Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 300929
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
429 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

RC

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

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

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

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

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

$$

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