Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 151545 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1145 AM EDT WED APR 15 2015 .SYNOPSIS... HIGH PRESSURE TODAY PROVIDES DRY WEATHER AND WARMER THAN NORMAL TEMPERATURES. DRY BUT SEASONABLY COOL WEATHER FOLLOWS THURSDAY. HIGH PRESSURE MOVES OFFSHORE FRIDAY WITH A PERIOD OF RAIN POSSIBLE. A COLD FRONT CROSSES THE AREA LATE SATURDAY. WEAK HIGH PRESSURE FOLLOWS SUNDAY. LOW PRESSURE APPROACHES EARLY NEXT WEEK WITH THE THREAT OF WIDESPREAD RAIN LATER MARATHON MONDAY INTO TUESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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11 AM UPDATE... OTHER THAN BANDS OF HIGH CLOUDS PASSING ACROSS N CT/RI/SE MA...SKIES WERE MAINLY CLEAR AT 15Z. TEMPS HAVE ALSO RECOVERED QUICKLY AFTER LOWS IN THE UPPER 20S AND 30S /EXCEPT 40-45 IN THE URBAN CENTERS/ TO THE LOWER-MID 60S AWAY FROM THE IMMEDIATE E COAST...CAPE COD AND THE ISLANDS. N-NE WINDS HAVE BEEN INCREASING THROUGH THE MORNING AND...WITH GOOD MIXING THROUGH 900 HPA AS NOTED ON THIS MORNING/S SOUNDINGS FROM KALY...KOKX AND KBOX...GUSTS TO AROUND 20 KT HAVE BEEN NOTED ACROSS CENTRAL AND WESTERN AREAS. CONDITIONS STILL REMAIN MARGINAL FOR FIRE WEATHER ISSUES...THOUGH DEWPTS OVER THE LAST FEW HOURS WERE LOWER THAN FORECAST. THE BIG QUESTION REMAINS WHETHER WINDS WILL REACH 25 KT CRITERIA. PLEASE SEE DETAILS ON FIRE WEATHER ISSUES BELOW. HAVE UPDATED NEAR TERM FORECAST TO BRING CONDITIONS CURRENT AND INCORPORATED TRENDS INTO REMAINDER OF THIS AFTERNOON/S FORECAST. ================================================================= FOCUS IS UPON THE FIRE WEATHER ENVIRONMENT. WILL SEE A DRY AIRMASS DROP S OUT OF CANADA WHICH YESTERDAY WAS ASSOCIATED WITH DEWPOINTS AROUND 20 DEGREES AND WIND GUSTS RANGING 25 TO 30 MPH. YET WITH THE PRESSURE GRADIENT RELAXING...NORTHERLY WINDS ADVECTING THE DRY AIRMASS SOUTH ARE NOT EXPECTED TO BE AS ROBUST. H925 SUSTAINED WINDS OF AROUND 30 KTS YESTERDAY DROP TO 20 KTS. SO EVEN THOUGH THE FORECAST RELATIVE HUMIDITY IS AT OR BELOW 30 PERCENT WITH HIGHS IN AROUND THE MID TO UPPER 60S WITH DEWPOINTS AROUND THE LOW-20S...WINDS ARE FORECAST TO BE MARGINAL WITH GUSTS AROUND 15 TO 20 MPH. BUT WITH A CONSENSUS OF THE FORECAST GUIDANCE HAVING 30 MPH N-WINDS AT THE TOP OF THE WELL-MIXED LAYER UP TO H8 CAN NOT RULE OUT 25 MPH GUSTS AT THE SURFACE...ESPECIALLY AS FOR MUCH OF THE MONTH OF APRIL MODEL WIND GUST FORECASTS HAVE BEEN UNDERDONE. SO CONFIDENCE IS THAT WE WILL SEE WIND GUSTS OF AROUND 25 MPH. HIGH CONFIDENCE WE WILL SEE THE DRY CONDITIONS. UPSTREAM DEWPOINTS DOWN TO 10-DEGREES WERE OBSERVED ACROSS S CANADA WITH TEMPERATURES NEAR 60-DEGREES. SO IN SHORT...THE COMBINATION OF MIX-DOWN OF FASTER MOMENTUM AND DRIER AIR TO THE SURFACE WILL RESULT IN CONDITIONS IN WHERE RELATIVE HUMIDITY WILL BE LESS THAN 30 PERCENT...AROUND 15 TO 20 PERCENT IN FACT /IMPROVING ALONG THE SHORES INTO THE AFTERNOON HOURS WITH ONSHORE WIND/...AND WIND GUSTS OF AROUND 25 MPH. PER COORDINATION WITH STATE FIRE WEATHER FOCAL POINTS...A RED FLAG WARNING HAS BEEN ISSUED FOR ALL OF MASSACHUSETTS EXCEPT NANTUCKET...WHILE FOR CT AND RI...WEATHER CONDITIONS MAY WARRANT A RED FLAG WARNING WHICH IS NOTED IN THE HAZARDOUS WEATHER OUTLOOK. FOR FURTHER DETAILS...PLEASE SEE THE FIRE WEATHER DISCUSSION BELOW.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... TONIGHT... WINDS RELAX AS HIGH PRESSURE BUILDS INTO THE REGION. EXPECTING LIGHT AND VARIABLE WINDS UNDER MOSTLY CLEAR CONDITIONS. SHOULD SEE DECENT RADIATIONAL COOLING AND THUS HAVE GONE WITH A CONSENSUS BLEND OF MOS GUIDANCE...DROPPING IT A COUPLE OF DEGREES ESPECIALLY IN SUSCEPTIBLE LOW-LYING AREAS PRONE TO RADIATIONAL COOLING. FROST AND FREEZE HEADLINES ARE NOT NECESSARY AT THIS TIME AS THE GROWING SEASON DOES NOT BEGIN TILL APRIL 21ST FOR LOW- LYING COASTAL AREAS. THURSDAY... HIGH PRESSURE PUSHES E ALLOWING FOR RETURN S-FLOW. MOSTLY CLEAR FORECAST WITH LOW DEWPOINTS AS TEMPERATURES WARM TO THE 60-DEGREE MARK. CONTINUED BOUNDARY-LAYER MIXING ALBEIT LIMITED TO H9 BY A DRY-AIR INVERSION. INFLUENCE OF HIGH PRESSURE SHOULD KEEP WINDS BELOW THE 25 MPH THRESHOLD...CAN NOT RULE OUT GUSTS UP TO 20 MPH WITH THE MIX-DOWN OF FASTER MOMENTUM AND DRIER AIR. WILL NEED TO RE-EVALUATE WITH THE NEXT FORECAST PERIOD WITH RESPECT TO THE FIRE WEATHER ENVIRONMENT. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... SYNOPTIC OVERVIEW... CLOSED LOW OVER THE FOUR CORNERS REGION SUPPORTS SPLIT FLOW ACROSS THE CONUS INTO EARLY THIS WEEKEND. THIS CLOSED LOW EJECTS SEVERAL PACKETS OF SOUTHERN STREAM MOISTURE NORTHEASTWARD INTO NEW ENGLAND WITH THE FIRST MOISTURE PLUME ARRIVING FRI. THE NEXT PACKET OF JET ENERGY AND MOISTURE TARGET SNE EARLY NEXT WEEK. THIS 2ND PRECIP EVENT MAY BE MORE WIDESPREAD AND ASSOCIATED WITH APPRECIABLE QPF AS STREAMS MERGE AND FORMS A COASTAL LOW. MEANWHILE THE NORTHERN STREAM UNDERGOES SOME AMPLIFICATION AS TROUGHING DEVELOPS VICINITY OF ALASKA WITH DOWNSTREAM RIDGING INTO WESTERN CANADA. THIS RESULTS IN A MODEST SURGE OF COOL AIR INTO THE NORTHEAST SAT NIGHT AND SUN MORNING BEHIND A DEPARTING NORTHERN STREAM SHORT WAVE TROUGH/COLD FRONT. MODEL/GUIDANCE EVALUATION... FIRST ITEM OF CONCERN ARE POPS AND QPF FOR FRI. 00Z GFS IS MOST BULLISH WITH QPF. MEANWHILE ALL OTHER GUIDANCE HAS LIGHTER AMOUNTS ALONG WITH PRECIP BECOMING FRAGMENTED ESPECIALLY EASTWARD WHICH SEEMS REASONABLE AS PRECIP ENTERS CONFLUENT FLOW ALOFT OVER NEW ENGLAND. GEFS POPS FOR 0.05 QPF CAPTURES THIS NICELY WITH POPS DIMINISHING FROM WEST TO EAST FRI. THUS WILL FOLLOW A NON GFS SOLUTION HERE YIELDING LESS QPF. NEXT ISSUE IS TIMING OF PRECIP FOR MARATHON MONDAY. DETERMINISTIC 00Z GFS AND 00Z ECMWF ALONG WITH GEFS ENSEMBLES IN GOOD AGREEMENT FOR DRY WEATHER MON MORNING WITH INCREASING CHANCES FOR RAIN IN THE AFTERNOON AND BEYOND. GIVEN GOOD MODEL AGREEMENT WILL FOLLOW THIS TIMELINE. DAILY SENSIBLE WEATHER... THU NIGHT...MILD NIGHT AS RETURN FLOW ADVECTS DEW PTS NEAR 50 ACROSS THE REGION. ANY RAIN SHOULD HOLD OFF TIL VERY LATE AT NIGHT OR FRI MORNING. FRIDAY...HIGH CERTAINTY FOR SCATTERED SHOWERS BUT STILL SOME UNCERTAINTY REGARDING HOW WIDESPREAD AND ASSOCIATED QPF. DOESN/T APPEAR AS A WASHOUT GIVEN FAST FLOW ALOFT MAY YIELD RAIN ENDING IN THE AFTERNOON WITH PARTIAL CLEARING POSSIBLE. SATURDAY...MILD START AND WARM ADVECTION AHEAD OF APPROACHING SHORT WAVE AND ATTENDING COLD FRONT SHOULD SUPPORT A WARM AFTERNOON WITH HIGHS IN THE U60S TO L70S. LEANED TOWARD THE WARMER MOS TEMPS COMPARED TO COOLER MODEL BLEND TEMPS. SOME UNCERTAINTY REGARDING POTENTIAL FOR AFTERNOON AND EVENING SHOWERS. BEST INSTABILITY /STEEPENING LAPSE RATES/ AND FORCING FOR ASCENT APPEARS ACROSS NORTHERN AND EASTERN MA. THUS HIGHEST POPS ACROSS THIS REGION. SUNDAY...COOLER AND DRY BEHIND DEPARTING SHORT WAVE AND ATTENDING COLD FRONT. ALTHOUGH SEASONABLY MILD WITH HIGHS U50S TO L60S...FEW DEGS ABOVE NORMAL. EARLY NEXT WEEK INCLUDING MARATHON MONDAY...FAIRLY HIGH CONFIDENCE IN WIDESPREAD RAIN SOMETIME LATER MONDAY INTO MONDAY NIGHT AND AT LEAST EARLY TUE. RAIN COULD BE WIDESPREAD IN AREAL COVERAGE ALONG WITH APPRECIABLE RAINFALL GIVEN GULF MOISTURE...STREAMS MERGING RESULTING IN A COASTAL LOW TRACKING NEAR OR OVER SOUTHERN NEW ENGLAND. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
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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 THURSDAY/...HIGH CONFIDENCE. 12Z UPDATE... NOT MUCH CHANGE TO 06Z TAFS. EARLIER DISCUSSION BELOW. ============================================================== VFR. N WINDS GUSTING UP TO 25 KTS. WILL SEE AN ONSHORE NE FLOW EMERGE TOWARDS MIDDAY AND LINGER INTO EVENING FOR COASTAL TERMINALS TODAY. LIGHT / VARIABLE FLOW OVERNIGHT FOLLOWED BY RETURN S-FLOW INTO THURSDAY AS HIGH-CLOUDS INCREASE OUT OF THE W. KBOS TAF...HIGH CONFIDENCE IN TAF. THINKING NE-ONSHORE FLOW DEVELOPS AROUND 15Z. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY... THURSDAY NIGHT...HIGH CONFIDENCE FOR VFR FRIDAY...MODERATE CONFIDENCE. MAINLY VFR BUT WITH PERIODS OF MVFR IN SCATTERED RAIN SHOWERS. SATURDAY...MOST LIKELY VFR WITH A MODEST WEST WIND BECOMING NORTHWEST. SUNDAY...MOST LIKELY VFR ALONG WITH DIMINISHING WINDS.
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&& .MARINE...
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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 THURSDAY/...HIGH CONFIDENCE. THIS AFTERNOON...EXPECT N-NE WINDS GUSTING UP TO 25 KT. SEAS REMAIN BELOW 5 FT...BUT MAY POSSIBLY SEE BRIEF SWELLS UP TO 5 FT ACROSS THE FAR SOUTHERN OUTER WATERS. TONIGHT AND THURSDAY...LIGHT AND VARIABLE WINDS OVERNIGHT AS HIGH PRES MOVES ACROSS THE WATERS...THEN SHIFTS E ON THURSDAY ALLOWS FOR RETURN S FLOW THAT BECOMES BRISK WITH GUSTS UP TO 20 KTS TOWARDS THE END OF THE DAY. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY... THURSDAY NIGHT AND FRIDAY...MODEST WSW WINDS AS HIGH PRES SLIPS SOUTH OF NEW ENGLAND. STRONGEST WINDS NORTHERN WATERS AND NEAR SHORE. VSBY MAY LOWER AT TIMES IN PERIODS OF RAIN. SATURDAY...LOW PRES MOVING ACROSS EASTERN QUEBEC INTO NEW BRUNSWICK WILL YIELD A MODEST WSW WIND ACROSS THE WATERS. COLD FRONTAL PASSAGE LATE SAT YIELDS A WIND SHIFT TO THE WNW WITH MODEST WIND GUSTS. SUNDAY...DIMINISHING WIND AND SEAS AS HIGH PRES CREST OVER NEW ENGLAND AND NEARBY COASTAL WATERS. DRY WEATHER RESULTS IN GOOD VSBY.
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&& .FIRE WEATHER...
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11 AM UPDATE... DEWPTS HAVE DROPPED BELOW FORECASTED VALUES AS N-NE WINDS INCREASED TO 10-15 KT ACROSS A GOOD PORTION OF THE REGION BY LATE THIS MORNING. INCORPORATED THESE DOWNWARD TRENDS INTO THIS AFTERNOON/S FORECAST...AND NOTED MINIMUM RELATIVE HUMIDITIES DOWN TO 15-25 PERCENT FOR MOST AREAS EXCEPT HIGHER ACROSS THE MID AND OUTER CAPE AND NANTUCKET. AFTER COLLABORATION WITH STATE FIRE WEATHER OFFICIALS AT MID MORNING...CONTINUED THE RED FLAG WARNING FOR MOST OF MASSACHUSETTS /EXCEPT NANTUCKET/ WHILE KEEPING IT DOWN FOR N CT AND RI. KEPT MENTION OF ELEVATED FIRE WEATHER POTENTIAL FOR THOSE AREAS IN THE HAZARDOUS WEATHER OUTLOOK. PREVIOUS DISCUSSION... A LACK OF RAIN COMBINED WITH DRY CONDITIONS ACROSS THE REGION HAS ALLOWED SMALL FINE FUEL FIRES TO IGNITE THE PAST FEW DAYS. WILL SEE WEATHER CONDITIONS TODAY THAT ONLY EXACERBATE THE ISSUE. DRY AIR AND BREEZY NORTH WINDS ASSOCIATED WITH HIGH PRESSURE BUILDING SOUTH OUT OF CANADA WILL RESULT IN MINIMUM RELATIVE HUMIDITIES ACROSS THE REGION OF AROUND 10 TO 20 PERCENT AS NORTHERLY WINDS GUST 20 TO 25 MPH FROM MID-MORNING INTO THE EVENING HOURS TODAY. WILL CONTINUE TO MONITOR CONDITIONS AND UPDATE HEADLINES AS CONDITIONS WARRANT.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...RED FLAG WARNING UNTIL 7 PM EDT THIS EVENING FOR MAZ002>023- 026. RI...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...NOCERA/EVT SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL/EVT FIRE WEATHER...EVT/DUNTEN

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