Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 272053
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
353 PM EST THU NOV 27 2014

.SYNOPSIS...
SCATTERED LIGHT SNOW SHOWERS/FLURRIES POSSIBLE THIS AFTERNOON.
TONIGHT...A TROUGH OF LOW PRESSURE MAY PRODUCE ACCUMULATING SNOW
ACROSS EASTERN MA INCLUDING THE BOSTON AREA. HIGH PRESSURE MOVES
OVER NEW ENGLAND FRIDAY AND SHIFTS OFFSHORE OVER THE WEEKEND. A
WARM FRONT MOVES ACROSS THE REGION LATE SATURDAY NIGHT AND EARLY
SUNDAY. A COLD FRONT THEN SWINGS THROUGH NEW ENGLAND MONDAY.
ANOTHER WARM FRONT/COLD FRONT COMBINATION WILL MOVE THROUGH THE
REGION WEDNESDAY AND WEDNESDAY NIGHT.

&&

.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
LIGHT SNOW SHOWERS AND FLURRIES MOVE OVER SOUTHERN NEW ENGLAND AS A
SHORTWAVE APPROACHES SOUTHERN NEW ENGLAND.  MOST OF THESE
SHOWERS/FLURRIES SHOULD REMAIN SOUTH OF THE MASS PIKE THOUGH A FEW
MAY GRAZE THE NORTHWESTERN ZONES.

AT THE SAME TIME...LOW PRESSURE DEVELOPS OFF THE COAST OF NORTH
CAROLINA.  THIS WILL BECOME IMPORTANT FOR OUR WEATHER LATE TONIGHT
INTO FRIDAY MORNING AS AN INVERTED TROUGH DEVELOPS OFF THIS LOW INTO
PORTIONS OF NEW ENGLAND.

TEMPERATURES REMAIN IN THE 30S FOR MOST OF SOUTHERN NEW ENGLAND THIS
AFTERNOON.  WHILE TEMPERATURES WILL DROP AFTER SUNSET...WITH
OVERCAST SKIES IN PLACE...THEY WILL BE SLOW TO DROP...STAYING IN THE
LOWER 30S THROUGH MIDNIGHT.

&&

.SHORT TERM /MIDNIGHT THROUGH 6 PM FRIDAY/...
*** ACCUMULATING SNOW POSSIBLE LATE TONIGHT INTO EARLY FRI AFTERNOON
  ACROSS EASTERN MA FROM CAPE ANN TO BOSTON TO CAPE COD ***

AS MENTIONED IN THE NEAR TERM SECTION...LOW PRESSURE OFF OF NORTH
CAROLINA WILL MOVE NORTHEASTWARD...PASSING WELL OUTSIDE THE
BENCHMARK.  HOWEVER...AN INVERTED TROUGH WILL DEVELOP AS THE
SHORTWAVE CROSSES SOUTHERN NEW ENGLAND. THESE TWO FEATURES WILL
PROVIDE ENOUGH LIFT AND INSTABILITY ALONG THE EAST COAST OF NEW
ENGLAND TO PRODUCE A NARROW BAND OF RAIN/SNOW SHOWERS.  THE MAIN
QUESTION IS JUST WHERE DOES THIS TROUGH SET UP AND HOW CLOSE TO THE
COAST DOES IT GET.

THESE FEATURES LEAVE A LOT OF UNCERTAINTY AS A SHIFT OF 10 TO 20
MILES TO THE EAST WILL LEAVE MOST AREAS WITHOUT SNOW.  HOWEVER...
MODELS HAVE CONSISTENTLY BEEN FORECASTING UP TO HALF AN INCH OF QPF
ALONG THE EAST COAST OF MASSACHUSETTS TO JUST OFF THE COAST FOR THE
LAST THREE MODEL RUNS. THAT LENDS SOME LEVEL OF CERTAINTY TO THE
POTENTIAL FOR A QUICK FEW INCHES OF SNOW.  IN ADDITION...STEEP LOW
LEVEL LAPSE RATES AND TOTAL TOTALS OVER 50 BOTH INDICATE PLENTY OF
INSTABILITY THAT WILL BE REALIZED.

AT THIS POINT...GENERALLY HAVE SNOWFALL TOTALS JUST UNDER ADVISORY
CRITERIA /3 INCHES/. HOWEVER...THERE ARE A FEW POCKETS OF AROUND 3
INCHES RIGHT AROUND THE BOSTON AREA.  DUE TO THE POTENTIAL FOR A
CHANGE IN AMOUNTS IF HIGHEST QPF ENDS UP OVER LAND RATHER THAN OVER
THE OCEAN...AM OPTING TO ISSUE A WINTER WEATHER ADVISORY ALONG THE
IMMEDIATE EAST COAST FROM CAPE ANN SOUTH THROUGH COASTAL PLYMOUTH
COUNTY.  EXPECT SNOW TO BEGIN SHORTLY AFTER MIDNIGHT AND CONTINUE
THROUGH THE MORNING HOURS ON FRIDAY.  WHILE THERE IS QUITE A BIT OF
UNCERTAINTY WITH THESE SYSTEMS...GIVEN THE NUMBER OF SHOPPERS AND
TRAVELERS WHO MAY BE OUT AND ABOUT FRIDAY MORNING...FELT AN ADVISORY
WOULD BE A GOOD IDEA.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
BIG PICTURE... ZONAL FLOW THIS WEEKEND WITH 500 MB HEIGHTS BUILDING
OVER NEW ENGLAND WHILE A SHORTWAVE TROUGH DROPS THROUGH WESTERN
CANADA INTO THE PACIFIC NORTHWEST. THE SHORTWAVE THEN RACES EAST TO
CROSS NEW ENGLAND MONDAY NIGHT. ANOTEHR SHORTWAVE RACES EAST ACROSS
THE NORTHERN TIER DURING THE WEEK.  THERE ARE DIFFERENCES BETWEEN
THE ECMWF AND GFS REGARDING THE AMPLITUDE AND SPEED OF THIS
SHORTWAVE WITH THE GFS FASTER/LESS AMPLIFIED.

WE FAVOR A MODEL BLEND FOR MOST OF THE LONG TERM.  MOVEMENT OF
SHORTWAVES THROUGH ZONAL FLOW LEADS TO QUESTIONS ON TIMING SO
CONFIDENCE IS AT BEST MODERATE. LATE IN THE LONG TERM WE TEND CLOSER
TOWARD THE ECMWF. AS NOTED BY HPC...THE GREATER AMPLITUDE TROUGH
SHOWN BY THE ECMWF IS MORE REASONABLE DUE TO DEEP LOW PRESSURE IN
THE BERING SEA AND RESULTING BUILDING OF A RIDGE ALONG THE PACIFIC
COAST.

THE DAILIES...

FRIDAY NIGHT-SATURDAY... HIGH PRESSURE BUILDS OVER NEW ENGLAND WITH
DRY CHILLY WEATHER. CROSS SECTIONS SHOW INCREASING MID AND HIGH
LEVEL MOISTURE SATURDAY AS THE HIGH SHIFTS EAST AND WARMER AIR
STARTS MOVING IN OVER THE TOP OF THE COLDER AIR. SO WE EXPECT MOSTLY
CLEAR SKIES FRIDAY NIGHT AND INCREASING SKY COVER ON SATURDAY. WE
STAYED CLOSE TO A COMPOSITE OF GUIDENCE FOR TEMPS BOTH PERIODS.

SATURDAY NIGHT THROUGH MONDAY... A WARM FRONT APPROACHES SATURDAY
NIGHT. THIS WILL MAINTAIN CLOUDS OVER THE REGION. LOW LEVEL PROFILES
LOOK RATHER DRY AND LIFT IS WEAK. SO ANY PCPN SHOULD BE LIMITED. WE
SHOWED SLIGHT CHANCE POPS MAINLY ALONG AND NORTH OF THE MASS PIKE
SATURDAY NIGHT AND IN SRN NH SUNDAY MORNING. THE WARM FRONT LIFTS
NORTH ON SUNDAY ALLOWING FOR MILDER TEMPS AND DEWPOINTS AS WELL AS A
GENERALLY DRY DAY.

THE MODELS SHOW DIFFERENCES IN TIMING THE PASSAGE OF THE COLD FRONT.
THIS IS NOT A SURPRISE AS WE WILL BE IN A ZONAL FLOW. THE GFS IS
FASTEST WITH PASSAGE MONDAY MORNING. THE ECMWF IS SLOWER WITH
PASSAGE MONDAY EVENING. WE USED A BLEND OF THIS DATA WITH CHANCE
POPS IN THE WEST IN THE MORNING...SLIGHT CHANCE ALL AREAS AFTN...AND
CHANCE ALL AREAS EARLY MONDAY NIGHT. AT BEST MODERATE CONFIDENCE IN
THIS TIMING.

TUESDAY... HIGH PRESSURE BUILDS OVER THE REGION WITH COLDER AIR.
MIXING WILL BE LIMITED TO 925 OR 950 MB...AND TEMPS AT THAT LEVEL
SUPPORT MAX TEMPS IN THE UPPER 20S AND 30S.

WEDNESDAY-THURSDAY... SHORTWAVE MOVES OUT OF THE PACIFIC NORTHWEST
AND PUSHES A COLD FRONT ACROSS THE NORTHERN TIER OF STATES TUESDAY-
WEDNESDAY. THIS WILL DRAW A SOUTHWEST LOW LEVEL JET OF 40-45 KNOTS
LEADING THE COLD FRONT UP TO OUR AREA BY WEDNESDAY.

THIS JET WILL SUPPLY MOISTURE AND GENERATE SUFFICIENT LIFT FOR
CLOUDS AND A CHANCE OF PCPN. CONFIDENCE IN TIMING IS LOW BUT AS
NOTED ABOVE WE FAVORED THE TIMING SHOWN BY THE ECMWF FOR ONSET OF
CLOUDS AND ANY PCPN. LOW LEVEL TEMPERATURES WILL DETERMIN PCPN
TYPE...BUT TREND SHOULD BE FROM SNOW TO RAIN EARLY WEDNESDAY AND
WEDNESDAY MORNING. LINGERING COLD AIR AT THE SURFACE MAY SUPPORT A
PERIOD OF SLEET OR FREEZING RAIN DURING THE TRANSITION DURING THE
MORNING...THEN TEMPS SHOULD BE WARM ENOUGH FOR PCPN TO FALL AS RAIN
ANY OTHER TIME OF THE DAY. TIMING OF THE COLD FRONT PER THE ECMWF
WOULD BE LATE WEDNESDAY OR EARLY WEDNESDAY NIGHT.

HIGH PRESSURE BRINGS DRIER WEATHER ON THURSDAY.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
FORECASTER CONFIDENCE LEVELS...

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

.SHORT TERM /THROUGH FRIDAY/...MODERATE CONFIDENCE.

THROUGH 00Z...A MIX OF CIGS ACROSS THE AREA THOUGH MOSTLY
VFR/MVFR. IFR CIGS ON THE OUTER CAPE. -SHSN MOVE INTO SOUTHERN NEW
ENGLAND FROM NYS THROUGH THE AFTERNOON.

TONIGHT...MVFR CIGS MOVE ACROSS THE REGION. PRECIP DEVELOPS ACROSS
E MA INTO RI...POSSIBLY AS FAR W AS KORH-KIJD...AS INVERTED
TROUGH TAKES SHAPE NEAR THE COAST AFTER 06Z. AREAS OF MVFR-IFR
VSBYS DEVELOP IN RAIN AND/OR SNOW. VSBYS SHOULD REMAIN MAINLY VFR
ACROSS CENTRAL AND WESTERN AREAS...THOUGH PATCHY FOG MAY FORM LATE
AT NIGHT.

FRIDAY...SNOW/RAIN SHOWERS WILL CONTINUE THROUGH MID-MORNING ALONG
THE E COAST OF MASS...POSSIBLY AS FAR INLAND AS ORH-IJD. PRECIP
COMES TO AN END AFTER NOON AND CONDITIONS WILL IMPROVE TO VFR BY
FRIDAY EVENING.

KBOS TERMINAL...HIGH CONFIDENCE TODAY...LOWER CONFIDENCE TONIGHT IN
EXACT TIMING AS PRECIP DEVELOPS.

KBDL TERMINAL...HIGH CONFIDENCE.

OUTLOOK...FRIDAY NIGHT THROUGH TUESDAY...MODERATE CONFIDENCE

FRIDAY NIGHT AND SATURDAY...VFR. INCREASING SKY COVER SATURDAY.
NORTHWEST WINDS BECOME SOUTHWEST BUT REMAIN LIGHT.

SATURDAY NIGHT-SUNDAY...LOWERING CLOUDS SATURDAY NIGHT WITH
POTENTIAL FOR MVFR CIGS/VSBYS IN WIDELY SCATTERED PCPN LATE AT NIGHT
AND SUNDAY MORNING. LOW LEVEL WINDS...AROUND 2000 FEET...WILL
INCREASE OVERNIGHT AND SUNDAY TO 40-45 KNOTS AND MAY CREATE LOW
LEVEL WIND SHEAR.

MONDAY...VFR WITH SCATTERED SHOWERS AS A COLD FRONT MOVES THROUGH.
SOUTHWEST WINDS AHEAD OF THE COLD FRONT WILL SWITCH TO NORTHWEST
AFTER THE FRONT MOVES THROUGH.

TUESDAY...VFR WITH NORTH TO NORTHEAST WINDS.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

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

SEAS DIMINISH SLOWLY TONIGHT BEFORE INCREASING AGAIN AS INVERTED
TROUGH DEVELOPS OVER THE WATERS.  GENERALLY NORTHWESTERLY WINDS
EXPECTED OVER THE WATERS THOUGH A FEW NORTHEASTERLY WINDS ARE
POSSIBLE ON THE EASTERN WATERS.  WINDS INCREASE FRIDAY...GUSTING TO
NEAR 25 KTS.  HAVE SMALL CRAFT ADVISORIES UP FOR MOST OF THE COASTAL
WATERS FOR EITHER SEAS...GUSTY WINDS OR BOTH.

OUTLOOK...FRIDAY NIGHT THROUGH TUESDAY...MODERATE CONFIDENCE.

FRIDAY NIGHT...DIMINISHING WINDS AND SEAS. LINGERING 5 FOOT SEAS ON
THE OUTER WATERS BEFORE MIDNIGHT MAY REQUIRE A SMALL CRAFT ADVISORY.

SATURDAY...WINDS AND SEAS SHOULD REMAIN BELOW SMALL CRAFT THRESHOLDS.

SUNDAY...SOUTHWEST WINDS INCREASE TO 25 KNOTS AND SEAS BUILD TO 5-7
FEET. A SMALL CRAFT ADVISORY MAY BE NEEDED ON MOST WATERS.

MONDAY...A COLD FRONT MOVES THROUGH DURING THE AFTERNOON OR EVENING.
SOUTHWEST WINDS SHIFT TO NORTHWEST LATER IN THE DAY...WITH SPEEDS 20
TO 25 KNOTS. SEAS DIMINISH A LITTLE BUT REMAIN AT OR ABOVE 5 FEET ON
THE EXPOSED WATERS.  A SMALL CRAFT ADVISORY MAY STILL BE NEEDED.

TUESDAY...NORTH WINDS BECOME NORTHEAST WITH GUSTS AROUND 25 KNOTS.
SEAS LINGER AT 5 TO 6 FEET ON THE OUTER WATERS.  A SMALL CRAFT
ADVISORY MAY BE NEEDED.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...WINTER WEATHER ADVISORY FROM 1 AM TO NOON EST FRIDAY FOR
     MAZ007-015-016-019.
NH...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ231-
     232.
     SMALL CRAFT ADVISORY UNTIL 6 PM EST FRIDAY FOR ANZ235-237-250-
     251-254>256.

&&

$$
SYNOPSIS...WTB/RLG
NEAR TERM...RLG
SHORT TERM...RLG
LONG TERM...WTB
AVIATION...WTB/RLG
MARINE...WTB/RLG



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