FXUS63 KIWX 090038
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
738 PM EST TUE DEC 8 2009

.AVIATION...

MIX BAG OF PRECIPITATION BEING REPORTED ACROSS THE AREA THIS
EVENING AND CAUSING PROBLEMS AT PRACTICALLY EVERY TERMINAL. MVFR
CONDITIONS EXPECTED THROUGH THE TAF PD WITH BRIEF PERIODS OF IFR
POSSIBLE...WHICH IS ALREADY BEING REPORTED AT KSBN AND HAVE
COVERED THIS WITH A TEMPO GROUP. SURGE OF WARMER AIR IS TAKING
LONGER THAT ORIGINALLY THOUGHT TO MOVE UP FROM THE SOUTH AND WEST
SO HELD ON TO A MIX OF RASNPL UNTIL 06/08Z AT KFWA/KSBN
RESPECTIVELY. LOOK FOR THE COLD FRONT TO MOVE THROUGH WEDNESDAY
MORNING AFTER 12Z WHICH WILL CHANGE ANY PRECIPITATION OVER TO
SNOW BY LATE MORNING/EARLY AFTERNOON. 

EXPECT WINDS TO INCREASE OVER THE NEXT SEVERAL HOURS
OF UPWARDS OF 15-20KTS WITH GUSTS UP TO 35KTS AND EVEN STRONGER
TOWARDS THE END OF THE TAF PERIOD. 

ANY SNOW THAT DOES FALL AND ACCUMULATES ON WEDNESDAY, MAINLY AT THE KSBN/KBEH
TERMINALS, WILL SEE BLOWING SNOW AND VISBYS DROP. HAVE STARTED
TRENDING THIS AT THE END OF THE TAF PD BUT WILL NEED TO BE MONITORED
WITH LATER TAF ISSUANCES. 

&&

.PREV DISCUSSION... /ISSUED 252 PM EST TUE DEC 8 2009/ 

SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT

DEEP TROUGH AND ASSOCIATED POWERHOUSE 150 KT PLUS UPR JET NOW JUST 
EJECTING INTO THE CENTRAL HIGH PLAINS WILL PIVOT NEWD INTO THE MID MS 
VALLEY TONIGHT WHILE TAKING ON A NEGATIVE TILT. 12 HR 7-5H HEIGHT 
FALLS OF NEARLY 20 DAM ACROSS THE CENTRAL PLAINS/MID MS VALLEY...AND 
IMPRESSIVE 5-3H Q-VECTOR CONV/DPVA WILL YIELD A ROBUST LOW LVL 
RESPONSE...WITH THETA-E ADV WITHIN 40-50KT CROSS ISOBARIC ISENTROPIC 
FLOW. PRECIP SHIELD ASSOCIATED WITH THIS WILL MOVE INTO THE FA FROM 
SW TO NE EARLY THIS EVE...WITH THE SYSTEM DRY SLOT POISED TO SLIDE 
IN BY LATE TONIGHT. 12Z GUIDANCE REMAINED RELATIVELY CONSISTENT IN 
TRACKING THE SFC LOW TO NEAR CHICAGO BY 12Z WED AND INTO NRN LOWER 
MI BY WED AFTN...WITH THE 7H LOW NW OF THAT. THIS TRACK IS OBVIOUSLY 
NOT A GOOD TRACK FOR HEAVY SNOW LOCALLY. HOWEVER...THERMAL PROFILES 
LOOK INITIALLY FAVORABLE FOR A BRIEF BURST OF SNOW/SLEET LATE THIS 
AFTN AND EVE MAINLY NORTH OF HIGHWAY 30. MAYBE AN INCH OR TWO AT 
MOST NORTH OF ROUTE 6. THE SNOW/SLEET WITH THE INITIAL OMEGA SURGE 
WILL CHANGE OVER TO ALL RAIN THIS EVE AS WARM AIR SURGES NWD ON THE 
EASTERN FLANK OF THE RAPIDLY DEEPENING MID LATITUDE CYCLONE. AREAS 
SOUTH OF HIGHWAY 30 WILL SEE MAINLY RAIN LATE THIS AFTN/EVE...WITH 
SOME SLEET POSSIBLE LATE THIS AFTN PER UPSTREAM OBS. DRY SLOT WITH 
LOW CLOUDS/DRIZZLE WILL SETTLE IN LATE TONIGHT INTO THE FIRST PART 
OF WED MORNING AS THE CYCLONE WRAPS UP WEST OF HERE.

STRONG CDFNT WILL TRANSLATE THROUGH WED MORNING...WITH STAUNCH CAA 
AND STRONG WINDS IN ITS WAKE LATE WED MORNING INTO WED AFTN/EVE. SFC 
LOW WILL DEEPEN TO AROUND 975MB IN NRN LOWER MI PER LATEST MODEL 
SOLUTIONS. RESULTANT SFC PRESSURE GRADIENT...ISOLLABARIC 
COUPLET...AND NAM BUFKIT MOMENTUM PROGS SUGGEST WIND GUSTS NEAR 50 
MPH WILL BE POSSIBLE WED/WED EVE. NAM INDICATING THAT A HIGH WIND 
WARNING MAY BE NEEDED WITH 50 KNOT WINDS AT 92H. CURRENT THINKING IS 
THAT MIXING THIS TO THE SFC MAY BE TOUGH GIVEN THE PROGGED LOW LVL 
SHEAR. WILL COVER WITH A WIND ADVISORY FOR NOW. OTHER CONCERN IS 
SNOW/BLOWING SNOW CHANCES IN FAR NC IN AND SW LOWER MI WED AFTN INTO 
WED NIGHT. WEAKENING DEFORMATION AXIS/SYNOPTIC SUPPORT WILL ROTATE 
THROUGH THE NW WED AFTN. THIS SYNOPTIC MOISTURE COMBINED WITH 
INCREASING LAKE INSTABILITY PER CAA WILL LIKELY BE ENOUGH TO PRODUCE 
SCT/NUM SNOW SHOWERS. HOWEVER...ACCUMULATIONS IN THE FAR NW SHOULD 
NOT BE MORE THAN AN INCH OR TWO WED AFTN GIVEN BNDRY LAYER WESTERLY 
FLOW OF 40-50 KNOTS LIMITING PARCEL RESIDENCE TIME. SRN/EASTERN 
PORTIONS OF THE FA WILL LIKELY SEE LINGERING SHRAS CHANGE OVER TO A 
FEW SNOW SHOWERS/FLURRIES ON WED. WESTERLY FLOW WILL DISSIPATE A BIT 
BY WED NIGHT WITH ANY SYNOPTIC SUPPORT SHIFTING OFF TO THE NE. 
LIGHTER WESTERLY FLOW AND DELTA T/S IN UPPER TEENS WITH LAKE INDUCED 
EQUILIBRIUM LVLS INCREASING TO BTW 8-10 KFT SHOULD RESULT IN SOME 
ORGANIZATION TO THE SNOW ACROSS THE FAR NORTH...ESPECIALLY NRN 
CASS/BERRIEN COUNTIES IN MI. AN ADDITIONAL COUPLE OF INCHES OF SNOW 
WILL BE POSSIBLE HERE WED NIGHT...WITH MOST LOCATIONS RECEIVING 
LITTLE IF ANY SNOW ACCUMULATION OUTSIDE OF BERRIEN/CASS AND MAYBE ST 
JOE COUNTIES IN MI. WILL PROBABLY NEED SOME TYPE OF HEADLINE UP IN 
THESE COUNTIES FOR WED AFTN/NIGHT/THU GIVEN THE POTENTIAL FOR 
BLOWING SNOW AND ACCUMULATIONS OF 2-5 INCHES. HELD OFF ON ANY 
HEADLINE FOR NOW.  

LONG TERM...

STRONG SYSTEM WILL HAVE EXITED THE REGION BY THE BEGINNING OF LONG 
TERM WITH VERY COLD AIR FOLLOWING IN ITS WAKE.  H85 TEMPS FALL 
QUICKLY TO -20C 12Z THU...RESULTING IN HIGHS ACROSS THE CWA WHICH 
MAY PEAK BELOW 20 IN MOST LOCATIONS AS HANDLED BY A BLEND OF MET 
GUIDANCE...WHICH COOLED THIS CYCLE...WITH WARMER MAV. WITH WINDS 
STILL 15-20MPH THIS WILL MAKE FOR A VERY UNCOMFORTABLE DAY DROPPING WIND 
CHILL READINGS NEAR ZERO. THURSDAY NIGHT WILL BE THE COLDEST...AND 
EVEN STEADY GRADIENT WINDS WORKING AGAINST RADIATIONAL COOLING 
OVERNIGHT LOWS WILL SETTLE NEAR 10 WITH SOME LOCATIONS FALLING TO 
SINGLE DIGITS.

WITH COLD AIR AND WESTERLY WINDS...LAKE EFFECT WILL GEAR UP AND LAST 
THROUGH FRIDAY NIGHT AS WINDS REMAIN WEST TO WSW AND DELTA T/S STAY 
NEAR 20C THROUGH THURSDAY EVENING...AND 15C BY FRIDAY EVENING BEYOND 
WHICH WARMING TEMPS AND BACKING WINDS SHUT THINGS DOWN. GIVEN WIND 
DIRECTION MAIN IMPACT WILL ONCE AGAIN BE LIMITED TO MICHIGAN 
COUNTIES.  EQL LEVELS ARE JUST ABOVE GROWTH ZONE BUT AMOUNTS MAY BE 
STUNTED INITIALLY BY DRY AIR AND BRISK WIND SPEEDS KEEPING MODE 
MULTICELLULAR THROUGH THURSDAY NIGHT.

FLOW BECOMES MORE ZONAL THROUGH THE WEEKEND WITH TEMPS MODERATING 
BACK TO LOW 30S FOR HIGHS.  BEYOND THIS...MODEL AGREEMENT BECOMES 
QUITE POOR AS UPPER FLOW OVER CANADA IS HANDLED VERY DIFFERENTLY. 
AN ARGUMENT COULD BE MADE TO PULL SATURDAY POPS WITH NO SUPPORT FROM 
THE 12Z ECMWF...BUT WILL LET THEM RIDE GIVEN 12Z GFS AND ENSEMBLE 
STILL SHOWING WEAK LOWER/MID LEVEL WAVE.  KEPT POPS DRY BEYOND THIS 
AS CONFIDENCE IN ANY SOLN IS VERY LOW AS MODELS ATTEMPT TO RETURN 
EASTERN TROUGH BUT DISAGREE ON EVOLUTION OF UPPER PATTERN AND 
PLACEMENT OF WAVES WITHIN FLOW.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WIND ADVISORY FROM 10 AM EST /9 AM CST/ WEDNESDAY TO 1 AM EST 
     /MIDNIGHT CST/ THURSDAY FOR INZ003>009-012>018-020-022>027-
     032>034.

     WINTER WEATHER ADVISORY UNTIL 1 AM EST /MIDNIGHT CST/ WEDNESDAY 
     FOR INZ003>009-012>018.

MI...WIND ADVISORY FROM 10 AM WEDNESDAY TO 1 AM EST THURSDAY FOR 
     MIZ077>081.

     WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR MIZ077>081.

OH...WIND ADVISORY FROM 10 AM WEDNESDAY TO 1 AM EST THURSDAY FOR 
     OHZ001-002-004-005-015-016-024-025.

     WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR OHZ001-002-
     004-005-015.

LM...GALE WARNING FROM 10 PM THIS EVENING TO 7 PM EST THURSDAY FOR 
     LMZ043-046.

&&

$$

SHORT TERM...STEINWEDEL
LONG TERM...LUDINGTON
AVIATION...WEISSER