691 FXUS61 KBOX 072150 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 450 PM EST Sun Feb 7 2021 .SYNOPSIS... A quick hitting winter storm will bring accumulating snow to much of Southern New England today with the highest amounts across Rhode Island and Southeast Massachusetts. The snow will start as a brief period of rain across eastern New England before changing to all snow during the afternoon. Drier weather returns on Monday. Additional snow and rain storms are possible on Tuesday...Thursday/Friday....and Sunday. && .NEAR TERM /UNTIL MIDNIGHT TONIGHT/... 415 PM Update... * 1-2 inches per hour snowfall rates through early this evening across Eastern MA and RI before winding down. * Winds pick up this evening along the coast as the low pressure deepens, with the risk for power outages due to combination of heavy, wet snow. What a snow event this has been for S New England! A quasi- stationary mesoscale band set up from NE CT to metrowest Boston, producing 2-3 inches, with localized 4 inches per hour snowfall rate. The primary surface low has undergone rapid cyclogenesis, deepened to 994 mb and is tracking near the 70W/40N benchmark. Also noticed that a secondary, more expansive band has set up near the south coast, and is forecast to track along the Cape and Islands. This is in response to an impressive 700-925mb frontogenetic band that has set up just off the south coast. The heaviest snow tends to occur just north and west of the best forcing. When it's all said and done, we will have had widespread 6-10 inches along a swath from NE CT to Metrowest Boston, with 2-5 inches total for the Cape and Islands due to the more marginal temperatures yielding more heavy, wet snow and melting effect. Also expect winds to pick up along the coast as the surface low continues to deepen and lift into the Gulf of Maine this evening, with 30-40 mph gusts possible. Nantucket would be on the fringe of a 60-70 kt 925mb low level jet so may see gusts 45 mph at times. Concern will be possible power outages with strong winds and heavy wet snow across SE MA. Headlines wise, have opted to keep the existing winter weather headlines and the Wind Advisory for Nantucket given the ongoing weather event. && .SHORT TERM /MIDNIGHT THROUGH 6 PM MONDAY/... Cold front blasts through the region tonight, yielding 925mb temperatures between -12 to -14C by around daybreak. A 30 to 40 kt 925mb jet moves across the area overnight so it will be gusty with west winds 20 to 30 mph at times. Lows generally in the teens to near 20. A well-mixed atmosphere should preclude single digit lows. Dry but cold weather is on tap for Monday. A 496 Dm upper low continues to sit over Northern Quebec, sending with upper jet flow around the low and across the northern tier of CONUS. We do not quite get a direct hit by the arctic blast currently experienced across the Midwest. The result is smaller shortwaves moving through this during this work week. See the long-term discussion for details about potential systems to watch this week. Expect Monday to feature filtered sunshine as a -32 to -34C cold pool moves over S New England, steepening mid-level lapse rates to 6-7C/km. 700-850mb RH falls to less than 30 percent for the first half of Monday before increasing for the afternoon hours out ahead of the Tuesday system. Highs will be around 5 to 10 degrees below average, generally in the mid 20s to low 30s. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... Big Picture... Low pressure sits over Central Canada through much of the week, then ejects east across Canada next weekend. Upper jets and associated shortwaves will move around the low and across the northern tier of the USA. One weak shortwave looks good to cross New England on Tuesday/Tuesday evening. Timing on later shortwaves is less confident, but roughly Thursday/Friday and again on next Sunday. Mass and thermal fields of the long-range models are similar through midweek, but by Thursday the GFS shifts colder as it moves the core of the Canada low south to the USA border. The model maintains this separation through the remainder of the week, thus a trend to a colder forecast from the GFS. Forecast confidence is moderate-high Tuesday, but trends to low by the weekend. Details... Monday night-Tuesday-Wednesday... As the shortwave approaches, expect increasing clouds Monday night. Weak lift ahead of the weather system may generate an area of snow that moves into Western/Central MA and Nrn CT late Monday night. Departing high pressure will maintain enough subsidence for dry weather in Eastern MA/RI. Temperatures will dip into the teens and low 20s, but the increasing clouds will bring temps up about 5F late at night. Even so, temps will be well below freezing as the precipitation moves in. Surface low with the upper shortwave will redevelop off Long Island Tuesday, then move east of Nantucket by 7 PM. South to southeast winds will turn from west and Northwest at that time and start to dry the airmass. Temperatures maintain below freezing during the morning, but trend warmer by midday. The 1000-850 mb thickness climbs above 1300m along the immediate South Coast and Islands. This suggests mainly snow north of that line, and snow mixing/changing to rain along the South Coast/Islands. Snowfall amounts of approximately 2-4 inches would be possible away from the coast with this track. Low level temps Tuesday support 30s along the south coast and mid 20s to around 30 inland. Northwest wind and colder lower layer temps support Tuesday night min temps roughly 15-25F. High pressure approaching from the Northern Plains will maintain northwest wind and drying air Tuesday night and Wednesday. Northwest gusts may reach 20 kt/25 mph. Mixing is forecast to reach at least 925-mb. Mixing to 925-mb or 900-mb suggests max temps in the 20s, but local effects may allow coastal areas to reach the low 30s. Thursday-Friday... High pressure builds in Eastern Canada Thursday as the next shortwave approaches through the Ohio Valley. This shortwave and the associated upper jet will favor a redevelopment along the coast Thursday afternoon. The pressure gradient between high pressure north and low pressure south will bring northeast winds to Srn New England, further moistening the lower levels. This alignment suggests another period of precipitation for our area Thursday afternoon through Friday. The GFS is faster, the ECMWF slower and farther north. But all project a path along or south of 40N/70W. This path that would favor mainly snow for our area with potential for several inches accumulation, but leave potential for a mix or change to rain along the south coast/Islands. The upper shortwave moves east of our area late Friday, by which point surface winds should turn from northwest and diminish the precip by Friday night. Saturday-Sunday... High pressure and subsidence brings dry weather Saturday. One more shortwave moves through the upper flow, approaching Saturday night and passing through here on Sunday. The path is far enough south of us to suggest mainly snow. As noted above, confidence is low...will forecast low-end chance pops for now and monitor. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent 2145z Update... Through 00z...High Confidence on trends, moderate on timing. Widespread LIFR conditions have developed across the region with all terminals. Expect 1/4 to 1/2 mi vsby to persist through around 00z as the last of the heavy mesoscale snow band lifts out of Eastern MA. Terminals out west including BAF and BDL are already seeing improvement to IFR as snowfall rate lightens. NNE winds 10 to 15 kt turning N by around 23z. These winds will gust between 25 and 35 knots across the Cape/Islands and up to 40 knots across Nantucket. Tonight...High confidence on trends, moderate on timing. The bulk of the snow will exit eastern New England by 01z or 02z. MVFR-IFR ceilings will linger a bit longer, but most locations should improve to VFR from west to east by or shortly after midnight. N wind gusts of 25 to 35 knots across the Cape and Islands will shift to the NW and diminish a bit, but still remain gusty overnight, Monday...High confidence. VFR with NW winds 10 to 15 kt. KBOS TAF...High confidence on trends, moderate on timing. KBDL TAF...High confidence on trends, moderate on timing. Outlook /Monday Night through Friday/... Monday Night: VFR. Slight chance SN. Tuesday: Mainly IFR, with local MVFR possible. Breezy. Chance SN. Tuesday Night: Mainly VFR, with areas IFR possible. Breezy. Slight chance SN. Wednesday through Wednesday Night: VFR. Breezy. Thursday: Mainly MVFR, with local IFR possible. Slight chance SN. Thursday Night: Mainly IFR, with areas MVFR possible. Breezy. Chance SN. Friday: IFR. Breezy. Chance SN. && .MARINE... * Gale Warnings continue for all outer waters this evening. * Freezing Spray Advisory hoisted for all outer waters for Monday. Today and Tonight...High confidence. Low pressure tracking just southeast of the Benchmark will result in winds shifting from the E to more northerly early this evening. Despite lack of high pressure to our north, enough of a pressure gradient should result in a period of N wind gusts of 30 to 40 knots. Gale headlines continue for all open waters into this evening. Seas will be quite rough on all waters. Late tonight, strong cold advection behind the departing system will result in NW wind gusts of 25 to 35 knots. We will likely need to extend marginal gale headlines or go with strong small craft headlines. Given it is marginal will defer this to the next shift. Have also hoisted Freezing Spray Advisories for Monday for all outer waters due to strong cold air advection, winds and rough seas. Outlook /Monday Night through Friday/... Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain, chance of snow. Local visibility 1 nm or less. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain. Visibility 1 to 3 nm. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow. Local visibility 1 to 3 nm. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of snow. Visibility 1 nm or less. Friday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain, chance of snow. Visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory until 1 AM EST Monday for CTZ002>004. MA...Winter Weather Advisory until 1 AM EST Monday for MAZ002>012- 014-024-026. Winter Storm Warning until 1 AM EST Monday for MAZ013-015>023. Wind Advisory until 10 PM EST this evening for MAZ024. RI...Winter Weather Advisory until 1 AM EST Monday for RIZ008. Winter Storm Warning until 1 AM EST Monday for RIZ001>007. MARINE...Freezing Spray Advisory from midnight tonight to 7 PM EST Monday for ANZ231-232-250-251-254. Gale Warning until 3 AM EST Monday for ANZ231>235-237-250-251- 254>256. Freezing Spray Advisory from midnight tonight to 1 PM EST Monday for ANZ233>235-237-255-256. Small Craft Advisory until 3 AM EST Monday for ANZ230-236. && $$ SYNOPSIS...WTB/Chai NEAR TERM...Chai SHORT TERM...Chai LONG TERM...WTB AVIATION...WTB/Chai MARINE...WTB/Chai