Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 211736
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1236 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 18Z...

* GUSTY NORTH/NORTHWEST WINDS...POSSIBLY SHIFTING NORTH/NORTHEAST
  LATE THIS AFTERNOON OR EARLY THIS EVENING.
* MVFR CIGS THRU EARLY EVENING.
* CHANCE OF SHRA THIS AFTERNOON. CMS

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

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 18Z...

* MEDIUM FOR WIND SPEEDS/GUSTS/DIRECTIONS THROUGH THE PERIOD.
* HIGH FOR MVFR CIGS THIS AFTERNOON.
* LOW FOR SHRA THIS AFTERNOON. 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...
313 AM CDT

LOW PRESSURE HAS MOVED INTO LOWER MICHIGAN AND WILL CONTINUE TO
SLIDE EAST THROUGHOUT THE AFTERNOON...REACHING THE EASTERN GREAT
LAKES REGION BY THIS EVENING. MEANWHILE THE PRESSURE GRADIENT
ALONG THE WESTERN PERIPHERY OF THE LOW HAS TIGHTENED...AND WAS
EXPECTED TO MOVE ACROSS LAKE MICHIGAN THIS MORNING. GUIDANCE HAS
CONTINUED TO INDICATE THAT GALE FORCE WINDS WILL DEVELOP...HOWEVER
IT APPEARS TO BE MARGINAL WITH GUSTS GENERALLY AROUND 35 KT TO
POSSIBLY A FEW GUSTS UP TO 38KT IN THE SOUTHERN HALF OF THE LAKE.
HAVE GONE AHEAD AND UPGRADED THE GALE WATCH TO A GALE
WARNING...BUT ALSO TRIMMED THE END TIME AS IT APPEARS GALE
CONDITIONS WILL QUICKLY COME DOWN BY THIS AFTN. THE OTHER
CHALLENGE HAS BEEN HOW TO HANDLE THE GALE WATCH THAT WAS IN EFFECT
FOR THE INDIANA NEARSHORE WATERS. THIS APPEARS TO BE SLIGHTLY LESS
FAVORABLE SO HAVE MIGRATED THE GALE WATCH TO A SMALL CRAFT
ADVISORY...BUT FEEL AN OCCASIONAL GALE FORCE GUST IS POSSIBLE LATE
THIS MORNING THROUGH THE AFTERNOON. WHILE THE GRADIENT WILL
QUICKLY DIMINISH TONIGHT...WAVES WILL LIKELY REMAIN ELEVATED FOR
THE SOUTHERN HALF OF THE LAKE. HAVE NUDGED THE END TIME TO THE
SMALL CRAFT ADVISORY FOR THE INDIANA NEARSHORE INTO MON AFTN. HIGH
PRESSURE ACROSS THE CENTRAL PLAINS WILL CONTINUE TO BUILD EAST
TONIGHT...THEN REMAIN OVER LAKE MICHIGAN THROUGH WEDNESDAY BEFORE
DRIFTING EAST. THIS WILL MAINTAIN MUCH LIGHTER WINDS AND LOWER
WAVES FOR TUESDAY AND WEDNESDAY.

BEACHLER

&&

.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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