Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 172232 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 532 PM EST WED DEC 17 2014 .SYNOPSIS...
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SCATTERED RAIN OR SNOW SHOWERS ARE POSSIBLE TONIGHT AS AN UPPER LEVEL DISTURBANCE CROSSES NEW ENGLAND. HIGH PRESSURE WILL SLOWLY PASS ACROSS NORTHERN NEW ENGLAND LATE THIS WEEK...BRINGING DRY AND SEASONABLE CONDITIONS. LOW PRESSURE WILL PASS WELL SOUTH OF THE REGION...BRINGING A PERIOD OF SCT RAIN AND/OR SNOW SHOWERS THIS WEEKEND INTO EARLY NEXT WEEK. STRONGER LOW PRESSURE WELL WEST OF NEW ENGLAND LOOKS TO BRING RAIN AND GUSTY ONSHORE WINDS THE MIDDLE OF NEXT WEEK.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 225 PM UPDATE... SEEING A FEW BREAKS IN CLOUD COVER ACROSS SOUTHERN NEW ENGLAND THIS AFTERNOON...BUT EXPECT THESE TO FILL BACK IN AS WE APPROACH SUNSET DUE TO LEFTOVER MOISTURE AND PRESENCE OF UPPER LEVEL TROUGH OVER REGION. STILL LOOKING AT DRY WEATHER THROUGH AT LEAST THIS EVENING PER HIGH-RES MODELS...BEFORE SCATTERED RAIN/SNOW SHOWERS DEVELOP EARLY TONIGHT IN RESPONSE TO APPROACHING SHORT WAVE. MOST OF THIS ACTIVITY SHOULD BE FOCUSED NORTH OF MASS PIKE...BUT COULD SEE A FEW RAIN OR SNOW SHOWERS INTO PARTS OF N CT...RI AND SE MA AS WELL. NOT LOOKING OVERLY IMPRESSIVE FOR ANY SNOW SQUALLS PER BTV 4KM WRF AND OTHER HIGH-RES MODELS. DESPITE PRESENCE OF MOISTURE AND UPPER TROUGH MOVING THROUGH NEW ENGLAND...LACKING GOOD INSTABILITY AND LAPSE RATES. SO OUR THINKING IS WE WILL SEE DUSTING TO PERHAPS AN INCH OF ACCUMULATION OF SNOW AT MOST...MAINLY ACROSS HIGHER TERRAIN. LOWS TONIGHT WILL DROP BACK INTO 30S...WITH FREEZING LINE PROBABLY STAYING JUST W OF I-495 CORRIDOR IN E MA BY DAYBREAK THU. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... EXPECT TO SEE FEW LINGERING SNOW SHOWERS THU MORNING ACROSS NE MA AS SYSTEM DEPARTS. OTHERWISE DRY WEATHER WILL PREVAIL THU AND THU NIGHT. GUSTY W/NW WINDS /30-35 MPH/ ANTICIPATED AS A RESULT OF LOW PRESSURE DEEPENING OVER MARITIMES. THIS SHOULD HELP TO SCOUR OUT CLOUDINESS A BIT...BUT DO NOT EXPECT TOTAL CLEARING AS UPPER TROUGH STILL HANGS BACK FROM NEW ENGLAND TO GREAT LAKES...EVEN THROUGH THU NIGHT. STAYED CLOSE TO BLEND OF MODEL GUIDANCE WHICH RESULTS IN HIGHS FROM UPPER 30S NW TO MID 40S SE THU...AND LOWS MAINLY IN 20S THU NIGHT. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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HIGHLIGHTS... * DRY WEATHER AND NEAR OR SLIGHTLY BELOW TEMPS FOR FRIDAY AND SAT * LOW PRESSURE WILL PASS S OF NEW ENGLAND THIS WEEKEND...BUT WILL STILL SEE SCT LIGHT RAIN AND/OR SNOW SHOWERS * STRONGER LOW PRESSURE DEVELOPING WELL WEST OF THE REGION LOOKS TO BRING PERIODS OF HEAVY RAIN AND GUSTY WINDS BY CHRISTMAS EVE OVERVIEW AND MODEL PREFERENCES... 12Z MEDIUM RANGE MODEL SUITE WAS IN GENERALLY GOOD AGREEMENT... THOUGH TIMING AND TRACK ISSUES DID COME INTO PLAY FOR WEAK LOW PRES PASSING WELL S OF THE REGION SUN NIGHT/MON...THEN WITH THE STRENGTHENING LOW PRES CENTER ACROSS THE GREAT LAKES ASSOCIATED WITH A LONG WAVE NEG TILT TROUGH WHICH WILL WRAP IN MOISTURE BY AROUND CHRISTMAS EVE DAY. MID AND UPPER LEVEL STEERING CURRENTS REMAIN IN A SPLIT FLOW ACROSS NORTH AMERICA EARLY IN THIS FORECAST CYCLE. MODELS IN VERY GOOD AGREEMENT THAT THIS PATTERN EVOLVES INTO AN AMPLIFIED TROUGH/RIDGE SET UP...WITH LONG WAVE TROUGH DIGGING THROUGH THE CENTRAL U.S. TO THE WESTERN GULF OF MEXICO COAST BY EARLY NEXT WEEK. 12Z ECMWF AND GFS BOTH CONTINUE TO EVOLVE CUTOFF H5 LOW PRES...WHICH WILL CAUSE THE LONG WAVE TROUGH TO BECOME NEGATIVELY TILTED ACROSS THE SE U.S. WHILE BOTH MODELS DID SIGNAL THIS EVOLUTION...TIMING IS IN QUESTION...ESPECIALLY WITH THE DEVELOPMENT OF LOW PRES AND A SLUG OF HEAVY RAINFALL MOVING UP THE EASTERN SEABOARD WITH THE POSSIBILITY OF SOME MIXED PRECIP TO START WELL INLAND AROUND TUESDAY THAT WILL CHANGE TO RAIN WITH GUSTY EAST TO SOUTHEAST WINDS BRINGING MILDER AIR BY CHRISTMAS EVE DAY. ONE THING TO NOTE ON THIS PATTERN EVOLUTION...CONSIDERING WE ARE TALKING ABOUT A SYSTEM ABOUT A WEEK AWAY...THE 12Z GFS/EC OP RUNS WERE RATHER CLOSE WITH THE STRENGTH OF THE PARENT LOW OVER THE OHIO VALLEY MOVING INTO THE GREAT LAKES EARLY NEXT WEEK. HOWEVER...THERE ARE TIMING AND TRACK ISSUES FOR THE LATE MON-WED TIMEFRAME OF THE LOW AND SHORT WAVE WRAPPING AROUND IT WHICH LOOKS TO AFFECT THE REGION...WHICH LENDS TO SOMEWHAT LOWERED CONFIDENCE. DO FEEL THERE IS A GOOD SHOT FOR PRECIP...IT IS A MATTER OF THE ONSET AND ENDING OF THIS PRECIP. SO...LEANED TOWARD THE WPC GUIDANCE AS WELL AS BLEND OF THE GFS/EC ENSEMBLES ALONG WITH A BIT OF THE GFS/EC OP RUNS. DETAILS... FRIDAY AND SATURDAY...HIGH CONFIDENCE. AS UPPER LOW MOVES INTO THE MARITIMES EARLY FRIDAY...UPPER LEVEL RIDGE AND BUBBLE CUTOFF HIGH OVER CENTRAL CANADA WILL SHIFT ACROSS QUEBEC DURING THIS TIMEFRAME. ASSOCIATED SURFACE HIGH WILL SLOWLY SHIFT E AS WELL...BRINGING MAINLY DRY CONDITIONS FRIDAY INTO EARLY SATURDAY. EXPECT TEMPS TO RUN CLOSE TO OR SLIGHTLY BELOW SEASONAL NORMS. DURING MID TO LATE SATURDAY...AS THE AXIS OF THE HIGH PASSES OVER SOUTHERN QUEBEC...WINDS SHIFT TO E-NE. ALL MEDIUM RANGE MODELS BRING LIGHT PRECIP TOWARD THE COAST BY SATURDAY EVENING AND...WITH MARGINAL TEMPS AWAY FROM THE COAST...HAVE INCLUDED SLIGHT CHANCE TO LOW CHANCE POPS FOR RAIN AND/OR SNOW SHOWERS WITH THE BEST SHOT RIGHT ALONG THE COAST. MAY ALSO SEE PATCHY DRIZZLE AND FOG DEVELOP. LOW PRES WILL APPROACH THE MID ATLC COAST LATE SAT NIGHT...SO APPEARS SOME MOISTURE FROM THIS SYSTEM WILL WORK N INTO CT/S RI DURING THE PRE-DAWN HOURS...SO COULD SEE SOME SCT RAIN/SNOW SHOWERS THERE. SUNDAY AND MONDAY...LOW TO MODERATE CONFIDENCE. THIS WAS A TOUGH PORTION OF THE FORECAST AS PATTERN BEGINS TO UNDERGO CHANGE TO THE WEST. A RATHER FLAT SHORT WAVE WORKS OFF THE MID ATLC COAST WITH ASSOCIATED SURFACE REFLECTION. THIS SYSTEM OUT OF THE SOUTHERN STREAM DOES NOT LOOK TO PHASE UP WITH ANYTHING IN THE NORTHERN STREAM. HOWEVER...WILL STILL SEE PERIODS OF SCT RAIN AND/OR SNOW SHOWERS WITH THE CONTINUED ONSHORE FLOW AS THIS SOUTHERN LOW SLOWLY SHIFTS OFFSHORE WHILE THE HIGH TO THE N SLOWLY MOVES E AS THE OVERALL STEERING PATTERN SLOWS DOWN AND BECOMES MORE AMPLIFIED WITH THE DIGGING LONG WAVE TROUGH OVER THE CENTRAL U.S. WITH THE ONSHORE WINDS...EXPECT ANY MIXED RAIN/SNOW TO CHANGE TO RAIN ACROSS EASTERN MA/RI/PORTIONS OF N CT...WHILE SCT LIGHT SNOW SHOWERS CONTINUE INLAND. NOT MUCH IN THE WAY OF QPF...SO NOT EXPECTING TOO MUCH SNOW ACCUMULATIONS MAINLY ACROSS THE HIGHER INLAND TERRAIN. EXPECT HIGHS BOTH DAYS IN THE MID-UPPER 30S WELL INLAND TO THE MID 40S ALONG THE COAST. TUESDAY AND WEDNESDAY...LOW CONFIDENCE...MAINLY FOR TIMING. ANOTHER LOW THAT DEVELOPS ACROSS THE EASTERN GULF OF MEXICO WILL PASS WELL S OF THE REGION DURING TUESDAY...BUT WILL KEEP EASTERLY WINDS IN PLACE. THIS WILL ALSO KEEP THE CHANCE FOR LIGHT PRECIP ACROSS THE REGION. NOTING SOME PLACEMENT ISSUES FOR THE AXIS OF THIS MOISTURE AND HOW FAR N IT WILL SHIFT FROM THE SECOND PASSING LOW. WITH CONTINUED ONSHORE FLOW...TEMPS WILL BE A LITTLE BIT MILDER WITH HIGHS FROM THE UPPER 30S OVER THE HIGHEST INLAND TERRAIN TO THE MID AND UPPER 40S ALONG THE S COAST. IN THE MEANTIME...THE UPPER LEVEL PATTERN WILL TAKE SHAPE BY TUESDAY ACROSS THE CENTRAL U.S...WITH LONG WAVE TROUGH DIGGING TO THE GULF OF MEXICO. H5 CUTOFF LOW FORMS ACROSS THE UPPER MID WEST /THOUGH PLACEMENT ISSUES IN PLAY/...WHILE SURFACE LOW PRES FORMS ACROSS THE MISSISSIPPI VALLEY. THE UPPER TROUGH BECOMES NEGATIVELY TILTED BY 12Z WED...WHICH WILL ALLOW THE SURFACE SYSTEM TO DEEPEN AS IT ROTATES ACROSS WESTERN PA/CENTRAL VA. A SLUG OF QPF...TAPPED FROM THE TROPICS...WILL SHIFT UP THE EASTERN SEABOARD DURING WED. NOTED PWATS ON ORDER OF 1.3 TO 1.4 INCHES...WHICH IS ABOUT +2 SD ABOVE SEASONAL NORMALS FOR MID TO LATE DECEMBER. WILL ALSO SEE E-SE WINDS INCREASE WITH STRONG LOW LEVEL JET WORKING UP THE COAST /H85 WINDS BRIEFLY INCREASE TO 60-70 KT AS JET CROSSES DURING WED/. HAVE PRETTY GOOD CONFIDENCE IN PRECIP MOVING IN DURING WEDNESDAY INTO CHRISTMAS EVE AS MODELS CONTINUE TO SIGNAL THIS...BUT BIG QUESTION WILL BE THE ONSET AND ENDING OF THIS SLUG OF PRECIP. ALSO...SINCE TEMPS WILL BE CHILLY TO START WELL INLAND...WILL SEE PERIOD OF MIXED PRECIP THERE TO START BEFORE CHANGING OVER TO RAIN. HAVE CARRIED LIKELY POPS FOR THIS TIMEFRAME...THOUGH STILL QUESTIONS ON EXACT TIMING. TEMPS WILL RISE WITH THE INCREASING ONSHORE FLOW... LIKELY TO AS MUCH AS 10 DEGREES ABOVE SEASONAL NORMS.
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&& .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH THURSDAY NIGHT/...MODERATE CONFIDENCE. MVFR CIGS WILL PREVAIL THROUGH THIS EVENING. CIGS LIFT TO VFR ACROSS MOST OF AREA TONIGHT WITH INCREASING W/NW WINDS...GUSTING TO 25KT ESPECIALLY NEAR COAST. ALSO EXPECT SCATTERED RAIN/SNOW SHOWERS...MAINLY ACROSS NORTHERN MA WITH BRIEF MVFR CIGS/VSBYS. VFR CIGS DOMINATE THU AFTER LEFTOVER MVFR CIGS DURING MORNING... PERHAPS SCATTERED RAIN/SNOW SHOWERS ACROSS NE MA. NW WINDS GUST AS HIGH AS 25-30KT. KBOS TERMINAL...MODERATE CONFIDENCE. LOW-END MVFR CIGS THROUGH EVENING PUSH. COULD SEE CIGS IMPROVE TO OVC025 AS BEST CASE...BUT NOT LIKELY AT THIS TIME. KBDL TERMINAL...HIGH CONFIDENCE. OUTLOOK...FRIDAY THROUGH MONDAY... FRIDAY...HIGH CONFIDENCE. VFR. SATURDAY...LOW TO MODERATE CONFIDENCE. VFR TO START...THEN DEVELOPING MVFR CONDITIONS ESPECIALLY ACROSS THE COAST MAINLY SAT AFTERNOON/NIGHT. SUNDAY AND MONDAY...LOW CONFIDENCE. LOW END VFR TO MVFR CIGS. PATCHY MVFR TO LOCAL IFR VSBYS IN SCT RAIN AND/OR SNOW SHOWERS.
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&& .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...MODERATE CONFIDENCE. SCA REMAINS POSTED FOR ALL WATERS THROUGH THU...AND FOR OUTER WATERS THROUGH THU NIGHT. LOW PRESSURE DEEPENING OVER MARITIMES WILL RESULT IN STRONG W/NW WINDS ACROSS WATERS...SOLIDLY 25-30KT GUSTS WITH OUTSIDE CHANCE OF SOME 35KT GUSTS ON OUTER WATERS. HOWEVER WE ARE NOT CONFIDENT ENOUGH TO UPGRADE TO GALE WARNINGS AT THIS TIME. PEAK GUSTS SHOULD OCCUR LATE TONIGHT THROUGH THU AFTERNOON. WINDS GRADUALLY SUBSIDE THU NIGHT BUT SEAS WILL TAKE A BIT LONGER TO DIMINISH. MAY SEE SCATTERED RAIN/SNOW SHOWERS ON E MA WATERS LATE TONIGHT INTO THU MORNING...ESPECIALLY NEAR CAPE ANN AND MERRIMACK RIVER. OUTLOOK...FRIDAY THROUGH MONDAY... MODERATE TO HIGH CONFIDENCE THROUGH SUNDAY...THEN LOW CONFIDENCE MONDAY. FRIDAY...NW WIND GUSTING UP TO 20 KT. SEAS START OFF AROUND 5 FT ACROSS THE OUTER WATERS EARLY FRI...BUT SHOULD SUBSIDE BY FRI EVENING. SATURDAY AND SUNDAY...WINDS AND SEAS BELOW SMALL CRAFT CRITERIA. WIND SHIFT TO E-NE DURING SUN AND SEAS BUILD UP TO 4 FT ON THE OUTER WATERS. MONDAY...EXPECT NE WINDS GUSTING UP TO 20 KT. LOW PROB OF 25 KT GUSTS AS WELL AS 5 FT SEAS.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...NONE. MA...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR ANZ232>235- 237. SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR ANZ230-236. SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ231-250-251- 254>256.
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&& $$ SYNOPSIS...EVT/JWD NEAR TERM...JWD SHORT TERM...JWD LONG TERM...EVT AVIATION...EVT/JWD MARINE...EVT/JWD

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