Area Forecast Discussion
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000
FXUS61 KBOX 210220
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
918 PM EST SAT DEC 20 2014

.SYNOPSIS...
SCATTERED SNOW/RAIN SHOWERS WILL AFFECT THE REGION THROUGH SUN.
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 SUNDAY MORNING/...

915 PM UPDATE...

A RATHER TRICKY FORECAST OVERNIGHT WITH INVERTED TROUGH/COASTAL
FRONT RESULTING IN SOME MESOSCALE PROCESSES.  MAIN BAND OF SNOW THAT
HAS DROPPED A NARROW BAND OF 1 TO 2 INCHES OF SNOW ACROSS PORTIONS
OF BOSTON/S SOUTH SHORE WAS GRADUALLY PRESSING SOUTHWEST THIS
EVENING.  THIS PARTLY IN RESPONSE TO A SUBTLE COASTAL FRONT THAT WAS
ALSO SHIFTING FURTHER WEST INTO PLYMOUTH AND EVEN FAR EASTERN
NORFOLK COUNTY.  MILDER AIR WAS ALSO CAUSING SOME OF THESE AREAS TO
MIX WITH OR CHANGE TO RAIN.

OVERALL...STILL THINK THAT A COATING TO AT MOST 2 INCHES WILL COVER
IT FOR MOST OF SOUTHERN NEW ENGLAND INTO SUNDAY.  WE DID OPT TO
SHIFT THE BEST RISK FOR THE 1 TO 2 INCHES A BIT FURTHER SOUTH AND
WEST BASED ON RADAR RETURNS AND LATEST GUIDANCE.  LOW RISK OF
ISOLATED 3 INCH AMOUNTS REMAINS POSSIBLE.

THE RAIN/SNOW LINE WILL LIKELY HANG OUT ACROSS FAR EASTERN
NORFOLK/PLYMOUTH AND PERHAPS FAR SOUTHEAST BRISTOL COUNTIES.  THE
MODELS MAY BE SLIGHTLY UNDER ESTIMATING THE WESTWARD PUSH OF THIS
LINE...SO SOMETHING TO WATCH BUT DO NOT THINK IT WILL GET MUCH
FURTHER WEST THAN THAT.

FINALLY...SCATTERED SNOW SHOWERS MAY ALSO DEVELOP INTO WESTERN
MA/NORTHERN CONNECTICUT OVERNIGHT INTO SUNDAY MORNING WITH A
APPROACHING SHORTWAVE.  MODEL GUIDANCE DIFFERS ON EXACTLY HOW THIS
WILL UNFOLD...BUT INCREASING EAST TO SOUTHEAST FLOW JUST OFF THE
GROUND SHOULD ALLOW FOR AT LEAST SOME ACTIVITY IN OUR WESTERN ZONES
BY DAYBREAK.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
RAIN/SNOW SHOWERS WILL CONTINUE INTO THE MORNING HOURS...THEN TAPER
OFF AS INVERTED TROUGH PULLS AWAY FROM SOUTHERN NEW ENGLAND AND HIGH
PRESSURE STARTS TO BUILD IN.  MOST LIKELY AREAS FOR CONTINUING
SHOWERS WILL BE ALONG THE IMMEDIATE EAST COAST OF MASSACHUSETTS.

AS THE DAY GOES ON...EXPECT A SLOW DRYING TREND AS HIGH PRESSURE
BUILDS INTO THE REGION.  CLOUDS WILL STICK AROUND WITH TEMPS
GENERALLY IN THE 30S.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
BIG PICTURE... SHORTWAVE ENTERING THE PACIFIC NORTHWEST CROSSES THE
ROCKIES OVER THE WEEKEND DRIVEN BY A 160-KNOT JET.  THIS DIGS A
SUBSTANTIAL TROUGH OVER THE PLAINS MONDAY-TUESDAY WHILE PACIFIC HIGH
PRESSURE BUILDS ALONG THE PACIFIC COAST. THIS IN TURN WILL ALLOW AN
UPPER RIDGE TO BUILD ALONG THE ATLANTIC COAST AND SLOWLY SHIFT EAST
OF THE COAST.  THE JET ENERGY WORKS ITS WAY AROUND THE BASE OF THE
PLAINS TROUGH AND MOVES UP THE APPALACHANS MIDWEEK.  THIS SUPPORTS A
TRANSITION OF THE TROUGH TO NEGATIVE TILT AND SLOWER MOVEMENT...WITH
WARM MOIST AIR FOR THE ATLANTIC COAST. THE TROUGH AXIS SWINGS OVER
NEW ENGLAND CHRISTMAS DAY FOLLOWED BY A WEAK RIDGE. ANOTHER
SHORTWAVE MOVES ASHORE FROM THE PACIFIC MIDWEEK AND MOVES ACROSS THE
PLAINS BY THE END OF THE WEEK AND APPROACHES THE NORTHEAST USA
SATURDAY.

THERE IS SOME SPREAD IN DETAILS AMONG THE LONG RANGE MODELS...BUT
ALL SHOW A SIMILAR SCENARIO BOTH FOR THE MIDWEEK SYSTEM AND THE END
OF WEEK SYSTEM.  WE USED A BLEND OF GFS/ECMWF.

THE DAILIES...

SUNDAY NIGHT-MONDAY... HIGH PRESSURE REMAINS NORTH OF THE REGION
BRINGING A MOIST EAST FLOW ACROSS SOUTHERN NEW ENGLAND. UPPER
PATTERN SHOWS WEAK RIDGING AS THE PLAINS TROUGH DIGS...BUT SURFACE
FIELDS SUGGEST A LINGERING INVERTED TROUGH ALONG OR JUST OFFSHORE.
THIS SHOULD MAINTAIN CONSIDERABLE CLOUDS. COULD BE SOME DRIZZLE OR
FLURRIES NEAR THE EAST COAST BUT SUPPORTING LARGE SCALE ASCENT IS
LACKING SO PCPN SHOULD BE LIMITED.

MONDAY NIGHT-TUESDAY... LOW PRESSURE FORMS ALONG A STALLED WARM
FRONT OFF THE MID ATLANTIC COAST. AS THE LOW DEVELOPS...IT BRINGS
AN INCREASED PRESSURE GRADIENT AGAINST HIGH PRESSURE MOVING
THROUGH THE MARITIMES. THE RESULT WILL BE A STRENGTHENING LOW
LEVEL EAST- SOUTHEAST JET. THIS WILL INCREASE THE MOIST INFLOW
OVER SOUTHERN NEW ENGLAND. ALSO...AS THE JET CONVERGES ON THE
INVERTED SURFACE TROUGH IT WILL GENERATE INCREASED LOW LEVEL LIFT
AND INCREASE THE CHANCE OF PCPN. WE WILL HAVE CLOUDS AND CHANCE
POPS. TEMPS IN NORTHWEST MASS WILL BE COLD ENOUGH SO THAT THERE
MAY BE A MIX OF PCPN TYPES DURING THE MORNING.

TUESDAY NIGHT-WEDNESDAY... PLAINS UPPER TROUGH DIGS DEEPER AND MOVES
EAST...PUSHING THE UPPER RIDGE TO OUR EAST. ALSO...THE STRONG UPPER
SOUTHWEST JET MOVES UP OVER THE EASTERN USA. THIS SETUP WILL TAKE
THE PRIMARY SURFACE LOW UP THROUGH THE WESTERN GREAT LAKES.
SECONDARY LOWS FORMING ON THE SYSTEM COLD FRONT WILL MOVE OUT OF THE
GULF OF MEXICO TOWARD THE GREAT LAKES. A SOUTHWEST LOW LEVEL JET
WILL MOVE UP THE ATLANTIC COAST ON WEDNESDAY AND OVER THE TOP OF THE
EAST-SOUTHEAST FLOW AT THE SURFACE. THE RESULT WILL BE PLENTY OF LOW
LEVEL LIFT THE GENERATE PCPN.

PRECIPITABLE WATER VALUES ARE FORECAST TO EXCEED 1.5 INCHES...WHICH
IS 3 STD DEVIATIONS ABOVE NORMAL FOR DECEMBER.  THIS MEANS A LOT OF
WATER AVAILABLE AS PCPN. TEMPERATURE PROFILES WILL BE ABOVE FREEZING
SO PTYPE SHOULD BE RAIN. MODEL QPF SHOWS POTENTIAL RAINFALL OF OVER
2 INCHES. THIS WOULD SUGGEST POTENTIAL URBAN/POOR DRAINAGE FLOODING
ISSUES WEDNESDAY.

STRONG LOW LEVEL WINDS WILL ALSO BE A CONCERN ESPECIALLY WEDNESDAY
NIGHT. THE ECMWF SHOWS EAST-SOUTHEAST WINDS 30-35 KNOTS ALONG HE
EAST MASS COAST AT 1000 MB. THEN WEDNESDAY NIGHT WINDS AT 925 MB
INCREASE TO 60-75 KNOTS AND MOVE ACROSS COASTAL RI AND SOUTHEAST
MASS. 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.

MAINTAINED A LIMITED MENTION OF THUNDER...AS CONVECTIVE PARAMETERS
ARE MARGINAL...SI VALUES WILL BE JUST ABOVE ZERO AND K INDEX WILL BE
IN THE LOW 30S WEDNESDAY NIGHT.

UPPER LOW WILL SWING THE SURFACE COLD FRONT THROUGH SOUTHERN NEW
ENGLAND WEDNESDAY NIGHT. WINDS WILL THEN SHIFT TO WEST AND PCPN
SHOULD COME TO AN END AROUND THE TIME THAT SANTA ARRIVES.

CHRISTMAS DAY... WEST WINDS WILL BRING A DRYING OF THE AIRMASS
DURING THE DAY. SO THE TREND SHOULD BE TO AT LEAST PARTIAL CLEARING.
SUFFICIENT COLD ADVECTION AT ALL LEVELS THURSDAY WILL ALLOW SOME
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-SATURDAY... WEAK HIGH PRESSURE BUILDS OVER THE AREA FRIDAY
AND BRING A SUNNY DAY. THE NEXT PACIFIC SHORTWAVE APPROACHES
SATURDAY 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 /02Z SUNDAY THROUGH THURSDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SUNDAY/...

TONIGHT AND SUNDAY...MVFR CIGS/VSBYS IN RAIN/SNOW SHOWERS MOVING
WEST OFF THE OCEAN INTO SOUTHEASTERN MASS. THESE WILL SPREAD
FARTHER WEST INTO RI/CENTRAL MASS/NORTHEAST CT. LOCAL IFR
CIGS/VSBYS POSSIBLE WITH THE STRONGEST SHOWERS.

WINDS ARE ENE ALONG THE IMMEDIATE SOUTHEAST MASS COAST WITH NORTH
TO NORTHWEST WINDS ELSEWHERE. THIS WINDSHIFT MAY NUDGE FARTHER
WEST WITH THE SHOWERS EARLY TONIGHT.

MVFR CIGS MAY REACH THE CT VALLEY LATE TONIGHT BUT LOW CONFIDENCE
ABOUT ANY SIGNIFICANT REDUCTION IN VSBY THERE.

MVFR CIGS WILL LINGER MOST AREA ON SUNDAY. ANY CIGS THAT RISE
ABOVE MVFR SHOULD ONLY REACH AROUND 4000 FEET.

KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. FLURRIES AND SNOW
SHOWERS THROUGH 06Z WITH POTENTIAL FOR WINDSHIFT TO 040 DURING
THIS TIME.

KBDL TERMINAL...MODERATE CONFIDENCE IN TAF.

OUTLOOK...SUNDAY NIGHT THROUGH THURSDAY...MODERATE CONFIDENCE

SUNDAY NIGHT-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-SOUTHEST
SURFACE WINDS MAY GUST TO 35 KNOTS ALONG THE EAST MASSACHUSETTS
COAST. 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 CONFIDENCE. HIGH PRESSURE ACROSS QUEBEC WILL RESULT IN
PERSISTENT NORTHEAST WINDS ACROSS THE WATERS THROUGH THE WEEKEND.
WIND GUSTS UP TO 20 KNOTS WITH SEAS BETWEEN 2 AND 4 FEET ARE
EXPECTED FOR MOST WATERS...SO NO HEADLINES PLANNED.

THERE IS A LOW PROBABILITY THAT A BRIEF SURGE OF NORTHEAST WIND
GUSTS NEAR 25 KNOTS WITH MARGINAL 5 FOOT SEAS COULD AFFECT OUR
NORTHERN WATERS LATE TONIGHT INTO SUN MORNING...BUT NOT CONFIDENT
ENOUGH TO ISSUE ANY HEADLINES AT THIS POINT.

OUTLOOK...SUNDAY NIGHT THROUGH THURSDAY...MODERATE CONFIDENCE

SUNDAY NIGHT-MONDAY...EAST TO NORTHEAST WINDS GUSTING AROUND 15
KNOTS OR LESS.  SEAS WILL HOLD AROUND 3-4 FEET.

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 5-10 FEET HEIGHTS ON THE EXPOSED WATERS.
A GALE WARNING MAY BE NEEDED.

CHRISTMAS DAY... WEST SOUTHWEST WINDS WILL CONTINUE TO GUST 35-40
KNOTS...SO A GALE WARNING MAY CONTINUE TO BE NEEDED. SEAS OF 10-15
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. BREAKING IT DOWN...ON TUESDAY HIGH TIDE
AT BOSTON WILL BE 11.6 FT. THERE WILL BE EAST WINDS DURING THIS
HIGH TIDE ALLOWING FOR MINOR SPLASHOVER ALONG THE MASS COAST. IF
WIND GUSTS INCREASE THEN COULD POSSIBLE SEE MINOR COASTAL
FLOODING.

ON WEDNESDAY...WINDS WILL SWITCH TO A MORE SOUTHEASTERLY FLOW DURING
THE DAY AND INCREASE QUICKLY DUE TO THE APPROACHING SYSTEM.
WEDNESDAY AFTERNOON HIGH TIDE IN BOSTON IS 11.7 FT...AND AN
APPRECIABLE EAST OR SOUTHEAST WIND SHOULD PUSH LEVELS HIGHER THAN ON
TUESDAY.  THIS WOULD PROBABLY BE THE BEST CHACNE OF MINOR COASTAL
FLOODING ALONG THE EAST COAST.

THE WEDNESDAY EVENING HIGH TIDE WILL BE A LITTLE LOWER...BUT THE
WIND BECOMES SOUTH WITH 50-60 KNOTS AT 2000 FEET ABOVE THE SURFACE
AVAILABLE TO BE BROUGHT DOWN IN GUSTS. HIGH TIDE IN PROVIDENCE WILL
BE 5.2 FT. MINOR COASTAL FLOODING COULD OCCUR ALONG THE SOUTH
COASTS OF RI AND MASS...AND COULD BE CHANNELED IN NORTH-SOUTH AXIS
BAYS SUCH AS NARRAGANSETT BAY.

&&

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

&&

$$ SYNOPSIS...WTB/RLG
NEAR TERM...FRANK
SHORT TERM...RLG
LONG TERM...WTB
AVIATION...WTB/RLG
MARINE...WTB/RLG
TIDES/COASTAL FLOODING...STAFF


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