000 FXUS61 KBOX 140202 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1002 PM EDT Tue Apr 13 2021 .SYNOPSIS... High pressure over eastern Canada will result in dry weather and mild temperatures Wednesday, except for the immediate eastern MA coast where it will remain cool. By Thu, low pressure emerges off the NJ coast, then intensifies as it slowly tracks along the coast or into Southeast Massachusetts Fri, yielding a widespread windswept rain late Thursday into Friday. Accumulating wet snow is possible across the Berkshires of Western Massachusetts. Gradual improvement is expected over the weekend as the storm exits out to sea, with dry milder weather likely Sunday. Rain may return early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 10 PM Update... Still some pockets of mainly clear skies across eastern CT into southeast MA and RI. However, model cross sections indicate that mid level cloudiness will be increasing overnight. We can already see this occurring on the GOES-16 Nighttime Satellite Imagery. This as a result of a weak trough axis backing in from the west across our region. Forcing and deep moisture will be quite limited, so dry weather will continue overnight other than the low risk of a brief sprinkle or two across eastern MA. Otherwise, temperatures should mainly drop into the lower to middle 40s by daybreak. However, some spots across southeast New England may briefly drop into the middle to upper 30s before more clouds overspread the region. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... A warmer day on tap for Wednesday, especially for the western areas as a thermal ridge aloft builds in from the west. 925 hPa temps from 5-10 C will support surface temperatures high temperatures in the upper 50s/low 60s for the majority of southern New England with cooler temperatures along The Cape Islands (low 50s) and warmer temperatures in the CT River Valley (upper 60s). Some mid-level cloudiness to start the day will be followed by clearing and eventually a mix of sun and clouds for the afternoon. Weak surface high pressure will support light and variable winds that will eventually become a light southeasterly wind as the surface high moves offshore by late afternoon tomorrow. .Wednesday Night. As the upper-level ridge axis slides east over the Atlantic waters on Wednesday evening, a closed low at 500 hPa will be approaching the northeast from the west. This will support the development of low-pressure off the coast of VA/NC that will eventually bring substantial precipitation and likely snowfall (at higher elevations) to southern New England on Thursday. Prior to the arrival of this low-pressure system, deformation aloft will support showers for the western half of the forecast area on Wednesday night. At this point the latest guidance suggests that showers wouldn't begin until after Midnight Wednesday into Thursday and would be confined to the western counties of MA/CT (Franklin, Hampshire, Hampden,Hartford). Low temperatures on Wednesday night will be similar to Tuesday night with lows falling into the upper 30s/low 40s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Widespread moderate to heavy rainfall late Thu into Fri * Accumulating wet snow possible Western MA Thu ngt/Fri * Drying trend Saturday and moderating temps Sunday Thursday... Impressive closed low moves from MI to PA, inducing cyclogenesis near the NJ/NYC coast. Rain maybe heavy at times across Western MA/CT, in response to strong wind anomalies and high PWATs within the warm conveyor belt (WCB) along with elevated instability on the nose of the dry slot. This heavy rain overspreads the remainder of the region Thu night from west to east. Again, periods of heavy rain given impressive WCB along with elevated instability. It will be a windswept rain as low level ESE jet moves across the area. Rain likely changes over to snow across high elevations of Western MA, as cold air aloft with mid level low overspreads this area and combined with dynamical and diabatic cooling processes from heavy qpf. Snow accumulations very challenging at this time range, as snow to liquid ratios (SLR) will be on the order of 8 to 1 or so. In addition, with surface temps 33/34, likely be a big difference in snow accums from paved vs unpaved surfaces. Earlier model runs were farther southeast with track of mid level low, but 12z guidance has trended farther northwest. This has resulted in dry slot tracking farther NW across much of Southern New England. Therefore, this has reduced the threat of heavy wet snow over the Worcester Hills and confined to Western- Northwest MA for now. Most of the time this NW trend rarely reverses and sometimes continues to trend NW. Will just have to monitor later model runs, but for now decided to follow a more conservative snowfall forecast approach given the time range and this new NW trend. For now, preliminary snowfall forecast is for 3-6 inches across the higher terrain of W/NW MA. Definitely a heavy wet snow but with fully leaved trees not an issue yet in mid April, power outages not as great of a concern vs mid May. Friday... Low becomes occluded/vertically stacked somewhere over Southeast MA, with WCB rains lifting north and exiting MA into NH/VT, with rain intensity likely diminishing as the day progresses. A chilly/raw/damp day with snow possible across the high terrain of W/NW MA. Gusty NE winds likely confined to NE MA/Cape Ann area. Chilly with highs only in the 40s. Lighter comma-head rain (snow high terrain) likely Fri night as occluded low slowly moves east of MA. Chilly/raw night with lows in the mid to upper 30s. The Weekend... Dry trend Sat but rather chilly with 850 mb temps around -3C, only supporting highs in the upper 40s and lower 50s, with morning clouds giving way to partial afternoon sunshine Sat. Dry and milder Sunday with highs in the 50s, possibly pushing 60 in the CT river valley. Early Next Week... Milder given SW flow aloft but could be unsettled with precip at times depending on amplitude and track of individual short waves embedded in the broad SW flow aloft. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 23z Update...high confidence. No change from previous TAFs, with VFR conditions along with dry weather. Light to modest NNE winds along the coast, light and variable inland. Earlier discussion below. ================================================================= Tonight/Wed/Wed night...moderate Confidence Generally VFR conditions with BKN/OVC mid-level clouds above 3000 feet through tomorrow afternoon. MVFR conditions at Cape/Islands terminals improving to VFR between 21-00Z as ceilings lift to around 3500 feet. This will lead to pre- dominantly VFR conditions overnight with perhaps some embedded MVFR over The Cape/Islands terminals. Gusty north/northeasterly winds along coastal areas will transition to light/variable overnight as well. KBOS TAF...Moderate Confidence in TAF. KBDL TAF...High Confidence in TAF. Outlook /Thursday through Sunday/... Thursday: Mainly VFR, with areas MVFR possible. Breezy. Chance RA. Thursday Night: Mainly IFR, with areas MVFR possible. Windy with local gusts up to 30 kt. RA. Friday: Mainly MVFR, with areas IFR possible. Windy with gusts up to 30 kt. RA likely. Friday Night: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Chance RA. Saturday: Mainly VFR, with local IFR possible. Breezy. Saturday Night: VFR. Breezy. Sunday: Mainly VFR, with local MVFR possible. && .MARINE... Weak high pressure builds over the Atlantic waters tonight and tomorrow resulting in a gradual weakening of the northeasterly winds over the coastal waters. 4-5 foot seas will linger across the outer waters through Wednesday night.Winds eventually pick up out of east early Thursday as low-pressure system approaches southern New England. Outlook /Thursday through Sunday/... Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain. Thursday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Rough seas up to 10 ft. Rain. Areas of visibility 1 to 3 nm. Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 15 ft. Chance of rain. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 14 ft. Chance of rain. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 14 ft. Saturday Night: Winds less than 25 kt. Areas of rough seas. Sunday: Winds less than 25 kt. Local rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 11 PM EDT Wednesday for ANZ250-254- 255. Small Craft Advisory until 8 AM EDT Wednesday for ANZ256. && $$ SYNOPSIS...Nocera/RM NEAR TERM...Frank SHORT TERM...RM LONG TERM...Nocera AVIATION...Nocera/RM MARINE...Nocera/RM