939  
FXUS61 KBOX 221729  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
129 PM EDT WED MAY 22 2024  
   
SYNOPSIS
 
 
A HIGH PRESSURE REMAINS JUST SOUTHEAST OF NEW ENGLAND, SETTING  
THE STAGE FOR SUMMERLIKE WARMTH THROUGH THURSDAY AWAY FROM THE  
IMMEDIATE SOUTH COAST. GENERALLY DRY WEATHER IS EXPECTED THROUGH  
TODAY, BUT AN APPROACHING COLD FRONT MAY BRING A ROUND OF  
SCATTERED SHOWERS AND THUNDERSTORMS THURSDAY AFTERNOON AND  
EVENING. A FEW STRONG TO SEVERE STORMS ARE POSSIBLE. MAINLY DRY  
ON FRIDAY WITH IT REMAINING MILD. UNSETTLED THROUGH THIS WEEKEND  
WITH HIT OR MISS SHOWERS AND THUNDERSTORMS. TURNING MORE  
SEASONABLE EARLY NEXT WEEK WITH A BETTER OPPORTUNITY FOR  
WIDESPREAD RAINS.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
THE LAST OF THE VALLEY FOG HAS ERODED IN NORTHWEST MA LEAVING  
COMPLETELY CLEAR SKIES ACROSS ALL OF SNE FOR OUR HOTTEST DAY OF  
THE YEAR SO FAR. FORECAST IS ON TRACK!  
 
PREVIOUS DISCUSSION...  
 
STILL CLOSELY TRACKING THE PROGRESS OF A STRATUS BANK JUST OFF  
THE SOUTH COAST OF NEW ENGLAND. SATELLITE DATA CONTINUED TO HINT  
AT THIS STRATUS APPROACHING, BUT AS OF THIS WRITING THERE HAS  
BEEN NO INDICATION OF IT FROM THE SURFACE OBSERVATIONS. SOME OF  
THE MORE RELIABLE NEAR TERM GUIDANCE STILL SUGGESTS IT MAY TAKE  
UNTIL SOME TIME BETWEEN 4-6 AM FOR THESE CLOUDS TO OVERSPREAD  
THE CAPE AND ISLANDS. PUTTING THESE SOURCES TOGETHER, PREFERRED  
THE GLAMP GUIDANCE FOR TIMING THE STRATUS AND FOG THIS MORNING.  
 
NOT MUCH CHANGE TO THE SYNOPTIC PATTERN, WITH A HIGH PRESSURE  
STILL LINGERING OFF THE SOUTH COAST OF NEW ENGLAND. OTHERWISE,  
NOT MUCH ELSE TO DRIVE SHOWERS AND THUNDERSTORMS OTHER THAN  
DAYTIME HEATING. MOST OF THE CONVECTION-ALLOWING MODELS DEPICT  
THE GREATEST RISK STAYS TO OUR WEST INTO THIS EVENING. HOWEVER,  
WITH HIGH TEMPERATURES 85-90 ACROSS MUCH OF INTERIOR SOUTHERN  
NEW ENGLAND AND DEW POINTS AROUND 60 DEGREES, THERE IS AT LEAST  
A GREATER CHANCE TOWARDS WESTERN MA THIS AFTERNOON AND EVENING.  
 
STILL EXPECTING MUCH COOLER CONDITIONS TOWARDS THE IMMEDIATE  
SOUTH COAST, WITH HIGHS GENERALLY IN THE 60S. A SHARP  
TEMPERATURE GRADIENT SHOULD EXTEND ACROSS SOUTHERN RI INTO  
SOUTHEAST MA.  
 

 
   
SHORT TERM /THURSDAY/
 
 
MID LEVEL LAPSE RATES ARE PROJECTED TO BE SLIGHTLY STEEPER THAN  
MOIST ADIABATIC THIS EVENING. THUS, DESPITE NOT HAVING MUCH  
SYNOPTIC SUPPORT, SHOWERS AND THUNDERSTORMS COULD LAST A WHILE  
PAST SUNSET. ANY SUCH SHOWERS OR THUNDERSTORMS WOULD BE  
WEAKENING AS THEY MOVED FARTHER EAST TONIGHT.  
 
THURSDAY STILL APPEARS TO BE A MORE ACTIVE WEATHER DAY AS A  
COLD FRONT IS PROJECTED TO ARRIVE DURING THE TIME OF PEAK  
HEATING. SOME LINGERING CLOUDS FROM THE LEFTOVER CONVECTION  
SHOULD MEAN SLIGHTLY LOWER HIGH TEMPERATURES, BUT STILL PLENTY  
WARM AND HUMID ENOUGH TO SUPPORT SOME STRONGER THUNDERSTORMS  
DURING THE AFTERNOON AND EVENING. DAMAGING WINDS AND LARGE HAIL  
ARE THE MAIN THREATS.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
 
 
HIGHLIGHTS  
 
* SHOWERS AND THUNDERSTORMS EXITING THU NIGHT INTO EARLY FRI AS  
A COLD FRONT EXITS.  
 
* DRY AND QUIET WEATHER FOR THE REST OF FRI WITH ABOVE NORMAL TEMPS.  
 
* TEMPS REMAIN MILD THROUGH THE WEEKEND. STILL A LOT OF  
UNCERTAINTY WITH HOW THE PATTERN EVOLVES, BUT LOOKS UNSETTLED.  
NO WASHOUTS ANTICIPATED AT THIS POINT.  
 
* STILL UNSETTLED EARLY NEXT WEEK WITH BETTER OPPORTUNITIES FOR  
MORE WIDESPREAD RAINS. TEMPS MAY RETURN TO MORE SEASONABLE  
LEVELS.  
 
THURSDAY NIGHT INTO EARLY FRIDAY...  
 
A SHORTWAVE TROUGH OVER THE MID ATLANTIC THU NIGHT WILL LIFT  
INTO SOUTHERN NEW ENGLAND BY EARLY FRI. THE SHORTWAVE MOVES  
OFFSHORE BY MID/LATE FRI AM. A COLD FRONT WILL BE SITUATED  
NEARBY OR OVER SOUTHERN NEW ENGLAND THU EVE. SOME UNCERTAINTY  
WITH WHERE THE FRONT WILL BE, BUT IT WILL BE PUSHING FURTHER  
OFFSHORE EARLY FRI.  
 
FAIR AMOUNT OF UNCERTAINTY DURING THIS PERIOD AS SOME GUIDANCE  
ALREADY HAS THE COLD FRONT OFFSHORE BY THU EVENING, WHILE OTHERS  
NOT UNTIL EARLY ON FRI. TOUGH TO RESOLVE AT THIS POINT AS  
CONVECTIVE INFLUENCES WILL ALSO BE AT PLAY FROM ACTIVITY EARLIER  
ON THU. IN GENERAL HAVE STUCK WITH THE NBM AT THIS POINT IN  
TIME, BUT THERE ARE SIGNALS THAT GIVEN THE SLOWER MOVING FRONTAL  
BOUNDARY WE COULD SEE SOME HEAVY DOWNPOURS.  
 
DUE TO THE UNCERTAINTY HAVE LARGELY STUCK WITH PROBABILISTIC  
GUIDANCE, BUT SHOULD NOTE THAT THE UKMET HAS BEEN CONSISTENT  
FROM THE LAST 4 RUNS AND IS CONCERNING WITH A HEAVY RAINFALL  
RISK (1-3+ INCHES OVERNIGHT). THOUGH WILL NOTE THE EXACT  
PLACEMENT OF THE HEAVY RAIN AXIS HAS SHIFTED A BIT FROM RUN TO  
RUN. MOST OF THE OTHER GUIDANCE CLIP THE SOUTH COAST OR HAVE THE  
HEAVIEST PRECIP OFFSHORE. BOTH THE NAEFS AND EPS GUIDANCE  
INDICATE PWATS OF 1.5-2 STD ABOVE MODEL CLIMATOLOGY FOR THE BOX  
AREA AND A PLUME OF ROUGHLY 1.25-1.5 INCHES IMPINGING ON OUR  
AREA. THIS MATCHES UP WELL WITH THE LATEST DETERMINISTIC  
GUIDANCE, WHICH ALSO SHOW WARM CLOUD LAYER DEPTHS OF 2.5-3.5 KM.  
INSTABILITY WILL BE WANING DUE TO THE LOSS OF HEATING, BUT  
THERE MAY STILL BE UP TO A FEW HUNDRED J/KG OF MUCAPE IN PLACE.  
DEEP LAYER SHEAR MAY STILL BE HIGH ENOUGH THAT THERE ARE A FEW  
LINGERING STRONG STORMS. ALL SOURCES OF ENSEMBLE GUIDANCE,  
GEPS/GEFS AND EPS INDICATE LOW TO MOD PROBS (10-60 PERCENT) OF  
24 HR QPF AOA 0.5 INCHES. THE RISK IS HIGHEST OFFSHORE OF THE  
SOUTH COAST AND PROBS HAVE BEEN TRENDING OFFSHORE FROM RUN TO  
RUN. THE GEPS IS THE MOST AMPED UP OUT OF THE ENSEMBLES AND EVEN  
HAS SOME LOW PROBS OF 1+ INCHES OF QPF OFFSHORE. BASED ON THIS  
DID BUMP UP OUR QPF A BIT, BUT KEEP THE HEAVIEST OVER THE WATERS  
AT THIS POINT.  
 
WILL BE MILD ACROSS SOUTHERN NEW ENGLAND UNDER SWLY FLOW AHEAD  
OF THE FRONT AND W/WNW BEHIND IT. LOW TEMPERATURES RANGE FROM  
THE MID 50S TO THE LOW 60S.  
 
FRIDAY...  
 
A RIDGE AXIS EXTENDS FROM THE WESTERN/CENTRAL GREAT LAKES INTO  
THE TN VALLEY EARLY ON FRI. THE RIDGE BUILDS INTO THE EASTERN  
GREAT LAKES/MID ATLANTIC BY LATE FRI. IN RESPONSE A WEAK HIGH  
NUDGES INTO SOUTHERN NEW ENGLAND.  
 
DRY AND QUIET WEATHER ANTICIPATED DURING THIS TIMEFRAME. EXPECT  
ANOTHER MILD DAY ACROSS SOUTHERN NEW ENGLAND, BUT IN WAKE OF  
THE FRONT WILL BE A BIT LESS MUGGY. WILL HAVE WNW TO NW FLOW AT  
925 HPA WITH TEMPS OF 19-21 CELSIUS. BASED ON THIS AND CONSENSUS  
AMONGST MODELS HAVE BUMPED UP OUR HIGHS TO THE 75TH PERCENTILE  
OF GUIDANCE AS WE SHOULD HAVE GOOD DOWNSLOPING. THE RESULT ARE  
FAIRLY WIDESPREAD 80S. THOUGH WINDS MAY STAY ENOUGH TO THE SW  
ACROSS THE IMMEDIATE SOUTH COAST WHERE TEMPS WILL STRUGGLE TO  
GET OUT OF THE 70S.  
 
THIS WEEKEND INTO EARLY NEXT WEEK...  
 
STILL A CONSIDERABLE AMOUNT OF UNCERTAINTY THROUGH THIS  
TIMEFRAME. ESPECIALLY WITH HOW THE BLOCKY PATTERN EVOLVES OUT ON  
THE NORTHERN PLAINS/PACIFIC NW. THERE ARE SEVERAL WAVES THAT  
LIFT THROUGH SOUTHERN NEW ENGLAND, THOUGH THE BETTER SHOT FOR A  
DEEPER TROUGH COMES EARLY NEXT WEEK.  
 
GIVEN THE UNCERTAINTIES MENTIONED HAVE JUST STUCK WITH THE NBM.  
THOUGH SHOULD NOTE TEMPS HAVE TAKEN A SWING FROM 24 HRS AGO TO  
MILDER READINGS THROUGH THE WEEKEND, BEFORE WE TURN MORE  
SEASONABLE EARLY NEXT WEEK. BOTH DAYS OVER THE WEEKEND FEATURE  
SPOTTY SHOWER OPPORTUNITIES, BUT NO WASHOUTS ARE ANTICIPATED.  
ENSEMBLE GUIDANCE NOT SHOWING MUCH SIGNAL WISE FOR IMPACTFUL  
WEATHER WITH PWATS AROUND NORMAL RELATIVE TO MODEL CLIMO.  
TEMPERATURES STILL MILD.  
 
BEST SHOT FOR THE WASHOUT/HEAVIER PRECIP COMES EARLY NEXT WEEK.  
THE NAEFS/EPS GUIDANCE INDICATE PWATS AROUND 1-2 STD ABOVE  
MODEL CLIMO ALONG WITH THAT DEEPER TROUGH LIFTING IN. THE EPS  
INDICATES THERE ARE LOW TO MOD PROBS (10-40 PERCENT) OF 24 HR  
QPF AOA 1 INCH. THE GEPS/GEFS ARE MORE MUTED AND FIRMLY IN LOW  
PROBS AT THIS POINT. WILL BE ANOTHER PERIOD WE WILL HAVE TO  
MONITOR IN THE COMING DAY, BUT FOR NOW HAVE STUCK WITH THE NBM.  
 

 
   
AVIATION /18Z WEDNESDAY THROUGH SUNDAY/
 
 
FORECAST CONFIDENCE LEVELS:  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
THIS AFTERNOON...HIGH CONFIDENCE.  
 
VFR. SW WINDS 5-10 KTS.  
 
TONIGHT...MODERATE CONFIDENCE.  
 
LIGHT SW WINDS CONTINUE 5-10 KTS. IFR/MVFR CIGS IN STRATUS/FOG  
POSSIBLE OVER SOUTHEAST MA TERMINALS, BUT LOW CONFIDENCE IN  
AREAL EXTENT. COULD ALSO SEE SOME STATUS IN THE LOWER CT RIVER  
VALLEY. AREAS MVFR IN WEAKENING SHOWERS AND THUNDERSTORMS,  
MAINLY ACROSS WESTERN AND CENTRAL MA.  
 
THURSDAY...LOW TO MODERATE CONFIDENCE.  
 
MAINLY VFR, WITH AREAS MVFR/IFR IN HEAVIER SHOWERS AND  
THUNDERSTORMS. BEST CHANCE OF THUNDERSTORMS IS BETWEEN 15Z AND  
00Z.  
 
THURSDAY NIGHT...LOW TO MODERATE CONFIDENCE.  
 
MAINLY VFR, BUT AREAS OF MVFR/IFR IN ANY LINGERING SHOWERS AND  
THUNDERSTORMS WHICH MAY STICK AROUND FOR SOUTHEASTERN TERMINALS  
THROUGH AS LATE AS 06Z, AND EVEN LATER FOR ACK/FMH/HYA.  
 
KBOS TAF...HIGH CONFIDENCE IN TAF.  
 
KBDL TAF...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /FRIDAY THROUGH SUNDAY/...  
 
FRIDAY THROUGH FRIDAY NIGHT: VFR.  
 
SATURDAY THROUGH SATURDAY NIGHT: VFR. SLIGHT CHANCE SHRA.  
 
SUNDAY: VFR. SLIGHT CHANCE SHRA, ISOLATED TSRA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS:  
 
LOW - LESS THAN 30 PERCENT.  
MEDIUM - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
THROUGH THURSDAY...HIGH CONFIDENCE.  
 
HIGH PRESSURE SOUTH OF THE WATERS MAINTAINS RELATIVELY LIGHT  
WINDS AND SEAS THROUGH THURSDAY. THE MAIN CONCERN WILL BE POOR  
VISIBILITY IN AREAS OF FOG REDUCING VISIBILITY TO LESS THAN 1  
MILE AT TIMES INTO TONIGHT.  
 
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...  
 
THURSDAY NIGHT: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS,  
ISOLATED THUNDERSTORMS.  
 
FRIDAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
FRIDAY NIGHT: WINDS LESS THAN 25 KT.  
 
SATURDAY THROUGH SATURDAY NIGHT: WINDS LESS THAN 25 KT. SLIGHT  
CHANCE OF RAIN SHOWERS.  
 
SUNDAY: WINDS LESS THAN 25 KT. SLIGHT CHANCE OF RAIN SHOWERS,  
ISOLATED THUNDERSTORMS.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...AIR QUALITY ALERT UNTIL 11 PM EDT THIS EVENING FOR MAZ004>007-  
010>016-026.  
RI...NONE.  
MARINE...NONE.  
 

 
 

 
 
SYNOPSIS...BELK/BL  
NEAR TERM...BELK/BW  
SHORT TERM...BELK  
LONG TERM...BL  
AVIATION...BW/BL  
MARINE...BELK/BL  
 
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