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FXUS61 KBOX 172101 AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
401 PM EST SUN FEB 17 2019

SYNOPSIS... 

ACCUMULATING SNOW OVERSPREADS THE REGION LATE THIS EVENING AND OVERNIGHT FROM WEST TO EAST AND CONTINUES INTO MONDAY, IN ASSOCIATION WITH A LOW PRESSURE TRACKING SOUTH OF NEW ENGLAND. DRIER AND COLDER CONDITIONS FOLLOW MONDAY NIGHT INTO WEDNESDAY. ANOTHER LOW APPROACHES THE REGION WHICH WILL BRING SNOW WEDNESDAY NIGHT, LIKELY CHANGING TO A WINTRY MIX INLAND, AND OVER TO RAIN ALONG THE COAST BEFORE ENDING THURSDAY. DRY CONDITIONS SHOULD RETURN FRIDAY INTO SATURDAY.

&&


NEAR TERM /UNTIL 10 PM THIS EVENING/...  

4 PM UPDATE...

DRY WEATHER PREVAILS THROUGH ABOUT 9 OR 10 PM THIS EVENING, BUT WE WILL SEE A SIGNIFICANT INCREASE IN MID/HIGH LEVEL CLOUDINESS AHEAD OF THE APPROACHING LOW PRESSURE SYSTEM. TEMPERATURES WILL FALL BACK TO THE MIDDLE 20S TO THE LOWER 30S OVER THIS TIME.

&&


SHORT TERM /10 PM THIS EVENING THROUGH 6 PM MONDAY/...    

HIGHLIGHTS...

* SNOW DEVELOPS BETWEEN 10 PM AND 2 AM FROM SOUTHWEST TO NORTHEAST * HEAVIEST SNOW OCCURS THROUGH 9 AM NEAR AND ESP SOUTH OF PIKE * SNOW CONTINUES MON AFTERNOON WITH FOCUS ACROSS CENTRAL/EASTERN MA

1) OVERVIEW AND IMPACTS:

APPROACHING SHORTWAVE WILL INCREASE THE FORCING FOR ASCENT AND ALLOW SNOW TO OVERSPREAD THE REGION ROUGHLY BETWEEN 10 PM AND 2 AM MONDAY MORNING. THE HEAVIEST SNOW IS EXPECTED NEAR AND ESPECIALLY SOUTH OF THE MA TURNPIKE OVERNIGHT. THIS IS WHERE THE BEST FORCING RESIDES AND THE GUIDANCE INDICATES A FEW HOURS OF OMEGA EXCEEDING 20 UNITS IN THE SNOW GROWTH REGION. THERE ALSO IS A -EPV SIGNATURE PRESENT ALONG WITH 700 MB LAPSE RATES ON THE ORDER OF 6-7 C/KM. THIS IS SUPPORTIVE FOR A WINDOW OF 1 TO PERHAPS 2 INCH PER HOUR SNOWFALL RATES. WHILE THIS IS RELATIVELY A SHORT WINDOW, IT LOOKS TO IMPACT RI AND SE MA DURING THE MORNING COMMUTE (ALBEIT LESS TRAFFIC THAN USUAL GIVEN THE HOLIDAY). PTYPE SHOULD MAINLY BE SNOW, BUT ENOUGH MID LEVEL WARMTH MAY INVADE THE IMMEDIATE SOUTH COAST AND PARTICULARLY THE CAPE/ISLANDS FOR A CHANGE TO SLEET/RAIN TOWARDS 12Z MONDAY.

THE FIRST PHASE OF THE STORM SHOULD COME TO AN END BY MID MORNING MONDAY. HOWEVER, THERE IS A SECOND PORTION OF THIS EVENT WE NEED TO DISCUSS. AN INVERTED TROUGH FEATURE ALONG WITH MOIST LOW LEVEL ONSHORE FLOW WILL ALLOW FOR PERIODS OF GENERALLY LIGHTER SNOWFALL TO LINGER INTO THE AFTERNOON. IN FACT, THE AREA NEEDED FOR ICE NUCLEATION DRIES OUT ACROSS PORTIONS OF WESTERN MA/NORTHERN CT FOR A TIME. THIS MAY RESULT IN SOME FREEZING DRIZZLE TOO.

WHILE LIGHTER SNOWFALL WILL BE THE RULE WITH THE SECOND PORTION OF THE STORM, WE WILL NEED TO WATCH CENTRAL AND EASTERN MA FOR LOCALLY HEAVIER BANDS. MOIST ONSHORE FLOW MAY RESULT IN SOME ENHANCEMENT OF THE SNOW ALONG THE EAST SLOPES OF THE WORCESTER HILLS AND PERHAPS EVEN THE BERKS. ALONG THE EASTERN MA COAST, THE LAND/SEA INTERFACE MAY RESULT IN OCEAN ENHANCEMENT. A LOOK AT THE MODEL CROSS SECTIONS REVEALS SATURATED SOUNDINGS IN THE OPTIMAL SNOW GROWTH REGION. SO THERE MIGHT BE A FEW BANDS OF MODERATE TO PERHAPS EVEN BRIEFLY HEAVY SNOW LATER IN THE MORNING INTO THE LATE AFTERNOON IN THIS REGION.

OUTSIDE OF THESE BANDS OF MORE SIGNIFICANT SNOW ACROSS CENTRAL AND EASTERN MA, ROADS MAY BE MANAGEABLE GIVEN LIGHTER SNOWFALL RATES AND MARGINAL TEMPERATURES. LIGHT SNOW SHOWERS MAY LINGER INTO THE THE EARLY EVENING HOURS, BUT ANY ACCUMULATIONS AFTER 7 OR 8 PM SHOULD BE LESS THAN AN INCH.

2) HEADLINES AND SNOW ACCUMULATIONS:

BASED ON THE LATEST DATA FEEL A WIDESPREAD 3 TO 6 INCHES OF SNOW IS IN STORE FOR MUCH OF THE REGION. GUIDANCE ALSO POINTS TO A SWATH OF POTENTIALLY 4 TO 7 INCH AMOUNTS IN THE PVD-TAN-PYM-EWB CORRIDOR. WILL GO AHEAD AND UPGRADE THIS REGION TO A MARGINAL WINTER STORM WARNINGS. WE ALSO WILL HAVE TO WATCH THE CAPE AND SOUTH COASTS OF RI, BUT MORE MARGINAL TEMPERATURES AND THE POTENTIAL FOR A PERIOD OF SLEET/RAIN, DID NOT FEEL CONFIDENT ENOUGH TO GO WITH A WARNING. THE REST OF OUR COUNTY WARNING AREA WILL BE UNDER A WINTER WEATHER ADVISORY. THERE IS A LOW RISK THOUGH THAT MARGINAL WARNING CRITERIA IS REALIZED ALONG THE EAST SLOPES OF THE BERKS/ORH HILLS WITH BETTER RATIOS AND PERHAPS EVEN BOSTON ITSELF WITH THE INVERTED TROUGH. AGAIN THOUGH JUST WAS NOT CONFIDENT ENOUGH IN THIS REGION.

THE BOTTOM LINE IS A MODERATE SNOW EVENT IS IN THE CARDS FOR THE REGION. BIGGEST IMPACT WILL THE MORNING COMMUTE NEAR AND ESPECIALLY SOUTH OF THE MA TURNPIKE. ALSO, THE AFTERNOON COMMUTE MAY BE AN ISSUE FROM THE WORCESTER HILLS AND ONTO THE EASTERN MA COAST FROM THE INVERTED TROUGH.

&&


LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...    

* DRY BUT TURNING COLDER MONDAY NIGHT INTO WEDNESDAY * ANOTHER CHANCE OF SNOW WEDNESDAY NGT BUT LIKELY CHANGING TO A WINTRY MIX INLAND AND RAIN ALONG THE COAST THURSDAY * DRY WEATHER FOLLOWS FRIDAY AND LIKELY LINGERS INTO SATURDAY

OVERVIEW...

LARGE SCALE FLOW ACROSS THE CONUS THIS PERIOD FEATURES A HIGH AMPLITUDE WESTERN TROUGH AND A DOWNSTREAM SOUTHEAST/SUBTROPICAL RIDGE ALONG WITH CONFLUENT FLOW ACROSS NEW ENGLAND AS NORTHERN STREAM REMAINS SOMEWHAT AMPLIFIED. FORECAST DILEMMA THIS PERIOD REVOLVES AROUND AMPLITUDE OF NORTHERN STREAM WHICH WILL DICTATE POSITION OF CONFLUENT FLOW ACROSS NEW ENGLAND/MARITIMES AND ACCOMPANYING DRY/COLD AIRMASS. THIS WILL ULTIMATELY DETERMINE THE STORM TRACK AND PTYPE FOR WED NIGHT/THU EVENT.

DETAILS...

MON NIGHT/TUE/WED ...

DRYING TREND DEVELOPS MON NIGHT AS COASTAL LOW EJECTS OUT TO SEA IN RESPONSE TO NORTHERN STREAM SHORT WAVE MOVING ACROSS NEW ENGLAND. GOOD COLD AIR ADVECTION (CAA) BEHIND THIS DEPARTING SHORT WAVE WITH 925 MB TEMPS DROPPING TO -10C TO -12C ACROSS SOUTHERN NEW ENGLAND MON NGT INTO WED. THIS WILL SUPPORT TEMPS COLDER THAN NORMAL WITH HIGHS ONLY IN THE UPPER 20S TO LOWER 30S BOTH TUE AND WED AND TEENS AT NIGHT. BLUSTERY NW WINDS MON NGT AND TUE WILL PROVIDE COLD WIND CHILLS AS WELL. WINDS DIMINISH WED AS 1030+ MB HIGH PRES BUILDS OVER THE REGION.

WED NIGHT/THURSDAY ...

NEXT SURGE OF MOISTURE APPROACHES FROM THE SOUTHWEST WED NGT. COLUMN IS INITIALLY COLD ENOUGH TO SUPPORT ALL SNOW. HOWEVER WITH SOUTHEAST EAST RIDGE BUILDING UP THE EASTERN SEABOARD STORM TRACK SHIFTS FARTHER NORTH CLOSER TO NEW ENGLAND. ALSO WITH MID LEVEL TROUGH TRACKING WELL NORTHWEST OF NEW ENGLAND MID LEVEL WARM AIR OVERSPREADS THE AREA THU. HOWEVER WITH NORTHERN STREAM SHORT WAVE SLOW TO EXIT NEWFOUNDLAND, COLD HIGH PRES WILL LINGER OVER THE MARITIMES AND PROVIDE COLD AIR DAMMING ACROSS INTERIOR SOUTHERN NEW ENGLAND FOR AT LEAST AT TIME INTO EARLY THU. THIS WILL INCREASE THE ODDS OF SHALLOW COLD AIR LINGERING ACROSS THE INTERIOR AND SUPPORTING A WINTRY MIX. CLOSER TO THE COAST SNOW LIKELY CHANGES TO RAIN GIVEN A STORM TRACK ALONG OR NEAR THE SOUTH COAST. ALTHOUGH GIVEN EVENT IS STILL 96+ HRS OUT IN TIME WE DON'T WANT TO LOCK INTO ONLY ONE WEATHER SCENARIO.

FRIDAY/SATURDAY ...

COASTAL LOW AND ASSOCIATED MID LEVEL TROUGH FROM THU MOVES EAST OF NEW ENGLAND AND IS REPLACED BY DRY NW FLOW ALOFT AND SEASONABLE TEMPS FRI INTO SAT. NEXT SYSTEM APPROACHES SAT NIGHT/SUNDAY WITH THE THREAT FOR ANOTHER ROUND OF WINTRY PRECIP.

&&


.AVIATION /21Z SUNDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH MONDAY/...  HIGH CONFIDENCE.

TONIGHT AND MONDAY...MAINLY VFR EARLY THIS EVENING. SNOW OVERSPREADS THE REGION FROM SOUTHWEST TO NORTHEAST BETWEEN 03Z AND 07Z. THIS WILL RESULT IFR TO LIFR CONDITIONS DEVELOPING OVERNIGHT AND PERSISTING THROUGH MONDAY AFTERNOON. HEAVIEST SNOW OCCURS NEAR AND ESPECIALLY SOUTH OF THE MA TURNPIKE THROUGH ABOUT 13Z OR 14Z MONDAY, WHERE LIFR CONDITIONS WILL BE MOST PREVALENT.

GENERALLY LIGHTER SNOWS LINGER LATER MONDAY MORNING INTO THE AFTERNOON AND THERE MAY EVEN BE POCKETS OF FREEZING DRIZZLE IN WESTERN MA/NORTHERN CT. DESPITE THE OVERALL DIMINISHING SNOW INTENSITY, LOCALIZED BANDS OF MODERATE TO EVEN BRIEFLY HEAVIER SNOW WILL REMAIN POSSIBLE ACROSS CENTRAL AND EASTERN MA INTO MON AFTERNOON. PTYPE SHOULD BE ALL SNOW EXCEPT FOR THE IMMEDIATE SOUTH COAST AND ESPECIALLY THE CAPE/ISLANDS, WHERE A CHANGE TO SLEET/RAIN MAY OCCUR FOR A TIME MONDAY MORNING. TOTAL SNOW ACCUMULATIONS OF 3 TO 6 INCHES ARE ANTICIPATED FOR MUCH OF THE REGION.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF.

OUTLOOK /MONDAY NIGHT THROUGH FRIDAY/...

MONDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. BREEZY. SLIGHT CHANCE SN.

TUESDAY THROUGH TUESDAY NIGHT: VFR. BREEZY.

WEDNESDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. CHANCE SN.

WEDNESDAY NIGHT: MAINLY IFR, WITH AREAS MVFR POSSIBLE. BREEZY. SN LIKELY, PL LIKELY, FZRA LIKELY.

THURSDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY. CHANCE RA, CHANCE FZRA, CHANCE PL.

&&



MARINE...  
   FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH MONDAY/...  HIGH CONFIDENCE.

TONIGHT AND MONDAY...HIGH CONFIDENCE. GENERALLY LIGHT WINDS AND FLAT SEAS THIS EVENING. 5 FOOT SMALL CRAFT SEAS AND NORTHEAST WIND GUSTS UP TO 25 KNOTS DEVELOP ACROSS THE SOUTHERN WATERS NEAR DAYBREAK MONDAY AND CONTINUE INTO THE AFTERNOON. A FEW GUSTS APPROACHING 25 KNOTS ARE POSSIBLE MONDAY ACROSS SOME OF THE SOUTHERN SOUNDS AND BAYS, BUT FELT IT WAS TO MARGINAL FOR HEADLINES AT THIS POINT. PERIODS OF RAIN, SLEET, AND SNOW OVERNIGHT INTO MONDAY WILL REDUCE VSBYS AT TIME FOR MARINERS.

OUTLOOK /MONDAY NIGHT THROUGH FRIDAY/...

MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. CHANCE OF SNOW. AREAS OF VISIBILITY 1 TO 3 NM.

TUESDAY THROUGH TUESDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.

WEDNESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT. SLIGHT CHANCE OF SNOW. AREAS OF VISIBILITY 1 TO 3 NM.

WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT. RAIN LIKELY, CHANCE OF SNOW, SLEET LIKELY, FREEZING RAIN LIKELY. VISIBILITY 1 TO 3 NM.

THURSDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT. CHANCE OF RAIN, FREEZING RAIN LIKELY.

&&


.TIDES/COASTAL FLOODING...

HIGH ASTRONOMICAL THIS WEEK WITH SEVERAL 12 FT TIDES IN BOSTON WED AND THU! THUS WON'T TAKE MUCH ONSHORE FLOW TO PRODUCE MINOR COASTAL FLOODING ALONG THE EASTERN MA COASTLINE. GREATEST RISK COMES LATE WED INTO THU AS SURFACE WAVE TRACKS ALONG OR NEAR SOUTH COAST COMBINING WITH MARITIME HIGH PRESSURE TO PROVIDE INCREASING ONSHORE FLOW.

&&


BOX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM EST MONDAY FOR CTZ002>004. MA...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 4 PM EST MONDAY FOR MAZ022>024. WINTER STORM WARNING FROM 11 PM THIS EVENING TO 4 PM EST MONDAY FOR MAZ017>021. WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 4 PM EST MONDAY FOR MAZ002>008-010-013>016-026. WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM EST MONDAY FOR MAZ009-011-012. RI...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 4 PM EST MONDAY FOR RIZ006>008. WINTER STORM WARNING FROM 11 PM THIS EVENING TO 4 PM EST MONDAY FOR RIZ001>005.
MARINE...  SMALL CRAFT ADVISORY FROM 1 AM TO 5 AM EST TUESDAY FOR ANZ232. SMALL CRAFT ADVISORY FROM MIDNIGHT MONDAY NIGHT TO 5 AM EST TUESDAY FOR ANZ233-234. SMALL CRAFT ADVISORY FROM 10 PM MONDAY TO 6 AM EST TUESDAY FOR ANZ231-251. SMALL CRAFT ADVISORY FROM 11 PM MONDAY TO 6 AM EST TUESDAY FOR ANZ235-237. SMALL CRAFT ADVISORY FROM 3 PM MONDAY TO 6 AM EST TUESDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 6 AM MONDAY TO 6 AM EST TUESDAY FOR ANZ254>256.

&&
SYNOPSIS...FRANK/NOCERA NEAR TERM...FRANK SHORT TERM...  FRANK LONG TERM...  NOCERA AVIATION...  FRANK/NOCERA
MARINE...  FRANK/NOCERA TIDES/COASTAL FLOODING...STAFF
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