942  
FXUS61 KBOX 210333  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
1133 PM EDT SAT JUL 20 2019  
   
SYNOPSIS
 
 
EXTREME HEAT AND HUMIDITY CONTINUES INTO SUNDAY WITH DANGEROUS  
HEAT INDICES BETWEEN 100 AND 110 DEGREES DURING THE AFTERNOON  
AND EARLY EVENING. THE HEAT AND HUMIDITY MAY TRIGGER A FEW  
ISOLATED SHOWERS/THUNDERSTORMS FROM LATE SATURDAY THROUGH  
SUNDAY. OTHERWISE MOST LOCATIONS EXPERIENCE DRY WEATHER. LOW  
PRESSURE THEN TRACKS ALONG A FRONTAL BOUNDARY INTO SOUTHERN NEW  
ENGLAND MONDAY AND TUESDAY, AND WILL BE ACCOMPANIED BY SHOWERS  
AND THUNDERSTORMS WITH TROPICAL DOWNPOURS AND STRONG WINDS  
POSSIBLE. EVENTUALLY MUCH COOLER AND LESS HUMID AIR MOVES INTO  
THE REGION LATE TUE INTO WED. MAINLY DRY WEDNESDAY THROUGH  
FRIDAY WITH SEASONABLE TEMPERATURES AND COMFORTABLE HUMIDITY  
LEVELS.  
 

 
   
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
 
 
*** EXCESSIVE HEAT WARNING CONTINUES THROUGH SUNDAY ***  
*** NEAR RECORD WARMTH TONIGHT ***  
 
11 PM UPDATE...  
 
A FEW ISOLATED SHOWERS AND THUNDERSTORMS CROSSED N CENTRAL CT  
AS WELL AS FROM EASTERN HAMPDEN COUNTY ACROSS SOUTHERN WORCESTER  
COUNTY AFTER 2330Z. QUITE A BIT OF LIGHTNING DEVELOPED AROUND  
0015Z OR SO AS IT MOVED INTO SW WORCESTER COUNTY NEAR BRIMFIELD  
AND CHARLTON, MAINLY ALONG ROUTE 20. THIS CELL STRENGTHENED AS  
IT CROSSED OXFORD AND AUBURN HEADING FOR SUTTON BY AROUND  
0045Z. THE STORM DID STRENGTHEN BRIEFLY AS IT CROSSED S CENTRAL  
WORCESTER COUNTY WHICH PROMPTED THE SVR.  
 
ANOTHER AREA OF SHOWERS/THUNDERSTORMS MOVED OUT OF E CENTRAL NY  
AND BERKSHIRE COUNTY INTO FRANKLIN AND HAMPSHIRE COUNTIES, BUT  
THE CONVECTION REMAINED BELOW WARNING CRITERIA. NOTED WIND GUSTS  
UP TO 27 KT AT KORE AS THE STORMS CROSSED THERE. THE CONVECTION  
CONTINUED TO WEAKEN AS THE PRECIP MOVED ACROSS NW MASS, THOUGH  
A FEW THUNDERSTORMS DID CROSS CENTRAL AND E FRANKLIN COUNTY  
THROUGH AROUND 02Z, BUT FINALLY DISSIPATED.  
 
SCATTERED SHOWERS CONTINUED ACROSS NW AND W MASS AT 03Z, BUT  
SHOULD DISSIPATE BY AROUND 05Z OR SO.  
 
EXPECT SULTRY CONDITIONS ACROSS THE REGION OVERNIGHT AS  
DEWPOINTS REMAIN MAINLY IN THE LOWER-MID 70S, THOUGH THE  
DEWPOINT WAS 77 DEGREES AT KBOS AT 03Z. TEMPS OVERNIGHT WILL  
BOTTOM OUT IN THE MID 70S TO LOWER 80S, WARMEST IN THE URBAN  
CENTERS AS WELL AS EASTERN INTERIOR MASS.  
 
HAVE UPDATED TO BRING CONDITIONS CURRENT.  
 
PREVIOUS DISCUSSION...  
 
GIVEN DEWPTS ARE IN THE LOW TO MID 70S WITH A FEW UPPER 70S,  
ONLY EXPECTING TEMPS TO COOL OFF INTO THE MID TO UPPER 70S  
OVERNIGHT. EVEN WARMER IN THE URBAN CENTERS OF BOSTON,  
PROVIDENCE AND HARTFORD WHERE TEMPS MAY ONLY FALL INTO THE LOW  
80S, WHICH IS NEAR RECORD WARMTH FOR OVERNIGHT LOWS.  
 

 
   
SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/
 
 
415 PM UPDATE ...  
 
SUNDAY...  
 
*** EXCESSIVE HEAT WARNING CONTINUES SUNDAY ***  
*** NEAR RECORD HIGHS POSSIBLE ***  
 
STILL CAPPED ENVIRONMENT SUNDAY WITH ONLY SUBTLE HEIGHT FALLS  
AND WARM TEMPS PERSIST ALOFT. NOT MUCH CYCLONIC CURVATURE TO THE  
MID LEVEL FLOW, THUS LITTLE IF ANY SYNOPTIC SCALE LIFT. HOWEVER  
DEEP LAYER SHEAR INCREASES A BIT FROM 15 KT TODAY TO ABOUT 25 KT  
SUNDAY AFTERNOON, STILL A HIGH CAPE LOW SHEAR ENVIRONMENT.  
ALTHOUGH WITH BLYR WINDS BECOMING WEST AND INCREASING TO 15-20  
KT IN THE AFTERNOON, THIS WILL LIMIT SURFACE CONVERGENCE AND  
ALSO DRY OUT THE BOUNDARY LAYER WITH DEW PTS FALLING INTO THE  
MID AND UPPER 60S. SO A NOTCH LESS OPPRESSIVE TOMORROW BUT THIS  
WILL ALSO LOWER CAPE VALUES DOWN TO 1000-2000J/KG, PLENTY OF  
INSTABILITY TO SUPPORT DEEP CONVECTION BUT DEFINITELY LESS  
INSTABILITY THAN TODAY. CONVERSELY MID LEVEL LAPSE RATES MORE  
IMPRESSIVE TOMORROW AS EML CURRENTLY OVER THE GREAT LAKES AND OH  
VALLEY ADVECTS ACROSS SNE. THUS MIXED SIGNALS FOR CONVECTION  
TOMORROW BUT MORE UNFAVORABLE THAN FAVORABLE PARAMETERS. AS A  
RESULT MOST OF THE CAMS MODELS SUPPRESS CONVECTION SUNDAY.  
 
OTHERWISE ANOTHER VERY HOT DAY WITH TEMPS PERHAPS A FEW DEGS  
HIGHER THAN TODAY GIVEN WEST WINDS WILL INCREASE TOMORROW TO  
15-20 MPH, PROVIDING MORE DOWNSLOPE ADIABATIC WARMING. SO WHILE  
TEMPS MAY BE A FEW DEGS HIGH TOMORROW, DEW PTS WILL LIKELY FALL  
INTO THE UPPER 60S AND LOWER 70S, SO NOT QUITE AS OPPRESSIVE  
HUMIDITY. NEVERTHELESS THE COMBINATION OF HIGHS TOMORROW 95-100  
COUPLED WITH DEW PTS IN THE UPPER 60S TO LOWER 70S YIELDING HEAT  
INDICES OF 100-110 WILL CONTINUE WITH CURRENT HEADLINES.  
 
SUNDAY NIGHT...  
 
STILL VERY WARM BUT NOT AS OPPRESSIVE AS TONIGHT WITH SLIGHTLY  
DRIER AIRMASS OVER THE REGION. ANY ISOLATED LATE DAY STORMS  
SHOULD DISSIPATE BY LATE EVENING. OTHERWISE DRY WEATHER  
PREVAILS.  
 

 
   
LONG TERM /MONDAY THROUGH SATURDAY/
 
 
HIGHLIGHTS...  
 
* SHOWERS/THUNDERSTORMS LIKELY MON INTO TUE WITH EVENTUALLY MUCH  
COOLER LESS HUMID AIR MOVING INTO THE REGION  
 
* MAINLY DRY WITH SEASONABLE TEMPERATURES WED THROUGH SATURDAY WITH  
COMFORTABLE HUMIDITY  
 
DETAILS...  
 
MONDAY AND TUESDAY...  
 
THE BIG IDEA FOR MONDAY AND TUESDAY WILL BE A VERY WET STORM SYSTEM  
WHICH MOVES THROUGH BRINGING HEAVY RAINFALL AND SOME SCATTERED  
THUNDERSTORMS TO THE REGION. BEGINNING MONDAY MID LEVEL FLOW  
AMPLIFIES, DIGGING A DEEP TROUGH OVER THE EASTERN US WITH A LARGE  
RIDGE OVER THE INTERMOUNTAIN WEST. AS THIS DEEPENING TROUGH  
APPROACHES SOUTHERN NEW ENGLAND FLOW BECOMES SOUTHWEST PULLING IN  
DEEP, MOISTURE RICH AIR AHEAD OF IT (PWATS NEAR 2"). THE FRONT  
STALLED SOUTH OF THE COAST WHICH BROUGHT SOME RELIEF FROM THE HEAT  
AND HUMIDITY WILL LIFT NORTH AGAIN ON MONDAY PUTTING A PORTION OF  
SNE IN THE WARM SECTOR, THOUGH THERE IS STILL CONSIDERABLE  
UNCERTAINTY IN JUST HOW FAR NORTH THAT MOVES. BEST CHANCE NOW WOULD  
BE THAT IT STAYS ALONG OR SOUTH OF THE MA PIKE, AND THIS IS WHERE  
WE'LL SEE THE BEST INSTABILITY AND CHANCE FOR THUNDERSTORMS MONDAY  
AFTERNOON AND OVERNIGHT. WITH INSTABILITY ON THE ORDER OF 1500 J/KG  
CAPE AND GOOD DEEP LAYER SHEAR (40-45 KTS) THERE IS POTENTIAL FOR A  
FEW STRONG TO SEVERE THUNDERSTORMS IN THE WARM SECTOR. HOWEVER, THE  
GREATEST RISK WILL LIKELY BE FROM HEAVY RAIN AND POTENTIAL FLOODING  
AS DETAILED BELOW.  
 
AS THE UPPER TROUGH DIGS A SURFACE LOW IS GENERATED ALONG THE  
STALLED FRONTAL BOUNDARY, STRENGTHENING OVER EASTERN PA ON MONDAY  
BEFORE MOVING INTO NEW ENGLAND, POTENTIALLY AS A DOUBLE BARREL  
LOW. THIS WOULD BRING TWO ROUNDS OF VERY HEAVY RAIN TO THE  
REGION. PLENTY OF MOISTURE IS PRESENT AS MENTIONED EARLIER. THIS  
WITH APPROACHING FRONTAL CONVERGENCE, THE RRQ OF A 110KT 300MB  
JET, AND A 30-35KT LLJ MEANS WE HAVE POTENTIAL TO SEE A  
PROLONGED PERIOD(S) OF HEAVY RAIN FROM LATE MONDAY THROUGH  
TUESDAY. WPC CURRENTLY HAS WESTERN MA/CT IN A SLIGHT RISK OF  
EXCESSIVE RAINFALL, WITH A MARGINAL RISK FOR THE REST OF THE  
AREA. WE'LL HAVE TO MONITOR FOR THE POTENTIAL OF FLOODING WITH  
THIS SYSTEM GIVEN DEEP LAYER MOISTURE AND STRONG UNIDIRECTIONAL  
SHEAR. THE LOW SHOULD LIFT OUT LATE TUESDAY BRINGING RAIN TO AN  
END. COOLER AND DRIER AIR MOVES IN BEHIND THE SYSTEM WHICH ALONG  
WITH CLOUD COVER SHOULD KEEP HIGH TEMPS ON TUESDAY IN THE 70S.  
 
WEDNESDAY THROUGH SATURDAY...  
 
A COOLER, MORE SEASONABLE, AND DRIER PERIOD IS ON TAP FOR MID WEEK  
INTO THE WEEKEND. THE UPPER TROUGH MOVES OVERHEAD WITH BUILDING HIGH  
PRESSURE AT THE SURFACE. 850MB TEMPS AROUND 10C TEMPERATURES WILL  
MAKE SURFACE TEMPS FEEL COOL RELATIVE TO THIS WEEKEND, IN THE MID  
80S; SHOULD FEEL DRIER AS WELL, WITH PWATS <1" AND DEWPOINTS IN THE  
50S AND LOW 60S.  
 

 
   
AVIATION /03Z SUNDAY THROUGH THURSDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SUNDAY NIGHT/...MODERATE TO HIGH CONFIDENCE.  
 
03Z UPDATE...  
 
VFR AND MAINLY DRY. MAY SEE SPOTTY MVFR CONDITIONS IN PATCHY FOG  
OR ANY LEFTOVER SHOWERS, WHICH WILL CROSS N CENTRAL AND W MASS  
THROUGH AROUND 05Z, THEN SHOULD DISSIPATE. MAY ALSO SEE MVFR  
CONDITIONS ACROSS OUTER CAPE COD AND NANTUCKET IN FOG THROUGH  
12Z. PATCHY MVFR IN PATCHY FOG ALSO THE INTERIOR VALLEYS. LIGHT  
W-SW WINDS INLAND, THEN SW UP TO 10 KT ALONG THE IMMEDIATE  
COAST.  
 
SUNDAY AND SUNDAY NIGHT...MODERATE CONFIDENCE.  
 
MORE OF THE SAME. VFR CONDITIONS WITH ANY T-STORMS VERY  
ISOLATED IN AREAL COVERAGE. WEST WINDS A BIT MORE THAN TODAY  
15-20 KT.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /MONDAY THROUGH THURSDAY/...HIGH CONFIDENCE.  
 
MONDAY: VFR. SHRA LIKELY, CHANCE TSRA.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. BREEZY. SHRA  
LIKELY, CHANCE TSRA.  
 
TUESDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY. CHANCE  
SHRA.  
 
TUESDAY NIGHT THROUGH THURSDAY: VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SUNDAY NIGHT/...HIGH CONFIDENCE.  
 
11 PM UPDATE...  
 
OVERNIGHT...MAINLY LIGHT S-SW WINDS, EXCEPT 10-15 KT WITH GUSTS  
UP TO 20 KT ACROSS THE SOUTHERN WATERS TO E OF CAPE COD. PATCHY  
FOG NEAR AND OFFSHORE OF CAPE COD AND THE ISLANDS.  
 
SUNDAY AND SUNDAY NIGHT...S-SW WINDS BECOMING W-NW LATE SUNDAY  
INTO SUNDAY NIGHT. ISOLATED T-STORM POSSIBLE. PATCHY FOG  
POSSIBLE SUNDAY MORNING BUT IMPROVING.  
 
OUTLOOK /MONDAY THROUGH THURSDAY/...HIGH CONFIDENCE.  
 
MONDAY: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS, SLIGHT  
CHANCE OF THUNDERSTORMS.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. RAIN SHOWERS LIKELY, CHANCE OF THUNDERSTORMS.  
 
TUESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 25 KT. LOCAL ROUGH SEAS. CHANCE OF RAIN SHOWERS, CHANCE OF  
THUNDERSTORMS.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE  
OF RAIN SHOWERS.  
 
WEDNESDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY  
APPROACHING 5 FT.  
 
THURSDAY: WINDS LESS THAN 25 KT.  
 

 
   
CLIMATE
 
 
RECORD HIGHEST MIN TEMPS FOR SATURDAY JULY 20:  
 
BOS: 80 IN 1977  
BDL: 73 IN 1977  
PVD: 76 IN 1977  
ORH: 72 IN 1977  
 
RECORD HIGHS FOR SATURDAY JULY 20:  
 
BOS: 99 IN 1991  
BDL: 100 IN 1991  
PVD: 101 IN 1991  
ORH: 95 IN 1991  
 
RECORD HIGHEST MIN TEMPS FOR SUNDAY JULY 21:  
 
BOS: 81 IN 1991  
BDL: 74 IN 1977  
PVD: 77 IN 1980  
ORH: 73 IN 1991  
 
RECORD HIGHEST MAX TEMPS FOR SUNDAY JULY 21  
 
BOS: 102 IN 1977  
BDL: 101 IN 1991  
PVD: 102 IN 1991  
ORH: 95 IN 1926  
 
LAST OCCURRENCE OF 100F OR HIGHER TEMPERATURES  
BOS: 7/22/2011 (103F)  
BDL: 7/18/2012 (100F)  
PVD: 7/22/2011 (101F)  
ORH: 7/4/1911 (102F)  
 
NOTABLE HIGH DEW POINTS IN PAST YEARS FOR JULY 20 AND JULY 21:  
 
SATURDAY JULY 20  
 
BOS 76 IN 2013 (LAST OF MULTIPLE YEARS)  
BDL 76 IN 2005  
PVD 76 IN 2013 (LAST OF MULTIPLE YEARS)  
ORH 76 IN 2013  
 
SUNDAY JULY 21  
 
BOS 76 IN 1994  
BDL 78 IN 1972  
PVD 81 IN 1977 (TIED FOR HIGHEST ALL-TIME AT PVD)  
ORH 76 IN 2011 (LAST OF MULTIPLE YEARS)  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...AIR QUALITY ALERT UNTIL 11 PM EDT THIS EVENING FOR CTZ002>004.  
EXCESSIVE HEAT WARNING UNTIL 8 PM EDT SUNDAY FOR CTZ002>004.  
MA...AIR QUALITY ALERT UNTIL 11 PM EDT THIS EVENING FOR MAZ017>024.  
AIR QUALITY ALERT FROM 11 AM TO 11 PM EDT SUNDAY FOR  
MAZ020>024.  
EXCESSIVE HEAT WARNING UNTIL 8 PM EDT SUNDAY FOR MAZ002>021-  
026.  
HEAT ADVISORY UNTIL 8 PM EDT SUNDAY FOR MAZ022-023.  
RI...AIR QUALITY ALERT UNTIL 11 PM EDT THIS EVENING FOR RIZ001>008.  
AIR QUALITY ALERT FROM 11 AM TO 11 PM EDT SUNDAY FOR  
RIZ003>008.  
EXCESSIVE HEAT WARNING UNTIL 8 PM EDT SUNDAY FOR RIZ001>007.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...NOCERA/BW  
NEAR TERM...EVT/BW  
SHORT TERM...NOCERA  
LONG TERM...BW  
AVIATION...NOCERA/EVT/BW  
MARINE...NOCERA/EVT/BW  
CLIMATE...  
 
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