605  
FXUS61 KBOX 132043  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
343 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. AN ADDITIONAL DISTURBANCE MAY MERGE  
WITH THIS SYSTEM, EXTENDING THE THE CHANCE OF SNOW INTO  
WEDNESDAY NIGHT. DRY WEATHER RETURNS FOR THE LATE WEEK.  
 

 
   
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 SUNDAY NIGHT/
 
 
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 /MONDAY THROUGH SATURDAY/
 
 
BIG PICTURE...  
 
LONGWAVE PATTERN THROUGH NEXT FRIDAY SHOWS TROUGH OVER THE EASTERN  
USA AND A RIDGE OVER THE WESTERN USA. THIS TRENDS TO A FLATTER FLOW  
BY NEXT SATURDAY.  
 
SHORTWAVE PATTERN SHOWS A SHORTWAVE OVER THE CANADIAN ARCTIC  
SWEEPING SOUTH THIS WEEKEND AND THEN DIGGING OVER THE GREAT LAKES.  
THIS TROUGH THEN SWEEPS EAST, CROSSING NEW ENGLAND MIDWEEK. QUIETER  
FLOW FOR FRIDAY-SATURDAY WITH BUILDING HEIGHTS.  
 
MODEL MASS FIELDS ARE SIMILAR THROUGH TUESDAY, BUT CONTINUE TO SHOW  
DIFFERENCES IN THE EVOLUTION OF THE EASTERN TROUGH WEDNESDAY-  
THURSDAY. THE GFS AND GGEM ARE MORE PROGRESSIVE WITH THE TROUGH, THE  
ECMWF HOLDS IT CLOSER TO THE COAST. THE GFS AND ECMWF BOTH DEVELOP  
SECONDARY LOWS LATE WEDNESDAY, BUT THE GFS AND 12Z ECMWF CARRY IT  
WELL OFFSHORE WHILE THE 00Z ECMWF KEPT IT CLOSE TO THE COAST.  
ENSEMBLE RUNS SHOW SOLUTIONS IN BETWEEN. THE VARIATIONS BETWEEN  
MODELS AND BETWEEN MODEL RUNS DO NOT GENERATE CONFIDENCE. WE REMAIN  
AGNOSTIC BETWEEN THE TWO OPPOSING SOLUTIONS AT THIS TIME.  
 
CONFIDENCE IN THE FORECAST REMAINS HIGH THROUGH TUESDAY NIGHT, THEN  
LOW WEDNESDAY-THURSDAY AND MODERATE FRIDAY-SATURDAY.  
 
DETAILS...  
 
MONDAY...  
 
TWO WEATHER SYSTEMS...HIGH PRESSURE CENTERED NORTH OF MAINE AND A  
STORM WELL OUT TO SEA. THESE WILL COMBINE TO BRING A NORTHEAST  
SURFACE FLOW OVER SOUTHERN NEW ENGLAND. SURFACE WIND SPEEDS OF 10-15  
KNOTS AND MOISTURE BELOW 850 MB SUGGEST OCEAN EFFECT CLOUDS AND  
SCATTERED SNOW SHOWERS MOVING ASHORE OVER CAPE COD AND MUCH OF EAST  
COASTAL MA. AN INCH OF SNOW POSSIBLE IN THE MORE SIGNIFICANT  
SNOW SHOWERS. CLOUDS MAY EXTEND TO RI AND CENTRAL MASS.  
 
RIDGING FROM THE HIGH EXTENDS OVER SOUTHERN NEW ENGLAND AND SHOWS A  
COLD-AIR DAMMING SIGNAL. SO TEMPERATURES REMAIN COLD WITH 950 MB  
TEMPS SUPPORTING MAX SFC TEMPS MAINLY IN THE 20S AND LOW 30S.  
 
CLOUDS AND A LIGHT FLOW WILL KEEP TEMPS A LITTLE LESS COLD THAT THE  
PREVIOUS NIGHT. BASED ON FORECAST DEW POINTS, WE WELL GO WITH MIN  
TEMPS IN THE TEENS INLAND AND 20S ALONG THE COAST.  
 
TUESDAY-WEDNESDAY-THURSDAY...  
 
LOW PRESSURE FROM THE CANADIAN ARCTIC WILL SWEEP SOUTH TO THE GREAT  
LAKES MONDAY, THEN TURN EAST AND CROSS NEW ENGLAND. THIS SYSTEM WILL  
DRAW ON PRECIP WATER VALUES ON THE HIGH SIDE OF NORMAL BUT NOT BY  
MUCH. EXPECT TEMPERATURES WOULD SUGGEST LIGHT SNOW. QPF OF ROUGHLY  
0.25 INCHES IS POSSIBLE, WHICH WOULD SUPPORT A FEW INCHES SNOW. AN  
ADVISORY MAY EVENTUALLY BE NEEDED FOR THIS EVENT.  
 
AS NOTED ABOVE, THE ECMWF AGREES WITH CONSENSUS ON BRINGING THIS  
FIRST SYSTEM THROUGH ON TUESDAY-EARLY WEDNESDAY. THE 00Z ECMWF HAS A  
SLOWER-MOVING UPPER TROUGH WHICH PLACES THE SUPPORTING UPPER JET  
ALONG THE EAST COAST DURING WEDNESDAY WITH A FAVORABLE LEFT EXIT  
REGION OF ONE JET SEGMENT OVER THE CAROLINA COAST. THIS DEVELOPS A  
COASTAL LOW THAT MOVES UP THE COAST AND THEN NEAR THE 40N/70W  
BENCHMARK WEDNESDAY NIGHT. THE GFS AND 12Z ECMWF SHOW SIMILAR  
CYCLOGENESIS, BUT MUCH FARTHER EAST OF NORTH CAROLINA...NEAR 70W  
LONGITUDE...AND TRACK THE STORM TOO FAR OFFSHORE TO BRING ANY PCPN  
TO SOUTHERN NEW ENGLAND EXCEPT POSSIBLY CAPE/ISLANDS. THE 00Z ECMWF  
SCENARIO WOULD BRING A SECOND BURST OF PCPN LATE WEDNESDAY/WEDNESDAY  
NIGHT ENDING THURSDAY MORNING WITH ADDITIONAL SNOW ACCUMULATION  
POSSIBLE. THE GFS/12Z ECMWF SCENARIO WOULD MEAN DRY WEATHER LATE  
WEDNESDAY THROUGH THURSDAY. WE ARE NOT CONFIDENT ON EITHER SOLUTION  
AT THIS TIME, BUT WILL KEEP OUR OPTIONS OPEN BY MENTIONING POPS  
THROUGH WEDNESDAY NIGHT.  
 
FRIDAY-SATURDAY...  
 
HIGH PRESSURE OVER THE SOUTHERN USA BUILDS NORTH AND BRINGS DRY  
WEATHER TO SOUTHERN NEW ENGLAND. A WEAK SHORTWAVE RACES ACROSS  
DURING THIS TIME AND COULD BRING A PERIOD OF CLOUDS BUT NO  
PRECIPITATION. TEMPERATURES AT ALL LEVELS TREND WARMER WITH  
POTENTIAL FOR ABOVE NORMAL MAX TEMPS AND MIN TEMPS DURING THIS TIME.  
 

 
   
AVIATION /21Z SATURDAY THROUGH THURSDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SUNDAY NIGHT/...  
 
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 THURSDAY/...  
 
MARTIN LUTHER KING JR DAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE  
IN EASTERN MASSACHUSETTS. BREEZY. CHANCE SHSN.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE IN EASTERN  
MASSACHUSETTS.  
 
TUESDAY THROUGH TUESDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE.  
CHANCE SN.  
 
WEDNESDAY AND WEDNESDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE,  
IMPROVING TO VFR DURING WEDNESDAY NIGHT. BREEZY. CHANCE SN.  
 
THURSDAY: VFR. BREEZY.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SUNDAY NIGHT/...  
 
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 /MONDAY THROUGH THURSDAY/...  
 
MARTIN LUTHER KING JR DAY: WINDS LESS THAN 25 KT. SEAS UP TO  
5 FT. CHANCE OF SNOW SHOWERS. VISIBILITY 1 TO 3 NM.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. SLIGHT  
CHANCE OF SNOW SHOWERS. AREAS OF VISIBILITY 1 TO 3 NM.  
 
TUESDAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS. SLIGHT  
CHANCE OF SNOW. AREAS OF VISIBILITY 1 TO 3 NM.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE  
OF SNOW. VISIBILITY 1 TO 3 NM.  
 
WEDNESDAY THROUGH WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. SEAS  
UP TO 5 FT. CHANCE OF SNOW. VISIBILITY 1 TO 3 NM.  
 
THURSDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 30 KT. LOCAL ROUGH SEAS. SLIGHT CHANCE OF SNOW. AREAS OF  
VISIBILITY 1 TO 3 NM.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR  
ANZ230>237-250-251-254>256.  
 

 
 

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