Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 131127 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 727 AM EDT SAT SEP 13 2014 .SYNOPSIS... ONE LOW PRESSURE SYSTEM WILL MOVE INTO QUEBEC WHILE ANOTHER WEAK LOW PRESSURE CENTER WILL PASS SOUTHEAST OF NANTUCKET THIS EVENING. THESE TWO SYSTEMS WILL BRING SCATTERED SHOWERS TO THE AREA LATE THIS AFTERNOON AND EARLY THIS EVENING. HIGH PRESSURE BRINGS DRY WEATHER WITH SLIGHTLY BELOW NORMAL TEMPERATURES SUNDAY INTO MONDAY. THE NEXT COLD FRONT WILL LIKELY BRING A PERIOD OF SHOWERS LATE MONDAY NIGHT INTO TUESDAY. MAINLY DRY WEATHER EXPECTED NEXT WEDNESDAY THROUGH FRIDAY WITH SLIGHTLY BELOW NORMAL TEMPERATURES CONTINUING. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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730 AM UPDATE... TRENDS IN THE FORECAST REMAIN ON TRACK. STRATO CU HAS OVERSPREAD A GOOD PORTION OF THE AREA AND EXPECT THIS TO REMAIN FOR THE REMAINDER OF THE DAY. NORTHERLY WINDS WILL SWITCH TO THE EAST TODAY KEEPING AN ONSHORE FLOW. OTHERWISE SCATTERED SHOWERS WILL DEVELOP LATER THIS AFTERNOON. PREVIOUS DISCUSSION... CLOUDS WILL BE ON THE INCREASE TODAY AS THE PRIMARY UPPER SHORT WAVE TROUGH AND SURFACE LOW HEADS FOR THE ST LAWRENCE RIVER. A SECONDARY SURFACE LOW WILL PASS SOUTHEAST OF NANTUCKET THIS EVENING. A CHALLENGING PART OF THE FORECAST IS THAT THE FORECAST AREA WILL FOR THE MOST PART LIE IN BETWEEN THE TWO SOURCES OF ENERGY AND THE SHOWER ACTIVITY IS PROBABLY NOT GOING TO BE THAT ORGANIZED. HAVE GONE HIGH CHANCE TO LOW LIKELY POPS FOR THE AREA THINKING THAT AT ANY ONE TIME THE SHOWERS WILL LIKELY BE SCATTERED BUT OVER THE COURSE OF 4 OR 5 HOURS AT LEAST HALF OF THE AREA IS LIKELY TO RECEIVE A MEASURABLE AMOUNT OF RAIN. THINK MOST AREAS WILL RECEIVE A QUARTER OF AN INCH OR LESS OF RAINFALL EXCEPT POSSIBLY A LITTLE MORE BERKSHIRES TO MONADNOCKS AND OVER CAPE AND ISLANDS. TEMPERATURES ARE LIKELY TO BE HELD IN THE MID TO UPPER 60S BY THE CLOUD COVER AND ONSHORE FLOW.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... TONIGHT...EVENING SHOULD START OFF WITH CLOUDS AND SCATTERED SHOWERS...BUT THE SHOWERS SHOULD DIMINISH/END WEST TO EAST BETWEEN 8 PM AND MIDNIGHT. EXPECT CLEARING SKIES OVERNIGHT...ALTHOUGH MAY BE SOME POCKETS OF FOG WHERE SUFFICIENT RAIN FALLS FOR A TIME. EVENTUALLY...THINK THE LOWERING DEWPOINTS AND MIXING FROM THE NW GRADIENT WILL CLEAR OUT MOST OF THE FOG PATCHES LATE AT NIGHT. SUNDAY...LOOKS LIKE PLENTY OF SUNSHINE AND TYPICAL EARLY FALL HIGH TEMPERATURES OF 65 TO 70 AS HIGH PRESSURE BUILDS INTO NEW ENGLAND AND H85 TEMPERATURES SLIP TO BETWEEN 8C AND 10C DURING THE AFTERNOON. THERE COULD BE A FEW WIND GUSTS FROM THE NORTHWEST TO 20 MPH IN THE MORNING ALONG THE COASTAL PLAIN BUT THE GRADIENT THEN SLACKENS DURING THE DAY. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... HIGHLIGHTS... * LOW RISK OF PATCHY FROST SUN NIGHT ACROSS DISTANT INTERIOR * A PERIOD OF SHOWERS LIKELY LATE MON NIGHT/TUE * DRY WEATHER/SLIGHTLY BELOW NORMAL TEMPS NEXT WED-FRI OVERVIEW... OVERALL MODEL GUIDANCE IS IN AGREEMENT WITH A BROAD TROUGH OVER THE EASTERN HALF OF THE CONTINENT AND A FULL-LATITUDE RIDGE OVER WESTERN NORTH AMERICA. IN FACT APPEARS THAT THE NORTHERN BRANCH OF THE JET STREAM REMAINS FAIRLY PROGRESSIVE ESP SINCE THE NAO TRENDING MORE POSITIVE FOR THE FIRST HALF OF THIS FORECAST. THE FLOW DOES BEGIN TO BECOME MORE AMPLIFIED TOWARDS THE END OF THE PERIOD AS A TROUGH DIGS OVER THE EASTERN PACIFIC LEADING TO A RIDGE IN THE CENTRAL CONUS....ABOUT WHEN THE NAO BECOMES MORE NEUTRAL. HOWEVER IT LOOKS LIKE THE EASTERN CONUS WILL STILL REMAIN IN A TROUGH PATTERN THROUGH THE WORK WEEK WITH A POSSIBLE CHANGE IN THE PATTERN BY NEXT WEEKEND. ONLY MAJOR WEATHER MAKE TO WATCH FOR AT THE MOMENT IS THE SHORTWAVE PASSING THROUGH MONDAY NIGHT/TUESDAY BRINGING SHOWERS TO THE REGION. LOW CONFIDENCE ON EXACT TIMING BUT CONFIDENCE IS INCREASING THAT PRECIP WILL OCCUR. OTHERWISE HIGH PRESSURE WILL PREVAIL WITH TEMPS AT OR BELOW AVERAGE FOR THIS TIME OF YEAR. IN FACT SUNDAY NIGHT AND MID TO LATE NEXT WEEK MAY NEED TO WATCH FOR FROST HEADLINES. DETAILS... MONDAY... A MODIFIED CANADIAN HIGH WILL BUILD INTO NEW ENGLAND DURING THIS PORTION OF THE FORECAST...CRESTING OVER THE REGION ON MONDAY. LOWS ON SUN NIGHT WILL BE QUITE CHILLY FOR SEPTEMBER. ALTHOUGH RECORD COLD IS NOT EXPECTED...WE MAY STILL SEE SOME MIDDLE TO UPPER 30S ACROSS PORTIONS OF SOUTHWEST NH/NORTHWEST MA...WHERE THIS IS A LOW RISK FOR SOME PATCHY FROST IN THE TYPICALLY COOLEST OUTLYING LOCATIONS. FOR MONDAY HIGHS...EVEN WITH FULL SUNSHINE TEMPS WILL ONLY REACH INTO THE MID 60S TO LOWER 70S...SINCE THE SUN ANGLE IS LOW. DRY WEATHER WILL PREVAIL. MONDAY NIGHT INTO TUESDAY... THE NEXT SHOT FOR ANY SHOWERS WILL BE LATE MONDAY NIGHT INTO TUESDAY AS ANOTHER SHORTWAVE MOVES THROUGH THE FLOW. OVERALL GUIDANCE HAS TRENDED TO BE ON THE WETTER SIDE SO CONFIDENCE IS INCREASING THAT PRECIP WILL OCCUR. RIGHT NOW LOOKS AS IF DROUGHT STRICKEN RI AND SE MASS HAVE THE BETTER SHOT FOR THE HIGHER QPF AMOUNTS. ALTHOUGH THE EC DOES HAVE A QPF BULLS-EYE FOR THE REGION...NOTICED THAT THE GFS HAS TICKED UP SO OVER 0.25 TO 0.5 INCHES IS NOT OUT OF THE QUESTION...ESPECIALLY SINCE PWAT VALUES DO NOSE IN AT ABOUT 1.5 INCHES. INSTABILITY LOOKS FAIRLY LIMITED...SO WILL NOT INCLUDE THUNDER IN THE FORECAST AT THIS TIME. HIGHS SHOULD BE IN THE 60S TO AROUND 70. END OF THE WORK WEEK... HIGH PRESSURE FROM CANADA WILL SET UP OVER THE NORTHEAST ON WED INTO FRIDAY. THE GFS BRING AN ARCTIC FRONT ACROSS THE REGION ON WED WHILE THE EC HOLDS IT UP UNTIL THURSDAY NIGHT. EITHER WAY GUIDANCE IS SHOWING 850 MB TEMPS DROPPING BELOW 0C. THIS WILL KEEP TEMPS WELL BELOW AVERAGE...IN THE 60S RESULTING IN CRISP FALL LIKE TEMPS. BECAUSE OF THE DIFFERENCE...WILL CONTINUE WITH A BLEND OF PREV FORECAST AS WELL AS THE ENSEMBLES FOR NOW. EITHER WHICH WAY WE MAY NEED TO BEGIN TO WATCH FOR THE RISK FOR SOME FROST IN SOUTHWEST NH/NORTHWEST MA...WHERE WINDS CAN DECOUPLE. && .AVIATION /12Z 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. CONFIDENCE IS MODERATE FOR TODAY AND TONIGHT...THEN HIGH FOR SUNDAY. TODAY...MOST OF AREA WILL PROBABLY EXPERIENCE MVFR TO VFR CONDITIONS FOR MID MORNING THROUGH EARLY AFTERNOON. AFTER ABOUT 20Z...ANTICIPATE CIGS TO LOWER TO LOW MVFR LEVELS W TO E WITH PATCHY IFR CIGS POSSIBLE 22Z TO 02Z ACROSS SE COASTAL LOCATIONS. SCATTERED SHOWERS WILL REDUCE VISIBILITIES FOR A TIME OR TWO LATE AFTERNOON AND EARLY EVENING. TONIGHT...SHOWERS SHOULD END W TO E BETWEEN 00Z AND 04Z. FOG PATCHES MAY LINGER FOR A WHILE BUT BELIEVE LOWERING DEWPOINTS AND MIXING IN THE NW GRADIENT WILL RESULT IN VFR CONDITIONS TAKING HOLD MOST AREAS OVERNIGHT. SUNDAY...LOOKS LIKE VFR CONDITIONS WITH NO CIGS AND EXCELLENT VSBY. KBOS TERMINAL...MODERATE TO HIGH CONFIDENCE. GENERALLY MVFR/VFR CONDITIONS THROUGH ABOUT 22Z. HIGHER CONFIDENCE THAT A PERIOD OF MVFR CIGS/VSBYS ANTICIPATED IN SCATTERED SHOWERS GENERALLY 22Z TO 02Z SUN. CONDITIONS SHOULD IMPROVE TO VFR LATE TONIGHT AS NW FLOW MIXES THE AIR MASS AND DEWPOINTS LOWER. KBDL TERMINAL...MODERATE TO HIGH CONFIDENCE. GENERALLY MVFR/VFR CONDITIONS THROUGH ABOUT 20Z. HIGHER CONFIDENCE THAT A PERIOD OF MVFR CIGS/VSBYS ANTICIPATED IN SCATTERED SHOWERS GENERALLY 20Z TO 00Z SUN. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY...HIGH CONFIDENCE. MAINLY VFR CONDITIONS OVER THIS TIME...EXCEPT FOR A PERIOD OF MVFR- IFR CONDITIONS LATE MON NIGHT/TUE IN A ROUND OF SHOWERS.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. FORECAST CONFIDENCE IS MODERATE TODAY AND TONIGHT...AND HIGH FOR SUNDAY. HAVE MADE A QUICK UPDATE OF THE MARINE FORECAST TO ISSUE A SMALL CRAFT ADVISORY FOR THE REST OF THE MORNING FOR THE COASTAL WATERS EAST OF MASSACHUSETTS INCLUDING MASS BAY AND STELLWAGEN BANK. BOTH JEFFREYS LEDGE AND BOSTON BUOYS WERE REPORTING SEAS OF 5 FT AT 5AM...AND BOSTON BUOY HAS REPORTED NE WIND GUSTS TO 23 KT AT BOTH 4 AND 5 AM. ALTHOUGH STRONGER THAN INITIALLY EXPECTED...BELIEVE THE GRADIENT WILL LIKELY PERSIST THROUGH MOST OF THE MORNING AND THEN SHOULD SLACKEN THIS AFTERNOON AS SURFACE PRESSURES BEGIN TO DROP TO THE NORTHWEST. HAVE PUT THE ADVISORY OUT UNTIL NOON. LATER SHIFTS WILL NEED TO ASSESS WHETHER ANY TIME OR SPACE EXTENSION WILL BE NECESSARY. MARINE FORECAST IS ALSO A LITTLE TRICKY FOR LATE TONIGHT. IN THE WAKE OF A WEAK LOW PRESSURE SYSTEM MOVING NE ACROSS GEORGES BANK TONIGHT...COULD SEE A PERIOD OF N TO NW WINDS GUSTING BETWEEN 20 AND 25 KT DURING EARLY SUNDAY MORNING. CONFIDENCE IS NOT HIGH ENOUGH AT THIS POINT TO ISSUE A SMALL CRAFT ADVISORY FOR THIS TIME PERIOD...BUT THE SITUATION WILL NEED TO BE WATCHED AND A HEADLINE MAY BECOME NECESSARY FOR SOME OF THE WATERS FOR A TIME SUNDAY MORNING. OUTLOOK...SUNDAY NIGHT THROUGH WEDNESDAY.... MONDAY INTO TUE MORNING...MODERATE TO HIGH CONFIDENCE. HIGH PRESSURE NEARBY WILL RESULT IN A WEAK PRESSURE GRADIENT KEEPING WINDS/SEAS BELOW SCA THRESHOLDS. TUESDAY AFTERNOON INTO WEDNESDAY...MODERATE CONFIDENCE. MAY SEE SOME MARGINAL SCA WINDS/SEAS ACROSS THE OUTER-WATERS BEHIND A COLD FRONT/LOW PRESSURE SYSTEM IN THE COOL AIR ADVECTION PATTERN. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT TODAY FOR ANZ250-251. && $$ SYNOPSIS...DUNTEN/THOMPSON NEAR TERM...DUNTEN/THOMPSON SHORT TERM...THOMPSON LONG TERM...DUNTEN AVIATION...DUNTEN/THOMPSON MARINE...DUNTEN/THOMPSON

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