FXUS63 KIWX 022345
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
645 PM EST WED DEC 2 2009

.AVIATION /00Z TAFS/...

POOR FLYING CONDITIONS OVERNIGHT AS SURFACE LOW TAKES TRACK FROM
NEAR LOUISVILLE NORTHEAST TO JUST WEST OF CLEVELAND TOWARDS
DAYBREAK. SHARP WESTERN EDGE OF PRECIP HAS ALLOWED SBN TO REMAIN
VFR AND DRY WITH FWA NOW OCCASIONALLY SEEING IFR CIGS/VSBYS IN
MODERATE RAIN. FOR THE OVERNIGHT...EXPECT CONTINUED OCCASIONAL IFR
CONDITIONS TO BECOME MORE PREDOMINATE AT FWA. AT SBN...EXPECT THAT
IT WILL TAKE UNTIL AFTER MIDNIGHT FOR THE LOWER CIGS TO MOVE
IN...WITH ONLY SOME VERY LIGHT RAIN BETWEEN NOW AND THEN. TOWARDS
DAYBREAK...RAIN WILL PULL OUT OF FWA LEAVING SOME REMNANT DRIZZLE.
AT SBN...LAKE EFFECT PRECIPITATION WILL TAKE OVER AS THE SYNOPTIC
PRECIPITATION COMES TO AN END. ALSO...TEMPS WILL BE GRADUALLY
COOLING...WITH A MIX/CHANGE TO SNOW POSSIBLE TOWARDS MORNING.  

FOR THE DAY ON THURSDAY...EXPECT MVFR SHRASN AT SBN WITH THE
POSSIBILITY THAT A BAND OF STRONGER PRECIP OFF OF LAKE MICHIGAN
CHANGES PRECIPITATION OVER TO ALL SNOW WITH IFR VSBYS. AT
FWA...GRADUAL IMPROVEMENT IS EXPECTED WITH CIGS MVFR MOST OF THE
DAY...LIKELY BECOMING VFR TOWARDS EVENING. A SPRINKLE/FLURRY CAN/T
BE RULED OUT HERE DURING THE DAY...BUT WITH NO ADDITIONAL IMPACT
ON FLIGHT CONDITIONS. 

NORTHERLY WINDS 10-15KTS WILL GRADUALLY BACK TO NORTHWEST DURING
THE OVERNIGHT 10-15KTS. FOR THURSDAY...NORTHWEST WINDS 12G20KTS
ARE EXPECTED...BACKING WESTERLY IN THE AFTERNOON AND DECREASING TO
10-15KTS.  

&&

.PREV DISCUSSION... /ISSUED 313 PM EST WED DEC 2 2009/ 

SHORT TERM...

..TONIGHT THROUGH THURSDAY NIGHT...

WATER VAPOR SHOWS POTENT UPPER LOW LIFTING NORTHEAST OUT OF GULF 
COAST REGION INTO MIDWEST WHILE NORTHERN STREAM SHORT WAVE SINKS 
SOUTH ACROSS THE DAKOTAS. THESE TWO FEATURES AND MESOSCALE LAKE 
EFFECT EVENT WILL BE CONCERNS IN THE SHORT TERM PERIOD. 

REGIONAL RADAR MOSAIC SHOWING RAIN INCREASING IN COVERAGE AND 
SPREADING NORTH AHEAD OF UPPER WAVE LIFTING OUT OF SOUTH. EXPECT 
THIS TO CONTINUE TO SPREAD NORTH ACROSS ALL OF FORECAST AREA THIS 
EVENING. FAR NORTHWEST AREAS WILL LIKELY BE SKIMMED BY THIS SYNOPTIC 
SYSTEM WITH ONLY LIGHT RAIN AMOUNTS. A LITTLE HIGHER QPF AS YOU GO 
FURTHER SOUTH AND EAST ACROSS OUR AREA WITH AMOUNTS NEAR A HALF INCH 
POSSIBLE INTO NORTHWEST OHIO. 

FORECAST CHALLENGE BECOMES TRANSITION TO SNOW THURSDAY MORNING. 12Z 
MODEL SUITE IN RATHER GOOD AGREEMENT ON KEEPING BOUNDARY LAYER WARM 
ENOUGH FOR ALL LIQUID ALL AREAS THROUGH JUST ABOUT 12Z THURSDAY. 
SURFACE WET BULB TEMPS SHOWN TO REMAIN IN MID AND UPPER 30S THROUGH 
ABOUT 15Z BEFORE GRADUALLY BEGINNING TO FALL THROUGH THE DAY. 925MB 
WET BULB ZERO LINE MOVES THROUGH A LITTLE QUICKER BUT STILL NOT 
UNTIL AT LEAST 12Z IN WEST. 1000-850MB THICKNESS VALUES SIMILAR TO 
925MB WET BULB WITH 1300M CRITICAL THICKNESS LINE INTO WESTERN AREAS 
NEAR 12Z AND NOT THROUGH EASTERN AREAS UNTIL AFTER 18Z. HAVE USED A 
BLEND OF MODEL CONSENSUS FOR TRANSITION WHICH BASICALLY CONTINUES 
PREVIOUS TRENDS OF SLOWING CHANGEOVER TO ALL SNOW BY SEVERAL HOURS. 
THIS MAKES ACCUMULATING SNOW AWAY FROM LAKE EFFECT AREAS LESS LIKELY 
AS DEEPER MOISTURE BEGINS PULLING OUT OF THE AREA AFTER 06Z TONIGHT. 
WILL LEAVE A RAIN OR SNOW MENTION IN FAR NORTHWEST TONIGHT BEFORE 12Z 
BUT TRANSITION ALL OTHER AREAS TO JUST RAIN. HAVE KEPT A LOW CHANCE 
POP OR FLURRY/SPRINKLE MENTION ALL AREAS ON THURSDAY WITH COLD AIR 
ADVECTION AND ANY LINGERING MOISTURE...THOUGH MEASURABLE PCPN 
BECOMING DOUBTFUL AWAY FROM LAKE EFFECT. 

LAKE EFFECT AREAS POSE THEIR OWN CHALLENGES FOR THIS EVENT. LAKE 
ENHANCED BAND STILL LOOKS PLAUSIBLE TOWARD 12Z THU AS SYNOPTIC LOW 
EXITS THE EAST AND COLD AIR ADVECTION BEGINS IN WEST. MUCH COLDER 
AIR OVER NORTHERN LAKE MICHIGAN WILL BE QUICKLY MOVING SOUTH ACROSS 
LAKE AS LOW LEVEL FLOW QUICKLY BACKS FROM NORTHEAST TO NORTHWEST AND 
EVENTUALLY WEST. ITS THE PERIOD FROM ABOUT 09Z TO 18Z THAT IS OF 
SOME CONCERN IN FAR NW AREAS AS MODELS 925MB PLUME ANALYSIS INDICATE 
GOOD LIFT AND MOISTURE WITH LONG FETCH. QUESTION IS WHETHER DELTA T 
VALUES WILL BE COLD ENOUGH THIS EARLY FOR GOOD INSTABILITY AND HOW 
FAST MID LEVEL SYNOPTIC MOISTURE DRIES OUT AND WHETHER ANY ORGANIZED 
BAND CAN FORM. GIVEN THE QUICKLY BACKING WINDS EXPECT ANY LAKE PLUME 
TO BE RATHER TRANSITORY EARLY WHICH WOULD LIMIT ANY ACCUMULATIONS. 
IN ADDITION...WET BULB TEMPS LOOK TO STILL BE IN LOW TO MID 30S 
WHICH MAY ALLOW ANY SNOW TO MIX WITH RAIN AT TIMES OR MELT QUICKLY. 
HAVE CONTINUED LIKELY POPS IN FAVORED LAKE EFFECT REGION WITH ONLY 
SMALL ACCUMS. FLOW BECOMES MORE WESTERLY THU NIGHT WHICH SHOULD 
SHIFT ANY LAKE EFFECT INTO EXTREME NORTHERN INDIANA AND MAINLY 
SOUTHWEST LOWER MICHIGAN. BERRIEN AND CASS REMAIN FAVORED LOCATIONS 
WITH SOME ACCUMS POSSIBLE THU NIGHT DEPENDING AGAIN ON AMOUNT OF 
MOISTURE IN MIXED LAYER GIVEN SHORTEST FETCH POSSIBLE ACROSS LAKE.

LONG TERM /FRIDAY THROUGH WEDNESDAY/...

BRUNT OF THE COLD BLAST WILL BE SETTLING OVER THE AREA AT THE START 
OF THE PERIOD. 850 MB TEMPS OF -12 TO -14C WILL LEAD TO A COLD DAY 
ACROSS THE AREA COMPARED TO WHAT WE HAVE SEEN RECENTLY. AVERAGE 
HIGHS THIS TIME OF YEAR ARE IN THE UPPER 30S SO DEFINITELY BELOW 
NORMAL. MOST AREAS WILL BE DRY EXCEPT FOR LOCATIONS IN FAR SOUTHERN 
LOWER MI...WHERE LAKE EFFECT MACHINE WILL BE IN FULL SWING WITH 
DELTA T'S AROUND 20 C. GIVEN SHORT FETCH IN THE WSW TO SW 
FLOW...AMOUNT OF MSTR TO BE CONTRIBUTED TO THESE BANDS REMAINS 
TRICKY. AS SUCH HAVE MAINTAINED LIKELY POPS FRIDAY IN BERRIEN 
COUNTY. HIGHEST POPS WILL REMAIN ACROSS NORTHERN AND CNTRL OF THE 
COUNTY WHERE A FEW INCHES OF ACCUMULATION WILL BE POSSIBLE. THE 
CHANCES FOR SNOW WILL CONTINUE INTO SATURDAY MORNING WITH A SLOW 
DOWNWARD TREND AS THE FLOW BEGINS TO SHIFT...DELTA T'S AND MSTR 
DECREASES.  FOR THE REMAINDER OF THE AREA...HAVE KEPT WITH PARTLY 
CLOUDY SKIES AS DRY AIRMASS SHOULD ALLOW FOR SUNSHINE BUT STILL COOL 
TEMPS. 

A FAST MOVING WAVE WILL ARRIVE SOMETIME MONDAY OR MONDAY NIGHT. AT 
THIS POINT IT APPEARS TO BE MSTR STARVED AND WILL PROBABLY DO LITTLE 
MORE THAN ALLOW FOR SLIGHTLY WARMER TEMPS AHEAD OF IT AND A 
REINFORCING SHOT OF COLD AIR BEHIND IT. PAST GRIDS HAD THIS HANDLE 
SO WILL LEAVE CHC POPS MON/MON NGT. SOME POTENTIAL TO REMOVE POPS 
FROM MONDAY NIGHT BUT GIVEN VARIANCE OF MODELS LATELY DON'T WANT TO 
MESS AROUND WITH IT. 

FINAL FOCUS WILL TURN TOWARD NEXT SOMEWHAT DEEPER TROUGH SET TO DIG 
INTO THE PLAINS AS THE MONDAY SYSTEM IS MOVING THROUGH. GFS SHOWS A 
RATHER POTENT SYSTEM TAKING SHAPE AND AFFECTING MUCH OF THE EASTERN 
US. GFS ENSEMBLE MEMBERS FOR PRECIP CHANCES DEPICT 60 TO 70% CHANCE 
OF A TENTH OF AN INCH OR MORE MAINLY ON WEDNESDAY. WHILE THIS WOULD 
LEAD NORMALLY TO INCREASED CONFIDENCE...THE FACT THAT THE MEDIUM 
RANGE MODELS HAVE BEEN DOING RATHER HORRIBLE IN TERMS OF CONSISTENCY 
OF LATE AND THAT THIS AREA IS LIKELY TO CHANGE IN LOCATION OVER THE 
NEXT SEVERAL DAYS...MAKES IT HARD TO LEAN THAT HEAVILY ON GUIDANCE 
POINT TOWARDS ABOVE CLIMO POPS. NOW THAT BEING SAID...GIVEN THE 
SIGNS OF THE ACTIVE PATTERN AND LARGE PIECE OF NORTHERN STREAM 
ENERGY SET TO BREAK OFF AND DROP TOWARDS THE AREA...STAGE MAY BE SET 
FOR A SOMETHING TO BE MONITORED IN LATER FORECASTS. FOR NOW HAVE 
WENT UNDER CLIMO/GUIDANCE VALUES AND INTRODUCED 30 POPS TUES 
NGT/WEDS WITH PLENTY OF TIME TO WATCH EVOLUTION OF THE MODELS. 

ONE THING TO NOTE IS LARGE POLAR LOW THAT WILL BE MOVING ACROSS 
NORTHERN CANADA TOWARDS THE END OF THIS FORECAST PERIOD WITH A CORE 
OF -40 C 850 MB TEMPS. WILL SOME OF THIS MAKE IT DOWN OUTSIDE THE 
LONG TERM PERIOD...STAY TUNED.  

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST FRIDAY FOR LMZ043-046.

&&

$$

SHORT TERM...LASHLEY
LONG TERM...FISHER
AVIATION...ARNOTT