334  
FXUS61 KBOX 120247  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
947 PM EST THU JAN 11 2018  
   
SYNOPSIS
 
 
MULTIPLE LOW PRESSURE AREAS ALONG AN APPROACHING COLD FRONT WILL  
BRING HEAVY RAINFALL, FLOODING AND POSSIBLE GUSTY WINDS FRIDAY  
INTO EARLY SATURDAY. A SHARP TURN TO MUCH COLDER WEATHER  
OCCURS RAPIDLY LATE FRIDAY NIGHT THROUGH SATURDAY FROM WEST TO  
EAST. THIS MAY ALLOW RAIN TO CHANGE TO A PERIOD OF ICE BEFORE  
ENDING, MAINLY IN THE INTERIOR ALONG WITH A FLASH FREEZE ACROSS  
ALL SOUTHERN NEW ENGLAND. MAINLY DRY BUT VERY COLD WEATHER IS  
EXPECTED SUNDAY AND MONDAY, BUT WILL HAVE TO WATCH THE POTENTIAL  
FOR SOME SNOW AND/OR MIXED PRECIPITATION TUESDAY INTO  
WEDNESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
945 PM UPDATE...  
 
IMPRESSIVE SOUTHWEST LOW LEVEL JET ON THE ORDER OF 40 TO 50  
KNOTS WILL CONTINUE TO ALLOW LOW LEVEL MOISTURE TO INCREASE  
OVERNIGHT. DEWPOINTS IN THE 40S WILL ALSO ALLOW FOR  
AREAS OF FOG TO DEVELOP...BUT WHETHER IT BECOMES DENSE REMAINS  
UNCERTAIN. SO FAR THIS EVENING...THERE IS JUST ENOUGH WIND  
MIXING DOWN FROM THE LOW LEVEL JET TO PREVENT DENSE FOG. THE MOS  
GUIDANCE GENERALLY KEEPS ENOUGH SURFACE WIND TO PREVENT DENSE  
FOG...BUT SOMETIMES IT IS TOO STRONG WITH THE WINDS AND WILL  
HAVE TO WATCH FOR POTENTIAL DECOUPLING ESPECIALLY AFTER  
MIDNIGHT. GIVEN DEWPOINTS IN THE 40S AND A DEEP SNOWPACK...DENSE  
FOG MAY FORM QUITE QUICKLY "IF" WINDS DECOUPLE. NO DENSE FOG  
ADVISORY YET...BUT WILL REISSUE THE SPECIAL WEATHER STATEMENT  
HIGHLIGHTING THE CONCERN. GREATEST RISK IS ACROSS THE INTERIOR  
AND NEAR THE SOUTH COAST.  
 
AS FOR PRECIPITATION...BULK OF SYNOPTIC SCALE FORCING/DEEPER  
MOISTURE WILL REMAIN WEST OF OUR REGION. THEREFORE...EXPECT DRY  
WEATHER TO DOMINATE BUT MAY SEE A FEW SPOT SHOWERS DEVELOP  
ACROSS THE INTERIOR TOWARD DAYBREAK. TEMPERATURES MAINLY  
IN THE 40S OVERNIGHT...BUT READINGS MAY REACH OR EXCEED  
50 ACROSS PORTIONS OF THE COASTAL PLAIN BY DAYBREAK.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
 
 
***UNSEASONABLY MILD FRIDAY WITH HEAVY RAINFALL AND SIGNIFICANT  
URBAN/STREET FLOODING THREAT FOR THE LATE DAY/EVENING COMMUTE***  
 
***FREEZING RAIN AND ICING POSSIBLE TOWARD DAYBREAK SATURDAY  
ACROSS INTERIOR NORTHERN AND WESTERN MA***  
 
HEAVY RAINFALL AND FLOODING...  
 
SLOW MOVING COLD FRONT APPROACHING FROM THE WEST WITH MULTIPLE  
WAVES OF LOW PRESSURE COMBINED WITH HIGHLY ANOMALOUS PWATS AND A  
GOOD LOW LEVEL JET WILL BRING HEAVY RAINFALL AND FLOODING THREAT  
TO SNE. INITIAL PERIOD OF HEAVY RAINFALL ASSOCD WITH A POTENT  
LOW LEVEL JET IS EXPECTED TO MOVE ACROSS SNE DURING FRIDAY FROM  
WEST TO EAST WITH HEAVIEST RAINFALL IN THE INTERIOR. A SECOND  
WAVE APPROACHING FROM THE SOUTH AS POTENT SOUTHERN STREAM  
SHORTWAVE LIFTS NE TOWARD NEW ENG WILL BRING ANOTHER ROUND OF  
HEAVY RAINFALL LATE FRIDAY INTO FRIDAY NIGHT. THIS WILL LIKELY  
BE FOCUSED SOMEWHERE FROM THE I-95 CORRIDOR TO CAPE COD AS  
PERSISTENT LOW LEVEL JET SETS UP IN THIS AREA.  
 
HIGHLY ANOMALOUS PWATS OF 1.50-1.75" WHICH IS 4-5 STANDARD  
DEVIATIONS ABOVE NORMAL COMBINED WITH +3SD LOW LEVEL JET IS A  
STRONG SIGNAL FOR HEAVY RAINFALL. HIGH CONFIDENCE OF WIDESPREAD  
RAINFALL OF 1.5 TO 3 INCHES WITH LOCALIZED 4 INCH AMOUNTS  
POSSIBLE. ISOLD THUNDER IS ALSO POSSIBLE GIVEN THE STRONG LOW  
LEVEL JET DYNAMICS AND MARGINAL ELEVATED INSTABILITY. HEAVIEST  
RAINFALL AMOUNTS EXPECTED SOMEWHERE ACROSS EASTERN HALF NEW ENG  
WITH FOCUS FROM I95 CORRIDOR TO CAPE COD. CONFIDENCE IS LOWER IN  
AXIS OF HEAVIEST RAINFALL DUE TO POTENTIAL CONVECTION AND  
MESOSCALE FACTORS AND IT IS POSSIBLE THIS AXIS COULD SHIFT.  
 
TEMPS WILL SOAR WELL INTO THE 50S TO EVEN LOWER 60S ACROSS RI  
AND SE MA WITH HIGH DEWPOINTS RESULTING IN MOST IF NOT ALL THE  
SNOWPACK RAPIDLY MELTING. THE RAPID SNOWMELT COMBINED WITH HEAVY  
RAINFALL WILL RESULT IN AN INCREASED RISK FOR SIGNIFICANT  
URBAN AND POOR DRAINAGE FLOODING, ESPECIALLY IN VICINITY OF SNOW  
CLOGGED DRAINS.  
 
EXPECT SHARP RISES ON RIVERS AND STREAMS BUT MOST RIVERS ARE  
EXPECTED TO REMAIN BELOW FLOOD STAGE. THE NERFC FORECAST HAS  
THE ASSABET RIVER AT MAYNARD AND THE PAWCATUCK RIVER AT  
WESTERLY REACHING FLOOD STAGE, BUT NOT UNTIL LATE SATURDAY NIGHT  
OR EARLY SUN.  
 
STRONG WIND...  
 
POTENT LOW LEVEL JET WITH 60-70 KTS DOWN TO 925 MB DEVELOPS  
ACROSS SE NEW ENG LATER FRI INTO FRIDAY NIGHT. SOUNDINGS NOT  
SUPPORTIVE OF MUCH LOW LEVEL MIXING. HOWEVER, WHERE TEMPS  
APPROACH OR EXCEED 60 DEGREES WILL ENHANCE MIXING AND POTENTIAL  
FOR STRONGER WIND GUSTS 40-50 MPH. THE BEST CHANCE FOR THESE  
STRONGER GUSTS WILL BE ACROSS RI AND SE MA WHERE MILDEST TEMPS  
EXPECTED. WIND ADVISORIES MAY EVENTUALLY BE NEEDED IF CONFIDENCE  
INCREASES IN THESE HIGHER GUSTS.  
 
FREEZING RAIN AND ICING...  
 
LATE FRI NIGHT, GUIDANCE INDICATES COLD FRONT WILL DROP SOUTH  
ACROSS WESTERN HALF OF SNE. SHARPLY COLDER AIR WILL MOVE IN  
BEHIND THE FRONT WITH POTENTIAL FOR RAIN CHANGING TO FREEZING  
RAIN WITH TEMPS DROPPING RAPIDLY INTO THE UPPER 20S. THERE IS  
STILL UNCERTAINTY WITH TIMING OF FRONT AND LOW LEVEL COLD AIR  
BUT BEST CHANCE OF ICING BEFORE DAYBREAK SAT WILL BE ACROSS  
INTERIOR NORTHERN AND WESTERN MA, MAINLY NORTH AND WEST OF BAF-  
FIT.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
*/ HIGHLIGHTS...  
 
- ICING HAZARDS SATURDAY, COMBINATION OF FREEZING RAIN AND  
FLASH FREEZE  
 
- COLD SUNDAY THROUGH MONDAY, OCEAN-EFFECT SNOWS OVER CAPE/ISLANDS  
 
- POTENTIAL WINTER STORM TUESDAY INTO WEDNESDAY  
 
*/ OVERVIEW...  
 
UNTIL A H3 JET IMPULSE / H5 VORT MAX IS ABLE TO CASCADE E, THE WAVE  
BREAK / SPLIT FLOW REGIME LIES OFFSHORE OF THE NE PACIFIC. H5 RIDGE  
PREVAILING OVER THE W CONUS AS THE H5 ATLANTIC RIDGE AND EMBEDDED  
TRAFFIC SLOW THE DOWNSTREAM FLOW, A H5 TROF PATTERN IS PREFERRED  
OVER THE E CONUS THROUGH WHICH BOTH N AND S STREAM ENERGY ROTATE,  
INFLUENTIAL UPON THE SW-NE BAROCLINIC ZONE / COLD FRONT SWEEPING E  
THROUGH THE REGION FRIDAY INTO SATURDAY, STALLING OFFSHORE AGAINST  
THE PROMINENT H5 ATLANTIC RIDGE. A SERIES OF STORM SYSTEMS EXPECTED  
INTO EARLY NEXT WEEK UNTIL THE FLOW SEEMING RELAXES, MOVING TOWARDS  
A THAWING PATTERN AS MILD, PACIFIC AIR COMES ASHORE AND SWEEPS THE  
CONUS. THOSE STORM SYSTEMS AND ASSOCIATED IMPACTS ADDRESSED BELOW.  
 
*/ SATURDAY...  
 
THROUGH THE PREFERRED H5 TROF PATTERN, N/S PIECES COMING TOGETHER  
AIDING IN MID-LEVEL ASCENT BENEATH THE RRQ OF THE UPPER-LEVEL JET.  
CONVEYOR BELT MOTIONS PULLING TOGETHER, ANTI-CYCLONIC WCB PULLED TO  
THE W, THE DCB DRAWN FROM THE SW, AS THE CCB WRAPS IN FROM THE N/W.  
EVIDENT ANAFRONTAL CHARACTERISTICS VIA UPSLOPE ALONG THE ISENTROPES,  
SW-NE LOW TO MID LEVEL FRONTOGENETICAL BANDING REARWARD OF A SHARP  
SURFACE COLD FRONT AS AIRMASSES CLASH AND CONSIDERABLY COLDER AIR  
UNDERCUTS, THE DENDRITIC GROWTH ZONE DRIED OUT.  
 
FREEZING RAIN...  
 
ASSUMING THERE IS NO ICE WITHIN THE COLUMN, COLDER AIR UNDERCUTTING  
QUICKLY WITH FAVORABLE LIFT / ASCENT ALOFT PRIOR TO DRY AIR ERODING  
THE COLUMN, LOOKING AT A ROUGHLY 3-6 HOUR WINDOW OF FREEZING RAIN /  
DRIZZLE OVER N/W INTERIOR S NEW ENGLAND, ROUGHLY W OF INTERIOR ESSEX  
COUNTY MA, WORCESTER AND TOLLAND HILLS. THERE IS THE POTENTIAL OF  
REACHING THE I-95 CORRIDOR, SOME UNCERTAINTY ON THE SPEED AT WHICH  
COLDER AIR MOVES IN WITH PRECIPITATION ONGOING, BUT EXPECTING THE  
COLUMN TO DRY OUT INTO AFTERNOON LESSENING THE CHANCE. COLLABORATING  
WITH WPC AND NEIGHBORING WFOS, UPWARDS OF A TENTH OF AN INCH OF ICE  
ACCRETION, THE HIGHEST AMOUNTS IN THE BERKSHIRES / NW MA, FORECAST.  
MAJORITY OF IMPACTS AROUND SUNRISE INTO EARLY AFTERNOON DRYING OUT  
THEREAFTER, PERHAPS JUST FREEZING DRIZZLE LINGERING BEFORE ALL IS  
SAID AND DONE. HELD OFF ON WINTER WEATHER ADVISORIES AS WE'RE COMING  
UP TO A POTENTIAL FLOODING EVENT, WILL LET THE OVERNIGHT CREW HAVE  
ANOTHER LOOK AS THE 11.12Z NAM / CANADIAN ARE A BIT FASTER WITH THE  
SURFACE COLD FRONT AND DRYING OVER GLOBAL GUIDANCE.  
 
FLASH FREEZE...  
 
CONSIDERING A SHARPER TEMPERATURE GRADIENT, FASTER TEMPERATURE DROP,  
LEANING WITH HIGHER-RES GUIDANCE FROM THE NAM / CANADIAN. LOOKING AT  
TEMPERATURES RANGING FROM 40S TO 50S AROUND SUNRISE. BY NOON FALLING  
INTO THE 20S AND 30S FOR ALL BUT SE-COASTAL NEW ENGLAND, TEENS FOR  
THE BERKSHIRES, THEN BY EVENING SINGLE DIGITS TO TEENS, 20S ALONG  
THE COAST. RESIDUAL WET SURFACES, A 20-30 DEGREE TEMPERATURE DROP IN  
ROUGHLY A 6-HOUR PERIOD, EXPECT ANY UNTREATED SURFACES TO QUICKLY  
FREEZE RESULTING IN POTENTIAL HAZARDOUS TRAVEL CONDITIONS.  
 
*/ SATURDAY NIGHT THROUGH MONDAY...  
 
ARCTIC HIGH PRESSURE BUILDING ACROSS THE REGION. MONITORING OCEAN  
EFFECT SNOWS OVER THE CAPE AND ISLANDS. WHETHER UNI-DIRECTIONAL N/NE  
FLOW WITHIN THE BOUNDARY LAYER, RELATIVE HUMIDITY FAVORABLY AT OR  
ABOVE 70 PERCENT, BENEATH CYCLONIC FLOW. OVERALL THINKING OUTCOMES  
WILL BE LIGHT. SHEAR WITHIN THE LAYER SOMEWHAT DISRUPTIVE AS LAPSE  
RATES DERIVE FROM TEMPERATURE DIFFERENCES OF 10-13 DEGREES. NOTING  
THE WARM OCEAN TEMPERATURES OF 40 DEGREES, THE TEMPERATURE OF THE  
TOP OF THE LAYER, OCEAN INDUCED CAPE ONLY AS HIGH AS 200 J/KG, NCAPE  
UP TO 0.15. WOULD LIKE TO SEE HIGHER VALUES. EXPECTING LIGHT SNOW  
OUTCOMES OF TENTHS FROM FALMOUTH OF CHATHAM GIVEN THE WIND DIRECTION  
THROUGHOUT THE FORECAST PERIOD, BETTER CHANCE SEEMINGLY SUNDAY NIGHT  
INTO MONDAY WITH MID-LEVEL ASCENT PROVIDED BY AN IMPULSE ROTATING  
THROUGH THE CYCLONIC FLOW. COLDEST TEMPERATURES AROUND SUNDAY, GOING  
TO BE IN THE FREEZER. POSSIBLE WIND CHILL HEADLINES NEEDED FOR THE  
BERKSHIRES OTHERWISE EXPECTING VALUES AS LOW AS 10 BELOW ZERO.  
 
*/ TUESDAY INTO WEDNESDAY...  
 
CLIPPER LOW TRANSFERRING ENERGY OFFSHORE OVER THE BETTER BAROCLINIC  
ZONE / STALLED COLD FRONT UP AGAINST THE ATLANTIC H5 RIDGE. COASTAL  
LOW DEVELOPING PER CONSENSUS OF ENSEMBLE MEMBER / MEAN GUIDANCE. AS  
TO OUTCOMES, STILL UNCERTAIN WITH RESPECT TO INTENSITY, PROXIMITY,  
MOVEMENT AND TIMING, DETAILS WHICH WILL BE OUTLINED AS WE GET CLOSER  
TO THE EVENT. ONE THING WORTH NOTING IS THE POSITIVE-TILTED H5 TROF  
AXIS LEADING INTO THE EVENT BECOMING NEGATIVE AFTERWARD. SEEMINGLY  
DEVELOPING ACROSS NEW ENGLAND BUT DEEPER AND MORE EXPLOSIVE DOWN-  
STREAM. LOOKING LIKE A RAIN / SNOW EVENT, SNOW TO LIQUID RATIO  
DEPENDENT RESPECTIVE TO REGIONS OF FAVORABLE LIFT / ASCENT, JUST TOO  
EARLY TO GET ON AMOUNTS AND EXACT IMPACTS.  
 

 
   
AVIATION /03Z FRIDAY THROUGH TUESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH FRIDAY NIGHT/...  
 
TONIGHT...MODERATE CONFIDENCE. WIDE VARIETY OF CONDITIONS THIS  
EVENING WILL TEND TO DETERIORATE TO AT LEAST LOW END MVFR ALONG WITH  
IFR/LIFR CONDITIONS. LOW CLOUDS AND FOG WILL INCREASE IN AREAL  
COVERAGE OVERNIGHT ESPECIALLY ACROSS THE INTERIOR. BIGGEST  
UNCERTAINTY IS IF THE WINDS DECOUPLE ENOUGH TO ALLOW FOR AREAS  
OF DENSE FOG. WILL CONTINUE TO MONITOR CLOSELY. LLWS ALSO A  
CONCERN ESPECIALLY TOWARD DAYBREAK.  
 
FRIDAY INTO FRIDAY NIGHT...MODERATE CONFIDENCE.  
WIDESPREAD IFR-VLIFR. RA/+RA WITH FG ALONG WITH INCREASING S WINDS  
WITH GUSTS UP AROUND 20-30 KTS, STRONGEST OVER INTERIOR SE NEW  
ENGLAND TERMINALS. LLWS WITH STRONGEST S/SW 2 KFT WINDS UP TO 60  
KTS OVER SE NEW ENGLAND. -RA CHANGING TO FZRA/FZDZ TOWARDS SATURDAY  
SUNRISE OVER N/W MA AND CT.  
 
KBOS TERMINAL...MODERATE CONFIDENCE IN TAF.  
 
KBDL TERMINAL...MODERATE CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. WINDY WITH GUSTS  
TO 30 KT. RA, CHANCE FZRA, AREAS FG, SLIGHT CHANCE FZDZ.  
 
SATURDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR POSSIBLE. BREEZY.  
SLIGHT CHANCE SN.  
 
SUNDAY THROUGH SUNDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR  
POSSIBLE.  
 
MARTIN LUTHER KING JR DAY: MAINLY VFR, WITH LOCAL MVFR  
POSSIBLE. SLIGHT CHANCE SN.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. BREEZY.  
CHANCE SN.  
 
TUESDAY: 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 FRIDAY NIGHT/...  
 
TONIGHT...HIGH CONFIDENCE. SOUTHWEST WIND GUSTS OF 20 KNOTS  
EXPECTED WITH SEAS BUILDING TO 5 FT OVER THE SOUTHERN WATERS.  
 
FRIDAY INTO FRIDAY NIGHT...MODERATE CONFIDENCE. POTENT LOW  
LEVEL JET DEVELOPS OVER THE WATERS BUT A RATHER STRONG LOW  
LEVEL INVERSION IS PRESENT WHICH WILL PREVENT STRONGER WINDS  
FROM MIXING DOWN. WE WILL CERTAINLY SEE SCA WIND GUSTS, BUT BEST  
CHANCE FOR GALES WILL BE OVER THE NEARSHORE WATERS AND BOSTON  
HARBOR AND NARRAGANSETT BAY WHERE BEST MIXING ANTICIPATED. WE  
WILL HOLD ON TO THE GALE WATCH OVER THESE WATERS AND NE MA  
COASTAL WATERS AS CONFIDENCE NOT HIGH ENOUGH FOR WARNINGS, WITH  
SCA ELSEWHERE. RISK FOR GALES OVER THE OUTER SOUTHERN WATERS IS  
LOW. LOW VSBYS EXPECTED IN RAIN AND FOG.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 35 KT.  
ROUGH SEAS UP TO 16 FT. CHANCE OF RAIN, AREAS FOG, CHANCE OF  
FREEZING RAIN, CHANCE OF FREEZING DRIZZLE. LOCAL VISIBILITY  
1 NM OR LESS.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. ROUGH SEAS UP TO 11 FT.  
CHANCE OF SNOW.  
 
SUNDAY: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS. SLIGHT  
CHANCE OF SNOW.  
 
SUNDAY NIGHT THROUGH MARTIN LUTHER KING JR DAY: WINDS LESS THAN  
25 KT. SEAS UP TO 5 FT. SLIGHT CHANCE OF SNOW.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF ROUGH SEAS.  
CHANCE OF SNOW.  
 
TUESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 25 KT. ROUGH SEAS UP TO 9 FT. CHANCE OF SNOW.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...FLOOD WATCH FROM 6 AM EST FRIDAY THROUGH SATURDAY AFTERNOON  
FOR CTZ002>004.  
MA...FLOOD WATCH FROM 6 AM EST FRIDAY THROUGH SATURDAY AFTERNOON  
FOR MAZ002>024-026.  
RI...FLOOD WATCH FROM 6 AM EST FRIDAY THROUGH SATURDAY AFTERNOON  
FOR RIZ001>008.  
MARINE...GALE WATCH FROM FRIDAY AFTERNOON THROUGH FRIDAY EVENING FOR  
ANZ230>234-236-250-251.  
SMALL CRAFT ADVISORY FROM 3 AM FRIDAY TO 7 AM EST SATURDAY FOR  
ANZ235-237-254>256.  
 

 
 

 
SYNOPSIS...KJC/SIPPRELL  
NEAR TERM...FRANK  
SHORT TERM...KJC/SIPPRELL  
LONG TERM...SIPPRELL  
AVIATION...FRANK/KJC/SIPPRELL  
MARINE...KJC/SIPPRELL  
 
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