Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 050211 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1011 PM EDT Wed Oct 4 2023 .SYNOPSIS... Other than overnight and morning fog, high pressure continues to provide dry and very pleasant weather through Thursday. A strong frontal system then slowly moves into Southern New England Friday night into Saturday. While rain amounts are still uncertain, there is growing confidence on widespread showers for late Friday into Saturday evening. Rain could be heavy at times, as tropical moisture from Philippe tracks northward. Rain comes to an end early Saturday night, ushering in blustery conditions and a cooler air mass to Southern New England for Sunday into early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Update: 10pm Forecast does remain on track this evening, but the challenge will be how widespread and dense it becomes. Already seeing areas of dense fog from Newport to New Bedford along with the Islands; which have vis less than 0.25 mile. Will issue and SPS to bring more awareness to the fog development overnight. If it continues, Dense Fog Advisory will become likely, just in time for the Thursday morning ride into work/school. Previous Discussion... * Another mild night with fog more widespread tonight This evening & overnight... Gorgeous late afternoon/early evening in progress, courtesy of a high amplitude ridge (590 dam) remains across SNE, providing dry, mild and very pleasant conditions into this evening. Dew pts in the 60s combined with light onshore flow will promote areas of fog to develop after sunset (621 pm Boston, 628 pm Hartford). Given the light onshore flow and stronger/lower subsidence inversion, the fog overnight is likely to be more widespread (and locally dense at times) than last night. Higher dew pts will also result in a mild night, with lows only 55-60.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... 330 PM update... * Morning fog eventually burns off to afternoon sunshine * Warm and humid for October, highs 75-80 & dew pts in the 60s Thursday... Expecting morning fog to be more widespread (and locally dense) than previous mornings, therefore it may take until late morning to burn off and perhaps midday-ish for coastal areas. Column is fairly dry with PWATs below 1 inch, so as blyr warms some of this dry air aloft should mix down and help erode fog. Thus, partly to mostly sunny conditions should develop. Still a warm airmass over the region, however with SE winds more established blyr not as warm as previous days, with 925 mb temps down from 20/21C Wed to 17/18C Thu. This will support highs in the mid to upper 70s away from the coastline. Still about 10 degs warmer than normal. Looks to be another beautiful late morning and afternoon, with sunshine, light SE winds and a warm away from the coast. Even at the shoreline, despite the light onshore winds, it will feel mild with dew pts in the 60s. Thursday night... As ridge axis moves farther offshore, low level moisture begins to stream northward toward SNE. This is evident on both NAM and GFS bufkit time sections. This should translate to widespread low clouds and fog overnight. All the guidance has some very light qpf. Given the moisture is very shallow, most likely looking at areas of drizzle/mist. Another mild night given relatively high dew pts. Lows mainly 55-60. SE winds persist. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Highlights: * Increasing clouds Fri, with mainly light rain showers for interior MA/CT. Heavier rain arrives overnight. * Steady and heavier rain Sat morning to Sat early evening. Locally heavy rain totals are possible in interior Southern New England, although there is more uncertainty on rain amounts in eastern MA and RI. * Cooler than normal weather and blustery/breezy Sunday. Remains cooler and unsettled for early next week. Details... Friday through Sunday... You`ve heard it before and here we are we approach the weekend more rain is on the way. Friday through Saturday night looks to be the most active period of weather in the extended forecast period as a frontal system from the Great Lakes combined with moisture from what is now Tropical Storm Phillipe brings soaking rain and even some thunderstorms to southern New England. Friday will be a bit of a transition day between the drier pattern we`ve enjoyed to the very wet pattern of Saturday. This, as the surface ridge breaks down with the arrival of a mid level trough digging into the eastern Great Lakes. Eventually this trough will become negatively tilted as it crosses SNE and ushers the remnants of what is now Tropical Storm Phillipe into Nova Scotia. So conditions will begin to deteriorate on Friday as isentropically forced showers move in with warm advection on E/SE winds. This direction of flow will also favor orographic ascent which serves to enhance rainfall amounts over the high terrain of central and western MA/CT. Overall, though, not expecting big rainfall amounts out of Friday`s showers, most likely a few hundredths to a few tenths. The heavier and steadier rain then arrives overnight Friday and especially on Saturday. As for placement of the heaviest amounts (1+inches) ensemble guidance is continuing to highlight two maxima, one over western MA/CT associated with the frontal system and another either fully offshore or scraping eastern MA associated with Phillipe. This leaves much of central/eastern MA and RI in the area of greatest uncertainty as to how much rain we`ll see. There will exist a decent amount of instability Friday night into Saturday as well which introduces some variability because anywhere that sees convection could see very localized high rainfall amounts. Overall, rainfall amounts for our area are do not scream "flash flooding concern". The cold front then ushers the bulk of the moisture out of the area sometime around Saturday night/Sunday morning. Cold air advection behind the front then steepens the lapse rate and brings a starkly colder and breezy post frontal airmass on Sunday. There remains a good deal of uncertainly on the timing of the front and arrival of the dry slot, though, so there`s a chance rain sticks around for some of Sunday morning. Even beyond Sunday morning, the upper low remains overhead and this cyclonic flow/cold pool aloft will promote clouds and widely scattered rain showers on Sunday. Monday through Wednesday... The upper low mentioned above isn`t in any hurry to exit and will in fact stick around through at least the first half of the week. Thus, while it won`t be a washout, a cool and unsettled pattern will be with us for the duration. Given 850 mb temps just a few degrees above zero this puts us solidly in the cooler than average boat, with highs only in the mid to upper 50s or low 60s each day. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z Update: Tonight...High confidence in trends but lower on exact details. Widespread fog developing and likely at least MVFR with areas of IFR/LIFR. Light SE winds. Thursday...High Confidence in trends but lower on exact timing details. IFR/LIFR at 12z in fog but slowly trending upward toward MVFR and eventually VFR between 15z-18z. Winds SSE less than 10kt. Thursday night...high confidence in trends but lower in exact timing details. VFR/MVFR at 00z in developing fog, then trending IFR/LIFR overnight in light SSE winds. Could be some patchy drizzle/mist in the areas of dense fog. KBOS Terminal...high confidence in TAF trends, but uncertainty on how quickly fog develops this evening and then how quickly erodes Thu morning. KBDL Terminal...high confidence in TAF trends, but uncertainty on how quickly fog develops this evening and then how quickly erodes Thu morning. Outlook /Friday through Monday/... Friday: MVFR/IFR conditions possible. Slight chance SHRA. Friday Night: Mainly IFR, with local MVFR possible. Chance SHRA, isolated TSRA, patchy BR. Saturday: IFR. Breezy. SHRA, isolated TSRA, patchy BR. Saturday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SHRA, isolated TSRA, patchy BR. Sunday: VFR. Windy with areas of gusts up to 30 kt. Slight chance SHRA. Sunday Night through Columbus Day: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 330 PM update... Tranquil boating weather late morning through the afternoon, then fog develops late evening and overnight. Fog could locally be dense at times with vsby less than 1/4 mile. Mainly dry weather prevails until Thursday night, when mist/drizzle accompanies another round of fog. With high pressure offshore, seas only 1-3 ft on the ocean, even less in the bays/harbors/sounds. Outlook /Friday through Monday/... Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Friday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 11 ft. Rain showers likely, patchy fog. Visibility 1 to 3 nm. Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain showers, patchy fog. Local visibility 1 to 3 nm. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of rain showers. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 9 ft. Columbus Day: Moderate risk for Small Craft Advisory winds with gusts up to 20 kt. Seas up to 5 ft. && .CLIMATE... Record Daily High Temperatures for October 4th BOS 86 in 2007 BDL 86 in 2007 PVD 85 in 1941 and 1959 ORH 85 in 1898 and 1931 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera NEAR TERM...Nocera/BW/Dooley SHORT TERM...Nocera LONG TERM...BW AVIATION...Nocera/BW MARINE...Nocera/BW CLIMATE...STAFF is the U.S. government's official web portal to all federal, state and local government web resources and services.