Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191358 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 1000 AM EDT SUN APR 19 2015 .SYNOPSIS... CANADIAN HIGH PRESSURE BRINGS MUCH COOLER WEATHER TODAY. A WIND SWEPT SOAKING RAIN IS EXPECTED MONDAY INTO MONDAY NIGHT. SCATTERED SHOWERS AND MILD TEMPS TUESDAY MORNING GIVE WAY TO A DRYING TREND DURING THE AFTERNOON. THEN MUCH COOLER WEATHER OVERSPREADS THE AREA MID TO LATE NEXT WEEK ALONG WITH THE RISK OF SCATTERED SHOWERS...ESPECIALLY DURING THE AFTERNOON AND EVENING. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 AM UPDATE... HIGH PRESSURE OVER QUEBEC WILL GENERATE EAST TO NORTHEAST SURFACE WINDS ACROSS SOUTHERN NEW ENGLAND TODAY. DESPITE PLENTY OF SUNSHINE...ONSHORE FLOW THIS TIME OF YEAR MEANS HIGHS WILL HOLD IN THE UPPER 40S AND LOWER 50S ALONG THE IMMEDIATE COAST INCLUDING BOSTON. IT WILL TURN MILDER THE FURTHER AWAY YOU GET FROM THE OCEAN...WITH HIGHS EXPECTED TO REACH INTO THE LOWER TO MIDDLE 60S ACROSS THE LOWER CONNECTICUT RIVER VALLEY. IN BETWEEN THE COAST AND LOWER CT RIVER VALLEY...EXPECT HIGHS WELL UP INTO THE 50S TO NEAR 60.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... TONIGHT... HIGH PRESSURE SHIFTS E AS LOW PRESSURE APPROACHES FROM THE W. WINDS ENHANCE OUT OF THE E/SE AS CLOUDS LOWER AND THICKEN WITH A CHANCE OF SHOWERS ACROSS W NEW ENGLAND TOWARDS MONDAY MORNING. YET BELIEVE LOW MARINE STRATUS MAY BECOME AN ISSUE BEFOREHAND AS LONG E-FETCH OFF THE WATERS COULD YIELD MOISTURE POOLING BENEATH THE DRY-INVERSION PER LINGERING HIGH PRESSURE THAT CONDENSES WITH NOCTURNAL COOLING AS WELL AS PROXIMITY OF COOLER WATERS. NOT THINKING SO MUCH FOG WITH BRISK E/SE SURFACE WINDS BUT NOT OUT OF THE QUESTION. CHILLY OVER- NIGHT WITH E/SE ONSHORE FLOW...LOWS AROUND THE UPPER-30S. MONDAY INTO MONDAY NIGHT... BREAKING THIS DOWN INTO TWO PARTS. THE FIRST PART BEING THE LOW- TO MID-LEVEL WARM FRONT LIFTING NE ACROSS THE REGION MONDAY. SYNOPTIC FRONTOGENETICAL FORCING OF DEEP-LAYER MOISTURE. DECENT H85-7 THETA-E MOIST PLUME OF SUB-TROPICAL ORIGINS FUNNELED N BY ANOMALOUSLY STRONG LOW-LEVEL S-FLOW OF 50-60 KNOTS THE H925-85 CONVERGENT NOSE OF WHICH IS COLLOCATED ALONG AND REARWARD OF THE WARM FRONT. PWATS UP TO 1.5- INCHES...ROUGHLY AROUND +2 STANDARD DEVIATIONS ABOVE NORMAL FOR THE MONTH OF APRIL ACROSS THE NORTHEAST. COLLOCATION OF BEST INGREDIENTS AROUND MID-MORNING INTO EARLY EVENING MONDAY DURING WHICH TIME THERE IS THE EXPECTATION OF A BROAD SWATH OF RAIN WITH EMBEDDED HEAVIER SHOWERS. LACK OF INSTABILITY SO NOT THINKING ANY THUNDER. WARM FRONT SHOULD BE PROGRESSIVE WITH H85-3 30-40 KNOT S/SW-FLOW SO FOR THIS TIMEFRAME THINKING AVERAGE PRECIPITATION AMOUNTS AROUND 0.75-INCHES WITH LOCALLY HEAVIER AMOUNTS. NOT OUT OF THE QUESTION TO SEE LOCALES EXCEED AN INCH. BUT THIS IS OVER A NEARLY 12-HOUR PERIOD. EVALUATING SREF PROBABILITIES ALONG WITH FORECAST THINKING...PERHAPS NUISANCE URBAN FLOODING BUT A LOW RISK OF FLASH FLOODING. NO LONGER ANY SNOW COVER EITHER...AND THERE IS A BREAK IN THE ACTION OUTLINED BELOW. EXPECTING A LULL BETWEEN PARTS AS DRIER AIR ENTRAINS REARWARD OF THE WARM FRONT WITHIN THE WARM SECTOR. DEEP-LAYER MOISTURE FILLS BACK IN AHEAD OF THE MID-LEVEL POSITIVELY-TILTED TROUGH. ACCOMPANYING LEFT- FRONT-QUADRANT OF A JET STREAK ROUNDING THE BASE OF THE TROUGH HAS THE POTENTIAL OF INVOKING A SURFACE REFLECTION OF LOW PRESSURE OVER THE NE-CONUS...THAT OR STOUT BROADSCALE DIFFLUENCE ALOFT. COLLOCATED WEAK INSTABILITY / CONDITIONALLY UNSTABLE MOIST ADIABATIC PROFILE... AND THERE IS THE LIKELIHOOD OF CONTINUED WET WEATHER WITH POTENTIAL ELEVATED THUNDER. NOT ABSOLUTELY CERTAIN ON OUTCOMES BUT THE FORCING SEEMS APPARENT WITHIN A FAVORABLE ENVIRONMENT TO RESULT IN SOMETHING AT LEAST SHOWERY...BUT CAN NOT RULE OUT POSSIBLE HEAVY RAIN AND AS PREVIOUSLY MENTIONED THUNDER. SHOWALTERS < 0 WITH TOTAL-TOTALS > 50 IN ADDITION TO ELEVATED INSTABILITY. WILL GO CHANCE THUNDER. ONCE AGAIN...NUISANCE FLOODING CONSIDERATIONS ESPECIALLY IN URBAN CENTERS BUT LOW RISK FLASH FLOODING. IN ALL LOOKING AT STORM-TOTAL RAINFALL FOR ROUGHLY A 24-HOUR PERIOD OF 1.0-1.5 INCHES. WIDESPREAD RAIN. EMBEDDED HEAVY SHOWERS. CHANCE THUNDER. SUBSEQUENT NUISANCE POOR-DRAINAGE FLOODING. BREEZY ONSHORE SE-WINDS WITH GUSTS UP TO AROUND 35 MPH ALONG THE COAST. VISIBILITY ISSUES WITH A COMBINATION OF FOG AND/OR HEAVY RAIN. FIRST SET OF IMPACTS MID-MORNING INTO EVENING MONDAY...A LULL...THEN MORE WET WX IS ANTICIPATED LATE MONDAY NIGHT. HAVE THE UMBRELLA HANDY. && .LONG TERM /TUESDAY THROUGH SATURDAY/... HIGHLIGHTS... * TUE...SCATTERED MORNING SHOWERS THEN AN AFTERNOON DRYING TREND * WED-SAT...COOLER WITH PERIODS OF SHOWERS...MAINLY DIURNAL SYNOPTIC OVERVIEW AND MODEL PREFERENCES... AMPLIFYING NORTHERN STREAM PHASES WITH SOUTHERN PLAINS CUTOFF LOW TODAY TO FORM AN ANOMALOUS LOW/VORTEX OVER THE GREAT LAKES TUE. THEREAFTER THIS UPPER LOW WILL BE VERY SLOW TO MOVE AS HIGH LATITUDE BLOCKING DEVELOPS WITH POSITIVE HEIGHT ANOMALY EVOLVING OVER THE SOUTHERN DAVIS STRAIT. THIS RESULTS IN A VERY SLOW MOVING VORTEX FROM THE NORTHERN GREAT LAKES WED TO ONLY ADVANCING EASTWARD INTO MAINE BY NEXT WEEKEND! WHILE THIS SEEMS EXTREME IT/S DOES HAVE SUPPORT FROM TELECONNECTIONS AS AO/NAO AND EPO AS ALL THREE INDICES GO NEGATIVE. GIVEN GOOD MODEL AGREEMENT A BLEND OF OPERATIONAL GUIDANCE WILL WORK BEST AS A BASELINE FOR THIS PORTION OF THE FORECAST. DAILY DETAILS... TUESDAY...TRAILING SHORT WAVE TROUGH AND ATTENDING COLD FRONT ALONG WITH TRIPLE POINT LOW WILL BE MOVING ACROSS THE AREA DURING THE MORNING. THIS WILL LIKELY YIELD A ROUND OF SHOWERS TO THE REGION. INSTABILITY ALOFT MAY BE SUFFICIENT FOR ELEVATED THUNDER. IF NOT AT THE VERY LEAST THIS INSTABILITY WILL ENHANCE SHOWER INTENSITY AND ASSOCIATED DOWNPOURS. BY AFTERNOON DRY SLOT WILL BE WORKING ITS WAY AROUND THE SYSTEM AND INTO THE REGION. SO SUSPECT WITH DEEPENING DRY LAYER AND COLD ADVECTION TUE AFTERNOON WILL FEATURE A DRYING TREND FROM SOUTH TO NORTH. IN ADDITION...MILD START TO THE DAY COMBINED WITH BREAKS OF AFTERNOON SUNSHINE POSSIBLE AND WEAK COLD AIR ADVECTION HIGHS WILL WARM INTO THE 60S. WED AND THU...WHILE BOTH ENSEMBLES AND DETERMINISTIC GUIDANCE ARE IN VERY GOOD AGREEMENT ON THE TIMING AND TRACK OF MID LEVEL CLOSED LOW...AS EXPECTED MODELS ARE STRUGGLING WITH THE AMPLITUDE AND TIMING OF INDIVIDUAL SHORT WAVES CIRCULATE AROUND THE VORTEX. THUS LOW CONFIDENCE ON TIMING SHOWER THREAT THIS PERIOD. TRENDING COOLER AS MID LEVEL LOW AND ASSOCIATED COLD POOL ALOFT ADVECT EASTWARD INTO THE REGION. COOLER THU THAN WED. FRIDAY AND SATURDAY...ECENS/EPS SUGGEST CORE OF COLD AIR ALOFT SETTLES OVER THE AREA AS MID LEVEL LOW TRACKS ACROSS NORTHERN NY STATE AND NORTHERN NEW ENGLAND WITH 850 TEMPS COOLING TO -2C TO -5C! RISK OF SHOWERS TOO GIVEN COLD AIR AND CYCLONIC FLOW ALOFT. NOT OUT OF THE QUESTION THAT SCATTERED RAIN SHOWERS MIX WITH SOME SNOW AT TIMES ACROSS THE HIGHER TERRAIN! && .AVIATION /14Z 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 MONDAY NIGHT/... TODAY...HIGH CONFIDENCE. VFR. NORTHEAST WINDS WILL GRADUALLY TURN MORE EAST THIS AFTERNOON. INCREASING HIGH-CLOUD LATE AS WINDS VEER E/SE TOWARDS EVENING. TONIGHT...HIGH CONFIDENCE. ENHANCING SE-WINDS WITH GUSTS UP TO 20 KTS ALONG THE COAST AS CIGS LOWER AND THICKEN. POSSIBLE MVFR-IFR VSBYS WITH PATCHY FOG...AS WELL AS -SHRA OVER W NEW ENGLAND. MONDAY...HIGH CONFIDENCE. WIDESPREAD RAIN WITH EMBEDDED +RA. VSBY RESTRICTIONS SUBSEQUENTLY ALONG WITH PATCHY FOG. MVFR-IFR CIGS. E/SE WINDS WITH GUSTS UP TO 30 KTS ALONG THE COAST. MONDAY NIGHT...MODERATE CONFIDENCE. SHRA WITH CHANCE TSRA. IFR CIGS WITH PATCHY FOG. CONTINUED E/SE WINDS WITH GUSTS UP TO 30 KTS ALONG THE COAST. OUTLOOK...TUESDAY THROUGH THURSDAY... TUE...MODERATE CONFIDENCE...SO UNCERTAINTY HOW QUICKLY CONDITIONS WILL IMPROVE. IFR/MVFR TUE AM IN SCATTERED SHOWERS SHOULD IMPROVE TO MVFR/VFR DURING THE AFTERNOON WITH DRYING TREND. WED AND THU...LOW CONFIDENCE GIVEN UNCERTAINTY ON EXACT AMPLITUDE AND TIMING OF INDIVIDUAL COLD FRONTS AND ATTENDING SHORT WAVE TROUGHS THIS FAR OUT.
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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 MONDAY NIGHT/... TODAY...HIGH CONFIDENCE. NORTH TO NORTHEAST WINDS GUSTING AROUND 25 KNOTS ACROSS NANTUCKET SOUND AND POINTS SOUTHEAST. THOUGHT ABOUT A SHORT FUSED SMALL CRAFT HEADLINE...BUT SINCE WE HAVE LONG DURATION HEADLINES MONDAY INTO MONDAY NIGHT OPTED TO LET IT GO SINCE WINDS SHOULD DIMINISH SOME OVER THE NEXT FEW HOURS. TONIGHT...HIGH CONFIDENCE. ENHANCING SE-WINDS WITH GUSTS UP TO 20 KTS ACROSS THE WATERS BY MORNING. MARINE STRATUS DEVELOPING. MAYBE SOME FOG ISSUES OVER THE WATERS. SEAS BUILDING TO 5 FEET ON THE S-WATERS. MONDAY...HIGH CONFIDENCE. WIDESPREAD RAIN WITH EMBEDDED HEAVIER SHOWERS. VSBY RESTRICTIONS SUBSEQUENTLY ALONG WITH PATCHY FOG. E/SE WINDS WITH GUSTS UP TO 30 KTS ALONG THE COAST. LOW RISK OF GALES ON THE E OUTER WATERS. SEAS 8 TO 10 FEET. UP TO 12 FEET ON THE S OUTER WATERS. MONDAY NIGHT...MODERATE CONFIDENCE. SHOWERS WITH THE CHANCE OF THUNDERSTORMS. PATCHY FOG AND VISIBILITY RESTRICTIONS REMAIN AN ISSUE. CONTINUED E/SE WINDS WITH GUSTS UP TO 30 KTS ALONG THE COAST. LOW RISK OF GALES ON THE E OUTER WATERS. SEAS 10 TO 12 FEET ON THE OUTER WATERS. OUTLOOK...TUESDAY THROUGH THURSDAY... TUE...STRONG LOW LEVEL JET MON NIGHT MOVING OFFSHORE...THUS WINDS DIMINISHING THRU THE DAY. LEFTOVER SE SWELLS WILL REMAIN LARGE. HIGH FORECAST CONFIDENCE. WED INTO THU...MODERATE CONFIDENCE. SOMEWHAT DRIER WITH IMPROVED VSBYS FROM TUE AM. ANY PRECIP WILL BE MAINLY DIURNAL AND IN THE FORM OF SCT SHOWERS.
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&& .TIDES/COASTAL FLOODING...
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HIGH ASTRONOMICAL TIDES AND A PERIOD OF STRONG ONSHORE WINDS MAY YIELD MINOR COASTAL FLOODING ALONG THE RI AND MA COASTLINE. HIGHEST TIDE MON EVENING AND OVERNIGHT...AROUND 11 PM SOUTH COAST AND 2 AM EASTERN MA. AT THE MOMENT MUCH OF THE MODEL GUIDANCE HAVE GREATEST WIND AND SURGE OCCURRING AROUND LOW TIDE MON EVENING. ALTHOUGH HAVE TO WATCH THIS CLOSELY GIVEN ONLY 6 HR TIME DIFFERENCE BETWEEN LOW AND HIGH TIDE. ESTOFS APPEARED MORE REASONABLE AND BULLISH THAN ETSS WITH SURGE VALUES MON AFTN AND EVENING 1.0 TO 1.5 FT. WAVE MODELS SUGGEST SEAS NEAR SHORE WAVES 10-15 FT AT THIS TIME. LIKELY NOT SUFFICIENT TO SUPPORT A WATCH.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM 5 AM MONDAY TO 6 AM EDT TUESDAY FOR ANZ230>237-250-251-254>256. && $$ SYNOPSIS...NOCERA/SIPPRELL NEAR TERM...FRANK SHORT TERM...SIPPRELL LONG TERM...NOCERA AVIATION...FRANK/NOCERA/SIPPRELL MARINE...FRANK/NOCERA/SIPPRELL TIDES/COASTAL FLOODING...STAFF

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