Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261049 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 649 AM EDT Mon Oct 26 2020 .SYNOPSIS... Weak low pressure passing southeast of New England will bring areas of light rain and drizzle into tonight. A cold front will move across the region late tonight followed by high pressure and dry weather Tuesday and Wednesday. The remnants of Zeta may bring a soaking wind swept rain Thursday into Friday, with rain possibly ending as snow Friday across the high terrain of northern Massachusetts. Behind this departing system, dry but blustery and cold weather follows later Friday/Fri night. High pressure returns next weekend with dry but chilly weather Saturday followed by milder temperatures Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM update... 1032 mb high over the Maritimes providing cool/damp NE flow into Southern New England this morning, with temps in the 40s to near 50. Short wave trough moving across the northern Great Lakes today is accompanied by a modest low and mid level southerly jet over NYS into Northern New England. This is resulting in weak warm air advection up and over the cool low level airmass across Southern New England. As this jet/forcing for ascent lifts/exits into Northern New England, rain will taper off to drizzle this afternoon. However Maritime high will maintain cool temps here thru the afternoon, with highs only in the 50s, upper 40s high terrain! Previous forecast captures these details nicely and remains on track. Thus no major changes with this forecast update. Earlier discussion below. ================================================================== Putting it rather frankly...we are looking at a fairly raw and cloudy Monday with periods of very light rain or drizzle, and we`ll add some mist or fog for the afternoon. Early this morning, a ridge/wedge of high pressure extended southward through Southern New England into the mid-Atlantic region. A weak inverted trough/ill-defined surface low is located over the southern waters. Periods of mainly light rain, rain which is barely resulting in measurable precip, is falling into the ridge in an easterly onshore flow. Following trends and the latest short-term high res models, these light rains project to continue at least through mid to late morning, gradually shifting northward as it does so with surface low passing just to our east. Noting the low clouds, fog and periods of drizzle or light showers prevalent early this AM across much of the I-95 corridor in PA/NJ into southern NY. With model soundings showing lots of low-level RH left behind across most of Southern New England this afternoon, it`s anticipated that we`ll see similar conditions settle in by the late- morning/early-afternoon hrs and continue through the rest of the day. All told, not looking at a washout with QPF values only a few hundreths. Modest warm advection does take place today, but abundant cloudiness and periods of rain and drizzle will make for a very slow rise to temperatures. Looks like today is one of those days where the high temperature occurs later tonight (ahead of a cold front, more on that below) as opposed to typical diurnal/late-afternoon. Current temps in the mid 40s to low 50s may only rise a couple degrees into the upper 40s to the mid 50s through the day today, with upper 50s across Cape Cod and the Islands. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight: Southeast flow allows for continued warm advection to occur, ahead of a cold front which crosses through Southern New England for the second half of tonight. Temperatures should continue to undergo a slow rise into the low to mid 50s through about midnight, amid continued overcast skies with intervals of drizzle and fog/mist. A cold front then approaches interior western MA overnight tonight and continues to progress eastward toward pre-dawn/early Tues AM. A return to cooler and drier conditions on NW flow should allow for some greater clearing but appears unlikely to happen any sooner than late-overnight/pre-dawn hrs of Tuesday. Lows by Tuesday AM should dip back into the 40s, though a few low 50s towards the South Coast and Cape Cod. Tuesday: Surface ridge from the Great Lakes ridges into Southern New England for Tuesday, with moderate cold advection occurring as the day progresses. 925 mb temps fall from the low teens Celsius to around +3 to +5C in that cold advection. Will be somewhat blustery early on Tuesday with northwest winds around 10-15 mph, though diminishing by afternoon. Partial sun will offset the cold advection to bring highs in the mid 40s to lower 50s. Some indication late in the day that a weak vort max in fast west- southwest flow allows for increasing clouds from west to east. A few models break out some showers as this feature mostly passes to our north. However forecast soundings show some drier mid to low-level air that probably results in more virga than anything else. Did leave slight chance PoPs for late in the day, but many areas should be dry. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights * Mainly dry & seasonably cool weather Tue night/Wed/Wed night * Remnants of Zeta may result in a wind driven soaking rain late Thu into early Fri, possibly ending as snow across the high terrain * Blustery & cold late Fri into early Sat, then milder Sunday Precipitation... Northern stream energy drives frontal boundary farther south of New England with high pressure advecting into the region Tue night/Wed/Wed night. This will promote mainly dry weather Tue and is evident as PWATs lower to about a 0.5 inches. Then our attention shifts to Tropical Storm Zeta as it emerges out of the Gulf of Mexico Wed. Closed low over west TX will eject Zeta northeast. Confluent flow across New England will steer remnant Zeta to track along or near 40N. Expecting two rounds of precip late this week with first round associated with remnants of Zeta late Thu/Thu night. Periods of moderate to heavy rain given tropical moisture running up and over cooler low level airmass, combined with banding Fgen potential from confluent flow aloft. Then second round of potential moderate to heavy precip late Thu night into early Fri, as closed low over TN Valley ejects northeast and potentially mergers with northern stream energy as this features approach New England. This northern stream s/wv will drive colder air into northwest portion of precip shield, possibly changing rain to snow late Thu night into Fri morning across northern MA, especially over the high terrain. Will have to watch closely the evolution of this as there is a low probability of minor snow accumulation across the high terrain. Then drying trend likely follows late Fri into Sat as system appears progressive, as trailing northern stream short wave serves as a kicker, rather than close system off. Next trough/cold front may approach our area Sun/Sun night, but amplitude and moisture remain uncertain. Temperatures... 1020+ mb high pressure delivers temperatures at or slightly cooler than normal with highs in the low to mid 50s Wed, then lows in the 30s Tue night and 40s Wed night. Seasonably cool Thu with highs in the 50s but will feel cooler given rain overspreading the region along with increasing ENE winds, as low pres/remnants of Zeta track south of New England. Very chilly Friday with highs only in the 40s, upper 30s high terrain, becoming blustery and even colder Fri night as intensifying coastal low exits and 1030+ mb high over Great Lakes advects toward New England. Cold air advection on gusty north winds will yield lows in the 20s Fri night and wind chills possibly in the teens! NNE winds may gusts up to 45 mph late Fri/Fri night. Given trees remain fully to partially leaved across Cape Cod and the Islands, potential for some wind impacts here. Chilly but dry weather Sat with highs only in the 40s to near 50s, but milder Sunday ahead of next short wave/cold front, with highs rebounding into the 50s to near 60. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 11z TAF Update: no major changes from previous TAFs. Earlier discussion below. ============================================================= Today: Moderate confidence. MVFR through most of the morning, with periods of light rain interspersed with drizzle. Light rain comes to an end around late-AM/early-PM, but ceilings deteriorate toward IFR/LIFR with into the afternoon mist/fog, drizzle and stratus. Generally higher confidence in these trends, but exact timing when categories deteriorate below MVFR levels is less clear. East winds 6-12 kt (around 15 kt at ACK, gusts lower-20s kt), then lighten and become southeast around 4-8 kt. Tonight: Moderate confidence. IFR/LIFR with continued drizzle, mist/fog and low stratus for the first part of the evening. A cold front arrives late tonight that should bring about improvement towards VFR- MVFR levels. This improvement may start in the far west around 05-07z and towards early Tue AM towards the eastern coast. Light south winds shift to northwest and increase to around 7-12 kt, occasional gusts around 20 kt near eastern MA and Cape Cod toward early Tue AM. Tuesday: High confidence. Improvement toward SCT-BKN VFR ceilings. Ceilings may lower towards VFR-MVFR levels late for western TAFs as a weak disturbance aloft approaches but should be predominantly VFR. Very light showers possible underneath this deck late in the day but may be more virga. KBOS Terminal...Moderate confidence in TAF. MVFR cigs develop into the AM push, possibly as soon as 09z. IFR cigs develop in the aftn. KBDL Terminal...Moderate confidence in TAF. MVFR cigs develop around ~07-09z. IFR cigs develop in the aftn. Outlook /Tuesday Night through Friday/... Tuesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Wednesday: Mainly VFR, with areas MVFR possible. Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. Thursday: Mainly MVFR, with areas VFR possible. RA. Thursday Night: Mainly MVFR, with areas IFR possible. Strong winds with local gusts up to 40 kt. RA. Friday: Mainly MVFR, with local IFR possible. Strong winds with gusts up to 40 kt. Chance RA, SN likely. && .MARINE... SCAs continue on most southern waters through today, though will continue into early tonight on the southern outer waters. On the eastern waters, long-period seas have been running around 4 ft and opted to drop the SCA for these waters. A weak surface low will bring light rains with periods of fog and some enhancement to east winds early today. East winds may bring about a period of gusts to SCA levels on the southern waters through the morning, with seas in the 4-6 ft range on the outer waters. Winds to decrease a bit and shift to SE by afternoon, with gusts to around 15 kt. Seas will still be in the SCA range until early tonight. Periods of mist, drizzle and fog (visbys 1 to 3 SM) this afternoon into a good part of tonight. Late-overnight tonight into early Tuesday, a cold front will cross the waters allowing for a period of NW wind gusts. It`s possible that gusts may briefly approach SCA levels on the eastern waters but speeds decrease around mid to late AM. Seas mainly in the 3-4 ft range for Tuesday. Outlook /Tuesday Night through Friday/... Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Wednesday: Winds less than 25 kt. Slight chance of rain showers. 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. Rain. Thursday Night: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 10 ft. Rain. Friday: gale force winds with gusts up to 45 kt. Rough seas up to 11 ft. Rain likely. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ254>256. Small Craft Advisory until 5 PM EDT this afternoon for ANZ235- 237. && $$ SYNOPSIS...Nocera/Loconto NEAR TERM...Nocera/Loconto SHORT TERM...Loconto LONG TERM...Nocera AVIATION...Nocera/Loconto MARINE...Nocera/Loconto

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