Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 051638
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1138 AM CDT SUN JUL 5 2015

.UPDATE...
1123 AM CDT

THE DEVELOPING LAKE BREEZE HAS STARTED TO BRING COOLER LOW 70S
TEMPERATURES ONSHORE IN AREAS IMMEDIATELY ADJACENT TO THE LAKE.
SOUTHERLY FLOW AT LOCATIONS FARTHER OUT IS HELPING WARM MOST OF
THE AREA INTO THE UPPER 70S AND LOWER 80S AS OF LATE MORNING.
SCATTERED TO BROKEN CUMULUS HAVE ALSO STARTED BREAKING OUT OF THE
THIN HAZY OVERCAST. LATEST ACARS SOUNDINGS FROM AIRCRAFT AT ORD
SHOW A WELL MIXED LAYER FROM THE SFC TO ABOUT 875 MB AND THEN A
WARM CAPPING LAYER ABOVE THAT. DEWPOINTS LOCALLY ARE IN THE LOW TO
MIDDLE 60S...WHILE MUCH FARTHER WEST ACROSS IOWA THEY ARE REACHING
VALUES IN THE UPPER 60S TO MIDDLE 70S. OVERNIGHT SHOWERS IN THAT
AREA HAVE MOSTLY DISSIPATED...BUT SHORT TERM RAP GUIDANCE SUGGESTS
PRONOUNCED MOISTURE FLUX INTO THAT AREA WILL SUPPORT RENEWED
CONVECTION IN THE SPC SLIGHT TO ENHANCED RISK FOR THE NORTH
CENTRAL CONUS TODAY. IN THE LOCAL AREA...THE WARM CAPPING LAYER
ALOFT AND LACK OF MOISTURE CONVERGENCE AT LOW LEVELS WILL PROVIDE
FOR A QUIET AND SEASONABLY WARM AFTERNOON AND EVENING.

LENNING

&&

.SHORT TERM...
328 AM CDT

THROUGH MONDAY NIGHT...

FAIRLY QUIET CONDITIONS ACROSS THE AREA POST INDEPENDENCE DAY
CELEBRATIONS...THE EXCEPTION BEING SOME LINGERING HAZY SKIES
POSSIBLY MIXED WITH SOME PATCHES OF FOG. SPLIT FLOW REGIME IN PLACE
UPSTAIRS WITH MORE DOMINANT UPPER JET HEADING NORTH TOWARD HUDSON
BAY AND WITH ANOTHER WEAKENING JET HEADED SOUTH INTO THE CENTRAL AND
SOUTHERN PLAINS THANKS TO A MID LEVEL RIDGE MOVING EAST THROUGH THE
REGION. VERY DRY UPPER AIR SOUNDINGS AT KDVN AND KILX AND UPSTREAM
SUGGEST LITTLE IN THE WAY OF CLOUDINESS TODAY..THOUGH SOME HIGH
CLOUDS FROM LOW PRESSURE IN THE OHIO VALLEY WILL CLIP THE AREA ALONG
WITH LINGERING SKY OBSCURATION DUE TO CANADIAN WILDFIRE SMOKE.

AT THE SURFACE...FRONTS LIE WELL AWAY FROM THE AREA WITH ONE
BOUNDARY IN SOUTHERN ILLINOIS...AND ANOTHER WELL NORTHWEST BACK IN
THE UPPER MIDWEST.  STRONG LOW LEVEL LAPSE RATES WITH AN INVERSION
AROUND 850 MB STILL LOOKS TO SUPPORT SOME SHALLOW AFTERNOON CUMULUS
TODAY AS WELL. 850/925 TEMPS GET A 2-3C DEGREE BOOST AND WITH THE
MIXING DOES SOLIDLY SUPPORTS MID TO UPPER 80S.  LOCAL CLIMO
SUGGESTING A 90 NOT IMPOSSIBLE IN THE FAR WEST...BUT KEPT TEMPS
UNDER THAT GIVEN THE SMOKE STILL PRESENT IN THE AREA. AGAIN A LAKE
BREEZE SEEMS A GOOD BET...BUT WITH MIXING TO 850 TAPPING SLIGHTLY
HIGHER WINDS...FEELING AT THIS POINT THAT IT REMAINS EAST OF
ORD/MDW. ENOUGH TO KEEP LAKESHORE AREAS AT OR BELOW 80.

MONDAY LOOKS TO BE THE BEST CHANCE AT ECLIPSING THE 90 DEGREE MARK.
THE FRONTAL BOUNDARY DOWN IN SOUTHERN ILLINOIS GETS A NORTHWARD
SHOVE IN RESPONSE TO SOUTHERLY FLOW AHEAD OF LOW PRESSURE
EAST/NORTHEASTWARD THROUGH THE UPPER MIDWEST AND INTO THE NORTHERN
GREAT LAKES. SOME MID LEVEL FORCING IN THE LATE MORNING/EARLY
AFTERNOON MOVES THROUGH AS THE MID LEVEL FRONTAL BOUNDARY SHIFTS
NORTHWARD...BUT SOUNDINGS GENERALLY PRETTY DRY DURING THIS TIME.
GUSTY SOUTH/SOUTHWEST WINDS SHOULD HOLD A LAKE BREEZE AT BAY.

ATTENTION FOCUSES ON THE APPROACHING COLD FRONT FROM THE NORTHWEST
MONDAY LATE AFTERNOON AND MONDAY NIGHT. SEVERAL LOW PRESSURE WAVES
RIDING ALONG THE FRONT LOOK TO SLOW ITS PROGRESS DOWN FROM ITS
SPEEDIER CURRENT TRACK...AS THE UPPER JET INITIALLY REMAINS PARALLEL
TO THE LOWER LEVEL FRONT. THE FRONT WORKS ITS WAY THROUGH MONDAY
NIGHT INTO EARLY TUESDAY...BRINGING A DECENT SHOT OF
RAIN/THUNDERSTORMS AREA WIDE...SLOWEST IN THE SOUTHEAST. THE STRONG
LOW LEVEL WIND SPEEDS AND HIGH PWAT AIR MASS SHOULD ALLOW FOR SOME
RELATIVELY EFFICIENT RAINFALL PRODUCTION AND GUSTY
WINDS...COINCIDENT WITH A MARGINAL RISK FOR SEVERE STORMS MONDAY
LATE AFTERNOON AND EVENING.

KMD

&&

.LONG TERM...
328 AM CDT

TUESDAY THROUGH SATURDAY...

THERE COULD BE SOME LINGERING PRECIP BEHIND THE FRONT TUESDAY
MORNING BEFORE HIGH PRESSURE MOVES BACK IN. NORTHERLY FLOW WILL
USHER IN A MUCH COOLER AIR MASS AS ADDITIONAL COOL AIR CONTINUES
TO POUR IN OFF THE LAKE. TEMPS GRADUALLY MODULATE THROUGH THE
REMAINDER OF THE WEEK.

THE SOUTHEASTERN U.S. RIDGE ATTEMPTS TO REESTABLISH ITSELF...WHILE
TROUGHING SETS UP IN THE SOUTHWESTERN U.S. INITIALLY DRY AND
COOLER STABLE AIR WILL LIMIT PRECIP CHANCES THROUGH TUESDAY
NIGHT...BUT LATER WEDNESDAY THROUGH WEEKS END LOOK FOR OCCASIONAL
WAVES TO BRING OCCASIONAL CHANCES OF SHOWERS/STORMS.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* LAKE BREEZE TO REMAIN EAST OF TERMINALS TODAY.

RODRIGUEZ/MM

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST ISSUE IS IN THE NEAR TERM...WITH VIS RESTRICTION
STILL IN PLACE ACROSS THE TERMINALS. SMOKE/HAZE/FOG IN PLACE FROM
OVERNIGHT WONT LIKELY DIMINISH OR MIX OUT UNTIL WINDS PICK
UP...LIKELY IN THE NEXT TWO TO THREE HOURS. HOWEVER...VIS SHOULD
BE SLOWLY IMPROVING THROUGH THAT TIME. VFR SKIES WITH SOUTHERLY
WINDS ARE THEN LIKELY THROUGH THE FORECAST PERIOD...WITH WIND
SPEEDS INCREASING TOWARDS THE END OF THE PERIOD.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM CONFIDENCE ON WINDS REMAINING SOUTH TODAY.

RODRIGUEZ/MM

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

MONDAY NIGHT...TSRA LIKELY.

TUESDAY...CHANCE MORNING TSRA. NORTH-NORTHEAST WINDS.

WEDNESDAY...SLIGHT CHANCE SHRA.

THURSDAY...CHANCE TSRA.

FRIDAY...CHANCE TSRA.

SATURDAY...CHANCE TSRA.

RODRIGUEZ

&&

.MARINE...
309 AM CDT

INCREASING SOUTHERLY FLOW OVER THE LAKE WILL BE OBSERVED TODAY AS
HIGH PRESSURE SHIFTS TO THE EAST...AND A TROUGH OF LOW PRESSURE
SLOWLY APPROACHES FROM THE WEST. SOUTHERLY FLOW OF 10 TO 20 KT
WILL BE LIKELY ALL ACROSS THE LAKE BY THIS AFTERNOON...WITH THIS
WIND PERSISTING TONIGHT. WITH THE APPROACH OF THE SYSTEM ON
MONDAY...EXPECT WINDS TO CONTINUE TO INCREASE TO INITIALLY 15 TO
25 KT...BUT THEN INCREASING TO 30KT THROUGHOUT THE DAY. AT THIS
TIME...IT DOES APPEAR THAT THE 30KT WINDS WILL BE CONFINED ACROSS
THE NORTHERN HALF. HOWEVER...THERE IS SOME SLIGHT UNCERTAINTY WITH
REGARDS TO THE EVOLUTION OF THIS SYSTEM AND LOCATION OF STRONGEST
SPEEDS. STILL THINK THAT HAZARDOUS WINDS FOR SMALL CRAFT WILL BE
OBSERVED ACROSS THE NEARSHORES ON MONDAY. ALTHOUGH GALES DONT
APPEAR LIKELY AT THIS TIME...CANNOT COMPLETELY RULE OUT A WINDOW
OF AT LEAST GALE FORCE GUSTS OVER THE NORTH HALF LATE MONDAY
AFTERNOON INTO THE EVENING. HAVE EXCLUDED ANY MENTION OF GALES AT
THIS TIME...BUT WILL CONTINUE TO MONITOR LATEST GUIDANCE. AS THIS
SYSTEM DEPARTS MONDAY NIGHT INTO TUESDAY...WINDS WILL SHIFT TO THE
NORTH AND INCREASE ONCE AGAIN...WITH LINGERING HIGHER WAVES
POSSIBLE OVER THE SOUTH HALF AND NEARSHORE WATERS ON TUESDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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