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FXUS61 KBOX 141145 AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
645 AM EST FRI DEC 14 2018

SYNOPSIS... 

HIGH PRESSURE MOVES E OF NEW ENGLAND THROUGH TODAY WITH A MILD S FLOW DEVELOPING. A SERIES OF LOW PRESSURE SYSTEMS TRACKING S OF NEW ENGLAND MAY BRING A PERIOD OF RAIN FRIDAY NIGHT INTO EARLY SATURDAY ... AND AGAIN SUNDAY INTO SUNDAY NIGHT WITH MIXED PRECIP AND ICE POSSIBLE IN THE INTERIOR. A COLD FRONT SWEEPS ACROSS THE REGION MONDAY FOLLOWED BY BLUSTERY AND COLD WEATHER TUESDAY. MODERATING TEMPERATURES BY WEDNESDAY INTO THURSDAY. ANOTHER STORM SYSTEM POSSIBLE BY LATE WEEK INTO WEEKEND.

&&


NEAR TERM /UNTIL 6 PM THIS EVENING/...  

7 AM UPDATE...

CONTINUED CLEARING AS WEAK S FLOW ROUNDING A DEPARTING HIGH PRESSURE SCOURS OUT LOW CLOUDS WESTWARD. SUBSEQUENTLY, FOR THOSE REGIONS E/SE, WITH CLEAR CONDITIONS AND LIGHT WINDS, TEMPERATURES HAVE DROPPED SHARPLY IN THE LAST 1-3 HOURS. UPDATED THE FORECAST TO ACCOUNT FOR THE LATEST TRENDS. WITH FLOW TURNING MORE W DURING THE DAY, SHOULD SEE LOW CLOUDS PUSH BACK TOWARDS THE E ALONG WITH THE INCREASING CHANCES OF SHOWERS, ESPECIALLY ALONG S-COASTAL NEW ENGLAND, TOWARDS EVENING.

CONCERNING THE THREAT OF FREEZING DRIZZLE, PARTICULARLY WITHIN THE CT RIVER VALLEY, FEEL THIS IS MOSTLY CONCLUDED WITH WESTWARD PUSH OF DRIER AIR, CEILINGS LIFTING, AND TEMPERATURE - DEWPOINT DEPRESSIONS RISING EVER SLIGHTLY. INCREASING S FLOW ALONG WITH DAYTIME HEATING, SHOULD WARM UP NICELY INTO THE 40S WITH DRY CONDITIONS.

&&


SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...    

IT STILL APPEARS THAT CONFLUENT MID LEVEL FLOW WILL DEVELOP OVER OUR REGION LATER TONIGHT. THE MAIN IMPACT OF THIS WILL BE TO STEER A LOW PRESSURE TO OUR SOUTH, LIMITING THE RISK FOR SIGNIFICANT RAINFALL. UNTIL THIS CONFLUENCE DEVELOPS, WE WILL HAVE TO CONTEND WITH A WEAK SHORTWAVE AND WEAK FRONT. THESE TWO FEATURES SHOULD BE ENOUGH TO TRIGGER SCATTERED AREAS OF LIGHT RAIN EARLY THIS EVENING. WINDS SHOULD REMAIN LIGHT S TO SW, SO TEMPERATURES SHOULD HOLD NEARLY STEADY OVERNIGHT.

HIGH PRESSURE MOVING INTO THE SAINT LAWRENCE VALLEY SATURDAY SHOULD BRING DRIER WEATHER FROM N TO S DURING THE DAY. WINDS TURN MORE FROM THE N SATURDAY AFTERNOON, STARTING THE RETURN OF COLDER AIR.

&&


LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...    

*/ HIGHLIGHTS...

- WINTRY MIX AROUND SUNDAY - TURNING COLDER MONDAY THROUGH TUESDAY - MILD CONDITIONS RETURN WEDNESDAY INTO THURSDAY - ANOTHER STORM SYSTEM POSSIBLE LATE WEEK / WEEKEND

*/ OVERVIEW...

ENSEMBLE MEAN WAFFLING OF THE N PACIFIC H5 TROF LENDS TO VARIABLE TRENDS WITHIN WPO / EPO TELECONNECTIONS. OF CERTAINTY, CONTINUATION OF A PROGRESSIVE, MILD PACIFIC JET LENDS TO RELOADING SHOTS OF WARM AIR ACROSS N AMERICA ECHOED UP THROUGH THE STRATOSPHERE, SEEMINGLY SHUNTING THE STRATOSPHERIC VORTEX AND COLDER ARCTIC AIR TO THE OTHER SIDE OF THE N HEMISPHERE. PERSISTENT STREAM OF PACIFIC ENERGY, AN ACTIVE MID TO LATE DECEMBER PATTERN IS LIKELY, HOWEVER JUXTAPOSITION OF RIDGING / TROUGHING ACROSS THE CONUS IS NOT. PRESENT TRANSITION TOWARDS A RIDGE-TROF REGIME MAY REVERSE COME THE HOLIDAYS, N-WINDS INITIALLY, MORE S FURTHER OUT IN TIME. SOME SIGNAL GLEANED FROM EC WEEKLIES AND CFS OF HOLIDAY WARMTH, BUT NO TRUE CONFIDENCE AT THIS TIME.

FOR NOW, A H5 RIDGE-TROF SETUP, DOWNSHEARING POTENTIAL VORTICITY AND COLDER AIR, TAPPING INTO THE S-STREAM SUB-TROPICAL PACIFIC JET. YET ARCTIC AIR BOTTLED UP N. COHESION BETWEEN THE TWO GOING INTO THIS WEEKEND, THERE IS THE POTENTIAL FOR WINTER WEATHER OUTCOMES WHICH ARE HIGHLIGHTED IN THE DISCUSSION BELOW ALONG WITH FORECAST MODEL PREFERENCE. AS NOTED BY THE PRIOR FORECASTER, KEY TO THE DISCUSSION IS THE COHESION / PHASE TIMING WITH RESPECT TO CYCLOGENESIS RELATIVE TO THE 40N/70W BENCHMARK.

*/ DISCUSSION...

SATURDAY NIGHT THROUGH SUNDAY NIGHT...

POSSIBLE INTERIOR WET SNOW. CONSENSUS TREND, DOWNSHEARED PV-STREAMER AND ATTENDANT TROP-FOLD FROM CANADA INTO THE NE CONUS DRAWS INWARD A SUB-TROPICAL PACIFIC S-STREAM CLOSED LOW THRU CYCLONIC CONVERGENCE AND ASCENT BENEATH LOWERING HEIGHTS. HOWEVER, INDIVIDUAL FORECAST MODEL GUIDANCE STRUGGLING ON THIS TRANSITION PARTICULAR TO LOCATIONS OF SURFACE TO MID-LEVEL FEATURES RELATIVE TO THE 40N/70W BENCHMARK, AS WELL AS SUBSEQUENT INTERIOR IMPACTS RELATED TO DEFORMATION, LOW LEVEL CONVERGENT FORCING, AND BROADSCALE ASCENT. ASIDE, GOOD MODEL AGREEMENT ON THICKNESSES ILLUSTRATING AN ARCTIC AIR DISCONNECT, THE STORM HAVING TO MANIFEST ITS OWN COLD TOWARDS WINTRY PRECIP-TYPES, ONLY DOING SO THROUGH DYNAMIC COOLING AND SURFACE WET-BULBING THAT IS PROPORTIONAL TO GREATER STORM STRENGTH. DOWNSTREAM PROGRESSIVE FLOW PATTERN, BOMBOGENESIS INTO SE CANADA, CONSISTENT MODEL SIGNALS OF INCREASING LIFT, DEFORMATION, TROWALING, STEEP LAPSE RATES, EVEN POTENTIAL INSTABILITY WRAPPING AROUND THROUGH THE SNOW GROWTH REGION AS THE STORM LIFTS OUT, BECOMING CYCLONIC NEGATIVELY-TILTED, CLOSING OFF INTO A DEEPER LOW WITH BROADER DIFFLUENCE ALOFT. PERHAPS WITH, HOWEVER, SOME DRY AIR ISSUES AND SUBSEQUENT ICE PRESENCE LENDING TO MIXED PRECIP-TYPES, THE POSSIBILITY OF SLEET AND/OR FREEZING RAIN.

ROUGHLY DAYTIME INTO EVENING EVENT, MILD THICKNESSES, UNCERTAINTY WITH STORM TRACK AND ASSOCIATED SYNOPTIC FEATURES, EXPECT INTERIOR WINTER PRECIP GOING WITH HIGH-RES 2M TEMPERATURES AND WET-BULB PROCESSES YET HOWEVER LOWER CONFIDENCE ANY WET SNOWS WILL MEET OR EXCEED THE 3-INCH THRESHOLD FOR ADVISORY-LEVEL CRITERIA. NOT MUCH CONFIDENCE GAINED FROM ENSEMBLE MEANS AND PROBABILISTICS, AND LEFT FEELING AS IF CIPS ANALOGS ARE CONTAMINATED BY POORLY ASSOCIATED ANALOGS TO THE FORECAST MASS FIELDS.

A MIX-BAG, WINTRY-PRECIP EVENT GIVEN MARGINAL THERMAL FIELDS AS DESCRIBED ABOVE BY THICKNESSES, AND THE POSSIBLE PRESENCE OF DRY AIR. NON-GFS PREFERENCE WITH A CLOSER TRACK TO S NEW ENGLAND. A WORTHY MENTION IN THE HAZARDOUS WEATHER OUTLOOK. CONTINUED TRACK UNCERTAINTY WITH RESPECT TO EXACT SPECIFICS, STAY TUNED FOR LATER FORECAST UPDATES.

MONDAY INTO TUESDAY...

STORM LIFTING OUT, BOMBING OVER SE CANADA. ISALLOBARIC / GRADIENT WIND RESPONSE, EXPECT BLUSTERY NW WINDS MIXING DOWN EASILY TO THE SURFACE AS COLD AIR ADVECTION PROCEEDS. POTENTIAL FOR WIND ADVISORY HEADLINES WITH GUSTS AT OR EXCEEDING 45 MPH. LAKE EFFECT MACHINE ONGOING, SNOW SHOWER / FLURRY ACTIVITY INTO THE BERKSHIRES THAT DISSIPATES WITH TIME AS HIGH PRESSURE SLOWLY BUILDS IN FROM THE W. CONSIDERING COLDEST 2M TEMPERATURE GUIDANCE GOING INTO WEDNESDAY MORNING AS WINDS TURN LIGHT UNDER MOSTLY CLEAR CONDITIONS.

WEDNESDAY INTO THURSDAY...

MODERATING TEMPERATURE TREND AS HIGH PRESSURE SHIFTS E AND S-FLOW RETURNS. MORE SEASONABLE CONDITIONS EXPECTED WITH INCREASING CLOUDS LATE AHEAD OF A STORM SYSTEM FOR THE LATE-WEEK TIMEFRAME.

FRIDAY INTO THE WEEKEND...

SERIES OF STORM SYSTEMS FOLLOWED BY SHOTS OF COLDER AIR. FAR OUT IN TIME AND DISCREPANCIES AMONG DETERMINISTIC GUIDANCE. PREFERENCE TO ENSEMBLE MEANS WITH LOW CONFIDENCE.

&&


.AVIATION /12Z FRIDAY THROUGH TUESDAY/...

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SATURDAY/...  MODERATE CONFIDENCE.

TODAY... SCT-BKN LOW END VFR CIGS WITH LIGHT S WINDS.

TONIGHT... BKN-OVC LOW-END VFR CIGS LOWERING INTO MVFR. SCT -SHRA MAINLY S OF THE MA PIKE.

SATURDAY... IMPROVING TOWARDS VFR N TO S AS S WINDS SHIFT NW. -SHRA PUSHING S AS WELL, OUT OVER THE WATERS, WITH TIME TOWARDS SATURDAY EVENING.

KBOS TERMINAL...HIGH CONFIDENCE IN TAF.

KBDL TERMINAL...HIGH CONFIDENCE IN TAF.

OUTLOOK /SATURDAY NIGHT THROUGH TUESDAY/...

SATURDAY NIGHT: VFR. BREEZY.

SUNDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. WINDY WITH GUSTS TO 35 KT. CHANCE RA, CHANCE FZRA, SLIGHT CHANCE SN.

SUNDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. WINDY WITH GUSTS TO 35 KT. CHANCE RA, CHANCE FZRA, CHANCE SN.

MONDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. WINDY WITH LOCAL GUSTS TO 30 KT. SLIGHT CHANCE RA, SLIGHT CHANCE FZRA.

MONDAY NIGHT: VFR. WINDY WITH GUSTS TO 35 KT.

TUESDAY: VFR. STRONG WINDS WITH LOCAL GUSTS TO 40 KT.

&&



MARINE...  
  

FORECASTER CONFIDENCE LEVELS...

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

SHORT TERM /THROUGH SATURDAY/...  HIGH CONFIDENCE.

TRANQUIL BOATING CONDITIONS TO PREVAIL THROUGH SATURDAY ACROSS MOST OF THE COASTAL WATERS. THE EXCEPTION WILL BE A RISK FOR SOME GUSTS UP TO 25-30 KT ACROSS THE COASTAL WATER EAST OF MA AS A FRONT CROSSES LATE THIS EVENING INTO TONIGHT. AFTER MORE CONSIDERATION, DECIDED TO ISSUE A SMALL CRAFT ADVISORY FOR THE COASTAL WATERS EAST OF MA FOR TONIGHT.

CHANCE FOR LIGHT RAIN TONIGHT INTO SATURDAY ACROSS THE SOUTHERN WATERS.

OUTLOOK /SATURDAY NIGHT THROUGH TUESDAY/...

SATURDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP TO 30 KT. LOCAL ROUGH SEAS. SLIGHT CHANCE OF RAIN.

SUNDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 40 KT. ROUGH SEAS UP TO 9 FT. CHANCE OF RAIN.

SUNDAY NIGHT: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 35 KT. ROUGH SEAS UP TO 9 FT. CHANCE OF RAIN.

MONDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP TO 30 KT. ROUGH SEAS UP TO 9 FT. SLIGHT CHANCE OF RAIN.

MONDAY NIGHT: STRONG WINDS WITH GUSTS UP TO 35 KT. ROUGH SEAS UP TO 9 FT. SLIGHT CHANCE OF RAIN.

TUESDAY: GALE FORCE WINDS WITH GUSTS UP TO 40 KT. ROUGH SEAS UP TO 9 FT. SLIGHT CHANCE OF SNOW.

&&


BOX WATCHES/WARNINGS/ADVISORIES...


CT...NONE. MA...NONE. RI...NONE.
MARINE...  SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 8 AM EST SATURDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 6 AM EST SATURDAY FOR ANZ251.

&&


SYNOPSIS...BELK/SIPPRELL NEAR TERM...BELK/SIPPRELL SHORT TERM...  BELK LONG TERM...  SIPPRELL AVIATION...  BELK/SIPPRELL
MARINE...  BELK/SIPPRELL
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