FXUS63 KIWX 072027
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
327 PM EST MON DEC 7 2009
.SHORT TERM...
...TONIGHT THROUGH TUESDAY NIGHT...
FORECAST FOCUS REMAINS ON POTENT WINTER STORM THAT WILL MOVE THROUGH
THE GREAT LAKES REGION WITH IMPACTS BEGINNING HERE AS EARLY AS TUE
AFTERNOON. HOWEVER...MUST FOCUS SOME ATTENTION ON POSSIBLE LIGHT
LAKE EFFECT SNOW TONIGHT WITH WHAT APPEARS TO BE A TYPE 6
LASHLEY-HITCHCOCK MESO LOW OVER CENTRAL LAKE MICHIGAN THIS AFTERNOON.
WITH RESPECT TO LAKE EFFECT TONIGHT...NAM12 HAS A DECENT HANDLE ON
AFOREMENTIONED MESO LOW AND SATELLITE SHOWS THIS FEATURE NICELY EAST
OF MKE...DRIFTING SOUTHEAST WITH A WEAK SINGLE BAND TO ITS NORTH.
PLUME ANALYSIS BRINGS THIS ONSHORE INTO BERRIEN COUNTY WHERE WEAK
SNOW SHOWERS HAVE PERSISTED MOST OF THE DAY. HAVE FOLLOWED NAM12
PLUME ANALYSIS FOR TONIGHT WITH SCATTERED SNOW SHOWERS IN BERRIEN
COUNTY THIS EVENING. AS OFFSHORE WINDS INCREASE TONIGHT WITH WEAK
SYNOPTIC FLOW EXPECT WEAKENING SNOW BAND TO DRIFT SOUTH AND WEST
INTO LAPORTE COUNTY AND EVENTUALLY WEST OF THERE IF IT DOES NOT DIE
OUT COMPLETELY. INLAND PENETRATION DIFFICULT TO ASSESS BUT COULD SEE
SOME SNOW SHOWERS INTO SOUTH BEND. EXPECT ACCUMULATIONS GENERALLY AN
INCH OR LESS BUT THESE MESO LOWS HAVE A TENDENCY TO CARRY BRIEF
BURSTS IN MORE EXTREME DELTA T ENVIRONMENTS. COULD SEE SOME LOCALLY
HEAVIER AMOUNTS BUT WILL HAVE TO MONITOR TRENDS THIS EVENING.
OPERATIONAL MODELS REMAIN IN SURPRISINGLY GOOD AGREEMENT FOR
UPCOMING WINTER STORM SYSTEM AS THEY HAVE FOR LAST COUPLE DAYS.
CONCERN THOUGH AS ENSEMBLE FORECASTS FROM SREF AND NCEP CLUSTER
CONTINUE TO DIVERGE WITH SURFACE LOW TRACK AND THUS PLACEMENT OF
HEAVY SNOW POTENTIAL.
GFS AND CMC ENSEMBLES HAVE SEVERAL PERTURBATIONS INDICATING SURFACE
LOW TRACK FURTHER SOUTH ACROSS NORTH CENTRAL INDIANA INTO NORTHWEST
OHIO AND HAVE BEEN SHOWING THIS FOR SEVERAL RUNS..BUT A GRADUAL
TREND NORTH IN LAST FEW RUNS. MEANWHILE...SREF ENSEMBLES ARE RATHER
TIGHTLY CLUSTERED AROUND A MORE NORTHERN TRACK THROUGH NORTHEAST
IL...SOUTHEAST WI AND CENTRAL MICHIGAN...SIMILAR BUT A BIT NORTH OF
OPERATIONAL NAM AND GFS. ECMWF WHICH HAD BEEN A SOUTHERN TRACK
PROPONENT SHIFTED NORTH TOWARD OTHER OPERATIONAL MODELS WITH ITS 00Z
RUN AND CONTINUES THERE WITH ITS 12Z RUN. HENCE FOCUS ON OPERATIONAL
MODELS INDICATE GOOD CONFIDENCE IN NORTHERN STORM TRACK ACROSS OUR
FAR NORTHWEST AREA. THE SOUTHERN ENSEMBLE SOLUTIONS ARE SOURCES OF
CONCERN THAT CONTINUE TO LEAD TO A LITTLE HEDGING AT THIS FORECAST
PROJECTION TIME. GIVEN OUR LOCAL STUDY OF NEGATIVELY TILTED SYSTEMS
HELPING TRACK SURFACE LOWS FARTHER NORTH...THIS GIVES US MORE
CONFIDENCE IN THE NORTHERN CLUSTER OF SOLUTIONS.
PREVIOUS GRID FORECASTS HAVE TRENDED TOWARD THE NORTHERN SOLUTIONS
WITH A BIT OF HEDGE TO THE SOUTHERN POSSIBILITIES GIVEN THE NUMBER
OF GFS ENSEMBLE MEMBERS THAT HAVE CONTINUED TO SHOW THIS. HAVE NO
REASON OR NEED TO DEVIATE FROM THIS IDEA. PLAN TO STAY WITH IDEA OF
MID LEVEL 850MB AND 700MB LOW TRACKS WELL TO OUR NORTHWEST ACROSS
NORTHERN IL AND WI INTO CENTRAL MI...WHERE HEAVIEST SNOW BAND WILL
FOLLOW. OUR AREA RELEGATED TO WARM AIR ADVECTION SURGE AND
PRECIPITATION DEVELOPMENT IN THIS REGION WHEN COLD AIR WILL STILL BE
ENTRENCHED...ESPECIALLY NORTH. CHALLENGE WILL LIE WITH HOW FAST WARM
SURGE MOVES NORTH AND HOW FAST PCPN WILL DEVELOP IN COLD AIR BEFORE
WARM AIR CHANGES PCPN OVER TO RAIN MOST AREAS. LEANING TOWARD NAM12
AND SREF SOLUTIONS OF MOISTENING LOWER LEVELS TUE AFTERNOON WITH
SNOW DEVELOPING AS THERMAL PROFILES REMAIN BELOW 0C. A QUICK BURST
OF SNOW WITH ACCUMULATIONS FROM 1 TO 3 INCHES EXPECTED FROM TUE AFTN
TO TUE EVENING WITH LIGHTER AMOUNTS IN SOUTHERN AREAS AND HEAVIER
AMOUNTS FAR NORTH. WARM SURGE ON NOSE OF 50KT LOW LEVEL JET SHOULD
QUICKLY TURN SNOW TO RAIN JUST ABOUT OVER ENTIRE AREA DURING THE
EVENING PER 12Z NAM AND 09Z SREF SOLUTIONS. BUFKIT SOUNDINGS SUGGEST
AN HOUR OR TWO OF FREEZING RAIN AND SLEET POSSIBLE WITH LIGHT ICING.
THIS REASONABLE AND ESPECIALLY IN LIGHT OF ROADS TODAY SHOWING ICING
WITH MELTING LIGHT SNOW THAT FELL. THUS HAVE ADDED A MENTION OF
LIGHT FREEZING RAIN TO NORTHERN AREAS BEFORE TRANSITION TO ALL RAIN.
NO HEADLINES PLANNED WITH THIS PACKAGE BUT EXPECT ADVISORIES MAY BE
NEEDED WITH MIXED PRECIPITATION.
FINALLY BY LATE TUE NIGHT SURFACE LOW MOVES TO CENTRAL LAKE MICHIGAN
AND DEEPENS RAPIDLY ALLOWING ISALLOBARIC WIND TO INCREASE IN ITS
WAKE. THIS WILL HELP SURGE COLD AIR IN FROM WEST WITH POSSIBLE
CHANGEOVER TO SNOW AGAIN IN WEST. DRY SLOT BEING DEPICTED TO BE
QUITE STRONG AND FAST BY NAM12 AND SREF AND THIS MAY LIMIT
ADDITIONAL ACCUMS. HOWEVER...WINDS WILL INCREASE IN 25 TO 35 MPH
RANGE WITH GUSTS TO AROUND 40 MPH POSSIBLE LATE TUE NIGHT.
&&
.LONG TERM...
PRECIPITATION WILL BE ONGOING ACROSS THE CWA AT THE ONSET OF THE EXTENDED
ALTHOUGH THERE IS SOME DOUBT AS TO COVERAGE AS 12Z MODELS PULL DRY
SLOT INTO THE AREA WHICH WILL NEED TO BE REASSESSED. FOR NOW KEPT
LIKELY POPS ON WED AS SFC LOW TRACK IS STILL TOO UNCERTAIN TOO ADD
GRANULAR DETAIL. CHANGED WORDING AFTER 18Z TO SHOWERS AS BACK SIDE
OF THE SYSTEM SPORTS LESS WRAPAROUND AND PERSISTENT PRECIP IS LESS
LIKELY THAN A SHOWERY NATURE. AS SFC LOW WORKS INTO SOUTHERN LOWER
MICHIGAN COLD AIR MAKES A RETURN CHANGING PTYPE BACK TO SNOW FROM
WEST TO EAST. PREFER NAM/SREF FOR TRACK/TIMING AS THEY HAVE THE
FURTHEST NW SFC LOW TRACK WITH NAM BUFR SOUNDINGS AND SREF TEMP PROFILES
BRINGING PHASE CHANGE INTO THE NW AFTER 12Z AND THROUGH THE ENTIRE CWA
BY 21Z. AMOUNTS RECEIVED ON THE BACK SIDE OF THIS SYSTEM SHOULD BE
LIGHT...BUT STRONG WINDS WILL COMPLICATE MATTERS SIGNIFICANTLY IF
ANYTHING SUBSTANTIAL IS RECEIVED. STRONG PRESS RISE/FALL COUPLET FLANKING
THE CWA WITH WINDS 25-30 MPH AND HIGHER GUSTS HAS PROMPTED THE
ISSUANCE OF A HIGH WIND WATCH.
AS VERY COLD AIR FOLLOWS IN SYSTEMS WAKE...H85 TEMPS DOWN TO -20C
SETS UP IMPRESSIVE DELTA T/S FOR LAKE RESPONSE. FETCH IS WESTERLY
WHICH RELEGATES MAJOR IMPACT TO NORTHERN TIER OF COUNTIES...AND WIND
SPEEDS OVER THE LAKE ARE QUITE FAST FOR SUCH A SHORT FETCH
SIGNIFICANTLY REDUCING RESIDENCE TIME OVER THE LAKE....SO SNOW
FORECAST REMAINS CONSERVATIVE AT THIS TIME.
TEMPS WILL TAKE A PLUNGE AS COLD AIR MASS MOVES IN QUICKLY. MEX
GUIDANCE DOES NOT GET SOUTH BEND OUT OF THE TEENS ON THURSDAY WITH
LOW 20S IN THE SOUTHEAST. WITH WINDS AROUND 20MPH THURSDAY WILL
BE A RAW DAY INDEED. SLOW RECOVERY IN TEMPS BACK TO NEAR FREEZING
FOR HIGHS BY THE WEEKEND WITH A WEAK WAVE KEEPING SNOW CHANCES IN
THE GRIDS FOR SATURDAY.&&
.AVIATION...18Z TAFS
WEAK ASCENT NOW EAST OF THE FA...ASSOCIATED WITH A LEAD
SHRTWV...HAS ALLOWED THE WIDESPREAD -SN TO COME TO AN END...WITH
JUST A FEW LINGERING FLURRIES EXPECTED FOR THIS AFTN. ABUNDANT LOW
LVL MOISTURE NEAR A WEAKENING CDFNT JUST WEST OF THE FA HAS
ALLOWED WIDESPREAD MVFR AND PATCHY IFR CIGS TO ENGULF MUCH OF
INDIANA WESTWARD INTO IL AND EASTERN IA. EXPECT SOME GRADUAL
IMPROVEMENT TO AT LEAST HIGH END MVFR CIGS/VIS AT FWA THIS AFTN
WITH NORMAL DIURNAL EFFECTS AND DRYING ALOFT. TOUGHER FCST AT SBN
AS LAKE EFFECT PROCESS LOOKS TO DOMINATE. ALREADY ENOUGH
MIXING/INSTABILITY TO BREAK UP THE STRATUS WITH VFR CIGS AS OF
17Z. THINK THIS WILL FILL IN WITH TIME YIELDING AT LEAST HIGH END
MVFR CONDITIONS AFTER 19/20Z. BNDRY LAYER FLOW WILL VEER MORE
WESTERLY BEHIND THE WEAK CDFNT BY LATE THIS AFTN AT SBN...ALLOWING
FOR SOME LAKE EFFECT SNOW SHOWERS AND MVFR CIGS/VIS THIS EVENING.
WILL LIKELY SEE A PERIOD OF IFR CIGS/VIS BUT NOT ENOUGH CONFIDENCE
TO ADD.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...HIGH WIND WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY
NIGHT FOR INZ003>009-012>018-020-022>027-032>034.
MI...HIGH WIND WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY
NIGHT FOR MIZ077>081.
OH...HIGH WIND WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY
NIGHT FOR OHZ001-002-004-005-015-016-024-025.
LM...GALE WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY EVENING FOR
LMZ043-046.
&&
$$
SHORT TERM...LASHLEY
LONG TERM...LUDINGTON
AVIATION...STEINWEDEL
