FXUS63 KIWX 301133
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
633 AM EST MON NOV 30 2009

.AVIATION /12Z TAFS/...

EXPECT VFR CONDITIONS TO PERSIST THROUGH THE TAF PERIOD. EARLIER
MVFR CIGS CAUSED BY LAKE EFFECT MOISTURE HAVE IMPROVED TO VFR AND
SEE NO REASON WHY CIGS WILL GO BACK DOWN THIS MORNING. THERE HAVE
BEEN A FEW LOWER CIGS FLOATING AROUND...AND CAN/T COMPLETELY RULE
OUT A SHORT PERIOD OF MVFR RESTRICTIONS...BUT BELIEVE THE MUCH
HIGHER LIKELIHOOD SCENARIO IS FOR THE MORNING TO BE VFR...AND HAVE
LEFT OUT TEMPO MVFR MENTION IN THIS ISSUANCE. THIS EVENING A
CLIPPER-LIKE LOW PRESSURE SYSTEM WILL RACE BY THE TERMINALS TO THE
NORTHEAST...BRINGING WITH IT A CHANCE FOR SOME FLURRIES. EXPECT
THESE TO BE UNABLE TO PRODUCE ANY VSBY RESTRICTIONS.  

NORTHWEST WINDS 5-10KTS WILL BACK WESTERLY AND INCREASE TO
10G16KTS FOR THE AFTERNOON. TONIGHT...THE WINDS WILL CONTINUE TO
BACK SOUTHWESTERLY AND INCREASE TO 14G22KTS FOR THE OVERNIGHT.
LLWS A CONCERN AS THE LLEVEL GRADIENT WILL BE SQUEEZED ON THE
SOUTHWESTERN FLANK OF THE ABOVE MENTIONED LOW PRESSURE SYSTEM. THE
NAM IS AWFULLY ROBUST WITH 50KTS OF 2KFT FLOW...AND WON/T GO QUITE
THIS STRONG IN THE TAFS. FOR NOW...WILL STICK TO 40KTS AT 2KFT
WHICH MAKES IT A MARGINAL SITUATION GIVEN DECENT LLEVEL MIXING.
HOWEVER...BELIEVE A HEAD/S UP IS WARRANTED GIVEN THE POTENTIAL
STRENGTH OF THE FLOW.  

&&

.PREV DISCUSSION... /ISSUED 417 AM EST MON NOV 30 2009/ 

SHORT TERM /TODAY THROUGH TUESDAY NIGHT/...

SHORTWAVE TROUGH AXIS NEARING OUR LONGITUDE AS OF THIS WRITING AND 
WILL RAPIDLY SHIFT EAST UNDER POTENT NORTHERN STREAM FLOW TODAY.  
THIS WILL END ANY REMAINING MID LEVEL SUPPORT FOR ASCENT AND...IN 
ITS WAKE BRING TROPOSPHERE-DEEP SUBSIDENCE FOR THE DAY TODAY.  MAIN 
CHALLENGE THROUGH TODAY WILL BE REMAINING LAKE EFFECT 
CLOUDINESS/PRECIP AS WELL ALIGNED EARLY MORNING 340-350 FLOW AND 
T85S CONTINUING TO COOL TOWARDS -6 - -7C SUGGEST A CONTINUED WEAK 
LAKE RESPONSE. THE LLEVEL FLOW WILL BACK TODAY AS THE H85 TROUGH 
AXIS SHIFTS EAST...BUT SIGNIFICANT BACKING /AS WELL AS SIGNIFICANT 
H85 WARMING WILL LIKELY HOLD OFF UNTIL ABOUT NOON.  THUS EXPECT 
QUITE A FEW CLOUDS THROUGH THE DAY...PARTICULARLY OVER WESTERN AREAS 
EARLY...WITH THESE CLOUDS SHIFTING EAST AS THE DAY GOES ON.  ANY 
PRECIP WILL BE VERY LIGHT AS WITH REGIONAL RADAR RETURNS SHOWING 
ONLY VERY SPOTTY LIGHT RETURNS ATTM.  IN THE GRIDS...WILL CARRY ONLY 
SPRINKLE/FLURRY MENTION TO COVER THIS. PREVIOUS FORECAST HIGHS LOOK 
TO BE IN VERY GOOD SHAPE GIVEN T92 SUPPORTING LOWER 40S FULLY MIXED 
BUT LIKELY CLOUD COVER RESTRICTING MIXING OVER THE NORTHEAST THIS 
AFTERNOON...WHERE HIGHS WILL STRUGGLE TO REACH 40. 

RAPIDLY MOVING CLIPPER-TYPE SYSTEM WILL BRUSH THE AREA TONIGHT.  
MODELS HAVE TRENDED DEEPER WITH THIS SYSTEM AS MORE OF IT/S ENERGY 
BECOMES RESOLVABLE IN THE 00Z MODEL SUITE/S INITIALIZATION.  A SURGE 
OF POSITIVE THETAE ADVECTION AT H85 WILL GENERATE A RAPIDLY MOVING 
BUT PRETTY POTENT SWATH OF ISENTROPIC LIFT.  GIVEN IT/S CANADIAN 
ORIGIN AND RAPID MOVEMENT...MOISTURE WILL BE QUITE LIMITED.  
HOWEVER...SURFACE OBSERVATIONS EAST OF THE CANADIAN ROCKIES EARLY 
THIS MORNING SUGGEST A MODESTLY MOIST AIRMASS...WILL DEWPOINTS NEAR 
30F.  THUS...EXPECT THE LIFT TO BE ENOUGH FOR SOME PRECIP 
GENERATION...PARTICULARLY OVER NORTHEASTERN AREAS WHERE THE LIFT 
WILL BE A LITTLE DEEPER GIVEN CLOSER PROXIMITY TO FAVORABLE QG 
FORCING NEAR THE MID LEVEL VORT MAX.  PRECIP TYPE NOT A CERTAINTY 
GIVEN ONLY MARGINALLY COLD ENOUGH BL TEMPS.  WILL KEEP LIGHT SNOW 
MENTION FOR MOST OF THE AREA AS WET BULB PROFILES STILL SUGGEST SN 
SHOULD DOMINATE...BUT ADD MIX MENTION OVER FAR SOUTHWEST MICHIGAN 
WHERE THE SOUTHWESTERLY FLOW WILL BE ONSHORE AND PRETTY POTENT AS 
THE GRADIENT SQUEEZES SOUTH OF THE SURFACE LOW.  NO SNOW ACCUMS ARE 
EXPECTED. THE ABOVE MENTIONED WINDS WILL LIKELY KEEP TEMPS FROM 
FALLING THAT FAR THROUGH THE OVERNIGHT...PARTICULARLY WITH THE 
EXPECTED CLOUD COVER.  WILL KEEP LOWS ABOVE MOS VALUES...AND CLOSER 
TO THEIR THREE HOURLY PREDICTIONS.  THIS WILL YIELD LOWS GENERALLY 
IN 32-35F RANGE.  

NICE DAY IN STORE FOR TUESDAY AS SHORTWAVE RIDGING BUILDS IN BEHIND 
DEPARTING CLIPPER.  AS NEXT...MORE POTENT NORTHERN STREAM SHORTWAVE 
DIVES INTO THE UPPER MIDWEST...WARM ADVECTION UNDER WESTERLY H85 
FLOW WILL CONTINUE.  I DON/T EXPECT TOO MUCH IN THE WAY OF 
CLOUDINESS AS THE MAJORITY OF THE UPPER LEVEL CLOUDINESS WILL BE 
BOTH NORTH AND SOUTH OF THE AREA NEAR THE POLAR AND SUBTROPICAL JET 
AXES...RESPECTIVELY.  SUBSIDENCE THROUGH MOST OF THE COLUMN UNDER 
THE SHORTWAVE RIDGE ALONG WITH A PRETTY DRY LLEVEL AIRMASS /DRIER BY 
AFTERNOON AS TEMPS REBOUND NICELY/ SHOULD PRECLUDE MUCH CU FORMATION 
AS WELL.  EXPECT FULL MIXING TO WARMING T92S WHICH WILL INCREASE TO 
+5C OR BETTER TOWARDS EVENING.  THEREFORE...WILL BUMP UP PREVIOUS 
HIGHS A FEW DEGREES TO AROUND 50 AND THIS MAY STILL BE CONSERVATIVE 
IF CURRENT THINKING HOLDS.  

SECOND CLIPPER-LIKE SYSTEM NEARS THE REGION TUESDAY NIGHT...BUT 
SURFACE COLD FRONT SHOULD REMAIN NORTHWEST OF THE CWA.  EXPECT 
GRADUALLY INCREASING CLOUD COVER GIVEN THE APPROACH OF THIS 
WAVE...AND UPPER LEVEL MOISTURE LIKELY STREAMING NORTHEAST FROM THE 
DEVELOPING LOW OVER THE GULF...BUT THINGS LOOK NO WORSE THAN PCLOUDY 
ATTM.  BLENDED MOS LOWS IN THE MID 30S LOOK REASONABLE GIVEN THE 
WARMER AIRMASS THAN THE NIGHT PRIOR AND LINGERING SOUTHWESTERLY 
WINDS THROUGH THE NIGHT.  

LONG TERM...

MIDWEEK SYSTEM AND TRAILING LAKE EFFECT STILL THE MAIN FOCUS FOR THE 
EXTENDED PERIOD.  DIGGING GULF OF ALASKA WAVE COMBINED WITH 
DEEPENING HUDSON BAY VORTEX WILL SERVE TO AMPLIFY FLOW OVER NOAM AND 
ALLOW DEEP TROUGHING TO TAKE SHAPE OVER CENTRAL CONUS.  UPPER LOW 
STILL DRIFTING SLOWLY SOUTH OVER THE GULF OF CALIFORNIA IS PROGGED 
TO BE BOOTED EAST BY SOUTHERN STREAM AND PHASE WITH DIGGING TROUGH 
JUST TO OUR SOUTHEAST. THE MODEL SUITE HAS SHIFTED WEST WITH TIME 
AND IT NOW APPEARS MORE LIKELY THAT PRECIPITATION WILL MOVE INTO THE 
CWA FROM THE SOUTH BEGINNING AS RAIN.  THEREAFTER...CONSIDERABLE 
SPREAD IN THE TIMING OF PHASING AND PATH OF THE LLEVEL WAVE  
CONTINUES TO MANIFEST THUS THROWING A WRENCH INTO PTYPE 
CONCERNS...BUT AT THIS TIME PREFER THE ECMWF WHICH IN ITS 12Z RUN KEPT 
THE SFC/850/700 LOW MORE CLOSELY TIED TO THE H5 LOW BEFORE PHASING 
AND EVEN THOUGH THERE IS MORE SPREAD IN THE 00Z RUN IS STILL THE 
TIGHTEST GROUPING TAKING CONTINUITY INTO ACCOUNT...AND BEST HEDGE 
AGAINST A MORE WESTERLY TRACK OF THE LLEVEL FEATURE...AS BEFORE 
PHASING THE SETUP RESEMBLES SCENARIO WITH NEGATIVE TILT MID LEVEL 
TROUGH AND A MODEL EASTERLY BIAS WITH THE SFC/H85 LOW. THIS IS ALSO 
REASON NOT TO THROW OUT THE VERY WARM 00Z/06Z NAM WHICH AT 09Z THU 
IS +6C AT AOH WHILE THE 03Z SREF/00Z GFS ARE ALL DROPPING SFC WET 
BULBS BELOW ZERO AND CHANGING TO SNOW AS EARLY 03Z THU. OBVIOUSLY 
LARGE UNCERTAINLY STILL LOOMS AND THIS WILL REQUIRE CLOSE SCRUTINY 
IN FOLLOWUP CYCLES.

MORE CERTAIN IS THAT BEHIND THIS SYSTEM COLD AIR SETTLES IN AND 
THERE HAS BEEN GOOD RUN TO RUN CONTINUITY IN THE GFS/ECMWF WRT LAKE 
EFFECT SNOW SETUP AS H85 TEMPS OF -13C SETTLE IN ALONG WITH NW WINDS 
BACKING TO WESTERLY FRIDAY AND FINALLY SOUTHWEST FRIDAY 
NIGHT...TAKING THE ACTION NORTH OF THE CWA FOR SATURDAY.  PREV SHIFT 
RAISED TO LIKELY IN BERRIEN/CASS COUNTY THURSDAY NIGHT SO JUST A 
NUDGE UPWARD IN SAME LOCALES ON FRIDAY FOR THIS ISSUANCE. GUIDANCE IS 
BEGINNING TO GRASP THE COLD AIR LATE WEEK WITH THE 00Z MEX DOWN TO 
30 FOR A FRIDAY HIGH IN FWA. THUS MAIN TEMP ADJUSTMENT WAS TO MOVE 
FRIDAY HIGHS GENEROUSLY IN THIS DIRECTION.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 1 PM EST TUESDAY FOR LMZ043-046.

&&

$$

SHORT TERM...ARNOTT
LONG TERM...LUDINGTON
AVIATION...ARNOTT