748  
FXUS61 KBOX 131018  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
427 AM EST SAT JAN 13 2018  
   
SYNOPSIS
 
 
HEAVY RAIN ENDS THIS MORNING AS A BIT OF ICE ACROSS WESTERN MA WITH  
A FLASH FREEZE THE MAIN STORY ACROSS THE REST OF THE REGION AS  
TEMPERATURES CRASH TODAY. 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/
 
 
***HEAVY RAIN/URBAN STREET FLOODING THREAT ENDS BY MID MORNING***  
 
***A BIT OF ICE ACROSS WESTERN MA THIS MORNING BUT THE MAIN STORY  
WILL BE A FLASH FREEZE TODAY AS TEMPERATURES CRASH***  
 
1) HEAVY RAIN/FLOODING AND COASTAL WIND EARLY THIS MORNING...  
 
HEAVY RAIN IMPACTING EASTERN MA/RI WHERE 80+ KNOT LOW LEVEL JET WAS  
IMPINGING ON PWATS 4-5 STANDARD DEVIATIONS ABOVE NORMAL. SIGNIFICANT  
URBAN STREET FLOODING WILL CONTINUE TO BE AN ISSUE IN THIS REGION  
THROUGH DAYBREAK. IN ADDITION...THE HEAVY RAIN AND ASSOCIATED  
CONVECTIVE ELEMENTS WERE TAPPING SOME OF THAT LOW LEVEL JET ALLOWING  
40 TO 50 MPH WIND GUSTS ALONG AND SOUTHEAST OF THE BOS-PVD CORRIDOR.  
WILL CONTINUE WIND ADVISORY BUT SHOULD SEE THESE WINDS DIMINISH FROM  
WEST TO EAST BY MID MORNING...AS LOW LEVEL JET EXITS THE REGION. AS  
THE LOW LEVEL JET SHIFTS EAST OF THE REGION...PRECIPITATION WILL  
DECREASE IN AREAL COVERAGE/INTENSITY DRAMATICALLY BY MID MORNING.  
 
2) WESTERN MA LIGHT ICING WITH FLASH FREEZE THE MAIN STORY TODAY:  
 
TEMPERATURES WERE MAINLY IN THE UPPER 50S TO THE LOWER 60S VERY  
EARLY THIS MORNING...BUT HAVE DROPPED INTO THE 30S ALONG THE EAST  
SLOPES OF THE BERKS EARLY THIS MORNING BEHIND A VERY STRONG COLD  
FRONT. THIS COLD FRONT WILL CROSS WESTERN MA BY 12Z...REACH THE  
BOSTON TO PROVIDENCE CORRIDOR BY 15 OR 16Z AND THEN OFF THE  
SOUTHEAST NEW ENGLAND COAST BY 18Z. ENOUGH PRECIPITATION WILL  
REMAIN FOR A BRIEF PERIOD OF LIGHT FREEZING RAIN/SLEET ACROSS  
WESTERN MA. FOR THE REST OF THE REGION...THE COLD AIR  
SHOULD COME IN PRETTY MUCH AFTER THE PRECIPITATION HAS ENDED.  
HOWEVER...MAY STILL SEE AN HOUR OR TWO OF SPOTTY -FZDZ AS THE SURGE  
OF COLD AIR INITIALLY COMES IN SHALLOW AND THERE IS SOME LEFT OVER  
LOW LEVEL MOISTURE FOR A 1 TO 3 HOUR PERIOD.  
 
THE MAIN CONCERN THOUGH IS THE EXPECTED FLASH FREEZE AND DRAMATIC  
DROP IN TEMPERATURES TODAY. MOST OF OUR FLASH FREEZES OCCUR WHEN  
OUR WINDS TURN NORTH NORTHEAST WHICH PREVENT DRYING. IN THIS  
CASE...THE WINDS WILL TURN NORTHWEST WHICH SHOULD ALLOW FOR AT LEAST  
SOME DRYING. HOWEVER...GIVEN THE DRAMATIC TEMPERATURE DROP FROM  
READINGS IN THE UPPER 50S TO LOWER 60S VERY EARLY THIS MORNING AND  
INTO THE 20S IN MOST LOCATIONS BY MID AFTERNOON IS QUITE UNUSUAL IN  
THIS PART OF THE COUNTRY. GIVEN ALL THE RECENT RAIN/STREET  
FLOODING/STANDING WATER THINK WILL SEE SOME ICING ISSUES AND WILL  
CONTINUE THE WINTER WEATHER ADVISORY ALONG AND NORTHWEST OF THE  
BOSTON TO PROVIDENCE CORRIDOR.  
 

 
   
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 /09Z SATURDAY THROUGH WEDNESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH TONIGHT/...  
 
THROUGH 12Z THIS MORNING...MODERATE TO HIGH CONFIDENCE. LOW END  
MVFR TO IFR CONDITIONS IN RAIN THROUGH 12Z. LLWS ALONG WITH  
SOUTHERLY WIND GUSTS OF 35 TO 40 KNOTS EXPECTED ALONG AND SOUTHEAST  
OF THE BOS-PVD CORRIDOR. STRONG COLD FRONT SHOULD BE THROUGH WESTERN  
MA BY 12Z ALLOWING PTYPE TO CHANGE TO -FZRA/IP.  
 
AFTER 12Z TODAY...MODERATE TO HIGH CONFIDENCE. IFR TO MVFR  
CONDITIONS SHOULD IMPROVE TO MAINLY VFR FROM WEST TO EAST THIS  
AFTERNOON. STRONG COLD FRONT REACHES THE BOS-PVD CORRIDOR BY  
15Z-16Z AND PROBABLY OFF THE SOUTHEAST NEW ENGLAND COAST BY 18Z.  
MOST OF THE LIGHT -FZRA/IP SHOULD BE CONFINED TO WESTERN AND  
NORTH CENTRAL MA...BUT A BRIEF PERIOD OF SPOTTY -FZDZ MAY OCCUR  
FOR AN HOUR OR TWO BEHIND THE FRONT ACROSS THE REST OF THE  
REGION. MAIN ISSUE WILL BE A FLASH FREEZE AS TEMPERATURES  
TUMBLE BELOW FREEZING AND INTO THE 20S IN MOST LOCATIONS BY MID  
AFTERNOON.  
 
KBOS TERMINAL...MODERATE TO HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...MODERATE TO HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SUNDAY THROUGH WEDNESDAY/...  
 
SUNDAY: VFR. BREEZY.  
 
SUNDAY NIGHT: VFR.  
 
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...MODERATE TO HIGH CONFIDENCE. POTENT SOUTHERLY LOW LEVEL JET  
WAS ALLOWING FOR SSW WIND GUSTS UP TO 40 KNOTS ON MANY OF OUR WATERS  
EARLY THIS MORNING...ESPECIALLY IN HEAVIER RAIN WHICH WAS ALLOWING  
SOME OF THE STRONGER WINDS TO MIX DOWN. WINDS SHOULD DROP BELOW  
GALE FORCE WIND GUSTS FROM WEST TO EAST BY MID MORNING AS LOW LEVEL  
JET EXITS THE REGION. HOWEVER, STRONG COLD FRONT CROSS THE WATERS  
LATER THIS MORNING AND EARLY AFTERNOON WITH NW WIND GUSTS AROUND 25  
KNOTS. GALES WILL NEED TO BE CONVERTED TO SMALL CRAFT HEADLINES.  
 
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:  
 
BOS 61 IN 2017,1975  
PVD 62 IN 2018  
BDL 60 IN 2018  
ORH 59 IN 2018  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...FLOOD WATCH UNTIL 1 PM EST THIS AFTERNOON FOR CTZ002>004.  
WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 4 PM EST  
THIS AFTERNOON FOR CTZ002>004.  
MA...FLOOD WATCH UNTIL 1 PM EST THIS AFTERNOON FOR MAZ002>024-026.  
DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR  
MAZ020-021.  
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 4 PM EST  
THIS AFTERNOON FOR MAZ005>007-013>019.  
WIND ADVISORY UNTIL 9 AM EST THIS MORNING FOR MAZ018>024.  
WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR MAZ013-  
015>017.  
WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR  
MAZ002-003-008>011.  
WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 4 PM EST  
THIS AFTERNOON FOR MAZ004-012-026.  
DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR MAZ022>024.  
RI...FLOOD WATCH UNTIL 1 PM EST THIS AFTERNOON FOR RIZ001>008.  
DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR  
RIZ006>008.  
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 4 PM EST  
THIS AFTERNOON FOR RIZ002>005.  
WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR RIZ002-004-  
006-007.  
WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 4 PM EST  
THIS AFTERNOON FOR RIZ001.  
MARINE...GALE WARNING UNTIL 9 AM EST THIS MORNING FOR ANZ231>234-250-  
251-254>256.  
GALE WARNING UNTIL 7 AM EST THIS MORNING FOR ANZ230-235-236.  
SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ237.  
 

 
 

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