Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222330 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 630 PM EST THU JAN 22 2015 .SYNOPSIS... HIGH PRESSURE WILL CONTINUE TO BUILD OVER THROUGH TOMORROW. A COASTAL STORM WILL IMPACT MUCH OF THE REGION SATURDAY INTO SATURDAY NIGHT WITH THE POTENTIAL FOR HEAVY SNOW ACROSS PARTS OF THE AREA. MORE SNOW IS POSSIBLE MONDAY IF LOW PRESSURE TRACKS CLOSE ENOUGH TO THE COAST...BUT EITHER WAY VERY COLD WEATHER FOLLOWS NEXT WEEK. && .NEAR TERM /THROUGH FRIDAY/... 630 PM UPDATE... RADAR SHOWS LAST OF FLURRIES NEAR OUTER CAPE WHICH SHOULD DIMINISH LATER THIS EVENING. STILL SEEING SOME PATCHY CLOUDS ACROSS CENTRAL AND SE MA AS WELL AS E CT AND RI...BUT LIKEWISE THESE WILL CLEAR OUT BY MIDNIGHT OR SO. LOOKS LIKE JUST ENOUGH OF A LOW LVL PRES GRADIENT TO MAINTAIN SOME W-NW FLOW THROUGH THE OVERNIGHT AND GIVEN THAT CLOUDS MAY TAKE SOME TIME TO ERODE...WILL MITIGATE RADIATIONAL COOLING POTENTIAL. ALSO NOTE THAT GUIDANCE WHICH INITIALIZED DWPTS WELL...ARE A BIT HIGHER THIS ROUND THAN PREVIOUS SUGGESTING LESS ROOM FOR COOLING. THEREFORE...FEEL THAT WHILE THE MOS MINS MAY BE A BIT TOO WARM GIVEN THE CLEARING...MINS LEFTOVER FROM PREVIOUS SHIFT LOOK RIGHT IN LINE...SO NO MAJOR CHANGES TO OVERNIGHT MINS FROM PREVIOUS FORECAST. && .SHORT TERM /FRIDAY NIGHT THROUGH 6 PM FRIDAY/... TOMORROW... RIDGE OF HIGH PRES WILL CREST ACROSS THE REGION DURING THE AFTERNOON TOMORROW. THEREFORE...DRY WX CONTINUES TO PREVAIL. A SLIGHT UPTICK IN MID LVL WARM ADVECTION SHOULD FOLLOW THE RIDGE PASSAGE UNDER VERY WEAK RETURN FLOW. THEREFORE...WITH A FAIR AMOUNT OF AFTERNOON SUN...SUSPECT HIGHS WILL BE A BIT WARMER TOMORROW THAN THEY WERE TODAY...WITH MAINLY MID 30S TO EVEN A FEW SPOTS NEAR 40 BY LATE AFTERNOON. TOMORROW NIGHT... INCREASING CLOUDS AND MODEST WARM ADVECTION EXPECTED AHEAD OF DEVELOPING LOW PRES IN THE MID ATLANTIC. THEREFORE...ALTHOUGH MINS ARE LIKELY TO FALL BACK BELOW FREEZING...SUSPECT THEY WILL BE WARMER TOMORROW NIGHT THAN THE LAST FEW. WITH MORE WIDESPREAD UPPER TEENS TO MID 20S. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... HIGHLIGHTS... * FAST MOVING COASTAL STORM SAT INTO SAT NIGHT * MORE SNOW POSSIBLE MON IF LOW TRACKS CLOSE ENOUGH TO OUR REGION * VERY COLD AIR FOLLOWS NEXT WEEK DETAILS... SAT AND SAT NIGHT... RAPIDLY DEEPENING MID LEVEL SHORT WAVE WILL CAUSE SURFACE LOW TO BOMB OUT AS IT PASSES BY SAT EVENING. 12Z MODELS HAVE COME INTO BETTER AGREEMENT WITH TRACK OF COASTAL LOW...TAKING IT OVER OR JUST INSIDE 40/70 BENCHMARK. DESPITE GOOD MODEL AGREEMENT...FORECAST REMAINS VERY DIFFICULT AND CONFIDENCE IS LOWER THAN WE WOULD LIKE AT THIS TIME FRAME SINCE ANY WOBBLES IN TRACK HAS HUGE INFLUENCE IN PRECIPITATION TYPE AND SNOWFALL AMOUNTS. ON LARGER SCALE...PATTERN IS NOT FAVORABLE FOR WIDESPREAD SIGNIFICANT SNOWS IN SOUTHERN NEW ENGLAND. IN ADDITION THERMAL PROFILES ARE MARGINAL WITH LACK OF STRONG SURFACE HIGH TO NORTH...AND WITHOUT STRONG THERMAL GRADIENT PRECIPITATION SHIELD ON ITS NW SIDE WILL BE MORE LIMITED THAN THAT WE NORMALLY EXPECT WITH WINTER STORMS. BUT RAPID DEEPENING SHOULD HELP TO COMPENSATE SOMEWHAT...ESPECIALLY ON BACKSIDE OF STORM SAT AFTERNOON/EVENING WHEN WE COULD SEE BURST OF ACCUMULATING SNOW. 1) PRECIPITATION TYPE AND HEAVY SNOW... PRECIPITATION LOOKS TO BEGIN SAT MORNING FROM S TO N...STARTING AS SNOW ACROSS MUCH OF AREA EXCEPT FOR RAIN ON CAPE COD AND ISLANDS. STILL LOOKING AT POTENTIAL FOR NARROW BAND OF HEAVY WET SNOW...MOST LIKELY FROM N CENTRAL CT INTO WORCESTER HILLS...NW RI AND INTERIOR NE MA. DESPITE WARMING ALOFT...FORECAST SOUNDINGS IN THIS REGION ARE NEARLY ISOTHERMAL...SO POTENTIAL EXISTS FOR ACCUMULATING SNOW WHERE IT COMES DOWN HEAVY AND ACROSS HIGHER ELEVATIONS. WE ISSUED A WINTER STORM WATCH FOR THESE AREAS WHERE WE HAVE 50 PERCENT CONFIDENCE ON REACHING WARNING CRITERIA...ALBEIT THE LOWER END /6 OR 7 INCHES/. ALSO HAVE TO BE CONCERNED WITH POSSIBILITY OF DOWNED TREE LIMBS AND WIRES WHERE SNOWFALL EXCEEDS 5 INCHES DUE TO WET NATURE OF SNOW. FARTHER S AND E...THERE SHOULD BE CHANGE TO RAIN AS MILDER AIR ARRIVES WITH LITTLE IF ANY ACCUMULATION. HOWEVER WE DO EXPECT ALL AREAS TO CHANGE TO SNOW LATER SAT AFTERNOON AND SAT EVENING... EVEN DOWN TO CAPE COD AND ISLANDS...AS STORM RAPIDLY DEEPENS AND DRAWS COLDER AIR INTO REGION. OUR THINKING IS WE MAY NEED TO ISSUE WINTER WEATHER ADVISORIES ACROSS REST OF RI AND E MA IN LATER FORECASTS...EITHER FOR 2-4" TOTALS OR A BRIEF PERIOD OF HEAVY SNOW AND GUSTY WINDS RESULTING IN DANGEROUS TRAVEL...OR BOTH! 2) STRONG WINDS ACROSS THE CAPE/ISLANDS... RAPID DEEPENING OF LOW AS IT PASSES 40/70 SHOULD BRING PERIOD OF STRONG N/NW WINDS SAT NIGHT TO CAPE COD AND ISLANDS. FORECAST SOUNDINGS SHOW POTENTIAL 40-45KT...BUT IF MODELS ARE UNDERDOING STRENGTH OF LOW WINDS COULD BE HIGHER. WE WILL PROBABLY NEED TO ISSUE WIND ADVISORIES IN LATER FORECASTS...BUT CONFIDENCE IS NOT YET HIGH ENOUGH TO DO SO NOW. 3) COASTAL FLOODING... REFER TO COASTAL FLOOD SECTION BELOW FOR DETAILS. SUNDAY AND MONDAY... 12Z GFS SHOWS POTENTIAL FOR A SIGNIFICANT WINTER STORM SUN NIGHT AND MON AS UPPER LOW CLOSES OFF S OF NEW ENGLAND AND DEVELOPS POTENT SURFACE LOW WHICH PASSES S OF US AS WELL. ON OTHER HAND WE HAVE 12Z ECMWF WHICH DOES NOT CARVE OUT AS DEEP OF UPPER TROUGH AND HAS MORE SUPPRESSED/WEAKER SOLUTION...BUT ITS TREND HAS BEEN TO COME A LITTLE FARTHER N ON THIS RUN. WHILE UNCERTAINTY IS HIGH THIS FAR OUT...GFS LOOKS TO BE OUTLIER BUT WE DO THINK WE STAND CHANCE AT SOME ACCUMULATING SNOW. TUESDAY THROUGH THURSDAY... GENERALLY DRY...BLUSTERY AND VERY COLD WEATHER PREVAILS WITH POTENTIAL FOR SOME OCEAN EFFECT SNOWS MAINLY FOCUSED OFFSHORE. AS MENTIONED BEFORE COLD AIR IS FAIRLY SHALLOW SO NEED TO KEY ON TEMPERATURES BELOW 850 MB WHICH ARE A BIT MISLEADING. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH FRIDAY NIGHT/...HIGH CONFIDENCE. FLURRIES NEAR OUTER CAPE WILL DIMINISH BY 02Z...WITH LINGERING VFR CIGS ACROSS CENTRAL MA...RI AND SE MA CLEARING OUT 03-05Z. VFR FRI WITH W/NW WINDS AOB 10KT...THEN VFR CIGS AOA 120 FRI NIGHT. KBOS TAF...HIGH CONFIDENCE IN TAF. KBDL TAF...HIGH CONFIDENCE IN TAF. OUTLOOK /SATURDAY THROUGH TUESDAY/... SATURDAY AND SATURDAY NIGHT...MODERATE CONFIDENCE. MVFR/IFR IN RAIN AND WET SNOW...MAINLY RAIN ON CAPE COD AND ISLANDS BEFORE CHANGE TO SNOW SAT EVENING WHEN N/NW WINDS COULD GUST TO 45KT. SUNDAY...HIGH CONFIDENCE. VFR. NW WINDS GUSTING TO 30 KT. MONDAY...LOW CONFIDENCE. MVFR/IFR POSSIBLE IN SNOW. TUESDAY...MODERATE CONFIDENCE. VFR. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH TOMORROW NIGHT/...HIGH CONFIDENCE. LOW PRES CONTINUES TO DEEPEN AND MOVE OFFSHORE THROUGH THE OVERNIGHT HOURS. THIS WILL YIELD A FEW MORE LIGHT OCEAN EFFECT SHOWERS THROUGH THE EVENING. OTHERWISE...EXPECT A BUILDING SWELL ON THE E OUTER WATERS TO REACH ABOUT 5-6 FT LATE TONIGHT...SO WILL BE HOISTING A SMALL CRAFT ADVISORY BEGINNING AFTER MIDNIGHT AND CONTINUING INTO TOMORROW. A PERIOD OF CONDITIONS BELOW SCA IS EXPECTED LATE TOMORROW INTO TOMORROW NIGHT. OUTLOOK /SATURDAY THROUGH TUESDAY/... SATURDAY AND SATURDAY NIGHT...MODERATE TO HIGH CONFIDENCE. LOW PRESSURE BOMBS OUT AS IT RAPIDLY MOVES NORTHEAST AND CROSSES NEAR 40/70 BENCHMARK SAT EVENING. STRONGEST WINDS EXPECTED SAT AFTERNOON AND SAT NIGHT WITH N/NW GALES ON MOST OF WATERS. GALE WATCHES HAVE BEEN POSTED. RAIN SAT SHOULD CHANGE TO SNOW SAT EVENING. SUNDAY...HIGH CONFIDENCE. DIMINISHING WINDS AND SEAS...BUT PROBABLY STAYING IN SCA ON OUTER WATERS. MONDAY AND TUESDAY...LOW CONFIDENCE. LOW PRESSURE TRACKS S OF NEW ENGLAND...BUT SHOULD COME CLOSE ENOUGH TO BRING INCREASING N/NE WINDS AND BUILDING SEAS. GALE FORCE WINDS POSSIBLE LATE MON INTO EARLY TUE. && .TIDES/COASTAL FLOODING... MINOR IMPACTS ARE POSSIBLE WITH THE WEEKEND SYSTEM ALONG PORTIONS OF THE MASSACHUSETTS EAST COAST. THERE ARE COUNTERACTING FACTORS. FACTORS THAT COULD LEAD TO SOME EROSION AND COASTAL FLOODING WILL BE THE RAPID DEEPENING OF THE SYSTEM WHICH LEADS TO ISALLOBARIC FORCING AND THE FACT THE ASTRO TIDE IS RELATIVELY HIGH STILL THIS WEEKEND. HOWEVER...FACTORS MITIGATING EROSION AND INUNDATION INCLUDE A VERY PROGRESSIVE SYSTEM THAT WILL LIMIT DURATION OF ANY SIGNIFICANT ONSHORE FETCH. AND AS LUCK HAS IT...THE SHORT PERIOD OF ANY CONSEQUENTIAL STORM SURGE WILL LIKELY OCCUR AROUND THE SATURDAY EVENING LOW TIDE. THE SURGE WILL BE JUST STARTING TO BUILD FOR THE SATURDAY AFTERNOON HIGH TIDE...POSSIBLY .5 TO 1.0 FEET...AND A DIMINISHING SURGE...PROBABLY NO MORE THAN 1 TO 1.5 FEET...WILL OCCUR AT THE TIME OF THE VERY EARLY SUNDAY MORNING HIGH TIDE WHEN SURFACE WINDS WILL HAVE BACKED AROUND TO NW. NEARSHORE SEAS ALONG THE OPEN COASTLINE WILL LIKELY BE ONLY ABOUT 5 TO 7 FEET EARLY SATURDAY AFTERNOON AND BETWEEN 10 AND 15 FEET EARLY SUNDAY MORNING...LIKELY NOT LARGE ENOUGH TO POSE A SIGNIFICANT OVERWASH RISK. CONSIDERING THE VARIOUS FACTORS...WE ANTICIPATE A POTENTIAL FOR MINOR COASTAL FLOODING ALONG VULNERABLE EAST FACING SHORELINES FROM BOSTON SOUTH AT THE TIME OF THE SATURDAY EARLY AFTERNOON HIGH TIDE...GENERALLY 2 TO 230 PM. THERE IS ALSO A CHANCE OF SOME MINOR COASTAL FLOODING AND BEACH EROSION ALONG NE AND N FACING SHORELINES AT THE TIME OF THE EARLY SUNDAY MORNING HIGH TIDE...GENERALLY 230 AM TO 3 AM. SHOULD THE SYSTEM APPROACH SOONER...THEN THE IMPACT COULD BE SOMEWHAT MORE FOR THE SATURDAY AFTERNOON HIGH TIDE. IF THE SYSTEM SHOULD SLOW DOWN SOME...WHICH HAS NOT BEEN THE MODEL TREND OF LATE...THEN THERE COULD BE A LITTLE MORE IMPACT FOR EARLY SUNDAY MORNING HIGH TIDE. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY EVENING FOR CTZ002>004. MA...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY EVENING FOR MAZ004>006-011>014-026. RI...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SATURDAY EVENING FOR RIZ001. MARINE...GALE WATCH FROM SATURDAY AFTERNOON THROUGH SUNDAY MORNING FOR ANZ231>235-237-250-254>256. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EST FRIDAY FOR ANZ250-254. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 7 AM EST FRIDAY FOR ANZ255. && $$ SYNOPSIS...DOODY/JWD NEAR TERM...DOODY/JWD SHORT TERM...DOODY LONG TERM...JWD AVIATION...DOODY/JWD MARINE...DOODY/JWD TIDES/COASTAL FLOODING...THOMPSON

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