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000
FXUS63 KLOT 111742
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1142 AM CST WED DEC 11 2013

.DISCUSSION...
333 AM CST

PRIMARY FORECAST CHALLENGES INCLUDING DEALING WITH ENDING SNOW THIS
MORNING...CRASHING TEMPS/WIND CHILLS THIS AFTERNOON AND
EVENING...THEN THE FRIDAY NIGHT INTO SATURDAY SYSTEM.

AREA OF SNOW CONTINUES TO BLANKET MUCH OF NORTHERN ILLINOIS AS OF
09Z WITH VSBYS MOSTLY IN THE 1.5-3SM RANGE. SHORT RANGE GUIDANCE HAS
BEEN PRETTY CONSISTENT IN SHOWING A SLIGHT WEAKENING IN THE FORCING
THIS MORNING SO WOULD NOT ANTICIPATE ANY BIG RAMP UP IN THE
INTENSITY OF THE SNOW OUT THERE NOW. HEAVIEST BATCH OF SNOW JUST
NORTH OF THE QUAD CITIES IS SHOULD MOVE EAST-SOUTHEAST TOWARD
CHICAGO AND ESPECIALLY THE SOUTHERN CHICAGO SUBURBS IN THE NEXT
COUPLE/FEW HOURS. BASED ON THE FEW UPSTREAM REPORTS WE`VE SEEN SO
FAR THINK THAT TOTALS WILL END UP MOSTLY IN THE 1-3 INCH RANGE BUT
IMPACT STILL SHOULD BE FAIRLY HIGH SO NOT PLANNING TO ALTER ONGOING
HEADLINES. WINTER WX ADVISORY SHOULD BE ABLE TO BE CANCELLED EARLY
OVER NORTH CENTRAL AND POSSIBLY NORTHEAST ILLINOIS WITH ACCUMULATING
SNOW WRAPPING UP PRIOR TO 10 AM.

SKIES WILL CLEAR OUT BEHIND THE SNOW THIS AFTERNOON...BUT THE
SUNSHINE WILL BE QUITE DECEIVING AS AN ARCTIC FRONT WILL SWEEP
THROUGH LATER THIS MORNING INTO EARLY THIS AFTERNOON RESULTING IN
FALLING TEMPERATURES THIS AFTERNOON. LOW TEMPS TONIGHT WILL BE
TRICKY. WINDS NOT EXPECTED TO GO CALM...BUT AT LEAST SEVERAL HOURS
OF CLEAR SKIES THIS EVENING PLUS THE FRESH SNOW COVER AND ARCTIC AIR
MOVING IN SHOULD ALLOW TEMPS TO CRASH BELOW ZERO MOST AREAS THIS
EVENING. HAVE CONTINUED THE TREND FROM THE PREVIOUS FORECASTS OF
UNDERCUTTING GUIDANCE...THOUGH ADMITTEDLY AM CONCERNED ABOUT THE
HIGHER THAN AVG BUST POTENTIAL. AS WE SAW MONDAY EVENING...POTENTIAL
EXISTS FOR TEMPS TO CRASH LOWER THAN FORECAST WITH COLDEST LOCATIONS
POTENTIALLY REACHING THE MID TO UPPER TEENS BELOW ZERO. CONVERSELY
IF CLOUDINESS ARRIVES EARLIER IT MAY NOT BE QUITE AS FRIGID.
REGARDLESS OF HOW LOW TEMPS FALL THIS EVENING...THEY SHOULD BECOME
STEADY AND EVENTUALLY SLOWLY RISE AFTER MIDNIGHT AS CLOUD COVER
INCREASES...WINDS TURN SOUTHERLY...AND PRETTY IMPRESSIVE WARM AIR
ADVECTION BEGINS. MODERATELY GUSTY WINDS THIS AFTERNOON AND WINDS
AROUND 10 MPH THIS EVENING WILL RESULT IN WIND CHILLS CRASHING TO
DANGEROUSLY LOW LEVELS. SAME CAVEAT EXISTS WITH WIND CHILLS AS WITH
LOW TEMPS...BUT BEST GUESS AT THIS POINT IS THAT WIND CHILLS SHOULD
BOTTOM OUT BETWEEN 15 TO 30 BELOW THIS EVENING...THEN SLOWLY RECOVER
AFTER MIDNIGHT AS TEMPS BEGIN TO RISE. WILL BE HOISTING A WIND CHILL
ADVISORY STARTING LATE THIS AFTERNOON NC IL AND EARLY EVENING ELSE
WHERE AND RUN IT THROUGH TONIGHT FOR ALL BUT FAR SE CWA.

IMPRESSIVE WARM AIR ADVECTION AND STRENGTHENING SOUTHERLY WINDS
SHOULD ALLOW TEMPS TO REBOUND NICELY ON THURSDAY. H8 TEMPS ARE
PROGGED TO WARM 10-15C IN ABOUT 18 HOURS AND DESPITE THE SNOW COVER
THINK TEMPS SHOULD WARM CONSIDERABLY...MUCH LIKE WHAT WEE SAW
TUESDAY. ANOTHER WEAKER COLD FRONT WILL DROP SOUTH BACK THROUGH THE
AREA FRIDAY BUT PUSH OF COLDER AIR BEHIND THIS FRONT IS RELATIVELY
TAME COMPARED TO WHAT WE`VE BECOME ACCUSTOMED TO OF LATE.

NEXT METEOROLOGICAL HEADACHE IS WHAT HAPPENS WITH THE UPPER LOW
MEANDERING OFF THE SOCAL COAST THIS MORNING. UPSTREAM SHORTWAVE
TROUGH IS DIGGING SOUTH AND EXPECTED TO PROVIDE THE NEEDED OOMPH TO
PUSH THE UPPER LOW EASTWARD ONSHORE AND THEN EVENTUALLY INTO THE
SOUTHERN PLAINS. BOTH THE UPPER LOW AND UPSTREAM KICKER ARE OFFSHORE
AND UNSAMPLED BY THE UPPER AIR NETWORK INCREASING THE FORECAST
UNCERTAINTY IN THE MODELS` HANDLING OF THIS CONVOLUTED MESS OF VORT
MAXES. BIG PICTURE-WISE...GFS/ECMWF HAVE AGREED ON THE IDEA UPPER
LOW OPENING UP AND WEAKENING AS IT MOVES TOWARD THE OHIO VALLEY
SUNDAY INTO AN INCREASINGLY CONFLUENT FLOW AS NORTHERN STREAM TROUGH
AMPLIFIES OVER THE GREAT LAKES/UPPER MISSISSIPPI VALLEY. WHILE
CONFIDENCE IN TIMING AND INTENSITY OF THIS SYSTEM IS LOW...STILL
APPEARS LIKELY THAT A SWATH OF ACCUMULATING SNOW WILL FALL TO THE
NORTH OF THE TRACK OF THE LOW...WITH OUR CWA (ESPECIALLY SOUTHERN)
CERTAINLY WELL WITHIN THE "CONE OF UNCERTAINTY" FOR ACCUMULATING
SNOW. NOT LOOKING LIKE A BLOCKBUSTER SNOWSTORM BY ANY STRETCH OF THE
IMAGINATION...BUT WHERE EVER THE ACCUMULATING SNOW BAND DOES OCCUR
SEVERAL INCHES LOOK VERY POSSIBLE. FULLY EXPECT MODELS TO ADJUST THE
FORECAST TRACK AND PROBABLY TIMING AND INTENSITY OF THIS SYSTEM OVER
THE NEXT COUPLE DAYS AS IT BECOMES BETTER SAMPLED...SO I`D STAY
TUNED BEFORE PLACING IN BETS ON HOW IT WILL PAN OUT.

ALONG WITH THE UNCERTAINTY WITH THIS WEAKENING UPPER LOW...THERE IS
ALSO NOW DOUBTS AS TO HOW MUCH OF AN ARCTIC INTRUSION WILL TAKE
PLACE LATER THIS WEEKEND. AFTER A COUPLE RUNS OF TRENDING MUCH
COLDER THE 00Z EC HAS FLOPPED BACK TOWARD MORE OF A GLANCING BLOW OF
COLD FOR OUR AREA FOLLOWED BY A QUICK REBOUND IN TEMPS. OVERALL
CONFIDENCE IS LOW SO DIDN`T STRAY FROM THE MODEL CONSENSUS
INITIALIZATION GRIDS.

IZZI

&&

.AVIATION...

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

* OCCASIONAL FLURRIES THROUGH EARLY AFTERNOON.

* GUSTY NORTHWESTERLY WINDS DEVELOPING BY 17-18Z THROUGH SUNSET.

* GUSTY SOUTHWESTERLY WINDS DEVELOPING LATE TOMORROW MORNING.

KREIN

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

THE BULK OF THE SNOW ASSOCIATED WITH A WEAK CLIPPER-TYPE SYSTEM
AND A SFC COLD FRONT HAS PUSHED WELL SOUTH AND EAST OF THE
TERMINALS. HOWEVER...A LINGERING PATCH OF BKN/OVC STRATOCU WITH
MVFR CIGS OVER NERN IL WILL PRODUCE SOME SCATTERED FLURRIES FOR
ANOTHER HOUR OR SO BEFORE SKIES FINALLY SCATTER OUT. WINDS HAVE
ALREADY BEGUN TO SHIFT TO NWLY WITH GUSTINESS INCREASING AS AN
AREA OF PRESSURE RISES AND STRONG COLD ADVECTION MOVES IN BEHIND
THE COLD FRONT. EXPECT THAT GUSTINESS SHOULD SUBSIDE WITH SUNSET.
A WEAK SFC RIDGE MOVING OVER THE REGION OVERNIGHT WILL HELP DROP
WINDS TO AROUND 5KT. FOLLOWING THE PASSAGE OF THE SFC
RIDGE...WINDS WILL BACK SWLY AND INCREASE THROUGH THE
MORNING...WITH GUSTS TO ARND 20KT FROM LATE MORNING THROUGH LATE
AFTERNOON.

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

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

THURSDAY NIGHT THROUGH FRIDAY...VFR.
LATE FRIDAY NIGHT THROUGH SATURDAY...SNOW LIKELY. IFR/MVFR.
SUNDAY...IMPROVING TO VFR.
MONDAY THROUGH TUESDAY...CHC FOR SNOW. PERIODS OF IFR PSBL.

BMD

&&

.MARINE...
214 AM CST

WINDS HAVE DIMINISHED BELOW GALES BUT WILL REMAIN BREEZY THROUGH AT
LEAST LATE THURSDAY AS A STRONG HIGH BUILDS ACROSS THE PLAINS
TOWARDS THE MID MISSISSIPPI VALLEY RESULTING IN A MODERATE PRESSURE
GRADIENT OVER THE LAKE. WILL HOIST A SMALL CRAFT ADVISORY FOR THE
ILLINOIS AND INDIANA NEARSHORE WATERS STARTING MID MORNING TODAY.
THE ADVISORY FOR THE ILLINOIS WATERS WILL RUN THROUGH LATE THIS
EVENING WHEN WINDS SHOULD DROP BELOW CRITERIA OVERNIGHT WITH
OFFSHORE FLOW. THE INDIANA SHORES THOUGH WILL LIKELY EXPERIENCE
HAZARDOUS CONDITIONS FOR SMALL CRAFT THROUGH MID TO LATE THURSDAY AS
WAVES SLOWLY DIMINISH IN THE MODERATE NORTHWEST FLOW. WINDS BRIEFLY
ABATE THURSDAY NIGHT INTO EARLY FRIDAY AS A NEUTRAL POINT PUSHES
OVER THE REGION...BUT THEN ARE EXPECTED TO PICK UP AGAIN OUT OF THE
EAST/NORTHEAST LATE FRIDAY AS LOW PRESSURE DEEPENS OVER THE LOWER
MISSISSIPPI VALLEY AND LIFTS INTO THE OHIO VALLEY SATURDAY. A RIDGE
WILL BUILD ACROSS THE LAKE LATE NEXT WEEKEND AND SHOULD ALLOW FOR
ANOTHER LULL IN THE WINDS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012...3 PM WEDNESDAY TO 5 AM THURSDAY.

     WIND CHILL ADVISORY...ILZ006-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
     ILZ022-ILZ023-ILZ032...6 PM WEDNESDAY TO 5 AM THURSDAY.

IN...WIND CHILL ADVISORY...INZ001-INZ002...6 PM WEDNESDAY TO 5 AM
     THURSDAY.

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

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 3 PM THURSDAY.

&&

$$

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