642  
FXUS61 KBOX 191942  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
342 PM EDT FRI JUL 19 2019  
   
SYNOPSIS
 
 
EXTREME HEAT AND HUMIDITY IS ON TAP FOR THE WEEKEND WITH DANGEROUS  
HEAT INDICES BETWEEN 105 AND 115 DEGREES DURING BOTH AFTERNOONS. DRY  
WEATHER DOMINATES THIS WEEKEND, BUT A FEW THUNDERSTORMS ARE POSSIBLE  
SUNDAY AFTERNOON AND NIGHT. A BETTER CHANCE FOR SOME SHOWERS AND  
THUNDERSTORMS WILL BE NEXT MONDAY INTO TUESDAY WITH EVENTUALLY MUCH  
COOLER AND LESS HUMID AIR MOVING INTO THE REGION. MAINLY DRY WITH  
SEASONABLE TEMPERATURES FAVORED WEDNESDAY THROUGH NEXT FRIDAY  
ALONG WITH COMFORTABLE HUMIDITY LEVELS.  
 

 
   
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
 
 
345 PM UPDATE...  
 
TONIGHT ...  
 
WARM SECTOR AIRMASS OVERSPREADING THE REGION THIS AFTERNOON WITH  
MANY INTERIOR LOCATIONS (BDL-BAF-FIT-BED-OWD-BOS) INTO THE LOW 90S  
AS OF 3 PM ALONG WITH DEW PTS 70-75. THEN THERE IS NANTUCKET AT 70  
DEGS IN 1/2 MILE FOG. GOTTA LOVE NEW ENGLAND WEATHER.  
 
CU-SCU CLOUDS WILL ERODE WITH SUNSET AND GIVE WAY TO A VERY WARM  
EVENING/NIGHT GIVEN DEW PTS OF 70-75. THUS OVERNIGHT MINS ONLY IN  
THE 70S, TO NEAR 80 IN THE URBAN AREAS OF BOSTON, PROVIDENCE AND  
HARTFORD. THIS HUMID AIRMASS COMBINED WITH SW WINDS WILL LIKELY  
RESULT IN PATCHY FOG AND STRATUS REVISITING CAPE COD AND THE ISLANDS  
WITH PLENTY OFFSHORE SOUTH OF MVY-BID AND LONG ISLAND VIA LATEST  
GOES-16 SATELLITE IMAGERY. SOME PATCHY INTERIOR FOG AS WELL.  
 

 
   
SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/
 
 
*** EXCESSIVE HEAT WARNING CONTINUES ***  
*** NEAR RECORD HIGH TEMPERATURES ***  
 
SATURDAY ...  
 
OFF TO A VERY WARM START WITH MORNING LOWS ONLY 75-80. THIS COMBINED  
WITH 850 MB TEMPS OF +22C TO +23C ADVECTING ACROSS THE REGION,  
BOUNDARY LAYER EXTENDING UP TO 800 MB AND WEAK DOWNSLOPING WEST  
WINDS OF 10-15 KT WILL SUPPORT HIGHS 95-100 AWAY FROM THE SOUTH  
COAST AND 100-105 POSSIBLE IN THE CT RIVER VALLEY AND MERRIMACK  
VALLEY OF NORTHEAST MA. THESE NEAR RECORD HIGHS WILL COMBINE WITH  
DEW PTS OF 70-75 TO YIELD HEAT INDICES OF 105-110 WITH A FEW SPOTS  
IN THE CT RIVER VALLEY AND MERRIMACK VALLEY APPROACHING 115! THUS  
DANGEROUS HEAT AND HUMIDITY AND AS A RESULT EXCESSIVE HEAT WARNINGS  
REMAIN POSTED.  
 
GIVEN THIS ANOMALOUS AIRMASS DERIVED HIGHS WITH THE WARMEST  
GUIDANCE.  
 
MID LEVEL SUBTROPICAL RIDGE AND ASSOCIATED SUBSIDENCE SHOULD CAP ANY  
POTENTIAL CONVECTION TOMORROW. THEREFORE EXPECTING DRY WEATHER.  
 
SATURDAY NIGHT ...  
 
NEAR RECORD WARMTH WITH LOW TEMPS ONLY FALLING BACK TO 75-80 WITH  
LOW 80S LIKELY IN THE URBAN CENTERS OF BOSTON, PROVIDENCE AND  
HARTFORD. THUS NO RELIEF WITH THESE TEMPS AND DEW PTS REMAINING IN  
THE 70S. SSW WINDS AND DRY WEATHER SHOULD PREVAIL.  
 

 
   
LONG TERM /SUNDAY THROUGH FRIDAY/
 
 
HIGHLIGHTS...  
 
* DANGEROUS HEAT/HUMIDITY SUN: HEAT INDEX VALUES BETWEEN 105 AND 115  
AND IT IS POSSIBLE A FEW ALL TIME RECORD HIGHS ARE APPROACHED  
 
* HIGH UNCERTAINTY IF ANY CONVECTION DEVELOPS SUN PM, BUT IT NEEDS  
TO BE MONITORED GIVEN EXTREME INSTABILITY/EML IN PLACE  
 
* SOME SHOWERS/THUNDERSTORMS LIKELY MON AND/OR TUE WITH EVENTUALLY  
MUCH COOLER LESS HUMID AIR MOVING INTO THE REGION  
 
* MAINLY DRY WITH SEASONABLE TEMPERATURES FAVORED WED THROUGH NEXT  
FRI ALONG WITH COMFORTABLE HUMIDITY LEVELS  
 
DETAILS...  
 
SUNDAY...  
 
EVERYTHING REMAINS ON TRACK FOR EXTREME HEAT/HUMIDITY FOR THIS PART  
OF THE COUNTRY. STRONG UPPER LEVEL RIDGE TO THE SOUTH WILL CONTINUE  
TO PUMP A VERY HIGHLY ANOMALOUS AIRMASS INTO SOUTHERN NEW ENGLAND.  
850T AROUND +22C AND WESTERLY FLOW WILL RESULT IN NEAR RECORD HIGH  
TEMPERATURES. IN FACT, MANY OF THE NAEFS/GEFS ARE SHOWING  
TEMPERATURE PROFILES OUTSIDE THE MODELS CLIMATOLOGY. THEREFORE, WE  
EXPECT HIGHS TO RANGE BETWEEN 98 AND 103 DEGREES IN MANY LOCATIONS  
AWAY FROM ANY LOCALIZED MARINE INFLUENCES. WHETHER WE END UP ON THE  
HIGHER/LOWER SIDE OF THESE NUMBERS WILL DEPEND UPON AMOUNT OF SOLAR  
INSOLATION. IF EVERYTHING TURNS OUT TO BE IDEAL IT IS NOT OUT OF  
THE QUESTION THAT A FEW ALL TIME RECORD HIGHS ARE CHALLENGED.  
 
MORE IMPORTANT THOUGH WILL BE THE DANGEROUS HEAT INDEX VALUES. GIVEN  
THE EML IN PLACE, DEWPOINTS WILL TEND TO STAY QUITE HIGH REMAINING  
IN THE 70S. THIS WILL RESULT IN EXTREME HEAT INDEX VALUES CLIMBING  
TO BETWEEN 105 TO 115 DEGREES DURING PEAK AFTERNOON HEATING.  
 
THE OTHER CONCERN SUNDAY AFTERNOON AND EVENING WILL BE THE POTENTIAL  
FOR CONVECTION, BUT THIS REMAINS QUITE UNCERTAIN. THE HIGHLY  
ANOMALOUS HEAT/HUMIDITY COUPLED WITH AN EML IN PLACE WILL RESULT IN  
A TREMENDOUS AMOUNT OF INSTABILITY FOR THIS PART OF THE COUNTRY. WE  
WILL PROBABLY SEE CAPE VALUES ON THE ORDER OF 4,000 J/KG. A COLD  
FRONT WILL BE DROPPING SOUTH INTO THE REGION, BUT THERE IS LIMITED  
UPPER SUPPORT. THAT MEANS THERE IS UNCERTAINTY IF WE ARE ABLE TO  
BUST THE CAP. IF THE CAP HOLDS, WE MAY REMAIN COMPLETELY DRY. ON  
THE OTHER HAND IF IT BREAKS, THERE IS SOME HIGH END SEVERE WEATHER  
POTENTIAL GIVEN THE ENVIRONMENT IN PLACE. WILL HAVE A BETTER IDEA  
ONCE WE GET INTO THE WHEELHOUSE OF THE HIGH RESOLUTION MODELS.  
 
MONDAY AND TUESDAY...  
 
INTERESTING SETUP MON INTO TUE AS MODEL GUIDANCE INDICATES A FEW  
WAVES OF LOW PRESSURE FORMING ALONG THE FRONT TO OUR SOUTH. LATEST  
MODEL GUIDANCE INDICATES WE MAY ENTER THE WARM SECTOR AGAIN FOR A  
TIME MONDAY WITH ONE OF THE WAVES OF LOW PRESSURE. EITHER WAY,  
THERE WILL BE THE THREAT FOR SOME SHOWERS AND THUNDERSTORMS MON INTO  
TUE. PLENTY OF UNCERTAINTY ON TIMING, BUT GIVEN HIGH PWATS LOCALLY  
HEAVY RAINFALL WILL BE A CONCERN. WE ALSO WILL HAVE TO WATCH FOR  
THE RISK FOR LOCALIZED SEVERE WEATHER NEAR ANY FRONTAL BOUNDARIES.  
 
WEDNESDAY THROUGH FRIDAY...  
 
MAINLY DRY AND SEASONABLE WEATHER APPEARS TO BE ON TAP FOR THE  
MIDDLE AND LATTER HALF OF THE NEXT WORK WEEK. LATEST MODEL GUIDANCE  
SHIFTS THE FRONT SOUTHEAST OF OUR REGION AS HIGH PRESSURE BUILDS IN  
FROM THE WEST. THE RESULT WILL BE PLEASANT SUMMERLIKE TEMPERATURES  
BUT WITH COMFORTABLE HUMIDITY LEVELS. A BIG RELIEF FROM WHAT WE  
WILL EXPERIENCE THIS WEEKEND.  
 

 
   
AVIATION /20Z FRIDAY THROUGH WEDNESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SATURDAY NIGHT/...MODERATE CONFIDENCE.  
 
1755Z UPDATE ...  
 
THRU 00Z ... VFR WITH OCCASIONAL IFR/MVFR AT NANTUCKET. SSW  
WINDS.  
 
AFTER 00Z ... VFR BUT IFR/MVFR DRIFTING BACK INTO CAPE COD AND  
THE ISLANDS AS THE NIGHT PROGRESSES. SSW WINDS CONTINUE.  
 
SATURDAY ... ANY LEFTOVER MVFR/IFR ACROSS CAPE COD AND THE  
ISLANDS WILL ERODE AND GIVE WAY TO VFR BY MIDDAY OR EARLIER. VFR  
ELSEWHERE WITH MODEST WEST WINDS, SOUTHWEST ALONG THE COAST. DRY  
WEATHER PREVAILS.  
 
SATURDAY NIGHT ... VFR AND DRY WEATHER LIKELY.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SUNDAY THROUGH WEDNESDAY/...HIGH CONFIDENCE.  
 
SUNDAY: VFR. BREEZY. CHANCE SHRA, CHANCE TSRA.  
 
SUNDAY NIGHT: VFR. CHANCE SHRA, CHANCE TSRA.  
 
MONDAY: MAINLY MVFR, WITH AREAS VFR POSSIBLE. SHRA LIKELY, TSRA  
LIKELY.  
 
MONDAY NIGHT: MAINLY MVFR, WITH AREAS VFR POSSIBLE. BREEZY.  
CHANCE SHRA, SLIGHT CHANCE TSRA.  
 
TUESDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. BREEZY. CHANCE  
SHRA, SLIGHT CHANCE TSRA.  
 
TUESDAY NIGHT THROUGH WEDNESDAY: VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SATURDAY NIGHT/...HIGH CONFIDENCE.  
 
345 PM UPDATE...  
 
TONIGHT ... SSW WINDS BUT LOW CLOUDS AND FOG WILL IMPACT THE  
SOUTHERN WATERS FROM CAPE COD SOUTHWARD.  
 
SATURDAY / SAT NIGHT ... SSW WINDS WITH PERIODS OF LOW CLOUDS AND  
FOG SOUTHERN WATERS.  
 
OUTLOOK /SUNDAY THROUGH WEDNESDAY/...HIGH CONFIDENCE.  
 
SUNDAY THROUGH SUNDAY NIGHT: WINDS LESS THAN 25 KT. SEAS  
LOCALLY APPROACHING 5 FT. CHANCE OF RAIN SHOWERS, CHANCE OF  
THUNDERSTORMS.  
 
MONDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
RAIN SHOWERS LIKELY, THUNDERSTORMS LIKELY.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT. RAIN SHOWERS LIKELY, THUNDERSTORMS LIKELY.  
 
TUESDAY: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE OF  
RAIN SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT. SLIGHT CHANCE OF RAIN SHOWERS, ISOLATED THUNDERSTORMS.  
 
WEDNESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT.  
 

 
   
CLIMATE
 
 
RECORD HIGHEST MIN TEMPS FOR SATURDAY JULY 20:  
 
BOS: 75 IN 2016  
BDL: 73 IN 1975  
PVD: 77 IN 1983  
ORH: 72 IN 2013  
 
RECORD HIGHS FOR SATURDAY JULY 20:  
 
BOS: 99 IN 1991  
BDL: 100 IN 1991  
PVD: 101 IN 1991  
ORH: 92 IN 1901  
 
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...EXCESSIVE HEAT WARNING UNTIL 8 PM EDT SUNDAY FOR CTZ002>004.  
AIR QUALITY ALERT UNTIL 11 PM EDT THIS EVENING FOR CTZ002-003.  
MA...AIR QUALITY ALERT FROM 11 AM TO 11 PM EDT SATURDAY FOR  
MAZ017>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 FROM 11 AM TO 11 PM EDT SATURDAY FOR  
RIZ001>008.  
EXCESSIVE HEAT WARNING UNTIL 8 PM EDT SUNDAY FOR RIZ001>007.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...NOCERA/FRANK  
NEAR TERM...NOCERA  
SHORT TERM...NOCERA  
LONG TERM...FRANK  
AVIATION...NOCERA/FRANK  
MARINE...NOCERA/FRANK  
CLIMATE...STAFF  
 
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