704  
FXUS61 KBOX 150252  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
1052 PM EDT TUE AUG 14 2018  
   
SYNOPSIS
 
 
LOW PRESSURE AND ITS ATTENDING COLD FRONT WILL MOVE ACROSS THE  
REGION TONIGHT ALONG WITH SCATTERED SHOWERS AND THUNDERSTORMS  
WITH LOCALLY HEAVY RAIN AND GUSTY WINDS. THE FRONT EXITS  
OFFSHORE WEDNESDAY WITH A DRYING TREND DURING THE AFTERNOON  
ALONG WITH WARM BUT SLIGHTLY LESS HUMID CONDITIONS. IT WILL  
REMAIN VERY WARM THURSDAY ALONG WITH SLIGHTLY LESS HUMID  
CONDITIONS. TROPICAL HUMIDITY RETURNS FRIDAY INTO SATURDAY WITH  
INCREASING RISK OF SHOWERS AND THUNDERSTORMS AS A COLD FRONT  
APPROACHES. COOLER WEATHER FOLLOWS FOR SUNDAY AND MONDAY, THEN  
TROPICAL WEATHER RETURNS YET AGAIN ON TUESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
 
 
1025 PM UPDATE...  
 
NOTING A FEW LEFTOVER SHOWERS/THUNDERSTORMS MOVING N OUT OF  
FRANKLIN AND NW WORCESTER COUNTIES, AS WELL AS SOME MOVING INTO  
HARTFORD COUNTY ON THE LATEST NE REGIONAL 88D RADAR MOSAIC. THE  
PRECIP WAS MOVING A BIT W OF DUE N AROUND THE PERIPHERY OF THE  
H5 CUTOFF LOW PRESSURE THAT WILL SLOWLY SHIFT E OUT OF E NY  
STATE OVERNIGHT AS THE LOW WEAKENS TO AN OPEN WAVE.  
 
WILL KEEP AN EYE ON MORE SHOWERS/THUNDERSTORMS THAT WILL WRAP  
AROUND THE UPPER LOW INTO N NJ AND SE NY THAT MAY TRY TO PUSH  
INTO N CENTRAL CT/W MASS, BUT IT COULD REMAIN S OF THE REGION AS  
WELL.  
 
OTHERWISE, WILL SEE SULTRY CONDITIONS CONTINUE WITH DEWPOINTS IN  
THE MID 60S TO LOWER 70S. WITH LOW T/TD SPREADS, WILL LIKELY SEE  
AREAS OF FOG REDEVELOP OVERNIGHT.  
 
HAVE UPDATED TO BRING CONDITIONS CURRENT AND INCORPORATE TRENDS  
INTO THE OVERNIGHT FORECAST.  
 
PREVIOUS DISCUSSION...  
 
THE UPPER LOW ITSELF WILL MOVE OVERHEAD DURING THE NIGHT  
BRINGING A PERIOD OF CLOUDS TO ALL AREAS OVERNIGHT. THIS IS  
ALREADY STARTING IN OUR WESTERN SECTIONS, AND SHOULD SPREAD  
OVER THE COASTAL PLAIN AFTER MIDNIGHT.  
 
OTHERWISE WARM SECTOR AIRMASS WILL PROVIDE A WARM AND MUGGY  
NIGHT WITH LOWS ONLY FALLING BACK TO 65-70, LOW 70S SOUTH COAST  
INCLUDING CAPE COD AND ISLANDS. AREAS OF FOG POSSIBLE GIVEN  
HUMID AIRMASS AND ESPECIALLY WHERE HEAVY RAIN HAS FALLEN TODAY.  
 

 
   
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/
 
 
WEDNESDAY...  
 
UPPER TROUGH AND FRONTAL BOUNDARY STILL OVER THE REGION AT 12Z,  
THUS SCATTERED SHOWERS AND ISOLATED T-STORM ESPECIALLY OVER  
SOUTHEAST MA. AS THE TROUGH AND FRONTAL BOUNDARY MOVE OFFSHORE  
HEIGHT RISES THRU THE DAY ALONG WITH FLOW BECOMING MORE  
ANTICYCLONIC WILL SUPPORT A DRYING TREND ALONG WITH SLIGHTLY  
LESS HUMIDITY. OVERALL A REAL NICE SUMMER AFTERNOON ALTHOUGH IT  
WILL BE VERY WARM WITH HIGHS IN THE MID TO UPPER 80S.  
 
WEDNESDAY NIGHT...  
 
RIDGING PROVIDES DRY AND WARM CONDITIONS. SOME PATCHY FOG  
POSSIBLE BUT NOT WIDESPREAD AS AIRMASS NOT QUITE AS HUMID AS  
TODAY WITH DEW PTS FALLING INTO THE 60S.  
 

 
   
LONG TERM /THURSDAY THROUGH TUESDAY/
 
 
BIG PICTURE...  
 
ZONAL FLOW JET STREAM ACROSS CANADA WHILE SUBTROPICAL HIGH REMAINS  
IN CONTROL ACROSS THE SOUTHERN USA. THE USA NORTHERN TIER IS IN  
BETWEEN, WITH A LIGHTER WEST-EAST FLOW OVERHEAD WHILE MOST OF THE  
JET ENERGY STAYS TO OUR NORTH. THIS PATTERN LINGERS UNTIL THE  
WEEKEND. AT THAT TIME HIGH PRESSURE BUILDS OVER THE WESTERN USA,  
WHICH IN TURNS ALLOWS A TROUGH TO DIG OVER THE GREAT LAKES/MIDWEST.  
WEST ATLANTIC HIGH REMAINS OFF OUR COAST.  
 
FOR US, THIS MEANS A COUPLE OF SHORTWAVES MOVING EAST ACROSS NEW  
ENGLAND FRIDAY THROUGH SUNDAY. AFTER THAT, OUR UPPER FLOW TURNS FROM  
THE SOUTHWEST FOR EARLY NEXT WEEK AS THE MIDWEST TROUGH DIGS.  
THAT WOULD TREND US BACK INTO THE TROPICAL AIR AGAIN ON TUESDAY.  
 
MODEL MASS FIELDS ARE SIMILAR THROUGH SUNDAY. DIFFERENCES ARISE FROM  
THE TROUGH DIGGING FROM CANADA INTO THE MIDWEST, ALTHOUGH THESE  
SCENARIOS ALL BRING A SOUTHWEST FLOW TO OUR AREA. CONFIDENCE REMAINS  
HIGH THROUGH FRIDAY, THEN MODERATE OVER THE WEEKEND AND LOW EARLY  
NEXT WEEK.  
 
CONCERNS...  
 
FRIDAY-SATURDAY CONVECTION...  
 
SHORTWAVE ON THE SOUTHERN EDGE OF THE ZONAL FLOW APPROACHES NEW  
ENGLAND FRIDAY AND CROSSES THE REGION SATURDAY. JET SUPPORT IS  
MOSTLY TO OUR WEST DURING FRIDAY, BUT MOVES OVER SOUTHERN NEW  
ENGLAND FRIDAY EVENING THROUGH SATURDAY MORNING. LOW LEVEL WINDS ARE  
FORECAST 10-20KTS, WHILE MID LEVEL FORECASTS TOP OUT AROUND 35  
KNOTS. CAPE IS FORECAST TO BUILD TO 1500-2500 J/KG...THE NAM EVEN  
SUGGESTS A CORE OF 3000 J/KG. THETA-E RIDGE BUILDS OVER THE HUDSON  
VALLEY FRIDAY AFTERNOON AND MOVES EAST ACROSS OUR AREA BY EVENING.  
GFS/ECMWF SHOW 0-1KM HELICITY AT 100-200 DURING THE  
AFTERNOON/EVENING, MOSTLY ACROSS NORTHERN MASS. PRECIPITABLE WATER  
BUILDS TO 2-2.25 INCHES BY FRIDAY.  
 
THIS SUGGESTS INCREASED RISK OF SHOWERS AND THUNDER. THE HIGH  
MOISTURE VALUES SUGGEST LOCAL DOWNPOURS. THE WINDS ARE BORDERLINE  
FOR DAMAGING CONVECTION, BUT COMBINED WITH THE STABILITY PARAMETERS  
AND HELICITY THIS SUGGESTS POTENTIAL FOR STRONG WIND GUSTS AND HAIL  
IN ANY CONVECTION...THIS WILL NEED TO BE MONITORED.  
 
TIMING THE DEPARTURE OF THE UPPER TROUGH AND SURFACE COLD FRONT  
HOLDS LESS CONFIDENCE, BUT CURRENT DATA SUPPORTS CONVECTION DURING  
THE FIRST HALF OF THE DAY, SHIFTING OFFSHORE DURING  
AFTERNOON/EVENING.  
 
SUNDAY NIGHT-MONDAY SOUTHERN OFFSHORE SYSTEM...  
 
THE NEXT SHORTWAVE SWEEPS EAST FROM THE GREAT LAKES, FORMING A  
SURFACE LOW OVER/NEAR VIRGINIA ON SUNDAY. THIS MOVES EAST-NORTHEAST  
SUNDAY NIGHT WITH THE SURFACE LOW PASSING TO OUR SOUTH MONDAY.  
 
WEAK HIGH PRESSURE THEN BUILDS ACROSS EASTERN CANADA. THIS SHOULD  
BRING FAIR WEATHER TO US FOR SUNDAY AND MONDAY. MAIN CONCERN IS THE  
POSITION OF THE HIGH CENTER, WITH RESULTING NORTHEAST LOW LEVEL FLOW  
AND ITS EFFECT ON TEMPS AND SKY COVER. THIS HAS POTENTIAL TO BRING  
SHOWERS TO OUR AREA SUNDAY NIGHT/MONDAY.  
 

 
   
AVIATION /03Z WEDNESDAY THROUGH SUNDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH WEDNESDAY NIGHT/...  
 
OVERNIGHT...MODERATE CONFIDENCE.  
 
SCATTERED SHOWERS AND ISOLATED THUNDER MAY MOVE INTO W MASS/N  
CENTRAL CT TERMINALS OVERNIGHT WITH MIX OF MVFR-IFR CONDITIONS.  
MODERATE CONFIDENCE GIVEN UNCERTAINTY ON AREAL COVERAGE OF  
CONVECTION. ALSO MAY SEE IFR CIGS/VSBYS IN AREAS OF FOG.  
 
WEDNESDAY...HIGH CONFIDENCE.  
 
ANY MORNING IFR-MVFR IMPROVES TO VFR BY MID TO LATE MORNING.  
SCATTERED SHOWERS/STORMS FOCUSED OVER SOUTHEAST MA IN THE  
MORNING THEN MOVING OFFSHORE. CAN'T RULE OUT AN ISOLATED SHOWER  
DURING THE AFTERNOON BUT VFR CONDITIONS PREVAIL.  
 
WEDNESDAY NIGHT...HIGH CONFIDENCE.  
 
VFR AND DRY WEATHER.  
 
KBOS TERMINAL...TRICKY FORECAST REGARDING WIND DIRECTION AND  
CIGS/VSBYS. WHILE LIGHT E-NE WINDS PREVAIL AT 03Z, VFR  
CONDITIONS IN PLACE. MAY SEE MVFR-IFR VSBYS IN PATCHY FOG FOR A  
TIME, THEN LIGHT/VARIABLE WIND SHIFTS TO S-SW BY AROUND 06Z-07Z  
(EXACT TIMING UNCERTAIN), WITH MVFR TO LOW END VFR CONDITIONS.  
SCATTERED SHOWERS/STORMS THRU 21Z THEN DIMINISHING. ISOLATED  
SHOWERS/THUNDERSTORMS POSSIBLE OVERNIGHT INTO THE WED MORNING  
PUSH.  
 
KBDL TERMINAL...MAINLY VFR, BUT MVFR AT TIMES IN SCATTERED  
SHOWERS/ISOLATED STORMS. HEAVY RAIN IS MAIN CONCERN.  
 
OUTLOOK /THURSDAY THROUGH SUNDAY/...  
 
THURSDAY: VFR.  
 
THURSDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. SLIGHT  
CHANCE SHRA, ISOLATED TSRA, PATCHY BR.  
 
FRIDAY: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY. CHANCE  
SHRA, SLIGHT CHANCE TSRA.  
 
FRIDAY NIGHT: MAINLY VFR, WITH AREAS IFR POSSIBLE. BREEZY.  
CHANCE SHRA, SLIGHT CHANCE TSRA, PATCHY BR.  
 
SATURDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. CHANCE SHRA,  
SLIGHT CHANCE TSRA.  
 
SATURDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. SLIGHT  
CHANCE SHRA, PATCHY BR.  
 
SUNDAY: 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.  
 
SHORT TERM /THROUGH WEDNESDAY NIGHT/...  
 
OVERNIGHT...S-SW WINDS INCREASING 15-20 KT WITH GUSTS TO 25 KT  
SOUTH WATERS OF MA/RI WHERE SMALL CRAFTS REMAIN POSTED.  
TROPICAL AIRMASS YIELDS PATCHY DENSE FOG AT TIMES ALONG WITH  
HEAVY DOWNPOURS IN ISOLATED SHOWERS/THUNDERSTORMS.  
 
WEDNESDAY...SW WINDS EARLY BECOMING W-SW WITH FRONTAL PASSAGE.  
SCATTERED MORNING SHOWERS GIVES WAY TO A DRYING TREND DURING THE  
AFTERNOON.  
 
WEDNESDAY NIGHT...LIGHT WEST WINDS. DRY WEATHER AND GOOD VSBY.  
 
OUTLOOK /THURSDAY THROUGH SUNDAY/...  
 
THURSDAY: WINDS LESS THAN 25 KT.  
 
THURSDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. LOCAL VISIBILITY 1 TO 3 NM.  
 
FRIDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
CHANCE OF RAIN SHOWERS, SLIGHT CHANCE OF THUNDERSTORMS.  
 
FRIDAY NIGHT THROUGH SATURDAY: WINDS LESS THAN 25 KT. AREAS OF  
SEAS APPROACHING 5 FT. CHANCE OF RAIN SHOWERS, SLIGHT CHANCE OF  
THUNDERSTORMS.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS  
APPROACHING 5 FT. SLIGHT CHANCE OF RAIN SHOWERS, ISOLATED  
THUNDERSTORMS.  
 
SUNDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT CHANCE  
OF RAIN SHOWERS.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT WEDNESDAY FOR ANZ235-255-  
256.  
 

 
 

 
SYNOPSIS...WTB/NOCERA  
NEAR TERM...WTB/EVT  
SHORT TERM...NOCERA  
LONG TERM...WTB  
AVIATION...WTB/NOCERA/EVT  
MARINE...WTB/NOCERA/EVT  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MA Page
The Nexlab RI Page
The Nexlab NH Page
The Nexlab CT Page Main Text Page