FXUS63 KIWX 240503
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1203 AM EST THU DEC 24 2009

.AVIATION /06Z TAFS/...

VFR AT BOTH TERMINALS ATTM AS LIGHT FZRA CONTINUES JUST NORTHWEST
OF SBN WITH FWA IN THE CLEAR. FOR THE OVERNIGHT...COULD SEE
ANOTHER LIGHT BOUT OF FZRA AT SBN FOR THE NEXT FEW HOURS...BUT
OVERALL VFR CONDITIONS SHOULD PERSIST. BAND OF HEAVIER PRECIP WILL
APPROACH THE TERMINALS FROM THE WEST AND SOUTH ON THURSDAY.
EXPECT THAT THIS WILL BEGIN REACHING THE AREA BY AFTERNOON AND
START AS A FZRA/PL MIX BEFORE GOING TO ALL RAIN TOWARDS 00Z.
VSBYS/CIGS WILL ALSO DETERIORATE TO MVFR DURING AND THROUGH THE
EVENING HOURS.

EAST WINDS 15 KTS WILL CONTINUE OVERNIGHT AND THROUGH THE DAY
THURSDAY BEFORE STRENGTHENING TO 18G28KTS THURSDAY NIGHT. LLWS A
CONCERN BY AFTERNOON AT SBN AND EVENING AT FWA AS 2KFT WINDS
INCREASE TO AROUND 50KTS FROM THE SOUTHEAST. THESE ROBUST
WINDS...COUPLED WITH A STRONG LLEVEL INVERSION PORTENDS A CLASSIC
SETUP FOR STRONG LLWS.  

&&

.PREV DISCUSSION... /ISSUED 1053 PM EST WED DEC 23 2009/ 

UPDATE...

HAVE UPDATED TO TAKE STARKE/LAPORTE/BERRIEN UP TO AN ICE STORM
WARNING GIVEN REPORTS NEARING 0.25 INCHES OF ICING AS OF THIS
WRITING. ALTHOUGH ZR WILL GENERALLY BE LIGHT FOR THE REMAINDER OF
WHILE PRIMARY BAND OF HEAVIER PRECIP ASSOCIATED WITH BAND OF
POSITIVE H85 THETAE ADVECTION WILL LIFT NORTH OVERNIGHT...NUMEROUS
UPSTREAM RIPPLES IN THE FLOW ALONG THE EASTERN FLANK OF DEEP
MOISTURE PLUME SUGGEST A CONTINUATION OF LIGHT ZR. WITH THIS
ADDITIONAL ICING...AND WIND GUSTS TO 30 MPH...EXPECT SOME
SCATTERED POWER OUTAGES IN THE WARNING REGION. ALSO...HAVE RUN THE
WARNING THROUGH 00Z FRIDAY FOR ADDITIONAL ICING AS NEW ROUND OF
PRECIP ON THURSDAY WILL LIKELY START AS ZR BEFORE TRANSITIONING TO
RAIN...THUS THE WATCH IN THIS LOCATION HAS BEEN CANCELED. HAVE
KEPT THE ADVISORY BASICALLY IN TACT FOR NOW...BUT EXTENDED IT TO
DAYBREAK GIVEN THAT THIS AREA WILL BE ON THE EASTERN EDGE OF THE
ABOVE MENTIONED PRECIP FOR THE OVERNIGHT WITH SLICK TRAVEL
CONTINUING.

MATCHED WX/POPS TO ABOVE THINKING AND TWEAKED TEMPS...BUT OVERALL
LITTLE OTHER CHANGE TO THE GRIDS. LEFT EVERYTHING ALONE AFTER 12
THURSDAY MORNING.  

UPDATED GRIDS/PRODUCTS ARE OUT.  

PREV DISCUSSION... /ISSUED 703 PM EST WED DEC 23 2009/ 

UPDATE...
GRIDS IN DECENT SHAPE AT THIS POINT...BUT ADVISORY NEEDED SOME
CHANGES TO UPDATED ZONES AND WSW FORTHCOMING. 

OVERALL COVERAGE OF PRECIP HAS BEGUN TO DIMINISH SOMEWHAT BUT
POCKETS OF HIGHER RETURNS INDICATIVE OF POCKETS OF SLEET AND
FREEZING RAIN ARE STILL SHOWN. AS EXPECTED...AFTER THE INITIAL
BAND OF MIXED PRECIP THAT HAS MOVED ACROSS NEARLY ALL OF THE CWA
AT SOME POINT...THE BEST COVERAGE HAS BECOME MORE CONFINED TO WEST
OF INTERSTATE 69 AND ESPECIALLY ALONG AND WEST OF STATE ROUTE 15
ACROSS INDIANA. NUMEROUS REPORTS OF SLIDE-OFFS AND LIGHT GLAZING
HAS BEEN REPORTED ACROSS THE PREVIOUS ADVISORY AREA. OUTSIDE OF
THE HIGHER RETURNS...SOME FREEZING DRIZZLE IS STILL BEING SEEN AND
UPSTREAM OBSERVATIONS AND RADAR DATA OUT OF ILLINOIS SHOWS THIS
MAY CONTINUE INTO THE EVENING. TO HELP COVER ANY EVENING TRAVEL
AND PREVIOUS HEADLINES OUT TILL 6Z...HAVE EXTENDED PORTIONS OF THE
ADVISORY THAT WERE SET TO EXPIRE AT 00Z TO 6Z. HAVE ALSO EXPANDED
THE ADVISORY ONE TIER EAST TO COVER REPORTS OF SOME ICING ON
SURFACES. SUSPECT THAT COUNTIES WILL BE ABLE TO BE DROPPED PRIOR
TO THE EXPIRATION ESPECIALLY EAST...BUT WITH STRENGTH OF LIFT AND
OBVIOUS CONTINUED FEED OF MSTR...DON'T WANT TO CUT THINGS OFF TOO
PREMATURE. 

AFTER MIDNIGHT...STEADIER PRECIP MAY MOVE BACK IN TO FAR WESTERN
AREAS...BUT WILL REEVALUATE THINGS IN A FEW HOURS. 

PREV DISCUSSION... /ISSUED 407 PM EST WED DEC 23 2009/

SHORT TERM...
INITIAL BAND OF WAA PRECIP ASSOCIATED WITH DEEPENING SFC LOW OVER 
THE SRN PLAINS WAS MOVG ACROSS THE CWA THIS AFTN. ZR BEING REPORTED 
A LITTLE FARTHER NE THAN PREVIOUS ADVISORY AREA, SO HAVE EXPANDED 
ADVISORY NE A COUPLE OF COUNTIES IN NORTH CENTRAL INDIANA AND 
SOUTHWEST MICHIGAN FOR THIS EVENING. SHOULD BE A LULL IN THE PRECIP 
AS STRONGER WAA SHIFTS TO THE NW OF OUR CWA AS LOW CONTS TO 
INTENSIFY...HOWEVER...SOME LIGHT FREEZING RAIN MAY PERSIST ALONG OUR 
WRN BORDER LATE TONIGHT AND INTO THU MORNING. FOR NOW CONTD WITH 
ENDING TIME OF ADVISORY AT 1AM BUT THIS MAY NEED TO BE EXTENDED OVER 
NW INDIANA. 

COLD FRONT ASSOCIATED WITH VERY STRONG PLAINS LOW WILL APPROACH THE 
CWA FROM THE SW ON THURSDAY. CONTINUED EASTERLY SFC WINDS WILL LIMIT 
WARMUP AHEAD OF THE CDFNT AS SGFNT BAND OF RAIN MOVES TOWARD THE 
AREA. STILL APPEARS THAT INITIAL RAINFALL WITH THIS HEAVIER BAND OF 
PRECIP MAY OCCUR INTO FREEZING SFC TEMPS OVER NRN PORTIONS OF THE 
CWA LATE THU/THU EVE, BEFORE WAA RAISES TEMPS ABOVE FREEZING. THUS, 
HAVE CONTINUED WITH A WINTER STORM WATCH FOR THU AFTN/NGT WHERE 
PREVIOUSLY ISSUED ACROSS SRN MI AND FAR NRN INDIANA, THOUGH AT THIS 
POINT SEEMS MORE LIKELY THAT EVENTUAL HEADLINE WILL BE FOR AN 
ADVISORY RATHER THAN WARNING DUE TO SHORT DURATION OF SUB-FREEZING 
TEMPS DURING THE WATCH PERIOD. ADDED MENTION OF HEAVY RAIN THU NGT 
AS STRONG FORCING COMBINED WITH GULF MOISTURE ADVECTING INTO THE 
AREA AHEAD OF THIS SYSTEM'S COLD FRONT SHOULD RESULT IN A PERIOD OF 
HEAVY RAIN. APPEARS THIS WILL MOVE THROUGH THE AREA QUICKLY ENOUGH 
THAT FLOODING WILL NOT BE A CONCERN.&&

LONG TERM...
FRIDAY THROUGH WEDNESDAY...FOR THIS PACKAGE...FAVOR A BLEND OF THE 
SLOWER CANADIAN GEM AND THE OPERATIONAL ECMWF. THESE MODELS ARE 
SLOWER THEN THE GFS ENSEMBLE MEAN. THE GFS APPEARS TO BE SHOWING THE 
TYPICAL BIAS OF TRYING TO EJECT THIS TYPE OF SYSTEM EAST TOO FAST. 
THERE WILL BE A RATHER COMPLEX FUJIWHARA INTERACTION OF 2 UPPER 
LEVEL SYSTEMS FRIDAY. THE MOIST CONVEYOR BELT OF WARM AIR WILL BE 
COMPLETELY CUT OFF AS THE SYSTEM BECOMES OCCLUDED. THE DRY SLOT 
SHOULD BE MOVING INTO THE AREA FRIDAY MORNING WITH THE HEAVIEST 
PRECIPITATION NORTHEAST OF THE AREA. TEMPERATURES SHOULD WARM TO 
AROUND 40F OVER MOST OF THE AREA BEFORE THE COLD FRONT MOVES IN FROM 
THE SOUTHWEST. SOME CONCERN EXISTS FOR FLOODING FROM OVERNIGHT 
RAINFALL AMOUNTS THURSDAY NIGHT PLUS SNOWMELT FRIDAY. THE RAINFALL 
COMBINED WITH SNOW MELT WILL LIKELY BRING RISES TO AREA RIVERS 
FRIDAY. AT THIS TIME...FEEL POTENTIAL FLOOD ISSUES WILL BE MAINLY 
AREA RIVER RISES...BUT ISOLATED FLOODING OF LOW AREAS ARE 
POSSIBLE...ESPECIALLY IF STORM DRAINS BECOME PLUGGED BY DEBRIS OR 
MELTING SNOW AND ICE. MUCH COLDER CONDITIONS WILL OCCUR EARLY FRIDAY 
NIGHT WITH FLASH FREEZING LIKELY. THE UPPER LOW SHOULD THEN EJECT 
OUT OVER THE FORECAST AREA OVER THE WEEKEND. HAVE RAISED SNOW 
CHANCES TO HIGH CHANCE. GIVEN THIS PATTERN...BELIEVE THERE WILL 
PROBABLY BE ANOTHER 1-4 INCHES OF SNOW OVER THE WEEKEND BASED ON THE 
DURATION OF LIGHT SNOW. THE POTENTIAL FOR LAKE EFFECT SNOW LOOKS 
MARGINAL EARLY...BUT SHOULD INCREASE LATE IN THE PERIOD AS WINDS 
BECOME NORTHWEST. HAVE INDICATED THIS POTENTIAL WITH A CHANCE FOR 
LAKE EFFECT SNOW SUNDAY NIGHT THROUGH MONDAY NIGHT.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...ICE STORM WARNING UNTIL 6 PM CST THURSDAY FOR INZ003-012.

     WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR INZ004-005-
     013>016-020-022.

     WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY 
     MORNING FOR INZ004>007.

MI...ICE STORM WARNING UNTIL 7 PM EST THURSDAY FOR MIZ077.

     WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR MIZ078.

     WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY 
     MORNING FOR MIZ078>081.

OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST THURSDAY FOR LMZ043-046.

     GALE WARNING FROM 7 AM THURSDAY TO 1 PM EST FRIDAY FOR LMZ043-
     046.

&&

$$

SHORT TERM...JT
LONG TERM...SKIPPER
AVIATION...ARNOTT
UPDATE...ARNOTT