Area Forecast Discussion
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000
FXUS61 KBOX 212056
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
356 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/...
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 /21Z SUNDAY 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/...

THROUGH TONIGHT...MODERATE CONFIDENCE. MAINLY MVFR/IFR CONDITIONS
THROUGH TONIGHT. EXCEPTION RIGHT NOW IS THE CAPE AND ISLANDS WHERE
VFR CONDITIONS ARE IN PLACE. BELIEVE CONDITIONS WILL DETERIORATE
LATER TONIGHT THERE. WIDESPREAD LIGHT SNOW SHOWERS ARE AFFECTING
ALL OF SOUTHERN NEW ENGLAND THIS AFTERNOON. EXPECT THIS ACTIVITY
TO BECOME MORE SCATTERED IN NATURE. RAIN SHOWERS ACROSS MOST OF
PLYMOUTH COUNTY AND ONTO THE CAPE/ISLANDS WITH SNOW SHOWERS NORTH
AND WEST.

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.  HAVE ISSUED A SMALL CRAFT
ADVISORY FOR THE EASTERN WATERS BEGINNING MIDDAY MONDAY AND
CONTINUING 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...RLG
SHORT TERM...RLG
LONG TERM...WTB
AVIATION...WTB/RLG
MARINE...WTB/RLG
TIDES/COASTAL FLOODING...


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