Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 170801 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 401 AM EDT FRI APR 17 2015 .SYNOPSIS...
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A COLD FRONT WILL BRING A PERIOD OF SHOWERS TO THE REGION THIS MORNING FOLLOWED BY A DRYING TREND IN THE AFTERNOON. WARM WEATHER RETURNS SAT AHEAD OF A COLD FRONT. CANADIAN HIGH PRESSURE BRINGS COOLER WEATHER SUNDAY. THEN A COASTAL LOW DELIVERS A WIND SWEPT SOAKING RAIN TO THE REGION LATE MON INTO MON NIGHT. COOLER WEATHER SHOULD DOMINATE NEXT WEEK WITH A FEW SHOWERS FROM TIME TO TIME.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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WIDESPREAD RAIN WITH EMBEDDED HEAVIER SHOWERS TO PREVAIL THRU MIDDAY WITH DEEP-LAYER FORCING OF AVAILABLE MOISTURE /PWATS IN EXCESS OF 1- INCH/ AHEAD OF AN ATTENDANT COLD FRONT TO THE OPEN-WAVE TROUGHING PATTERN ALOFT. PROGRESSIVE IN NATURE...SHOULD SEE ONLY A TENTH OR TWO OF PRECIP. ENOUGH TO WET THE ROADS BUT DO LITTLE ELSE OF HARM. HEAVIEST AMOUNTS ACROSS THE W-SLOPES OF HIGHER TERRAIN AS OROGRAPHIC LIFT AIDS IN FORCING. AS THE FRONT SLOWS TOWARDS THE S-COAST DURING THE LATER HALF OF THE DAY...PERSISTENT SW-FLOW COMBINED WITH PARTIAL CLEARING ALLOWS FOR STEEPENING LOW-LEVEL LAPSE RATES AND DEVELOPMENT OF SOME MARGINAL INSTABILITY. AS NOTED BY THE PREVIOUS FORECASTER...COULD SEE SOME DIURNALLY-DRIVEN SHOWER ACTIVITY...MAINLY THINKING CT AND POINTS SW. COULD SEE SOME HEAVY DOWNPOURS WITH THIS ACTIVITY BUT WITH MOST OF THE INSTABILITY BELOW THE FREEZING-LEVEL...MAY NOT SEE MUCH IF ANY IN THE WAY OF THUNDER. HIGHS AROUND THE LOW- TO MID-60S.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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TONIGHT... WEAK RIDGE OF HIGH PRESSURE SETTLES ACROSS THE REGION ALLOWING WINDS TO BECOME LIGHT AND VARIABLE. WITH CLEARING CONDITIONS...BELIEVE RADIATIONAL COOLING WOULD PREVAIL. THINKING RESIDUAL MOISTURE PER EARLIER RAINS WITH DEWPOINTS AROUND THE MID-40S...COLD AIR DRAINAGE INTO THE VALLEYS...PATCHY DENSE FOG NOT OUT OF THE QUESTION. FOCUS IS ACROSS N/W MA AND THE SANDIER SOILS OF SE MA OUT ONTO THE CAPE AND ISLANDS...AS WELL AS NW CT...SO LONG AS WINDS REMAIN LIGHT. LOWS AROUND THE LOW- TO MID-40S WITH THE WARM-SPOTS ACROSS HIGH TERRAIN. SATURDAY... CONSENSUS OF FORECAST GUIDANCE PLACES THE GREATEST FOCUS ACROSS S NH INTO NE MA WHERE POSITIVE VORTICITY ADVECTION MAXIMIZES BENEATH THE LEFT-FRONT-QUADRANT OF THE UPPER-LEVEL-JET. SUBSEQUENT REFLECTION OF SURFACE LOW PRESSURE LENDS TO CONVERGENCE OF THERMAL- AND MOIST-AXES WHERE INSTABILITY DEVELOPS AS TEMPERATURES WARM INTO THE 70S BENEATH AN UNSTABLE PROFILE OF STEEP LAPSE RATES UP TO H6. LOOKING AT MUCAPE VALUES OF 500 J/KG COLLOCATED WITH SHOWALTERS < 0. CONSIDERING UNI- DIRECTIONAL SHEAR WITHIN A THIN MID-LEVEL CAPE PROFILE ENCOMPASSED IN A SUB-FREEZING REGIME ABOVE AN INVERTED-V SOUNDING PROFILE...CAN NOT RULE OUT WITH ANY THUNDERSTORMS THE THREAT OF STRONG TO DAMAGING WINDS AND SMALL HAIL. LIKELY POPS ACCORDINGLY. MAY BE GOING A LITTLE TOO FAR OUT IN LEFT FIELD WITH THE FORECAST...BUT FEEL THE SIGNALS CAN NOT BE IGNORED. ADDITIONAL ACTIVITY COULD DEVELOP SW OF THE AFOREMENTIONED AREA OF FOCUS ALONG AN ATTENDANT COLD FRONT TO THE SURFACE LOW. INSTABILITY APPARENT ALBEIT WEAKER WITH LESSER DEEP BOUNDARY-LAYER PROFILE. ALSO LESS FORCING PER PROXIMITY TO THE POTENT SHORTWAVE DIVING SE ACROSS NEW ENGLAND. WILL PREVAIL CHANCE POPS AWAY FROM NE MA WITH ISOLATED THUNDER. SOME FORECAST UNCERTAINTY DEPENDENT ON THE PLACEMENT OF FEATURES AND FOCUS OF THERMAL- AND MOIST-AXES TO WHICH MODELS EXHIBIT DISCREPANCY AND ARE NOT NECESSARILY SUCCINCT. FOR MORE ON POTENTIAL FIRE WEATHER CONDITIONS...PLEASE CONSULT THE FIRE WEATHER DISCUSSION BELOW. WILL SEE HIGHS AROUND THE UPPER-60S AS WINDS GUST OUT OF THE W AS HIGH AS 40 MPH. DRIEST CONDITIONS SETTLE TOWARDS THE SW ACROSS THE CT-RIVER VALLEY WITH MINIMUM RELATIVE HUMIDITY VALUES FORECAST AROUND 30-PERCENT.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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HIGHLIGHTS... * TURNING MUCH COOLER SAT NIGHT AND SUN * WIND SWEPT SOAKING RAIN LATE MON INTO EARLY TUE * COOLER WITH PERIODS OF SHOWERS MID TO LATE NEXT WEEK SYNOPTIC OVERVIEW... ZONAL FLOW CURRENTLY ACROSS THE NORTHERN TIER STATES AND SOUTHERN CANADA BECOMES MUCH MORE AMPLIFIED THIS WEEKEND WHICH EVOLVES INTO A TYPICAL SPRING-LIKE BLOCKY PATTERN BY THE MIDDLE TO END OF NEXT WEEK. AT THIS TIME THE UPPER AIR CONFIGURATION FEATURES A CLOSED LOW OVER THE NORTHERN GREAT LAKES INTO ONTARIO ALONG WITH A POSITIVE HEIGHT ANOMALY OVER THE SOUTHERN DAVIS STRAITS. THIS WILL RESULT IN UNSETTLED AND COOLER WEATHER MUCH OF NEXT WEEK ESPECIALLY MID TO LATE WEEK. MODEL PREFERENCES... DETERMINISTIC AND ENSEMBLE GUIDANCE IN VERY GOOD AGREEMENT THRU TUE. ECMWF IS SLIGHTLY FASTER THAN GFS WITH ONSET OF RAIN MON...WHICH IS A FLIP-FLOP OF THE TYPICALLY FASTER/MORE PROGRESSIVE GFS. HOWEVER THIS TIME THE GFS MAY BE ON TO SOMETHING...AS NORTHERN STREAM SHORT WAVE TROUGH THAT MOVES ACROSS THE REGION SAT EVOLVES INTO A CLOSED LOW OVER THE NW ATLC SUN-MON. THIS WOULD FAVOR A SLOWER/LESS PROGRESSIVE SOLUTION FOR UPSTREAM MOISTURE TO ARRIVE MON. THUS WILL LEAN TOWARD THE SLOWER GFS SOLUTION. THEN MID TO LATE NEXT WEEK THE ECMWF DIGS THE GREAT LAKES CLOSED LOW FARTHER SOUTH THAN THE GFS. THE ECENS ENSEMBLES SUGGEST SOMETHING IN BETWEEN THE GFS AND ECMWF IS MORE PLAUSIBLE. THEREFORE WILL LEAN TOWARD A MODEL BLEND HERE. DAILY SENSIBLE WEATHER DETAILS... SATURDAY NIGHT AND SUNDAY...HIGH FORECAST CONFIDENCE AS ROBUST NORTHERN STREAM SHORT WAVE EXITS OFFSHORE MUCH COOLER AIR ADVECTS ACROSS THE AREA. LOW LEVEL FLOW TURNS TO THE N-NE WHICH WILL USHER IN A COOL MARITIME AIRMASS INTO THE REGION...VERY SIMILAR TO YESTERDAY/THU. THIS WIND SHIFT OFF THE CHILLY EASTERN MA OCEAN WATERS WILL RESULT IN RAPID TEMP DROP WITH READINGS AROUND 70 SAT AFTN FALLING RAPIDLY INTO THE 40S SAT EVENING AND EVENTUALLY MU30S SAT NIGHT! MARITIME AIRMASS REMAINS OVER THE AREA SUNDAY WHICH WILL RESULT IN COOL TEMPS /50S/ ACROSS EASTERN MA AND RI BUT WARMING NOTICEABLY /L60S/ WESTWARD INTO THE CT RVR VLY. MONDAY AND MONDAY NIGHT...MODERATE TO HIGH CONFIDENCE. SOUTHERN AND NORTHERN STREAMS MERGE FORMING A DYNAMIC SYSTEM WITH A TRIPLE POINT/COASTAL LOW IMPACTING SOUTHERN NEW ENGLAND FROM LATE MON THRU MON NIGHT AND POSSIBLY INTO TUE MORNING. MODELS SIGNALING AN IMPRESSIVE WARM/MOIST CONVEYOR DEVELOPING ALONG THE EASTERN SEABOARD INTO NEW ENGLAND. WITHIN THIS MOISTURE PLUME GULF OF MEXICO AND ATLC INFLOW YIELDS PWATS RISING TO NEAR +2 SD DEVIATIONS ABOVE CLIMO. THIS IS COURTESY OF ANOMALOUS /+2 TO +3 SD DEVIATIONS FROM CLIMO/ 925 MB /60 KT/ AND 850 MB JET CORES OFF THE OCEAN INTO NEW ENGLAND. THESE MOISTURE AND WIND ANOMALOUS YIELDS THE RISK FOR A PERIOD OF HEAVY RAINFALL LATE MON INTO EARLY TUE. DETERMINISTIC AND ENSEMBLE GUIDANCE BOTH SUGGEST 1-2" OF RAINFALL POSSIBLE. AS FOR TEMPS...IT WILL BE CHILLY/RAW WITH STRONG ONSHORE FLOW OFF THE COLD OCEAN WATERS. IN ADDITION WITH STRONG LOW LEVEL JET EXPECT A WIND SWEPT RAIN ESPECIALLY ALONG THE COAST. TUESDAY THROUGH THURSDAY...MODERATE CONFIDENCE. CLOSED LOW OVER WESTERN GREAT LAKES SLOWLY MEANDERS INTO THE EASTERN LAKES AND POSSIBLE NY STATE OR NEW ENGLAND BY LATE NEXT WEEK. THESE LOWERING HEIGHTS AND ASSOCIATED COLD POOL AND CYCLONIC FLOW ALOFT WILL FAVOR DIURNAL CLOUDS AND SHOWERS POSSIBLE ALONG WITH COOLER TEMPS.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH SATURDAY/...HIGH CONFIDENCE. VFR LOWERING TO MVFR AS -SHRA SWEEP THE TERMINALS TOWARDS MIDDAY. -SHRA CONCLUDE ACROSS S/SE-COASTAL TERMINALS DURING THE AFTERNOON. SW-WINDS PREVAIL WITH GUSTS AROUND 20 KTS...STRONGEST OVER SE MA. SOME IMPROVEMENT OVERNIGHT...YET PATCHY IFR-LIFR FOG EXPECTED OVER SELECT TERMINALS. FOG ERODES DURING THE MORNING AS W-WINDS INCREASE TO 30 KTS ON SATURDAY. SHRA/TSRA POTENTIAL FOR NE MA. KBOS TAF...HIGH CONFIDENCE. KBDL TAF...HIGH CONFIDENCE. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY... SAT NIGHT...VFR WITH WINDS BECOMING N-NE AND GUSTY ALONG THE EASTERN MA COASTLINE. HIGH CONFIDENCE. SUN...VFR AND DIMINISHING WINDS. HIGH CONFIDENCE. MON...MVFR/IFR DEVELOPING IN RAIN/FOG BY AFTERNOON. E/SE WIND GUSTING TO 25-30KT NEAR COAST. MODERATE CONFIDENCE. TUE...MVFR POSSIBLE IN SCT SHOWERS. MODERATE CONFIDENCE.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE. AS SHOWERS ENCOMPASS THE WATERS TOWARDS EVENING...SW-WINDS WILL GUST 20-25 KTS GENERATING SWELL IN EXCESS OF 5 FEET. DID NOT UNDERCUT THE WINDS WITH THIS FORECAST AS THE FORECAST WAS DOING WELL WITH PRESENT WAVE HEIGHTS. SMALL-CRAFT ADVISORIES ACCORDINGLY. WILL SEE A LULL IN WINDS OVERNIGHT DURING WHICH TIME FOG MAY DEVELOP... ESPECIALLY MORE SO ACROSS THE INNER WATERS...WHICH WOULD RESULT IN VISIBILITY RESTRICTIONS. THE THREAT SHOULD CONCLUDE INTO SATURDAY AS WINDS GUSTS OUT OF THE W UP TO 25 KTS. SMALL-CRAFT LIKELY NEEDED AGAIN ACROSS THE INNER- WATERS. BEST CHANCE FOR RAIN ON SATURDAY ACROSS THE E-WATERS. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY... SATURDAY NIGHT...SOME UNCERTAINTY ON WIND SPEEDS. FAST MOVING LOW PRES ZIPS ACROSS THE GULF OF MAINE AND MAY YIELD A PERIOD OF N-NE WINDS 20-25 KT...STRONGEST WINDS OVER EASTERN MA WATERS. THUS LOW PROB SCA HEADLINE MAY BE REQUIRED. SUNDAY...HIGH CONFIDENCE. HIGH PRES MOVES ACROSS NEW ENGLAND. LIGHT WINDS AND SUBSIDING SEAS. MONDAY...MODERATE CONFIDENCE. INCREASING E/SE WINDS EXPECTED MON WITH BUILDING SEAS...PROBABLY REQUIRING SCA WITH GUSTS REACHING 25-30KT. OUTSIDE CHANCE OF REACHING MARGINAL GALES /35KT/ ESPECIALLY ON SOUTHERN WATERS. SEAS COULD REACH AS HIGH AS 8-10 FT ON OUTER WATERS MON NIGHT. RAIN AND FOG WILL LIMIT VSBY MON AFTERNOON AND AND MON NIGHT. TUESDAY...MODERATE CONFIDENCE. CONDITIONS IMPROVE SOMEWHAT TUE AS WINDS SUBSIDE AND SEAS GRADUALLY DIMINISH...BUT SEAS SHOULD REMAIN ROUGH ON OPEN WATERS THROUGH MOST OF DAY WHICH WOULD REQUIRE SCA.
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&& .FIRE WEATHER...
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WITH ONLY A TENTH OR TWO OF RAINFALL EXPECTED TODAY...THERE IS A POTENTIAL FOR ELEVATED FIRE WEATHER CONDITIONS ON SATURDAY AS DRY AIR SETTLES ACROSS THE REGION AND MIXING HEIGHTS EXTEND UP TO 7 KFT. SO IN ADDITION TO MINIMUM RELATIVE HUMIDITIES AROUND 30 PERCENT WITH THIS LATEST FORECAST...WITH THE POTENTIAL OF BEING LOWER DOWN TO 20 PERCENT...WESTERLY WIND GUSTS IN EXCESS OF 25 TO 30 MPH ARE EXPECTED. HIGH PRESSURE MOVES IN ON SUNDAY KEEPING THE WINDS GUSTS AT BAY... BUT ALLOWING FOR RH/S TO DROP NEAR 30 PERCENT AGAIN. CONDITIONS WILL TURN MORE WET BY NEXT WEEK WITH SEVERAL CHANCES OF SHOWERS AND COOLER WEATHER THROUGHOUT THE WORK WEEK.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 6 PM EDT THIS EVENING FOR ANZ230>236-250-251. SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 8 PM EDT THIS EVENING FOR ANZ254>256.
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&& $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL FIRE WEATHER...WFO BOX STAFF

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