Area Forecast Discussion
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000
FXUS61 KBOX 200608
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
107 AM EST SAT DEC 20 2014

.SYNOPSIS...
A WEAK DISTURBANCE AND ONSHORE FLOW WILL RESULT IN A PERIOD OF
LIGHT SNOW/RAIN SHOWERS MAINLY ACROSS EASTERN NEW ENGLAND THIS
WEEKEND INTO EARLY NEXT WEEK. LOW PRESSURE WILL PASS SOUTH OF NEW
ENGLAND...BRINGING ANOTHER PERIOD OF PRECIPITATION. A MUCH
STRONGER STORM PASSING WEST OF NEW ENGLAND WILL BRING HEAVY
RAINFALL...GUSTY WINDS AND COASTAL FLOODING CONCERNS TO THE
REGION WEDNESDAY INTO WEDNESDAY EVENING. DRY BUT VERY WINDY
CONDITIONS FOLLOW FOR CHRISTMAS DAY INTO FRIDAY.

&&

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

105 AM UPDATE...

LOW CLOUDS BEGINNING TO BACK IN OFF THE OCEAN VERY EARLY THIS
MORNING.  THIS IN RESPONSE TO AN APPROACHING SHORTWAVE RESULTING IN
WINDS AT 925 MB BECOMING EAST.  SHOULD SEE LOW CLOUDS CONTINUE TO
EXPAND ACROSS EASTERN NEW ENGLAND THROUGH DAYBREAK...WHILE THE
INTERIOR HAS CLEAR TO PARTLY CLOUDY SKIES.  TEMPS WILL REMAIN IN THE
20S THROUGH DAYBREAK...EXCEPT LOWER TO MIDDLE 30S ACROSS PORTIONS OF
THE CAPE/ACK WITH AN ONSHORE COMPONENT TO THE WIND.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
HIGH PRES BUILDS ACROSS N MAINE AND THE MARITIMES WITH LOW LEVEL
FLOW VEERING TO THE E WHILE SFC WINDS MOSTLY NE. THIS WILL RESULT
IN LOW CLOUDS EXPANDING WEST ACROSS SNE DURING SAT AS LOW LEVEL
MOISTURE INCREASES. NOT REALLY LOOKING AT A PURE OCEAN EFFECT
SITUATION AS INSTABILITY IS MARGINAL. HOWEVER...HI-RES GUIDANCE
PICKING UP ON A DEVELOPING COASTAL FRONT ACROSS CAPE COD VICINITY
WITH E WINDS TO THE E OF THE BOUNDARY AND N/NE WINDS TO THE WEST.
LOW LEVEL FORCING COMBINED WITH DEEPENING MOISTURE AS MID LEVEL
SHORTWAVE MOVES IN FROM THE WEST WILL RESULT IN RAIN/SNOW SHOWERS
EXPANDING WEST FROM CAPE COD INTO EASTERN HALF NEW ENG. WHILE SOME
LIGHT PRECIP IS POSSIBLE IN THE MORNING...ESPECIALLY CAPE
COD...BULK OF PRECIP OCCURS LATER SAT INTO SAT NIGHT ASSOCD WITH
DEEPER MOISTURE AND LOW LEVEL LIFT FROM THE COASTAL FRONT/INVERTED
TROF.

PTYPE/SNOW ACCUM...
LOOKING AT MOSTLY RAIN FOR CAPE/ISLANDS AND POSSIBLY INTO SE
COASTAL PLYMOUTH COUNTY WHERE E WINDS WILL SUFFICIENTLY WARM THE
BOUNDARY LAYER KEEPING TEMPS IN THE MID/UPPER 30S. HOWEVER...JUST
INLAND AND NORTH FROM THE IMMEDIATE SE COAST AND WEST OF THE
COASTAL FRONT WHERE WINDS ARE FORECAST TO BE MORE
NORTHERLY...EXPECT MOSTLY SNOW ALTHOUGH THERE COULD BE A MIX AT
THE START. FREEZING DRIZZLE IS NOT LIKELY AS THE COLUMN MOISTENS
LATE SAT INTO SAT NIGHT WITH TEMPS -10C IN THE MOIST LAYER WHICH
IS COLD ENOUGH FOR ICE CRYSTAL PRODUCTION.

NAM IS PICKING UP ON SOME ENHANCEMENT IN N PLYMOUTH COUNTY INTO
NORFOLK COUNTY WITH QPF UP TO A THIRD OF AN INCH. THIS LIKELY
ASSOCD WITH A 20-25 KT E/NE LOW LEVEL JET THAT THE NAM IS
FORECASTING. HOWEVER...THIS MIGHT BE OVERDONE AS HI-RES WRF QPF
IS LESS AND OTHER MODELS ARE WEAKER WITH THE LOW LEVEL NE FLOW.
DONT WANT TO COMPLETELY IGNORE THE NAM AS IT SOMETIMES CAN PICK
UP ON HEAVIER MESOSCALE PRECIP IN THESE SITUATIONS SO USED A
BLEND OF NAM/GFS QPF TO TEMPER NAM OUTPUT. MAINLY LOOKING AT A
COATING TO AN INCH FOR EASTERN NEW ENG...HIGHEST AMOUNTS ACROSS E
MA AWAY FROM THE IMMEDIATE COAST. LOCALIZED AMOUNTS UP TO 2 INCHES
POSSIBLE...ESPECIALLY JUST SW OF BOSTON.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
HIGHLIGHTS...

* SCT SNOW/RAIN SHOWERS LINGER ON SUNDAY WITH SLIGHTLY BELOW
  NORMAL TEMPS
* WEAK LOW PRES WILL PASS SOUTH OF NEW ENGLAND MONDAY NIGHT AND
  TUESDAY BRINGING LIGHT PRECIPITATION...AS WELL AS A WINTRY MIX
  TO THE INTERIOR
* STRENGTHENING LOW PRES WILL WRAP UP AROUND ANOMALOUS VORTEX
  ACROSS THE GREAT LAKES...BRINGING HEAVY RAIN...GUSTY WINDS AND
  COASTAL CONCERNS TO THE REGION LATE WEDNESDAY INTO CHRISTMAS EVE

OVERVIEW AND MODEL PREFERENCES...

MEDIUM RANGE MODEL SUITE CONTINUES TO SIGNAL DEVELOPMENT OF
AMPLIFIED UPPER LEVEL PATTERN ACROSS NORTH AMERICA THROUGH THIS
FORECAST PERIOD. AN H5 CUTOFF VORTEX WILL DOMINATE ACROSS THE GREAT
LAKES AND ITS EXTENDING LONG WAVE TROUGH WRAPPING AROUND TO THE
EASTERN SEABOARD AS IT BECOMES NEGATIVELY TILTED. WITH OVERALL SW
FLOW IN PLACE...WILL SEE WEAK SYSTEMS WORK TOWARD THE REGION EARLY
IN THE PERIOD. A STRONGER LOW WILL DEVELOP NEAR OR JUST OFF THE SE
U.S. COAST AROUND EARLY WED AND PASS W OF THE REGION WED NIGHT...
BRINGING GUSTY WINDS...HEAVY RAINFALL WITH A FEW THUNDERSTORMS
POSSIBLE AS WELL AS POSSIBLE COASTAL CONCERNS.

WHILE THERE ARE STILL SOME TIMING AND TRACK VARIANCES WITH THE MID
WEEK SYSTEM...MODELS AND ENSEMBLES REMAIN IN GOOD AGREEMENT WITH THE
DEVELOPMENT OF THIS AMPLIFIED PATTERN...AS WELL AS THE UPPER
LEVEL VORTEX ACROSS THE GREAT LAKES AND SURFACE SYSTEM THAT WILL
MORE THAN LIKELY AFFECT THE REGION DURING THE WEDNESDAY-WEDNESDAY
NIGHT TIMEFRAME.

USED A BLEND OF AVAILABLE GUIDANCE AS WELL AS GFS/EC ENSEMBLE MEANS
FOR THIS FORECAST WHICH SHOWED GOOD CONTINUITY TO THE PREVIOUS
FORECAST.

DETAILS...

SUNDAY AND MONDAY...MODERATE TO HIGH CONFIDENCE.

LEFTOVER MOISTURE WILL LINGER SUNDAY MORNING WITH LIGHT RAIN
AND/OR SNOW SHOWERS MAINLY ACROSS E MA/RI THOUGH COULD SEE SOME
ISOLD ACTIVITY FURTHER INLAND AS COASTAL FRONT WEAKENS. RIDGING
WILL NOSE DOWN THE COAST FROM HIGH PRES OVER NORTHERN NEW ENGLAND
AND QUEBEC SUN NIGHT INTO MONDAY...BRINGING A BRIEF DRY PERIOD
THOUGH CLOUDS WILL LINGER WITH A CONTINUED ONSHORE WIND
FLOW...ALBEIT WEAK. EXPECT TEMPS TO RUN NEAR OR SLIGHTLY BELOW
NORMAL...THOUGH WILL BE A BIT MILDER ALONG THE S COAST DURING MON.

BY LATE MONDAY...MAY START TO SEE SOME PRECIP WORK INTO THE LOWER
CT VALLEY AS A WEAK LOW MOVES OFF THE MID ATLC COAST.

MONDAY NIGHT-TUESDAY...MODERATE CONFIDENCE.

WEAK COASTAL LOW WILL PASS OFF THE SOUTH COAST...BUT WILL BRING
ENOUGH MOISTURE AND LIFT FOR PRECIP TO MOVE IN FROM S-N. TEMPS
WILL STILL BE CHILLY THOUGH...ESPECIALLY INLAND THERE THE COLDER
AIR WILL BE TRAPPED... SO WILL SEE SOME MIXED PRECIP /SLEET AND/OR
FREEZING RAIN/. EVEN THOUGH QPF WILL BE LIGHT...COULD BE ENOUGH TO
CAUSE SOME LIGHT GLAZING PROBLEMS LATE MON NIGHT INTO TUE MORNING.
STILL SOME TIMING ISSUES AS WELL AS QUESTIONS WITH THERMAL
PROFILES...BUT MAY NEED WINTER WX HEADLINES DURING THIS TIMEFRAME.
SOMETHING TO MONITOR CLOSELY.

BY TUE AFTERNOON...TEMPS SHOULD RECOVER WITH GRADUALLY INCREASING
E-SE WINDS...SO WILL SEE ALL RAIN BY THEN. HIGHS ON TUE WILL
RANGE FROM THE UPPER 30S ACROSS THE HIGHER INLAND TERRAIN TO THE
MID AND UPPER 40S ALONG THE COAST.

ONE OTHER ISSUE THAT MAY NEED ATTENTION WILL BE THE LONG EASTERLY
FETCH AND INCREASING ASTRONOMICAL TIDES ON TUESDAY. BOSTON
HARBOR/S HIGH TIDE OCCURS AT 1142 AM AT 11.6 FEET. SURFACE WINDS
LOOK TO REMAIN AT 15 KT OR LESS BUT...WITH THE MAINLY EASTERLY
WIND DIRECTION OVER SEVERAL DAYS...MAY SEE SOME GROUND SWELLS WORK
IN WHICH COULD CAUSE SOME POSSIBLE SPLASHOVER DURING THE MIDDAY
TIDE.

WEDNESDAY AND THURSDAY...HIGH CONFIDENCE IN SYSTEM DEVELOPMENT AND
EFFECTS...LOW TO MODERATE CONFIDENCE ON TIMING DETAILS.

WILL SEE STRONG SURFACE SYSTEM AND ITS ASSOCIATED H5 CUTOFF
VORTEX WILL BE INTENSIFYING DURING THIS TIMEFRAME...WHILE LONG
WAVE TROUGHING WILL BECOME NEGATIVELY TILTED AROUND THE MID ATLC
OR SE U.S. COAST. A SECONDARY LOW...WITH ENERGY AND TROPICAL
MOISTURE WORKING IN FROM THE GULF OF MEXICO...WILL INTENSIFY
DURING WED AS IT WRAPS AROUND THE LARGER UPPER LEVEL CIRCULATION.
LOOKS LIKE THIS LOW WILL PASS W OF THE REGION...BUT WILL BE IN THE
AREA OF BEST MOISTURE CONVERGENCE AND TRANSPORT UP THE EASTERN
SEABOARD. THE 12Z GFS IS BULLISH IN BRINGING SLUG OF HEAVY QPF
ACROSS THE REGION. BOTH THE 12Z EC AND GGEM ALSO SIGNAL THIS
INFLUX THOUGH NOT QUITE AS HIGH ON THE PRECIP AMTS.

STILL NOTING PWATS AT 1.4 TO 1.5 INCHES...RUNNING 2-3SD ABOVE
SEASONAL NORMALS AT ABOUT THE TIME OF THE HEAVIEST PRECIP LATE
WED INTO WED EVENING. ON TOP OF THIS...SOME GOOD INSTABILITY MOVES
ACROSS WITH K INDICES IN THE LOWER-MID 30S AND TOTAL TOTALS IN THE
LOWER 50S. WOULD NOT BE SURPRISED TO SEE SOME ISOLD THUNDER SO
MENTIONED IN THE FORECAST MAINLY DURING WED NIGHT...ALONG WITH
HEAVY RAINFALL FROM THE CONVECTION. LOW LEVEL JET ON ORDER OF
40-55 KT AT H85 AND 50-60 KT AT H925...SO COULD ALSO SEE GUSTY
WINDS ESPECIALLY WITH ANY STORMS. OH...ONE MORE THING...THERE
WILL BE A BRIEF BURST OF MILDER AIR THAT WORKS IN WITH THIS
SYSTEM. EXPECT TEMPS TO RISE TO THE MID 40S WELL INLAND TO THE
MID 50S AT THE COAST...BUT WILL NOT TOP OFF UNTIL CLOSE TO
MIDNIGHT WED NIGHT...WHICH WILL HELP SUPPORT THE INSTABILITY.

MODELS CONTINUE TO SIGNAL FAST MOVEMENT OF THE SURFACE SYSTEM
LATE WED NIGHT...WITH DRY SLOT WORKING ACROSS THE REGION AFTER
MIDNIGHT WITH DRY CONDITIONS BY DAWN ON CHRISTMAS MORNING. WINDS
WILL QUICKLY SHIFT AROUND TO W-SW AND WILL BECOME VERY GUSTY WITH
THE LOW LEVEL JET IN PLACE AND COLDER AIR WRAPPING IN.

MAY HAVE SOME COASTAL FLOODING ISSUES WITH HIGHEST ASTRONOMICAL
TIDES OF THE MONTH OCCUR ON WED AND THU...UP TO 11.7 FT AND 11.5
FT RESPECTIVELY FOR BOSTON. ANY EASTERLY COMPONENT WILL PUSH THE
TIDE ABOVE FLOOD...SO COASTAL FLOODING IS POSSIBLE AS WELL AS
BEACH EROSION ON THE WED TIDE ALONG E FACING BEACHES. THE SOUTH
COASTLINE WILL ALSO HAVE TO BE WATCH CLOSELY ON THU AS WINDS SHIFT
TO W- SW...THOUGH E COASTAL AREAS COULD SEE PROBLEMS WITH
CONTINUED E SWELLS. AS MENTIONED ABOVE...STRONG SOUTHERLY JET
DEVELOPS WED INTO THU AND...WITH ASTRONOMICAL HIGH TIDES...COULD
ALSO SEE MINOR TO MODERATE COASTAL FLOODING. ANOTHER ISSUE IS THE
POTENTIAL PRESSURE FALLS IF THIS SYSTEM STRENGTHENS EVEN
MORE...IT COULD ADD ANOTHER FOOT ONTO THE SURGE.

FRIDAY...LOW CONFIDENCE.

ONCE UPPER LOW AND SURFACE SYSTEM MOVES INTO SOUTHERN CANADA...
EXPECT A RATHER FAST UPPER W FLOW IN PLACE. MAY SEE SOME LEFTOVER
SNOW SHOWERS ACROSS THE E SLOPES OF THE BERKSHIRES. GUSTY W-SW
WINDS CONTINUE AS TEMPS FALL BACK TO MORE SEASONABLE LEVELS.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SUNDAY/...

105 AM UPDATE...

TODAY...MODERATE CONFIDENCE.  MVFR CIGS WILL CONTINUE TO OVERSPREAD
EASTERN NEW ENGLAND THIS MORNING AND EVENTUALLY INTO THE INTERIOR
THIS AFTERNOON.  SCATTERED PRECIPITATION WILL OVERSPREAD
SOUTHEAST MA/CAPE/ISLANDS THIS AFTERNOON.  PTYPE MAINLY SNOW SHOWERS
NORTHWEST OF THE SOUTHEAST PLYMOUTH COUNTY COAST AND RAIN SHOWERS
SOUTHEAST OF THAT REGION. LOCALIZED IFR CONDITIONS POSSIBLE JUST
INLAND FROM THE SOUTHEAST NEW ENGLAND COAST...WHERE PTYPE IS SNOW.

TONIGHT AND SUNDAY...MODERATE CONFIDENCE.  MVFR CONDITIONS DOMINATE
IN LOWER CLOUDS AND SCATTERED PRECIPITATION.  LOCALIZED IFR
CONDITIONS POSSIBLE WITH THE BEST CHANCE IN SNOW SHOWERS.
PRECIPITATION AFFECTS MAINLY EASTERN NEW ENGLAND BUT STILL SOME
SCATTERED ACTIVITY ACROSS WESTERN NEW ENGLAND. PTYPE MAINLY SNOW
SHOWERS NORTHWEST OF THE SOUTHEAST PLYMOUTH COUNTY COAST AND RAIN
SHOWERS SOUTHEAST OF THAT REGION.

KBOS TERMINAL...MODERATE CONFIDENCE IN TAF.  SNOW SHOWERS MAY ARRIVE
TOWARDS 00Z THIS EVENING.

KBDL TERMINAL...MODERATE CONFIDENCE IN TAF.

OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY...

MONDAY...MODERATE CONFIDENCE. MAINLY VFR.

MONDAY NIGHT-TUESDAY...MODERATE CONFIDENCE. DEVELOPING RAIN OR
MIXED PRECIP FROM S-N MON NIGHT WITH MVFR CONDITIONS. MAY SEE
-FZRA/-PL ACROSS CENTRAL AND WESTERN AREAS AROUND OR AFTER
MIDNIGHT INTO TUE MORNING THEN SHOULD CHANGE TO RAIN AS TEMPS
RISE. E-SE WINDS GUSTING TO 20-25 KT ALONG S COAST TUE.

TUESDAY NIGHT-WEDNESDAY...MODERATE CONFIDENCE. MVFR-IFR
CONDITIONS IN RAIN...HEAVY AT TIMES DURING WED. ISOLD THUNDER
POSSIBLE WED AFTERNOON/EVENING. E WINDS SHIFTING TO SE-S LATE TUE
NIGHT/WED WITH GUSTS UP TO 25-30 KT...HIGHEST ACROSS CAPE COD AND
THE ISLANDS.

&&

.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.

HIGH PRESSURE BUILDING EAST TO MAINE AND THE MARITIMES WILL KEEP
WINDS/SEAS BELOW SCA THRESHOLDS THROUGH SATURDAY NIGHT...WITH WIND
SPEEDS LESS THAN 20 KT. NORTHERLY WINDS TONIGHT BECOMING NE
SAT/SAT NIGHT. GUSTS UP TO 20 KT POSSIBLE SAT NIGHT ACROSS NE MA
COASTAL WATERS.

OUTLOOK...SUNDAY THROUGH WEDNESDAY...MODERATE TO HIGH CONFIDENCE.

SUNDAY THROUGH MONDAY NIGHT...WINDS AND SEAS BELOW SMALL CRAFT
CRITERIA. E WINDS GUSTING UP TO 20 KT MON NIGHT.

TUESDAY-WEDNESDAY...E WINDS INCREASE...GUSTING TO 30 KT TUE THEN
SHIFT TO SE GUSTING TO 30-35 KT WED...HIGHEST ON THE OUTER
WATERS. SEAS BUILD UP TO 7-11 FT BY WED. GALES ON THE OUTER WATERS
LIKELY.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...NONE.

&&

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


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