FXUS63 KLOT 040417
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1017 PM CST THU DEC 3 2009

.DISCUSSION...

309 PM...MAIN FORECAST CONCERN IS SNOW POTENTIAL THIS EVENING
ACROSS NORTHERN IL...ALONG WITH SNOWFALL POTENTIAL SUNDAY NIGHT
INTO MONDAY AND AGAIN TUESDAY INTO WEDNESDAY.

A RATHER STRONG SHORTWAVE ROTATING SOUTHEAST ACROSS THE NORTHERN
PLAINS WILL TURN EAST OVER IOWA THIS AFTERNOON THEN MOVE ACROSS 
SOUTHERN WI THIS EVENING. LOW LEVEL INSTABILITY INCREASES AS THIS
FEATURE APPROACHES...BUT APPEARS THE BEST INSTABILITY WILL REMAIN
ACROSS SOUTHERN WI. SNOW ALSO EXPECTED TO BE MORE CONVECTIVE IN
NATURE...THUS MAKING SNOWFALL FORECASTS A BIT DIFFICULT...AS ONE
AREA MAY GET AN INCH OR TWO WHILE OTHERS BARELY SEE A DUSTING.
WITH THE EXPECTATION OF THE HEAVIEST SNOW FALLING ACROSS SOUTHERN
WI AND LIKELY IN A NARROW CORRIDOR...HAVE RAPIDLY DECREASED CAT 
POPS AT THE IL/WI STATE LINE TO JUST CHANCE FROM ROUGHLY RPJ TO
MDW. THINK MOST AREAS ACROSS THE NORTHERN 4 COUNTIES WILL SEE AN
INCH OR TWO BUT TO ACCOUNT FOR POSSIBLE ISOLATED HEAVIER AMOUNTS
WILL GO WITH 1 TO 3 INCHES...HIGHEST NEAR THE WI BORDER. SNOWFALL
AMOUNTS WILL ALSO RAPIDLY DROP OFF WITH JUST A DUSTING POSSIBLE
SOUTH OF THE NORTHERN 4 COUNTIES. SNOW WILL LIKELY BE TAPERING 
OFF TO FLURRIES BY/SHORTLY AFTER MIDNIGHT.

AS COLDER AIR CONTINUES TO SPREAD ACROSS THE AREA LATER TONIGHT
AND FRIDAY...TEMPS WILL DROP INTO THE LOWER/MID 20S TONIGHT AND
WITH THE COLDEST AIR ALOFT SPREADING ACROSS THE AREA FRIDAY...
EXPECT LITTLE IF ANY RECOVERY IN TEMPS ON FRIDAY WITH MOST AREAS
REMAINING IN THE UPPER 20S...PERHAPS A FEW LOCATIONS TAGGING 
LOWER 30S...BRIEFLY...ACROSS EASTERN AREAS. A FEW FLURRIES ALSO
POSSIBLE FRIDAY. FRIDAY NIGHT THRU SUNDAY LOOKS QUIET WITH TEMPS
SLOWLY RISING BACK INTO THE UPPER 30S BY SUNDAY.

WEAK UPPER TROUGH/SFC LOW SWINGS ACROSS THE MIDWEST LATE SUNDAY
NIGHT INTO MONDAY MORNING. TEMPS PLENTY COLD ENOUGH FOR PRECIP 
TO BE ALL SNOW AND MODEL QPF WOULD SUGGEST AT LEAST A DUSTING TO
PERHAPS AN INCH OR TWO. VERY PROGRESSIVE SYSTEM...SO DURATION OF
SNOW WILL LIKELY BE SHORT. HOWEVER...TIMING ISN/T VERY GOOD AS 
IT ARRIVES JUST BEFORE A MONDAY MORNING RUSH HR.

NEXT SYSTEM THAT ARRIVES TUESDAY/TUESDAY EVENING REMAINS IN 
DECENT AGREEMENT AMONG THE MODELS...BUT CONTINUES TO SHIFT A
LITTLE FURTHER NORTH WITH NEW RUNS. NEW 12Z ECMWF BRINGS THE SFC
LOW RIGHT ACROSS NORTHERN IL WITH AT LEAST A HALF INCH OF QPF.
IF CURRENT TRENDS HOLD...THIS SYSTEM WILL HAVE THE POTENTIAL TO
PRODUCE AN ACCUMULATING SNOW...PERHAPS ACROSS THE CWA BUT STILL
TOO EARLY TO SAY WHEN OR WHERE. BEYOND THIS SYSTEM...12Z GFS HAS
BACKED OFF WITH JUST -15C OR SO AT 850MB BY NEXT THURSDAY
MORNING...PREVIOUS 06Z RUN WAS DOWN TO -20C. SHOULD BE NOTED THAT
THE ECMWF IS WARMER...BUT MINOR DIFFERENCES BETWEEN MODELS OR
MODEL RUNS PROBABLY WON/T MATTER TOO MUCH IF THERE IS A SNOW PACK
AS THE TREND WILL BE COLDER. CMS

&&

.AVIATION...
1017 PM CST

0600 UTC TAFS...CURRENT TAFS SEEM TO BE IN DECENT WORKING ORDER AS
THE BULK OF THE SNOW SHOWERS AND SUB VFR CONDITIONS REMAIN FURTHER
NORTH ACROSS SOUTHERN WISCONSIN. EXPECT THAT THIS WILL BE THE
TREND OVERNIGHT AS THE MAIN SFC TROF SWINGS EASTWARD ACROSS THE
SOUTHERN HALF OF THE LAKE AND TAKES THE CORE OF SNOW ALONG WITH
IT. STILL COULD SEE AN INCREASE IN REALLY LIGHT SNOW SHOWERS INTO
FRIDAY MORNING AS THE MAIN UPPER TROF MOVES THROUGH...BUT THE
BETTER DYNAMICS WITH IT SEEM TO BE WEAKENING. STILL LOOKS LIKE
THERE MAY BE A BETTER CHANCE FOR HIGH END MVFR CIGS TO DEVELOP
FRIDAY MORNING AROUND/AFTER DAYBREAK WITH THE MAIN TROF COMING
THROUGH. FOR THE VERY NEAR TERM THOUGH...SKIES HAVE ACTUALLY GONE
CLEAR AT ORD...WHICH WILL BE SHORT LIVED AS THE NEXT BATCH OF 4KFT
CIGS AND 10SM -SN COMES IN. WESTERLY WINDS HAVE REMAINED GUSTY ON
UP TO AROUND 20KT AND SHOULD REMAIN UP OVERNIGHT TOWARD DAYBREAK.

EXPECT MAINLY VFR CONDITIONS THROUGH DAYBREAK WITH SOME BRIEF MVFR
CIGS POSSIBLE...PARTICULARLY TOWARD RFD. 

HALBACH

&&

.MARINE...
144 PM CST

LOW PRESSURE CONTINUES TO PULL AWAY ACROSS NORTHERN NEW ENGLAND THIS 
AFTERNOON...WITH A TROUGH LINGERING ACROSS THE LAKES AND UPPER 
MIDWEST. WHILE THE SFC PRESSURE GRADIENT HAS WEAKENED A BIT WITH THE 
DEPARTURE OF THE SURFACE LOW CENTER...A LINGERING MODEST WEST TO 
NORTHWEST GRADIENT WILL COMBINE WITH RELATIVELY COLD AIR IN THE LOW 
AND MID LEVELS TO MAINTAIN SOMEWHAT GUSTY WINDS ACROSS LAKE MICHIGAN 
INTO THE WEEKEND. WHILE WINDS WILL GENERALLY REMAIN IN THE 15-20 KT 
RANGE...A FEW PERIODS OF SLIGHTLY ENHANCED WINDS CAN BE EXPECTED 
PUSHING GUSTS INTO THE 25 KT RANGE. ONE OF THESE PERIODS WILL BE 
WITH THE PASSAGE OF A MID LEVEL DISTURBANCE TONIGHT ON SOUTHERN LAKE 
MICHIGAN...AND ANOTHER IS AHEAD OF THE COLD FRONT SUNDAY. ANOTHER
AREA OF LOW PRESSURE WILL MOVE ACROSS THE WESTERN LAKES ON MONDAY...
THOUGH LONGER RANGE MODEL GUIDANCE DIFFERS ON THE EVENTUAL
TRACK/STRENGTH OF THIS SYSTEM. CURRENT FORECAST REPRESENTS A BLEND
OF LONG RANGE GUIDANCE WITH THIS SYSTEM...BETWEEN STRONGER/DEEPER
GFS AND WEAKER ECMWF REPRESENTATION OF LOW BY 12Z MONDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM FRIDAY.

&&

$$