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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
958 PM EST SUN DEC 21 2014

.SYNOPSIS...
SCATTERED SNOW/RAIN SHOWERS CONTINUE THROUGH MONDAY. WEAK LOW
PRESSURE WILL PASS SOUTH OF NEW ENGLAND BRINGING ANOTHER PERIOD OF
PRECIPITATION MONDAY NIGHT AND TUESDAY. A MUCH STRONGER STORM
PASSING WEST OF NEW ENGLAND WILL BRING HEAVY RAINFALL... GUSTY
WINDS AND COASTAL FLOODING CONCERNS TO THE REGION WEDNESDAY AND
WEDNESDAY NIGHT. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR
CHRISTMAS DAY. HIGH PRESSURE BRINGS DRY WEATHER FRIDAY. ANOTHER
DEVELOPING SYSTEM MAY BRING RAIN AND SNOW NEXT SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

1000 PM UPDATE...

LATEST RADAR IMAGERY SHOWS LIGHT RADAR ECHOES ACROSS PORTIONS OF
SOUTHERN NEW ENGLAND...ESP SOUTH OF THE PIKE. DUE TO MOIST ONSHORE
FLOW FOR THE REMINDER OF THE NIGHT BELIEVE FLURRIES/LIGHT SNOW
SHOWERS WILL CONTINUE. NOT MUCH ACCUMULATION IS ANTICIPATED.
TEMPERATURES AT OR NEAR FREEZING COMBINED WITH HIGHER DEWPOINTS
MAY LEAD TO A FEW SLICK SPOTS OVERNIGHT INTO TOMORROW MORNING.
DRIVERS ARE URGED TO USE CAUTION. 

PREVIOUS DISCUSSION...
SHORTWAVE RIDGING BUILDS OVER SOUTHERN NEW ENGLAND OVERNIGHT. IN
ADDITION...HIGH PRESSURE IN QUEBEC BUILDS OVER THE REGION AS WELL.
THEREFORE...THERE WILL BE NO FOCUSING MECHANISM FOR PRECIP.
HOWEVER...ONSHORE FLOW AND DECENT MID LEVEL LAPSE RATES WILL ALLOW
FOR A FEW SCATTERED SNOW/RAIN SHOWERS ACROSS THE AREA OVERNIGHT.
EXPECT SNOW SHOWERS TO REMAIN ROUGHLY NORTH AND WEST OF A NEWPORT
TO TAUNTON TO SCITUATE LINE. ANY ADDITIONAL SNOWFALL WILL AMOUNT
TO A DUSTING TO ABOUT AN INCH. TEMPERATURES WILL FALL INTO THE MID
20S ACROSS THE NORTHWEST TO THE MID 30S ON THE CAPE AND ISLANDS.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
MONDAY...CLOUDY...DAMP...AND RAW CONDITIONS WILL CONTINUE THROUGH 
THE DAY WITH CONTINUED ONSHORE FLOW AND SCATTERED SNOW/RAIN SHOWERS. 

MONDAY NIGHT...WEAK LOW PRESSURE MOVING UP THE COAST TO JUST OFF THE 
DELMARVA PENINSULA WILL PRODUCE WARM ADVECTION OVER SOUTHERN NEW 
ENGLAND.  THIS IN TURN WILL LIKELY RESULT IN SOME PRECIPITATION 
DEVELOPING OVERNIGHT.  HIGH PRESSURE MOVING INTO THE MARITIMES WILL 
ALLOW FOR SOME COLD AIR DAMMING...PARTICULARLY INTO INTERIOR 
SOUTHERN NEW ENGLAND.  THIS SCENARIO IS A GOOD SET UP FOR SOME 
FREEZING RAIN ACROSS THE INTERIOR.  THE MAIN QUESTION IS HOW FAR 
NORTH THE WARMER AIR GETS AS THIS WILL DETERMINE PTYPE.  FOR 
NOW...WILL MAKE MENTION OF THE POTENTIAL FOR AN AREA OF FREEZING 
RAIN IN THE HAZARDOUS WEATHER OUTLOOK. IF FREEZING RAIN LOOKS TO BE 
MORE CERTAIN...WE WILL NEED TO ISSUE A WINTER WEATHER ADVISORY.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
BIG PICTURE... 

TUESDAY STARTS WITH UPPER RIDGES ON EACH COAST AND A DEEP UPPER 
TROUGH/CLOSED LOW OVER THE PLAINS. BY WEDNESDAY THE CLOSED LOW 
EJECTS NORTHEAST THROUGH LAKE SUPERIOR INTO CANADA. THIS SWEEPS THE 
TROUGH AXIS EAST AND PASSES ACROSS NEW ENGLAND CHRISTMAS DAY. 
ANOTHER SHORTWAVE MOVES ONSHORE IN THE PACIFIC NORTHWEST WEDNESDAY 
AND PHASES WITH A SECOND DROPPING SOUTH FROM NORTHERN CANADA.  THIS 
REESTABLISHES THE UPPER TROUGH OVER THE NORTHERN PLAINS/GREAT LAKES 
SATURDAY.

CONTOUR HEIGHTS WILL BE ABOVE NORMAL MIDWEEK...TRENDING BELOW NORMAL 
OVER THE WEEKEND AS THE SECOND UPPER TROUGH SHIFTS EAST. THIS POINTS 
TO A COOLING TREND AFTER CHRISTMAS.

THE GFS AND ECMWF ARE SIMILAR IN HANDLING THE HOLIDAY STORM. THERE 
ARE DIFFERENCES BETWEEN THE MODELS IN HANDLING THE SUNDAY SYSTEM. WE 
USED A BLEND MOST OF THE LONG TERM PERIOD...BUT MANUALLY ADJUSTED 
POPS FOR SUNDAY WITH LOW CONFIDENCE IN MODEL VALUES.

THE DAILIES... 

TUESDAY... HIGH PRESSURE OVER THE MARITIMES WITH RIDGING DOWN THE 
ATLANTIC COAST. COASTAL LOW PRESSURE WAVE DEVELOPS ALONG STALLED 
WARM FRONT AND MOVES NORTH.  AS THE COASTAL LOW MOVES NORTH IT WILL 
RUN UP AGAINST THE MARITIME HIGH. THIS WILL INCREASE THE LOW LEVEL 
PRESSURE GRADIENT AND INCREASE THE LOW LEVEL SOUTHEAST WINDS. 
RESULT...A SOUTHEAST LOW LEVEL JET RUNS OVER THE RIDGING ALONG THE 
COASTAL PLAIN INDUCING LOW LEVEL LIFT. THE MOIST LAYER EXPANDS ABOVE 
800 MB...NOT DEEP BUT DEEP ENOUGH FOR THE LIFT TO GENERATE LIGHT 
PCPN. PTYPE WILL BE RAIN MOST PLACES...BUT THERE COULD BE SPOTS OF 
LIGHT FREEZING RAIN IN NORTHWEST MASSACHUSETTS. WE WILL MAINTAIN 
CHANCE POPS BUT INCREASE TO AROUND 50 PCT...THE HIGH END OF THE 
CHANCE RANGE.

LOW LEVEL SOUTH JET MOVES UP THE COAST TUESDAY NIGHT REACHING THE 
COOLER AIR OVER NEW ENGLAND AFTER MIDNIGHT AND BEFORE SUNRISE. THIS 
WILL GENERATE ADDITIONAL LIFT AS WELL AS INCREASING AND DEEPENING 
MOISTURE. THIS SUGGESTS INCREASING POPS OVERNIGHT.  TEMPERATURES 
SHOULD REMAIN ABOVE FREEZING SO PTYPE SHOULD BE RAIN.

WEDNESDAY-THURSDAY... SOUTH 40-50 KNOT LOW LEVEL JET MOVES OVER NEW 
ENGLAND WEDNESDAY GENERATING STRONG LIFT AND TRANSPORTING HIGH 
VALUES OF PRECIPITABLE WATER INTO THAT LIFT. THE MOISTURE VALUES ARE 
MORE THAN 3 STD DEVIATIONS ABOVE NORMAL FOR DECEMBER...AND ACTUALLY 
NEAR THE MAXIMUM PREVIOUSLY OBSERVED VALUE. THIS SUGGESTS RAIN WITH 
SOME HEAVY DOWNPOURS. COLD FRONT APPROACHES LATE WEDNESDAY NIGHT AND 
CROSSES SOUTHERN NEW ENGLAND CHRISTMAS MORNING. THE FRONT WILL HAVE 
DYNAMIC SUPPORT FROM A 140-150 KNOT UPPER JET. THE FOREWARD PROGRESS 
OF THE FRONT WILL SLOW BECAUSE MOST OF THE MOTION IN THE UPPER JET 
WILL BE PARALLEL TO THE FRONT. THIS WILL MEAN CONTINUED RAIN/HEAVY 
RAIN THROUGH THE NIGHT INTO THURSDAY MORNING. 
 
THE OBVIOUS CONCERN FOR THIS PERIOD WILL BE FLOODING FROM HEAVY 
RAINFALL. RAIN AMOUNTS OF 2 TO 3 INCHES ARE EXPECTED. THIS SHOULD BE 
SUFFICIENT FOR AT LEAST URBAN AND POOR DRAINAGE FLOODING. A FLOOD 
WATCH MAY BE NEEDED.

A SECOND CONCERN WILL BE WIND. THE LOW LEVEL JET WEDNESDAY WILL BE 
SOUTH 40-50 KNOTS...AND INCREASE TO 55-65 KNOTS WEDNESDAY NIGHT. 
CONVENTIONAL MIXING WILL NOT BE DEEP...BUT HEAVY DOWNPOURS COULD 
CREATE A MOIST ADIABATIC CHANNEL THAT BRINGS DOWN SOME STRONGER WIND 
GUSTS. MODEL GRIDS ARE RATHER LIGHT ON WIND GUSTS...15 TO 30 KNOTS.  
WE WILL MANUALLY ADJUST THESE VALUES UP TO 25-35 KNOTS OVER LAND AND 
A LITTLE STRONGER OVER WATER.

A THIRD CONCERN WILL BE COASTAL FLOODING. MORE DETAILS ON THIS IN 
THE TIDE/COASTAL FLOOD SECTION.

WINDS SHIFT TO WEST BEHIND THE FRONT ON CHRISTMAS DAY. THIS WILL 
BRING DRIER AIR AND SO END THE RAINFALL. COLD ADVECTION WILL PROMOTE 
MIXING TO NEAR 850 MB IN THE AFTERNOON AND TAP 25-35 KNOT WIND 
GUSTS...POSSIBLY 40 KNOT GUSTS. A WIND ADVISORY MAY BE NEEDED FOR 
THESE WEST WINDS THURSDAY.

FRIDAY THROUGH SUNDAY.... HIGH PRESSURE MOVES OVER THE REGION FRIDAY 
BRINGING DRY WEATHER.  SHORTWAVE MOVING THROUGH THE GREAT LAKES 
SWINGS A COLD FRONT THROUGH NEW ENGLAND SATURDAY. THE SURFACE 
REFLECTION OF THE SHORTWAVE MOVES UP THE ST LAWRENCE VALLEY AND JET 
SUPPPORT WILL MOSTLY BE NORTH OF THE BORDER...SO PCPN WILL BE 
LIMITED.  QUESTION FOR SUNDAY WILL BE WHETHER A WAVE FORMS ON THE 
DEPARTING COLD FRONT...IF SO IT MIGHT BRING PCPN TO NEW ENGLAND. THE 
ECMWF THINKS SO BUT THE GFS DOES NOT. WE BROUGHT IN A CHANCE OF RAIN 
AND SNOW SHOWERS.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH MONDAY NIGHT/...

TONIGHT...MODERATE CONFIDENCE. MAINLY MVFR CONDITIONS THROUGH
TONIGHT. ONE EXCEPTION IS OVER BOSTON AND ESSEX COUNTY WHERE THE
1500 FOOT CEILING BROKE TO 6500 FEET AND MAY STAY LIKE THAT
THROUGH THE EARLY NIGHT. BUT WITH CONTINUED ONSHORE FLOW AND A FEW
RAIN/SNOW SHOWERS UPSTREAM IT IS POSSIBLE CIGS WILL DROP BACK TO
1500 FEET IN ANY SHOWERS. THE OVERALL MOIST FLOW SHOULD ALSO BRING
LEVELS BACK TO MVFR OVERNIGHT. SECOND EXCEPTION IS OVER CAPE COD AND
THE ISLANDS WHERE VFR CONDITIONS CONTINUE IN PLACE. BELIEVE THESE
CONDITIONS WILL ALSO DETERIORATE OVERNIGHT IN THE ONSHORE
NORTHEAST FLOW. 

MONDAY AND MONDAY NIGHT...MODERATE CONFIDENCE. MAINLY MVFR
CONDITIONS CONTINUE IN SCATTERED LIGHT SNOW SHOWERS. LIGHT FZRA
POSSIBLE LATE MONDAY NIGHT ACROSS NW MASSACHUSETTS.

KBOS TERMINAL...MODERATE CONFIDENCE. 

KBDL TERMINAL...MODERATE CONFIDENCE. 

OUTLOOK...TUESDAY THROUGH FRIDAY...MODERATE CONFIDENCE

TUESDAY...MVFR CIGS AND VSBYS IN LIGHT RAIN.  EAST SOUTHEAST 
WINDS...WITH FREQUENT GUSTS TO 25 KNOTS ON THE CAPE AND ISLANDS.

LATE TUESDAY NIGHT-WEDNESDAY-THURSDAY... CONDITIONS LOWERING TO 
IFR/LIFR IN RAIN/HEAVY RAIN. SOUTHEAST WINDS GUSTING 25 TO 35 KNOTS 
WEDNESDAY AND SOUTH WINDS SIMILAR SPEEDS WEDNESDAY NIGHT...EXCEPT 30 
TO 40 KNOTS CAPE COD AND ISLANDS. WINDS AT 2000 FEET MAY REACH 55 TO 
65 KNOTS BY WEDNESDAY NIGHT CREATING LOW LEVEL WIND SHEAR. ISOLATED 
THUNDERSTORMS WEDNESDAY AFTERNOON AND NIGHT. COLD FRONT SWINGS 
THROUGH ON THURSDAY MORNING BRINGING A WIND SHIFT TO WEST WITH GUSTS 
30-40 KNOTS.  CONDITIONS IMPROVE TO VFR AFTER THE WIND SHIFT.

FRIDAY...VFR.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

HIGH PRESSURE ACROSS QUEBEC AND THE MARITIMES WILL RESULT IN 
PERSISTENT NORTHEASTERLY TO EASTERLY WINDS ACROSS THE WATERS THROUGH 
MONDAY.  THIS WILL RESULT IN BUILDING SEAS ON THE EASTERN WATERS 
DESPITE WIND GUSTS UP TO 20 KNOTS.  SEAS BUILD TO AT LEAST 5 FEET ON 
THE EASTERN WATERS BY MIDDAY MONDAY. A SMALL CRAFT ADVISORY
CONTINUES FOR THE EASTERN WATERS FOR THE PERIOD FROM MIDDAY
MONDAY THROUGH TUESDAY MORNING. WINDS INCREASE TO NEAR 25 KTS ON
THE SOUTHERN WATERS BY 12Z TUESDAY.

OUTLOOK...TUESDAY THROUGH FRIDAY...MODERATE CONFIDENCE

TUESDAY...EAST WIND GUSTING TO 25 KNOTS...BECOMING SOUTHEAST AT 
NIGHT. SEAS 5 TO 7 FEET ON THE EXPOSED WATERS.  A SMALL CRAFT 
ADVISORY WILL BE NEEDED.

WEDNESDAY-THURSDAY... SOUTH WINDS WITH FREQUENT GUSTS 35 TO 40 KNOTS 
BY WEDNESDAY AFTERNOON AND CONTINUING THROUGH THE NIGHT. WINDS SHIFT 
WEST THURSDAY MORNING WITH SIMILAR SPEEDS THROUGH THE AFTERNOON. 
SEAS WILL BUILD TO 7 TO 12 FEET ON THE EXPOSED WATERS BY WEDNESDAY 
NIGHT AND THURSDAY.  A GALE WARNING MAY BE NEEDED.

FRIDAY...WINDS DIMINISHING TO 25 KNOTS FRIDAY MORNING AND BELOW 25 
KNOTS BY AFTERNOON.  SEAS LINGERING AT 5 TO 7 FEET ON THE EXPOSED 
WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED.

&&

.TIDES/COASTAL FLOODING...
HIGH ASTRONOMICAL TIDES WILL OCCUR TUESDAY THROUGH THURSDAY. 

TUESDAY...HIGH TIDE AT BOSTON WILL BE 11.6 FT. WINDS WILL BE FROM
THE EAST...SO THERE WILL BE ONSHORE FLOW DURING THIS HIGH TIDE
ALLOWING FOR MINOR SPLASHOVER. IF WINDS INCREASE THEN COULD SEE
SOME POCKETS OF MINOR COASTAL FLOODING.
 
WEDNESDAY...WINDS SHIFT TO A MORE SOUTHEASTERLY FLOW DURING THE DAY 
AND INCREASE QUICKLY AS AN APPROACHING SYSTEM BRINGS PRESSURE
FALLS OF 1 MB/HR. THE WEDNESDAY AFTERNOON HIGH TIDE IN BOSTON IS
11.7 FT AND STRONG SOUTHEASTERLY WINDS WILL BE JUST OFFSHORE.
RIGHT NOW BELIEVE MINOR COASTAL FLOODING IS POSSIBLE ALONG THE
EAST COAST.

WEDNESDAY EVENING...SOUTHERLY WINDS ARE EXPECTED AND ASTRONOMICAL 
TIDES INCREASE ALONG THE SOUTH COAST. HIGH TIDE IN PROVIDENCE WILL 
BE 5.2 FT. 925 MB LLJ STRENGTHENS TO 55-65 KTS WHICH COULD PUSH A
DECENT SURGE UP ALONG THE SOUTH COAST DURING THE TIME OF HIGH
TIDE. THINKING THAT MINOR COASTAL FLOODING COULD OCCUR BUT CANNOT
RULE OUT MODERATE ALONG THE SOUTH COAST...ESPECIALLY IF LLJ
CONTINUES TO STRENGTHEN.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM MONDAY TO 7 AM EST TUESDAY FOR 
     ANZ250.
     SMALL CRAFT ADVISORY FROM 10 PM MONDAY TO 7 AM EST TUESDAY FOR 
     ANZ251-255.
     SMALL CRAFT ADVISORY FROM 1 PM MONDAY TO 7 AM EST TUESDAY FOR 
     ANZ254.

&&

$$
SYNOPSIS...WTB/RLG
NEAR TERM...DUNTEN/RLG
SHORT TERM...RLG
LONG TERM...WTB
AVIATION...WTB/RLG
MARINE...WTB/RLG
TIDES/COASTAL FLOODING...

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