204  
FXUS61 KBOX 152122  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
422 PM EST SAT DEC 15 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE BUILDS ACROSS NORTHERN NEW ENGLAND TONIGHT  
PROVIDING DRY CHILLY WEATHER. LOW PRESSURE APPROACHES NEW  
ENGLAND FROM THE SOUTH WITH RAIN OVERSPREADING THE REGION FROM  
SOUTH TO NORTH SUNDAY, ALTHOUGH THE STEADIEST AND HEAVIEST RAIN  
ARRIVES SUNDAY EVENING AND OVERNIGHT. PRECIPITATION WILL LIKELY  
BE A MIX OF SLEET AND FREEZING RAIN ACROSS NORTHWEST CT INTO  
WESTERN-CENTRAL MASS, THEN TRENDING TOWARD LIGHT SNOW SUNDAY  
NIGHT. GREATEST IMPACT WILL BE AT THE HIGHER ELEVATIONS WHERE  
TEMPERATURES WILL BE BELOW FREEZING. COLD AIR WILL PUSH ACROSS  
THE REGION MONDAY AFTERNOON THROUGH TUESDAY AS HIGH PRESSURE  
BUILDS ACROSS THE NORTHEAST. AS THE HIGH MOVES OFF THE EASTERN  
SEABOARD AROUND MID WEEK, MILDER AIR WILL WORK IN. LOW PRESSURE  
WILL DEVELOP ACROSS THE SOUTHEAST LATE THURSDAY, THEN WILL SHIFT  
TOWARD THE REGION LATE NEXT WEEK BRINGING A SWATH OF RAIN  
THURSDAY NIGHT INTO EARLY NEXT WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
 
 
330 PM UPDATE...  
 
FRONTAL BOUNDARY HAS NOW REACHED THE SOUTH COAST WITH EARLIER  
LIGHT RAIN OFFSHORE. DEW PTS STILL AROUND 50 ALONG THE SOUTH  
COAST BUT DEW PTS DROP OFF INTO THE 30S ACROSS NORTHERN MA IN  
THE DEEPER POST FRONTAL AIRMASS. AS NORTHERN STREAM SHORT WAVE  
CURRENTLY OVER MAINE MOVES EAST THIS WILL DRIVE FRONTAL BOUNDARY  
FARTHER SOUTH WITH DEW PTS FALLING INTO THE 20S AND 30S  
OVERNIGHT. THUS DRY WEATHER PREVAILS AND NOT EXPECTING ANY FOG  
GIVEN THE DRIER AIRMASS. ALTHOUGH MAY BE ENOUGH MOISTURE FOR  
FROST WHERE TEMPS FALL BELOW FREEZING, MAINLY NORTH AND WEST OF  
HFD-PVD-BOS. HOWEVER, UNTIL THE CORE OF THE COLDER/DRIER  
AIRMASS ARRIVES ENJOY TEMPS OF 50-55 LATE THIS AFTERNOON!  
 
LATER TONIGHT AS LOW PRESSURE APPROACHES FROM THE SOUTH, 1025 MB  
HIGH OVER MAINE WILL SQUEEZE THE PGRAD AND RESULT IN INCREASING  
NE WINDS ALONG THE SOUTH COAST INCLUDING CAPE COD.  
 

 
   
SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/
 
 
UPDATED 330 PM...  
 
*** WINTRY MIX OF PRECIP INLAND ESPECIALLY HIGH TERRAIN ***  
 
SYNOPTIC OVERVIEW...  
 
NORTHERN STREAM SHORT WAVE CURRENTLY ACROSS ME MOVES EAST  
TONIGHT AND DELIVERS A BURST OF LOW LEVEL COLD AIR ADVECTION  
TONIGHT INTO SUNDAY, SETTING THE STAGE FOR A WINTRY MIX OF  
PRECIP INLAND SUNDAY/SUNDAY NIGHT BEFORE ENDING MONDAY MORNING.  
THE KEY HERE IS THE COLD AIR IS FAIRLY SHALLOW (BELOW 850 MB)  
SUNDAY, THUS NOT DEEP ENOUGH TO SUPPORT SNOW UNTIL SUNDAY NIGHT  
WHEN THE COLUMN BEGINS TO COOL FROM THE TOP DOWN COURTESY OF  
HEIGHT FALLS AS THE VERTICALLY STACKED LOW DEEPENS SUNDAY NIGHT  
AS IT TRACKS OVER OR NEAR THE BENCHMARK. THIS IS TYPICALLY A  
FAVORABLE TRACK FOR HEAVY SNOW, HOWEVER THE ANTECEDENT AIRMASS  
IS NOT VERY COLD AS MENTIONED ABOVE AND THIS IS A SOUTHERN  
STREAM SYSTEM THAT DOESN'T PHASE WITH ANY NORTHERN STREAM  
ENERGY. THUS NO INFUSION OF COLD AIR.  
 
SUNDAY...  
 
MODEL SOUNDINGS SHOW DRY LAYER BETWEEN 800-900 MB WHICH DELAYS  
NORTHWARD PROGRESSION OF RAIN SHIELD DURING THE DAY. THUS  
STEADIEST RAIN OCCURS LATE IN THE DAY ACROSS CT-RI AND SOUTHEAST  
MA WITH JUST SPOTTY LIGHT RAIN ELSEWHERE. CONCERN IS SUNDAY  
MORNING THERE MAY BE ENOUGH LOW LEVEL MOISTURE FOR SOME SPOTTY  
DRIZZLE ACROSS NORTHERN CT AND OVER THE BORDER INTO SOUTHWEST MA  
EASTWARD INTO SOUTHERN WORCESTER COUNTY. THEREFORE THERE IS A  
VERY LOW RISK FOR SOME SPOTTY FREEZING DRIZZLE ACROSS THIS  
REGION. WILL ISSUE A SPECIAL WEATHER STATEMENT TO ADDRESS THIS.  
 
OTHERWISE RAIN SHIELD SLOWLY OVERSPREADS THE REGION FROM SOUTH  
TO NORTH SUNDAY ESPECIALLY DURING THE AFTERNOON. MOST LOCATION  
THE COLUMN IS WARM ENOUGH ALONG WITH SURFACE TEMPS TO SUPPORT  
ALL RAIN. HOWEVER FROM NORTHWEST HARTFORD COUNTY INTO WESTERN-  
CENTRAL MA A MIX OF FREEZING RAIN AND SLEET IS LIKELY WITH THE  
GREATEST TRAVEL IMPACT AT ELEVATIONS ABOVE 1000 FT DURING THE  
DAY WHERE TEMPS WILL BE NEAR FREEZING. AGAIN MOST OF THE REGION  
WILL HAVE TEMPS ABOVE FREEZING SO JUST EXPECTING WET ROADWAYS.  
 
NE WINDS CONTINUE TO INCREASE ESPECIALLY ALONG THE SOUTH COAST  
INCLUDING CAPE COD AND THE ISLANDS AS LOW PRES APPROACHES WITH  
ATTENDING LOW LEVEL ENE JET.  
 
SUNDAY NIGHT...  
 
COASTAL LOW CONTINUES TO SLOWLY DEEPEN AS IT TRACKS OVER OR NEAR  
THE BENCHMARK. THIS CAUSES THE COLUMN TO COOL FROM TOP DOWN IN  
RESPONSE TO HEIGHT FALLS WITH MID LEVEL WARM LAYER ERODING  
ACROSS NORTHWEST CT INTO WESTERN-CENTRAL MA. THIS IS WHERE SLEET  
AND FREEZING RAIN WILL TRANSITION TO MAINLY LIGHT SNOW  
OVERNIGHT. THUS A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR  
THIS REGION FOR A PERIOD OF WINTRY MIX (SLEET AND FREEZING RAIN)  
FOLLOWED BY A COATING TO 2 INCHES OF SNOW POSSIBLE. GREATEST  
FORECAST CONFIDENCE FOR IMPACT WILL BE ACROSS THE HIGHER TERRAIN  
WHERE TEMPS WILL BE AT OR BELOW FREEZING, SO EXPECTING SLIPPERY  
TRAVEL HERE. THUS THE ADVISORY HAS BEEN CONFINED TO THE HIGHEST  
ELEVATIONS. AT LOWER ELEVATIONS IN THE ADVISORY AREA ROADS MAY  
JUST HAVE A MINOR SLUSHY ACCUMULATION OR PERHAPS JUST WET IN THE  
VALLEYS. IF LATER TRENDS SUGGEST A COLDER SCENARIO THE ADVISORY  
MAY HAVE TO BE EXPANDED SOUTH AND EAST. BUT FOR NOW ANY TRAVEL  
IMPACTS SHOULD BE CONFINED THE HIGH TERRAIN OF NORTHWEST CT INTO  
WESTERN-CENTRAL MA.  
 
ELSEWHERE ESPECIALLY FROM HFD-PVD-BOS TO THE COASTLINE JUST  
EXPECTING PERIODS OF RAIN OVERNIGHT AND WIND GUSTS UP TO 40 MPH  
OVER CAPE COD AND THE ISLANDS. HELD OFF ON A WIND ADVISORY AS  
WIND GUSTS WILL BE MARGINAL GIVEN LACK OF COLD AIR AND STEEP LOW  
LEVEL LAPSE RATES IN ADDITION TO STRONGEST WINDS STILL BEYOND 36  
HRS. LATER SHIFTS WILL HAVE TO MONITOR TRENDS HERE.  
 
MONDAY MORNING...  
 
VERTICALLY STACKED LOW JUST NE OF THE 40N/70W BENCHMARK REMAINS  
PROGRESSIVE AND MOVES FARTHER OFFSHORE WITH MORNING PRECIP  
ENDING AND GIVING WAY TO AT LEAST PARTIAL CLEARING BY MIDDAY OR  
SO.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
 
 
HIGHLIGHTS...  
 
* MAINLY DRY, BLUSTERY AND COLD MONDAY AFTERNOON AND TUESDAY  
* MILD TEMPERATURES RETURN WEDNESDAY THROUGH LATE NEXT WEEK  
* RAIN, HEAVY AT TIMES FROM THURSDAY NIGHT THROUGH FRIDAY  
* A FEW LINGERING SHOWERS ON SATURDAY WITH SOMEWHAT COOLER  
TEMPERATURES  
 
OVERVIEW...  
 
H5 TROUGH ACROSS THE NORTHEAST U.S. PUSHES E ACROSS THE  
MARITIMES LATE MONDAY INTO TUESDAY. NORTHERN STREAM STORM TRACK  
LIFTS INTO SOUTHERN CANADA BY MID WEEK, WHILE H5 TROUGH DIGS  
ACROSS THE CENTRAL PLAINS DURING THE WED-THU TIMEFRAME. THIS  
WILL ALLOW MILDER TEMPERATURES TO PUSH NORTHWARD AS W-SW WIND  
FLOW AT THE SURFACE AND ALOFT SETS UP AHEAD OF DIGGING LONG WAVE  
TROUGH FROM THE WESTERN GREAT LAKES DOWN THE MISSISSIPPI RIVER  
VALLEY. NOTING CUTOFF H5 LOW DEVELOPS AROUND 12Z FRI ON LONG  
RANGE MODELS, RIDING ACROSS THE OHIO/TENNESSEE VALLEYS. DEEP  
TROUGH PUSHES SLOWLY E, ALLOWING SOUTHERLY FLOW TO WORK UP THE  
EASTERN SEABOARD LATE THU INTO FRI, BRINGING DEEP MOISTURE FEED  
UP THE COAST AS LOW PRESSURE RIDES UP THE APPALACHIANS INTO  
QUEBEC INTO NEXT WEEKEND.  
 
DETAILS...  
 
MONDAY AFTERNOON THROUGH TUESDAY NIGHT...  
 
H5 CUTOFF LOW S OF NOVA SCOTIA MONDAY AFTERNOON WILL WEAKEN AS  
ANOTHER COLD POOL SHIFTS SE OUT OF NORTHERN NEW ENGLAND INTO THE  
MARITIMES MONDAY NIGHT. PERSISTENT CYCLONIC FLOW WILL KEEP LOW  
LEVEL MOISTURE ACROSS EASTERN AREAS THROUGH MONDAY AFTERNOON.  
COULD SEE LINGERING LIGHT RAIN ACROSS PORTIONS OF CAPE COD,  
WHILE LIGHT SNOW LINGERS ACROSS THE E SLOPES OF THE BERKSHIRES  
INTO MONDAY NIGHT. RAIN ACROSS THE OUTER CAPE WILL TAPER TO SNOW  
SHOWERS MONDAY NIGHT, BUT WILL LINGER INTO TUESDAY WITH COLD,  
BLUSTERY NW WINDS IN PLACE.  
 
COLD POOL WORKS INTO NY STATE AND NEW ENGLAND BY MONDAY NIGHT  
WHICH WILL SPREAD ACROSS THE REGION OVERNIGHT. H85 TEMPS WILL  
DROP DOWN TO -12C TO -15C BY 12Z TUESDAY. EXPECT HIGHS TO ONLY  
REACH THE MID TO UPPER 20S ACROSS THE HIGHER TERRAIN TO THE  
LOWER 30S ACROSS THE COASTAL PLAIN, RUNNING 5 TO 10 DEGREES  
BELOW SEASONAL LEVELS. LOWS TUESDAY NIGHT WILL BE MAINLY IN THE  
TEENS TO AROUND 20, EXCEPT IN THE 20S ACROSS THE COASTAL PLAIN.  
 
WEDNESDAY AND THURSDAY...  
 
LARGE HIGH PRESSURE BUILDS ACROSS THE EASTERN U.S. WEDNESDAY,  
WITH DRY CONDITIONS AND SEASONAL TEMPERATURES. AS THIS HIGH  
MOVES OFFSHORE, THE RETURN SW FLOW WILL BRING MILDER CONDITIONS  
ON THURSDAY WITH READINGS IN THE UPPER 30S ACROSS THE E SLOPES  
OF THE BERKSHIRES TO THE UPPER 40S ACROSS E RI INTO SE MASS.  
 
CLOUDS WILL INCREASE DURING THURSDAY WELL AHEAD OF DEVELOPING  
LOW PRESSURE ACROSS THE SE STATES. SCATTERED LIGHT RAIN MAY  
REACH INTO THE CT VALLEY BY LATE IN THE DAY.  
 
THURSDAY NIGHT THROUGH SATURDAY...  
 
SURGE OF MOISTURE WORKS UP THE EASTERN SEABOARD WITH DEEP  
SOUTHERLY WIND FLOW AT THE SURFACE AND ALOFT. ALSO NOTING PWAT  
MOISTURE PLUME WORKING UP THE COAST BY AROUND MIDNIGHT THURSDAY  
NIGHT, UP TO 2 TO 3 SD ABOVE SEASONAL NORMALS BY FRI MORNING.  
COULD SEE SOME HEAVIER RAINFALL AS THIS PLUME MOVES ACROSS  
DURING FRIDAY, WITH THE BEST SHOT ACROSS CENTRAL AND EASTERN  
AREAS.  
 
AS THE LOW SHIFTS NE ACROSS THE APPALACHIANS FRIDAY NIGHT INTO  
EARLY SATURDAY, DRY SLOT WILL WORK INTO THE COASTAL PLAIN ON  
SATURDAY, THOUGH SHOWERS MAY LINGER ACROSS THE CENTRAL AND  
WESTERN AREAS.  
 

 
   
AVIATION /22Z SATURDAY THROUGH THURSDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH MONDAY/...MODERATE CONFIDENCE.  
 
330 PM UPDATE...  
 
TONIGHT...  
 
VFR WITH THE EXCEPTION OF SOME LEFTOVER MVFR ALONG THE SOUTH  
COAST THAT WILL MOVE OFFSHORE SHORTLY. NE WINDS INCREASE TO 30  
KTS TOWARD MORNING ACROSS SOUTH COASTAL RI/MA.  
 
SUNDAY...  
 
A MIX OF MVFR AND VFR TRENDING TOWARD IFR/MVFR AS THE DAY  
PROGRESSES AS RAIN OVERSPREADS THE AREA FROM SOUTH TO NORTH.  
FREEZING RAIN AND SLEET LIKELY ACROSS THE HIGHER ELEVATIONS  
INCLUDING KORH. NE WINDS UP TO 35 KT POSSIBLE LATE IN THE DAY  
ALONG SOUTH COAST OF RI/MA INCLUDING CAPE COD AND ISLANDS.  
 
SUNDAY NIGHT...  
 
IFR/LIFR IN RAIN EXCEPT FREEZING RAIN AND SLEET CHANGING TO ALL  
SNOW ACROSS THE INTERIOR WITH MINOR ACCUMULATIONS POSSIBLE  
HIGHER ELEVATIONS. NE WINDS UP TO 35 KT CAPE COD AND ISLANDS.  
 
MONDAY MORNING...  
 
MVFR/IFR IN RAIN TRENDING UP TO MVFR/VFR BY MIDDAY OR SO. GUSTY  
NORTH WIND SHIFTING TO NW AROUND NOON.  
 
KBOS TERMINAL...  
QUIET WEATHER TONIGHT WITH LOWERING CIGS SUNDAY. MUCH OF THE DAY  
MAY BE DRY WITH RAIN POSSIBLY HOLDING OFF UNTIL AFTER 21Z  
SUNDAY. RAIN MAY CHANGE TO A PERIOD OF SLEET AND SNOW BEFORE  
ENDING MONDAY MORNING.  
 
KBDL TERMINAL...  
QUIET WEATHER TONIGHT BUT LOWERING CIGS TOWARD 12Z SUNDAY.  
SPOTTY LIGHT FREEZING DRIZZLE POSSIBLE SUNDAY MORNING. OTHERWISE  
ALL RAIN SUNDAY THEN POSSIBLY MIXING WITH SLEET AND SNOW SUNDAY  
NIGHT.  
 
OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...  
 
MONDAY NIGHT: VFR. WINDY WITH GUSTS TO 35 KT.  
 
TUESDAY: VFR. STRONG WINDS WITH LOCAL GUSTS TO 40 KT.  
 
TUESDAY NIGHT: VFR. WINDY WITH GUSTS TO 35 KT.  
 
WEDNESDAY THROUGH WEDNESDAY NIGHT: VFR. BREEZY.  
 
THURSDAY: VFR. SLIGHT CHANCE RA.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH MONDAY/...HIGH CONFIDENCE.  
 
*** NE GALES LIKELY LATE SUNDAY INTO SUNDAY NIGHT ***  
 
TONIGHT...QUIET WEATHER WITH NE WINDS INCREASING TO 30 KT BY  
SUNDAY MORNING.  
 
SUNDAY...NE WINDS INCREASE TO 35 KT LATE SOUTHERN WATERS. VSBY  
LOWERING IN RAIN FROM SOUTH TO NORTH.  
 
SUNDAY NIGHT...NE WINDS UP TO 35 KT WITH STRONGEST WINDS AROUND  
THE CAPE COD WATERS.  
 
MONDAY...GALE CENTER JUST NE OF 40N/70W MOVES SEAWARD WITH  
NORTHERLY GALES DIMINISHING AND BECOMING NW BY MIDDAY.  
 
OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...  
 
MONDAY NIGHT: MODERATE RISK FOR GALE FORCE WINDS WITH GUSTS UP  
TO 40 KT. ROUGH SEAS UP TO 10 FT. CHANCE OF SNOW SHOWERS.  
 
TUESDAY: MODERATE RISK FOR GALE FORCE WINDS WITH GUSTS UP TO  
40 KT. ROUGH SEAS UP TO 11 FT. SLIGHT CHANCE OF SNOW SHOWERS.  
 
TUESDAY NIGHT: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO  
35 KT. AREAS OF ROUGH SEAS.  
 
WEDNESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT.  
 
WEDNESDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 20 KT. SEAS LOCALLY APPROACHING 5 FT.  
 
THURSDAY: WINDS LESS THAN 25 KT.  
 

 
   
TIDES/COASTAL FLOODING
 
 
330 PM UPDATE...  
 
HIGH TIDE 4 AM MONDAY IS ONLY AROUND 9 FT AND ONLY EXPECTING A  
STORM SURGE OF 0.75 FT TO 1.5 FT, ALONG WITH SEAS ONLY 7 TO 15  
FT OFFSHORE. THIS WILL RESULT IN TOTAL WATER LEVELS BELOW FLOOD  
STAGE AND INSUFFICIENT WAVE ACTION TO YIELD ANY COASTAL  
FLOODING.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...WINTER WEATHER ADVISORY FROM 6 AM SUNDAY TO 7 AM EST MONDAY  
FOR CTZ002.  
MA...WINTER WEATHER ADVISORY FROM 6 AM SUNDAY TO 7 AM EST MONDAY  
FOR MAZ002>004-008>011-026.  
RI...NONE.  
MARINE...GALE WARNING FROM 9 AM SUNDAY TO MIDNIGHT EST SUNDAY NIGHT FOR  
ANZ231>235-237.  
SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 6 AM EST MONDAY FOR  
ANZ230.  
SMALL CRAFT ADVISORY FROM 2 AM SUNDAY TO 6 AM EST MONDAY FOR  
ANZ236.  
GALE WARNING FROM 3 PM SUNDAY TO 6 AM EST MONDAY FOR ANZ250-  
254.  
SMALL CRAFT ADVISORY FROM 5 AM SUNDAY TO 6 AM EST MONDAY FOR  
ANZ251.  
GALE WARNING FROM 6 AM SUNDAY TO MIDNIGHT EST SUNDAY NIGHT FOR  
ANZ255-256.  
 

 
 

 
SYNOPSIS...NOCERA/EVT  
NEAR TERM...NOCERA  
SHORT TERM...NOCERA  
LONG TERM...EVT  
AVIATION...NOCERA/EVT  
MARINE...NOCERA/EVT  
TIDES/COASTAL FLOODING...  
 
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