Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 010958 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 458 AM EST Thu Dec 1 2016 .SYNOPSIS... Showers over southern New England during the predawn hours will exit the region at or shortly before sunrise...followed by dry...breezy and mild conditions later this morning and afternoon. Other than the risk of a few snow showers or flurries Friday night...expect mainly dry conditions through much of the weekend, with a trend toward cooler temperatures. Weak low pressure may bring spotty light rain and/or snow showers Sunday night into Monday. Into the middle of next week, there is some potential for wintry precipitation Tuesday night into Wednesday, but timing and track remain uncertain. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 300 am Update... *** Dry weather and sunshine return later this morning *** At 3 am surface analysis has parent low pressure over northern NY state with its attending warm front along the south coast of MA and RI. Temperatures north of the front are in the 40s while 50s to near 60 are being observed from Block Island to Marthas Vineyard to Nantucket. Welcome to December 1st! Strong pressure falls over southern New England at 3 am on the order of 5 to 6 mbs in the past 3 hrs suggest triple point low beginning to form and will track across the region. This will advect warm sector farther north into RI and southeast MA thru sunrise. So expect a mild start to the day across this region. Meanwhile water imagery shows leading edge of dry slot beginning to overspread southern New England. As a result rain shield has moved offshore and has been replaced by low top showers...as cyclonic branch of the warm conveyor belt becomes the main lifting mechanism for precip now thru 09z west...12z east. Lead short wave and associated triple point low move offshore around sunrise with rapid clearing/drying from west to east. This will be accompanied by a wind shift to the west. Winds will immediately become gusty after sunrise as modest pressure-rise fall couplet enhances wind gusts potential. Model soundings supports west winds gusting up to 35-40 mph after sunrise...then settling back to 20 to 30 mph this afternoon. Sunshine returns later this morning and this coupled with a mild start and CAA delayed to later today...highs of 55-60 will be common across RI and eastern MA...50-55 elsewhere with coolest readings over the high terrain. Normal high for Dec 1st is 42F-48F for southern New England. Not as much sunshine across the hilly terrain as strato- cu overspreads this area later this morning and continues thru the afternoon. This cloudiness holds off until mid to late afternoon farther east across RI and eastern MA. So overall not very winter-like for the 1st day of Dec. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight... Dry but cooler with 850 temps falling to about -3C. This combined with a modest west wind will make it feel noticeably cooler. Temps will fall back into the 30s but still running 5-8 degs above normal for early Dec. Some cloudiness expected across northwest MA as lake effect clouds spill up and over the Berkshires. However mainly dry conditions should prevail. Friday... CAA continues and low level flow veers more to the west. This trajectory may be more favorable for lake effect clouds to impact northern MA and possibly farther southward. Both NAM and GFS have increasing low level lapse rates of 6.5C/km to 7.0C/km in the 925-700 mb layer. Given this layer is nearly saturated along with cyclonic flow aloft...could see some lake effect streamers make it over the Berkshires into northern MA. Thus have including very low probs of light showers/sprinkles with snow showers/flurries for the high terrain. Otherwise a typical early Dec day with highs in the mid to upper 40s along with a chilly west wind of 15 to 25 mph. More clouds across northern MA with some partial sunshine expected over CT/RI and southeast MA. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Mainly dry conditions with cooling temperatures through the weekend * Low confidence in wintry precip Sunday night into Monday * Another low may approach sometime Tuesday night or Wednesday, but low confidence on timing and track continue Overview... 00Z models and ensembles were in fairly good agreement through this weekend in keeping mainly dry conditions in place, though will see temperatures cool through this timeframe as the cutoff H5 low spins across Atlantic Canada. There is continued uncertainty with regards to precipitation in the mid range models. The Canadian, GFS, and GEFS members all keep southern New England dry throughout the long term period. The EPS members have two low pressures approaching southern New England sometime Sunday night into Monday, one from the north and the other from the south. However, the members are well spread out as far as path and timing. The operational ECMWF indicates a similar solution but slower, delayed until Tuesday into Wednesday. Reading previous forecast discussions, this time period has been very uncertain with models flip flopping, so will keep with a blend of the models for the forecast. Details... Friday night through Sunday...Moderate to high confidence. Cutoff upper level low over Quebec will shift into the Maritimes, but broad troughing extends westward across northern New England into N NY state through Saturday. May see some widely sct snow showers across the E slopes of the Berkshires Fri night into early Sat morning. There has been model consistency over the last couple of nights in the development of ocean effect showers over the eastern waters as colder air works across the warmer waters. They have been trying to bring some isolated showers into outer Cape Cod Sat into Sat night, though some question whether they will get in with a mainly NW flow in place. Usually need a more northerly flow to get the moisture to work across the arm of the Cape. Kept only slight chance POPs going for this aspect. Noting a fairly tight pressure gradient across the region during this timeframe between the exiting low and strong high pressure building out of the Ohio River valley to the mid Atlantic states. Will see gusty winds especially along the coast, up to 30-35 mph at times mainly Saturday into Saturday night. Temperatures on Saturday will be close to seasonal normals for early December, then will be cooler as mid level heights lower. Sunday night through Wednesday...Low confidence. High pressure will build across the region early Sunday night. May see as weak low approach Sunday night into Monday morning. Lack of good support or moisture should mean spotty light precip if that. Still uncertain on the evolution of this system as it approaches. At this point, have slight chance POPs in the forecast. Beyond this, H5 ridge looks to build over the northeast U.S. into eastern Canada, while SW U.S. cutoff low becomes captured by this building ridge in the developing SW flow aloft. This may approach the region around the Tuesday to Wednesday timeframe, but very uncertain on this track and timing. With the building ridge, temperatures should moderate somewhat but will need to monitor for possible cold air damming that may set up as any precip approaches. Will continue to monitor. && .AVIATION /09Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 120 am update... Short Term /through Friday/... Thru 12z...High confidence in trends but lower in exact timing. IFR and MVFR in periods of heavy rain will begin to improve from 07z west to 09z east as back edge of rain sweeps across the area. Additional improvement from 09z to 12z with conditions lifting to VFR west to IFR-MVFR RI and eastern MA. Also expect a wind shift to the SW between 09z to 12z. After 12z...High confidence but slightly lower on exact timing this morning. West winds increase to 25 to 35 kt around or shortly after sunrise. Then wind gusts not quite as strong in the afternoon...closer to 25 kt. Any leftover showers in MVFR-IFR over RI and eastern MA at 12z quickly improves to VFR. Across CT and western-central MA...should be VFR at 12z however marginal MVFR- VFR cigs quickly move back into the area and will overspread RI and eastern MA during the afternoon. Tonight...High confidence. VFR but areas of MVFR cigs across the higher terrain. West winds 5 to 10 kt except 15 to 25 mph along the coast and especially Cape Cod and the Islands. Friday...moderate confidence with some uncertainty on extent of lake effect snow/rain showers entering MA/RI/CT. Marginal VFR-MVFR cigs as lake effect rain/snow showers spilling over the Berkshires into northern MA and eventually CT/RI and southeast MA later in the day. West winds somewhat gusty up to 25 kt. KBOS TAF...Rain shield moving rapidly eastward with dry weather and IFR cigs improving to MVFR by 09z-11z. Moderate confidence. KBDL TAF...Rain shield moving rapidly eastward with dry weather and IFR cigs improving to MVFR by 08z-10z. Moderate confidence. Outlook /Friday Night through Monday/... Friday night through Sunday...High confidence. Mainly VFR. May see some spotty light -SHRA Friday night into Saturday across outer Cape Cod, with spotty -SHSN over the E slopes of the Berkshires Fri night. W-NW wind gusts up to 25-30 kt Fri night into Sat night, mainly along the S coast. Sunday night and Monday...Low confidence. May see patchy MVFR conditions in spotty -SHRA/-SHSN Sunday night into Monday morning, then should be mainly VFR. Timing is uncertain, though. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Today... Triple point low moves across southern New England at sunrise and then into the Gulf of ME. S-SE winds 20-30 kt during the predawn hours shift to the SW at sunrise and then west later this morning at 20-30 kt. A few gusts to 35 kt possible near shore. Showers and fog move offshore and improve with the wind shift around sunrise. Tonight... West winds 20-25 kt. Mainly dry weather and good vsby. Friday... More of the same...west winds 20-25 kt along with mainly dry weather and good vsby. Outlook /Friday Night through Monday/...Moderate confidence. Friday night through Saturday night...Expect NW winds gusting up to 25-30 kt across most of the waters /except Boston Harbor and Narragansett Bay/. Seas will range up to 5-6 ft over the outer waters. Winds should diminish after midnight Sat night. Sunday through Monday...Seas may linger around 5 ft early Sunday, otherwise winds and seas should diminish below small craft criteria. N winds may gust up to 20 kt late Mon on the outer waters. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 PM EST Friday for ANZ231>235-237- 250-251-254>256. Small Craft Advisory from 8 AM this morning to 7 PM EST this evening for ANZ230-236. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT

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