894  
FXUS61 KBOX 130238  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
938 PM EST FRI JAN 12 2018  
   
SYNOPSIS
 
 
MULTIPLE LOW PRESSURE AREAS ALONG AN APPROACHING COLD FRONT WILL  
BRING HEAVY RAINFALL, POTENTIAL FLOODING AND GUSTY WINDS  
THROUGH TONIGHT. A SHARP TURN TO MUCH COLDER WEATHER OCCURS  
RAPIDLY SATURDAY WHICH WILL ALLOW RAIN TO END AS A BIT OF LIGHT  
FREEZING RAIN AND SLEET, BUT MORE IMPORTANTLY A FLASH FREEZE IS  
EXPECTED ACROSS ALL OF SOUTHERN NEW ENGLAND. 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 AM SATURDAY MORNING/
 
 
935 PM UPDATE...  
 
***PERIODS OF HEAVY RAIN OVERNIGHT ALONG WITH SIGNIFICANT URBAN  
STREET FLOODING***  
 
***RAIN CHANGING TO FREEZING RAIN/SLEET ACROSS WESTERN MA  
TOWARDS 12Z***  
 
1) HEAVY RAIN/FLOODING...  
 
ANOMALOUS AIRMASS IN PLACE WITH PWATS 4-5 S.D. ABOVE NORMAL  
ALONG WITH STRONG FORCING AHEAD OF A COLD FRONT WILL CONTINUE TO  
RESULT IN PERIODS OF HEAVY RAINFALL OVERNIGHT. RAINFALL TOTALS  
OF 2-3 INCHES WITH LOCALIZED 4 INCH AMOUNTS ARE POSSIBLE. THE  
MAIN FOCUS FOR THE HEAVIEST RAIN SHOULD BE ACROSS EASTERN MA/RI  
WHERE A POTENT LOW LEVEL JET TAPS THIS ANOMALOUS AIRMASS. GIVEN  
THE STRONG FORCING IN PLACE AND MUCAPES OF A FEW HUNDRED  
J/KG...A RUMBLE OR TWO OF THUNDER CAN NOT BE RULED OUT.  
 
THE RESULT OF THIS HEAVY RAINFALL AND THE RAPID SNOWMELT WILL  
RESULT IN A CONTINUED SIGNIFICANT URBAN STREET FLOODING THREAT.  
ALSO...SOME MINOR RIVER/STREAM FLOODING IS ALSO EXPECTED.  
 
2) STRONG WINDS ON THE COASTAL PLAIN:  
 
IMPRESSIVE 925 MB LOW LEVEL JET WILL INCREASE FURTHER TOWARDS  
MIDNIGHT TO OVER 80 KNOTS ALONG THE SOUTHEAST NEW ENGLAND COAST.  
DESPITE THE INVERSION IN PLACE...SOME OF THOSE WINDS MAY BE  
BROUGHT DOWN IN HEAVIER RAIN AND ANY POTENTIAL CONVECTION.  
WHILE LLJ IS NOT QUITE AS STRONG IN THE BOS-PVD  
CORRIDOR...MILDER TEMPS AROUND 60 WILL ALLOW FOR BETTER MIXING.  
THEREFORE...WIND ADVISORY CONTINUES THROUGH DAYBREAK ALONG AND  
SOUTHEAST OF THE BOSTON TO PROVIDENCE CORRIDOR. THIS IS FOR  
SOUTHWEST WIND GUSTS OF 40 TO 50 MPH AT TIMES.  
 
3) DENSE FOG ALONG THE SOUTH COAST/CAPE/ISLANDS:  
 
OPTED TO EXTEND THE DENSE FOG ADVISORY THROUGH DAYBREAK ACROSS  
THE SOUTH COAST, CAPE AND ISLANDS. VERY HIGH DEWPOINT AIR  
CONTINUES TO STREAM OVER THE RELATIVELY WARM OCEAN. THIS WILL  
RESULT IN CONTINUED FOG...WHICH WILL BE DENSE AT TIMES.  
 
4) RAIN CHANGING TO A BIT OF ICE TOWARDS 12Z ACROSS WESTERN MA:  
 
IMPRESSIVE SURGE OF VERY COLD AIR WILL WORK INTO WESTERN MA BY  
12Z BEHIND A STRONG COLD FRONT. MANY LOCATIONS WITH CURRENT  
TEMPS IN THE UPPER 50S TO NEAR 60 WILL SEE READINGS DROP BELOW  
FREEZING IN A MATTER OF JUST A COUPLE HOURS IN WESTERN MA. STILL  
SOME TIMING DIFFERENCES...BUT THE COLD AIR COMES IN INITIALLY  
SHALLOW ENOUGH FOR PTYPE TO CHANGE TO SOME LIGHT FREEZING  
RAIN/SLEET IN THIS REGION WITH ENOUGH RESIDUAL LOW LEVEL  
MOISTURE. THE BIGGER ISSUE WILL BE A FLASH FREEZE THAT WILL  
SWEEP ACROSS THE REST OF THE REGION SATURDAY WITH RAPIDLY  
FALLING TEMPS.  
 

 
   
SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/
 
 
***FLASH FREEZE ALL SNE ALONG WITH A BRIEF PERIOD OF FREEZING  
RAIN/SLEET, ESPECIALLY INTERIOR***  
 
COLD FRONT MOVES THROUGH REST OF SNE SAT MORNING FOLLOWED BY A  
RAPID TEMP DROP. BEST CHANCE FOR A PERIOD OF FREEZING RAIN AND  
POSSIBLY SOME SLEET BEFORE THE PRECIP ENDS WILL BE IN THE  
INTERIOR. LOWER CHANCES FOR FREEZING RAIN TOWARD THE COAST AS  
GUIDANCE SHOWS PRECIP MOVING OUT AS COLDER AIR RUSHES IN. IT  
WILL BE A RACE BETWEEN THE COLDER MOVING IN AND PRECIP MOVING  
OUT. HOWEVER, THE GREATER CONCERN IS THE FLASH FREEZE  
POTENTIAL AS TEMPS RAPIDLY DROP FROM THE 50S TO BELOW FREEZING  
IN ABOUT A 3 HOUR PERIOD. EXACT TIMING OF THE COLDER AIR IS A  
BIT UNCERTAIN DUE TO TIMING DIFFERENCES IN THE MODELS AND FLASH  
FREEZE TIMING MAY BE OFF BY A FEW HOURS. OUR FORECAST HAS THE  
FLASH FREEZE OCCURRING DURING THE MORNING IN THE INTERIOR AND  
LATE MORNING INTO EARLY AFTERNOON IN THE COASTAL PLAIN. EVEN  
WITH NW WINDS, THE RAPID TEMP DROP BELOW FREEZING AND LEFTOVER  
WET SURFACES WILL RESULT IN ICY SPOTS DEVELOPING.  
 
TEMPERATURES BY LATE AFTERNOON WILL BE FALLING INTO THE TEENS  
AND 20S.  
 

 
   
LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/
 
 
BIG PICTURE...  
 
LONGWAVE PATTERN THROUGH NEXT FRIDAY SHOWS TROUGH OVER THE EASTERN  
USA AND A RIDGE OVER THE WESTERN USA. SHORTWAVE PATTERN SHOWS A  
SHORTWAVE OVER THE CANADIAN ARCTIC SWEEPING SOUTH THIS WEEKEND AND  
THEN DIGGING OVER THE GREAT LAKES. THIS TROUGH MAINTAINS A  
PROGRESSIVE AXIS THROUGH TUESDAY. THE GFS AND ECMWF SHOW THE TROUGH  
THEN FORMING A CLOSED LOW ALONG THE NE USA COAST WEDNESDAY-THURSDAY.  
 
MODEL MASS FIELDS ARE SIMILAR THROUGH WEDNESDAY MORNING, THEN SHOW  
DIFFERENCES THROUGH FRIDAY. THERMAL FIELDS ALSO ARE SIMILAR THROUGH  
WEDNESDAY MORNING, THEN DIVERGE. CONFIDENCE IS HIGH THROUGH TUESDAY  
NIGHT, THEN LOW-MODERATE THE LATTER HALF OF THE WEEK.  
 
DETAILS...  
 
SATURDAY NIGHT THROUGH MONDAY...  
 
HIGH PRESSURE OVER THE MIDWEST/PLAINS WILL BE IN TRANSITION AS IT  
BUILDS INTO NEW ENGLAND. THE AXIS STARTS THE WEEKEND NNW-SSE, A COLD  
WEATHER SIGNATURE, AND MORPHS TO A NE-SW AXIS SUNDAY BEFORE LIFTING  
OUT THROUGH THE MARITIMES MONDAY. THE DEPARTING RIDGE LEAVES A COLD-  
AIR DAMMING SIGNATURE ACROSS NEW ENGLAND MONDAY NIGHT.  
 
EXPECT DRY WEATHER DURING THIS TIME WITH COLDER-THAN-NORMAL  
TEMPERATURES. TEMPERATURES ARE BORDERLINE FOR OCEAN-EFFECT  
CLOUDS/SNOW. BUT WIND DIRECTION TURNS FROM THE NORTH SUNDAY AND  
NORTHEAST MONDAY. MOISTURE/RH CROSS SECTIONS SHOW INCREASING VALUES  
BELOW 850 MB. NORTH WIND SUPPORTS CLOUDS AND SCATTERED SHOWERS ON  
THE CAPE AND ISLANDS SUNDAY. NORTHEAST WIND SUPPORTS THIS ACROSS  
EAST COASTAL MASS MONDAY. TEMPS IN THE MIXED LAYER SUPPORT MAX SFC  
TEMPS IN THE 20S TO AROUND 30. DRY AIR WILL SUPPORT MIN TEMPS IN THE  
SINGLE NUMBERS AND LOWER TEENS, EXCEPT A LITTLE HIGHER ON THE  
CAPE/ISLANDS.  
 
TUESDAY-WEDNESDAY...  
 
LOW PRESSURE FROM THE CANADIAN ARCTIC WILL SWEEP SOUTH TO THE GREAT  
LAKES MONDAY, THEN TURN EAST AND CROSS NEW ENGLAND ON  
TUESDAY/WEDNESDAY. TIMING OF FAST-MOVING SYSTEMS IS A CHALLENGE,  
ESPECIALLY 4-5 DAYS IN THE FUTURE. THE GFS FAVORS TUESDAY, THE 00Z  
ECMWF FAVORS WEDNESDAY. EXPECT A PERIOD OF LIGHT ACCUMULATING  
SNOW DURING THIS TIME.  
 
THURSDAY-FRIDAY...  
 
LOW-MODERATE CONFIDENCE, BUT THE GFS AND ECMWF SHOW POTENTIAL FOR AN  
UPPER LOW TO CLOSE OFF NEAR THE MID ATLANTIC COAST WITH UPPER SSW  
JET ALONG THE EASTERN USA COAST. THE JET AXIS PLACEMENT FAVORS  
DEVELOPMENT OF A COASTAL LOW OFF THE CAROLINAS. THE GFS AND GGEM  
MAINTAIN ENOUGH OF A PROGRESSIVE PATTERN TO MOVE THE LOW OUT TO SEA,  
WHILE THE ECMWF TURNS THE UPPER FLOW FROM THE SOUTH AND DIRECTS THE  
COASTAL LOW UP THE COAST TO OUTER CAPE COD. THIS LATTER SOLUTION  
SHOWS ENOUGH WARM AIR FOR RAIN IN EASTERN MASS/RI, AND POSSIBLY ALL  
THE WAY TO THE BERKSHIRES. AS IT IS THE MINORITY SOLUTION, WE OPTED  
FOR THE DRIER GFS FORECAST.  
 

 
   
AVIATION /02Z SATURDAY THROUGH WEDNESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SATURDAY/...  
 
TONIGHT...MODERATE CONFIDENCE.  
 
CONDITIONS LOWERING WITH WIDESPREAD IFR/LIFR EXPECTED AS  
ADDITIONAL RAIN OVERSPREADS THE REGION FROM THE SOUTH. RAIN  
CHANGING TO A PERIOD OF FZRA WESTERN MA 09-12Z. SOUTH WIND GUSTS  
TO 40-45 KT THROUGH TONIGHT ACROSS RI AND EASTERN MA WITH WINDS  
LIKELY PEAKING BETWEEN MIDNIGHT AND DAYBREAK SAT. WIDESPREAD  
LLWS.  
 
SATURDAY...MODERATE CONFIDENCE.  
RAIN CHANGES TO A BRIEF PERIOD OF FZRA INTERIOR BEFORE ENDING IN  
THE MORNING. LOW RISK OF BRIEF FZRA MAKING IT INTO THE COASTAL  
PLAIN BEFORE THE PRECIP ENDS. GREATER CONCERN IS FLASH FREEZE AS  
TEMPS RAPIDLY DROP FROM 50S TO BELOW FREEZING IN 2-3 HOURS.  
WIDESPREAD IFR/LIFR IMPROVING TO VFR IN THE AFTERNOON FROM WEST  
TO EAST.  
 
KBOS TERMINAL...MODERATE CONFIDENCE IN TAF.  
 
KBDL TERMINAL...MODERATE CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY NIGHT THROUGH WEDNESDAY/...  
 
SATURDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY.  
SLIGHT CHANCE FZRA.  
 
SUNDAY: VFR. BREEZY.  
 
SUNDAY NIGHT: VFR.  
 
MARTIN LUTHER KING JR DAY: MAINLY VFR, WITH LOCAL MVFR  
POSSIBLE ALONG THE EAST COAST OF MASSACHUSETTS. BREEZY.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE.  
 
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 SATURDAY/...  
 
TONIGHT...MODERATE CONFIDENCE.  
GALE WARNINGS CONTINUE AND EXPANDED TO BOSTON HARBOR AND  
NARRAGANSETT BAY. 70-80 KT LOW LEVEL JET DEVELOPS THROUGH  
TONIGHT. STRONGEST GUSTS TO 40 KT WILL OCCUR OVER NEARSHORE  
WATERS WHERE MIXING IS BETTER. LESS WIND EXPECTED OVER THE OUTER  
WATERS DUE TO INVERSION BUT RISK OF GALES CONTINUE, ESPECIALLY  
IN ANY CONVECTIVE ELEMENTS. VSBYS BELOW 1 MIL E IN AREAS OF  
HEAVY RAIN AND FOG.  
 
SATURDAY...HIGH CONFIDENCE.  
SOUTHERLY GALES IN THE MORNING, THEN WINDS DIMINISHING AS LOW  
LEVEL JET MOVES OFFSHORE. WINDS SHIFTING TO NW LATE MORNING  
THROUGH AFTERNOON WITH GUSTS 20-25 KT.  
 
OUTLOOK /SATURDAY NIGHT THROUGH WEDNESDAY/...  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. ROUGH SEAS UP TO 12 FT.  
SLIGHT CHANCE OF SNOW SHOWERS. LOCAL VISIBILITY 1 TO 3 NM.  
 
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 FOR TODAY JANUARY 12  
 
BOS 61 IN 2017,1975  
PVD 60 IN 2017  
BDL 57 IN 1913  
ORH 57 IN 2017  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...FLOOD WATCH THROUGH SATURDAY AFTERNOON FOR CTZ002>004.  
WINTER WEATHER ADVISORY FROM 9 AM TO 4 PM EST SATURDAY FOR  
CTZ002>004.  
MA...FLOOD WATCH THROUGH SATURDAY AFTERNOON FOR MAZ002>024-026.  
DENSE FOG ADVISORY UNTIL 5 AM EST SATURDAY FOR MAZ020-021.  
WINTER WEATHER ADVISORY FROM 11 AM TO 4 PM EST SATURDAY FOR  
MAZ005>007-013>019.  
WIND ADVISORY UNTIL 9 AM EST SATURDAY FOR MAZ018>024.  
WIND ADVISORY UNTIL 6 AM EST SATURDAY FOR MAZ013-015>017.  
WINTER WEATHER ADVISORY FROM 5 AM TO 4 PM EST SATURDAY FOR  
MAZ002-003-008>011.  
WINTER WEATHER ADVISORY FROM 9 AM TO 4 PM EST SATURDAY FOR  
MAZ004-012-026.  
DENSE FOG ADVISORY UNTIL 9 AM EST SATURDAY FOR MAZ022>024.  
RI...FLOOD WATCH THROUGH SATURDAY AFTERNOON FOR RIZ001>008.  
DENSE FOG ADVISORY UNTIL 5 AM EST SATURDAY FOR RIZ006>008.  
WINTER WEATHER ADVISORY FROM 11 AM TO 4 PM EST SATURDAY FOR  
RIZ002>005.  
WIND ADVISORY UNTIL 6 AM EST SATURDAY FOR RIZ002-004-006-007.  
WINTER WEATHER ADVISORY FROM 9 AM TO 4 PM EST SATURDAY FOR  
RIZ001.  
MARINE...GALE WARNING UNTIL 9 AM EST SATURDAY FOR ANZ231>234-250-251-  
254>256.  
GALE WARNING UNTIL 7 AM EST SATURDAY FOR ANZ230-235-236.  
SMALL CRAFT ADVISORY UNTIL 7 PM EST SATURDAY FOR ANZ237.  
 

 
 

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