Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250013 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 713 PM EST Fri Jan 24 2020 .SYNOPSIS... High pressure over the Maritimes brings dry weather to New England tonight and Saturday morning. Low pressure over the Midwest redevelops over the Mid Atlantic states. This will bring a period of heavy rain and gusty coastal winds late Saturday and Saturday night as it tracks across interior southern New England. It may be preceded by some light freezing drizzle over the Berkshires. Mainly dry and mild conditions return Sunday then dry and seasonable for much of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 7 PM Update... Increased sky cover as ocean stratus has advected in due to the northeasterly flow within the lower levels. In addition, there may be some fog development across the higher elevations of the interior late tonight along with patchy drizzle/freezing drizzle due to the increasing easterly flow. Rest of the forecast remains on track. Previous discussion... High pressure centered over the Maritimes brings a northeast surface flow over Southern New England. Satellite imagery shows low clouds over the Gulf of Maine just south of the Maine coast. These clouds are moving west and have run into the coast near Portsmouth NH. Increasing east flow will encourage cloud growth south over Southern New England. Upslope areas could see some patchy drizzle or freezing drizzle, but most areas will remain dry. Temperatures will fall to near dew point, so expect min temp range in the mid 20s west to mid 30s southeast. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Closed upper low over the Great Lakes with a 100-kt southern jet feeding in. This will generate a secondary low during the night that moves up over our area late Saturday and Saturday night. Low level wind forecasts show a 50-60 kt low level jet moving up over New York City early afternoon and along the South Coast of New England late afternoon and early night. The combination of these two jets will generate strong lift over Southern New England during the late afternoon and early night. This will generate rain from mid afternoon through around midnight. PW values of 0.75 to 1.0 inches suggest some heavy showers. The PW values are above normal for January, but the system is moving fast enough to limit any flooding threat to urban/poor drainage concerns. The rain tapers off a little before midnight in the west and a little after midnight in the east. That low level jet moves over the region early Saturday night. The low level inversion will limit the amount of wind to reach the surface, but gusts of 25-35 kt should be possible especially along the South Coast and Islands. Winds will diminish after midnight as the system moves past. A 1 to 2 ft surge is expected along the south coast around the high tide Sat evening as the low level jet is moving through. Astronomical tides are rather low and no coastal flooding is expected. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Temperatures slowly trending downward through the extended. * Dry and quiet through the extended. The only exception is across the eastern slopes of the Berkshires Sunday into late on Monday where light scattered rain and snow showers are possible. Details... Sunday AM through Tuesday AM... Initially a cutoff low will be situated over the eastern Great Lakes. The cutoff will gradually rotate northeastward into northern New England by Sunday evening. Expect -5 to -8 degree Celsius westerly cold air to advect in. Will see a mixture of sunshine and clouds across the region on Sunday. There are chances of light rain and snow showers across the eastern slopes of the Berkshires. Little to no snowfall accumulation is anticipated. Temperatures will be slightly warmer when compared to Saturday. Readings range from the mid 30s across the Berkshires to the mid to upper 40s along the coast. The cutoff low will rotate across northern New England on Monday. A shortwave will rotate from the eastern Great Lakes late on Sunday through southern New England on Monday. Winds will shift to the northwest and continue advecting cold air into the region. Increased cloud cover a bit compared to the previous forecast. There will be chances of snow showers across the eastern slopes of the Berkshires. Suspect that these chances could linger further east as suggested by several GEFS members, especially during the day time. The combination of the shortwave sliding through, cold air advection and diurnal heating could bring scattered shower activity. Confidence is low to moderate at this point in time, so have kept things dry at this point in time. Temperatures on Monday range from the low 30s across the Berkshires to the low to mid 40s along the coast. Tuesday through Friday... Confidence in the forecast significantly lowers Tuesday until the end of the long term. Model guidance is all over the place with several shortwaves sliding through with large differences between individual models and run to run differences. At this point in time it appears that we will remain dry, but under cyclonic flow aloft. Temperatures should continue trending downward as colder air advects in. Next shot for precipitation is late in the week and heading into the weekend. High temperatures cool to the 30s by the end of the extended. Low temperatures cool to the teens and 20s above zero. && .AVIATION /00Z SATURDAY 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/... Tonight...Moderate confidence. MVFR ceilings continue to spread in from the ocean and NH due to increasing easterly flow. This primarily impact BOS, BED and ORH over the next 6 hours. Will see ceilings lower to IFR at ORH along with fog development, but am not confident on visibilities at this point in time. BOS will particularly be tricky as the HRRR and GLAMP keep the terminal on the edge of MVFR/VFR. Leaned toward VFR from roughly 06Z until 14Z based on the latest HRRR. Other terminals will see ceilings lower to MVFR closer to 12Z. Saturday and Saturday night...Moderate to high confidence. Widespread MVFR with IFR conditions. Still expect patchy fog with drizzle or higher elevation freezing drizzle in the morning. Best opportunity for IFR/LIFR is when the heavier precipitation moves in. Heaviest precipitation timeframe looks like 21Z to 06Z at this point. East winds gust 25 to 35 knots over Cape Cod and the Islands during the afternoon and into the evening. Rain tapering off close to midnight in the CT River Valley and eastern coastal MA after midnight. Precipitation becoming lighter after midnight. KBOS Terminal...Low to moderate confidence until 12Z. On the fence between MVFR/VFR conditions due to ocean stratus. Moderate confidence after 12Z with MVFR/IFR ceilings expected. KBDL Terminal...Moderate to high confidence until 12Z. Moderate confidence after 12Z. MVFR/IFR conditions spreading in. Potential for LIFR as heavier precipitation moves in late in the afternoon. Outlook /Sunday through Monday/ ... Sunday through Monday: Mainly VFR, with local MVFR possible. Breezy. Monday Night through Tuesday: VFR. Breezy. && .MARINE... Short Term /through Saturday Night/...High confidence. Northeast wind around 10 kt tonight will increase to 20-25 kt by late Saturday and early Saturday night. Wind gusts will be 30-40 kt at that time. Strongest gusts will be on the eastern MA waters. Winds then diminish after midnight as the weather system moves past. Winds at that time will shift out of the southwest. Gale Watch continues on the waters east of Massachusetts for Saturday and Saturday night. Small Craft Advisory continues on all other waters through Sunday. Outlook /Sunday through Wednesday/... Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Monday: Winds less than 25 kt. Areas of rough seas. Monday Night: Winds less than 25 kt. Seas up to 5 ft. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from noon Saturday to 7 PM EST Sunday for ANZ232. Small Craft Advisory from noon Saturday to 1 AM EST Sunday for ANZ233-234. Small Craft Advisory from 3 PM Saturday to 5 AM EST Sunday for ANZ230. Gale Watch from Saturday evening through late Saturday night for ANZ231-251. Small Craft Advisory from noon Saturday to 11 AM EST Sunday for ANZ236. Small Craft Advisory from 7 AM Saturday to 7 PM EST Sunday for ANZ235-237. Gale Watch from Saturday evening through late Saturday night for ANZ250-254. Small Craft Advisory from 4 AM Saturday to 7 PM EST Sunday for ANZ255-256. && $$ SYNOPSIS...WTB NEAR TERM...WTB/BL SHORT TERM...WTB LONG TERM...BL AVIATION...WTB/BL MARINE...WTB/BL

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