Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 210815
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 AM CDT SUN SEP 21 2014

.DISCUSSION...
311 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 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.

JEE

&&

.AVIATION...

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

* ISOLATED TSRA ENDING BY 7Z.

* WEST WINDS VEERING NORTHWEST BY DAYBREAK. SPEEDS GENERALLY ARND
  10-14KT WITH GUSTS DEVELOPING AFT DAYBREAK TO 20-24KT.

* MVFR CIGS DEVELOPING ARND 10Z AND LIKELY PERSISTING THRU EARLY
  AFTN.

BEACHLER

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

LINE OF SHOWERS AND THUNDERSTORMS MOVING THRU AT TAF TIME...SHUD
QUICKLY END BY 630Z FOR ORD/MDW...GYY WILL BE CLOSER TO 7Z.
ELSEWHERE STORMS HAVE MOVED TO THE EAST WITH MAINLY VFR CIGS
PUSHING IN. HOWEVER FURTHER NORTH ACROSS WISCONSIN MVFR CIGS HAVE
DEVELOPED AND WILL CONTINUE TO SLIDE SOUTHEAST TOWARDS NORTHERN IL
AIRFIELDS...BUT HOLD OFF UNTIL ARND DAYBREAK. WINDS HAVE MAINLY
BECOME WESTERLY WITH SPEEDS ARND 10-14KT...AND AS DAYBREAK NEARS
GUSTS WILL BE DEVELOPING TO NEAR 20-24KT. GUIDANCE INDICATES THAT
WITH THE MID-LVL SYSTEM DROPPING SOUTHEAST TOWARDS THE TAF
SITES...MVFR CIGS WILL BE DEVELOPING AND LIKELY PERSIST THUR EARLY
AFTN. IN ADDITION IT APPEARS SOME VCSH OR LGT SHRA WILL ACCOMPANY
THE LOW CIGS LATER THIS MORNING THRU EARLY AFTN. WINDS WILL ALSO
BE TURNING NORTHWEST THEN NORTH BY THIS AFTN. THEN DRIER AIR WILL
ARRIVE AND SCOUR THE LOW CLOUDS BY SUNSET.

BEACHLER

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

* HIGH CONFIDENCE IN WIND DIR/SPEED/GUSTS.

* MEDIUM CONFIDENCE IN PRECISE TIMING OF CIGS...HIGH CONFIDENCE IN
  MVFR CIGS DEVELOPING THOUGH.

* MEDIUM CONFIDENCE IN TIMING AND PLACEMENT OF SHRA LATER TODAY.

BEACHLER

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

MONDAY AND TUESDAY...VFR.

WEDNESDAY THROUGH FRIDAY. VFR. SOUTHEAST WINDS.

KMD

&&

.MARINE...
123 PM CDT

FRONT THROUGH THE MIDDLE MISSISSIPPI VALLEY.  THE FIRST ROUND GALES
HAS SUBSIDED AND THE STRONGER...SMALL CRAFT ADVISORY LEVEL WINDS
OVER THE NEARSHORE WATERS ARE SUBSIDING AS WELL AS THE FRONTAL
TROUGH APPROACHES THE LAKE AND THE GRADIENT WEAKENS.  AS THE LOW
LIFTS TO THE NORTHEAST THROUGH QUEBEC...IT WILL DRAG A COLD FRONT
ACROSS THE LAKE...TURNING WINDS NWLY AND THEN NLY BY MID DAY
SUNDAY.  THE STRONGEST PUSH OF COLD ADVECTION SHOULD BE OVER THE
SOUTHERN PORTIONS OF THE LAKE...SO...THERE IS STILL A CHANCE FOR
MARGINAL NLY GALES OVER THE SOUTHERN PORTIONS OF THE LAKE.  WILL
MAINTAIN THE GOING GALE WATCH FOR SUNDAY AND NOT UPGRADE TO A GALE
WARNING JUST YET SINCE THERE IS STILL SOME UNCERTAINTY AS TO THE
TIMING...DURATION AND EXTENT OF GALES.  THE FRONT WILL FINALLY PUSH
SOUTH OF THE LAKE BY MID DAY SUNDAY WITH HIGH PRESSURE BUILDING OVER
THE CENTRAL PLAINS...MAINTAINING NLY WINDS THROUGH SUNDAY NIGHT OR
EARLY MONDAY MORNING.  BY MONDAY AFTERNOON...THE CENTER OF THE HIGH
WILL SLIDE JUST SOUTH OF THE LAKE AND THEN MOVE TO THE EASTERN GREAT
LAKES TUESDAY...ALLOWING WINDS TO TURN SOUTHERLY AGAIN.
HOWEVER...DO NOT EXPECT THE SLY WINDS TO GET TOO STRONG...PERHAPS
10-15KT...SINCE THE AREAL EXTEND OF THE HIGH WILL SPREAD FROM THE
EAST COAST TO THE MIDDLE MISSISSIPPI VALLEY...SETTING UP A WEAK SLY
GRADIENT.  THE NEXT UPSTREAM TROUGH DEVELOPING IN THE LEE OF THE
ROCKIES THURSDAY AND FRIDAY IS NOT EXPECTED TO MAKE MUCH EWD
PROGRESS UNTIL SATURDAY NIGHT OR SUNDAY...SO THE LIGHT SLY WINDS
SHOULD PREVAIL OVER THE LAKE THROUGH THE WEEKEND.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...9 AM
     SUNDAY TO 3 PM SUNDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...7 AM SUNDAY TO 10
     AM MONDAY.

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

&&

$$

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