144  
FXUS61 KBOX 170309  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
1009 PM EST WED JAN 16 2019  
   
SYNOPSIS
 
 
A COLD FRONT SWEEPS ACROSS THE REGION EARLY TONIGHT WITH COLD  
DRY AIR WEATHER INTO THURSDAY EVENING. ONE WEATHER SYSTEM SLIPS  
PAST SOUTHERN NEW ENGLAND FRIDAY, BRINGING A PERIOD OF SNOW  
CHANGING TO RAIN THURSDAY NIGHT AND FRIDAY. ALL EYES ARE ON A  
SECOND STORM THAT BRINGS A MIX OF WINTRY WEATHER FOR SATURDAY  
NIGHT AND SUNDAY. ARCTIC AIR RETURNS FOR EARLY NEXT WEEK.  
ANOTHER WEATHER SYSTEM MAY BRING RAIN AND SNOW NEXT WEDNESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
10 PM UPDATE...  
 
MAIN UPDATE WAS TO RAISE TEMPS A BIT OVER THE NEXT FEW HOURS,  
SLOWING THE PROGRESSION OF THE COLD FRONT A BIT IN LINE WITH  
OBSERVATIONS. CURRENTLY THE FRONT IS DRAPED FROM SOUTHWEST TO  
NORTHEAST ACROSS SNE IN THE VICINITY OF THE BDL-PVD-BOS  
CORRIDOR. IT'S JUST PASSED BOSTON IN THE LAST HALF HOUR AS  
EVIDENCED BY A SLIGHT WIND SHIFT, 25 KT WIND GUST, AND DEWPOINTS  
DROPPING INTO THE LOW TEENS. STILL SEEING TDS IN THE 20S OVER  
SOUTHEAST MA WHICH ARE EXPECTED TO DROP OVERNIGHT AS A DRIER  
POST FRONTAL AIR MASS IS USHERED IN.  
 
PREVIOUS DISCUSSION...  
 
710 PM UPDATE...  
 
COLD FRONT OVER WESTERN MASS AT 6 PM WILL SWEEP ACROSS SOUTHERN  
NEW ENGLAND TONIGHT. RADAR SHOWS FLURRIES ALONG/AHEAD OF THE  
FRONT, AND WITH THE LOW DEW POINTS IN PLACE THAT SHOULD BE AS  
MUCH AS WE SEE FOR PRECIPITATION TONIGHT.  
 
MSAS SHOWS PRESSURE RISES OF UP TO 3 MB/HOUR BEHIND THE FRONT  
OVER NRN NEW ENGLAND/NEW YORK/QUEBEC, WHICH SHOULD SUPPORT NW  
WINDS AND COLD ADVECTION OVERNIGHT. DEW POINTS BEHIND THE FRONT  
FALL TO THE SINGLE NUMBERS IN NRN NEW ENGLAND AND NRN NY. THIS  
WILL MOVE INTO OUR AREA OVERNIGHT.  
 
IF WINDS DIMINISH ENOUGH OVERNIGHT, THEN TEMPERATURES MAY REACH  
7-9 IN SOME SPOTS. MOST PLACES WILL CHILL INTO THE TEENS.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/
 
 
THU...  
HIGH PRES CRESTS OVER THE REGION. THE AIRMASS ATTENDANT TO THIS  
HIGH IS GENERALLY COLDER THAN THAT WHICH IS IN PLACE NOW. WITH A  
COLD START THANKS TO EARL AM RADIATIONAL COOLING, EXPECTING  
HIGHS TO GENERALLY REMAIN BELOW NORMAL FOR THE DAY, MAINLY IN  
THE 20S WITH A FEW SPOTS IN THE LOW 30S NEAR THE COASTLINES.  
LIGHT WINDS GRADUALLY SHIFT AROUND TO THE E AHEAD OF A WARM  
FRONTAL APPROACH THU NIGHT.  
 
THU NIGHT...  
WARM FRONT APPROACHES FROM THE SW, COLUMN SUFFICIENTLY DRY FOR  
EARLY BREAKS IN CLOUDS ALLOWING DIURNAL TEMPS TO DROP INITIALLY,  
INTO THE TEENS TO MID 20S. THIS IS BEFORE MOISTURE FLUX ALLOWS  
FOR RISING DWPTS THROUGHOUT THE COLUMN. AT THE ONSET OF  
PRECIPITATION, MAINLY AFTER 06Z, TEMPS SHOULD BE COLD ENOUGH FOR  
ALL SNOW, AND ALLOW SOME ACCUMULATIONS ON ROADWAYS LEFT  
UNTREATED DUE TO COLD SFC TEMPS. SNOW CONTINUES, ALTHOUGH  
THANKFULLY LIGHT INTO THE MORNING COMMUTE.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
BIG PICTURE...  
 
LONGWAVE SCALE CONTINUES TO SHOW RIDGE-WEST/TROUGH-EAST THROUGH THE  
LONG-TERM PERIOD, SUGGESTING WARM WEST AND COLD EAST. SHORTWAVE  
SCALE SHOWS SEPARATE NORTHERN AND SOUTHERN STREAMS FRIDAY WITH  
A WEAK SHORTWAVE RACING THROUGH NEW ENGLAND. THE STREAMS THEN  
MERGE SATURDAY, ALTHOUGH LATEST MODELS SHOW A LITTLE MORE  
DIFFICULTY IN THE MERGE. DEEP TROUGH OVER THE GREAT LAKES MOVES  
EAST ACROSS NEW ENGLAND SUNDAY NIGHT OR MONDAY. THE GFS AND  
ECMWF MAINTAIN CYCLONIC FLOW OVER THE REGION THROUGH TUESDAY.  
 
MODEL FIELDS ARE IN GENERAL AGREEMENT THROUGH SATURDAY, AND CLEARLY  
DIVERGENT LATER MONDAY THROUGH WEDNESDAY. CONFIDENCE IS MODERATE  
FRIDAY-SATURDAY AND LOW MONDAY TO WEDNESDAY.  
 
CONCERNS...  
 
THREE PERIODS OF UNSETTLED WEATHER... FRIDAY, SATURDAY NIGHT-SUNDAY,  
AND WEDNESDAY. COLD/DRY OR SEASONABLY COLD/DRY THE REMAINDER OF THE  
PERIOD. STRONG NORTHWEST WIND GUSTS POSSIBLE SUNDAY NIGHT AND MONDAY  
DRAWING UNSEASONABLY COLD ARCTIC AIR INTO SOUTHERN NEW ENGLAND.  
 
FRIDAY...  
 
SHALLOW NORTHERN STREAM SHORTWAVE IN A SPLIT-STREAM FLOW REGIME  
SUGGESTS ONLY LIMITED MOISTURE AMOUNTS AND WEAK LIFT. GFS CROSS  
SECTIONS SHOW DEEP MOISTURE, BUT PRECIPITABLE WATER VALUES ONLY A  
LITTLE ABOVE NORMAL. CONSENSUS MSLP FIELDS SHOW A SURFACE LOW  
TRACKING JUST SOUTH OF OUR SOUTH COAST, SUGGESTING THERMAL FIELDS  
WILL SUPPORT MAINLY SNOW, WITH A CHANGE TO RAIN ALONG THE COAST.  
TEMPS ALOFT SUGGEST MAX SFC TEMPS IN THE AFTERNOON IN THE 30S TO LOW  
40S. CLEARING SKIES, DIMINISHING WIND, AND DEWPTS IN THE TEENS AND  
LOW 20S SUGGEST FRIDAY NIGHT MIN TEMPS IN THE TEENS AND LOW 20S.  
 
SATURDAY NIGHT AND SUNDAY...  
 
PHASED-STREAM FLOW BRINGS HIGHER MOISTURE AMOUNTS TO THIS SYSTEM.  
CROSS SECTIONS AGAIN SHOW DEEP MOISTURE. PRECIP WATER VALUES HAVE  
DIMINISHED A LITTLE, BUT STILL SHOW VALUES AROUND 1 INCH FEEDING  
INTO SOUTHERN AND EASTERN PARTS OF OUR AREA. THESE PW VALUES ARE  
WELL ABOVE NORMAL IN MID JANUARY.  
 
STILL UNCERTAINTY IN THIS FORECAST AS THE MODELS CONTINUE TO SHIFT.  
MOST CONFIDENCE IS IN THE ECMWF AND ALLIED MODELS WHICH HAVE BEEN  
THE MOST CONSISTENT IN SHOWING A CENTER TRACK ALONG OR NEAR THE  
SOUTH COAST. THE GFS SOLUTION HAS SHIFTED TOWARD THE ECMWF. THIS IS  
A COLDER SOLUTION, AND SUPPORTS MORE SNOW AND ICE IN THE FORECAST  
THAN PREVIOUSLY.  
 
BASED ON THIS, THE FORECAST STARTS WITH SNOW EVERYWHERE SATURDAY  
NIGHT, THEN BRINGS RAIN INTO THE SOUTH COAST BY MORNING. RAIN  
SPREADS UP TO BOSTON AND THE NORTH SHORE SUNDAY, ALSO ACROSS RI AND  
MUCH OF NRN CT. NORTH OF THAT ZONE WILL BE A BAND OF SLEET/FREEZING  
RAIN IN THE INTERIOR...AND SNOW IN PARTS OF NORTHWEST MASS. SHIFTS  
IN THE FORECAST STORM PATH NORTH AND SOUTH WILL OF COURSE SHIFT  
THESE PRECIPITATION BANDS NORTH AND SOUTH.  
 
STRONG EAST WINDS WILL REACH 35-50 MPH SPEEDS ALONG THE COAST,  
ESPECIALLY OVER CAPE COD AND ISLANDS. INLAND SPEEDS WILL BE MORE  
LIKE 25-35 MPH.  
 
SUNDAY NIGHT-MONDAY  
 
THE STORM PASSES OUR AREA BETWEEN 1 PM AND 7 PM SUNDAY. WINDS  
WILL QUICKLY SHIFT OUT OF THE NORTH AND NORTHWEST. STRONG  
PRESSURE GRADIENT AT THE SURFACE WILL GENERATE STRONG SUSTAINED  
WINDS, AND COLD ADVECTION WILL DRAW STRONG WINDS ALOFT DOWN TO  
THE SURFACE WITH GUSTS OF 25-40 MPH POSSIBLE. THE COMBINATION OF  
WIND AND COLD AIR WILL BRING WIND CHILLS TO SINGLE DIGITS AND  
BELOW ZERO SUNDAY NIGHT AND MONDAY.  
 
WEDNESDAY...  
 
ANOTHER WEATHER SYSTEM MOVES UP THE OHIO VALLEY, SPREADING RAIN  
AND SNOW INTO SOUTHERN NEW ENGLAND WEDNESDAY/WEDNESDAY NIGHT.  
THE UPPER FLOW FAVORS THE SOUTHERN STREAM, BUT THE DAY 7 TIME  
PERIOD LEAVES MUCH UNCERTAINTY.  
 

 
   
AVIATION /03Z THURSDAY THROUGH MONDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY NIGHT/...HIGH CONFIDENCE.  
 
TONIGHT...  
 
VFR. WINDS FROM THE WSW WILL TURN FROM THE NW TONIGHT AS A COLD  
FRONT MOVES THROUGH. GUSTS MAY REACH 20-24 KT FOR A FEW HOURS,  
THEN DIMINISH LATE TONIGHT.  
 
THU AND THU NIGHT...  
MAINLY VFR. LOWERING CIGS THROUGH THE OVERNIGHT HOURS. WINDS  
SHIFT FROM NW TO E-SE OVERNIGHT.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRIDAY: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. CHANCE SN.  
 
FRIDAY NIGHT: VFR. BREEZY.  
 
SATURDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE LATE. CHANCE SN.  
 
SATURDAY NIGHT: IFR/LIFR. WINDY WITH GUSTS TO 35 KT. SN, FZRA.  
 
SUNDAY: MVFR/IFR CONDITIONS POSSIBLE. STRONG WINDS WITH GUSTS  
TO 40 KT. RA, FZRA, PL, SN.  
 
SUNDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. STRONG WINDS WITH  
LOCAL GUSTS TO 40 KT. CHANCE SN, FZRA LIKELY.  
 
MARTIN LUTHER KING JR DAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE.  
WINDY WITH GUSTS TO 30 KT.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY NIGHT/...  
 
W-SW WINDS WILL CONTINUE TO GUST AROUND 22 KT EARLY TONIGHT,  
THEN BECOME NW OVERNIGHT AS A COLD FRONT MOVES ACROSS THE  
WATERS. PRESSURE RISES BEHIND THE FRONT WILL GENERATE INCREASED  
WINDS ACROSS THE WATERS FOR A FEW HOURS TONIGHT.  
 
HIGH PRESSURE BUILDS OVER NEW ENGLAND THURSDAY, BRINGING  
LIGHTER WINDS TO THE WATERS. THE HIGH THEN MOVES OFF TO THE EAST  
THURSDAY NIGHT. THIS WILL BRING QUIETER BOATING WEATHER TO THE  
WATERS.  
 
AN APPROACHING WEATHER SYSTEM WILL SPREAD SNOW AND RAIN OVER THE  
WATERS AFTER MIDNIGHT THURSDAY NIGHT, WITH REDUCED VSBYS BY  
MORNING.  
 
OUTLOOK /FRIDAY THROUGH MONDAY/...  
 
FRIDAY: WINDS LESS THAN 25 KT. SNOW LIKELY, CHANCE OF RAIN.  
AREAS OF VISIBILITY 1 TO 3 NM.  
 
FRIDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
SATURDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT. SLIGHT CHANCE OF SNOW. LOCAL VISIBILITY 1 TO 3 NM.  
 
SATURDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS  
WITH GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS. SNOW LIKELY, RAIN.  
VISIBILITY 1 TO 3 NM.  
 
SUNDAY: MODERATE RISK FOR GALE FORCE WINDS WITH GUSTS UP TO  
45 KT. ROUGH SEAS UP TO 13 FT. RAIN, FREEZING RAIN.  
 
SUNDAY NIGHT: MODERATE RISK FOR GALE FORCE WINDS WITH GUSTS UP  
TO 40 KT. ROUGH SEAS UP TO 13 FT. CHANCE OF SNOW, FREEZING RAIN  
LIKELY, CHANCE OF SLEET. VISIBILITY 1 TO 3 NM.  
 
MARTIN LUTHER KING JR DAY: LOW RISK FOR GALE FORCE WINDS WITH  
GUSTS UP TO 35 KT. ROUGH SEAS UP TO 12 FT. CHANCE OF SNOW.  
VISIBILITY 1 TO 3 NM.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EST THURSDAY FOR ANZ231>235-  
237.  
SMALL CRAFT ADVISORY UNTIL 1 AM EST THURSDAY FOR ANZ230.  
SMALL CRAFT ADVISORY UNTIL 10 AM EST THURSDAY FOR ANZ250.  
SMALL CRAFT ADVISORY UNTIL 7 AM EST THURSDAY FOR ANZ251-255-  
256.  
SMALL CRAFT ADVISORY UNTIL 11 AM EST THURSDAY FOR ANZ254.  
 

 
 

 
SYNOPSIS...WTB/DOODY  
NEAR TERM...WTB/DOODY/BW  
SHORT TERM...DOODY  
LONG TERM...WTB  
AVIATION...WTB/DOODY  
MARINE...WTB/DOODY  
 
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