Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240027 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 727 PM EST Thu Feb 23 2017 .SYNOPSIS... High pressure offshore of New England will bring unseasonably warm conditions into Saturday. A warm front may trigger a few showers across northern Massachusetts tonight and Friday morning, with light spotty drizzle elsewhere. Otherwise mainly dry weather prevails. A strong cold front will cross the region Saturday night, bringing areas of rain and patchy fog. There will be a low chance for isolated thunderstorms as the front passes. Dry but blustery conditions return on Sunday into Monday with normally cool temperatures. A couple of fast moving low pressure areas may bring unsettled conditions to the region around the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 7 PM Update... Low stratus clouds already returning along the S coast this evening, though some breaks in the clouds noted at KACK at 23Z. With temps falling to the dewpts, which are mainly in the lower-mid 40s, the low clouds will fill in by 02Z-03Z. May start to see some of the lower clouds filter northward on the light S-SW winds. Will need to monitor for possible dense fog advisories mainly near or after midnight for some areas mainly along the S coast. With dry conditions expected through most of the night, remainder of forecast in good shape. Have updated the early portion to bring conditions current and incorporated into trends through 05Z-06Z. Previous Discussion... After a record setting day of warm temperatures (BOS 68, PVD 66, BDL 66 and ORH 64) a pleasant early evening is ahead with mild temps and winds diminishing. However, attention turns to low clouds and patchy fog along the south coast that continues to dissipate. This trend will continue this evening but as the blyr continues to cool, the low level moisture is likely to return in the form of low clouds and fog tonight. However couple of wildcards here...1) additional area of low clouds and fog upstream along the south coast of Long Island that continues to advect northeast toward Block Island and RI south coast. 2) second wildcard is SC/CU clouds over to the west across PA and NY. Models have this lifting into a mid deck of clouds and overspreading our region later this evening and overnight. This may help keep temp up a bit and large enough dew pt depressions to preclude low clouds and fog becoming widespread. Nonetheless the trend tonight will be for mainly clear skies to become mostly cloudy. Frontal boundary to the northwest of SNE may bleed southward tonight but then lift north as warm front late tonight. This may be sufficient for some spotty light rain especially across northern MA. Elsewhere mainly dry conditions likely prevail other than some spotty light drizzle overnight. Will remain in the warm sector so a very mild night ahead with lows in the 40s...more typical of our daytime highs for late Feb. Given dewpts are in the 40s (again AOA our normal daytime highs), as mentioned above expect at least patchy fog to develop as the night progresses. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Updated 410 PM... Friday... Warm front across northern MA in the morning lifts slowly north. Thus at least some sunshine across CT/RI and southeast MA with more clouds across northern MA especially in the morning. This boundary may yield some spotty light rain over northern MA in the morning along with spotty light drizzle elsewhere, but the trend will be towards drier weather for the afternoon. Given we`ll remain in the warm sector expecting another day of highs in the 60s across CT/RI along and south of the MA pike. Route 2 corridor northward to the VT/NH border will be slightly cooler with highs in the upper 50s given cool side of the boundary. Boston and the north shore may have seabreezes that limit highs to the 50s. However let`s keep in mind it`s still late Feb when normal daytime highs should be only in the lower 40s. Thus spring fever continues and 60s possibly lingering into Sat too! Friday night... More of the same, warm sector airmass remains over the region so very mild conditions prevail with temps only falling into the 40s along with another round of patchy fog and drizzle. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * Mild with showers late Saturday and Saturday night * Blustery and seasonably cool Sunday and Monday * Progressive steering pattern around the middle of next week may bring a few weather systems and unsettled conditions Overview... 12Z model suite remains in pretty good agreement through Sunday, then model solutions diverge greatly after this timeframe thanks to a redeveloping broad upper level steering pattern across the lower 48 through the middle of next week. Have low confidence in timing and track of individual systems from Mon through Thu due to the fast flow aloft. Strong H5 short wave moves quickly across the region late Sat and Sat night, with its associated cold front. Will see normally cool but blustery conditions move in for Sunday and Monday as high pressure moves across. Beyond this, really tough resolving sensible weather with low continuity amongst the model suite through the middle of next week. Monday is a good example, with the GFS continuing to develop a wave of low pres in the developing SW flow aloft, while the Canadian GGEM and ECMWF keep dry conditions. Do note some model to model consistency with a couple of systems during the Tue night to Thu timeframe, but timing is still in question. Used a blend of available guidance through Sunday with rather good confidence. Into next week, transitioned to the model ensembles which showed a bit better continuity than individual model solutions. Details... Saturday into Saturday night... Models continue to signal strong short wave moving quickly eastward as it wraps around cutoff H5 low over western Hudson Bay during this timeframe. Its associated surface cold front will cross the region during Sat night. Will continue to see low clouds and areas of fog Sat morning, which may break briefly as S-SE winds increase with the increasing pres gradient ahead of the cold front during the afternoon. Clouds look to linger through the day, along with some scattered showers as low level moisture remains underneath the inversion. May also see some patchy drizzle mainly along the S coast where best low level moisture pooling will take place with the onshore wind. Strong low level S jet will push toward the region during Sat, increasing to 35-45 kt at H925 up to 50 kt at H85 by 00Z Sun as front approaches. Best mixing is noted behind the front, but some of this could mix down with any moderate rain that may push across. Southern stream swath of higher PWATs sweep into the region on the strong winds aloft. While the PWATs are only about 1 inch, this is about 2 SD above climo for late February. Noted that the higher QPF amounts have shifted a bit further N into N New England and upstate NY with the 12Z run, along with the faster forward progress of the front once it reaches the region overnight. At this point, expect about 0.25 to 0.5 inches with highest amounts across the E slopes of the Berkshires, with around 0.1 inches or less along the coast. With the precip mainly near and behind the front, colder air will work in while some of the precip is across the region. Will see mix/changeover to snow mainly across the higher terrain of the Berkshires and northern Worcester hills. Will still see precip quickly shut off as system clears the coast between 06Z and 09Z Sun. Expecting mainly a dusting of snow, with an outside shot of up to 1/2 inch, which could occur near the border with Berkshire county. May see some lingering rain along the E Mass coast toward daybreak. Still noting good instability as the front approaches, with TT into the lower 50s, LIs at or just below zero and TQ values in the upper teens to around 20. Some signals for elevated convection, considering low level capping in place on BUFKIT soundings until the front approaches. May see some brief heavy rainfall near the Berkshires into parts of the northern CT valley, which could also bring brief strong wind gusts down. Have kept isold thunder in the forecast from about 22Z through 06Z. One other aspect after this system passes will be rising water levels across the watershed into early next week. Much if not all the snowpack has or will have melted across this region, but still much more upstream that will push into the headwaters and head downstream. Will need to monitor in case some river levels approach action stage. Sunday through Tuesday... High pressure builds to the mid Atlantic coast Sunday, keeping good shot of cold air advection working across in the W-NW wind flow at the surface and aloft. H85 temps drop from -4C (east) to -10C (west) at 12Z Sunday down to -9C to -11C at 18Z. Excellent low level mixing also works in, with a 50 kt jet at H85 moving across Sunday, and 30-35 kt jet at both H9 and H95. So, will likely see wind gusts up to 30-35 mph during the day Sunday, highest gusts across the higher terrain and along the coast. At least skies will be mainly sunny. Remains seasonably cool and blustery on Monday, but some big model differences especially on the 12Z GFS. This model continues to signal a fast moving weak system working NE around the backside of the departing high pres off the mid Atlantic coast Mon night and Tue. Low confidence continues. Most models showing a bit better continuity with another system in the Tuesday timeframe. Looks like good lift ahead of another warm front as low pressure moves across the Great Lakes. Again, looks like the GGEM and ECMWF are in better agreement with the GFS the outlier. Went with chance POPs with this system, though low confidence remains. Wednesday-Thursday... Upper level pattern remains progressive, with H5 trough migrating across the central U.S. during this timeframe. Timing of the associated low pres and cold front still in question, but looks like another decent shot of precip with it some time late Wednesday into Thursday. Lower than average confidence during this timeframe. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... 7 PM update... Tonight...Low to moderate confidence for timing of low conditions. Already noting IFR-LIFR CIGS along the S coast, and expect to expand northward. Patchy drizzle may accompany these low clouds as well with low risk of a few light spotty showers northern MA late. Friday...Moderate confidence. Combination of IFR-MVFR in the morning with slow improvement to from south to north. Low risk of some spotty light rain across northern MA. Friday night...MVFR likely with light spotty showers/drizzle possible. KBOS TAF...high confidence until about 00z then diminishing tonight and thereafter. KBDL TAF...high confidence until about 00z then diminishing tonight and thereafter. Outlook /Saturday through Tuesday/... Saturday...Moderate confidence. MVFR-IFR conditions in areas of fog and low clouds. May see spotty drizzle along the S coast Sat morning. Isolated TSTMS approach the E slopes of the Berkshires around 21Z-22Z, then shift steadily E Sat evening. Brief heavy rain possible across W Mass with any thunder. Precip mixing with or changes to -SN around midnight or so across the higher inland terrain ending after 06Z. May see local IFR-LIFR conditions in any -SN. Conditions improve rapidly toward daybreak across central and western areas. W winds gusting to 20-25 kt after midnight. Sunday...Moderate confidence. VFR conditions. NW winds gusting to 25-30 kt, highest along the immediate coast and across the higher terrain. Monday...Low confidence. Mainly VFR conditions. SW winds gusting to around 25 kt, highest along S coast. May see local MVFR in isold -SHRA mainly S of the Mass Pike Mon afternoon/night. Tuesday...Low confidence due to timing of weather features. May see scattered -SHRA with local MVFR conditions. May mix with or change to -SHSN during the nighttime hours mainly across the higher terrain. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. Other than some gusts near 25 kt early this evening near shore, S-SW winds will be fairly light along with low seas. Biggest concern will be vsby lowering to below a mile at times in patchy fog tonight thru Fri night. Outlook /Saturday through Tuesday/... Saturday...Moderate confidence. SE winds shift to S Sat night gusting to 25-30 kt. Seas build up to 6-9 ft, highest on the outer waters. Reduced visibilities in areas of fog and scattered showers Sat, then in rain Sat night and patchy fog Sat night. Low chance of isold thunderstorms Sat evening through around midnight. Winds shift to W after midnight Sat night, gusting to 25-30 kt. Conditions improve with the wind shift. Sunday...High confidence. W-NW winds gusting to 25-30 kt across the open waters. Low chance for gale force gusts on the eastern outer waters. Seas up to 6-9 ft, though will slowly subside as winds diminish Sun night. Good visibilities. Monday-Tuesday...Low confidence due to timing of weather features. SW winds may gust to around 25 kt at times on the outer waters Mon and Mon night, then diminish Tue. Local visibility restrictions possible in scattered showers Mon night-Tue, though timing in question. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera/EVT SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.