Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 162018 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 418 PM EDT TUE SEP 16 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. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... SHOWERS HAVE ALL BUT DISSIPATED AS THE COLD FRONT CONTINUES TO WORK THROUGH THE REGION. SCATTERED TO BROKEN CUMULUS ASSOCIATED WITH BOUNDARY LAYER MIXING OF THE REARWARD MOIST-COLD POOL TO THE FRONT SHOULD DISSIPATE AS WE GO INTO THE EVENING AS TEMPERATURES FALL INTO THE 50S. TONIGHT... COLD FRONT PUSHES OFFSHORE AS HIGH PRESSURE BUILDS FROM THE W. WITH THE PRESSURE GRADIENT RELAXING...WINDS BECOMING LIGHT AND VARIABLE. CONDITIONS GRADUALLY CLEAR ALLOWING GOOD RADIATIONAL COOLING. LOWS FALLING TOWARDS THE UPPER-30S FOR PORTIONS OF N/W MA AND S NH...IN THE 40S ELSEWHERE /WARMER ALONG THE SHORES AND WITHIN URBAN HEAT CENTERS/. LOW CONFIDENCE CONCERNING FROST...BUT WILL NEED TO MONITOR THOSE AREAS WHICH ARE NOTORIOUS FOR RADIATE OUT WELL DURING SUCH SITUATIONS OUTLINED ABOVE. NOTING DAYTIME SHOWERS AND DEWPOINTS AROUND THE LOW-50S DURING MAX- HEATING OF THE DAY...THERE IS A GOOD POSSIBILITY FOR PATCHY DENSE FOG...ESPECIALLY FOR THE W- AND CENTRAL-INTERIOR AROUND THE MID-CT RIVER VALLEY...AS WELL AS THE MERRIMACK RIVER VALLEY. COULD ALSO SEE A FEW SPOTS ACROSS INTERIOR S NEW ENGLAND. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... WEDNESDAY... HIGH PRESSURE IN CONTROL. LIGHT AND VARIABLE WINDS CONTINUE. MOSTLY SUNNY CONDITIONS. SEA-BREEZES ALONG THE SHORES. COOLER AIRMASS ALOFT IN WAKE OF THE COLD FRONT WITH H85 TEMPERATURES AROUND +5C WILL MAKE IT FEEL LIKE A CRISP COOL DAY AT THE SURFACE WITH HIGHS AROUND THE UPPER-60S TO LOW-70S...ROUGHLY 5 DEGREES BELOW-NORMAL. SCATTERED DIURNAL CU AROUND 5 KFT ACROSS THE INTERIOR /ESPECIALLY OVER THE HIGH TERRAIN/...SANDWICHED BELOW A STOUT DRY-INVERSION. WEDNESDAY NIGHT... ANOTHER NIGHT OF HIGH PRESSURE WITH LIGHT / VARIABLE WINDS. SOME QUESTION AS TO WHETHER CONDITIONS WILL REMAIN CLEAR. POSSIBILITY OF SOME HIGH CLOUDS FILTERING ACROSS THE REGION AHEAD OF A SHARP COLD FRONT DIVING S OUT OF E-CANADA /DECENT CYCLONIC FLOW AND JET- DYNAMICS ALOFT/. THIS WOULD LIMIT RADIATIONAL COOLING AND POTENTIAL FOG DEVELOPMENT. CAN NOT RULE OUT SOME SPOTTY AREAS OF FOG. WILL HOLD WITH THE PREVIOUS FORECAST OF LOWS DOWN INTO THE 40S EXCEPT ALONG THE IMMEDIATE COAST. && .LONG TERM /THURSDAY THROUGH TUESDAY/... BIG PICTURE... UPPER TROUGH OVER THE NORTHEAST USA MOVES OFF BY FRIDAY WITH THE FLOW CONVERTING TO ZONAL FOR FRIDAY AND SATURDAY. SHORTWAVE FROM THE GULF OF ALASKA MERGES WITH ENERGY FROM THE CANADIAN ARCTIC LATE WEEK WHILE AN UPPER RIDGE BUILDS OVER THE PACIFIC COAST. BOTH OF THESE ACTIONS WILL DIG AN UPPER TROUGH OVER THE GREAT LAKES...WHICH MOVES INTO THE NORTHEAST USA EARLY NEXT WEEK. UPPER HEIGHTS ARE BELOW NORMAL THURSDAY-FRIDAY BUT MODERATE TO 60 METERS ABOVE NORMAL BY SUNDAY. THIS SUGGESTS A COOL FINISH TO THE WEEK FOLLOWED BY A SMALL WARMING TREND OVER THE WEEKEND...THEN COOLING AGAIN BY TUESDAY AS THE UPPER TROUGH AND COLDER TEMPS ALOFT MOVE BACK IN. THE DAILIES... THURSDAY... UPPER SHORTWAVE MOVES ACROSS SOUTHERN NEW ENGLAND AND PUSHES A WEAK SECONDARY FRONT THROUGH. SUFFICIENT MOISTURE FOR SOME CLOUDS ESPECIALLY NORTH OF THE MASS PIKE. BUT COLD ADVECTION ALOFT IS WEAK AS IS INSTABILTIY...TOTALS IN THE MID 40S AND MID LEVEL LAPSE RATES A LITTLE OVER 5.5C/KM...SO WE/RE NOT BIG ON CONVECTION. MOST LIKELY A FEW SHOWERS. TEMPS AT 850 MB 5-7C SUPPORT MAX TEMPS MID 60S TO LOWER 70S. HIGH PRESSURE BUILDS OVERHEAD THURSDAY NIGHT. MOSTLY CLEAR SKIES AND LIGHT WINDS WILL ALLOW RADIATIONAL COOLING. DEW POINTS WILL BE IN THE 30S AWAY FROM THE COAST AND LOW 40S COAST AND ISLANDS. EXPECT MIN TEMPS 35-40 AWAY FROM THE COAST AND 40S ALONG THE COAST. IF MVY AIRPORT DECOUPLES...IT WILL BE NEAR 40 OR LOW 40S. THESE TEMPS WILL MEAN A POTENTIAL FOR PATCHY FROST. MOSTLY LIKELY AREAS WOULD BE SOUTHWEST NH AND NORTHWEST MASS. FRIDAY-SATURDAY...HIGH PRESSURE OVER THE REGION FRIDAY SHIFTS EAST SATURDAY...BUT PROVIDES DRY WEATHER BOTH DAYS. LIGHT WINDS FRIDAY...DEVELOPING SOUTH WIND SATURDAY. MODEL WIND GUSTS FOR SATURDAY DO NOT REFLECT WINDS ALOFT IN THE MIXED LAYER. SO WE BUMPED VALUES UP TO NEAR 20 KTS. FRIDAY TEMPS ALOFT 0-2C SUPPORTS MAX SFC TEMPS UPPER 50S TO MID 60S...SATURDAY TEMPS ALOFT 4-6C SUPPORTS MAX SFC TEMPS MID 60S TO LOWER 70S. RADIATIONAL COOLING AGAIN FRIDAY NIGHT BUT DEW POINTS WILL BE A LITTLE HIGHER...35-45...SO MIN SFC TEMPS UPPER 30S AND 40S. SOUTH WINDS WILL BRING HIGHER DEW POINTS SATURDAY NIGHT WITH MIN TEMPS UPPER 40S AND 50S. SUNDAY... INCREASING SOUTH WIND SUNDAY WITH SOME INCREASE IN CLOUDS AS A COLD FRONT APPROACHES. BUT THE DAY SHOULD REMAIN DRY WITH PLENTY OF SUN. MODEL GUST FORECASTS ARE AGAIN LOWER THAN THA MIXED LAYER WOULD SUGGEST. SOUTHWEST WINDS SHOW A GUST POTENTIAL TO 25 KNOTS AND POSSIBLY AS HIGH AS 30 KNOTS. WE BUMPED THE SUNDAY WIND GUSTS UP INTO THE LOW 20S. TEMPS ALOFT AROUND 10C AND POSSIBLY TO 12C. THIS MEANS MID TO UPPER 70S...AND WITH SUFFICIENT MIXING THERE MAY BE SOME SPOTS WITH LOW 80S. SOUTHWEST WIND MAY BUFFER THESE VALUES WHERE IT COMES OFF THE OCEAN. SUNDAY NIGHT-MONDAY...COLD FRONT MOVES THROUGH OUR AREA EARLY MONDAY MORNING THROUGH MIDDAY. BEST DYNAMICS MOVE FROM NEW YORK UP THROUGH VERMONT. BUT SUFFICIENT LOW LEVEL CONVERGENCE AND MOISTURE TO FORECAST SHOWERS WITH COLD FROPA. MONDAY NIGHT-TUESDAY...COLDER AIR ADVECTS IN BEHIND THE COLD FRONT. MEANWHILE THE UPPER TROUGH MOVES EAST FROM THE GREAT LAKES WITH COOLING TEMPS ALOFT. TEMPS ALOFT 0-2C SUPPORTING UPPER 50S TO MID 60S. && .AVIATION /20Z TUESDAY 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. TONIGHT... IFR-VLIFR DENSE FOG CERTAINLY POSSIBLE ACROSS INTERIOR NEW ENGLAND WITH 1/2SM VV002. HIGHEST CONFIDENCE FOR THOSE TERMINALS WHICH SAW RAIN EARLIER TODAY AND ARE SHELTERED FROM THE WIND AND TYPICALLY PRONE TO FOG. WEDNESDAY INTO WEDNESDAY NIGHT... IFR-VLIFR FOG BURNS OFF IN THE MORNING. FEW-SCT CIGS AROUND 5 KFT FOR INTERIOR TERMINALS. SEA-BREEZES ALONG THE SHORES TOWARDS MIDDAY...ERODING TOWARDS EVENING. NOT ENOUGH CONFIDENCE AT THIS TIME TO BELIEVE THERE WILL BE FOG ISSUES TOWARDS THURSDAY MORNING. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. PRESENT N/NE WINDS WILL BECOME VRB WITH COLD FRONTAL PASSAGE THIS AFTERNOON...TURNING W/NW INTO THE OVERNIGHT. LOW CONFIDENCE ON FOG. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. THERE IS SOME CONFIDENCE OF POTENTIAL FOG IMPACTS TOWARDS WEDNESDAY MORNING. OUTLOOK...THURSDAY THROUGH SUNDAY...HIGH CONFIDENCE. VFR THROUGH THE PERIOD. SOUTHWEST WINDS SATURDAY MAY GUST TO 20 KNOTS. SOUTHWEST WINDS SUNDAY MAY GUST 25 KNOTS...POSSIBLY A LITTLE HIGHER. && .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. WITH EDOUARD...ITS INTENSITY AND PROXIMITY TO SOUTHERN NEW ENGLAND SHOULD RESULT IN LONG-PERIOD SWELL OF AROUND 14 SECONDS THAT LOOKS TO REMAIN AT OR BELOW 5 FEET. WITH FORECAST GUIDANCE THAT HAS BEEN OVERZEALOUS WITH WAVE AND SWELL ACTION WITH COMPARISON TO THE LATEST BUOY OBSERVATIONS... WILL HOLD OFF ON THE ISSUANCE OF SMALL CRAFT ADVISORIES FOR HAZARDOUS SEAS. IT IS CERTAINLY PLAUSIBLE TOWARDS MIDWEEK THAT THE OUTER WATERS WILL SEE 5 FOOT SEAS. THIS ALONG WITH THE LONG- PERIOD SWELL...BELIEVE THAT THE RIP CURRENT RISK WILL REMAIN IN THE MODERATE-RANGE FOR THE S-ATLANTIC FACING SHORELINES NEGATING THE NEED FOR RIP CURRENT STATEMENTS AT THIS TIME. HAVE GREATEST CONFIDENCE WITH THE EC WAVE MODEL AND WNA-HURRICANE WAVE GUIDANCE WITH RESPECT TO WAVE AND SWELL ACTION. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY... HIGH PRESSURE BUILDS JUST NORTH OF THE WATERS. NORTH WINDS 15 KNOTS OR LESS. LINGERING 5 FEET ON THE EASTERN OUTER WATERS FROM SWELL...BUT THIS WILL BE SUBSIDING. FRIDAY...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 WILL INCREASE TO 5- 7 FEET IN THIS NORTHEAST FLOW...DIMINISHING AS THE WINDS DIMINISH FRIDAY EVENING. SATURDAY-SUNDAY...HIGH PRESSURE MOVES OFF THROUGH THE MARITIMES. THE WINDS WILL SHIFT TO SOUTH SATURDAY AND SOUTHWEST SUNDAY. GUSTS TO 20 KNOTS 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...WTB/SIPPRELL NEAR TERM...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...WTB AVIATION...WTB/SIPPRELL MARINE...WTB/SIPPRELL

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