Area Forecast Discussion
Issued by NWS Boston, MA

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885 FXUS61 KBOX 251110 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 710 AM EDT Mon Sep 25 2017 .SYNOPSIS... High pressure covering the Northeast USA will bring fair warm weather to Southern New England through Wednesday. A cold front combined with moisture from Maria may impact the region with possibly scattered showers Wednesday into Thursday. Behind the front, turning much cooler and lower humidity later Thursday and continuing into the weekend. Hurricane Maria will bring dangerous rough surf and rip currents to the south coast this week, before passing well southeast of New England late this week. && .NEAR TERM /UNTIL 7 PM THIS EVENING/...
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7 AM Update... Summer-like morning with temps already in the low 70s in a few locations along with dew pts in the 60s! The exception is across Cape Cod and the Islands where low clouds and fog exist. This low level moisture may take most of the morning to burn off given the lower sun angle now that it`s late Sep. Near record highs today with temps soaring to 85-90 away from the coastline. Dry weather prevails given deep layer ridge over the area. However SPC mesoanalysis indicates very moist 850 mb and 925 mb dew pts across the region. Despite the absence of a forcing mechanism, this abundant moisture may combine with differential heating across the high terrain for a spot shower this afternoon. Previous forecast captures these details nicely so no major changes with this update. Today... Lingering fog will dissipate this morning. High pressure will provide subsidence and maintain a warm humid airmass over us. Thus we expect another sunny day. Dew points remain in the 60s, so the humidity will be noticeable. The mixed layer per the GFS reaches to about 850 mb, similar to yesterday. The ECMWF is similar, but more like 880-890 mb. Temps at the top of the layer are about 16-17C, with a few hints of 18C. This would support max sfc temps in the upper 80s and around 90 inland. Weak winds will again allow a seabreeze, which will buffer temps this afternoon and keep places near the coast cooler.
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&& .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM TUESDAY/... High pressure means light wind continue. This means fair weather with patchy fog inland. Meanwhile, the coastal fog and stratus should again advect up across Cape Cod and Islands. There is a low risk that the fog could advance farther northwest into Southeast Mass. High pressure remains in control Tuesday, with a light wind inland and light southeast wind at the shore. The NAM and GGEM show showers moving into South Coastal MA and RI tonight. The GGEM then spreads showers across all of Southern New England Tuesday. Dynamic features show no support for this, and convective parameters are stable through the period. We will favor the GFS and ECMWF which keep any showers offshore, and will show slight chance pops along the South Coast late in the day. With dew points in the 60s, min temps should also be in the 60s. Sunshine and mixing on Tuesday will again bring the layer up to about 850 mb, where temps are forecast at 16-17C. This favors mid 80s inland and cooler toward the shore. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Very warm and humid weather persist into Wednesday * Scattered showers possible Wednesday into Thursday * Pattern change to much cooler and less humid weather late Thu into the weekend Overall good model agreement on the large scale flow between the EC, GFS, their ensembles, the UKMET and NAM. Thus above average forecast confidence this period. Ridge lingers across the region into Wed and will result in warm (highs 80-85) and humid conditions (dew pts 65-70!). Despite Hurricane Maria remaining well south of New England mid level moisture advects (K indices on the rise) northward into our area beginning Wed and continuing into Thu. Not much forcing for ascent Wed given ridge axis lingers across the area. Thus perhaps dry weather prevails Wed. However by Wed night and especially into Thu approaching short wave and attending cold front will act on PWATs of +2 STD from Maria and provide a focus for showers late Wed into Thu. Some signs this could take the form of a PRE - Predecessor Rainfall Event given frontal boundary and upper level jet streak. Thus looks like a small window of opportunity for a period of heavy rain over southeast MA Thu especially Cape Cod and the islands. Will have to watch closely given tropical airmass. Then big improvement with a noticeable cool down late Thu into the weekend as low level flow becomes N-NE behind departing fropa and Maria. Seasonable for this time of year with highs 65-70 Fri/Sat/Sun and lows in the 40s along with low humidity. A touch of fall for sure. Mainly dry too with the exception of a few isolated brief diurnal showers possible Sat with cold pool aloft and cyclonic flow. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Today... High confidence. 7 AM update... VFR and mainly dry weather today, other than a spot shower over the high terrain this afternoon. Seabreezes develop. IFR conditions over Cape Cod and the Islands may take much of the morning to dissipate. Earlier discussion below. ================================================================ VFR. Areas of IFR/LIFR early on Cape Cod and Islands due to fog, but the fog will lift and thin during the morning. Light east to southeast wind. Tonight... Moderate-High confidence. VFR inland with patchy fog late. Meanwhile, fog and low clouds move back over Cape Cod and Islands with areas of 1/4 mile vsbys. Areas of IFR/LIFR in any fog. Tuesday... High confidence. VFR. Areas of IFR/LIFR early on Cape Cod and Islands due to fog. Light southeast wind. KBOS TAF...High confidence in TAF. Seabreeze redevelops by 15z, becoming south toward 00Z-02Z. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/... High Confidence. Tue night...VFR but trending toward MVFR late south coast, along with low risk for some rain south coast. Wed...Marginal MVFR-VFR with very low risk of rain. Thu...Marginal MVFR-VFR southeast MA along with risk of showers. Elsewhere improving to VFR and mainly dry. Fri...VFR, dry weather and light winds.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. Winds will remain light through Tuesday with high pressure overhead. Meanwhile, increasing long period south swell from Hurricane Maria will be moving into the waters with potential for 5 to 7 foot seas over southern waters tonight and 7 to 9 feet on Tuesday. SCA for hazardous seas will continue. In addition, areas of fog will result in poor vsbys at times, especially south and east of Cape Cod. Outlook /Tuesday Night through Friday/...Confidence...High Tue night and Wed...Light winds with ridge overhead however increasing large southerly swells from Hurricane Maria. Low risk of scattered showers especially southern waters. Given moist airmass rounds of fog expected. Wed night into Thu...Some heavy rain possible southeast MA waters as moisture from Maria combine with approaching cold front. In addition areas of dense fog may be an issue. Friday...Big improvement with front offshore and high pres building in. && .TIDES/COASTAL FLOODING... Long period swell from Hurricane Maria will be moving north into the south coastal waters. WNAWave guidance indicating increasing swell of 5-7 feet with a period of 15 seconds moving reaching the south coastal waters tonight and up to 9 ft on Tuesday. This will result in increasing high surf and dangerous rip currents. High surf advisory will continue and will extend through Tue. It is likely the high surf will continue through the week even as Maria likely recurves out to sea well southeast of New England. && .CLIMATE... Record high Sunday was broken at BDL with a temp of 92 degrees. Record high Sunday was broken at ORH with a temp of 86 degrees. Two of four climate sites broke max temp records yesterday. Another chance for record high temps again today, 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 two days...Today and Tuesday...are: BOS 89/1926 95/1881 ORH 85/1970 91/1930 BDL 90/2007 93/2007 PVD 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...High Surf Advisory until 6 PM EDT Tuesday for MAZ020-022>024. RI...High Surf Advisory until 6 PM EDT Tuesday for RIZ006>008. MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT Tuesday for ANZ235-237. Small Craft Advisory for hazardous seas until 7 AM EDT Wednesday for ANZ254>256. && $$ SYNOPSIS...WTB/Nocera NEAR TERM...WTB/Nocera SHORT TERM...WTB LONG TERM...Nocera AVIATION...WTB/Nocera MARINE...WTB/Nocera TIDES/COASTAL FLOODING... CLIMATE...

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