Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220241 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1041 PM EDT TUE APR 21 2015 .SYNOPSIS... A COLD FRONT WILL BRING A ROUND OF SCATTERED TO NUMEROUS SHOWERS...AND PERHAPS A FEW THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING. UNSEASONABLY COOL WEATHER FOLLOWS THURSDAY THROUGH THIS WEEKEND WITH SPOTTY SHOWERS FROM TIME TO TIME. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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1040 PM UPDATE... NO MAJOR CHANGES TO THE FORECAST REQUIRED THIS EVENING. DID TWEAK FORECAST THROUGH DAYBREAK TO REFLECT LATEST OBSERVED TRENDS. STILL WATCHING ISOLATED SHOWERS TO OUR WEST. THESE SHOWERS WERE JUST STARTING TO GRAZE PORTIONS OF NORTHWEST MASSACHUSETTS. SO FAR... DO NOT HAVE RELIABLE REPORTS OF MEASURABLE RAINFALL. BASED ON RADAR REFLECTIVITY...THESE SHOWERS ARE MAINLY VERY LIGHT TO THIS POINT. OF COURSE THIS COULD CHANGE OVER THE NEXT FEW HOURS. PREVIOUS DISCUSSION... A SHORTWAVE MOVES ACROSS THE REGION OVERNIGHT. HOWEVER...MOISTURE AND INSTABILITY IS QUITE LIMITED IN THE WAKE OF TODAY/S COLD FRONTAL PASSAGE. THEREFORE MAINLY DRY WEATHER EXPECTED...BUT CAN/T RULE OUT A LOW RISK OF AN ISOLATED SPOT SHOWER. OTHERWISE...SKIES SHOULD BE PARTLY CLOUDY WITH LOW TEMPS MAINLY IN THE 40S...WITH SOME MIDDLE TO UPPER 30S POSSIBLE ACROSS THE NORMALLY COOLEST OUTLYING LOCATIONS...ESPECIALLY IN NORTHWEST MA.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... ***HIGH CONFIDENCE IN SCATTERED TO NUMEROUS SHOWERS WED AFTERNOON/EVENING*** ***LOW CONFIDENCE ON WHETHER WE SEE ANY THUNDER/SMALL HAIL/GUSTY WINDS WED AFTERNOON/EVENING*** WEDNESDAY AND WEDNESDAY NIGHT... WHILE A FEW SHOWERS ARE POSSIBLE WEDNESDAY MORNING...MUCH OF THE MORNING PROBABLY ENDS UP DRY AS FORCING WILL STILL BE TO OUR WEST. THINGS GET A BIT MORE INTERESTING WEDNESDAY AFTERNOON AND EVENING AS A POTENT SHORTWAVE/COLD FRONT APPROACH THE REGION. HIGH CONFIDENCE THAT SCATTERED TO NUMEROUS SHOWERS DEVELOP WEDNESDAY AFTERNOON AND CONTINUE INTO THE EVENING. IN FACT...FEEL MOST LOCATIONS WILL SEE A PERIOD OF RAIN SHOWERS SO WILL CONTINUE WITH LIKELY POPS. THE BIGGEST UNCERTAINTY IS WHETHER OR NOT WILL BE ABLE TO MUSTER ENOUGH INSTABILITY FOR ANY THUNDER/SMALL HAIL OR GUSTY WINDS. ITS QUITE COLD ALOFT WITH VERY STEEP MID LEVEL LAPSE RATES ON THE ORDER OF 7 TO 8 C/KM. WIND FIELDS ALOFT ARE QUITE IMPRESSIVE AS WELL. HOWEVER...THERE IS ONE BIG AND KEY INGREDIENT MISSING WHICH IS INSTABILITY. IF WE CAN MANAGE A FEW HUNDRED J/KG OF CAPE IT MIGHT BE ENOUGH TO RESULT IN ISOLATED THUNDERSTORMS. GIVEN COLD AIR ALOFT WOULD NOT BE SURPRISED TO SEE SOME GRAUPEL/SMALL HAIL AND GUSTY WINDS WITH HEAVIER SHOWERS EVEN IF WE DO NOT END UP SEEING THUNDER. ALSO COULD END UP WITH JUST RAIN SHOWERS...GIVEN VERY MARGINAL SETUP. FOR NOW WE WENT WITH A SLIGHT CHANCE OF THUNDER WITH THE RISK OF SMALL HAIL/GUSTY WINDS IN THE FORECAST. REGARDLESS...DOES NOT LOOK LIKE WILL HAVE ENOUGH INSTABILITY FOR SEVERE WEATHER. BULK OF THE ACTIVITY SHOULD END WEDNESDAY EVENING...BUT A FEW SHOWERS MAY LINGER AFTER MIDNIGHT GIVEN STRONG SHORTWAVE. AS FOR TEMPERATURES...IT WILL BE BREEZY WEDNESDAY AFTERNOON BUT HIGHS SHOULD REACH FROM NEAR 60 ACROSS THE HIGHER TERRAIN TO MAINLY LOWER TO MIDDLE 60S ELSEWHERE. && .LONG TERM /THURSDAY THROUGH TUESDAY/...
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HIGHLIGHTS... * UNSEASONABLY COOL THU-SUN WITH WIDELY SCATTERED SHOWERS AT TIMES * UNCERTAINTY IN OVERALL WEATHER PATTERN EARLY NEXT WEEK OVERVIEW AND MODEL PREFERENCES... 12Z MODEL SUITE AND ENSEMBLES CONTINUE TO SIGNAL COOLER THAN NORMAL TEMPERATURES THROUGH THIS TIMEFRAME. BLOCKING PATTERN ACROSS THE LOWER 48 SEEN...WITH CUTOFF H5 LOW PRESSURE ACROSS THE NORTHEASTERN U.S. AS WELL AS NEAR OR JUST OFF THE PACIFIC NW COAST. WITH COLD POOL OVERHEAD THROUGH THIS WEEKEND...LOOKS LIKE THERE WILL BE SPOTTY SHOWERS MAINLY DURING THE DAYLIGHT INTO THE EARLY EVENING HOURS EACH DAY. PINNING DOWN LOCATIONS OF ANY PRECIP WILL BE TOUGH THOUGH DUE TO TRACK OF ANY SHORT WAVE THAT MOVES ALONG IN THE UPPER W-NW FLOW. MODELS TRY TO SLOWLY PUSH THE UPPER LOW E TOWARD THE MARITIMES AROUND THE LATE SUN OR MON TIMEFRAME...BUT MODEL TIMING IS IN QUESTION. USED A BLEND OF AVAILABLE GUIDANCE FOR THIS FORECAST...WHICH SHOWED GOOD CONTINUITY WITH THE PREVIOUS FORECAST. DETAILS... THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE. THE COMBINATION OF THE COLD POOL SITTING ACROSS THE REGION...ANY WEAK SHORT WAVES THAT MOVE AROUND THE BASE OF THE UPPER LOW TO THE N AS WELL AS DIURNAL HEATING ALLOWING FOR INCREASING LAPSE LOW LEVEL LAPSE RATES...SCT SHOWERS SHOULD DEVELOP MAINLY IN THE LATE MORNING THROUGH THE EVENING HOURS ON MOST DAYS THROUGH THIS WEEKEND. WHILE THERE IS A DECENT SHOT OF SHOWER DEVELOPMENT...A LOT OF QUESTIONS WHERE THE LIGHT RAIN WILL FALL. LOOKS LIKE BEST SHOT OF PRECIP WILL BE BOTH THU AND FRI ESPECIALLY AWAY FROM THE COAST. SOME QUESTION AS TO WHETHER THE UPPER LOW WILL START TO MIGRATE E LATE SUN OR SUN NIGHT. TIMING IS STILL IN QUESTION...BUT HAVE LOWERED POPS THOUGH DID KEEP SLIGHT CHANCE GOING MAINLY NEAR AND N OF THE MASS PIKE. TEMPS WILL CONTINUE TO RUN ON THE COLD SIDE...ON THE ORDER OF 5 TO 10 DEGREES BELOW SEASONAL NORMS FOR LATE APRIL. HIGHS WILL MAINLY BE IN THE 50S...WITH A FEW UPPER 40S SEEN ACROSS THE HIGHER INLAND TERRAIN. MONDAY-TUESDAY...LOW CONFIDENCE. WIDE VARIANCE WITH MODEL SOLUTIONS AS WELL AS THE ENSEMBLES ON TIMING THE UPPER LOW FAR ENOUGH TO THE E TO BRING DRIER CONDITIONS. IT DOES LOOK LIKE...FOR NOW...WILL SEE A MAINLY DRY DAY ON MONDAY BUT STILL CAN NOT RULE OUT A STRAY SHOWER OR TWO MAINLY ACROSS N MA. AS FOR TUESDAY...A LOT OF QUESTIONS AS TO WHETHER ANOTHER CUTOFF UPPER LOW MAY WORK INTO THE SE U.S...THEN MAY TRY TO WORK NE. MODELS HAVING A LOT OF TROUBLE TRACKING THIS SYSTEM SO VERY LOW CONFIDENCE DURING THIS TIMEFRAME.
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&& .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH WEDNESDAY NIGHT/... OVERNIGHT...HIGH CONFIDENCE. MAINLY VFR CONDITIONS. WEDNESDAY AND WEDNESDAY NIGHT...HIGH CONFIDENCE THAT VFR CONDITIONS DOMINATE. HOWEVER...A COLD FRONT WILL BRING A BAND OF SCATTERED TO NUMEROUS SHOWERS WEDNESDAY AFTERNOON INTO WEDNESDAY EVENING RESULTING IN BRIEFLY LOWER CIGS/VSBYS. A FEW ISOLATED THUNDERSTORMS CAN NOT BE RULED OUT...WHICH MAY CONTAIN LOCALIZED GUSTY WINDS/SMALL HAIL GRAUPEL BUT CONFIDENCE IN THAT IS LOW. KBOS TAF...HIGH CONFIDENCE IN MAINLY VFR THROUGH WEDNESDAY MORNING. KBDL TAF...HIGH CONFIDENCE IN MAINLY VFR THROUGH WEDNESDAY MORNING. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY THROUGH SATURDAY...HIGH CONFIDENCE. MAINLY VFR. CONDITIONS MAY LOWER TO MVFR QUICKLY IN A BRIEF DIURNALLY DRIVEN WIDELY SCT SHOWERS MAINLY DURING THE LATE MORNING INTO THE EVENING HOURS EACH DAY. SUNDAY...HIGH CONFIDENCE. MAINLY VFR. MAY SEE A BRIEF SHOWER OR TWO ACROSS NORTHERN AND EASTERN MA DURING THE MIDDAY AND AFTERNOON HOURS. LOW PROB OF BRIEF MVFR CONDITIONS IN ANY SHOWERS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... TONIGHT THROUGH WEDNESDAY NIGHT...MODERATE TO HIGH CONFIDENCE. LEFT OVER SOUTHEAST SWELL WILL CONTINUE TO GENERATE SMALL CRAFT SEAS ACROSS MOST OF OUR OPEN WATERS INTO WED NIGHT. WILL ALSO HOIST A NEAR SHORE SMALL CRAFT ADVISORY LATE WEDNESDAY MORNING AND AFTERNOON. BUFKIT SUPPORTS NEAR SHORE SOUTHWEST 25 TO 30 KNOT WIND GUSTS WEDNESDAY AFTERNOON WITH GOOD MIXING AHEAD OF AN APPROACHING COLD FRONT. THE OTHER CONCERN WILL BE FOR A BAND OF SHOWERS LATE WEDNESDAY AFTERNOON AND NIGHT. IF ENOUGH INSTABILITY CAN BE REALIZED...A FEW OF THE HEAVIER SHOWERS MAY CONTAIN GUSTY WINDS/SMALL HAIL. LOW RISK OF A FEW THUNDERSTORMS AS WELL. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY THROUGH SATURDAY...HIGH CONFIDENCE. EXPECT W WINDS TO GUST UP TO 25-30 KT THROUGH MOST OF THE PERIOD MAINLY OVER THE OPEN WATERS. SEAS ON THE OUTER WATERS UP TO 5-7 FT THROUGH THE DAYLIGHT HOURS SAT. WINDS AND SEAS SHOULD DIMINISH SAT NIGHT. GENERALLY GOOD VSBYS. SUNDAY...HIGH CONFIDENCE. W WINDS DIMINISH BELOW SMALL CRAFT CRITERIA AS WEAK HIGH PRES BUILDS ACROSS. SEAS BELOW 5 FT. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 7 PM EDT WEDNESDAY FOR ANZ230>234-236. SMALL CRAFT ADVISORY UNTIL 8 AM EDT THURSDAY FOR ANZ235-237- 250-254>256. SMALL CRAFT ADVISORY UNTIL 3 AM EDT THURSDAY FOR ANZ251. && $$ SYNOPSIS...FRANK/EVT NEAR TERM...BELK/FRANK/EVT SHORT TERM...FRANK LONG TERM...EVT AVIATION...FRANK/EVT MARINE...FRANK/EVT

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