Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 261903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
203 PM CDT THU MAR 26 2015

.SHORT TERM...
219 AM CDT

THROUGH TONIGHT...
IR IMAGERY EARLY THIS MORNING DISPLAYS THE CHANNEL OF MOISTURE
POSITIONED ACROSS THE MID-MISSOURI VALLEY STRETCHING NORTHEAST
THROUGH LOWER MICHIGAN. REGIONAL RADAR MOSAIC ALSO SHOWS THE BULK
OF THE PRECIP OVER SOUTHERN IL/CENTRAL IN...WITH SOME SHOWERS
LINGERING ACROSS THE SOUTHERN FORECAST AREA INTO A PORTION OF
NORTHWEST INDIANA. DRY AIR WILL CONTINUE TO SLIDE SOUTHEAST ACROSS
THE REGION...WITH SOME THINNING IN THE CLOUDS LATER THIS MORNING.
GUIDANCE HAS BEEN INDICATING THAT ANY THINNING OF THE SOLAR SHIELD
WOULD BE BRIEF...AS WINDS WILL BE TURNING NORTHERLY LATER THIS
AFTERNOON ALLOWING LAKE MOISTURE TO DEVELOP AND ADVECT ACROSS
NORTHERN IL/NORTHWEST IN. MIXING WILL INCREASE LATER THIS
MORNING...WITH AN INCREASE IN THE LOW LEVEL GRADIENT...THIS SHOULD
ALLOW FOR SOME GUSTS BETWEEN 20 AND 25 MPH.

500MB TROUGH AXIS WILL ARRIVE THIS AFTN COUPLED WITH AN UNSEASONABLY
COOL THERMAL TROUGH IN THE LOW LEVELS. THE COMBINATION WILL LIKELY
LOCK SFC TEMPS THIS AFTN IN THE LOW/MID 40S...AND POSSIBLY IN THE
UPR 30S CLOSER TO LAKE MICHIGAN. WINDS WILL STEADILY TURN NORTHERLY
LATE THIS AFTN/EARLY EVENING...WITH THE LAKE SFC-850MB TEMP GRADIENT
INCREASING AS A RESULT OF THE ANOMALOUS THERMAL TROUGH ADVECTING
SOUTH ACROSS THE WESTERN GREAT LAKES. THIS WILL LIKELY ALLOW LAKE
MOISTURE TO INCREASE...WITH SOME LAKE INDUCED RAIN SHOWERS
BECOMING MIXED WITH SNOW...THEN TRANSITIONING TO ALL SNOW LATE
TONIGHT. HI-RES LOCAL GUIDANCE HAS DONE A DECENT JOB DEPICTING
THIS FROM RECENT CYCLES. SOME LIGHT ACCUMS WILL BE
POSSIBLE...HOWEVER THIS WILL HINGE UPON WHEN PRECIP TRANSITIONS TO
ALL SNOW. EXPECT ANY ACCUMS TO BE LESS THAN 1 INCH AND MORE LIKELY
LESS THAN 0.5...MAINLY FOR AREAS ADJACENT TO LAKE MICHIGAN.

LAKE CLOUDS WILL LIKELY HELP TO KEEP SFC TEMPS A FEW DEGREES WARMER
IN THE LOW/MID 20S TONIGHT CLOSER TO LAKE MICHIGAN...WHILE LOCATIONS
ALONG AND WEST OF MENDOTA TO CRYSTAL LAKE WILL DIP TO AROUND 20 FOR
OVERNIGHT LOWS.

BEACHLER

&&

.LONG TERM...
331 AM CDT

FRIDAY THROUGH WEDNESDAY...

AN AMPLIFIED UPPER LEVEL FLOW PATTERN ACROSS NORTH AMERICA WILL ACT
TO DRIVE THE HEART OF AN UNSEASONABLY COLD AIRMASS SOUTHWARD ACROSS
THE GREAT LAKES REGION ON FRIDAY. THE COLD AIRMASS IS PROGGED TO
FEATURE NEAR -15 DEGREE CELSIUS TEMPERATURES AT 850 MB  AND -8 TO -
10 925 MB TEMPERATURES. THIS WILL LIKELY RESULT IN SURFACE
TEMPERATURES STRUGGLING TO GET INTO THE LOW TO MID 30S ACROSS MUCH
OF THE AREA. IN ADDITION TO THE COLD...SOME LINGERING LIGHT LAKE
EFFECT SNOW SHOWERS COULD LINGER INTO FRIDAY...ESPECIALLY ACROSS
NORTHWESTERN INDIANA.

A CANADIAN SURFACE RIDGE IS EXPECTED TO MOVE OVERHEAD BY SATURDAY
MORNING...AND THIS SHOULD ALLOW TEMPERATURES LATE FRIDAY NIGHT TO
DROP INTO THE TEENS IN MOST AREAS OUTSIDE OF CHICAGO. IN SPITE OF A
GOOD AMOUNT OF SUNSHINE ON SATURDAY...WITH THE SURFACE HIGH
OVERHEAD...HIGH TEMPERATURES WILL ONLY LIKELY BE ABLE TO CLIMB INTO
THE MID TO UPPER 30S IN MOST AREAS.

THE WEATHER PATTERN BEGINS TO CHANGE FOR THE SECOND HALF OF THE
WEEKEND AS A SIGNIFICANT NORTHERN PACIFIC WAVE IS FORECAST TO SHIFT
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST. THE SYSTEM IS
EXPECTED TO MOVE ATOP THE WESTERN CONUS RIDGE AND SHIFT OVER THE
GREAT LAKES REGION BY SUNDAY EVENING. SOME GUSTY SOUTHWEST WINDS AND
A PERIOD OF LIGHT RAIN IS POSSIBLY SUNDAY AS THIS SYSTEM IMPACTS THE
GREAT LAKES REGION.

WARMER CONDITIONS STILL LOOK TO RETURN TO THE REGION NEXT WEEK AS
THE STORM TRACK LOOKS TO FAVOR SYSTEMS TRACKING EASTWARD ACROSS THE
NORTHERN CONUS. IN FACT...WE COULD SEE TEMPERATURES BACK INTO THE
60S BY THE END OF THE FORECAST PERIOD.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LOW VFR CIGS 3000-4000 FT LOWERING TO MVFR OVERNIGHT.

* NORTHWEST WINDS TODAY INCREASING A BIT TO 10-13 KTS WITH GUSTS
  TO 20 KT POSSIBLE. EXPECT WINDS TO BE QUITE VARIABLE BETWEEN 280
  AND 340. WINDS SHIFT MORE NORTHERLY BY THIS EVENING AND NORTH-
  NORTHEAST TONIGHT.

* LAKE BREEZE THIS AFTERNOON...POSSIBLY REACHING CLOSE TO MDW LATE
  THIS AFTERNOON. SPEEDS

* CHANCE OF LAKE EFFECT RAIN/SNOW SHOWERS THIS EVENING/OVERNIGHT.

KMD

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

LOW END VFR CIGS CONTINUE TO STREAM IN FROM THE NORTHWEST THIS
AFTERNOON. EXPECT CIGS TO HOVER ABOVE 3000 FT FOR MOST LOCATIONS
THROUGH THE AFTERNOON. WINDS HAVE BEEN VARIABLE BETWEEN 280 AND
340 DEGREES THIS AFTERNOON...BUT HAVE GENERALLY SETTLED AROUND
310-320 DEGREES. EXPECT GUSTS TO 20 KT OR SO. WINDS WILL
GRADUALLY SHIFT TO NORTHERLY THIS EVENING...AND EVEN NORTHEASTERLY
CLOSER TO THE LAKEFRONT. FOCUS SHIFTS TO LAKE EFFECT SHOWER
POTENTIAL OVERNIGHT. MOISTURE REMAINS RATHER SHALLOW THIS
EVENING...BUT OVERNIGHT IT LOOKS LIKE MOISTURE...LOW LEVEL
INSTABILITY...AND HIGHER INVERSION HEIGHTS WOULD SUPPORT A PERIOD
OF SNOW SHOWERS AFTER MIDNIGHT THROUGH DAYBREAK. NOT SUPER
CONFIDENT AS TO HOW ORGANIZED THE SHOWERS WILL BE...BUT
ORD...MDW...AND GYY ARE ALL SUSCEPTIBLE. WAS DEBATING ON A TEMPO
WHICH MAY BE MORE HOW IT PLAYS OUT...BUT WANTED TO KEEP THINGS
SIMPLE WITH THE MVFR -SHSN MENTION DURING THE MOST LIKELY TIME
PERIOD. BEST LIFT IS BELOW THE DENDRITIC GROWTH ZONE...THUS THE
LOWER CONFIDENCE IN RINGING OUT SNOW AND IT MAY NOT BE QUITE AS
EFFICIENT. EITHER WAY...MVFR CONDITIONS ARE EXPECTED OVERNIGHT.

WINDS REMAINING NNE ON FRIDAY WITH FLURRIES TAPERING DURING THE
MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH IN WIND TRENDS TODAY...MEDIUM TONIGHT WITH TIMING OF SHIFT
  TO NORTH-NORTHEAST DIRECTION.

* MEDIUM THAT LAKE BREEZE STAYS EAST OF MDW. IF IT REACHES MDW IT
  WOULD BE LATE THIS AFTERNOON.

* HIGH IN CIGS REMAINING VFR THIS AFTERNOON...MEDIUM-HIGH IN
  RETURNING TO MVFR OVERNIGHT.

* MEDIUM CONFIDENCE IN LAKE EFFECT SNOW AND ASSOCIATED IMPACTS.

KMD

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

FRIDAY NIGHT...VFR. NORTH WINDS TURNING NORTHEAST.

SATURDAY...VFR. LIGHT NORTHEAST WINDS TURNING SOUTHEAST.

SUNDAY...CHANCE RAIN THROUGH THE DAY...POSSIBLY MIXING WITH SNOW
EARLY. MVFR CIGS/VIS POSSIBLE. GUSTY SOUTHWEST WINDS.

MONDAY...VFR. WEST WINDS.

TUESDAY...VFR. SOUTHWEST WINDS.

WEDNESDAY...SLIGHT CHANCE OF RAIN. MAINLY VFR.

BEACHLER

&&

.MARINE...
203 PM CDT

MAIN MARINE FORECAST CONCERNS FOCUS ON A COUPLE OF PERIODS OF
STRONGER WINDS...THE FIRST FROM THE NORTH LATE TONIGHT THROUGH
FRIDAY EVENING AND THE SECOND A STRONGER PERIOD OF SOUTH WINDS AND
POTENTIAL GALES SATURDAY NIGHT THROUGH SUNDAY AND THEN BECOMING
WEST AND VERY SLOWLY DIMINISHING SUNDAY NIGHT INTO MONDAY.

LOW PRESSURE WAS LIFTING NORTHEAST THROUGH THE OHIO VALLEY THIS
AFTERNOON...WHILE HIGH PRESSURE WAS PUSHING SOUTHWARD FROM CENTRAL
CANADA. IN ADDITION...A WEAK SURFACE TROUGH WAS PUSHING SOUTH
ACROSS THE LAKE...WITH COLDER AIR AND A TIGHTENING GRADIENT AHEAD
OF THE APPROACHING HIGH STARTING TO SHIFT WINDS MORE TO THE NORTH-
NORTHWEST WITH GUSTS NEAR 30 KT ON THE NORTH END OF THE LAKE. THIS
TROUGH WILL CONTINUE TO MOVE SOUTH DOWN THE LAKE THROUGH THIS
EVENING...WITH WINDS BECOMING NORTHERLY AND INCREASING TO 30 KT
TONIGHT AND SLOWLY EASING TO 25 KT OR SO THROUGH LATE FRIDAY. THIS
NORTHERLY FETCH WILL LEAD TO WAVES BUILDING INTO THE 8 FOOT
RANGE...AND WILL HAVE A SMALL CRAFT ADVISORY IN EFFECT AFTER 06Z
FRI/1 AM CDT FOR THE IL/IN NEARSHORE WATERS. WINDS WILL CONTINUE
TO DIMINISH MORE QUICKLY LATER FRIDAY NIGHT AND SATURDAY...THOUGH
WILL HAVE THE SCA RUN THROUGH 21Z SAT/4 PM CDT AS WAVES SUBSIDE
MORE SLOWLY.

THE SURFACE HIGH WILL CONTINUE TO SPREAD SOUTHEAST ACROSS THE
WESTERN LAKES AND INTO THE OHIO VALLEY BY SATURDAY EVENING...
ALLOWING WINDS TO SHIFT BACK TO THE SOUTH. A DEEPENING AREA OF LOW
PRESSURE IS EXPECTED TO DEVELOP AND MOVE EAST THROUGH MANITOBA AND
INTO ONTARIO SATURDAY NIGHT INTO SUNDAY...TIGHTENING THE GRADIENT
AND INCREASING SOUTH WINDS TO 35-40 KT GALES BY SUNDAY MORNING.
WINDS LOOK TO EAST A BIT LATE SUNDAY AND SHIFT WEST AS THE
TRAILING COLD FRONT MOVES ACROSS THE LAKE. WESTERLY WINDS THEN
CONTINUE TO DIMINISH MONDAY.

SOUTH GALES APPEAR TO BE FAIRLY LIKELY FOR DURING THE DAY
SUNDAY... THOUGH ON DAY 4 STILL A LITTLE BEYOND THE TIME PERIOD
FOR A GALE WATCH. IF FORECAST GUIDANCE CONTINUES TO DEPICT A
SIMILAR SCENARIO WILL LIKELY NEED A GALE WATCH IN THE NEXT DAY OR
SO.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...1 AM FRIDAY TO 4 PM SATURDAY.

&&

$$

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