Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 022038
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
338 PM CDT TUE JUN 2 2015

.SHORT TERM...
142 PM CDT

THROUGH WEDNESDAY NIGHT...

A RELATIVELY QUIET AND DRY PERIOD OF WEATHER IS SETTING UP FOR NRN
IL/NWRN IN THROUGH AT LEAST WEDNESDAY NIGHT.  FOR THE REMAINDER OF
THIS AFTERNOON...A RIDGE OF HIGH PRESSURE EXTENDING FROM THE ERN
GREAT LAKES THROUGH THE MIDDLE MISSISSIPPI VALLEY WILL HELP KEEP
SKIES MOSTLY SUNNY WITH LIGHT WINDS.  THE RIDGE IS ALSO ASSOCIATED
WITH A RATHER DRY AIRMASS...WITH DEWPOINTS ONLY IN THE LOWER TO
MIDDLE 40S ACROSS MUCH OF THE REGION.  UNDER AMPLE SUNSHINE AND WITH
DRY AIR IN PLACE...EXPECT THAT TEMPERATURES SHOULD TOP OUT IN THE
MIDDLE 70S THIS AFTERNOON.  THE EXCEPTION WILL BE THE
LAKEFRONT...WHERE A WEAK PRESSURE GRADIENT...LIGHT WINDS AND STRONG
DIFFERENTIAL HEATING BETWEEN THE COOL LAKE WATERS AND THE WARMER
LAND WILL SET UP A LAKE BREEZE.  SO...LAKEFRONT
LOCATIONS...INCLUDING DOWNTOWN CHICAGO SHOULD SEE HIGH TEMPS TODAY
ONLY IN THE UPPER 50S TO AROUND 60F.  FOR TONIGHT...MOSTLY CLEAR
SKIES...LIGHT WINDS AND DRY AIR SHOULD ALLOW FOR TEMPERATURES TO
DROP OFF INTO THE LOWER 50S.  SOME ISOLATED...SHELTERED LOCATIONS
COULD EVEN SEE TEMPS DROP INTO THE MIDDLE TO UPPER 40S.  THE URBAN
HEAT ISLAND OF THE CHICAGO METRO AREA SHOULD REMAIN A BIT
WARMER...WITH LOWS IN THE MIDDLE TO UPPER 50S.

WEDNESDAY SHOULD BE A NEAR REPEAT PERFORMANCE...THOUGH WITH THE HIGH
SHIFTING TO THE EAST...WHILE THE WESTERN PLAINS LOW REMAINS OVER WRN
KS...LOW LEVEL FLOW WILL BECOME MORE SSELY AS THE RIDGE AXIS SHIFTS
TO THE OHIO VALLEY.  THE REGION WILL REMAIN CUT OFF FROM GULF
MOISTURE...SO MOSTLY SUNNY SKIES ARE LIKELY AGAIN...WITH TEMPS A BIT
HIGHER...TOPPING OUT IN THE UPPER 70S TO AROUND 80F.  A WEAK
GRADIENT WILL ALLOW FOR LAKE BREEZE DEVELOPMENT AGAIN
TOMORROW...HOWEVER...THE LAKE BREEZE IS EXPECTED TO SET UP A LITTLE
LATER IN THE AFTERNOON THAN TODAY...SO LAKE FRONT LOCATIONS SHOULD
GET A LITTLE WARMER...WITH HIGHS IN THE MIDDLE 60S.  FOR WEDNESDAY
NIGHT...STILL EXPECTING QUIET WEATHER...BUT WITH INCREASING CLOUD
COVER AS THE CANADIAN LOW BEGINS TO DRAG A COLD  FRONT ACROSS THE
UPPER MISSISSIPPI VALLEY TO NEAR THE NORTHERN END OF LAKE MICHIGAN.
THE RIDGE IS EXPECTED TO REMAIN NEARLY STATIONARY ALONG THE OHIO
VALLEY...SO ANY PCPN ASSOCIATED WITH THE SYSTEM WILL BE SHUNTED TO
THE NORTH OF THE CWA...MAINLY IN WISCONSIN AND ERN IOWA BY LATE
WEDNESDAY NIGHT.  INCREASING CLOUD COVER AND RISING SFC DEWPOINTS
SHOULD LIMIT OVERNIGHT COOLING...WITH LOWS BY EARLY THURSDAY MORNING
EXPECTED TO BE IN THE UPPER 50S TO LOWER 60S.

KREIN

&&

.LONG TERM...
335 PM CDT

THURSDAY THROUGH TUESDAY...

THE AREA WILL STAY ON EASTERN PERIPHERY OF MID/UPPER RIDGING OVER
CENTRAL CONUS THURSDAY THROUGH SATURDAY...WITH A FEW CONVECTIVELY
DRIVEN DISTURBANCES PIVOTING AROUND RIDGE AXIS. MODELS INDICATE
DECAYING CONVECTION TRYING TO MAKE IT INTO OUR AREA ON
THURSDAY...MOST BULLISH ON THE LATEST 12Z ECMWF...BUT HAVE FAVORED
GUIDANCE THAT WEAKENS REMNANT CONVECTION AND KEPT POPS LOW IN
NORTHWEST 1/2 OF CWA. UNLESS THERE IS MORE IMPACT FROM
CLOUDS/CONVECTION THAN EXPECTED...HIGHS SHOULD REACH THE LOWER TO
MID 80S...WITH UPPER 70S ALONG IL SHORE AS A LAKE BREEZE FORMS
DURING THE AFTERNOON. A LAKE ENHANCED FRONT WILL BE DRIVEN
SOUTHWARD LATE THURSDAY NIGHT INTO FRIDAY...SO A MUCH COOLER DAY
WILL RESULT NEAR LAKE MICHIGAN...BUT SOUTH OF THE FRONT MID 70S TO
LOW 80S APPEAR PROBABLE. UNCERTAINTY ON POPS...AS NAM AND
ESPECIALLY GFS ARE STRONGER AND FARTHER NORTH WITH A MIDLEVEL
DISTURBANCE. GENERALLY MAINTAINED HIGH CHANCE POPS FROM PREVIOUS
FORECAST FOR SHOWERS/SCT`D TSRA.

SATURDAY LOOKS QUIETER AND FAIRLY COOL ESPECIALLY NEAR THE LAKE
WITH ONSHORE FLOW THEN RETURN FLOW QUICKLY RETURNS ON SUNDAY AS A
SURFACE LOW TRACKS SOMEWHERE NEARBY..WITH RESULTING SHOWER AND
TSRA CHANCES. DESPITE A UPPER LOW/TROUGH SETTING UP OVER THE
NORTHERN LAKES ON MONDAY AND TUESDAY...AIR MASS WILL REMAIN
SEASONABLY WARM BEHIND SUNDAY FROPA WITH GENERALLY LOW POPS...BUT
ANOTHER LAKE ENHANCED FROPA COULD OCCUR ON TUESDAY.

RC


&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* EASTERLY WINDS AT TIMES AROUND 10 KT THROUGH MID-AFTERNOON.

* ANOTHER LAKE BREEZE TURNING WINDS EASTERLY ON WEDNESDAY
  AFTERNOON.

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

A HIGH PRESSURE RIDGE REMAINS ANCHORED ACROSS THE LOCAL AREA. THIS
HAS PROVIDED DEVELOPMENT OF A LAKE BREEZE THAT TURNED WINDS
EASTERLY AT ORD AND MDW. THESE WINDS WILL CONTINUE THROUGH THE
AFTERNOON WITH SOME UNDULATION LIKELY...INCLUDING SPORADIC GUSTS
AROUND 15 KT EARLY THIS AFTERNOON. WIND SPEEDS WILL SHOW A GRADUAL
DIMINISHING DURING DUSK.

THE WEATHER REGIME ON WEDNESDAY IS FAVORABLE AGAIN FOR A LAKE
BREEZE DEVELOPMENT...THOUGH A LATER MORE TRADITIONAL PASSAGE TIME
THAN TODAY AND NOT AS SUPPORTIVE FOR 10 KT WINDS.

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM IN WIND SPEEDS THIS AFTERNOON AND MEDIUM-HIGH IN SPEEDS
  DIMINISHING BELOW 9 KT BY 23Z.

* MEDIUM-HIGH IN WINDS AND TIMING OF SHIFT ON WEDNESDAY
  AFTERNOON.

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

* WEDNESDAY NIGHT AND THURSDAY...DRY/VFR. SOUTHEAST WINDS.
* FRIDAY...CHANCE OF SHRA/TSRA. MVFR LIKELY. NORTHEAST WINDS.
* SATURDAY...SLIGHT CHANCE OF SHRA. MVFR POSSIBLE. NORTHEAST
  WINDS.
* SUNDAY...CHANCE OF SHRA/TSRA. SOUTH WINDS.
* MONDAY...SLIGHT CHANCE OF SHRA/TSRA. GUSTY WEST WINDS.

MTF/CMS

&&

.MARINE...
122 PM CDT

A PERIOD OF QUIET WEATHER SETTING UP FOR LAKE MICHIGAN AS A SERIES
OF HIGH PRESSURE SYSTEMS CROSS THE GREAT LAKES REGION.  AS OF
TUESDAY AFTERNOON...HIGH PRESSURE IS CENTERED OVER LAKE HURON WITH A
RIDGE AXIS EXTENDING SOUTHWEST ACROSS SOUTHERN LAKE MICHIGAN AND
THEN TO THE LOWER MISSISSIPPI VALLEY WHILE LOW PRESSURE DEVELOPS IN
THE LEE OF THE ROCKIES.  LITTLE CHANCE IS EXPECTED TO THE PATTERN
THROUGH TOMORROW AFTERNOON WITH GENERALLY LIGHT WINDS WITH A
GENERALLY SOUTHERLY FETCH.  THE EXCEPTION WILL BE THE SOUTHERN LAKE
MICHIGAN NEARSHORE WATERS WHERE THE WEAK PRESSURE GRADIENT
ASSOCIATED WITH THE RIDGE IN PLACE WILL SET UP ONSHORE FLOW DUE TO
LAKE BREEZE FORMATION.  BY WEDNESDAY EVENING...THE HIGH WILL PUSH
ACROSS NEW ENGLAND AS A COMPLEX TROUGH OF LOW PRESSURE EXTENDS FROM
JAMES BAY...THROUGH THE UPPER MISSISSIPPI VALLEY...TO A DEEPENING
LOW PRESSURE CENTER OVER THE SOUTH HIGH PLAINS.  THIS WILL MAINTAIN
THE SOUTHERLY FETCH OVER LAKE MICHIGAN WITH WINDS INCREASING IN
RESPONSE TO A STRENGTHENING GRADIENT OVER THE LAKE.  HOWEVER...EVEN
WITH THIS STRENGTHENING GRADIENT...WINDS SHOULD STILL ONLY BE IN THE
10 TO 20 KT RANGE.  THE NORTHERN STREAM SYSTEMS...OVER CANADA WILL
BE MUCH MORE PROGRESSIVE THAN SYSTEMS OVER THE CENTRAL PLAINS...AS
THE LOW PRESSURE OVER CANADA QUICKLY MOVES TO NERN CANADA...WHILE AT
THE OTHER END OF THE TROUGH...LOW PRESSURE REMAINS NEARLY STATIONARY
OVER WRN KS.  THE NRN SYSTEM WILL DRAG A COLD FRONT ACROSS NRN LAKE
MICHIGAN BY THURSDAY EVENING.  ANOTHER AREA OF HIGH PRESSURE
BUILDING OUT OF SOUTHERN ONTARIO AND ACROSS THE UPPER GREAT LAKES
WILL HELP PUSH THE COLD FRONT DOWN THE LENGTH OF THE LAKE...CLEARING
THE SOUTHERN TIP OF THE LAKE BY FRIDAY EVENING.  THIS HIGH WILL VERY
SLOWLY SAG TO THE EAST AND SOUTH...KEEPING PREVAILING EASTERLY WINDS
OVER THE LAKE INTO THE WEEKEND...BEFORE VEERING TO SOUTHERLY BY
SUNDAY AS THE TROUGH OVER THE WESTERN PLAINS FINALLY LIFTS OUT
TOWARD THE UPPER MISSISSIPPI VALLEY.

KREIN

&&

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

$$

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