579  
FXUS61 KBOX 232336  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TAUNTON MA  
636 PM EST THU NOV 23 2017  
   
SYNOPSIS
 
 
QUIET WEATHER THROUGH FRIDAY WITH DRY AND COOL CONDITIONS.  
MILDER AIR RETURNS SATURDAY AHEAD OF A COLD FRONT. THAT COLD  
FRONT SWINGS THROUGH SOUTHERN NEW ENGLAND LATE SATURDAY AND  
EARLY SATURDAY NIGHT. BLUSTERY AND COOLER WEATHER FOLLOWS  
SUNDAY. CONDITIONS TREND TOWARD DRY AND MILDER AGAIN TUESDAY  
AND WEDNESDAY, AND THEN COOL AGAIN THURSDAY BEHIND ANOTHER COLD  
FRONT.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
635 PM UPDATE...  
 
SATELLITE IMAGES SHOW HIGH CLOUDS MOVES ACROSS NEW ENGLAND, AND  
AN AREA OF MID-LEVEL CLOUDS DIMINISHING AS IT APPROACHES FROM OUR  
WEST. NO PRECIP UPSTREAM. SO EXPECT A FAIR WEATHER NIGHT WITH  
PATCHY CLOUDS OVERNIGHT. WE MADE A FEW MINOR ADJUSTMENTS BASED  
ON OBSERVED TEMPERATURES AND DEW POINTS, BUT OTHERWISE NO  
SIGNIFICANT CHANGES TO THE FORECAST.  
 
PREVIOUS DISCUSSION...  
 
SCATTERED TO BROKEN MID TO HIGH CLOUD DECKS FILTERING ACROSS  
THE REGION COULD PUT A BLANKET ON THANKSGIVING FESTIVITIES  
KEEPING TEMPERATURES SLIGHTLY WARMER. POSITIVELY- TILTED OPEN  
WAVE AND ATTENDANT WEAK VORTMAX SWEEPS THROUGH THE REGION EARLY  
ACROSS THE N-STREAM, A FLATTENING FEATURE, AS ENERGY SWEEPS UP  
FROM THE SE. MID TO HIGH CLOUDS SWEEPING THROUGH HOWEVER INTO A  
REGION OF DRIER AIR AND SUBSIDENCE, CAN ALREADY SEE SOME EROSION  
IN THE LATEST GOES-16 SATELLITE. PERHAPS SOME BLANKET /  
INSOLATION IMPACTS SO DID NOT GO WITH COLDEST OF MOS GUIDANCE.  
TOWARDS THE LOWER END WITH FORECAST LIGHT WINDS, LOOKING AT LOWS  
DOWN INTO THE 20S, WARMER ALONG THE SHORE.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
 
 
NICE DAY ON TAP. WITH DAYTIME MIXING UNDER MOSTLY CLEAR CONDITIONS,  
THE MID TO HIGH CLOUDS ERODING OUT, WINDS TURN S/SW. WARM AIR  
ADVECTION PROCEEDING ALOFT, MIXING IS LIMITED TO AROUND H95.  
LOOKING AT HIGHS IN THE UPPER 40S TO LOW 50S, EDGING TOWARDS THE  
WARMER END OF GUIDANCE.  
 
WITH BOTH N AND S STREAM ENERGY STILL NEIGHBORING OUR REGION,  
DRY SUBSIDENCE INVERSION PREVAILS. AS WE GO TOWARDS EVENING, THE  
CAP WELL IN PLACE, MIXING UP TO JUST BENEATH, AND THE BOUNDARY  
LAYER COOLS, LIKELY TO SEE THE MOISTURE POOLING CONDENSE AND  
SUBSEQUENTLY COULD SEE THE DEVELOPMENT OF LOW-LEVEL STRATUS  
EVENING AND OVERNIGHT ESPECIALLY OVER SE NEW ENGLAND. LOWS DOWN  
INTO THE 30S MOST PLACES, BUT WARMER SE AROUND THE LOW 40S. WITH  
DAYTIME MIXING, DEWPOINTS SHOULD BE LOW ENOUGH THAT 5 TO 10  
DEGREE DEWPOINT DEPRESSIONS PREVAIL. SO DESPITE THE OVERNIGHT  
N/W LOOKING FAVORABLE FOR RADIATIONAL COOLING, DO NOT EXPECT FOG  
TO BE AN ISSUE.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
BIG PICTURE...  
 
LONGWAVE SCALE SHOWS A BROAD TROUGH ALONG THE USA EAST COAST AND  
WEST ATLANTIC, A SECOND TROUGH OVER THE EASTERN PACIFIC, AND A RIDGE  
OVER THE THE PLAINS. THE EASTERN TROUGH LINGERS MUCH OF THE WEEK  
WHILE THE OVERALL FLOW TRENDS ZONAL.  
 
MODEL CONSENSUS SHOWS NORTHERN STREAM SHORTWAVES CROSSING NEW  
ENGLAND SATURDAY NIGHT/SUNDAY AND AGAIN WEDNESDAY. THE MODELS ALSO  
SHOW A SOUTHERN STREAM LOW CROSSING THE SOUTHEAST USA THURSDAY  
TRAILING THE WEDNESDAY NORTHERN SHORTWAVE.  
 
THE MASS AND THERMAL FIELDS ARE SIMILAR THROUGH MON NIGHT/TUESDAY,  
BUT THEN DIVERGE BY SHOWING DIFFERENT TIMING OF THE NORTHERN AND  
SOUTHERN STREAM FEATURES. THE FEATURE THAT BECOMES THE NORTHERN AND  
SOUTHERN SHORTWAVES NEXT WEEK IS CURRENTLY OVER THE ALEUTIANS AND  
DIVING SOUTH OVER THE PACIFIC OCEAN...AND IT REACHES THE USA WEST  
COAST BY MONDAY. EXPECT CHANGEABLE SOLUTIONS REGARDING THIS FEATURE  
UNTIL THAT TIME.  
 
CONTOUR HEIGHTS AND THERMAL FIELDS ARE A LITTLE ABOVE NORMAL  
SATURDAY, TREND COLDER THAN NORMAL SUNDAY-MONDAY, THEN TREND ABOVE  
NORMAL MIDWEEK NEXT.  
 
DETAILS...  
 
SATURDAY...  
 
LOW PRESSURE PASSES WELL OFFSHORE. GENERAL AGREEMENT THAT THE  
SOUTHERN SHORTWAVE REMAINS UNPHASED WITH THE NORTHERN TROUGH.  
MEANWHILE, THE NORTHERN TROUGH DOESN'T DIG MUCH UNTIL THE OFFSHORE  
LOW IS MOVING PAST US. SO EXPECT THE PRECIPITATION TO REMAIN OVER  
THE OCEAN.  
 
COLD FRONT APPROACHES DURING THE AFTERNOON AND PASSES THROUGH  
SOUTHERN NEW ENGLAND DURING THE EVENING/EARLY NIGHT. MOISTURE IS  
LIMITED BELOW 700 MB MUCH OF THE TIME, BUT RUNS DEEP BRIEFLY DURING  
THE EVENING. PRECIPITABLE WATER VALUES CLIMB TO ABOUT 0.85 INCHES  
DURING THE EVENING, WHICH IS ABOVE NORMAL FOR LATE NOVEMBER. WE WILL  
SHOW LOW-END CHANCE POPS DURING THE LATE AFTERNOON/EVENING.  
 
TEMPS IN THE MIXED LAYER ARE FORECAST AT 850-MB EQUIV OF -1C TO -4C,  
SO EXPECT MAX SFC TEMPS IN THE 50S. BEHIND THE FRONT, THE AIRMASS  
COOLS AND DRIES SLOWLY, SO MIN TEMPS AT NIGHT SHOULD ONLY FALL TO  
THE 30S AND LOW 40S.  
 
SUNDAY-MONDAY...  
 
UPPER TROUGH DIGS OVER NEW ENGLAND SUNDAY. COLD POOL WILL BE IN  
PLACE WITH 500-MB TEMPS AT -28C WORKING TO DESTABILIZE THE AIRMASS.  
MOISTURE LINGERS BELOW 800 MB DURING THIS TIME. EXPECT QUITE A FEW  
CLOUDS TO POP DURING THE DAY, BUT MOISTURE IS TOO LIMITED FOR  
SHOWERS. MIXED LAYER TEMPS WILL SUPPORT MAX SFC TEMPS IN THE UPPER  
30S AND 40S.  
 
THE TROUGH MOVES OFF ON MONDAY AND HIGH PRESSURE BUILDS SURFACE AND  
ALOFT. EXPECT A FAIR DAY WITH MAX SFC TEMPS IN THE 40S.  
 
TUESDAY THROUGH THURSDAY...  
 
ANOTHER COLD FRONT CROSSES US MIDWEEK, DRIVEN BY THE NORTHERN STREAM  
SHORTWAVE. AS NOTED ABOVE, THERE ARE TIMING UNCERTAINTIES AMONG THE  
MODELS, SO WE USED A BLEND. THIS FAVORS A WEDNESDAY PASSAGE AT THIS  
TIME, BUT THE UNCERTAINTIES NOTED ABOVE MAY CHANGE THAT EXACT  
TIMING. THIS WILL NEED TO BE MONITORED. THE BLEND OF MODEL DATA  
SUPPORTS SLIGHT CHANCE POPS WEDNESDAY WITH THE COLD FROPA AND MAINLY  
DRY THURSDAY.  
 

 
   
AVIATION /23Z THURSDAY 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/...HIGH CONFIDENCE.  
 
VFR. W/NW WINDS DIMINISH OVERNIGHT, TURNING S/SW INTO FRIDAY.  
BKN-OVC MVFR CIGS POSSIBLE FOR SE NEW ENGLAND INTO FRIDAY NIGHT.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY THROUGH SATURDAY NIGHT: MAINLY VFR, WITH LOCAL MVFR  
POSSIBLE. BREEZY. SLIGHT CHANCE SHRA.  
 
SUNDAY: VFR. WINDY WITH LOCAL GUSTS TO 30 KT.  
 
SUNDAY NIGHT THROUGH TUESDAY: VFR. BREEZY.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH FRIDAY NIGHT/...  
 
SMALL CRAFT ADVISORIES ADJUSTED TO ACCOUNT FOR SEAS. SHOULD  
CONCLUDE INTO FRIDAY MORNING. HIGH PRESSURE MAINLY IN CONTROL.  
GOOD BOATING WEATHER AS SWELLS DIMINISH.  
 
OUTLOOK /SATURDAY THROUGH TUESDAY/...  
 
SATURDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT. SLIGHT CHANCE OF RAIN SHOWERS.  
 
SUNDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS  
UP TO 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 
SUNDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS.  
 
MONDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP  
TO 25 KT. LOCAL ROUGH SEAS.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING  
5 FT.  
 
TUESDAY: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING 5 FT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...NONE.  
MA...NONE.  
RI...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 7 PM EST THIS  
EVENING FOR ANZ250.  
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 7 AM EST FRIDAY  
FOR ANZ254>256.  
 

 
 

 
SYNOPSIS...WTB/SIPPRELL  
NEAR TERM...WTB/BELK/SIPPRELL  
SHORT TERM...SIPPRELL  
LONG TERM...WTB  
AVIATION...WTB/SIPPRELL  
MARINE...WTB/SIPPRELL  
 
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