY.

HIGH MVFR CIGS EXTEND WELL NORTH INTO WI AND EXPECT MVFR CIGS FOR
MUCH OF THE AFTERNOON SLOWLY LIFTING BY LATE AFTERNOON OR EARLY
EVENING THEN SCATTERING OUT THIS EVENING WITH SKC OVERNIGHT INTO
MONDAY MORNING EXPECTED. CMS

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

* MEDIUM FOR WIND SPEEDS/GUSTS/DIRECTIONS THROUGH THE PERIOD. CMS

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

MONDAY NIGHT THROUGH TUESDAY...VFR.

WEDNESDAY THROUGH SATURDAY...VFR. WINDS TURNING SOUTHEASTERLY.

BEACHLER

&&

.MARINE...
202 PM CDT

DEEPENING LOW PRESSURE IS MOVING THROUGH SOUTHERN ONTARIO AS A
SECONDARY COLD FRONT PUSHING DOWN THE LAKE.  WINDS HAD ALREADY BEGUN
TO STRENGTHEN FOLLOWING THE PASSAGE OF THE PRIMARY COLD FRONT
OVERNIGHT LAST NIGHT AND EARLIER TODAY...BUT WERE FROM A SWLY TO WLY
DIRECTION.  FOLLOWING THE PASSAGE OF THE SECONDARY COLD
FRONT...WINDS ARE TURNING TO NLY.  WLY GALE FORCE WINDS HAD
DEVELOPED OVER THE SRN PORTIONS OF THE LAKE IN THE WAKE OF THE
PASSAGE OF THE FIRST COLD FRONT WHILE THE SFC LOW WAS STILL
DEEPENING OVER LOWER MICHIGAN TO GEORGIAN BAY...BUT THE STRONGER
COLD ADVECTION AND ADDITIONAL PRESSURE FALLS ASSOCIATED WITH THE LOW
DEEPENING OVER SRN ONTARIO HAS LEAD TO GALE FORCE WINDS OVER THE NRN
PORTIONS OF THE LAKE AS WELL.  ALSO...WITH A NORTHERLY FETCH
DEVELOPING AT THE FAR SOUTHERN TIP OF THE LAKE...GALES ARE LIKELY FOR
FOR THE INDIANA NEARSHORE WATERS.  SO...HAVE EXPANDED THE GOING GALE
WARNING TO INCLUDE ALL OF THE OPEN WATERS AS WELL AS THE INDIANA
NEARSHORE WATERS.  THE ILLINOIS NEARSHORE WATERS SHOULD GENERALLY
REMAIN BELOW GALE FORCE WITH THE INITIAL OFFSHORE FLOW...AND EVEN
WHEN WINDS TURN NLY...SOME SHELTERING UPSTREAM FROM THE WISCONSIN
SHORE SHOULD HELP LIMIT WINDS GENERALLY TO ARND 30KT...THOUGH AN
OCCASIONAL GALE FORCE GUST IS CERTAINLY NOT OUT OF THE QUESTION THIS
AFTERNOON.  BY THIS EVENING...THE SFC LOW SHOULD LIFT INTO SRN
QUEBEC WHILE HIGH PRESSURE SPREADS ACROSS THE CENTRAL PLAINS AND
INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEY.  WHILE WIND DIRECTION
WILL REMAIN NORTHERLY...SPEEDS SHOULD BEGIN TO DROP OFF THROUGH THE
EVENING TO BELOW GALE FORCE.  THE HIGH SHOULD CONTINUE TO SPREAD
EAST OVERNIGHT...FURTHER DIMINISHING WIND SPEEDS...BUT A SMALL CRAFT
ADVISORY WILL REMAIN IN EFFECT INTO MONDAY AFTERNOON OR EARLY
EVENING...ESPECIALLY FOR THE INDIANA NEARSHORE WATERS AS RESIDUAL
HIGH WAVE ACTION WILL BE SLOW TO DAMPEN.  BY MONDAY EVENING...THE
CENTER OF THE HIGH PRESSURE WILL SLIDE JUST SOUTH OF THE
LAKE...BACKING WINDS THOUGH WLY...BUT AS THE CENTER OF THE HIGH
QUICKLY SLIDES TO THE EAST INTO THE OHIO VALLEY AND EASTERN GREAT
LAKES...WINDS WILL CONTINUE TO BACK TO SLY BY TUESDAY EVENING.  THE
FORECAST MODELS CONTINUE TO INDICATE THAT THE HIGH SHOULD CONTINUE
TO MOVE OFF TO THE EAST WHILE A TROUGH OF LOW PRESSURE DEVELOPS IN
THE LEE OF THE ROCKIES.  THIS SFC PRESSURE PATTERN WILL KEEP SLY
WINDS OVER THE LAKE...BUT SINCE THE TROUGH IS STILL EXPECTED TO
REMAIN OVER THE WRN PLAINS THROUGH LATE THIS WEEK AND THE HIGH
REMAINS PARKED OVER THE NERN CONUS...RELATIVELY LIGHT...GENERALLY
SOUTHERLY WINDS SHOULD PREVAIL OVER THE LAKE THROUGH NEXT WEEKEND.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ743-LMZ744-LMZ745-
     LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878
     UNTIL 7 PM SUNDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...7 PM SUNDAY TO 5
     PM MONDAY.

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

&&

$$

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