Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 132306
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
705PM EDT SAT SEP 13 2014

.SYNOPSIS...
LOW PRESSURE SYSTEM WILL MOVE FROM THE SAINT LAWRENCE RIVER REGION
NORTHEAST INTO SOUTHEAST QUEBEC TONIGHT. ANOTHER LOW SOUTH OF LONG
ISLAND WILL PASS EAST OF NANTUCKET OVERNIGHT. THESE TWO SYSTEMS
WILL BRING LIGHT RAIN TO SOUTHERN NEW ENGLAND BEFORE MIDNIGHT.
HIGH PRESSURE WILL BRING SUNNY SKIES AND CLEAR NIGHTS SUNDAY INTO
MONDAY WITH SLIGHTLY BELOW NORMAL TEMPERATURES. A COLD FRONT WILL
LIKELY BRING A PERIOD OF SHOWERS LATE MONDAY NIGHT INTO TUESDAY.
MAINLY DRY WEATHER EXPECTED NEXT WEDNESDAY THROUGH FRIDAY WITH
SLIGHTLY BELOW NORMAL TEMPERATURES CONTINUING.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

705 PM UPDATE...

ALREADY SEEING THE RAIN ENDING ACROSS SOUTHERN NH/WESTERN MA AND
NORTHERN CT EARLY THIS EVENING.  SHOULD SEE THE RAIN WIND DOWN
ACROSS EASTERN MA/RHODE ISLAND BETWEEN 8 AND 9 PM...BUT WILL LINGER
A BIT LONGER ACROSS THE CAPE AND ISLANDS.  STILL CAN/T RULE OUT A
SPOT SHOWER OR TWO ACROSS THE REST OF THE REGION THROUGH
MIDNIGHT...BUT AGAIN OTHER THAN THE CAPE AND ISLANDS MOST AREAS
WILL BE MAINLY DRY AFTER 9 PM.

EAST WINDS WILL TURN TO THE NORTH AND NORTHWEST ONCE THE LOW
PASSES EAST OF NANTUCKET OVERNIGHT. SKIES ARE FORECAST TO CLEAR
OUT FROM WEST TO EAST AFTER MIDNIGHT BUT THERE COULD BE SOME
SCATTERED FOG PATCHES DEVELOPING DUE TO THE EARLIER RAINFALL.
THIS FOG MIGHT BE LOCALLY DENSE IN AREAS ACROSS THE INTERIOR...IF
WINDS CAN DECOUPLE FOR TIME.  HOWEVER...MUCH OF THE REGION WILL NOT
DECOUPLE AS A RESULT OF COOL AIR ADVECTION BEHIND THE COLD FRONT.

TOWARD DAYBREAK...WINDS MAY BRIEFLY GUST TO 20 TO 25 MPH ESPECIALLY
NEAR THE COAST. OVERNIGHT LOWS WILL RANGE FROM THE MID 40S IN SW
NH AND NW MA...TO THE UPPER 50S NEAR THE CAPE AND ISLANDS.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
SUNDAY...NORTHWEST WINDS MAY GUST TO 20 TO 25 MPH IN RI AND
EASTERN MA EARLY IN THE MORNING FOR A FEW HOURS DUE TO THE
GRADIENT BEHIND DEPARTING LOW PRESSURE AND ADVANCING STRONG HIGH
PRESSURE...THEN WINDS WILL DROP OFF. OTHERWISE...A BRIGHT SUNNY
DAY IS IN STORE WITH HIGH TEMPERATURES 65 TO 70 EXCEPT 60 TO 65 IN
SOUTHERN NH.

SUNDAY NIGHT...CRYSTAL CLEAR SKIES WILL ALLOW FOR GOOD RADIATIONAL
COOLING. OVERNIGHT LOWS WILL MAINLY BE IN THE 40S BUT COULD DIP
INTO THE UPPER 30S IN SOUTHWEST NH. THERE IS A VERY LOW
PROBABILITY THAT SOME FROST COULD FORM IN SOUTHWEST NH.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

HIGHLIGHTS...
*SHOWERS POSSIBLE FROM COLD FRONTAL PASSAGE MON NIGHT/TUE
*BELOW NORMAL TEMPS OBSERVED AFTER LATE WEEK FRONTAL PASSAGE
*LESS HUMIDITY AS DEW POINTS ARE BELOW 60F FOR THE ENTIRE PERIOD

OVERVIEW...

THIS PERIOD IS CHARACTERIZED BY A RIDGE IN THE WEST AND A TROUGH IN
THE EAST OR THE TYPICAL POSITIVE PNA PATTERN AT LEAST TO START. WITH
THE UPPER LEVEL LOW PRESSURE SYSTEM DROPPING SOUTH OUT OF
CANADA...EXPECT THE ARCTIC OSCILLATION TO DROP MORE NEGATIVE. ALSO
EXPECTING THE NAO TO DROP FROM POSITIVE TO MORE NEUTRAL INDICATING
A SLOWING PATTERN.

MODELS HANDLE THIS PERIOD FAIRLY WELL AND WITH ADEQUATE AGREEMENT
ASIDE FROM THE HANDLING OF A SHORTWAVE THAT MOVES THROUGH THE
REGION. THE 6Z GFS IS FASTER AND WEAKER WITH THE MOVEMENT OF THAT
SHORTWAVE THROUGH THE REGION THAN THE ECMWF. THE LATTER HAS A
STRONGER SHORTWAVE...WHICH FORMS A LOW PRESSURE SYSTEM SOUTH OF THE
AREA. HAVE GONE WITH A BLEND OF THE MODELS TO ELIMINATE THE GFS BIAS
TOWARDS QUICKER EVOLUTION THROUGH THE REGION AND THE HEAVIER
PRECIPITATION FROM THE ECMWF. LATER IN THE PERIOD...A COLD FRONT
PUSHES SOUTH THROUGH NEW ENGLAND WITH MORE MODEL DISAGREEMENT. THE
ECMWF ALLOWS FOR A LATER PASSAGE OF THE FRONT LATE THURSDAY NIGHT
WHILE THE GFS PUSHES IT THROUGH LATE WEDNESDAY/EARLY THURSDAY.
FOLLOWING THE ENSEMBLES AND WPC...HAVE GONE WITH AN EARLY THURSDAY
FRONTAL PASSAGE.

DAILIES...

 MONDAY...A HIGH PRESSURE SYSTEM MOVES FROM WEST TO EAST CHANGING
WINDS TO THE SOUTHWEST AHEAD OF A SHORTWAVE FROM CANADA. WITH MIXING
UP TO AROUND 850 MB THAT WOULD GIVE HIGH TEMPS IN THE MID TO UPPER
60S

 TUESDAY...EVEN WITH THE SOUTHWEST WARMING WINDS...THE HUMIDITY
REMAINS LOW WITH PWATS ONLY AROUND 1 INCH AND THE TOTAL OF TOTALS
ONLY AROUND 40. FEEL A LOWER END EVENT MAY OCCUR FROM THIS WITH THE
QUICK MOVING LOW PRESSURE SYSTEM. HAVE LEANED AWAY FROM THE
ECMWF...BUT FEEL THE GFS MAY BE TOO LOW. ALSO DON/T SEE MUCH IN
THE WAY OF INSTABILITY FOR THUNDER.

WEDNESDAY THROUGH FRIDAY...AREAS OF HIGH PRESSURE PINWHEEL AROUND
THE UPPER LEVEL LOW IN SOUTHEASTERN CANADA. A COLD FRONT LOOKS TO
PASS THROUGH EARLY THURSDAY WITH TEMPERATURES AS COLD AS JUST OVER
2 SDS BELOW NORMAL AT 850MB OR 1.5 KM INTO THE SKY. AM EXPECTING A
FEW CUMULUS CLOUDS TO BE AROUND...BUT NOT OVERCAST AT ALL. BEST
CHANCE TO SEE THURSDAY OVERNIGHT TEMPS DIP BELOW 40F AND WOULD
THEREFORE HAVE TO WATCH FOR FROST IN THOSE AREAS...NAMELY
NORTHWESTERN MA AND SOUTHEASTERN NH.

SATURDAY...THE 6Z GFS IS SHOWING A COLD FRONT...BUT WITH THE NAO
BEGINNING TO GO NEGATIVE AND INDICATING A SLOWING PATTERN...WILL
STICK WITH WHAT THE ECMWF AND OTHER ENSEMBLE MODELS ARE SHOWING
AND ALLOW HIGH PRESSURE TO SLOWLY EXIT THE REGION.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
FORECASTER CONFIDENCE LEVELS...

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

CONFIDENCE IS LOW FOR TONIGHT...THEN HIGH FOR SUNDAY AND
SUNDAY NIGHT.

TONIGHT...BAND OF RAIN NOW ACROSS EASTERN MA/RHODE ISLANDS SHOULD
EXIT MOST OF THIS AREA BY 1Z.  THE EXCEPTION WILL BE THE CAPE AND
ISLANDS WHERE IT WILL LINGER A BIT LONGER.  OTHERWISE...CAN/T RULE
OUT A SPOT SHOWER OR TWO THROUGH 4Z BUT MOST OF THE REST OF THE
NIGHT WILL BE DRY.

CIGS/VSBYS FORECAST IS OF LOW CONFIDENCE TONIGHT.  A WIDE VARIETY OF
CONDITIONS RANGING FROM IFR TO VFR WERE OCCURRING EARLY THIS
EVENING. MVFR PROBABLY DOMINATE FOR THE FIRST PART OF THE
NIGHT...WITH SOME LOCATIONS ALONG THE COASTAL PLAIN IMPROVING TO
VFR.  HOWEVER...PARTIAL CLEARING WILL RESULT IN SOME MVFR-IFR VSBYS
TO DEVELOP ACROSS THE INTERIOR.  WINDS WILL NOT DECOUPLE IN ALL
LOCATIONS SO UNSURE HOW WIDESPREAD ANY FOG WILL BE.

SUNDAY AND SUNDAY NIGHT...VFR WITH CLEAR SKIES AND EXCELLENT
VISIBILITY AFTER ANY EARLY MORNING LOW CLOUDS/FOG PATCHES.

KBOS TERMINAL...MODERATE CONFIDENCE.  MVFR CONDITIONS WILL LINGER
INTO THE EVENING BUT SHOULD IMPROVE TO VFR.  RAIN ENDS BY AROUND 1Z.

KBDL TERMINAL...LOW CONFIDENCE. IFR CONDITIONS SHOULD IMPROVE AT
LEAST TEMPORARILY LATER THIS EVENING.  HOWEVER...WE MAY SEE SOME
FOG DEVELOP AFTER MIDNIGHT BUT THAT IS UNCERTAIN BECAUSE UNSURE IF
THE TERMINAL WILL BE ABLE TO COMPLETELY DECOUPLE.

OUTLOOK...MONDAY THROUGH THURSDAY...HIGH CONFIDENCE.

MONDAY...VFR CONDITIONS EXPECTED.

TUESDAY...SHOWERS BEGIN IN THE EARLY MORNING HOURS WITH MVFR
CONDITIONS EXPECTED. THEN BECOMING VFR AS SHOWERS EXIT IN THE MID
AFTERNOON HOURS.

WEDNESDAY AND THURSDAY...VFR CONDITIONS EXPECTED.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

FORECAST CONFIDENCE IS MODERATE TONIGHT THROUGH SUNDAY NIGHT.

TONIGHT...E WINDS 15 TO 20 KT WITH SOME HIGHER GUSTS ALONG THE
COAST WILL SHIFT TO THE N AND NW WELL AFTER MIDNIGHT AS LOW
PRESSURE SOUTH OF LONG ISLAND MOVES NE AND PASSES TO THE E OF
NANTUCKET. A BAND OF LIGHT TO OCCASIONALLY MODERATE RAIN WILL PASS
OVER THE WATERS AND MAY RESTRICT VISIBILITIES MAINLY TO 3 TO 5
MILES.

SUNDAY...THE GRADIENT BETWEEN THE DEPARTING LOW PRESSURE AND
ADVANCING STRONG HIGH PRESSURE MAY CAUSE A BRIEF PERIOD OF NW WIND
GUSTS TO 25 KT WITHIN A FEW HOURS EITHER SIDE OF DAYBREAK SUNDAY.
AS A RESULT A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE EASTERN
MA COASTAL WATERS. THE WINDS SHOULD DIMINISH BY LATE MORNING...BUT
SEAS COULD LINGER NEAR 5 FT OVER THE OUTER WATERS EAST OF MA...SO
THE SMALL CRAFT ADVISORY EXTENDS INTO THE AFTERNOON FOR THOSE
AREAS.

SUNDAY NIGHT...WINDS AND SEAS BELOW SMALL CRAFT ADVISORY CRITERIA.

OUTLOOK...MONDAY THROUGH THURSDAY...

MONDAY INTO TUE MORNING...MODERATE TO HIGH CONFIDENCE.  HIGH
PRESSURE NEARBY WILL RESULT IN A WEAK PRESSURE GRADIENT KEEPING
WINDS/SEAS BELOW SCA THRESHOLDS.

TUESDAY AFTERNOON INTO WEDNESDAY...MODERATE CONFIDENCE. SWELLS BEGIN
TO BUILD TO BETWEEN 5 AND 7FT BEHIND THE DEPARTING LOW PRESSURE
SYSTEM AND COLD FRONT. THIS IS ABOVE SCA LEVELS AND THEREFORE A SCA
MAY BE NEED.

THURSDAY...AS NEXT HIGH PRESSURE SYSTEM APPROACHES WITH WEAKER
PRESSURE GRADIENT...EXPECT SWELLS TO DIE DOWN DURING THE DAY TO
BELOW SCA THRESHOLD.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...NONE.
NH...NONE.
RI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 11 AM EDT SUNDAY FOR ANZ231-
     232-251-255.
     SMALL CRAFT ADVISORY FROM 6 AM TO 4 PM EDT SUNDAY FOR ANZ250-
     254.

&&

$$
SYNOPSIS...GAF/HR
NEAR TERM...FRANK/GAF
SHORT TERM...GAF
LONG TERM...HR
AVIATION...GAF/HR
MARINE...FRANK/GAF/HR



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