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Area Forecast Discussion
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000
FXUS61 KBOX 212024
AFDBOX

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

.SYNOPSIS...
SCATTERED SNOW/RAIN SHOWERS CONTINUE THROUGH THIS AFTERNOON. 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.

&&

.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/...
HIGHLIGHTS...

* WEAK SHORTWAVE ON MON NIGHT/TUESDAY COULD BRING WINTRY 
  MIX/FREEZING RAIN TO THE INTERIOR
* ANOMALOUS SYSTEM ACROSS THE GREAT LAKES WILL BRING HEAVY 
  RAIN...GUSTY WINDS AND COASTAL FLOODING CONCERNS AROUND CHRISTMAS 
  EVE
* BLUSTERY BUT AIRMASS WILL BE DRYING OUT ON CHRISTMAS DAY

OVERVIEW...

THE MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR AND PREDICTABLE 
LARGER SCALE MID TO UPPER LEVEL PATTERN EVOLUTION FOR MUCH OF THE 
UPCOMING WEEK. THIS ACTIVE FLOW REGIME DEVELOPS SEVERAL MID-UPPER 
LEVEL TROUGH AND ASSOCIATED/UNSETTLING LEAD SURFACE LOW/FRONTAL 
SYSTEMS AND PCPN SWATHS PROGRESS STEADILY ACROSS THE LOWER 48. THE 
FIRST AMPLIFIED/DEEP LEAD SYSTEM WORKS ACROSS THE ERN/NERN US INTO 
ERN CANADA CHRISTMAS EVE INTO CHRISTMAS ALLOWING FOR A MOIST/WARMED 
AIRMASS IN ADVANCE OF FRONTAL APPROACH WITH HEAVIEST LEAD QPF 
POTENTIAL OVER NEW ENGLAND. BIGGEST QUESTION IS THE EVOLUTION OF THE 
SECONDARY LOW PRESSURE SYSTEM. 00Z GUIDANCE HAS BACKED OFF ON THE 
STRENGTH OF THE LOW AND IS HAVING ISSUES ON HOW TO HANDLE ITS 
EVOLUTION. THE EC AND GFS HAVE SLOWED DOWN THE SYSTEM SLIGHTLY WITH 
THE EC HAVING MORE OF A NEGATIVE TROUGH VS THE GFS. BELIEVE THE 
UKMET IS A GOOD COMPROMISE AT IS WAS THE FIRST DETERMINISTIC 
GUIDANCE ON TAMPERING DOWN THE FIRST MAIN LOW...WHILE THE CMC IS OUT 
TO LUNCH. REGARDLESS THIS IS A VERY ANOMALOUS SYSTEM THAT IS ABOUT 4 
STANDARD DEVIATIONS AWAY. 

A SECONDARY SYSTEM DEEPENS ACROSS THE FOUR CORNERS ON FRIDAY AND 
WITH THE STUBBORN TROUGH OVER THE CENTRAL U.S...IT WILL PUSH A 
SYSTEM TOWARDS SOUTHERN NEW ENGLAND BY SUNDAY. THIS SYSTEM MAY 
SUPPORT A MODEST SWATH OF OVERRUNNING SNOW OVER SOUTHERN NEW 
ENGLAND. 

DETAILS...
 
TUESDAY...MODERATE CONFIDENCE.

A WEAK WAVE OF LOW PRESSURE DEVELOPS ALONG THE SOUTHEAST COAST 
MONDAY...AND WILL BE ON A DEVELOPING WARM FRONTAL BOUNDARY. THIS LOW 
REMAINS WEAK AS THE WARM FRONT MOVES SLOWLY NORTH MONDAY NIGHT INTO 
TUESDAY. APPEARS THAT THERE IS DECENT WARM ADVECTION AHEAD OF THIS 
WAVE. SEVERAL HI-RES GUIDANCE MODELS SHOW THAT THERE IS THE 
POTENTIAL FOR COLD AIR DAMMING ACROSS THE INTERIOR INTO TUESDAY.  
BIGGEST QUESTION WILL BE IS THERE ENOUGH MOISTURE FOR PRECIP DURING 
THIS TIME FRAME. DUE TO A STRENGTHENING LLJ PROVIDING A GOOD SOURCE OF 
LIFT ANTICIPATE PRECIP TO DEVELOP AND OVERSPREAD ACROSS SOUTHERN NEW 
ENGLAND. IF THIS PLAYS OUT WITH COLD AIR DAMMING AND WARM AIR 
ADVECTION...THEN WE COULD SEE FREEZING RAIN/DRIZZLE ACROSS THE I-91 
CORRIDOR LATE MONDAY INTO TUESDAY MORNING. DURING THE DAY ON 
TUESDAY...GOOD AMOUNT OF WARM AIR WILL PUSH SURFACE TEMPS ABOVE 
FREEZING BY THE LATE MORNING ALLOWING FOR ANY PRECIP TO BE MORE OF 
THE LIQUID VARIETY AHEAD OF THE CHRISTMAS EVE STORM. HOWEVER 
GUIDANCE IS ALWAYS TOO FAST IN SCOURING TEMPS OUT ESP ACROSS THE CT 
VALLEY SO WE WILL NEED TO MONITOR THIS CLOSELY...ESP DUE TO LIGHT 
WINDS AND THE HIGH IN EASTERN CANADA. A WINTER WX ADVISORY MAY BE 
NEEDED FOR THE LIGHT ICING POTENTIAL. 

WE COULD ALSO SEE SOME MINOR COASTAL FLOODING CONCERNS ON TUESDAY. SEE 
BELOW FOR MORE DETAILS. 

WEDNESDAY INTO THURSDAY...HIGH CONFIDENCE IN SYSTEM LOW CONFIDENCE 
ON DETAILS. 

ANOMALOUS SYSTEM WILL STRENGTHEN OVER THE GREAT LAKES TUESDAY INTO 
WEDNESDAY. A SECONDARY SHORTWAVE WILL ROUND THE DEEP TROUGH AND 
DEVELOP A SECONDARY LOW PRESSURE ALONG THE COLD FRONT. THIS 
SECONDARY LOW WILL STRENGTHEN AND PASS WEST OF SOUTHERN NEW ENGLAND. 
THIS SYSTEM WILL CONTINUE TO DEEPEN AS IT MOVES TOWARDS EASTERN 
CANADA SWINGING A COLD FRONT ACROSS THE NORTHEAST. 

STRONG SOUTHERLY JET OUT AHEAD OF THE FRONT WITH A GULF MOISTURE 
CONNECTION WILL IMPACT SOUTHERN NEW ENGLAND ON CHRISTMAS EVE. THIS 
STRONG JET WILL YIELD FOR PCPN IN THE LIQUID VARIETY.  PW ANOMALIES 
ARE BETWEEN +4 TO +5 STANDARD DEVIATIONS ABOVE NORMAL WHICH IS QUITE 
ANOMALOUS FOR THIS TIME OF YEAR. IN FACT CURRENT PWATS ARE PROGGED 
ABOVE 1.6 INCHES WITH MODEL QPF OVER 2 INCHES...AT THE VERY LEAST 
COULD SEE URBAN AND POOR DRAINAGE FLOODING. LATEST EC EVEN SHOWS 
OVER 2.5 INCHES OF QPF...AND WITH THE TROPICAL CONNECTION AND STRONG 
SOUTHERLY FLOW COULD SEE HIGHER AMOUNTS DUE TO TOPOGRAPHY 
ENHANCEMENTS. RAINFALL RECORDS MAY FALL IF EVERYTHING FALLS INTO 
PLACE. 

AHEAD OF THE FRONT...SOUTHERN NEW ENGLAND WILL WARM SECTOR WED INTO 
THUR MORNING ALLOWING FOR TEMPERATURES TO BE WELL ABOVE AVERAGE. IN 
FACT WE MAY BE CLOSE AT BREAKING RECORD HIGH TEMPS IF TEMPS WARM TO 
60F OR ABOVE ON CHRISTMAS EVE. SINCE WE WILL BE IN THE WARM 
SECTOR...AND SHOWALTERS CLOSE TO ZERO...ISOLATED THUNDER IS STILL 
POSSIBLE. 

STRONG LOW LEVEL WINDS WILL ALSO BE A CONCERN ESPECIALLY WEDNESDAY 
NIGHT. THE ECMWF SHOWS EAST-SOUTHEAST WINDS 30-40 KNOTS ON WEDNESDAY 
INCREASING TO 60-75 KNOTS BY WEDNESDAY NIGHT. STRONG DOWNPOURS MAY 
OVERCOME THE LOW LEVEL INVERSION AND BRING STRONG GUSTS OF AT LEAST 
30-40 KNOTS ESPECIALLY ALONG THE SOUTH COAST. A WIND ADVISORY MAY BE 
NEEDED IN SOME AREAS.

CHRISTMAS DAY...MODERATE CONFIDENCE.

AS THE COLD FRONT PASSES THROUGH EARLY CHRISTMAS DAY...THE WEST 
WINDS WILL HELP DRY THE AIRMASS ALLOWING FOR PARTLY SUNNY SKIES. 
STRONG CAA ON THURSDAY WILL ALLOW DESCENT MIXING. WINDS IN THE SFC-
850 MB LAYER WILL BE 30-40 KNOTS AND POSSIBLY A LITTLE 
HIGHER...WHICH WOULD REQUIRE A WIND ADVISORY FOR MUCH OF THE AREA.

FRIDAY-SUNDAY...LOWER CONFIDENCE 

WEAK HIGH PRESSURE BUILDS OVER THE AREA FRIDAY INTO SATURDAY. THE 
NEXT SHORTWAVE APPROACHES LATE SATURDAY INTO SUNDAY AND SHOULD BRING 
INCREASING CLOUDS FROM WEST TO EAST ALONG WITH A CHANCE OF RAIN OR 
SNOW SHOWERS MAINLY IN THE AFTERNOON AND AT NIGHT.

&&

.AVIATION /20Z 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...MONDAY THROUGH THURSDAY...MODERATE CONFIDENCE. 

MONDAY...MVFR CIGS CONTINUE IN RI/EASTERN MASS IN MARINE EAST FLOW. 
VFR IN THE WEST.

TUESDAY...VFR WITH SCATTERED MVFR IN ANY RAIN/SNOW SHOWERS.

WEDNESDAY...CONDITIONS LOWERING TO IFR IN RAIN/HEAVY RAIN. ISOLATED 
THUNDERSTORMS POSSIBLE ESPECIALLY WEDNESDAY NIGHT. EAST-SOUTHEAST 
SURFACE WINDS MAY GUST TO 35-45 KNOTS. WINDS AT 2000 FEET AGL WILL 
REACH 50-60 KNOTS WEDNESDAY AFTERNOON AND EARLY NIGHT CREATING LOW 
LEVEL WIND SHEAR CONCERNS.

CHRISTMAS DAY...WEST WIND GUSTING 30-40 KNOTS. CONDITIONS IMPROVING 
TO VFR AS THE WIND BRINGS IN COOLER DRIER AIR.

&&

.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

MONDAY...EAST TO NORTHEAST WINDS GUSTING AROUND 15 KNOTS OR LESS.  
SEAS WILL HOLD AROUND 3-4 FEET...MAY INCREASE TO 5FT IN NORTHEAST 
FLOW AS GUIDANCE MAY BE UNDERDONE.

TUESDAY... INCREASING EAST WINDS WITH FREQUENT GUSTS 25 TO 30 KNOTS. 
SEAS WILL BUILD TO 5-6 FEET ON THE EXPOSED WATERS.  A SMALL CRAFT 
ADVISORY MAY BE NEEDED.

WEDNESDAY...RAIN WILL BE HEAVY AT TIMES PRODUCING POOR VISIBILITY. 
INCREASING SOUTHEAST WINDS 20-25 SUSTAINED AND 40 KNOT GUSTS.  WINDS 
SHOULD SHIFT TO SOUTH WEDNESDAY NIGHT AND SOUTHWEST TOWARD THURSDAY 
MORNING. RAIN WILL TAPER OFF WITH THE WIND SHIFT TO SOUTHWEST. SEAS 
WILL CONTINUE TO BUILD WITH 7-11 FEET HEIGHTS ON THE EXPOSED WATERS. 
A GALE WARNING WILL BE NEEDED...WITH A LOW PROB OF A FEW STORM FORCE 
GUSTS ACROSS THE EASTERN OUTER WATERS.

CHRISTMAS DAY... WEST SOUTHWEST WINDS WILL CONTINUE TO GUST 35-40 
KNOTS...SO A CONTINUED GALE WARNING MAY BE NEEDED. SEAS OF 7-15 FEET 
ARE POSSIBLE ON THE EXPOSED WATERS...AND 5 FEET IS POSSIBLE ON SOME 
OF THE NEARSHORE WATERS.

&&

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

TUESDAY...HIGH TIDE AT BOSTON WILL BE 11.6 FT. 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 DECENT PRESSURE 
FALLS. 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 50-60 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...NONE.

&&

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



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