Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270219 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1019 PM EDT SUN JUL 26 2015 .SYNOPSIS... A VERY WEAK BOUNDARY WILL STALL ACROSS THE AREA THROUGH THURSDAY...WHICH WILL BRING A RISK FOR SHOWERS AND THUNDERSTORMS EACH AFTERNOON. SOME STORMS MAY PRODUCE HEAVY RAIN...AND A FEW MAY BECOME STRONG TO SEVERE. HOT AND HUMID TUESDAY THROUGH THURSDAY. A COLD FRONT MAY BRING SCATTERED THUNDERSTORMS LATE THURSDAY AND THURSDAY NIGHT. WARM AND DRY WEATHER IS EXPECTED FRIDAY INTO NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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1030 PM UPDATE... BOUNDARY LAYER STABILIZING AS TEMPERATURES COOL AT THE SURFACE. BUT THAT IS LIKELY NOT GOING TO STOP THE SHOW. AS DERIVED FROM THE SPC MESOANALYSIS WE ARE STILL BENEATH A BROAD AREA OF LOW PRESSURE WITH CYCLONIC FLOW ALOFT. A FAIR AMOUNT OF ELEVATED INSTABILITY AT DISPOSAL OF AROUND 1-2K J/KG. SHEAR IS WEAK OR HARDLY PRESENT. THE FOCUS FOR THIS EVENING INTO THE OVERNIGHT IS THE DEVELOPMENT OF SCATTERED SHOWERS / THUNDERSTORMS WHEREVER LIFT WITHIN THE LOW- TO MID-LEVELS ABOVE THE BOUNDARY LAYER CAN BE GENERATED. PERHAPS SOME OROGRAPHIC LIFT AIDING TO THE CAUSE. MID-LEVEL LAPSE RATES ARE AROUND 6C/KM SUBSEQUENTLY CONDITIONALLY UNSTABLE. THUS SOME CORES COULD GET QUITE UP THERE WITH HEIGHT THROUGH THE ATMOSPHERE. FREEZING LEVELS AROUND 13 KFT WITH THE -10 / -20C AT 19 AND 23 KFT RESPECTIVELY. THE PRIMARY THREATS WITH ANY STORMS IS HEAVY RAIN AND LOCALIZED FLOODING CONSIDERING THE LIGHT MEAN WIND FLOW THROUGH THE LAYER. ALSO HAVE TO CONTEND WITH LIGHTNING. SOME SECONDARY THREATS POSSIBLE OF HAIL AND GUSTY WINDS. WITH SHEAR BEING SO WEAK...WITH ANY HAIL IT WILL BE SMALL. UPDRAFTS LIKELY NOT TO SUSTAIN. OTHERWISE A MILD AND SOMEWHAT MUGGY NIGHT. LOWS DOWN INTO THE 60S AND THERE IS LIKELY TO BE SOME PATCHY FOG IN SPOTS CONSIDERING THE ANTECEDANT RAINS OF EARLIER TODAY AND DEWPOINTS IN THE LOW- TO MID-60S. ANYWHERE WHERE IT CAN CLEAR OUT EVER BRIEFLY WITH THE LIGHT SURFACE WINDS MAY RESULT IN QUICK FOG DEVELOPMENT. NEAR-TERM FORECAST GUIDANCE USED WITH THIS FORECAST BUT BLENDED WITH SREF PROBABILITIES AND MOS GUIDANCE. IT IS ANYONES GUESS AS TO WHERE CONVECTION WILL DEVELOP. BEST THING TO CONVEY IS THE CHANCE AND THE POTENTIAL THREATS.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... MONDAY... REMNANT BOUNDARY /PREVIOUS COLD FRONT WEAKENING/ DRIFTS INTO OUR AREA FROM THE WEST ON MONDAY. LOW LEVEL SOUTHERLY FLOW WILL CONTINUE TO KEEP MOISTURE INTO OUR AREA...WITH SURFACE DEWPOINTS IN THE MID AND UPPER 60S...AND PWATS AROUND 1.5 INCHES. POTENTIAL FOR SURFACE- BASED INSTABILITY TO INCREASE TO 1000-2000 J/KG FOR THE AFTERNOON. THE INSTABILITY ACCOMPANIED BY THE REMNANT BOUNDARY WILL ALLOW FOR SHOWER/THUNDERSTORM DEVELOPMENT. WILL WARRANT CHANCE POPS. WITH THE MEAN WIND FLOW AROUND 10 MPH OUT OF THE W...THREATS CONSIDERED ARE HEAVY RAIN / MARGINAL HAIL / PERHAPS STRONG TO DAMAGING WINDS FROM PULSE-TYPE CONVECTION /WEAK SHEAR ENVIRONMENT/. POTENTIAL LOCALIZED URBAN/POOR DRAINAGE FLOODING. WARM AND HUMID WITH HIGHS MOSTLY IN THE 80S. MONDAY NIGHT...ANY T-STORMS SHOULD SLOWLY DIMINISH IN THE EVENING...WITH ONLY A SLIGHT CHANCE SHOWERS LATE EVENING AND ON WITH THE NE-SW ORIENTED BOUNDARY LINGERING IN OUR AREA. OTHERWISE...A PARTLY CLOUDY AND MUGGY NIGHT WITH PATCHY FOG. && .LONG TERM /TUESDAY THROUGH SUNDAY/... HIGHLIGHTS... * VERY WARM WITH SCATTERED THUNDERSTORMS STILL POSSIBLE TUESDAY. * HOT WEDNESDAY AND THURSDAY WITH HIGHS IN THE LOWER TO MID 90S. * SCATTERED STORMS POSSIBLE LATE THURSDAY AND THURSDAY NIGHT. OVERVIEW AND MODEL PREFERENCES... AFTER A FINAL SHORTWAVE MOVES THROUGH THE REGION TUE...THE REMAINDER OF THE MID TERM WILL BE DEFINED BY RIDGE BUILDING AND WARM ADVECTION THEREIN. THE RIDGE/WARMING WILL LEAD TO A PERIOD OF ABOVE NORMAL HEAT/HUMIDITY MAINLY WED AND THU. UPSTREAM...A CUTOFF LOW PRES NEAR BAFFIN ISLAND IS EXPECTED TO PHASE WITH ROBUST SHORTWAVE ENERGY CURRENTLY RESIDING OVER THE PAC NW. THE FIRST EXPERIENCE OF THIS FEATURE WILL COME FRI...WITH THE PASSAGE OF A WEAK COLD FRONT WHICH WILL RELIEVE THE AREA OF MUCH OF THE HEAT. AS THE CUTOFF SETTLES OVER QUEBEC AND N NEW ENGLAND NEXT WEEKEND...THE COMBINATION OF CYCLONIC CURVATURE ALOFT AND A CONDUIT FOR SEVERAL SHORTWAVES SUGGEST A COOLER...AND POTENTIALLY MORE UNSETTLED PERIOD. DETAILS... TUE... WARMING AT MID/LOW LVLS BEGINS BUT WILL BE LIMITED BY THE PASSAGE OF A WEAK SHORTWAVE DIVING S DOWNSTREAM OF AN AMPLIFYING TROF. A NEARLY WASHED OUT FRONTAL BOUNDARY REMAINS DRAPED ACROSS THE ERN HALF OF THE REGION. THE COMBINATION OF THESE FEATURES WITHIN AN AIRMASS WHERE H85 INCREASE TO NEARLY +18C...H5 TEMPS DROP BRIEFLY TO AROUND -10C...AND MODEST K-INDICES/PWATS SUGGEST SLOW MOVING POP-UP SHOWERS AND THUNDERSHOWERS ARE POSSIBLE DURING THE AFTERNOON/EVENING HOURS. AM NOTING A CORRIDOR OF 1000-1500J/KG SFC CAPE ACROSS THE ERN THIRD OF THE REGION WHICH SUPPORTS THIS THINKING. THEREFORE...WILL BE INCREASING POPS...MAINLY E OF A IJD- ORH-AFN LINE DURING THE AFTERNOONS. THE CU FIELD GENERATED WILL ALSO LIMIT WARMING...SO WHILE SOME LOCATIONS MAY MAKE THEIR FIRST RUN AT 90F...SOME ARE LIKELY TO REMAIN JUST SHORT. WED AND EARLY THU... POSSIBLY ONE OF THE HOTTEST AND MORE UNCOMFORTABLE PERIODS AS H85 TEMPS INCREASE FROM AROUND +18C/H92 23C WED...TO H85 +21C/H92 26C ON THU. THESE TEMPS SHOULD BE EASILY REALIZED AND MORE AS OVERNIGHT MINS ARE LIKELY TO STALL IN THE MID-UPPER 60S AND EVEN LOW 70S THANKS TO HIGHER DWPTS /MORE ON THIS LATER/. THEREFORE...WITH DOWNSLOPING WESTERLY COMPONENT TO THE WIND...SEVERAL LOCATIONS MAKE THEIR RUNS INTO THE LOW-MID 90S EACH DAY. AS THETA-E RIDGE BUILDS WITHIN THE MASS-FIELD RIDGING...GRADUAL INCREASE IN SFC DWPT IS EXPECTED FROM THE MID 60S WED...TO NEAR 70 ON THU. A LOCAL CLIMATE STUDY SUGGESTS THAT THE LOW 60S ARE NEAR SEASONAL NORMALS FOR DWPTS IN SRN NEW ENGLAND WHILE THE 70F MARK ABOUT 1 STD DEVIATION HIGHER THAN NORMAL. CERTAINLY AN UNCOMFORTABLE PERIOD REGARDING HUMIDITY WITH 90+ AMBIENT TEMPERATURES. MAY NEED TO MONITOR FOR LOCALIZED HEAT ADVISORIES ESPECIALLY THU WITH THE INCREASE IN DWPTS ALTHOUGH THE RISK IS CERTAINLY NON-ZERO WED. LATE THU INTO FRI... COLD FRONTAL PASSAGE EXPECTED ALTHOUGH STILL SOME UNCERTAINTY ON EXACT TIMING WHICH WILL PLAY A ROLE IN POTENTIAL CONVECTIVE ACTIVITY. MODIFIED EML POSSIBLE AS MOST GUIDANCE FAVORS NEAR 6.5C/KM MID LVL LAPSE RATES. THE ISSUE IS H7 TEMPS NEAR +10C SUGGEST CAPPING WHICH MAY LIMIT THE POTENTIAL FOR CONVECTION EVEN WITH THE LOW LVL SOURCE OF LIFT. WILL CONTINUE WITH SLIGHT TO CHANCE POPS DURING THE PERIOD OF THE EXPECTED FROPA BUT WITH TS ONE CATEGORY BELOW THE OVERALL POP VALUE. STILL A PERIOD TO WATCH AS ABOVE THE INVERSION...THANKS TO THE EML CAPE VALUES ARE PROGGED TO BE QUITE HIGH. THE WEEKEND... WITH CUTOFF LOW PRES SETTLING JUST TO THE N...THE COMBINATION OF COOLER MID LVL TEMPS AND CYCLONIC CURVATURE ARE LIKELY TO YIELD BUILDING DIURNAL CU EACH DAY IN SPITE OF LOW LVL HIGH PRES RIDGE. THE CURVED FLOW WILL ALSO ALLOW FOR WEAK SHORTWAVES TO MOVE THROUGH WHICH IS DIFFICULT TO TIME AT 7 DAYS. H85 TEMPS DROP BACK TO AN AVERAGE OF +16 SO ALTHOUGH STILL SUMMER-LIKE CONDITIONS WILL BE MUCH MORE SEASONABLE THEN THE MID-WEEK PERIOD. && .AVIATION /02Z MONDAY THROUGH FRIDAY/...
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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 MONDAY/... 2Z UPDATE... TONIGHT...MODERATE CONFIDENCE. ISO TO SCT SHRA/TSRA. +RA WITH LIGHTNING MAIN THREATS. TEMPO MVFR TO IFR POSSIBLE. SPECIFICITY AS TO TIMING AND TERMINALS HIGHLY UNCERTAIN. LIGHT S-FLOW WITH THE POTENTIAL FOR IFR FOG. OTHERWISE A MIX OF VFR-MVFR. MONDAY...MODERATE CONFIDENCE. MAINLY VFR...EXCEPT SCATTERED MVFR/IFR CIGS/VSBYS IN SHRA/TSRA DEVELOPING MAINLY FOR THE AFTERNOON. A FEW STORMS MAY PRODUCE GUSTY WINDS AND LOCALLY HEAVY RAINFALL. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. MAINLY VFR. WILL KEEP SHRA/TSRA OUT OF THE TERMINAL. LOW CHANCE OF PATCHY FOG ISSUES. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. MAINLY VFR. NO RAIN AT THE TERMINAL TODAY. LESSER CONFIDENCE OF PATCHY FOG ISSUES. SOME MVFR CLOUDS AT TIMES NOT OUT QUESTION. OUTLOOK /TUESDAY THROUGH FRIDAY/... TUE AND WED...HIGH CONFIDENCE. MAINLY VFR. ALTHOUGH THERE IS A THREAT FOR A FEW SHOWERS OR THUNDERSTORMS MAINLY ACROSS E MA AND RI TUE AFTERNOON. OTHERWISE...HOT. THU...MODERATE CONFIDENCE. EXACT TIMING IS UNCERTAIN...BUT A COLD FRONT COULD BRING ABOUT SHOWERS AND THUNDERSTORMS LATE IN THE DAY ON THU AND THU EVENING. FRI...MODERATE CONFIDENCE. DEPENDING ON COLD FRONTAL TIMING...BUT A PERIOD OF DRY WEATHER IS EXPECTED TO FOLLOW.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH MONDAY NIGHT/...HIGH CONFIDENCE. TONIGHT... EARLY EVENING CHANCES FOR SHOWERS/ISOLATED THUNDER DIMINISHING THROUGH THE EVENING HOURS. S-WINDS CONTINUING WITH THE POTENTIAL FOR GUSTS UP AROUND 20 KTS. SEAS BELOW 4-FEET. MONDAY... WET-WEATHER MAY HOLD MORE ACROSS THE INTERIOR THAN OVER THE WATERS AS BREEZY S-WINDS CONTINUE WITH THE POTENTIAL FOR GUSTS UP 15 KTS. SEAS REMAINING BELOW 4-FEET THE HIGHEST OF WHICH ARE ANTICIPATED OVER THE E/NE-WATERS. MON NIGHT...HIGH CONFIDENCE. WINDS AND SEAS BELOW SMALL CRAFT ADVISORY THRESHOLDS. A SHOWER OR THUNDERSTORM IS POSSIBLE IN THE EVENING WITH LOCALLY ROUGH CONDITIONS. OUTLOOK /TUESDAY THROUGH FRIDAY/... TUE AND WED...HIGH CONFIDENCE. MAINLY QUIET BOATING WEATHER ALTHOUGH A BRIEF SHOWER/THUNDERSHOWER MAY PRODUCE LOCALLY ROUGHER CONDITIONS ON TUE. THU...MODERATE CONFIDENCE. A BUILDING SWELL TO THE S WILL MOVE UP THE COASTLINE ALONG WITH SOME GUSTIER SW WINDS MAINLY AROUND 20 KT. THE SWELL HAS THE CHANCE TO PEAK AT ABOUT 5 FT ON THE OUTER SRN WATERS ON THU...SO SMALL CRAFT ADVISORIES MAY BE REQUIRED. OTHERWISE...ANOTHER LOW RISK FOR THUNDERSTORMS LATE IN THE DAY ON THU. FRI...MODERATE CONFIDENCE. LOOKS LIKE AFTER THE SWELL RESIDES BOATING WX SHOULD ONCE AGAIN BECOME QUIET. && .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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