644  
FXUS61 KBOX 101159  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
659 AM EST WED JAN 10 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE MOVES EAST OF THE REGION TODAY AND TONIGHT  
BRINGING MILDER WEATHER ON THURSDAY. UNSEASONABLY MILD  
TEMPERATURES ARE ANTICIPATED FRIDAY INTO FRIDAY NIGHT ALONG WITH  
PERIODS OF HEAVY RAIN, GUSTY WINDS ALONG WITH THE POTENTIAL FOR  
SOME FLOODING. THE RAIN MAY END AS SOME ICE ACROSS THE INTERIOR  
ON SATURDAY IF THE MUCH COLDER AIR ARRIVES BEFORE THE  
PRECIPITATION ENDS. DRY AND VERY COLD WEATHER IS FAVORED SUNDAY  
INTO MONDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
7AM UPDATE...  
IT TOOK SOME TIME, BUT THE SKC CONDITIONS AND DECOUPLING HAVE  
ALLOWED FOR A RAPID TEMP DROPOFF WITHIN THE LAST COUPLE OF  
HOURS. WHILE THIS WAS FORECAST, THE SLOWER RESPONSE AND SLIGHTLY  
ELEVATED DEWPOINTS ARE LIKELY TO LIMIT THE DROPOFF COMPARED TO  
THE PREVIOUS FORECAST. THEREFORE, WILL BE ADJUSTING THE  
TEMPS/DWPTS WITH THIS UPDATE AND MAY ALLOW FOR SLIGHTLY WARMER  
HIGHS GIVEN THE WARMER START. THIS IS IN SPITE OF THE LIMITED  
MIXING AND STRONG SUBSIDENCE.  
 
PREVIOUS DISCUSSION...  
 
LARGE HIGH PRESSURE WILL SLOWLY MOVE EAST OF THE REGION TODAY.  
THE RESULT WILL BE MAINLY SUNNY SKIES AND LIGHT WINDS. DESPITE  
WARMING TEMPS ALOFT...THE LOW JANUARY SUN ANGLE AND LIMITED  
MIXING SHOULD KEEP HIGH TEMPS MAINLY IN THE MIDDLE TO UPPER 30S.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/
 
 
TONIGHT...  
 
INCREASING SOUTHWEST LOW LEVEL JET/WARM ADVECTION ALOFT WILL  
RESULT IN SKIES BECOMING MOSTLY CLOUDY TONIGHT...ESPECIALLY  
ACROSS THE INTERIOR. MOISTURE/FORCING IS QUITE LIMITED SO  
GENERALLY DRY WEATHER IS EXPECTED TONIGHT. HOWEVER, THERE MAY BE  
JUST ENOUGH MOISTURE FOR A BRIEF PERIOD OF SPOTTY LIGHT FREEZING  
RAIN ACROSS NORTHWEST MA. CONFIDENCE ON WHETHER THIS IMPACTS OUR  
REGION OR STAYS TO OUR NORTH IS UNCERTAIN...BUT LATER SHIFTS MAY  
NEED TO CONSIDER A SPECIAL WEATHER STATEMENT IF CONFIDENCE  
INCREASES. LOW TEMPS THIS EVENING SHOULD RANGE FROM THE MIDDLE  
20S TO THE LOWER 30S...BUT EXPECT TEMPS TO RISE AFTER MIDNIGHT  
WITH INCREASING SOUTHWEST FLOW.  
 
THURSDAY...  
 
A RATHER MILD DAY IS ON TAP FOR THE REGION WITH CONTINUED SOUTHWEST  
FLOW/WARM ADVECTION. THE WARM ADVECTION PATTERN WILL PROBABLY  
RESULT IN AN ABUNDANCE OF CLOUDS...BUT SOME PEEKS OF SUN ARE  
STILL ANTICIPATED. WHILE WE CAN NOT RULE OUT A SPOT SHOWER OR  
TWO...UPPER LEVEL RIDGING AND LACK OF SYNOPTIC SCALE FORCING  
SHOULD RESULT IN GENERALLY DRY WEATHER. HIGH TEMPS SHOULD MAINLY  
BE IN THE UPPER 40S TO THE LOWER 50S.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
 
 
HIGHLIGHTS...  
 
* HEAVY RAIN YIELDS A FLOODING RISK FRI AND SAT.  
* RAPID FREEZING POSSIBLE LATE SAT.  
* A RETURN OF COLDER THAN NORMAL CONDITIONS EARLY NEXT WEEK.  
 
OVERVIEW AND MODEL PREFERENCES...  
A GRADUAL TRANSITION IN A SLIGHT POSITIVE NAO/AO REGIME AS  
SUBTROPICAL HIGH BEGINS TO FORM BLOCK IN THE W ATLANTIC,  
ALLOWING THE TROF OVER SOCAL PHASES WITH A WEAKER N STREAM WAVE,  
LEADING TO A DRAW OF TROPICAL MOISTURE AND HIGH LATENT HEAT  
THROUGH A MEAN SW-NE ORIENTED JET. TWO WAVES WILL TRAVERSE THE  
ATTENDANT SFC FRONT FRI AND SAT WHICH LOOKS TO LEAD TO PERIODS  
OF HEAVY RAINFALL. THEREAFTER, AS THE RIDGE CONTINUES TO FORM A  
BLOCK OFFSHORE, THE LONGWAVE WILL PHASE WITH ARCTIC WAVE AND  
ALLOW ANOTHER ROUND OF ARCTIC AIR TO FOLLOW THE WET/UNSETTLED  
PERIOD. 10.00Z MODEL GUIDANCE SUITE CONTINUES TO SHOW GENERALLY  
GOOD SYNOPTIC SCALE AGREEMENT THROUGH THE WEEKEND. WHILE THERE  
CONTINUES TO BE MESO-SCALE AND THERMAL PROFILE DISAGREEMENTS,  
THESE WILL SLOWLY BECOME RESOLVED NOW THAT THE INITIATING WAVE  
(THE CUTOFF CURRENTLY IMPACTING SOCAL) IS ONSHORE AND BEING  
BETTER SAMPLED. GIVEN THE AGREEMENT AT THIS LEVEL, WILL CONTINUE  
TO LEAN MOST HEAVILY ON ENSEMBLES. THIS IS MAINLY DUE TO THE  
ANOMALOUS TROPICAL MOISTURE EVENT EXPECTED DURING THIS PERIOD,  
AND THE LOW RISK FOR THE INFLUENCE OF LOW LVL COLD AIR ON SAT  
(SOMETHING THAT AT LEAST A FEW MEMBERS REFLECT).  
 
DETAILS...  
 
THU NIGHT INTO FRI...  
DEEPENING LONGWAVE REACHES THE GULF OF MEXICO, ALLOWING THE  
ADVECTION OF HIGH PWAT AIR (NEARLY 1.5 INCHES, WHICH IS ALMOST 5  
STD DEVIATIONS ABOVE JANUARY NORMALS) TOWARD NEW ENGLAND. WHILE  
THE FIRST IN A SERIES OF FRONTAL WAVES MOVING ALONG A SLOW  
MOVING BAROCLINIC ZONE TO THE NW IS EXPECTED TO SHIFT THROUGH  
THE GREAT LAKES INTO QUEBEC, A 60+ KT LLJ WITH STRONG FRONT END  
CONVERGENCE WILL YIELD A PERIOD OF MOD-HEAVY RAIN EARLY FRI  
MORNING INTO THE DAYTIME ON FRI. THIS WILL BE THE SHORTER LIVED  
AND GENERALLY WEAKER OF THE TWO WAVES, BUT STILL, QPF VALUES  
COULD APPROACH 1.00-1.50 UNTIL DRY AIR FILTERS IN ALOFT, LEADING  
TO DIMINISHING RAINFALL RATES THROUGH THE LATE AFTERNOON AND  
EVENING. THIS IS IN ADVANCE OF STRONGER LATENT HEAT RELEASE  
UPSTREAM NEAR THE S TAIL OF THE APPALACHIANS WHICH WILL FORM A  
STRONGER FRONTAL WAVE MOVING THROUGH ON SAT. MORE ON THIS BELOW,  
ALONG WITH THE POTENTIAL IMPACTS OF HEAVY RAIN BOTH FRI AND  
SAT. TEMPS REMAIN MILD THANKS TO H92 TEMPS NEAR +10C, YIELDING  
HIGHS IN THE LOW-MID 50S.  
 
FRI NIGHT INTO SAT NIGHT...  
SECONDARY FRONTAL WAVE, THIS ONE ASSOCIATED WITH A NEARLY 70+  
LLJ (EVEN AS LOW AS H92) WILL PASS ALONG THE FRONT AS IT MOVES  
ACROSS S NEW ENGLAND. THE TIMING IS CRITICAL HERE, AS THIS LOW  
COULD ULTIMATELY PASS DIRECTLY OVER, TO THE W OR TO THE E OF NEW  
ENGLAND. ENSEMBLES STILL YIELD A LOT OF SPREAD AT THIS TIME,  
BUT THIS WILL NEED TO BE WATCHED. A W OR DIRECT TRACK WOULD  
ALLOW FOR HEAVIER RAIN WITH CONVECTIVE ELEMENTS AS K-VALUES  
SHIFT WELL ABOVE 30 AND CONDITIONALLY UNSTABLE SOUNDINGS YIELD  
MODEST MU CAPE. THESE TRACKS COULD ALSO BE THE MEANS BY WHICH  
SOME OF THE MOMENTUM FROM THIS STRONG LLJ IS ABLE TO MIX TO THE  
SFC, HOWEVER WITH SOME LINGERING SNOWPACK AND AN IMPLIED  
INVERSION ON SOUNDINGS, A LACK OF NEAR SFC MIXING MAY BE ABLE  
TO KEEP IT ALOFT. STILL SOMETHING TO WATCH. OTHERWISE, A FURTHER  
E TRACK COULD ALLOW FOR SHALLOW, NEAR SFC COLD AIR IN FAST  
ENOUGH (THANKS TO ISALLOBARIC NORTH AND NORTHWESTERLIES) BEFORE  
THE MAIN PRECIP SHIELD DISSIPATES, ALLOWING FOR SOME WINTRY MIX  
(MOST LIKELY FZRA) ACROSS THE INTERIOR. AS MENTIONED ABOVE,  
THESE ARE MESOSCALE FEATURES WHICH WILL GRADUALLY EVOLVE.  
 
IN ANY CASE, ANOTHER ROUND OF HEAVY RAIN IS LIKELY WITH  
CONVECTIVE THE HELP. THE HEAVY RAIN, WILL COMBINE WITH HIGH  
DWPTS TO YIELD SNOWMELT BEGINNING FRI AND CONTINUING ON SAT.  
WITH FULL QPF FROM BOTH WAVES YIELDING A POTENTIAL BETWEEN  
1.50-4.00 INCHES (EVEN MORE IN SPECIFIC RUNS), THE ADDITIONAL  
SNOWMELT, COMBINED WITH A POTENTIAL FOR SNOW CLOGGED DRAINS  
COULD YIELD SOME URBAN AND POOR DRAINAGE FLOODING, AS WELL AS  
SOME FLOODING SPECIFICALLY IN FLASHIER SMALL STREAMS.  
 
FOLLOWING THE FLOODING RISK, THE INFLUENCE OF COLD AIR TIMING  
WILL BE IMPORTANT, AS A FREEZE IS POSSIBLE IMMEDIATELY FOLLOWING  
HEAVY RAIN. OVERNIGHT MINS ARE LIKELY TO DIP BELOW FREEZING  
BEFORE SUN MORNING.  
 
SUN...  
AS LOW PRES SHIFTS INTO THE MARITIMES, COLDER AIR BEGINS TO  
FILTER IN FROM THE W, ALTHOUGH ARCTIC HIGH PRES REMAINS ACROSS  
THE GREAT LAKES. TEMPS ALOFT, NEARLY ISOTHERMAL THROUGH H85,  
HOVER BETWEEN -10C AND -12C. THIS IS NEAR THE STANDARD FOR MID  
JANUARY, SO EXPECT HIGHS SUN TO REMAIN NEAR SEASONAL NORMALS,  
BUT COLDER THAN PREVIOUS 48 HOURS. SUN NIGHT MINS HOWEVER WILL  
BE DEPENDENT ON CENTER OF HIGH PRES, BUT THERE IS A POSSIBILITY  
FOR RADIATIONAL COOLING, WITH LOWS IN THE SINGLE DIGITS OR LOW  
TEENS.  
 
EARLY NEXT WEEK...  
ARCTIC INFLUENCED AIRMASS REMAINS IN PLACE WITH HIGH PRES  
ESPECIALLY THROUGH TUE. HOWEVER, WILL NEED TO WATCH WAVES  
ROTATING THROUGH THE LONGWAVE TROF, WHICH COULD BRING ABOUT A  
SNOWFALL EVENT. CONFIDENCE IS LOW IN TIMING OR DETAILS AT THIS  
TIME.  
 

 
   
AVIATION /11Z WEDNESDAY THROUGH SUNDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY/...  
 
TODAY...HIGH CONFIDENCE.  
VFR. WINDS REMAIN LIGHT, BUT SLOWLY BACK TO THE SSW THROUGH THE  
AFTERNOON.  
 
TONIGHT...HIGH CONFIDENCE IN MAINLY VFR CONDITIONS. LOW RISK FOR  
A BRIEF PERIOD OF SPOTTY LIGHT FREEZING RAIN IN NORTHWEST MA.  
 
THURSDAY...MODERATE CONFIDENCE. TIMING UNCERTAIN BUT THREAT FOR  
MVFR TO IFR CONDITIONS WILL INCREASE MAINLY ACROSS THE INTERIOR  
DURING THE AFTERNOON AND ESPECIALLY EARLY EVENING.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...  
 
THURSDAY NIGHT: MVFR/IFR CONDITIONS POSSIBLE. BREEZY. RA,  
PATCHY BR.  
 
FRIDAY: MAINLY MVFR, WITH AREAS IFR POSSIBLE. WINDY WITH GUSTS  
TO 35 KT. RA.  
 
FRIDAY NIGHT: MAINLY IFR, WITH AREAS MVFR POSSIBLE. WINDY WITH  
LOCAL GUSTS TO 30 KT. RA, PATCHY BR.  
 
SATURDAY: MAINLY MVFR, WITH AREAS IFR POSSIBLE. WINDY WITH  
GUSTS TO 35 KT. RA, SLIGHT CHANCE FZRA.  
 
SATURDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. BREEZY.  
SLIGHT CHANCE SHRA.  
 
SUNDAY: VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH THURSDAY/...  
 
TODAY...HIGH CONFIDENCE. HIGH PRESSURE BUILDS ACROSS THE WATERS ALLOWING  
ANY LEFT OVER WINDS AND SEAS TO FALL BELOW SMALL CRAFT ADVISORY  
THRESHOLDS BY DAYBREAK. QUIET WEATHER CONTINUES ON THE WATERS  
FOR THE REST OF THE DAY.  
 
TONIGHT AND THURSDAY...HIGH CONFIDENCE. SOUTHWEST WINDS OF 10 TO  
15 KNOTS WITH SOME GUSTS INTO THE LOWER 20 KNOTS ARE  
ANTICIPATED. GIVEN THE INVERSION OVER THE RELATIVELY COLD  
OCEAN...FEEL CONDITIONS WILL GENERALLY REMAIN BELOW SMALL CRAFT  
HEADLINES INTO THURSDAY AFTERNOON.  
 
OUTLOOK /THURSDAY NIGHT THROUGH SUNDAY/...  
 
THURSDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. RAIN LIKELY.  
 
FRIDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH LOCAL  
GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS. RAIN.  
 
FRIDAY NIGHT: WINDS LESS THAN 25 KT. ROUGH SEAS UP TO 13 FT.  
RAIN.  
 
SATURDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 30 KT. ROUGH SEAS UP TO 13 FT. RAIN.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. ROUGH SEAS UP TO 11 FT.  
SLIGHT CHANCE OF RAIN SHOWERS.  
 
SUNDAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...NONE.  
 

 
 

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