766 FXUS61 KBOX 200739 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 339 AM EDT Fri Mar 20 2020 .SYNOPSIS... A warm front will move north over Southern New England this morning, bringing showers followed by mild air this afternoon. A cold front then sweeps across the region, bringing scattered showers and isolated thunderstorms late afternoon and evening. A few strong storms are possible across western MA/CT with gusty winds and heavy rain. Behind the cold front, dry and cooler weather arrives for the weekend. A developing storm could bring rain or snow early next week. && .NEAR TERM /THROUGH TODAY/... Southern stream shortwave moves over the Great Lakes today. At the same time, a northern stream shortwave digs over the Great Lakes, turning the upper flow more southwest. This southwest flow should push a warm front northeast through Srn New England today, with milder air over the region this afternoon. The warm advection will generate lift along and ahead of the warm front, supporting showers. One area of showers moves through early morning, a second mid morning. Warm advection will bring a very moist airmass, with PW values climbing to between 1.25 and 1.5 inches. This is at least as moist as airmasses in this area get in mid to late March. Expect showers in the warm sector, possibly with heavy downpours during the afternoon and evening. Temperatures at 950 mb are forecast at 16-18C, which would support max temps in the upper 60s and lower 70s. If mixing can reach a little higher, temps in the mid 70s would be possible. VAD Wind profiles show 30-40 kt at 3000 feet AGL, and 50 kt at 5000 feet. BUFKIT soundings show these speeds getting a little lower by the afternoon, with 40 kts to 1500 feet AGL and 50 kt near 2000 feet. This suggests surface gusts reaching 25-30 kt/30-35 mph. Finally, convection will be a concern. The 00Z HiRes WRF brings 200 J/Kg air east to the Berkshires 3-4 PM with strong low level shear as just noted. This low CAPE/high shear environment will be concentrated in low levels. It will generate convection, but the column is forecast to be dry at the minus 12C to minus 18C layer after 2 PM. Lacking the ice crystals for the collision/friction process may mean no lightning. But with 40-50 kt winds at 1500-3000 feet AGL, bringing that wind down to the surface in a shower/downpour would be enough to create some damage. SPC has our Western and Central areas in a Marginal Risk zone for this afternoon/evening. Will also note that the chance of a tornado, while quite small, is non- zero. && .SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/... Tonight... Cold front moves through during the evening/early night and offshore 7-9 PM. Northern stream shortwave passes around midnight, turning the upper flow from the WNW. Drier and cooler air moves in behind the front overnight. Cross sections and BUFKIT soundings agree on northwest winds 30-40 kt in position to be mixed to the surface in gusts. Temperatures fall to the upper 20s and 30s by morning. Saturday... High pressure builds in from central Canada. The center of the high passes north of New England, so winds will blow from the north. Cross sections show dry air at all levels, supporting a sunny day. The sun and cold advection will support mixing to 850 mb, where temps of minus 6C to minus 8C will bring max sfc temps in the 40s. Winds in the mixed layer may support gusts around 20 kt in the morning, diminishing in the PM. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights... * A coastal storm could bring accumulating snowfall to southern New England late Monday into early Tuesday, but the track of the system is still uncertain. Folks will want to stay tuned to the forecast. * Dry weather for much of Tuesday, but another round of precipitation is possible on Wednesday. Details... Saturday night and Sunday... The pressure gradient really relaxes on Sunday as the high builds in, so do not expect it to be breezy. Temperatures trend downward through the weekend as the position of the ridge will keep us under northerly/northwesterly cold air advection through the weekend. Did nudge down overnight lows Saturday night into Sunday morning toward the 25th percentile of guidance as strong radiational cooling is anticipated. Did not go with the coldest guidance as winds may not completely decouple. Monday into Tuesday AM... High pressure will build over or just east of Nova Scotia on Monday. A trough will lift from the Mid Mississippi/Ohio River Valley early on Monday into the Appalachians and become negatively tilted. This develops low pressure just east of Delaware/New Jersey, which will lift northeastward and potentially bring accumulating snow to the region late on Monday into early Tuesday, but this is all dependent on the track of the surface low. Confidence in a particular solution is very low at this point in time as run to run and model to model solutions vary in the track of the system. The latest GEFS, GFS, UKMET, ECMWF and EPS guidance have been trending with the system tracking further east. Will need to continue to monitor this because significant accumulating snowfall will be possible if the latest ECMWF/GEM verify. The GFS tracks the system much further east which would bring little to no snowfall to the region. The other ingredient that we have in place ahead of the system is the strong high building to the north/northeast, which will help lock colder air into the lower levels. This system lifts northeast of the region by Tuesday morning. Due to the uncertainty have kept the NBM guidance, but capped precipitation chances at chance due to the uncertainty. Rest of Tuesday and Wednesday... High pressure builds in behind the exiting system. This will bring dry and quiet weather to the region. Temperatures rebound as high pressure builds in. Highs range from the low 40s to the low 50s across southern New England. Another trough swings in with nearly the same track as the storm late on Monday into early Tuesday. This may bring another coastal storm to the region. Still lots of uncertainty in the strength of the trough and associated surface low. The GFS and GEM depict a strong coastal storm, whereas the latest ECMWF features a fairly innocuous broad low. Have kept the NBM guidance due to the uncertainty. && .AVIATION /07Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...Moderate-High confidence. Widespread IFR and some LIFR ceilings/vsbys in the morning, improving to MVFR in the afternoon. Showers this morning as the leading edge of mild air moves in. Scattered showers this afternoon in the heart of the mild air. A thunderstorm is possible, mainly in Central and Western section. VCTS has been noted in the afternoon for Worcester, Bradley, and Westfield TAFs. Finally, strong low level winds with 40-50 kts expected from 1500 to 3000 feet AGL...so LLWS is noted for all TAFs. Strong wind gusts may occur from heavier showers that are absent lightning. Tonight... A cold front moves through Srn New England in the evening/early night. Expect drier air to move in behind the front. That will mean clearing skies, with conditions improving to VFR the first part of the night. Saturday... High pressure builds north of New England. Expect mostly clear skies and NNW winds gusting to 20 kt. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday Night through Tuesday/... Saturday Night: VFR. Sunday through Sunday Night: VFR. Breezy. Monday: Mainly MVFR, with local IFR possible. Breezy. Chance RA, chance SN. Monday Night: Mainly IFR, with areas MVFR possible. Breezy. Chance RA, chance SN. Tuesday: Mainly VFR, with local MVFR possible. Breezy. && .MARINE... Today... Warm front lifts north across the waters, with winds turning from the southwest. Strong southwest winds just off the surface will generate gusts of 25 to 30 kts at the ocean surface. This will maintain seas of 5 to 8 feet on the exposed waters. Reduced vsbys in showers and fog. A Small Craft Advisory is in place for all waters today and continuing into Saturday. Tonight... Evening showers along and ahead of a cold front. Winds then shift from the northwest, followed by clearing skies and improving vsbys. Winds will continue to gust 25 to 30 kt. Seas remain 5 to 9 feet on the exposed waters. Saturday... High pressure builds north of New England. This will bring north to northwest winds to the waters. Winds may gust to 20 kts in the morning, but will trend lighter in the afternoon. the diminishing wind will allow seas to diminish, with 5 foot values lingering on just the outer waters late in the day. Outlook /Saturday Night through Tuesday/... Saturday Night through Sunday: Winds less than 25 kt. Seas up to 5 ft. Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain. Local visibility 1 to 3 nm. Monday Night: Winds less than 25 kt. Rough seas up to 9 ft. Chance of rain. Tuesday: Winds less than 25 kt. Rough seas up to 10 ft. Slight chance of rain. && .CLIMATE... Expecting mild temperatures Friday, but not record high level. Min temps will be high Friday night, but a few degrees too cool early Friday morning. Record Highs for Today March 20 (1 AM to 1 AM) BOS 79/1945 ORH 77/1945 BDL 81/1945 PVD 83/1945 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT Saturday for ANZ231>235- 237-251. Small Craft Advisory from 2 PM this afternoon to 8 AM EDT Saturday for ANZ230-236. Small Craft Advisory until 8 PM EDT Saturday for ANZ250- 254>256. && $$ SYNOPSIS...WTB/Nocera/BL NEAR TERM...WTB/Nocera SHORT TERM...WTB/Nocera LONG TERM...BL AVIATION...WTB/Nocera/BL MARINE...WTB/Nocera/BL CLIMATE...