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000
FXUS63 KLOT 090053
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
653 PM CST SUN DEC 8 2013

.DISCUSSION...
630 PM CST

TEMPERATURES AND SKY ARE ON TRACK...BUT ADJUSTED PRECIP TRENDS FOR
THIS EVENING INTO TONIGHT. LIGHT TO MODERATE SNOW CONTINUES TO
FALL ACROSS THE REGION AS THE SYSTEM CONTINUES OFF TO THE
NORTHEAST. REPORTS OF FZRA AND FREEZING DRIZZLE HAVE MAINLY
REMAINED SOUTH OF THE CWA OVER ILX/S CWA...BUT THINKING SNOW WILL
MIX AND THEN TRANSITION TO FREEZING DRIZZLE OVER THE NEXT FEW
HOURS SOUTH OF A STREATOR ILLINOIS TO DE MOTTE INDIANA LINE. THE
FREEZING DRIZZLE WILL PRODUCE A THIN GLAZE AT BEST...BUT ENOUGH TO
CREATE SLICK CONDITIONS. AS SUCH ISSUED A FREEZING RAIN ADVISORY
FOR THE SOUTHERN COUNTIES THROUGH MIDNIGHT.

SNOW WILL MIX WITH FREEZING DRIZZLE ACROSS THE AREA AS SNOW COMES
TO AN END LATE THIS EVENING...BUT NOT EXPECTING MUCH OF AN IMPACT
FOR AREAS NOT INCLUDED IN THE ADVISORY. ALL IN ALL PRECIP SHOULD
COME TO AN END BY 9Z AS PREVIOUSLY THOUGHT. IN FACT WONDERING IF
PRECIP WILL END SOONER THAN CURRENTLY FORECAST.

JEE

&&

.PREV DISCUSSION...
257 PM CST

TONIGHT...
LIGHT SNOW BEGAN EARLIER TODAY...AS A SEEDER-FEEDER MECHANISM
DEVELOPED ACROSS FAR NORTHEAST ILLINOIS. A WEAK MESO-LOW OVER THE
SOUTHERN TIP OF LAKE MICHIGAN THIS MORNING HAS SHIFTED NORTH...WHICH
RESULTED IN A BURST OF SNOWFALL ACROSS FAR SOUTHEAST WISCONSIN AND
FAR NORTHEAST LAKE COUNTY IL. THIS HAS SINCE PUSHED FURTHER NORTH.
TEMPERATURES HAVE SLOWLY WARMED AT THE SFC INTO THE MID 20S...WITH
DEW POINTS HOVERING AROUND 20 DEG. GUIDANCE CONTINUES TO INDICATE
DECENT LIFT/OMEGA ALONG A CHANNEL CURRENTLY LIFTING NORTH ACROSS
CENTRAL IL AND STRETCHING WEST INTO SOUTHEAST IOWA...EXPECT THIS TO
BLOSSOM THE SNOWFALL ACROSS NORTHERN IL LATE THIS AFTN/EARLY
EVENING BEFORE THE DEEPER MOISTURE BEGINS TO PEEL OFF TO THE NORTH
BY LATE TONIGHT. THE BEST OMEGA DOES APPEAR TO DIMINISH ARND
04Z...HOWEVER THE ENVIRONMENT REMAINS RATHER MOIST BELOW THE
DENDRITIC GROWTH ZONE. WHICH RAISES SOME CONCERN THAT SOME PATCHY
FREEZING DRIZZLE MAY DEVELOP IN THE WAKE OF THE LOW LATER THIS
EVENING. HAVE TRENDED BACK FROM THE COVERAGE OF THE FREEZING
DRIZZLE...HOWEVER EXPECT THERE MAY BE A PERIOD OF SOME LIGHT
FREEZING DRIZZLE BEFORE ALL PRECIP ENDS LATER TONIGHT. THE FOCUS
APPEARS TO BE SOUTH OF I-80.

BASED ON COBB P-TYPE ALGORITHMS WITH THIS NEXT CHANNEL OF SNOW THAT
IS BEGINNING TO DEVELOP...SNOWFALL RATES MAY APPROACH 0.5"/HR WITHIN
THE 22-02Z WINDOW. MANY OF THE POINTS INDICATING THIS ARE ALONG THE
FAR NORTHERN ROW OF COUNTIES IN IL...WHICH COULD ALLOW FOR SNOWFALL
THIS AFTN/EVE OF AN ADDITIONAL 1-2". FURTHER SOUTH THE SNOW TOTALS
WILL BE MUCH LIGHTER...WITH GENERALLY ARND 1". THE BEST LIFT DOES
APPEAR TO REMAIN JUST BELOW THE FAVORED DGZ...SO DENDRITIC SIZE MAY
REMAIN SMALLER AND MORE DIFFICULT TO GET THE BETTER ACCUMS TO OCCUR.
EITHER WAY...WITH THE SMALLER FLAKES VSBYS WILL FALL TO ARND 1/2
MILE UNDER THE STRONGEST SNOWFALL.

CONFIDENCE IN SNOWFALL TOTALS...MEDIUM/HIGH.
CONFIDENCE IN FREEZING DRIZZLE...MEDIUM.

MONDAY THROUGH TUESDAY...
EARLY MON THE DEPARTING SFC LOW WILL BE OVER NORTHERN LOWER
MICHIGAN...WITH A 500MB TROUGH AXIS PIVOTING EAST ACROSS THE CENTRAL
PLAINS. STRONG THERMAL TROUGH WILL REMAIN OVERHEAD...KEEPING TEMPS
ALOFT IN THE -8 TO -12 DEG C RANGE. THE COMBINATION OF SLOW EROSION
IN THE CLOUDS WITH WESTERLY WINDS WILL HELP TO HOLD TEMPS FOR MUCH
OF THE DAY IN THE UPPER TEENS TO LOW 20S...THEN POSSIBLY WARM INTO
LOW 20S ACROSS THE FAR SOUTHEASTERN CWFA.

HIGH PRESSURE WILL THEN BUILD EAST ACROSS THE REGION...SETTING THE
STAGE FOR A VERY COLD NIGHT MONDAY NIGHT. ARCTIC AIR ALOFT OF -20 TO
-22 DEG C DOES REMAIN JUST NORTH OF THE FORECAST AREA MON
NGT...HOWEVER WITH SKIES THINNING FURTHER TEMPS SHOULD EASILY
RADIATE INTO THE SINGLE DIGITS ABOVE ZERO. WITH WINDS REMAINING
LIGHT FROM THE WEST/SOUTHWEST...THIS SHOULD PREVENT TOO MANY AREAS
FROM COOLING TO ARND 0 TO JUST BELOW. ALTHOUGH WIND CHILL READINGS
IN MANY AREAS WILL BE WELL BELOW ZERO AND CLOSE TO -10 DEG C
READINGS EARLY TUE MORNING.

HIGH PRESSURE ELONGATES AND BEGINS TO DRIFT SOUTH TUE...AS A CLIPPER
BEGINS TO PUSH SOUTHEAST INTO THE UPPER MIDWEST EARLY TUE. THIS WAVE
WILL EVENTUALLY ARRIVE ACROSS THE FORECAST AREA TUE EVE. THIS WILL
SPREAD LIGHT SNOW ACROSS THE CWFA TUE NIGHT...WITH THE POSSIBILITY
OF LIGHT ACCUMS.

CONFIDENCE...HIGH.

WEDNESDAY THROUGH SATURDAY...
ENSEMBLES ARE BEGINNING TO SUGGEST THE ARCTIC AIRMASS THAT HAS
PUSHED SOUTHEAST ACROSS THE NORTHERN CONUS WILL BEGIN TO WEAKEN
TOWARDS THE SECOND HALF OF THE WEEK. GUIDANCE IS DEPICTING A WEAK
MID-LVL RIDGE...WITH SOME MODERATION TO THE TEMPS. TOWARDS NEXT
WEEKEND THE FLOW DOES BEGIN TO FLATTEN OUT...HOWEVER CONSIDERABLE
DIFFERENCES AMONGST THE ENSEMBLE MEMBERS DOES EXIST. THIS INDICATES
CONFIDENCE LOWERING AND PERHAPS THE DEVELOPMENT OF YET ANOTHER RIDGE
ACROSS THE PAC-NW. THIS COULD BE SETTING THE STAGE FOR A RETURN TO
COLD AIR BEYOND THE CURRENT EXTENDED FORECAST.

CONFIDENCE...MEDIUM.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* STEADY SNOW DECREASING IN COVERAGE/INTENSITY TOWARD 02/03Z.

* -FZDZ MAY DEVELOP AS SNOW ENDS DURING THE LATE
  EVENING...PRIMARILY ENDING AROUND MIDNIGHT IF IT OCCURS.

* IFR VSBY IMPROVES TO MVFR AND EVENTUALLY VFR. CIGS MAINLY MVFR
  WITH PERIODIC IFR NEXT 1-2 HOURS. MVFR LIKELY CONTINUES
  OVERNIGHT.

* WINDS SHIFT TO SOUTHEAST NEXT FEW HOURS THEN MORE QUICKLY TO
  SOUTH-SOUTHWEST MID EVENING...THEN SOUTHWEST TOWARD MIDNIGHT.

MDB

//DISCUSSION...UPDATED 00Z...

LOW PRESSURE CONTINUES TO BECOME SOMEWHAT BETTER ORGANIZED TO THE
SOUTHWEST WITH AN UPPER LEVEL WAVE CROSSING OVER THE LOCAL AREA.
WIDESPREAD SNOW CONTINUES ACROSS THE TERMINALS WITH IFR VSBY BUT
SNOW COVERAGE WILL BE DECREASING TOWARD MID EVENING. THE NEXT
CONCERN IS FREEZING DRIZZLE POTENTIAL WHICH LOOKS LIKELY SOUTH OF
THE TERMINALS BUT MORE QUESTIONABLE OVER THE TERMINALS THEMSELVES.
HAVE ADDED -FZDZ MENTION TO ALL BUT RFD AS THE SNOW
INTENSITY/COVERAGE WINDS DOWN AND THE SURFACE LOW ARRIVES. THREAT
LOOKS TO END AROUND OR JUST AFTER MIDNIGHT AS WINDS TURN SOUTHWEST
BEHIND THE PASSING LOW AND UPPER LEVEL FORCING DIMINISHES. IN
TERMS OF CEILINGS...SOME IFR IS OCCURRING WITH THE SNOWFALL BUT
THE TREND LOOKS TO BE TOWARD PERSISTENT MVFR THROUGH THE NIGHT
WITH IMPROVEMENT MONDAY MORNING. WINDS WILL TURN SOUTHEAST OVER
THE NEXT FEW HOURS THEN FLIP SOUTHWEST AS THE LOW PASSES OVER THE
AREA LATER THIS EVENING. WIND SPEEDS WILL DIMINISH AS THE LOW
PASSES AND THE SHIFT OCCURS BUT SPEEDS SHOULD COME UP BEHIND THE
LOW.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN SNOW INTENSITY/COVERAGE DECREASING 02/03Z.

* LOW-MEDIUM CONFIDENCE IN -FZDZ OCCURRING MID/LATE EVENING.

* HIGH CONFIDENCE IN IFR VSBY IMPROVING THROUGH THE
  EVENING...MEDIUM CONFIDENCE IN RATE OF IMPROVEMENT. HIGH
  CONFIDENCE IN VARIABLE IFR/MVFR CIGS NEXT FEW HOURS. MEDIUM
  CONFIDENCE THAT MVFR WILL PREVAIL OVERNIGHT.

* HIGH CONFIDENCE IN WIND TRENDS...MEDIUM-HIGH CONFIDENCE IN
  TIMING.

MDB

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

TUESDAY...VFR.

TUESDAY NIGHT AND WEDNESDAY...CHANCE FOR -SN AND MVFR CIGS/VSBY.

THURSDAY AND FRIDAY...VFR.

FRIDAY NIGHT AND SATURDAY...CHANCE FOR -SN AND MVFR.

MDB

&&

.MARINE...
337 PM CST

HIGH PRESSURE OF OVER SOUTHERN QUEBEC AND NEW ENGLAND WILL
CONTINUE TO MOVE EAST TONIGHT AND BE CENTERED OVER NEW BRUNSWICK
AND NOVA SCOTIA BY MON MORNING. MEANWHILE...LOW PRESSURE WILL
MOVE NORTHEAST FROM THE MID MS VALLEY TO THE EASTERN U.P. OF MI.
AS THE LOW DEEPENS AND CONTINUES ON ACROSS ONTARIO AND TO NEAR
SOUTHERN JAMES BAY DURING MON A COLD FRONT WILL MOVE EASTWARD
THROUGH THE UPPER GREAT LAKES SHIFTING WINDS TO OUT OF THE WEST
WITH SPEEDS INCREASING TO STRONG BREEZES FROM MID MORNING THROUGH
THE EVENING. OUTSIDE OF A FEW GUSTS AT OR JUST ABOVE GALE FORCE
SPEEDS ARE NO LONGER EXPECTED TO REACH GALE FORCE MON SO THE GALE
WATCH HAS BEEN CANCELLED.

A RIDGE OF HIGH PRESSURE WILL MOVE EAST FROM THE UPPER MIDWEST TO
THE EASTERN GREAT LAKES WITH A LOW MOVING FROM SD EAST TO WESTERN
LAKE SUPERIOR. THIS LOW CONTINUES EASTWARD TUE WITH A TRAILING
COLD FRONT MOVING ACROSS LAKE MI. BEHIND THE LOW AND THE COLD
FRONT WEST WINDS WILL LIKELY INCREASE TO NEAR GALE OR LOWER END
GALES TUE. HIGH PRESSURE WILL BE MOVING FROM ALBERTA AND
SASKATCHEWAN SOUTHEAST ACROSS THE NORTHERN PLAINS TO THE UPPER MS
VALLEY AND THE MID MO VALLEY TUE NIGHT AND WED...AND THEN EAST
OVER THE OH VALLEY THU AND THU NIGHT.

WINDS AND WAVES ARE NO LONGER EXPECTED TO REACH SMALL CRAFT
ADVISORY CRITERIA TONIGHT FOR THE IL AND IN NEARSHORE WATERS.
HOWEVER...WINDS ARE EXPECTED TO INCREASE TO AND ABOVE CRITERIA
MON SO THE SMALL CRAFT ADVISORY STAT TIME HAS BEEN PUSHED BACK
UNTIL MID MON MORNING.

TRS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FREEZING RAIN ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL
     MIDNIGHT MONDAY.

IN...FREEZING RAIN ADVISORY...INZ010-INZ011-INZ019 UNTIL MIDNIGHT
     MONDAY.

LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...9 AM MONDAY TO 10 PM MONDAY.

&&

$$

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