920  
FXUS61 KBOX 261050  
AFDBOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BOSTON/NORTON MA  
650 AM EDT SAT MAY 26 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE SOUTHEAST OF NEW ENGLAND WILL BRING ANOTHER DAY OF  
WARM TEMPERATURES TODAY. A COLD FRONT WILL PUSH SOUTH ACROSS THE  
REGION LATE TODAY INTO THIS EVENING, BRINGING SCATTERED SHOWERS AND  
A FEW THUNDERSTORMS. MUCH COOLER AND UNSETTLED CONDITIONS WILL  
LINGER SUNDAY, WITH IMPROVING CONDITIONS BY MONDAY. HIGH  
PRESSURE BRINGS MAINLY DRY AND WARMER WEATHER TUESDAY THROUGH  
THURSDAY. AN APPROACHING WEATHER SYSTEM BRINGS SHOWERS FRIDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
650 AM UPDATE...  
 
SOME THIN CIRRUS OVERHEAD, OTHERWISE A SUNNY MORNING. SATELLITE  
IMAGERY SHOWS THICKER CLOUDS IN VT-NH-MAINE, WITH MORE UPSTREAM  
OVER NORTHERN NY AND ONTARIO. EXPECT THE THICKER CLOUDS TO MOVE  
IN DURING THE AFTERNOON/EVENING, BUT DRY WEATHER FOR MUCH OF THE  
DAY. NO SIGNIFICANT CHANGES TO THE FORECAST.  
 
MASSACHUSETTS JOINED IN THIS MORNING WITH AN AIR QUALITY ALERT  
FOR AREAS ADJACENT TO CT AND RI AND EXTENDING ACROSS SE MASS. RI  
AND CT CONTINUE WITH THEIR EXISTING AQA. TIME IS 11 AM TO 11 PM.  
 
PREVIOUS DISCUSSION...  
 
SKIES WERE MAINLY PARTLY CLOUDY ACROSS THE REGION AT 08Z AS SEEN  
ON LATEST GOES-EAST NIGHTTIME MICROPHYSICS SATELLITE IMAGERY AND  
ON OBSERVATIONS. MOST OF THE HEAVIER CLOUDS LOOKED CONFINED  
ACROSS CENTRAL NH/VT NORTHWARD AS THE FRONT SITS ACROSS FAR N  
MAINE. SCATTERED SHOWERS AND A FEW THUNDERSTORMS SEEN ON THE NE  
REGIONAL 88D RADAR CROSSING N NY INTO CENTRAL AND N NH/ME  
HEADING TO THE GULF OF MAINE AT 0820Z.  
 
WILL SEE DRY CONDITIONS FOR MOST AREAS THROUGH THE DAY. EXPECT  
TO SEE CLOUDS INCREASE ACROSS N MASS BY AROUND MIDDAY, THEN  
WILL SHIFT S THROUGH THE AFTERNOON. THE MAJORITY OF THE 00Z  
MODEL SUITE SIGNALING A SLOW MOVEMENT TO THE FRONT, BUT SHOULD  
START TO APPROACH THIS AFTERNOON. CURRENT TIMING SUGGESTS THAT  
THE FRONT SHOULD REACH NE MASS BY AROUND 18Z-20Z, THEN WILL PUSH  
TO AROUND THE MASS PIKE BY AROUND 00Z OR SO.  
 
NOTING RATHER GOOD INSTABILITY ASSOCIATED WITH THE FRONT, WITH  
SLIS IN THE ZERO TO -2 RANGE, TQ VALUES AROUND 20 AND K INDICES  
IN THE LOWER 30S. HOWEVER, THE LAPSE RATES ARE NOT THAT GREAT,  
ON THE ORDER OF 6 TO 6.5C/KM, BUT STILL EXPECT SCATTERED  
THUNDERSTORMS EMBEDDED WITH THE SHOWERS AS THE FRONT APPROACHES,  
BUT APPEARS THE MAJORITY OF THE ACTIVITY WILL ARRIVE TONIGHT.  
 
HAVE CARRIED CHANCE POPS ACROSS N CENTRAL AND NE MASS BY AROUND  
20Z-21Z, WITH SLIGHT CHANCE POPS FURTHER S AND W.  
 
WHAT WILL HELP WITH THE INSTABILITY WILL BE THE WARM SUMMER LIKE  
TEMPS, WHICH ARE EXPECTED TO REACH THE MID AND UPPER 80S AWAY  
FROM THE IMMEDIATE S COAST. A FEW SPOTS MAY EVEN TOUCH 90. AS  
THE FRONT CROSSES NE MASS, TEMPS WILL START TO FALL QUICKLY BY  
EVENING AS WINDS SHIFT TO E-NE  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/
 
 
TONIGHT...  
 
THE COLD FRONT CONTINUES TO SLOWLY PUSH SOUTHWARD ACROSS THE  
REMAINDER OF THE REGION, THEN WILL START TO STALL NEAR OR JUST  
OFF THE S COAST BY AROUND 12Z SUNDAY. WINDS WILL SHIFT TO E-NE  
AND TEMPS WILL FALL QUICKLY WITH THE SURGE OF COLDER AIR DOWN  
THE COAST BEHIND THE FRONT. STILL SOME INSTABILITY LINGERING, SO  
CAN NOT RULE OUT A FEW THUNDERSTORMS NEAR AND AHEAD OF THE FRONT  
AS IT PASSES.  
 
ANOTHER IMPULSE MOVES ALONG THE PASSING FRONT AS IT REACHES THE  
S COAST THROUGH AROUND 03Z OR SO, SO WILL SEE A BETTER SHOT FOR  
SHOWERS AND A FEW THUNDERSTORMS THERE. HAVE CARRIED HIGH CHC  
POPS THERE, ALONG WITH THE THUNDER. AS THE COLDER AIR MOVES IN,  
WILL SEE THE CONVECTION DIMINISH, BUT WILL CAN NOT RULE OUT AN  
ISOLATED T-STORM THROUGH THE NIGHT ACROSS N CT/RI/SE MASS.  
 
TEMPS WILL FALL BACK TO THE LOWER-MID 50S.  
 
SUNDAY...  
 
WITH THE FRONT NEARLY STATIONARY S OF THE REGION, WILL SEE  
CONTINUED CHANCE FOR SHOWERS. STILL CAN'T RULE OUT A RUMBLE OF  
THUNDER ALONG S COASTAL AREAS THROUGH MIDDAY AS MARGINAL  
INSTABILITY LINGERS. WILL SEE GUSTY E-NE WINDS MOVING IN ACROSS  
E COASTAL AREAS WITH GUSTS UP TO 20-25 KT, HIGHEST ACROSS OUTER  
CAPE COD AND NANTUCKET.  
 
TEMPS WILL BE COOLEST ACROSS EASTERN MASS WITH HIGHS ONLY IN THE  
MID-UPPER 50S, RANGING TO THE LOWER 60S ACROSS THE CT VALLEY,  
WHERE THE PRECIP WILL SLOWLY TAPER OFF AROUND MIDDAY OR EARLY  
AFTERNOON.  
 

 
   
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
 
 
BIG PICTURE...  
 
TODAY'S DRAMATIS COELUS...WEATHER OF THE DRAMA?...FEATURES A  
ZONAL UPPER FLOW ALONG THE NORTHERN TIER OF THE USA, A CLOSED  
LOW OVER THE WESTERN USA, ANOTHER CLOSED LOW ALONG THE ALASKA  
COAST, CLOSED LOW OVER THE GULF OF MEXICO HELD IN PLACE BY  
RIDGES CENTERED OVER MEXICO AND THE WEST INDIES.  
 
ONE SHORTWAVE IN THE ZONAL FLOW MOVES EAST OF NEW ENGLAND  
MONDAY, ALLOWING SOME DRYING OVER OUR AREA. A SHARPER SHORTWAVE  
IN THE ZONAL FLOW MOVES ACROSS EASTERN CANADA TUESDAY, WITH  
MODEL CONSENSUS SHOWING A WINDSHIFT OVER OUR AREA AS THE  
SHORTWAVE MOVES PAST. THE CLOSED WESTERN LOW GETS KICKED OUT OF  
POSITION AS THE ALASKA LOW MOVES DOWN THE COAST AND ASHORE. THE  
WESTERN LOW THEN EJECTS INTO THE ZONAL FLOW, DRAWS THE GULF OF  
MEXICO LOW NORTH AND MERGES, THEN MOVES THROUGH NEW ENGLAND AT  
THE END OF THE WEEK.  
 
MODEL SOLUTIONS SHOW ABOVE NORMAL CONTOUR HEIGHTS THROUGH THE  
FORECAST PERIOD, AND THERMAL FIELDS ALSO INDICATE ABOVE NORMAL  
TEMPERATURES.  
 
MODEL SOLUTIONS REMAIN SIMILAR THROUGH THURSDAY MORNING, THEN  
SHOW A SIMILAR BROAD PATTERN WITH DIFFERENCES IN DETAIL. THIS  
GIVES US HIGH CONFIDENCE IN THE FORECAST THROUGH MIDWEEK AND  
MODERATE CONFIDENCE LATE WEEK.  
 
CONCERNS...  
 
SUNDAY NIGHT-MONDAY...  
 
WAVE ALONG THE STALLED COLD FRONT MOVES OUT TO SEA WHILE  
RIDGELINE FROM THE MARITIMES HOLDS OVER SOUTHERN NEW ENGLAND.  
CROSS SECTIONS SHOW PLENTY OF MOISTURE BELOW 700 MB BUT SHALLOW  
AND DIMINISHING LIFT. THE POSITIONING OF THE RIDGE LINE SHOULD  
MAINTAIN EAST- NORTHEAST WINDS THROUGH MONDAY MAINTAINING A  
MOIST LOW-LEVEL FLOW. WILL CONTINUE TO INDICATE CHANCE POPS  
SUNDAY NIGHT, THEN MOSTLY CLOUDY SKIES MONDAY.  
 
TUESDAY THROUGH THURSDAY...  
 
SECOND, SHARPER SHORTWAVE PASSES TO OUR NORTH ON TUESDAY. THIS  
BRINGS A WINDSHIFT FROM WESTERLY TO NORTHERLY, BUT LOTS OF DRY  
AIR IN PLACE AT THE TIME. HIGH PRESSURE SURFACE AND ALOFT BRINGS  
SUBSIDENCE, AND DRY AIR LINGERS THROUGH THURSDAY. EXPECT MOSTLY  
CLEAR SKIES AND LIGHT WIND. LIGHT FLOW SHOULD SUPPORT SEA  
BREEZES ON WEDNESDAY.  
 
THURSDAY NIGHT AND FRIDAY...  
 
MOISTURE FIELDS INCREASE AT THE CIRRUS LEVEL THURSDAY, THEN  
CLOSER TO THE SURFACE THURSDAY EVENING AND NIGHT. TIMING OF  
ONSET OF SHOWERS IS DEPENDENT ON THE EJECTING SHORTWAVE AND ITS  
INTERACTIONS WITH THE GULF OF MEXICO LOW. CURRENT INFO SUGGESTS  
SHOWERS STARTING SOMETIME THURSDAY NIGHT AND CONTINUING INTO  
FRIDAY.  
 

 
   
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SUNDAY/...HIGH CONFIDENCE.  
 
TODAY... MAINLY VFR CONDITIONS THROUGH MOST OF THE DAY. CLOUDS  
LOWER ACROSS N MASS TO NEAR THE MASS PIKE DURING THE AFTERNOON.  
ISOLD SHRA/TSRA AFTER 19Z-20Z MAINLY FROM THE MASS PIKE  
NORTHWARD, BEST CHANCE ACROSS NE MASS. W-SW WINDS 5-10 KT EXCEPT  
UP TO 15 KT ALONG S COAST. WIND SHIFT TO E-NE AFTER 21Z ACROSS  
NE MASS.  
 
TONIGHT...  
MAINLY VFR THROUGH 05Z-06Z, THEN CIGS LOWER TO AREAS OF IFR FROM  
NE-SW. PATCHY LIFR CIGS ACROSS HIGHER TERRAIN AND ALONG S COAST  
TOWARD DAYBREAK. VSBYS LOWER TO MVFR-IFR ACROSS E MASS/RI IN  
AREAS OF FOG. WINDS SHIFT TO E-NE FROM N-S OVERNIGHT WITH GUSTS  
TO AROUND 20 KT ALONG E COASTAL AREAS AFTER 08Z. SCATTERED SHRA,  
CHANCE TSRA.  
 
SUNDAY...  
MVFR-IFR CIGS LINGER THROUGH MOST OF THE DAY. SCATTERED SHRA  
THROUGH THE DAY. ISOLATED TSRA MAINLY S OF THE MASS PIKE BY  
MIDDAY, THEN OFFSHORE LATE IN THE DAY. VSBYS IMPROVE TO VFR N OF  
MASS PIKE AROUND MIDDAY, BUT MVFR-IFR IN PATCHY FOG ALONG S  
COAST THROUGH THE DAY.  
 
KBOS TERMINAL...HIGH CONFIDENCE IN TAF, EXCEPT MODERATE  
CONFIDENCE IN TIMING OF WIND SHIFT TODAY. SW WIND AROUND 10 KT.  
BACK DOOR COLD FRONT MOVES ACROSS AROUND 19Z-21Z WITH A WIND  
SHIFT FROM W TO E-NE. WIND GUSTS TO AROUND 20 KT AFTER 03Z  
TONIGHT.  
 
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.  
LIGHT S-SW WINDS BECOME W 5-10 KT BY MIDDAY. BACK DOOR COLD  
FRONT SHOULD HOLD OFF UNTIL AROUND 00Z-02Z WHEN WIND SHIFTS  
TO NE.  
 
OUTLOOK /SUNDAY NIGHT THROUGH WEDNESDAY/...MODERATE TO HIGH  
CONFIDENCE.  
 
SUNDAY NIGHT: MAINLY IFR, WITH LOCAL MVFR POSSIBLE. BREEZY.  
AREAS BR, SLIGHT CHANCE SHRA, ISOLATED TSRA.  
 
MEMORIAL DAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE IN THE  
MORNING.  
 
MONDAY NIGHT: MAINLY VFR, WITH LOCAL IFR POSSIBLE. PATCHY BR.  
 
TUESDAY: VFR. BREEZY.  
 
TUESDAY NIGHT THROUGH WEDNESDAY: VFR.  
 

 
   
MARINE
 
 
FORECASTER CONFIDENCE LEVELS...  
 
LOW - LESS THAN 30 PERCENT.  
MODERATE - 30 TO 60 PERCENT.  
HIGH - GREATER THAN 60 PERCENT.  
 
SHORT TERM /THROUGH SUNDAY/...HIGH CONFIDENCE.  
 
TODAY... SMALL CRAFTS WILL END BY MID MORNING ACROSS BI/RI  
SOUNDS, OTHERWISE WILL CONTINUE FOR THE SOUTHERN OUTER WATERS  
THROUGH THE DAY. SW WINDS DIMINISH AHEAD OF THE APPROACHING BACK  
DOOR COLD FRONT, WHICH SHOULD PUSH ACROSS THE EASTERN WATERS  
DURING THE AFTERNOON, THEN APPROACHING CAPE COD BY 00Z. WILL SEE  
CHANCE OF SHOWERS/ISOLATED THUNDERSTORMS MOVE ACROSS THE  
EASTERN WATERS AFTER 18Z, WITH A WIND SHIFT TO E-NE AS THE FRONT  
PASSES WITH GUSTS UP TO 20 KT.  
 
TONIGHT...  
WINDS SHIFT TO E-NE ACROSS THE SOUTHERN WATERS THIS EVENING.  
WILL SEE WINDS GUSTING UP TO AROUND 25 KT ACROSS THE EASTERN  
WATERS TO E OF CAPE COD OVERNIGHT. GUSTS UP TO 25-30 KT AND SEAS  
BUILD TO 3-5 FT ACROSS THE EASTERN OUTER WATERS TOWARD  
DAYBREAK, WHERE SMALL CRAFTS HAVE BEEN ISSUED. SCATTERED  
SHOWERS/ISOLATED THUNDERSTORMS LINGER THROUGH THE NIGHT. AREAS  
OF FOG WITH REDUCED VISIBILITY.  
 
SUNDAY...  
E-NE WINDS INCREASE ACROSS ALL WATERS AS THE COLD FRONT SHIFTS  
S. GUSTS UP TO 25-30 KT, HIGHEST ON THE EASTERN OPEN WATERS.  
SEAS BUILD UP TO 5-8 FT ON THE EASTERN WATERS AS WELL. SMALL  
CRAFTS WILL BE NEEDED ON THE SOUTHERN WATERS DURING THE DAY.  
SHOWERS CONTINUE, WITH BEST CHANCE ALONG THE SOUTHERN WATERS.  
REDUCED VISIBILITY IN AREAS OF FOG.  
 
OUTLOOK /SUNDAY NIGHT THROUGH WEDNESDAY/...MODERATE CONFIDENCE.  
 
SUNDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH  
GUSTS UP TO 25 KT. AREAS OF ROUGH SEAS. CHANCE OF RAIN SHOWERS,  
AREAS FOG, SLIGHT CHANCE OF THUNDERSTORMS. VISIBILITY 1 TO  
3 NM.  
 
MEMORIAL DAY: WINDS LESS THAN 25 KT. SEAS UP TO 5 FT.  
 
MONDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS APPROACHING  
5 FT.  
 
TUESDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.  
 
TUESDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL VISIBILITY 1 TO  
3 NM.  
 
WEDNESDAY: WINDS LESS THAN 25 KT.  
 

 
   
BOX WATCHES/WARNINGS/ADVISORIES
 
 
CT...AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS  
EVENING FOR CTZ002>004.  
MA...AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS  
EVENING FOR MAZ011>013-016>021.  
RI...AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS  
EVENING FOR RIZ001>008.  
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EDT THIS MORNING FOR  
ANZ232>234.  
SMALL CRAFT ADVISORY UNTIL 10 AM EDT THIS MORNING FOR ANZ235-  
237.  
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EDT SUNDAY  
FOR ANZ250.  
SMALL CRAFT ADVISORY FROM 1 AM TO 6 PM EDT SUNDAY FOR ANZ251.  
SMALL CRAFT ADVISORY UNTIL 6 PM EDT SUNDAY FOR ANZ254.  
SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR ANZ255-  
256.  
 

 
 

 
SYNOPSIS...WTB/EVT  
NEAR TERM...WTB/EVT  
SHORT TERM...EVT  
LONG TERM...WTB  
AVIATION...WTB/EVT  
MARINE...WTB/EVT  
 
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