932  
FXUS61 KBOX 132335  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
635 PM EST SAT JAN 13 2018  
   
SYNOPSIS
 
 
ARCTIC HIGH PRESSURE OVER THE HIGH PLAINS BUILDS INTO NEW  
ENGLAND THROUGH MONDAY NIGHT, PROVIDING A RETURN TO COLDER THAN  
NORMAL TEMPERATURES. LOW PRESSURE MAY BRING SNOW TO THE REGION  
FROM TUESDAY INTO WEDNESDAY NIGHT FOLLOWED BY ANOTHER BURST OF  
COLD WEATHER THURSDAY THROUGH SATURDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
 
 
630 PM UPDATE...  
 
TWO AREAS OF CLOUDS ON THE SATELLITE. ONE IS MOVING SOUTH ACROSS  
THE EASTERN WATERS AND ACROSS PLYMOUTH AND CAPE COD. THESE  
CLOUDS WILL SWEEP SOUTH ACROSS THE ISLANDS EARLY TONIGHT, WITH  
SUBSEQUENT CLEARING IN ALL AREAS. ANOTHER AREA OF CLOUDS LINGERS  
OVER THE BERKSHIRES, FED BY LAKE-EFFECT MOISTURE OFF LAKE  
ONTARIO. WE CONTINUE TO EXPECT THESE CLOUDS TO DISSIPATE  
OVERNIGHT AS WINDS DIMINISH.  
 
WITH COLDER AIR MOVING IN, AND WITH SUFFICIENT NORTH-NORTHWEST  
WINDS IN PLACE, WE CONTINUE TO EXPECT OCEAN-EFFECT CLOUDS TO  
DEVELOP EAST OF MASSACHUSETTS AND MOVE SOUTH INTO CAPE COD  
EITHER OVERNIGHT OR FIRST THING SUNDAY MORNING.  
 
ASIDE FROM EARLY NIGHT CLOUDS, NO SIGNIFICANT CHANGES TO THE  
FORECAST AT THIS TIME.  
 
PREVIOUS DISCUSSION...  
 
1042 MB ARCTIC HIGH PRES OVER THE HIGH PLAINS LATE THIS AFTERNOON  
BUILDS EAST TONIGHT. NOW GIVEN THE LACK OF SNOW COVER OVER NEW  
ENGLAND AND UPSTREAM THIS AIRMASS MODIFIES SOMEWHAT AS IT APPROACHES  
AND THEN ACROSS THE AREA WITH 925 MB AND 850 MB TEMPS LOWERING TO  
ABOUT -10C BY SUNDAY MORNING. THIS SUPPORTS LOW TEMPS TONIGHT IN THE  
TEENS ACROSS MUCH OF RI AND EASTERN MA WITH SINGLE DIGITS OVER MUCH  
OF NORTHERN CT AND WESTERN-CENTRAL MA. HOWEVER IT WILL FEEL COLDER  
WITH A MODEST NNW WIND PROVIDING WIND CHILLS FROM ABOUT -5F TO +5F.  
 
CLOUDS AND FLURRIES ACROSS WESTERN MA WILL COME TO AND THIS EVENING  
AND LOW LEVEL FLOW SHIFTS FROM WNW TO NNW, CUTTING OFF LOW LEVEL  
MOISTURE FROM THE LAKE ONTARIO.  
 
WATCHING AREA OF STRATO-CU CLOUDS OVER THE SEACOAST OF NH/ME SLIDING  
SOUTHWARD IN DEVELOPING NORTHERLY FLOW. THESE CLOUDS WILL CLIP  
EASTERN ESSEX COUNTY, POSSIBLY BOSTON AREA FOR A BRIEF TIME THIS  
EVENING AND THEN DOWN ACROSS CAPE COD.  
 
REGARDING OCEAN EFFECT SNOW POTENTIAL...AS WINDS BECOME NNW LATER  
THIS EVENING AND LOW LEVEL CAA INCREASES, LOW LEVEL LAPSE RATES WILL  
INCREASE GIVING WAY TO BANDS OF OCEAN EFFECT SNOW SHOWERS ACROSS MA  
BAY, CAPE COD BAY AND THE ADJACENT OCEAN WATERS ACROSS THE OUTER  
CAPE COD AND POSSIBLY NANTUCKET. SNOW SHOWERS WILL BE VERY BANDED  
(NARROW BANDS) WITH SOME TOWNS RECEIVING A DUSTING OR A COATING  
WHILE NEIGHBORING LOCATIONS RECEIVE LITTLE IF ANY SNOWFALL. USED  
ARW/NMM AND HREF TO DERIVE QPF/SNOW ACCUMS.  
 

 
   
SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/
 
 
415 PM UPDATE...  
 
SUNDAY...  
 
COLDER THAN NORMAL TEMPS CONTINUE WITH ARCTIC 1040 MB HIGH PRES OVER  
NY STATE. 925 MB TEMPS LOWER TO -14C. THIS WILL ONLY SUPPORT HIGHS  
IN THE 20S WITH UPPER TEENS ACROSS THE HIGH TERRAIN. A MODEST  
NORTHERLY WIND COMBINED WITH THIS FRIGID TEMPS WILL YIELD WIND  
CHILLS IN THE SINGLE DIGITS AND TEENS. MOSTLY CLEAR SKIES SUNDAY BUT  
GIVEN THE LOW JAN SUN ANGLE AND ARCTIC AIRMASS WILL CALL IT  
INEFFECTIVE SUNSHINE.  
 
CAPE COD AND NANTUCKET MAY REMAIN OVERCAST GIVEN THE MOIST NNE WIND  
ACROSS THE REGION ALONG WITH SCATTERED OCEAN EFFECT SNOW SHOWERS  
CONTINUING, BUT BECOMING MORE FRAGMENTED FROM DIURNAL HEATING  
PROVIDING ENOUGH DISRUPTION TO THE LOW LEVEL CIRCULATION.  
 
SUNDAY NIGHT...  
 
DRY BUT FRIGID WITH ARCTIC HIGH PRES ANCHORED ACROSS NEW ENGLAND.  
RIDGE AXIS ACROSS THE INTERIOR AND WILL PROVIDE IDEAL RADIATIONAL  
COOLING. THUS LEANED TOWARD THE COLDER MOS TEMPS HERE WITH LOWS ZERO  
TO MINUS 5 ACROSS WESTERN MA. NOT MUCH OF A WIND CHILL HERE GIVEN  
THE LIGHT WINDS. MUCH OF THE REGION WILL SEE MINS IN THE SINGLE  
DIGITS TO ABOUT 10 DEGS IN BOSTON AND PROVIDENCE URBAN AREAS TO  
TEENS ALONG THE SOUTH COAST.  
 
NOT AS COLD HERE GIVEN NNE WINDS OFF THE OCEAN. HOWEVER THIS WILL  
CREATE LOWER WIND CHILLS AND ALSO OCEAN EFFECT SNOW SHOWERS  
SPREADING MORE ONSHORE INTO PLYMOUTH COUNTY AND POSSIBLE INTO BOSTON  
AND THE NORTH SHORE. COULD BE SOME MINOR ACCUMULATIONS INCLUDING THE  
RT-3 CORRIDOR OF PLYMOUTH COUNTY. WILL HAVE TO WATCH THIS GOING INTO  
THE MONDAY MORNING COMMUTE. NOT A LOT OF SNOW BUT PERHAPS A COATING  
TO AN INCH, ENOUGH FOR SNOW COVERED ROADS. AGAIN WILL WATCH TRENDS  
ON HI RES MODELS. MAY NOT BE ENOUGH FOR A WINTER WEATHER ADVISORY  
BUT PERHAPS A SPECIAL WEATHER STATEMENT TO INCREASE PUBLIC AWARENESS  
ON SOME SLIPPERY TRAVEL SUN NIGHT INTO MON MORNING.  
 

 
   
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 /23Z 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/...  
 
TONIGHT... HIGH CONFIDENCE.  
 
VFR AND DRY WEATHER WITH N WINDS 10-20 KT, HIGHEST  
WINDS OVER CAPE COD AND ISLANDS. ONE CLOUD DECK MOVES OVER THE  
CAPE AND ISLANDS EARLY TONIGHT, WITH CLEARING BY MIDNIGHT. MORE  
CLOUDS WILL DEVELOP OVER MASSACHUSETTS BAY AS COLD AIR FLOWS IN.  
THIS WILL GENERATE MORE CLOUDS WITH MVFR CIGS, WHICH WILL MOVE  
INTO CAPE COD AND ISLANDS EITHER LATE TONIGHT OR SUNDAY MORNING.  
SCATTERED OCEAN EFFECT SNOW SHOWERS MAY BE ASSOCIATED WITH THESE  
LATE CLOUDS AND MAY PRODUCE 3-4 MILE VSBYS.  
 
SUNDAY...HIGH CONFIDENCE.  
 
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/...  
 
TONIGHT...  
 
WNW WINDS UP TO 25 KT EARLY SLACKENING A BIT AS WINDS TURN FROM  
THE NNW DURING THE NIGHT. SNOW SHOWERS DEVELOP 11 PM TO 2 AM  
ACROSS EASTERN MA WATERS WITH SOME LOWER VSBYS. AS WINDS BECOME  
NORTHERLY AND COMBINE WITH LEFTOVER SOUTHERLY SWELLS, SEAS WILL  
BECOME VERY CHAOTIC AND CHOPPY. SOME LIGHT FREEZING SPRAY  
POSSIBLE.  
 
SUNDAY...  
 
NNE WINDS 10-20 KT WITH ARCTIC HIGH PRES OVER NY STATE. ROUGH SEAS  
ACROSS THE EASTERN MA WATERS. SCATTERED SNOW SHOWERS LOWER VSBY AT  
TIMES OVER EASTERN MA WATERS. SOME LIGHT FREEZING SPRAY POSSIBLE.  
 
SUNDAY NIGHT...  
 
NNE WINDS INCREASE TO 15-20 KT WITH ARCTIC HIGH PRES ANCHORED OVER  
SOUTHEAST QUEBEC. SNOW SHOWERS OVER EASTERN MA WATERS LOWERS VSBY AT  
TIMES. SOME LIGHT FREEZING SPRAY POSSIBLE.  
 
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.  
 

 
   
HYDROLOGY
 
 
HEAVY RAINFALL AND COMPLETE MELTING OF OUR SNOWPACK RESULTED IN  
SIGNIFICANT RISES ON RIVERS AND STREAMS. FLOOD WARNINGS ARE IN  
EFFECT FOR SEVERAL RIVERS (PLEASE REFER TO OUR FLOOD STATEMENTS AND  
WARNINGS). IN ADDITION, THE WARM TEMPS HAVE LED TO NUMEROUS ICE  
JAMS. MUCH COLDER AIR IS RUSHING INTO SNE AND TEMPS ARE EXPECTED TO  
FALL INTO THE SINGLE NUMBERS AND LOWER TEENS TONIGHT WHICH WILL  
EVENTUALLY END THE RUNOFF. FOR DETAILS ON SPECIFIC AREA RIVERS,  
INCLUDING OBSERVED AND FORECAST RIVER STAGES, PLEASE VISIT THE  
ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON OUR  
WEBSITE.  
 

 
   
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/NOCERA  
NEAR TERM...WTB/NOCERA  
SHORT TERM...NOCERA  
LONG TERM...WTB  
AVIATION...WTB/NOCERA  
MARINE...WTB/NOCERA  
HYDROLOGY...  
 
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