Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 181741
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
1241 PM EST THU DEC 18 2014

.SYNOPSIS...
SCATTERED RAIN AND SNOW SHOWERS WILL QUICKLY COME TO AN END BY MID
MORNING.  OTHERWISE...HIGH PRESSURE SLOWLY BUILDING ACROSS EASTERN
CANADA WILL RESULT IN DRY AND SEASONABLY CHILLY TEMPERATURES THROUGH
FRIDAY. SCATTERED SNOW SHOWERS WILL DEVELOP SATURDAY NIGHT INTO
SUNDAY WITH A LOW PRESSURE SYSTEM MOVING NEAR THE REGION TUESDAY.
AN ANOMALOUS SYSTEM WILL IMPACT THE EASTERN UNITED STATES
WEDNESDAY INTO THURSDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1230 PM UPDATE...
LOTS OF DIURNAL STRATO-CU HAVE DEVELOPED ACROSS SNE WITH COLD
POOL ALOFT WITH 500 MB TEMPS -26C ACTING ON RESIDUAL LOW LEVEL
MOISTURE. WE SHOULD SEE A DECREASE IN CLOUD COVER LATE
AFTERNOON/EVENING...ESPECIALLY IN THE COASTAL PLAIN. GUSTY W/NW
WILL CONTINUE THIS AFTERNOON. ADJUSTED SKY GRIDS...OTHERWISE
FORECAST ON TRACK.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
TONIGHT...

LOW PRESSURE IN THE CANADIAN MARITIMES WILL CONTINUE TO LIFT
NORTHEAST.  THIS WILL ALLOW THE PRESSURE GRADIENT TO WEAKEN A
BIT...BUT NOT ENOUGH FOR WINDS TO COMPLETELY DECOUPLE EVEN IN THE
VALLEY LOCATIONS.  THEREFORE...LOW TEMPS SHOULD MAINLY BE IN THE 20S
TO AROUND 30 WITH PARTLY CLOUDY SKIES.

FRIDAY...

LARGE HIGH PRESSURE OVER THE GREAT LAKES SHOULD PUSH EAST INTO
QUEBEC.  WHILE WERE NOT TOO COLD AT 850 MB...THIS HIGH PRESSURE
SYSTEM SHOULD ALLOW SOME SHALLOW COLD AIR TOO OOZE SOUTH...KEEPING
HIGH TEMPS IN THE 30S FOR MOST LOCATIONS.  SHOULD SEE A MIXTURE OF
CLOUDS AND SUN WITH LESS WIND THAN TODAY.

&&

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

* SCT SNOW/RAIN SHOWERS SAT INTO SUNDAY WITH BELOW AVG TEMPS
* WEAK WAVE OF LOW PRESSURE ON TUESDAY
* ANOMALOUS SYSTEM ACROSS THE GREAT LAKES WILL BRING HEAVY
  RAIN...GUSTY WINDS AND COASTAL CONCERNS AROUND CHRISTMAS EVE

OVERVIEW...

OVERALL 00Z GUIDANCE IS IN AGREEMENT SYNOPTICALLY WITH ISSUES ON
TIMING AND SMALLER SCALE FEATURES. AMPLIFIED PATTERN SET TO RETURN
TO THE U.S. AS THE STRONG W PACIFIC JET TRANSLATES DOWNSTREAM THIS
WEEKEND INTO THE PAC NW. BUILDING HEIGHTS OVER SE CANADA SHOULD ALSO
HELP DIG THE TROUGH INTO THE OHIO VALLEY MIDWEEK AND LIKELY CLOSE
OFF AS IT SWINGS INTO SOUTHERN CANADA ON CHRISTMAS DAY.
MODELS/ENSEMBLES HAVE BEEN FAIRLY CONSISTENT IN RECENT RUNS ON THIS
AMPLIFIED PATTERN AND THE MOST RECENT GEFS/ECMWF ENSEMBLE GUIDANCE
SHOW GOOD CORRELATION TO NEXT THURSDAY.

DURING THIS SYNOPTIC TRANSITION...HIGH PRESSURE AND UPPER LEVEL
RIDGE WILL BE OVER THE NORTHEAST SATURDAY INTO SUNDAY. DIGGING
TROUGH OVER THE CENTRAL CONUS WILL PUSH A SHORTWAVE ACROSS THE SE
INTO THE MID-ATLANTIC. APPEARS THAT A WEAK COASTAL LOW WILL DEVELOP
MOVING TOWARDS THE REGION MONDAY INTO TUESDAY. THE GFS BRINGS THIS
LOW OVER THE BENCHMARK WHERE THE EC PUSHES WELL EASTWARD THANKS TO
BUILDING HIGH PRESSURE OVER EASTERN CANADA. THIS SYSTEM IS WEAK SO
COASTAL REGIONS HAVE THE BEST SHOT FOR PRECIP. AS THIS SYSTEM DEPART
APPEARS ANOMALOUS LOW OVER THE GREAT LAKES WILL DEVELOP A SECONDARY
LOW CLOSER TO NEW ENGLAND. THE GFS IS STILL A TAD FASTER COMPARED TO
THE EC BUT OVERALL EXCELLENT MODEL AGREEMENT 6+ DAYS OUT.

DETAILS...

SATURDAY INTO SUNDAY...HIGH CONFIDENCE.

HIGH PRESSURE IN EASTERN CANADA WILL BUILD ACROSS THE REGION FRIDAY
NIGHT INTO SATURDAY. HOWEVER IT APPEARS ON FRIDAY NIGHT INTO
SATURDAY NORTHERLY FLOW MAY ALLOW FOR SOME OCEAN EFFECT CLOUDS/SNOW
SHOWERS TO IMPACT THE CAPE. SURFACE TO 850 MB TEMP DIFFERENCE IS 14C
WHICH IS UNSTABLE ENOUGH FOR SNOW SHOWERS ON SATURDAY FOR THE CAPE.
AM NOT ANTICIPATE MUCH IN THE WAY OF ACCUMULATIONS BUT A DUSTING
CANNOT BE RULED OUT.

WEAK WAVE WILL MOVE THROUGH THE FLOW ON SATURDAY NIGHT AND WITH HIGH
PRESSURE SHIFTING EASTWARD EXPECT ONSHORE EASTERLY FLOW. GUIDANCE
CONTINUES TO SHOW QPF MOVING ONSHORE AND WITH MOISTURE AND THE LIFT
COULD SEE SNOW SHOWERS MOVING INLAND SATURDAY NIGHT INTO SUNDAY.
BIGGEST QUESTION IS WILL THE MOISTURE SATURATE ENOUGH TO -6C. IF NOT
THEN THE POTENTIAL FOR FREEZING DRIZZLE IS POSSIBLE. FOR NOW BELIEVE
THAT THERE IS ENOUGH MOISTURE SO A QUICK HALF INCH TO AN INCH IS
POSSIBLE PER SOUNDINGS EAST OF THE WORCESTER HILLS.

MONDAY INTO TUESDAY...MODERATE CONFIDENCE.

WEAK COASTAL LOW PRESSURE SYSTEM WILL DEVELOP AND MOVE SOMEWHERE
BETWEEN THE BENCHMARK AND WELL OFFSHORE. BELIEVE A SOLUTION FATHER
OUT TO SEA IS POSSIBLE DUE TO STRONG HIGH PRESSURE IN EASTERN
CANADA. REGARDLESS A ROUND OF SHOWERS WILL MOVE ACROSS THE REGION
WITH THE COASTAL AREAS HAVING THE BEST SHOT TO SEE PRECIP. THERMAL
PROFILES WILL ALLOW FOR SNOW AT NIGHT AND RAIN DURING THE DAY.

TEMPERATURES WILL SLOWLY BEGIN TO WARM AS SOUTHERLY FLOW BECOMES
DOMINATE OUT AHEAD OF STRONGER SYSTEM TO THE EAST.

TUESDAY HIGH TIDE WILL BE 11.6 IN BOSTON DURING THE LATE MORNING AND
WITH ANY EASTERLY FLOW MAY ALLOW FOR MINOR COASTAL FLOODING.

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

STRONG ANOMALOUS SYSTEM WILL STRENGTHEN OVER THE GREAT
LAKES...DEVELOPING A SECONDARY SURFACE LOW JUST WEST OF SOUTHERN NEW
ENGLAND. STILL A LOT OF DETAILS TO WORK OUT AS THIS SYSTEM IS STILL
6 DAYS AWAY...HOWEVER ENSEMBLES SHOW THAT THIS SYSTEM IS AROUND 2 TO
3 STANDARD DEVIATIONS ALLOWING FOR INCREASING CONFIDENCE THAT A
POTENT STORM WILL OCCUR. LATEST 00Z GUIDANCE SHOWS THAT MOST PRECIP
WILL BE LIQUID WITH A DEEP SUBTROPICAL CONNECTION BACK ACROSS
MEXICO... PW ANOMALIES FORECAST TO RISE TO BETWEEN +1 TO +3
/OR HIGHER/...AND TEMPERATURES WELL ABOVE AVERAGE. IN FACT WE MAY BE
CLOSE AT BREAKING RECORD HIGH TEMPS IF TEMPS WARM TO 60F OR ABOVE ON
CHRISTMAS EVE.  AS THE SYSTEM WRAPS UP INTO CANADA...COLD AIR
ADVECTION SHOULD CIRCULATE AROUND AND BEGIN A TRANSITION FROM
SOUTHWEST TO NORTHEAST IN TURNING P-TYPE TO SNOW.

THIS SYSTEM IS QUITE STRONG SO WE WILL NEED TO WATCH FOR POSSIBLE
URBAN FLOODING ISSUES AS WELL AS WIND ISSUES. GUIDANCE RIGHT NOW IS
SHOWING A 40 TO 50 KT JET AT 925 MB WHICH MAY WARRANT WIND
ADVISORIES BUT THIS SYSTEM COULD STRENGTHEN EVEN MORE SO A STRONGER
JET IS POSSIBLE. LASTLY COASTAL FLOODING ISSUES WILL NEED TO BE
ADDRESS AS HIGH TIDE ON WED AND THUS ARE 11.7 AND 11.5 RESPECTIVELY.
ANY ONSHORE COMPONENT WILL PUSH THE TIDE ABOVE FLOOD SO COASTAL
FLOODING IS POSSIBLE AS WELL AS BEACH EROSION.

&&

.AVIATION /18Z THURSDAY 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 THE OUTER CAPE 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 MONDAY...

SATURDAY INTO SUNDAY...HIGH CONFIDENCE. MOSTLY VFR WITH MVFR
CONDITIONS ANY SCT SNOW/RAIN SHOWERS.

MONDAY...LOW CONFIDENCE. VFR CONDITIONS.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TODAY THROUGH FRIDAY/...MODERATE TO HIGH CONFIDENCE.

TODAY...SCA HEADLINES FOR ALL WATERS.  HIGH PRESSURE OVER THE GREAT
LAKES AND LOW PRESSURE OVER THE CANADIAN MARITIMES WILL RESULT IN A
TIGHT PRESSURE GRADIENT.  NORTHWEST WIND GUSTS OF 25 TO 30 KNOTS
EXPECTED ACROSS ALL WATERS.  A FEW GUSTS NEAR 35 KNOTS ARE POSSIBLE
ACROSS OUR SOUTHERN AND EASTERN OUTER-WATERS...BUT DO NOT THINK THEY
WILL BE WIDESPREAD ENOUGH FOR GALE WARNINGS.

TONIGHT...SCA HEADLINES WILL CONTINUE FOR MOST OPEN WATERS.  WINDS
WILL DIMINISH SOME BUT STILL THINK WINDS WILL GUST UP TO 25 KNOTS
FOR MUCH OF THE NIGHT.

FRIDAY...HIGH PRESSURE BUILDING INTO QUEBEC WILL ALLOW THE PRESSURE
GRADIENT TO WEAKEN.  STILL EXPECT NORTHWEST WINDS TO GUST TO 20
KNOTS IN THE COLD AIR ADVECTION PATTERN...BUT BELOW SMALL CRAFT
ADVISORY THRESHOLDS.  LINGERING SMALL CRAFT SEAS ACROSS THE
SOUTHEAST WATERS SHOULD DIMINISH BY LATE MORNING.  OTHERWISE...NO
HEADLINES ARE ANTICIPATED.

OUTLOOK...FRIDAY NIGHT INTO MONDAY...MODERATE TO HIGH CONFIDENCE.

FRIDAY NIGHT INTO SUNDAY...ANTICIPATE DIMINISHING WINDS AND SEAS
SUBSIDING LATE THU NIGHT INTO SATURDAY LEADING TO BELOW SMALL CRAFT
ADVISORY LEVELS.

MONDAY...EXPECT NE WINDS GUSTING UP TO 20 KT. LOW PROB OF 25 KT
GUSTS AS WELL AS 5 FT SEAS.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 3 AM EST FRIDAY FOR ANZ232>235-237.
     SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ230-
     236.
     SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ231-250-251-
     254>256.

&&

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


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