891  
FXUS61 KBOX 150740  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
340 AM EDT SUN SEP 15 2019  
   
SYNOPSIS
 
 
ANY LINGERING SHOWERS AT SUNRISE OVER CAPE COD AND THE ISLANDS WILL  
MOVE OFFSHORE AND GIVE WAY TO A DRY WARM SUNDAY AFTERNOON BEHIND A  
DEPARTING COLD FRONT. A SECONDARY TRAILING COLD FRONT MAY RESULT IN  
A FEW SHOWERS SUNDAY NIGHT INTO MONDAY. OTHERWISE AN EXTENDED PERIOD  
OF DRY WEATHER IS EXPECTED BEGINNING TUESDAY AND LIKELY CONTINUING  
INTO NEXT WEEKEND AS CANADIAN HIGH PRESSURE CREST OVER THE REGION.  
THE HIGH WILL INITIALLY BE ACCOMPANIED BY UNSEASONABLY COOL WEATHER  
TUE INTO THU MORNING. BUT A GRADUAL WARMUP IS EXPECTED WITH  
TEMPERATURES POSSIBLY REBOUNDING INTO THE 80S FRIDAY AND  
SATURDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM THIS MORNING/
 
 
2 AM UPDATE...  
 
WHILE THE COLD FRONT AS PUSHED INTO CENTRAL VT INTO THE  
BERKSHIRES AT 05Z, THE PRECIP OUT AHEAD LIES ACROSS THE EASTERN  
WATERS TO THE S COAST AS SEEN ON LATEST NE REGIONAL 88D RADAR  
IMAGERY.  
 
SCATTERED SHOWERS WILL LINGER THROUGH ACROSS THE SOUTHERN  
WATERS AND THE ISLANDS THROUGH MOST IF NOT THROUGH DAYBREAK.  
EXPECT MAINLY DRY CONDITIONS ACROSS THE REMAINDER OF THE AREA.  
HOWEVER, WITH LOW LEVEL LIGHT OR CALM WINDS AND MOISTURE TRAPPED  
NEAR THE SURFACE, AREAS OF LOW CLOUDS AND FOG WILL LIKELY DEVELOP  
MAINLY ACROSS CENTRAL AND WESTERN AREAS, ESPECIALLY ACROSS MOST  
OF THE CT VALLEY. ALSO NOTING SOME PATCHY FOG DEVELOPING ACROSS  
PORTIONS OF THE S COAST AS WELL AS INTERIOR E MASS. THE FOG MAY  
BECOME LOCALLY DENSE AT TIMES THROUGH DAYBREAK WITH DEWPOINT  
DEPRESSIONS FROM ZERO TO 2 DEGREES AT QUITE A FEW LOCATIONS.  
 
TEMPS WILL FALL BACK TO THE MID 50S TO NEAR 60 ACROSS WESTERN  
AREAS BY DAYBREAK, RANGING TO THE LOWER-MID 60S ELSEWHERE.  
 
WITH THE BEST DEEP MOISTURE IN PLACE ALONG THE S COAST, SHOULD  
SEE MORE SHOWERS/ISOLATED THUNDER DEVELOP AHEAD OF THE  
APPROACHING COLD FRONT, SO KEPT LKLY POPS MAINLY ALONG S COASTAL  
AREAS THROUGH DAYBREAK, WITH SOME LEFTOVER SHOWERS LINGERING  
INTO SE MASS AND E CENTRAL CT. COLD FRONT LOOKS TO CROSS INTO NE  
AND CENTRAL MASS INTO NW CT BY AROUND 12Z.  
 
PREVIOUS DISCUSSION...  
 
THETAE AXIS COLLOCATED WITH DEEP LAYER MOISTURE ALL THE WAY  
THROUGH H5 UNDERGOING WEAK OF MODERATE ASCENT COURTESY OF A  
STRETCHED MID-LEVEL VORTMAX. BUT JUST THE INITIAL WAVE. AS  
SURMISED EARLIER, STILL A FAIRLY LOW LEVEL MOIST ENVIRONMENT  
BENEATH FALLING HEIGHTS, CYCLONIC FLOW, SOME LOW LEVEL  
CONVERGENT WIND TENDENCIES, AND OROGRAPHIC SUPPORT, ALL OF WHICH  
PRECEDING THE MAIN COLD FRONT OVER THE E GREAT LAKES  
ACCOMPANIED BY ADDITIONAL STRETCHED MID-LEVEL VORTMAX ENERGY,  
THERE REMAINS THE CHANCE OF LIGHT TO MODERATE SHOWERS GOING INTO  
THIS EVENING. KEEP WITH CHANCE TO LIKELY POPS. SOME PLACES HAVE  
ALREADY SEEING UPWARDS OF A TWO TO THREE TENTHS, NOT RULING  
THAT OUT FOR OTHER LOCATIONS.  
 

 
   
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/
 
 
TODAY INTO TONIGHT...  
 
PLEASANT AND DRY CONDITIONS TODAY, PERHAPS THE RETURN OF LIGHT  
SHOWER ACTIVITY OVERNIGHT. WASHING OUT WITH DRIER AIR,  
SUBSIDENCE BUILDING FROM THE N WITH AN ASSOCIATED 1020+ HIGH.  
SURFACE COLD FRONT LINGERS SE JUST OFFSHORE, SOME SPOT SHOWER  
ACTIVITY FOR NANTUCKET ESPECIALLY, WILL GO WITH SUNDAY MORNING  
CHANCE POPS THEN DRYING. OTHERWISE, PLEASANT AND DRY, LIGHT W  
WINDS WHICH SHOULD ALLOW NEAR-SHORE SEA-BREEZES AS HIGHS WARM  
INTO THE MID TO UPPER 70S (THE AIRMASS ALOFT RELATIVELY  
UNCHANGED OTHER THAN BEING DRIER). MIXING UP TO H9, SOME DRAW  
DOWN OF FASTER WINDS, LOWER DEWPOINTS ESPECIALLY INTO THE 50S.  
 
AMPLIFYING H5 TROF LATE INTO THE OVERNIGHT PERIOD TONIGHT WITH  
ACCOMPANYING VORTMAX DROPPING S, CYCLONICALLY ROTATING THROUGH.  
CAMS A BIT MORE ROBUST ON OUTCOMES VERSUS GLOBAL GUIDANCE. GIVEN  
THE MODEST LIFT AND FORCING ALONG A REINFORCING COLD FRONT, ANY  
CONTINENTAL-MOIST AIRMASS TO WHICH CONSENSUS OF GUIDANCE SIGNAL  
IN SOME VARIATION OF MAGNITUDE SHOULD SQUEEZE OUT SOME LIGHT  
SHOWER ACTIVITY. SUGGESTION OF SLIGHT CHANCE POPS TOWARDS MONDAY  
MORNING SEEMS WARRANTED. HIGH CONFIDENCE ON CLOUD COVER THAT  
SHOULD KEEP OVERNIGHT LOWS MILD IN THE UPPER 50S TO LOW 60S.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
 
 
UPDATED 340 AM ...  
 
HIGHLIGHTS...  
 
* AN EXTENDED PERIOD OF DRY WEATHER IS LIKELY TUESDAY THRU SATURDAY  
* FALL-LIKE TUE/WED WITH HIGHS ONLY IN THE 60S AND LOWS IN THE 40S  
* SUMMER-LIKE WARMTH POSSIBLE FRI AND SAT WITH HIGHS IN THE 80S  
 
PRECIPITATION ...  
 
LOOKS LIKE AN EXTENDED PERIOD OF DRY WEATHER AS HIGH AMPLITUDE  
PATTERN EVOLVES WITH DEEP CLOSED MID LEVEL LOW OVER THE NORTHWEST  
ATLANTIC ALONG WITH UPSTREAM 588 DAM RIDGE FROM THE MS VALLEY INTO  
THE GREAT LAKES. THIS SETUP SUPPORTS DRY NORTHWEST FLOW INTO NEW  
ENGLAND. THUS DRY WEATHER SHOULD PREVAIL TUE THRU SAT PER ENSEMBLES  
AND DETERMINISTIC GUIDANCE. DEFINITELY A PLEASANT STRETCH OF WEATHER.  
 
TEMPERATURES ...  
 
VERY PLEASANT FALL-LIKE WEATHER THIS PERIOD FEATURING MILD DAYS AND  
COOL NIGHTS. COOLER AIR BEGINS TO ADVECT INTO THE REGION MONDAY  
NIGHT INTO TUE AS TRAILING SHORT WAVE ENERGY DIVES INTO THE BASE OF  
MARITIME TROUGH. EC ENSEMBLES HAVE CORE OF COOL AIR CENTERED OVER  
EASTERN MA WED INTO THU MORNING WITH 850 MB TEMPS DOWN TO ONLY +3C!  
THIS WILL TRANSLATE TO HIGHS ONLY IN THE 60S TUE AND WED DESPITE  
PLENTY OF SUNSHINE. NORMAL HIGH THIS TIME OF YEAR IS 70-75. LOWS  
WILL BE MAINLY IN THE 40S, LOW 50S IN THE URBAN AREAS. AS 588 DAM  
RIDGE OVER THE OH VALLEY BUILDS EASTWARD INTO NEW ENGLAND EXPECT A  
NOTICEABLE WARMUP WITH SUMMER-LIKE WARMTH POSSIBLE FRI AND SAT AS  
HIGHS LIKELY CLIMB INTO THE 80S WITH EC ENSEMBLES OFFERING +15C AT  
850 MB. GIVEN 1025+ MB CANADIAN HIGH PRESSURE OVER THE REGION MUCH  
OF NEXT WEEK, WEAK PGRADIENT/LIGHT WINDS AND DRY AIRMASS WILL  
SUPPORT RADIATIONAL COOLING. THUS WILL LEAN TOWARD THE COOLER MOS  
NIGHTTIME TEMPS. LIGHT PGRADIENT WILL ALSO SUPPORT AFTERNOON  
SEABREEZES.  
 
TROPICAL STORM HUMBERTO ...  
 
GOOD MODEL AGREEMENT THAT HUMBERTO WILL TRACK AWAY FROM THE EAST  
COAST NEXT WEEK AND THEN POSSIBLY IMPACT BERMUDA AROUND THURSDAY.  
THEREAFTER THE ECMWF CONTINUES ITS THEME OF ANOMALOUS WESTERN  
ATLANTIC TROUGH CAPTURING HUMBERTO AND LIFTING THE TROPICAL CYCLONE  
NORTHWARD ACROSS EASTERN GEORGES BANK AND TOWARDS NOVA SCOTIA  
FRI/SAT. WHILE THIS TRACK IS STILL SOUTHEAST OF NEW ENGLAND IT'S  
CLOSE ENOUGH TO WATCH CLOSELY. AT THE VERY LEAST THIS TRACK WOULD  
YIELD LARGE SWELLS FOR MA/RI WATERS AND WITH TEMPS LIKELY WARMING  
INTO THE 80S FRI/SAT, ROUGH SURF AND STRONG RIP CURRENTS COULD BE A  
CONCERN FOR OCEAN EXPOSED BEACHES. THE ECMWF SOLUTION IS A LOW  
PROBABILITY BUT WILL HAVE TO BE WATCHED GIVEN OTHER EC ENSEMBLE  
MEMBERS SUPPORT THE OPERATIONAL RUN.  
 

 
   
AVIATION /08Z SUNDAY THROUGH THURSDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH MONDAY/...HIGH CONFIDENCE.  
 
THROUGH 12Z...  
AREAS OF MVFR-IFR CIGS/VSBYS, WITH LOCAL LIFR CONDITIONS WILL  
LINGER THROUGH THE REMAINDER OF THE NIGHT. NOTING AREAS OF VFR  
CONDITIONS ACROSS NE INTERIOR MASS AS WELL AS THE MID AND LOWER  
CT VALLEY, BUT CONDITIONS WILL VARY WITH THE LINGERING LOW  
CLOUDS AND PATCHY FOG THERE. MAY SLOWLY IMPROVE ACROSS N  
CENTRAL/NE MASS AFTER 09Z. SW WINDS 5-10 KT WITH SOME GUSTS TO  
AROUND 15-20 KT ACROSS S RI/S COASTAL MASS TERMINALS, WHICH ARE  
BEGINNING TO SHIFT TO W-NW ACROSS THE BERKSHIRES AS WELL AS  
HIGHER TERRAIN SUCH AS WORCESTER.  
 
TODAY...  
MVFR-IFR CONDITIONS MAY LINGER ALONG THE S COAST AS WELL AS THE  
SOUTHERN ISLANDS AND COASTAL WATERS THROUGH A GOOD PORTION OF  
THE DAY. A FEW SHOWERS AND PATCHY FOG MAY LINGER ACROSS PORTIONS  
OF THE MID AND OUTER CAPE AS WELL AS NANTUCKET THROUGH MOST OF  
THE DAY. OTHERWISE, INLAND FOG SHOULD LIFT WITH CONDITIONS  
IMPROVING TO VFR BY MID TO LATE MORNING. W-NW WINDS AT 5-10 KT,  
THOUGH HOLDING FROM THE SW ACROSS CAPE COD AND THE ISLANDS  
THROUGH MOST OF THE DAY.  
 
TONIGHT...  
CLOUDS INCREASE FROM NW-SE DURING THE NIGHT AS ANOTHER WEAK  
SYSTEM APPROACHES. SCATTERED SHOWERS MAY PUSH INTO INTO N  
CENTRAL AND NW MASS AFTER 06Z WITH THE NEXT SYSTEM. LIGHT W-NW  
OR CALM WINDS.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF TRENDS.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF TRENDS.  
 
OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...HIGH CONFIDENCE.  
 
VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH MONDAY/...HIGH CONFIDENCE.  
 
SW WINDS CONTINUE, WITH SOME GUSTS UP TO 20 KT. MAY SEE SIMILAR  
GUSTS AHEAD OF THE COLD FRONT TOWARD DAYBREAK AROUND CAPE ANN  
AREA. SEAS 4 FT OR LESS.  
 
EXPECT WINDS TO DIMINISH AFTER FRONTAL PASSAGE THIS MORNING,  
THOUGH WILL STALL ALONG THE S COAST OR ACROSS THE COASTAL WATERS  
BY THIS EVENING. EXPECT W WINDS UP TO ABOUT 10 KT ON THE EASTERN  
WATERS, BUT LIGHT W-SW WINDS ON THE SOUTHERN WATERS. MAINLY GOOD  
VISIBILITY, BUT LOW CLOUDS/FOG MAY LINGER ACROSS THE WATERS  
NEAR THE MID AND OUTER CAPE WITH VISIBILITY RESTRICTIONS.  
 
DRY CONDITIONS ACROSS THE WATERS TONIGHT. VISIBILITY RESTRICTIONS  
LINGER EARLY TONIGHT ACROSS THE SOUTHERN WATERS TO THE WATERS E  
OF CAPE COD, BUT SHOULD IMPROVE BY 05Z-06Z.  
 
OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...MODERATE CONFIDENCE.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT.  
 
TUESDAY THROUGH THURSDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS  
APPROACHING 5 FT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...NOCERA  
NEAR TERM...EVT  
SHORT TERM...SIPPRELL  
LONG TERM...NOCERA  
AVIATION...NOCERA/EVT  
MARINE...NOCERA/EVT  
 
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