Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 311759 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 159 PM EDT SUN AUG 31 2014 .SYNOPSIS... WARM HUMID FLOW OVER THE NORTHEAST U.S. A UPPER LEVEL SHORT WAVE FROM THE GREAT LAKES DIVES EAST THROUGH NEW ENGLAND LATE AFTERNOON/EVENING BRINGING POTENTIAL THUNDERSTORMS WITH HEAVY DOWNPOURS AND STRONG WINDS. SHOWERS AND THUNDERSTORMS WILL LINGER INTO MONDAY EVENING...WITH THE BEST CHANCE ACROSS CT/RI AND SOUTH OF THE MASS PIKE. ANOTHER COLD FRONT APPROACHES LATER TUESDAY INTO TUESDAY NIGHT. WARM BUT LESS HUMID WEATHER WILL THEN FOLLOW FOR WEDNESDAY THROUGH FRIDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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150 PM UPDATE... LOWER CLOUDS ARE HANGING TOUGH ACROSS SNE WHICH HAS KEPT INSTABILITY IN CHECK SO FAR. TEMPS UPPER 70S TO LOWER 80S WITH SBCAPES 500-1000 J/KG. 0-6KM SHEAR 35-40 KT. THERE ARE SOME THIN SPOTS IN THE CLOUDS SO STILL EXPECT PARTIAL SUNSHINE AT TIMES WHICH SHOULD ALLOW TEMPS TO REACH MID 80S IN A FEW SPOTS. EXPECTED SBCAPES 1000-1500 J/KG WITH DEWPOINTS NEAR 70 SHOULD ALLOW SCT CONVECTION TO DEVELOP MID/LATE AFTERNOON IN THE INTERIOR. HI-RES GUIDANCE HINTING AT LATE SHOW WITH CONVECTION FIRING 21-00Z AS MID LEVEL SHORTWAVE MOVES IN FROM THE WEST. DELAYED HIGHER POPS BY A FEW HOURS...OTHERWISE NO CHANGES TO CURRENT FORECAST. PREVIOUS DISCUSSION... LOTS OF LOWER CLOUDS HAVE MOVED IN/DEVELOPED ACROSS SNE THIS MORNING. PLENTY OF CLOUDS ACROSS NY/PA BUT THERE ARE SOME BREAKS MOVING INTO SNE. ALSO SOME CLEARING ACROSS COASTAL NJ AND S OF LONG ISLAND WHICH MAY BRING SOME BREAKS OF SUN TO THE REGION. THE SKY COVER WILL BE AN IMPORTANT FACTOR IN HOW MUCH INSTABILITY IS REALIZED THIS AFTERNOON. TROPICAL PLUME OF MOISTURE ADVECTS INTO THE REGION WITH PWATS AROUND 2.25" BY 00Z. THIS IS 2-3 SD ABOVE NORMAL AND SFC DEWPOINTS WILL BE REACHING 70 MAKING FOR A VERY HUMID DAY. 850 TEMPS AROUND 17C BUT CLOUD COVER WILL LIMIT FULL HEATING POTENTIAL SO EXPECT MAXES REACHING THE LOW TO MID 80S...COOLER SOUTH COAST. THIS WILL BE ENOUGH TO GENERATE SBCAPES 1000-1500 J/KG...BUT LESS INSTABILITY IF NO SUNSHINE. INSTABILITY PARAMETERS ARE FAVORABLE FOR SHOWERS/TSTMS TO DEVELOP THIS AFTERNOON. HI-RES GUIDANCE SUPPORTS THIS SCENARIO WITH CONVECTION DEVELOPING IN THE INTERIOR LATE AFTERNOON INTO THE EVENING AS MID LEVEL SHORTWAVE APPROACHES FROM THE WEST AROUND 00Z. 0-6KM SHEAR INCREASES TO 35-40 KT THIS AFTERNOON AND EVENING SO POTENTIAL FOR ORGANIZED CONVECTION AND SEVERE WEATHER IF CAPES CAN EXCEED 1000 J/KG. MID LEVEL LAPSE RATES ARE QUITE MEAGER AROUND 5 C/KM WHICH IS A LIMITING FACTOR...BUT ENOUGH INSTABILITY AND DEEP MOISTURE TO SUPPORT A FEW STRONG TO SEVERE STORMS. MAIN THREAT IS HEAVY RAINFALL/LOCALIZED FLASH FLOODING OF URBAN AND POOR DRAINAGE AREAS GIVEN ANOMALOUS PWAT PLUME...BUT STRONG TO DAMAGING WINDS POSSIBLE IF INSTABILITY IS REALIZED.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... TONIGHT... CONVECTION LINGERS INTO AT LEAST THE START OF THE NIGHT. SIGNS IN THE MODEL DATA THAT THE SURFACE BOUNDARY MAY LINGER OVER SOUTHEAST MASS/RI/CT LATER AT NIGHT. THIS MAY PROVIDE A FOCUS FOR AT LEAST SCATTERED CONVECTION CONTINUING OVERNIGHT IN THIS AREA. NO AIRMASS CHANGE SO IT SHOULD BE A WARM AND HUMID NIGHT WITH DEWPOINTS AROUND 70...AND SO MIN TEMPS SHOULD BE AROUND 70 OR IN THE LOWER 70S. MONDAY... WARM HUMID AIRMASS LINGERS OVER THE REGION. PRECIP WATER VALUES CONTINUE ABOVE 2 INCHES SOUTH OF THE MASS PIKE AND 1.5 TO 2.0 INCHES NORTH. DYNAMICS WILL BE DIMINISHING...BUT SOUTHERN NEW ENGLAND WILL CONTINUE UNDER THE RIGHT ENTRANCE REGION OF THE DEPARTING UPPER JET FOR AT LEAST PART OF THE DAY. WE WILL CONTINUE WITH CHANCE POPS FOR SHOWERS/TSTMS...AND WITH LOCALLY HEAVY DOWNPOURS. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... OVERVIEW AND MODEL PREFERENCES... BROAD RIDGING IS THE DOMINATE FEATURE ACROSS THE EASTERN U.S. THROUGH MOST OF THIS FORECAST PERIOD...MORE TYPICAL FOR THE MIDDLE OF SUMMER RATHER THAN EARLY SEPTEMBER. HOWEVER...EARLY IN THIS PERIOD...THERE WILL BE A COUPLE OF FAST MOVING SYSTEMS IN THE BROAD NORTHERN STREAM FLOW THAT WILL AFFECT THE REGION. THE RIDGE FINALLY BECOMES ESTABLISHED AROUND MID WEEK...WITH WARM BUT DRY CONDITIONS THROUGH THE END OF THE WEEK. SOME QUESTIONS AS TO WHEN THE RIDGING MAY BREAK DOWN...AS MODEL SOLUTIONS LATE IN THE RUN TRY TO BREAK DOWN THE RIDGE WHILE BRINGING DOWN A H5 CUTOFF LOW ACROSS NORTH CENTRAL CANADA INTO NORTHERN QUEBEC. A LOT OF SOLUTION DIVERGENCE DURING THAT PORTION OF THE FORECAST...HOWEVER. OVERALL...HAVE FAIRLY GOOD CONFIDENCE WITH MOST OF THE FORECAST... THOUGH SOME QUESTION AS TO TIMING THE FRONT OFF THE COAST EARLY MONDAY NIGHT AS THE H5 PATTERN MAY BRIEFLY HANG UP...THEN MORE QUESTIONS WITH THE POSSIBLE CHANGES IN THE STEERING PATTERN OVER THE NORTHERN TIER LATE IN THE CYCLE. HAVE LEANED TOWARD A BLEND OF AVAILABLE GUIDANCE INTO FRIDAY...THEN PUSHED TOWARD A BLEND OF THE ECENS AND GEFS MEANS WHICH SHOWED A SLOWER BREAKDOWN OF THE RIDGING ACROSS THE REGION...WITH LOWER CONFIDENCE IN THE FRIDAY-SATURDAY TIMEFRAME. DAILIES... MONDAY NIGHT... H5 SHORT WAVE HANGS UP A BIT ALONG THE S COAST EARLY MON NIGHT WHICH WILL KEEP CHANCE FOR SCT SHOWERS/TSTMS THROUGH ABOUT MIDNIGHT. FAIR AMOUNTS OF INSTABILITY MOVE ALONG WITH THIS FRONT...WITH K INDICES IN THE LOWER-MID 30S AND TOTAL TOTALS APPROACHING 50. WILL REMAIN RATHER HUMID AND...WITH ANY LOW LEVEL MOISTURE FROM RAINFALL...WILL SEE SOME PATCHY FOG REDEVELOP AFTER MIDNIGHT. WILL REMAIN STICKY OVERNIGHT WITH LOWS IN THE 65 TO 70 DEGREE RANGE. TUESDAY... ANOTHER FRONTAL SYSTEM STEADILY WORKS ITS WAY ACROSS OUT OF NY STATE DURING TUESDAY...THOUGH SOME TIMING ISSUES IN PLACE AMONGST THE OPERATIONAL MODEL SUITE. FOR NOW...DID INTRODUCE CHANCE POPS ACROSS SW NH/W MA AROUND MIDDAY /THOUGH THIS MAY BE A BIT TOO FAST/...THEN PUSHES ACROSS THE REMAINDER OF THE INTERIOR DURING THE AFTERNOON. MAY HOLD OFF UNTIL EVENING /IF THEN/ FOR COASTAL AREAS. LOOKS LIKE MOST ENERGY WILL REMAIN ACROSS THE INTERIOR AS THE H5 HEIGHTS LIFT BACK INTO NORTHERN NEW ENGLAND AND SOUTHERN QUEBEC TUE NIGHT. EXPECT THE FRONT TO CLEAR THE COAST LATE TUE NIGHT WITH ANY LEFTOVER PRECIP ENDING. WEDNESDAY... EXPECT DRIER AIR TO SLOWLY WORK ACROSS THE REGION DURING THE DAY ON LIGHT W WINDS. HIGH PRES RIDGE WILL BUILD OUT OF THE APPALACHIANS. TEMPS WILL REMAIN WARM WITH A GENERAL W WIND FLOW THROUGHOUT THE LAYER. HIGHS WILL BE IN THE LOWER-MID 80S. THURSDAY AND FRIDAY... EXPECT DRY AND MILD CONDITIONS CONTINUING WITH DEWPTS DOWN TO THE 50S...THOUGH AROUND 60 ALONG THE IMMEDIATE COAST. HIGHS WILL BE IN THE UPPER 70S TO MID 80S BOTH DAYS. A DRY FRONT MAY PUSH THROUGH EARLY FRI WITH LITTLE MORE THAN A WIND SHIFT. SATURDAY... LOTS OF QUESTIONS DURING THIS TIMEFRAME AS A COLD FRONT TRIES TO WORK ACROSS THE NORTHERN TIER...MAINLY DUE TO UPPER LEVEL PATTERN THAT MAY TRY TO CHANGE ACROSS NORTH CENTRAL CANADA. TIMING IS VERY MUCH IN QUESTION...THOUGH FOR NOW HAVE MENTIONED CHANCE POPS AS THE FRONT MAY TRY TO WORK IN. LOW CONFIDENCE WITH THIS FEATURE. && .AVIATION /18Z SUNDAY 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 NIGHT/...HIGH CONFIDENCE IN TRENDS BUT LOWER CONFIDENCE IN PRECISE DETAILS AND TIMING. THROUGH THIS EVENING...AREAS OF MVFR CIGS WILL LINGER THIS AFTERNOON. SW GUSTS TO 25 KT ALONG THE COAST. SCT TSTMS EXPECTED TO DEVELOP 20-00Z ACROSS THE INTERIOR WITH BRIEF IFR CONDITIONS POSSIBLE ALONG WITH HEAVY DOWNPOURS AND GUSTY WIND. TONIGHT...CONVECTION MAY LINGER TONIGHT AND MOVE ACROSS THE COASTAL PLAIN BEFORE DIMINISHING. AREAS OF STRATUS AND PATCHY FOG EXPECTED TO DEVELOP AND EXPAND ACROSS THE REGION...BUT HIGHEST PROBABILITY NEAR THE S COAST. EXACT TIMING UNCERTAIN. MONDAY...MVFR/IFR CIGS/VSBYS MAY LINGER MOST OF THE DAY ALONG THE SOUTH COAST...BUT IMPROVING TO VFR IN THE INTERIOR AND ESPECIALLY FAR N AREAS AS DRIER AIR MOVES IN FROM THE N. SCT SHOWERS/TSTMS EXPECTED TO DEVELOP WITH BRIEF MVFR/IFR POSSIBLE IN ANY TSTMS. MONDAY NIGHT...AREAS OF IFR STRATUS AND FOG EXPECTED TO REDEVELOP BUT UNCERTAINTY ON AREAL EXTENT. A FEW SHOWERS/TSTM MAY LINGER INTO THE EVENING ALONG THE SOUTH COAST. KBOS TERMINAL...HIGH CONFIDENCE IN TAF REGARDING TRENDS BUT LOWER CONFIDENCE ON PRECISE DETAILS AND TIMING. KBDL TERMINAL...HIGH CONFIDENCE IN TAF REGARDING TRENDS BUT LOWER CONFIDENCE ON PRECISE DETAILS AND TIMING. OUTLOOK...TUESDAY THROUGH THURSDAY... TUESDAY...MODERATE CONFIDENCE. MVFR-IFR VSBYS THROUGH AROUND 14Z IN PATCHY FOG...THEN BRIEF PERIOD OF VFR. MAY SEE PERIODS OF MVFR IN SCT SHOWERS/TSTMS ESPECIALLY INLAND DURING THE AFTERNOON/EVENING. PRECIP SHOULD TAPER OFF AFTER MIDNIGHT. PATCHY FOG RETURNS AFTER 05Z-06Z WITH MVFR-IFR VSBYS IN NORMALLY PRONE INLAND LOCATIONS. WEDNESDAY AND THURSDAY...MODERATE CONFIDENCE. EXPECT MAINLY VFR CONDITIONS AS HIGH PRESSURE BUILDS IN. LOCAL MVFR- IFR VSBYS IN PATCHY FOG THROUGH 14Z WED. MAY AGAIN SEE LOCAL MVFR- IFR VSBYS IN PATCHY FOG AROUND DAYBREAK THU OVER THE FAR INTERIOR /SW NH AND N CENTRAL-W MA/.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. MODERATE CONFIDENCE TODAY THROUGH MONDAY. 1030 AM UPDATE... WE EXPANDED SCA FOR SOUTH COASTAL NEARSHORE WATERS FOR EXPECTATION OF SOME G25 KT AFT 18Z INTO THIS EVENING AS MODEST LLJ DEVELOPS. TODAY... DRY WEATHER FOR MUCH OF THE DAY. POTENTIAL FOR SHOWERS/TSTMS AFTER 4 PM...EXCEPT AFTER 2 PM NORTH OF CAPE ANN. ANY STORMS WILL HAVE STRONG WIND GUSTS AS WELL AS POOR VISIBILITY IN HEAVY DOWNPOURS. SOUTHWEST WIND WILL GUST TO 20-22 KNOTS WHICH IS CLOSE TO SMALL CRAFT LEVELS. THE PERSISTENCE OF THE WIND WILL BUILD SEAS A TAD WITH 5 FOOT HEIGHTS MOVING INTO THE OUTER WATERS LATE IN THE DAY. A SMALL CRAFT ADVISORY HAS BEEN PUT IN EFFECT ON THE OUTER WATERS STARTING THIS EVENING. IT IS MAINLY FOR THE 5 FOOT SEAS...BUT WINDS WILL BE CLOSE TO THRESHOLD AND SO WE WILL KEEP THE HEADLINE NON-SPECIFIC. TONIGHT... THE POTENTIAL FOR 5 FOOT SEAS WILL EXTEND INTO RI SOUND ON THE SOUTHWEST WIND. GAVE SOME THOUGHT ABOUT SIMILAR POTENTIALS FOR BLOCK ISLAND SOUND AND BUZZARDS BAY...BUT PREFERRED THE BETTER FETCH INTO RI SOUND WHERE A SMALL CRAFT ADVISORY WILL BE IN EFFECT. SHOWERS AND THUNDERSTORMS MAY MOVE ACROSS THE WATERS. BEST CHANCE ON TIMING OF THE STORMS WOULD BE THE FIRST PART OF TONIGHT...BUT CONDITIONS WILL REMAIN FAVORABLE THROUGH THE NIGHT. ANY STORMS WOULD HAVE STRONG WIND GUSTS EARLY TONIGHT AND POOR VISIBILITY IN HEAVY DOWNPOURS AT ANY TIME. MONDAY... WINDS AND SEAS DIMINISH BELOW SMALL CRAFT LEVELS. SMALL CRAFTS WILL LINGER OVER THE OUTER WATERS DURING THE MORNING. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY... MONDAY NIGHT...MODERATE CONFIDENCE. SW WINDS DIMINISH DURING THE NIGHT. LEFTOVER 5 FT SEAS MAY LINGER ACROSS THE FAR OUTER WATERS S AND E OF NANTUCKET EARLY MON NIGHT...THEN SHOULD SUBSIDE. TUESDAY THROUGH THURSDAY...MODERATE CONFIDENCE. EXPECT WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. MAY SEE SOME SW WIND GUSTS UP TO 20 KT TUE NIGHT BEFORE SHIFTING TO W-NW AND DIMINISHING BY WED MORNING. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR ANZ231>234. SMALL CRAFT ADVISORY UNTIL 2 AM EDT MONDAY FOR ANZ235-237. SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 5 AM EDT MONDAY FOR ANZ250. SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 11 AM EDT MONDAY FOR ANZ254>256.
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&& $$ SYNOPSIS...WTB/EVT NEAR TERM...KJC SHORT TERM...WTB LONG TERM...EVT AVIATION...KJC/EVT MARINE...WTB/KJC/EVT

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