937 FXUS61 KBOX 012059 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 359 PM EST Fri Mar 1 2019 .SYNOPSIS... Coastal storm tonight into Saturday with mostly snow, a wintry mix with rain along the immediate south coast of New England. Some blustery northeast winds as well. A second storm Sunday night into early Monday will bring snow, likely changing to rain in the coastal plain. Significant snow accumulations possible in the interior. Mainly dry weather, but much colder for the rest of the coming week with temperatures well below normal. && .NEAR TERM /THROUGH SATURDAY/... 4 pm update... Initially tranquil conditions early this evening, with increasing clouds from S to N. Then looking at a plowable snowfall event for much of the area during late tonight into Saturday. Low pressure over the southeastern states emerges off the Carolina coast, steadily deepening and strengthening as it tracks toward our area. 12Z GFS tracks the low center over the 40N/70W benchmark, 12Z NAM and ECMWF bring the low center slightly SE of the benchmark during Sat morning. Some favorable dynamics for this deepening low, with SNE getting into right rear quadrant of upper level jet. However looking at the mid levels, flow shows short wave energy but it is traversing thru a fast flow with only a modest amount of mid level troughing and a lack of a downstream block. This will keep this system progressive, moving steadily thru and then NE of our area during late tonight thru Saturday afternoon. The expedient track of this low brings a challenge to determining snowfall amounts, the shorter residence time limiting accumulations. Although models not fully consistent on QPF amounts, there is model agreement that the highest QPF will be over SE MA, with amounts tapering over the interior. Heaviest snow expected to fall between 4 am and noon. Marginal thermal fields indicate the potential for a heavier, wet snow over SE MA and RI, and some wintry mix closer to the coastline as well as the Cape/Islands. Precip type all snow over the interior, where the snow to liquid ratios will be higher. A Winter Storm Warning is now in effect for Bristol and Plymouth Counties in MA for 4 to 7 inches of snow. Then a Winter Weather Advisory is in effect for the remainder of the BOX County Warning Area, except for a portion of NW MA and also Nantucket where amounts are expected to be lower (in Nantucket's case, mixing with rain). Generally a 3 to 6 inch event in the Advisory area. Winds will be out of the NE, becoming N and increasing during the day Saturday. Gusts 20 to 30 mph along the east coastal MA and coastal RI locales, except gusts 30 to 40 mph Cape and Islands. With surface dewpoints in the teens and low 20s, there will be some wet bulbing overnight as precip approaches. Looking at overnight lows mainly in the 20s, except around 30 Cape and Islands. Highs on Saturday mostly in the low to mid 30s, except upper 30s on Nantucket. && .SHORT TERM /SATURDAY NIGHT/... Saturday night... The coastal low continues to rapidly deepen but is moving steadily away from our area, east of Halifax by 06Z. There is the potential for some lingering wraparound light snow during the evening, and have slight chance to chance pops for that timeframe. Then after midnight, dry with partial clearing as surface ridging briefly moves into our area. Winds shift from the North to the West and become light. Seasonably cold with lows mainly in the 20s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Another coastal storm will likely bring significant snow accumulation to the interior Sunday night into early Monday * Snow likely changes to rain near the coast * Much colder for the rest of next week with temps well below normal Sunday... Dry weather holds on for much of the day as high pres gradually shifts to the east. Clouds will be increasing and some light snow may reach western MA/CT toward evening, otherwise a dry day with highs in the 30s to around 40. Sunday night into Monday... High confidence that a winter storm will impact the region but there is still uncertainty with respect to specific details regarding where rain-snow line sets up and specific snow accums across the region. GFS remains furthest south and east with low track near the benchmark and coldest of the guidance and would suggest significant snowfall across the coastal plain. ECMWF is furthest north with track across the Cape with heaviest snow in the distant interior with rain-snow line getting west of the I-95 corridor. NAM is somewhat of a compromise. Given the lack of a blocking downstream ridge and mean trough axis back across the Lakes, we think GFS is to far offshore so favored a track closer to the ECMWF but will blend with NAM thermal profiles as a basis for the forecast. Enough cold air in place for precip to start as snow across all SNE Sun evening, but expect an eventual change to rain overnight along the south coast and the coastal plain near the I-95 corridor from PVD to BOS with mostly snow to the north and west. This area has greatest uncertainty regarding snowfall amounts as ptype transition zone expected to be nearby. A period of heavy snow with 1-2"/hr snowfall rates will possible in the interior overnight Sun night but duration of heavy snowfall rates should will be limited as this will remain an open wave with no closed mid level low developing. Regarding snowfall, prelim thinking is max snowfall axis of 6-10" across the interior west of I-95 corridor, with highest amounts across interior MA and portions of northern CT. Expect 4-7" along the I-95 corridor into interior SE MA, 2-4" PVD-TAN-PYM and 1-2" near the south coast. However, it is important to note that any shift in the storm track will result in changes to these numbers. There is a risk of isolated to scattered power outages, especially from northern CT, NW RI through NE MA where risk of 6+ inches of wet snow. The snow should be drier further back across central and western MA with lower risk of power outages here. The heaviest snow should be winding down Mon morning, but there will be a significant impact to the morning commute, especially in the interior with snow covered roads. Tuesday through Friday... Unseasonably cold airmass settles over New Eng with 850 mb temps 2-3 SD below normal. The coldest period should be around Wed/Thu with 850 mb temps down around -20C. Looks mostly dry during this period with NW flow aloft, but will have to watch next approaching shortwave and low pres which could bring more snow/wintry precip sometime late Fri into Sat. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Thru 00Z... VFR. Localized sea breezes end, with prevailing wind becoming light from the SE. Tonight into Saturday... SN spreading across the terminals. Wintry mix with IP/RA along the immediate S-coast, Cape and Islands. MVFR- LIFR impacts, especially with SN, to both CIG and VSBY. SE winds becoming NE overnight, increasing to 10 to 20 sustained along E/SE New England. During Sat, gusts 25 to 30 kts eastern MA/RI, except gusts 30 to 35 kts possible Cape/Islands. Saturday night...Lingering MVFR cigs with some light -SN possible during the evening. Then becoming VFR after midnight with partial clearing. KBOS Terminal...VFR, then lowering cigs/vsbys late tonight w/SN moving in around 10Z Saturday, diminishing after 20Z. Expect reductions in both CIGs and VSBYs as SN accumulates on runways anywhere around 3 to 6 inches. KBDL Terminal... VFR, then lowering cigs/vsbys late tonight w/SN moving in around 10z Saturday and persisting thru 17Z. Looking at accumulations on runways of 2 to 4 inches. Outlook /Sunday through Wednesday/... Sunday: VFR. Sunday Night: Mainly IFR, with local MVFR possible. Breezy. SN, RA, FZRA. Monday: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Chance SN. Monday Night through Wednesday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Tonight...Low pressure system emerges off the Carolina coastline tonight, strengthening as it tracks towards the coastal waters. Winds/seas increase overnight, Shifting from the S to E/SE with gusts 25 to 30 knots on the southern coastal waters late tonight. Seas on the southern waters building to 3 to 6 feet. Reduced vsbys late in areas of rain and snow. Saturday...Gale Warnings in effect for the southern outer coastal waters and waters east of Cape Cod, as well as Nantucket Sound. NE winds becoming N, intensifying with gusts up to 35 kts. Elsewhere along the waters, SCA headlines hoisted with gusts to 30 kts during the day. Seas 5 to 10 feet. Reduced vsbys in areas of rain and snow, mainly in the morning. Saturday night...Coastal Storm rapidly pulls NE-ward away from our area. Will still have some gusts to 25 kts to start, along the outer coastal waters. Then winds diminish during the overnight. Outlook /Sunday through Wednesday/... Sunday: Winds less than 25 kt. Local rough seas. Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Rain, snow. Local visibility 1 nm or less. Monday: Moderate risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain. Local visibility 1 to 3 nm. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Local visibility 1 to 3 nm. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Slight chance of snow showers. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory from 1 AM to 7 PM EST Saturday for CTZ002>004. MA...Winter Weather Advisory from 1 AM to 7 PM EST Saturday for MAZ004>007-009>016-022-023-026. Winter Storm Warning from 1 AM to 7 PM EST Saturday for MAZ017>021. RI...Winter Weather Advisory from 1 AM to 7 PM EST Saturday for RIZ001>008. MARINE...Gale Warning from 7 AM to 6 PM EST Saturday for ANZ232. Small Craft Advisory from 3 AM to 7 PM EST Saturday for ANZ233- 234. Small Craft Advisory from 7 AM to 5 PM EST Saturday for ANZ230. Small Craft Advisory from 6 AM Saturday to 3 AM EST Sunday for ANZ231-251. Small Craft Advisory from 6 AM to 5 PM EST Saturday for ANZ236. Small Craft Advisory from 3 AM Saturday to 3 AM EST Sunday for ANZ235-237. Small Craft Advisory from 6 AM Saturday to 5 AM EST Sunday for ANZ250. Gale Warning from 7 AM to 7 PM EST Saturday for ANZ254>256. && $$ SYNOPSIS...KJC/NMB NEAR TERM...NMB SHORT TERM...NMB LONG TERM...KJC AVIATION...KJC/NMB MARINE...KJC/NMB