000
FXUS63 KLOT 091946
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
146 PM CST MON DEC 9 2013

.DISCUSSION...
327 AM CST

IN THE SLIGHTLY MODIFIED WORDS OF FRANK SINATRA...THE WORST IS YET
TO COME AND IT WON`T BE THAT FINE. AFTER WADING AROUND IN THE
SHALLOW END OF THE ARCTIC POOL THE PAST FEW DAYS IT LOOKS LIKE OUR
AREA IS POISED TO MEANDER INTO THE DEEP END OF THE POOL FOR BIT THIS
WEEK. AND FOR GOOD MEASURE IT IS LOOKING INCREASINGLY LIKELY THAT
PORTIONS OF THE AREA COULD FRESHEN UP OUR NEW SNOW PACK WITH A
COUPLE MORE POORLY TIMED INCHES AROUND RUSH HOUR WEDNESDAY MORNING.
THE ONE SILVER LINING...IT DOES LOOK LIKE THE ARCTIC AIR WILL LOOSEN
ITS GRIP ON THE AREA LATER THIS WEEK INTO THE WEEKEND THOUGH IT
SHOULD REMAIN COLD...JUST A MORE TYPICAL BRAND OF COLD.

SYSTEM RESPONSIBLE FOR SUNDAY`S SNOW IS PULLING OUT WITH ANY
LINGERING SPITS OF FREEZING SNIZZLE OR FLURRIES LIKELY TO EXIT THIS
AREA BY SUNRISE...WITH CLEARING LINE ARRIVING SHORTLY THEREAFTER.
DESPITE CLEARING SKIES...BLUSTERY WEST WINDS AND COLD AIR ADVECTION
SHOULD RESULT IN TEMPS FALLING A FEW DEGREES THIS MORNING FOLLOWED
BY A POSSIBLE SLIGHT EARLY AFTERNOON RECOVERY BEFORE FALLING OFF
QUICKLY TOWARD EARLY THIS EVENING. WILL PROBABLY SEE SOME CLEARING
TONIGHT AND LESSENING OF THE WINDS THIS EVENING AS WEAK RIDGE AXIS
PASSES BY...WHICH COULD RESULT IN TEMPS REALLY TANKING THIS EVENING
WITH THE FRESH SNOW COVER. SOME REMAINING WIND FOLLOWED BY WARM AIR
ADVECTION STARTING UP AFTER MIDNIGHT WILL HOPEFULLY KEEP TEMPS FROM
GETTING TOO OUT OF HAND...BUT POTENTIAL EXISTS FOR SOME OF THE HOLES
TO DIP BELOW ZERO. THOSE HEADING TO THE BEARS GAME THIS EVENING WILL
REALLY NEED TO BUNDLE UP WITH WIND CHILLS NEAR OR JUST BELOW
ZERO...WHICH IS ONE HECK OF A CONTRAST FROM THE LAST HOME GAME WHICH
FEATURED SEVERE THUNDERSTORMS AND TEMPERATURES NOT FAR FROM 70 BACK
ON NOV 17TH!

CLIPPER PASSING TO OUR NORTH LATE TONIGHT AND TUESDAY COULD ALLOW
TEMPS TO BEGIN TO RISE LATE TONIGHT WITH THAT RISE CONTINUING INTO
TUESDAY WITH A BRIEF SHOT OF "WARM" AIR ADVECTION. SECONDARY COLD
FRONT ARRIVES IN THE AFTERNOON AND AFTER A QUICK REBOUND COULD SEE
TEMPS BEGIN TO FALL AGAIN IN THE AFTERNOON WITH THE NEXT SHOT OF
ARCTIC AIR. TUESDAY LOOKS TO BE VERY WINDY...SO WIND CHILLS NOT
EXPECTED TO GET MUCH ABOVE ZERO ALL DAY AS WEST WINDS GUST TO OVER
30 MPH. THE GUSTY WEST WINDS COULD RESULT IN SOME BLOWING SNOW IN
OPEN/RURAL AREAS BUT NOT EXPECTING IT TO BE A HUGE DEAL.

NEXT CLIPPER SHOULD RESULT IN WARM AIR ADVECTION STARTING UP AGAIN
TUESDAY NIGHT...WITH YET ANOTHER PERIOD WITH AN ATYPICAL DIURNAL
TEMP TREND AS WE SEE TEMPS BEGIN TO RATHER QUICKLY RISE AFTER
EVENING LOWS. TUES NIGHT CLIPPER IS PROGGED TO TRACK FARTHER SOUTH
AND BETTER FORCING IS FARTHER SOUTH PLACING OUR AREA IN THE
POTENTIAL SWATH OF SNOW. MOISTURE IS LIMITED AND FORCING NOT
TREMENDOUS...BUT PRETTY GOOD MODEL AGREEMENT IN THIS SYSTEM LAYING
OUT A SWATH OF ABOUT A TENTH OF AN INCH OF LIQUID OVER NORTHERN
ILLINOIS. BEING SUCH A SUBTLE SHORTWAVE...MODELS MAY WELL CHANGE
THEIR TUNE SOME IN THE NEXT 12-24 HOURS...BUT GIVEN CURRENT PROGS IT
WOULD SEEM REASONABLE THAT A SWATH OF 1-3 INCHES OF FLUFFY SNOW
COULD FALL WITH THIS SYSTEM. CURRENT FORECAST PATH WOULD FAVOR AREAS
NORTH OF I-80 AGAIN WITH TIMING LOOKING TO BE AFTER MIDNIGHT TUES
NIGHT THROUGH RUSH HOUR WEDNESDAY MORNING.

YET ANOTHER RE-ENFORCING BLAST OF ARCTIC AIR ARRIVES WEDNESDAY
AFTERNOON IN THE WAKE OF THIS CLIPPER. ECMWF/GFS/WRF-NAM ARE ALL IN
GOOD AGREEMENT ON BRINGING WHAT APPEARS TO BE REMARKABLY COLD AIR
FOR SO EARLY IN THE SEASON WITH 850MB AND 925MB TEMPS BOTH PROGGED
TO DROP TO AROUND -19C...WHICH LOOKING BACK TO 1979 WE HAVE ONLY
SEEN COLD OF THIS MAGNITUDE A FEW TIMES DURING THE FIRST 15 DAYS OF
DECEMBER. ONE OF THE EVENTS WAS 12/15/1989 WHEN ORD GOT TO -8 AND
RFD -16...ANOTHER WAS 12/14-15/1985 WHEN ORD ONCE AGAIN HIT -8 AND
RFD -11. IT DOESNT LOOK LIKE IT WILL GET THAT COLD THIS TIME AROUND
THANKS TO THE PROGRESSIVE NATURE OF THE PATTERN...HOWEVER THAT DOES
GIVE SOMEWHAT OF A BASELINE FOR WHAT AN AIR MASS LIKE THIS ONE CAN
BRING. THINKING NOW THAT TEMPS WILL FOLLOW ANOTHER ATYPICAL DIURNAL
TREND WEDNESDAY WITH STEADILY FALLING TEMPS WED AFTERNOON...PROBABLY
INTO THE SINGLE DIGITS BY SUNSET OVER MOST OF THE AREA WITH WIND
CHILLS WELL BELOW ZERO.

WEDNESDAY NIGHT SHOULD BE COLDEST NIGHT OF THE SEASON...AND POSSIBLY
ONE OF THE COLDEST NIGHTS IN YEARS. WHILE NOT AN IDEAL RADIATIONAL
COOLING SET-UP WITH SOME GRADIENT PERSISTING THROUGH THE NIGHT AND
WARM AIR ADVECTION ALOFT...IT DOES LOOK LIKE SKIES COULD BE MOSTLY
CLEAR AND WITH A FRESH SNOW PACK THINK THAT LOWS WILL DROP BELOW
ZERO OVER MOST OF THE CWA OUTSIDE OF THE URBAN HEAT ISLAND OF
CHICAGO. CONSERVATIVELY KNOCKED LOWS DOWN TO 5 TO 10 BELOW IN THE
COLDEST SPOTS...BUT IF WINDS DECOUPLE AND WE STAY CLEAR THEN LOWS
COLDER THAN 10 BELOW WOULD NOT BE A STRETCH AT ALL FOR PLACES LIKE
ARR/RPJ. OFFICIALLY IT WILL BE CLOSE FOR CHICAGO OHARE...BUT IF WE
DROP BELOW ZERO IT WOULD BE ONLY THE SECOND TIME IN THE LAST 30
YEARS THAT TEMPS HAVE DROPPED BELOW ZERO IN CHICAGO THIS EARLY IN
THE SEASON. WIND CHILLS LOOK TO BOTTOM OUT IN THE 10 TO 20 BELOW
RANGE...GETTING CLOSE TO THE -20 WIND CHILL ADVISORY CRITERIA OVER
NORTH CENTRAL ILLINOIS FOR TIME WED NIGHT.

WARM AIR ADVECTION SHOULD TAKE HOLD THURSDAY WITH TEMPS REBOUNDING
NICELY FROM THE BITTERLY COLD MORNING LOWS. HAVE GONE A SMIDGE BELOW
GUIDANCE OUT OF FEAR OF THE SNOW COVER AND VERY COLD START TO THE
DAY MAKING IT HARD TO REBOUND MORE THAN 20F. WARM AIR ADVECTION
CONTINUES THURSDAY NIGHT WITH TEMPS PROBABLY NOT FALLING MUCH FROM
DAY TIME HIGHS AND LIKELY TO END UP 20F+ WARMER THAN THE PREVIOUS
NIGHT IN MANY AREAS.

ANOTHER SHORTWAVE COULD AFFECT THE AREA LATE FRIDAY INTO EARLY
SATURDAY...THOUGH MODELS ARE NOT IN GREAT AGREEMENT IN THEIR
HANDLING OF THAT SYSTEM JUST YET. AT THIS TIME NOT LOOKING LIKE A
BLOCK-BUSTER...BUT COULD BE COLD ENOUGH FOR MOSTLY SNOW IF IT DOES
IMPACT THE CWA. MORE MODERATE BRAND OF COLD EXPECTED TO ARRIVE IN
THE WAKE OF THIS SYSTEM...BUT STILL BELOW AVERAGE.

IZZI

&&

.AVIATION...

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

* GUSTY WEST WINDS TODAY.
* VERY GUSTY SOUTHWEST WINDS TUESDAY MORNING FOLLOWED BY VERY
  GUSTY WESTERLY WINDS TUESDAY AFTERNOON. WIND GUST OF 30 TO 35 KT
  POSSIBLE.
* CHANCE OF SOME LIGHT SNOW SHOWERS AND LOWER CIGS MID TO LATE
  TUESDAY MORNING.

KJB

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

SURFACE HIGH PRESSURE IS CURRENTLY SET UP ACROSS THE PLAINS...WHILE
LOW PRESSURE CONTINUES TO DEEPEN AS IT LIFTS NORTHWARD ACROSS
EASTERN ONTARIO. OVERALL...THESE PRESSURE PATTERNS WILL SUPPORT SOME
GUSTY WESTERLY WINDS THROUGH THE REMAINDER OF THE AFTERNOON. THE
MVFR CIGS ARE FINALLY BEGINNING TO MOVE OUT OF NORTHEASTERN
ILLINOIS...WITH VFR CONDITIONS EXPECTED FOR THE REST OF THE DAY.

THE MAIN WEATHER CONCERNS WILL BE DURING THE DAY ON TUESDAY. ANOTHER
WEAK...BUT FAST MOVING CLIPPER SYSTEM...WILL MOVE FROM THE
DAKOTAS...EAST SOUTHEASTWARD ACROSS SOUTHERN WISCONSIN ON TUESDAY.
THIS SYSTEM COULD PRODUCE A PERIOD OF LIGHT SNOW AND FLURRIES ACROSS
THE TERMINALS...MAINLY DURING THE MORNING. HOWEVER...THE MAIN
WEATHER CONCERN WITH THIS SYSTEM WILL BE THE WINDS. IT APPEARS THE
THE WINDS WILL SWITCH OUT OF THE SOUTH-SOUTHWEST AND INCREASE EARLY
TUESDAY MORNING. WIND GUSTS OF 25 TO 30 KT APPEAR LIKELY BY MID
MORNING. THEN...AS THE SURFACE SYSTEM SHIFTS ACROSS THE AREA WINDS
WILL SHIFT OUT OF THE WEST BY MID DAY. A PERIOD OF EVEN STRONGER
WINDS (30 TO 35 KT) ARE EXPECTED FOLLOWING THIS WIND SHIFT.

KJB

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

* LOW TO MEDIUM FOR THE CHANCE OF LIGHT SNOW AND LOWER CIGS
 TUESDAY MORNING.
* HIGH FOR ALL OTHER ELEMENTS.

KJB

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

TUESDAY NIGHT...SNOW LIKELY LATE...ACCUMULATIONS POSSIBLE. DROPPING
TO IFR.
WEDNESDAY...SNOW ENDING. IMPROVING TO VFR.
THURSDAY...VFR.
FRIDAY...CHC SNOW. BECOMING IFR/MVFR.
SATURDAY...CHC SNOW. IFR/MVFR.
SUNDAY...IMPROVING TO VFR.

BMD

&&

.MARINE...
145 PM CST

MAIN MARINE FORECAST CONCERNS ARE A COUPLE OF PERIODS OF GALE FORCE
WINDS OVER NORTHERN LAKE MICHIGAN THIS AFTERNOON/EVENING...AND AGAIN
TUESDAY AND TUESDAY NIGHT ACROSS THE ENTIRE LAKE. HAVE UPGRADED GALE
WATCH TO A GALE WARNING FOR TUESDAY AND TUESDAY NIGHT.

STRENGTHENING LOW PRESSURE WAS LOCATED JUST NORTH AND NORTHEAST OF
LAKE SUPERIOR THIS AFTERNOON...AND WILL CONTINUE TO DEEPEN AS IT
LIFTS TOWARD JAMES BAY THIS EVENING. AS THE LOW DEEPENS...A PERIOD
OF TIGHTENING SURFACE PRESSURE GRADIENT WAS RESULTING IN LOW-END
WEST GALES ACROSS MAINLY NORTHERN LAKE MICHIGAN WITH GRAND TRAVERSE
LIGHT GUSTING 34 KTS AS OF NOON CST. GALES WILL LINGER TONIGHT AS
THE LOW PULLS AWAY...GRADUALLY EASING AFTER MIDNIGHT ACROSS THE FAR
NORTHERN PORTION OF THE LAKE AS WEAK HIGH PRESSURE RIDGING MOVES
ACROSS THE WESTERN LAKES. THE LULL LOOKS TO BE BRIEF HOWEVER...AS A
FAST MOVING CLIPPER SYSTEM CURRENTLY MOVING ACROSS FAR SOUTHERN
SASKATCHEWAN TRAVELS QUICKLY TO THE UPPER MISSISSIPPI VALLEY
OVERNIGHT...AND ACROSS THE NORTHERN/WESTERN GREAT LAKES REGION ON
TUESDAY. THIS WILL INDUCE A QUICK RE-TIGHTENING OF THE SURFACE
PRESSURE GRADIENT ACROSS LAKE MICHIGAN TUESDAY MORNING...WITH STRONG
SURFACE-BASED MIXING AND COLD ADVECTION EXPECTED TO PRODUCE WESTERLY
40 KT GALES BASED ON MODEL FORECAST SOUNDINGS. GALES LOOK TO PERSIST
INTO TUESDAY EVENING ACROSS THE SOUTH HALF OF THE LAKE...AND PAST
MIDNIGHT FARTHER NORTH. HIGH PRESSURE THEN BUILDS SOUTHEAST FROM THE
CENTRAL PLAINS THROUGH THE MID/LOWER MISSOURI AND LOWER OHIO RIVER
VALLEYS WEDNESDAY AND WEDNESDAY NIGHT...ALLOWING GALES TO EASE
THOUGH WINDS REMAIN WESTERLY IN THE 20-30 KT RANGE IN THE TIGHTER
GRADIENT NORTH OF THE SURFACE HIGH AND SOUTH OF LOW PRESSURE WHICH
LINGERS OVER HUDSON BAY. WEST WINDS WILL LINGER THROUGH THURSDAY AS
THE HIGH SPREADS EAST THROUGH THE OHIO VALLEY...AND ANOTHER WEAK LOW
CROSSES THE NORTHERN LAKES.

IN THE NEAR TERM...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE
ILLINOIS AND INDIANA NEAR SHORE WATERS THROUGH EARLY TUESDAY... WITH
WINDS/WAVES DIMINISHING MORE QUICKLY ALONG THE ILLINOIS SHORE
TONIGHT. THE GALE WARNING TUESDAY/TUESDAY EVENING INCLUDES THE NEAR
SHORE WATERS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 3
     AM TUESDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...4 PM
     TUESDAY TO 3 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 8 AM TUESDAY.

     GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
     LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...8 AM TUESDAY TO 9 PM
     TUESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 PM
     MONDAY.

&&

$$

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

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