190  
FXUS61 KBOX 230152  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
952 PM EDT THU AUG 22 2019  
   
SYNOPSIS
 
 
A COLD FRONT MOVES ACROSS SOUTHERN NEW ENGLAND OVERNIGHT, THEN  
STALLS JUST OFF THE SOUTH COAST. A WAVE OF LOW PRESSURE THEN  
MOVES ALONG THE FRONT AND CLOSE TO THE REGION. SCATTERED  
SHOWERS AND EMBEDDED THUNDER MAY IMPACT MUCH OF CT/RI AND  
SOUTHEAST MA THROUGH FRIDAY MORNING. THE FRONT MOVES FARTHER  
OFFSHORE FRIDAY AFTERNOON WITH DRIER AND LESS HUMID WEATHER TO  
FOLLOW. CANADIAN HIGH PRESSURE THEN PROVIDES DRY WEATHER  
SATURDAY WITH A MILD AFTERNOON AND COOL NIGHT. ONSHORE FLOW  
SUNDAY WILL YIELD COOLER CONDITIONS ALONG WITH A FEW SHOWERS  
POSSIBLE. COOL WEATHER LIKELY LINGERS INTO EARLY NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
COLD FRONT HAS MOVED INTO NORTHERN MA. POSITION OF THE FRONT IS  
WELL INDICATED BY DEW POINTS. DEW POINTS AT 9 PM IN CT-RI-SE MA  
WERE 70 TO 75 (OPPRESSIVE HUMIDITY) WHILE VALUES AT PITTSFIELD,  
NORTH ADAMS, ORANGE, FITCHBURG, AND LAWRENCE WERE IN THE MID TO  
UPPER 50S. RADARS SHOW SHOWERS OVER NYC AND SW CT MOVING EAST.  
THIS BATCH IS MOSTLY A CONCERN OF OUR SOUTH COAST AREAS FROM  
AROUND 1130 PM TO 230 AM.  
 
SBCAPE FROM THE SPF RAP SHOWS 500-1000 J/KG LINGERING OVER CT-  
RI-SE MA THROUGH MIDNIGHT, THEN DIMINISHING. THIS SHOULD SUPPORT  
THE SHOWERS MOVING ACROSS FROM NYC.  
 
SYNOPTIC SUPPORT INCREASES LATER TONIGHT AS CANADIAN UPPER  
TROUGH SWINGS SOUTH, AND OUR AREA MOVES UNDER THE RIGHT ENTRANCE  
REGION OF THE SUPPORTING UPPER JET. PW VALUES ARE FORECAST  
AROUND 2 INCHES OVERNIGHT, SUPPLYING MOISTURE FOR CLOUDS AND  
SHOWERS/THUNDER.  
 
WE WILL CONTINUE TO SHOW AN AREA OF SCATTERED SHOWERS/THUNDER  
DEVELOPING OVERNIGHT ALONG AND SOUTH OF THE COLD FRONT, MAINLY  
AREAS SOUTH OF THE MASS PIKE.  
 
MIN TEMPS WILL BE HIGHLY DEPENDANT ON THE DEW POINTS. SOUTH OF  
THE FRONT TEMPS AND DEWS WILL LINGER IN THE LOW TO MID 70S.  
NORTH OF THE FRONT WE EXPECT TEMPS TO FALL INTO THE 60S, EXCEPT  
MID TO UPPER 50S ALONG THE BERKSHIRE EAST SLOPES AND PARTS OF  
NORTHERN WORCESTER COUNTY.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
 
 
4 PM UPDATE ...  
 
FRIDAY ...  
 
SHOWERS WITH EMBEDDED THUNDER AND HEAVY RAIN POSSIBLE DURING THE  
MORNING ACROSS CT-RI AND SOUTH OF THE MA PIKE, ESPECIALLY SOUTH  
COAST OF RI/MA. FOR WHAT IT'S WORTH THE NEW 12Z EC HAS TRENDED  
SLOWER WITH THE DEPARTING RAIN SHIELD, HOWEVER ALL GUIDANCE  
INCLUDING THE CAMS SUPPORT A DRYING TREND IN THE AFTERNOON ALONG  
WITH SUNSHINE DEVELOPING FROM NORTHWEST TO SOUTHEAST.  
 
SHOULD TURN OUT TO BE A NICE AFTERNOON WITH HIGHS IN THE UPPER  
70S TO LOWER 80S (SEASONABLE FOR LATE AUG) BUT VERY COMFORTABLE  
HUMIDITY WITH DEW PTS FALLING INTO THE UPPER 40S AND LOWER 50S!  
 
FRIDAY NIGHT ...  
 
DRY POST FRONTAL AIRMASS OVERSPREADING THE REGION WITH A COOL  
NORTH DRAINAGE FLOW. THUS LEANED TOWARD THE COOLER GUIDANCE WITH  
LOWS IN THE 50S REGIONWIDE, UPPER 40S FOR NW MA AND AROUND 60  
FOR THE BIG CITY OF BOSTON.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
4 PM UPDATE ...  
 
HIGHLIGHTS...  
 
* MILD TEMPERATURES AND DRY CONDITIONS SATURDAY  
* COOLER THAN NORMAL TEMPERATURES EXPECTED SATURDAY THROUGH MONDAY,  
WITH SPOTTY LIGHT RAIN OR SHOWERS AT TIMES  
* TEMPERATURES MODERATE BY MID WEEK, WITH ANOTHER CHANCE FOR SHOWERS  
TUESDAY THROUGH THURSDAY  
 
DETAILS...  
 
SATURDAY AND SUNDAY...  
 
THE WEEKEND LOOKS OVERALL PLEASANT AND COOLER, WITH A VERY  
COMFORTABLY DRY AIRMASS IN PLACE. A LARGE AREA OF HIGH PRESSURE AT  
THE SURFACE MOVES EAST FROM SOUTHERN CANADA INTO NORTHERN NEW  
ENGLAND AND REMAINS ANCHORED THERE THROUGH THE WEEKEND. WHILE SOME  
LINGERING WEAK TROUGHING AND COLD POOL ALOFT REMAIN, HIGH PRESSURE  
AND AN ESPECIALLY DRY COLUMN SHOULD KEEP RAIN CHANCES TO A MINIMUM.  
BEST CHANCE OF SOME SHOWERS WILL BE ON SUNDAY AS MOIST LOW LEVEL  
ADVECTION INCREASES ON NORTH EASTERLY FLOW WHICH COULD ALLOW FOR  
SOME SHALLOW SHOWERS...CAN'T RULE OUT A POP UP SHOWER FOR MOST OF  
THE REGION BUT THE BEST CHANCE WOULD BE ALONG THE SOUTH AND EAST  
COASTS AND COASTAL PLAIN. SPEAKING OF NORTHEASTERLY FLOW AROUND THAT  
SURFACE HIGH, THE PRESSURE GRADIENT TIGHTENS ON THE SOUTHERN END,  
BRINGING GUSTY NORTHEAST WINDS ON SUNDAY (AND TO A LESSER EXTENT  
ON MONDAY), MAINLY ALONG THE SOUTH COAST INTO CAPE COD WHERE  
WINDS COULD GUST TO 25-35 MPH.  
 
COMFORTABLE CONDITIONS BOTH DAYS UNDER A DEEP COLD POOL. H85 TEMPS  
DOWN AROUND 6-8C WILL SUPPORT BELOW AVERAGE HIGH TEMPERATURES IN THE  
70S EACH DAY...60S ALONG THE EAST COAST ON SUNDAY GIVEN INCREASED  
ONSHORE FLOW. DEWPOINTS REMAIN COMFORTABLE IN THE 50S.  
 
MONDAY THROUGH THURSDAY...  
 
MONDAY LOOKS TO REMAIN MOSTLY DRY WITH CONTINUED INFLUENCE OF HIGH  
PRESSURE AND ONLY A SLOWLY MOISTENING ATMOSPHERIC COLUMN. WINDS  
ALONG THE SOUTH COAST REMAIN GUSTY BUT START COMING DOWN. IT'S NOT  
UNTIL MONDAY NIGHT/TUESDAY THAT WE REALLY SEE SIGNS OF A WARM  
FRONTAL FEATURE AHEAD OF TWO INCOMING LOW PRESSURE SYSTEMS...ONE  
MOVING FROM THE GREAT LAKES INTO CANADA, AND ANOTHER POTENTIALLY  
APPROACHING SOUTHERN NEW ENGLAND UP THE EAST COAST. HIGH DEGREE OF  
UNCERTAINTY ON HOW THESE FEATURES PLAY OUT AND INTERACT WITH EACH  
OTHER, BUT THE GENERAL IDEA WILL BE INCREASING MOISTURE AS DEWPOINTS  
SURGE BACK INTO THE UPPER 60S TUESDAY, INTO THE 70S BY WEDNESDAY  
INTO LATE WEEK. OVERALL AN UNSETTLED PATTERN WITH AT LEAST PERIODIC  
RAIN CHANCES TUESDAY THROUGH THURSDAY AS SEVERAL FRONTAL BOUNDARIES  
AND SHORTWAVES MOVE THROUGH. NOT MUCH INSTABILITY FOR THUNDER, AT  
LEAST THROUGH MID WEEK GIVEN COOL NORTHEAST FLOW. TEMPERATURES  
REMAIN A BIT BELOW NORMAL TUESDAY, IN THE 70S, BEFORE REBOUNDING  
INTO THE LOW 80S BY MID-LATE WEEK AS WARMER SUBTROPICAL AIR IS  
PULLED UP THE COAST DOWNSTREAM OF THE TROUGH.  
 

 
   
AVIATION /02Z FRIDAY THROUGH TUESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH FRIDAY NIGHT/...MODERATE CONFIDENCE.  
 
TONIGHT...  
 
MAINLY DRY INITIALLY. VFR-MVFR CIGS/VSBYS MOVING INTO CT-RI-SE  
MASS 03Z TO 06Z. ISOLATED THUNDER POSSIBLE. MAINLY VFR AND DRY  
NORTH OF THE MA PIKE.  
 
FRIDAY...  
 
SHOWERS IN MVFR-VFR POSSIBLE DURING THE MORNING ACROSS RI/CT AND  
SOUTHEAST MA, ESPECIALLY ALONG THE SOUTH COAST AND ISLANDS.  
OTHERWISE TREND WILL BE FOR VFR, DRY WEATHER AND NW WINDS.  
 
FRIDAY NIGHT...  
 
VFR, DRY WEATHER AND NORTHERLY WINDS.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...MODERATE CONFIDENCE  
 
SATURDAY: VFR.  
 
SATURDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.  
 
SUNDAY THROUGH SUNDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR  
POSSIBLE. BREEZY. SLIGHT CHANCE SHRA.  
 
MONDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY. CHANCE  
SHRA.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY.  
SLIGHT CHANCE SHRA.  
 
TUESDAY: VFR. BREEZY. SLIGHT CHANCE SHRA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE.  
 
TONIGHT ... SCATTERED SHOWERS AND ISOLATED THUNDER ESPECIALLY  
11 PM TO 2 AM ALONG THE SOUTHERN WATERS. ADDITIONAL SHOWERS  
ARRIVE ON MOST WATERS AFTER 2 AM. SW WINDS SLOWLY SHIFTING TO  
NW AS A COLD FRONT STALLS OVER THE SOUTHERN WATERS. SEAS  
LINGERING AT 5 FEET SOUTH OF BLOCK ISLAND, BUT EXPECTED TO  
DIMINISH. WE WILL CONTINUE THE SMALL CRAFT ADVISORY TO 2 AM.  
 
FRIDAY ... SCATTERED SHOWERS WITH ISOLATED THUNDER AND HEAVY  
DOWNPOURS POSSIBLE IN THE MORNING, THEN TRENDING DRYING IN THE  
AFTERNOON FROM NW TO SE.  
 
FRIDAY NIGHT ... COLD FRONT OFFSHORE WITH WNW WINDS AND DRY  
WEATHER.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...MODERATE CONFIDENCE.  
 
SATURDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS  
APPROACHING 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
SUNDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 30 KT. SEAS UP TO 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
SUNDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. SEAS UP TO 5 FT. CHANCE OF RAIN SHOWERS.  
 
MONDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 25 KT. SEAS UP TO 5 FT. CHANCE OF RAIN SHOWERS.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT  
CHANCE OF RAIN SHOWERS.  
 
TUESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 25 KT. SEAS UP TO 5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT FRIDAY FOR ANZ254>256.  
 

 
 

 
SYNOPSIS...NOCERA/BW  
NEAR TERM...WTB/NOCERA/BW  
SHORT TERM...NOCERA  
LONG TERM...BW  
AVIATION...WTB/NOCERA/BW  
MARINE...WTB/NOCERA/BW  
 
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