-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 081800
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
100 PM EST SUN DEC 8 2013

.SYNOPSIS...

LARGE HIGH PRESSURE WILL SETTLE OVER NEW ENGLAND TODAY. ANOTHER
LOW PRES MOVING UP FROM THE SOUTH WILL BRING A WINTRY MIX OF
PRECIPITATION LATE TONIGHT INTO MON. DRY AND UNSEASONABLY COLD
WEATHER FOLLOWS FOR THE MIDDLE AND END OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

-- Changed Discussion --
1 PM UPDATE...

WILL HOLD OFF ON ANY FURTHER DISCUSSION UNTIL THE 4 PM FORECAST
ISSUANCE.

PREVIOUS DISCUSSION...

LOOKING DOWNSTREAM WITH THE 12Z OKX /UPTON NY/ SOUNDING...LOTS OF
DRY AIR BELOW H5 AS THE ENTIRE COLUMN REMAINS BELOW FREEZING.
NORTHERLY FLOW PREVAILING AT THE SURFACE SUSTAINING COLD AND DRY
AIR OVER SOUTHERN NEW ENGLAND. THOUGH SURFACE HIGH PRESSURE
REMAINS IN CONTROL...BROAD-SCALE DIFFLUENCE ASSOCIATED WITH THE
UPPER-LEVEL JET IS ALLOWING FOR ISENTROPIC LIFT OF SUB-TROPICAL
FLOW /PER WATER VAPOR SATELLITE/ OVER THE COLD DOME OF AIR ACROSS
THE REGION. EXTENSIVE CLOUD COVER HAS RESULTED.

PER RADAR...PRECIPITATION ALONG AND SOUTH OF SOUTHERN NEW ENGLAND
HAVING DIFFICULTY MOVING NORTH. CLOSEST REPORTS OF PRECIPITATION
REACHING THE GROUND ARE JUST NORTH OF WASHINGTON DC /THAT BEING OF
SNOW/. OF MORE IMPORTANT NOTE IS THE OBVIOUS SIGNAL OF COLD-AIR
DRAINAGE SOUTHWARD FROM THE HIGH TOWARDS THE DEVELOPING LOW.
EXPECTING A SIMILAR OUTCOME IN SIGNAL ACROSS SOUTHERN NEW ENGLAND
AS THE LOW DRIFTS NORTH AND EAST TOWARDS THE CAPE. WILL HOLD OFF
POPS INTO THE SOUTHERN-MOST REGION UNTIL SUN-DOWN. DOWNSTREAM
SNOW/S COMBINED WITH THE EXTENSIVE CLOUD COVER AT OR ABOVE SNOW
GROWTH REGIONS GIVE CONFIDENCE TO THE LATER FORECAST OF SEEING A
PERIOD OF SNOW TONIGHT INTO MONDAY.

CLOUD COVER AND COLD AIRMASS ACROSS THE REGION...WILL CONTINUE
WITH HIGHS AROUND THE LOW-30S /WARMER ALONG THE SHORES/.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...

STRONG HIGH PRES RETREATS NE INTO THE MARITIMES AND WILL SUPPLY
LOW LEVEL COLD AIR FOR A WINTRY MIXED PRECIP EVENT LATER TONIGHT
INTO MONDAY AS MILDER AIR STREAMS IN ALOFT. MODEL GUIDANCE IN GOOD
AGREEMENT WITH TRACK OF A WEAK COASTAL LOW ACROSS SE NEW ENG
MONDAY AND ALSO SUGGEST A LIGHT TO MODERATE QPF EVENT WITH QPF
LESS THAN 0.50".

THERE ARE RED FLAGS WHICH INDICATE THIS WILL NOT BE A SIGNIFICANT
QPF EVENT. WHILE PWATS ARE MODEST...U-WIND ANOMALIES ARE NEUTRAL
AND THE COLUMN NEVER SATURATES WITH ONLY MODEST FORCING FOR
ASCENT. IN FACT...MOISTURE IN THE SNOW GROWTH REGION WHICH IS
ABOVE 700 MB IS RATHER LIMITED FOR THE EVENT. HOWEVER...LOW
LEVELS ARE QUITE COLD AT THE ONSET OF THE PRECIP AND ICE
GENERATION MAY INITIALLY OCCUR BELOW 850 MB SUPPORTING A PERIOD
OF SNOW AT THE ONSET.

MODEL DIFFERENCES IN THE THERMAL PROFILE EXIST...PARTICULARLY IN
THE LOW LEVELS. GFS IS QUICKEST TO ERODE LOW LEVEL COLD AIR AND IS
LIKELY TOO FAST GIVEN COLD AIR DAMMING SIGNATURE. NAM/ECMWF HOLD
ON TO THE COLD AIR LONGER WHICH SEEMS MORE LIKELY AS TRACK OF LOW
PRES SUPPORTS LIGHT N/NE WINDS IN THE INTERIOR WHICH WILL MAKE IT
DIFFICULT TO SCOUR OUT THE COLD AIR. MEANWHILE MODELS AGREE THAT
WARMER AIR ALOFT AROUND 800 MB WILL QUICKLY LIFT NORTH ACROSS THE
REGION LATE TONIGHT THROUGH MONDAY SETTING THE STAGE FOR A PERIOD
OF SLEET AND FREEZING RAIN.

PROFILE IS COLD ENOUGH FOR PRECIP TO BEGIN AS SNOW EVERYWHERE
INCLUDING THE S COAST. ONSET OF SNOW WILL BE AROUND OR JUST BEFORE
MIDNIGHT IN THE S AND WELL AFTER MIDNIGHT NE MA AND S NH.
HOWEVER...WARMING ALOFT WILL RESULT IN A GRADUAL CHANGEOVER TO
SLEET...FREEZING RAIN AND RAIN FROM SOUTH TO NORTH...AROUND 09Z S
COAST...12-15Z MASS PIKE REGION AND 18Z S NH. THE TRANSITION TO
PLAIN RAIN WILL BE QUICKEST ALONG THE COAST AS EAST WINDS QUICKLY
WARM THE BOUNDARY LAYER.

SNOW ACCUM WILL LIKELY BE LIMITED TO AN INCH OR 2 AWAY FROM THE
COAST WITH LOCALLY HIGHER AMOUNTS IN THE BERKSHIRES AND
MONADNOCKS...BUT THE GREATER CONCERN IS FOR A PERIOD OF FREEZING
RAIN AND FREEZING DRIZZLE. BEST CHANCE FOR MINOR ICE ACCUM WILL BE
ACROSS THE CT VALLEY INTO CENTRAL MA...BUT SOME ICING IS POSSIBLE
INTO THE COASTAL PLAIN LATE TONIGHT INTO MON MORNING...ESPECIALLY
RI AND INTERIOR SE MA BEFORE CHANGING TO RAIN.

WE ISSUED WINTER WEATHER ADVISORIES FOR MUCH OF THE REGION AWAY
FROM THE IMMEDIATE COAST AND AS FAR SE AS PVD-TAN AS TIMING OF
FZRA COULD AFFECT THE MORNING COMMUTE. AFTER COORD WITH GYX WE
HELD OFF ON AN ADVISORY FOR S NH DUE TO LATER TIMING

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...

HIGHLIGHTS...

*MAINLY DRY AND COLD AFTER PRECIP ENDS MON EVENING
*   UNCERTAINTY FOR THE WEEKEND

OVERVIEW AND MODEL PREFERENCES...
08/00Z MODEL GUIDANCE CONTINUES TO SHOW GOOD SYNOPTIC SCALE
AGREEMENT THROUGH THE END OF THE WEEK...WITH SIGNIFICANT
TIMING/AMPLITUDE DIFFERENCES BY THE WEEKEND. GIVEN THE AGREEMENT A
GENERAL CONSENSUS BLEND OF THE MODELS WILL BE USED AS A BASELINE.
THIS BLEND TAKES INTO ACCOUNT THE EXTREMES IN AN ENVELOPE OF
SOLUTIONS FOR TWO FEATURES OF NOTE...THE FIRST BEING A WEAK
FRONTAL WAVE TUE...AND THE SECOND A STRONGER LONGWAVE TROF
DEVELOPING BY THE WEEKEND AS NOTED BY THE PREVIOUS FORECASTER.

THE BULK OF THE PERIOD WILL BE MARKED BY NEARLY ZONAL FLOW ACROSS
SRN NEW ENGLAND AT THE BASE OF A LONGWAVE TROF STEMMING FROM
HUDSON BAY CUTOFF. THIS FEATURE WILL REMAIN IN PLACE THROUGH MUCH
OF THE WORK WEEK...SUGGESTING A MAINLY DRY AND COLD SETUP FOR THE
AREA DESPITE SEVERAL WEAK SHORTWAVES /AND ATTENDANT CLIPPER
SYSTEMS/ SLIDING THROUGH THE FAST ZONAL FLOW. WX FOR THE WEEKEND
WILL BE DEPENDENT ON STREAM PHASING REGARDING A ROBUST AND
DEEPENING SHORTWAVE WHICH WILL MOVE ONTO THE PACIFIC COAST BY MID-
LATE WEEK. THE TWO EXTREMES IN SOLUTIONS HAVE TO DO WITH WHETHER
THIS WAVE PHASES WITH THE NRN STREAM AND EACH EXTREME ARE PLAYED
IN THE DETERMINISTIC ECMWF AND GFS. THE ECMWF APPEARS TO
PHASE...GENERATING A STRONGER COASTAL SYSTEM. THE GFS DOES NOT
PHASE THE STREAMS...WITH THE NRN WAVE PUSHING ITS ATTENDANT LOW
PRES THROUGH THE ST LAWRENCE VALLEY. GEFS/ECENS MEMBERS ARE LITTLE
HELP AS EACH HAS MEMBERS THAT SUPPORT EITHER SCENARIO. GIVEN THE
PRIMARY SRN STREAM SHORTWAVE IN QUESTION WILL NOT MOVE ONSHORE
UNTIL MID WEEK...ONCE IT IS BETTER OBSERVED BY LAND BASED REMOTE
SENSING AND RAOBS GUIDANCE IS LIKELY TO COME BETTER IN LINE. THE
CONSENSUS BLEND TAKES INTO ACCOUNT BOTH THE COLDER AND WARMER
SOLUTIONS.

DETAILS...

MON NIGHT INTO TUE NIGHT...
COLD FRONT FROM LOW PRES SLIDING THROUGH QUEBEC AND WEAK COASTAL
LOW PRES BOTH BEGIN TO QUICKLY MOVE OFFSHORE ALLOWING STRONG
STACKED NW FLOW TO DEVELOP...INITIATING STRONG COLD ADVECTION. ANY
PRECIPITATION SHOULD RAPIDLY COME TO AN END MON EVENING AS THE
COLD ADVECTION DEVELOPS...LEADING TO PARTIAL CLEARING AND BRISK NW
FLOW. THE KEY TO THIS TIME PERIOD WILL BE THE STALLED FRONTAL
BOUNDARY TO THE S AS IT PARALLELS STEERING FLOW. A WEAK SECONDARY
FRONTAL WAVE LOOKS TO DEVELOP AND SLIDE S OF THE REGION LATE IN
THE DAY TUE...WHICH MAY LEAD TO A FEW -SHSN TO DEVELOP ALONG THE
IMMEDIATE S COAST. ECMWF NOW CLOSER IN LINE TO GFS SHOWING JUST A
SLIGHT BIT OF QPF WITH WEAK DEFORMATION AXIS TO THE N OF THE WAVE.
THEREFORE...WILL MAINTAIN SOME CHANCE POPS FOR S COASTAL
LOCATIONS. SNOW ACCUMS ARE LIGHT AS LIFT IS WEAK AND CONFLUENT
FLOW ALOFT MAY LIMIT COLUMN MOISTURE TO THE NEAR SFC LAYER. TEMPS
LIKELY BEGIN TO DIP BELOW NORMAL...BUT THE MAIN COLD DOME ARRIVES
FOLLOWING THE FRONTAL WAVE.

WED INTO FRI...
LIKELY THE COLDEST PERIOD OF THE WEEK. DRY CP AIRMASS SLIDES IN
PLACE WITH STRONG 1035+ HIGH PRES TO THE W. THE BULK OF THE COLD
AIR RESTS WITH A SECONDARY ARCTIC AIRMASS WHICH LOOKS TO ARRIVE
WED NIGHT-THU ACCOUNTING FOR TIMING UNCERTAINTY. COLUMN VERY DRY
WITH THIS FROPA SO EXPECTING LITTLE IN THE WAY OF PRECIP SAVE FOR
THE POSSIBILITY OF SOME OCEAN EFFECT SNOWS ACROSS CAPE/ISLANDS
DEPENDING ON WIND TRAJECTORY. SST-H85 TEMP DIFFERENCE AS MUCH AS
20C. AM NOTING H85 TEMPS DIPPING TO AN AVERAGE OF -15 TO -18C BY
00Z FRI SUGGESTING TEMPS MAY STRUGGLE TO BREAK OUT OF THE 20S
DURING THE DAY THU. IN ESSENCE...A PERIOD OF DRY BUT ANOMALOUSLY
COLD...WITH TEMPS POSSIBLE 10-15 DEGREES BELOW MID DEC NORMS.

THIS COMING WEEKEND...
AS MENTIONED ABOVE...THE KEY PLAYERS IN THE WEEKEND SOLUTION ARE
YET TO BE FORMED OR PROPERLY SAMPLED SO A LOT OF UNCERTAINTY
EXISTS. HOWEVER...WITH SHORTWAVE ENERGY MOVING IN AND LONGWAVE
TROF ONLY SLOWLY EXITING TO THE N AND E...A PERIOD OF MORE
UNSETTLED WX IS PLAUSIBLE. EXACTLY WHICH TYPE WILL BE DEPENDENT
TRACK OF THE HIGH PRES IN MAINTAINING THE LOW LVL COLD AIR AND THE
TRACK OF ANY ATTENDANT LOW PRES SYSTEMS. TEMPERATURES DO SHOW
SIGNAL OF MODERATION...BUT ONLY SLIGHTLY AS THE LONGWAVE TROF TO
THE N LIFTS OUT.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...

-- Changed Discussion --
FORECASTER CONFIDENCE LEVELS...

LOW...LESS THAN 30 PERCENT.
MODERATE...30 TO 60 PERCENT.
HIGH...GREATER THAN 60 PERCENT.

18Z UPDATE...

WILL UPDATE THE DISCUSSION WITH 21Z TAFS. PRESENT DISCUSSION STILL
APPLIES WITH CURRENT FORECAST THINKING.

PREVIOUS DISCUSSION...

NEAR-TERM /THROUGH MONDAY/...OVERALL HIGH CONFIDENCE. BUT LOWER
CONFIDENCE ON P-TYPE TRANSITION AND TIMING OF LOWER CATEGORIES LATE
TONIGHT INTO MONDAY.

VFR TODAY WITH LOWERING CIGS TO LOW-END VFR LATE. OVERNIGHT...
CIGS CONTINUING TO DROP. EXPECT MVFR-IFR OUTCOMES AS -SN INITIALLY
TRANSITIONS SOUTH TO NORTH DURING THE MORNING HOURS TO -PL/UP/FZRA
TO -RA DURING THE MID-MORNING HOURS INTO MIDDAY. TRANSITIONS TO
OCCUR IMMEDIATELY ALONG THE COASTS AND WORK GRADUALLY TOWARDS THE
INTERIOR. WINTRY MIX MAY HOLD ON THE LONGEST ACROSS THE CT RIVER
VALLEY. WORST OF VSBYS LIKELY WITH -SN. LOWEST CIGS IFR/LIFR...
WITH VLIFR ON ELEVATED TERMINALS. CONDITIONS IMPROVE INTO MONDAY
NIGHT...CIGS LIFTING AND PRECIPITATION ENDS.

KBOS TAF...HIGH CONFIDENCE IN TRENDS. LOW CONFIDENCE IN TIMING OF
PRECIPITATION TRANSITIONS. EXPECTING -SN TO QUICKLY TRANSITION TO
-RA DURING THE MORNING WITH ONSHORE EASTERLY FLOW.

KBDL TAF...HIGH CONFIDENCE IN TRENDS. LOW CONFIDENCE IN TIMING OF
PRECIPITATION TRANSITIONS. -SN WILL GRADUALLY TRANSITION TO A
WINTRY MIX...BUT THAT MIX MAY HOLD LONGER WITH SHALLOW COLD AIR
BELOW-FREEZING OVER THE TERMINAL.

OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...

MON NIGHT...HIGH CONFIDENCE.
MIX OF MVFR/IFR IN REMNANT -SHRA/SHSN/FZRA WILL BE RAPIDLY ENDING
DURING THE EVENING...GIVING WAY TO VFR EVERYWHERE. NW WINDS LIKELY
TO BE GUSTY OVERNIGHT...20+ KT POSSIBLE.

TUE INTO TUE EVE...MODERATE CONFIDENCE.
MAINLY VFR ESPECIALLY AWAY FROM THE S COAST. MVFR/ISOLATED IFR
POSSIBLE IN A FEW SNOW SHOWERS ALONG THE IMMEDIATE S
COAST...CAPE...AND ISLAND TERMINALS.

WED INTO THU...HIGH CONFIDENCE.
MAINLY VFR. COLD FRONT LATE WED COMES THROUGH DRY BUT INCREASES
NW WINDS SOMEWHAT AND MAY LEAD TO ISOLATED MVFR/IFR CONDITIONS IN
OCEAN EFFECT SNOW SHOWERS OVER CAPE COD AND NANTUCKET.
-- End Changed Discussion --

&&

.MARINE...

FORECASTER CONFIDENCE LEVELS...

LOW...LESS THAN 30 PERCENT.
MODERATE...30 TO 60 PERCENT.
HIGH...GREATER THAN 60 PERCENT.

HIGH CONFIDENCE THROUGH MONDAY.

LIGHT WINDS TODAY...THEN INCREASING E WINDS LATE TONIGHT INTO
MONDAY AS COASTAL LOW LIFTS N ACROSS THE WATERS. A PERIOD OF
G25-30 LIKELY...ESPECIALLY S COASTAL WATERS AND WE ISSUED SMALL
CRAFT ADVISORIES. WINDS SHIFT TO WEST LATE MONDAY INTO MON
EVENING.

OUTLOOK...MONDAY NIGHT THROUGH THURSDAY...

MONDAY NIGHT AND TUESDAY...MODERATE TO HIGH CONFIDENCE.

MON NIGHT...MODERATE CONFIDENCE.
WINDS SHIFT TO THE W MONDAY AND GRADUALLY RECEDE BELOW SCA
THRESHOLDS...HOWEVER SEAS REMAIN ELEVATED PARTICULARLY ON THE
OCEAN WATERS AT 6-8 FT. SMALL CRAFT ADVISORIES LIKELY TO CONTINUE.

TUE INTO WED...HIGH CONFIDENCE.
SEAS SLACKEN SOMEWHAT TUE BUT ARE LIKELY TO REMAIN ABOVE SCA
THRESHOLDS ON THE OCEAN WATERS. OVERNIGHT TUE NIGHT...WINDS SHIFT
NW AND INCREASE AGAIN WITH 25-30 KT GUSTS POSSIBLE AND SEAS ONCE
AGAIN BUILD.

THU...MODERATE CONFIDENCE.
AFTER ANOTHER BRIEF LULL...NW WINDS AND SEAS LIKELY TO REMAIN
ABOVE SMALL CRAFT THRESHOLDS.

IN ESSENCE...ALTHOUGH THERE ARE LIKELY TO BE BRIEF PERIODS WHERE
WINDS AND/OR SEAS DROP BELOW SMALL CRAFT ADVISORY THRESHOLDS...IT
IS LIKELY CONDITIONS WILL REMAIN ABOVE SCA THRESHOLDS MUCH OF THE
TIME.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 10 AM EST
     MONDAY FOR CTZ002>004.
MA...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 10 AM EST
     MONDAY FOR MAZ013-017.
     WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 1 PM EST
     MONDAY FOR MAZ002>005-008>012-014-026.
NH...NONE.
RI...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 10 AM EST
     MONDAY FOR RIZ001>004-006.
MARINE...SMALL CRAFT ADVISORY FROM 5 AM TO 1 PM EST MONDAY FOR
     ANZ231>234.
     SMALL CRAFT ADVISORY FROM 3 AM TO 6 PM EST MONDAY FOR ANZ235-
     237-254>256.
     SMALL CRAFT ADVISORY FROM 7 AM TO 6 PM EST MONDAY FOR ANZ250.
     SMALL CRAFT ADVISORY FROM 7 AM TO 1 PM EST MONDAY FOR ANZ251.

&&

$$

SYNOPSIS...KJC/DOODY
NEAR TERM...SIPPRELL
SHORT TERM...KJC
LONG TERM...DOODY
AVIATION...SIPPRELL/DOODY
MARINE...KJC/DOODY