Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 020759 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 359 AM EDT TUE SEP 2 2014 .SYNOPSIS... HOT AND HUMID ACROSS THE REGION TODAY...ALTHOUGH A COLD FRONT WILL CROSS THE REGION OVERNIGHT. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE LATE TODAY AND THIS EVENING AHEAD OF THIS FRONT. DRIER BUT WARM WEATHER FOLLOWS THE FRONT WEDNESDAY AND THURSDAY. HUMIDITY WILL ONCE AGAIN INCREASE BY THE END OF THE WEEK...AS THE NEXT COLD FRONT BRINGS THE RISK FOR MORE SCATTERED SHOWERS/THUNDERSTORMS BY SATURDAY. COOLER AND LESS HUMID WEATHER FOLLOWS BY NEXT SUNDAY AND MON. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... ASIDE FROM SOME LOW CLOUDS OVER THE CAPE AND ISLANDS THIS MORNING...MANY LOCATIONS ARE PRIMED TO SEE THE SUNRISE THANKS TO WEAK MESO-RIDGE IN PLACE BETWEEN THE CONVECTIVE ACTIVITY FROM SUN NIGHT AND A COLD FRONT APPROACHING FROM THE E. WITH THIS IN PLACE...AND PLENTY OF SUNSHINE AWAY FROM WHERE THIS MARINE STRATUS IS LOCATED. EXPECT PLENTY OF MIXING THROUGH THE DAY ALLOWING TEMPS TO REACH TO AROUND 90 IN THE WARMER SPOTS LIKE THE MERRIMACK AND CT RIVER VALLEYS. UPPER 80S ARE LIKELY ELSEWHERE. TROPICAL AIRMASS REMAINS IN PLACE AS WELL...WHERE SFC DWPTS AROUND 70F ARE LIKELY THROUGH THE DAY UNDER A COLUMN WHICH IS SUPPORTING PWATS NEAR 2.0 INCHES. GIVEN THE HOT HUMID AIRMASS IN PLACE...NOT OUT OF THE QUESTION THAT A FEW AIRMASS-TYPE THUNDERSTORMS/SHOWERS POP THIS AFTERNOON THANKS THE SFC HEATING ALONE /THERE IS A LACK OF OTHER LIFT UNTIL PRE FRONTAL TROF ARRIVES LATE/. IN FACT EVEN UNDER RELATIVELY MODEST MID LVL LAPSE RATES...SB CAPE VALUES OF 500-1000J/KG AND MU CAPES AROUND 1000-1500J/KG ARE POSSIBLE. DURING THE DAY...LLJ AND THEREFORE SHEAR IS LOW. THEREFORE...GIVEN THE HIGH PWATS...EXPECT HEAVY RAINFALL TO BE THE PRIMARY THREAT WITH ANY THUNDERSTORMS THAT OCCUR. MOVEMENT WILL ALSO BE SLOW...BUT COVERAGE IS LIKELY TO SCT AT BEST...SO ANY THREAT FOR URBAN/POOR DRAINAGE FLOODING IS THERE...BUT ISOLATED. HAVE HIGHEST POPS IN THE HIGHER TERRAIN OF NW MA AND SW NH...BUT HAVE AT LEAST SLIGHT CHANCE POPS CLOSER TO THE COASTLINES GIVEN THE HOT/HUMID AIRMASS IN PLACE. HOWEVER...IT COULD BE...AS STRONGER CONVECTION DEVELOPS TO THE W CLOSER TO THE COLD FRONT...THAT AIRMASS CONVECTION DIMINISHES TOWARD EVENING...UNTIL THE COLD FRONTAL CONVECTION ARRIVES AFTER 00Z. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... TONIGHT... SFC COLD FRONT WILL BE RAPIDLY APPROACHING FROM THE W...WITH TIMING GENERALLY AGREED UPON BY GUIDANCE. EXPECT IT TO BE IN E NY BY 00Z...CENTRAL BOX CWA BY 06Z AND THEN OFFSHORE BETWEEN 09Z AND 12Z. SUSPECT THERE WILL BE ONGOING CONVECTION /POTENTIALLY STRONG/ ACROSS ERN NY BY ABOUT 00Z THIS EVENING. INITIALLY...THE BEST LLJ ENERGY WILL BE SHIFTING NNE SUGGESTING SLOW E PROGRESSION...SO SUSPECT IT MAY TAKE UNTIL AS LATE AS 03Z FOR ANY OF THIS CONVECTION TO ARRIVE IN W MA/CT AND SW NH. THE KEY IS HOW MUCH OF THIS HOLDS TOGETHER INTO THE BOX CWA GIVEN THAT BY 03Z...ALMOST 3 HOURS WITHOUT SIGNIFICANT SFC HEATING WILL HAVE ELAPSED. DO NOTE THAT AS IT APPROACHES WITH THE COLD FRONT...THERE IS AN INCREASE LLJ ENERGY TO ABOUT 35-40 KT AT H85. THEREFORE...30 KT OF 0-3 KM SHEAR AND NEARLY 40 KT OF 0-6KM ARE POSSIBLE AS THIS CONVECTION APPROACHES. REGARDING SFC CONDITIONS...DO NOTE A POCKET OF HELICITY NEAR 100 AS WELL. HOWEVER...WILL BE GRADUALLY LOSING THE NEAR 1000-1200J/KG OF SFC CAPE WITH DIURNAL STABILIZATION. THEREFORE...IT/S A BALANCING ACT BETWEEN THE STABILIZATION OF THE COLUMN AND THE INCREASE IN LOCALIZED SHEAR. DO FEEL THAT THE GUIDANCE SHIFTING QPF OUT OF THE REGION IS LIKELY TOO DRY ESPECIALLY IN THE W HALF OF THE REGION. FEEL THAT MAINTAINING THE THREAT FOR T-STORMS INTO AT LEAST 03-06Z IS WARRANTED. NOT OUT OF THE QUESTION THAT AN ISOLATED SEVERE STORM IS NOTED GIVEN THE SHEAR...BUT NOT CONFIDENT ENOUGH TO INCLUDE ENHANCED WORDING WITH THIS UPDATE GIVEN STABILIZATION. WILL HOWEVER MAINTAIN WORDING FOR HEAVY RAIN...AS HIGH PWATS COULD STILL PROMOTE AN ISOLATED FLASH FLOOD THREAT. ALL THIS THINKING COINCIDES NICELY WITH LATEST SPC DAY 1. OUTSIDE OF THE HEAVY RAIN/THUNDER POTENTIAL...MAY NEED TO WATCH ESPECIALLY E AREAS FOR THE RETURN OF SOME OVERNIGHT FOG AND STRATUS THANKS TO DWPTS HOLDING NEAR 70 FOR MUCH OF THE NIGHT. MINS ARE LIKELY TO REMAIN WARM AS THE COOLER AIR WILL LAG THE FRONT UNTIL MAINLY AROUND OR AFTER SUNRISE. WED... RAPID IMPROVEMENT FOLLOWING THE FRONT THANKS TO DRY AIR MOVING IN. WILL LIKELY SEE DWPTS FALL BACK INTO THE 50S DURING THE DAY. THE COLUMN AS A WHOLE IS DRY ALSO...SO AFTER LEFTOVER DEBRIS CLOUDS DIMINISH DURING THE MORNING EXPECT A MAINLY SUNNY DAY. H85 TEMPS STILL REMAIN CLOSE TO +13C...SO HIGHS ARE LIKELY STILL TO REACH THE MID TO UPPER 80S. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... HIGHLIGHTS: * DRY THU/FRI WITH VERY WARM AFTERNOON/S * HUMID WITH SCT SHOWERS/STORMS POSSIBLE SAT * COOLER AND LESS HUMID SUN INTO MON DETAILS: WEDNESDAY NIGHT... HIGH PRESSURE OVERHEAD WILL RESULT IN MAINLY CLEAR SKIES AND LIGHT WINDS. THIS WILL ALLOW LOW TEMPS TO BOTTOM OUT MAINLY IN THE 50S...TO LOWER 60S. PATCHY FOG MAY DEVELOP LATE IN THE TYPICALLY PRONE LOCATIONS. THURSDAY AND FRIDAY... HIGH PRESSURE IN CONTROL WILL KEEP THE WEATHER DRY WITH WARM AFTERNOON/S...PARTICULARLY BY FRIDAY. HIGH TEMPS SHOULD BE WELL UP INTO THE 80S ON THURSDAY...BUT HUMIDITY WILL BE IN CHECK. AS THE HIGH MOVES FURTHER OFF THE COAST BY FRIDAY...850 MB TEMPS REACH +16C AS SOUTHWEST FLOW ALOFT INCREASES. THIS SHOULD ALLOW HIGHS WELL UP INTO THE 80S TO NEAR 90. HUMIDITY WILL ALSO INCREASE ON FRIDAY...ALTHOUGH IT WILL NOT BE OPPRESSIVE. SATURDAY... A COLD FRONT WILL APPROACH THE REGION AND LIKELY TRIGGER SCATTERED SHOWERS/THUNDERSTORMS DURING THE DAY SATURDAY. NOT EXPECTING THE ENTIRE DAY TO BE A WASHOUT...BUT APPEARS ENOUGH INSTABILITY/MOISTURE AND FORCING AVAILABLE FOR CONVECTION. PWATS APPROACHING 2 INCHES WILL MAKE HEAVY RAIN AND VERY LOCALIZED FLOODING THE MAIN CONCERN. WHILE MORE CLOUDS WILL LIKELY KEEP TEMPS A FEW DEGREES LOWER THAN FRIDAY...IT WILL BE QUITE HUMID AHEAD OF THE COLD FRONT WITH DEWPOINTS NEAR 70. SUNDAY AND MONDAY... THE COLD FRONT SHOULD HAVE EXITED THE SOUTHEAST NEW ENGLAND COAST EARLY SUNDAY. THIS WILL ALLOW COOLER AND LESS HUMID AIR TO WORK INTO THE REGION SUNDAY AND MONDAY. WILL ALSO HAVE TO WATCH A COUPLE WAVES OF LOW PRESSURE OFF THE MID ATLANTIC COAST. FOR NOW MOST OF THE MODELS KEEP THEM FAR ENOUGH AWAY TO RESULT IN MAINLY DRY WEATHER AND THAT WILL BE SHOWN IN OUR DETERMINISTIC FORECAST. HOWEVER... THERE CERTAINLY IS AT LEAST A LOW PROBABILITY THAT ONE OF THEM ENDS UP FURTHER NORTH AND WE END UP WITH A PERIOD OF SHOWERS. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... 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...LOWER CONFIDENCE IN TIMING. THROUGH TODAY... MAINLY VFR MOST LOCATIONS EXCEPT FOR SOME EARLY MORNING FOG AND LOW CLOUDS ESPECIALLY CAPE/ISLAND TERMINALS. ALTHOUGH MAY NEED TO WATCH RI TERMINALS AS WELL. CONDITIONS IMPROVE A COUPLE OF HOURS AFTER SUNRISE EXCEPT ACK WHERE LOW CLOUDS MAY LINGER INTO MID DAY. OTHERWISE TODAY...A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE...MAINLY W OF AN IJD-ORH-MHT LINE THIS THREAT CONTINUES INTO THE EVENING. TONIGHT... ANY SHOWERS AND THUNDERSTORMS END ESPECIALLY AFTER 06Z. WITH WINDS SHIFTING GRADUALLY TO THE W. SOME MORE FOG AND LOW CLOUDS ESPECIALLY ACROSS SE MA UNTIL WINDS SHIFT DURING THE EARLY MORNING HOURS. WED... VFR. KBOS TERMINAL...HIGH CONFIDENCE IN TRENDS. MAY BE A SHOWER OR THUNDERSHOWER LATE IN THE DAY TODAY OR THIS EVENING. SEA BREEZE UNLIKELY UNDER STRONGER S-SW WINDS. KBDL TERMINAL...HIGH CONFIDENCE IN TRENDS. LOWER CONFIDENCE ON TIMING. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY... WEDNESDAY NIGHT THROUGH FRIDAY...HIGH CONFIDENCE. MAINLY VFR CONDITIONS OTHER THAN LATE NIGHT/EARLY MORNING PATCHY GROUND FOG IN THE TYPICALLY PRONE LOCATIONS. FRIDAY NIGHT AND SATURDAY...MODERATE CONFIDENCE. A PERIOD OF MVFR- IFR CONDITIONS EXPECTED IN LOW CLOUDS/FOG PATCHES AND SCT SHOWERS/THUNDERSTORMS. TIMING HIGHLY UNCERTAIN AT THIS POINT. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. HIGH CONFIDENCE THROUGH THE PERIOD WEDNESDAY. SW FLOW CONTINUES TODAY...AND A FEW GUSTS TO AROUND 20 KT ARE POSSIBLE MAINLY NEAR THE SHORELINES OF CAPE COD AND THE ISLANDS. BY TONIGHT...WINDS WILL SHIFT TO THE W-NW AND CONTINUE IN THIS DIRECTION INTO WED FOLLOWING A COLD FRONTAL PASSAGE. LOW CHANCE FOR SOME SHOWERS OR THUNDERSHOWERS THIS EVENING. SEAS MAY APPROACH 5 FT ON THE S OCEAN WATERS THIS EVENING...BUT SHOULD REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGH THE DAY ON WED. OTHERWISE...SOME FOG MAY LEAD TO VSBY REDUCTIONS EARLY THIS MORNING AND AGAIN TONIGHT. OUTLOOK...WEDNESDAY NIGHT THROUGH SATURDAY... MODERATE CONFIDENCE THROUGH THIS PERIOD. WEDNESDAY NIGHT AND THURSDAY...HIGH CONFIDENCE. WEAK PRESSURE GRADIENT SHOULD KEEP WINDS/SEAS BELOW SCA THRESHOLDS. GOOD VISIBILITIES SHOULD MAKE FOR NICE BOATING WEATHER. FRIDAY...MODERATE TO HIGH CONFIDENCE. NEAR SHORE SOUTHWEST WIND GUSTS OF 20 TO 25 KNOTS MAY DEVELOP IN THE AFTERNOON WITH GOOD MIXING OVER THE LAND. SEAS SHOULD REMAIN BELOW SCA THRESHOLDS...BUT MAY BECOME CHOPPY ESPECIALLY NEAR SHORE. FRIDAY NIGHT AND SATURDAY...MODERATE CONFIDENCE. AREAS OF FOG MAY AFFECT THE SOUTHERN WATERS. SOUTHWEST WIND GUSTS AROUND 20 KNOTS ARE EXPECTED AHEAD OF AN APPROACHING COLD FRONT. THERE WILL BE THE RISK OF SCT SHOWERS AND THUNDERSTORMS DURING THE DAY SATURDAY. && .EQUIPMENT... THE BOURNE/HYANNIS NOAA WEATHER RADIO TRANSMITTER...KEC-73... BROADCASTING ON 162.550 MHZ...CONTINUES TO EXPERIENCE OCCASIONAL OUTAGES. THE TECHNICAL ISSUES ARE BEING WORKED ON PRESENTLY. WE APOLOGIZE FOR THE INCONVENIENCE. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANK/DOODY NEAR TERM...DOODY SHORT TERM...DOODY LONG TERM...FRANK AVIATION...FRANK/DOODY MARINE...FRANK/DOODY EQUIPMENT...STAFF

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