Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 192048 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 448 PM EDT FRI SEP 19 2014 .SYNOPSIS... CLEAR SKIES AND CHILLY TEMPERATURES WILL BE IN PLACE TONIGHT ACROSS THE REGION AS HIGH PRESSURES CRESTS ACROSS THE REGION. AS THE HIGH MOVES OFFSHORE...MILDER TEMPERATURES WILL BRIEFLY RETURN FOR SATURDAY AND SATURDAY NIGHT. A COLD FRONT CROSSES NEW ENGLAND SUNDAY NIGHT...WHILE A LOW PRESSURE CENTER RAPIDLY PASSES SOUTHEAST OF NANTUCKET ON ITS WAY TO NOVA SCOTIA. AFTER THIS COLD FRONT PASSES OFFSHORE MONDAY MORNING...HIGH PRESSURE DOMINATES THROUGH ALL OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... THROUGH 00Z...SKIES HAVE BEEN MAINLY CLEAR ACROSS MOST OF THE REGION THROUGH EARLY THIS AFTERNOON. THE ONLY EXCEPTION HAS BEEN ACROSS E COASTAL MA INTO E RI WHERE OCEAN CLOUDS HAVE BEEN MOVING ONSHORE WITH THE NE WIND. HOWEVER...THE CLOUDS HAVE BEEN DISSIPATING ACROSS MOST OF THE COASTAL AREAS AS WINDS HAVE BEEN SLOWLY DIMINISHING AND VEERING TO EAST. SOME CLOUDS STILL LINGER ACROSS CAPE COD AND THE ISLANDS BUT SHOULD DISSIPATE BY THIS EVENING. TEMPS HAVE REMAINED MAINLY IN THE MID-UPPER 50S ACROSS MOST AREAS...WITH SOME REPORTS IN THE LOWER-MID 60S ACROSS THE MID AND LOWER CT VALLEY INTO NE CT/INTERIOR RI. NOTING RATHER LOW DEWPTS...MAINLY IN THE UPPER 20S TO LOWER 30S ACROSS S NH INTO N CENTRAL MA...RANGING TO THE MID 30S ALONG THE IMMEDIATE E COAST... CAPE COD AND THE ISLANDS. THESE READINGS ARE 2-4 DEGS LOWER THAN FORECAST. EXPECT GENERALLY CLEAR CONDITIONS WITH WINDS CONTINUING TO DIMINISH INTO THIS EVENING. TONIGHT...HIGH PRES CENTER WILL CREST ACROSS EASTERN AREAS THIS EVENING...THEN PUSH OFFSHORE. TIMING OF THIS WILL BE A BIG QUESTION...AS LIGHT E WINDS WILL LIKELY DECOUPLE AND DROP OFF IN THE NORMALLY PRONE INTERIOR AREAS ESPECIALLY ACROSS PORTIONS OF S NH/N CENTRAL AND NW MA. AS NOTED ABOVE...DEWPTS ARE LOWER THAN FORECAST. HOW QUICKLY THESE RISE OVERNIGHT...AS CURRENTLY INDICATED BY SHORT RANGE MODEL GUIDANCE...WILL BE CRITICAL FOR OVERNIGHT LOWS ACROSS THE INTERIOR. CURRENT FORECASTED LOWS ARE IN THE MID-UPPER 30S WELL INLAND. IF TEMPS FALL LOWER THAN FORECAST...POSSIBLE SHORT FUSED HEADLINES FOR FROST OR FREEZE MAY NEED TO BE ISSUED. THIS ASPECT WILL BE MONITORED CLOSELY. OTHERWISE...EXPECT MAINLY CLEAR...DRY AND MAINLY CALM CONDITIONS. MAY START TO SEE SOME HIGH CLOUDS WORK INTO WESTERN AREAS WELL AFTER MIDNIGHT. LOWS WILL RANGE FROM THE MID 30S TO AROUND 40 INLAND TO THE MID 40S TO AROUND 50 ALONG THE IMMEDIATE SHORE. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... SATURDAY...HIGH PRES WILL SHIFT E OF THE REGION DURING THE DAY. MILD S-SW FLOW TAKES OVER. TEMPS WILL RESPONSE TO THIS AS RIDGE REMAINS ACROSS REGION. THE SW FLOW MAY BECOME GUSTY /AROUND 20 KT/ DURING THE AFTERNOON ACROSS INLAND AREAS WITH GOOD MIXING IN PLACE. WILL ALSO NOTICE INCREASING HUMIDITY AS DEWPTS STEADILY RISE DURING THE DAY. HIGHS WILL REACH THE LOWER 70S FOR MOST AREAS...THOUGH A BIT COOLER ACROSS THE HIGHER TERRAIN AND ALONG THE IMMEDIATE S COAST WITH THE ONSHORE WIND. NOTING A BROAD INVERTED TROUGH STARTING TO TAKE SHAPE ALONG THE MID ATLC AND SE U.S. COAST...ALONG WITH LOW PRES OFF THE GA/FL COAST EARLY SAT. SOME MOISTURE MAY START TO MOVE UP TOWARD THE REGION LATE IN THE DAY. SATURDAY NIGHT...AS LOW PRES DEVELOPS AND MOVES NE UP THE COAST...A PIECE OF MOISTURE MAY WORK INTO CENTRAL AND SOUTHERN AREAS FOR A TIME OVERNIGHT. HAVE CARRIED LOW CHANCE POPS ACROSS RI/NE CT THOUGH PLACEMENT OF THE AXIS OF THIS MOISTURE IS UNCERTAIN. WILL CONTINUE TO SEE S WINDS ALONG WITH MILD AND HUMID CONDITIONS. MAY SEE SOME PATCHY FOG DEVELOP MAINLY AFTER MIDNIGHT AS WELL. TEMPS WILL ONLY FALL BACK TO THE MID 50S TO LOWER 60S. && .LONG TERM /SUNDAY THROUGH FRIDAY/... * CHANCE OF SHOWERS SUNDAY INTO SUNDAY NIGHT WITH COLD FRONT PASSAGE * DRY CONDITIONS LIKELY NEXT WEEK OVERVIEW...NOT MUCH CHANGE IN THE 19/12Z GUIDANCE SUITE FROM PREVIOUS RUNS. WE STILL EXPECT A FAIRLY SHARP SHORTWAVE TROUGH AND A COLD FRONT 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 THIS COLD FRONT. SINCE THIS LOW PRESSURE SYSTEM MAY CONTAIN TROPICAL PROCESSES...CONFIDENCE IN HOW THIS SYSTEM WILL INTERACT WITH THE MID LATITUDE SHORTWAVE AND COLD FRONT IS LOW. THE 19/12Z GUIDANCE STILL PROJECTS THE DRAMATIC DEVELOPMENT OF AN ASSOCIATED UPPER JET WITH THIS COASTAL LOW FROM 80 TO 100+ KT IN LESS THAN 12 HOURS SUNDAY NIGHT...AND FURTHER INTENSIFIES THIS JET MONDAY. THE MODEL CONSENSUS CONTINUES TO KEEP THIS SYSTEM DISTINCTLY SEPARATE FROM THE FRONTAL SYSTEM UNTIL WELL PAST NEW ENGLAND. AND THERE REMAINS SOME SIGNALS THAT MUCH OF SOUTHERN NEW ENGLAND COULD BE CAUGHT IN A SUBSIDENCE ZONE BETWEEN THE FRONT AND COASTAL SURFACE LOW...WITH RESULTING MINIMAL RAINFALL. AS NOTED BY PREVIOUS FORECASTER...IF THIS 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 SOUTHEAST NEW ENGLAND. ALSO AS BEFORE...WE KEPT THE FORECAST CONSERVATIVE AND WENT NO HIGHER THAN A CHANCE OF RAIN SHOWERS SUNDAY AND SUNDAY NIGHT...DUE TO HIGHER THAN NORMAL UNCERTAINTY FOR THIS TIME RANGE OF THE FORECAST. ONCE OUR REGION IS CLEAR OF BOTH THIS COASTAL LOW AND COLD FRONT MONDAY MORNING...MEDIUM RANGE MODELS ARE IN FAIRLY CLOSE AGREEMENT ON A HIGH AMPLITUDE UPPER RIDGE BUILDING OVER EASTERN NORTH AMERICA. THIS MEANS VERY LITTLE CHANCE OF RAIN FOR THE FORESEEABLE FUTURE ACROSS 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. DETAILS... SUNDAY...THINKING THAT MUCH OF AREA WILL REMAIN DRY WITH TWO NOTABLE EXCEPTIONS. ONE EXCEPTION COULD BE ACROSS NORTHWEST MA AND SOUTHWEST NH...WHERE AIR MASS BECOMES MARGINALLY UNSTABLE AND MORE MOIST AHEAD OF AN APPROACHING COLD FRONT. CONTINUED TO INDICATE A CHANCE OF SHOWERS WITH ISOLATED THUNDERSTORMS ROUGHLY NORTHWEST OF A MANCHESTER NH-WORCESTER MA-HARTFORD CT 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 OTHER EXCEPTION WILL BE ACROSS CAPE COD AND THE ISLANDS. HAVE GREATEST CONFIDENCE IN SCATTERED SHOWERS ACROSS NANTUCKET BY LATE SUNDAY AFTERNOON. THIS TIMING IS RATHER UNCERTAIN. DECIDED TO ONLY MENTION A SLIGHT CHANCE OF SHOWERS FOR THE VINEYARD AND THE CAPE. THIS COULD CHANGE IF THE TIMING IS ALTERED BY ONLY A COUPLE OF HOURS...EITHER FASTER OR SLOWER. WILL NEED TO MONITOR THIS AREA TO TRACK THE INFLUX OF MOISTURE. 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 TOWARDS NORTHWEST MA AND EXTREME SOUTHWEST NH...COULD CONTAIN STRONG WINDS. MONDAY...LINGERING CHANCE OF SHOWERS ACROSS THE CAPE AND ISLANDS EARLY. OTHERWISE DRIER AS SURFACE HIGH PRESSURE BUILDS INTO THE REGION. MAY BE BREEZY FROM THE NORTHWEST DUE TO COMBINATION OF MODERATE SURFACE PRESSURE GRADIENT AND MODERATE COLD AIR ADVECTION. TUESDAY THROUGH FRIDAY...RELATIVELY HIGH CONFIDENCE OF DRY CONDITIONS THROUGH THIS 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 SOUTHWEST NH AND NORTHWEST 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. && .AVIATION /14Z 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 NIGHT/...HIGH CONFIDENCE. THROUGH 00Z...VFR. ANY LEFTOVER CLOUDS AT 3-4KFT ACROSS S COASTAL MA/E RI WILL DISSIPATE BY EARLY EVENING. TONIGHT...MAINLY VFR...EXCEPT FOR PATCHY FOG AFTER MIDNIGHT ACROSS INTERIOR AREAS WITH LOCAL MVFR-IFR CONDITIONS POSSIBLE. SATURDAY AND SATURDAY NIGHT...EXPECT MAINLY VFR CONDITIONS THROUGH THE PERIOD. ANY LEFTOVER PATCHY FOG SHOULD DISSIPATE BY 14Z AT THE TYPICAL TERMINALS. WINDS OUT OF THE S-SW ON SAT...WITH AFTERNOON GUSTS TO 20 KT POSSIBLE. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...SUNDAY THROUGH TUESDAY... HIGH CONFIDENCE THROUGH THE PERIOD...EXCEPT MODERATE CONFIDENCE SUNDAY AFTERNOON AND NIGHT. 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. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE. THROUGH 00Z...CONDITIONS ACROSS MOST OF THE WATERS HAVE SUBSIDED SO WHERE SMALL CRAFTS WERE STILL IN EFFECT HAVE BEEN DROPPED. KEPT SMALL CRAFTS GOING FOR OUTER WATERS S AND E OF CAPE COD AND NANTUCKET INTO THIS EVENING FOR LEFTOVER 5 FOOT SEAS. TONIGHT...EXPECT WINDS TO DIMINISH SOMEWHAT AS THEY VEER TO E-SE DURING THE NIGHT. SATURDAY...S-SW WIND FLOW TAKES OVERNIGHT. MAY SEE SOME GUSTS CLOSE TO SMALL CRAFT CRITERIA...SOMETHING TO MONITOR. SEAS SHOULD REMAIN BELOW 5 FT. SATURDAY NIGHT...MAINLY S WINDS IN PLACE. GUSTS UP TO 25 KT MAY LINGER EARLY ON THE EASTERN OUTER WATERS. HOWEVER...SEAS MAY REACH 5 FT ON THE OUTER WATERS OVERNIGHT. OUTLOOK...SUNDAY THROUGH TUESDAY...MODERATE CONFIDENCE. 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...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ254- 255. && $$ SYNOPSIS...BELK/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...BELK AVIATION...BELK/EVT MARINE...BELK/EVT

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