FXUS63 KIWX 110516
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1216 AM EST FRI DEC 11 2009

.AVIATION...
06Z TAF...CONTINUED WESTERLY SURFACE FLOW OVER LAKE MICHIGAN WILL
PRODUCE LAKE EFFECT SNOW JUST NORTH OF SOUTH BEND AIRPORT. WEAK
SHORTWAVE VISIBLE IN THE WATER VAPOR IMAGERY IS MOVING INTO LOWER
WISCONSIN AT THIS TIME AND WILL HELP TO ENHANCE CLOUD COVER OVER
THE NORTHERN PORTION OF THE COUNTY WARNING AREA...PRODUCING MVFR
CONDITIONS IN SOUTH BEND. FORT WAYNE WILL BE VFR MOST OF THE
PERIOD AND WITH THE PRESSURE GRADIENT RELAXING LATER IN THE
PERIOD...GUSTS WILL GRADUALLY DIMINISH.

&&

.PREV DISCUSSION... /ISSUED 256 PM EST THU DEC 10 2009/ 

SHORT TERM...
TONIGHT THROUGH FRIDAY NIGHT...
ONGOING LES ALONG WITH WINDY AND VERY COLD CONDITIONS MAIN FOCUS IN 
THE SHORT TERM. KIWX RADAR SHOWING LES BANDS CONTINUING OVER MUCH OF 
BERRIEN AND NORTHERN CASS COUNTIES. NOT MUCH IN THE WAY OF RADAR 
ECHOES BUT STILL SEEING SOME VSBY RESTRICTIONS IN ST. JOE MI AS 
WELL. SFC ANALYSIS HAS LOW PRESSURE WELL TO THE NE IN QUEBEC WITH 
HIGH PRESSURE MOVING INTO WESTERN TN VALLEY. BROAD CYCLONIC FLOW 
WILL CONTINUE TO DOMINATE IN THE GREAT LAKES REGION THROUGH TONIGHT. 
SFC TROUGH CURRENTLY MOVING INTO IOWA WILL ROTATE THROUGH THE AREA 
TONIGHT AND EXPECTED TO VEER SW FLOW TO MORE WESTERLY COMPONENT 
WHICH WILL ALLOW LES BANDS TO PERSIST OVERNIGHT. WILL THEREFORE 
EXTEND WARNING FOR BERRIEN COUNTY THROUGH 12Z FRIDAY...DOWNGRADE 
CASS TO ADV ALONG WITH ST. JOE. NOT MUCH LET UP IN WINDS AS 20G30 
SHOULD ONLY DROP OFF TO 15G25 TONIGHT WHICH WILL MAINTAIN BLOWING 
SNOW TO ANY ADDITIONAL LES ACCUMULATIONS. OUTSIDE OF THE LAKE EFFECT 
AREA SCT/BKN CLOUDS EXPECTED TO GIVE WAY TO CLEARING SKIES THIS 
EVENING. SFC TROUGH PASSING THROUGH OVERNIGHT WILL REINFORCE 
EXISTING THERMAL TROUGH OVER THE AREA WHICH SHOULD SEND OVERNIGHT 
TEMPS AOB THIS MORNINGS LOWS. SFC RIDGE SLIDES TO EASTERN TN VALLEY 
ON FRIDAY ALONG WITH LOW LEVEL THERMAL TROF SO EXPECT SOME 
MODERATION IN TEMPS WITH SOME SUNSHINE...BUT STILL LEANING HEAVILY 
TOWARD COOLER MET GUIDANCE. SOUTHERLY FLOW TO FINALLY SHUT DOWN LES 
FRIDAY NIGHT WHILE REST OF THE CWA WILL SEE MAINLY CLEAR SKIES AND 
LIGHT WINDS...AGAIN FAVORING COOLER LOWS.&&

LONG TERM...

EXTENDED BEGINS WITH NEARLY ZONAL FLOW ALOFT ABOVE SOUTHERLY FLOW IN 
THE LOWER LEVELS AS CENTER OF SFC RIDGE HAS PROGRESSED EASTWARD TO 
THE MID ATLANTIC STATES.  295K SFC SHOWING A BROAD AREA OF 
ASCENT BEGINNING SATURDAY AND LASTING INTO SUNDAY EVENING BUT 
MOISTURE IS LACKING UNTIL SATURDAY NIGHT WHEN LIGHT PRECIP WILL BE 
POSSIBLE.  WITH SOUNDINGS SHOWING WARMING ALOFT OVER COLD NEAR SFC 
LAYER HAVE INCLUDED A MENTION OF FZRA IN SOUTHERN HALF FOR SATURDAY 
NIGHT.  ON SUNDAY WARMING CONTINUES TAKING SFC TEMPS ABOVE FREEZING 
AND CHANGING TO A BORDERLINE RAIN/SNOW MIX. 

COLD MID/UPPER VORTEX OVER CENTRAL CANADA THEN DIGS TROUGH THE 
NORTHERN PLAINS PHASING WITH SOUTHERN STREAM AND PROGRESSING INTO 
THE GREAT LAKES BY TUESDAY NIGHT.  DECENT AGREEMENT ON SFC FRONTAL 
PASSAGE MONDAY EVENING/NIGHT CONTINUING NEED FOR CHC POPS STARTING 
AS ALL RAIN WITH TRANSITION POSSIBLE AS COLDER AIR ARRIVES BUT WITH 
LITTLE WINDOW FOR OPPORTUNITY AMOUNTS APPEAR VERY LIGHT.

12Z ECMWF HAS TRENDED SIGNIFICANTLY TOWARDS THE GFS WITH DEPTH OF 
TROUGH INTO THE GREAT LAKES MID/LATE WEEK AND GRIDDED TEMPS HAVE 
BEEN NUDGED DOWN ACCORDINGLY WITH COLD DRY SFC HIGH PRESSURE TAKING 
CONTROL. THIS COULD FORESHADOW LAKE EFFECT POTENTIAL IF COLDER GFS 
SOLN VERIFIES...BUT FOR NOW WITH ECMWF H85 TEMPS BORDERLINE FOR LAKE 
RESPONSE...WILL KEEP GRIDS DRY TO BE SURE THIS TREND IS
MEANINGFUL. 

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR MIZ078-
     079.

     WINTER STORM WARNING UNTIL 7 AM EST THIS MORNING FOR MIZ077.

OH...NONE.
LM...GALE WARNING UNTIL 6 AM EST EARLY THIS MORNING FOR LMZ043-046.

&&

$$

SHORT TERM...LEWIS
LONG TERM...SKIPPER
AVIATION...LEWIS