Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 170608 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 108 AM EST Sun Nov 17 2019 .SYNOPSIS... High pressure will shift east across northern New England tonight, keeping dry conditions and cold air across the region. As the high pushes away Sunday, temperatures will gradually moderate but remain below normal. A coastal storm will then bring rain and strong coastal winds late Sunday night into Monday, with some light icing in the interior at the onset. The storm moves to the Maritimes Tuesday with high pressure building south of New England Wednesday and Thursday. A cold front may bring a round of showers sometime Thursday night into Friday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1 AM update... Strato-cu developing across SE coastal MA as coastal front sets up with NE flow bringing shallow low level moisture. Expect clouds to expand across SE MA early this morning and possibly into RI toward daybreak. Temps not quite as cold as previously forecast as northerly winds just strong enough to disrupt ideal radiational cooling. Raised mins a bit with lows mostly in the teens interior and 20s RI and eastern MA but holding in the 30s Cape/Islands east of the coastal front. Previous discussion... Clear skies across much of SNE this evening but some lower clouds have developed on the upper Cape and there are clouds just offshore and flirting with ACK. Cross sections show increasing low level moisture across eastern New Eng where skies will likely become mostly cloudy late tonight and toward daybreak. But remaining mostly clear further into the interior. Clear skies, light wind and dry airmass with strong high pres to the north will result in excellent radiational cooling conditions away from the coast. Lows here will bottom out in the single numbers and teens, coldest across western MA. Along the coast, a NE wind will keep temps mostly in the 20s with low to mid 30s outer Cape/Islands where gusts to 20-30 mph expected overnight as a coastal front develops. In fact temps will likely rise into the 30s across east coastal MA as NE winds increase. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Sunday... Will see E-NE winds continue to increase through the day as the northern periphery of the moisture from the SE low pres works toward the region. Clouds will continue to increase and lower, especially during the afternoon. Some question how quickly the moisture will work up the coast, which will be dependent upon how quickly the high across NH and Maine lifts to the Maritimes. At this point, should remain dry across the majority of the region through the day, but will start to see the leading edge of the light rain reach the S coast around or after 21Z. Temps will recover especially along the coast with the persistent onshore winds. Readings will top off in the lower-mid 40s along the shore, ranging to the mid-upper 30s well inland, coldest across the higher inland terrain. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... Coastal Low and Potential Impacts Sun night into Mon: * Light icing/light freezing rain likely at the onset across parts of the interior late Sun night/Mon am before ptype changes to rain * Periods of rain late Sun night and Mon which may be heavy at times especially across eastern MA/RI * Northeast wind gusts of 35 to 45 mph with a few gusts up to 50 mph possible across the immediate coast late Sun night/Mon * Minor Coastal Flooding possible along the eastern MA coast on Mon Tuesday Through Saturday... * Dry and seasonable weather follows Tue/Wed and into Thu * A round of showers possible sometime Thu night into Fri Details... Sunday night into Monday... The main concern continues to revolve around a coastal low pressure system Sun night into Mon, which will pass east of Nantucket. The high resolution models tend to be faster and further northwest when compared to the EC/GFS. We think there will be somewhat of a compromise in the models, so blended the timing for now. Thinking that much of Sun evening may end up dry other than some light drizzle along the coast. However, should see precipitation overspread the region from southeast to northwest after midnight. 1) Interior Light Icing Potential: Ptype should mainly be rain in most locations. However, given the low pressure system tracking offshore and lingering high pressure over eastern Canada some light icing/freezing rain is likely across portions of the interior at the onset. We are most confident in this occurring across the high terrain of the Worcester Hills and east slopes of the Berks. Up to one tenth of an inch of ice accretion is possible and untreated roads will be icy for the morning commute. There also is a possibility for a brief period of light freezing rain across the lower elevations of interior northeast MA and into parts of CT, but it also could end up a few degrees too warm. Regardless, Ptype should change to rain Mon morning in all locations. 2) Strong Wind Potential Along The Coast: Offshore low pressure tracking east of Nantucket will be associated with a modest northeast LLJ of 45 to 55 knots across eastern MA and RI. This should result in northeast wind gusts of 35 to 45 mph with a few gusts near 50 mph along the coast. The strongest of these winds will be late Sun night into Mon especially across the Cape/Islands. Since we do not have a rapidly bombing low pressure system or anomalously high surface pressures in eastern Canada, think this will mainly be a wind advisory event along portions of the eastern MA coast. Fortunately, given most leaves are off the trees these wind speeds should not cause too many issues other than a few downed tree limbs etc. 3) Rainfall: Given we have a well developed coastal low pressure system tracking east Nantucket, periods of rain will impact the region late Sun night into Mon. The guidance continues to differ with rainfall amounts given uncertainty how close the system tracks to the coast. With a closed 700 mb low expecting a general 0.50 to 1.50 inches of rainfall with the higher amounts across eastern MA and RI. We may see some 2 inch amounts across eastern MA and RI, depending on the exact track. Regardless, rainfall amounts are not expected to be high enough to result in any fresh water flooding issues. 4) Minor Coastal Flooding Potential: Fairly decent E/NE fetch combined with several hours of strong winds should bring a storm surge of 1.5 to 2.0 feet with Monday afternoon high tide in eastern MA, which is a little higher than storm surge guidance from ESTOFS/ETSS. Astronomical high tide is (10.3 ft at Boston and 3.7 ft at Nantucket Harbor) so this would bring the potential for pockets of minor coastal flooding to much of the eastern MA coast including Nantucket and Martha`s Vineyard. Seas offshore of 14-18 ft are not expected to significantly add to the impact along coast but may bring minor beach erosion. So in a nutshell, while some pockets of minor coastal flooding seem reasonable do not think winds/storm surge will be enough to result in a significant coastal flood event. Monday night and Tuesday... The system departs Monday night into early Tuesday morning. It is possible there is a touch of wintry precipitation on the backside of the system across the high terrain of western MA. Any amounts though should be light. Otherwise, dry weather expected for most of Tue with highs recovering into the 40s to the lower 50s. Wednesday through Saturday... Another low pressure system and associated cold front may bring a period of showers sometime Thu night into Fri. Otherwise, dry weather expected with seasonable temps dominating. The exception might be Fri as we may have a period of mild temps in the warm sector ahead of the next cold front. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...Moderate confidence. Through 12z... Mainly VFR, but some MVFR cigs develop across SE MA. NE gusts increase to 25 kt across ACK. Today... Low end VFR to MVFR cigs expected to expand west across SNE reaching the CT valley this afternoon. NE gusts 20-25 kt over the Cape and increasing to 30 kt over ACK. Tonight... Widespread MVFR with areas of IFR. Patchy drizzle or interior freezing drizzle possible in the evening, then steadier rain overspreading eastern New Eng overnight with pockets of light freezing rain in the interior. NE gusts 20-30 kt along the coast and 35 kt over the Islands. Monday... MVFR/IFR in rain and fog. Pockets of freezing rain possible in the morning in the interior. NE gusts 20-30 kt in the coastal plain and 30-40 kt Cape/Islands. KBOS TAF...Moderate confidence in TAF. Expect MVFR cigs developing today. KBDL TAF...Moderate confidence in TAF. Expect MVFR cigs developing this afternoon. Outlook /Monday Night through Thursday/... Monday Night: Mainly MVFR, with areas IFR possible. Windy with gusts up to 35 kt. Chance SHRA. Tuesday: Mainly VFR, with local MVFR possible. Tuesday Night: VFR. Wednesday through Wednesday Night: VFR. Breezy. Thursday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA, slight chance FZRA. && .MARINE... Through Tonight... Expect NE winds to briefly diminish to 15-20 kt this evening, then will become E-NE 20-30 kt, highest on the southern outer waters mainly after midnight. Gusts will increase to around 35 kt on the southern outer waters, where Gale Warnings remain in place. Seas will build to 5-8 ft on the outer waters. Good visibility. Sunday... Expect E-NE winds will increase to gale force across the waters E and S of Cape Cod as well as the southern near shore waters from midday through the afternoon. Gale Warnings are in effect there. On the eastern waters, winds will gust up to 25-30 kt. Seas will build up to 6-10 ft, highest on the southern outer waters. Good visibility continues, but will see light rain reach the southern waters toward nightfall. Outlook /Monday Night through Thursday/... Sunday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 18 ft. Rain. Local visibility 1 to 3 nm. Monday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 17 ft. Rain, patchy fog. Visibility 1 to 3 nm. Monday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 13 ft. Chance of rain showers. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Wednesday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning from 4 PM this afternoon to 7 PM EST Monday for ANZ231>235-237. Gale Warning from 3 AM to 5 PM EST Monday for ANZ230-236. Gale Warning from 10 PM this evening to 10 PM EST Monday for ANZ250-251. Gale Warning from 1 PM this afternoon to 10 PM EST Monday for ANZ254. Gale Warning until 7 PM EST Monday for ANZ255-256. && $$ SYNOPSIS...Frank/EVT NEAR TERM...KJC SHORT TERM...EVT LONG TERM...Frank AVIATION...KJC/Frank MARINE...Frank/EVT

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