Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251958 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 358 PM EDT MON AUG 25 2014 .SYNOPSIS... HIGH PRESSURE OVER NEW ENGLAND WILL DRIFT SOUTH OF THE AREA THROUGH MIDWEEK BRINGING DRY WEATHER AND WARMER THAN NORMAL TEMPERATURES. A COLD FRONT MOVES THROUGH WEDNESDAY BRINGING A CHANCE OF AN ISOLATED SHOWER AND/OR THUNDERSTORM. DRY...SOMEWHAT COOLER WEATHER RETURNS FOR THE LATER PART OF THE WEEK FOLLOWED BY POSSIBLY A PERIOD OF WET WEATHER OVER THE HOLIDAY WEEKEND INTO NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... *** PVD HITS 90 AT 312 PM TODAY FOR THE FIRST TIME SINCE 7/8/14 *** PLEASANT WEATHER ACROSS SOUTHERN NEW ENGLAND INTO THIS EVENING AND OVERNIGHT AS BOTH UPPER LEVEL RIDGE AND SURFACE HIGH PRES CREST OVER THE REGION. THIS PROVIDES A DEEP COLUMN OF SUBSIDENCE AND ASSOCIATED DRY AIR. LATE DAY SEABREEZES WILL ERODE LATER THIS EVENING. GIVEN THE LIGHT WINDS AND RELATIVELY DRY AIRMASS TEMPS WILL FALL MODESTLY WITH SUNSET PER RADIATIONAL COOLING. NOT QUITE AS COOL AS LAST NIGHT BUT STILL MOST LOCATIONS OUTSIDE OF THE URBAN AREAS WILL SEE MINS IN THE U50S TO L60S...WITH M60S IN THE URBAN CENTERS. NEVERTHELESS VERY COMFORTABLE. THIS RADIATIONAL COOLING WILL LEAD TO PATCHY FOG IN THE TYPICAL INTERIOR VALLEYS AND LOW LYING SECTIONS OF EASTERN MA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... TUESDAY... MORE OF THE SAME...DEEP LAYER RIDGE AXIS OVER THE REGION IN THE MORNING AND SLOWLY SAGS SOUTH TO THE COAST BY DAYS END. THIS PROVIDES ANOTHER DAY OF DRY WEATHER...ABUNDANT SUNSHINE AND LIGHT/VARIABLE WINDS BECOMING SSW IN THE AFTERNOON. AUG SUN CONTINUES TO MODIFY AIRMASS WITH BOTH 850 MB AND 925 MB TEMPS WARMING BY A FEW DEGS. THIS SUGGEST MU80S TO AROUND 90 WILL BE MORE COMMON TOMORROW AWAY FROM THE SOUTH COAST. SSW WINDS WILL KEEP SOUTH COASTAL AREAS/BEACHES IN THE 75 TO 80 DEG RANGE. DEW PTS STILL REASONABLE IN THE U50S TO L60S. NONETHELESS ANOTHER FABULOUS DAY. TUESDAY NIGHT... EAST COAST RIDGE BEGINS TO SLOWLY ERODE WITH SUBTLE HEIGHT FALLS OVER NEW ENGLAND AS NORTHERN STREAM TROUGH ENTERS THE GREAT LAKES. ANTICYCLONIC MID LEVEL FLOW CONTINUES SO DRY WEATHER PREVAILS. AREAS OF FOG NOT AS WIDESPREAD AS TONIGHT AS SURFACE WINDS BECOME MORE WSW AS COLD FRONT APPROACHES. THIS WILL ALSO RESULT IN A MILDER NIGHT WITH LOWS IN THE 60S REGIONWIDE. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... */ 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 /20Z 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 NIGHT...HIGH CONFIDENCE. EAST SWELLS OF 3-4 FT CONTINUE MAINLY ACROSS THE EASTERN MA WATERS. WINDS REMAIN LIGHT THRU TUE NIGHT AS HIGH PRES HOVERS OVER THE AREA. VSBY MAY BRIEFLY LOWER NEAR SHORE LATE AT NIGHT/EARLY MORNING...OTHERWISE GOOD VSBY SHOULD PREVAIL ALONG WITH DRY WEATHER. ANY LARGE SWELLS FROM TROPICAL STORM CRISTOBAL SHOULD NOT ARRIVE INTO THE SOUTH COASTAL WATERS UNTIL WED. OUTLOOK...WED THROUGH FRIDAY... WED 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...NOCERA NEAR TERM...NOCERA SHORT TERM...NOCERA LONG TERM...SIPPRELL AVIATION...NOCERA/SIPPRELL MARINE...NOCERA/SIPPRELL

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