Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 281255 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 855 AM EDT TUE JUL 28 2015 .SYNOPSIS... A TROUGH OF LOW PRESSURE ALOFT WILL BRING A RISK OF SCATTERED SHOWERS AND THUNDERSTORMS TO EASTERN MASSACHUSETTS AND POSSIBLY RHODE ISLAND TODAY. HOT AND HUMID CONDITIONS EXPECTED THROUGH THURSDAY. A COLD FRONT MAY BRING SCATTERED THUNDERSTORMS LATE THURSDAY AND THURSDAY NIGHT. WARM BUT DRIER AND LESS HUMID WEATHER IS EXPECTED FRIDAY INTO NEXT WEEKEND. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... 855 AM UPDATE... CANCELLED DENSE FOG ADVISORY ACROSS WESTERN MA AS VISIBILITIES WERE RAPIDLY IMPROVING ACROSS MUCH OF THE REGION BY MID MORNING. ISOLATED POCKETS OF PATCHY FOG IN THIS REGION WILL STILL BE POSSIBLE UNTIL ABOUT 10 AM...BUT SHOULD IMPROVE QUICKLY IN THIS REGION AS WELL. OTHERWISE...AN AREA OF LOW CLOUDS COVERED EASTERN CT/RHODE ISLAND AND SOUTHEAST MA BUT THESE SHOULD BURN OFF IN THE NEXT FEW HOURS. PARTLY TO MOSTLY SUNNY SKIES ARE ANTICIPATED ACROSS THE ENTIRE REGION BY NOON. WILL HAVE MORE ON THE CONVECTIVE POTENTIAL LATER THIS MORNING...MAINLY ACROSS EASTERN NEW ENGLAND. STILL A LOT OF UNCERTAINTY AS OUTLINED BELOW. TODAY... *** A FEW STRONG TO POSSIBLE A SEVERE STORM TODAY ACROSS EASTERN MASSACHUSETTS *** TRICKY CONVECTIVE FORECAST TODAY AS STRONG LEAD SHORT WAVE INTRUDING ACROSS VT/NH AND INTO NORTHERN MA AT 7 AM. SHOWER ACTIVITY WITH THIS FEATURE CONTINUES TO WEAKEN AS CONVECTION DEPARTS THE ELEVATED TERRAIN. BEHIND THIS FEATURE H5 TEMPS COOL TO ABOUT -12C WITH COLDEST VALUES OVER EASTERN MA. THIS WILL STEEPEN MID LEVEL LAPSE RATES. HOWEVER BEHIND THIS DEPARTING SHORT WAVE THERE IS WEAK MID LEVEL SUBSIDENCE WITH THE COLUMN DRYING FROM THE TOP DOWNWARD. IN FACT AFTER 18Z HEIGHTS ALOFT BEGIN TO RISE ALONG WITH H5 TEMPS WARMING. THIS MAY SUPPRESS CONVECTION SOMEWHAT. THE HI RES GUID SUPPORTS THIS IDEA WITH VERY LITTLE CONVECTION AND MAINLY CONFINED TO THE NH SEACOAST SOUTHWARD INTO CAPE ANN...BOSTON AND THEN COASTAL PLYMOUTH AND CAPE COD. WHAT/S LIKELY HAPPENING HERE IS LOW LEVEL CONVERGENCE FROM SEABREEZE BOUNDARIES IN EASTERN MA IS PROVIDING THE ADDITIONAL FORCING FOR ASCENT ALONG WITH HIGHER DEW PT AIR/SBCAPES YIELDING GREATER INSTABILITY ALONG THE EASTERN MA COAST. A GOOD AMOUNT OF SUBSTANCE WILL BE OVER THE REGION ON THE BACKSIDE OF THE POTENT SHORTWAVE DEPARTING THE NORTHERN NEW ENGLAND COAST. BELIEVE THE MID-LEVEL DRYING WILL LIMIT THE COVERAGE OF SHOWERS/THUNDERSTORMS FOR TODAY. ANTICIPATE CONVECTIVE COVERAGE TO BE MORE ISOLATED TO SCATTERED IN NATURE. THE BEST AREA TO SEE THUNDERSTORMS WILL BE ACROSS EASTERN MASS...ALONG THE SEA BREEZE BOUNDARY WHICH WILL BE THE MAIN FORCING. CANNOT RULE OUT A FEW POP-UP SHOWERS AND THUNDERSTORMS ACROSS THE INTERIOR WHEN LOCATIONS REACH THE CONVECTIVE TEMPERATURE. BEST LOCATION WITHIN THE INTERIOR WILL BE ACROSS THE TERRAIN. APPEARS THAT SHOWERS WILL BEGIN TO DEVELOP AFTER 18Z WITH THE BEST CHANCE BETWEEN 21-00Z. THUNDERSTORMS TODAY COULD CONTAIN GUSTY WINDS...HEAVY RAINFALL THANKS TO A DESCENT AMOUNT OF INSTABILITY AND SHEAR OVER THE REGION. IN FACT GUIDANCE SHOWS ABOUT 1500 TO 2000 J/KG OF MUCAPE WITH 0-6KM SHEAR VALUES AROUND 30-40 KTS. INVERTED V SOUNDINGS ALSO FAVOR THE POTENTIAL FOR GUSTY WINDS. PWAT VALUES WILL BE AROUND 1.5 INCHES AND IF ANY STORMS DEVELOP ALONG THE BOUNDARY...THEY MAY TRAIN RESULTING IN URBAN AND POOR DRAINAGE FLOODING. OVERALL...MANY AREAS WILL REMAIN DRY TODAY AS IT WILL BE A HIT OR MISS TYPE OF COVERAGE. HOWEVER HIGHEST CONFIDENCE IS ACROSS EASTERN MASS WHERE CONVECTION COULD DEVELOP ALONG THE SEABREEZE BOUNDARY WHICH COULD CAUSE...HEAVY RAIN AND GUSTY WINDS. OTHERWISE A HOT AND HUMID DAY WILL BE IN STORE WITH A FEW SITES HITTING AT OR NEAR 90F WITH DEWPOINTS IN THE IN THE UPPER 60S TO LOW 70S. THIS WILL RESULT IN HEAT INDEX VALUES IN THE LOW TO MID 90S. && .SHORT TERM /7 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... TONIGHT INTO TOMORROW... A FEW LINGERING SHOWERS ARE POSSIBLE AFTER 00Z. OTHERWISE EXPECT A QUIET NIGHT AS MID-LEVEL RIDGE BEGINS TO BUILD INTO THE REGION. WEAK FLOW AND INCREASING LOW LEVEL MOISTURE WILL ALLOW FOR ANOTHER ROUND OF FOG TO DEVELOP. ALTHOUGH BELIEVE THAT IT WONT BE AS WIDESPREAD AS TONIGHT. BEST CHANCE IS ACROSS THE CAPE AND ISLANDS AND WHERE PRECIP OCCURS TODAY. OVERNIGHT TEMPS WILL DROP INTO THE UPPER 60S TO LOW 70. HIGH PRESSURE BUILDS ACROSS SOUTHERN NEW ENGLAND TOMORROW BRINGING 18-19C 850MB TEMPS. THIS WILL ALLOW FOR TEMPS TO REACH IN THE LOW TO MID 90S. DEWPOINTS WILL STILL BE IN THE UPPER 60S TO LOW 70S LEADING TO HEAT INDEX VALUES IN THE MID 90S. CANNOT RULE OUT A SPOT SHOWER ON WEDNESDAY IF LOCATIONS REACH THEIR CONVECTIVE TEMPERATURES...ESP ACROSS THE HIGHER TERRAIN. BECAUSE OF THE UNCERTAINTY KEPT FORECAST DRY. && .LONG TERM /THURSDAY THROUGH MONDAY/... 350 AM UPDATE... HIGHLIGHTS... * VERY WARM AND HUMID THU * SCATTERED STORMS POSSIBLE LATE THU/THU NIGHT * DRIER/LESS HUMID FRI THRU MON BUT STILL WARM WED NIGHT/THU/THU NIGHT... GOOD MODEL AGREEMENT ON SHORT WAVE RIDGING OVER THE AREA WED NIGHT INTO THU. THUS DRY WEATHER TO START THIS PERIOD HOWEVER THE RISK OF SHOWERS/T-STORMS INCREASES LATE THU INTO THU NIGHT AS POTENT NORTHERN STREAM TROUGH CURRENTLY EXITING THE NORTHERN ROCKIES INTO THE HIGH PLAINS BEGINS TO APPROACH NEW ENGLAND FROM THE WEST. APPEARS TIMING OF THE FRONT COMES THROUGH OVERNIGHT...WELL AFTER PEAKING HEATING. THIS COMBINED WITH MARGINAL SHEAR KEEPS THE RISK LOW FOR STRONG CONVECTION LATE THU INTO THU NIGHT. HOWEVER GOOD SYNOPTIC SCALE LIFT WITH THIS TROUGH SUGGEST AT LEAST SHOWERS SHOULD BE ABLE TO HOLD TOGETHER AND MOVE ACROSS THE AREA LATE THU AND THU NIGHT. PWATS ABOVE NORMAL AND DEW PTS 65 TO 70 WILL INCREASE THE RISK FOR HEAVY DOWNPOURS. ALTHOUGH STILL 2 DAYS AWAY WILL NEED TO MONITOR LATER MODEL TRENDS. OTHERWISE VERY WARM AND HUMID CONDITIONS THU AHEAD OF APPROACHING COLD FRONT. A MODEL BLEND OFFERS HIGHS U80S TO L90S. FRIDAY THROUGH MONDAY... ANOMALOUS CLOSED LOW/VORTEX SETS UP OVER HUDSON/JAMES BAY THIS TIME PERIOD. THIS RESULTS IN BELOW NORMAL HEIGHTS AND MEAN TROUGH OVER THE GREAT LAKES INTO THE NORTHEAST. THIS WILL KEEP TEMPERATURES NEAR NORMAL /HIGHS MU80S/ AND LOWS IN THE 60S ALONG WITH TOLERABLE HUMIDITY AS DEW PTS AVERAGE IN THE 50S DURING THE DAYLIGHT HOURS. HOWEVER WITH THE NORTHERN STREAM JET SUPPRESSED SOUTHWARD INTO THE GREAT LAKES AND NORTHEAST THERE WILL BE THE RISK OF SCATTERED DIURNAL SHOWERS/T-STORMS JUST ABOUT EVERY DAY. TOO DIFFICULT AT THIS TIME RANGE TO TIME INDIVIDUAL SHORT WAVES. NOT A WASHOUT BUT THE RISK OF CONVECTION FROM TIME TO TIME. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY AFTERNOON/... 7 AM UPDATE... IFR AND MVFR WILL SLOWLY IMPROVE THIS MORNING AND SHOULD BE VFR BY MIDDAY. THE EXCEPTION WILL BE OVER THE ISLANDS WHERE IFR/MVFR MAY LINGER MUCH OF THE DAY. OTHERWISE NO MAJOR CHANGES FROM 06Z/09Z TAFS. EARLIER DISCUSSION BELOW. =========================================================================== BEFORE 00Z...MODERATE CONFIDENCE. DRY WEATHER DOMINATES OVERNIGHT...A FEW SPOT SHOWERS ARE POSSIBLE IN NE MASS AROUND DAYBREAK. OTHERWISE...LOW CLOUDS AND FOG WILL OCCUR ACROSS THE SOUTH COAST AND CT VALLEY. LOCALLY DENSE FOG IS POSSIBLE DROPPING TERMINALS TO LIFR. TODAY...MODERATE TO HIGH CONFIDENCE. ANY LOW CLOUDS AND FOG PATCHES SHOULD IMPROVE TO VFR BY LATE MORNING. SCATTERED SHOWERS/THUNDERSTORMS WILL DEVELOP GENERALLY ACROSS EASTERN MA AFTER 18Z WHILE ACTIVITY WILL BE HIT AND MISS...THE POTENTIAL IS THERE FOR ISOLATED STRONG STORMS WITH LOCALLY HEAVY RAINFALL. TONIGHT...MODERATE CONFIDENCE. VFR FOR MOST SITES. CANNOT RULE OUT IFR IN STRATUS AND FOG ACROSS SE MASS INCLUDING THE CAPE AND ISLANDS. WEDNESDAY...HIGH CONFIDENCE. VFR WITH DIURNAL CU DEVELOPING AROUND 5K. A SPOT SHOWER IS POSSIBLE. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZE AROUND 14-16Z. LOW CONFIDENCE ON STRONG/SEVERE THUNDERSTORM HITTING THE TERMINAL. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. LOW CLOUDS AND SOME FOG MAY DEVELOP EARLY THIS MORNING. OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/... 350 AM UPDATE... WED NGT/THU...PATCHY MVFR/IFR IN FOG WED NGT BUT QUICKLY IMPROVING TO VFR THU MORNING. LOW PROB THAT MVFR/IFR IN STRATUS LINGERS ALONG THE SOUTH COAST THU. THEN UNCERTAINTY ON HOW QUICK THIS FOG/STRATUS BURNS OFF SOUTH COAST. THU NIGHT...VFR-MVFR IN SCATTERED SHOWERS/T-STORMS. SOME UNCERTAINTY ON HOW WIDESPREAD PRECIP WILL BE. FRI AND SAT...VFR LIKELY. HIGH FORECAST CONFIDENCE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY/...HIGH CONFIDENCE. WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH WEDNESDAY. A FEW SPOT SHOWERS AND PERHAPS A THUNDERSTORM WILL BE POSSIBLE TODAY. THESE THUNDERSTORMS COULD CONTAIN GUSTY WINDS. SPECIAL MARINE WARNINGS MAY BE NEEDED WITH THE HIGHEST RISK ACROSS OUR WATERS ADJACENT TO EASTERN MA. OTHERWISE FOG AND STRATUS WILL BE THE ISSUE TONIGHT...WITH DRY WEATHER EXPECTED ON WEDNESDAY. OUTLOOK /WEDNESDAY NIGHT THROUGH SATURDAY/... 350 AM UPDATE... WED NIGHT AND THU...FAIRLY TRANQUIL WIND AND SEAS. POSSIBLE PATCHY FOG IN HUMID AIRMASS. THU NIGHT...MODEST SSW WIND AHEAD OF APPROACHING COLD FRONT. SCATTERED SHOWERS WITH EMBEDDED THUNDER POSSIBLE. FRI AND SAT...COLD FRONT SLOWLY MOVES OFFSHORE. ANOTHER WEAK FRONT MAY ENTER THE WATERS SAT. WSW WINDS EXPECTED. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...NOCERA/DUNTEN NEAR TERM...FRANK/NOCERA/DUNTEN SHORT TERM...DUNTEN LONG TERM...NOCERA AVIATION...NOCERA/DUNTEN MARINE...NOCERA/DUNTEN

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