Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 171121 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 721 AM EDT WED SEP 17 2014 .SYNOPSIS... HIGH PRESSURE WILL BUILD INTO THE REGION BRINGING COOLER AND DRIER WEATHER THROUGH THE REMAINDER OF THE WEEK. SOME FROST IS POSSIBLE EARLY FRIDAY MORNING IN SOME AREAS. THE HIGH WILL THEN SLIP OFFSHORE AND SOUTHWEST FLOW BEHIND IT WILL ALLOW TEMPERATURES TO WARM TO NEAR OR ABOVE NORMAL SUNDAY AND MONDAY. A COLD FRONT MOVES THROUGH ON MONDAY...FOLLOWED BY COOLER WEATHER BY TUESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM UPDATE... ASIDE FROM A FEW REMAINING PATCHES OF FOG ACROSS THE REGION...MAINLY SKC CONDITIONS AWAY FROM THE S COAST...WHERE SOME CI FROM AN OFFSHORE SYSTEM MOVE THROUGH. THEREFORE...PLENTY OF SUNSHINE TO GO AROUND...WHICH WILL LEAD TO A RAPID INCREASE IN TEMPS THIS MORNING EVEN AFTER THE COOL START. CURRENT FORECAST STILL REFLECTS THESE TRENDS NICELY...SO NO MAJOR CHANGES NEEDED WITH THIS UPDATE. PREVIOUS DISCUSSION... CALM WINDS...CLEAR SKIES...AND A BIT OF LEFTOVER MOISTURE FROM THE SCATTERED RAIN SHOWERS YESTERDAY HAS ALLOWED PATCHY FOG TO DEVELOP ACROSS THE REGION. THIS FOG IS LOCALLY DENSE...REDUCING VISIBILITIES BELOW A MILE IN MANY LOCATIONS AND BELOW A QUARTER OF A MILE IN SOME AREAS. HIGH PRESSURE BUILDS INTO THE REGION TODAY AS LOW PRESSURE MOVES INTO SOUTHERN ONTARIO. EXPECT MOSTLY SUNNY SKIES AND TEMPERATURES CLIMBING INTO THE UPPER 60S TO LOWER 70S. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... TONIGHT...LIGHT WINDS TURN TO THE SOUTHWEST AHEAD OF A COLD FRONT STEMMING FROM A WEAK LOW PRESSURE SYSTEM IN SOUTHEASTERN CANADA. THIS WILL KEEP TEMPERATURES ON THE COOL SIDE BUT STILL IN THE MID 40S TO MID 50S. THURSDAY...THE COLD FRONT WILL MOVE THROUGH SOUTHERN NEW ENGLAND DURING THE DAY...SHIFTING WINDS TO THE NORTHWEST. THE FRONT APPEARS TO BE MOISTURE STARVED BY THE TIME IT MOVES INTO THE AREA SO EXPECT NOTHING MORE THAN A FEW CLOUDS. MAIN CONCERN WITH THE FRONT WILL BE IT USHERING IN COOLER TEMPERATURES. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... OVERVIEW AND MODEL PREFERENCES... THE PRIMARY INFLUENCE IN THE SENSIBLE WX THROUGH THE LONG TERM CONTINUES TO BE TWO REASONABLY DEEP LONGWAVE TROFS. THE FIRST WILL GRADUALLY LIFT OUT TOWARD THE END OF THE WEEK AS MID LVL RIDGE SLIDES W-E ACROSS THE CONUS...YIELDING RISING HEIGHTS AND MORE ZONAL FLOW. HOWEVER...THE NEAR HUDSON BAY CUTOFF HOLDS EVEN AS THE HEIGHTS RISE ACROSS SRN CANADA AND THE NORTHEAST...SO...WHEN A SECOND STRONG/COLD SHORTWAVE SLIDES OUT OF THE ALASKAN REGION...THE LONGWAVE TROF REDEVELOPS EARLY NEXT WEEK. THEREFORE...EXPECT...AFTER A COOL END OF THE WORK WEEK...A PERIOD OF WARMING AND MILDER WX FOR THE WEEKEND FOLLOWED BY ANOTHER RETURN TO COOL CONDITIONS BY THE EARLY HALF OF NEXT WEEK. GIVEN BOTH ENSEMBLES AND OPERATIONAL GUIDANCE HAS GENERAL AGREEMENT WITH THESE SYNOPTIC SCALE FEATURES...WILL USE A BLEND AS A BASELINE FOR THIS FORECAST. DETAILS... THU NIGHT INTO FRI NIGHT... POTENTIAL FOR THE COOLEST PORTION OF THE FORECAST. A WEAK COLD FRONT WILL SLIDE THROUGH THE AREA LATE THU...BUT ALLOW FOR GRADUAL CLEARING WITH COLD HIGH PRES BUILDING OVER THU NIGHT. DWPTS SHOULD FALL BACK INTO THE 30S...SO ASSUMING CLEARING OCCURS QUICKLY ENOUGH WITH RADIATIONAL COOLING...TEMPS COULD FALL INTO THE MID 30S IN NW MA/SW NH VALLEYS WHICH MAY REQUIRE FROST ADVISORIES. ELSEWHERE...STILL A COOL MORNING FRI...UPPER 30S AND LOW 40S POSSIBLE. THIS COOL START AND HIGH PRES MEANS DRY WX WITH HIGHS TOPPING OUT IN THE UPPER 50S TO MID 60S IN THE WARMEST SPOTS. GOOD SETUP FOR RADIATIONAL COOLING AGAIN FRI NIGHT...BUT RETURN FLOW AND RISING DWPTS MAY MEAN MINS ARE A BIT WARMER THAN THU NIGHT. SAT AND SUN... WEAK WARM FRONT SLIDES THROUGH THE REGION ON SAT. AT THIS POINT...IT LOOKS LIKE HIGH PRES REMAINS IN CONTROL WITH SUBSIDENCE SUPPRESSING ANY WEAK LIFT ASSOCIATED WITH THE FRONT. SO WILL KEEP THE FORECAST DRY. IN FACT...SUBSIDENCE BETWEEN A LOW PRES MOVING THROUGH SRN CANADA...AND OFFSHORE OF THE MID ATLANTIC THROUGH THE WEEKEND IS LIKELY TO YIELD MAINLY DRY CONDITIONS THROUGHOUT. MODELS DO INDICATE THIS AS AN INVERTED RIDGE FROM HIGH PRES IN THE MARITIMES. OTHERWISE...RISING HEIGHTS AND H85 TEMPS APPROACHING +12C ON SAT...THEN +14C ON SUN SUGGEST TEMPS RISE ABOVE NORMAL BY SUN. THEREFORE...LOOKING AT HIGHS IN THE LOW-MID 70S ARE EXPECTED SAT...REACHING CLOSE TO 80 BY SUN. SUN NIGHT INTO MON... COLD FRONT ASSOCIATED WITH THE NRN SYSTEM WILL CROSS THERE REGION DURING THIS PERIOD. STILL A FEW ISSUES TO WORK OUT REGARDING TIMING. HOWEVER...WITH AT LEAST MODEST PWATS /AROUND 1.5 INCHES/ AND SOME LIFT SUSPECT A PERIOD OF SHOWERS ARE POSSIBLE WITH THIS FRONTAL PASSAGE. ECMWF GOES BACK AND FORTH BETWEEN A DRY AND FRONTAL PASSAGE AND A WET ONE WITH SECONDARY LOW PRES DEVELOPMENT. BUT FEEL THAT AT LEAST SOME SLIGHT TO CHANCE POPS ARE WARRANTED...ESPECIALLY AS K-VALUES APPROACH 30. TUE AND WED... LONGWAVE TROF AND CUTOFF LOW PRES DEVELOP IN VICINITY OF THE GREAT LAKES. MODELS INDICATE THAT THICKNESS VALUES COULD DROP TO AROUND 540-550DM. THEREFORE...CONDITIONS LOOK RIPE FOR ANOTHER COOL DOWN EARLY NEXT WEEK. && .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 WEDNESDAY/...HIGH CONFIDENCE. THROUGH 12Z...MODERATE CONFIDENCE. MAINLY VFR. LOCALLY DENSE FOG HAS DEVELOPED ACROSS PORTIONS OF THE REGION REDUCING VISIBILITIES TO MVFR/IFR. TODAY THROUGH THURSDAY...HIGH CONFIDENCE. VISIBILITIES SHOULD IMPROVE QUICKLY AS FOG DISSIPATES. VFR CONDITIONS EXPECTED. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY...HIGH CONFIDENCE. MAINLY VFR THROUGH THE PERIOD. ALTHOUGH SOME OVERNIGHT FOG AT TYPICALLY PRONE AIRPORTS MAY LEAD TO IFR CONDITIONS...PARTICULARLY FRI NIGHT INTO SAT NIGHT. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH WEDNESDAY NIGHT/...MODERATE CONFIDENCE. MODERATE TO HIGH CONFIDENCE. SWELL FROM HURRICANE EDOUARD WILL SLOWLY BUILD INTO THE COASTAL WATERS WITH INCREASING SEAS. REGULAR FORECAST GUIDANCE HAS BEEN UNRELIABLE BUT HURRICANE WAVE WATCH GUIDANCE LOOKS MUCH MORE REASONABLE SO HAVE USED THAT. EXPECT SEAS TO REMAIN BELOW 5 FEET EXCEPT PERHAPS A FEW HOURS THURSDAY MORNING. WINDS REMAIN BELOW 15 KTS THROUGH THE PERIOD. OUTLOOK...THURSDAY NIGHT THROUGH SUNDAY...MODERATE CONFIDENCE. THU NIGHT FRI...HIGH PRESSURE NORTH OF THE WATERS WILL BRING A STRONGER NORTHEAST WIND WITH POTENTIAL FOR 20 KNOTS ESPECIALLY AROUND NANTUCKET AND ON THE SOUTHERN OUTER WATERS. SEAS MAY INCREASE TO 4-6 FEET IN THIS NORTHEAST FLOW...DIMINISHING AS THE WINDS DIMINISH FRIDAY EVENING. SMALL CRAFT ADVISORIES MAY BE NEEDED FOR SEAS. SATURDAY-SUNDAY...HIGH PRESSURE MOVES OFF THROUGH THE MARITIMES. THE WINDS WILL SHIFT TO SOUTH SATURDAY AND SOUTHWEST SUNDAY. GUSTS 20-25 KTS BOTH DAYS WITH POTENTIAL FOR 25 KNOT GUSTS ON SUNDAY. MOST SEAS WILL REMAIN BELOW 5 FEET...BUT THE WATERS EAST OF MASS BAY AND IPSWICH BAY MAY SEE SEAS RISE AGAIN TO AROUND 5 FEET. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...DOODY/RLG NEAR TERM...DOODY/RLG SHORT TERM...RLG LONG TERM...DOODY AVIATION...DOODY/RLG MARINE...DOODY/RLG

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