Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 011254 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 754 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/... 720 AM Update... Drier air is quickly working across the region, with the last of the showers moving across E Mass, Cape Cod and the islands. Noting a quick spike of temperatures across E Mass at 12Z, up to the lower 60s in some spots. Have also seen some brief gusts up to 20-25 kt across central and western areas as winds shifted to W. With conditions drying out, have updated to bring conditions current and incorporated trends into near term forecast. Previous Discussion... Lead short wave and associated triple point low pushes to the Gulf of Maine with rapid clearing/drying from west to east. This will be accompanied by a wind shift to the west. Winds will immediately become gusty 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 by mid-late morning. 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. Should see mainly dry conditions through Sunday. From Sunday night onward, uncertainty continues with regards to how the models handle the ejection of cutoff mid level low pressure out of the SW U.S. as high amplitude H5 ridge builds across the eastern U.S. into eastern Canada. Noting wide model solution spread as next system works its way across the midwest and Ohio Valley early next week. One weak low looks to approach Sunday night into Monday, but not a lot of moisture with this system. The surface system associated with the progressive cutoff mid level system may approach around the late Tuesday into Wednesday timeframe, but with low consistency with the track and timing of this system, low confidence at this time, but could see a wintry mix depending upon the temperature regime as the system approaches. 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 /13Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Today...High confidence but lower on exact timing this morning. Leftover MVFR-IFR CIGS/VSBYS in patchy fog and band of -SHRA across E Mass and on the islands will improve to VFR by around 14Z-15Z. Elsewhere, VFR conditions. Winds shift to W and will briefly gust up to around 25 kt as low pressure exits to the Gulf of Maine. May see some gusts up to 30 kt through midday. After skies briefly become mostly clear, diurnal clouds will redevelop by mid-late morning across western areas, with BKN deck at 3000-4000 ft, which will move across the remainder of the region through 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... S-SE winds shift to SW through mid morning across the eastern waters as low pressure moves NE of the waters. Winds then become W 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 until 7 PM EST this evening for ANZ230- 236. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera/EVT SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT

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