Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 252033 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 433 PM EDT SAT JUL 25 2015 .SYNOPSIS...
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UNSETTLED WEATHER EXPECTED THROUGH EARLY NEXT WEEK...WITH MAINLY DIURNAL SHOWERS AND THUNDERSTORMS. SCATTERED STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE AGAIN SOMETIME SUNDAY INTO SUNDAY NIGHT. RISK FOR THUNDERSTORMS CONTINUES MONDAY. THE NEXT MAIN WEATHER HEADLINE WILL BE A POSSIBLE HEAT WAVE TUESDAY THROUGH THURSDAY. A COLD FRONT MAY BRING SCATTERED THUNDERSTORMS LATE THURSDAY AND THURSDAY NIGHT.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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415 PM UPDATE... THRU EARLY THIS EVENING... DIURNAL HEATING OVER WESTERN MA AND CT HAS ALLOWED FOR SOME ISOLATED SHOWERS TO POP UP. SOME SHALLOW LOW LEVEL INSTABILITY EXISTS IN THIS AREA. WILL HAVE A CONTINUED RISK FOR ISOLATED/DIURNALLY DRIVEN...LOW- TOPPED SHOWERS ACROSS THE EAST SLOPES OF THE BERKS/PIONEER VALLEY AND NORTHERN CT INTO EARLY THIS EVENING. EASTERN HALF OF CWA HAS BEEN LARGELY SHOWER-FREE DUE TO MARINE INFLUENCE KEEPING MAX TEMPS LOWER AND AIRMASS MORE STABLE. EXCEPTION: CAPE COD AREA DID GET INTO THE 70S TODAY AND A LOCAL BOUNDARY PICKED UP ON SURFACE OBS IN THE AREA SHOWED CONSISTENT LOW LEVEL CONVERGENCE FROM 16Z THRU THIS AFTERNOON. SLOW MOVING SHOWER/S/ DEVELOPED RIGHT IN THIS AREA...AND MOVEMENT WAS MINIMAL AT 20Z. EXPECTING THIS AREA IS AT A CONTINUED RISK FOR SHOWERS FOR A COUPLE MORE HOURS...SO HAVE LOCALIZED POPS IN THIS AREA. OTHERWISE...PARTLY TO MOSTLY CLOUDY SKIES EXPECTED ACROSS SNE THRU EARLY THIS EVENING. TONIGHT... PREVIOUS BACKDOOR BOUNDARY MAKES AN EASTWARD RETURN INTO OUR AREA TONIGHT AS A WARM FRONT. MID-LEVEL FORCING PER H5 VORTMAX ALOFT SWEEPING ACROSS THE NE-CONUS THRU THE BROADER CYCLONIC FLOW AN OVER-RUNNING PRECIP SETUP SEEMS LIKELY. CHANCE TO LIKELY POPS ACCORDINGLY FOR SHOWERS. BASED ON MODEL SOUNDINGS...WILL MENTION ISOLATED THUNDER AS IT IS ANTICIPATED THAT PARCELS WILL UNDERGO FORCING WITHIN THE LOW- TO MID-LEVELS. INSTABILITY LOOKS TO BE MARGINAL...SO AT THIS TIME NOT EXPECTING LOW LEVEL HELICITY TO TRANSLATE TO ISSUES AT THE SURFACE. LOWS TONIGHT IN THE LOW-MID 60S AND HUMID WITH SURFACE S-SE ONSHORE FLOW AND THE POSSIBILITY FOR PATCHY DENSE FOG.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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SUNDAY... MID-LEVEL SHORT WAVE AND ACCOMPANYING TROUGH AXIS LIFT NORTHEAST INTO MAINE THROUGH THE DAY. WARM FRONT LIFTS NORTH OF OUR REGION AND SHOWERS WITH ISOLATED THUNDER POSSIBLE IN THE MORNING. THEN ANTICIPATING AFTERNOON SHOWERS AND T-STORMS WITH DIURNAL INSTABILITY. GREATER INSTABILITY DEVELOPS THOUGH IN WHAT APPEARS TO BE A MARGINAL-SHEAR ENVIRONMENT. MODELS SHOW 0-1/0-3 KM HELICITY DECREASES DURING THE DAY...BUT THIS WILL BE SOMETHING TO KEEP AN EYE ON AS SUNDAY UNFOLDS. POSSIBILITY FOR SHOWERS/SCATTERED T-STORMS ON SUNDAY FROM LOW-LEVEL CONVERGENCE...AIRMASS INSTABILITY/RAPID DESTABILIZATION...AND/OR OROGRAPHIC LIFT. ANY ONE OR A COMBINATION OF WHICH SEEMS TO LEND TO SCATTERED SHOWER AND THUNDERSTORM ACTIVITY. MEAN-WIND FLOW IS RATHER MEAGER AROUND 15 KTS...SO SOME CONCERN WITH RESPECT TO SOME LOCALIZED HEAVY RAINFALL. PWATS 1.25-1.5 INCHES SO NOT EXPECTING WIDESPREAD ISSUES WITH HEAVY RAINFALL. CAPE GENERALLY 1000-2000 J/KG SUNDAY AFTERNOON. COULD BE LOOKING AT A PERIOD OF STRONG TO SOME SEVERE T-STORMS WITH POSSIBILITY OF LARGE HAIL...DAMAGING WINDS...MAYBE A LOW CHANCE OF A TORNADO. NOT ENOUGH CONFIDENCE IN GOING WITH ENHANCED WORDING IN THE FORECAST...LOW CONFIDENCE. SUNDAY NIGHT...SHOWERS AND THUNDERSTORMS WILL GRADUALLY DIMINISH OVERNIGHT. AREAS OF FOG WILL LIKELY DEVELOP. LOWS IN THE 60S.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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HIGHLIGHTS... * SCATTERED T-STORMS MONDAY. * HEAT WAVE POSSIBLE TUESDAY THROUGH THURSDAY. * SCATTERED STORMS POSSIBLE LATE THURSDAY AND THURSDAY NIGHT. OVERVIEW AND MODEL PREFERENCES... FINALLY WE WILL BE MOVING ONE CUTOFF LOW PRES ACROSS ATLANTIC CANADA OUT TOWARD GREENLAND...ALLOWING SUBTROPICAL RIDGING TO TAKE CONTROL THROUGH MUCH OF THE WEEK. FOLLOWED BY YET ANOTHER ONE. GUIDANCE IN PRETTY GOOD AGREEMENT AT THE SYNOPTIC SCALE WITH THIS THINKING. THEREFORE...HAVE HIGH CONFIDENCE IN ECHOING PREVIOUS FORECASTER THAT A HEAT WAVE FOR SOME /OR AT THE VERY LEAST ABOVE NORMAL TEMPERATURES/ IS LIKELY FOR THE TUE-FRI TIMEFRAME. UNCERTAINTY IN TIMING OF ANY PRECIP PARTICULARLY TUE- FRI AS WELL...AS GUIDANCE CONTINUES TO INDICATE QPF BUT IN AN UNFAVORABLE REGIME. FEEL THAT AS A SECONDARY CUTOFF SETTLES ACROSS QUEBEC AND NRN NEW ENGLAND THE THREAT FOR PRECIP WILL INCREASE...BUT THE MID TERM IS LIKELY TO BE MORE DRY THAN WET...WITH THE ONE EXCEPTION BEING MON...BUT MORE ON THAT BELOW. GIVEN THE REASONABLE SYNOPTIC AGREEMENT...A BLEND OF OPERATIONAL GUIDANCE AND ENSEMBLES WILL BE USED. THIS SHOULD ALSO SMOOTH OUT ANY OF THE QPF ANOMALIES MENTIONED ABOVE. DETAILS... MON... GFS HAS NOW JOINED THE ECMWF AND INDICATES HIGHER K-INDICES AND MODEST P-WATS AVAILABLE TO WORK WITH A STALLED AND DISSIPATING FRONT ACROSS SRN NEW ENGLAND MON. THIS INCREASE IN MOISTURE LEADS TO DECENT SFC BASED CAPE VALUES APPROACHING 1500-2000J/KG UNDER NEARLY 6.5C/KM LAPSE RATES. AT ODDS WILL BE HOW MUCH CLEARING IS OBSERVED AND WHETHER THE BULK OF THIS CAPE CAN EVEN BE REALIZED IN SPITE OF THE FORCING MECHANISM. BEST CHANCE WILL BE WRN MA/CT WHERE DRIER AIR WILL BE MOVING IN...BUT THIS WILL ALSO LEAD TO SOME CAPPING. THEREFORE...NOT AN IDEAL SETUP HERE...SHEAR NOT IMPRESSIVE EITHER AND WILL LIKELY BE TOO LOW TO MAKE UP THE DIFFERENCE. IN ANY CASE...LOW END CHANCE POPS WITH SOME MENTION OF THUNDER STILL SEEMS LIKE A REASONABLE FORECAST FOR MON...PRIOR TO THE HEATING OF MID WEEK. TUE THROUGH THU... BUILDING RIDGE WILL ALSO LEAD TO INCREASING LOW-MID LVL TEMPS THROUGH THE PERIOD. H92 TEMPS START AROUND 22-23C AND H85 16-17C. BY THU...THEY TOP OUT AROUND 26-28C AT H92 AND 20-22C AT H85. THIS SUGGESTS A CAP WHICH IS LIKELY TO PREVENT DEVELOPMENT DIURNAL CONVECTION AND WITH LIMITED PWATS /NEAR JULY NORMALS/ TUE AND WED...SUSPECT SOUNDING IS TOO DRY TO SUPPORT THE QPF THAT THE GFS IS ESPECIALLY ROBUST WITH. BY THU HUMIDITY/PWATS INCREASE TO NEARLY 2 STD DEVIATIONS ABOVE NORMAL BUT DEEP LAYER RIDGING AND CONTINUED CAPPING SHOULD LIMIT RISK FOR SHOWERS/STORMS. THEREFORE...WILL GO WITH A MAINLY DRY PERIOD...BUT WITH GRADUALLY MODERATING TEMPERATURES. W COMPONENT TO THE FLOW DOES INDICATE DOWNSLOPING...SO TEMPERATURES ARE LIKELY TO OVERACHIEVE TYPICAL MIXING EACH DAY. SOME LOCATIONS COULD BE HEADING FOR A TRUE HEAT WAVE...BUT SEVERAL LOCATIONS WILL LIKELY SEE THE LOW 90S BY THU. FRI... THE FIRST IN A SERIES OF SHORTWAVES WHICH WILL HELP TO DIG A CUTOFF LOW PRES AND ASSOCIATED TROF TO THE S MOVES THROUGH ON FRI. TIMING DIFFERENCES ARE NOTED WITH TYPICAL BIASES...AS IN GFS IS FASTER THAN THE THE MORE AMPLIFIED ECMWF. FOR NOW...WILL TIME THE ATTENDANT FRONTAL BOUNDARY RIGHT DOWN THE MIDDLE OF THESE SOLUTIONS...SUGGESTING A LATE THU NIGHT/EARLY FRI PASSAGE. RISK FOR THUNDERSTORMS WILL BE DEPENDENT ON EROSION OF THE CAP AND LEFTOVER CAPE VALUES DURING THE OVERNIGHT HOURS. ONCE AGAIN SHEAR IS LIMITED...SO WILL BE INCREASING POPS BUT APPLYING THUNDER UNDER THE HIGHEST POP THRESHOLD. INDEED EVEN MODELS CAPABLE OF RESOLVING CONVECTION ARE NOT OVERLY IMPRESSIVE AT THIS POINT. HOWEVER...GIVEN THE AIRMASS IN PLACE ABOVE THE CAP...WILL NEED TO KEEP AN EYE ON THIS PERIOD...AS A LATER PASSAGE COULD MEAN SOMETHING ENTIRELY DIFFERENT. SAT... WILL GENERALLY LEAN ON A DRY PERIOD...BUT WITH THE SETTLING CUTOFF AND NEAR STALLING FRONTAL BOUNDARY TO THE S...THIS TOO COULD CHANGE. AT ANY RATE...COOLER AIRMASS IN PLACE WITH TEMPERATURES TRENDING BACK TOWARD SEASONAL NORMALS.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT-TERM /THROUGH SUNDAY/...MODERATE CONFIDENCE. EARLY THIS EVENING...MODERATE CONFIDENCE. 4 PM UPDATE... CIGS ACROSS EASTERN HALF OF MA HAD MOSTLY IMPROVED TO VFR BUT SOME PATCHY MVFR CIGS LINGERED. EXPECT CONTINUED CIG IMPROVEMENT INTO EARLY THIS EVENING. SHOWER ACTIVITY MAY LINGER THRU 22-23Z OVER LOCALIZED BOUNDARY MID-CAPE. MAINLY VFR CONDITIONS EXPECTED WEST OF FIT/ORH IN MA AS WELL AS RI AND NORTHERN CT. CHANCE FOR ISOLATED MVFR -SHRA. LIGHT NE/E WINDS BECOMING SE/S THIS EVENING. TONIGHT...MODERATE CONFIDENCE. EXPECTING MAINLY VFR CONDITIONS TO START TONIGHT...THEN MVFR CIGS/VSBYS BECOME POSSIBLE IN PATCHY FOG AND SCATTERED SHOWERS. LOCALIZED IFR CONDITIONS POSSIBLE IN DENSE FOG AND/OR ISOLATED TSRA. SUNDAY...LOW CONFIDENCE. MAINLY VFR DURING THE DAY...BUT MVFR-IFR IMPACTS POSSIBLE WITH TSRA WHICH MAY ALSO CONTAIN MULTIPLE CONVECTIVE THREATS SUCH AS HAIL AND GUSTY WINDS. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. E/SE ONSHORE WINDS THRU TONIGHT THIS EVENING. PREDOMINANTLY BKN BUT VFR CIGS THRU 00Z...WITH POTENTIAL FOR MVFR CIGS/VSBYS WITH FOG RETURNING LATER TONIGHT. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. MAINLY VFR WITH SOME FOG POSSIBLE LATER TONIGHT. ISOLATED -SHRA POTENTIALLY DEVELOPING LATE THIS AFTERNOON. OUTLOOK /MONDAY THROUGH THURSDAY/... MON AND TUE...MODERATE CONFIDENCE. A FRONTAL BOUNDARY WILL STALL OVER...OR JUST OFFSHORE OF NEW ENGLAND. THIS WILL PROVIDE A FOCUS FOR CONTINUED SHOWER/T-STORMS DURING THE AFTERNOON HOURS. OTHERWISE VFR DURING THE DAY. FOG POSSIBLE AT TYPICALLY PRONE AIRPORTS EACH NIGHT. WED AND THU...HIGH CONFIDENCE. MAINLY VFR WITH WEAK HIGH PRES.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH SUNDAY/...HIGH CONFIDENCE. TONIGHT...ISOLATED SHOWERS REMAIN POSSIBLE IN VICINITY OF NANTUCKET SOUND THRU 00Z. INCREASING CHANCES FOR SHOWERS TOWARDS MORNING OUT OF THE W POSSIBLY ACCOMPANIED WITH THUNDER. WINDS VEERING SE AND INCREASING. POTENTIAL FOR PATCHY DENSE FOG AROUND THE CAPE AND ISLANDS. SUNDAY... CONTINUED CHANCES OF WET-WEATHER...ESPECIALLY OVER THE E-WATERS. SE-WINDS CONTINUE TO VEER S WITH THE POTENTIAL FOR GUSTS OF 15-20 KTS. SEAS BUILD UP TO AROUND 4-FEET. SUNDAY NIGHT... DIMINISHING CHANCES FOR SHOWERS/THUNDER...WITH WINDS/SEAS BELOW SCA CONDITIONS. OUTLOOK /MONDAY THROUGH THURSDAY/... MON AND TUE...HIGH CONFIDENCE. A FRONTAL BOUNDARY WILL STALL OVER OR JUST INLAND OF THE SRN NEW ENGLAND WATERS...THEN MOVE OFFSHORE ON TUE. THIS BOUNDARY IS LIKELY TO HAVE LITTLE IMPACT ON SEAS/WINDS EACH DAY...CONDITIONS SHOULD GENERALLY REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS...ALTHOUGH NEAR SHORE WATERS SURROUNDING CAPE COD/ISLANDS MAY APPROACH 20-25 KT OUT OF THE SW. AN OCCASIONAL SHOWER OR THUNDERSTORM IS POSSIBLE WITH LOCALLY ROUGH CONDITIONS...BUT THIS THREAT SHOULD DROP BY TUE NIGHT. WED AND THU...MODERATE CONFIDENCE. WEAK HIGH PRES WILL BUILD OVER THE WATERS WITH WARMING CONDITIONS. EXPECT WINDS/SEAS TO REMAIN BELOW SCA CONDITIONS SAVE FOR MAYBE THU...WHERE INCREASING SW FLOW MAY LEAD TO 5 FT SWELLS MOVING UP THE COASTLINE AND IMPACTING THE SRN WATERS.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...DOODY/NMB NEAR TERM...NMB SHORT TERM...NMB LONG TERM...DOODY AVIATION...DOODY/NMB MARINE...DOODY/NMB

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