Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220024 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 724 PM EST Tue Feb 21 2017 .SYNOPSIS...
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A weak cold front dissipates as it crosses New England late tonight. Unseasonably mild temperatures will remain across southern New England late this week as weak low pressure systems pass west of the region. A strong cold front will cross the region Saturday afternoon and evening, bringing showers and possibly a few thunderstorms. Near seasonable temperatures will return early next week, with blustery conditions on Sunday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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7 PM Update... Bands of high clouds crossing the region out of NY state as seen on latest NE regional IR satellite imagery. Also noting some mid level clouds on latest surface OBS across the northeast. Noting some light precip moving E out of NY state, but appears most if not all has not reached the ground. Rather wide T/Td spreads of 15-20 degrees per 00Z OBS across the CT valley. SE winds across NE Mass at 00Z shifted to S-SW further W, though remaining light as high pressure pushes SE off of Nantucket. Looks like it will take a while for precip to reach the ground, if it does with the dewpt depressions. They may decrease overnight with slowly increasing low level moisture. Have left previous forecast intact for the remainder of the overnight hours. Still could see a little precip reach the ground, so warrants the CHC POPS going. Have updated near term forecast to bring conditions current. Previous Discussion... High pres moves offshore tonight with weak warm advection developing along with weakening shortwave moving into New England. Forcing for ascent is limited but models indicating deep moisture plume moving across SNE 06z-12z. A few showers possible mainly after midnight as this moisture plume and weak shortwave moves through but some areas may remain dry. Will maintain low chc pops for late tonight. The main issue is the potential for patchy light freezing rain across interior N MA as the precip moves in and temps will be near freezing here. Elsewhere, expect temps will be mostly above freezing. Since temps will be marginal and some areas may remain dry, no advisory will be issued but will address potential for some spotty icy spots in an SPS.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... Moisture axis will be oriented south of the Pike by 12z and moving south of the coast during the morning. Clouds and a few showers are possible in the morning across CT/RI and SE MA, otherwise mid level drying moving in from the north should allow ptsunny skies to develop late morning into the afternoon from north to south. SW flow will bring milder temps into SNE with highs likely reaching the low/mid 50s across most locations but cooler Cape/Islands and higher terrain. However, potential for upper 50s to near 60 in the coastal plain if there is sufficient sunshine. Cloud cover may limit full heating. Wednesday night... Mainly dry conditions and above normal temps with modest SW flow persisting. Patchy low clouds and fog may develop overnight. Lows will range through the 30s. && .LONG TERM /THURSDAY THROUGH TUESDAY/...
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Highlights... * Record warmth remains possible Thursday * Scattered showers possible with mainly mild temps on Friday * Widespread showers expected Saturday-Saturday night, with a few thunderstorms possible * Blustery and seasonably cool Sunday-Monday Overview... Overall upper level pattern continues across the lower 48 late this week, with building H5 ridge across the eastern U.S. as a trough digs out of the Rockies into the Plains states. This trough will slow surface systems down on Thu and Fri, with high pressure pushing offshore. A weak cold front may briefly work into northern areas Fri, but will retreat quickly north as S-SW winds pick up so could see another mild day for most areas. The big question is the timing of the surface system/developing cutoff H5 low that will work slowly east either Fri or Sat. Models seem to have a decent handle on the movement and shearing of the mid level system into Quebec, but some question as to the timing of the associated cold front. At this point, looks like it should push across Saturday into Saturday night. This will likely bring a decent amount of rainfall, and may even see a few thunderstorms ahead of the front. Beyond this, cutoff low pres over central Canada should keep progressive pattern in place through the remainder of the weekend into early next week with seasonable temperatures returning. Details... Thursday... High pressure off the eastern seaboard will keep steady stream of mild air pushing northward across the region. Could see some isolated showers move across western areas during the day, but models having a tough time handling the low level moisture field. Noting mainly light QPF during Thu night. Leaned toward the drier solution with the weakening system, at least with any shower activity during the day Thu. Noting a strong low level jet pushing across the region Thu afternoon and night ahead of weakening cold front. Low level mixing is marginal, though does improve between H925 and H95 after 00Z Fri across S coastal areas, so could see brief gusts up to 20-25 kt. Area of clouds may linger, especially across central and western areas during the day, which may cut back on the full heating potential. Depending upon how much mixing takes place up to H925, where readings will be around +10C to +11C, and whether the clouds could actually clear for a time, temps may reach the lower-mid 60s. Record highs may be close at KPVD and KORH, but may be tougher to reach at KBOS and KBDL. Low level capping seen on 12Z BUFKIT soundings Thu night, which could trap low level moisture along the S coast with the SW winds in place. Have mentioned patchy drizzle during the nighttime hours for those areas. May also see some isolated showers during the overnight as well, mainly across central and western areas, but precip will be light. Friday... Cold front stalls just S of the region Fri morning, but temps will not get too cool as H925 and H85 temps remain on the mild side. Light E-SE winds in place early in the day will shift to S-SW again as system returns as a warm front during the afternoon. This will be ahead of low pressure moving across the Great Lakes. May see scattered showers mainly from the Mass Pike northward during the day ahead and with the front. With a light onshore flow on both coasts, temps will be a bit cooler there. However, another mild day on tap for inland areas though not quite as warm as expected on Thursday. Readings away from the coast and into the inland valley could approach or exceed 60 in some spots. Otherwise temps mainly reaching the 50s. Saturday... Will be an active day. Low pressure will push into Quebec during the day with the weakening upper level cutoff low. However, its associated short wave will wrap across the region. Strong vorticity ribbon with this short wave, along with band of instability. Noted LI/s near zero, total totals in the lower 50s and TQ values up to 18-19 for elevated convection. So, have also mentioned a slight chance for thunderstorms Sat afternoon and evening for now. Have also noting good low level southerly jet up to 35-45 kt ahead of the front, so could see some of this mix down with any convection. Cold air will wrap in quickly overnight Sat night as the precip tends to cut off. Could still see a quick mix or changeover to snow showers across central and western areas. System pushes offshore quickly though, so may not see much of a wintry mix toward the coastal plain as the moisture ends quickly. Highs on Saturday may reach the lower 60s across interior E Mass and the CT valley, otherwise readings mainly in the 50s. Temps fall quickly overnight, bottoming out in the 30s at most locations, except around 40 on the outer Cape and the mid-upper 20s over the higher inland terrain. Sunday through Tuesday... Cold front pushes offshore by 12Z Sun, so should see mainly dry conditions for Sunday. Blustery NW winds in place, with gusts up to 25-30 kts, highest along the immediate coast and higher terrain. The gusty winds will make it feel more like temperatures in the mid 20s to mid 30s during the day, though actual highs will be close to seasonal normals /mid 30s to mid 40s/. May see another weak short wave quickly move across Sunday night-Monday. Have only carried slight chance POPs with this system as it appears to be moisture starved in the W-NW flow aloft. This is ahead of another reinforcing cold front. Timing of this system is in question though with fast flow aloft. For now, Tuesday should be a dry and seasonable day as high pressure builds across. Winds should diminish. Systems continue to move quickly in progressive flow aloft, so timing this far out is in question.
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&& .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/... Through 00z... VFR with increasing high clouds. Coastal seabreezes developing. Tonight...Moderate confidence. VFR cigs, but areas of MVFR developing late tonight in western MA and portions of northern CT. A few showers possible mainly after midnight with low risk of patchy freezing rain in interior northern MA. Wednesday...Moderate confidence. Patchy MVFR cigs/vsbys in the morning, mainly from CT valley to the south coast, improving to VFR in the afternoon. Low risk of a morning shower near the south coast. Wednesday night...Moderate confidence. Areas of MVFR/IFR cigs may develop along with patchy fog. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Thursday through Sunday/... Thursday...Moderate confidence. Mainly VFR across most of E Mass. MVFR-IFR CIGS lingering along the S coast, Cape Cod and the islands, possibly into the CT valley Thu afternoon/night. Patchy fog may develop overnight as well with local MVFR-IFR VSBYS. Friday...Low confidence. Leftover MVFR-IFR VSBYS through mid morning in patchy drizzle/fog. CIGS improve to VFR, though may see patchy MVFR-IFR CIGS as warm front pushes N during the day, especially across central and N Mass. Scattered showers linger across the interior. Light E-SE winds shift to S from S-N Fri afternoon and evening. May see gusts up to 20 kt along the S coast. Saturday...Moderate confidence. Areas of MVFR-IFR CIGS/VSBYS in showers and patchy fog. Low risk for isolated thunderstorms Sat afternoon/evening. A few snow showers possible across western areas before precip ends. Conditions may improve to VFR after midnight across western areas. Sunday...Moderate confidence. A few rain and/or snow showers may linger across central and eastern areas through mid morning Saturday with local MVFR conditions. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. Persistent SW flow through the period with windspeeds and seas remaining below SCA. However, may see a few gusts 20-25 kt late tonight into Wed morning across eastern MA waters. Outlook /Thursday through Sunday/... Thursday...High confidence. S-SW winds in place, gusting up to around 20 kt during the afternoon. Gusts up to 25 kt and seas building to around 5 ft on the outer waters Thu night. May see patchy drizzle and fog develop Thu night along the S coast with reduced visibilities. Friday...Low confidence. Winds should become light N-NE across the eastern waters Fri morning, with light/variable winds on the southern waters. Expect winds to shift back to S-SW during the day as warm front pushes N. May see gusts up to 20 kt on the outer water Fri night. Local visibility restriction in patchy fog. Saturday...Moderate confidence. S winds increase, gusting to around 25 kt. Small crafts likely. Seas build up to 5-8 ft on the southern outer waters. Reduced visibilities in showers and patchy fog. Low chance for thunderstorms Sat afternoon/evening. Sunday...Moderate confidence. Winds shift to W and gust up to 25-30 kt. Seas up to 6-9 ft on the open waters. && .CLIMATE... Record Highs for Thu Feb 23 BOS...65/1990 BDL...68/1990 PVD...60/1990 ORH...61/1990 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/EVT NEAR TERM...KJC/EVT SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/EVT MARINE...KJC/EVT CLIMATE...Staff

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