Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 190631 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 231 AM EDT SAT JUL 19 2014 .SYNOPSIS... HIGH PRESSURE OVER THE NORTHEAST USA WILL MOVE OFFSHORE OVER THE WEEKEND. LOW PRESSURE DEVELOPING OFF THE CAROLINAS WILL PASS SOUTHEAST OF NANTUCKET SUNDAY. HIGH PRESSURE MAINTAINS DRY WEATHER THROUGH THE EARLY WEEK. A COLD FRONT FROM CANADA MOVES OVER NEW ENGLAND MIDWEEK. && .NEAR TERM /THROUGH TODAY/... 230 AM UPDATE... UPDATED FORECAST TO ACCOUNT FOR CURRENT TRENDS. OTHERWISE...NO SIGNIFICANT CHANGES NEEDED TO THE ONGOING FORECAST. TODAY... HIGH PRESSURE MOVES FARTHER OFFSHORE TODAY. EXPECTING DRY WEATHER WITH INCREASING MID AND HIGH LEVEL CLOUDS. LIGHT WINDS WILL ONCE MORE RESULT IN SEA BREEZES. EVENTUALLY A SOUTHEAST SYNOPTIC FLOW WILL DEVELOP THIS AFTERNOON. THIS ONSHORE FLOW WILL BUFFER THE WARMTH ALONG THE COASTS. MOS TEMPERATURES HAVE BEEN TOO HIGH THE PAST FEW DAYS ALONG THE IMMEDIATE COAST. WITH MORE CLOUDS THAN YESTERDAY...AS WELL AS A STRONGER ONSHORE FLOW...LOWERED TEMPERATURES BELOW MOS ALONG THE COASTS. OVERALL MAX TEMPERATURES SHOULD BE NEAR OR SLIGHTLY LOWER THAN FRIDAY. && .SHORT TERM /TONIGHT THROUGH 6 PM SUNDAY/... TONIGHT...AN OFFSHORE HIGH PRESSURE WILL KEEP THE WEATHER DRY MOST PLACES...AS A SURFACE RIDGE EXTENDS WEST ACROSS SOUTHERN NEW ENGLAND. WE CONTINUE TO WATCH A SOUTHERN STREAM SHORTWAVE THAT IS EXPECTED TO GENERATE A COASTAL LOW OFF THE CAROLINAS BY THIS EVENING. WITH SOUTHWEST FLOW ALOFT...WE EXPECT THIS WEAK LOW PRESSURE WILL MOVE TOWARD OUR REGION TONIGHT. THE QUESTION WHICH REMAINS IS HOW CLOSE THIS LOW PRESSURE WILL GET. JUST ABOUT ALL OF THE 19/00Z GUIDANCE BRINGS SOME PRECIPITATION INTO CAPE COD AND THE ISLANDS. SOME GUIDANCE SOURCES BRING SOME RAINFALL EVEN FARTHER NORTHWEST. THINKING THE SURFACE RIDGE WILL HOLD STRONG...SO HAVE KEPT THE BRUNT OF THE RAINFALL OFFSHORE. THIS IS SIMILAR TO PREVIOUS FORECAST THINKING. SUNDAY...BEST CHANCE OF SHOWERS WILL BE ACROSS THE CAPE/ISLANDS WITH A MOIST ONSHORE FLOW...WHILE A RIDGE OF HIGH PRESSURE SHOULD CURTAIL THE RAINFALL FROM MAKING FURTHER NORTH/WEST. HOWEVER... THIS WILL HAVE TO BE CLOSELY MONITORED. THERE WILL BE CONSIDERABLE CLOUDINESS...WITH A GRADUAL CLEARING TREND GETTING UNDERWAY... ESPECIALLY LATER IN THE DAY. AN ONSHORE FLOW WILL KEEP COASTAL AREAS IN PARTICULAR COOLER. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... HIGHLIGHTS... * FAIR WEATHER W/SEASONABLE TEMPS AND INCREASING HUMIDITY MONDAY. * TEMPERATURES IN THE UPPER 80S TO LOWER 90S TUESDAY...WEDNESDAY AND POSSIBLY THURSDAY...WITH DEWPOINTS IN THE MID 60S. * BEST CHANCE OF SHOWERS AND THUNDERSTORMS IN THE WEDNESDAY AND THURSDAY TIMEFRAME WITH THE APPROACH OF A COLD FRONT. OVERVIEW AND MODEL PREFERENCES... MID-LEVEL TROUGH EJECTS OUT OF THE NORTHEAST US AND INTO THE CANADIAN MARITIMES ON MONDAY. A RIDGE BUILDS OVER THE REGION TUESDAY AND WEDNESDAY AND THE NEXT TROUGH APPROACHES THURSDAY. THERE IS DISAGREEMENT IN THE MODELS EARLY IN THE PERIOD WITH THE SPEED OF AN OFFSHORE LOW IN THE SUNDAY - MONDAY PERIOD... WITH THE ECMWF PLACING THE LOW SOUTH OF THE BENCHMARK AT 12Z SUNDAY...MEANWHILE THE GFS PLACES IT NEAR CAPE HATTERAS ATTM. THIS IMPACTS JUST HOW QUICKLY SKIES CLEAR ON SUNDAY AND WENT WITH A COMPROMISE SOLUTION FOR NOW THAT CLEARS SKIES OUT SUNDAY NIGHT. THE GFS ALSO APPEARS A BIT OVERDONE ON IT/S NORTHWEST EXTENT OF QPF ON SUNDAY...ESPECIALLY WITH HIGH PRESSURE DRAPED ACROSS THE REGION...SO KEPT CHANCE POPS ON THE CAPE/ISLANDS. LATER IN THE PERIOD...THE GFS IS MORE PROGRESSIVE WITH A FRONTAL PASSAGE ON THURSDAY WHILE THE ECMWF STALLS THE FRONT ACROSS THE REGION INTO FRIDAY. DETAILS... MONDAY...HIGH PRESSURE BUILDS IN WITH PARTLY SUNNY SKIES AND DRY WX EXPECTED. AN ONSHORE FLOW WILL PERSIST BEHIND THE DEPARTING LOW...AND AS THE PRESSURE GRADIENT RELAXES...A SEA-BREEZE COMPONENT TOO. THEREFORE EXPECT COASTAL AREAS COOLER WITH SEASONABLE TEMPS OVER THE INTERIOR. IT WILL BECOME NOTICEABLY MORE HUMID LATER MONDAY...AND THERE MAY BE FOG/LOW CLOUDS ALONG THE SOUTH COAST MONDAY NIGHT WITH THE APPROACH OF A WARM FRONT. TUESDAY...WARM FRONT MOVES THROUGH THE REGION. ALTHOUGH SOME MODELS INDICATE LIGHT QPF /ESPECIALLY NORTHWEST/...COLUMN IS DRY AND THERE IS LITTLE SUPPORT FOR THIS...SO LEFT FORECAST DRY. SUN AND MXG TO 850 HPA SUPPORTS HIGHS 85 TO 90...EVEN ALONG THE COAST...AS THE PRESSURE GRADIENT LOOKS TO SUPPRESS THE SEA-BREEZE. WEDNESDAY...TROUGH APPROACHES FROM THE WEST. AT THIS POINT...THERE APPEARS TO BE MORE THAN ADEQUATE INSTABILITY FOR CONVECTION...BUT SHEAR IS MINIMAL. THERE MAY ALSO BE SOME SLIGHT RIDGING AT MID- LEVELS WHICH COULD KEEP THE ATMOSPHERE CAPPED AND WHETHER OR NOT THERE IS SUFFICIENT MOISTURE IN THE COLUMN IS QUESTIONABLE. THE BEST CHANCE OF CONVECTION MAY HOLD OFF UNTIL WEDNESDAY NIGHT. ANOTHER HOT DAY IS IN STORE WITH 850 HPA TEMPS SUPPORTING HIGHS IN THE UPPER 80S TO LOWER 90S...AND ONCE AGAIN...THE PRESSURE GRADIENT APPEARS TO INHIBIT THE SEA-BREEZE. THURSDAY AND FRIDAY...FRONT MOVES THROUGH THE REGION SOMETIME DURING THIS TIMEFRAME WITH THE BEST CHANCE OF SHOWERS AND THUNDERSTORMS ALONG WITH TEMPERATURES RETURNING TO MORE SEASONABLE LEVELS BEHIND THE FRONT. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY NIGHT/... THROUGH 12Z...HIGH CONFIDENCE. VFR. PATCHY FOG/LOW CLOUDS IN NORTHWEST MASS/SOUTHWEST NH WITH IFR/LIFR CIGS AND VSBYS. TODAY...HIGH CONFIDENCE. VFR. SEA BREEZES DEVELOP BY LATE AM. TONIGHT...HIGH CONFIDENCE. VFR. SHOWERS MAY BRING BRIEF MVFR VSBYS TO THE ISLANDS LATE AT NIGHT. SUNDAY...MODERATE CONFIDENCE. MVFR/IFR POSSIBLE IN LOW CEILINGS AND SHRA MAINLY CONFINED TO CAPE COD AND THE ISLANDS. VFR EXPECTED ELSEWHERE. KBOS TAF...HIGH CONFIDENCE IN TAF. SEA BREEZE DEVELOPS AROUND 14-15Z TODAY. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY... MONDAY THROUGH WEDNESDAY...LOW CONFIDENCE. MVFR/IFR POSSIBLE IN FOG AND LOW CLOUDS ALONG THE SOUTH COAST...ESPECIALLY MONDAY NIGHT INTO TUESDAY MORNING. MVFR/IFR POSSIBLE NORTHWEST IN SHRA/TSRA LATE WED. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. THROUGH SUNDAY...HIGH CONFIDENCE. WAVE MODELS CONTINUE TO OVERFORECAST WAVE HEIGHTS OFF OUR COAST BY ABOUT A FOOT. LOWERED THE WAVE HEIGHT GUIDANCE BY 20 PERCENT THROUGH THE FORECAST PERIOD. TRANQUIL BOATING WEATHER EXPECTED WITH HIGH PRESSURE OVERHEAD. LIGHT WINDS TREND TO SOUTHEAST TODAY AS THE HIGH MOVES OFFSHORE... THEN TO EAST TONIGHT. WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT THRESHOLDS THROUGH SUNDAY. COASTAL LOW PRESSURE DEVELOPING OFF THE CAROLINAS TODAY WILL MOVE UP THE COAST TONIGHT. CURRENT FORECAST TRACK WOULD KEEP MOST OF THIS STORM WELL OFFSHORE. BUT FORECAST MODELS AGREE ON LIGHT SHOWERS INTO OUR SOUTHERN WATERS AFTER MIDNIGHT TONIGHT... ESPECIALLY SOUTH AND EAST OF NANTUCKET. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY... MODERATE CONFIDENCE. HIGH PRESSURE BUILDS IN ON MONDAY. A WARM FRONT MOVES THROUGH ON TUESDAY AND A COLD FRONT WILL APPROACH ON THURSDAY. SCA FOR SEAS POSSIBLE...ESPECIALLY OVER THE OUTER WATERS...DURING THE SUNDAY-MONDAY TIMEFRAME. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...BELK/99 NEAR TERM...BELK SHORT TERM...BELK LONG TERM...99 AVIATION...BELK/99 MARINE...BELK/99

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