006  
FXUS61 KBOX 211950  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
350 PM EDT SAT SEP 21 2019  
   
SYNOPSIS
 
 
HIGH PRESSURE REMAINS IN CONTROL INTO MONDAY WITH SUMMER-LIKE  
TEMPERATURES AND DRY WEATHER. A COLD FRONT WILL BRING A PERIOD OF  
SHOWERS LATE MONDAY, MONDAY NIGHT INTO TUE FOLLOWED BY COOLER, BUT  
SEASONABLY WEATHER THROUGH THE REST OF NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
 
 
350 PM UPDATE ...  
 
ANOMALOUS (588 DAM) DEEP LAYER RIDGE OVER THE NORTHEAST LATE THIS  
AFTERNOON PROVIDING WARM BUT PLEASANT CONDITIONS WITH 3 PM TEMPS 80-  
85 INLAND, 75-80 ELSEWHERE. DEW PTS 55-60 SO HUMIDITY FAIRLY  
COMFORTABLE. GIVEN THIS DEEP LAYER RIDGE MOVES ACROSS THE AREA  
TONIGHT DRY WEATHER WILL CONTINUE. 1025 MB SURFACE HIGH OFF THE MID  
ATLC COAST BUT WITH PRESSURE GRADIENT WEAK ACROSS SOUTHERN NEW  
ENGLAND EXPECTING MOST LOCATIONS TO DECOUPLE. THUS LIGHT WINDS,  
CLEAR SKIES AND DEW PTS IN THE 50S WILL SUPPORT LOWS LATE TONIGHT IN  
THE 50S AS WELL. THEREFORE SIDED WITH THE COOLER MOS GUIDANCE  
FOR MIN TEMPS. PATCHY RADIATIONAL FOG INLAND EXPECTED.  
 
ONLY WEATHER CONCERN LATE TODAY IS LEFTOVER ESE SWELLS OF AROUND 4  
FT WITH A PERIOD OF EVERY 11 SECONDS CONTINUES ACROSS THE MA WATERS.  
THUS ELEVATED RISK OF STRONG RIPS WITH MODEST SURF ACROSS OCEAN  
FACING BEACHES UNTIL SUNSET.  
 

 
   
SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/
 
 
350 PM UPDATE ...  
 
SUNDAY ...  
 
EVEN WARMER THAN TODAY AWAY FROM THE SOUTH COAST WITH 925 MB TEMPS  
PUSHING +21C ACROSS NORTHERN MA, THAT'S UP FROM +19C THIS AFTERNOON.  
THUS MID 80S TO PERHAPS UPPER 80S SHOULD BE COMMON ACROSS THE  
MERRIMACK VALLEY OF NORTHEAST MA INTO BOSTON AS SW PRESSURE GRADIENT  
SHOULD BE SUFFICIENT IN THE AFTERNOON TO PRECLUDE SEABREEZE  
DEVELOPMENT. LOW 80S ELSEWHERE EXCEPT 70S ALONG THE SOUTH COAST. IT  
WILL FEEL WARMER TOMORROW THAN TODAY AS DEW PTS CLIMB INTO THE 60S  
ESPECIALLY SOUTH COAST. IN FACT SOUTH COAST BEACHGOERS MAY  
EXPERIENCE SOME STRATUS AND FOG THRU THE DAY AS THIS HIGHER DEW PT  
SURGES NORTHWARD. PLYMOUTH COUNTY NORTHWARD SHOULD BE STRATUS/FOG  
FREE GIVEN MORE SW LAND TRAJECTORY.  
 
IT WILL BECOME BREEZY LATE IN THE DAY WITH SSW WINDS UP TO 20 MPH.  
 
UPPER LEVEL CLOSED LOW CURRENTLY OVER LAKE ONTARIO THIS AFTERNOON  
ONLY GENERATING SOME SHALLOW CU/SCU GIVEN ATMOSPHERE IS DRY LOW TO  
MID LEVELS. EXPECT THE SAME OUTCOME AS THIS FEATURE MOVES ACROSS  
SOUTHERN NEW ENGLAND SUNDAY. THUS NO SENSIBLE WEATHER IMPACTS.  
 
SUNDAY NIGHT ...  
 
WARM NIGHT AHEAD OF LOW LEVEL WAA INCREASES WITH APPROACHING FRONT  
YIELDING TIGHTENING SW PRESSURE GRADIENT. GIVEN DEW PTS IN THE 60S  
EXPECT LOWS TO BE IN THE 60S AS WELL ALONG WITH PATCHY FOG WITH DEW  
PTS HIGHER THAN AVG NIGHTTIME LOW. THIS WILL SERVE FOR A VERY WARM  
START TO THE DAY MONDAY. GIVEN SW GRADIENT BREEZY CONDITIONS ALONG  
THE COAST, CAPE COD, ISLANDS AND HIGH TERRAIN.  
 

 
   
LONG TERM /MONDAY THROUGH SATURDAY/
 
 
*/ HIGHLIGHTS...  
 
- RAIN ANTICIPATED LATE MONDAY INTO MONDAY NIGHT  
- THEREAFTER MILD DAYS, COOL NIGHTS, DRY THE REMAINDER OF THE WEEK  
- TEMPERATURES RUNNING ABOVE AVERAGE THROUGHOUT  
 
*/ OVERVIEW...  
 
AMPLIFYING PATTERN. IMPRESSIVE N PACIFIC JET SIGNALED BY A +WPO/+EPO  
THAT CASCADES ENERGY AND MILD AIR OVER THE CONUS INITIALLY. KICKING  
DOWNSHEARED ENERGY ACROSS THE 4-CORNERS REGION, A CLOSING MID-LEVEL  
LOW LATCHED ONTO CONTINENTAL MOISTURE, THERE'S A CHANCE FOR RAINFALL  
AROUND MONDAY NIGHT DISCUSSED IN MORE DETAIL BELOW. HOWEVER BY LATE  
SEPTEMBER A PATTERN-AMPLIFICATION EMERGES. ONE-TWO PUNCH, NW PACIFIC  
TAPAH BECOMING POST-TROPICAL, INGESTED INTO THE BERING STRAIGHT LOW,  
SUBSEQUENT LATENT HEAT RELEASE AMPLIFIES THE LONGWAVE TROF THAT RE-  
CAPTURES EARLIER CUT-OFF N PACIFIC ENERGY. HEIGHTENED AK RIDGE THAT  
ULTIMATELY DOWNSHEARS A DEEP TROF ACROSS THE W CONUS INTO THE END OF  
SEPTEMBER, PNA BECOMES LARGELY NEGATIVE AS DOES THE EPO/WPO. WITH A  
CONTINUED ACTIVE N ATLANTIC TROPICS EMPHASIZED BY THE PHASE 1 MJO,  
AN IMPRESSIVE HEAT PUMP AND ANOMALOUSLY HIGHER HEIGHTS EMERGE OVER  
THE E CONUS. NO SURPRISE TO SEE ABOVE AVERAGE TEMPERATURE TRENDS AND  
BELOW AVERAGE PRECIPITATION PER CPC. HOWEVER ALONG THE NE-PERIPHERY  
OF THE HEAT-BUBBLE NO-TROUBLE, THERE ARE OPPORTUNITIES FOR COOLER  
AIR AND RAINFALL CHANCES ALONG SE-SWEEPING COLD FRONT BOUNDARIES. SO  
NOT ENTIRELY CONVINCED WE'LL SEE THE BRUNT OF THE HEAT EXPECTED FOR  
THE SE CONUS N INTO THE MID-ATLANTIC. PERHAPS JUST ON THE CUSP YET  
HOWEVER FOR LATE SEPTEMBER IS STILL ABOVE AVERAGE WHEN HIGHS ARE  
NORMALLY AROUND 70 AND LOWS NORMALLY AROUND 50. A PATTERN OF MILD  
DAYS AND COOL NIGHTS, SOME SHOTS OF WET-WEATHER IN-BETWEEN. BREAK  
DOWN THE DETAILS BELOW.  
 
*/ DISCUSSION...  
 
MONDAY INTO MONDAY NIGHT...  
 
WIDESPREAD SHOWERS AND APPRECIABLE RAINFALL REMAINS POSSIBLE. LEAN  
TOWARDS WETTER SOLUTIONS GIVEN CONSENSUS FORECAST MID-LEVEL CLOSED-  
LOW SOLUTION ACTING ON A NARROW-RIBBON OF CONTINENTAL MOISTURE. MUCH  
OF THE SAME, PRECIPITABLE WATERS UP AROUND 1.75-INCHES, WARM-CLOUD  
LAYER UP AROUND 12 KFT PRECEDING THE SWEEPING COLD FRONT. A MOIST-  
ADIABATIC, CONDITIONALLY-UNSTABLE PROFILE, ALBEIT BRIEF AND RIGHT  
ALONG THE FRONT, EXPECTED LIFT, LOW-LEVEL CONVERGENT FORCING, AND  
SYNOPTIC ASCENT BENEATH CYCLONIC FLOW AND DIFFLUENCE ALOFT MAKES A  
CASE OF DECENT UPWARD MOTIONS THAT SHOULD PROMOTE COLLISION AS WELL  
AS COALESCENCE SUCH THAT DECENT RAINS SHOULD DEVELOP. POSITIVE TO A  
NEUTRAL TILT TROF WITH MODEST W/SW SHEAR PRECEDING, INSTABILITY IS  
IN QUESTION GIVEN MARGINAL, MOIST-ADIABATIC LAPSE RATES. RUMBLES OF  
THUNDER NOT RULED OUT, NOR HEAVIER DOWNPOURS. CHANCE TO LIKELY POPS.  
THERE'S INCREASING SIGNAL OF THE POSSIBILITY OF SIGNIFICANT RAINFALL  
WITH AMOUNTS AROUND 0.50 INCHES.  
 
REST OF THE WEEK...  
 
RAIN CHANCES AROUND THURSDAY NIGHT APPEAR SUPPRESSED BY THE WEIGHT  
OF INCREASING HEIGHTS ACROSS THE E CONUS. HOWEVER WITH THE PRIOR  
MENTIONED AMPLIFIED PATTERN TIGHTENING OVER THE W AND CENTRAL CONUS  
THAT NEW ENGLAND FINDS ITSELF BENEATH NW FLOW ALOFT, THE OPPORTUNITY  
FOR SOME SLIGHTLY COOLER AIR AND RAINFALL CHANCES ALONG SE SWEEPING  
COLD FRONTS OVER THE WEEKEND INTO EARLY NEXT WEEK. HOWEVER OVERALL  
TEMPERATURES STILL LOOK TO RUN ABOVE AVERAGE.  
 

 
   
AVIATION /20Z SATURDAY 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/...HIGH CONFIDENCE.  
 
18Z UPDATE (NO MAJOR CHANGES)...  
 
THRU 00Z ... VFR, DRY WEATHER AND LIGHT WINDS WITH SEABREEZES  
AT THE COAST  
 
AFTER 00Z ... VFR, DRY WEATHER AND LIGHT WINDS. ISOLATED  
MVFR/IFR INLAND DUE TO PATCHY FOG.  
 
SUNDAY ... VFR AND DRY WEATHER. COULD BE SOME PATCHY FOG/IFR-  
MVFR ALONG THE SOUTH COAST AT TIMES. LIGHT/VARIABLE WIND IN THE  
MORNING BECOMING SSW AND INCREASING 15-20 KT.  
 
SUNDAY NIGHT ... VFR AND DRY WEATHER. HOWEVER PATCHY IFR/MVFR IN  
FOG MAY LINGER AT TIMES ALONG THE SOUTH COAST. MODEST SSW WINDS  
CONTINUE WITH STRONGEST WINDS ALONG THE SOUTH COAST AND ISLANDS.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /MONDAY THROUGH THURSDAY/...  
 
MONDAY: VFR. BREEZY. CHANCE SHRA.  
 
MONDAY NIGHT: VFR. BREEZY. SHRA LIKELY, SLIGHT CHANCE TSRA.  
 
TUESDAY: VFR. SLIGHT CHANCE SHRA.  
 
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 SUNDAY NIGHT/...HIGH CONFIDENCE.  
 
345 PM UPDATE ...  
 
EASTERLY SWELLS FROM HUMBERTO HAVE NOW DIMINISHED TO 3 TO 4 FT. THUS  
HAVE DROPPED THE SCA. OTHERWISE LIGHT WINDS TONIGHT INTO SUNDAY  
MORNING THEN SSW WINDS INCREASE TO 15-20 KT SUNDAY AFTERNOON AND  
EVENING WITH GUSTS UP TO 25 KT POSSIBLE TOWARD SUNRISE MONDAY.  
PATCHY FOG AND LOW CLOUDS MAY LIMIT VSBY SUNDAY AFTERNOON THRU  
SUNDAY NIGHT. DRY WEATHER PREVAILS.  
 
OUTLOOK /MONDAY THROUGH THURSDAY/...MODERATE CONFIDENCE.  
 
SUNDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 
MONDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 25 KT. AREAS OF ROUGH SEAS. CHANCE OF RAIN SHOWERS.  
 
MONDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. AREAS OF ROUGH SEAS. RAIN SHOWERS LIKELY,  
SLIGHT CHANCE OF THUNDERSTORMS.  
 
TUESDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
CHANCE OF RAIN SHOWERS.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
WEDNESDAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...HIGH RIP CURRENT RISK UNTIL 8 PM EDT THIS EVENING FOR MAZ022-  
024.  
RI...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...NOCERA  
NEAR TERM...NOCERA  
SHORT TERM...NOCERA  
LONG TERM...SIPPRELL  
AVIATION...NOCERA/SIPPRELL  
MARINE...NOCERA/SIPPRELL  
 
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