FXUS63 KIWX 020040
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
740 PM EST TUE DEC 1 2009
.AVIATION...
A SFC LOW WILL RACE NORTHEAST TOWARD THE OHIO RIVER WEDNESDAY. THE
DEFORMATION ZONE OF THIS SYSTEM SHOULD SPREAD OVER NORTHERN
INDIANA BY LATE IN THE DAY. IT LOOKS LIKE THE PRECIPITATION SHOULD
START AS RAIN TOWARD THE END OF THE TAF PERIOD. CIGS/VSBYS MAY
BECOME MVFR VERY LATE...BUT FOR NOW...KEPT CONDITIONS VFR WITH
RAIN STARTING LATE. WINDS SHOULD BECOME NORTHEAST...AND THEN
INCREASE AND BACK TO THE NORTH TOWARD 00Z.
&&
.PREV DISCUSSION... /ISSUED 338 PM EST TUE DEC 1 2009/
SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
UNSEASONABLY WARM START TO DECEMBER FOR THE AREA WITH EVERYONE
GENERALLY INTO THE 50 TO 54 DEGREE RANGE...A GOOD 10 DEGREES OR MORE
ABOVE NORMAL. FEW THIN HIGH CLOUDS TRYING TO SCOOT INTO SOUTHERN
AREAS BUT NOT REALLY AMOUNTING TO MUCH. HIGH CLOUDS WILL CONTINUE TO
DRIFT IN TONIGHT...ALLOWING FOR MOSTLY CLEAR SKIES AND LOWS LIKELY
AT OR ABOVE FREEZING ACROSS THE AREA.
SKIES WILL GENERALLY BE PARTLY TO MOSTLY SUNNY TO START THE DAY WITH
CONDITIONS STARTING TO GO DOWNHILL BY LATE AFTERNOON AS STORM SYSTEM
THAT HAS BEEN DISCUSSED FOR SEVERAL DAYS TAKES SHAPE AND BEGINS ITS
RAPID MOVE TOWARDS THE OHIO VALLEY. MAJORITY OF THE MODELS TRACK THE
SFC LOW ACROSS SE OHIO WEDS EVE WITH THE GFS SOMEWHAT FURTHER EAST.
AS A RESULT...GFS IS RATHER DRY FOR MUCH OF THE FA EXCEPT SE AREAS.
CONSIDERING THE DEGREE OF INTENSIFICATION EXPECTED WITH THIS
SYSTEM...CONSENSUS IS TO LEAN AGAINST THE GFS WITH A MORE NW TRACK
EXPECTED...POTENTIALLY EVEN A BIT FURTHER NW THAN MODELS ARE
CURRENTLY SHOWING. THIS BEING SAID...RAIN WILL BEGIN TO ARRIVE IN
SOUTHEASTERN AREAS DURING THE AFTERNOON AND EXPAND NORTHWEST OVER
TIME AS THE LOW DRAWS CLOSER. MOST FAVORABLE TIME FRAME LOOKS TO BE
IN THE 00Z TO 9Z RANGE. PRECIP TYPE NOT AN ISSUE TILL AFTER 3Z WITH
MODELS VARYING ON HOW FAST THE COLD AIR ARRIVES. MIXTURE OF RAIN AND
SNOW COULD BEGIN AS 1000-850 MB THICKNESS VALUES BEGIN TO APPROACH
CRITICAL 1300 M THRESHOLDS. AFTER 6Z...ECMWF AND GEM CRASH THICKNESS
VALUES BELOW 1300 M WITH A CHANGE TO ALL SNOW...VS GFS AND NAM WHICH
ARE SOMEWHAT SLOWER. GOING MIDDLE OF THE ROAD AT THIS POINT BUT IN
GENERAL EVERYONE SHOULD BE CHANGED OVER BY 9Z.
FOCUS THEN TURNS TOWARDS INCREASING THREAT FOR LAKE ENHANCED SET UP
AS NORTHERLY FLOW SETS UP AND COMBINES WITH DEPARTING BUT SUFFICIENT
SYNOPTIC MSTR AND LIFT TO CAUSE AN INCREASED CHANCE OF SNOWFALL
ACROSS BERRIEN AND LAPORTE COUNTIES. LIGHT ACCUMS ARE POSSIBLE
DEPENDING ON TIMING OF CHANGE OVER SO A MENTION OF ACCUMS UP TO 1
INCH HAS BEEN INTRODUCED.
LONG TERM...
..THURSDAY THROUGH TUESDAY...
SYNOPTIC LOW WILL BE EXITING THE REGION THURSDAY MORNING WITH
STRONGEST COLD AIR ADVECTION OF THE SEASON UNDERWAY. 850MB TEMPS
WILL BE DROPPING THROUGH THE DAY WITH DELTA T VALUES RISING INTO UPPER
TEENS BY END OF THE DAY. LATEST NAM12 925MB PLUME ANALYSIS SUGGEST A
LAKE ENHANCED EVENT MAY BE ONGOING ACROSS THE FAR NORTHWEST AT
BEGINNING OF PERIOD AS RESIDUAL LOW LEVEL MOISTURE FROM DEPARTING
SYNOPTIC SYSTEM INTERACTS WITH INCREASING INSTABILITY OVER LAKE WITH
COLD AIR ADVECTION. HAVE INCREASED POPS FAR NORTHWEST TO LIKELY
THURSDAY FOR THIS SCENARIO. AS SYNOPTIC MOISTURE WANES DURING THE
DAY SHOULD SEE QUICK TRANSITION TO PURE LAKE EFFFECT BY LATE
MORNING. WITH MOISTURE BECOMING SHALLOWER THROUGH THE DAY EXPECT
MORE CELLULAR LAKE BANDS IN THE AFTERNOON. DEEPER MOISTURE ARRIVES
AGAIN THU NIGHT AND SHOULD SEE AN INCREASE IN ACTIVITY THOUGH FLOW
WILL BECOME MORE WESTERLY AND CONFINE BULK OF ACTIVITY TO NEAR AND
NORTH OF TOLL ROAD. FLOW CONTINUES TO BACK WITH SOUTHWEST FLOW BY
FRIDAY MORNING. DELTA T VALUES WILL BE AROUND 20C BY FRIDAY MORNING
AND BUFKIT SHOWING A LARGE MIXED LAYER NEARLY SATURATED THROUGH
7KFT. THINK THIS COULD BE A DECENT EVENT WITH SEVERAL HOURS OF LIGHT
TO MODERATE SNOW ACROSS CENTRAL AND NORTHERN BERRIEN COUNTY AND
POSSIBLY WESTERN CASS COUNTY DEPENDING ON WIND DIRECTION. HAVE KEPT
THESE AREAS IN LIKELY POPS WITH NUMEROUS SNOW SHOWER WORDING. THE
SHORT FETCH HAS ME CONCERNED FOR ACCUMULATIONS RIGHT NOW BUT IF NAM
EXTREME DELTA T VALUES AND MOISTURE DEPTH IS INDEED REALIZED...COULD
SEE SEVERAL INCHES FOR THE EVENT IN THIS FAR NORTHWEST REGION.
OUTSIDE OF LAKE EFFECT REGION WILL LIKELY SEE VARIABLY CLOUDY SKIES
THROUGH THE PERIOD WITH TEMPS BELOW NORMAL BUT STILL SEASONABLE FOR
EARLY DECEMBER.
A WEAK SHORT WAVE AND SURFACE FRONT BEING PROGGED TO APPROACH LATER
SUNDAY. MEDIUM RANGE MODELS SHOWING LIMITED MOISTURE BUT A
REINFORCEMENT TO COLD AIR THAT WILL ALREADY BE IN PLACE. WOULD NOT
BE SURPISED IF THIS SHORT WAVE ENDS UP BEING A BIT STRONGER WITH
BAROCLINIC ZONE AND BETTER RESOLUTION BY UPPER AIR NETWORK AS TIME
APPROACHES. AT THIS TIME LOOKS LIKE SOME FLURRIES OR VERY LIGHT SNOW
SHOWERS WOULD BE POSSIBLE BUT VERY LOW PROBABILITY AT THIS TIME
RANGE SO NO PLANS TO INTRODUCE ANY MENTION.
MODEL UNCERTAINTY CONTINUES MONDAY AND TUESDAY WITH A WAVE LIFTING
OUT OF WEST AND POSSIBLE OVERRUNNING IN OUR AREA. 12Z ECMWF IS
STRONGER AND FURTHER WEST WITH A RAIN EVENT BEING SHOWN BY TUESDAY.
WILL HAVE A LOW CHANCE POP FOR RAIN OR SNOW ON DAY 7 AT THIS POINT
BUT MUCH WILL CHANGE WITH THIS SYSTEM FOR SURE.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LMZ043-046.
&&
$$
SHORT TERM...FISHER
LONG TERM...LASHLEY
AVIATION...SKIPPER
