FXUS63 KIWX 062342
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
642 PM EST SUN DEC 6 2009

.AVIATION...
A WEAK UPPER LEVEL SYSTEM WILL MOVE NORTHEAST OVER THE AREA
MONDAY. AHEAD OF THIS SYSTEM...VFR CONDITIONS SHOULD TO CONTINUE
AS HIGH PRESSURE MOVES EAST. LIGHT SNOW IS POSSIBLE BY
DAYBREAK...BUT VSBYS SHOULD REMAIN VFR. MVFR CIGS ARE POSSIBLE
DURING THE DAY AS THE LOWER LEVELS TRY TO SATURATE. ANY SNOW
SHOULD END DURING THE AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 505 PM EST SUN DEC 6 2009/ 

SHORT TERM...

..TONIGHT THROUGH MONDAY NIGHT...

HIGH PRESSURE WAS SLIDING OFF TO OUR EAST AND RETURN FLOW WAS 
ALREADY BRINGING HIGH CLOUDS BACK INTO THE AREA. EXPECT CLOUDS TO 
THICKEN AND LOWER THIS EVENING AHEAD OF WEAK LEAD SHORT WAVE THAT 
WILL MOVE THROUGH LATE TONIGHT AND MONDAY. MODELS NOT AS AGRESSIVE 
TODAY WITH THETA E ADVECTION BUT STILL SHOWING WEAK LIFT AND 
MOISTURE ADVECTION IN LOWER LEVELS VERY LATE TONIGHT AND MONDAY. 
MODEL SOUNDINGS SHOW DRY LOWER LEVELS TAKING UNTIL MID DAY MONDAY TO 
SATURATE...BY WHICH TIME BEST LOW LEVEL MOISTURE ADVECTION IS COMING 
TO AN END. SURFACE OBSERVATIONS SUPPORT DRY LOW LEVEL AIRMASS WITH 
DEW POINTS IN THE UPPER TEENS TO LOWER 20S FROM LOWER MICHIGAN TO 
SOUTHWEST MO THIS AFTERNOON. ENOUGH WEAK FORCING AND INDICATIONS OF 
MOISTENING LOWER LEVELS TO CONTINUE LOW CHANCE POPS FOR THIS EVENT 
BUT CERTAINLY QUESTION MEASURABLE QPF. LIGHT...NON MEASURABLE SNOW 
SHOWERS OR FLURRIES MOST LIKELY EXPECTATION FROM THIS WEAK SYSTEM 
THUS ONLY SOME MINOR TWEEKS TO CURRENT GRIDS.

ANY LINGERING LIGHT PCPN SHOULD BE DONE BY MID AFTERNOON. NAM12 
DEVELOPING A LOW LEVEL INVERSION AND LOCKING IN ANY LOW CLOUDS THAT 
DEVELOP DURING THE DAY. GFS SIMILAR BUT NOT AS STRONG WITH 
INVERSION. NAM VERY AGGRESSIVE WITH DEVELOPING A NEARLY SATURATED 
LOWEST 15HFT MONDAY NIGHT WHICH MAY LEAD TO ADDITIONAL LOW CLOUD 
DEVELOPMENT OR POSSIBLY DENSE FOG AS WINDS WILL BE LIGHT IN WAKE OF 
WEAK SYSTEM AND WEAK HIGH PRESSURE OVER THE AREA. WILL KEEP IT 
MOSTLY CLOUDY FOR NOW AND SEE IF ANY PCPN ACTUALLY FALLS WHICH WOULD 
HELP FOG DEVELOPMENT MONDAY NIGHT.  

LONG TERM...SATURDAY THROUGH THURSDAY...

..MID WEEK SYSTEM IN THE CROSSHAIRS...

ALL EYES REMAIN ON MAJOR MID WEEK STORM SYSTEM WITH MODELS IN 
GENERAL AGREEMENT ON TRACK THAT MORE THAN LIKELY KEEPS MOST IF NOT 
ALL OF THE KIWX CWA OUT OF A "BIG SNOW."  AS ALWAYS...UNCERTAINTY 
EXISTS...BUT ATTM PROBS FOR A MAJOR SNOWSTORM RELATIVELY LOW WITH 
CONCERNS MORE CENTERED ON PTYPE ISSUES...MODERATE RAIN THAT MAY 
RESULT IN SOME MINOR FLOODING...AND POSSIBLE WARNING CRITERIA WINDS 
AS THE STORM EXITS WED AFTERNOON/NIGHT.

ONE MAJOR PLAYER IN EVOLUTION OF EVENT IS SIGNIFICANT PIECE OF 
ENERGY FROM THE REMNANTS OF SUPER TYPHOON NIDA THAT THAT IS HELPING 
PINCH OFF A HIGHLY ANOMOLOUS 5780M H5 HIGH OVER ALASKA ATTM. AS SEEN 
ON LATEST WATER VAPOR...A PORTION OF THIS ENERGY HAS ROUNDED THE 
BASE OF THE ALEUTIAN LOW AND IS PRIMED TO CREST OVER THE UPR HIGH 
LATER THIS WEEK AND BECOME PARTIALLY RESPONSIBLE FOR DRAGGING IN THE 
COLDEST AIR OF THE SEASON THURSDAY. THE OTHER...UNDERCUTTING PORTION 
OF THIS NRN PAC ENERGY WILL COMBINE WITH A SWD DIVING MERIDIONALLY 
ORIENTED JET STREAK INDUCED BY INTENSE HORIZONTAL HEIGHT DIFFERENCES 
OVER NRN CANADA TO STRENGTHEN NRN CALI SFC LOW AND BEGIN TO EJECT IT 
SE. EXPECT GRADUAL INTENSIFICATION AS THIS SYSTEM MOVES FROM THE 
FOUR CORNERS 12Z TUE TO SOMEWHERE NEAR CHICAGO AROUND 12Z WED. 

AS EXPECTED...MODEL DIFFERENCES ABOUND AS TO EXACT LOCATION OF SFC 
LOW AND STRENGTH OF WAA AND SUBSEQUENT PTYPES OVER THE CWA. 
SOLUTIONS RANGE FROM A SREF SFC LOW TRACK OF DAVENPORT TO MILWAUKEE 
TO A ECMWF TRACK FROM LAFAYETTE TO SAGINAW WITH NAM, GFS, AND GEM IN 
BETWEEN. ATTM...THINKING IS THAT MODELS ARE EXHIBITING SOME EWD BIAS 
AS IS USUAL BUT PROBABLY NOT AS MUCH AS THEY TYPICALLY DO GIVEN H5 
OPEN WAVE PATTERN VERSUS DEEP CLOSED UPR LOW AND THEREFORE PREFER A 
SFC LOW TRACK OVER CHICAGO. THEREFORE...FOR THIS PACKAGE PREFERENCE 
LIES WITH THE NAM AS BELIEVE SFC LOW TRACK AND LOW LVL THERMAL 
FIELDS TO BE MOST REPRESENTATIVE THOUGH ALL MODELS LIKELY EXHIBITING 
TYPICAL BIAS OF UNDERDOING WAA WITH DEEPENING SFC LOWS.

TUESDAY...
THOUGH BETTER PRECIP PROBS HOLD OFF UNTIL AFTER 00Z...LEFT A CHC OF 
PRECIP IN FOR LATE AFTERNOON WITH PTYPE MORE LIKELY SNOW THAN RAIN 
IN THE NW CWA AS SURGE OF WARMER LOW LVL AIR HOLDS OFF UNTIL AFTER 
00Z.  OTHERWISE...EXPECT TUESDAY TO BE THE CALM BEFORE THE STORM 
WITH MAINLY CLOUDY CONDITIONS AND SEASONAL TEMPS. 

TUESDAY NIGHT...
IMPRESSIVE ISENTROPIC ASCENT WITH 6 G/KG MIXING RATIO SOURCE REGION 
AIR TO LIKELY RESULT IN INTENSE WAA PRECIP BAND TUESDAY EVENING WITH 
BIGGEST CONCERNS LYING WITH PTYPE (AS MODEL LOW LVL THERMAL 
SCENARIOS VARY SIGNIFICANTLY) AND INTENSITY/ACCUMULATION OF INITIAL 
PRECIP BURST. INITIAL PRECIP FALLING THROUGH AN UNSATURATED COLUMN 
WILL ALLOW SFC TEMPS TO FALL TO WET BULBS AND COMBINED WITH DYNAMIC 
COOLING...EXPECT MORE SNOW THAN RAIN IN THE NWRN CWA THROUGH 03Z 
BEFORE SURGE OF WARM AIR ALLOWS MORE RAIN TO MIX IN WHICH WILL 
LIKELY KEEP SNOW ACCUMS DOWN.  OVER THE SE HALF OF THE CWA...EXPECT 
SNOW ACCUMS TO BE MINIMAL IF AT ALL AS H85 TEMPS WILL LIKELY PUSH 
+6C OR HIGHER.  USED A NON-DIURNAL TEMPERATURE CURVE THROUGH THE 
NIGHT AND INTO WEDNESDAY AS TEMPS WILL LIKELY BE IN THE 40S IN MANY 
AREAS LATE TUE NIGHT/EARLY WEDNESDAY MORNING.  DEEPENING LOW WITH 
IMPRESSIVE UVVS MAY EVEN SUPPORT A RUMBLE OF THUNDER IN SERN CWA 
AFTER MIDNIGHT...BUT WILL LEAVE MENTION OUT AT THIS TIME AS ELEVATED 
INSTABILITY LOOKS TO BE QUITE MINIMAL.

WEDNESDAY...
A STRONG COLD FRONT WILL CRASH THROUGH THE CWA WEST TO EAST EXITING 
THE LIMA AREA IN THE LATE AFTERNOON.  BUMPED TEMPS SEVERAL DEGREES 
HIGHER AND USED A NON-DIURNAL CURVE TO ATTEMPT TO ACCOUNT FOR THIS 
AND WOULD NOT BE SURPRISED IF HIGHS IN THE SERN PORTION OF THE CWA 
SURGE EVEN HIGHER THAN CURRENTLY PROGGED MID 40S. WRAP AROUND 
SNOWFALL WILL RECEIVE LITTLE LAKE ENHANCEMENT AND SHOULD BE 
GENERALLY LIGHT OVERALL BUT VERY STRONG WINDS PER EXTREMELY TIGHT 
SFC PRES GRAD COULD REDUCE VISIBILITIES NONETHELESS CREATING 
HAZARDOUS CONDITIONS.

WEDNESDAY NIGHT AND THURSDAY...
COLD WILL BE THE WORD AS RELEASE OF VERY COLD AIR THAT HAS BEEN 
BOTTLED UP IN CANADA CONTINUES. A FEW LAKE EFFECT SNOW SHOWERS WILL 
BE POSSIBLE WITH LOW LVL FLOW DIRECTION SUPPORTING MAINLY MICHIGAN 
COUNTIES AGAIN BUT SYNOPTIC DRYING WILL LIKELY YIELD ONLY A LIGHT TO 
MODERATE EVENT.  CUT TEMPS ANOTHER COUPLE OF DEGREES ON THU BUT AM 
PROBABLY STILL TOO WARM WITH HIGHS IN THE TEENS DEFINITELY NOT OUT 
OF THE QUESTION AS H85 TEMPS CRASH TO -20C.

FRIDAY...
PULLED POPS OUTSIDE OF LAKE EFFECT AREAS AS STG MODEL AGREEMENT 
EXISTS WITH SFC RIDGING SQUEEZING IN FROM THE SOUTH. CUT TEMPS A 
LITTLE BUT STILL EXPECTING A DECENT REBOUND FROM THU WITH HIGHS IN 
THE MID TO UPR 20S.

SAT/SUN...
DESPITE DECENT AGREEMENT ON OVERALL SYNOPTIC FLOW PATTERN... 
SIGNIFICANT DISAGREEMENTS BEGIN TO ARISE IN THE MODELS TOWARDS END 
OF PERIOD WRT LL THERMAL FIELDS AND WILL CHOOSE TO HEDGE SLIGHTLY 
BELOW CLIMO FOR TEMPS WITH MAINLY DRY WX AS GENERAL FLOW PATTERN 
LOOKS FAIRLY FLAT ZONAL WITH ANY WEAK SYSTEMS NEARLY IMPOSSIBLE TO 
TIME AT THIS POINT. JUST THE SLIGHTEST BIT OF CONCERN DOES EXIST FOR 
ANOTHER BIG SYSTEM OVER THE WEEKEND AS THE MODELS HAVE BEEN TRYING 
TO DEVELOP A SRN STREAM EAST COAST LOW AND HANDLING OF ERN U.S. 
SYSTEMS HAS BEEN SUSPECT AT BEST IN THE FAR REACHES OF THE EXTENDED 
WITH INCREDIBLE WWD SHIFTS NOTED THIS SEASON.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SHORT TERM...LASHLEY
LONG TERM...SIMPSON
AVIATION...SKIPPER