Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 151033 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 633 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/... 630 AM UPDATE... ONLY CHANGE TO PREVIOUS FORECAST WAS TO ADJUST HOURLY TEMPS AND DEW PTS TO BETTER REFLECT CURRENT CONDITIONS. LARGE VARIATION IN TEMPERATURES ACROSS THE AREA THIS MORNING WITH LOCATIONS LACKING WIND HAVING TEMPS IN THE 30S AND EVEN A FEW U20S. WHERE LIGHT NW WINDS EXIST TEMPS ARE IN THE 40S TO NEAR 50! THUS COOLER LOCATIONS WILL WARM UP QUICKLY WITHIN THE NEXT FEW HOURS AS COOL AIR IS VERY SHALLOW. GORGEOUS DAY COMING UP WITH TEMPS RISING WELL INTO THE 60S ALONG WITH LOW HUMIDITY AND A NNW BREEZE. COOLER ALONG THE EASTERN MA COASTLINE AS WINDS MAY TURN TO THE NORTHEAST THIS AFTERNOON. EARLIER DISCUSSION BELOW. ================================================================= 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. && .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 /12Z WEDNESDAY THROUGH SUNDAY/... 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. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY/...HIGH CONFIDENCE. NE-WINDS GUSTING UP TO 20 KTS THROUGH THE DAY WILL GENERATE SEAS OF AROUND 3-4 FEET. CAN NOT RULE OUT THE POTENTIAL FOR 5-FOOT SWELL AND AS SUCH WILL CONTINUE WITH THE SMALL-CRAFT ADVISORY FOR HAZARDOUS SEAS WITH EXTENSION TO ANZ254. LIGHT AND VARIABLE WINDS FOLLOW FOR THE OVERNIGHT PERIOD BENEATH HIGH PRESSURE. SHIFTING TO THE 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. && .FIRE WEATHER... 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 AND WARRANT THE ISSUANCE OF A RED FLAG WARNING FOR PORTIONS OF THE FORECAST AREA PER COLLABORATION AMONG STATE FIRE WEATHER FOCAL POINTS...AN ACKNOWLEDGEMENT OF ELEVATED FIRE WEATHER POTENTIAL FOR OTHERS WITHIN THE HAZARDOUS WEATHER OUTLOOK. 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 SHOULD THE WEATHER AND/OR FORECAST CHANGE...WILL UPDATE HEADLINES AS NECESSARY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...RED FLAG WARNING FROM 11 AM THIS MORNING TO 7 PM EDT THIS EVENING FOR MAZ002>023-026. RI...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM THIS AFTERNOON TO 11 PM EDT THIS EVENING FOR ANZ254>256. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...NOCERA/SIPPRELL SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL FIRE WEATHER...SIPPRELL

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