Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 250249
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
948 PM EST TUE FEB 24 2015

.SYNOPSIS...
FAST MOVING LOW PRESSURE WILL BRING A PLOWABLE SNOWFALL TO RHODE
ISLAND AND EASTERN MASSACHUSETTS LATE TONIGHT INTO VERY EARLY
WEDNESDAY MORNING. A REINFORCING SURGE OF COLD BUT DRY WEATHER
RETURNS WEDNESDAY NIGHT THROUGH FRI NIGHT. TEMPS SLOWLY MODERATE
SAT AS HIGH PRES BUILDS INTO THE REGION...THEN A FRONTAL SYSTEM
MAY BRING SOME SNOW LATE SUN INTO MON.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
*** PLOWABLE SNOW ACROSS EASTERN MA/RI LATE TONIGHT BUT SHOULD BE
  OVER FOR MOST BY THE WEDNESDAY MORNING COMMUTE ***

945 PM UPDATE...

VERY LIGHT SNOW SHOWERS AND FLURRIES HAS BROKEN OUT ACROSS MUCH OF
THE REGION.  LOOKS LIKE SOME SHALLOW LIFT OVER THE ARCTIC DOME AT
THE SURFACE WITH EVEN SOME OCEAN EFFECT ON SOUTH WINDS THE RESULT.
NOT REALLY EXPECTING MUCH MORE THAN A COATING OR SO FROM THIS
ACTIVITY.

THE MAIN UNCERTAINTY ARE THE RADAR RETURNS BLOSSOMING SOUTH OF LONG
ISLAND.  THE HRRR/RAP HAVE VERY LITTLE SNOW MAKING IT NORTHWEST OF
EVEN THE CAPE COD CANAL.  THIS CERTAINLY IS CONCERNING...BUT WE ARE
NOT READY TO COMPLETELY BITE ON THOSE SOLUTIONS BASED ON BLOSSOMING
RADAR.  THE REST OF THE GUIDANCE HAS ABOUT 0.10 TO 0.20 INCHES OF
QPF ALONG THE BOS TO PVD CORRIDOR POINTS SOUTH AND EAST.  GIVEN A
PERIOD OF GOOD LIFT IN THE SNOW GROWTH REGION RESULTING IN DECENT
RATIOS...COULD EASILY TRANSLATE TO 1 TO 4 INCHES OF SNOW.
HOWEVER...IF THINGS END UP SHIFTING EAST BY 20 OR SO MILES AT THE
LAST SECOND MUCH OF THE ADVISORY AREA WOULD BE LOOKING AT JUST A
COATING TO 1 INCH.

ALL IN ALL...BASED ON THE LATEST RADAR TRENDS AND 00Z NAM NOT
PLANNING TO MAKE ANY CHANGES TO THE GOING FORECAST.  IF WE START TO
SEE THE RADAR RETURNS TAKE A MORE EASTERLY TRAJECTORY AND THE OTHER
00Z GUIDANCE BACK OFF AS WELL...WILL HAVE TO LOWER SNOW ACCUMS.
HOWEVER...JUST NOT ENOUGH CONFIDENCE TO MAKE CHANGES AT THIS TIME
ESPECIALLY WITH THOSE IMPRESSIVE RETURNS LIGHTING UP SOUTH OF LONG
ISLAND.

PREVIOUS DISCUSSION...

SYNOPTIC OVERVIEW...

IMPRESSIVE NORTHERN STREAM SHORT WAVE TRAVERSING THE GREAT LAKES PER
LATEST WATER VAPOR IMAGERY. GOOD MODEL AGREEMENT ON STRONG SYNOPTIC
SCALE FORCING /MID LEVEL Q-VECTOR CONVERGENCE/ WITH THIS FEATURE AS
IT CROSSES THE AREA TONIGHT...CENTERED ON 06Z. THE SHORT WAVE TROUGH
HAS SUFFICIENT AMPLITUDE TO THE BACK THE MID LEVEL ENOUGH TO CAPTURE
SOUTHERN STREAM MOISTURE SOUTH OF NEW ENGLAND. IN TURN THIS INDUCES
AN INVERTED TROUGH OVER THE AREA EXTENDING FROM A SOUTHERN STREAM
SYSTEM TRACKING WELL SOUTH OF NEW ENGLAND. THIS IS AN INDICATION OF
THE STRONG FORCING FOR ASCENT FROM THIS NORTHERN STREAM SHORT WAVE.

TIMING...SNOW ACCUMULATIONS...UNCERTAINTY AND HEADLINES...

GOOD MODEL AGREEMENT ON SNOW COMING ONSHORE TO THE SOUTH COAST OF MA
AND RI BETWEEN 10 PM AND MIDNIGHT...THEN QUICKLY OVERSPREADING THE
REMAINDER OF THE AREA AFTER MIDNIGHT. HEAVIEST SNOW FALLS
APPROXIMATELY 2 AM TO 5 AM FROM SW TO NE AND THEN TAPERS OFF BY 6-7
AM.

THIS SYSTEM REMAINS VERY PROGRESSIVE AND TYPICALLY WOULD NOT PRODUCE
MUCH SNOWFALL. HOWEVER AS NOTED BY PREVIOUS FORECASTERS THERE ARE
SEVERAL ATTRIBUTES THAT SUPPORT A 2-4" SNOWFALL FOR MUCH OF RI AND
EASTERN MA. THIS INCLUDES BRIEF BUT STRONG SYNOPTIC SCALE
FORCING...MODEST MID LEVEL FGEN COLLOCATED WITH AN AREA OF WEAK
INSTABILITY /-EPV/ AND RELATIVELY HIGH SLR PER GOOD LIFT IN THE SNOW
GROWTH REGION. SO WHILE HEAVIEST QPF /0.20-0.35/ IS OVER CAPE COD
AND THE ISLANDS...WARMING BLYR WILL YIELD LOWER SLR AND POSSIBLY
RAIN MIXING IN FOR A TIME AT NANTUCKET. FARTHER INLAND SPECIFICALLY
THE I-95 CORRIDOR OF RI AND EASTERN MA INCLUDING THE BOS-PVD
CORRIDOR...MLVL FGEN/MESOSCALE SNOW BAND AND HIGHER SLR WILL LIKELY
RESULT IN HIGHER SNOWFALL THAN MODEL QPF SUGGEST. IN FACT HIGHEST
SNOW TOTALS LIKELY OCCUR SOMEWHERE ALONG THE I-95 CORRIDOR SOUTHEAST
TO THE CAPE COD CANAL PER MID LEVEL BANDING SIGNATURE AND GOOD SNOW
GROWTH. THUS OUR SNOW GRAPHIC HAS A LARGE AREA OF 2-4" SNOWFALL FROM
BOS-PVD SOUTHEAST TO THE CAPE. IF ALL PARAMETERS ABOVE COME TOGETHER
YIELDING A MORE ROBUST MESOSCALE SNOW BAND THERE IS A LOW RISK FOR A
FEW LOCATIONS COMING CLOSE TO 5 OR 6". HOWEVER THE MORE LIKELY
SCENARIO IS FOR 2-4". THUS NO CHANGE FROM PREVIOUS HEADLINES.

CHARACTER OF THE SNOW WILL BE DRY/FLUFFY EXCEPT A BIT WETTER/HEAVIER
FOR THE OUTER CAPE AND ISLANDS. THERE WILL BE A SHARP CUTOFF TO THE
WEST SPECIFICALLY NW OF BOS-PVD AND VERY LITTLE IF ANY SNOW WEST OF
I-91/CT RVR VLY.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
WEDNESDAY...

ANY SNOW AT SUNRISE WILL BE CONFINED TO EXTREME EASTERN MA AND WILL
EXIT OFFSHORE BY 7 AM...PERHAPS 8 AM FOR OUTER CAPE COD AND CAPE
ANN.

BEHIND THE DEPARTING SHORT WAVE NW WINDS PICK UP TO 20-30 MPH BY
MIDDAY AND CONTINUE INTO THE AFTERNOON. SO DESPITE TEMPS CLIMBING
INTO THE U20S AND L30S...A GUSTY NW WIND WILL PROVIDE A BIT OF A
WIND CHILL. ALTHOUGH NOT NEARLY AS COLD AS WE HAVE EXPERIENCED
RECENTLY. SUNSHINE DEVELOPS BY MID TO LATE MORNING.

WED NIGHT...

A TRAILING SHORT WAVE TROUGH BRINGS A REINFORCING SURGE OF COLD AIR
TO THE REGION...ALTHOUGH NOT NEARLY AS COLD AS RECENT DAYS. MIN
TEMPS BY SUNRISE THU WILL BE IN THE SINGLE DIGITS INLAND...AROUND 10
BOSTON AND PROVIDENCE TO TEENS ALONG THE SOUTH COAST...CAPE COD AND
ISLANDS.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
HIGHLIGHTS...

*  OCEAN EFFECT SNOW POSSIBLE ON THE CAPE THURSDAY
*  HIGH PRESSURE EXPECTED THROUGH THE WEEKEND
*  COLD FRONT BRINGS WINTRY PRECIP SUNDAY INTO MONDAY
*  ANOTHER STORM POSSIBLE TUESDAY

MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH THE WEEKEND.  THEN THEY
DIVERGE A BIT...PARTICULARLY WITH A LOW PRESSURE SYSTEM EXPECTED TO
IMPACT SOUTHERN NEW ENGLAND ON TUESDAY.  HIGH PRESSURE BUILDS INTO
SOUTHERN NEW ENGLAND FROM THE MIDWEST THROUGH SATURDAY.  THEN THE
HIGH PRESSURE MOVES OFFSHORE...ALLOWING LOW PRESSURE TO MOVE THROUGH
QUEBEC AND BRING A COLD FRONT THROUGH SOUTHERN NEW ENGLAND LATE
SUNDAY.  THIS WILL BRING A PERIOD OF WINTRY WEATHER TO THE REGION.
THEN HIGH PRESSURE BUILDS BACK IN BRIEFLY LATE MONDAY.  THE MODELS
DIFFER ON THE STRENGTH...DEVELOPMENT...AND TRACK OF A LOW PRESSURE
SYSTEM EXPECTED TO AFFECT SOUTHERN NEW ENGLAND TUESDAY.  THE ECMWF
HAS THE MORE TYPICAL PATTERN OF A LOW MOVING THROUGH THE GREAT LAKES
AND A SECONDARY LOW DEVELOPING OFF THE COAST OF NEW JERSEY AND
TRACKING ACROSS THE 40/70 BENCHMARK.  THE GFS KEEPS THE LOW PRESSURE
AS AN INSIDE RUNNER...TRACKING UP THROUGH PENNSYLVANIA AND NEW YORK
STATE.  THESE TWO DIFFERENT SOLUTIONS WILL AFFECT EVERYTHING FROM
TEMPERATURES TO PRECIPITATION TYPES.  BUT THIS IS 7-8 DAYS OUT SO WE
EXPECT THINGS TO CHANGE QUITE A BIT BETWEEN NOW AND THEN.

THURSDAY AND FRIDAY...HIGH PRESSURE BUILDS INTO THE REGION.  LOW
PRESSURE SYSTEMS TRACKING WELL SOUTH OF SOUTHERN NEW ENGLAND MAY
BRING SOME OCEAN EFFECT SNOW TO THE CAPE AND ISLANDS.

SATURDAY...HIGH PRESSURE CENTERS OVER SOUTHERN NEW ENGLAND BRINGING
DRY WEATHER AND MODERATING TEMPERATURES.

SUNDAY AND MONDAY...HIGH PRESSURE MOVES OFFSHORE.  LOW PRESSURE OVER
HUDSON BAY WILL TRACK EASTWARD THROUGH QUEBEC BRINGING A COLD FRONT
THROUGH SOUTHERN NEW ENGLAND.  THIS WILL RESULT IN A PERIOD OF
WINTRY PRECIP THROUGHOUT THE AREA.  RIGHT NOW...THERMAL PROFILES
INDICATE THAT THIS IS LIKELY TO BE IN THE FORM OF SNOW SHOWERS.  A
CHANGE IN THERMAL PROFILE COULD RESULT IN A WINTRY MIX OF PRECIP
DURING THIS TIME.

THE OTHER CONCERN DURING THIS TIME IS THE POTENTIAL FOR GUSTY WINDS.
THE ECMWF INDICATES A RATHER STRONG LOW LEVEL JET DEVELOPING WHILE
THE GFS KEEPS THE LOW LEVEL WINDS RATHER CALM.  AT ANY RATE...EXPECT
ADVISORY LEVEL WINDS WOULD BE THE MOST WE WOULD NEED TO BE CONCERNED
ABOUT.  WILL KEEP AN EYE ON THIS THROUGHOUT THE WEEK.

TUESDAY...A COUPLE OF DIFFERENT SOLUTIONS FORECAST IN THE MODELS.
THE ECMWF HAS A LOW PRESSURE SYSTEM MOVING THROUGH THE GREAT LAKES
WITH A SECONDARY LOW FORMING OFF THE NEW JERSEY COAST AND PASSING
JUST INSIDE THE 40/70 BENCHMARK.  THE GFS HAS THE LOW TRACKING
THROUGH PENNSYLVANIA AND NEW YORK BRINGING A WARM FRONT THROUGH
SOUTHERN NEW ENGLAND.  THESE TWO SOLUTIONS HAVE VASTLY DIFFERENT
THERMAL PROFILES AND THIS WOULD AFFECT PRECIPITATION TYPES.  WE HAVE
AWHILE TO GO ON THIS STORM SO WILL ALLOW LATER RUNS TO BETTER
RESOLVE THIS PARTICULAR STORM.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TODAY THROUGH WEDNESDAY/...

TONIGHT...DRY WEATHER THRU ABOUT 03Z THEN SNOW COMES ONSHORE TO
THE SOUTH COAST OF MA AND RI BETWEEN 04Z-05Z...THEN OVERSPREADS
THE REMAINDER OF RI AND EASTERN MA THEREAFTER. BRIEF MODERATE TO
HEAVY SNOW 07Z-10Z OVER RI AND EASTERN MA THEN EXITS OFFSHORE
11Z/12Z. MVFR AND IFR CONDITIONS IN THIS AREA WITH 2-4" SNOWFALL
FOR BOS/PVD/HYA/FMH AND ACK ALONG WITH NEIGHBORING TERMINALS.

ELSEWHERE...VFR TO MVFR CIGS WITH LITTLE IF ANY SNOW.

WED/WED NIGHT...VFR AND DRY WEATHER WITH MODEST NW WINDS.

KBOS TAF...HIGH CONFIDENCE IN VFR CONDITIONS THRU 03Z/04Z. THEN BURST
OF MODERATE TO EVEN BRIEFLY HEAVY SNOW EXPECTED BETWEEN 07Z AND
10Z WED. QUICKLY IMPROVING THEREAFTER. 2-4" SNOWFALL LIKELY.
DRY/FLUFFY SNOW.

KBDL TAF...HIGH CONFIDENCE IN TAF.  BRIEF MVFR CONDITIONS POSSIBLE
BETWEEN 04Z AND 08Z IN A BAND OF LIGHT SNOW.

OUTLOOK...THURSDAY THROUGH SUNDAY...

THURSDAY THROUGH FRIDAY...HIGH CONFIDENCE.  VFR. LOW PROBABILITY OF
MVFR/IFR CONDITIONS ON THE OUTER CAPE AND NANTUCKET IN OCEAN EFFECT
SNOW SHOWERS.

SATURDAY...HIGH CONFIDENCE. VFR.

SUNDAY...MODERATE CONFIDENCE.  MVFR/IFR CONDITIONS LIKELY IN SNOW
SHOWERS.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...

TONIGHT...MODEST SOUTH WINDS BECOME NW TOWARD SUNRISE. SNOW LIMITS
VSBY TO LESS THAN A MILE ROUGHLY 11 PM TO 5 AM.

WED...NW WINDS 20-30 KT BEGINNING MID MORNING. ANY SNOW MOVES WELL
OFFSHORE BY 8-9AM.

WED NIGHT...NW WINDS DIMINISH AND BECOME NORTHERLY.OUTLOOK...THURSDAY
THROUGH SUNDAY...

OUTLOOK...THURSDAY THROUGH SUNDAY...

MODERATE CONFIDENCE.  SMALL CRAFT SEAS LINGER ON THE OUTER WATERS
THURSDAY AND FRIDAY.  HIGH PRESSURE STARTS BUILDING OVER THE WATERS
THROUGH THE WEEKEND...KEEPING WINDS AND SEAS BELOW SMALL CRAFT
CRITERIA.  PERIODS OF OCEAN EFFECT SNOW THURSDAY AND FRIDAY NEAR THE
CAPE AND ISLANDS MAY REDUCE VISIBILITIES AND MORE WIDESPREAD
SNOW/RAIN WILL BE POSSIBLE LATE SUNDAY AS A COLD FRONT APPROACHES
THE WATERS.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR MAZ006-
     007-013>024.
RI...WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR RIZ002-
     004>008.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM WEDNESDAY TO 1 AM EST THURSDAY
     FOR ANZ230>237-250-251-254>256.

&&

$$
SYNOPSIS...NOCERA/RLG
NEAR TERM...FRANK/NOCERA
SHORT TERM...NOCERA
LONG TERM...RLG
AVIATION...NOCERA/RLG
MARINE...NOCERA/RLG



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