966  
FXUS61 KBOX 282012  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
412 PM EDT FRI APR 28 2017  
   
SYNOPSIS
 
 
ANOTHER MILD NIGHT TONIGHT WITH A RISK FOR SHOWERS AND  
THUNDERSTORMS FOR SOME IN THE MORNING. WARM CONDITIONS FOLLOW  
ONCE AGAIN FOR THE DAYTIME TOMORROW. AFTER A COLD FRONTAL  
PASSAGE TOMORROW NIGHT HIGH PRESSURE BUILDS OVER NEW ENGLAND  
SUNDAY WITH DRY BUT COOLER AIR. SPRAWLING LOW PRESSURE IN THE  
PLAINS WILL PUSH A WARM FRONT THROUGH OUR AREA MONDAY, THEN  
SWING A COLD FRONT THROUGH ON TUESDAY. ANOTHER STORM MOVES UP  
FROM THE GULF OF MEXICO LATE THURSDAY OR FRIDAY.  
 

 
   
NEAR TERM /THROUGH SATURDAY/
 
 
THE PESKY SC AND MARINE STRATUS THAT HAS SO PLAGUED OUR WX OVER  
THE LAST 72 HOURS OR SO HAS FINALLY ERODED ENOUGH THANKS TO A  
COMBINATION OF DRY AIR ENTRAINMENT AND W FLOW TO ALLOW FOR  
MAINLY SUNNY SKIES ACROSS THE REGION THIS AFTERNOON. TEMPS HAVE  
SHOT-UP AS A RESULT, THANKS TO H85 TEMPS AROUND +12C WE SEE  
SEVERAL LOW 80S AND UPPER 70S WHICH WILL LINGER INTO THE EARLY  
EVENING HOURS.  
 
THE MAINLY CLEAR CONDITIONS WILL PERSIST INTO THE EVENING.  
HOWEVER, STILL NOTING A BAND OF MARINE STRATUS/FOG WELL SE OF LI  
WHICH WILL NEED TO BE MONITORED AS THE W-SW WINDS COULD ONCE  
AGAIN BRING IT INTO THE ISLAND AND CAPE COD LATE THIS EVENING,  
YIELDING ANOTHER ROUND OF POTENTIAL DENSE FOG. NOT CONFIDENT  
ENOUGH TO HOIST AN ADVISORY GIVEN THAT THE W COMPONENT OF THE  
FLOW IS TYPICALLY NOT CONDUCIVE TO MARINE FOG OVER LAND, BUT IT  
WILL NEED TO BE WATCHED. OTHERWISE, INCREASING MID-UPPER CLOUDS  
AND HIGH DWPTS FROM THE WASHED OUT FRONT THIS AFTERNOON WILL  
LIMIT OVERNIGHT MINS TO THE UPPER MID AND UPPER 50S.  
 
THE ONE KEY TO THE FORECAST FOR THE OVERNIGHT AND EARLY TOMORROW  
IS A BURST OF ELEVATED INSTABILITY ASSOCIATED WITH THE REMNANT  
COLD POOL FROM A DEVELOPING MCS ACROSS THE LOWER OH VALLEY LATE  
THIS EVENING. NOTING AN INJECTION OF MOISTURE INTO THE COLUMN  
FROM THE REMNANTS OF THE MCS, AND WITH STEADY LAPSE RATES  
LEFTOVER FROM THIS AFTERNOON/EVENING NEAR 6.0-6.5C/KM, THIS WILL  
YIELD MU/ELEVATED CAPE PROFILES NEAR 500J/KG BETWEEN 09Z (5AM  
LOCAL) AND 15Z (11AM LOCAL). THIS IS ALSO ASSOCIATED WITH A  
MODEST LLJ AROUND 40 KT YIELDING ABOUT 45-50 KT OF 0-6KM SHEAR.  
THEREFORE, THE INGREDIENTS ARE AVAILABLE FOR A SECOND ROUND OF  
EARLY AM ELEVATED CONVECTION.  
 
ONE CAVEAT AS IS OFTEN THE CASE WITH UPSTREAM MCS DEVELOPMENT IS  
STEERING OF THE CONVECTION. MCS IS LIKELY TO TURN SOMEWHAT S,  
FOLLOWING THE GRADIENT OF HIGHEST SFC BASED INSTABILITY, BUT  
GIVEN THE INCREASE IN ELEVATED STABILITY FURTHER N (OVER SNE),  
THE THREAT RISK REMAINS. COULD BE A TWO PART TYPE OF EVENT, ONE  
WATCHING THE ACTUAL REMNANTS OF THE MCS RELATIVE TO ITS COLD  
POOL, AND THE SECOND FURTHER N ALONG A WEAK SHORTWAVE/LLJ. GIVEN  
THESE FACTORS, HAVE FOCUSED THE HIGHEST POPS/CHANCES FOR TSRA  
ACROSS CT/RI AND SE MA SIMILAR TO THIS MORNING, HOWEVER THE RISK  
IS DEFINITELY NON-ZERO FURTHER N. SEVERE RISK IS LOW GIVEN THE  
BULK OF THE INSTABILITY IS ELEVATED BUT THE INFLUENCE OF THE  
LLJ DOES SUGGEST A FEW GUSTY WINDS ARE POSSIBLE IF STRONGER TSRA  
ARE OBSERVED.J  
 
OTHERWISE, AFTER THE SHORTWAVE/INSTABILITY SHIFTS E IN THE LATE  
MORNING, EXPECT ANOTHER GRADUAL CLEARING WITH ONLY DIURNAL SC  
THROUGH THE AFTERNOON. AIRMASS SIMILAR TO TODAY SUGGESTS ANOTHER  
ROUND OF HIGHS IN THE UPPER 70S TO LOW 80S, WARMEST AWAY FROM  
THE S COAST. A BIT MORE BREEZY HOWEVER, AS THE LINGERING LLJ  
COULD YIELD SOME WIND GUSTS TO AROUND 25 MPH.  
 

 
   
SHORT TERM /SATURDAY NIGHT/
 
 
MORE TYPICAL SETUP FOR SPRING OVERNIGHT TOMORROW. LINGERING  
CLOUDS BUT MORE ROOM FOR COOLING AS DRIER DWPTS BEGIN TO FILTER  
IN THROUGH THE AFTERNOON AND EVENING TOMORROW. HOWEVER,  
EXPECTING SLOW BACKDOOR COLD FRONT PROGRESSION DURING THE LATE  
NIGHT INTO SUN TIMEFRAME. THEREFORE, LOOKING AT MOSTLY LOWS IN  
THE UPPER 40S AND LOW 50S. WHICH IS CLOSER TO SEASONABLE NORMALS  
THAN WE HAVE EXPERIENCED WITH THE MOISTURE OF THE PAST FEW  
DAYS.  
 

 
   
LONG TERM /SUNDAY THROUGH FRIDAY/
 
 
BIG PICTURE...  
 
LONGWAVE PATTERN SHOWS RIDGES OFF EACH COAST WITH A TROUGH OVER THE  
MIDWEST. THIS PATTERN STARTS SHIFTING EAST LATE NEXT WEEK.  
 
SHORTWAVE PATTERN SHOWS TWO SYSTEMS OF INTEREST IN THE LONG TERM.  
THE FIRST IS A CLOSED LOW OVER THE SOUTHERN ROCKIES DURING THE  
WEEKEND THAT EJECTS THROUGH THE GREAT LAKES TUESDAY AND IS ABSORBED  
INTO THE HUDSON BAY LOW THEREAFTER. THIS DRAWS A STRONG UPPER JET  
ACROSS NEW ENGLAND MONDAY NIGHT AND TUESDAY. THE SECOND SYSTEM IS A  
SHORTWAVE SOUTH OF THE ALEUTIANS THIS WEEKEND THAT REACHES THE  
WASH/BC COAST MONDAY AND DIGS A CLOSED LOW OVER THE SOUTHERN STATES  
BY FRIDAY.  
 
MODEL MASS FIELDS ARE SIMILAR THROUGH WEDNESDAY THEN DISAGREE ON THE  
LATE WEEK SYSTEM...THE GFS SHOWS A COASTAL STORM WHILE THE ECMWF  
SHOWS IT TRACKING NORTH THROUGH CENTRAL NY. THE GGEM SHOWS A LITTLE  
OF BOTH. ALSO LARGE RUN-TO-RUN CHANGES. AS THE SYSTEM IS WELL OUT  
OVER THE NORTH PACIFIC, WE ALSO NOTE TIME AND SAMPLING ISSUES. THIS  
MEANS AT LEAST MODERATE CONFIDENCE IN THE EARLY WEEK SYSTEM BUT LOW  
CONFIDENCE IN THE LATE WEEK SYSTEM.  
 
DETAILS...  
 
SUNDAY...  
 
HIGH PRESSURE BUILDS OVER THE REGION WITH A LIGHT EAST TO SOUTHEAST  
WIND. WARM FRONT STALLED OVER THE MID ATLANTIC COULD COMBINE WITH  
THE EAST FLOW TO SPREAD SOME CLOUDS INTO THE AREA, BUT AIRMASS LOOKS  
OTHERWISE DRY. EXPECT COOLEST TEMPS AT THE EAST MA SHORE, WARMEST IN  
THE CT RIVER VALLEY.  
 
THE HIGH SHIFTS OFFSHORE SUNDAY NIGHT AND THE WARM FRONT SHIFTS  
NORTH. THIS SHOULD BRING AN INCREASE IN SKY COVER. CAN/T RULE OUT  
SCATTERED SHOWERS AT THIS TIME FROM THE ONSHORE FLOW, BUT THESE  
SHOULD BE LOCALLY GENERATED AS THE SOUTHWEST LOW LEVEL JET WILL BE  
TOO FAR AWAY TO GENERATE LIFT OVER THE FRONT.  
 
MONDAY-TUESDAY...  
 
LOW PRESSURE IN THE GREAT LAKES LIFTS NORTHEAST, PULLING THE WARM  
FRONT NORTH THROUGH NEW ENGLAND MONDAY OR EARLY MONDAY NIGHT.  
QUESTIONS REMAIN REGARDING TIMING OF THE WARM FRONT AND ASSOCIATED  
WIND SHIFT. BECAUSE OF THIS WE HAVE NUDGED GUIDANCE TEMPS ABOUT 2  
DEGREES COOLER. SOME LINGERING SHOWERS ESPECIALLY NORTH OF THE MASS  
PIKE. BUT EXPECT MOST OF THIS TO MOVE OFF TO THE NORTH. LOW LEVEL  
SOUTHWEST JET MOVES UP THE COAST WITH 40 KNOT WINDS AT 2000 FEET,  
HELPING GENERATE GUSTS TO 20 KNOTS.  
 
COLD FRONT SWEEPS EAST FROM NEW YORK MONDAY NIGHT. SECOND LOW LEVEL  
SOUTHWEST JET MOVES IN WITH 50-60 KNOT WINDS AT 2000 FEET. UPPER JET  
WITH 110 KNOTS MOVES OVER NEW ENGLAND AFTER MIDNIGHT AND PROVIDES  
UPPER VENTING AS THE FRONT MOVES THROUGH AND PROVIDES LOW LEVEL  
CONVERGENCE. STABILITY PARAMETERS LOOK FAVORABLE FOR THUNDER WITH  
FORECASTS OF TOTALS 48-50 AND LI 0 TO -2. PRECIP WATER FORECAST AT  
1.7 INCHES. EXPECT A PERIOD OF SHOWERS AND SCATTERED THUNDER WITH  
THE FRONT MONDAY NIGHT AND EARLY TUESDAY. LOCALLY HEAVY SHOWERS  
POSSIBLE.  
 
DRIER AIR MOVES IN ON TUESDAY. SOME UNCERTAINTY AS TO HOW DEEP THE  
MIXING WILL BE BEHIND THE COLD FRONT, ALTHOUGH MODEL CROSS SECTIONS  
SHOW IT AS HIGH AS 800 MB. TEMPS IN THIS LAYER WILL SUPPORT MAX  
SURFACE TEMPS TO AT LEAST 70F AND POSSIBLY TO THE MID 70S. WINDS IN  
THE LAYER REACH AS HIGH AS 30 KNOTS, SO A GUSTY AFTERNOON IN STORE.  
 
WEDNESDAY...  
 
SURFACE LOW OVER THE MARITIMES AND CLOUD SHIELD INTO NORTHERN NEW  
ENGLAND. UPPER SHORTWAVE LINGERS OVER NORTHERN MAINE ALONG WITH  
COLD POOL OVER NORTHERN NEW ENGLAND. THIS SHOULD GENERATE SOME  
DIURNAL CLOUDS, ESPECIALLY NORTH OF THE MASS PIKE. TEMPS ALOFT  
SUPPORT MAX SFC TEMPS IN THE 60S.  
 
THURSDAY-FRIDAY...  
 
AS NOTED ABOVE, LONG RANGE MODELS SEEM TO AGREE THAT A STORM WILL  
AFFECT THE NORTHEAST USA BUT DISAGREE ON HOW IT WILL DO SO. THIS  
AND THE FACT THAT THIS IS A DAY 6/7 FORECAST WILL LIMIT FORECAST  
POPS TO 30-40 PCT. MODEL CONSENSUS ON TIMING WOULD BRING RAIN INTO  
OUR AREA THURSDAY MID TO LATE AFTERNOON, BUT WE DO NOTE THE ECMWF IS  
SIX HOURS FASTER THAN CONSENSUS. BEST CHANCE LOOKS TO BE THURSDAY  
NIGHT AND FRIDAY.  
 

 
   
AVIATION /19Z 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.  
 
THROUGH 04Z (MIDNIGHT LOCAL)...MODERATE CONFIDENCE.  
VFR NOW THROUGH THIS EVENING FOR ALL TAF SITES EXCEPT ACK, WHICH  
MAY LINGER IN THE LOW CIGS FOR A BIT LONGER BUT TRANSITIONING TO  
A RISK FOR SOME MVFR/IFR CIGS WITH SHRA/TSRA (SEE BELOW). TERMINALS  
FROM WST EAST THE CAPE/ISLANDS MAY ONCE AGAIN SEE A PERIOD OF  
LATE EVENING LOW CIGS AND LIFR CONDITIONS, MOST LIKELY ON  
ACK/MVY. SOUTHERLY SEA BREEZES LIKELY THIS AFTERNOON, LOWER RISK  
FOR E COAST.  
 
AFTER 04Z THROUGH TOMORROW...MODERATE CONFIDENCE.  
STILL HAVE TO WATCH LIFR/IFR CONDITIONS MAINLY COASTAL RI AND S  
COASTAL MA IN LOW CIGS/FOG. OTHERWISE VFR MAINLY INLAND BUT WITH  
A RISK FOR SOME SHRA/TSRA. BEST CHANCE FOR THESE WOULD BE ACROSS  
CT/RI/SE MA BETWEEN 09Z AND 14Z FROM W-E. LOWER RISK FURTHER N.  
AFTER THESE MOVE THROUGH EXPECT SCT-BKN LOW END VFR CLOUDS  
THROUGH THE DAY. WINDS SHIFT FROM SW TO W IN THE MORNING WITH A  
FEW GUSTS AROUND 20 KT DURING THE AFTERNOON.  
 
TOMORROW NIGHT...HIGH CONFIDENCE.  
W FLOW AND MAINLY VFR.  
 
KBOS TAF...GENERALLY HIGH CONFIDENCE IN TAF. IF SEA BREEZE  
OCCURS THIS AFTERNOON/EVENING IT WOULD BE RELATIVELY SHORT  
LIVED.  
 
KBDL TAF...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/... MODERATE CONFIDENCE.  
 
SUNDAY... HIGH CONFIDENCE.  
 
VFR.  
 
SUNDAY NIGHT TO TUESDAY... MODERATE CONFIDENCE.  
 
CEILINGS LOWER TO MVFR/IFR SUNDAY NIGHT AND THE START OF MONDAY IN  
LOW CLOUDS AND FOG/DRIZZLE. BRIEF IMPROVEMENT TO VFR POSSIBLE  
MONDAY, THEN A COLD FRONT MOVES THROUGH MONDAY NIGHT AND EARLY  
TUESDAY WITH SHOWERS AND SCATTERED THUNDER. LOW LEVEL WIND SHEAR  
LEADING THE COLD FRONT WITH SOUTHWEST WINDS OF 50-60 KNOTS AT 2000  
FEET AGL. THE COLD FRONT MOVES OFFSHORE TUESDAY MORNING FOLLOWED BY  
CLEARING SKIES AND SOUTHWEST WINDS GUSTING 25-30 KNOTS.  
 
WEDNESDAY... MODERATE CONFIDENCE.  
 
VFR. WEST WINDS GUSTING TO 20 KNOTS.  
 

 
   
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.  
 
LINGERING OFFSHORE SWELL CONTINUES ON THE WATERS, HOLDING AT 5-6  
FT. THEREFORE, OFFSHORE SMALL CRAFT ADVISORIES WILL CONTINUE  
INTO THE EVENING HOURS UNTIL THIS SWELL SUBSIDES A BIT MORE.  
OTHERWISE, ANOTHER ROUND OF FOG THIS EVENING AND THEN ANOTHER  
RISK FOR SHOWERS OR A THUNDERSTORM ON THE WATERS DURING THE  
EARLY MORNING HOURS.  
 
AFTER THE SHOWERS/STORMS AND FOG DISSIPATE DURING THE MORNING  
HOURS TOMORROW, W WINDS BECOME A BIT MORE BREEZY, ESPECIALLY  
NEAR SHORE WITH GUSTS TO 20 KT, HOWEVER FEEL THESE WILL REMAIN  
BELOW SMALL CRAFT ADVISORY THRESHOLDS THROUGHOUT THE DAY. THERE  
IS A LOW RISK FOR SLIGHTLY STRONGER W GUSTS DURING THE OVERNIGHT  
HOURS ALONG WITH SEAS REACHING NEAR 5 FT, BUT THIS IS VERY  
MARGINAL AND DOESN'T WARRANT ANOTHER ADVISORY AT THIS TIME.  
LATER SHIFTS CAN RE-EVALUATE.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/... MODERATE CONFIDENCE.  
 
SUNDAY...  
 
EAST WINDS LESS THAN 20 KNOTS AND SEAS LESS THAN 5 FEET.  
 
MONDAY...  
 
WARM FRONT MOVES NORTH OF THE WATERS LATE MONDAY. EAST WINDS TURN  
FROM THE SOUTHEAST AND EVENTUALLY FROM THE SOUTH BUT REMAIN LESS  
THAN 25 KNOTS. SEAS LESS THAN 5 FEET MOST OF MONDAY, THEN BUILD 5-8  
FEET MONDAY NIGHT ON THE EXPOSED SOUTHERN WATERS. WINDS 2000 FEET  
ABOVE THE SURFACE WILL INCREASE TO 50-60 KNOTS, SO POTENTIAL FOR  
GUSTS TO 30 KNOTS MONDAY NIGHT. SHOWERS AND POSSIBLY THUNDER MONDAY  
NIGHT. A SMALL CRAFT ADVISORY WILL PROBABLY BE NEEDED.  
 
TUESDAY...  
 
COLD FRONT MOVES ACROSS THE WATERS EARLY TUESDAY. WINDS WILL SHIFT  
FROM THE SOUTHWEST AFTER THE FRONT MOVES THROUGH. SHOWERS/THUNDER  
END AFTER THE WIND SHIFT. SOUTHWEST WINDS MAY GUST 25-30 KNOTS  
TUESDAY. SEAS REMAIN 5 TO 8 FEET ON THE SOUTHERN WATERS EXPOSED TO A  
SOUTHWEST FLOW. A SMALL CRAFT ADVISORY WILL PROBABLY BE NEEDED.  
 
WEDNESDAY...  
 
WEST WINDS WILL BE 20 KNOTS OR LESS. SEAS OF 5-6 FEET LINGER ON THE  
SOUTHERN OUTER WATERS.  
 

 
   
TIDES/COASTAL FLOODING
 
 
* ISOLATED MINOR COASTAL FLOODING IMPACTS DURING ASTRONOMICALLY  
HIGH TIDE TONIGHT ALONG THE EAST COAST  
 
THE ASTRONOMICAL HIGH TIDES REMAIN VERY ELEVATED INTO THIS  
WEEKEND.  
 
GIVEN A LINGERING SWELL OFFSHORE AND ITS REMNANT SURGE, WITH HIGH  
TIDE VALUES ONLY A FEW TENTHS SHY OF TYPICAL MINOR FLOODING LEVELS,  
A COASTAL FLOOD STATEMENT CONTINUES FOR THE HIGH TIDE NEAR 2 AM  
TONIGHT FOR EAST COASTAL LOCATIONS. AT THIS TIME, WE ANTICIPATE  
ONLY MINIMAL IMPACTS AT TYPICALLY PRONE LOCATIONS.  
 
ALSO, DUE TO THE BREADTH OF THE FETCH, WE MAY ENCOUNTER ENOUGH  
WAVE ACTION WITH LENGTHENING PERIODS ON TOP OF AN ELEVATED TIDE  
TO CAUSE POCKETS OF EROSION TONIGHT ALONG THE MARTHA'S VINEYARD  
SOUTH COAST, NANTUCKET SOUTH AND EAST COASTS, AND THE OUTER  
CAPE OCEAN SIDE FROM TRURO TO CHATHAM.  
 
BOSTON HIGH TIDES (FLOOD STAGE AT BOSTON 12.5 FEET)...  
 
12.14 FEET / SATURDAY 12:56 AM  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR ANZ250.  
SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ254>256.  
 

 
 

 
SYNOPSIS...WTB/DOODY  
NEAR TERM...DOODY  
SHORT TERM...DOODY  
LONG TERM...WTB  
AVIATION...WTB/DOODY  
MARINE...WTB/DOODY  
TIDES/COASTAL FLOODING...STAFF  
 
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