FXUS61 KCAR 221603
AFDCAR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CARIBOU ME
1103 AM EST TUE DEC 22 2009

.SYNOPSIS...
A TROUGH OF SURFACE LOW PRESSURE EXTENDING NORTHWEST FROM LOW
PRESSURE WELL EAST OF NOVA SCOTIA WILL SLOWLY BACK WESTWARD INTO
THE REGION TODAY THROUGH WEDNESDAY AS AN UPPER LEVEL LOW FROM
EASTERN ONTARIO SLIDES SOUTHEAST INTO THE GULF OF MAINE. THE
TROUGH WILL WEAKEN LATE WEDNESDAY AS HIGH PRESSURE SLOWLY BUILDS
OVER THE AREA WEDNESDAY NIGHT AND THURSDAY.
&&

.NEAR TERM /THROUGH TONIGHT/...
DECISION WAS TO DROP OFF MEZ029 FROM THE WARNING AND ADJUST
SNOWFALL AMOUNTS A BIT FURTHER NORTH ACROSS NORTH CENTRAL MAINE.

UPDATED THE GRIDS AND ZFP TO GO W/OCNL SNOW THIS MORNING ACROSS
THE NORTHERN 1/2 OF THE CWA. SOME LIGHT FREEZING DRIZZLE HAS MIXED
IN AT TIMES ACROSS THE HOULTON AND MILLINOCKET AREAS AND INCLUDED
THIS WORDING AS WELL. TEMPERATURES WERE ADJUSTED TO FIT CURRENT
CONDITIONS.

A TROUGH EXTENDING BACK FROM THE STRONG STORM SYSTEM EAST OF THE
MARITIMES IN COMBINATION WITH A POTENT UPPER LEVEL DISTURBANCE
WILL BRING A MODERATE TO HEAVY SNOWFALL ACROSS MUCH OF NORTHERN
AND DOWNEAST MAINE. THE MAIN CHALLENGE WILL BE WITH REGARD TO
FORECASTING THE AXIS OF HEAVIEST SNOWFALL BANDING. APPEARS AS IF
THE HEAVIEST SNOW BAND WILL SET UP ON A NORTHWEST TO SOUTHEAST
AXIS LATE TONIGHT IN ASSOCIATION WITH STRONG FGEN FORCING AND
CONVERGENCE ALONG THE TROF EXTENDING BACK ACROSS THE AREA. EXPECT
THE STEADIEST SNOW TO OVERSPREAD THE FA IN EARNEST LATER THIS
AFTERNOON AND THEN CONTINUE INTO THIS EVENING HEAVY AT TIMES
OVERNIGHT...AS HEAVIEST AXIS OF SNOW SINKS SOUTH. OF COURSE THE
KEY TO THE UPCOMING FORECAST WILL BE WITH REGARD TO THE EXACT
ORIENTATION AND WIDTH OF THE HEAVIEST SNOW BANDING...SINCE ANY
DEVIATION CAN RESULT IN A SHARP GRADIENT IN THE FORECASTED
SNOWFALL AMOUNTS. 

GFS AND NAM TM SECTIONS INDICATE DENDRITES AND SECTOR PLATES
DOMINATING SN CRYSTAL DEVELOPMENT IN THE VICINITY OF THE BEST LIFT
AND FRONTAL ZONE TNGT INTO WED MORN WITH WEAK NEGATIVE EQUIVALENT
POTENTIAL VORTICITY INDICATING SOME INSTABILITY ALG THE UPPER PTN
OF THE FRONTAL SFC ALF. LIQ EQUIV-SN RATIOS MAY REACH CLOSE TO 20:1
ATTMS JUST E OF THE CNTRL ME HIGHLANDS WHERE IN ADDITION TO THE
AFOREMENTIONED MICRO-CLD PHYSICS...TERRAIN SHADOWING MAY LOWER
WIND SPEEDS IN THIS AREA...RESULTING LESS FRACTURING OF SN CRYSTALS.
&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
CONSENSUS OF LATEST MODELS INDICATES MODERATE TO HEAVY SNOW
BANDING CONTG OVR CNTRL PTNS OF THE THE FA INTO THE MORN HRS
WITH SNFL HVY ATTMS REFERENCED BEFORE THE BANDING STRUCTURE
BEGINS TO BREAK DOWN DURING THE AFTN HRS. HEAVIEST STORM TOTALS
WILL LIKELY REACH THE 12 TO 20 INCH RANGE IN A ZONE EXTENDING FROM
THE NW TO SE PTN OF THE FA...CENTERED OVR THE E CNTRL ME HIGHLANDS
AND ADJACENT AREAS JUST E OF THESE HIGHLANDS WHERE A COMBO OF
HIGHER TERRAIN ENHANCED QPF AND SN RATIOS WILL CONTRIBUTE TO THESE
TOTALS. FURTHER N AND E...TOTALS BECOME MORE UNCERTAIN WITH
CONSTRAINTS OF BAND WIDTH AND PSN PLAYING CRITICAL ROLES IN THE
UPCOMING EVENT.

ANY STEADY SNFL ERLY WED EVE WILL TAPER TO SCT SN SHWRS LATER WED
NGT AND SHOULD END BY THU AS BOTH THE SFC TROF AND UPPER LOW MOVE
SE FROM THE REGION. WHATS LEFT OF THE SFC HIGH FROM THE LARGE
UPPER LVL BLOCK THAT HAS RESIDED OVR NRN CAN WILL RIDGE INTO THE
FA ON THU...BRINGING AT LEAST PTL CLRG TO THE FA AND A REPLACEMENT
OF THE SEMI ATLC MARITIME AIR WITH SOMEWHAT COOLER DRIER AIR.
&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
THE ONLY CHGS MADE TO THE LONG TERM WAS TO RAISE LOW TEMPS FOR
SAT NGT AND POPS TO LIKELY CATEGORY AS WELL AS INTRODUCE MIXED
PRECIP FOR CNTRL AND RAIN FOR DOWNEAST AREAS THIS PD. DUE TO TIME
CONSTRAINTS IN PREPARING FCST GRIDS FOR UPCOMING SNOW EVENT FOR
LATER TDY INTO WED...THE REST OF THE LONG TERM WAS LEFT UNCHGD.
&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
NEAR TERM: EXPECT WIDESPREAD IFR AND AT TIMES LIFR CONDITIONS TO
SPREAD ACROSS ALL THE TAF SITES LATE TODAY AND CONTINUE THROUGH
TONIGHT.

SHORT TO LONG TERM: IFR WILL CONT WED MORN IN SN WITH SLOW N TO S
IMPROVEMENT TO MVFR WED AFT/NGT. VFR SHOULD RETURN TO ALL SITES BY
THU AND CONT INTO SAT MORN...BEFORE LOWERING TO MVFR IN MIXED
PRECIP LATE SAT.
&&

.MARINE...
NEAR TERM: EXPECT SCA CONDITIONS TO CONTINUE INTO THIS
AFTERNOON. WINDS WILL DIMINISH LATER THIS AFTERNOON AS TROF
CROSSES THE WATERS AND GRADIENT RELAXES.

SHORT TERM TO LONG TERM: MSLY SCA OR NO HDLNS DURG THIS PD...WITH
THE NEXT CHC OF GALES SAT NGT AHEAD OF SECONDARY LOW PRES XPCTD TO
TRACK E OFF THE CNTRL ME COAST.
&&

.CAR WATCHES/WARNINGS/ADVISORIES...
ME...WINTER STORM WARNING UNTIL 3 PM EST WEDNESDAY FOR MEZ001-002.
     WINTER STORM WARNING UNTIL 6 PM EST WEDNESDAY FOR MEZ003>006-
     010-011-031-032.
     WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 1 AM EST 
     THURSDAY FOR MEZ015>017-030.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR 
     ANZ050>052.

&&

$$
NEAR TERM...HEWITT/MWALKER
SHORT TERM...VJN
LONG TERM...VJN
AVIATION...HEWITT/MWALKER
MARINE...HEWITT/MWALKER/VJN