Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 212210
AFDLOT

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

.DISCUSSION...
320 PM CDT

QUIET WEATHER WILL BE IN PLACE THROUGH MUCH IF NOT ALL OF THE
FORECAST PERIOD THANKS TO UPPER RIDGING AND SURFACE HIGH PRESSURE
THAT WILL SET UP ACROSS THE REGION. EARLY AFTERNOON WATER VAPOR
IMAGERY SHOWS AN UPPER LOW SPINNING SOUTHEASTWARD ACROSS THE LOWER
GREAT LAKES. A LARGE UPPER RIDGE IS SPREAD FROM THE U.S. ROCKIES
WELL INTO CENTRAL CANADA WITH A CUTOFF UPPER LOW OVER
CALIFORNIA/NEVADA. A LARGE UPPER TROUGH IS OFF THE CANADIAN AND
NORTHWEST U.S. COAST AND SLOWLY MOVING EASTWARD. AT THE
SURFACE...LOW PRESSURE IS OVER LAKE ONTARIO WITH SEVERAL TROUGH AXES
ROTATING AROUND ITS PERIPHERY...ONE OF WHICH IS WORKING SOUTHWARD
ACROSS THE LOCAL AREA THIS AFTERNOON. STRONG HIGH PRESSURE IS OVER
THE CENTRAL AND NORTHERN PLAINS AND MOVING EAST.

TONIGHT...THE UPPER TROUGH WILL QUICKLY EXIT TO THE SOUTH AND EAST
BY MONDAY MORNING WITH THE LEADING EDGE OF THE BIG UPPER RIDGE
ENTERING THE AREA. ANY SHOWER ACTIVITY WILL BE ENDING BY EARLY
EVENING AS THE UPPER WAVE DEPARTS. THE LONGER FETCH NORTHERLY FLOW
DOWN THE LAKE WILL LIKELY KEEP LAKE STRATUS IN PLACE ALONG THE
ILLINOIS SHORE AND ACROSS MUCH OF NW INDIANA. INVERSION HEIGHTS ARE
QUITE LOW SO AM NOT EXPECTING SHOWERS AT THIS POINT BUT SOME
SPRINKLES ARE POSSIBLE...MAINLY THROUGH THE EVENING WHEN LAKE-H85
DELTA TS ARE GREATEST. OTHERWISE EXPECT MOSTLY CLEAR SKIES
ELSEWHERE. WINDS WILL DIMINISH OVERNIGHT ALLOWING FOR RADIATIONAL
COOLING INTO THE LOW TO MID 40S AWAY FROM THE LAKE...WITH THE
COLDEST READINGS ACROSS NORTH CENTRAL ILLINOIS WHERE A FEW SITES
COULD FALL JUST BELOW 40.

MONDAY...THE SURFACE HIGH WILL QUICKLY MOVE EASTWARD ACROSS THE AREA
AND BE CENTERED OVER CENTRAL IL/IN BY MONDAY EVENING. H85 TEMPS WILL
START OUT AROUND 7C BUT WARM TO AROUND 10C BY LATE IN THE DAY THANKS
TO THE APPROACHING UPPER RIDGE. MAY SEE SOME SCATTERED STRATOCU
DEVELOP TOWARD MIDDAY BUT OTHERWISE EXPECT MOSTLY SUNNY TO SUNNY
SKIES WITH GENERALLY LIGHT WIND THAT WILL TURN WESTERLY THROUGH THE
AFTERNOON. THE EXCEPTION WILL BE NEAR THE LAKE WHERE WINDS WILL
LIKELY TURN NORTH-NORTHEAST. WITH HIGHS EXPECTED TO BE IN THE MID TO
UPPER 60S THE INLAND PUSH OF LAKE AIR MAY BE MINIMAL BUT LAKESHORE
AREAS WILL BE HELD TO THE LOW TO MID 60S. A FEW SPOTS MAY REACH 70
ACROSS THE FAR WESTERN AND SOUTHERN CWA. CALM/LIGHT WINDS WILL SET
UP AGAIN MONDAY NIGHT WITH CLEAR SKIES SUPPORTING MORE RADIATIONAL
COOLING. WITH THE HIGH POSITIONED OVER OHIO AND A RIDGE AXIS
EXTENDING WESTWARD THE SOUTHEASTERN CWA MAY SEE THE COOLEST READINGS
WITH LOW TO MID 40S...WITH MID TO UPPER 40S ELSEWHERE.

TUESDAY THROUGH SUNDAY...THE UPPER RIDGE AXIS WILL CREST THE AREA
WEDNESDAY WHILE THE CUTOFF UPPER LOW OVER CA/NV TODAY SLOWLY TRACKS
NORTHEAST INTO THE CENTRAL/NORTHERN PLAINS. LATEST GUIDANCE
CONTINUES TO SUPPORT THE IDEA THAT THIS LOW WILL TRACK NORTH AND
REMAIN WEST OF THE AREA INTO THURSDAY...THOUGH THERE ARE DIFFERENCES
IN THE DETAILS OF WHAT HAPPENS TO THE TROUGH. A BIG UPPER TROUGH
WILL REMAIN OFF THE WEST COAST AND HELP FORCE ANOTHER UPPER RIDGE TO
AMPLIFY NORTHEASTWARD ACROSS THE WESTERN U.S. INTO THURSDAY THEN
PROGRESS EASTWARD AND PARKING OVER THE EASTERN U.S. OVER THE
WEEKEND. TUESDAY THROUGH MOST IF NOT ALL OF WEDNESDAY WILL BE QUIET
WITH MODERATING TEMPS AND AM EXPECTING THAT THE REST OF THE WEEK
WILL BE QUIET AND DRY AS WELL. WILL NEED TO MONITOR THE PROGRESS OF
THE CUTOFF UPPER LOW WEDNESDAY/EARLY THURSDAY AS A SHIFT IN ITS
TRACK COULD RESULT IN INCREASED CLOUD COVER OR POSSIBLY SOME MINIMAL
POPS. OTHERWISE...THE NEXT CHANCE FOR POPS WILL BE TOWARDS
SUNDAY/MONDAY AS GULF MOISTURE WRAPS AROUND THE BACK SIDE OF THE
DEPARTING SURFACE HIGH IN CONJUNCTION WITH A DEVELOPING UPPER TROUGH
OVER THE ARKLATEX/GULF COAST. TEMPS WILL MODERATE INTO THE 70S BY
TUESDAY WITH A WARMING TREND THROUGH THE REST OF THE WEEK.
SOUTHEASTERLY WINDS WILL LIKELY PREVAIL WITH THE SURFACE HIGH TO THE
EAST AND SOME ENHANCED LAKE FLOW/PUSH OF COOLER AIR MAY OCCUR JUST
ABOUT EVERY DAY SO LAKESHORE AREAS WILL BE SEVERAL DEGREES COOLER
THROUGH THE WEEK.

MDB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NORTHEAST WINDS ABOVE 10 KT THROUGH EARLY THIS EVENING.

RODRIGUEZ

//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 22Z...

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//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...INDIANA NEARSHORE WATERS UNTIL 5 PM MONDAY.

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

&&

$$

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