Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251752 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 152 PM EDT MON AUG 25 2014 .SYNOPSIS... HIGH PRESSURE CONTINUES TO BUILD SOUTH OF NEW ENGLAND THROUGH MIDWEEK BRINGING DRY WEATHER AND WARMER THAN NORMAL TEMPERATURES. A COLD FRONT MOVES THROUGH WEDNESDAY BRINGING A CHANCE OF SHOWERS AND THUNDERSTORMS. DRY...COOLER WEATHER RETURNS FOR THE LATER PART OF THE WEEK FOLLOWED BY POSSIBLY A PERIOD OF WET WEATHER OVER THE WEEKEND INTO NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 145 PM UPDATE... SPECTACULAR WEATHER ACROSS SOUTHERN NEW ENGLAND THIS AFTERNOON WITH ABUNDANT SUNSHINE...TEMPS IN THE 80S INLAND ALONG WITH COMFORTABLE HUMIDITY WITH DEW PTS IN THE 50S. CLOSER TO THE COAST TEMPS ARE COOLER...IN THE 70S AS LIGHT SEABREEZES ARE IN PROGRESS. DEW PTS A LITTLE HIGHER HERE /U50S TO L60S/ GIVEN ON THE ONSHORE FLOW. ONLY FLY IN THE OINTMENT ARE MODEST 3-4 FT EASTERLY SWELLS YIELDING SOME ROUGH SURF AND RIP CURRENTS ACROSS EASTERN MA BEACHES FROM CAPE COD NORTHWARD TO SALISBURY BEACH. THESE SWELLS ARE NOT FROM TS CRISTOBAL BUT RATHER FROM A STALLED FRONT IN THE CENTRAL ATLC WITH AT LEAST ONE WAVE OF LOW PRES ON THIS FRONT GENERATING THE HIGHER SEAS OFFSHORE. PREVIOUS DISCUSSION... NO MAJOR CHANGES FROM PREVIOUS FORECAST. 12Z OBSERVED SOUNDINGS FROM CHATHAM MA AND PORTLAND ME INDICATE DEEP MID LEVEL SUBSIDENCE INVERSION AS H5-H7 RIDGE AXIS OVER THE ST LAWRENCE RIVER VLY PROVIDES LARGE SCALE SUBSIDENCE ACROSS NEW ENGLAND. THIS WILL PROVIDE LOTS OF SUNSHINE TODAY ALONG WITH A FEW DECORATIVE DIURNAL CU/SCU CLOUDS. DESPITE 2 MONTHS REMOVED FROM THE SUMMER SOLSTICE AUGUST SUNSHINE STILL ABLE TO MODIFY AIRMASS WITH 850 MB AND 925 MB TEMPS A FEW DEGS WARMER THAN YESTERDAY. THUS EXPECTED HIGHS TODAY 85-90 INLAND AWAY FROM COOLING AFTERNOON SEABREEZES AT THE COAST. WITH OCEAN TEMPS IN THE U60S TO AROUND 70...EXPECT BEACHES AND COASTAL AREAS TO ONLY COOL OFF INTO THE MU 70S. MODERATELY HUMID ALONG THE COAST WITH DEW PTS IN THE L60S. HOWEVER INLAND FAIRLY DEEP BLYR MIXING UP TO ABOUT 850 MB PER BUFKIT SOUNDINGS SHOULD RESULT IN DEW PTS FALLING INTO THE MU 50S DURING PEAK HEATING THIS AFTERNOON. EARLIER DISCUSSION BELOW. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... TONIGHT... UPPER LVL RIDGE WILL CREST ACROSS THE REGION AS CENTER OF HIGH PRES AND OVERALL RIDGE SHIFTS TO THE S COAST. THEREFORE...WITH A RELATIVELY WEAK PRES GRADIENT AND LITTLE MOISTURE THROUGH THE COLUMN ANOTHER NIGHT FOR RADIATIONAL COOLING IS LIKELY. EVEN WITH A WARMER START IN THE EVENING...SUSPECT MANY LOCATIONS WILL ONCE AGAIN MAKE A RUN INTO THE 50S THANKS TO DWPTS STAYING IN THE 50S THROUGH THE DAY TODAY. A FEW 40S NOT OUT OF THE QUESTION EITHER...IN THE COOLER VALLEYS OF NW MA AND SW NH. SOME PATCHY VALLEY FOG ALSO POSSIBLE IN TYPICALLY PRONE SPOTS. TUESDAY... WITH HIGH PRES SHIFTING TO THE S AND A COLD FRONT SLOWLY APPROACHING FROM THE NW...INCREASING PRES GRADIENT WILL LEAD TO MODERATE RETURN FLOW THROUGH THE DAY. EXPECT INCREASING DWPTS... ALTHOUGH ONLY TO AROUND THE 60 MARK. ALSO THIS FLOW WILL LIMIT SEA BREEZES ON THE E COAST...AND MAY EVEN KEEP THEM OFFSHORE ENTIRELY. THEREFORE...AWAY FROM THE S COAST...MORE LOCATIONS MAKE A RUN AT THE MID 80S AND UPPER 80S WHERE THE DOWNSLOPING IS MAXIMIZED. CONDITIONS REMAIN MOSTLY DRY...JUST SOME DIURNAL CU EXPECTED. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... */ HIGHLIGHTS... - CHANCES OF SHOWERS / THUNDERSTORMS FOR WEDNESDAY - SEASONABLE WEATHER UNDER HIGH PRESSURE THURSDAY INTO FRIDAY - HOT AND HUMID CONDITIONS AND WET WEATHER RETURN FOR THE WEEKEND */ OVERVIEW AND MODEL PREFERENCE... ENSEMBLE SIGNALS OF A NEGATIVE NAO AND PNA INTO THE END OF THE MONTH WOULD INDICATE PREFERRED TROUGHING AND RIDGING ACROSS THE E-CONUS RESPECTIVELY. CONFUSED? CONSIDER THAT WITH A NEGATIVE PNA TROUGHING OCCURS OVER THE W-CONUS WITH RIDGING E...WHILE WITH A NEGATIVE NAO RIDGING IS PREFERRED ACROSS THE NW-ATLANTIC INTO THE DAVIS STRAIGHT RESULTING IN TROUGHING TO THE W. CONSEQUENTIALLY...THE STRENGTH OF EITHER DETERMINES CONDITIONS ACROSS THE AREA OF WHICH THERE IS EVEN THE POTENTIAL FOR BALANCE RESULTING IN CONVERGENT ZONAL FLOW ACROSS THE REGION /TROUGH TO THE N...RIDGE TO THE S/. EVALUATING DETERMINISTIC/ENSEMBLE GUIDANCE...THERE APPEARS TO BE NO BIG SYSTEMS ON THE HORIZON /MINUS CRISTOBAL/ BUT RATHER AN AVERAGE ZONAL FLOW. WITH MORE PRONOUNCED W-CONUS TROUGHING...EXPECT HIGHER HEIGHTS WITHIN THE ZONAL FLOW...AND WEAKER TROUGH DISTURBANCES WITH ATTENDANT LOW PRESSURE CENTERS STAYING WELL TO THE N. SO IN SUMMARY...EXPECTING A WARMER-THAN-AVERAGE PATTERN INTO EARLY SEPTEMBER. AS IT HAS BEEN THE CASE ACROSS THE MID-ATLANTIC AS OF LATE...THE NE CONUS COULD NOW FIND ITSELF PARKED BENEATH THE STALLED BOUNDARY OF AIRMASSES ALONG WHICH INDIVIDUAL WAVES WOULD YIELD AN ACTIVE- AND WET-WEATHER PATTERN. IF ENSEMBLE MEMBERS ARE CORRECT... THIS COULD BREAK LATER IN TIME AS THE PNA SHIFTS TOWARDS A POSITIVE MODE RESULTING IN A PREFERRED TROUGHING-MODE OVER THE NE-CONUS. HIGHLIGHTS/CONFIDENCE ARE BROKEN DOWN IN THE DAILY DISCUSSION BELOW. */ DAY-TO-DAY DETAILS... TUESDAY NIGHT INTO THURSDAY NIGHT... CRISTOBAL SWEEPS NE WELL OFFSHORE OF NEW ENGLAND AS AN OPEN-WAVE TROUGH AMPLIFIES OVER THE NE-CONUS. EXPECT SWELL ASSOCIATED WITH CRISTOBAL DURING A PERIOD OF NORMAL ASTRONOMICAL TIDES. MODERATE TO HIGH RISK OF RIP CURRENTS. WITH THE TROUGH...AN ATTENDANT COLD FRONT WILL SWEEP ACROSS SNE LATE WEDNESDAY INTO WEDNESDAY NIGHT. ACTIVITY IS EXPECTED TO BE DIFFUSE AS LOW- TO MID-LEVEL FLOW IS WESTERLY AND MORE CONTINENTAL-ORIGIN. IN ADDITION...WITHIN THE RIGHT-EXIT-REGION OF THE UPPER-LEVEL-JET YIELDS PREFERRED SUBSIDENCE AND LESSER DEEP- LAYER ASCENT PER JET-COUPLING WITH THE SURFACE FRONT. WILL GO WITH ONE MORE DAY OF HEAT/HUMIDITY FOR WEDNESDAY WITH H85 TEMPERATURES AROUND +14/16C. HIGHS BREAKING 90-DEGREES FOR SEVERAL SPOTS ALONG WITH INCREASING CLOUDS AND THE CHANCE OF SHOWERS AND THUNDERSTORMS. CONVECTIVE THRESHOLDS ARE MET WITHIN MINOR-MODEST INSTABILITY IN A REGION OF WESTERLY WIND-SHEAR AND PWATS UP TO 1.75 INCHES. THEREAFTER HIGH PRESSURE BUILDS IN FROM THE W RESULTING IN CLEARING CONDITIONS AS WINDS BECOME LIGHT AND VARIABLE BENEATH A +8- 10C AIRMASS FOR THURSDAY. EXPECTING A MOSTLY CLEAR DAY WITH MORE SEASONABLE CONDITIONS. FRIDAY INTO FRIDAY NIGHT... WILL HOLD WITH A DRY FORECAST WITH HIGH PRESSURE IN CONTROL. EXPECT SEASONABLE CONDITIONS WITH MILDER AIR RETURNING LATE UNDER S/SE FLOW BENEATH INCREASING MID- TO HIGH-LEVEL CLOUDS. SATURDAY ONWARD... RETURN S-FLOW AHEAD OF A COLD FRONT RESULTS IN THE RETURN OF HOT AND HUMID CONDITIONS ALONG WITH THE CHANCES OF SHOWERS / THUNDERSTORMS. POSSIBLE THE FRONTAL BOUNDARY STALLS WITHIN POTENTIAL CONVERGENT ZONAL FLOW THROUGH WHICH ADDITIONAL WAVES OF ENERGY YIELD CONTINUED CHANCES OF SHOWERS / THUNDERSTORMS ALONG WITH THE THREAT OF HEAVY RAIN. NO CERTAINTY THIS FAR OUT IN THE FORECAST...BUT FEEL A BLEND OF THE DETERMINISTIC 25.0Z GFS AND 24.12Z ECMWF IS WARRANTED AS THERE IS DECENT AGREEMENT WITH ITS ENSEMBLE COUNTERPARTS. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM...THROUGH TUESDAY NIGHT...HIGH CONFIDENCE. 2 PM UPDATE... VFR EXCEPT FOR SOME LOCALIZED MVFR-IFR FOG ACROSS THE INTERIOR VALLEYS AND LOW LYING AREAS OF EASTERN MA LATE TONIGHT. MORE OF THE SAME TUE AND TUE NIGHT INCLUDING NEAR SHORE TERMINALS WITH LATE MORNING SEA BREEZES DEVELOPING. KBOS TERMINAL...HIGH CONFIDENCE IN TAF WITH SLIGHTLY LOWER CONFIDENCE ON EXACT TIMING OF SEA BREEZE TUE. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...WED THROUGH FRIDAY... WED AND WEDNESDAY NIGHT...MODERATE CONFIDENCE. SCT-BKN 4-6 KFT CIGS ALONG WITH THE CHANCES OF SHRA/TSRA. MIX OF MVFR-IFR CONDITIONS POSSIBLE WITH ANY WEATHER. COLD FRONT SWEEPING TERMINALS LATE WEDNESDAY INTO WEDNESDAY NIGHT WITH WINDS TURNING NW AND WEATHER CONCLUDING. THURSDAY INTO FRIDAY NIGHT...MODERATE CONFIDENCE. VFR. BREEZY NW FLOW THURSDAY TURNING LIGHT / VARIABLE OVERNIGHT INTO FRIDAY. S-WINDS TOWARDS SATURDAY MORNING ALONG WITH INCREASING MID- TO HIGH-LEVEL CLOUDS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM...THROUGH TUESDAY...HIGH CONFIDENCE. 10 AM UPDATE... PLEASANT BOATING CONDITIONS TODAY WITH LIGHT WINDS AS HIGH PRES CREST OVER THE WATERS. LIGHT WINDS YIELD VERY LITTLE IF ANY WIND WAVES. SEAS WILL CONSIST MAINLY OF A 3 FT EASTERLY SWELL WITH A PERIOD AROUND 9 SECONDS. EARLIER DISCUSSION. ================================================================= HIGH PRES BUILDS OVER THE WATERS THROUGH TUESDAY WITH MAINLY QUIET BOATING WEATHER EXPECTED. WINDS SHIFT FROM THE NE TODAY TO THE S-SW LATE IN THE DAY AND TOMORROW. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY... TUESDAY NIGHT INTO WEDNESDAY NIGHT...MODERATE CONFIDENCE. COLD FRONT SWEEPING THE WATERS WEDNESDAY NIGHT AS CRISTOBAL LIFTS NE OUT TO SEA WELL OFFSHORE OF NEW ENGLAND. SUBSEQUENT SWELL FROM CRISTOBAL WILL RESULT IN WAVE HEIGHTS UP TO 7 FEET ON THE OUTER WATERS. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE AHEAD OF THE COLD FRONT FOLLOWED BY HIGH PRESSURE. BREEZY SW WINDS BACKING OUT OF THE NW WITH PASSAGE. THURSDAY INTO FRIDAY NIGHT...MODERATE CONFIDENCE. SWELL DIMINISHING ALONG WITH WAVE HEIGHTS. HIGH PRESSURE BUILDING OVER THE WATERS WITH BREEZY NW FLOW THURSDAY TURNING LIGHT / VARIABLE OVERNIGHT INTO FRIDAY. S-WINDS TOWARDS SATURDAY MORNING. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...DOODY/SIPPRELL NEAR TERM...NOCERA SHORT TERM...DOODY LONG TERM...SIPPRELL AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/DOODY/SIPPRELL

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