000
FXUS63 KLOT 021355
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
755 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 12Z...

* WEST-NORTHWEST WINDS UNDER 10 KT BECOMING LIGHT/VARIABLE THIS
  AFTERNOON BEFORE FLOPPING SOUTHEAST BY EARLY EVENING. SOUTH-
  SOUTHEAST WINDS BECOMING GUSTY 15-20 KT BY TUESDAY MORNING.

* SNOW...MIXING WITH SLEET THEN CHANGING TO FREEZING RAIN/RAIN
  EARLY TUESDAY MORNING. VFR CONDITIONS TO QUICKLY DETERIORATE TO
  IFR/LIFR IN PRECIP.

RATZER/KB

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SPREADING EAST ACROSS THE REGION TODAY WILL RESULT
IN WEST-NORTHWEST WINDS NEAR 10 KT EARLY DIMINISHING TO 5 KT OR
LESS AND FLOPPING AROUND TO SOUTHEAST BY LATE AFTERNOON. SOUTH-
SOUTHEAST WINDS WILL THEN INCREASE LATE TONIGHT AS A LOW PRESSURE
SYSTEM TAKES SHAPE ACROSS THE PLAINS TO OUR WEST...WITH WINDS
160-170 DEG GUSTING AROUND 20 KT BY TUESDAY MORNING.

PATCHY VFR HIGH CLOUDS WILL INCREASE FROM THE SOUTHWEST TODAY AND
WILL GRADUALLY THICKEN AND LOWER THROUGH THE MID-LEVELS THIS
EVENING. FORECAST MODELS CONTINUE TO SHOW GOOD AGREEMENT IN
DEVELOPING PRECIPITATION NORTHWARD INTO THE AREA AHEAD OF A WARM
FRONT TOWARD SUNRISE TUESDAY. COLUMN IS INITIALLY ENTIRELY BELOW
FREEZING...THOUGH STRONG WARM PUSH ALOFT IS EXPECTED TO RESULT IN
PRECIPITATION INITIALLY IN THE FORM OF SNOW BECOMING MIXED
WITH/CHANGING TO SLEET AND THEN FREEZING RAIN DURING THE MORNING.
SURFACE TEMPERATURES WILL SLOWLY WARM WITH THE GUSTY SOUTH-
SOUTHEAST WINDS...THOUGH DO NOT LOOK TO REACH FREEZING OR ABOVE
UNTIL ABOUT NOON. WITH THE ONSET OF PRECIPITATION...VFR CIG/VIS
SHOULD RAPIDLY DETERIORATE THROUGH MVFR TO IFR/LIFR.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM IN WIND DIRECTION THIS AFTERNOON DURING FLOP FROM WNW TO
  SE.

* MEDIUM-HIGH IN PRECIP TIMING/TREND EARLY TUESDAY. MEDIUM IN
  CIG/VIS IMPACTS.

* HIGH ALL OTHER ELEMENTS.

RATZER/KB

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

TUESDAY NIGHT...MVFR CIGS. GUSTY WEST WINDS.

WEDNESDAY...MVFR CIGS.

THURSDAY AND FRIDAY...VFR.

SATURDAY AND SUNDAY...MVFR CIGS POSSIBLE.

RATZER

&&

.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/WEDNESDAY WITH 25+ 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 6 PM WEDNESDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO