968  
FXUS61 KBOX 131810  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
110 PM EST SAT JAN 13 2018  
   
SYNOPSIS
 
 
A STRONG COLD FRONT EXITS OFFSHORE EARLY THIS AFTERNOON WITH  
TEMPERATURES CRASHING INTO THE 20S THIS AFTERNOON. MAINLY DRY  
BUT VERY COLD WEATHER FOLLOWS TONIGHT THROUGH MONDAY. MAINLY DRY  
BUT COLD WEATHER IS EXPECTED SUNDAY AND MONDAY. LOW PRESSURE  
DIVING SOUTH FROM THE CANADIAN ARCTIC WILL BRING A CHANCE OF  
SNOW TUESDAY AND WEDNESDAY. DRY WEATHER MAY RETURN THURSDAY AND  
FRIDAY. WE WILL BE WATCHING A POTENTIAL COASTAL STORM THAT COULD  
CHANGE THAT THURSDAY FORECAST.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
115 PM UPDATE...  
 
AT 1 PM COLD FRONT WAS ON THE VERGE OF MOVING ACROSS THE OUTER  
CAPE AND NANTUCKET. OTHERWISE POST FRONTAL AIRMASS HAS  
OVERSPREAD THE REGION WITH TEMPS FALLING RAPIDLY INTO THE 20S  
AND 30S REGIONWIDE ON GUSTY WNW WINDS UP TO 35 MPH. THIS IS  
RESULTING IN WIND CHILLS IN THE TEENS AND 20S. THE GUSTY WNW  
WINDS AND RAPID DRYING POST FRONTAL AIRMASS HAS ENDED THE FLASH  
FREEZE THREAT. THEREFORE HAVE EXPIRED THE WINTER WEATHER  
ADVISORY AND WILL LET THE SPS EXPIRE ON ITS OWN AT 19Z.  
 
HYDRO...  
 
CANCELLED THE FLOOD WATCH GIVEN RAINFALL HAS ENDED. HOWEVER MANY  
RIVERS/STREAMS ARE IN FLOOD GIVEN ICE JAMS AND RISING WATER  
LEVELS. PLEASE REFER TO OUR FLOODING WARNINGS AND STATEMENTS FOR  
ADDITIONAL INFORMATION.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/
 
 
TONIGHT...  
 
VERY COLD AIR WILL BE USHERED IN ON NORTH TO NORTHWEST WINDS.  
ALTHOUGH WE WON/T BE EXTREMELY COLD AT 850 MB THIS AIRMASS WILL COME  
DOWN SHALLOW AND EXPECT OVERNIGHT LOW TEMPS TO MAINLY BE IN THE  
SINGLE DIGITS TO LOWER TEENS IN MOST LOCATIONS. WE MAY EVEN FLIRT  
WITH WIND CHILL ADVISORY CONDITIONS ALONG THE EAST SLOPES  
OF THE BERKS...BUT IT WAS TOO MARGINAL TO ISSUE AT THIS TIME.  
MEANWHILE ON THE OUTER-CAPE...NNW WINDS MAY ALLOW  
FOR SOME OCEAN EFFECT SNOW SHOWERS TO DEVELOP OVERNIGHT BUT WITH  
ACCUMS OF ONLY A DUSTING TO LESS THAN 1 INCH ARE EXPECTED.  
 

 
   
LONG TERM /SUNDAY THROUGH FRIDAY/
 
 
HIGHLIGHTS...  
 
- COOL AND MAINLY DRY EXCEPT LIGHT SNOW ACROSS EXTREME SE MA.  
 
- ADVISORY OR EVEN WINTER STORM SNOW POSSIBLE TUE INTO EARLY  
THU DEPENDING ON TRACK.  
 
- SEASONABLE LATE WEEK.  
 
OVERVIEW AND MODEL PREFERENCES...  
THE FORMATION OF AN UPSTREAM REX-BLOCK, SIGNALING A STRONG  
POSITIVE PNA, COMBINED WITH BLOCKING CUTOFF HIGH PRES AT H5  
NEAR THE AZORES, ALLOWS MEANDERING CUTOFF TO SETTLE NEAR THE  
GREAT LAKES EARLY IN THE WEEK. THIS IS A PV LOBE ASSOCIATED WITH  
A CURRENT BAFFIN ISLAND VORTEX, SO IT WILL CARRY WITH IT  
ANOTHER ROUND OF ARCTIC INFLUENCED AIR AS IT SETTLES JUST  
UPSTREAM. THE PRIMARY FOCUS ASSOCIATED WITH THIS CUTOFF WILL BE  
A CLIPPER SYSTEM INITIALLY. HOWEVER, THERE IS SOME INDICATION OF  
SECONDARY DEVELOPMENT AS THE TROF BEGINS TO TRANSITION TOWARD A  
NEGATIVE TILT ALONG THE COAST. WHILE THE ECMWF AND MANY OF ITS  
ENSEMBLES LEAD THE CHARGE, THERE REMAINS ENOUGH UNCERTAINTY THAT  
A BLEND OF ENSEMBLES FROM BOTH THE ECENS AND GEFS IS PREFERRED  
AS IT WILL TAKE INTO ACCOUNT BOTH THE MORE PROGRESSIVE AND MORE  
AMPLIFIED SOLUTIONS. AS THE TROF SHIFTS ENE, WILL MAINTAIN THIS  
BLEND INTO THE WEEKEND.  
 
DETAILS...  
 
SUN THROUGH MON...  
ARCTIC AIRMASS ONCE AGAIN SETTLES JUST TO THE W OF NEW ENGLAND,  
BUT NOT WITHOUT ITS IMPACTS. H92 TEMPS DIP AS LOW -13C BY EARLY  
MON MORNING. THIS SUGGEST COOL HIGHS EACH DAY, MAINLY IN THE  
20S, ALTHOUGH WITH HIGH PRES CRESTING WIND CHILLS SHOULD BE  
LIMITED. OVERNIGHT LOWS, HOWEVER ARE PRIMED FOR RADIATIONAL  
COOLING, BUT WILL BE MITIGATED BY THE NOW LACK OF A SNOWPACK.  
STILL WILL LIKELY SEE MINS FALL AS LOW AS THE SINGLE DIGITS IN  
SHELTERED VALLEYS TO THE TEENS ELSEWHERE. STRONG SUBSIDENCE IS  
IMPLIED IN SOUNDINGS, WHICH SUGGESTS MAINLY DRY CONDITIONS. H85  
TEMPS ARE WARMER UNDER THIS INVERSION THAN TEMPS BELOW. WITH NNW  
FLOW GRADUALLY SHIFTING TOWARD THE NNE, THE DELTA-T VALUES FROM  
SST TO H85 HOVERS AROUND 15C, WHILE TO H9, IT IS CLOSER TO 20C.  
THEREFORE, ALTHOUGH SHALLOW WILL LIKELY SEE LIGHT (GIVEN ONLY  
MOISTURE IS AT THE TOP OF THE MIXED LAYER) SNOW SHOWERS ACROSS  
MAINLY THE OUTER PORTIONS OF CAPE COD AND POSSIBLY PLYMOUTH  
COUNTY SUN NIGHT INTO MON AS THE WINDS TAKE ON A SLIGHT E  
COMPONENT. ACCUMS SHOULD WILL REMAIN LIGHT.  
 
TUE INTO THU...  
AS CUTOFF SETS UP NEAR THE GREAT LAKES AND ITS ATTENDANT  
LONGWAVE TROF CONTINUES TO DIG, THE FINAL DEPTH AND TILT WILL  
ULTIMATELY DETERMINE THE POSSIBILITY OF SECONDARY COASTAL  
DEVELOPMENT NEAR THE MID ATLANTIC, AFTER A WEAKENING CLIPPER  
IMPACTS THE REGION. AT THIS TIME, ENSEMBLE LOW LOCATIONS FOR THE  
POTENTIAL COASTAL LOW RANGE FROM NON-EXISTENT, TO AN INSIDE  
RUNNER TO CLOSE TO BERMUDA, WITH SOME CLUSTERING NEAR THE 40/70  
BENCHMARK. HOWEVER, THIS MUCH SPREAD IS LIKELY TO CONTINUE INTO  
SUN, UNTIL THE PV ANOMALY CURRENTLY WRAPPED UP THE ARCTIC  
BECOMES BETTER SAMPLED. THE CLIPPER DOES INGEST SOME MOISTURE ON  
TUE AS IT APPROACHES THE ATLANTIC. THIS DOES YIELD DECENT  
MOISTURE IN THE DGZ, HOWEVER OVERALL LIFT IS WEAK, SO SLRS ARE  
UNLIKELY TO BE MAXIMIZED. SO A MORE PROGRESSIVE SOLUTION  
FAVORED BY THE GFS, WITH QPF RANGING ONLY BETWEEN 0.1-0.25  
INCHES COULD STAY BELOW ADVISORY CRITERIA. MEANWHILE, THE MORE  
ROBUST SOLUTION WOULD QUICKLY FOLLOW THE CLIPPER WITH INFLUENCE  
OF COASTAL LOW PRES WED-THU WITH BETTER LIFT IN THE DGZ AND  
OVERALL MORE LATENT-HEAT ENERGY. THERE IS SOME PRECEDENT FOR  
THIS SOLUTION GIVEN SOME OF THE ENSEMBLES AND OVERALL  
AMPLIFICATION OF THE PATTERN, AND SHOULD IT VERIFY, IT HAS  
CLOSER TO 0.5-1.00 INCHES OF QPF WHICH MAY WARRANT WINTER  
STORMS. TOO EARLY TO CALL ON TOTALS AT THIS TIME, ESPECIALLY  
SINCE THE MORE AMPLIFIED SOLUTION ALSO INTRODUCES WARMER AIR  
(H92 TEMPS AVERAGE +3C ACROSS SE MA). ELSEWHERE, WITH H92 TEMPS  
GENERALLY BETWEEN  
-2C AND -6C, MAINLY SN IS EXPECTED, ALONG WITH HIGHS CLOSER TO  
SEASONAL NORMALS IN THE UPPER 20S TO LOW 30S AND LOWS IN THE  
TEENS TO MID 20S. SOMETHING TO WATCH ESPECIALLY LATE WEEKEND  
INTO MON.  
 
FRI INTO THE WEEKEND...  
ENOUGH BREAKDOWN OF THE UPSTREAM REX TO SIGNAL A TRANSITION. AS  
OPENING WAVE TRANSITIONS E AND MODERATES, TEMPS LOOK TO RETURN  
TO MORE SEASONABLE LEVELS, ALONG WITH MAINLY DRY AIR.  
 

 
   
AVIATION /18Z SATURDAY THROUGH THURSDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TONIGHT/...  
 
1815Z UPDATE...  
 
THRU 00Z...HIGH CONFIDENCE.  
 
VFR AND DRY WEATHER. WNW WINDS UP TO 30 KT WILL SHIFT TO THE NNW  
TOWARD 00Z AND DECREASE IN SPEED.  
 
AFTER 00Z...HIGH CONFIDENCE.  
 
VFR AND DRY WEATHER WITH N WINDS 10-20 KT, HIGHEST WINDS OVER  
CAPE COD AND ISLANDS. ALSO THIS IS WHERE MVFR CIGS WILL DEVELOP  
ALONG WITH SCATTERED OCEAN EFFECT SNOW SHOWERS TONIGHT.  
 
SUNDAY...HIGH CONFIDNECE.  
 
VFR AND DRY WEATHER EXCEPT MVFR IN SCATTERED SNOW SHOWERS OVER  
CAPE COD AND NANTUCKET. MODEST NORTH WINDS 10-20 KT.  
 
SUNDAY NIGHT...MODERATE CONFIDENCE. SOME UNCERTAINTY ON TIMING  
AND AREAL COVERAGE OF MVFR CONDITIONS.  
 
MVFR IN SCATTERED SNOW SHOWERS CONTINUES OVER CAPE COD AND  
NANTUCKET. HOWEVER AS WINDS SHIFT FROM N TO NE THESE MVFR  
CONDITIONS SPREAD WESTWARD INTO EASTERN MA TOWARD DAYBREAK MON.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF THRU SUNDAY THEN SOME  
UNCERTAINTY IF SNOW SHOWERS MAKE IT WESTWARD INTO LOGAN SUN NGT.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /MONDAY THROUGH WEDNESDAY/...  
 
MARTIN LUTHER KING JR DAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE  
ALONG EXTREME SOUTHEAST MA IN SOME LIGHT SHSN. BREEZY.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE ALONG EXTREME  
SOUTHEAST MA IN SOME LIGHT SHSN.  
 
TUESDAY: MVFR/IFR CONDITIONS POSSIBLE. CHANCE SN.  
 
TUESDAY NIGHT: MAINLY IFR, WITH LOCAL MVFR POSSIBLE. CHANCE SN.  
 
WEDNESDAY: MAINLY VFR, WITH AREAS IFR POSSIBLE. BREEZY. CHANCE  
SN.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TONIGHT/...  
 
TODAY...STRONG COLD FRONT CROSS THE WATERS LATER THIS MORNING  
AND EARLY AFTERNOON WITH NW WIND GUSTS AROUND 25 KNOTS.  
 
TONIGHT...HIGH CONFIDENCE. NNW WIND GUSTS AROUND 20 KNOTS IN THE  
COLD AIR ADVECTION PATTERN...BUT SEAS WILL REMAIN ABOVE SMALL CRAFT  
THRESHOLDS EVEN THOUGH SWELL WILL BE ON THE DOWNWARD TREND.  
 
OUTLOOK /SUNDAY THROUGH WEDNESDAY/...  
 
SUNDAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS. LOCAL  
VISIBILITY 1 TO 3 NM.  
 
SUNDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. SLIGHT  
CHANCE OF SNOW SHOWERS. LOCAL VISIBILITY 1 TO 3 NM.  
 
MARTIN LUTHER KING JR DAY: WINDS LESS THAN 25 KT. SEAS UP TO  
5 FT. SLIGHT CHANCE OF SNOW SHOWERS. AREAS OF VISIBILITY 1 TO  
3 NM.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
TUESDAY: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE OF  
SNOW, CHANCE OF RAIN. VISIBILITY 1 TO 3 NM.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT. CHANCE  
OF SNOW. VISIBILITY 1 TO 3 NM.  
 
WEDNESDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT. CHANCE OF SNOW. VISIBILITY 1 TO 3 NM.  
 

 
   
CLIMATE
 
 
RECORD HIGH TEMPS SET YESTERDAY:  
 
PVD 62 IN 2018  
BDL 60 IN 2018  
ORH 59 IN 2018  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 7 AM EST SUNDAY FOR ANZ231>235-237-  
250-251-254>256.  
SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ230-  
236.  
 

 
 

 
SYNOPSIS...FRANK/DOODY  
NEAR TERM...NOCERA  
SHORT TERM...FRANK  
LONG TERM...DOODY  
AVIATION...NOCERA/DOODY  
MARINE...FRANK/DOODY  
CLIMATE...  
 
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