Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 281459
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
959 AM EST SAT FEB 28 2015

.SYNOPSIS...

A FAST MOVING LOW PRESSURE SYSTEM WILL BRING ACCUMULATING SNOW TO
THE REGION LATE SUNDAY INTO SUNDAY NIGHT...WITH THE HIGHEST AMOUNTS
EXPECTED SOUTH OF THE MASSACHUSETTS TURNPIKE AND AWAY FROM THE
IMMEDIATE SOUTH COAST. ANOTHER STORM IS LIKELY TUESDAY NIGHT INTO
WEDNESDAY...WITH SNOW AND MIXED PRECIPITATION LIKELY CHANGING TO
RAIN. COLD AND DRY CONDITIONS RETURN FOR THE END OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...

10 AM UPDATE...

NO MAJOR CHANGES. ONLY MODIFICATIONS TO TEMPERATURES AND
DEWPOINTS TO BRING THEM MORE IN-LINE WITH TRENDS.

PREVIOUS DISCUSSION...

HIGH PRESSURE OVERHEAD WILL ALLOW FOR SUNNY SKIES AND LIGHT WINDS.
TEMPERATURESS SHOULD RECOVER INTO THE MIDDLE TO UPPER 20S IN MOST
LOCATIONS...BUT THAT IS STILL AROUND 15 DEGREES BELOW NORMAL FOR
THE LAST DAY OF FEBRUARY. HOWEVER...THE INCREASING LATE FEBRUARY
SUN ANGLE AND LIGHT WINDS WILL MAKE IT SOMEWHAT MORE BEARABLE THAN
OUR RECENT COLD WAVES.

TONIGHT...

HIGH PRESSURE OVERHEAD WILL ALLOW FOR ANOTHER EXCELLENT NIGHT OF
RADIATIONAL COOLING.  THE NORMALLY COLDEST OUTLYING LOCATIONS WILL
DROP TO BETWEEN 5 AND 15 BELOW ZERO...WHILE MAINLY SINGLE DIGITS CAN
BE EXPECTED FOR THE REST OF THE REGION.  THE ONE FLY IN THE OINTMENT
IS WE ARE EXPECTING SOME MID/HIGH CLOUDS TO INCREASE FROM THE WEST
AFTER MIDNIGHT.  IF THEY COME IN A BIT EARLIER THEN EXPECTED OUR
TEMPERATURE FORECAST MIGHT BE TOO COLD.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...

*** ACCUMULATING SNOW LATE SUNDAY AND ESPECIALLY SUNDAY NIGHT WITH
  THE HIGHEST AMOUNTS EXPECTED SOUTH OF THE MA TURNPIKE AND AWAY
  FROM THE IMMEDIATE SOUTH COAST ***

A DIGGING SHORTWAVE WILL DROP TOWARDS THE GREAT LAKES ON SUNDAY.
THIS WILL ALLOW FOR AN OVERRUNNING SETUP ACROSS SOUTHERN NEW
ENGLAND. A NICE FRONTOGENESIS SIGNATURE WITH A DEVELOPING LOW
LEVEL JET SHOULD RESULT IN A GOOD SLUG OF PRECIPITATION SUNDAY
EVENING INTO SUNDAY NIGHT. MOST MODELS ARE SHOWING A WEAK
SECONDARY LOW PRESSURE DEVELOPING NEAR THE SOUTH COAST. THIS WILL
HELP TO BACK AND STRENGTHEN THE LOW LEVEL JET ALONG WITH SOME
SURFACE CONVERGENCE RESULTING IN THE RISK FOR SOME HIGH
PRECIPITATION TOTALS SOUTH OF THE MA TURNPIKE WHICH WILL EXPLAIN
MORE BELOW.

1} TIMING AND PTYPE:

DRY WEATHER SHOULD PREVAIL SUNDAY MORNING. MID LEVEL WARM
ADVECTION SHOULD ALLOW LIGHT SNOW TO DEVELOP DURING THE AFTERNOON
ACROSS THE INTERIOR...REACHING THE COASTAL PLAIN BY LATE
AFTERNOON/EARLY EVENING. THE SNOW WILL INITIALLY BE LIGHT...BUT
EXPECT THE SNOW TO PICKUP IN INTENSITY SUNDAY EVENING AND
OVERNIGHT AS THE LOW LEVEL JET/FORCING INCREASE. MODEL SOUNDINGS
SHOW A PERIOD OF DECENT OMEGA IN THE PRIME SNOW GROWTH REGION.
SYSTEM IS FAIRLY PROGRESSIVE...SO THE SNOW SHOULD BE OVER EARLY
MONDAY MORNING AND BEFORE RUSH HOUR STARTS.

PTYPE WILL PROBABLY BE ALL SNOW FOR A LOT OF THE REGION. IT BECOMES
MORE UNCERTAIN ACROSS SOUTHERN RI AND FAR SOUTHEAST MA. THE NAM
MODEL IS AN OUTLIER AND MOST AGGRESSIVE IN BRINGING A SURGE OF
WARM MID LEVEL AIR NORTHWARD...WHICH WOULD CHANGE PTYPE TO RAIN
FOR JUST ABOUT ALL OF RHODE ISLAND AND SOUTHEAST MA SUN NIGHT.
HOWEVER...MOST OF THE OTHER GUIDANCE KEEPS PTYPE SNOW EXCEPT FOR
AREAS NEAR THE SOUTH COAST/CAPE/ISLANDS. SO FOR NOW WILL KEEP THE
CHANGE OVER LINE JUST SOUTH OF THE TAUNTON TO PROVIDENCE
CORRIDOR...BUT THIS MAY NEED TO BE ADJUSTED BASED ON LATEST MODEL
DATA.

2)SNOW ACCUMULATIONS AND HEADLINES:

THIS LOOKS TO BE A HIGH END WINTER WEATHER ADVISORY OR LOW END
WARNING FOR MUCH OF THE REGION. WE ARE GENERALLY EXPECTING
SNOWFALL AMOUNTS OF BETWEEN 3 AND 7 INCHES...AWAY FROM THE SOUTH
COAST WHERE PTYPE ISSUES WILL BE MORE PROBLEMATIC. THE NAM IS
HEAVIER ON QPF AND WE OPTED TO GO WITH A GFS/ECMWF BLEND. EVEN
THESE MODELS STILL HAVE BETWEEN 0.40 TO 0.60 INCHES OF PRECIP FROM
NEAR THE PIKE TO THE SOUTH COAST. THIS SEEMS TO BE IN RESPONSE TO
A WEAK WAVE DEVELOPING NEAR THE SOUTH COAST...ALLOWING FOR A MORE
BACKED LOW LEVEL JET AND BETTER SURFACE CONVERGENCE. WITH PRETTY
GOOD OMEGA IN THE SNOW GROWTH REGION...SNOWFALL RATIOS MAY BE
BETTER THAN 10 TO 1 RATIOS.

WITH THAT SAID...FELT IT IS WORTH A WINTER STORM WATCH FROM NEAR THE
PIKE TO AREAS INLAND FROM THE SOUTH COAST...WHERE PTYPE WILL
PROBABLY END UP AS MAINLY SNOW.  THIS IS FOR THE POTENTIAL OF 4 TO 7
INCHES OF SNOW. WE ARE FAIRLY CONFIDENCE IN WIDESPREAD 3 TO 4
INCH AMOUNTS...BUT CONFIDENCE IS LOWER ON WHETHER OR NOT WE SEE
THE 6 TO 7 INCH AMOUNTS. HOWEVER...WE ONLY NEED 50 PERCENT
CONFIDENCE IN THOSE HIGHER TOTALS OCCURRING TO ISSUE THE WATCH AND
IT GIVES THE NEXT SHIFT SOME MORE OPTIONS.

3) FORECAST UNCERTAINTY:

HOW MUCH SNOW WE ACTUALLY RECEIVE WILL HAVE A LOT TO DO WITH HOW
QUICKLY THE SECONDARY WAVE OF LOW PRESSURE DEVELOPS AND HOW FAR
NORTH THE RAIN/SNOW LINE GETS. THE NAM MODEL IS STRONGEST WITH
THE DEVELOPMENT OF THIS WAVE AND HENCE HAS THE HIGHEST QPF...BUT
DOES INTRODUCE MORE PTYPE ISSUES. MEANWHILE...THE GGEM IS THE
WEAKEST WITH THIS DEVELOPMENT AND BARELY HAS ADVISORY LEVEL SNOW
FOR THE REGION. CURRENTLY WE ARE LEANING TOWARDS A GFS/ECMWF
COMPROMISE...RESULTING IN 3 TO 7 INCHES OF SNOW WITH THE HIGHEST
AMOUNTS SOUTH OF PIKE AND AWAY FROM THE SOUTH COAST.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...

HIGHLIGHTS...

*  CONDITIONS IMPROVE MONDAY
*  ANOTHER STORM POSSIBLE TUE NIGHT INTO WED...WITH SNOW OR
   MIXED PRECIP LIKELY CHANGING TO RAIN
*  COLD AND DRY TOWARD THE END OF THE WEEK

OVERVIEW AND MODEL PREFERENCES...

ONE THING IS FOR CERTAIN...WITH LITTLE CHANGE IN THE NAO/AO AND
THE PNA EXPECTED TO REBOUND FROM NEGATIVE VALUES BACK TOWARD A
MORE NEUTRAL SOLUTION...THE COLD AIR AND LONGWAVE TROF LOOK TO
REMAIN THROUGH THE LONG TERM FORECAST. THE ONLY CAVEAT WILL BE IN
THE LOW LVLS ON WED...WHEN A ROBUST SW LLJ WILL ALLOW LOW-MID LVL
TEMPS TO WARM CLOSER TO ABOVE CLIMATOLOGICAL NORMALS. HOWEVER...
THE COLD AIR INITIALLY IN PLACE WILL LEAD TO P-TYPE ISSUES FOR THE
MID WEEK SYSTEM. ECMWF DETERMINISTIC REMAINS THE MOST ROBUST OF
THE OPERATIONAL MODELS...WITH HIGHER AMPLIFICATION IN THE FLOW
PATTERN THAN THE GFS AND UKMET. IT STARTS MUCH COLDER...BUT ENDS
MUCH WARMER. HOWEVER...DO NOTE THAT SOME OF THE GEFS AND ECENS
ENSEMBLES AGREE WITH THE ECMWF. THEREFORE...WILL BE USING THE
ENSEMBLE BLEND AS A BASELINE AS THIS TAKES INTO ACCOUNT BOTH THE
MORE PROGRESSIVE /AND ULTIMATELY LESS ROBUST WITH THE THERMAL
DIFFERENCES/ AND THE POTENTIAL FOR A MORE DYNAMIC SYSTEM. WILL USE
THIS BLEND THROUGH THE REMAINDER OF THE FORECAST AS WELL.

DETAILS...

MONDAY...

MORNING SNOWS COME TO AN END EARLY ACROSS E MA...AND FLURRIES
DISSIPATE THROUGH THE BERKSHIRES AND LITCHFIELD HILLS AS DRY NW
FLOW MOVES IN. BLUSTERY CONDITIONS EXPECTED...AND EVEN THROUGH
HIGHS WILL STILL BE MAKING IT INTO THE LOW-UPPER 30S...NW WINDS
WITH GUSTS 25-35 MPH AT TIMES WILL YIELD WIND CHILLS STRUGGLING
INTO THE LOW 20S.

MONDAY NIGHT INTO TUESDAY...

HIGH PRES WILL MOVE ACROSS THE REGION. DRY CONDITIONS DOMINATE
ALTHOUGH WITH TEMPS REMAINING BELOW NORMAL.

TUESDAY NIGHT INTO THURSDAY...

MODEL CONSENSUS IS NOW GENERALLY IN AGREEMENT THAT BOTH THE NRN
AND SRN STREAMS PHASE IN SOME FASHION ACROSS THE CENTRAL CONUS
WITH THE FORMATION OF LOW PRES WHICH IS EXPECTED TO SLIDE ACROSS
SRN CANADA. WARM FRONT WILL APPROACH...BUT GIVEN DEEP SNOWPACK THE
LOW LVL FRONT MAY ACTUAL STALL NEAR THE S COAST AS THE LOW MOVES
OVER AS THE UPPER WARM FRONT SLIDES INTO CENTRAL NEW ENGLAND. THIS
PRESENTS A GOOD OVERRUNNING SITUATION WITH STRONG 50-60 KT H92 LLJ
OUT OF THE SW. GIVEN THAT THIS SYSTEM IS ASSOCIATED WITH THE SRN
STREAM...IT ALSO CARRIES WITH IT A FAIR AMOUNT OF MOISTURE AS
PWATS LOOK TO REACH 2-3 STD DEVIATIONS ABOVE NORMAL

SO ALL IN ALL..PLENTY OF INGREDIENTS FOR HEAVY PRECIP ACROSS THE
AREA. THE QUESTION WILL BE TYPE...ALL GUIDANCE BEGIN COLD ENOUGH
FOR SNOW AT ONSET TUE NIGHT INTO EARLY WED. ECMWF WOULD SUGGEST
MUCH MORE AND BETTER LIFT IN THE SNOW GROWTH REGION...SO THERE IS
THAT TO CONSIDER. IN ANY CASE...WILL NEED TO AT LEAST WATCH FOR
POTENTIAL WARNING LEVEL SNOWFALL BEFORE THE WARM AIR BEGINS TO
BUILD IN FROM S TO N THROUGH THE DAY ON WED. EVEN THOUGH THE ECMWF
STARTS THE COLDEST...IT ENDS AS THE WARMEST SOLUTION...BRINGING
THE H92 +8C LINE ALL THE WAY INTO CENTRAL MA. SO WE DO EXPECT A
GRADUAL SHIFT TO A WINTRY MIX INCLUDING SLEET AND FREEZING RAIN
FOR A TIME GIVEN THE DEEP SNOWPACK ACROSS THE REGION. SOME AREAS
OF WRN MA...AND THE HILLS OF NRN CT MAY ACTUALLY STAY AS A MIX OF
SLEET FREEZING RAIN AND EVEN MAYBE SOME SNOW GIVEN THAT THE SFC
WARM FRONT MAY STALL. WILL HAVE TO WATCH FOR ICY CONDITIONS WITH
AS MUCH AS A QUARTER INCH OF ICE NOT OUT OF THE QUESTION WHERE IT
DOESN/T SWITCH TO RAIN WITH MELTING /BEST CHANCE OF RAIN/MELT IS
IN RI/CT AND PORTIONS OF MASS E OF I-495 AND S OF THE MASS PIKE/.
HEAVY RAIN A THREAT TOO GIVEN UPPER LVL INSTABILITY AND ROBUST
LLJ...SO WHERE MELTING AND HEAVY RAIN ARE OBSERVED...POOR DRAINAGE
FLOODING IS A POSSIBILITY WHERE SNOW CLOGS AREA DRAINS.

THIS HEAVY MIXED PRECIP EVENT COULD LINGER INTO THU...THE MORE
AMPLIFIED ECMWF AND SEVERAL ECENS/GEFS MEMBERS SUGGEST THAT THE
LEFTOVER COLD FRONT STALLS WITH YET ANOTHER WEAK WAVE OF LOW PRES
MOVING THROUGH THU. OTHER SOLUTIONS ARE MORE PROGRESSIVE AND HAVE
LESS QPF /SNOW POTENTIALLY/ ON THE BACK END. HOWEVER...BY THU
AFTERNOON/EVENING...CONDITIONS SHOULD BE IMPROVING /ALTHOUGH WITH
RAPID TEMPERATURE DROP/.

LATE NEXT WEEK...

EVEN THOUGH THERE IS UNCERTAINTY WITH HOW AMPLIFIED THE PATTERN
IS BY LATE WEEK. IT APPEARS A PERIOD OF DRY BUT COLD WX IS LIKELY
AS ARCTIC AIR ONCE AGAIN SHIFTS IN BEHIND THE EXITING MID WEEK
SYSTEM.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TODAY THROUGH SUNDAY NIGHT/...

15Z UPDATE...NO CHANGES.

TODAY AND TONIGHT...HIGH CONFIDENCE. VFR.

SUNDAY MORNING...MODERATE CONFIDENCE. VFR. INCREASING MID-LEVEL
CLOUDS.

SUNDAY AFTERNOON INTO MONDAY MORNING...

SNOW OVERSPREADS THE REGION W-E. CIGS/VSBYS DETERIORATE TO MVFR-
IFR BY EARLY EVENING...WIDESPREAD IFR-LIFR SUNDAY NIGHT. SN MAY
MIX WITH OR CHANGE TO RA FOR A TIME ACROSS PORTIONS OF S RI AND
FAR SE MA...ESPECIALLY IMMEDIATE S-COAST/CAPE AND ISLANDS. PRECIP
SHOULD RAPIDLY END FROM W-E TOWARD DAYBREAK MONDAY....IMPROVING
CONDITIONS.

KBOS TAF...HIGH CONFIDENCE. VFR INTO SUNDAY MORNING.

KBDL TAF...HIGH CONFIDENCE. VFR INTO SUNDAY MORNING.

OUTLOOK...MONDAY THROUGH WEDNESDAY...

MONDAY...HIGH CONFIDENCE.

CONDITIONS IMPROVE EARLY FROM IFR/MVFR IN SNOWS AND LOW CIGS...
WITH VFR EXPECTED EVERYWHERE BY AFTERNOON. NW WINDS IN THE
AFTERNOON WITH GUSTS 25-30 KT.

MON NIGHT INTO TUE...HIGH CONFIDENCE.

MAINLY VFR. GRADUALLY LOWERING CIGS ON TUE.

TUE NIGHT INTO WED...MODERATE CONFIDENCE.

MIXED WINTRY PRECIP LIKELY STARTS AS ALL SNOW...TRANSITIONS TO A
MIX OF SLEET AND FREEZING RAIN...THEN TO ALL RAIN DURING THE DAY
ON WED. SOME SNOW AND ICE ACCUMULATIONS ARE LIKELY WITH IFR OR
POTENTIALLY EVEN LIFR CONDITIONS AT TIMES.

&&

.MARINE...

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE.

10 AM UPDATE...NO MAJOR CHANGES.

HIGH PRESSURE NEARBY WILL KEEP WINDS/SEAS WELL BELOW SMALL CRAFT
ADVISORY THRESHOLDS INTO SUNDAY MORNING. A WEAK WAVE OF LOW
PRESSURE MOVES ACROSS THE WATERS LATE SUN INTO SUN NIGHT...BUT
WEAK PRESSURE GRADIENT SHOULD KEEP WINDS/SEAS BELOW SMALL CRAFT
THRESHOLDS.

OUTLOOK...SUNDAY THROUGH WEDNESDAY...

MONDAY INTO MONDAY NIGHT...HIGH CONFIDENCE.

SW WINDS SHIFT TO THE NW DURING THE DAYLIGHT HOURS AS A COLD
FRONT SWEEPS ACROSS THE WATERS. ONCE WINDS SHIFT NW IN THE
AFTERNOON EXPECT GALE FORCE GUSTS 35-40KT. COLDER AIR TUE NIGHT
COULD LEAD TO LIGHT FREEZING SPRAY.

TUESDAY...MODERATE CONFIDENCE.

WINDS GRADUALLY DIMINISH OUT OF THE W-NW BUT SEAS ARE LIKELY TO
REMAIN ELEVATED 5-8FT ON THE OCEAN WATERS. SMALL CRAFT ADVISORIES
WILL LIKELY BE NEEDED.

TUESDAY NIGHT INTO WEDNESDAY...MODERATE CONFIDENCE.

SNOW CHANGES TO RAIN TUE NIGHT WITH LOW VSBYS OVER THE WATERS.
WINDS OUT OF THE S MAINLY AROUND 25-30 KT AT MOST. SEAS BUILD
12-15 FT BY DAYTIME ON WED ON SE OCEAN WATERS. SMALL CRAFT
ADVISORIES WILL LIKELY BE NEEDED.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH LATE SUNDAY
     NIGHT FOR CTZ002>004.
MA...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH LATE SUNDAY
     NIGHT FOR MAZ009-011>013-015>019.
RI...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH LATE SUNDAY
     NIGHT FOR RIZ001>004.
MARINE...NONE.
LEFT OVER SMALL CRAFT SEAS ACROSS THE OUTER-WATERS WILL DIMINISH
EARLY THIS MORNING.  OTHERWISE...
&&

$$

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


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