Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 020852
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
252 AM CST MON MAR 2 2015

.SHORT TERM...
250 AM CST

THROUGH TUESDAY...

HIGH PRESSURE CENTERED OVER THE MID MISSOURI VALLEY THIS MORNING
WILL TRANSLATE EAST ACROSS NORTHERN ILLINOIS THIS AFTERNOON AND THEN
OFF THE ATLANTIC COAST BY EARLY TUESDAY. MEANWHILE...CLOSED UPPER
LOW WITHIN A DEEP TROUGH IS IN PLACE ACROSS THE WEST COAST AND LEAD
WAVE IS PROGGED TO EJECT NORTHEAST FROM THE DESERT SOUTHWEST THIS
EVENING WITH A SURFACE LOW DEVELOPING OVER THE COLORADO FRONT RANGE
WHICH WILL LIFT INTO THE UPPER MIDWEST TUESDAY. THIS WILL BE A
CHALLENGING SYSTEM WITH THE POTENTIAL FOR MODEST SNOW ACCUMULATIONS
ON THE FRONT END...IN ADDITION TO LIGHT ICE ACCUMULATIONS...BEFORE
PRECIPITATION CHANGES OVER TO ALL RAIN. THESE DETAILS OF COURSE WILL
HINGE ON THE TRACK AND STRENGTH OF THE LOW WHICH MODELS CONTINUE TO
STRUGGLE WITH. THE 00Z EUROPEAN MODEL FITS WELL WITHING THE BEST
CLUSTERING OF THE GEFS AND HAS SHIFTED NORTH FROM PREVIOUS RUNS...A
MOVE THE GFS MADE WITH EARLIER GUIDANCE...THOUGH THE LATEST RUN IS
NORTH OF THE GEFS MEAN. SREF IS EVEN AN FARTHER NORTHERN OUTLIER.
CONTINUE TO LEAN HEAVILY ON THE ECMWF GUIDANCE BUT WITH A NORTHERN
STREAM SYSTEM PUSHING EAST ACROSS THE CANADIAN PRAIRIES AND HIGH
PRESSURE ALONG THE EAST COAST...WOULDNT BE SURPRISE TO SEE FARTHER
SHIFTS NORTH WHICH WOULD LIKELY LESSEN THE IMPACTS FROM FROZEN
PRECIP TYPE.

CURRENT EXPECTATIONS ARE THAT PRECIPITATION WILL BEGIN AS SNOW WITH
LIGHT ACCUMULATIONS POSSIBLE BEFORE MID LEVELS WARM ENOUGH FOR A
TRANSITION TO SLEET AND FREEZING RAIN DURING THE MORNING. AS
SURFACE/BOUNDARY LAYER TEMPS CONTINUE TO WARM...PRECIP SHOULD CHANGE
OVER TO RAIN FOR MOST IF NOT ALL OF THE CWA BY AFTERNOON. GIVEN THE
RAPID WARMUP...ANY SNOW/ICE ACCUMULATIONS WOULD LIKELY QUICKLY MELT
OFF. UNFORTUNATELY THE BEST CHANCES FOR FROZEN PRECIP WILL BE RIGHT
AROUND THE MORNING COMMUTE. MID LEVEL DRY SLOT PUNCHES INTO THE
REGION MID AFTERNOON INTO THE EARLY EVENING AND PRECIPITATION WILL
LIKELY TRANSITION TO A LIGHT RAIN OR DRIZZLE...THEN MOST OF THE
REMAINING PRECIPITATION SHOULD START TO PUSH EAST OF THE FORECAST
AREA THROUGH THE EVENING.

DEUBELBEISS

&&

.LONG TERM...
250 AM CST

TUESDAY NIGHT THROUGH SUNDAY...

HIGH PRESSURE WILL GRADUALLY BUILD FROM THE NORTHERN PLAINS TUESDAY
NIGHT TO THE MIDWEST THURSDAY THEN TO THE MID-ATLANTIC COAST FRIDAY
INTO SATURDAY. RIDGING WILL BE IN PLACE ACROSS NORTHERN ILLINOIS
MUCH OF THE PERIOD BRINGING AN EXTENDED PERIOD OF DRIER WEATHER. THE
HIGH WILL BE ACCOMPANIED BY COLDER AIR...WITH H85 TEMPS PUSHING -20C
MOVING ACROSS NORTHERN ILLINOIS WEDNESDAY NIGHT AND THURSDAY
MORNING. THIS WILL BE THE COLDEST MORNING IN THE FORECAST WITH NEAR
OR BELOW ZERO LOWS EXPECTED. A LOW PRESSURE SYSTEM WILL MOVE ACROSS
NORTHERN ONTARIO FRIDAY WITH A THERMAL RIDGE OVERSPREADING NORTHERN
ILLINOIS RESULTING IN WARMER CONDITIONS BY THE END OF THE WEEK INTO
THE WEEKEND.

DEUBELBEISS

&&

.AVIATION...

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

* LIGHT WEST-NORTHWEST WINDS FLOPPING TO LIGHT SOUTHEAST BY
  EVENING. MAY BE A PERIOD OF VARIABLE DIRECTION 5 KT OR LESS THIS
  AFTERNOON. SOUTH-SOUTHEAST WINDS INCREASING TOWARD TUESDAY
  MORNING.

* SNOW/MIXED PRECIP EXPECTED TO DEVELOP BY 12Z TUESDAY
  MORNING...WITH CIG/VIS QUICKLY DETERIORATING TO MVFR/IFR/LIFR
  JUST BEYOND END OF ORD 30 HOUR TAF.

RATZER

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

HIGH PRESSURE BUILDING EAST ACROSS THE TERMINALS MONDAY...AND
MOVING OFF TO THE EAST BY MONDAY EVENING. CURRENT WEST WINDS
10-12 KTS WILL DIMINISH TO LESS THAN 10 KT THIS MORNING AS
GRADIENT WEAKENS. WINDS WILL CONTINUE TO DIMINISH AND WILL LIKELY
BECOME VARIABLE IN DIRECTION AS THE HIGH PASSES OVERHEAD EARLY
THIS AFTERNOON...EVENTUALLY SETTLING TO A LIGHT SOUTHEAST THIS
EVENING AS THE HIGH PULLS AWAY TO THE EAST. SOUTH-SOUTHEAST WINDS
EXPECTED TO INCREASE ABOVE 10 KT TOWARD TUESDAY MORNING...PROBABLY
WITH GUSTS 20+ KT BEYOND 12Z.

VFR HIGH/MID CLOUDS WILL GRADUALLY INCREASE FROM THE SOUTHWEST
THROUGH THIS AFTERNOON AS MOISTURE BEGINS TO SPREAD NORTH AHEAD OF
AN AREA OF A LOW PRESSURE SYSTEM WHICH WILL DEVELOP ACROSS THE
PLAINS LATER TODAY/TONIGHT. CLOUDS WILL CONTINUE TO THICKEN AND
LOWER TONIGHT IN ADVANCE OF A WARM FRONT WHICH WILL LIFT TOWARD
THE AREA TUESDAY MORNING. FORECAST MODELS ARE IN FAIRLY GOOD
AGREEMENT IN PRECIPITATION DEVELOPING FROM THE SOUTHWEST ROUGHLY
10-12Z EARLY TUESDAY...LIKELY INITIALLY IN THE FORM OF SNOW. A
QUICK DETERIORATION FROM VFR TO MVFR/IFR/POTENTIALLY LIFR IS EXPECTED.

RATZER

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

* LOW IN WIND DIRECTION THIS AFTERNOON...BUT HIGH IN SPEEDS LESS
  THAN 10 KT.

* MEDIUM-HIGH IN TIMING ONSET OF SNOW TUESDAY MORNING.

* HIGH ALL OTHER ELEMENTS.

RATZER

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

TUESDAY...SNOW MIXING WITH FREEZING RAIN AND SLEET. IFR LIKELY.

WEDNESDAY...MVFR CIGS.

THURSDAY THROUGH SATURDAY...MAINLY VFR. POSSIBLE MVFR CIGS
SATURDAY.

BEACHLER

&&

.MARINE...
217 AM CST

HIGH PRESSURE SPREADING EAST FROM THE PLAINS EASTWARD TO THE MIDWEST
AND GREAT LAKES TODAY WILL ALLOW WESTERLY WINDS TO DIMINISH QUICKLY
THIS MORNING...AS THE GRADIENT WEAKENS WITH THE APPROACH OF THE
SURFACE RIDGE AXIS. WINDS WILL BACK TO THE SOUTH-SOUTHEAST BY
TONIGHT AS THE HIGH PULLS AWAY TO THE EAST...AND WILL INCREASE INTO
THE 25 KT RANGE BY TUESDAY MORNING AS AN AREA OF LOW PRESSURE LIFTS
NORTHEAST FROM THE PLAINS TO THE MID-MISSOURI VALLEY. THE LOW IS
EXPECTED TO TRACK NORTHEAST ACROSS WISCONSIN AND NORTHERN LAKE
MICHIGAN TUESDAY...WITH WINDS FURTHER INCREASING INTO THE 30-35 KT
RANGE ON THE SOUTHERN 2/3 OR SO OF THE LAKE DURING THE DAY. CURRENT
MODEL RUNS ARE NOT AS BULLISH IN DEEPENING THE LOW AS IT APPROACHES
AND IT APPEARS THAT A BRIEF PERIOD OF MARGINAL GALE FORCE WINDS
MIDDAY-AFTERNOON TUESDAY. WILL CONTINUE TO MENTION GALE FORCE GUSTS
BUT WILL HOLD SHORT OF A GALE WARNING AT THIS TIME. WINDS WILL THEN
EASE JUST A BIT BY TUESDAY EVENING AS THE TRAILING COLD FRONT MOVES
ACROSS THE LAKE...BUT ARE EXPECTED TO REMAIN NEAR 30 KT AS THE SHIFT
TO THE WEST-NORTHWEST TUESDAY NIGHT AS COLD AIR SPREADS ACROSS THE
LAKE AND ANOTHER LARGE HIGH PRESSURE SYSTEM BUILDS FROM CANADA
SOUTHEAST ACROSS THE PLAINS. WINDS LOOK TO HOLD IN THE 25-30 KT
RANGE WEDNESDAY AS WELL...AS THE CENTER OF THE HIGH SLOWLY TRACKS
SOUTHEAST...EVENTUALLY MOVING INTO THE LOWER OHIO VALLEY BY LATE
THURSDAY. THIS WILL ALLOW WINDS TO GRADUALLY DIMINISH AND BACK TO
THE SOUTHWEST THURSDAY NIGHT. GUSTY SOUTH-SOUTHWEST WINDS RETURN
FRIDAY AS THE HIGH MOVES OFF TO THE SOUTHEAST AND LOW PRESSURE
TRACKS NORTH OF THE LAKES.

WHILE MOST OF THE IL/IN NEAR SHORE WATERS APPEAR ICE COVERED PER
SATELLITE AND WEBCAM IMAGERY...WILL CARRY A SMALL CRAFT ADVISORY
TUESDAY/TUESDAY EVENING WITH 25-30 KT WINDS DURING THAT PERIOD.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...6 AM TUESDAY TO 10 PM TUESDAY.

&&

$$

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