510  
FXUS61 KBOX 180819  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
419 AM EDT THU OCT 18 2018  
   
SYNOPSIS
 
 
UNSEASONABLY CHILLY AND WINDY WEATHER TODAY WILL BE FOLLOWED BY  
DIMINISHING WINDS BUT SUB-FREEZING LOW TEMPERATURES IN MANY  
LOCATIONS TONIGHT. MILDER TEMPERATURES RETURN FRIDAY AFTERNOON  
ALONG WITH PLENTY OF SUNSHINE. SERIES OF SWEEPING COLD FRONTS  
LATE WEEK INTO THE WEEKEND. LIGHT SHOWERY WEATHER SURROUNDING,  
NOTHING OF A WASHOUT, ALONG WITH BREEZY WINDS. IN WAKE, CANADIAN  
HIGH PRESSURE, FROST / FREEZE CONDITIONS FOR AN OVERNIGHT  
PERIOD BEFORE TEMPERATURES REBOUND.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
* WINDY AND UNSEASONABLY CHILLY TODAY  
 
STRONG COLD ADVECTION BEHIND LAST EVENING/S COLD FRONT WILL  
ALLOW 850T TO DROP TO BETWEEN -8C AND -10C THROUGH MID  
AFTERNOON. MODEL CROSS SECTIONS INDICATE A LOT OF DRY AIR  
THROUGH THE COLUMN...SO EXPECT PLENTY OF SUNSHINE.  
NONETHELESS...THE ANOMALOUS COLD AIR ALOFT WILL RESULT IN HIGH  
TEMPERATURES ONLY IN THE LOWER 40S ACROSS THE HIGHER TERRAIN  
WITH MAINLY UPPER 40S ELSEWHERE.  
 
THE ATMOSPHERE WILL BE SUPER ADIABATIC AND ALLOW STRONGER WINDS  
ALOFT TO MIX DOWN. ALTHOUGH MUCH OF THE REGION SHOULD REMAIN  
BELOW WIND ADVISORY CRITERIA...EXPECT A BRIEF PERIOD OF 30 TO 35  
KNOT WIND GUSTS ROUGHLY BETWEEN 10Z AND 15Z. WE CAN NOT RULE OUT  
A FEW GUSTS NEAR 40 KNOTS FOR A VERY SHORT TIME. WITH ALL THAT  
SAID DROPPED THE WIND ADVISORY FOR MUCH OF THE REGION...BUT  
OPTED TO KEEP IT FOR THE WORCESTER HILLS AND NORTHEAST MA WHERE  
THE GREATEST POTENTIAL EXISTS FOR CRITERIA BEING APPROACHED.  
WE ALSO CONTINUED THE ADVISORY FOR ACK/CAPE COD. EVEN IF GUSTS  
ONLY APPROACH 35 KNOTS...MINOR TREE DAMAGE/ISOLATED POWER  
OUTAGES ARE POSSIBLE GIVEN THE FULLY LEAFED TREES.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/
 
 
* WIDESPREAD FROST/FREEZE CONDITIONS OVERNIGHT  
 
TONIGHT...  
 
A RIDGE OF HIGH PRESSURE WILL BUILD SOUTH OF OUR REGION FROM THE  
WEST. THIS WILL ALLOW WINDS TO DECOUPLE IN MANY LOCATIONS AND  
WITH MAINLY CLEAR SKIES AN IDEAL NIGHT OF RADIATIONAL COOLING  
CONDITIONS ARE EXPECTED. LOW TEMPS SHOULD RANGE FROM THE MIDDLE  
20S IN THE NORMALLY COLDEST OUTLYING LOCATIONS...TO THE UPPER  
20S AND LOWER 30S IN MOST OTHER LOCATIONS. FREEZE/FROST  
HEADLINES ARE POSTED OVERNIGHT FOR MANY LOCATIONS WHERE THE  
GROWING SEASON HAS NOT OFFICIALLY ENDED. EVEN ALONG THE  
IMMEDIATE COAST...LOW TEMPERATURES SHOULD DROP WELL DOWN INTO  
THE 30S AND FROST HEADLINES ARE POSTED FOR MANY OTHER LOCATIONS.  
THE EXCEPTION IS DOWNTOWN BOSTON/NANTUCKET, WHERE LOW TEMPS  
SHOULD GENERALLY REMAIN IN THE UPPER 30S.  
 
FRIDAY...  
 
THE RIDGE OF HIGH PRESSURE WILL MOVE EAST OF THE MID ATLANTIC  
COAST FRIDAY. THE RESULT WILL BE A QUICK RETURN TO A MUCH MILDER  
SOUTHWEST FLOW OF AIR. IN FACT...850T WILL RISE TO +8C TO +10C  
BY FRIDAY AFTERNOON. GIVEN THE COLD START AND THE LOWERING  
OCTOBER SUN ANGLE...THIS MID LEVEL WARMTH WILL NOT BE COMPLETELY  
REALIZED AT THE SURFACE. NONETHELESS...STILL EXPECT A  
SIGNIFICANTLY MILDER DAY WITH MANY LOCATIONS REACHING THE LOWER  
60S. GUSTY SOUTHWEST WINDS SHOULD DEVELOP ALONG THE COASTAL  
PLAIN DURING THE AFTERNOON.  
 

 
   
LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/
 
 
*/ HIGHLIGHTS...  
 
- TEMPERATURE UNDULATIONS AROUND SWEEPING COLD FRONTS  
- WITH ANY FRONTAL PASSAGES, EXPECT SHOWERY WEATHER, BREEZY WINDS  
- IN WAKE, FROST / FREEZE CONDITIONS POSSIBLE  
 
*/ OVERVIEW...  
 
UNDULATING AIRMASSES OF AUTUMN. NE ATLANTIC ANTI-CYCLONIC WAVE BREAK  
EVOLVES INTO AN OMEGA BLOCK SLOWING THE UPSTREAM H5 LONGWAVE PATTERN  
ALLOWING STORM MATURATION OVER E CANADA NE TOWARDS THE NORWEGIAN SEA.  
OBTAINING GREATER CURVATURE / ANGULAR MOMENTUM, STORM DEEPENING NETS  
CROSS-POLAR FLOW INTO EASTERN N AMERICA THROUGH A PREFERRED H5 TROF  
AIDED BY A +PNA / +AO TREND. UP AGAINST AN UPSTREAM -EPO AND SPLIT-  
FLOW REGIME, PREFERRED H5 TROF WAVERS AT TIMES, RELOADING WHEN +PNA  
W CONUS H5 RIDGE SURGES. STRENGTH CRUCIAL WHEN IT COMES TO H5 TROF  
DIPS OVER BAROCLINIC REGIONS, WHERE MORE FAVORABLE STORM DEVELOPMENT  
WILL OCCUR, WHETHER ACTING ON THE S-STREAM.  
 
ASIDE, WITH H5 TROF DIPS, ISALLOBARIC / PRESSURE-GRADIENT RESPONSE  
TO PATTERN AMPLIFICATION, DOWNWARD REFLECTION WITH SURFACE - H85  
COLD AIR ADVECTION ROUGHLY -1 TO -2 STANDARD DEVIATION AIDING IN  
STEEP LOW-LEVEL LAPSE RATES, SUBSEQUENT MIX-DOWN OF FASTER MOMENTUM  
AND DRIER AIR. WET-WEATHER CHANCES ALONG ASSOCIATED SWEEPING COLD  
FRONTS.  
 
ROSSBY WAVE TRANSITION INTO THE END OF OCTOBER, A +EPO EVOLVES. W  
CONUS ONSHORE PACIFIC AIR, THE UPSTREAM PREFERRED H5 TROF PATTERN  
LOOKS TO BREAK, ALBEIT BRIEFLY, LESS ACTIVE PATTERN.  
 
*/ DISCUSSION...  
 
FRIDAY NIGHT INTO SATURDAY NIGHT ... CHANCE POPS UPON A CONTINENTAL  
AIRMASS UNDERGOING ASCENT ABOVE A LIFTING COLD FRONT. SHOWERY, NOT A  
WASHOUT. WIND WATCH. BREEZY SW WINDS WITH ADVISORY-LEVEL CONCERNS  
GIVEN POTENTIAL MIXING TO H8 WHERE 45 MPH WINDS ARE MODELED. A LULL  
LATE SATURDAY INTO SATURDAY EVENING WITH COLD FRONTAL PASSAGE, THEN  
FOCUS ON COLD AIR ADVECTION, STEEPENING LAPSE RATES, ALLOWANCE OF  
FAST NW WINDS TO MIX DOWN.  
 
SUNDAY INTO SUNDAY NIGHT ... BREEZY NW WINDS DIMINISHING. CLEARING  
UNDER HIGH PRESSURE INFLUENCE SHIFTING SE. LIGHT WINDS, COLD ALOFT.  
FROST / FREEZE CONCERNS INTO MONDAY MORNING.  
 
MONDAY THRU WEDNESDAY ... TEMPERATURE SWINGS ROUND ANOTHER SWEEPING  
COLD FRONT TUESDAY EVENING. CHANCE POPS WITH SHOWERY WEATHER, FAIRLY  
VOID OF MOISTURE, ANOTHER CONTINENTAL AIRMASS. BREEZY WINDS POSSIBLE  
AGAIN WITH FROST / FREEZE CONCERNS IN COLD FRONTAL WAKE.  
 
LATE WEEK ONWARD ... WAY TOO MUCH DETERMINISTIC / ENSEMBLE MODEL  
SPREAD TO MAKE ANY DETERMINATION. -EPO HAVING WEAKENED, LOW PRESSURE  
DEVELOPING OVER THE GULF OF AK, N PACIFIC OPENS AND MILD PACIFIC AIR  
STREAMS ASHORE SEEMS CERTAIN, HOWEVER DOWNSTREAM OUTCOMES ARE WIDELY  
UNKNOWN.  
 

 
   
AVIATION /08Z THURSDAY THROUGH MONDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH FRIDAY/...  
 
TODAY...HIGH CONFIDENCE IN VFR. NW WIND GUSTS OF 25 TO 35 KNOTS.  
 
TONIGHT...HIGH CONFIDENCE. VFR WITH DIMINISHING WINDS THIS  
EVENING.  
 
FRIDAY...HIGH CONFIDENCE. VFR CONDITIONS CONTINUE. SW WIND GUSTS  
INCREASE TO BETWEEN 20 AND 25 KNOTS DURING THE AFTERNOON ALONG  
THE COASTAL PLAIN. A FEW GUSTS AROUND 30 KNOTS EXPECTED ACROSS  
THE FAR SOUTHEAST NEW ENGLAND COAST.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
 
OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...MODERATE-HIGH CONFIDENCE.  
 
FRIDAY NIGHT: VFR. WINDY WITH GUSTS TO 30 KT. SLIGHT CHANCE  
SHRA.  
 
SATURDAY: VFR. WINDY WITH GUSTS TO 35 KT. CHANCE SHRA.  
 
SATURDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.  
 
SUNDAY THROUGH SUNDAY NIGHT: VFR. WINDY WITH AREAS GUSTS TO  
30 KT.  
 
MONDAY: 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/...HIGH CONFIDENCE.  
 
TODAY...GALE WARNINGS REMAIN POSTED THIS MORNING FOR ALL  
WATERS WITH NORTHWEST WIND GUSTS OF 30 TO 40 KNOTS. THE  
STRONGEST OF THE WINDS WILL GRADUALLY DIMINISH FROM WEST TO EAST  
THIS AFTERNOON...BUT WILL NEED TO CONTINUE GALE HEADLINES  
THROUGH LATE AFTERNOON ACROSS MOST OUTER-WATERS.  
 
TONIGHT...WHILE WIND GUSTS SHOULD DROP BELOW 25 KNOTS THIS  
EVENING...SMALL CRAFT HEADLINES WILL STILL BE NEEDED FOR MUCH  
OF TONIGHT ACROSS THE OUTER-WATERS FOR LEFT OVER  
SEAS...ALTHOUGH THEY WILL BE ON THE DOWNWARD TREND.  
 
FRIDAY...SMALL CRAFT HEADLINES WILL BE REQUIRED FOR ALL WATERS  
AS HIGH PRESSURE MOVES FURTHER EAST AND AWAY FROM THE MID  
ATLANTIC COAST. THIS WILL GENERATE SOUTHWEST WIND GUSTS OF 20 TO  
30 KNOTS AND ROUGH SEAS...PARTICULARLY ON THE SOUTHERN WATERS  
WITH LONG FETCH.  
 
OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...MODERATE TO HIGH  
 
FRIDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS. SLIGHT CHANCE OF RAIN  
SHOWERS.  
 
SATURDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 35 KT.  
AREAS OF ROUGH SEAS. CHANCE OF RAIN SHOWERS.  
 
SATURDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE  
OF RAIN SHOWERS.  
 
SUNDAY: STRONG WINDS WITH AREAS OF GUSTS UP TO 30 KT. AREAS OF  
ROUGH SEAS. SLIGHT CHANCE OF RAIN SHOWERS.  
 
SUNDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 30 KT. LOCAL ROUGH SEAS.  
 
MONDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
 

 
   
CLIMATE
 
 
RECORD LOW MAXIMUM TEMPERATURES FOR TODAY  
 
BOS 45 IN 1898  
ORH 36 IN 1989  
BDL 44 IN 2009  
PVD 46 IN 1939  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR  
CTZ002>004.  
MA...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR  
MAZ007-014-019-022-023.  
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR  
MAZ005-006-009>013-017-018-020-021.  
WIND ADVISORY UNTIL 11 AM EDT THIS MORNING FOR MAZ004>007-  
012>016-022-024-026.  
RI...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR  
RIZ002-004>007.  
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR  
RIZ001-003.  
MARINE...GALE WARNING UNTIL 2 PM EDT THIS AFTERNOON FOR ANZ231-232-251.  
GALE WARNING UNTIL 11 AM EDT THIS MORNING FOR ANZ230-233>237.  
GALE WARNING UNTIL 4 PM EDT THIS AFTERNOON FOR ANZ250-254>256.  
 

 
 

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