067  
FXUS61 KBOX 112247  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
647 PM EDT TUE MAY 11 2021  
   
SYNOPSIS
 
 
WEAK LOW PRESSURE OVER THE MARITIMES WILL CIRCULATE COOLER THAN  
NORMAL AIR WITH A RISK OF A FEW SHOWERS AND EMBEDDED THUNDER  
WEDNESDAY AFTERNOON. MAINLY DRY AND MILDER CONDITIONS THURSDAY  
AND FRIDAY, THEN SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS  
EXPECTED THIS WEEKEND BUT NOT A WASHOUT. MORE UNSETTLED EARLY  
NEXT WEEK WITH BETTER CHANCES FOR SHOWERS BUT TIMING IS  
UNCERTAIN.  
 

 
   
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
 
 
645 PM UPDATE...  
 
DIURNAL CU DECREASING ACROSS SNE, BUT AREA OF ENHANCED MOISTURE  
IN THE 850-700 MB LAYER WILL RESULT IN SOME EXTRA CLOUD COVER  
ALONG THE SOUTH COAST THIS EVENING BEFORE CLEARING. OTHERWISE,  
SOME LOW-LEVEL MOISTURE WILL STREAM IN FROM THE NORTHWEST DURING  
THE PREDAWN HOURS AND PRODUCE A SHORT PERIOD OF CLOUD COVER  
ESPECIALLY ACROSS THE INTERIOR.  
 
SHORTWAVE PASSAGE WILL MAINTAIN FAIRLY BRISK WINDS TONIGHT,  
ESPECIALLY ALONG THE COAST AND HIGHER TERRAIN AS STRONG  
PRESSURE GRADIENT IN PLACE. CLOUD COVER AND MIXING WILL LIMIT  
THE LOW TEMPERATURES OVERNIGHT. HOWEVER WE SHOULD STILL SEE SOME  
FAIRLY LOW TEMPERATURES IN THE UPPER 30S TO MID 40S.  
 

 
   
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/
 
 
WEDNESDAY...  
 
RELATIVELY STRONG PRESSURE GRADIENT AT THE SURFACE WILL STILL BE IN  
PLACE BY TOMORROW. THIS WILL CONTINUE TO SUPPORT MODERATE SUSTAINED  
WINDS OUT OF THE WEST/NORTHWEST. AS A RESULT PARTLY CLOUDY SKIES  
ACROSS THE INTERIOR EARLY SHOULD MIX OUT BY MID-LATE MORNING.  
HOWEVER THE NORTHWEST FLOW AND CAA ALOFT WILL SETTLE A COLD-POOL  
ALOFT OVER SOUTHERN NEW ENGLAND. THIS WILL ALLOW THE ATMOSPHERE TO  
DESTABILIZE AND WITH THE HELP OF SOME MID-LEVEL MOISTURE WE SHOULD  
SEE SOME DIURNAL CUMULUS DEVELOP DURING THE AFTERNOON HOURS.  
ADDITIONALLY A SHORT-WAVE AT 500 HPA AND ASSOCIATED POSITIVE  
VORTICITY ADVECTION MAY SUPPORT ENOUGH ASCENT TO PRODUCE SOME SPOTTY  
INSTABILITY SHOWERS DURING THE AFTERNOON HOURS. THERE MAY ALSO BE  
ENOUGH CAPE TO SUPPORT SOME ISOLATED THUNDER SHOWERS.  
 
BUFKIT SOUNDINGS CURRENTLY INDICATE THE POTENTIAL TO MIX UP TO ABOUT  
800HPA WHICH SHOULD SUPPORT HIGH TEMPERATURES IN THE LOW-MID 60S AT  
THE SURFACE TOMORROW AFTERNOON. WINDS AT 850 HPA TOMORROW AFTERNOON  
ARE NOT FORECAST TO BE AS STRONG AS TODAY THUS THE POTENTIAL FOR  
STRONG WIND GUSTS WILL BE SOMEWHAT LIMITED. ALL IN ALL WITH THE  
EXCEPTION OF SOME SPOTTY SHOWERS WEDNESDAY IS SHAPING UP TO BE A  
PLEASANT SPRING DAY.  
 
WEDNESDAY NIGHT...  
 
MID-LEVEL CLOUDS MOVE EAST OVER THE ATLANTIC OVERNIGHT WEDNESDAY  
INTO THURSDAY WITH A 500 HPA SHORTWAVE ALOFT. ATMOSPHERE SHOULD  
DECOUPLE ENOUGH TO GET SOME PRETTY GOOD RADIATIONAL COOLING. THUS  
LEANED ON THE LOWER MOS GUIDANCE FOR LOW TEMPERATURES THURSDAY  
MORNING WHICH ARE FORECAST TO ONCE AGAIN BOTTOM OUT IN THE UPPER 30S  
TO LOW 40S. WINDS WILL REMAIN OUT OF THE NORTHWEST IN THE 5-10 MPH  
RANGE.  
 

 
   
LONG TERM /THURSDAY THROUGH TUESDAY/
 
 
HIGHLIGHTS...  
 
* DRY AND SEASONABLY MILD THU/FRI. LOW RISK FOR A FEW SHOWERS FRI  
AFTERNOON IN THE INTERIOR  
 
* SCATTERED SHOWERS/ISOLATED T-STORMS SAT/SUN BUT NOT A WASHOUT.  
MILD TEMPS NEAR OR SLIGHTLY ABOVE NORMAL  
 
* INCREASING RISK OF SHOWERS EARLY NEXT WEEK BUT TIMING UNCERTAIN  
 
DETAILS...  
 
THURSDAY INTO FRIDAY...  
 
MID LEVEL TROUGH LIFTS OUT THU WITH SLOWLY RISING HEIGHTS AS RIDGE  
BUILDS EAST FROM THE GT LAKES. RESULT WILL BE MOSTLY SUNNY SKIES BUT  
SOME DIURNAL CU GIVEN SHALLOW MOISTURE MOISTURE NOTED IN FORECAST  
SOUNDINGS. DESPITE STEEP LOW LEVEL LAPSE RATES, LACK OF MOISTURE  
WILL PRECLUDE ANY SHOWERS. DEEP BOUNDARY LAYER MIXING WITH 850 MB  
TEMPS 4-5C SUPPORT HIGHS WELL INTO THE 60S TO NEAR 70.  
 
A BIT MORE DIURNAL CLOUD COVER ON FRI AS MOISTURE SOMEWHAT DEEPER  
BUT STILL EXPECTING PARTLY TO MOSTLY SUNNY SKIES. MODELS INDICATING  
MARGINAL INSTABILITY AND DEEPER MOISTURE AS KI INCREASE TO NEAR 30  
SO CAN'T RULE OUT A FEW SHOWERS IN THE INTERIOR, OTHERWISE A DRY  
DAY. HIGHS SHOULD BE A FEW DEGREES WARMER THAN THU AS 925/850 MB  
TEMPS MODERATE, WITH LOWER 70S IN MOST LOCATIONS, BUT COOLER ALONG  
THE COAST WHERE SEA BREEZES LIKELY.  
 
SATURDAY AND SUNDAY...  
 
WEAK FLOW ALOFT BUT DECENT COLD POOL OVER NEW ENG WITH 500 MB TEMPS  
AROUND -25C. THIS WILL GENERATE SOME INSTABILITY WITH CAPES UP TO  
500-1000 J/KG AND TT INTO THE MID 50S. EXPECT A FEW AFTERNOON  
SHOWERS AND ISOLATED T-STORMS EACH DAY, ESPECIALLY INTERIOR BUT NOT  
A WASHOUT WITH A MIX OF SUN AND CLOUDS. HIGHS GENERALLY LOWER 70S,  
EXCEPT COOLER ALONG THE COAST WHERE SEA BREEZES ANTICIPATED.  
 
MONDAY AND TUESDAY...  
 
UNCERTAINTY INCREASES EARLY NEXT WEEK AS MODELS DIFFER ON THE UPPER  
LEVEL PATTERN. GFS MORE AMPLIFIED WITH APPROACHING MID LEVEL TROUGH  
AND OFFERS A WETTER SCENARIO THAN ECMWF BUT IT DOES APPEAR  
INCREASING CHANCES OF SHOWERS SOMETIME EARLY NEXT WEEK.  
 

 
   
AVIATION /22Z TUESDAY THROUGH SUNDAY/
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
00Z TAF UPDATE:  
 
TONIGHT...HIGH CONFIDENCE.  
 
VFR. WNW/W WIND GUSTS COME DOWN AFTER SUNSET TO SUSTAINED WINDS  
5 TO 15 KTS, BUT GUSTS TO 20KTS ESPECIALLY OVER THE HIGHER  
ELEVATIONS AND NEAR THE COAST.  
 
WEDNESDAY AND WEDNESDAY NIGHT...HIGH CONFIDENCE.  
 
VFR. NW WIND GUSTS TO 20 KTS DURING WED.  
 
KBOS TAF...HIGH CONFIDENCE IN TAF.  
 
KBDL TAF...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /THURSDAY THROUGH SUNDAY/...  
 
THURSDAY THROUGH THURSDAY NIGHT: VFR.  
 
FRIDAY: VFR. SLIGHT CHANCE SHRA.  
 
FRIDAY NIGHT: VFR.  
 
SATURDAY: VFR. CHANCE SHRA, ISOLATED TSRA.  
 
SATURDAY NIGHT: VFR.  
 
SUNDAY: VFR. CHANCE SHRA, ISOLATED TSRA.  
 

 
   
MARINE
 
 
TIGHT SURFACE PRESSURE GRADIENT WILL RESULT IN MODERATE  
SUSTAINED WINDS OUT OF THE WEST/NORTHWEST TONIGHT AND TOMORROW  
AFTERNOON. WINDY CONDITIONS AND CHOPPY SEAS HAVE WARRANTED AN  
EXTENSION OF SMALL CRAFT ADVISORIES FOR THE NEAR- SHORE WATERS  
THROUGH TOMORROW MORNING AND THE OUTER WATERS SOUTH AND EAST OF  
MARTHA'S VINEYARD THROUGH MID-AFTERNOON TOMORROW.  
 
OUTLOOK /THURSDAY THROUGH SUNDAY/...  
 
WINDS LESS THAN 25 KT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EDT WEDNESDAY FOR ANZ231>235-  
237-250-251.  
SMALL CRAFT ADVISORY UNTIL 4 PM EDT WEDNESDAY FOR ANZ254>256.  
 

 
 

 
SYNOPSIS...KJC/RM  
NEAR TERM...KJC/RM  
SHORT TERM...RM  
LONG TERM...KJC  
AVIATION...KJC/RM  
MARINE...KJC/RM  
 
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