Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210625 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 225 AM EDT SUN SEP 21 2014 .SYNOPSIS...
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SCATTERED SHOWERS AND PERHAPS A THUNDERSTORM OR TWO ARE EXPECTED INTO SUN MORNING...WITH MOST AREAS DRY AND RATHER MILD BY SUN AFTERNOON. A COLD FRONT CROSSES THE REGION BY DAYBREAK MONDAY WITH HIGH PRESSURE BRINGING DRY WEATHER FOR THE REST OF NEXT WEEK. TEMPS START OFF COOL EARLY NEXT WEEK...BUT MODERATE TO ABOVE NORMAL BY THE END OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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230 AM UPDATE... NOT MUCH CHANGE FROM PREVIOUS FORECAST...AS SHOWERS WITH LOCALLY HEAVY DOWNPOURS CONTINUE TO STREAM NORTHWARD FROM LONG ISLAND NORTHWARD ACROSS CT/WESTERN- CENTRAL MA FROM MID ATLC TROUGH. PREVIOUS FORECAST CAPTURES THIS NICELY SO NO MAJOR CHANGES WITH THIS UPDATE. EARLIER DISCUSSION BELOW. ================================================================= TROPICAL MOISTURE OFF THE CAROLINA AND MID ATLC COAST WILL CONTINUE TO STREAM NORTHWARD BETWEEN WESTERN ATLC SUBTROPICAL RIDGE AND APPROACHING MID LEVEL TROUGH ENTERING THE GREAT LAKES. SPC MESO ANALYSIS INDICATES PWATS APPROACHING 2 INCHES OFF THE MID ATLC ALONG WITH SURFACE DEW PTS IN THE MID 70S! 00Z OBSERVED UPPER AIR SOUNDING FROM OKX ON LONG ISLAND INDICATES COLUMN IS FAIRLY MOIST BELOW 700 MB. THIS MOISTURE WILL CONTINUE STREAMING NORTHWARD INTO SOUTHERN NEW ENGLAND THIS EVENING AND OVERNIGHT. DESPITE FORCING FOR ASCENT WEAK OVER THE REGION TONIGHT THERE IS SOME INSTABILITY ALOFT AS CONVECTION FIRES EAST OF NJ. THUS WEAK FORCING BUT COUPLED WITH INSTABILITY ALOFT AND PWATS CLIMBING TO +1 STD ABOVE CLIMO MAY YIELD SOME TROPICAL DOWNPOURS OVERNIGHT ACROSS CT AND INTO WEST- CENTRAL MA AFTER 06Z. AFTER 12Z SHOWERS MAY MOVE EASTWARD INTO RI AND EASTERN MA. 12Z ECMWF AND LATEST RUNS OF THE HRRR AND RAP13 APPEAR TO BE SIMULATING THIS CONVECTION FAIRLY WELL THRU 01Z. THEREFORE WILL FOLLOW CLOSELY AND ALSO MATCHES UP WELL WITH PREVIOUS FORECAST. RAP13 HAS STORM TOTAL QPF UP TO 0.60 INCHES BY 18Z ACROSS CT AND WEST-CENTRAL MA. OBVIOUSLY LOCALLY MUCH HIGHER AMOUNTS ARE POSSIBLE GIVEN THE TROPICAL CONNECTION AND WEAK INSTABILITY ALOFT MAY YIELD EMBEDDED TSTMS. EARLIER DISCUSSION IS BELOW.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
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OVERNIGHT INTO SUNDAY AFTERNOON... A SHORTWAVE/LOW PRESSURE SYSTEM OFF THE CAROLINA COAST WILL BE LIFTING NORTHEAST OVERNIGHT. THIS WILL INDUCE A 30 TO 40 KNOT SOUTHERLY LOW LEVEL JET...TRANSPORTING DEEPER MOISTURE NORTHWARD INTO SOUTHERN NEW ENGLAND. THIS WILL RESULT IN A BURST OF INSTABILITY AND A BAND OF SCATTERED SHOWERS MOVING FROM.HIGH CONFIDENCE IN TAF THROUGH 06Z. MODERATE CONFIDENCE AFTER 06Z. WEST TO EAST. TIMING LOOKS TO BE AFTER MIDNIGHT INTO SUNDAY MORNING...APPROXIMATELY BETWEEN 6Z AND 15Z. INSTABILITY PARAMETERS ARE MARGINAL...BUT THERE MIGHT BE ENOUGH ELEVATED CAPE FOR A FEW EMBEDDED THUNDERSTORMS. THIS RISK FOR SEVERE WEATHER IS EXTREMELY LOW SUNDAY MORNING. HOWEVER...WITH 0 TO 6 KM SHEAR OF 25 TO 30 KNOTS/0 TO 1 KM HELICITY AROUND 100...AND A FEW HUNDRED J/KG OF CAPE....CAN/T COMPLETELY RULE OUT AN ISOLATED STRONG STORM NEAR THE SOUTH COAST SUNDAY MORNING. AGAIN THOUGH...THAT APPEARS TO BE A VERY LOW PROBABILITY BUT SOMETHING WILL NEED TO WATCH. THE STEADY AND HEAVIEST RAIN WILL LIKELY REMAIN OFF THE COAST WITH THE SURFACE LOW PRESSURE SYSTEM GIVEN LIMITED BAROCLINICITY/FRONTOGENESIS. HOWEVER...IT STILL MAY SCRAPE THE FAR SOUTHEAST NEW ENGLAND COAST FOR A TIME WHERE PWATS APPROACH 2 INCHES SO BRIEF HEAVY RAIN IS POSSIBLE. IN A NUTSHELL...SCATTERED SHOWERS AND PERHAPS A FEW THUNDERSTORMS ARE EXPECTED MAINLY SUNDAY MORNING. WE ARE NOT EXPECTING A SOAKING RAIN BY ANY MEANS...BUT A PERIOD OF HEAVY RAIN IS POSSIBLE NEAR THE FAR SOUTHEAST NEW ENGLAND COAST IF THE PLUME OF TROPICAL MOISTURE CAN MAKE IT THAT FAR NORTHWEST. OTHERWISE...MOST OF SUNDAY AFTERNOON SHOULD BE DRY WITH JUST A LOT OF CLOUDS AROUND THE REGION...EXCEPT PERHAPS THE FAR SOUTHEAST NEW ENGLAND COAST WHERE SHOWERS MAY LINGER A BIT LONGER. LOW TEMPS OVERNIGHT WILL BE MUCH MILDER THAN LAST NIGHT WITH A DEVELOPING LOW LEVEL JET NOT ALLOWING WINDS TO DECOUPLE. LOWS WILL MAINLY BE IN THE UPPER 50S AND LOWER 60S BY DAYBREAK SUNDAY. HIGHS ON SUNDAY WILL BE IN THE MIDDLE TO UPPER 70S AND IT WILL FEEL A BIT HUMID WITH DEWPOINTS WELL INTO THE 60S! LATE SUNDAY AFTERNOON AND SUNDAY NIGHT... A COLD FRONT WILL APPROACH FROM THE WEST LATE SUNDAY AFTERNOON AND SLOWLY MAKE ITS WAY THROUGH THE REGION BY DAYBREAK MONDAY. A LOT OF MID LEVEL DRY AIR AND A LACK OF INSTABILITY WILL LIMIT PRECIPITATION POTENTIAL ALONG THE FRONT. THERE STILL MAY BE A FEW SP.HIGH CONFIDENCE IN TAF THROUGH 06Z. MODERATE CONFIDENCE AFTER 06Z.OT SHOWERS AND PERHAPS A THUNDERSTORM ACROSS THE INTERIOR LATE SUN AFTERNOON INTO THE EVENING ACROSS THE INTERIOR...BUT THAT IS ABOUT IT. MOST OF SUNDAY NIGHT SHOULD BE DRY IN A GIVEN LOCATION. LOW TEMPS WILL MAINLY IN THE UPPER 50S AND LOWER 60S BY DAYBREAK MONDAY.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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HEADLINES... *LOW CHANCE SHOWERS MON. THEN DRY THE REST OF THE WEEK *COOL TEMPERATURES DURING THE WEEK...MODERATING BY WEEKEND OVERVIEW... .HIGH CONFIDENCE IN TAF THROUGH 06Z. MODERATE CONFIDENCE AFTER 06Z. THE PERIOD STARTS OFF WITH GOOD AGREEMENT ON A TROUGH DRAPED OVER THE EAST COAST AND A RIDGE OVER THE WEST COAST. THE RIDGE SLOWLY MOVES EAST AS TIME GOES ON AND THE UPPER LEVEL MOVES NORTH INTO CANADA. GOOD AGREEMENT IN THE ENSEMBLE NAO AND AO TELECONNECTION FORECASTS TO STAY IN THE POSITIVE PHASES. THE PNA LOOKS TO START POSITIVE AND GO NEUTRAL AS TIME GOES ON...BUT THEN MODELS DIVERGE IN THEIR OUTPUTS AS A WEAKNESS IN THE RIDGE ALLOWS FOR SOME SPREAD. DAILIES... MONDAY...THE MORNING BEGINS WITH A DEPARTING COLD FRONT THAT IS FIGHTING WITH SOME DRY MIDLEVELS ALLOWING SOME OF THE PRECIP TO DRY UP. MOST OF THE PRECIPITATION SHOULD FALL IN NORTHWESTERN PORTIONS OF THE AREA AND OFFSHORE. BEHIND THE FRONT...STRONG MIXING OCCURS UP TO AROUND 850 MB WHERE 20 TO 25 KT WINDS EXIST SO GUSTS UP TO 25 KTS IS NOT OUT OF THE QUESTION. 850 MB TEMPS AHEAD OF THE FRONT ARE AROUND 10C SO MID TO UPPER 70S ARE NOT OUT OF THE QUESTION THERE. NORTHWESTERN SECTIONS WON/T GET THAT HIGH AS THE FRONT CROSS THROUGH TOO EARLY. TUESDAY THROUGH FRIDAY...BEHIND THE COLD FRONT...A STRONG 1035 MB HIGH PRESSURE SYSTEM COMES INTO THE REGION WITH COOLER TEMPERATURES...BUT NOT AS COLD AS THE PREVIOUS COLD FRONT. DRY WEATHER WILL ALSO PREVAIL DURING THIS PERIOD. SOME MODEL DISAGREEMENT AS TO THE PLACEMENT OF THE UPPER LEVEL JET APPROACHING THE REGION FROM THE SOUTH TOWARDS THE END OF THE PERIOD. THINK THE ECMWF MAY HAVE IT TOO FAR NORTH WHILE THE 6Z GFS HAS IT FURTHER SOUTH. THE EXACT PLACEMENT OF THIS JET WILL GIVE US WHEN CIRRUS CLOUDS MOVE NORTH FROM MOISTURE OFF OF THE SOUTHEAST US. WINDS WILL BE LIGHT DURING THIS PERIOD WITH THE UPPER JET UP NORTH SO BETTER CHANCE FOR COOLING TEMPS AT NIGHT ESPECIALLY WITH THE RECENT DRY SPELL WE/VE BEEN HAVING. IN PERIODS OF ONSHORE WINDS...FOG COULD OCCUR. SATURDAY...A COLD FRONT APPROACHES THE REGION FROM SOUTHEAST CANADA
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&& .AVIATION /06Z 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/... 230 AM UPDATE... THRU 12Z... MVFR CONDITIONS IN SHOWERS WILL BE FOCUSED ACROSS CT AND WESTERN- CENTRAL MA INTO SOUTHWEST NH. ELSEWHERE VFR BUT EVENTUALLY LOWERING TO MVFR AS SHOWERS SHIFT TOWARD RI AND EASTERN MA TOWARD 12Z. MODERATE CONFIDENCE. AFTER 12Z...MAINLY MVFR IN SCATTERED SHOWERS INLAND WITH EMBEDDED HEAVY RAIN. LOW PROB OF IFR ACROSS THE HIGHER TERRAIN. MORE WIDESPREAD SHOWERS MAY CLIP NANTUCKET AND CAPE COD. SHOWERS BEGIN TO TAPER OFF AND MOVE OFFSHORE AFTER 18Z. VERY LOW RISK OF AN ISOLATED TSTM ALONG SOUTH COAST. MODERATE CONFIDENCE..HIGH CONFIDENCE IN TAF THROUGH 06Z. MODERATE CONFIDENCE AFTER 06Z. TONIGHT...MAINLY VFR EXCEPT MVFR CAPE COD AND THE ISLANDS EARLY. CHANCE OF A BROKEN LINE OF SHOWERS AROUND 06Z ESPECIALLY WESTERN- CENTRAL MA INTO NH. MONDAY...VFR. MODEST W WIND. DRY RUNWAYS. KBOS TERMINAL..MODERATE CONFIDENCE IN TAF ON TIMING BUT LOWER CONFIDENCE ON AREAL COVERAGE OF SHOWERS. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. OUTLOOK...MONDAY NIGHT THROUGH THURSDAY... HIGH CONFIDENCE THROUGHOUT THE PERIOD .HIGH CONFIDENCE IN TAF THROUGH 06Z. MODERATE CONFIDENCE AFTER 06Z. VFR THRU THE PERIOD EXCEPT FOR ANY SHOWERS ON MONDAY IN THE NORTHWESTERN AREAS WHERE MVFR COULD BE NEEDED. WINDS AROUND 10KTS DURING THE DAY MONDAY WITH GUSTS TO 20 OR 25KTS IN PLACES. THESE WINDS DIE OFF ON TUESDAY AND FOR THE REST OF THE WEEK.
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&& .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... TONIGHT...MODERATE CONFIDENCE. SOUTH WINDS OF 10 TO 15 KNOTS WITH HIGH PRESSURE WELL OFF THE COAST. THERE IS A LOW PROBABILITY THAT 5 FOOT SEAS COULD DEVELOP FOR A TIME ACROSS THE OUTER-WATERS...BUT DECIDED TO KEEP WAVES JUST BELOW FOR NOW. LATER SHIFTS WILL HAVE TO KEEP A CLOSE EYE ON THIS POTENTIAL AND PERHAPS THE NEED FOR A SHORT FUSED SCA ADVISORY. SUNDAY AND SUNDAY NIGHT...MODERATE CONFIDENCE. SOUTHEAST WINDS AT 10 TO 15 KNOTS ON SUNDAY WILL SHIFT TO THE SOUTHWEST SUNDAY NIGHT AHEAD OF A COLD FRONT. HOWEVER...SWELL FROM LOW PRESSURE NEAR THE BENCHMARK WILL LIKELY RESULT IN SCA SEAS ACROSS THE OUTER-WATERS BY SUNDAY NIGHT. SINCE ITS MAINLY 3RD PERIOD...WILL DEFER THE ISSUANCE OF HEADLINES TO THE NEXT SHIFT. SCATTERED SHOWERS AND PERHAPS A THUNDERSTORM MAY AFFECT THE WATERS THIS MORNING. THERE MAY ALSO BE SOME VISIBILITY RESTRICTIONS IN PATCHY FOG...ESPECIALLY DURING THE SUNDAY MORNING. OUTLOOK...MONDAY THROUGH THURSDAY... HIGH CONFIDENCE... SEAS FROM 5 TO 8FT ON MONDAY AND INTO TUESDAY WITH THE PASSAGE OF A LOW TO THE SOUTHEAST OF THE REGION. EVEN WITH WINDS BELOW SCA THRESHOLDS...AN SCA MAY BE NEEDED FOR THIS PERIOD FOR THE SWELLS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANK/99 NEAR TERM...NOCERA SHORT TERM...FRANK LONG TERM...99 AVIATION...NOCERA/99 MARINE...FRANK/99

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