Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 171546 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1046 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/...
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1100 AM Update... Minor adjustments made to the forecast to account for latest trends. Positively tiled trough continues from the Great Lakes town into the Southeast. Meanwhile, a coastal low south of southern New England will slowly strengthen as it moves between the Benchmark and the Cape. The combination of these two systems interacting has resulted in widespread snowfall for the region. 12z and even some of the Hi-res models continue to struggle with this system, especially with the lull in precip across western MA/CT. The focus for snow and any banding is across eastern half of the region thanks to the persistent southwesterly flow and good upper level divergence from 300 mb jet streak. SPC meso analysis is also shows the region in a favorable 850 mb convergence region, which is helping support ongoing snow showers. However, this lull will appear to fill back end, but with lack of mid and upper level forcing do not expect more than an additional inch or two across western MA. For the rest of the region, precip shield while strong it is slowly beginning to break up which will help diminish any additions accumulations. Current thinking is that vsbys will increase to above 1 SM with light snow showers WAA continues across the I-95 corridor for the remainder. May need to look at some changes to headlines, but still trying to get a handle on what is occurring downstream. Snow may linger closer to 00z especially across NE MA as the low passes into the Gulf of Maine. Lingering lift and moisture may result in a couple of tenths of snow. Mixing line has pushed into the Cape and along the immediate south coast. Some locations have warmed into the mid 30s, but snowing just enough to keep ptype as snow. Latest 12z models keep the warm air across this location with perhaps making it to PYM. So the Cape may have seen its great snow this morning, which was a surprise 3 inches in some spots. Previous discussion... 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.
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&& .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 /16Z WEDNESDAY THROUGH SUNDAY/...
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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. 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.
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&& .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...
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1100 AM Update... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. 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.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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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 until 6 PM EST this evening for ANZ251. Small Craft Advisory until 6 PM EST Thursday for ANZ254>256.
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&& $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC/Dunten SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/Dunten/EVT MARINE...KJC/EVT HYDROLOGY...Staff

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