Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251109 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 709 AM EDT MON AUG 25 2014 .SYNOPSIS... HIGH PRESSURE CONTINUES TO BUILD SOUTH OF NEW ENGLAND THROUGH MIDWEEK BRINGING DRY WEATHER AND ABOVE-NORMAL TEMPERATURES. A COLD FRONT MOVES THROUGH WEDNESDAY BRINGING A CHANCE OF SHOWERS AND THUNDERSTORMS WITH IT. DRY...COOLER WEATHER RETURNS FOR THE LATER PART OF THE WEEK FOLLOWED BY POSSIBLY ANOTHER SHOT OF WET- WEATHER OVER THE WEEKEND INTO NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM UPDATE... NO MAJOR CHANGES IN THE FORECAST. THE PREVIOUS DISCUSSION SAYS IT ALL. PREVIOUS DISCUSSION... MAINLY SKC CONDITIONS ACROSS THE REGION THIS MORNING HAS ALLOWED FOR DECENT RADIATIONAL COOLING AND TEMPS ALREADY IN THE LOW-MID 50S ACROSS MUCH OF THE REGION. ONLY THE URBAN LOCALES ARE WARMER...IN THE 60S. THERE ARE A FEW CLOUDS MOVING OFF OF THE GULF OF MAINE EARLY THIS MORNING WHICH IS LIKELY TO LIMIT FURTHER COOLING THERE...HOWEVER NW VALLEYS IN MA AND SW NH COULD STILL MAKE A RUN AT THE 40S THANKS TO THE NEXT COUPLE OF HOURS OF FURTHER COOLING. OTHERWISE TODAY...A FAIR AMOUNT OF SUNSHINE OUT OF SOME DIURNAL CU ACROSS THE INTERIOR. H85 TEMPS CONTINUE TO RISE AS CENTER OF HIGH PRES GRADUALLY SHIFTS TO THE SW. WITH TEMPS AT THIS LVL AROUND +14C...SHOULD SEE HIGHS SHIFT INTO THE LOW-MID 80S WITH A FEW UPPER 80S IN THE WARMER VALLEYS THANKS TO A MODEST DOWNSLOPE COMPONENT TO THE WEAK FLOW. OVERALL FLOW IS RELATIVELY WEAK...BUT WILL GRADUALLY SHIFT TO THE S THROUGH THE DAY. SEA BREEZES KEEP NEAR SHORE LOCATIONS COOLER...MAINLY IN THE 70S. && .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 /11Z MONDAY THROUGH FRIDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM...THROUGH TUESDAY...HIGH CONFIDENCE. 12Z UPDATE... VFR. EXCEPT FOR SOME LOCALIZED MVFR-IFR FOG AT TYPICALLY PRONE AIRPORTS BOTH THIS MORNING AND AGAIN LATE TONIGHT. LIGHT FLOW SHIFTS TO THE S TODAY EXCEPT AT NEAR SHORE TERMINALS WITH SEA- BREEZES AROUND 15Z. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZES LIKELY START AROUND 14Z. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...TUESDAY NIGHT THROUGH FRIDAY... TUESDAY NIGHT INTO 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. 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...DOODY/SIPPRELL SHORT TERM...DOODY LONG TERM...SIPPRELL AVIATION...DOODY/SIPPRELL MARINE...DOODY/SIPPRELL

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