Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 141758 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1258 PM EST Thu Dec 14 2017 .SYNOPSIS... High pressure near Chicago builds eastward providing dry but cold conditions this afternoon into Friday morning. Two areas of low pressure, one tracking across the eastern Great Lakes and the other well offshore may bring a period of light snow or flurries late Friday into Friday evening. Temperatures will turn milder early next week, but will also bring the chance of rain and/or snow showers. Mainly dry conditions expected Tuesday into Wednesday, but some light precipitation may linger across portions of the region. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1 PM Update... Per latest satellite imagery back edge of the cloud shield moving across Cape Cod and the Islands and will be offshore shortly. Dry but cold this afternoon with good CAA to follow given -18C at 850 mb upstream over NY state, streaming this way. Also as ocean wave departs and intensifies will see WNW winds begin to increase 4p-7p today. Thus developing gusty WNW winds will add to the chilly conditions for the evening commute. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight... Clear skies and diminishing wind as high pres moves to the mid Atlc coast with ridging extending into New Eng. This will result in good radiational cooling which will be enhanced by fresh snow cover near the coast. Lows dropping into the single numbers, except teens near the coast. Friday... Next mid level trough and shortwave approaches from the west as coastal low pres develops well to the south. Sunshine will give way to increasing clouds in the afternoon as the column moistens. Modest large scale forcing develops late in the day ahead of the mid level trough with best chance for any late day snow showers across SE New Eng assocd with a weak inverted trough and increased low level moisture. Still rather cold with 925 mb temps -8 to -10C which will yield another day with highs mostly in the 20s, but winds will be lighter and less of a factor. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Overview... Overall, noting an active, progressive pattern in place across the lower 48, especially starting this weekend as the blocking high amplitude ridge across the western U.S. breaks down. This will bring weak mid level short waves eastward in the fast flow aloft. After several days of below normal temperatures, models continue to signal milder air starting to move into the northeast early next week. With any progressive pattern, however, noting widening model solution spread with the timing and track of weather systems especially across the northern stream, so have lower confidence with the track and timing of any systems beyond Monday. For now, will see a couple of weak lows passing near or SE of New England into this weekend, each bringing some light rain and/or snow showers but will move across rather quickly. As the upper pattern becomes nearly zonal, will start to see temperatures moderating closer to seasonal normals by early next week, though may still see some light precip into mid week mainly along coastal areas and across the E slopes of the Berkshires. Details... Friday night and Saturday... Light precipitation along the western periphery of low pressure moving well SE of the 40N/70W benchmark brings scattered snow showers Friday night. At this point, the best chance will occur along the immediate S coast, Cape Cod and the islands. Current timing suggests that the precip should push offshore by Sat morning. With light QPF amounts, less than 0.1 inches, should see less than an inch snow accumulations. As the low exits, W-NW winds will pick up as low level lapse rates increase during Saturday. Could see gusts up to 25-35 kt, highest across SE areas where the highest low level jet moves across. With temps running up to 10 degrees below seasonal normals, will see wind chill values in the teens to lower 20s during the day. Sunday and Monday... High pres ridge builds east across the eastern seaboard by Sunday morning, so winds will diminish by daybreak. Will see another cold day, however, as mid level winds continue from the NW, though will start to back to W later in the day. Another chilly day with highs from the mid-upper 20s across the higher inland terrain to the 30s across the coastal plain. A weak warm front will approach Sunday night, so may see some overrunning precip try to develop across western by around 00Z Monday, then pushing E quickly through the night and during Monday. Temps will hold mainly in the 20s except the lower-mid 30s along the immediate coast overnight as the precip develops. Thermal profiles suggest mainly light snow Sun night, but not a lot of precip to work with so not expect much in the way of snow accumulations at this point. As winds shift to SW, will see milder air finally push into the region. Expect spotty snow showers to change to rain during the morning, but may linger a bit longer across the higher inland terrain. Expect highs close to seasonal normals for mid December. Tuesday and Wednesday... With a nearly zonal mid level steering flow across most of the country, will see weak systems work eastward but tend to weaken as they approach. Not expect much in the way of precipitation either Tuesday or Wednesday, but timing and track of systems are in question with the fast flow aloft. Have mentioned only slight chance POPs across the higher inland terrain and near the coast through this timeframe, but confidence is low. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. 18z update... Thru 00z...high confidence. VFR and dry with developing WNW wind increasing to 15-20 kt, possibly up to 25 kt Cape Cod and islands. After 00z...high confidence. VFR and dry with gusty WNW winds 15-20 kt diminishing after midnight. Friday...some uncertainty how far north snow and MVFR conditions track VFR but trending toward MVFR south coast and islands including Cape Cod late in the day with light snow possible. Elsewhere VFR prevails. Light winds. Friday night...some uncertainty on northward extent of MVFR and snow during the evening. MVFR in light snow possible south coastal MA including Cape Cod and Islands. Elsewhere VFR. Light winds becoming WNW. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday through Monday/... Saturday through Saturday Night: VFR. Windy with local gusts to 30 kt. Sunday: VFR. Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHSN. Monday: Mainly VFR, with areas MVFR possible. Slight chance SHRA, slight chance SHSN. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Today... Diminishing winds through the morning, then W-NW winds will increase this afternoon with gusts to 25-30 kt. Area of snow this morning will reduce vsbys, mainly over south coastal waters. SCA all waters. Tonight... Lingering SCA wind gusts in the evening then diminishing winds overnight as high pres builds in from the west. Friday... NW winds shift to the SW in the afternoon. Speeds below 20 kt with seas below SCA. Outlook /Friday Night through Monday/... Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of snow showers. Saturday through Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of snow showers. Monday: Winds less than 25 kt. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ230-232>234. Small Craft Advisory until 4 AM EST Friday for ANZ231-251. Small Craft Advisory until 4 AM EST Friday for ANZ235-237. Small Craft Advisory until 7 AM EST Friday for ANZ250-254>256. && $$ SYNOPSIS...KJC/EVT NEAR TERM...Nocera SHORT TERM...KJC LONG TERM...EVT AVIATION...Nocera/EVT MARINE...KJC/EVT

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