000
FXUS63 KIWX 061155
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
655 AM EST TUE JAN 6 2009
.AVIATION...
LWRG CLOUD COVER/PRECIP RACING NEWD AND EXPANDING HAS LEAD TO
EARLIER START TIME FOR PRECIP ACRS NRN IN THIS AM. SHALLOW COLD LYR
TRAPPED NEAR SFC WITH WARM LAYER ALOFT AROUND 3-6KFT IN NERN IN TO
LKLY LEAD TO MIXED FREEZING AND FROZEN PRECIP FOR KFWA...MORE
SHALLOW WARM LYR FOR PRIMARILY FROZEN PRECIP AT KSBN SPCLY
TODAY...HOWEVER TONIGHT AS MSTR DEPTH BECOMES MORE SHALLOW
ANTICIPATE LACK OF ICE IN CLOUDS/SUPERCOOLED DROPLETS FOR LKLY LIGHT
FREEZING DRIZZLE/LIGHT SNOW MIX AS PRIMARY PTYPE. AS LLVLS SATURATE
IN PRECIP AS WARM/MOISTER AIR RIDES NWD CIGS WILL DETERIORATE WITH
TIME...AND HIGH CONFIDENCE FOR CIGS DOWN TO IFR RANGE WIDESPREAD
ACRS NRN BY EVENING AND MAINTAIN THRU NIGHT WITH MINIMAL STEERING
FLOW/DRYING AVAILABLE TO USURP TRAPPED MSTR BLO 5KFT INVERSION.
&&
.SHORT TERM...
INITIAL SHORTWAVE MOVG RAPDLY NEWD FM CNTL IL THIS AM WITH ZR/IP
REPORTS...HAVE UPPED ONSET TIME OF MIXED PRECIP. LEAN TWRD NAM
OVERALL...THOUGH WITH HIGHLY MENTAL MOD OF PRECIP GIVEN MSTR
XPORT ALONG I285K ISENT SFC WITH BROAD/GT 5 G/KG MSTR TAP
PERSISTING FM MO BOOTHILL NEWD INTO UPR OH VLY TDY. WARM LYR NEAR
825MB EDGING SLIGHTLY NWD TODAY...AS MIDLVL TROF TRANSITIONS FRM
HIGH POS TO NEUTRAL AXIS WILL AND WITH INITIAL MIX HAVE OPTED TO
HOIST A WINTER WX ADV WITH A BIT OF A HEDGE FARTHER NW ON NW
BORDER COUNTIES AND WITH INITAL MIX INTO CNTL IL LKLY OK...NW OF
ADVISORY ENTIRE DEPTH BLO 0 FOR A PRIMARILY LIGHT SNOW/SLEET EVENT
AND OPT OUT OF ADV. OPEN 7H TROF WITH LACK OF CENTRIC 12HR FALL
CENTER TO PROVIDE NO COHERENT/DOMINANT SFC REFLECTION TIL NRN AND
SRN PLAINS AND SEPARATE TN VLY WEAK SFC LOWS CONGEAL ACRS LWR
GRTLKS WED AFTN. SUBSEQUENTLY A RAPID ENERGY XFER IS UNDERWAY INTO
NRN NEW ENGLND COASTAL STORM DVLPMNT. MSTR DEPTH A CONCERN FOR
THIS FIRST EVENT... SPCLY TONIGHT WHEREAS TOTAL SNOW AMNTS WILL BE
HINDERED BY SHALLOW MOISTURE DEPTH LEADING TO FAILED TOTAL ICE
INTRODUCTION... MARGINALIZING LIQUID SNOW RATIOS...THUS HAVE
SCALED BACK FROM PREV FCST TOTAL EVENT SNOW TOTALS.
GFS APPEARS TOO STRONG WITH 7H COLD POOL DIVING SEWD INTO WRN/SRN
GRTLKS IN F36-54 TIMEFRAME...LEADING TO OVERESTIMATION OF MSTR
DEPTH AND WED SNOW POTL. FAVOR A MORE SUBDUED MSTR
PROFILE...THOUGH CYCLONIC LLVL FLOW WITH SECONDARY FRONT/TROF
PASSAGE WILL STILL MAINTAIN AT LEAST MID RANGE POPS/LOW
QPF...OUTSIDE OF FAVORED LAKE ENHANCED AREA FAR NRN TIER.
&&
.LONG TERM...
THURSDAY THROUGH MONDAY
VERY LITTLE CHANGES MADE TO THE EXTENDED PERIOD AS PREVIOUS FORECAST
REMAINS ON TRACK. BUILDING EASTERN PACIFIC RIDGE WILL SUPPORT MEAN
TROUGHING OVER THE EASTERN HALF OF THE CONUS...A CHARACTERISTIC OF A
STRONG POSITIVE PNA REGIME. THIS WILL SUPPORT ACTIVE NW FLOW WITH
SEVERAL CLIPPER EXPECTED TO IMPACT THE REGION AS NUMEROUS HEIGHT
ANOMALIES WILL EJECT OUT OF THE GULF OF ALASKA DEEP UPPER TROUGH.
MEAN SOLUTIONS OF THE NAEFS AND GEFS ALONG WITH THE DETERMINISTIC
RUNS OF THE GFS ARE HOLDING TOUGH ON THE ARRIVAL OF A LARGE H85
NEGATIVE T ANOMALY THIS WEEKEND. H85 T/S DOWN TO -20 C OVER THE
NORTHERN FA ARE PROGGED IN THE 00Z GFS...WITH 18Z MEAN ENSEMBLE RUNS
INDICATING SLIGHTLY WARMER SOLUTION DOWN TO -18C. THE ECMWF HAS BEEN
WAVERING ON THE INTENSITY OF THE CAA AND HAS DRASTICALLY WARMED H85
T/S SOME 7C OVER THE NORTHERN FA AT 00Z SUN WITH THE 00Z RUN. HAVE
PARTLY DISCOUNTED THIS SOLUTION GIVEN THE INCONSISTENT NATURE OF THE
ECMWF IN THIS PERIOD. ALTHOUGH THIS DOES INDICATE UNCERTAINTY IS
PRESENT...AND HAVE NOT WENT WITH A STRAIGHT GFS/NAEFS/GEFS SOLUTION
AS OF YET. GEFS CONFIDENCE GRAPHICS PER FSU ARE INDICATING NEAR
NORMAL CONFIDENCE IN THIS PERIOD....WITH ENSEMBLES CONVERGING ON A
DEEP H5 HEIGHT ANOMALY OVER THE GREAT LAKES BY DAY 6...FURTHER
SUPPORTED BY CIPS WINTER STORM ANALOG GUIDANCE. GIVEN THE
INTENSITY OF THE PACIFIC JET IN PLACE...TELECONNECTIONS WOULD EXPECT
A SHIFT TO A NORTHERLY FLOW DOMINATED REGIME...WITH MEAN THERMAL
FIELDS LOWERING LOCALLY WITH EACH CLIPPER PASSAGE...ESPECIALLY IF A
SNOW FIELD IS ESTABLISHED.
THUR...FIRST WAVE OF CAA WILL SUPPORT COLD CONDITIONS WITH LAKE SNOW
ONGOING AT THE STAR OF THE PERIOD. HAVE INCREASED POPS TO LIKELY
IN THE NW PER A DECENT H85 DELTA T/MODEST INVERSION HEIGHTS/AND LONG
FETCH NORTHERLY FLOW...SUPPORTING MODEST ACCUMS. THINGS WILL WIND
DOWN DURING THE DAY WITH FLOW BACKING WESTERLY AND INVERSION HEIGHTS
CRASHING.
FRI...CLIPPER SYSTEM WILL AFFECT THE REGION...WITH SNOW EXPECTED IN
THE WARM CONVEYOR BELT OF THE SYSTEM FRI...MAINLY IN THE NORTH WHERE
ASCENT AND FORCING WILL BE MAXIMIZED. HAVE RAISED POPS TO 50 IN THE
NE...WHERE A QUICK COATING TO AN INCH WILL BE POSSIBLE. WAA WILL
ALLOW SFC TEMPS TO INCREASE TO OR SLIGHTLY ABOVE FREEZING FRI NIGHT
AHEAD OF THE SFC TROUGH. GIVEN PROGGED THERMAL PROFILES
ALOFT...INDICATING SATURATION CONFINED BELOW THE ICE PRODUCTION
ZONE...HAVE ADDED CHANCE DRIZZLE MENTION...A COMMON CHARACTERISTIC
OF CLIPPER LOW ADVECTING OVER THE REGION.
SAT-MON...STRONG CAA BEHIND THE ADVANCING CLIPPER WILL ALLOW TEMPS
TO FALL INTO THE TEENS BY AFTERNOON ACROSS MUCH OF THE REGION.
STRONG PRESSURE GRADIENT IN PLACE/STRONG LL FLOW JUST OFF THE
SFC/COUPLED WITH STEEP LL LAPSE RATES WILL SUPPORT STRONG WESTERLY
WINDS. THIS MAY POSE A BLOWING SNOW THREAT IF SNOW PACK IS
ESTABLISHED AND REMAINS LOOSE DESPITE TEMPS WARMING TO NEAR 32F FRI
NIGHT. OTHERWISE...LAKE EFFECT SNOW SHOWERS ARE EXPECTED OVER THE
NW...BUT VERY DRY LL FLOW UPSTREAM /H85 RH AROUND 20 PERCENT WITH 20
TO 30 KNOTS OF SHEARED FLOW/ MAY HIGHLY LIMIT INTENSITY OF LK SNOWS
IF FLOW REMAINS LARGELY WESTERLY. EXPECT ANOTHER CLIPPER SYSTEM BY
EARLY NEXT WEEK WITH SNOW CHANCES ONCE AGAIN BY MON. HAVE KEPT T/S
SOME 10 TO 15 DEGREES F BELOW CLIMO...IN LINE WITH GFS/NAEFS/GEFS
PROGS...AND CIPS WINTER STORM ANALOG GUIDANCE.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 5 AM EST
WEDNESDAY FOR INZ008-009-018.
WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 5 AM EST
WEDNESDAY FOR INZ013-015>017-020-022>027-032>034.
MI...NONE.
OH...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 5 AM EST
WEDNESDAY FOR OHZ001-002-004-005-015-016-024-025.
LM...SMALL CRAFT ADVISORY FROM 1 PM WEDNESDAY TO 7 PM EST THURSDAY
FOR LMZ043-046.
&&
$$
SHORT TERM...MURPHY
LONG TERM...JC
AVIATION...MURPHY
