Area Forecast Discussion
Issued by NWS Boston, MA

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430 FXUS61 KBOX 240755 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 355 AM EDT Sun Sep 24 2017 .SYNOPSIS... High pressure covering much of the Eastern USA will bring warm and dry weather to Southern New England the first part of this week. Cold front approaches southern New England during Wednesday afternoon and triggers scattered showers. Cold front slowly moves through southern New England on Thursday and offshore Thursday night. Maria will bring swells to the south coast, but the center is expected to pass well southeast of New England late in the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Fog lingers early today, both as a broad area over Southeast Mass including the Cape and Islands and as smaller patches inland. The fog will dissipate during the morning. All areas will either start clear or become clear this morning. Expect sunny skies through the afternoon. A weak shortwave is projected to move across Northern New England, and could spread a few clouds our way. Subsidence under the ridge is likely to diminish any clouds and favor the mostly sunny forecast. Full sun will mean deep mixing, with the layer expected to reach to at least the 850 mb pressure level. The models have been known to underestimate this depth, so mixing above that level is a reasonable scenario, and would mean surface temperatures warmer than our estimates. Both the GFS and ECMWF project 850 mb temps of 17-19C, the NAM and GGEM 18-19C. This suggests inland areas will reach max sfc temps in the upper 80s and lower 90s. Light wind under the high pressure will allow sea breezes to develop later this morning. This will buffer temps, so expect lower max temps in Eastern Mass and RI especially along the coast. Interior climate sites are expected to reach max temps at or near record levels. The sea breeze at Boston should keep Logan Airport below its record. We do expect coolest temps to be found on Cape Cod. Should the fog linger longer than anticipated, temperatures may be a few degrees cooler still. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... High pressure remains over the region tonight and Monday. That means mostly clear skies and light winds. Dew points will mostly be in the 60s much of this time, so min temps tonight will be in the upper 50s and 60s. Expect a similar mixed layer Monday, with temps at 850 mb of 17-18C. So max temps should be similar to today, upper 80s and low 90s inland and cooler near the shore. Light flow will again allow sea breezes to form, buffering temperatures along the coastline. Patchy fog will again be possible overnight and early morning, favoring the usual inland fog spots as well as the South Coast. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Very warm temperatures persist into Wednesday * Scattered showers Wednesday afternoon through Thursday night * Maria will bring swells to the south coast but will sharply recurve out to sea southeast of New England late in the week Tuesday...H85 temperatures 16C to 18C will support very warm temperatures into Tuesday with surface temperatures reaching well into the 80s throughout most of the region. The light gradient flow, however, will set the stage for sea breezes along the coastal plain. Wednesday through Thursday night...A surface cold front and upper short wave trough will approach southern New England Wednesday afternoon. We anticipate scattered showers to develop ahead of the front Wednesday afternoon in moist, marginally unstable air mass. Model guidance suggests showalters near zero and K indices abov 30. Models have been giving a signal that tropical moisture from Maria may become entrained in the air mass just ahead of the front and increase the risk of a few heavy downpours, although there is uncertainty in the timing/duration of Maria`s moisture entrainment. The air mass appears to be unstable enough to support isolated thunder at least for Wednesday afternoon/evening. Due to the upper shortwave trough having to erode a very strong upper level ridge, the surface cold front will probably move slowly across southern New England and may not pass offshore until Thursday night. Thus, we anticipate scattered showers to persist Wednesday night into Thursday night. With tropical moisture from Maria and precipitable waters 1.7 to 2 inches, some the showers could contain very heavy downpours anytime late Wednesday to Thursday night. The air mass remains mild Wednesday into Thursday, but clouds will likely temper the high temperatures some. May still experience 70s to near 80 on Wednesday and probably mid to upper 70s on Thursday. Friday...Model consensus has the cold front passing offshore to the southeast of New England Friday morning, and Maria passing well southeast of our region. This will result in drier and cooler air moving into southern New England, although showers may linger into the morning for a while in southeast sections. Maria will become embedded in the westerlies on the leading edge of the mid latitude upper trough and likely pass out to sea well southeast of New England. H85 temperatures drop about 10C, and Friday`s high temperatures will be noticably cooler, albeit just closer to normal, even with plenty of sunshine and downsloping winds. Dewpoints in the upper 60s and 70s for most of the week will drop into the 40s most locations during Friday. Saturday...For now Saturday looks to be dry with near normal temperatures and very low humidity. && .AVIATION /08Z 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/... Today...Moderate-High confidence. Lingering MVFR ceilings in Western and Central sections while Eastern Mass and RI show IFR cigs and MVFR/IFR vsbys in fog and a few early morning showers. Drier air is moving in, so we expect clearing skies and VFR conditions arriving from west to east during the day. Low clouds may linger on Cape Cod and the Islands. North winds will diminish through the day, although some 20 knot gusts may linger this morning along the Cape/Islands/South Coast. Tonight...High confidence. Diminishing wind. VFR to start in most spots. Southeast Mass and RI will trend to IFR/LIFR in fog and low clouds. Areas of fog will also develop across the interior with IFR/LIFR conditions. Sunday... High confidence. Fog burns off during the morning. Most of the day will be VFR with light winds. Sea breezes expected along the coastlines, including BOS. KBOS TAF...Moderate confidence. IFR cigs and potential 4SM vsbys in low clouds and drizzle/fog early. Conditions should improve to VFR late this morning with clearing during mid to late afternoon. North to northeast winds will diminish through the day. KBDL TAF...High confidence in TAF. Borderline MVFR/VFR cigs will improve as clearing skies over the Berkshires sweep east this morning. Areas of fog may develop 06Z-12Z, although the chance of this is stronger over valley locations north of Springfield. Outlook /Monday Night through Thursday/... Confidence...High. Monday night through Tuesday...Mostly VFR except for patchy late night/early morning fog. Wednesday...Mostly VFR but scattered MVFR ceilings/visibilities in showers, main during the afternoon. Wednesday night through Thursday...MVFR ceilings and areas of IFR ceilings and visibilities in scattered showers and fog. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...High confidence. High pressure over the Eastern USA will bring light wind to the waters. The remnants of Jose well south of our area may favor a light east wind over our waters. Daytime heating of land areas will favor a sea breeze along the immediate coast. Locally dense fog may start the day over the waters around Cape Cod and Islands. This will mean a period of poor visibility to start the day. This fog should thin and dissipate over most waters by midday or early afternoon. Most seas are at 2-3 feet with a period of 10-15 seconds. This is leftover swell from Jose. Higher seas are found on the southern outer waters, and an additional south swell of 3-4 feet leading north from Maria will start showing itself in our southern waters later in the day. A High Surf Advisory remains in place in anticipation of this swell. Tonight and Monday... Light wind continues under high pressure. Seas will continue to build through the period as increasing swell moves north from Maria. South swell should reach 6-8 feet by Monday afternoon, affecting all of our exposed southern shoreline and possibly the southern beaches of the Outer Cape late Monday. Expect high surf and dangerous rip currents as a result of this swell. Outlook /Monday Night through Thursday/...Confidence...High Relatively light winds are expected through this period. However, swells from Maria will propagate into the southern coastal waters, beginning late Sunday night or Monday. Small Craft Advisories will likely need to be extended due to rough seas for the waters south of the MA and RI coast for all of this period. The swells from Maria will likely produce another round of high surf and dangerous rip currents. OUTLOOK...Sunday night through Thursday Confidence...High Relatively light winds are expected through Thursday. However, swells from Maria will impact the south coastal marine zones, and Small Craft Advisories will likely be needed due to rough seas. The swells from Maria will likely produce continuing high surf and dangerous rip currents, probably lasting most of the week. && .TIDES/COASTAL FLOODING... High Surf Advisories remain in effect through Monday along the south coast and the Outer Cape east coast. Swells from Maria will likely increase the surf and associated rip current risk across our ocean- exposed south coast starting later this afternoon and continuing through the week. This will be true even though Maria may eventually recurves out to sea well southeast of New England. && .CLIMATE... Best chance for record high temps will be Today and Monday, when records are 85-90. Records jump up Tuesday to 89-95, while less mixing will lead to lower max temps. So the chance for new records diminishes Tuesday. The current record max temps for the three days are BOS 90/1959 89/1926 95/1881 ORH 85/2010 85/1970 91/1930 BDL 89/1959 90/2007 93/2007 PVD 87/1959 89/1920 89/2007 Also... Dew points in the 60s, while high for this time of year, are not unprecedented. The daily extreme high values for dew points are still in the low 70s, except for a couple of 68 and 69 values at Worcester. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Dense Fog Advisory until 9 AM EDT this morning for MAZ022>024. High Surf Advisory until 6 PM EDT Monday for MAZ020-022>024. RI...Dense Fog Advisory until 9 AM EDT this morning for RIZ008. High Surf Advisory until 6 PM EDT Monday for RIZ006>008. MARINE...Small Craft Advisory for hazardous seas from 2 PM this afternoon to 6 PM EDT Monday for ANZ235-237. Small Craft Advisory for hazardous seas until 6 PM EDT Monday for ANZ254>256. && $$ SYNOPSIS...WTB/Thompson NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Thompson AVIATION...WTB/Thompson MARINE...WTB/Thompson TIDES/COASTAL FLOODING... CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.