995  
FXUS61 KBOX 210305  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
1105 PM EDT WED JUN 20 2018  
   
SYNOPSIS
 
 
SHOWERS ARE LIKELY OVERNIGHT S OF THE MA/CT/RI BORDER AS A LOW  
PRESSURE CENTER SWEEPS W TO E JUST S OF NEW ENGLAND. BIT COOLER  
WITH A SPOT SHOWERS THURSDAY. SEASONABLE FRIDAY WHILE TURNING  
UNSETTLED SATURDAY, CONTINUING THROUGH EARLY MONDAY WITH THE  
CHANCE OF SHOWERS AND THUNDERSTORMS. DRY WEATHER THEREAFTER  
THROUGH THURSDAY, WITH A RENEWED CHANCE OF WET- WEATHER FRIDAY  
INTO THE FOLLOWING WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
1030 PM UPDATE...  
 
AS LOW PRESSURE APPROACHES THE NJ COAST THIS EVENING, NOTING  
VERY SPOTTY SHOWER ACTIVITY ACROSS S COASTAL CT AND LONG ISLAND  
ON LATEST KBOX AND NE REGIONAL 88D RADAR IMAGERY. ONLY GROUND  
TRUTH SEEN AT 02Z WAS ACROSS CENTRAL LONG ISLAND, WHERE BOTH  
KISP AND KHWV WERE REPORTING -RA. PRETTY DRY AIRMASS IN PLACE  
AWAY FROM THE S COAST, WITH T/TD SPREADS FROM 10 TO 16 DEGREES.  
00Z NAM AND RAP BUFKIT SOUNDINGS ALSO SHOWING A DRY AIRMASS  
THROUGH THE LAYER, ESPECIALLY ON THE RAP MODEL DATA.  
 
CLOUDS AOB 5000 FT WERE REPORTED ACROSS A FEW SPOTS ON LONG  
ISLAND, WHILE MID AND HIGH CLOUDS WERE THE RULE FURTHER N.  
NOTING CLEARING LINE MOVING SLOWLY BUT STEADILY S ON LATEST  
GOES-EAST RGB MICROPHYSICS COMPOSITE AND IR SATELLITE IMAGERY.  
 
WITH THESE DRIER TRENDS, HAVE PUSHED THE NORTHERN EDGE OF THE  
PRECIP FURTHER S, BUT DID KEEP MENTION OF MAINLY CHC POPS  
ACROSS CENTRAL CT/CENTRAL RI AND S COASTAL MASS. HAVE LKLY POPS  
CONFINED TO THE IMMEDIATE S COAST AND ISLANDS AFTER MIDNIGHT.  
WITH A MAINLY STABLE AIRMASS, AS WELL AS NO LIGHTNING BEING  
REPORTED ANYWHERE ACROSS THE NE U.S., HAVE REMOVED MENTION OF  
THUNDER FROM THIS UPDATE.  
 
HAVE UPDATED NEAR TERM TO BRING CONDITIONS CURRENT AND  
INCORPORATED CURRENT THINKING INTO THE OVERNIGHT FORECAST.  
 
PREVIOUS DISCUSSION...  
 
RAIN MOVING IN JUST AROUND MIDNIGHT, EXITING THE EARLY MORNING  
HOURS ON THURSDAY. LATEST RADAR RETURNS JUST A PRE-CURSOR, ACTING  
TO MOISTEN THE ENVIRONMENT, HOWEVER LOW-LEVELS STILL CONSIDERABLY  
DRY AS SURFACE HIGH PRESSURE RETREATS OFF TO THE E.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/
 
 
THURSDAY INTO THURSDAY NIGHT...  
 
PRECIPITATION ALONG THE SOUTH COAST WILL BE ONGOING EARLY IN THE  
MORNING AS SURFACE LOW PRESSURE CONTINUE TO MOVE ACROSS THE SOUTHERN  
WATERS. APPROACHING WAVE FROM THE NORTHEAST WILL DRIVE THIS LOW  
SOUTH AND OFFSHORE LEADING TO AN END OF THE PRECIP. WILL HAVE TO  
WATCH FOR A SPOT SHOWER OR TWO DURING THE DAY ACROSS THE INTERIOR.  
INCREASING LOW LEVEL MOISTURE COMBINED WITH STEEP LAPSE RATES AND  
UPPER LEVEL TRIGGER COULD LEAD TO A FEW SHOWERS ESPECIALLY ALONG THE  
HIGHER TERRAIN. THUS HAVE INSERT A SLIGHT CHC FOR A SHOWER DURING  
THE AFTERNOON.  
 
TEMPERATURES ON THURSDAY WILL BE WARMER ACROSS THE CT VALLEY, BUT  
QUITE COOL ALONG THE EAST COAST. WINDS WILL SWITCH FROM THE  
SOUTHWEST TO THE NORTHEAST A FRONT PASSES THROUGH. THIS WILL BRING  
THE COOLER MARITIME AIRMASS ONSHORE. COULD SEE OVER A 10 DEGREE  
DIFFERENCE ACROSS THE REGION.  
 
TEMPERATURES OVERNIGHT WILL COOL OFF, BUT NOT AS MUCH AS PREV  
THROUGH. INCREASING LOW LEVEL MOISTURE TRAPPED WITHIN THE INVERSION  
WILL RESULT IN STRATUS AND FOG ACROSS THE AREA. STILL TRYING TO  
NARROW DOWN BEST LOCATION, BUT SOMETHING TO WATCH FOR IN THE COMING  
SHIFTS.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
*/ HIGHLIGHTS...  
 
- SATURDAY PERHAPS NOT A WASHOUT, SKIRTING RAINS S/E  
- SHOWERS / T'STORMS N/W SUNDAY, SWEEPING SE INTO MONDAY MORNING  
- PROLONGED DRY CONDITIONS DURING THE WEEK  
- WATCHING WEEKS-END FOR ADDITIONAL WET-WEATHER DISTURBANCES  
 
*/ OVERVIEW...  
 
SUMMER IS COMING. PREVAILING N PACIFIC H5 TROF DOWNSTREAM OF WHICH A  
SPLIT FLOW REGIME EMERGES OVER WESTERN N AMERICA. S TUG BY CASCADING  
SYSTEMS INTO A BAFFIN BAY GYRE, H85 TEMPERATURE WARM ANOMALIES BUILD  
INTO THE GREAT LAKES / ST. LAWRENCE RIVER VALLEY PER 5-DAY AVERAGES.  
SUBSEQUENT HIGHER HEIGHTS, MORE DOMINANT N ATLANTIC HIGH ESPECIALLY  
TOWARDS BERMUDA, INVOKING A S WARM, MOIST PUMP FROM THE GULF. WOULD  
APPEAR SEEMINGLY THAT A GENERAL H5 TROF PATTERN REMAINS OVER THE NE  
CONUS, HOWEVER WEAKER UNDER AN INCREASING WEIGHT OF HIGH PRESSURE,  
SUBSIDENCE. WEAK FRONTAL BOUNDARY PASSAGES WITH UNCERTAIN OUTCOMES,  
WHERE PRECIPITATION LOOKS PROMINENT UPSTREAM ONLY TO WASH OUT UPON  
ARRIVAL. CONFIDENT WARMING TREND INTO JULY, WHILE A NOD OF CONCERN  
OF DRIER THAN AVERAGE PRECIP, PERHAPS ENHANCING ONGOING ABNORMALLY  
DRY CONDITIONS. SOME UNKNOWNS, A NE ATLANTIC REX-BLOCK EVOLVING INTO  
W EUROPE, AND TROPICAL ACTIVITY OFF AFRICA INTO THE CARIBBEAN. WILL  
HIT ON ANY TARGETS OF OPPORTUNITY BELOW.  
 
*/ DISCUSSION...  
 
SATURDAY...  
 
LEAN AWAY FROM HEAVY RAIN WITH WEDGING HIGH PRESSURE, DRIER AIR, AS  
THE SUB-TROPICAL, +2" PRECIPITABLE WATER AIRMASS RESIDES S, PERHAPS  
SKIRTING SE NEW ENGLAND. HAVE SEEN THIS BEFORE WITH WINTER SYSTEMS  
IN WHERE ISALLOBARIC FLOW DAMS UP AGAINST AN APPROACHING OH RIVER  
VALLEY LOW. CAN'T RULE OUT SCATTERED SHOWER, THUNDERSTORM ACTIVITY  
TOWARDS DAYS END, BUT LEANING WITH 20.12Z GFS/NAM IN SE SKIRTING  
OUTCOMES FUELED BY LOW-LEVEL CONVERGENT INFLOW TOWARDS A HELD-UP  
WARM FRONTAL BOUNDARY. DE-AMPLIFYING MID-LEVEL TROF, WEAK FRONTAL  
BOUNDARY PARENT, PUSHES THE SUB-TROPICAL AXIS OFFSHORE AHEAD OF AN  
ONCOMING SHARPER H5 TROF AXIS FOR SUNDAY INTO MONDAY. NOT READY TO  
CALL THE DAY A WASHOUT.  
 
SUNDAY INTO MONDAY...  
 
AFTERNOON SHOWERS AND THUNDERSTORMS INTO EVENING, HOWEVER MAINLY N/W  
INTERIOR LOCALES. POSSIBLY STRONG BUT NOT THINKING SEVERE PER SHEAR  
AND 0-6 KM MEAN WIND ACCOMPANYING ALONG WITH MARGINAL INSTABILITY.  
BETTER SUB-TROPICAL, UNSTABLE AND MUGGY AIRMASS S/E, OFFSHORE, YET  
ENOUGH MOISTURE THAT WITH DESTABILIZATION SHOULD ALLOW ACTIVITY TO  
POP WITHIN CYCLONIC REGIME OUT AHEAD OF OVERNIGHT SHARP COLD FRONT,  
PUSHING OFFSHORE AROUND MONDAY MORNING. ACCOMPANYING VORTMAX, STRONG  
DEEP LAYER ASCENT, MAY HAVE TO WATCH SE NEW ENGLAND INTO MONDAY UP  
AGAINST A MORE MUGGY AIRMASS LINGERING OFFSHORE AS TO POTENTIAL OUT-  
COMES. THINKING A MAJORITY OF ACTIVITY IS NUISANCE.  
 
OVERALL, FOR THE 3-DAY PERIOD SATURDAY THROUGH MONDAY, COULD BE A  
SITUATION OF INTERIOR N/W DESTABILIZATION WITH S-SHORELINE SKIRTING  
SOAKERS. HIGH PRESSURE WEDGE FROM THE E, LOCATIONS UP THE ME COAST  
DOWN INTO NORTHEAST MA MAY END UP BEING THE PRECIPITATION LOSERS.  
 
END OF THE WEEK...  
 
SERIES OF FRONTAL BOUNDARIES, SLOWING, STALLING AGAINST THE BUILDING  
WALL OF ATLANTIC HIGH PRESSURE. HAVE TO WATCH CLOSELY STRENGTH OF  
SYNOPTIC FEATURES ROUND THE CONVERGENCE BOUNDARY, WHETHER THERE IS  
THE POSSIBILITY OF PROLONGED OUTCOMES OVER ANY ONE PARTICULAR AREA.  
NOTEWORTHY IS A SUDDEN TICK UPWARD OF PRECIPITATION WITHIN ENSEMBLE  
MEMBERS.  
 

 
   
AVIATION /03Z THURSDAY THROUGH MONDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY NIGHT/... HIGH CONFIDENCE.  
 
OVERNIGHT...  
MAINLY VFR. MAY SEE LOCAL MVFR AT TIMES ALONG THE IMMEDIATE S  
COAST, CAPE COD AND THE ISLANDS IN ANY -SHRA AND PATCHY FOG. LOW  
RISK OF BRIEF IFR CONDITIONS ACROSS THE ISLANDS MAINLY IN CIGS  
AFTER 06Z OR SO. SW WINDS UP TO ABOUT 10 KT SHIFTING TO LIGHT NW  
AFTER 08Z OR SO.  
 
THURSDAY...  
VFR. LINGERING S-COASTAL / ISLAND -SHRA WITH MVFR CIGS, A BRIEF  
THREAT OF IFR CIGS FOR ACK AROUND 12-18Z. IMPROVEMENT DURING THE  
AFTERNOON HOURS, CIGS LIFTING 4-7 KFT AGL, AS SPOT -SHRA DEVELOPS  
ACROSS INTERIOR S NEW ENGLAND AROUND ORH. N WINDS TURNING NE.  
 
THURSDAY NIGHT...  
VFR TO START BUT WITH NORTHEAST FLOW BELIEVE LOW LEVELS WILL  
SATURATE DROPPING CIGS AND VSBYS TO MVFR CONDITIONS.  
 
KBOS TERMINAL...  
KEEP -SHRA S OF THE TERMINAL OVERNIGHT. VFR PREVAILING.  
 
KBDL TERMINAL...  
EXPECT -SHRA TO BE IMMEDIATELY S OF THE TERMINAL. WILL GO LOW  
END VFR OVERNIGHT HOWEVER THERE IS A RISK OF SOME MVFR POSSIBLY  
SNEAKING IN PRIOR TO MORNING.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...MODERATE CONFIDENCE.  
 
FRIDAY: VFR.  
 
FRIDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.  
 
SATURDAY THROUGH SATURDAY NIGHT: SHRA LIKELY, CHANCE TSRA.  
 
SUNDAY THROUGH SUNDAY NIGHT: BREEZY. CHANCE SHRA, SLIGHT CHANCE  
TSRA.  
 
MONDAY: BREEZY. CHANCE SHRA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE.  
 
PASSING LOW PRESSURE SYSTEM ACROSS THE SOUTHERN WATERS WILL  
BRING SCATTERED SHOWERS WHICH COULD BRIEFLY REDUCE VISIBILITY.  
SEAS COULD BUILD TO 3 FEET. MAY SEE BRIEF GUSTS UP TO 20 KT  
ACROSS THE SOUTHERN NEAR SHORE WATERS THROUGH 06Z TONIGHT.  
OTHERWISE, SW WINDS WILL SHIFT TO A MORE NE DIRECTION TH  
LASTING INTO THU NIGHT. COULD SEE LOCAL VSBY RESTRICTIONS IN  
PATCHY FOG. CONDITIONS REMAIN BELOW SCA.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...MODERATE CONFIDENCE.  
 
FRIDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
 
FRIDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
SATURDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
CHANCE OF RAIN SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. RAIN SHOWERS LIKELY, CHANCE OF THUNDERSTORMS.  
 
SUNDAY: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE OF RAIN  
SHOWERS.  
 
SUNDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE  
OF RAIN SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.  
 
MONDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
CHANCE OF RAIN SHOWERS.  
 

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

 
 

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