Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250954 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 454 AM EST TUE NOV 25 2014 .SYNOPSIS... A WEAK FRONT WILL MOVE ACROSS THE REGION THIS MORNING. MILD CONDITIONS WILL HANG ON TODAY WITH GUSTY SOUTHWEST WINDS. LOW PRESSURE WILL BEGIN TO DEVELOP OFF THE CAROLINA COAST LATE TONIGHT...THEN WILL RAPIDLY INTENSIFY AS IT MOVES UP THE COAST EXPECT A MIX OF RAIN AND/OR SNOW ALONG WITH STRONG NORTHEAST WINDS WEDNESDAY INTO WEDNESDAY NIGHT. THE LOW WILL HEAD TO NOVA SCOTIA BY THANKSGIVING MORNING...WITH COLDER CONDITIONS AND LEFTOVER SNOW SHOWERS POSSIBLE. HIGH PRESSURE WILL PUSH ACROSS THE REGION FRIDAY INTO THIS WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE APPROACHING WEAK COLD FRONT APPEARS TO HAVE HUNG UP ACROSS W VT/UPSTATE NY AT 09Z. TEMPERATURES REMAIN IN THE 50S REGIONWIDE. NOTING A FEW READINGS IN THE LOWER 60S...WITH 64 DEGS AT KFIT AT 09Z. DEWPTS ALSO REMAIN IN THE LOWER-MID 50S INTO CENTRAL NH...THOUGH STARTING TO SEE LOWER DEWPTS INTO CENTRAL VT AND UPSTATE NY /KALB REPORTED 52 DEGS AT 08Z...DOWN TO 47 AT 09Z/. MID AND HIGH CLOUDS CONTINUE TO PUSH INTO NORTHERN NEW ENGLAND...WHILE LOW CLOUDS AND FOG REMAIN ALONG THE S COAST THOUGH VSBYS HAVE BEEN IMPROVING OVER THE LAST FEW HOURS. FOR TODAY...THE FRONT WILL WORK ITS WAY ACROSS THE REGION DURING THIS MORNING...AS SEEN ON BOTH THE 00Z NAM AND ECMWF OP MODEL RUNS. THE LINE OF LIGHT PRECIP NOTED EARLIER THIS MORNING ACROSS NORTHERN VT/NH HAS DISSIPATED AS IT MOVED NE...SO THIS IS MAINLY A DEWPT FRONT WHICH WILL PUSH E WITH THE SLOWLY LOWERING H5 HEIGHTS EVEN THOUGH THE REGION REMAINS IN A GENERAL SW FLOW AT THE SURFACE AND ALOFT. EXPECT WINDS TO GRADUALLY VEER TO W DURING THE AFTERNOON AND DIMINISH AS A WEAK RIDGE BUILDS E. WITH THIS RIDGE WILL BRING DRIER CONDITIONS...SO EXPECT THE MORNING CLOUDS TO PUSH OFFSHORE...THOUGH MAY LINGER ALONG THE S COAST...CAPE COD AND THE ISLANDS. COLDER AIR ADVECTS INTO THE REGION DURING THE AFTERNOON AS H85 TEMPS...WHICH START OFF FROM +7C TO +11C AT 12Z...WILL DROP BACK CLOSE TO 0C BY 00Z ACROSS SW NH/W MA...RANGING TO +6C ACROSS CAPE COD. WITH A HIGH LAUNCHING PAD AND SOME SUNSHINE WORKING IN...EXPECT TEMPS TO RISE AT LEAST A FEW DEGS THIS MORNING BEFORE FALLING BACK IN THE AFTERNOON. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... TONIGHT... WEAK RIDGE MOVES OFFSHORE AS LIGHT W WINDS CONTINUE TO VEER TO N. MEANWHILE...LOW PRES TAKES SHAPE OFF THE CAROLINA COAST LATE TONIGHT. WILL SEE PRECIP BLOSSOM S OF NEW ENGLAND OVERNIGHT...AND WILL PUSH INTO S COASTAL AREAS AFTER MIDNIGHT AND QUICKLY SHIFT N BY DAYBREAK. AS TEMPS FALL BACK CLOSE TO OR JUST BELOW FREEZING WELL INLAND...WILL SEE A MIX OF RAIN AND/OR SNOW GENERALLY FROM THE WORCESTER HILLS INTO THE HIGHER TERRAIN OF N CENTRAL CT WESTWARD. QPF DURING THIS TIME IS RATHER LIGHT...BUT COULD BE ENOUGH WELL INLAND TO CAUSE SOME PROBLEMS DURING THE MORNING COMMUTE. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... WEDNESDAY THROUGH THURSDAY MORNING... */ HIGHLIGHTS... - NOR`EASTER WILL IMPACT NEW ENGLAND WEDNESDAY INTO WEDNESDAY NIGHT - SIGNIFICANT IMPACTS WHICH WILL DISRUPT TRAVEL - PLOWABLE SNOWS ACROSS THE INTERIOR - POTENTIAL HEAVY RAIN ACROSS SE NEW ENGLAND /CAPE COD - ISLANDS/ - STRONG NE WINDS ACROSS E MA / CAPE COD / ISLANDS */ OVERVIEW AND MODEL CONSENSUS... OVERVIEW... INDIVIDUAL MODEL SOLUTIONS NARROWING IN ON A FOCUS OF A STORM TRACK AROUND THE 40N/70W BENCHMARK. BUT IT CONTINUES TO BE DIFFICULT TO RESOLVE SPECIFIC DETAILS ACROSS THE REGION. AGAIN...WE REALLY MAY NOT KNOW THE TRUE OUTCOMES TILL JUST A DAY OR TWO PRIOR. WEIGHED PREFERENCE UPON THE 24.15Z SREF / 24.12Z GFS ... AND NOW THE 24.12Z ECMWF HAS FINALLY COME ABOARD...HOORAY! NOW WITH A CONSISTENT STORM-TRACK...IMPACTS BEGIN WEDNESDAY MORNING...INCREASING INTO THE EVENING WITH THE HEIGHT OF THE STORM. MODEL CONSENSUS HAS THE STORM WINDING DOWN THURSDAY MORNING. SYNOPTICALLY... BASED ON A PREFERRED MODEL CONSENSUS ABOVE: LOW PRESSURE INTENSIFIES FROM THE GULF TUESDAY NE ACROSS THE 40N/70W BENCHMARK S OF NANTUCKET AROUND MIDNIGHT THURSDAY. ACCOMPANYING H85 LOW PASSES NE IN THE VICINITY OF THE CAPE COD CANAL TO NW OF THE 40N/70W BENCHMARK. DURING WEDNESDAY...BAROCLINIC LEAF / OVER-RUNNING PATTERN OF BROAD- SCALE ASCENT YIELDS TOP-DOWN MOISTENING DYNAMICALLY COOLING WITH TIME. WITH SURFACE INTERIOR N-FLOW WITH COASTAL NE-FLOW...AND DRIER AIR N/W...AM EXPECTING WETBULBING TOWARDS THE DEWPOINT TO AROUND THE FREEZING MARK THE DIVISION OF WHICH MAY BE ALONG A POSSIBLE COASTAL FRONT SETUP IMMEDIATELY N/W OF THE I-95 CORRIDOR. EXPECT INITIAL RAINS FOR INTERIOR LOCALES CHANGING OVER TO SNOW THROUGH THE DAY... AS TO THE TIMING OF THAT TRANSITION REMAINS UNCERTAIN AT THIS TIME. INTO WEDNESDAY NIGHT...INTENSIFYING LOW SWEEPS NE AROUND THE 40N/70W BENCHMARK S OF NANTUCKET. WITH A PROGRESSIVE FLOW-PATTERN /+NAO/ AND ABSENCE OF A CLOSED-LOW ABOVE H85 /MORE EMPHASIS OF AN ANTI-CYCLONIC BRANCH OF THE WARM CONVEYER BELT/...WITH LOW PRESSURE TROUGHING OVER THE GREAT LAKES ASSOCIATED WITH A STRONG POLAR-LOW HOLDS ARCTIC AIR REARWARD ACROSS C-CANADA /+AO/...EXPECTING THERMAL PROFILES AROUND THE FREEZING MARK OVER INTERIOR S NEW ENGLAND...WHILE MILD OVER THE IMMEDIATE COAST WITH CONTINUED THINKING OF MAINTAINED COASTAL-FRONT SETUP PRIOR TO STORM PASSAGE. PRECIPITATION OUTCOMES... A FRONT-END THUMP IS ANTICIPATED WITH SLANTWISE FORCING PER FRONTO- GENESIS NW OF H85 LOW EXTENDED E...ALONG WITH INDICATIONS OF WEAK TROWALING TOWARD THE NW-QUADRANT OF THE H85 LOW. BENEATH ENHANCED ASCENT PER MID-LEVEL IMPULSE AND RRQ OF THE UPPER-LEVEL-JET...STRONG DEEP-LAYER LIFT THROUGH MOIST DENDRITIC ZONES SHOULD YIELD A NW-SE PRECIPITATION GRADIENT ACROSS S NEW ENGLAND WITH HEAVIEST PRECIP IMMEDIATELY NW OF THE SURFACE LOW WHICH AGAIN SWEEPS NE AROUND THE 40N/70W BENCHMARK. COULD BE TALKING STORM-TOTAL PRECIPITATION AMOUNTS AROUND 1.5-2.0 INCHES FOR SE NEW ENGLAND WITH LESSENING AMOUNTS N/W WITH UP TO AROUND 0.75-INCHES FOR NW MA AND SW NH. SEE DETAILS BELOW IN THE THERMAL SETUP DISCUSSION THAT BREAKDOWN WHAT THOSE AMOUNTS COULD EQUATE TO IN TERMS OF SNOW. AGAIN...INITIAL PRECIP WILL LIKELY START OUT AS RAIN FOR SOME INTERIOR LOCATIONS BEFORE CHANGING TO SNOW. F-GEN SW-NE BANDING IS EVIDENT NW OF THE H85 LOW YET WITH MINOR INDICATIONS OF STATIC/INERTIAL INSTABILITY PER -EPV. CAN NOT RULE OUT THE POSSIBILITY OF SW-NE BANDS OF HEAVIER RETURNS PER WSR-88D RADAR DURING THE EVENT THAT WILL YIELD LOCALLY HIGHER PRECIPITATION AMOUNTS. ITS LIKELY WE WILL HAVE BETTER HANDLE IN ANALYZING SUCH OUTCOMES WHEN NEAR-TERM HIGH RESOLUTION GUIDANCE BECOMES AVAILABLE. THERMAL SETUP / SNOWFALL AMOUNTS... IF A COASTAL FRONT SETUP EMERGES BENEATH NEAR-ISOTHERMAL PROFILES AROUND -5C UP TO H7 THEN WOULD EXPECT SNOW-TO-LIQUID RATIOS RANGING FROM 10:1 TO 15:1 AS SREF METEOGRAMS SUGGEST ACROSS THE INTERIOR... WITH COASTAL RAINS. QUITE A RANGE THAT HAS SIGNIFICANT IMPLICATIONS ON SNOWFALL AMOUNTS. CHALLENGES OF SNOWFALL RATES DURING THE TIME OF DAY /LIKELY WILL SEE DIFFICULTY IN ACCUMULATING SNOWS DURING THE DAY WITH MARGINALLY COLD SURFACE TEMPERATURES/...ALSO WET-BULBING TO EQUILIBRIUM WITHIN THE FIRST 1 KFT ABOVE THE SURFACE...AND WHERE WE WILL EFFECTIVELY WET- BULB AND/OR WHERE AREAS ARE OVERCOME BY HEAVY SNOWFALL RATES. SO IN ADDITION TO THE INITIAL START/CHANGEOVER TO SNOW...SPEED OF THE SYSTEM AND IMPACTS TO PRECIPITATION AMOUNTS...AND RANGE OF SNOW- TO-LIQUID RATIOS...IT IS AN INCREDIBLY HUGE CHALLENGE TO NAIL DOWN SNOWFALL AMOUNTS. ONE KEY TO THIS ENTIRE FORECAST IS THE TRACK OF THE H85 LOW ALONG WITH H925 TEMPERATURES AT OR BELOW -2C. THE DIVIDING FREEZING LINE IS VARIED AMONG PREFERRED MODEL SOLUTIONS BUT NARROWING DOWN IN VICINITY OF THE AREA BETWEEN THE CT I-395 TO THE I-90/I-290/I-495 MA CORRIDOR TO THE I-95 CORRIDOR. SO AFTER PULLING OUT ALL MY HAIR...INTANGIBLES NOTED ABOVE MAKE THE SNOWFALL FORECAST TEDIOUS. FEEL DURING THE DAY SNOW ACCUMULATIONS WILL OCCUR AT 32-DEGREES OR BELOW WITH SNOW OCCURRING AT 36-DEGREES OR LOWER. THIS LOWERED SNOWFALL AMOUNTS FROM THE PRIOR SHIFT. IN COLLABORATION WITH WPC...BROAD AREA OF 6+ INCHES WITHIN THE WATCH AREA W OF NW MA TO NW RI ENCOMPASSING ALL OF CT EXCEPT COASTAL COMMUNITIES. AMOUNTS AROUND 8-10 INCHES POSSIBLE ACROSS THE HIGHER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS. CONTINUED THINKING THAT THERE WILL LIKELY BE WIGGLE ROOM OF THE RAIN- SNOW BAND DUE TO UNCERTAINTY IN THERMAL PROFILES IN THE FORECAST. EXPECT CHANGES WITHIN SNOWFALL AMOUNTS ALONG THE GRADIENT ADVERTISED AROUND THE AREA IMMEDIATELY W OF THE I-95 CORRIDOR. WINDS... CONSISTENT NE-FLOW OVER E MA INCLUDING CAPE COD AND THE ISLANDS. GUSTS EXCEEDING 45 MPH ARE POSSIBLE BUT DEPENDENT ON HOW STRONG THE STORM ACTUALLY GETS...WHICH AGAIN IS UNCERTAIN. WIND ADVISORY HEAD- LINES MAY BE NEEDED...BUT IF THEY ARE WOULD EXPECT THAT IT WOULD BE ON THE LOW-END OF CRITERIA WITH GUSTS AROUND 50 MPH. COASTAL FLOODING... FORECAST TIDES OF 10 FEET EXPECTED AT BOSTON SHORTLY AFTER MIDNIGHT THURSDAY. ANTICIPATING A SHORT-RESIDENCY TIME OF THE STORM...PERHAPS A MINOR SURGE AND MAYBE SOME SPLASHOVER IF THE NE-WINDS DISCUSSED ABOVE VERIFY. THURSDAY NIGHT THROUGH MONDAY... MEDIUM RANGE MODELS IN GOOD AGREEMENT THAT SERIES OF WEAK SHORTWAVES WILL ROTATE AROUND BROAD TROUGH IN PLACE OVER EASTERN STATES. THIS WILL MAINTAIN DRY WEATHER AND BELOW AVERAGE TEMPERATURES INTO WEEKEND...ALTHOUGH EXPECT SOME CLOUDINESS FROM TIME TO TIME. WE SHOULD SEE BRIEF MODERATION IN TEMPERATURES SUN AS SW FLOW DEVELOPS AHEAD OF NEXT COLD FRONT...WHICH WILL BRING REINFORCING SHOT OF COLD NEXT MON. MAY SEE FEW SHOWERS WITH PASSAGE OF FRONT SUN NIGHT/MON MORNING...BUT SHOULD BE ISOLATED AT BEST. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE. THROUGH 12Z...MAINLY VFR CIGS. S COAST OF RI/MA...IFR-LIFR CIGS/VSBYS IN FOG AND PATCHY -RA. SW WIND GUSTS UP TO 25-30 KT ACROSS CAPE COD AND THE ISLANDS SHOULD DIMINISH BY 10Z-11Z. TODAY...IFR TO LOCALLY LIFR CIGS/VSBYS SHOULD IMPROVE BY AROUND 15Z ALONG THE S COAST. OTHERWISE...EXPECT VFR CIGS AOA 10KFT. MAY SEE PATCHY CLOUDS AROUND 5-6KFT DURING THE AFTERNOON ACROSS RI/SE MA. SW WIND GUSTS UP TO 20-25 KT THROUGH MIDDAY ALONG S COAST. TONIGHT...EXPECT VFR CONDITIONS THROUGH THE NIGHT. KBOS TERMINAL...MODERATE CONFIDENCE IN TAF. KBDL TERMINAL...MODERATE CONFIDENCE IN TAF. OUTLOOK...WEDNESDAY THROUGH FRIDAY... WEDNESDAY INTO THURSDAY...MODERATE CONFIDENCE. NOR`EASTER ANTICIPATED. SIGNIFICANT ACCUMULATION SNOWS OVER INTERIOR TERMINALS IMMEDIATELY W OF THE I-95 CORRIDOR. +SN POSSIBLE. AROUND 40 KT NE-WINDS ACROSS E MA / CAPE COD / ISLANDS...ALONG WITH +RA. MIX OF IFR-VLIFR CONDITIONS. FRI...VFR. MODERATE CONFIDENCE. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE. TODAY...WINDS/SEAS HAVE DIMINISHED ACROSS MASS/IPSWICH BAYS TO ALLOW SMALL CRAFT TO EXPIRE AT 09Z. CONTINUED THE SMALL CRAFT ON THE SOUTHERN OUTER WATERS INTO RI/BI SOUNDS THROUGH THE DAY. SEAS UP TO 11 FT ON THE OPEN WATERS ON SW WINDS GUSTING TO 25 KT...WHICH SHOULD DIMINISH BY EVENING. TONIGHT...THE LULL BEFORE THE STORM. W WINDS DIMINISH AS THEY VEER TO NW-N DURING THE NIGHT. SEAS ON THE EASTERN OUTER WATERS AND DOWN TO THE SOUTHERN OPEN WATERS REMAIN AOA 5 FT. HOWEVER...AS NE WINDS INCREASE DURING WED...GALE AND STORM WATCHES HAVE BEEN ISSUED. OUTLOOK...WEDNESDAY THROUGH FRIDAY... WEDNESDAY INTO THURSDAY...MODERATE CONFIDENCE. NOR`EASTER ANTICIPATED PASSING NE AROUND THE 40N/70W BENCHMARK S OF NANTUCKET MIDNIGHT THURSDAY. LIKELY NE GALES OVER E MA / CAPE COD / ISLANDS...AND ALL WATERS. HEAVY RAIN LENDING TO REDUCED VISIBILITIES AT TIMES. FRI...MODERATE CONFIDENCE. SCA CONDITIONS SHOULD PERSIST ON OUTER WATERS DUE TO 25KT GUSTS AND 5 FT SEAS. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 10 AM EST THURSDAY FOR CTZ002. WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY MORNING FOR CTZ003-004. MA...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 10 AM EST THURSDAY FOR MAZ002>004-008>011. HIGH WIND WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY NIGHT FOR MAZ019-022>024. WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY MORNING FOR MAZ005>007-012>016-026. NH...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 10 AM EST THURSDAY FOR NHZ011. WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY MORNING FOR NHZ012-015. RI...HIGH WIND WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY NIGHT FOR RIZ008. WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY MORNING FOR RIZ001-003. MARINE...STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY EVENING FOR ANZ231>235-237-254>256. GALE WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY NIGHT FOR ANZ230-236-250-251. SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ235- 237-255-256. && $$ SYNOPSIS...SIPPRELL/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...JWD AVIATION...EVT/JWD MARINE...EVT/JWD

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