FXUS63 KIWX 151652
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1152 AM EST TUE DEC 15 2009

.UPDATE...
ZONES/GRIDS UPDATED TO REFLECT A DOWNWARD TREND IN LAKE EFFECT
POTENTIAL THIS AFTERNOON. DESPITE A DECENT FLOW AND VERY FAVORABLE
DELTA T'S...THE LACK OF DEEP MSTR IS PLAYING HAVOC WITH THE SNOW
SHOWERS ACROSS THE AREA WITH SEVERAL WEAKER BAND HAVING BEEN
HOLDING ON THIS MORNING WITH ONLY MINIMAL IMPACT. AFTER COLLAB
WITH KGRR HAVE LOWERED POPS TO SCT MENTION DOWNWIND OF THE LAKE
AND DROPPED ACCUMS TO UNDER AN INCH. ALSO...LARGE AREA OF
CLEARING WORKING IN FROM THE WEST THIS AFTERNOON TO BRING
INCREASING AMOUNTS OF SUN TO THOSE AREAS NOT DOWNWIND OF THE
LAKE...GENERALLY ALONG AND SE OF US 30. STILL EXPECTING A FALLING
TRENDS TO TEMPS ESPEICALLY AWAY FROM THE LAKE THIS AFTERNOON.

&&

.AVIATION /18Z TAFS/...
MVFR CIGS EXPECTED THROUGH AT LEAST 00Z AT KSBN WITH IMPROVING
CONDITIONS POSSIBLE AT KFWA BY LATE AFTERNOON. DRIER AIR IS
WORKING IN AND KFWA MAY GET TO SEE CIGS INCREASE AS THE AFTERNOON
PROGRESSES. HOWEVER...THEY ARE JUST CLOSE ENOUGH TO THE NW FLOW
OFF THE LAKE TO WARRANT HOLDING ONTO THE MVFR CIGS FOR NOW. QUITE
POSSIBLE THAT BY 00Z CHANGES WILL OCCUR TO BRING CIGS UP OR
ELIMINATE THEM. OTHERWISE...ANY SNOW THAT IS SEEN AT EITHER
LOCATION SHOULD NOT AMOUNT TO MUCH WITH MINIMAL IMPACT ON VSBYS. 

&&

.PREV DISCUSSION... /ISSUED 353 AM EST TUE DEC 15 2009/ 

SHORT TERM /TODAY THROUGH WEDNESDAY NIGHT/...

SFC LOW WHICH MOVED RAPIDLY NE ACROSS THE AREA YESTERDAY, WILL SLOW 
DOWN AND DEEPEN OVER NEW ENGLAND/CANADIAN MARITIMES TODAY/TNGT AS AN 
UPR LEVEL SHRTWV MOVES EAST ACROSS ONTARIO AND CLOSES OFF OVER 
QUEBEC. THIS IS EXPECTED TO RESULT IN ABOUT A 24HR PERIOD OF LAKE 
EFFECT SNOW DOWNWIND OF LAKE MICHIGAN AS SFC RIDGE OVER THE NRN 
PLAINS MOVES SLOWLY EAST TO THE OH VALLEY/WRN GRTLKS ON WEDNESDAY. 
MODELS CONT TO INDICATE RATHER LOW INVERSION OVER THE LAKE, AND THIS 
IS SUPPORTED BY LATEST UPSTREAM SOUNDINGS/TAMDAR. AIRMASS ALSO 
RATHER DRY UPSTREAM. A FAIRLY STRONG BAND WAS OVER ERN LAKE MICHIGAN 
ATTM ASSOCIATED WITH MESO LOW MOVG SE ACROSS SRN LWR MI BUT THIS 
BAND SHOULD MOVE IN OFF THE LAKE EARLY THIS MORNING WITH TRANSITION 
TO MULTIPLE BANDS SO STILL THINKING LIMITING FACTORS WILL KEEP LAKE 
EFFECT SNOWFALL BELOW ADVISORY CRITERIA IN OUR CWA. SFC RIDGE MOVG 
SLOWLY EAST ACROSS THE AREA WED AFTN/NGT WILL RESULT IN RETURN OF 
FAIR WX TO THE ENTIRE CWA. 

STRONG LOW LEVEL CAA SHOULD CAUSE SLOWLY FALLING TEMPS TODAY. H85 
THERMAL TROF WILL MOVE THROUGH THE CWA THIS EVE, BUT SFC CAA OFF 
SNOW FIELD TO THE NW WILL CONT OVERNIGHT. BASED ON UPSTREAM OBS 
ATTM, LATEST MOS MINS WHICH ARE A LITTLE COLDER THAN GOING TEMPS 
LOOK REASONABLE AND WERE FOLLOWED. WAA SHOULD OCCUR MAINLY ALOFT ON 
WED WITH LIGHT SFC FLOW AS RIDGE MOVES THROUGH THE AREA. THUS EXPECT 
TEMPS TO RESPOND SLOWLY DESPITE RETURN OF SUNSHINE AND FCST HIGHS IN 
THE M-U20S ACROSS THE AREA. WAA SHOULD STRENGTHEN WED NGT AS RIDGE 
MOVES TO THE EAST, HWVR, PERIOD OF GOOD RADIATIONAL COOLING STILL 
LOOKS LIKELY IN THE EVE, SO MAINTAINED GOING FCST MINS IN THE 
TEENS.  
  

LONG TERM...
FLAT FLW TO START THE SHRT TERM WILL GIVE WAY TO INCREASED TROUGHING 
ALG THE E COAST WWD INTO THE GREAT LAKES THIS PD...AND ESP THIS 
WEEKEND.

IN PRINCIPLE...PRIOR FCST HAD THIS HANDLED WELL W/A GENERAL DOWNWARD 
TREND IN TEMPS AND SNOW CHCS OVR THE WEEKEND ALTHOUGH IMPLIED MED 
RANGE DETAILS REMAIN SKETCHY. MAIN CHANGE WAS TO EXPAND POPS SWD SUN 
W/GREATER CONSENSUS ON TIMING OF RETROGRADING ERN TROUGH. HWVR THIS 
MAY CERTAINLY OCCUR FASTER GIVEN DOWNSTREAM BLOCK OVR GREENLAND LIKE 
00Z ECMWF SHOWS. OTHERWISE STG PUSH OF ARCTIC AIR XPCD SAT AS 
RETROGRADING TROUGH BEGINS TO SHIFT SWD ACRS THE WRN LAKES AND MARKS 
A RTN TO UNSEASONABLY COLD TEMPS LT WEEKEND AND INTO EARLY NXT WEEK.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 5 PM EST WEDNESDAY FOR LMZ043-046.

&&

$$

SHORT TERM...JT
LONG TERM...HOLSTEN
AVIATION...FISHER
UPDATE...WEISSER/FISHER