Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 301104 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 704 AM EDT THU JUL 30 2015 .SYNOPSIS... WARM AND VERY HUMID CONDITIONS TODAY. AN APPROACHING COLD FRONT WILL TRIGGER SHOWERS AND EMBEDDED THUNDERSTORMS THIS AFTERNOON AND EVENING WITH LOCALLY HEAVY RAINFALL...ESPECIALLY ACROSS WESTERN PORTIONS OF CT AND MA. NOT AS WARM AND LESS HUMID WEATHER ARRIVES FRIDAY AND CONTINUES INTO THE WEEKEND AND PROBABLY INTO MUCH OF NEXT WEEK. THERE IS A LOW RISK FOR A FEW SHOWERS AND AN ISOLATED THUNDERSTORM THIS WEEKEND INTO EARLY NEXT WEEK...HOWEVER MUCH OF THE TIME DRY WEATHER WILL PREVAIL. && .NEAR TERM /THROUGH TONIGHT/... 7 AM UPDATE... NOT MUCH CHANGE TO PREVIOUS FORECAST. STRATUS AND FOG LINGER ALONG THE SOUTH COAST OF MA AND RI. THIS WILL BURN OFF DURING THE NEXT FEW HOURS. CLOUDINESS ALONG THE NY/WESTERN NEW ENGLAND BORDER WILL SLOWLY OVERSPREAD THE REGION FROM WEST TO EAST TODAY. A FEW SHOWERS ARE POSSIBLE LATER THIS MORNING AND EARLY AFTERNOON ON THE LEADING EDGE OF HIGHER THETA-E AIRMASS ENTERING THE REGION. THESE SHOWERS ARE CURRENTLY OVER EASTERN NY STATE AND SLOWLY MOVING EAST. HOWEVER THE BULK OF SHOWERS AND T-STORMS WILL BE FOCUSED FROM 3 PM TO 9 PM...AS STATED BELOW BY PREVIOUS FORECASTER. UNTIL MOSTLY DRY WEATHER PREVAILS ESPECIALLY OVER RI AND EASTERN MA. OFF TO A VERY WARM START THIS MORNING WITH 7 AM TEMPS: 76 BOSTON...PROVIDENCE AND HARTFORD! VERY HUMID AS WELL WITH DEW PTS ALREADY IN THE L70S ACROSS CT/RI AND SOUTHEAST MA. EARLIER DISCUSSION BELOW. ===================================================================== TODAY AND TONIGHT... **STRONG TO POSSIBLE SEVERE THUNDERSTORMS WILL DEVELOP LATE THIS AFTERNOON BRINGING GUSTY WINDS AND LOCALIZED STREET FLOODING** STRONG UPPER LEVEL LOW WILL CONTINUE TO SPIN ACROSS HUDSON BAY. ASSOCIATED SHORTWAVE WILL MOVE THROUGH THE FLOW PUSHING A COLD FRONT ACROSS THE EASTERN GREAT LAKES INTO NEW ENGLAND LATE THIS AFTERNOON. THIS FRONT WILL BRING A ROUND OF SHOWERS AND THUNDERSTORMS FOR WESTERN MASS AND CONNECTICUT. FATHER EAST APPEARS THE CHANCE FOR A WETTING RAIN SEEMS TO BE LOWER AS FORCING ALONG THE FRONT WEAKENS. 00Z GUIDANCE ALSO SHOWS A WAVE MOVING UP FROM THE MID- ATLANTIC COAST WHICH COULD SLOW DOWN THE PASSAGE FRONT ACROSS THE CAPE AND ISLANDS TONIGHT. REGARDLESS APPEARS THAT THE FRONT WILL MOVE INTO WESTERN MASS AROUND 18-21Z AND OFFSHORE BY 06Z. DETAILS: AHEAD OF THE PASSAGE OF THE FRONT...SOUTHWESTERLY FLOW WILL PULL IN MOISTURE TODAY BRINGING DEWPOINTS INTO THE LOW 70S. CLOUD COVER WILL ALSO BE ON THE INCREASE WITHIN THE WAA PATTERN. WITH THIS AMOUNT OF MOISTURE...COULD SEE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS BREAK OUT ACROSS THE REGION BETWEEN 15-21Z. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH THIS ACTIVITY. AS THE FRONT APPROACHES THE REGION...BELIEVE MORE OF A CONVECTIVE LINE WILL DEVELOP ACROSS THE HUDSON VALLEY AND MOVE INTO WESTERN MASS. STRONG TO POSSIBLE SEVERE THUNDERSTORMS ARE POSSIBLE AS THE SYSTEM APPROACHES SNE. POOR MID LEVEL LAPSE RATES...5 C/KM AND CLOUD COVER WILL LIMIT INSTABILITY. HOWEVER...THE REGION SHOULD BE ABLE TO DEVELOP AROUND 1000-1500 MLCAPE ACROSS THE INTERIOR GIVEN THE 70+ DEWPOINTS. 0 TO 6 KM SHEAR IS RATHER MARGINAL...BUT DOES INCREASE TO 30 KNOTS ACROSS OUR NORTHWEST ZONES TOWARDS 00Z. SO ALTHOUGH THE INSTABILITY/SHEAR IS MARGINAL...WE ARE CLOSER TO THE BETTER FORCING AS HEIGHTS WILL BE DECREASING ALOFT. THEREFORE CANT RULE OUT THE POSSIBLE SEVERE THUNDERSTORM AS THE SYSTEM PASSES THROUGH. BIGGEST THREAT WITH THESE STORMS APPEARS TO BE HEAVY DOWNPOURS LEADING TO NUISANCE FLOODING AS PWAT VALUES ARE ABOUT 2+ INCHES. GUSTY WINDS/LOCALIZED DOWNBURST ALSO CANNOT BE RULE OUT DUE TO THE INVERTED-V SOUNDINGS. THERE IS ALSO THE POTENTIAL FOR A QUICK SPIN-UP DUE TO THE TROPICAL AIRMASS OVER THE REGION LEADING TO LOW LCL/S...BUT OVERALL CONFIDENCE IS LOW. AS THE FRONT PASSES...THE POTENTIAL FOR STRONG TO SEVERE STORMS DROPS OFF EAST OF THE WORCESTER HILLS. THIS IS DUE TO THE LOSS OF INSTABILITY FROM SUNSET AS WELL AS LACK OF BETTER FORCING. STILL CANT RULE OUT THUNDERSTORMS DURING THE OVERNIGHT HOURS DUE TO ELEVATED INSTABILITY. OTHERWISE TEMPERATURES WILL BE WARM ONCE AGAIN TODAY. HOWEVER NOT AS WARM AS YESTERDAY AS 925MB TEMPS ARE COOLER. SO TEMPERATURES WILL GENERALLY BE IN THE UPPER 80S WITH A FEW SPOT 90S. BEST LOCATION TO SEE 90+ WILL BE ACROSS THE MERRIMACK VALLEY...WHICH MAY SEE MORE SUN VERSUS THE REST OF THE AREA. FINALLY SOUTHWESTERLY LLJ WILL BE ON THE INCREASE THIS AFTERNOON ALLOWING FOR WIND GUSTS TO REACH BETWEEN 20-30 MPH ALONG THE SOUTH COAST. && .SHORT TERM /FRIDAY/... FRIDAY... FRONT WILL BE OFFSHORE BY FRIDAY MORNING LEADING TO A DESCENT DAY. ALTHOUGH TEMPERATURES WILL BE WARM...HUMIDITY WILL BE LOWER THAN THE PREVIOUS DAYS. ABUNDANT SUNSHINE WILL LEAD TO MIXING SO WINDS COULD GET A TAD GUSTY IN THE AFTERNOON. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... HIGHLIGHTS... * PATTERN CHANGE TO MORE SEASONABLE TEMPS AND LOWER HUMIDITY * LOW RISK OF A FEW SHOWERS SHOWERS/ISOLATED THUNDER EACH DAY BUT MUCH OF THE TIME REMAINING DRY SYNOPTIC OVERVIEW AND MODEL PREFERENCES... ANOMALOUS CANADIAN VORTEX OVER HUDSON AND JAMES BAYS THIS PERIOD RESULTS IN A MEAN MID LEVEL TROUGH DEVELOPING ACROSS THE GREAT LAKES INTO THE NORTHEAST AND WILL BE ACCOMPANIED BY BELOW NORMAL HEIGHTS. NUMEROUS SHORT WAVES WILL ROTATE THRU THIS BROAD TROUGH INTO NEW ENGLAND THIS TIME PERIOD AND WILL RESULT IN A REINFORCING SURGE OF DRIER AIR WITH EACH PASSING JET IMPULSE. THESE SHORT WAVE TROUGHS MAY YIELD A FEW SHOWERS/ISOLATED T-STORM WITH EACH FRONTAL PASSAGE. HOWEVER GIVEN THE LACK OF MOISTURE AND INSTABILITY MUCH OF THE PERIOD WILL FEATURE DRY WEATHER. DETERMINISTIC GUIDANCE IS DISPLAYING LARGE TIMING DIFFERENCES WITH THESE SHORT WAVES GIVEN THE FAST/BROAD FLOW ALOFT. THUS LOW FORECAST CONFIDENCE ON TIMING OF CONVECTIVE THREAT. GIVEN TIMING AND AMPLITUDE DIFFERENCES A MODEL BLEND PROVIDES THE MOST SKILL AND WILL USE THIS AS A BASIS FOR THIS FORECAST. DAILY SENSIBLE WEATHER DETAILS... FRI NIGHT...DRY WEATHER AND COMFORTABLE HUMIDITY /DEW PTS IN THE U50S TO L60S/ WITH POST FRONTAL AIRMASS OVER THE REGION. SATURDAY...LOW AMPLITUDE SHORT WAVE TROUGH MOVES ACROSS NY STATE INTO NORTHERN NEW ENGLAND. MOISTURE AND INSTABILITY IS LACKING AND THIS SHOULD LIMIT AREAL COVERAGE OF SHOWERS/T-STORMS TO WIDELY SCATTERED. THUS MOST LOCATIONS REMAIN DRY. SEASONABLY WARM WITH HIGHS IN THE 80S AND LOWS IN THE 60S. SUNDAY...SHOULD BE A MAINLY DRY DAY ALONG WITH SEASONABLE TEMPS /H85 +15/ WITH HIGHS IN THE 80S AND LOWS IN THE 60S. MONDAY...ANOTHER POTENTIAL SHORT WAVE TROUGH APPROACHES THE REGION FROM THE WEST. THUS LOW RISK OF SCATTERED SHOWERS/T-STORMS THIS PERIOD. SEASONABLY WARM WITH H5 TEMPS AROUND +15C. TUESDAY...CANADIAN VORTEX DIGS SOUTHWARD INTO QUEBEC WITH LOWERING HEIGHTS AND COOLER TEMPS ALOFT INTO NEW ENGLAND. THIS SHOULD YIELD A GREATER CHANCE FOR CONVECTION. WARMER AND MORE HUMID CONDITIONS LIKELY AHEAD OF MID LEVEL TROUGH AND ATTENDING COLD FRONT. WEDNESDAY...ITS DAY 7 BUT GOOD AGREEMENT AMONG DETERMINISTIC AND ENSEMBLE GUIDANCE THAT CLOSED LOW WILL BE OVER EASTERN QUEBEC WITH MEAN TROUGH AXIS ACROSS NEW ENGLAND. 925 MB AND 850 MB TEMPS ARE ABOUT -1 STD DEVIATION COOLER THAN CLIMO. THUS COULD HAVE A PERIOD OF SLIGHTLY COOLER THAN NORMAL WEATHER THIS PERIOD. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY NIGHT/... 7 AM UPDATE... NO MAJOR CHANGES FROM 06Z AND 09Z TAFS. EARLIER DISCUSSION BELOW. ================================================================== TONIGHT...HIGH CONFIDENCE. MAINLY VFR CONDITIONS EXCEPT ACROSS THE CAPE...ISLANDS AND SOUTH COAST WHERE FOG HAS DEVELOPED. CONDITIONS COULD DROP DOWN TO IFR. ALSO NEED TO WATCH THE CT VALLEY. BEFORE 18Z...HIGH CONFIDENCE. VFR TO START WITH LINGERING FOG ALONG SOUTHERN TERMINALS. SCT SHOWERS AND ISO THUNDER OUT AHEAD OF APPROACHING COLD FRONT COULD DROP CONDITIONS TO MVFR. WINDS ACROSS THE SOUTH COAST COULD GUST OUT OF THE SW AROUND 25-30 KTS. AFTER 18Z AND TONIGHT...MODERATE CONFIDENCE. WINDS AHEAD OF AN APPROACHING COLD FRONT WILL GUST BETWEEN 20-30 KTS...ESP ACROSS THE SOUTH COAST. COLD FRONT WILL MOVE ACROSS THE REGION FROM WEST TO EAST BEGINNING AROUND 18-21Z. THIS CONVECTIVE LINE COULD BRING STRONG TO SEVERE STORMS ACROSS WESTERN MASS BEFORE FIZZLING OUT ACROSS THE EASTERN HALF OF THE REGION. ANTICIPATE ANY LINGERING SHOWERS TO BE OUT OF THE REGION BY 06Z. PATCHY FOG COULD DEVELOP ACROSS THE NORMAL PRONE REGIONS OVERNIGHT. FRIDAY...HIGH CONFIDENCE. LINGERING FOG AND STRATUS WILL DISSIPATE. EXPECT VFR WITH DIURNAL CU AND GUSTY WINDS AROUND 15-20 KTS. KBOS TERMINAL...HIGH CONFIDENCE. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. THERE IS A PROBABILITY THAT A STRONG STORM COULD IMPACT THE TERMINAL THIS AFTERNOON. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... VFR MUCH OF THE TIME WITH A LOW RISK FOR SCATTERED SHOWERS SAT AND AGAIN MONDAY. GREATER RISK FOR THUNDER MON. MODERATE FORECAST CONFIDENCE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... TODAY AND TONIGHT...MODERATE TO HIGH CONFIDENCE. DEVELOPING LOW LEVEL JET WILL RESULT IN NEAR SHORE SOUTHWEST WIND GUSTS OF 25 TO 30 KNOTS DEVELOPING THIS AFTERNOON. IN ADDITION...LONG SOUTHWEST FETCH WILL ALLOW FOR SEAS TO BUILD TO BETWEEN 3 TO 5 FEET ACROSS MOST OPEN WATERS. SCA HEADLINES WILL CONTINUE TODAY AND TONIGHT. WINDS DIMINISH THIS EVENING...BUT WILL NEED TO KEEP HEADLINES UP THROUGH TONIGHT FOR THE OUTER- WATERS FROM THE LEFT OVER SWELL. HIGH PRESSURE WILL BUILD ON FRIDAY SO SCA MAY BE ALLOWED TO DROP. OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... FAIRLY TRANQUIL BOATING WEATHER THIS PERIOD WITH MODEST SW WINDS...GOOD VSBY AND MAINLY DRY WEATHER. LOW RISK OF SCATTERED SHOWERS AND T-STORMS MONDAY. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO 7 PM EDT THIS EVENING FOR ANZ230>234-236-251. SMALL CRAFT ADVISORY FROM NOON TODAY TO 11 PM EDT THIS EVENING FOR ANZ235-237. SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 AM EDT FRIDAY FOR ANZ250-254>256. && $$ SYNOPSIS...NOCERA/DUNTEN NEAR TERM...DUNTEN SHORT TERM...DUNTEN LONG TERM...NOCERA AVIATION...NOCERA/DUNTEN MARINE...NOCERA/DUNTEN

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