Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 182024
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
424 PM EDT SAT OCT 18 2014

.SYNOPSIS...
A STRONG COLD FRONT USERS IN A CHILLY AIRMASS ACROSS NEW ENGLAND
SUNDAY ALONG WITH BLUSTERY CONDITIONS. COLD TEMPERATURES SUNDAY
NIGHT WILL GIVE TO SOME MODERATION MON ALONG WITH A DIMINISHING WIND
AS HIGH PRES SLIDES SOUTH OF NEW ENGLAND. A LONG DURATION COASTAL
STORM IS LIKELY DURING THE MIDDLE TO END OF NEXT WEEK BUT THE AXIS
OF HEAVIEST RAIN AND STRONGEST WINDS REMAINS UNCERTAIN AT THIS TIME
RANGE.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
THROUGH 8 PM...A FEW SHOWERS HAVE POPPED OVER SOUTHERN NEW ENGLAND.
MOST CELLS HAVE HAD 40 DBZ VALUES TOPPING OUT BELOW 13K
FEET...LOWER THAN -10C. BUT A FEW HAVE REACHED 18K FEET AND
GENERATED A LITTLE THUNDER. TOTALS IN THE MID 40S IN OUR AREA AND
AROUND 50 IN NORTHERN NEW ENGLAND. SO THE POTENTIAL FOR THUNDER
IS PRESENT THROUGH THIS EVENING BUT EXPECT MOST ACTION TO BE AS
SHOWERS.

TEMPS IN THE MIDDLE TO UPPER 60S IN THE HIGHER TERRAIN...TO THE
LOWER 70S ACROSS PORTIONS OF THE COASTAL PLAIN...SHOULD START
COOLING THIS EVENING. WINDS GUSTS OF 20 MPH ARE POSSIBLE BEFORE
SUNSET.

TONIGHT...
INITIAL SHORTWAVE MOVES OFFSHORE...PUSHING A COLD FRONT THROUGH
OUR AREA. ANOTHER SHORTWAVE MOVES DOWN FROM ONTARIO TONIGHT AND
PUSHES THE TROUGH AXIS OVER NEW ENGLAND BY MORNING. THIS WILL
BRING COLDER TEMPS ALOFT WHICH WILL DESTABILIZE THE AIRMASS. THUS
EXPECT SHOWER COVERAGE TO DIMINISH EARLY TONIGHT...THEN INCREASE
AGAIN OVERNIGHT. EXPECT SCATTERED/CHANCE POPS FOR TONIGHT.

MIN TEMPS UPSTREAM IN ONTARIO WERE IN THE UPPER 30S AND
40S...THIS IS A REASONABLE TARGET FOR TONIGHT.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
SUNDAY...
SECOND SHORTWAVE AND TROUGH AXIS MOVE OFFSHORE IN THE MORNING.
THIS WILL ALLOW LINGERING SHOWERS IN THE MORNING...THEN A CLEARING
AND DRYING TREND BY AFTERNOON. NORTHWEST WINDS WILL BRING COLDER
AIR AT ALL LEVELS AND SUPPORT DAYTIME MIXING OF THE AIRMASS TO 850
MB. TEMPS AT 850 MB WILL BE -2C TO -5C...WHICH SUPPORTS MAX SFC
TEMPS IN THE UPPER 40S TO MID 50S. WINDS IN THE MIXED LAYER WILL
BE AT LEAST 25 KNOTS. WE WILL USE THESE VALUES.

SUNDAY NIGHT...
AS HIGH PRESSURE BUILDS OVER NEW ENGLAND THE WINDS WILL DIMINISH
DURNING THE EARLY NIGHT. MOSTLY CLEAR SKIES AND LIGHT WINDS WILL
ALLOW FOR RADIATIONAL COOLING. DEWPOINTS IN THE COLDER AIRMASS
WILL BE IN THE 20S...EXCEPT 30-35 ALONG THE COASTLINE AND ISLANDS.
THIS WILL SET UP THE POTENTIAL FOR WIDESPREAD TEMPERATURES AT AND
BELOW FREEZING ACROSS OUR AREA...THE COLDEST NIGHT OF THE SEASON
SO FAR. MOST AREAS ALONG THE COAST WILL COLD ENOUGH FOR A FROST.
WE WILL ISSUE A FREEZE WATCH FOR ALL AREAS AWAY FROM THE COAST
WHERE THE SEASON HAS NOT ALREADY ENDED.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

HIGHLIGHTS...

* TRANQUIL WEATHER MON WITH COOL TEMPS/SUNSHINE AND LIGHT WINDS

* A LONG DURATION COASTAL STORM WILL IMPACT NEW ENGLAND FROM TUE
  THROUGH FRI...HOWEVER AXIS OF HEAVIEST RAIN...STRONGEST WIND AND
  MAGNITUDE OF COASTAL FLOODING REMAINS UNCERTAIN AT THIS TIME

SYNOPTIC OVERVIEW AND MODEL/GUIDANCE EVALUATION...

NOT MUCH CHANGE FROM PREVIOUS MODEL RUNS WITH GOOD AGREEMENT ON AN
EVOLVING LONG DURATION HIGH AMPLTIUDE COASTAL STORM BEGINNING OFF
DELMARVA TUE/WED AND THEN TRACKING NORTHEAST OFF THE NEW ENGLAND
COAST THU/FRI. MODELS DIFFER ON FAR SOUTH DOWN THE EASTERN SEABOARD
CLOSED LOW INITIALLY DIGS...THEN HOW QUICKLY THE MID LEVEL
CIRCULATION CAPTURES THE SURFACE LOW /OCCLUSION/ WHICH WILL
DETERMINE TIMING/TRACK AND DURATION OF WARM CONVEYOR BELT RAINS OVER
THE REGION BEFORE DRY SLOT ARRIVES. AS EXPECTED THE DETERMINISTIC
GUIDANCE DISPLAYS SOME SMALL VARIATIONS FROM RUN TO RUN. THUS AT
THIS TIME RANGE THE MOST SKILLFUL SOLUTION IS A MODEL BLEND WHICH IS
VERY CLOSE TO THE 12Z GEFS AND 00Z ECENS ENSEMBLE MEANS.

DAILIES...

MONDAY...

OTHER THAN A CHILLY START TO THE DAY WITH MORNING LOWS IN THE 30S
REGIONWIDE...IT WILL BE A QUIET WEATHER DAY AS SHORT WAVE RIDGING
DEVELOPS OVER NEW ENGLAND AHEAD OF NORTHERN STREAM SHORT WAVE. WHILE
TEMPS WILL ONLY BE A FEW DEGS HIGHER THAN SUNDAY IT WILL FEEL
CONSIDERABLY WARMER GIVEN MORE SUNSHINE /LESS STRATO-CU/ AND LESS
WIND AS HIGH PRES SLIDES SOUTH OF NEW ENGLAND. EASILY THE PICK OF
THE WEEK.

TUESDAY THROUGH FRIDAY...

PROLONG PERIOD OF RAIN AND WIND OF VARYING INTENSITY AS LARGE
AMPLITUDE CLOSED MID LEVEL LOW DEVELOPS OVER THE MID ATLC REGION AND
EVENTUALLY SLIDES SOUTH OF NEW ENGLAND COAST. AS MENTIONED ABOVE
TIMING AND POSITION DIFFERENCES ON EXACT EVOLUTION WHICH CREATES
UNCERTAINTY ON STORM DETAILS...SUCH AS AXIS OF HEAVIEST RAIN...
STRONGEST WIND AND MAGNITUDE OF COASTAL FLOODING. THE NEW 12Z GEFS
INDICATES STRONGEST 925 MB AND 850 MB ONSHORE LOW LEVEL WIND
ANOMALIES /+3 STD/ OCCUR FROM 12Z WED TO 12Z THU ACROSS INTERIOR
SOUTHERN NEW ENGLAND AND THEN LIFTING INTO CENTRAL AND NORTHERN NEW
ENGLAND LATER THU INTO FRI. THIS WOULD SUGGEST THE STRONGEST WINDS
AND HEAVIEST RAINFALL LATE TUE NIGHT INTO EARLY THU FOR SOUTHERN NEW
ENGLAND BEFORE LIFTING INTO NORTHERN NEW ENGLAND WITH DRY SLOT
APPROACHING FROM THE SOUTH.

DETERMINISTIC RUNS OF THE 12Z GFS AND ECMWF CONCUR WITH THIS
EVOLUTION YIELDING EVENT RAINFALL TOTALS OF 1-2" ACROSS CT/RI AND
SOUTHEAST MA...INCREASING TO 3-4" OVER NORTHERN MA INTO SOUTHWEST
NH. LOCALLY HEAVIER AMOUNTS POSSIBLE ESPECIALLY IN THE UPSLOPE
REGIONS OF THE HIGHER TERRAIN OF MA AND NH. A SUPERBLEND OF ALL
MODEL SOURCES YIELDS THE SAME QPF RESULTS...AREAL COVERAGE AND IN
MAGNITUDE. THUS AT THIS TIME RANGE ENSEMBLES AND A MODEL BLEND OF
DETERMINISTIC GUID SUGGEST GREATEST THREAT OF FLOODING RAINS/STRONG
WINDS-DOWN TREE LIMBS-POWER OUTAGES AND COASTAL FLOODING WOULD BE
ACROSS NORTHERN MA INTO SOUTHERN NH. GIVEN THE TIME RANGE OBVIOUSLY
THIS CAN SHIFT FARTHER SOUTH OR NORTH. THUS NEED TO REMAIN
PROBABILISTIC AT THIS TIME RANGE.

REGARDING COASTAL FLOODING...AS MENTIONED ABOVE LATEST GUIDANCE AND
TRENDS CONTINUE TO SUGGEST LONGEST DURATION OF STRONGEST WINDS WILL
OCCUR FROM NORTHERN MA NORTHWARD ACROSS NH AND MAINE COASTLINE. THUS
GREATEST RISK OF COASTAL FLOODING AND EROSION IS CAPE ANN/SALISBURY
NORTHWARD. HOWEVER AT THIS TIME RANGE IT/S POSSIBLE FOR THIS RISK
AREA TO SHIFT SOUTHWARD OR NORTHWARD. WHILE ASTRO TIDES ARE SOMEWHAT
LOW THIS WILL LOWER THE RISK OF MORE SIGNIFICANT COASTAL FLOODING.
HOWEVER LONG DURATION EVENT OCCURRING OVER MULTIPLE TIDE CYCLES CAN
OFFSET THIS. FOR THIS REASON THE RISK OF EROSION APPEARS GREATER
THAN INUNDATION GIVEN LARGE SURF WILL BATTER THE COASTLINE FOR A
NUMBER OF CONSECUTIVE DAYS.

&&

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

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

SHORT TERM /THROUGH SUNDAY/...

THROUGH 00Z/8 PM...MODERATE CONFIDENCE. MAINLY VFR. BRIEF MVFR
CIGS POSSIBLE IN ANY SHOWERS/TSTMS. SOUTHWEST WIND GUSTS OF 20 TO
25 KNOTS EXPECTED BEFORE SUNSET.

TONIGHT...MODERATE TO HIGH CONFIDENCE. GENERALLY VFR WITH BRIEF
MVFR CIGS IN SCATTERED TO ISOLATED SHOWERS OVERNIGHT.

SUNDAY...HIGH CONFIDENCE. VFR. MORNING CLOUDS BREAK TO MOSTLY
CLEAR IN THE AFTERNOON. NORTHWEST WINDS WILL GUST TO 25 KT FROM
LATE MORNING THROUGH THE EVENING. SCATTERED SHOWERS ARE POSSIBLE
SUNDAY MORNING.

SUNDAY NIGHT...HIGH CONFIDENCE. VFR. MOSTLY CLEAR SKIES AND WINDS
BECOME LIGHT. TEMPERATURES AWAY FROM THE COAST WILL FALL TO NEAR
FREEZING OR A LITTLE BELOW...TURNING ANY WET SPOTS ON THE GROUND
INTO PATCHES OF ICE.

KBOS...HIGH CONFIDENCE IN TAF.

KBDL...HIGH CONFIDENCE IN TAF.

OUTLOOK...MONDAY THROUGH THURSDAY...

MON...HIGH CONFIDENCE. VFR/DRY RUNWAYS AND LIGHT WINDS.

TUESDAY/WEDNESDAY/THU...HIGH CONFIDENCE ON OVERALL THEME...WITH
CONDITIONS LOWERING TO MVFR/IFR IN DEVELOPING RAIN BUT LOW
CONFIDENCE ON EXACT TIMING OF DETAILS. STRONG EAST TO NORTHEAST
WINDS POSSIBLE WED INTO EARLY THU ACROSS NE MA AND S NH.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /TONIGHT THROUGH SUNDAY/...HIGH CONFIDENCE.

TONIGHT...SOUTHEAST SWELL FROM GONZALO CONTINUES TO AFFECT THE NEW
ENGLAND WATERS WITH A 14 SECOND PERIOD AND HEIGHTS OF 5 TO 8 FEET.
THIS WILL CONTINUE TONIGHT ON ALL EXPOSED WATERS. SOUTHWEST WINDS
GUSTING TO 20 KNOTS WILL BECOME WEST OVERNIGHT AS A COLD FRONT
MOVES THROUGH. SMALL CRAFT HEADLINES CONTINUE FOR ALL WATERS
EXCEPT BOS HARBOR/NARRAGANSETT BAY/MASSACHUSETTS BAY.

SUNDAY...NORTHWEST WINDS OVER THE WATERS WILL BRING GUSTS OF 25 TO
30 KNOTS TO THE SURFACE. SOUTHEAST SWELL WILL CONTINUE ALTHOUGH
DIMINISHED A LITTLE FROM SATURDAY. SMALL CRAFT ADVISORY IS IN
PLACE FOR ALL WATERS.

SUNDAY NIGHT...HIGH PRESSURE APPROACHES FROM THE WEST. NORTHWEST
WINDS WILL DIMINISH OVERNIGHT AS THE HIGH GETS CLOSER. SOUTHEAST
SWELL FROM GONZALO WILL DIMINISH OVERNIGHT. SMALL CRAFTS WILL END
ON THE NEARSHORE WATERS BUT LINGER ON THE OUTER WATERS.

OUTLOOK...MONDAY THROUGH THURSDAY...

*** POWERFUL/DANGEROUS EARLY SEASON COASTAL STORM TO MARINERS LIKELY
  WED/THU ***

MONDAY...WINDS SLACKEN AS HIGH PRES SLIDES SOUTH OF NEW ENGLAND.
THUS SUBSIDING SEAS. GOOD VSBY IN DRY WEATHER.

TUE/WED/THU...COASTAL STORM DEVELOPS OFF THE DE COAST YIELDING
INCREASING EAST WINDS BEGINNING TUE WITH STRONGEST E-NE WINDS LIKELY
WED INTO THU AS LOW PRES APPROACHES BETWEEN NANTUCKET AND THE
40N/70W BENCHMARK. E-NE GALES LIKELY WITH GREATEST RISK NORTHERN
WATERS ALONG WITH INCREASING SEAS OF 15+...AGAIN OCEAN WATERS
NORTHEAST OF BOSTON TO CAPE ANN. PERIODS OF HEAVY RAIN WILL REDUCE
VSBY.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...FREEZE WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY MORNING FOR
     CTZ002>004.
MA...FREEZE WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY MORNING FOR
     MAZ005-006-009>014-017-018.
NH...NONE.
RI...FREEZE WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY MORNING FOR
     RIZ001-003.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT MONDAY FOR ANZ231>235-237.
     SMALL CRAFT ADVISORY FROM 8 AM SUNDAY TO 2 AM EDT MONDAY FOR
     ANZ230-236-251.
     SMALL CRAFT ADVISORY UNTIL 8 AM EDT MONDAY FOR ANZ250-254>256.

&&

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



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