National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KLOT 090928
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
327 AM 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 09Z...

* POTENTIAL FOR A FEW FLURRIES THROUGH THE PREDAWN HOURS.
* GUSTY WEST WINDS INCREASING THROUGH THE PREDAWN HOURS.
* CIG TRENDS.

BMD

//DISCUSSION...UPDATED 09Z...

FLURRIES HAVE NOT DISSIPATED AS PREVIOUSLY EXPECTED...BUT IMPACT
APPEARS TO BE LIGHT AS VSBY IS MOSTLY STAYING IN THE 4-6SM RANGE.
CLEAR BACK EDGE TO THE STRATUS MOVING EAST INTO NORTH CENTRAL
ILLINOIS...THOUGH THERE ARE A FEW ADDITIONAL MVFR PATCHES EXPANDING
OVER EASTERN IOWA. RFD MAY BREAK OUT OF THE STRATUS IN THE NEXT
HOUR...BUT MAY BE IN AND OUT OF A FEW PATCHES OF MVFR CIGS THROUGH
THE PREDAWN HOURS. IF TERMINALS DO SEE THE STRATUS CLEAR OUT THIS
MORNING...WOULD STILL EXPECT AN MVFR STRATOCU DECK TO DEVELOP LATER
IN THE MORNING AFTER DAYBREAK.

PREVIOUS DISCUSSION...06Z...

LOW PRESSURE IS LIFTING ACROSS FAR SOUTHEAST WISCONSIN THIS
EVENING WITH A TRAILING COLD FRONT PUSHING ACROSS NORTH CENTRAL
ILLINOIS THIS HOUR. RADAR SHOWS INCREASING RETURNS IMMEDIATELY
AHEAD OF THE FRONT WHICH APPEARS TO BE AN AREA OF VERY LIGHT
DRIZZLE AND MIST. EXPECT THIS AREA TO CLEAR THE CHICAGO TERMINALS
IN A FEW HOURS AS THE FRONT SWEEPS ACROSS. FARTHER WEST...SNOW IS
PERSISTING BEHIND THE FRONT ACROSS PORTIONS OF IOWA. MODELS
INDICATE THIS AREA WILL DRY OUT AS IT LIFTS NORTHEAST...BUT STILL
HAS A DECENT CHANCE OF CLIPPING RFD THIS LATE EVENING. AT THE
MOMENT...DO NOT ANTICIPATE THIS AREA TO IMPACT THE CHICAGO
TERMINALS.

BEHIND THE FRONT...WESTERLY WINDS WILL INCREASE WITH GUSTS INTO THE
HIGH TEENS OVERNIGHT...AND FURTHER INCREASE INTO THE LOW 20 KT
RANGE DURING THE DAY MONDAY. COLD ADVECTION SHOULD KEEP THE LOWEST
LEVELS OF THE COLUMN MIXED PREVENTING IFR CIGS FROM FORMING
OVERNIGHT. CIGS SHOULD REMAIN MVFR THOUGH WITH A SLOW DIURNAL UPWARD
TREND...THEN MAY SCATTER OUT AROUND OR SHORTLY AFTER SUNSET MONDAY
EVENING.

BMD

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

* MEDIUM CONFIDENCE IN PRECIP TRENDS EARLY IN THE PERIOD.
* LOW-MEDIUM CONFIDENCE IN CIGS STAYING AT OR ABOVE 010 THROUGH
  THE PERIOD.
* HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM-HIGH CONFIDENCE IN
  GUST SPEEDS/TIMING.

BMD

//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...
249 AM CST

WITH A STRONG AREA OF HIGH PRESSURE OVER THE MISSISSIPPI AND OHIO
VALLEYS...AND A SERIES OF LOWS QUICKLY MOVING ACROSS THE NORTHERN
GREAT LAKES REGION...ANTICIPATE WINDS TO REMAIN ELEVATED WITH A
COUPLE PERIODS OF GALES EXPECTED. FIRST...LOW END PERIOD OF GALES
IS EXPECTED PRIMARILY ACROSS THE NORTHERN PORTIONS OF LAKE MICHIGAN
THIS AFTERNOON AND EVENING AS DEPARTING LOW PRESSURE DEEPENS AS IT
LIFTS TO NEAR JAMES BAY. HAVE HOISTED A SHORT DURATION 6 HR GALE
WARNING FOR THIS EVENT. WINDS DIMINISH BACK BELOW GALES MONDAY NIGHT
AS A TRANSIENT RIDGE MOVES ACROSS THE LAKE...BUT WINDS ARE EXPECTED
TO INCREASE BACK TO GALES AGAIN TUESDAY AS A CLIPPER SYSTEM MOVES
ACROSS THE LAKE. 40 KT GALES ARE EXPECTED ON THE SOUTH END OF THE
LAKE BY MID MORNING...AND SHOULD SPREAD NORTH ACROSS THE LAKE BY
AFTERNOON. WINDS WILL GRADUALLY TAPER WEDNESDAY INTO THURSDAY AS
HIGH PRESSURE BUILDS INTO THE UPPER MIDWEST TOWARDS THE OHIO
VALLEY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...9 AM MONDAY TO 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