Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 010202 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1002 PM EDT TUE MAR 31 2015 .SYNOPSIS... LIKELY RAIN/SNOW SLIDES ACROSS SOUTHERN PORTIONS OF CONNECTICUT... RHODE ISLAND AND MASSACHUSETTS OVERNIGHT WITH LITTLE IMPACT. HIGH PRESSURE YIELDS CHILLY BUT DRY WEATHER WEDNESDAY. WARMER THURSDAY AND ESPECIALLY FRI AHEAD OF A COLD FRONT. LOW PRESSURE DEVELOPS ON THE FRONT FRIDAY NIGHT AND MOVES ACROSS THE REGION EARLY SATURDAY BRINGING LOCALLY HEAVY RAIN SHOWERS. MAINLY DRY AND MUCH COLDER LATER SATURDAY AND SUNDAY. HIGH UNCERTAINTY NEXT WEEK WITH PERIODS OF UNSETTLED WEATHER POSSIBLE. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 10 PM UPDATE... LATEST MESOSCALE GUIDANCE...PARTICULARLY THE WRF CONTINUES TO OUTPERFORM REMAINING GUIDANCE REGARDING THE PRECIP SHIELD AND DEEPENING LOW PRES MOVING OFFSHORE. IT APPEARS THAT SOME CONVECTION IS LIKELY TO USURP MOISTURE/LIFT AS THE LOW PRES CONTINUES TO DEEPEN FURTHER OFFSHORE. THIS TIGHTENS THE PRECIP GRADIENT AND ALLOWS DRIER AIR TO MORE QUICKLY ENTRAIN FROM THE N. THEREFORE...WHAT FALLS THROUGH MIDNIGHT WILL LIKELY BE ALL THAT WE WILL SEE WITH THE ONE EXCEPTION BEING NANTUCKET...WHICH IS CLOSER TO THE LOW CENTER. PREVIOUS DISCUSSION... */OVERVIEW ... EVEN WITH THE 31.12Z FORECAST GUIDANCE...CONSENSUS HAS THE CLIPPER- LOW SWEEPING S OF NEW ENGLAND OFF THE DELMARVA COASTLINE ACROSS REGIONS OF BETTER BAROCLINICITY OFFSHORE. EXPECT A SHARP GRADIENT WITH RESPECT TO OUTCOMES AROUND THE CT-RI-MA BORDER DUE TO A COMBINATION OF THE FOLLOWING: 1) DECENT MOISTURE AND LIFT UP TO H5 WITH SYNOPTIC QG-FORCING / OMEGA ABOVE ... 2) A LOCALIZED GREATER FOCUS ALONG A PARENT H6-8 WARM FRONT ASSOCIATED WITH THE CLIPPER LOW AS W-E ZONAL MOIST FLOW IS SQUEEZED UP AGAINST A COLDER AND DRIER AIRMASS ASSOCIATED WITH HIGH PRESSURE BUILDING OUT OF THE NW. OUTCOMES COULD STILL WOBBLE SLIGHTLY N OR S. BUT TRUST THE NEAR- TERM MESOSCALE GUIDANCE TO BE NEARLY SPOT ON. WHILE IT APPEARS THE STRATIFORM-SHIELD PER WSR-88D RADAR RETURNS TO THE W WILL ENVELOPE MUCH OF S NEW ENGLAND...EROSION IS EXPECTED ALONG THE N PERIPHERY OF RETURNS /ALREADY BEING OBSERVED/ AS THE CLIPPER-LOW EMERGES OFF THE DELMARVA COAST INVOKING AN ISALLOBARIC RESPONSE TO THE WIND AND THE SUBSEQUENT ADVECTION OF COLDER AND DRIER AIR WITHIN THE LOW-LEVELS S ACROSS THE REGION. AGAIN...THE BATTLE LINE BETWEEN AIRMASSES AND WHERE THE BETTER AFOREMENTIONED LOW- TO MID-LEVEL BANDING ORIGINATES LOOKS TO BE AT OR S OF THE CT-RI-MA BORDER. WILL CONTINUE WITH HIGH CATEGORICAL POPS S OF THE BORDER...ESP ALONG THE S-COAST AND POINTS OFFSHORE. */ TOWARDS EVENING ... WITH ONLY LIGHT PRECIPITATION AT ONSET EXPECTED AND NOTING HOW TEMPERATURES TODAY WARMED TO THE 50-DEGREE MARK UNDER ABUNDANT SUNSHINE...IT WILL LIKELY TAKE LONGER FOR THE DRY LOW-LEVELS PER 12Z CHATHAM / UPTON SOUNDINGS TO DYNAMICALLY COOL AT THE SURFACE TO TEMPERATURES BELOW FREEZING. WITH A WARM BOUNDARY-LAYER...AM EXPECTING MUCH OF THE PRECIPITATION TO BE IN THE FORM OF RAIN WITH PERHAPS A WET-SNOWFLAKE MIXED IN. LITTLE TO NO IMPACT EXPECTED. */ EVENING AND TOWARDS MIDNIGHT ... BOTH NOCTURNAL COOLING AND AN INCREASING INTENSITY OF PRECIP IS LIKELY TO RESULT IN RAIN MIXING WITH AND / OR CHANGING OVER TO SNOW. TEMPS AROUND THE FREEZING MARK DURING THIS PERIOD...SNOW ACCUMULATION WILL LIKELY BE HARD TO COME BY...NO MORE THAN A COATING IF ANYTHING ON ELEVATED EXPOSED SURFACES. WET ROADWAYS LIKELY FOR THE MOST PART. BIGGEST IMPACT LIKELY IN THE FORM OF REDUCED VISIBILITIES AND ESPECIALLY MORE SO ALONG THE S-COASTLINE OF NEW ENGLAND. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... */ WEDNESDAY... COLD AIRMASS ALOFT IN WAKE OF THE CLIPPER-LOW. H85 TEMPS RANGING AROUND -4 TO -6C UP TO WHICH THE BOUNDARY-LAYER WILL MIX-DOWN DRIER AIR AND FASTER MOMENTUM. ANTICIPATING MOSTLY CLEAR CONDITIONS WITH BREEZY W-WINDS AS HIGHS TOP INTO THE LOW- TO MID-40S. */ WEDNESDAY NIGHT... MOSTLY CLEAR CONDITIONS PERSISTING PRIOR TO MORNING BY WHICH POINT THE LOW- TO MID-LEVEL RIDGE SWEEPS ACROSS THE REGION ALONG THE W- PERIPHERY OF WHICH IS THE CONVERGENT NOSE OF WARM-MOIST SW-FLOW UNDERGOING ISENTROPIC LIFT YIELDING MID- TO HIGH-LEVEL CLOUDS. FEEL THE MAJORITY OF THE OVERNIGHT PERIOD WILL BE CHARACTERIZED BY DRY WEATHER AND LIGHT AND VARIABLE FLOW ALLOWING A PERIOD OF GOOD RADIATIONAL COOLING. LOWS DROPPING INTO THE 20S FOR MOST LOCATIONS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... HIGHLIGHTS... * TEMPERATURES RISING TO NEAR NORMAL THU AND ABOVE NORMAL FRI * STORM SYSTEM BRINGS SHOWERS THU NIGHT INTO EARLY SAT * BLUSTERY AND COLDER LATE SAT INTO SUN OVERVIEW... NORTHERN STREAM REMAINS AMPLIFIED BY EARLY APRIL STANDARDS FOR LATER THIS WEEK AND WEEKEND. THIS RESULTS IN LARGE TEMP SWINGS FOR OUR AREA ALONG WITH A ROUND OF SHOWERS. LATE SUNDAY INTO EARLY NEXT WEEK UNCERTAINTY IS HIGH AS ENSEMBLE AND DETERMINISTIC GUIDANCE ARE AT ODDS WITH EACH OTHER. THE GEFS AND EPS ENSEMBLES SUGGEST THE UPPER AIR PATTERN DEAMPLIFIES WITH MORE OF A PACIFIC REGIME FLOODING THE CONUS AND SIGNS OF A SUBTROPICAL RIDGE BUILDING OVER THE SOUTHEAST STATES. THIS WOULD FAVOR MORE SEASONABLE TEMPS FOR SOUTHERN NEW ENGLAND NEXT WEEK. HOWEVER THE DETERMINISTIC GUIDANCE SUGGEST THE HUDSON BAY VORTEX WILL BE SLOWER TO DEPART...KEEPING REMNANT COLD AIR LONGER ACROSS SOUTHEAST QUEBEC INTO NEW ENGLAND. THUS POTENTIAL UNSETTLED WEATHER PATTERN AT LEAST EARLY NEXT WEEK AS PACIFIC MOISTURE STREAMS ACROSS THE NORTHERN STATES AND POTENTIAL INTERACTS WITH REMNANT COLD AIR OVER NEW ENGLAND. DAILY SENSIBLE WEATHER... THURSDAY...LOW RISK FOR A PERIOD OF MAINLY LIGHT RAIN IN THE MORNING AND POSSIBLY EARLY AFTERNOON AS WARM FRONT ALOFT PASSES ACROSS THE REGION. CLEARING DURING THE AFTERNOON. THE TRUE WARM SECTOR AIRMASS DOESN/T ARRIVE UNTIL SOMETIME FRI MORNING BUT TEMPS THU AFTERNOON SHOULD AT LEAST TOUCH 50 AWAY FROM THE SOUTH COAST GIVEN AFTERNOON SUNSHINE. IT WILL ALSO BECOME WINDY AS LOW LEVEL JET CRANKS UP TO ABOUT 55-65 KT BY 00Z AT 925 MB. NOT EXPECTING ALL OF THIS WIND TO MIX DOWN BUT NAM BUFKIT SOUNDINGS SUPPORT SSW WINDS GUSTING UP TO 35 MPH OR SO LATE IN THE DAY. THU NIGHT...LOW RISK OF A FEW ELEVATED TSTMS AS MID LEVEL LAPSE RATES STEEPEN TO ABOUT 7C/KM ALONG WITH WEAK MOIST CYCLONIC FLOW ALOFT. COULD SEE A FEW DOWNPOURS AS INSTABILITY WORKS WITH PWATS OF TO +2 STD ABOVE CLIMO FRI...FRONT STALLS OVER OR NORTH OF THE REGION AS WEST TO EAST MID LEVEL FLOW PARALLELS THE FRONT. MILD WITH WARM SECTOR REMAINING ACROSS MUCH OF THE REGION ESP CT/RI AND SOUTH OF THE MASS PIKE. ALL GUID SOURCES INCLUDING A MODEL BLEND HAVE TEMPS IN THE U50S AND L60S. DESPITE THE RISK OF SHOWERS IT WILL FEEL MILD/WARM AS DEW PTS CLIMB INTO THE L50S. THIS WILL PROMOTE CONDENSATION AND HELP ERODE REMAINING SNOWPACK. AS FOR COVERAGE OF SHOWERS DIFFICULT TO SAY AT THIS TIME RANGE HOW WIDESPREAD GIVEN MODELS DISAGREE ON HOW WAVY THE FRONT WILL BE. THUS FOR NOW WILL KEEP SHOWERS SCATTERED WITH POPS 30- 50%. FRI NIGHT INTO SAT...GOOD MULTI MODEL AGREEMENT ON FRONTAL WAVE BEING AN INSIDE RUNNER OR TRACKING OVER SOUTHERN NEW ENGLAND. THIS WILL LIKELY TRANSLATE TO HEAVIEST SHOWERS AND FRONTAL CONVERGENCE OVER THE INTERIOR INTO CENTRAL/NORTHERN NEW ENGLAND. FAIRLY STRONG JET DYNAMICS /WIND FIELDS +1 TO +2 STD ABOVE NORMAL/ COUPLED WITH PWATS +2 STD ABOVE CLIMO SUGGEST AT LEAST A MODEST SLUG OF QPF. BIG DISCREPANCY REGARDING EVOLUTION OF FRONTAL WAVE AS GFS IS MOST ROBUST WITH 979 MB LOW OVER MAINE 18Z SAT. GFS WOULD SUGGEST STRONG WINDS. MEANWHILE THE EC /985 MB/ AND UKMET /988 MB/ ARE SLIGHTLY WEAKER. SO FOR NOW LOOKS WINDY SAT BUT WILL HAVE TO WATCH LATER MODEL TRENDS FOR POSSIBLY STRONGER/DAMAGING WINDS IN COLD ADVECTION REGIME. SUNDAY...HIGH UNCERTAINTY GIVEN TIME RANGE AND FAST FLOW ALOFT. SHOULD BE DRY AND COOL TO START THE DAY BUT PACIFIC MOISTURE QUICKLY STREAMING IN FROM THE WEST LATE IN THE DAY OR AT NIGHT. THUS LOW RISK FOR A PERIOD OF RAIN/SNOW PENDING THERMAL PROFILES. NEXT WEEK...LOTS OF UNCERTAINTY AS MENTIONED ABOVE. LOOKS UNSETTLED WITH PACIFIC MOISTURE ENTERING THE NORTHEAST ALONG WITH POTENTIAL PTYPE ISSUES AS REMNANT COLD AIR LINGERS OVER QUEBEC INTO NEW ENGLAND. && .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 /THROUGH 12Z THURSDAY/... 7 PM UPDATE... NOT MUCH CHANGE FROM 21Z TAF UPDATE. LIGHT RAIN/SNOW CONFINED ACROSS CT...RI AND SOUTHEAST MA THIS EVENING THEN MOVING OFFSHORE OVERNIGHT. MVFR/IFR WILL BE CONFINED TO SOUTH COAST OF MA AND RI. EARLIER DISCUSSION BELOW. ====================================================================== */ INTO 6Z WEDNESDAY...HIGH CONFIDENCE. MIX LOW-END VFR / MVFR ESPECIALLY S OF CT-RI-MA BORDER ASSOC WITH -RA INITIALLY MIXING WITH AND / OR OVER TO -SN. LOW RISK OF IFR CIGS / VSBYS. LITTLE TO NO SNOW ACCUM. JUST WET RUNWAYS. */ 6Z WEDNESDAY INTO 12Z THURSDAY...HIGH CONFIDENCE. CONDITIONS IMPROVING AFTER 6Z VFR. W/NW-FLOW. 20 KT GUSTS DURING THE DAY...BECOMING VRB INTO EVENING AND OVERNIGHT. */ TERMINALS... KBOS TAF...HIGH CONFIDENCE. DRY. ANY OUTCOMES S OF TERMINAL. KBDL TAF...MODERATE CONFIDENCE. -RA / -SN MIX POSSIBLE YET EVER BRIEF AROUND 0Z DURING WHICH TIME MVFR IMPACTS IN THE FORM OF CIGS / VSBYS WILL BE POSSIBLE. */ OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY...VFR LIKELY. LOW RISK OF A PERIOD OF LIGHT RAIN IN THE MORNING AND EARLY AFTERNOON. GUSTY SSW WINDS DEVELOP. THURSDAY NIGHT AND FRIDAY...VFR BECOMING MVFR IN SCATTERED SHOWERS. LOW LEVEL WIND SHEAR EXPECTED THROUGHOUT THE REGION WITH SW 55-65 KT AT 2000-3000 FT. LOW RISK OF A FEW TSTMS THU NIGHT AND HEAVY DOWNPOURS. FRIDAY NIGHT INTO SAT MORNING...MVFR AND IFR CONDITIONS IN WIDESPREAD SHOWERS. AREAS OF FOG. LLWS POSSIBLE SOUTH COAST AND OFFSHORE. SAT AFTERNOON AND SUN...STRONG LOW PRES MOVES ACROSS NEW ENGLAND AND INTO THE MARITIMES SAT NIGHT WITH STRONG POST FRONTAL NW WINDS. TREND TOWARD DRY WEATHER SAT AFTN INTO SUN...ALTH POSSIBLY RAIN/SNOW LATE SUN/SUN NIGHT. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /TODAY THROUGH TUESDAY/...HIGH CONFIDENCE. */ TONIGHT... AREA OF LOW PRESSURE SWEEPS S OF NEW ENGLAND ACROSS THE S WATERS. MOSTLY RAIN BUT PERHAPS MIXING WITH SNOW AT TIMES. IMPACTS TO VISIBILITY POSSIBLE. W-WINDS BACKING N/NW WITH THE POTENTIAL OF GUSTS TO EXCEED 25 KTS BY MORNING. WAVES BUILDING IN EXCESS OF 5-FEET. */ WEDNESDAY... W/NW WINDS CONTINUING WITH GUSTS UP TO AROUND 20 KTS...SLOWLY DIMINISHING TOWARDS THE LATER-HALF OF THE DAY AS HIGH PRESSURE BUILDS IN FROM THE W. WAVES OF 5-7 FEET ON THE OUTER WATERS DIMINISH TOWARDS EVENING. */ WEDNESDAY NIGHT... WINDS BECOME LIGHT AS HIGH PRESSURE SETTLES IN. WAVES DROP BELOW 5-FEET BY MIDNIGHT THURSDAY. GOOD BOATING WEATHER PREVAILS. */ OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY...SSW WINDS DEVELOP WITH GUSTS UP TO 30 KT POSSIBLE NEAR SHORE LATE. LOW RISK OF A FEW TSTMS THU NIGHT. FRI...SSW WINDS INCREASE FRI NIGHT TO 20-30 KT AS POTENT LOW TRACKS INLAND OVER NEW ENGLAND. SHOWERS AND FOG REDUCE VSBY. SAT...SSW WINDS EARLY BUT NW GALES MAY DEVELOP SAT AFTN AND NIGHT AS STRONG LOW MOVES FROM MAINE INTO THE MARITIMES. MORNING RAIN GIVES WAY TO IMPROVING AFTN VSBY. SUN...LIGHTER WINDS AS FRONTAL BOUNDARY SLIDES ACROSS THE AREA. CHANCE OF RAIN/SNOW LATE OR AT NIGHT. && .CLIMATE... MODEL OUTPUT STATISTIC /MOS/ WILL SWITCH FROM COOL SEASON TO WARM SEASON EQUATIONS WITH TONIGHT/S 00Z 4/1 MODEL RUN. EARLY IN THE SPRING SEASON THIS SOMETIMES LENDS ITSELF TO MOS HAVING A WARM TEMP BIAS DURING ANOMALOUS COOL TEMP REGIMES. TOMORROW MAY BE AN EXAMPLE WHEN 925 AND 850 MB TEMPS RUN ABOUT -1 STD DEVIATION COLDER THAN CLIMO. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO 2 PM EDT WEDNESDAY FOR ANZ231-251-256. SMALL CRAFT ADVISORY FROM 2 AM TO NOON EDT WEDNESDAY FOR ANZ235-237. SMALL CRAFT ADVISORY FROM 2 AM TO 6 PM EDT WEDNESDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 2 AM WEDNESDAY TO 2 AM EDT THURSDAY FOR ANZ254-255. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...DOODY/SIPPRELL SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL CLIMATE...

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