FXUS63 KIWX 101724
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1225 PM EST THU DEC 10 2009

.AVIATION...
18Z TAFS...
GUSTY WEST/SOUTHWEST FLOW TO CONTINUE FOR REMAINDER OF DAYTIME HOURS 
BEFORE DIMINISHING TO SUSTAINED AROUND 15KTS OVERNIGHT. MORNING 
CLEARING HAS NOW GIVEN WAY TO SCT/BKN 3KFT DECK OVER MUCH OF THE 
AREA. WILL HIGHLIGHT THIS IN TAFS BEGINNING OF THE PERIOD AND CLEAR 
OUT AFTER SUNSET. WEAK SFC TROF AND UPPER LEVEL DISTURBANCE TO 
ROTATE THROUGH NW FLOW OVERNIGHT WHICH SHOULD VEER SW FLOW TO MORE 
WESTERLY COMPONENT OFF THE LAKE BY EARLY FRIDAY MORNING AND BRING 
SCT/BKN DECK BACK INTO KSBN HOWEVER ONGOING LES SHOULD REMAIN NORTH 
OF THE STATE LINE.  
&&

.PREV DISCUSSION... /ISSUED 356 AM EST THU DEC 10 2009/ 

SHORT TERM...

TODAY THROUGH FRIDAY NIGHT

SFC LOW WHICH BROUGHT A VAST ARRAY OF WINTER WEATHER TO THE 
CONUS...CONTINUES TO OCCLUDE AS IT PUSHES INTO WESTERN QUEBEC. 
STRONG LL PRESSURE GRADIENT IN PLACE IN REPONSE TO SFC RIDGING NOTED 
BY 3-4MB 3 HOUR PRESSURE TENDENCIES...CONTINUES TO OFFER BREEZY 
CONDITIONS WITH MANY PLACES STILL HOVERING IN THE 15-20 KNOT RANGE. 
CAA CONTINUES WITH TEMPS BEGINNING TO FALL INTO THE SINGLE DIGITS IN 
THE WESTERN FA. H85 TEMPS WILL CONTINUE TO FALL OVER THE FA...WITH 
VALUES OF -20 C EXPECTED BY AFTERNOON. CAA OVER THE WARM WATERS OF 
LAKE MICH CONTINUES TO SUPPORT A GROWING LAKE REPONSE AS LAKE 
INDUCED INSTABILITY CONTINUES TO RISE. SNOW SHOWERS CONTINUE IN 
PORTIONS OF SW MI...WITH A BRIEF LULL IN ACTIVITY. LL TROUGH AND 
HIGHLY CONVERGENT LL WIND FIELD IN PART TO INCREASINGLY GEOSTROPHIC 
FLOW OVER THE LAKE...SUPPORTED HEAVY SNOWS YESTERDAY EVENING. NOW 
THAT THE TROUGH FEATURE HAS EXITED THE REGION AND FLOW HAS SLACKENED 
SOME...SNOW SHOWER ACTIVITY HAS WANED SOME. HOWEVER...AS LAKE 
INDUCED INSTABILITY GROWS...DO EXPECT AN INCREASE IN ACTIVITY. 
OTHERWISE...DO EXPECT SOME BREAKS IN THE CLOUD DECK AWAY FROM LAKE 
MI FLOW....BY THIS AFTERNOON...WITH SFC HIGH PRESSURE BUILDING INTO 
THE REGION. HAVE UTILIZED THE NAM12/LOCAL WRF/AND GFS GIVEN LAKE 
EFFECT SNOW SETUP AND VERY GOOD INITIATION AS EVIDENCED IN 00Z 
MOMENTUM/THERMAL FIELD COMPARISON.

TODAY...MAIN CONCERN IN THE PERIOD IS ONGOING WINTER STORM WARNING 
AND LAKE EFFECT SNOW POTENTIAL. CAA WILL SUPPORT H85 DELTA T/S OF 
NEARLY 26 C...WITH LAKE INDUCED CAPE VALUES RISING TO NEARLY 800 
J/KG. WESTERLY FLOW WILL SUPPORT LAKE TROUGHINESS OVER THE WEST 
CENTRAL MI SHORELINE...WITH HIGHLY CONVERGENT LL FLOW 
DEVELOPING...SUPPORTING MAX UVM NEAR THE HOLLAND MKG AREA. THIS WILL 
FORCE THE MOMENTUM FIELD TO RESPOND THROUGH A BACKING WIND 
FIELD...WHICH IS ALREADY EVIDENT IN SFC OBS...MAINLY FROM 
GEOSTROPHIC TRENDED FLOW. GROWING INSTABILITY OVER THE LAKE WILL 
SUPPORT MAX NEGATIVE OMEGA IN OR NEAR THE DENDRITIC GROWTH 
ZONE...AND MODERATE TO HEAVY LAKE EFFECT SNOW WILL CONTINUE. THIS 
ONLY CONCERN IS THAT THE BULK OF SNOWFALL WILL OCCUR NORTH OF THE 
FA...WITH EXTREME NORTHERN BERRIEN AND CASS COUNTIES BEING IMPACTED 
MOST IN THE LOCAL FA. MODEL QPF GUIDANCE AND BUFR SNOW RATIO 
PROGS...SUPPORT ANOTHER 1-3 INCHES OF SNOW POSSIBLE ACROSS NORTHERN 
BERRIEN AND CASS COUNTIES AND EXTREME NW ST. JOE COUNTY MI THROUGH 
TODAY. FLOW LOOKS TO TURN WESTERLY TONIGHT WITH BANDING SHIFTING 
FARTHER SOUTH IN A VERY UNSTABLE REGIME GIVEN RAISED INVERSION 
HEIGHTS AND EQL OF 10KFT. EXPECTING ANOTHER 1-3 INCHES 
TONIGHT...WITH LOCALLY HEAVIER AMOUNTS POSSIBLE. IN ADDITION...GUSTY 
WESTERLY WINDS WILL CONTINUES TO SUPPORT BLOWING AND DRIFTING SNOW 
WITH WHITE OUT CONDITIONS STILL EXPECTED. WILL LET CURRENT WARNING 
END TIME REMAIN INTACT. HEADLINES MAY BE NEEDED TONIGHT...BUT 
LINGERING QUESTIONS ON FLOW ORIENTATION/HEIGHT ADJUSTMENT/AND 
SNOWFALL AMOUNTS PRECLUDES ANY CHANGES ATTM.

ELSEWHERE ACROSS THE FA.....EXPECT VERY COLD TEMPS WITH ONLY A VERY 
SLIGHT DIURNAL RISE. HAVE LOWERED HIGHS A TAD TO REFLECT CONCERNS ON 
CAA. SOME SUN MAY BE POSSIBLE LATE TODAY...ESPECIALLY IN THE SW. 
EXPECT WIND CHILL READINGS OF 5 TO 10 BELOW THIS MORNING AND AGAIN 
FRIDAY MORNING. LOOK FOR VERY COLD READINGS TONIGHT WITH LOWS IN THE 
SINGLE DIGITS. EVEN THOUGH SKIES WILL CLEAR ACROSS THE SOUTHERN 
THIRD OF THE FA...A MIXED BL IN THE PRESENCE OF VERY LITTLE SNOW 
COVER WILL TEND TO KEEP TEMPS FROM CRASHING BELOW ZERO.

FRIDAY...WARMING PROFILES AND LOWERING INVERSION HEIGHTS WILL 
SUPPORT A SLOW WANING TREND IN LAKE EFFECT SNOW. ANOTHER INCH OR TWO 
WILL BE POSSIBLE OVER THE CURRENTLY WARNED AREA...ESPECIALLY WESTERN 
CASS COUNTY. BUFR DATA STILL INDICATES DELTA T/S OVER 20C...AND 
GIVEN STRONG MODEL BIAS TO END LAKE EFFECT EVENTS TOO 
SOON...SNOWFALL TOTALS MAY BE HIGHER THAN CURRENT EXPECTATIONS. WILL 
DEFER ANY CHANGES TO THE DAYSHIFT...GIVEN THE NEED FOR MORE 
OBSERVATIONAL DATA CLOSER TO THE PERIOD. OTHERWISE...LOOK FOR 
CONTINUED COLD CONDITIONS WITH PARTLY TO MOSTLY SUNNY SKIES SOUTH OF 
THE LAKE FETCH. 

LONG TERM /SATURDAY THROUGH WEDNESDAY/...

WAA WILL BE UNDERWAY AT THE START OF THE PERIOD WITH PARTLY CLOUDY 
SKIES AND HIGH TEMPS RETURNING BACK TO NEAR FREEZING FOR SATURDAY. 
WARMEST SURGE OF AIR WILL ARRIVE SUNDAY INTO MONDAY AHEAD OF THE 
NEXT SYSTEM SET TO AFFECT THE REGION. WHILE SOLUTIONS VARY ON THE 
EXACT TRACK AND EFFECTS OF THIS SYSTEM IN THE 2ND HALF OF THE 
EXTENDED...MODELS AGREE AT LEAST ON 850 MB TEMPS CLIMBING NEAR OR 
ABOVE 0 C AND 1000-850 MB THICKNESS VALUES ABOVE 1300 M. MEX 
GUIDANCE POINTS TOWARDS HIGHS WELL INTO THE 40S BOTH SUNDAY AND 
MONDAY AND WHILE NOT A LARGE STRETCH DEPENDING ON THE EXACT 
TRACK...AM VERY HESITANT TO JUMP ON THAT BOAT GIVEN WHAT MAY STILL 
BE A COOL BOUNDARY LAYER. AS A RESULT HAVE INCREASED TEMPS SOMEWHAT 
BUT REMAINING UNDER MEX GUIDANCE. IN TERMS OF PRECIP WILL LEAVE CHC 
POPS IN FOR MONDAY AS FRONT APPROACHES. GIVEN ABOVE DETAILS AND 
COLLABORATION HAVE WENT WITH RAIN/SNOW MIX. CLOUD COVER MAY BE 
TRICKY DURING THE PERIOD AS WARM FRONT MOVES THROUGH WITH MODELS 
SHOWING POTENTIAL FOR A FAIR AMOUNT OF CLOUD COVER BY SUNDAY. WILL 
REMAIN CONSERVATIVE FOR NOW. 

AS MENTIONED...MODELS VARY GREATLY ON HANDLING OF NEXT POTENTIAL 
COLD SHOT STARTING MAINLY MONDAY NIGHT. TEMP PROFILES DO CONFIRM AT 
LEAST SOME COOLING. HOWEVER...GFS IS MUCH MORE AGGRESSIVE AND 
DRAMATIC ON COLD AIR WITH 850 MB TEMPS DROPPING BACK TO -16 TO -18 C 
BY TUES NIGHT COMPARED TO THE BRUNT OF THE COLD AIR REMAINING NE OF 
THE AREA AND 850 TEMPS ONLY DROPPING TO -2 TO -4 C WITH SIGNS OF 
WARMING ALREADY BY THE END OF THE PERIOD. GIVEN THIS DEGREE OF 
VARIANCE...HARD TO GRAB ONTO ONE SOLUTION AS GIVEN HISTORY PAST 
SEVERAL WEEKS ROLLER COASTER OF TEMPS IS EXPECTED. WILL STAY ON 
WARMER SIDE FOR NOW AND CONTINUE WITH PREV GRIDS. IF COLDER TEMPS DO 
ARRIVE THEN LAKE EFFECT WILL BECOME A CONCERN WITH ADDITION OF POPS 
BEING NEEDED STARTING MONDAY NIGHT. 

AVIATION...
DEPARTING SFC CYCLONE CONTINUES TO SUPPORT CAA INTO THE
FA...RESULTING IN LAKE EFFECT SNOW ACROSS THE NORTH...WITH
LINGERING WEAK VERTICAL ASCENT PER CONTINUED STRONG MECHANICAL
MIXING OVER THE REMAINDER OF THE FA. HIGH RH BOUNDARY LAYER WILL
NOT BEGIN TO DRY OUT UNTIL MID TO LATE MORNING WITH LIGHT SNOW
ACTIVITY EXPECTED TO PERSIST ACROSS MUCH OF THE FA...WITH MVFR TO
IFR VIS EXPECTED. OTHERWISE...NW AREAS WILL SEE CONTINUED LIGHT TO
MODERATE LAKE EFFECT SNOW SHOWERS GIVEN INCREASING LAKE INDUCED
INSTABILITY. BULK OF ACTIVITY IS EXPECTED TO REMAIN NORTH OF
SBN...WITH MAIN VIS RESTRICTIONS FROM BLSN THERE.

SFC HIGH PRESSURE WILL BUILD INTO THE REGION ON THUR...WITH VFR
CONDITIONS OVER THE MAJORITY OF THE FA...SAVE THE NNW WHERE LAKE
EFFECT CLOUDS AND SNOW SHOWERS WILL CONTINUE TO SUPPORT MVFR TO IFR
CONDITIONS. SBN WILL BE ON THE EDGE OF SNOW VIS RESTRICTIONS...BUT
GIVEN DIURNAL COOLING AND SLIGHT VEERING IN THE WIND PROFILE...DO
EXPECTED AT LEAST MVFR CIGS/VIS WITH POSSIBLE IFR CONDITIONS
RETURNING BY EVENING.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR MIZ077>079.
OH...NONE.
LM...GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LMZ043-046.

&&

$$

SHORT TERM...JC
LONG TERM...FISHER
AVIATION...LOGSDON