042  
FXUS61 KBOX 210005  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
705 PM EST THU FEB 20 2020  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL CONTINUE TO BRING DRY BUT COLD WEATHER  
TONIGHT AND FRIDAY. CONDITIONS REMAIN DRY THROUGH EARLY NEXT  
WEEK AS TEMPERATURES RISE TO ABOVE NORMAL LEVELS. NEXT CHANCE  
FOR WET WEATHER ARRIVES MONDAY NIGHT. UNSETTLED CONDITIONS MAY  
LINGER THROUGH THE MIDDLE OF NEXT WEEK WITH A COUPLE OF SURFACE  
LOWS MOVING ACROSS.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
650 PM UPDATE...  
 
NORTHERN EDGE OF MID AND HIGH CLOUDS FROM STORM ACROSS THE MID  
ATLC STATES HAS BEEN THINNING OUT OVER THE LAST COUPLE OF HOURS  
AS SEEN ON SKY COVER TRENDS ACROSS CENTRAL AND SOUTHERN AREAS ON  
THE GOES-EAST NIGHTTIME MICROPHYSICS RGB COMPOSITE SATELLITE  
IMAGERY. THIS IS LINED UP WELL WITH A WEAKENING TROUGH PUSHING  
ACROSS N CT/CENTRAL RI INTO SE MASS.  
 
STILL NOTING SOME LOWER CLOUDS AT AROUND 5-6KFT ACROSS THE  
ROUTE 2 AREA OF N MASS INTO S NH/VT AS RIDGING BUILDS ACROSS N  
VT/NH INTO CENTRAL MAINE. SHOULD SEE IMPROVING CONDITIONS THERE  
OVERNIGHT AS SUBSIDENCE SHIFTS SOUTHWARD.  
 
AS WINDS DROP OFF, TEMPS WILL FALL QUICKLY THROUGH THE NIGHT.  
OTHER THAN A FEW UPDATES TO BRING CONDITIONS CURRENT, OVERNIGHT  
FORECAST LOOKS ON TRACK.  
 
PREVIOUS DISCUSSION...  
 
TONIGHT...  
 
COLD AND DRY NW FLOW WITH ONE SHORT WAVE TROUGH MOVING THRU THIS  
EVENING FOLLOWED BY ANOTHER TOWARD MORNING. THE OVERALL NET EFFECT,  
COLD AIR ADVECTION WITH -20C AIR AT 850 MB NOW OVER NORTHERN NY INTO  
NORTHERN NEW ENGLAND, MAINLY STAYING TO OUR NORTH, HOWEVER ROBUST  
LOW LEVEL COLD AIR ADVECTION WITH 925 MB LOWERING FROM ABOUT -9C AT  
3 PM OVER SOUTHERN NEW ENGLAND TO -14C TO -15C BY 1 AM TO 7 AM  
FRI. THIS WILL SUPPORT LOWS IN THE SINGLE DIGITS AND TEENS  
OVERNIGHT, ONE OF THE COLDER NIGHTS THIS WINTER ESPECIALLY  
RECENTLY. A MODEST W-NW WIND BECOMING NORTHERLY OVERNIGHT AT  
5-15 MPH WILL PROVIDE A WIND CHILL A FEW DEGS COLDER THAN ACTUAL  
AIR TEMPS. GIVEN THE MAGNITUDE OF THE COLD AIR AND NORTHERLY  
DELIVERY (LACK OF DOWNSLOPE COMPONENT) OVERNIGHT BLENDED IN SOME  
OF THE COLDER GUIDANCE TO DERIVE MIN TEMPS.  
 
NNE WINDS COULD GUSTS UP TO 20 MPH LATE TONIGHT OVER CAPE COD AND  
NANTUCKET. GIVEN THE TRAJECTORY OF COLD AIR STREAMING ACROSS  
RELATIVELY WARM OCEAN WATERS OF AROUND 40F, EXPECTING LOTS OF OCEAN  
EFFECT CLOUDS LATER THIS EVENING ALONG WITH A FEW SNOW SHOWERS OR  
FLURRIES. NOT EXPECTING MUCH MORE THAN THAT AS SUBSIDENCE INVERSION  
FROM 1030 MB HIGH WILL LIMIT BOUNDARY LAYER DEPTH, CAPPING OCEAN  
EFFECT CONVECTIVE SNOW SHOWER THREAT.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
 
 
4 PM UPDATE ...  
 
FRIDAY ...  
 
VERY COLD START TO THE DAY AND TEMP RECOVERY WILL BE LIMITED AS  
GIVEN LACK OF THERMAL ADVECTION WITH RIDGE OF HIGH PRESSURE OVERHEAD  
AND ASSOCIATED SUBSIDENCE INVERSION LIMITING BOUNDARY LAYER MIXING.  
THUS SIMILAR HIGHS AS TODAY (UPPER 20S AND LOWER 30S) BUT IT WON'T  
FEEL AS COLD GIVEN MORE SUNSHINE AND LESS WIND. SUNSHINE MAY BE  
DELAYED UNTIL THE AFTERNOON FOR CAPE COD AND NANTUCKET AS OCEAN  
EFFECT CLOUDS LINGER MUCH OF THE MORNING.  
 
FRIDAY NIGHT ...  
 
RIDGE AXIS MOVES EAST OF THE AREA WITH WESTERLY WINDS DEVELOPING.  
HOWEVER AFTER SUNSET WHERE WINDS DECOUPLE (DEEPER VALLEYS AND  
POSSIBLY LOW LYING SPOTS OF EASTERN MA) TEMPS MAY FALL QUICKLY WITH  
DEW PTS IN THE SINGLE DIGITS AND CLEAR SKIES. HOWEVER NOT AS COLD  
ALONG THE COAST ESPECIALLY CAPE COD AND ISLANDS WHERE WINDS WILL NOT  
DECOUPLE, INCLUDING BOSTON AND HIGH TERRAIN.  
 
OTHERWISE, DRY AND QUIET WEATHER CONDITIONS.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
HIGHLIGHTS...  
 
* DRY CONDITIONS WITH NORMAL TEMPERATURES ABOVE NORMAL LATE  
THIS WEEKEND INTO EARLY NEXT WEEK  
 
* NEXT CHANCE FOR PRECIPITATION BEGINS MONDAY NIGHT, MAINLY  
RAIN EVENT  
 
* POTENTIAL FOR SOUTHERN STREAM MOISTURE SHIFTING OUT OF  
OHIO/TENNESSEE VALLEYS TOWARD THE NE U.S. THROUGH THE MIDDLE  
OF NEXT WEEK WITH CONTINUED MILD TEMPS  
 
* A CHANGEOVER TO LIGHT SNOW MAY OCCUR WED NIGHT INTO THU  
ACROSS PORTIONS OF THE INTERIOR  
 
DETAILS...  
 
SATURDAY THROUGH MONDAY...  
 
NOTING A GENERAL W-NW MID LEVEL STEERING FLOW FROM THE NORTHERN  
PLAINS STATES THROUGH NEW ENGLAND TO THE MID ATLC COAST TO  
START OFF SATURDAY MORNING. THIS KEEPS A DRY FLOW ACROSS THE  
NORTHEAST WITH A BROAD H5 RIDGE EXTENDING FROM ALBERTA AND  
SASKATCHEWAN THROUGH THE E SLOPES OF THE ROCKIES TO N TEXAS IN  
PLACE TO START OFF. THIS PATTER WILL TAKE A FEW DAYS TO BREAK  
DOWN, SO WILL SEE AN EXTENDED PERIOD OF DRY CONDITIONS AS  
SURFACE HIGH PRESSURE FROM EASTERN TEXAS TO THE MID ATLC COAST  
WILL SLOWLY SHIFT E THROUGH THE UPCOMING WEEKEND, THEN PUSHES  
OFF THE CAROLINA COAST BY AROUND 12Z MONDAY.  
 
WITH THE GENERAL LAND BASED WIND FLOW IN PLACE, ALONG WITH  
GRADUALLY RISING H5 HEIGHTS, TEMPS WILL START OFF CLOSE TO  
SEASONAL LEVELS ON SATURDAY ON W WINDS AT 10 MPH THAT MAY GUST  
UP TO 20 MPH. READINGS WILL CONTINUE TO MODERATE AS WINDS  
GRADUALLY BACK TO SW BY MONDAY. PART OF THE BACKING WINDS WILL  
BE THE BEGINNINGS OF A DIGGING LONG WAVE TROUGH THROUGH THE  
CENTRAL AND NORTHERN PLAINS STATES THAT WILL MERGE WITH A  
WEAKENING H5 CUTOFF LOW LATE SUNDAY AND MONDAY. H5 HEIGHTS WILL  
RISE TO AROUND 558 DM ON MONDAY. SO, WITH THE MILD SW WIND FLOW  
AND RISING HEIGHTS, WILL SEE MONDAY'S TEMPS RANGE FROM 5 TO 10  
DEGREES ABOVE SEASONAL LEVELS. HIGHS WILL TOP OFF IN THE LOWER  
50S ACROSS MOST AREAS, BUT ONLY IN THE MID-UPPER 40S ACROSS THE  
HIGHER TERRAIN AND ALONG THE S COAST WITH THE ONSHORE WIND.  
 
THE SW WINDS WILL BRING IN SOME MID AND UPPER LEVEL MOISTURE,  
SO CLOUDS WILL INCREASE FROM W-E DURING THE DAY. HOWEVER, WITH  
T/TD SPREADS AROUND 10 DEGREES, HAVE KEPT A DRY FORECAST GOING  
THROUGH MONDAY  
 
MONDAY NIGHT THROUGH TUESDAY NIGHT...  
 
WITH THE SW WIND IN PLACE BRINGING MILDER AIR AT THE SURFACE  
AND ALOFT, WILL SLOWLY BRING IN A DEEPENING MOISTURE LAYER AS A  
SURFACE LOW APPROACHES THE OH VALLEY BY 12Z TUE. SHOULD SEE  
LIGHT RAIN ARRIVE ACROSS THE CT VALLEY BY AROUND MIDNIGHT, THEN  
SPREADING E THROUGH THE REMAINDER OF THE NIGHT. TEMPS SHOULD  
REMAIN ABOVE FREEZING, SO NOT EXPECT PTYPE ISSUES AT THIS  
POINT.  
 
LOOKS LIKE BEST SHOT FOR PRECIP WILL OCCUR ALONG THE RI COAST,  
POSSIBLY REACHING INTO N CT BY AROUND DAYBREAK. NOT SEEING ANY  
SOUTHERN STREAM MOISTURE PLUME WORKING IN TO START OFF, SO  
SHOULD SEE LIGHT QPF VALUES MON NIGHT.  
 
BY TUESDAY MORNING, HOWEVER, WILL SEE INCREASING DEEP LAYER  
MOISTURE HEADING TOWARD THE REGION AS THE CENTRAL PLAINS H5  
TROUGH CONTINUES TO DIG. 12Z GEFS ENSEMBLE MEAN SIGNALING A PWAT  
PLUME ON THE ORDER OF 1 TO 2 SD ABOVE NORMAL (AROUND 1 TO 1.25  
INCHES). SO, COULD SEE STEADIER RAINFALL MAINLY S OF THE MASS  
PIKE FROM AROUND 18Z TUE TO 06Z WED, WITH POTENTIAL QPF TOTALS  
AROUND 0.5 TO 0.6 INCHES ACROSS NE CT/RI/SE MASS DURING THAT  
TIMEFRAME. SHOULD SEE PRECIP START TO TAPER OFF AS THE FIRST LOW  
WEAKENS AS IT MOVES ACROSS THE NORTHEAST. SO, SHOULD SEE PRECIP  
TAPERING OFF AROUND OR AFTER MIDNIGHT TUE NIGHT FROM W-E.  
 
HIGHS ON TUESDAY WILL RUN AROUND 5 DEGREES ABOVE NORMAL WITH  
READINGS MAINLY IN THE UPPER 40S TO AROUND 50, EXCEPT A BIT  
COOLER ACROSS THE HIGHER TERRAIN.  
 
WEDNESDAY AND THURSDAY...  
 
BY 12Z WEDNESDAY, WILL SEE DEEP, NEARLY MERIDIONAL H5 TROUGH  
FROM WESTERN ONTARIO SOUTHWARD THROUGH THE MS RIVER VALLEY  
DEVELOP. 12Z MODELS SIGNALING A BRIEF DRY PERIOD BETWEEN  
SYSTEMS THROUGH MIDDAY WEDNESDAY OR SO. THIS APPEARS TO BE  
SHORT LIVED AS SEVERAL MODEL MEMBERS DEVELOPING ANOTHER LOW  
PRES WAVE IN THE DELMARVA AREA BY 00Z THURSDAY. WITH AN E-SE  
WIND FLOW IN PLACE, MAY SEE ANOTHER AREA OF SHOWERS MOVE ACROSS.  
COULD SEE UP TO 0.3 INCHES ACROSS THE E SLOPES OF THE  
BERKSHIRES AFTER MIDNIGHT THU NIGHT, THEN PUSHES EASTWARD  
DURING THE DAY ON THURSDAY. SO, CURRENT FORECAST SUGGESTS  
ANOTHER 0.3 TO 0.5 INCHES OF RAINFALL DURING THE WED NIGHT-THU  
TIMEFRAME. STILL QUITE A BIT OF UNCERTAINTY WHETHER THIS  
SCENARIO, HOWEVER, AS THERE IS STILL QUITE A BIT OF MODEL  
SOLUTION SPREAD.  
 
ANOTHER CAVEAT MAY BE HOW QUICKLY COLDER AIR MAY FILTER IN  
BEHIND THE DEPARTING SECOND LOW ON THU. THERE IS THE POSSIBILITY  
OF A CHANGEOVER TO SNOW ACROSS THE HIGHER INLAND TERRAIN WED  
NIGHT THAT COULD SHIFT SE DURING THU. DEPENDING UPON HOW QUICKLY  
THIS WILL OCCUR, AS WELL AS WHETHER IT LASTS ACROSS THE HIGHER  
TERRAIN OF THE NORTHERN WORCESTER HILLS AND E SLOPES OF THE  
BERKSHIRES WHETHER THERE COULD BE SOME SNOW ACCUMULATION LATE  
WED NIGHT/THU.  
 

 
   
AVIATION /00Z FRIDAY THROUGH TUESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
00Z TAF UPDATE...HIGH CONFIDENCE THRU AT LEAST 12Z SATURDAY.  
 
VFR SCT-BKN CLOUDS FROM 050-070, MOST CLOUDS ACROSS N CT/RI/SE  
MASS TERMINALS THROUGH 03Z-05Z. EXCEPTION WILL BE ACROSS OUTER  
CAPE COD AND NANTUCKET WHERE MVFR CIGS DEVELOP IN RESPONSE TO  
WINDS BECOMING N-NE 10-20 KT AROUND OR AFTER 05Z. A FEW OCEAN  
EFFECT SNOW SHOWERS OR FLURRIES POSSIBLE ACROSS THIS AREA.  
 
FRIDAY...MVFR CIGS OVER MID TO OUTER CAPE COD AND NANTUCKET  
DURING THE MORNING, ALONG WITH A FEW SNOW SHOWERS/FLURRIES  
POSSIBLE, THEN SHOULD IMPROVE. OTHERWISE VFR, DRY WEATHER AND  
LIGHT/VARIABLE WINDS.  
 
FRIDAY NIGHT...VFR. DRY CONDITIONS AND LIGHT SW WINDS.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF. PERIOD OF SCT-BKN CLOUDS  
AT 050-060 THROUGH 03Z-04Z THIS EVENING.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY THROUGH SATURDAY NIGHT: VFR. BREEZY.  
 
SUNDAY THROUGH MONDAY: VFR.  
 
MONDAY NIGHT: MAINLY MVFR, WITH AREAS VFR POSSIBLE. CHANCE RA.  
 
TUESDAY: CHANCE RA.  
 

 
   
MARINE
 
 
4 PM UPDATE ...  
 
TONIGHT/FRIDAY/FRI NIGHT...  
 
DRY WEATHER AND GOOD VSBY. ONLY EXCEPTION WILL BE AS WINDS SHIFT  
FROM WNW LATE TODAY TO NNE OVERNIGHT (10-20 KT) A FEW SNOW SHOWERS  
MAY IMPACT THE WATERS AROUND CAPE COD AND NANTUCKET. LIGHT/VARIABLE  
WIND FRI FOLLOWED BY DEVELOPING MODEST WEST WIND FRI NIGHT BUT MAY I  
INCREASE TO 20-25 KT OUTER EASTERN MA WATERS LATE TOWARD GULF OF ME  
WATERS.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS  
APPROACHING 5 FT.  
 
SUNDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
 
SUNDAY NIGHT THROUGH MONDAY: WINDS LESS THAN 25 KT.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. CHANCE OF RAIN.  
 
TUESDAY: WINDS LESS THAN 25 KT. RAIN LIKELY.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...NONE.  
 

 
 

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