Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210143 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 943 PM EDT MON OCT 20 2014 .SYNOPSIS... A LONG DURATION COASTAL STORM WILL BRING PERIODS OF RAIN TUESDAY THROUGH THURSDAY WITH LINGERING SHOWERS FRIDAY AS THE STORM SLOWLY PULLS AWAY FROM NEW ENGLAND. MAINLY DRY WEATHER EXPECTED THIS WEEKEND WITH SEASONABLE TEMPERATURES. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 940 PM UPDATE... NO MAJOR CHANGES FROM PREVIOUS FORECAST. CHANCE OF RAIN BEGINS TO INCREASE AFTER 06Z/2AM AND ESPECIALLY TOWARD 12Z AND BEYOND PER LATEST 21Z SREF AND LATEST RAP13. ALTHOUGH MAY HAVE TO DELAY PRECIP A FEW MORE HOURS GIVEN 00Z UPSTREAM SOUNDING AT OKX WHICH INDICATES LOTS OF DRY AIR BETWEEN 850 MB TO 600 MB. THUS MUCH OF THE NIGHT MAY REMAIN DRY WITH RAIN HOLDING OFF UNTIL AFTER SUNRISE TUE AND BEYOND. WILL HAVE TO EVALUATE SATELLITE AND RADAR TRENDS AND 00Z NAM UPON ARRIVAL. REGARDING TEMPS...INCREASING LOW LEVEL WARM AIR ADVECTION WILL RESULT IN TEMPS HOLDING NEARLY STEADY OVERNIGHT ALONG WITH LOW TEMPS RUNNING 3-6 DEGS WARMER THAN NORMAL. QUITE A DIFFERENCE FROM LAST NIGHT. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... ***NARROW AXIS OF HEAVY RAIN POSSIBLE ON TUESDAY ACROSS EASTERN NEW ENGLAND*** TUESDAY... INTERESTING SETUP WITH A CLOSED UPPER LEVEL LOW TO OUR WEST AND A SURFACE TROUGH ACROSS EASTERN NEW ENGLAND. THE INTERACTION OF THE COLD POOL ALOFT...A SOUTHERLY LOW LEVEL JET AND AXIS OF SURFACE CONVERGENCE MAY LEAD TO SOME LOCALIZED HEAVY RAINFALL ACROSS EASTERN NEW ENGLAND. INTERESTING THAT THE HIGH RESOLUTION MODELS ARE SHOWING A NARROW AXIS OF 1 TO 2 INCHES OF RAIN SOMEWHERE NEAR THE I-95 CORRIDOR. EXACT LOCATION REMAINS UNCERTAIN AND IT COULD REMAIN OFFSHORE...BUT SOMETHING TO WATCH. WE MAY BE DEALING WITH LOCALIZED NUISANCE POOR DRAINAGE STREET FLOODING IN THIS REGION IF THIS NARROW AXIS OF HEAVY RAIN DEVELOPS. FURTHER TO THE WEST ACROSS INTERIOR SOUTHERN NEW ENGLAND...SCATTERED SHOWERS WILL BE POSSIBLE BUT BEST FORCING/MOISTURE WILL BE ACROSS OUR EASTERN ZONES...SO ACTIVITY SHOULD NOT BE AS WIDESPREAD. AS FOR CONVECTIVE POTENTIAL...500 MB TEMPS WILL BE BELOW -20C AND RESULT IN ELEVATED INSTABILITY. MODEL SOUNDINGS HAVE BEEN INDICATING MU CAPES ON THE ORDER OF 500 J/KG. HAVE INCLUDED ISOLATED THUNDERSTORMS IN THE FORECAST ACROSS SOME OF THE REGION. WHILE WE CAN/T RULE OUT AN ISOLATED THUNDERSTORM ACROSS MUCH OF THE REGION...BEST SHOT WILL BE ACROSS EASTERN NEW ENGLAND. HIGH TEMPS WILL MAINLY BE IN THE UPPER 50S AND LOWER 60S ACROSS THE REGION. TUESDAY NIGHT... APPEARS THAT THE DEEPER MOISTURE/LIFT TEMPORARILY SHIFTS TO THE NORTH OF OUR REGION AND INTO NORTHER NEW ENGLAND. NONETHELESS...CYCLONIC FLOW AROUND LOW PRESSURE WILL STILL RESULT IN SCATTERED SHOWERS AT TIMES. THE ACTIVITY WILL PROBABLY BE MOST WIDESPREAD ACROSS OUR FAR NORTHERN ZONES...CLOSER TO THE BETTER DYNAMICS AND FORCING. LOW TEMPS WILL ONLY DROP INTO THE UPPER 40S AND LOWER 50S IN MOST LOCATIONS. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... BIG PICTURE... CLOSED UPPER LOW OVER THE MID ATLANTIC COAST WEDNESDAY MIGRATES ACROSS NEW ENGLAND THURSDAY AND INTO THE MARITIMES FRIDAY. SHORTWAVE FROM THE PACIFIC NORTHWEST RACES ACROSS THE NORTHERN TIER OF STATES THIS WEEK AND CROSSES NEW ENGLAND SATURDAY. HIGH PRESSURE RIDGE THEN BUILDS OVER THE NORTHEAST USA SUNDAY AND MONDAY. HEIGHT CONTOURS ARE BELOW NORMAL MUCH OF THE WEEK UNDER THE INFLUENCE OF THE UPPER LOW...THEN RECOVER TO NORMAL LEVELS BY SUNDAY AS THE RIDGE BUILDS. THIS PATTERN FAVORS A COOL WET MID AND LATE WEEK...THEN DRY AND SEASONABLE BY SUNDAY AND MONDAY. MODERATE CONFIDENCE IN THE TYPES OF WEATHER...BUT LOW CONFIDENCE IN EXACT TIMING. THE DAILIES... WEDNESDAY-THURSDAY...COASTAL LOW SURFACE AND ALOFT WILL DOMINATE OUR WEATHER AS IT MOVES UP THE COAST. LOW PRESSURE TO OUR SOUTH AND AN EAST 50-60 KNOT LOW LEVEL JET ACROSS COASTAL MAINE AND WRAPPING INTO NH/VT. THIS MAY BRING ENHANCED ISENTROPIC LIFT ACROSS SOUTHERN NH AND NORTHERN MASS...WITH WEAKER LIFT FARTHER SOUTH. BY THURSDAY THE COLD CORE IS DIRECTLY OVERHEAD. SO WEDNESDAY IS A TRANSITION FROM STRATIFORM TO CONVECTIVE...THURSDAY MAINLY CONVECTIVE. SUFFICIENT INSTABILITY BOTH DAYS TO INDICATE A CHANCE OF THUNDER. FRIDAY...LOW PRESSURE SURFACE AND ALOFT WILL MOVE OFF TO THE EAST. COLD CORE STILL CLOSE ENOUGH TO PROVIDE CLOUDS AND SOME INSTABILITY. SHOULD CONTINUE TO BE A DIMINISHING CHANCE OF SHOWERS. SATURDAY...COLD FRONT ASSOCIATED WITH UPPER SHORTWAVE MOVES THROUGH LATER SATURDAY OR SATURDAY NIGHT. THE APPROACH OF THIS FRONT MAY ACTUALLY BE THE NUDGE THAT GETS THE LAST OF THE COLD POOL CLOUDS OUT OF OUR AREA. THE FRONT WILL BRING A PERIOD OF CLOUDS. THE POTENTIAL FOR SHOWERS IS LESS DEFINED AND SO WE FEATURE JUST SLIGHT CHANCE POPS IN SRN NH AND NRN MASS. TEMPS ALOFT SUPPORT DAYTIME MAX TEMPS IN THE 60S. SUNDAY-MONDAY...HIGH PRESSURE BUILDS OVER THE NORTHEAST WITH TEMPS ALOFT WARMER FROM SUNDAY TO MONDAY. TEMPS ALOFT SUPPORT 60S BOTH DAYS. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TUESDAY NIGHT/... 940 PM UPDATE... NO MAJOR CHANGES FROM 00Z TAFS. EARLIER DISCUSSION BELOW. ============================================================== TONIGHT...HIGH CONFIDENCE. VFR. SCATTERED SHOWERS AFTER MIDNIGHT BUT SHOULD NOT BRING LOWER CONDITIONS. TUESDAY...MODERATE CONFIDENCE. CONDITIONS DETERIORATE TO MAINLY MVFR THRESHOLDS IN MORNING NEAR COAST...BUT BRIEF IFR CIGS/VSBYS ARE POSSIBLE. SCATTERED SHOWERS EXPECTED WITH AN ISOLATED THUNDERSTORM OR TWO POSSIBLE. BULK OF THE FOCUS SHOULD BE ACROSS EASTERN NEW ENGLAND. TUESDAY NIGHT...MODERATE CONFIDENCE. LOW END MVFR TO PERHAPS IFR CONDITIONS DOMINATE IN LOW CLOUDS...SCATTERED SHOWERS AND FOG PATCHES. THE BULK OF THE ACTIVITY WILL LIKELY BE FOUND ACROSS OUR NORTHERN ZONES. KBOS...HIGH CONFIDENCE IN TAF TONIGHT WITH MODERATE CONFIDENCE ON TUESDAY. LOW PROBABILITY OF AN ISOLATED THUNDERSTORM ON TUESDAY. KBDL...HIGH CONFIDENCE IN TAF TONIGHT WITH MODERATE CONFIDENCE ON TUESDAY. OUTLOOK...WEDNESDAY THROUGH SATURDAY...MODERATE CONFIDENCE. WEDNESDAY-THURSDAY...PROLONGED PERIOD OF MIXED MVFR/IFR...WITH MORE IFR IN RAIN WEDNESDAY AND MORE MVFR IN SHOWERS THURSDAY. CHANCE OF THUNDER BOTH DAYS. CHANCE OF 30 KNOT EAST-NORTHEAST WIND GUSTS WEDNESDAY MORNING ALONG THE OUTER CAPE AND MASSACHUSETTS NORTH SHORE AREAS. FRIDAY-SATURDAY...VFR. AREAS OF MVFR CIGS/VSBYS IN SHOWERS ON FRIDAY...WITH THE BEST CHANCE IN SOUTHERN NH AND EASTERN MASS. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... 940 PM UPDATE... ONLY CHANGE TO PREVIOUS FORECAST IS TO INCREASE WIND SPEEDS A BIT OVERNIGHT TO 10-15 KT WITH GUSTS UP TO 20 KT. EARLIER DISCUSSION BELOW. ================================================================== TONIGHT...HIGH CONFIDENCE. HIGH PRESSURE WILL CONTINUE TO MOVE FURTHER EAST OF THE REGION. THIS WILL RESULT IN SOUTH TO SOUTHWEST WINDS OF 10 TO 15 KNOTS. HOWEVER...WINDS/SEAS SHOULD REMAIN BELOW SCA THRESHOLDS. TUESDAY AND TUESDAY NIGHT...MODERATE TO HIGH CONFIDENCE. DEVELOPING LOW PRESSURE SOUTH OF THE WATERS WILL COMBINED WITH A 1030 MB HIGH OVER EASTERN CANADA. EASTERLY WINDS ON TUESDAY WILL BEGIN TO SHIFT TO THE NORTHEAST TUESDAY NIGHT AS PRESSURE GRADIENT STRENGTHENS. PRETTY MUCH A LOCK THAT SCA SEAS WILL DEVELOP ACROSS OUR EASTERN AND PARTICULARLY OUR NORTHERN OUTER-WATERS TUE AFTERNOON INTO TUE NIGHT. IN FACT...BY DAYBREAK WEDNESDAY SEAS MAY BE APPROACHING 10 FEET ACROSS OUR FAR NORTHERN WATERS ALONG WITH GUSTS UP TO 30 KNOTS. SCA HEADLINES POSTED FOR THIS REGION. WE MAY ALSO SEE SOME 5 FOOT SEAS DEVELOP ACROSS THE SOUTHERN WATERS TOWARDS 12Z WEDNESDAY...BUT ITS TOO MARGINAL FOR LATE 3RD PERIOD SCA HEADLINES IN THIS REGION. OUTLOOK...WEDNESDAY THROUGH SATURDAY...MODERATE CONFIDENCE. WEDNESDAY-THURSDAY...LOW LEVEL EAST-NORTHEAST JET WILL BE FEEDING INTO THE MAINE MID-COAST WEDNESDAY. THE POTENTIAL FOR STRONG SURFACE WINDS SHOULD REMAIN NORTH OF OUR WATERS. WINDS OF 25-30 KNOTS MAY EXTEND AS FAR SOUTH AS THE MERRIMACK RIVER AND POSSIBLY CAPE ANN. WINDS DIMINISH AND BECOME VARIABLE THURSDAY AS THE COASTAL LOW MOVES ACROSS THE WATERS. SEAS WEDNESDAY REACH 5 FEET ON THE OUTER WATERS WITH 8 TO 10 FEET POSSIBLE FROM CAPE ANN TO MERRIMACK RIVER. BY THURSDAY THE PERSISTENT NORTHEAST FLOW WILL EXPAND THE AREA OF 8 TO 10 FOOT SEAS ACROSS THE EASTERN WATERS. SMALL CRAFT ADVISORY WILL BE NEEDED FOR THE EASTERN WATERS AND SOUTHERN OUTER WATERS. FRIDAY... AS THE COASTAL LOW PRESSURE MOVES OFF TOWARD THE MARITIMES...WINDS WILL BECOME NORTHWEST WITH GUSTS AROUND 20 KNOTS. WITH THE SHIFTING OF THE WIND DIRECTION TO OFFSHORE...WE EXPECT SEAS TO DIMINISH. BUT 5 FOOT SEAS MAY LINGER ON THE OUTER WATERS THROUGH THE DAY. SATURDAY...WINDS AND SEAS SHOULD REMAIN BELOW SMALL CRAFT LEVELS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON TUESDAY TO 8 AM EDT WEDNESDAY FOR ANZ250-254. SMALL CRAFT ADVISORY FROM 3 PM TUESDAY TO 8 AM EDT WEDNESDAY FOR ANZ251. && $$ SYNOPSIS...WTB/FRANK NEAR TERM...WTB/NOCERA SHORT TERM...FRANK LONG TERM...FRANK AVIATION...WTB/FRANK/JWD MARINE...WTB/FRANK

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