Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 020320 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1020 PM EST Thu Dec 1 2016 .SYNOPSIS... Other than the risk of a few snow showers or flurries Friday night, expecting mainly dry conditions through much of this weekend, with a trend toward cooler temperatures. A brief snow or rain shower is possible Sunday night into early Monday. Otherwise high pressure will provide dry weather Monday afternoon into Tuesday. Low pressure moving from the southeast states to the Mid-Atlantic coast may cause some mixed precipitation as far north as southern New England Tuesday night into Wednesday, but the track remains uncertain. && && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 1015 PM Update... Showers have dissipated, and clouds across SE MA were moving ESE with back edge likely moving out to sea between 11 PM and midnight. Otherwise, more stratocumulus clouds were spilling over the Berkshire crest and anticipate that will continue overnight. Temperatures were more or less on track with no significant changes needed. Gusty winds were persisting across the coastal plain but still expected to relax overnight over land. 650 PM update... Doppler radar shows a few light sprinkles across eastern NY, central MA, and northern CT. They were reported on the observations during the past hour at both Windsor Locks, CT and Worcester, MA. Have updated to add a slight chance of a light rain shower for the next few hours over interior southern New England. Otherwise, no changes to the forecast for the evening update. Previous discussion... Drier air continues to shift east overnight. West winds will continue to bring in more humid air from the Great Lakes. Variable clouds, with more clouds more likely to linger across the western half of southern New England. Temperatures expected to be 5-10 degrees lower than last night, but still above seasonable normals. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Gusty west winds continue through this period. While this should result in periods of clouds for most of the region, the possibility of showers is no so clear-cut. More clouds across northern MA, with partial sunshine expected over CT/RI and southeast MA. There should be enough of a cold pool aloft where scattered showers would be more favorable. However, west winds typically do not favor lake-effect showers very far east, as there is a decent downslope component in the CT River Valley. West winds also do not favor ocean-effect showers across the outer Cape and islands. Otherwise, expecting typical early December weather. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * A cool period with slightly below normal temperatures. * Low pressure to our south Tue night and Wed could cause some mixed precipitation this far north but track confidence is low. Saturday... High confidence. Cannot rule out a snow shower in western Franklin County MA early in the morning. Otherwise, with strong low pressure over the Canadian maritimes, it will be windy across southern New England with gusts to 20-30 mph at times from the northwest. Winds could approach 35 mph along the eastern MA coast. Despite partial sunshine...highs will be held to 40-45 except upper 30s in the northern slopes of the Berkshires. Sunday... High confidence. A mostly sunny and cool day is forecast with high pressure over southern New England. Highs from the upper 30s to lower 40s with diminishing winds. Sunday night and Monday morning... Moderate confidence. A band of clouds associated with a very weak short wave trough will spread across the area. Although the atmosphere is mainly dry, cannot rule out a few brief snow showers, which could perhaps leave a localized dusting. Overnight lows in the 20s except 30 to 35 Cape Cod and Islands. Rest of Monday and Tuesday... High confidence. Clear to partly cloudy conditions as a new high pressure system builds in from the west and north. Highs again both days in the upper 30s to lower 40s with lows in the 20s except lower to mid 30s Cape Cod and Islands. Tuesday night and Wednesday... Low confidence. Upper level low pressure from the southwestern U.S. will be lifting northeastward and weakening as it approaches New England in this time frame. The 12Z GFS spawns a decent low pressure system not too far to our south, but the GFS ensemble members are not as emphatic. The GFS and some GEFS members have a strong easterly low level jet that creates rain over the southeast half of our area and snow in the northwest half. It is notable that the 12Z operational run is farther southeast than previous runs, more in line with the ECMWF and Canadian models. The 12Z ECMWF is consistent with its prior runs and has precipitation knocking at our door Tuesday evening but then it shifts off the coast to our south, closer to the main low off the Mid-Atlantic coast. The Canadian model is also advertising a stronger persistent high over our region that prevents the northward advance of precipitation. As a result of the uncertainty, at this time we have forecast only 20-30 percent probabilities of mixed precipitation interior and rain in RI and eastern MA Tuesday night into Wednesday. Thursday... Low confidence. A strong cold front is forecast to approach southern New England from the west by Thursday evening. NCEP believes that the GFS is too fast with this approach. In general, continued chance PoPs for mainly showers Thu, but could end as snow showers by Thu. night. This will undoubtedly change in the next 7 days! && .AVIATION /03Z 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/... 10 pm update... Through 06Z...High confidence. Back edge of band of 5000-6000 ft BKN-OVC clouds will move across the Cape and Islands by 04Z. BKN-OVC clouds at 2500-3000 ft anticipated to persist overnight across the crest of the Berkshires with generally just SCT clouds making it past the east slopes of the Berkshires. Otherwise, VFR conditions expected. Wind gusts 20 to 25 KT across the coastal plain are expected to gradually diminish after 06Z. Friday and Friday Night...Moderate confidence. Some uncertainty on extent of lake effect snow/rain showers entering MA/CT during this time. Wind direction is not very favorable for ocean-effect showers across the outer Cape and islands. Temperatures would favor mostly rain showers across southern New England, where they develop. The exception would be across the east slopes of the Berkshires, where some light snow showers are possible. Will need to monitor the trends over the next 12-24 hours. KBOS TAF...High confidence in overall TAF. BOS anticipated to be CLR-SCT overnight. G25 KT anticipated to gradually diminish after 06Z. KBDL TAF...High confidence in overall TAF. Outlook /Saturday through Tuesday/... Saturday through Sunday...High confidence. Mainly VFR. May see some spotty light -SHRA Saturday across outer Cape Cod. NW wind gusts up to 25-30 kt Saturday into Sat night, especially in the higher terrain and along the south and east coasts. Sunday night and Monday morning...Low confidence. May see patchy MVFR conditions in spotty -SHRA/-SHSN Sunday night into Monday morning, then should be mainly VFR by Monday afternoon. Monday and Tuesday... High confidence. VFR. Increasing mid cloudiness in western sections Tuesday afternoon. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... Gusty west winds persist through the period. While there may be brief lulls in the winds, rough seas should not diminish as quickly. Overall, thinking Small Craft Advisory conditions will be met on most waters through Friday night. Some of the nearshore waters, like Boston Harbor and Narragansett Bay, may fall below advisory levels for a time. Still trying to work out if there will be a significant enough window where no advisory would be in effect. Outlook /Saturday through Tuesday/...Moderate confidence. Saturday through Saturday night...Expect NW winds gusting up to 25-30 kt across most of the waters. Seas will range up to 5-6 ft over the outer waters. Winds should diminish over Boston Harbor and Narragansett Bay after midnight Saturday night. Sunday through Monday...Seas may linger around 5 ft early Sunday, otherwise winds and seas should diminish below small craft criteria. NW to N winds may gust up to 20 kt late Mon. on the outer waters. Monday night and Tuesday... Winds and seas below small craft criteria. However, north to northeast winds will gust to 20 kt at times. Seas will build to near 5 ft over the waters south of Block Island and Marthas Vineyard toward Tuesday evening, as low pressure forms over the Mid-Atlantic region. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 AM EST Saturday for ANZ231>235- 237-250-251-254>256. Small Craft Advisory until 5 AM EST Friday for ANZ230. && $$ SYNOPSIS...Belk/GAF NEAR TERM...Belk/GAF/Thompson SHORT TERM...Belk LONG TERM...GAF AVIATION...Belk/GAF/Thompson MARINE...Belk/GAF

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