Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 050848 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 348 AM EST Mon Dec 5 2016 .SYNOPSIS... Brief period of light to moderate snow during the morning commute will result in snow covered roads especially across CT...western and central MA. Steadiest snow occurs early this morning then mix and/or change over to rain toward midday from south to north. Then partial clearing late in the day. Dry Monday night into Tuesday with high pressure. Low pressure off the mid Atlantic coast may bring some mixed light rain and/or snow into Southern New England Tuesday night into Wednesday. A polar front crosses the region late Thursday or Thursday night, with the chance for rain and snow showers. Very windy and cold conditions are then expected for Friday and next Saturday. && .NEAR TERM /THROUGH TODAY/... 345 am Update... *** Brief period of snow and slippery travel during the morning commute *** Snowfall... Warm advection snows entering NJ into eastern NY at 3 am. Column cold enough to support snow across all of southern New England. Bulk of the short wave energy tracks northwest of southern New England. Thus best forcing for ascent tracks across NY state into northern New England. Hence upward vertical motion is modest across our region. In addition system is very progressive limiting duration of precip. Furthermore deep layer moisture is lacking. This may be why bulk of guidance only has likely pops and not categorical. All of these parameters will limit snowfall potential. Both NAM and GFS show modest omega in the snow growth region from 09z to 12z across southern New England from west to east this morning. However during this time low level dry air hangs tough and by the time the column saturates dry air aloft is rapidly advecting eastward into the snow growth region. This will limit duration of steady/moderate snow to about only an hour or two (3 hrs at the most) this morning from 09z to 12z west to east. Given this leaned toward the lighter qpf from the 00z GFS/EC and RGEM. This yields snowfall potential of a coating to an inch across RI and eastern MA...before mixing or changing to rain later this morning before ending this afternoon. Farther inland (north and west of I-95)...given snow band is expected to weaken from west to east...slightly more snow inland with 1-2" likely. Low risk for a few spots receiving up to 3" across western CT/MA before snow band weakens eastward. Also low risk for a few interior spots receiving a brief period of freezing drizzle later this morning as dry air advects into the snow growth region...eroding ice crystals with supercooled droplets in warmer clouds below dominating. So in a nutshell some slippery travel for the morning commute along and northwest of I-95 corridor in RI and eastern MA. Southeast of this region duration of snow will be very brief. Temperatures... Cold this morning but once precip ends temps will rise into the upper 30s and lower 40s this afternoon. May even see a few breaks of sunshine mid to late afternoon CT...western-central MA and toward sunset RI and eastern MA. Winds will be fairly light today given weak pgrad, so not much of a wind chill to speak of. && .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/... 345 am update... Tonight... Strong mid level subsidence behind departing short wave which yields deep layer drying thru the column across southern New England tonight. Thus dry weather with mostly clear skies. Modest cold air advection behind this wave with blustery NW winds developing along the coast including Cape Cod and the islands. Seasonably cold with lows in the 20s...low 30s in Boston, Providence and the remainder of the immediate coastline including Cape Cod and the islands. Tuesday... Short wave ridging over the area will yield sunshine much of the day. However progressive upper air pattern with southern stream system approaching New England late in day resulting in clouds on the increase from SW to NE. Temps slightly colder than normal with highs in the upper 30s and low 40s. However it will feel seasonable given lots of sunshine and light winds with weak high pressure overhead. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Mixed precipitation possible Tuesday night into Wednesday morning * Very strong front crosses the region Thu or Thu night * Windy and cold into next weekend with strong gales over the waters Tuesday night through Wednesday night...Moderate confidence. Models continue to show a fast moving, weakening mid level short wave in SW flow moving thru our area, while a weak low pressure system emerges off the mid Atlantic coast Tuesday night. A potential secondary low pressure in southern Great Lakes region is expected to weaken as it moves E. Mid-Atlantic low center is forecast to track well south of 40N/70W, with our area having relatively light QPF totals. Best chance for measurable precip should be Tuesday night into Wed morning, then as low moves further offshore, precip becomes more spotty/diminishing for Wed afternoon. At this time thinking there is the potential for a wintry mix of light rain and snow to all light snow across much of the area Tue night, then on Wed precip winding down but a changeover to light rain at least along the coastal plain. Wednesday night should be mainly dry with our area in between systems. Thursday and Friday...Moderate confidence. There continue to be some timing and track differences regarding polar front wrapping around cutoff upper low across Hudson Bay. Digging mid level long wave trof will bring a surge of very cold air into our area. GFS timing of front is Thu day, while ECMWF timing is more Thu night. Will go with a model compromise for this timeframe. Mainly chance pops since exact timing of frontal passage is still uncertain. Chance for rain and/or snow showers across most of the region. Colder air will continue to sweep into the region during Friday as W- NW winds quickly increase. While at this time most of Friday/Friday night should be dry, cold air advection combined with WNW flow going thru eastern Great Lakes Region could translate to a few snow showers making their way into the east slopes of the Berkshires. Also the potential exists for a tightening pressure gradient as a low over the Canadian Maritimes intensifies, which could allow for gusts of 25-35 kts. Wind chills Fri night dip into the teens/single digits. Saturday and Sunday...Moderate confidence. While mainly dry conditions are anticipated for Saturday with high pressure working eastward, may see lingering snow showers across the east slopes of the Berkshires, as well as ocean effect snow showers off the coast. Our area could still be caught in a tight pressure gradient with a deepening low pressure over the Canadian Maritimes. Thus could have winds gusting to 25-35 kt, strongest winds along east coastal MA and the nearby coastal waters. During Sunday models show potential for a weak low pressure system moving eastward towards/into our area. While moisture does not look abundant with this feature, it could bring some light snowfall to the area. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 09Z update...high forecast confidence on trends but some uncertainty on exact timing of details. Leading edge of precip on radar not reaching the ground due to dry air eroding precip before reaching the surface. Snow overspreads CT/RI/MA between 09z-12z from west to east. Steady/moderate snow in MVFR-IFR for only an hour or two before becoming lighter and intermittent between 12z-15z. Then snow changes to rain 15z-18z across RI and eastern MA...possible much of CT too. Before then snow accumulations of a coating to an inch for RI and eastern MA...1-2" elsewhere with a low risk of a few amounts up to 3" across western CT/MA. Also low risk for a period of freezing drizzle 12z-15z across the interior. Precip ends 18z- 21z from west to east with conditions improving to MVFR/VFR 21z- 24z from west to east. Tonight...high forecast confidence. VFR likely along with increasing NW winds up to 25 kt across Cape Cod and Islands. Lighter winds elsewhere. Dry weather prevails. Tuesday...high forecast confidence. VFR and diminishing winds. Dry weather prevails with any risk for precip holding off until after sunset. KBOS TAF... MVFR with -SN around 12z-15z before mixing with and changing over to -RA 15z-18z. Snow accumulations of a coating to an inch possible. MVFR may improve to VFR toward 00z. KBDL TAF... MVFR in SN 09z-12z then possibly mixing or changing to rain 15z- 18z. Snow accumulations of 1 to 2 inches with a low risk of snowfall amounts up to 3 inches. Also low risk for a period of freezing drizzle 12z-15z. Outlook /Tuesday Night through Friday/... Tuesday night and Wednesday...Low to moderate confidence. MVFR to local IFR ceilings Tue night into Wed morning in light rain RI/SE Mass, a mix of rain/snow elsewhere. Improving to VFR Wed afternoon/night. Thursday...Moderate confidence. Mainly MVFR ceilings in areas of light rain showers ahead of approaching polar front. Depending on timing, rain showers could change to snow showers with local IFR conditions Thu afternoon/night. Friday...Moderate confidence. VFR except localized MVFR in isolated snow showers far interior MA. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... 345 am update... Today...high forecast confidence. Main issue will be vsby restriction in snow early this morning then snow changing to rain later this morning. Vsbys improve late today from west to east. Otherwise light winds today. Tonight...high forecast confidence. Low pressure develops east of New England resulting in NW winds of 20-25 kt. Thus SCA posted. Dry weather and good vsby. Tuesday...high forecast confidence. Diminishing winds as high pressure builds over New England. Dry weather and good vsby. Outlook /Tuesday Night through Friday/...Moderate confidence. Tuesday night through Wednesday night...Winds and seas remain below small craft criteria for most of the waters. NW winds Mon night will shift to E, gusting up to 20 knots at times. Thursday...Small craft advisories may be needed. Winds will shift to the SW-W and may gust up to 25 to 30 kt by late Thursday afternoon/night. Seas will be building to 4-6 ft over the outer waters. Friday...Strong W-NW gales expected to develop. There is the potential for some storm force gusts. Stay tuned for the latest forecast updates. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 7 PM this evening to 7 AM EST Tuesday for ANZ231>235-237-250-251-254>256. && $$ SYNOPSIS...Nocera NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...NMB AVIATION...Nocera/NMB MARINE...Nocera/NMB

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