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Area Forecast Discussion
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000
FXUS61 KBOX 182234
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
534 PM EST THU DEC 18 2014

.SYNOPSIS...
DRY AND SEASONABLE CONDITIONS WILL PREVAIL FRIDAY. AN UPPER LEVEL
DISTURBANCE AND MOIST NORTHEAST FLOW WILL BRING SOME LIGHT
PRECIPITATION SATURDAY INTO SUNDAY. LOW PRESSURE WILL LIKELY PASS
WELL SOUTH OF THE REGION TUESDAY...BUT STILL COULD BRING A PERIOD
OF LIGHT PRECIPITATION. A MUCH STRONGER STORM IS LIKELY TO BRING
HEAVY RAIN AND WIND TO SOUTHERN NEW ENGLAND WEDNESDAY INTO
WEDNESDAY EVENING. DRY BUT VERY WINDY CONDITIONS FOLLOW FOR
CHRISTMAS DAY.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
LOW PRES MOVES NE FROM THE MARITIMES BUT CYCLONIC FLOW WILL
PERSIST ALONG WITH SOME MOISTURE IN THE COLUMN WHICH WILL KEEP A
FEW CLOUDS ACROSS THE REGION ALTHOUGH DRY WEATHER EXPECTED. WHILE
GUSTY WINDS WILL DIMINISH TONIGHT...THERE IS ENOUGH PRESSURE
GRADIENT TO KEEP THE WINDS UP SO TEMPS WILL NOT DROP OFF THAT
QUICKLY. USED A BLEND OF AVAILABLE GUIDANCE WHICH SUGGESTS MIN
TEMPS MOSTLY IN THE 20S...WITH LOWER 30S OVER THE OUTER
CAPE/ISLANDS.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
FRIDAY...
HIGH PRES BUILDS ACROSS THE GRT LAKES WITH NW FLOW ACROSS NEW
ENG. TRICKY CLOUD FORECAST AS NAM INDICATING LOW LEVEL MOISTURE
TRAPPED BELOW INVERSION WITH WIDESPREAD LOW CLOUDS...WHILE GFS AND
ECMWF ARE DRIER IN THE LOW LEVELS. GIVEN LOW LEVEL FLOW IS STILL
NW...WE WILL LEAN MORE OPTIMISTIC THAN NAM WITH A MIX OF CLOUDS
AND SUN EXPECTED. TEMPS WILL LIKELY BE 3-5 DEGREES COLDER THAN
TODAY GIVEN COOLING AT 925 MB...WITH MAX TEMPS RANGING FROM NEAR
30 HIGHER TERRAIN IN NORTHERN AND WESTERN MA TO UPPER 30S IN THE
COASTAL PLAIN.

FRIDAY NIGHT...
MID LEVEL SHORTWAVE MOVES INTO W NEW ENG TOWARD DAYBREAK...BUT
FORCING IS WEAK THROUGH MOST OF THE NIGHT AND MOISTURE IS LIMITED
SO EXPECTING A MAINLY DRY NIGHT. HOWEVER...AS HIGH PRES BUILDS
EASTWARD ACROSS QUEBEC LOW LEVEL WINDS BECOME NE AND MODELS
INDICATE INCREASING LOW MOISTURE BACKING IN ACROSS SE NEW ENG
OVERNIGHT. DELTA T FROM SST TO THE TOP OF THE MIXED LAYER IS
AROUND 13C WHICH IS MARGINAL FOR OCEAN EFFECT AND OCEAN INDUCED
CAPES ARE NOT IMPRESSIVE...BUT LOW LEVEL LAPSE RATES ARE
INCREASING. MODELS DO SHOW SOME LIGHT QPF DEVELOPING SO THERE MAY
BE A FEW SNOW SHOWERS DEVELOPING OVER CAPE COD AND ACK OVERNIGHT
AND WE HAVE SOME LOW CHC POPS.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
HIGHLIGHTS...

* SCT LIGHT SNOW/RAIN SHOWERS SAT INTO SUN...WITH A PERIOD OF
  DRIZZLE/FREEZING DRIZZLE POSSIBLE SAT NIGHT INTO SUN MORNING
* WEAK WAVE OF LOW PRESSURE WILL PASS WELL OFFSHORE TUE BUT COULD
  STILL SEE LIGHT PRECIP
* ANOMALOUSLY STRONG STORM SYSTEM WILL BRING HEAVY RAIN...GUSTY
  WINDS AND COASTAL CONCERNS AROUND CHRISTMAS EVE

OVERVIEW AND MODEL PREFERENCES...
MEDIUM RANGE MODELS CONTINUE IN PRETTY GOOD AGREEMENT ON LARGE
SCALE AND UPPER LEVEL FEATURES THROUGH MOST OF THE FORECAST
PERIOD.

MODELS AND ENSEMBLES CONTINUE TO SIGNAL WEAK SHORT WAVES THAT
TRANSLATE ACROSS THE REGION EARLY IN THIS PERIOD...WITH A RATHER
POTENT BUT FAST MOVING ONE FOR SAT NIGHT/SUN TIMEFRAME WHICH IS
AIDED WITH LOW LEVEL ONSHORE MOISTURE...WITH A SECOND WEAK LOW FOR
LATE MON INTO TUE BRINGING ANOTHER PERIOD OF LIGHT PRECIP.

STILL QUITE A FEW PLACEMENT AND TIMING ISSUES WITH THE EVOLUTION
OF AN ANOMALOUSLY DEEP H5 CUTOFF LOW DEVELOPING ACROSS THE WESTERN
GREAT LAKES AROUND THE MON-TUE TIMEFRAME...THEN ROTATES NE
SOMEWHERE ACROSS S CENTRAL CANADA FOR CHRISTMAS DAY. BIG
IMPLICATIONS WITH THE ASSOCIATED LONG WAVE TROUGH...WITH GUIDANCE
CONTINUING TO INDICATE THE TROUGH BECOMING NEGATIVELY TILTED
ACROSS THE MID ATLC OR SE U.S. LATE IN THIS PERIOD. SECONDARY/
TRIPLE POINT LOW FORMS ON SURFACE FRONT OVER THE EASTERN GULF
AROUND TUESDAY...THEN WORKS UP ACROSS EASTERN PORTIONS OF THE SE
AND MID ATLC STATES. QUESTION IS IF THIS LOW APPROACHES WESTERN
PORTIONS OF NEW ENGLAND WED NIGHT.

STILL SEE THE SIGNALS FOR A FAST MOVING STORM WITH MULTIPLE
IMPACTS POSSIBLE...INCLUDING PERIOD OF HEAVY RAINFALL AND STRONG
WIND GUSTS...FIRST FROM THE SOUTH THEN SHIFTING TO THE WEST. COULD
EVEN SEE SOME COASTAL IMPACTS DURING THE HIGH TIDE CYCLE DURING
WED. TIMING REMAINS AN ISSUE...AS ONE WOULD EXPECT THIS FAR OUT.
MODEL GUIDANCE STILL DOING A RATHER GOOD JOB HANDLING GENERAL
FEATURES OF THIS SYSTEM AT THIS POINT.

USED A BLEND OF THE AVAILABLE GUIDANCE ALONG WITH WPC GUIDANCE. 

DETAILS...
 
SATURDAY INTO SUNDAY...HIGH CONFIDENCE.
HIGH PRES AT THE SURFACE AND ALOFT MOVES ACROSS QUEBEC INTO THE
MARITIMES DURING THIS WEEKEND...THEN TENDS TO SLOW ITS EASTWARD
PROGRESS WITH BLOCKING OVER THE WESTERN ATLC. RATHER POTENT SHORT
WAVE UNDERNEATH THE UPPER SYSTEM MOVES ACROSS THE REGION...AIDED
BY A LOW LEVEL E-NE WIND IN PLACE. A LOT OF LOW LEVEL MOISTURE IN
PLACE AS SEEN ON BUFKIT MODEL SOUNDINGS...SO WILL SEE SOME LIGHT
RAIN/SNOW SHOWERS DEVELOP FROM E-W DURING SATURDAY. EXPECTING
LITTLE IF ANY SNOW ACCUMULATIONS DURING SAT.

HOWEVER...AS TEMPS FALL BACK SAT NIGHT...ALONG WITH THE DEEP LOW
LEVEL MOISTURE FEED...WILL ALSO SEE AREAS OF DRIZZLE DEVELOP. BIG
PROBLEM WILL BE JUST AWAY FROM THE COAST WHERE TEMPS FALL BELOW
FREEZING WHICH MAY MEAN FREEZING DRIZZLE. DOES NOT TAKE MUCH TO
GET GLAZING ESPECIALLY ON UNTREATED SURFACES. WILL NEED TO MONITOR
THIS CLOSELY FOR POSSIBLE WINTER WEATHER HEADLINES ACROSS INTERIOR
E MA INTO RI...POSSIBLY EVEN FURTHER W. WITH THE LIGHT
SNOW...MIGHT SEE UP TO 1/2 INCH ACCUMULATIONS SAT NIGHT INTO SUN
MORNING.

ON SUNDAY...DRIZZLE WILL TAPER OFF DURING THE MORNING...THOUGH
LEFTOVER RAIN/SNOW SHOWERS WILL LINGER THOUGH TEND TO TAPER OFF
DURING THE AFTERNOON.

MONDAY INTO TUESDAY...MODERATE CONFIDENCE. 
ANOTHER COASTAL LOW LOOKS TO DEVELOP OFF THE SE U.S. COAST
AND...AS UPPER LEVEL TROUGH BEGINS TO DIG ACROSS THE CENTRAL
U.S...WILL SHIFT TO THE E-NE UNDERNEATH THE UPPER RIDGE. THE
MARITIMES SURFACE HIGH REMAINS PRETTY MUCH IN PLACE...WHICH WILL
HELP SHIFT THE MAIN EFFECTS OF THIS LOW WELL OFFSHORE /SE OF THE
40N/70W BENCHMARK/. HOWEVER...MODELS CONTINUE TO SIGNAL LIGHT
PRECIP REACHING THE COAST MAINLY MON NIGHT INTO TUE. EXPECT MAINLY
MIXED RAIN/SNOW SHOWERS WITH SPOTTY BRIEF PERIODS OF FREEZING
PRECIP AROUND DAYBREAK TUE ACROSS N CT/N RI INTO S CENTRAL MA.
EXPECT HIGH TEMPS ON TUE TO RUN ABOUT 5 DEGS ABOVE SEASONAL NORMS
AS WINDS BEGIN TO SHIFT MORE S- SE...THOUGH SOME TIMING ISSUES IN
PLACE FOR WIND SHIFT AMONGST OP MODELS.

ONCE THE LOW EXITS LATE TUE...WILL ALREADY START TO SEE MOISTURE
FEED UP THE COAST FROM THE DEVELOPING GULF LOW...SO NOT MUCH OF A
BREAK IN THE PRECIP BETWEEN SYSTEMS.

TUESDAY/S LATE MORNING HIGH TIDE WILL RUN UP TO 11.6 FT IN BOSTON
AND...WITH ANY EASTERLY WIND FLOW...THIS MAY CAUSE MINOR COASTAL
FLOODING. WILL MONITOR THIS ASPECT.

WEDNESDAY AND CHRISTMAS DAY...HIGH CONFIDENCE IN SYSTEM...LOW 
CONFIDENCE ON DETAILS. 

SECONDARY LOW FROM THE PARENT OVER THE NORTHERN GREAT LAKES
DEEPENS AS IT SHIFTS N. MODELS TRY TO PUSH THIS SYSTEM CLOSE TO OR
JUST INTO WESTERN NEW ENGLAND LATE WED/WED NIGHT...THOUGH STILL
TIMING ISSUES IN PLACE. AT THIS POINT...WILL SEE HEAVIEST SLUG OF
PRECIP MOVING ACROSS LATE WED INTO WED EVENING. GOOD TROPICAL
CONNECTION CONTINUES WITH PWATS FROM 1.25 TO 1.4 INCHES...RUNNING
ABOUT +2SD TO +3SD ABOVE NORMAL FOR LATE DECEMBER. GOOD SHOT OF
MILD AIR WORKS IN ON SE- S WINDS. MODELS CONTINUE TO SIGNAL H925
AND H85 FROM 50-65 KT...AND AT LEAST SOME WILL MIX DOWN ESPECIALLY
IF THE LOW PRES PASSES CLOSER /WITH RAPIDLY FALLING PRESSURE/.
HAVE HIGHS ON WED UP TO THE LOWER 50S ACROSS EASTERN AND SOUTHERN
AREAS...BUT COULD BE EVEN HIGHER WITH STRONG ONSHORE WINDS.

CURRENT TIMING SUGGESTS THE DRY SLOT SHOULD WORK INTO THE REGION
LATE WED NIGHT INTO CHRISTMAS MORNING...SO PRECIP SHOULD END. WILL
STILL SEE GUSTY WINDS...THOUGH QUICKLY SHIFTING TO W-SW AND
GUSTING UP TO 25-30 KT...HIGHEST ALONG THE S COAST.

MAY NEED HEADLINES WITH THIS SYSTEM...WITH POSSIBLE URBAN/POOR
DRAINAGE FLOODING IN HEAVY RAINFALL WED/WED NIGHT...STRONG WINDS
BOTH WED AND THU...AND MAYBE EVEN FOR COASTAL CONCERNS. NOTING
ASTRO HIGH TIDES CONTINUE /11.7 AND 11.5 FT AT BOSTON
RESPECTIVELY/... THOUGH TIMING OF WIND SHIFT MAY COME INTO PLAY
FOR CHRISTMAS EVE INTO CHRISTMAS MORNING.

FRIDAY...LOW CONFIDENCE MAINLY FOR TIMING.
ONCE UPPER LOW MOVES INTO SOUTHERN CANADA...EXPECT A RATHER FAST
UPPER W FLOW IN PLACE. MAY SEE LEFTOVER SNOW SHOWERS ACROSS THE E
SLOPES OF THE BERKSHIRES INTO THE MONADNOCKS. TEMPS WILL FALL BACK
CLOSE TO SEASONAL NORMS. ANOTHER LOW MIGHT MOVE INTO W NY STATE
FRI NIGHT.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...

THROUGH 00Z...LOW VFR/MVFR CIGS AROUND 3000-3500 FT. TREND SHOULD
BE FOR CLOUD DECK TO BECOME SCT TOWARD 00Z..ESPECIALLY NEAR THE
COAST. W/NW GUSTS TO 25-30 KT. 

TONIGHT...MODERATE CONFIDENCE. MAINLY VFR...BUT LINGERING MVFR
CIGS POSSIBLE IN THE WEST. DIMINISHING WIND. 

FRIDAY...LOW CONFIDENCE DUE TO UNCERTAINTY WITH EXTENT OF ANY MVFR
CIGS. WE HAVE MAINLY VFR IN THE TAFS WITH POCKETS OF MVFR...BUT
IT IS POSSIBLE MVFR CIGS COULD BE MORE EXPANSIVE IF LOW LEVEL
MOISTURE BECOMES TRAPPED BELOW THE INVERSION. LATER FORECASTS
WILL NEED TO REEVALUATE THIS.

FRIDAY NIGHT...MODERATE CONFIDENCE. MAINLY VFR...BUT MVFR CIGS
FROM THE OCEAN EXPANDING WEST ACROSS E MA. LOW PROB FOR SOME OCEAN
EFFECT SNOW SHOWERS OVER CAPE COD AND ACK AFTER MIDNIGHT.

KBOS TERMINAL...MODERATE CONFIDENCE. MAINLY VFR...BUT LOW PROB
FOR MVFR CIGS FRIDAY.

KBDL TERMINAL...MODERATE CONFIDENCE. SHOULD SEE MVFR CIGS SCATTER
OUT THIS EVENING. MVFR CIGS MAY RETURN FRI BUT THIS IS UNCERTAIN.

OUTLOOK...SATURDAY THROUGH TUESDAY...

SATURDAY INTO SUNDAY...HIGH CONFIDENCE. MAINLY VFR ACROSS CENTRAL
AND WESTERN AREAS. E MA INTO RI...AREAS MVFR CIGS/VSBYS IN ANY
RAIN/SNOW SHOWERS...AREAS OF DRIZZLE SAT NIGHT INTO SUN MORNING.

MONDAY-TUESDAY...MODERATE CONFIDENCE. MAINLY VFR. MAY SEE LOCAL
MVFR IN WIDELY SCT RAIN/SNOW SHOWERS MON NIGHT/TUE.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE.

TONIGHT...W/NW GUSTS 25-30 KT WILL LINGER OVER THE WATERS INTO
THIS EVENING BEFORE DIMINISHING OVERNIGHT. SCA HEADLINES WILL
CONTINUE TONIGHT.

FRIDAY...NW WINDS WILL BE BELOW SCA THRESHOLDS...BUT HAZARDOUS
SEAS WILL CONTINUE THROUGH THE MORNING OVER THE OUTER EASTERN 
WATERS...BEFORE SUBSIDING BELOW SCA. WILL LIKELY NEED TO EXTEND
THE SCA FOR SEAS INTO FRI MORNING. 

FRIDAY NIGHT...N/NW WINDS AND SEAS BELOW SCA. 

OUTLOOK...SATURDAY THROUGH TUESDAY...MODERATE TO HIGH CONFIDENCE.

SATURDAY THROUGH MONDAY...WINDS AND SEAS BELOW SMALL CRAFT
CRITERIA.
 
MONDAY NIGHT AND TUESDAY...EXPECT E-NE WINDS GUSTING UP TO 25 KT
WITH SEAS BUILDING UP TO 5-7 FT...HIGHEST ON THE EASTERN OUTER
WATERS.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST FRIDAY FOR ANZ231-232-251.
     SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR 
     ANZ233>235-237.
     SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ230-
     236.
     SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ250-254>256.

&&

$$
SYNOPSIS...KJC/EVT
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...EVT
AVIATION...KJC/EVT
MARINE...KJC/EVT



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