Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270214 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1014 PM EDT TUE AUG 26 2014 .SYNOPSIS... WARM TEMPERATURES CONTINUE WEDNESDAY ALONG WITH WIDELY SCATTERED THUNDERSTORMS AS A COLD FRONT SWEEPS ACROSS THE AREA LATE IN THE DAY. DRY...COOLER CONDITIONS RETURN THURSDAY AND FRIDAY BEHIND THE FRONT...HOWEVER HURRICANE CRISTOBAL DELIVERS ROUGH SURF AND RIP CURRENTS TO SOUTH COAST OCEAN BEACHES AS IT TRACKS WELL OFFSHORE. ANOTHER FRONT MAY BRING UNSETTLED CONDITIONS SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... QUIET NIGHT EXPECTED AS HIGH PRESSURE OVER THE REGION SHIFTS OFFSHORE. PRESSURE GRADIENT IS LIGHT...SO EXPECT WINDS TO BE LIGHT THROUGH THE NIGHT. SKIES ARE GENERALLY CLEAR...JUST SOME THIN CIRRUS IN SPOTS. SOME THICKER CLOUDS ARE MOVING INTO WESTERN NY...BUT EXTRAPOLATE TO THE CT VALLEY AROUND 12Z WEDNESDAY MORNING. DEW POINTS RANGE FROM THE UPPER 50S TO MID 60S. CLEAR SKIES AND LIGHT WINDS SHOULD ALLOW RADIATIONAL COOLING ALLOWING TEMPS TO FALL INTO OR NEAR THIS RANGE. THE COOLING MEANS THAT FOG WILL ALSO BE A CONCERN OVERNIGHT...ESPECIALLY ALONG THE SOUTH COAST WHERE SOUTHWEST FLOW OFF THE OCEAN MAY ADD TO THE MOISTURE CONTENT. FOG ALSO A CONCERN IN THE CT VALLEY AND IN TYPICAL FOG SPOTS ELSEWHERE...BED/OWN/IJD FOR EXAMPLE. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... CONVECTIVE POTENTIAL... BOTH 12Z ECMWF/NAM AND 12Z GFS HOLD OFF QPF TIL AFTER 18Z. THEREAFTER BOTH THE NAM AND GFS ARE MORE GENEROUS WITH THEIR QPF THAN THE ECMWF. THIS IS NOT SURPRISING AS BOTH THE NAM AND GFS ADVECTED HIGHER DEW PTS INTO SOUTHERN NEW ENGLAND WITH VALUES REACHING 70F. MEANWHILE THE MORE CONSERVATIVE AND REALISTIC ECMWF KEEPS SFC DEW PTS IN THE MU60S. THIS RESULTS IN THE ECMWF HAVING LESS SB INSTABILITY/CAPE (UP TO 1200J/KG) THAN BOTH THE NAM AND GFS (2500-3000J/KG)...AND RESULTING IN LESS CONVECTIVE QPF. FOR THIS REASON WE WILL LEAN TOWARD THE ECMWF INSTABILITY AND QPF FIELDS. AS FOR ANY STORMS BECOMING STRONG TO SEVERE...ALL MODEL GUIDANCE SUGGEST WEAK 0-6KM SHEAR AT 18Z WITH LESS THAN 20 KT. HOWEVER BY SUNSET SHEAR VALUES INCREASE TO 30-35 KT. ALTHOUGH BY THEN INSTABILITY BEGINS TO WANE AS BLYR COOLING COMMENCES...ESPECIALLY NOW WITH SUNSET CLOSER TO 730 PM. THUS INSTABILITY AND SHEAR ARE OUT OF PHASE. THIS WILL ONLY PROVIDE A SMALL WINDOW OF OPPORTUNITY FOR STORMS TO DEVELOP...PROBABLY CLOSER TO 21Z WHEN INSTABILITY AND SHEAR ARE BEST COLOCATED. ONE OR TWO STORMS MAY BE STRONG ENOUGH TO PRODUCE BRIEF HEAVY DOWNPOURS GIVEN DEW PTS IN THE MU60S AND PWATS +1 STANDARD DEVIATION FROM CLIMO ALONG WITH MARGINAL INSTABILITY FOR MODEST UPDRAFT POTENTIAL. LOW PROB OF SOME GUSTY WINDS IF A STRONGER STORM IS ABLE TO DEVELOP GIVEN INVERTED / SIGNATURE (LARGE DEW PT DEPRESSIONS GIVEN SFC TEMPS U80S-L90S). HOWEVER GIVEN THE LIMITED DEEP LAYER SHEAR AND LACK OF SURFACE CONVERGENCE AREAL COVERAGE OF T- STORMS WILL LIKELY BE CONFINED TO WIDELY SCATTERED. HENCE MANY LOCATIONS REMAIN DRY. FOR THIS REASON WILL NOT INCLUDE ANY ENHANCED WORDING IN OUR FORECAST. TEMPERATURES... LOW LEVEL WAA AHEAD OF THE FRONT RESULTS IN AIRMASS WARMING FURTHER WITH HIGHS WED IN THE U80S AND L90S. SW PGRAD WILL PRECLUDE SEABREEZES SO THESE WARMER TEMPS WILL BE REALIZED FROM CAPE ANN SOUTHWARD THRU BOSTON DOWN TO PLYMOUTH COUNTY. COOLER ALONG THE SOUTH COAST GIVEN THE WIND TRAJECTORY BUT STILL WARM WITH HIGHS U70S TO L80S. AGAIN WARMEST BEACHES WILL BE FROM PLYMOUTH COUNTY NORTHWARD TO CAPE ANN. SURF... APPEARS LARGE SWELLS FROM HURRICANE CRISTOBAL WILL HOLD OFF UNTIL VERY LATE IN THE DAY TOMORROW. THEREFORE BUILDING SURF WILL LIKELY HOLD OFF UNTIL SUNSET OR THEREAFTER WITH THE MOST DANGEROUS SURF LIKELY THU. LATER SHIFTS WILL HAVE TO MONITOR THIS CLOSELY. IF CRISTOBAL ACCELERATES A BIT MORE THAN EXPECTED BUILDING SURF COULD DEVELOP WED AFTERNOON AND WOULD REQUIRE THE ISSUANCE OF A HIGH RIP CURRENT RISK STATEMENT OR HIGH SURF ADVISORY. STAY TUNED. WED NIGHT...ANY LEFTOVER SHOWERS/T-STORMS SHOULD DIMINISH BY 9 PM OR 10 PM FOLLOWED BY THE FRONTAL LATER IN THE EVENING AND OVERNIGHT. DRIER AIR/LESS HUMID AIRMASS OVERSPREADS THE REGION FROM NORTH TO SOUTH LATER WED NIGHT. && .LONG TERM /THURSDAY THROUGH TUESDAY/... */ HIGHLIGHTS... - COOL AND DRY WEATHER UNDER HIGH PRESSURE THURSDAY AND FRIDAY - HOT AND HUMID CONDITIONS INTO THE WEEKEND - POSSIBLE THUNDERSTORMS SUNDAY...WITH HEAVY RAIN INTO MONDAY */ OVERVIEW AND MODEL PREFERENCE... CONTINUED DECENT SIGNAL OF A WARMER AND PERHAPS WETTER PATTERN INTO EARLY SEPTEMBER. DESPITE A NEARLY-EQUAL AMPLITUDE NEGATIVE NAO/PNA FORECAST...DOWNSTREAM RIDGING PER NEGATIVE PNA DOMINATES ESPECIALLY DURING THE SUMMER-MONTHS. NO SURPRISE TO SEE THE GEFS/NAEFS/CPC 6-10 AND 8-14 DAY ANOMALY FORECASTS HIGHLIGHTING NEAR- TO ABOVE-NORMAL CONDITIONS ACROSS THE REGION. CPC ALSO HINTS AT ABOVE-AVERAGE WETTER CONDITIONS LIKELY AS LOW-LEVEL HUMIDITY / PRECIPITABLE WATER VALUES ARE FORECAST TO BE ABOVE-AVERAGE PER ENSEMBLE FORECASTS PARENT WITH RIDGING AND ACCOMPANYING S-FLOW. EVALUATING DETERMINISTIC/ENSEMBLE GUIDANCE...THERE IS GOOD AGREEMENT WITHIN THE BROAD-SCALE PATTERN. BUT FINER DETAILS VARY...ESPECIALLY WITH REGARDS CONFLUENT SETUP INTO THE WEEKEND AND POTENTIAL WEAK- WAVE LOW INTO EARLY NEXT WEEK. MODELS APPEAR TO STRUGGLE WITH BOTH THE STRENGTH AND EVOLUTION OF THE W-ATLANTIC RIDGE / BERMUDA HIGH AND LOW OVER NE CANADA...BOTH OF WHICH INFLUENCE THE CONFLUENT SETUP AND ATTENDANT STALLED FRONTAL BOUNDARY. WOULD EXPECT A STRONGER BERMUDA HIGH TO HAVE GREATER INFLUENCE OVER THE REGIONS WEATHER AGAINST THE TROUGHING PATTERN WELL N. THIS COULD RESULT IN THE COMBINATION OF BOTH MOISTURE CONFLUENCE AND MID- TO UPPER-LEVEL DYNAMICS REMAINING N OF S NEW ENGLAND PRIOR TO A WEAK- WAVE LOW KICKER INTO EARLY NEXT WEEK. WITH THE MODEL VARIABILITY OF FRONTAL POSITION AND EVOLUTION OVER THE WEEKEND INTO EARLY NEXT WEEK...NO MODEL SOLUTION IS CERTAIN AND THUS WILL TREND WITH A CONSENSUS FORECAST. HIGHLIGHTS/CONFIDENCE ARE BROKEN DOWN IN THE DAILY DISCUSSION BELOW. */ DAY-TO-DAY DETAILS... THURSDAY... THE NE-CONUS FINDS ITSELF REARWARD OF A DEPARTING TROUGH AXIS WITHIN BRISK NW-FLOW AS A RIDGE BUILDS FROM THE W ALONG WITH SURFACE HIGH PRESSURE. THE BETTER COLD-POOL WITH ATTENDANT DYNAMICS AND ASCENT REMAINS N AND E. WHILE A DRY-SUBSIDENCE INVERSION BUILDS SE ACROSS THE REGION...CAN NOT RULE OUT THE POSSIBILITY OF SOME LIGHT SHOWER ACTIVITY ACROSS S NH INTO NE MA. NOT ENOUGH CONFIDENCE TO WARRANT POPS...BUT THE POTENTIAL SHOULD NOT BE IGNORED. EXPECTED SCATTERED TO BROKEN CLOUD DECKS OF CUMULUS BECOMING PANCAKE IN NATURE WITH THE SUBSIDENCE INVERSION BUILDING. MIXING UP TO H85 /+8-10C/ SHOULD ALLOW THE MIX-DOWN OF BREEZY NW-WINDS WITH GUSTS UP TO 25 MPH AND DRIER AIR TO THE SURFACE DURING THE DAY. EXPECTING SEASONABLE CONDITIONS WITH HIGHS AROUND THE MID- TO UPPER-70S. DRY AND QUIET OVERNIGHT UNDER LIGHT WINDS AS SURFACE HIGH PRESSURE EDGES CLOSER FROM THE W. EXPECTING AREAS OF EFFECTIVE RADIATIONAL COOLING...PERHAPS PATCHY DENSE FOG. AVERAGE LOWS AROUND THE REGION IN THE LOW- TO MID-50S...BUT WOULD NOT BE SURPRISED TO SEE SEVERAL AREAS IN THE UPPER-40S...ESPECIALLY THOSE AREAS WHICH RADIATE WELL. FRIDAY... HIGH PRESSURE IN CONTROL WITH LIGHT AND VARIABLE WINDS. WITH LITTLE CHANGE TO THE AIRMASS ALOFT /H85 +8-10C/...ANTICIPATE ANOTHER DAY OF SEASONABLE CONDITIONS UNDER MOSTLY CLEAR CONDITIONS. HIGHS AROUND THE MID- TO UPPER-70S...COOLER ALONG THE SHORES WITH EXPECTED SEA- BREEZES. OVERNIGHT...MAY SEE SOME MID- TO HIGH-LEVEL CLOUDS STREAM INTO THE REGION LATE AHEAD OF THE WEEKENDS WET-WEATHER. OTHERWISE LOWS AROUND THE LOW- TO MID-50S AS WINDS TURN S AND ONSHORE AS THE SURFACE HIGH PRESSURE SHIFTS OFFSHORE. SATURDAY INTO MONDAY... A CONFLUENT PATTERN BETWEEN AIRMASSES SETS UP ACROSS THE NE-CONUS PARENT TO WHICH A FRONTAL BOUNDARY STALLS AND BECOMES THE FOCUS FOR LOW- TO MID-LEVEL MOISTURE CONFLUENCE. STRETCHED MID-LEVEL ENERGY TRANSLATES ALONG THE BOUNDARY PROVIDING ASCENT AND YIELDING PERIODS OF RAIN...POSSIBLE THUNDERSTORMS. ACTIVITY APPEARS TO CONCLUDE AS A WEAK-WAVE LOW TRANSLATES ALONG THE FRONT PUSHING ACTIVITY OFFSHORE AROUND MONDAY. NO ONE MODEL SOLUTION IS PREFERRED. BELIEVE THE BERMUDA HIGH WILL HAVE A GREATER INFLUENCE OVER THE AREAS WEATHER INITIALLY SATURDAY INTO SUNDAY. DAILY OCCURRENCES OF SCATTERED SHOWERS / THUNDERSTORMS ARE POSSIBLE /THE GREATER PROBABILITY ON SUNDAY ACROSS INTERIOR NEW ENGLAND/...BUT WILL HOLD OFF HEAVIER RAIN TILL A WEAK-WAVE LOW ALONG THE FRONT ACTS AS A KICKER PUSHING ACTIVITY THROUGH THE REGION AND OFFSHORE AROUND MONDAY. CONSIDERING THE CONFLUENCE OF HIGH THETA-E MOIST TONGUE WITHIN THE LOW-LEVELS ALONG AND S OF THE STALLED FRONT YIELDING PWATS AROUND 1.75 AND 2.00 INCHES...GREATEST CONCERN IS FOR HEAVY RAIN AND THE POSSIBILITY OF FLOODING. UNCERTAIN AS TO THUNDERSTORM AND SEVERE WEATHER POTENTIAL. A CONDITIONALLY UNSTABLE PROFILE S OF THE FRONT IS MODELED IN A REGION OF FALLING HEIGHTS AND PERHAPS UPPER-LEVEL SUPPORT WITHIN THE RRQ OF THE UPPER-LEVEL JET. SOME INDICATIONS OF DECENT INSTABILITY WITHIN MODEST ROUGHLY UNI-DIRECTIONAL W-SHEAR. FREEZING LEVEL HEIGHTS ARE AROUND 14 KFT...SO IF ANY SEVERE THREATS WOULD LEAN TOWARDS DAMAGING WINDS AS 0-6 KM BULK SHEAR AND MEAN WIND ARE NEARLY PARALLEL. LOW CONFIDENCE AT THIS TIME. WE ARE STILL 5-6 DAYS OUT FROM THE FORECAST PERIOD. CAN ONLY SPECULATE FOR NOW AS THE RIDGE-TROUGH INTERSECT YIELDING THE CONFLUENT FLOW REGIME IS CRITICAL IN DETERMINING THE COLLOCATED FRONTAL BOUNDARY. EXPECTING WOBBLES IN THE FRONTAL POSITION WITH LATER FORECASTS RESULTING IN VARYING OUTCOMES. THIS IS WHY CHANCE OVER LIKELY POPS CONTINUE. WILL PREVAIL WITH CONDITIONS THAT ARE SLIGHTLY ABOVE-AVERAGE. INTO MIDWEEK... A BRIEF PERIOD OF QUIET WEATHER IS ANTICIPATED BEHIND THE WEAK-WAVE LOW. A FOLLOW-UP COLD FRONT IS POSSIBLE TOWARDS THE END OF THE WEEK. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /TONIGHT INTO WEDNESDAY NIGHT/...MODERATE CONFIDENCE. TONIGHT...VFR. CONCERNS WITH MVFR-IFR CIGS/VSBYS ASSOCIATED WITH LOW CLOUDS AND FOG...PERHAPS SOME PATCHY DRIZZLE. BEST CHANCE WOULD BE ALONG THE SOUTH COAST AND ISLANDS. SECOND BEST CHANCE IN THE CT VALLEY. ALSO POSSIBLE IN NORMAL FOG SPOTS. WEDNESDAY...LOW CLOUDS AND FOG MAY LINGER ON THE SOUTH COAST DURING THE MORNING. OTHERWISE...VFR. SCT TSRA/SHRA EXPECTED ROUGHLY FROM MHT-BDL AROUND 21Z. HAVE PREVAILED WITH VCSH FOR NOW REMOVING VCTS DUE TO LOW CONFIDENCE ON SPECIFICS. MIX OF MVFR-IFR POSSIBLE WITH TSRA WITH THE THREAT OF +RA AND GUSTY WINDS. WEDNESDAY NIGHT...GENERALLY VFR. ISOLATED SHRA/TSRA LINGER TOWARDS MIDNIGHT. WINDS SHIFTING NW BEHIND THE FRONT. A PERIOD OF MVFR-IFR CIGS/VSBYS POSSIBLE PRIOR TO FRONTAL PASSAGE ALONG CAPE COD AND THE ISLANDS. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. SW-WINDS PREVAILING. SCT SHRA/TSRA POSSIBLE AROUND 21Z...LOW CONFIDENCE SO WENT WITH VCSH. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. SW-WINDS PREVAILING. SCT SHRA/TSRA POSSIBLE AROUND 21Z...LOW CONFIDENCE SO WENT WITH VCSH. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY INTO FRIDAY...HIGH CONFIDENCE. VFR. BREEZY NW WINDS THURSDAY WITH GUSTS UP TO 25 KTS. SCT-BKN 5-6 KFT CIGS. SKC THURSDAY NIGHT INTO FRIDAY. LIGHT WINDS. PATCHY MVFR- IFR FOG POSSIBLE DURING THE OVERNIGHT PERIOD. SEA-BREEZES FRIDAY. SATURDAY INTO SUNDAY...MODERATE CONFIDENCE. VFR. INCREASING S-WINDS. BETTER CHANCES FOR SHRA/TSRA SUNDAY ACROSS THE INTERIOR. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /TONIGHT INTO WEDNESDAY NIGHT/...HIGH CONFIDENCE. TONIGHT...TRANQUIL WEATHER REGARDING WINDS AND SEAS. HOWEVER LOW CLOUDS...FOG AND POSSIBLY PATCHY DRIZZLE WILL LIKELY IMPACT THE SOUTHERN WATERS LATER TONIGHT. WEDNESDAY...LOW CLOUDS/FOG MAY LINGER INTO EARLY AFTERNOON ACROSS THE SOUTHERN WATERS. ELSEWHERE GOOD VSBY. LOW RISK OF A FEW SHOWERS/TSTMS TOWARD SUNSET. SW WINDS 10-15 KT POSSIBLY GUSTING TO 20 NEAR SHORE. 5 FT SOUTH SWELLS FROM HURRICANE CRISTOBAL ARRIVE IN THE SOUTHERN WATERS LATE IN THE DAY. WEDNESDAY NIGHT...SOUTH SWELLS FROM CRISTOBAL INCREASE RAPIDLY TO 6-9 FT BY DAYBREAK THU ACROSS THE SOUTHERN WATERS. A FEW TSTMS POSSIBLE WED EVENING. WIND SHIFT FROM SSW TO NW WITH THE FRONTAL PASSAGE. OUTLOOK...THURSDAY THROUGH SUNDAY... THURSDAY...HIGH CONFIDENCE. S-SWELL ASSOCIATED WITH CHRISTOBAL CONTINUES...BEGINNING TO DIMINISH INTO THE EVENING PERIOD. WITH BREEZY NW-FLOW WITH GUSTS UP TO 25 KTS POSSIBLE...AN OPPOSING WIND WILL MAKE FOR SOME CHOPPY CONDITIONS. WAVE HEIGHTS OF 8-10 FEET ARE FORECAST ACROSS THE ATLANTIC-EXPOSED S/SE WATERS. S-FACING BAYS AND HARBORS BEING SHELTERED FROM THE SWELL WILL HAVE LOWER WAVE HEIGHTS...BUT STILL HAVE THE NW-WIND THREAT. FRIDAY...HIGH CONFIDENCE. HIGH PRESSURE IN CONTROL. LIGHT WINDS. DIMINISHING SEAS WITH ONLY THE S/SE OUTER WATERS EXPERIENCING WAVE HEIGHTS IN EXCESS OF 5-FEET BY MORNING. GOOD BOATING WEATHER. SATURDAY INTO SUNDAY...MODERATE CONFIDENCE. INCREASING S-WINDS. FEEL MAJORITY OF WATERS WILL REMAIN DRY AS SHOWER AND THUNDERSTORM ACTIVITY IS ONGOING ACROSS INTERIOR NEW ENGLAND...MAINLY SUNDAY. SOME OF THE WET-WEATHER MAY DRIFT ACROSS THE E-WATERS POSING THREATS TO MARINERS...YET LOW CONFIDENCE AT THIS TIME. PROLONGED S-FETCH LENDING TO WAVE HEIGHTS IN EXCESS OF 5-FEET ACROSS THE S/SE WATERS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...AIR QUALITY ALERT FROM 1 PM TO 9 PM EDT WEDNESDAY FOR CTZ002>004. MA...NONE. NH...NONE. RI...AIR QUALITY ALERT FROM 11 AM TO 11 PM EDT WEDNESDAY FOR RIZ001>005. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 PM WEDNESDAY TO 6 PM EDT THURSDAY FOR ANZ235-237-254>256. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...WTB SHORT TERM...NOCERA LONG TERM...SIPPRELL AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL

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