Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 211408
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
908 AM 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 14Z...

* STRONG/GUSTY WEST/NORTHWEST WINDS SHIFTING NORTHERLY EARLY THIS
  AFTERNOON...THEN POSSIBLY NORTH/NORTHEAST LATE AFTERNOON/EARLY
  EVENING.
* MVFR CIGS MID MORNING THRU THIS AFTERNOON.
* CHANCE OF SHRA LATE MORNING THRU MID AFTERNOON. CMS

//DISCUSSION...UPDATED 14Z...

FORECAST SOUNDINGS IN GOOD AGREEMENT WITH GUSTS INTO THE MID 20
KT RANGE THIS MORNING...AS WIND DIRECTIONS TURN MORE NORTHWEST
THIS MORNING THEN NORTHERLY BY EARLY THIS AFTERNOON. SPECIFIC WIND
DIRECTIONS AND TIME SHIFTS REMAIN DIFFICULT BUT GOING FORECAST HAS
TRENDS HANDLED WELL AT THIS TIME. CMS

PREVIOUS 12Z DISCUSSION...

AN UPPER LEVEL LOW PRESSURE SYSTEM OVER WISCONSIN WILL PIVOT
SOUTHEAST ACROSS NORTHERN IL/NORTHWEST IN AIRFIELDS TODAY. VISIBLE
IMAGERY SHOWS A WEDGE OF CLEAR SKIES ACROSS NORTHERN IL AT
DAYBREAK...HOWEVER JUST NORTH INTO WISCONSIN CIGS HAVE ALREADY
DROPPED TO BKN020 TO BKN025. IN ADDITION IT APPEARS SOME VCSH OR
LGT SHRA WILL ACCOMPANY THE LOW CIGS LATER THIS MORNING THRU EARLY
AFTN. BREEZY WEST/NORTHWEST WINDS WITH GUSTS NEARING 25KT THRU
THIS AFTN. WINDS WILL SLOWLY TURN NORTH AND MAY BRIEFLY TURN
NORTHEAST AS DRIER AIR BEGINS TO WORK INTO THE REGION AND SHUD
START LIFTING THE CIGS ARND 00Z. DRIER AIR WILL CONTINUE TO SCOUR
THE CLOUDS...AND EXPECT JUST A FEW CLOUDS REMAINING OVERNIGHT WITH
THE EXCEPTION OF GYY.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH FOR WIND SPEEDS/GUSTS. MEDIUM FOR WIND DIRECTION CHANGES
  AND TIMING.
* HIGH FOR MVFR CIGS.
* LOW FOR SHRA. 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-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 PM SUNDAY.

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

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 5 PM MONDAY.

&&

$$

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