Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 022329
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
629 PM CDT THU JUL 2 2015

.SHORT TERM...
131 PM CDT

THIS AFTERNOON THROUGH FRIDAY...

LOWER CLOUDS HAVE BEEN SLOW TO LIFT GIVEN THE PRESENCE OF A THERMAL
INVERSION AROUND 3000 FT...BUT GRADUALLY CONTINUE TO DO SO AND
SPREAD WESTWARD WITH THE MEAN 925-850 MB WIND. HIGH CLOUDS
CONTINUE TO STREAM IN FROM THE NORTHWEST. GIVEN A STIFF ONSHORE
WIND AND CLOUDS...HIGHS HOLD ONLY IN THE 60S TO LOW 70S.

THE WEATHER PATTERN IS CHARACTERIZED BY NW FLOW ALOFT ON THE BACK
SIDE OF DEEPER UPPER LEVEL LOW PRESSURE IN QUEBEC. THE TROUGH AXIS
WITH THIS SYSTEM WILL LINGER BACK OVER OUR AREA THROUGH THE SHORT
TERM. DISTURBANCES IN THIS FLOW PATTERN WILL LARGELY BE SHUNTED AWAY
FROM THE REGION AS SURFACE HIGH PRESSURE...CURRENTLY ANCHORED OVER
NORTH CENTRAL WISCONSIN DRIFTS SLOWLY SOUTHWARD. WE WILL SEE
CONTINUED HIGH CLOUDINESS/HAZE AS THESE WAVES TRACK THROUGH. AS THE
HIGH SINKS SOUTH ON FRIDAY...WE MAINTAIN A NE FLOW OFF THE
LAKE...THOUGH THE ONSHORE WIND COMPONENT DOES EASE A BIT. THE AIR
MASS WARMS SOME...SO STILL EXPECT A MILDER DAY ON FRIDAY WHICH
LESS IN THE WAY OF MORNING CLOUDINESS. HIGHS LOOKS TO TAG THE
UPPER 70S TO 80 IN OUTLYING AREAS...WITH COOLER UPPER 60S TO LOW
70S ALONG THE LAKE.

KMD

&&

.LONG TERM...
229 PM CDT

FRIDAY NIGHT THROUGH THURSDAY...

A LARGE SCALE UPPER TROUGH WILL SHIFT EAST OF THE AREA SATURDAY AND
BE REPLACED BY AN UPPER RIDGE WHICH WILL BE AMPLIFYING ACROSS THE
WESTERN GREAT LAKES AND ONTARIO AHEAD OF A LARGER UPPER TROUGH OVER
WESTERN CANADA. THE RIDGING WILL BROADEN AND SHIFT TO THE EAST
SUNDAY WHILE THE UPPER TROUGH ADVANCES EAST-SOUTHEAST. THE PASSAGE
OF THIS TROUGH EARLY NEXT WEEK WILL USHER IN A MORE ZONAL BUT STILL
BROADLY TROUGHED UPPER FLOW.

AS FOR THE DETAILS...PLEASANT CONDITIONS WILL PERSIST THROUGH THE
WEEKEND AS SURFACE HIGH PRESSURE SETS UP RIGHT OVER THE AREA BY
SATURDAY MORNING. A WEAK COOL FRONTAL BOUNDARY WILL TRAIL A SURFACE
TROUGH MOVING ACROSS EASTERN ONTARIO/WESTERN QUEBEC AND DROP DOWN
LAKE MICHIGAN SATURDAY MORNING. THIS BOUNDARY LOOKS TO LOSE
DEFINITION AS IT APPROACHES THE SOUTHERN SHORES OF THE LAKE AS ITS
PARENT LOW PULLS OFF TO THE NORTHEAST AND IT ENCOUNTERS THE HIGH.
GIVEN THE PRESENCE OF THE HIGH...WINDS WILL BE LIGHT SO A LAKE
BREEZE IS LIKELY. THIS WILL KEEP LAKESHORE AREAS IN THE LOW TO MID
70S SATURDAY. HAZY SKIES FROM THE WILD FIRE SMOKE WILL PROBABLY
STILL BE IN PLACE DURING THE DAY BUT SHOULD START TO PEEL OFF TO THE
NORTH AS UPPER LEVEL FLOW SHIFTS SOUTHWESTERLY WITH THE ARRIVAL OF
THE RIDGE LATER IN THE DAY. SUNDAY WILL SEE A STEADIER SOUTHERLY LOW
LEVEL FLOW SO LAKE COOLING WILL BE MORE CONFINED TO SHORELINE AREAS.
OTHERWISE HIGHS WILL BE SIMILAR TO SATURDAY. A COLD FRONT WILL BE
WORKING ITS WAY TOWARDS THE AREA MONDAY AS THE UPPER TROUGH MOVES
ACROSS CENTRAL CANADA. STRONGER SOUTHERLY FLOW WILL BRING MORE HUMID
CONDITIONS TO THE AREA. THE SPEED OF THE FRONT IS STILL IN QUESTION
AND WESTERN AREAS MAY SEE SHOWER/THUNDER CHANCES LATER MONDAY
AFTERNOON ON THE EARLY SIDE. AM LEANING TOWARD A SLOWER PROGRESSION
BRINGING BETTER CHANCES MONDAY NIGHT AND FIRST THING TUESDAY BUT
WILL HAVE TO WATCH. THE FRONT WILL LIKELY STALL OUT SOMEWHERE SOUTH
OF THE AREA AND WHERE THIS OCCURS WILL DICTATE WHERE POPS MAY LINGER
THROUGH TUESDAY OR EVEN TUESDAY NIGHT. SOME MINIMAL POPS MAY BE
NEEDED WEDNESDAY/THURSDAY AS THE FLOW WILL BE FAVORABLE FOR
SHORTWAVE PASSAGES BUT SURFACE HIGH PRESSURE MAY WIN OUT. MONDAY
WILL BE THE WARMEST DAY WITH COOLER TEMPS TUESDAY AND WEDNESDAY
THANKS TO NORTHERLY LOW LEVEL WINDS. IT BECOMES INCREASINGLY
DIFFICULT TO PIN DOWN THE UPPER FLOW PATTERN BY LATE NEXT WEEK BUT
IT DOES APPEAR THAT PRECIP CHANCES MAY INCREASE DURING THAT TIME.

MDB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NORTHEAST WINDS AROUND 10 KT THROUGH EARLY-MID EVENING.

* LOW POTENTIAL FOR BR LATE TONIGHT INTO EARLY FRIDAY.

* LAKE BREEZE MAY CAUSE NORTHEAST WINDS TO INCREASE TO CLOSE TO 10
  KT FRIDAY AFTERNOON.

RC

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL REMAIN IN CONTROL THROUGH THE
PERIOD...CONTINUING QUIET AND GENERALLY VFR CONDITIONS. CANNOT
RULE OUT SOME BR/PATCHY GROUND FOG IN OUTLYING AREAS LATE TONIGHT
INTO EARLY FRIDAY...BUT HAVE NOT INCLUDED IN ANY TAFS GIVEN LIKELY
LOW COVERAGE IF IT OCCURS. NORTHEAST WINDS WILL DIMINISH BELOW 10
KT THIS EVENING AT ORD/MDW/GYYY AND POSITION OF HIGH PRESSURE ON
FRIDAY WILL YIELD LIGHTER SYNOPTIC EAST-NORTHEAST WINDS. THIS WILL
ENABLE A LAKE BREEZE TO PUSH INLAND AND INCREASE SPEEDS SOME
BEHIND IT...THOUGH IT IS UNCERTAIN WHETHER 10 KT THRESHOLD WILL BE
REACHED AT ORD. SCT TO POSSIBLY BKN VFR CU AT 035-045 IS EXPECTED
INLAND.

RC


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH IN WIND TRENDS THROUGH FRIDAY MORNING...LOW-MEDIUM IN WIND
  SPEEDS BEHIND LAKE BREEZE FRIDAY AFTERNOON.

* LOW IN BR LATE TONIGHT INTO EARLY FRIDAY.

* HIGH IN REMAINING ELEMENTS.

RC

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

SATURDAY AND SUNDAY...VFR.

MONDAY...

TUESDAY...

WEDNESDAY...

RC

&&

.MARINE...
229 PM CDT

HIGH PRESSURE IS CENTERED OVER NORTHERN LAKE MICHIGAN
THIS AFTERNOON AND WILL SETTLE SOUTHWARD THEN SPLIT INTO FRIDAY.
STEADIER NORTH TO NORTHEAST WINDS ACROSS SOUTHERN SECTIONS OF THE
LAKE THIS AFTERNOON WILL EASE UP THROUGH THE LATE EVENING. LOW
PRESSURE WILL MOVE ACROSS NORTHERN ONTARIO FRIDAY BRINGING A SHARPER
PRESSURE GRADIENT TO NORTHERN LAKE MICHIGAN AS THE HIGH SHIFTS SOUTH.
STEADY SOUTHWEST WINDS WILL DEVELOP NORTH THROUGH THE DAY WHILE
LIGHT AND NORTHEASTERLY WINDS SET UP SOUTH...WITH SOME VARIABILITY
IN DIRECTION EXPECTED. A WEAK COOL FRONT WILL TRAIL THE ONTARIO LOW
AND DROP ACROSS NORTHERN LAKE MICHIGAN SATURDAY TURNING WINDS
NORTHERLY BUT THE FRONT WILL LOSE FOCUS THROUGH THE DAY. HIGH
PRESSURE WILL THEN RE-FOCUS ACROSS LAKE MICHIGAN SATURDAY EVENING
ALLOWING FOR LIGHT AND VARIABLE WINDS. SOUTH TO SOUTHWEST WINDS WILL
DEVELOP THROUGH THE DAY SUNDAY AS THE HIGH SHIFTS EAST AND ANOTHER
LOW PRESSURE SYSTEM AND ASSOCIATED COOL FRONT MOVE ACROSS THE
CANADIAN PRAIRIES AND NORTHERN PLAINS. THE FRONT WILL CROSS THE LAKE
MONDAY EVENING OR TUESDAY MORNING BRINGING A SHIFT TO NORTHERLY
WINDS WHICH MAY DIMINISH FAIRLY QUICKLY AS HIGH PRESSURE WILL BUILD
IN RIGHT BEHIND IT. THE HIGH WILL SHIFT ACROSS THE LAKE THROUGH MID
WEEK KEEPING A FAIRLY LIGHT WIND REGIME IN PLACE.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 4 AM FRIDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 4 AM FRIDAY.

LM...NONE.
&&

$$

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