Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191814 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 114 PM EST Fri Jan 19 2018 .SYNOPSIS... Dry and seasonably cold conditions today, then a warming trend this weekend with continued dry weather. A storm system will bring the potential for heavy rain and strong coastal winds late Monday night into Tuesday, but there is a risk of some wintry mix/ice across the interior late Monday and Monday night. Blustery, dry and seasonably cold weather will follow Wednesday and Thursday. && .NEAR TERM /UNTIL MIDNIGHT TONIGHT/... 1 pm update... Wave clouds linger as low level moisture remains trapped beneath the stout H85 inversion as discerned via 12z sounding profiles. Weak mid-level ridging built across the region in wake of the morning H5 vortmax, diurnal heating as low level winds become more W/SW in advance of the approaching surface low into the N Great Lakes region, winds funneling N into the CT River Valley as temperatures warm into the 30s. Steering currents light within the low levels and both weak ridging and stout inversion stubborn, going to take awhile for low clouds to advect E across E/NE MA, likely to hang around towards evening before a brief break, possibly filling back. All in perspective along with increasing westerly winds as to be discussed below, not leaning too cold for the overnight period and in fact with winds becoming more W/SW, dewpoints rising, expecting to see low temperatures towards midnight and then holding stable or slowly rising thereafter. Lows down around the mid to upper 20s with the coldest conditions over the N/W high terrain coincident with the deepest snow pack. && .SHORT TERM /MIDNIGHT THROUGH 6 AM SUNDAY/... Through Saturday... Digging N-stream energy out of the Arctic reaches of Canada, capturing and stretching energy out of a sweeping H5 trof axis into the W CONUS, surface low continues to deepen across the N Great Lakes region into the St. Lawrence River Valley down to around 990 mb up against high pressure over the SE CONUS up to 1030 mb. A tightening pressure gradient emerges along with a subsequent jet streak, the threat is there of such winds mixing down to the surface requiring wind-related headlines, perhaps on sustained winds alone. H925 westerly winds 45 to 55 mph, the height of which is around Saturday morning. Accompanying stout inversion, strengthening, with pronounced warming through the H8-9 layer. Limitations on the potential mix down of faster momentum to the surface, however, if able to mix up to H95 / 1200 feet agl, then there is the possibility of getting wind gusts up around 40 to 45 mph. It`s a race of daytime heating and boundary layer mixing during the height of the winds. It could end up that the strongest winds will have passed by the point in which 2m temperatures are forecast to warm into the low 50s, the boundary layer by afternoon to mix up to H9 prior to a pre-frontal trough across the region late along which winds relax. Colder along the S-coast with onshore flow. Seemingly a marginal event, to no surprise is there low probability derived from both CIPS Analogs and ensemble probabilistic guidance of meeting or exceeding WIND ADVISORY criteria. If any one location has the best chance of seeing winds sustained over 30 mph and/or gusts over 45 mph it would be Nantucket. Roughly 30 to 40 mph gusts along the S/SE-coast with general 20 to 30 mph gusts elsewhere. Saturday night... Main surface cold front pushing S into the region, eroding beneath high pressure. Light winds expected with filtering mid to high level clouds across the region within the zonal pressure gradient aloft. Stout inversion building across the region down to H95, with higher dewpoint air lingering along with the likely boundary layer mixing of snowmelt and now cold air advection proceeding, expecting to seeing low clouds develop towards Sunday morning. Keeping it mild with lows around the upper 20s to low 30s for the timeframe. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Highlights... * Dry and mild Sunday * Risk of some wintry mix/ice in the interior late Mon/Mon night * A period of heavy rain and strong coastal winds likely late Mon night into Tue * Blustery and seasonably cold Wed/Thu Sunday... Less wind Sunday with NW flow but continued mild with temps in the 40s across much of the region. Expect mostly sunny skies as axis of mid/high level moisture across northern New Eng. Turning colder Sun night as cold front drops south across the region with strong high pres building across Canada and ridging nosing down into New Eng. Monday into Tuesday... Developing warm advection pattern ahead of warm front will lead to some light precip developing Mon afternoon and more likely Mon night. With high pres to the N/NE and good cold air damming signature, thermal profiles should be cold enough for some light snow/mix/ice in the interior with minor accum possible. A brief mix is also possible at the onset in the coastal plain. However, the main event will likely be late Mon night and especially Tue as potent mid level trough/low lifts NE across the Gt Lakes. Ptype mostly rain but ECMWF has low level cold air lingering into Tue morning across interior MA where some wintry mix/ice may continue before precip quickly changes to rain. Models indicate a strong pre-frontal low level jet which will advect high PWAT airmass northward into New Eng. PWAT and low level wind anomalies around +2SD which suggest potential for heavy rainfall and gusty winds. As previous forecaster noted, some convection also possible given steep mid level lapse rates. However, system is progressive which should limit excessive rainfall potential. Still, deterministic GFS/ECMWF/GGEM all indicate potential for 1"+ QPF and EPS has moderate probs of 1 inch rainfall. Temps may reach into the 50s in the coastal plain with 40s elsewhere. Wednesday and Thursday... Blustery and colder weather expected but dry conditions with NW flow. GEFS and EPS mean 850 mb temps around -8C Wed and -10C Thu so near seasonable temps expected, perhaps a bit below normal Thu. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Rest of today...High confidence. VFR. Low-end BKN-OVC CIGs will linger across the Berkshires most of the day, over N/NE MA towards the Cape this morning into midday. Light W winds overall, S through the CT River Valley. Tonight and Saturday...High confidence. VFR. Low-end VFR CIGs lingering mainly N of the MA-pike. Of greater concern is the increasing W winds. Strongest along the S-coast and over the Cape / Islands. Potential 40 kt gusts over ACK around 12-15z Saturday. Roughly 30-40 kts S/SE-coast, 20-30 kts elsewhere. Threat of LLWS roughly 9-15z with a 45-55 kt SW jet at and just above 2 kft agl. Saturday night...Moderate confidence. W winds diminishing, however low clouds potentially building across the region. Will keep low- end VFR with this forecast but there is the potential of IFR CIGs. KBOS Terminal...Low-end VFR CIGs around 4 kft agl through evening. Increasing W winds overnight into Saturday, gusts up to 30 kts possible. KBDL Terminal...Within a valley location, holding forecast increasing W winds into Saturday at or below 25 kts. Outlook /Sunday through Tuesday/... Sunday: VFR. Breezy. Sunday Night: VFR. Monday: Mainly VFR, with local IFR possible. Chance RA, chance SN. Monday Night: Mainly MVFR, with areas IFR possible. Breezy. RA likely, FZRA likely, chance SN. Tuesday: Mainly MVFR, with local IFR possible. Windy with gusts to 30 kt. RA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...High confidence. Increasing W winds overnight to gale force. Will potentially push seas to 10 feet as gusts up to 40 kts, sustained up to 30 kts, are forecast. Will be upgrading present headlines with GALE WARNINGS for the overnight into Saturday time frame. Outlook /Saturday Night through Tuesday/... Sunday through Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain likely. Tuesday: Strong winds with gusts up to 30 kt. Rough seas up to 12 ft. Rain. && .HYDROLOGY... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. 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...None. MA...None. RI...None. MARINE...Gale Watch from Saturday morning through Saturday afternoon for ANZ232>235-237-250. Small Craft Advisory from 1 AM to 8 AM EST Saturday for ANZ232>234. Small Craft Advisory from 7 AM to 4 PM EST Saturday for ANZ230. Small Craft Advisory from 1 AM to 5 PM EST Saturday for ANZ231. Small Craft Advisory from 2 AM to 4 PM EST Saturday for ANZ236. Small Craft Advisory from 10 PM this evening to 8 AM EST Saturday for ANZ235-237. Small Craft Advisory from midnight tonight to 8 AM EST Saturday for ANZ250. Small Craft Advisory from 2 AM to 7 PM EST Saturday for ANZ251. Gale Watch from late tonight through Saturday evening for ANZ254. Small Craft Advisory until 5 AM EST Saturday for ANZ254. Gale Watch from late tonight through Saturday evening for ANZ255-256. Small Craft Advisory until 3 AM EST Saturday for ANZ255-256. && $$ SYNOPSIS...KJC/Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...KJC AVIATION...KJC/Sipprell MARINE...KJC/Sipprell HYDROLOGY...WFO BOX

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