Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191128 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 728 AM EDT FRI SEP 19 2014 .SYNOPSIS... COOL TEMPERATURES PREVAIL TODAY...WITH THE POSSIBILITY OF SOME EARLY MORNING FROST SATURDAY MORNING. A COLD FRONT CROSSES NEW ENGLAND SUNDAY NIGHT NIGHT WHILE A LOW PRESSURE CENTER RAPIDLY PASSES SOUTHEAST OF NANTUCKET ON ITS WAY TO NOVA SCOTIA. AFTER THE COLD FRONT PASSES OFFSHORE MONDAY MORNING...HIGH PRESSURE DOMINATES THE REGION THROUGH ALL OF NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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715 AM UPDATE... WITH TEMPERATURES STILL IN LOW TO MID 30S ACROSS LARGE PORTION OF SW NH...WILL NEED TO KEEP THE FROST ADVISORY UP UNTIL 8 AM. AS SOME WIND DECOUPLING TOOK PLACE OVER THE NW INTERIOR...TEMPERATURES DROPPED RATHER QUICKLY WITH 7 AM TEMPERATURES AT AFN 32...AT EEN 34 AND ORE 35. SOME SCT-BKN MID CLOUDS ALONG THE SOUTH COAST...OTHERWISE MOSTLY CLEAR. HAD TO TWEAK MANY TEMPERATURES DOWN A COUPLE DEGREES OR SO AT THE OUTSET THIS MORNING BUT FORECAST HIGH TEMPERATURES TODAY STILL LOOK GOOD. PRIOR DISCUSSION... CONDITIONS ARE GRADUALLY MAKING THEIR WAY TOWARD SKC EARLY THIS MORNING AS COLD FRONT CONTINUES TO PUSH FURTHER OFFSHORE WITH TIME. A FEW MORE LOW-MID CLOUDS HAVE YET TO SCOUR OUT BUT THE TREND WILL BE TOWARD CLEARING THERE AS WELL. THEREFORE...MUCH OF THE REGION WILL BE SEEING THE SUNRISE THIS MORNING. HOWEVER IN SPITE OF THIS A MIXED BACK OF COOL N-NE FLOW...H85 TEMPS TOPPING OUT AROUND +3C BY PEAK HEATING AND SUBSIDENCE FROM CREST OF HIGH PRES LIMITING MIXING DEPTH WILL ALL LEAD TOWARD BELOW NORMAL HIGHS TODAY. IN FACT...EVEN IF FULL MIXING TO H85 IS ALLOWED...HIGHS ARE LIKELY TO TOP OUT ONLY AT ABOUT THE MID 60S. ACTUAL HIGHS ARE LIKELY TO RANGE FROM MID-UPPER 50S TO MID 60S EVEN WITH THE FULL SUN.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... TONIGHT... HIGH PRES WILL CREST EARLY IN THE EVENING THEN BEGIN TO SLIDE OFFSHORE. DRY WX PREVAILS ALTHOUGH WEAK INVERTED TROF MAY LEAD TO SOME BUILDING CLOUD COVER JUST W OF THE BOX CWA DURING THE EARLY MORNING HOURS...MORE ON THE IMPACTS OF THAT IN A BIT. THE KEY TONIGHT WILL BE POTENTIAL FOR COOL TEMPS AND ANOTHER ROUND OF POTENTIAL FROST. OVERALL...CONDITIONS ARE MORE RIPE FOR RADIATIONAL COOLING THAN THU NIGHT THANKS TO A MUCH WEAKENED PRES GRADIENT UNDER THE HIGH PRES AND ANOTHER START OF MAINLY SKC SKIES. HOWEVER THERE ARE SOME MITIGATING FACTORS TO CONSIDER...ONE BEING THE CLOUD COVER JUST MENTIONED...SHOULD THAT BUILD FAR ENOUGH INLAND OF THE HUDSON VALLEY REGION...ITS NOT OUT OF THE QUESTION THIS COULD LIMIT THE FALLING TEMPS. MODELS DO INDICATE THE TYPICAL DWPT RISE UNDER THE RETURN FLOW AS HIGH EXITS TO THE E...BUT FEEL THAT THIS IS LIKELY MUCH TOO FAST GIVEN THE VERY DRY START AND CONTINUED INFLUENCE OF THE HIGH ITSELF. WHILE EACH OF THESE MAY LIMIT FROST DEVELOPMENT...DO NOTICE THAT BIAS CORRECTED TEMPS SUPPORT SOME MID 30S PARTICULARLY IN NW MA AND SW NH AND EVEN A FEW OF THE TYPICALLY COOLER E MA SUBURBS. THEREFORE...MAY NEED TO MONITOR FOR ANOTHER ROUND OF FROST ADVISORIES TODAY. WILL HOLD OFF ON ISSUANCE THIS MORNING GIVEN CURRENT FROST ADVISORY IN PLACE...BUT THOSE WITH SENSITIVE VEGETATION MAY WISH TO TAKE ACTION TODAY NONETHELESS. SAT... HIGH PRES CONTINUES SLOW SLIDE TO THE E BUT REMAINS IN CONTROL AS INVERTED RIDGING. THIS IS ENHANCED BY SUBSIDENCE BETWEEN APPROACHING OCEAN SYSTEM AND COLD FRONT TO THE W. THEREFORE...ALTHOUGH UPPER LVL CLOUD COVER IS LIKELY TO INCREASE ACROSS THE W THROUGH THE DAY...FEEL MUCH OF THE DAY WILL REMAIN DRY. MID LVL TEMPS MODERATE UNDER S-SW FLOW TO ABOUT +8C TO +10C WHICH WITH FULL MIXING SUGGESTS TEMPS MAY RISE ABOVE SEASONAL NORMALS...HOWEVER THE COOL START TO THE DAY AND SLOW RISE IN THESE MID LVL TEMPS SUGGESTS THAT ACTUAL HIGHS MAY BE CLOSER TO NORMAL. MAINLY UPPER 60S AND LOW 70S. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... * CHANCE OF SHOWERS SUNDAY NIGHT WITH COLD FRONT PASSAGE * THEN PROBABLY DRY ALL NEXT WEEK OVERVIEW... FAIRLY SHARP SHORT WAVE TROF AND ASSOCIATED FRONT EXPECTED TO CROSS NEW ENGLAND SUNDAY NIGHT. A POTENTIALLY SIGNIFICANT COMPLICATION IN THE FORECAST IS THE LIKELY PASSAGE OF A SURFACE LOW JUST SE OF NANTUCKET AHEAD OF THE COLD FRONT. SINCE THIS LOW PRESSURE SYSTEM MAY CONTAIN TROPICAL PROCESSES...CONFIDENCE IN HOW THIS SYSTEM WILL INTERACT WITH THE MID LATITUDE SHORT WAVE AND COLD FRONT IS LOW. WE NOTE A DRAMATIC DEVELOPMENT OF AN ASSOCIATED UPPER JET WITH THE COASTAL LOW FROM 80 TO 100+ KT IN LESS THAN 12 HOURS SUNDAY NIGHT. THE MODEL CONSENSUS CONTINUES TO KEEP THIS SYSTEM DISTINCTLY SEPARATE FROM THE FRONTAL SYSTEM UNTIL WELL PAST NEW ENGLAND. AND THERE IS A STRONG HINT THAT MUCH OF SOUTHERN NEW ENGLAND COULD BE CAUGHT IN A SUBSIDENCE ZONE BETWEEN THE FRONT AND COASTAL SURFACE LOW WITH RESULTING MINIMAL RAINFALL. HOWEVER...IF THE COASTAL LOW PRESSURE SHOULD HAVE A MORE DISTINCT IDENTITY AS A TROPICAL OR SUBTROPICAL SYSTEM...THEN ONE MIGHT EXPECT A SOMEWHAT SLOWER SPEED AND BACK BUILDING OF THE UPPER JET TO AT LEAST BRING A HIGHER THREAT OF SIGNIFICANT RAINFALL TO SE NEW ENGLAND. FOR NOW PLAN TO TAKE A CONSERVATIVE APPROACH WITH POPS AND QPF BUT KEEP IN MIND THERE IS ABOVE AVERAGE UNCERTAINTY FOR THE LATE SUNDAY THROUGH SUNDAY NIGHT TIME FRAME. ONCE THE LOW OFF THE COAST PASSES BY AND THE COLD FRONT SWEEPS OFFSHORE MONDAY MORNING...MEDIUM RANGE MODELS ARE IN FAIRLY CLOSE AGREEMENT ON A HIGH AMPLITUDE UPPER RIDGE BUILDING OVER EASTERN NORTH AMERICA WITH VERY LITTLE CHANCE OF RAIN FOR THE FORESEEABLE FUTURE IN OUR AREA. WE WOULD ANTICIPATE RELATIVELY MILD DAYTIME TEMPERATURES AND COOL OVERNIGHT TEMPERATURES IN THIS PATTERN WITH RELATIVELY HIGH DIURNAL RANGES...NEAR TO ABOVE NORMAL AFTERNOON TEMPERATURES AND NEAR TO BELOW NORMAL LATE NIGHT/EARLY MORNING TEMPERATURES. MORE SPECIFICALLY... SATURDAY NIGHT...DRY AND MILDER AS RETURN FLOW ABOUT SURFACE HIGH PRESSURE EAST OF AREA AND APPROACHING COLD FRONT OVER THE GREAT LAKES BECOMES BETTER ESTABLISHED. SUNDAY...THINKING THAT MUCH OF AREA WILL REMAIN DRY WITH TWO NOTABLE EXCEPTIONS. ONE EXCEPTION COULD BE ACROSS NW MA AND SW NH WHERE AIR MASS BECOMES MARGINALLY UNSTABLE AND MORE MOIST AHEAD OF AN APPROACHING COLD FRONT. INTEND TO INDICATE CHANCE SHOWERS/THUNDERSTORMS ROUGHLY NW OF A MHT-ORH-BDL LINE. THERE WILL BE INCREASING VERTICAL SHEAR AND CANNOT RULE OUT AN ISOLATED STRONG OR EVEN SEVERE THUNDERSTORM NW MA AND SW NH LATE SUNDAY AFTERNOON OR EVENING. THE EXCEPTION IS THE SE PORTION OF THE FORECAST AREA. WILL RAISE POPS TO CHANCE IN SE AHEAD OF COASTAL LOW BY SUNDAY AFTERNOON AS MOISTURE MAY STREAM RAPIDLY NORTHWARD FROM COASTAL LOW PRESSURE SYSTEM TO THE SOUTH...WHICH IS EXPECTED TO TRIGGER A STRENGTHENING OF AN UPPER LEVEL JET ALONG/JUST OFF THE COAST. SUNDAY NIGHT...AS PER OVERVIEW SECTION WE HAVE ABOVE AVERAGE UNCERTAINTY FOR THIS FORECAST PERIOD AS RAIN CHANCES WILL DEPEND UPON INTERACTION BETWEEN COLD FRONT AND LOW PRESSURE PASSING JUST OFFSHORE. FOR NOW PLAN ON CHANCE POPS WITH HIGHEST VALUES FAR NW AND FAR SE. VERTICAL SHEAR INCREASES TO 40 TO 50 KT 0 TO 6 KM SUNDAY EVENING AND ANY THUNDERSTORMS...MOST LIKELY NW SECTIONS...COULD CONTAIN STRONG WINDS. MONDAY...LINGERING CHANCE OF SHOWERS FAR SE AND OTHERWISE DRY AS SURFACE HIGH PRESSURE BUILDS INTO THE REGION. MAY BE BREEZY FROM THE NW DUE TO COMBINATION OF MODERATELY TIGHT SURFACE PRESSURE GRADIENT AND MODERATE COLD AIR ADVECTION. TUESDAY THROUGH THURSDAY...RELATIVELY HIGH CONFIDENCE OF DRY CONDITIONS THROUGH THE PERIOD WITH MILD DAYS AND COOL NIGHTS. IT IS POSSIBLE THAT RADIATIONAL COOLING DURING TUESDAY NIGHT AND/OR WEDNESDAY NIGHT COULD BE ROBUST ENOUGH FOR SOME PATCHY FROST SW NH AND NW MA...BUT CONFIDENCE ON THIS IS QUITE LOW THIS FAR OUT. OTHERWISE...EXPECT THE MAIN STORY IS THAT WE WILL BE INCREASING A PRECIPITATION DEFICIT FOR MUCH OF AREA NEXT WEEK. DO NOT SEE ANY CREDIBLE RAIN THREAT IN THE FORESEEABLE FUTURE AFTER SUNDAY NIGHT. && .AVIATION /12Z 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. MAINLY VFR THROUGH THE PERIOD...EXCEPT SOME EARLY MORNING FOG IS POSSIBLE AT THE TYPICAL TERMINALS LATE TONIGHT/EARLY SAT. WINDS SUSTAINED AROUND 10 KT CONTINUE THROUGH THE EARLY HALF OF THE DAY WITH A FEW GUSTS TO 20 KT...ESPECIALLY SE COASTAL AREAS. THE WINDS DIMINISH TONIGHT. WINDS OUT OF THE S-SW ON SAT...WITH AFTERNOON GUSTS TO 20 KT POSSIBLE ONCE AGAIN. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY... HIGH CONFIDENCE THROUGH THE PERIOD EXCEPT MODERATE CONFIDENCE SUNDAY AFTERNOON AND NIGHT. SATURDAY NIGHT...VFR EXPECTED EXCEPT FOR POSSIBLY PATCHY VALLEY FOG. SUNDAY...VFR EXPECTED EXCEPT MVFR CIGS/VSBYS IN VICINITY OF SCATTERED SHOWERS/THUNDERSTORMS NW OF A MHT-ORH-BDL LINE SUNDAY AFTERNOON. A SECOND AREA OF MVFR CIGS/VSBYS MAY DEVELOP SUNDAY AFTERNOON ALONG AND S OF A BID-HYA-CQX LINE IN AREAS OF SHOWERS. SUNDAY NIGHT...MVFR CIGS/VSBYS POSSIBLE IN SHOWERS ACROSS THE REGION. MONDAY THROUGH TUESDAY...VFR CONDITIONS EXPECTED.
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&& .MARINE... 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. TODAY AND TONIGHT... COLD FRONT CONTINUES TO MOVE OFFSHORE THIS MORNING...HOWEVER N-NE WIND GUSTS UP TO 25 KT AND LINGERING WIND-WAVES AROUND 5-6 FT ON THE OCEAN WATERS SUGGEST THE NEED FOR SMALL CRAFT ADVISORIES TO CONTINUE THROUGH THE EARLY HALF OF THE DAY...AND INTO THE EVENING FOR THE SOUTHERN WATERS. CONDITIONS IMPROVE OVERNIGHT AS WINDS SHIFT TO THE S AND...ALONG WITH SEAS...DIMINISH. SAT... S-SW WINDS DOMINATE...WITH A FEW GUSTS TO AROUND 20 KT IN THE AFTERNOON...BUT SHOULD GENERALLY REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS. SEAS TOO WILL REMAIN GENERALLY 3-4 FT ON THE OCEAN WATERS AND LOWER NEAR SHORE. OUTLOOK...SATURDAY NIGHT THROUGH TUESDAY...MODERATE CONFIDENCE. SATURDAY NIGHT THROUGH SUNDAY...HIGH CONFIDENCE OF WINDS AND SEAS BELOW SMALL CRAFT ADVISORY LEVELS EXCEPT POSSIBLE BUILDING SWELL OVER THE SOUTHERN COASTAL WATERS LATE SUNDAY. SUNDAY NIGHT INTO MONDAY...MODERATE CONFIDENCE. MAY SEE SEAS BUILDING TO SMALL CRAFT ADVISORY LEVELS ACROSS AT LEAST THE OUTER WATERS SUNDAY NIGHT AND PERSISTING INTO MONDAY. IN ADDITION...MAY HAVE A PERIOD OF SMALL CRAFT ADVISORY GUSTS FROM THE NW DURING THE DAY MONDAY. LOW PRESSURE CENTER PASSING SE OF NANTUCKET MAY HAVE VERY SIGNIFICANT WINDS AND SEAS ON ITS EAST SIDE...BUT PROBABLY WELL OFFSHORE OF OUR COASTAL WATERS. TUESDAY...MODERATE TO HIGH CONFIDENCE OF WINDS AND SEAS BELOW SMALL CRAFT ADVISORY LEVELS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR NHZ011-015. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR ANZ232>235-237. SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR ANZ231- 251. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ250. SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ254-255. SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR ANZ256. && $$ SYNOPSIS...DOODY/THOMPSON NEAR TERM...DOODY/THOMPSON SHORT TERM...DOODY LONG TERM...THOMPSON AVIATION...DOODY/THOMPSON MARINE...DOODY/THOMPSON

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