Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 021117 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 717 AM EDT SAT MAY 2 2015 .SYNOPSIS... PROGRESSIVELY WARMER WEATHER IS EXPECTED THIS WEEKEND ESPECIALLY AWAY FROM THE COAST. DRY WEATHER DOMINATES...BUT MAY SEE A BRIEF SPOT SHOWER OR THUNDERSTORM IN NORTHERN MASSACHUSETTS SUNDAY AFTERNOON. HIGH PRESSURE BUILDS OVER THE REGION DURING EARLY NEXT WEEK. A COLD FRONT SWEEPS SOUTH ACROSS THE REGION TUESDAY AND THEN STALLS SOUTH OF NEW ENGLAND MIDWEEK. HIGH PRESSURE REBUILDS WITH DRY AND WARMING WEATHER THE REMAINDER OF THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 AM UPDATE... LINGERING STRATUS ACROSS RI AND EASTERN MASS WITH PATCHES OF LOW VSBYS DUE TO FOG. WITH LIGHT MARINE FLOW IN PLACE...EXPECT THE SUN TO ERODE THIS CLOUD LAYER THIS MORNING WITH ALL AREAS RETURNING TO MOSTLY CLEAR. FOR THIS UPDATE WE HAVE ADJUSTED SKY COVER PERCENTAGES AND TEMPS/DEWPOINTS TO REFLECT OBSERVED CONDITIONS. NO OTHER CHANGES AT THIS TIME. PREVIOUS DISCUSSION... THE INLAND CLOUD COVER HAS GENERALLY DISSIPATED THIS MORNING LEADING TO MOSTLY CLEAR SKIES. HOWEVER MODEST E COMPONENT TO THE FLOW HAS ALLOWED A BANK OF STRATUS TO GRADUALLY SHIFT INLAND FROM THE E COAST OF MA OVERNIGHT. IT/S TAKEN UNTIL ABOUT 08Z TO REACH THE PVD-BOS CORRIDOR...AND WITH SUNRISE ONLY A FEW MORE HOURS AWAY...AM THINKING IT WILL NOT GO TOO MUCH FURTHER BEFORE MIXING BEGINS TO ERODE IT. NAMDNG SEEMED TO SHOW THIS TREND WELL. OTHERWISE...THE LOW PRES SPINNING WELL TO THE S WILL CONTINUE TO USURP A FAIR AMOUNT OF THE DYNAMICS AND MOISTURE ACROSS THE REGION...SO EXPECT AWAY FROM A WEAK INSTABILITY TROF IN ERN NY AND W MA...FEEL THAT THE CHANCE FOR -SHRA ACTIVITY IS QUITE LOW TODAY. SLIGHT CHANCE POPS IN THE W. WARMER TEMPS AWAY FROM THE COAST TODAY. H85 TEMPS APPROACH +6C AND MIXING SHOULD HAVE LITTLE TROUBLE REACHING AT LEAST THIS HEIGHT...THEREFORE...WILL LIKELY SEE LOW 70S IN TYPICALLY WARMER SPOTS WITH UPPER 60S ELSEWHERE. CAVEAT IS THE NEAR COASTAL REGIONS...LIGHT FLOW MEANS SEA BREEZES...SO SUSPECT HIGHS TOP OUT ONLY IN THE 50S NEAR THE SHORE.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... TONIGHT... PARTLY CLOUDY CONDITIONS EXPECTED AS CLOUDS DIMINISH DURING THE EVENING. LIGHT FLOW SHOULD ALLOW FOR MODEST RADIATIONAL COOLING BUT OVERALL MOISTURE WILL BE INCREASING AS HIGH PRES CONTINUES TO MOVE OFFSHORE AND LIGHT RETURN FLOW DEVELOPS. MIN TEMPS FALL BACK INTO THE LOW TO MID 40S FOR THE MOST PART. SUN... ANOTHER PARTLY CLOUDY START. THIS SUNSHINE WILL ALLOW MIXING TO REACH HIGHER THAN H85 WHERE TEMPS WILL HAVE WARMED TO AN AVERAGE AROUND +9C. FLOW MAINLY S-SW. WITH THIS SLIGHT W COMPONENT INLAND...CT VALLEY CLOUD APPROACH 80F...OR AT LEAST THE UPPER 70S. WARMER ELSEWHERE TOO...EXCEPT COASTLINES WHERE THE LIGHT RETURN FLOW WILL ALLOW FOR THE DEVELOPMENT OF LATER DAY SEA BREEZES ONCE AGAIN. CONTINUE TO NOTE MODEST TROUGH IN MASS FIELDS MOVING INTO THE REGION DURING THE AFTERNOON FROM THE NW. THE COMBINATION OF THIS FEATURE AND SEA BREEZE FRONTS COULD ALLOW FOR THE DEVELOPMENT OF -SHRA ESPECIALLY E AND NE MA...BUT AS FAR SOUTH AS NRN CT/RI. SOME SFC BASE CAPE AROUND 200-500 J/KG ALSO AVAILABLE THANKS TO 6.5-7.0C/KM MID LVL LAPSE RATES. H5 TEMPS NEAR -20C AS WELL. THEREFORE...COULD BE AN ISOLATED RUMBLE OF THUNDER WITH ANYTHING THAT DEVELOPS. VERY LIGHT FLOW THROUGH THE WHOLE COLUMN...SO SHEAR FAR FROM AN ISSUE AND ANYTHING THAT DEVELOPS IS LIKELY TO COLLAPSE ON ITSELF AS IT FORMS. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... BIG PICTURE... NORTHERN AND SOUTHERN JET STREAMS THROUGH THE FORECAST PERIOD. UPPER RIDGE BUILDS OVER THE EASTERN USA WHILE GULF OF ALASKA LOW AND SOUTHERN STREAM SHORTWAVE MERGE TO FORM A CLOSED LOW WEST OF THE ROCKIES. THE BUILDING RIDGE SHOULD MAINTAIN TEMPS AT OR ABOVE NORMAL MUCH OF THE COMING WEEK. MODEL GUIDANCE IS SIMILAR THROUGH AT LEAST THURSDAY. EVEN FRIDAY ISN/T TOO DIFFERENT. A GENERAL BLEND OF MODEL DATA WAS USED FOR THE GRIDS. THE DAILIES... SUNDAY NIGHT-MONDAY... HIGH PRESSURE OFFSHORE BRINGS MOSTLY CLEAR SKIES AND LIGHT WIND. DEVELOPING SOUTHWEST WIND WILL ALSO BRING MILDER AIR AND DEW POINTS. SUNDAY NIGHT DEW POINTS WILL BE IN THE 40S WITH LIGHT WIND...SO MIN TEMPS WILL BE IN THE 40S AND LOWER 50S. SUNSHINE AND SOUTHWEST FLOW WILL BRING WARM TEMPS MOST PLACES MONDAY. EXPECT COOLER TEMPS ALONG THE SOUTH COAST AND ON CAPE ANN WHERE THE FLOW WILL BE OFF THE WATER. TEMPS AT 850 MB WILL BE AROUND 10C AT 2 PM AND 11-12C BY EVENING. FULL MIXING OF THIS SHOULD BRING MAX SFC TEMPS OF 77-81 AWAY FROM THE MARINE INFLUENCE. TUESDAY...UPPER SHORTWAVE SQUEEZES PAST THE UPPER RIDGE AND MOVES ACROSS NORTHERN NEW ENGLAND. WHILE MUCH OF THE DYNAMIC SUPPORT WILL BE NORTH OF OUR AREA...THIS WILL PUSH A COLD FRONT ACROSS SOUTHERN NEW ENGLAND GENERATING LOW LEVEL CONVERGENCE. THE AIRMASS WILL DESTABILIZE WITH DAYTIME HEATING. TOTALS WILL BE 45-50 WITH LI/S 0- 1. THE GFS SHOWS A CAPE OF 1000-1200 J/KG OVER CT-RI MID AFTERNOON. THE AIRMASS WILL BE MOIST WITH PRECIPITABLE WATER VALUES REACHING 1.4 INCHES WHICH IS ABOUT 2 STD DEVIATIONS ABOVE NORMAL. WE WILL MENTION CHANCE POPS FOR SHOWERS AND SLIGHT CHANCE OF THUNDER. TEMPS ALOFT WILL BE 8-9C...SO WILL FORECAST MAX SFC TEMPS IN THE 70S INLAND AND 60S ALONG THE SOUTH COAST. WEDNESDAY-THURSDAY-FRIDAY...HIGH PRESSURE BUILDS OVER THE REGION. WITH DRY WEATHER FOR THE LATTER PART OF THE WEEK. TEMPS ALOFT SUGGEST MAINLY 70S. BUT NORTHWEST FLOW ALOFT AND LIGHT FLOW AT THE SURFACE SUGGEST EITHER A SEA BREEZE IN EASTERN MASS OR A BACKDOOR COLD FRONT. THE ECMWF DOES SHOW A NORTHERN STREAM JET ACCOMPANYING A SHORTWAVE ACROSS MAINE AND THE MARITIMES WEDNESDAY-THURSDAY. THIS COULD PUSH A BACKDOOR FRONT INTO AT LEAST EASTERN MASS/RI. IT IS POSSIBLE TEMPERATURES IN EASTERN MASS WILL BE A FEW DEGREES COOLER THAN FORECAST. && .AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
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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 SUNDAY/... THROUGH TONIGHT...HIGH CONFIDENCE. IFR CIGS ALONG/EAST OF A ASH-WST LINE WILL BREAK BY 14Z EXCEPT ON THE CAPE AND ISLANDS WHERE THE CLOUDS COULD TAKE UNTIL 15-16Z. PATCHY IFR VSBYS IN FOG SHOULD QUICLY IMPROVE TO VFR THIS MORNING. VFR THROUGH THE PERIOD ELSEWHERE. E-SE WINDS TURN MAINLY S OVERNIGHT TONIGHT. SUN...HIGH CONFIDENCE. MAINLY VFR. OCCASIONAL -SHRA OR EVEN AN ISOLATED TSRA POSSIBLE ESPECIALLY ERN MA. KBOS TAF...HIGH CONFIDENCE IN TAF. MAY BE A BRIEF DIP TO LOW MVFR/IFR THIS MORNING AS THERE WILL BE A LOW CIG DECK JUST E OF THE AIRPORT. SEA BREEZES EXPECTED BOTH TODAY AND TOMORROW. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY...MODERATE CONFIDENCE. SUNDAY NIGHT AND MONDAY...VFR. PATCHY MVFR IN FOG EARLY MONDAY MORNING. SOUTHWEST WINDS GUSTING 15-20 KNOTS LATE MORNING AND AFTERNOON. TUESDAY...VFR. PERIOD OF MVFR CIGS/VSBYS POSSIBLE IN SHOWERS AS A COLD FRONT MOVES NORTH-SOUTH ACROSS THE REGION. WIDELY SCATTERED THUNDERSTORMS POSSIBLE WITH THE FRONT. WINDS SHIFT FROM SOUTHWEST TO NORTHWEST WITH THE FRONTAL PASSAGE. WEDNESDAY...VFR.
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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 SUNDAY/... CONDITIONS REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS AS HIGH PRES SLOWLY MOVES OVER THE WATER THIS WEEKEND. E-NE FLOW WILL SHIFT MAINLY TO THE S LATE TONIGHT INTO TOMORROW. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY...MODERATE CONFIDENCE. SUNDAY NIGHT-MONDAY...SOUTHWEST WINDS GUSTING TO 20 KNOTS. SEAS BELOW 5 FEET. NO HEADLINES EXPECTED. TUESDAY...A COLD FRONT MOVES ACROSS THE WATERS WITH SHOWERS. WINDS SHIFT WITH THE FRONTAL PASSAGE. SEAS 5-6 FEET ON THE OUTER WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR THE OUTER WATERS. WEDNESDAY...WINDS AND SEAS WILL BE BELOW SMALL CRAFT LEVELS. && .FIRE WEATHER...
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THE BIGGEST FIRE WEATHER CONCERN IS FOR MONDAY. MINIMUM AFTERNOON RELATIVE HUMIDITY VALUES DROPPING TO 30-35 PERCENT WITH AFTERNOON WIND GUSTS OF 20 TO PERHAPS 25 MPH. APPEARS JUST BELOW CRITERIA FOR ANY FIRE WEATHER HEADLINES...BUT WILL CONTINUE TO MONITOR SINCE ITS BEEN SO DRY OF LATE.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/DOODY NEAR TERM...WTB/DOODY SHORT TERM...DOODY LONG TERM...WTB AVIATION...WTB/DOODY MARINE...WTB/DOODY FIRE WEATHER...

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