Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 171156 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 656 AM EST Wed Jan 17 2018 .SYNOPSIS... Low pressure will track south of Nantucket today bringing accumulating snow to much of southern New England today, heaviest across western and central MA and northern CT. A changeover to rain is likely near the south coast. Mainly dry weather expected tonight into Sunday, with a warming trend during this weekend. Another low pressure should affect the region early next week with mostly rain, but there is a risk of some snow/mix/ice in the interior. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 650 AM update... Snow expanding across SNE this morning as low pres develops south of New Eng. Nice banding signature on radar across NE CT through central and NE MA lining up where omega increasing in the snow growth region. Also some higher returns across LI sound and coastal CT which will be moving across RI and SE MA this morning. Dual-pol radar shows rain-snow line approaching the south coast and Cape Cod which will change to rain shortly. Decent thump of snow early this morning has dropped 1-3 inches on the Cape. Models have trended colder as low pres tracks south of Nantucket, so rain-snow line expected to be confined near the south coast and may only briefly reach PVD-TAN-PYM later this morning and early afternoon. Brief period of moderate to heavy snow this morning, then tapering off this afternoon as low pres moves offshore and forcing for ascent diminishes. Generally looking at 2-4" RI and SE MA increasing to 5-8" across interior northern and western MA with a stripe of 4-6" in between from northern CT to NE MA. Previous discussion... Overview... 1023 hPa low pres continues to develop, located E of Cape May, NJ at 06Z per WPC surface analysis. Precip has taken its time developing across the interior as the first low has been weakening across upstate NY, but have seen good influx of low level moisture and lift on the SW flow aloft across S coastal Mass into S RI and SE CT since 05Z on NE regional 88D radar imagery. Noting a band of light snow from near Newport to KFMH and KHYA at 09Z. Also noting increasing radar reflectivities across W Mass into CT. With cooler temps across the interior, have seen light snow falling from near the mouth of the Merrimack River SE to KHFD through most of the night, but has been on the light side. However, have received some spotter reports up to 2.6 inches of snow in Worthington and 1.8 inches in Conway, out in western Franklin county. The only caveat is a dry slot between the two precip areas, which has kept some areas mainly dry. However, since 08Z, the precip is starting to fill in there as well, so should see snow develop through around 10Z. 00Z short range models have brought the track of the low back closer to the coast, though still expected to pass SE of Nantucket around midday before heading to the Gulf of Maine as the open H5 long wave trough steadily shifts E. S-SE winds in place across RI/SE Mass today, combined with low level flow around ridge sitting across eastern Maine and the Maritime, will bring somewhat milder temps. Further inland, temps will remain close to or a few degrees below freezing through the day. With the low further offshore, models have trended colder with the temps. However, the big change on this package is the lower QPF amounts forecasted along with a somewhat later start to the precip and steady movement offshore during this afternoon. QPF amounts are about 0.1 to 0.2 inches lower than previous forecasts, though the band of highest QPF remains across NE, central and W Mass. P-type... With the colder air remaining across most of the interior as well as from Cape Ann south to near Boston, will see mainly snow especially inland where the higher QPF values are along with the better snow growth region. With the onshore wind, milder surface to 950 hPa temps move in which will cause the mix and change over to rain across S RI/SE Mass. Based on this forecast, looks like the rain/snow line will run close to Route 44 from about central Plymouth county to Taunton and Providence into E central CT, but may still see some snow mixed in even down to the coast and to the lower Cape at times. However, this will hold down snow amounts. Snow Amounts/Hazards... Based on thermal and moisture fields, along with milder air working into SE areas, will see lowest amounts across RI/SE Mass. SHould see some light accumulations even down to the coast, but could melt away as precip mixes with or changes to rain. Expect around 1-2 inches there. For N RI and interior SE Mass, will see a bit more snow, on the order of 2-4 inches, highest across interior Providence county RI. Across the remainder of the region (N CT/NE, Central and W Mass), where the best snow growth is in place as well as highest QPF amounts and coldest temps, will see up 5-8 inches of snow. Have kept Winter Storm Warnings up from interior Essex county across through N Worcester and all of Franklin, Hampshire and Hampden counties. S of there, we converted several zones over to Winter Weather Advisories covering Cape Ann down to Boston and into portions of SE Mass, as well as N RI and N CT. Will still see some hazardous travel conditions this morning across interior Mass and N central CT as well as along the S coast. As the low shifts NE this afternoon, the back edge of the precip will start to push into the CT valley, allowing the snow and/or rain to taper off. Winds will also shift to NW but remain light. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Tonight... The low will push to the Gulf of Maine this evening, so will see conditions improve from W-E. Last of the precip should be offshore by around midnight. Another batch of cold air will push in as skies become mostly clear. May see some NW winds gusting up to around 20 kt along the immediate coast. Expect temps to bottom out mainly in the teens, though will hold in the 20s along the coast. Thursday... As the H5 trough moves across the region, will see high pressure ridging build E. Will see W-NW winds up to around 10-15 kt, highest along the coast. High temps will only reach to 25-30 across central and western areas, and the lower 30s across E Mass and RI. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Dry with a warming trend through this weekend * Another storm may bring mostly rain late Monday into Tuesday with a risk of some interior snow/mixed precip/ice Quiet pattern expected through the weekend with a moderating trend as amplified trough moves into the Plains with downstream ridging and rising heights across New Eng. Near normal temps Friday then warming above normal during the weekend with readings mostly in the 40s. The aforementioned high amplitude trough is forecast to lift NE toward New Eng early next week with a stormy period sometime Mon into Tue with decent low level jet moving across the region. Timing uncertain at this time range but given the amplitude of the pattern, prefer somewhat slower solution with bulk of the event occurring Mon night into Tue. Ptype also uncertain across interior as ECMWF would suggest some snow/mix/ice with strong high pres to the N/NE. GFS mostly rain. Will take several days to resolve these issues. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... Today...High confidence in trends. Moderate confidence in timing. Widespread IFR/MVFR conditions in snow this morning, slowly improving later this afternoon, especially western New Eng. Rain snow line advances along the south coast but likely not much further north. Tonight...High confidence. Any lingering MVFR-IFR conditions will improve to VFR across RI/E Mass by around midnight or so. NW wind gusts to around 20 knots around Nantucket and parts of Cape Cod from midnight onward. Thursday...High confidence. VFR. NW winds gusting up to 20-25 kt across S coastal areas, Cape Cod and the islands. KBOS Terminal...Moderate to high confidence in TAF. Expect continued low conditions during the remainder of the morning push, though should improve around or after 19Z. CIGS may remain low through 00Z. KBDL Terminal...High confidence in TAF. Morning push will continue to be impacted. Conditions should start to improve around midday as precip tapers off. Outlook /Thursday Night through Sunday/... Thursday Night: VFR. Breezy. Friday: VFR. Friday Night: VFR. Breezy. Saturday: VFR. Windy with local gusts to 30 kt. Saturday Night: VFR. Breezy. Sunday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Today...Seas remain at around 5 ft across the outer waters through midday, then will build again later today and tonight, up to 6-7 ft. Seas may reach into the waters E of Cape Ann, so have hoisted Small Craft Advisories there through this afternoon, then should subside this evening. Tonight and Thursday...NW winds will gust up to 20-25 kt, highest on the southern open waters. Seas will remain around 5 ft, though will subside may briefly subside across portions of the eastern outer waters. Have extended Small Craft Advisories through Thursday mainly for the waters from Cape Cod southward. Outlook /Thursday Night through Sunday/... Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Saturday Night: Winds less than 25 kt. Local rough seas. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .HYDROLOGY... 445 AM Update... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. The Flood Warning for at the Taunton River at Bridgewater was cancelled Monday night as the river level fell below flood stage. Cold conditions will persist through midweek which will limit additional runoff. Continued ice jams will remain on some of the rivers. There will be some increase of snow pack across interior southern New England as well. For details on specific area rivers, including observed and forecast river stages, please visit the Advanced Hydrologic Prediction Service (AHPS) graphs on our website. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory until 6 PM EST this evening for CTZ004. Winter Weather Advisory until 3 PM EST this afternoon for CTZ002-003. MA...Winter Weather Advisory until 1 PM EST this afternoon for MAZ017>019. Winter Weather Advisory until 6 PM EST this evening for MAZ007- 013>016. Winter Storm Warning until 3 PM EST this afternoon for MAZ002- 003-008>011. Winter Weather Advisory until 3 PM EST this afternoon for MAZ012. Winter Storm Warning until 6 PM EST this evening for MAZ004>006-026. RI...Winter Weather Advisory until 1 PM EST this afternoon for RIZ002>004. Winter Weather Advisory until 6 PM EST this evening for RIZ001. MARINE...Small Craft Advisory until 1 PM EST Thursday for ANZ250. Small Craft Advisory from noon today to 6 PM EST this evening for ANZ251. Small Craft Advisory until 6 PM EST Thursday for ANZ254>256. && $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC/EVT SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/EVT HYDROLOGY... is the U.S. government's official web portal to all federal, state and local government web resources and services.