226  
FXUS61 KBOX 291728  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
128 PM EDT THU JUL 29 2021  
   
SYNOPSIS
 
 
AN APPROACHING COLD FRONT WILL ALLOW SHOWERS TO DEVELOP ACROSS  
INTERIOR SOUTHERN NEW ENGLAND THIS AFTERNOON. SHOWERS AND EMBEDDED  
THUNDERSTORMS ARE EXPECTED TONIGHT AS THE COLD FRONT CROSSES THE  
REGION. A NOTICEABLY DRIER AIR MASS FILTERS INTO SOUTHERN NEW  
ENGLAND FRIDAY AFTERNOON INTO FRIDAY NIGHT, WITH NORTHWESTERLY  
BREEZES. SEASONABLE AND DRY ON SATURDAY. A FRONTAL SYSTEM BRINGS  
ANOTHER THREAT FOR SHOWERS SOMETIME SUNDAY AND/OR SUNDAY NIGHT. DRY  
WEATHER RETURNS FOR MONDAY BEFORE OUR WEATHER PATTERN TURNS MORE  
UNSETTLED INTO THE MIDDLE OF NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL MIDNIGHT TONIGHT/
 
 
1245 PM UPDATE...  
 
A FEW SHOWERS CAN BE SEEN ON RADAR ACROSS PORTIONS OF CT AND  
WESTERN MA THIS AFTERNOON. MODEL SOUNDINGS INDICATE WEAK  
INSTABILITY IN THESE AREAS WITH MLCAPE VALUES AROUND 200 J/KG.  
THERE IS SOME CIN TO OVERCOME RIGHT NOW, BUT WOULDN'T BE  
SHOCKED IF ONE OF THESE SHOWERS IS ABLE TO PRODUCE A RUMBLE OF A  
THUNDER.  
 
SHOWERS WILL EXPAND IN COVERAGE ACROSS THE WESTERN ZONES OVER  
THE NEXT COUPLE OF HOURS AS A SURFACE LOW PRESSURE SYSTEM TO  
OUR WEST/NORTHWEST LIFTS A WARM FRONT TOWARD SOUTHERN NEW  
ENGLAND. MOST OF THE FORECAST AREA IS EXPECTED TO STAY NORTH OF  
THE WARM FRONT AND OUTSIDE OF THE WARM SECTOR THIS AFTERNOON  
WHICH WILL LIMIT ORGANIZED THUNDERSTORM ACTIVITY FOR OUR AREA.  
NONETHELESS, WITH PWATS GREATER THAN 1.5 INCHES AND MODERATE  
FORCING FOR ASCENT WE COULD SEE SOME HEAVY DOWN POURS WITH THESE  
SHOWERS IN ADDITION TO ISOLATED THUNDER.  
 
AS SOUTHWEST FLOW ADVECTS HIGHER DEWPOINTS INTO SOUTHERN NEW  
ENGLAND WE WILL CONTINUE TO SEE THE ATMOSPHERE DESTABILIZE INTO  
THE EVENING HOURS. THE AREAS SOUTH OF THE I-90 CORRIDOR ARE IN A  
MARGINAL RISK FOR SEVERE THUNDERSTORMS THIS EVENING. EXPECT THE  
BEST CHANCE FOR ISOLATED STRONG TO SEVERE STORMS TO OCCUR  
OVERNIGHT AS THE SURFACE WARM FRONT LIFTS NORTHEAST OVER  
SOUTHERN NEW ENGLAND ALONG WITH A 40-50 KNOT 500 HPA JET.  
DAMAGING WINDS WOULD BE THE PRIMARY THREAT WITH ANY STORMS THAT  
BECOME SEVERE, BUT THE ENVIRONMENT WILL ALSO BE SUPPORTIVE OF  
AN ISOLATED TORNADO AS WELL.  
 

 
   
SHORT TERM /MIDNIGHT THROUGH 6 PM FRIDAY/
 
 
* MAIN THREAT FOR SEVERE WEATHER WILL BE TO OUR SOUTH, BUT THERE  
REMAINS A LOW RISK FOR ISOLATED SEVERE WEATHER/LOCALIZED FLOODING  
 
* MAINLY DRY WITH COMFORTABLE TEMPS RETURNING FOR MUCH OF FRIDAY  
 
TONIGHT...  
 
QUITE A CHALLENGING FORECAST TONIGHT REVOLVING AROUND THE TRACK OF  
THE CURRENT MCV AND HOW FAR NORTH THE TRUE WARM SECTOR WILL GET.  
HIGH RESOLUTION CAM/S HAVE IMPROVED OUR ABILITY TO FORECAST THESE  
TYPE OF SITUATIONS, BUT LOCATION/PLACEMENT OF VARIOUS FEATURES  
REMAINS QUITE DIFFICULT. THERE IS THE TENDENCY FOR THESE COMPLEXES  
TO MOVE FASTER AND GRAVITATE FURTHER SOUTH TOWARDS THE BETTER  
INSTABILITY THAN GUIDANCE INDICATES.  
 
THEREFORE, ODDS MAY FAVOR THAT THE TRUE WARM SECTOR STAYS SOUTH OF  
OUR REGION. WHILE WE WOULD STILL SEE SHOWERS AND EMBEDDED T-STORMS  
WITH LOCALLY HEAVY RAINFALL GIVEN STRONG DYNAMICS FROM THE NORTHERN  
STREAM ENERGY; THE MAIN SEVERE WEATHER THREAT WOULD REMAIN TO OUR  
SOUTH. THAT BEING SAID; THERE ARE SEVERAL PARAMETERS THAT HAVE US  
CONCERNED TONIGHT ESPECIALLY TOWARDS THE SOUTH COAST. STRONG  
DYNAMICS ARE PRESENT WITH 40+ KNOTS OF EFFECTIVE SHEAR ALONG WITH  
500 TO 1000 J/KG OF CAPE SOUTH OF THE MA TURNPIKE. IN ADDITION, 0-1  
KM HELICITY VALUES OF 150 TO 300 UNITS ARE ANTICIPATED ALONG A WARM  
FRONT. AS A RESULT SOME OF THE GUIDANCE; PARTICULARLY THE 00Z 3 KM  
NAM AS SPC SREF HAVE VARIOUS TORNADO PARAMETERS LIT UP ESPECIALLY  
TOWARDS THE SOUTH COAST. IF THE MESOSCALE PROCESSES COME TOGETHER  
JUST RIGHT THERE EXISTS A LOW PROBABILITY FOR ISOLATED SEVERE  
WEATHER INCLUDING A TORNADO/WATERSPOUT TOWARDS THE SOUTH COAST. THIS  
THREAT WOULD BE LOCALIZED, BUT WILL NEED TO BE MONITORED CLOSELY  
TONIGHT AS THESE THINGS CAN SPIN-UP QUICKLY. THE LIMITING FACTOR MAY  
END UP BEING THE NORTHERN STREAM SHORTWAVE FOCUSING ACROSS NORTHERN  
NEW ENGLAND AND THE MCV PASSING TO OUR SOUTH. THIS MAY KEEP A TRUE  
TRIPLE POINT/WARM FRONT FROM ALLOWING THE MESOSCALE PROCESSES TO  
ORGANIZE. LASTLY, THERE WILL BE A LOW RISK FOR LOCALIZED FLOODING  
GIVEN THE STRONG FORCING COUPLED WITH HIGH PWATS/WET ANTECEDENT  
CONDITIONS.  
 
FRIDAY...  
 
THE BULK OF THE SHOWERS AND EMBEDDED THUNDERSTORMS WILL BE OVER BY  
DAYBREAK AS THE COLD FRONT/SHORTWAVE EXIT THE REGION. A FEW LEFT  
OVER SHOWERS ARE POSSIBLE EARLY IN THE MORNING. OTHERWISE, MAINLY  
DRY WEATHER IS EXPECTED ON FRIDAY ALTHOUGH A FEW SPOT SHOWERS WILL  
REMAIN POSSIBLE INTO THE AFTERNOON GIVEN UPPER TROUGH/COLD POOL  
ALOFT. LOW PRESSURE WILL INTENSIFY AS IT LIFTS INTO THE CANADIAN  
MARITIMES ALLOW FOR A PLEASANT NORTHWEST BREEZE WITH PARTIAL  
SUNSHINE. HIGH TEMPERATURES WILL MAINLY BE IN THE UPPER 70S TO THE  
LOWER 80S, BUT SOME MIDDLE 80S ARE POSSIBLE NEAR THE SOUTH  
COAST.  
 

 
   
LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/
 
 
HIGHLIGHTS...  
 
* SATURDAY IS THE PICK OF THE WEEKEND WITH DRY WEATHER AND LOW  
HUMIDITY. CLOUDY WITH PERIODS OF RAIN ON SUNDAY.  
* UNSETTLED WEATHER WITH COOLER THAN NORMAL TEMPERATURES THROUGH  
MIDDLE OF NEXT WEEK.  
 
DETAILS:  
 
PERSISTENT UPPER LEVEL TROUGH DOMINATES OVER THE NORTHEAST US  
THROUGH EARLY NEXT WEEK, YIELDING BELOW NORMAL TEMPERATURES ON MOST  
DAYS. NORMAL HIGHS FOR THE LAST WEEK OF JULY ARE IN THE LOW TO MID  
80S. IN GENERAL, EXPECT HIGHS TO BE 5 TO 10 DEGREES BELOW NORMAL ON  
MOST DAYS WITH LOWER HUMIDITY TO BOOT. SO TALK ABOUT A TASTE OF  
EARLY FALL! PRECIPITATION WISE, MULTIPLE FRONTAL PASSAGES WILL  
PROVIDE THE CHANCES FOR SHOWERS AND THUNDERSTORMS WITH PERIODS OF  
DRY CONDITIONS SANDWICHED IN BETWEEN.  
 
A STRONG COLD FRONT SWEEPS THROUGH DURING THE DAY ON FRIDAY BUT IT  
DOES LOOK LIKE WE SHOULD WARM INTO THE UPPER 70S/LOW 80S ESPECIALLY  
ACROSS EASTERN MA/RI WITH SUNSHINE BUT WITH FALLING DEW POINTS AND  
BREEZY CONDITIONS. WITH DEW POINTS FALLING INTO THE 40S, SOME  
LOCATIONS COULD WAKE UP TO LOWS IN THE UPPER 40S IF WINDS COULD  
DECOUPLE ENOUGH. IT DOES LOOK LIKE THE WEEKEND WOULD FEATURE MOSTLY  
DRY AND PLEASANT CONDITIONS, WITH SATURDAY LOOKING LIKE THE PICK OF  
THE WEEKEND, WITH COOL AND CRISP CONDITIONS. IN FACT, IF THE WINDS  
DECOUPLE OVERNIGHT FRIDAY, SOME LOCATIONS COULD DROP INTO THE 40S ON  
SATURDAY MORNING AND SUNDAY MORNING WITH THE TROUGH AXIS CENTERED  
OVER NEW ENGLAND. TEMPERATURES AT 500MB DROP TO AROUND -12C TO -14C,  
WHICH IS CLOSE TO THE MINIMUM MOVING AVERAGE FOR LATE JULY ACCORDING  
TO THE SPC SOUNDING CLIMATOLOGY FOR CHATHAM, MA. SO TALK ABOUT A  
TASTE OF FALL! BRIEF RIDGING LOOKS TO OCCUR ON SUNDAY ALONG WITH A  
SURFACE WARM FRONT THAT COULD RESULT IN SHOWERS. THEN ANOTHER TROUGH  
SWINGS IN FROM SOUTHERN ONTARIO. SO COOLER THAN NORMAL TEMPERATURES  
LOOK TO CONTINUE INTO EARLY NEXT WEEK.  
 
FINALLY, THERE ARE INDICATIONS OF A COASTAL STORM SOMETIME IN THE  
TUESDAY TO WEDNESDAY TIME FRAME. WE GET INTO THE FAVORABLE RIGHT  
ENTRANCE REGION OF A 90 KT JET STREAK AND A SURFACE LOW TRACKS NEAR  
THE 70W/40N BENCHMARK. THIS SYNOPTIC SETUP, IF IT WERE TO  
MATERIALIZE, WOULD BE RATHER UNUSUAL FOR EARLY AUGUST. AND DEPENDING  
ON THE TRACK OF THE LOW, WE COULD BE LOOKING AT A NOR'EASTER!  
NONETHELESS, IT IS TOO PREMATURE TO OFFER ANY MORE FORECAST DETAILS  
AT THIS TIME. BUT THERE IS INCREASING CONFIDENCE OF A PATTERN CHANGE  
AS THE JET STREAM RETREATS BACK INTO CANADA AND THE BERMUDA HIGH  
STRENGTHENS. SO BY LATE NEXT WEEK, WE COULD BE LOOKING AT A RETURN  
TO ABOVE NORMAL TEMPERATURES AND THIS IS IN LINE WITH CPC'S 8-14 DAY  
OUTLOOK FOR ABOVE NORMAL CONFIDENCE FOR ABOVE NORMAL TEMPERATURES.  
 

 
   
AVIATION /18Z THURSDAY THROUGH TUESDAY/
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
18Z TAF UPDATE...  
 
THROUGH 00Z...HIGH CONFIDENCE  
 
GUSTY SOUTH/SOUTHWEST WINDS PERSIST THROUGH 00Z. MAINLY VFR WITH  
SOME PATCHES OF SCATTERED CLOUDS BELOW 3000 FEET. SHOWERS AND  
THUNDERSTORMS OVERSPREAD MOST OF SOUTHERN NEW ENGLAND THIS  
AFTERNOON AND EVENING. SHOWERS AND THUNDERSTORMS DON'T IMPACT  
THE CAPE TERMINALS UNTIL AFTER 00Z.  
 
TONIGHT...MODERATE CONFIDENCE. MVFR- IFR CONDITIONS WILL  
DOMINATE WITH ROUNDS OF SHOWERS AND EMBEDDED T-STORMS WITH  
LOCALLY LOCALLY HEAVY RAINFALL. SW WINDS OF 5 TO 15 KNOTS.  
 
FRIDAY...HIGH CONFIDENCE. MVFR CEILINGS EARLY IN THE MORNING SHOULD  
IMPROVE TO GENERALLY VFR BY AFTERNOON. WINDS BECOME NW AT 10 TO 15  
KNOTS WITH GUSTS OF 20-25 KNOTS EXPECTED.  
 
KBOS TERMINAL...MODERATE CONFIDENCE IN TAF.  
 
KBDL TERMINAL...MODERATE CONFIDENCE IN TAF.  
 
OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...  
 
FRIDAY NIGHT: VFR. WINDY WITH LOCAL GUSTS UP TO 30 KT.  
 
SATURDAY: VFR. BREEZY.  
 
SATURDAY NIGHT: VFR.  
 
SUNDAY: MAINLY VFR, WITH AREAS MVFR POSSIBLE. CHANCE SHRA.  
 
SUNDAY NIGHT: MAINLY MVFR, WITH LOCAL IFR POSSIBLE. CHANCE  
SHRA.  
 
MONDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. SLIGHT CHANCE  
SHRA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS.  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
TODAY...HIGH CONFIDENCE. HIGH PRESSURE MOVING OFF THE COAST WILL  
ALLOW FOR S WINDS OF 10 TO 20 KNOTS BY MID AFTERNOON. WE MAY SEE  
SOME 25 KNOT WIND GUSTS DEVELOP BY MID TO LATE AFTERNOON ACROSS OUR  
NORTHERN WATERS, SO WILL START SMALL CRAFT HEADLINES EARLIEST IN  
THIS REGION.  
 
TONIGHT AND FRIDAY...HIGH CONFIDENCE. MODEST SOUTHWEST LOW LEVEL JET  
SHOULD RESULT IN 25 KNOT WIND GUSTS TONIGHT AHEAD OF THE COLD FRONT.  
THIS COUPLED WITH THE LONG FETCH SHOULD YIELD 3 TO 6 FEET. WE MAY  
ALSO SEE A FEW STRONG THUNDERSTORMS OVERNIGHT WITH THE GREATEST RISK  
ACROSS OUR SOUTHERN WATERS. A COLD FRONT WILL CROSS THE REGION EARLY  
FRIDAY MORNING AND A DECENT PRESSURE GRADIENT SHOULD YIELD NW WIND  
GUSTS OF 20 TO 30 KNOTS. THEREFORE, SMALL CRAFT HEADLINES HAVE BEEN  
POSTED FOR ALL OPEN WATERS TONIGHT INTO FRIDAY.  
 
/OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...  
 
FRIDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 30 KT. SEAS UP TO 5 FT.  
 
SATURDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT.  
 
SUNDAY: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS.  
 
SUNDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. CHANCE OF RAIN SHOWERS.  
 
MONDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 

 
   
HYDROLOGY
 
 
NO ACTIVE RIVER FLOOD WARNINGS ARE IN EFFECT FOR RIVERS AND  
WATERWAYS ACROSS SOUTHERN NEW ENGLAND.  
 
HOWEVER, AFTER HAVING A TREMENDOUS AMOUNT OF RAINFALL FROM EARLY TO  
MID JULY, MANY RIVERS AND STREAMS CONTINUE TO RUN ABOVE TO MUCH  
ABOVE NORMAL ACROSS MOST OF MA, NORTHERN CT, AND FAR NORTHERN RI.  
THIS IS RESULTING IN SWIFT CURRENTS THAT WOULD NOT TYPICALLY BE SEEN  
IN THE SUMMER. THESE SWIFT CURRENTS CAN CATCH THOSE SWIMMING OR  
TUBING/KAYAKING ON AREA WATERWAYS OFF GUARD. THERE HAVE BEEN 3 TOTAL  
REPORTS OF DROWNINGS IN THE LAST WEEK ON THE FARMINGTON RIVER IN CT  
AND SQUANNACOOK RIVER IN MA GIVEN THE HIGHER THAN USUAL FLOWS AND  
SWIFT CURRENTS.  
 
THOSE WITH INTERESTS SWIMMING, TUBING OR KAYAKING ON AREA  
RIVERS AND WATERWAYS SHOULD BE AWARE THAT SWIFT CURRENTS DUE TO  
HIGH FLOWS ARE OCCURRING. THIS CAN RESULT IN DANGEROUS  
CONDITIONS, AND IT IS GENERALLY DISCOURAGED TO SWIM, INNER-TUBE,  
OR KAYAK UNTIL FLOWS DECREASE.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 8 PM EDT  
FRIDAY FOR ANZ231>235-237-254>256.  
SMALL CRAFT ADVISORY UNTIL 8 PM EDT FRIDAY FOR ANZ250-251.  
 

 
 

 
SYNOPSIS...FRANK/CHAI  
NEAR TERM...RM  
SHORT TERM...FRANK  
LONG TERM...CHAI  
AVIATION...RM  
MARINE...FRANK/CHAI  
HYDROLOGY...  
 
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