Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260228 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1028 PM EDT SAT JUL 25 2015 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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1030 PM UPDATE... PERHAPS AN INCREASING LEVEL OF CLARITY WITH RESPECT TO SYNOPTICS YET AN UNDERLYING UNCERTAINTY WITH RESPECT TO OUTCOMES. ONLY A MODERATE CONFIDENCE FORCAST. SEEING THE LOW- TO MID-LEVEL WARM FRONTAL BOUNDARY ALONG THE LEADING EDGE OF A NOSE OF WARM HIGH THETA-E AIR BENEATH A MID- LEVEL VORTEX AND ACCOMPANY TROUGH AXIS PUSH E INTO THE NE-CONUS. STRONG CONVERGENCE AND DECENT FORCING NOT OUT OF THE QUESTION IN AN ENVIRONMENT OF NOTEWORTHY 0-1/0-3 KM HELICITY AS E/SE-FLOW WITHIN THE LOW-LEVELS MEETS UP WITH PREDOMINANT W-FLOW ALOFT. BUT IT APPEARS BETTER INSTABILITY LAGS. MUCH OF THE ENVIRONMENT LOOKS TO TRANSLATE E WHILE REMAINING PRIMARILY ACROSS N NEW ENGLAND... BUT THERE IS A BOUNDARY STRETCH TO THE SW IGNITING SOME ACTIVITY OVER THE BINGHAMTON NY REGION. AS THE ENVIRONMENT PUSHES E INTO THE FORECAST AREA TOWARDS MORNING THINK WE ARE LOOKING AT A HIGH SHEAR LOW INSTABILITY SETUP. AND IN ADDITION THE AFOREMENTIONED SYNOPTICS ARE RUNNING UP AGAINST REMNANT MID-LEVEL RIDGING...AS WELL AS DRIER AIR ASSOCIATED WITH HIGH PRESSURE OVER THE GULF OF MAINE EVIDENT IN 0Z SOUNDINGS OUT OF GRAY AND CARIBOU MAINE. SO THERE IS A LIKELY EXPECTATION OF WET WEATHER TO PUSH E THOUGH THE OUTER EDGE MAY FACE SOME WEAKENING / EROSION UP AGAINST THE DRIER AND SUBSIDING AIRMASS TO THE E. NEVERTHELESS FEEL THE STRONG FORCING ALONG THE WARM FRONT SHOULD PUSH RAIN INTO THE AREA BY MORNING WITH EMBEDDED THUNDERSTORMS...MAINLY OVER N/W FORECAST ZONES. WILL NEED TO WATCH THE S-FLANK OF THE WARM FRONT TOWARDS BETTER THETA-E AND INSTABILITY AS NOTED EARLIER OVER BINGHAMTON NY. FORECAST WAS A BLEND OF HRRR/SREF BLENDS WITH MOS GUIDANCE. STRAYED FROM EXPLICIT NAM/WRF MODEL SOLUTIONS. PATCHY DENSE FOG THROUGH THE EVENING WITH LOWS GETTING DOWN TO AROUND THE LOW-60S.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... 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. && .LONG TERM /MONDAY THROUGH SATURDAY/... 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. && .AVIATION /02Z SUNDAY 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/... TONIGHT...MODERATE CONFIDENCE. MAINLY VFR THROUGH ABOUT 04Z...THEN PATCHY GROUND FOG POSSIBLE AT TYPICALLY PRONE AIRPORTS. SCT -SHRA MOVING INTO THE N/W TERMINALS TOWARDS MORNING WITH THE RISK OF TSRA. SUNDAY...HIGH 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. MAINLY VFR...BUT THERE IS THE LINGERING THREAT OF LATE NIGHT FOG/LOW CLOUDS WITH MVFR CONDITIONS. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. MAINLY VFR WITH SOME FOG POSSIBLE LATER TONIGHT. 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...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...DOODY/SIPPRELL/NMB SHORT TERM...NMB LONG TERM...DOODY AVIATION...DOODY/NMB MARINE...DOODY/NMB

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