626  
FXUS61 KBOX 262059  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
459 PM EDT WED JUL 26 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE REMAINS OVER THE REGION TONIGHT PROVIDING DRY  
COOL WEATHER. THE HIGH MOVES OFFSHORE THURSDAY GIVING WAY TO  
SLIGHTLY MORE HUMID CONDITIONS ALONG WITH THE RISK FOR A FEW  
SHOWERS AND AN ISOLATED THUNDERSTORM, BUT BY NO MEANS A WASHOUT.  
A DRYING TREND LIKELY DEVELOPS THU NIGHT INTO FRI AS A COLD  
FRONT MOVES THROUGH THE REGION AND THEN STALLS NEAR THE SOUTH  
COAST FRI. A COASTAL STORM WILL PUSH OFF THE MID ATLANTIC COAST,  
WHICH WILL BRING SHOWERS AND A FEW THUNDERSTORMS, ALONG WITH  
GUSTY ONSHORE WINDS WITH COOL TEMPERATURES FRIDAY INTO EARLY  
THIS WEEKEND. DRY AND SEASONABLE CONDITIONS RETURN BY EARLY NEXT  
WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
4 PM UPDATE...  
 
1020 MB HIGH OVER THE REGION LATE THIS AFTERNOON PROVIDING  
SPLENDID WEATHER WITH TEMPS MAINLY 75-80 ALONG WITH COMFORTABLE  
HUMIDITY. STABLE/COOL MARINE AIRMASS HAS COME ONSHORE VIA  
SEABREEZE CIRCULATION AND HAS RESULTED IN A LACK OF DIURNAL  
CLOUDS ALONG THE IMMEDIATE COAST PER LATEST GOES-16 IMAGERY. ALL  
OF THESE ATTRIBUTES WILL SET THE STAGE FOR VERY PLEASANT  
WEATHER THIS EVENING.  
 
THE ONLY ISSUE WILL BE WITH DRY AIRMASS /DEW PTS IN THE 50S -  
LOWEST INLAND/ IN PLACE COUPLED WITH LIGHT WINDS, TEMPS WILL  
FALL QUICKLY WITH SUNSET. SO EXPECT COOL CONDITIONS WITH SUNSET.  
OTHERWISE TRANQUIL WEATHER PREVAILS.  
 
LATER TONIGHT MID AND HIGH CLOUDS WILL OVERSPREAD THE REGION  
FROM NW TO SE AND THIS WILL STABILIZE TEMPS FROM FALLING MUCH  
MORE. HOWEVER GIVEN THE IDEAL RADIATIONAL COOLING CONDITIONS THE  
FIRST HALF OF THE NIGHT SIDED WITH THE COOLER MOS TEMPS FOR  
MINS. THUS ANOTHER COOL NIGHT WITH LOWS IN THE 50S EXCEPT AROUND  
60 IN THE URBAN AREAS.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/
 
 
4 PM UPDATE...  
 
THURSDAY...  
 
INCREASING CLOUDS AHEAD OF NEXT APPROACHING SHORT WAVE. WEAK  
LOW LEVEL WAA WILL RESULT IN SURFACE DEW PTS CLIMBING INTO THE  
LOW AND MID 60S, SO IT WILL FEEL MORE HUMID THAN TODAY. AIRMASS  
IS SLIGHTLY WARMER THAN TODAY BUT WITH INCREASING CLOUDS HIGHS  
TOMORROW WILL BE CLOSE TO VALUES OF TODAY, 75-80. IT WILL BE  
SLIGHTLY WARMER ALONG THE EASTERN MA COAST/BEACHES THAN TODAY  
GIVEN SSW WINDS TOMORROW. OVERALL A TYPICAL SUMMER DAY, PERHAPS  
A FEW DEGS BELOW AVERAGE.  
 
AS FOR THE RISK OF SHOWERS/T-STORMS, APPROACHING SHORT WAVE  
PROVIDES MODEST MID LEVEL MOISTURE ADVECTION (K INDEX LOW 30S)  
ALONG WITH WEAK FORCING/HEIGHT FALLS FOR ASCENT. THIS SHOULD BE  
SUFFICIENT FOR ISOLATED TO WIDELY SCATTERED SHOWERS. HOWEVER  
T-STORMS ESPECIALLY STRONG TO SEVERE APPEARS VERY LOW AS NW FLOW  
PRECLUDES TRUE WARM SECTOR AIRMASS FROM ADVECTING NORTHEAST  
INTO SOUTHERN NEW ENGLAND. THIS IS EVIDENT ON ALL MODEL GUIDANCE  
OFFERING LESS THAN 500 J/KG OF MUCAPE. THIS COMBINED WITH WEAK  
MID LEVEL LAPSE RATES (H5 TEMPS ONLY COOL FROM -9C TO -10C) WILL  
RESULT IN WEAK UPDRAFTS AND STRONGER STORMS LIKELY REMAINING IN  
THE WARM SECTOR ACROSS NYC/NJ/EASTERN PA. AFTER COLLABORATION  
WITH SPC THE SLIGHT RISK WAS REMOVED FROM SOUTHWEST CT FOR THU.  
 
SO ISOLATED TO WIDELY SCATTERED SHOWERS AND T-STORMS THU  
AFTERNOON, HOWEVER MANY HOURS OF DRY WEATHER TOO, SO BY NO MEANS  
A WASH OUT.  
 
THU NIGHT...  
 
GOOD DRYING THRU THE COLUMN PER DECREASING K INDEX VALUES AS  
SHORT WAVE TROUGH MOVES EAST OF THE AREA AND MID LEVEL  
ANTICYCLONIC FLOW AND ASSOCIATED SUBSIDENCE TAKE OVER. THIS WILL  
RESULT IN A DRYING TREND FROM NORTH TO SOUTH. SO ANY EVENING  
SHOWERS/T-STORMS WILL SHIFT SOUTH AND THEN OFFSHORE. HOWEVER  
FRONT WILL NOT REACH THE SOUTH COAST UNTIL FRI MORNING. SO  
EXPECT WARM AND HUMID CONDITIONS TO PERSIST MUCH OF THE NIGHT.  
THIS MOIST LOW LEVEL AIRMASS WILL INCREASE THE RISK OF PATCHY  
FOG AS WELL.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
HIGHLIGHTS...  
 
* RISK CONTINUES FOR SHOWERS AND A FEW THUNDERSTORMS POSSIBLE FRI  
NIGHT AND SAT, BEST CHANCE S COAST  
* GUSTY E-NE WINDS POSSIBLE ALONG COASTAL AREAS, HIGHEST ALONG S  
COAST, CAPE COD AND THE ISLANDS LATE FRI NIGHT INTO SAT EVENING  
* DRY CONDITIONS LIKELY SUNDAY INTO EARLY NEXT WEEK  
 
OVERVIEW AND MODEL PREFERENCES...  
CONTINUE TO SEE RATHER WIDE MODEL SOLUTION SPREAD FOR TRACK,  
STRENGTH AND TIMING OF LOW PRESSURE MOVING OFF THE MID ATLANTIC  
COAST AND S OF NEW ENGLAND. THE BIG QUESTION IS HOW FAR N THE  
PRECIP SHIELD MOVES INTO THE REGION AND HOW STRONG THE E-NE  
WINDS WILL BE ESPECIALLY LATE FRI NIGHT THROUGH INTO SATURDAY  
NIGHT, ESPECIALLY ALONG THE S COAST, CAPE COD AND THE ISLANDS.  
RATHER STRONG H5 SHORT WAVE ASSOCIATED WITH THIS SYSTEM,  
ESPECIALLY PRONOUNCED ON THE ECMWF ACROSS S NJ DURING SAT. COULD  
ALSO SEE GUSTY WINDS ALONG THE COAST, ESPECIALLY THE S COASTAL  
AREAS LATE FRI NIGHT INTO EARLY SAT NIGHT, BUT TIMING IS STILL  
AN ISSUE.  
 
MODELS SHOWING A BIT BETTER AGREEMENT AFTER THE LOW EXITS SAT  
NIGHT OR EVEN SUN MORNING, WITH DRY CONDITIONS AS HIGH PRESSURE  
BUILDS ACROSS. WILL SEE LEFTOVER COOL TEMPS ON SUNDAY, THEN  
BECOMING MORE SEASONABLE BY THE BEGINNING OF THE WORK WEEK.  
HOWEVER, STILL NOTING DEVELOPING H5 LONG WAVE TROUGHING ACROSS  
THE EASTERN U.S. WHILE ANOTHER HIGH AMPLITUDE RIDGE BUILDS  
ACROSS THE WESTERN STATES. SOME QUESTION AS TO TIMING OF ANOTHER  
COLD FRONT MOVING SE OUT OF SOUTHERN QUEBEC/ONTARIO, BUT  
APPEARS NOT A LOT OF UPPER SUPPORT WITH THIS SYSTEM. TIMING AND  
MOVEMENT STILL VERY MUCH IN QUESTION.  
 
DETAILS...  
 
FRIDAY...  
WILL START OFF DRY AND SEASONABLE EARLY FRIDAY, THEN SOME  
SHOWERS MAY START TO PUSH NE BY MIDDAY WELL AHEAD OF LOW PRES  
MOVING OFF THE S NJ COAST ALONG A STATIONARY FRONT S OF NEW  
ENGLAND. CLOUDS WILL INCREASE, ALONG WITH THE CHANCE FOR  
SHOWERS. MAY SEE SOME MARGINAL INSTABILITY FOR A FEW  
THUNDERSTORMS FRI AFTERNOON. LIGHT/VARIABLE WINDS BECOME LIGHT  
EASTERLY, THOUGH MAY START TO PICK UP ALONG THE S COAST BY  
EVENING. EXPECT HIGHS TO RUN A FEW DEGREES BELOW SEASONAL  
NORMALS DUE TO THE DEVELOPING ONSHORE WIND.  
 
FRIDAY NIGHT-SATURDAY...  
BEST CHANCE FOR SHOWERS ESPECIALLY FROM CENTRAL MASS SOUTHWARD.  
HAVE LIKELY POPS MENTIONED THERE FOR MOST OF THIS PERIOD.  
MARGINAL INSTABILITY REMAINS ACROSS THE REGION, SO HAVE KEPT IN  
SLIGHT CHANCE FOR THUNDERSTORMS AS WELL.  
 
BIG QUESTION WILL BE THE TRACK OF THE LOW AS IT DEEPENS TO A  
RATHER ANOMALOUS SYSTEM AS IT PASSES S OF NEW ENGLAND FRIDAY  
NIGHT TO MID DAY SATURDAY. VERY STRONG H925-H9 JET ASSOCIATED  
WITH THIS SYSTEM, WITH E-NE WINDS UP TO 40-50 KT S OF EASTERN  
LONG ISLAND AND BLOCK ISLAND BY AROUND MIDDAY SATURDAY. HOW MUCH  
MIXES DOWN IS IN QUESTION, BUT CAN NOT RULE OUT GUSTS TO 30-40  
KT ESPECIALLY OVER THE COASTAL WATERS. COULD SEE GUSTS THAT HIGH  
ACROSS CAPE COD AND THE ISLANDS DURING SATURDAY AS WELL.  
SOMETHING TO KEEP A CLOSE EYE ON.  
 
STILL NOTING CONVECTIVE FEEDBACK ISSUES, BUT RATHER GOOD SLUG  
OF PRECIP MOVES ACROSS. NOTING PWATS UP TO 2 TO 2.2 INCHES  
MOVING ACROSS CAPE COD AND THE ISLANDS SAT, SO COULD SEE SOME  
HEAVIER RAIN THERE FRI NIGHT/SAT. WILL BE A RATHER SHARP LINE  
WHERE HEAVIEST PRECIP FALLS, MAINLY ALONG S COAST, WITH ABOUT  
0.25 INCHES OR LESS FROM ABOUT N CT/RI TO S OF BOSTON NORTHWARD.  
 
AT THIS POINT, COULD SEE SOME IMPROVING CONDITIONS SATURDAY  
AFTERNOON/EVENING FROM W-E AS THE LOW SHIFTS OFFSHORE, BUT  
TIMING IS STILL IN QUESTION.  
 
SAT WILL BE ANOTHER CHILLY DAY BY JULY STANDARDS, WITH HIGHS  
ONLY IN THE LOWER-MID 70S.  
 
SATURDAY NIGHT THROUGH MONDAY...  
MID LEVEL LONG WAVE SHIFTS OFFSHORE DURING SAT NIGHT, WITH NW  
FLOW IN PLACE ALOFT INTO EARLY NEXT WEEK WHICH MAY SHIFT INTO  
QUEBEC. MEANWHILE, AT THE SURFACE, HIGH PRES BUILDS EASTWARD OUT  
OF THE OHIO VALLEY TO THE APPALACHIANS. GOOD RIDGING AND DRY  
CONDITIONS BUILD IN THIS PERIOD.  
 
WILL REMAIN ON THE COOL SIDE SUNDAY, WITH HIGHS RUNNING AROUND  
5 DEGREES BELOW SEASONAL NORMALS, BUT WILL WARM ON MONDAY  
ESPECIALLY ACROSS THE INTERIOR.  
 
TUESDAY-WEDNESDAY...LOW CONFIDENCE.  
ANOTHER COLD FRONT STARTS TO APPROACH DURING TUESDAY, THOUGH  
TIMING AND STRENGTH IN QUESTION. NOT A LOT OF MOISTURE  
ASSOCIATED WITH THE FRONT WITH THE GENERAL W-NW FLOW ALOFT IN  
PLACE. BROAD LONG WAVE TROUGH SETS UP ACROSS THE EASTERN U.S.,  
BUT NOT MUCH ENERGY TO WORK WITH. AT THIS POINT, MAY SEE A FEW  
SHOWERS TUE, THEN SHOULD BE DRY ON WED BUT TIMING OF FEATURES IN  
QUESTION.  
 

 
   
AVIATION /21Z WEDNESDAY THROUGH MONDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
18Z/2PM UPDATE...  
 
THRU 00Z...VFR WITH ANY BKN CIGS 4-5KFT. LIGHT S-SE WINDS  
CONTINUE.  
 
AFTER 00Z...VFR WITH WINDS BECOMING LIGHT AND VARIABLE, THEN SSW  
TOWARD MORNING.  
 
THURSDAY...VFR WITH BKN040-050 CIGS IN THE AFTERNOON ALONG WITH  
ISOLATED TO WIDELY SCATTERED T-STORMS.  
 
THURSDAY NIGHT...VFR BUT TRENDING TOWARD MVFR ESPECIALLY ACROSS  
CT/RI AND SOUTHEAST MA INCLUDING CAPE COD AND THE ISLANDS WHERE  
PATCHY FOG WILL FORM. SCATTERED SHOWERS AND ISOLATED T-STORM  
POSSIBLE IN THE EVENING HOURS.  
 
KBOS TERMINAL...HIGH CONFIDENCE. ISOLATED TO WIDELY SCATTERED  
SHOWERS/T-STORMS THU AFTERNOON/EARLY EVENING. STRONGEST STORMS  
WILL LIKELY REMAIN WELL SOUTHWEST OF THE REGION ACROSS NYC/NJ/PA  
AREA.  
 
KBDL TERMINAL...HIGH CONFIDENCE. ISOLATED TO WIDELY SCATTERED  
SHOWERS/T-STORMS THU AFTERNOON/EARLY EVENING. STRONGEST STORMS  
WILL LIKELY REMAIN WELL SOUTHWEST OF THE REGION ACROSS NYC/NJ/PA  
AREA.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRI...HIGH CONFIDENCE.  
A FEW SHOWERS AND THUNDERSHOWERS, MAINLY THU EVENING. THEN  
MAINLY NEAR THE S COAST ON FRI. OTHERWISE, PREDOMINANTLY VFR  
OUTSIDE OF SOME LOCALIZED GROUND FOG.  
 
FRI NIGHT AND SAT...MODERATE CONFIDENCE.  
POTENTIAL FOR IFR-MVFR CONDITIONS IN SHOWERS. PATCHY FOG DURING  
THE NIGHTTIME HOURS. SLIGHT CHANCE FOR THUNDERSTORMS, BEST  
CHANCE S COASTAL TERMINALS. E-NE WINDS WHICH COULD GUST 25-35 KT  
MAINLY NEAR THE COAST FROM KGHG SOUTHWARD SAT. RAINFALL,  
ESPECIALLY ALONG S COAST MAY BE HEAVY AT TIMES, THOUGH STILL  
UNCERTAIN HOW CLOSE THE HEAVY RAIN SHIELD WILL COME TO THE  
COAST. CONDITIONS SHOULD IMPROVE FROM W-E SAT AFTERNOON/EVENING.  
 
SATURDAY NIGHT THROUGH MONDAY...HIGH CONFIDENCE.  
VFR. N-NE WIND GUSTS TO AROUND 30 KT ACROSS CAPE COD AND THE  
ISLANDS EARLY SAT NIGHT, THEN DIMINISHING.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
4 PM UPDATE...  
 
SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE ON WIND AND  
WAVES BUT LOWER CONFIDENCE ON PROBABILITY OF SHOWERS/T-STORMS.  
 
TONIGHT...LIGHT ONSHORE WINDS CONTINUE. SMALL EAST SWELL OF 2-4 FT  
CONTINUES ACROSS THE OCEAN WATERS. OTHERWISE TRANQUIL WAVES NEAR  
SHORE. DRY WEATHER AND GOOD VSBY PREVAIL.  
 
THURSDAY...SSW WINDS 10-15 KT POSSIBLY INCREASING TO 20 KT IN GUSTS  
LATE IN THE DAY. ISOLATED SHOWER/T-STORM POSSIBLE. GOOD VSBY  
CONTINUES.  
 
THURSDAY NIGHT...SSW WINDS 10-15 KT SHIFTING TO WNW TOWARD DAYBREAK  
FRIDAY. ISOLATED SHOWER/T-STORM HOWEVER FOG MAY BECOME FAIRLY  
WIDESPREAD BUT IMPROVING TOWARD MORNING ACROSS THE NORTHERN WATERS  
GIVEN THE WIND SHIFT FROM SSW TO WNW.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRIDAY...HIGH CONFIDENCE.  
LIGHT/VARIABLE WINDS SHIFT TO E-SE BUT REMAIN LIGHT. SEAS 3 FT  
OR LESS.  
 
FRIDAY NIGHT INTO SATURDAY NIGHT...MODERATE CONFIDENCE.  
LOW PRES PASSES S OF NEW ENGLAND WHILE IT INTENSIFIES. STILL  
QUESTIONING HOW CLOSE THE LOW WILL APPROACH, BUT WINDS SHIFT TO  
E-NE AND PICK UP AFTER 06Z SAT. COULD SEE SUSTAINED WIND  
REACHING 20-25 KT BY 12Z SAT ACROSS THE SW WATERS. E-NE WINDS  
COULD GUST TO 30-40 KT DURING SAT, LIKELY HIGHEST ACROSS THE  
SOUTHERN WATERS TO N AND E OF CAPE COD, WITH SMALL CRAFT WINDS  
ELSEWHERE. SEAS MAY REACH AS HIGH AS 8-12 FT ON THE OPEN OCEAN  
WATERS. SHOWERS WITH ISOLATED THUNDERSTORMS, WITH PERIODS OF  
HEAVY RAIN ON THE SOUTHERN OUTER WATERS. WINDS SLOWLY DIMINISH  
SAT NIGHT, DOWN TO SMALL CRAFT LEVELS. SEAS WILL ALSO SLOWLY  
SUBSIDE BUT REMAIN AT OR ABOVE 5 FT.  
 
SUNDAY AND MONDAY...HIGH CONFIDENCE.  
IMPROVING CONDITIONS AS LEFTOVER SMALL CRAFT WINDS/SEAS  
DIMINISH BY SUNDAY EVENING, GIVING WAY TO QUIET BOATING  
CONDITIONS.  
 

 
   
EQUIPMENT
 
 
KBOX RADAR IS HAS RETURNED TO SERVICE.  
 

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

 
 

 
SYNOPSIS...NOCERA/EVT  
NEAR TERM...NOCERA  
SHORT TERM...NOCERA  
LONG TERM...EVT  
AVIATION...NOCERA/EVT  
MARINE...NOCERA/EVT  
EQUIPMENT...STAFF  
 
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