Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280807
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
307 AM CDT SAT MAR 28 2015

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

TO BE ISSUED SHORTLY.

&&

.AVIATION...

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

* LAKE BREEZE AIDING IN WINDS POSSIBLY TOPPING 9 KT THIS
  AFTERNOON.
* 40-45 KT SW WINDS BETWEEN 1000-2000 FT NEAR DAYBREAK SUNDAY
  POSSIBLY CREATING LLWS.

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

HIGH PRESSURE WILL REMAIN DIRECTLY OVER THE AREA THROUGH TODAY
BEFORE SHIFTING EAST TONIGHT. THIS WILL ALLOW FLOW FROM THE
NORTHEAST OR EAST-NORTHEAST TO INCREASE DURING THE EARLY
AFTERNOON...WITH SPEEDS OF 9 KT OR SLIGHTLY OVER POSSIBLE FOR AT
LEAST A COUPLE HOUR WINDOW DURING THE AFTERNOON. SURFACE WINDS
WILL TURN SOUTHERLY TONIGHT AS LOW PRESSURE APPROACHES FROM THE
NORTHWEST. SURFACE SPEEDS SHOULD GRADUALLY INCREASE LATE SATURDAY
NIGHT WHILE LOW-LEVEL JET WINDS INCREASE MARKEDLY ABOVE 1000 FT
OR SO...POSSIBLY RESULTING IN LLWS NEAR DAYBREAK SUNDAY.

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

* MEDIUM IN TIMING AND MAGNITUDE OF LAKE BREEZE. LOW IN DURATION
  OF SPEEDS AT 9+ KT.
* MEDIUM-HIGH IN 40-45KT SW LOW-LEVEL JET WINDS NEAR DAYBREAK
  SUNDAY. LOW IN TRUE LLWS.

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

SUNDAY...MVFR CIGS DEVELOPING WITH A PERIOD OF RAIN.

MONDAY...PRIMARILY VFR DURING DAY. CHANCE OF SHRA AT NIGHT.

TUESDAY...CHANCE OF MVFR CIGS EARLY.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF SHRA...OTHERWISE VFR.

MTF/IZZI

&&

.MARINE...
242 PM CDT

WINDS ARE COMING DOWN AS HIGH PRESSURE SLIDES EAST TOWARD THE
WESTERN LAKES.  HOWEVER WAVES WILL REMAIN HAZARDOUS TO SMALL CRAFT
INTO SATURDAY MORNING.  THE HIGH SHIFTS SOUTHEAST OVER THE OHIO
VALLEY SATURDAY EVENING WITH WINDS BECOMING SOUTHWEST TO 30 KT
OVERNIGHT.  THE NEXT LOW PASSES OVER ONTARIO SUNDAY AND WINDS
INCREASE TO GALES ACROSS THE LAKE.  MAX GUSTS OF 45 KT WILL BE OVER
THE NORTHERN END OF THE LAKE...AND WILL ISSUE A GALE WATCH FOR ALL
OF THE OPEN WATERS. GALES ARE POSSIBLE OVER THE NEARSHORE WATERS AS
WELL BUT WILL HOLD OFF ON ISSUING A WATCH AS CONFIDENCE IN NOT HIGH
ENOUGH FOR A WATCH AT THIS POINT.  THE LOWS COLD FRONT SWINGS OVER
THE LAKE SUNDAY EVENING WITH WINDS DIMINISHING AND BECOMING WEST TO
30 KT.  A WEAK RIDGE PASSES OVER THE LAKE MONDAY WITH A SURFACE LOW
MOVING OVER THE LAKE TUESDAY MORNING.  ANOTHER HIGH PRESSURE SYSTEM
REACHES THE WESTERN LAKES MID WEEK THEN A STRONG LOW SLIDES NORTH OF
THE LAKE THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SATURDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

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