Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 160800 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 300 AM EST Mon Jan 16 2017 .SYNOPSIS... High pressure maintains dry and seasonably cold conditions into Tuesday morning. Low pressure will push east out of the Ohio Valley toward the region, with the potential of snow and ice impacting much of the interior late Tuesday afternoon into Wednesday morning. This low pressure moves offshore by Thursday morning, but could see leftover spotty showers along the shore late this week. High pressure will build along the eastern seaboard with dry, milder conditions into next weekend. && .NEAR TERM /THROUGH TODAY/... A rather quiet January day, weather-wise. A large high pressure will be overhead, as it continues to move to the Mid Atlantic coast from the Great Lakes. Expecting a light west wind early, to become southwest later this morning, then increase slightly this afternoon. With plenty of sunshine, should see temperature slightly above normal this afternoon. && .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/... High pressure remains in control tonight, even with its core to our southwest. Not much moisture to work with, so a weak cold front late tonight should move through without much fanfare. Forecast gets much more complicated during Tuesday. Only have moderate confidence in the details at this point. 16/00Z guidance continues to suggest precipitation arrives during Tuesday afternoon, particularly across the western half of southern New England. The main issue there, will be low level humidity. It`s not expected to be very high to start, and am thinking it will take a while for the column to saturate, and permit the precipitation to reach the ground. However, that will have the consequence of evaporational cooling, which could lead to a wintry mix. Thinking a rain/snow mix would be most likely at the onset, before the arrival of warmer air aloft introduces the possibility of sleet and freezing rain as well. The Tuesday afternoon commute could get messy, particularly across the higher terrain of central and western MA. These details are not set in stone. Will need to monitor over the next 24-30 hours. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Possible significant icing event across portions of interior southern New England late Tuesday into Wednesday * Onshore winds will keep lingering clouds across the region into Friday * Dry and milder conditions should set up along the eastern seaboard by next weekend Overview... 12Z model suite and ensembles continue to signal slow but steady transitioning upper level steering pattern across the northern hemisphere through this timeframe. The fast, progressive flow, which has been persistent over the last few weeks, looks to feature more H5 amplification and the possibility of omega blocking setting up from the central U.S. to the western Atlantic by next weekend. Depending upon how this sets up, could see period of dry and milder conditions along the eastern seaboard. Prior to this, however, will see potential of significant icing and light snow accumulations across portions of interior southern New England Tue through Wed night as cold air gets trapped, which could allow for a wintry mix including sleet and/or freezing rain. As the low passes south of New England, should see winds become onshore during Wednesday, which should allow the mixed precipitation to change over to all rain as temps rise. Details... Tuesday night through Wednesday night...Low to moderate confidence. Big questions for this forecast will be how deep the cold air damming sets up, as well as how quickly the partial thicknesses rise overnight. Looks like the H85 to H7 thicknesses rise to critical 1540-1549m overnight while the H100 to H85 thicknesses remain at or below 1300m, which will allow IP/FZRA to develop across the higher inland terrain into the CT valley and N central Mass overnight. This, along with potential of 0.2 to 0.3" of QPF, where the best shot for freezing precip occurs, could see significant icing that may warrant winter weather headlines across portions of the interior. Will continue to monitor this very closely. May also see some light snow accumulations as well, and may even see some mixed snow/sleet as close as the eastern coastal plain for a time overnight Wed night. This will all depend upon the eventual temp profile. Winds will veer from N to easterly overnight into Wednesday, so this should bring milder air onshore far enough inland to bring a change to rain inland. Could still see some icing across the E slopes of the Berkshire and the northern Worcester hills into mid morning, but temps should rise above freezing then. As the ridge continues to shift E, the low should push off near or S of Cape Cod during Wed. Back edge of precip should work into western areas Wed afternoon, but will be slower to clear the east Wed night. Winds will back to N again, which will bring colder air back in. Precip could end as a mix of rain and snow showers even down to the coast. A lot to consider during this portion of the forecast. Thursday and Thursday night...Low to moderate confidence. As the low slowly pushes off the coast, it appears to stall over the western Atlantic with H5 omega blocking looks to set up. However, models and ensembles have some solution spread with its position of the low over the Atlantic as well as across the central U.S. Friday through Sunday...Low confidence. At this point, it looks like ridge at the surface and aloft sets up along the eastern seaboard. So, should see dry conditions during this timeframe. Should see mainly N-NE winds, which will keep temps milder than seasonal normals. However, this timing will be dependent upon movement of systems earlier in the week as well as the eventual set up of the blocking pattern across the central and eastern U.S., so lower than average confidence for this part of the forecast. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High Confidence. VFR. Dry weather and mainly light winds through Tuesday morning. MVFR developing from W to E Tuesday afternoon. Increasing risk fora wintry mix of RA, SN, FZRA and IP across the higher terrain of central and western MA Tuesday afternoon. Timing is not yet certain. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/...Moderate confidence. Tuesday Night through Wednesday night...Sleet could reach as far E as east coastal areas Tue night, though temps will slowly rise as winds become onshore overnight. Precip should change over to RA with lingering patchy fog Wed. Expect E winds gusting to around 25 kt along east coastal areas Wed, then back to N Wed night. Precip should taper off to showers Wed night, but could see mix back to IP/FZRA across N central and W Mass before ending. Patchy fog lingers through the night with MVFR-IFR VSBYS. Thursday-Friday...Will see MVFR to local IFR CIGS/VSBYS linger Thu morning as northerly winds keep low clouds/fog mainly across eastern areas. Should improve during Thu afternoon. Wind gusts up to 25 kt possible through Thu, then diminishing. Should see mainly VFR conditions Fri. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High Confidence. Today and tonight...High pressure moves south of the waters today. Southwest winds should develop as it does. Brief increase in the pressure gradient expected this afternoon and evening, leading to some gusts up to 25 kt. It`s marginal, but think these gusts will be widespread enough to warrant a Small Craft Advisory for some of the eastern coastal waters, especially the outermost waters. Dry weather and good visibility prevail. Tuesday...A weak cold front should move through during the morning, followed by a quick wind shift to the east; ahead of an approaching warm front. Good visibility should prevail, with only a chance of rain across the RI coastal waters late in the day. Outlook /Tuesday Night through Friday/...Moderate confidence. Tuesday Night-Wednesday...Winds veer from N to E during Tuesday, with gusts increasing to 25-30 kt Tue night and Wed across the eastern waters as low pressure moves across the southern waters. Seas will build up to 5-8 ft on the eastern waters Wed. Even with rather low astronomical tides, tide heights may reach 9-11 ft on both the Tue night and Wed tides along the east facing beaches as well as in Cape Cod Bay. Winds will back to N-NE but remain gusty Wed night across most of the waters as the low exits. Reduced visibilities in rain and patchy fog through Wed, then gradually improving. Thursday-Friday...N winds will continue to gust to 25-30 kt Thu, then will diminish Thu night. Seas remain very high, up to 8-11 ft on the eastern open waters through Thu night, then will slowly subside but remain well above 5 ft on most of the outer waters as well as the eastern near shores Fri. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 4 PM this afternoon to midnight EST tonight for ANZ250. Small Craft Advisory from 7 PM to 11 PM EST this evening for ANZ231-251. Small Craft Advisory from 6 PM this evening to 1 AM EST Tuesday for ANZ254. && $$ SYNOPSIS...Belk/EVT NEAR TERM...Belk/EVT SHORT TERM...Belk LONG TERM...EVT AVIATION...Belk/EVT MARINE...Belk/EVT

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