Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 212002 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 302 PM EST Sun Jan 21 2018 .SYNOPSIS...
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Warm air aloft moves north tonight and brings clouds to Southern New England. Some light precipitation is possible Monday. Most of it will be rain, but some light icing is possible in the interior. A fast moving storm system will bring a period of heavy rain to the region Tuesday along with strong winds on the coast. Blustery, dry and colder weather follows Wednesday through Friday, before above normal temperatures likely return next weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High pressure is situated to provide dry weather much of the night. Low level flow remains light most of this time, but shows signs of overrunning after midnight. Meanwhile, satellite images and sfc observations show a cloud deck over Eastern PA edging northeast. Between this and the favorable development of lift overnight, expect increasing clouds through the night. Can not rule out some light precip late, especially in Western MA and CT, but the chance before 12Z is rather low so we used slight chance pops. If any precipitation were to form late tonight, temperature profiles suggest rain in the south and a snow/sleet/freezing rain mix north. Clouds will limit the overnight cooling, and cold air damming signal does not show much until late night. We maintain a range of upper 20s north to mid 30s south coast.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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Monday... High pressure over Quebec Monday and increasing cold air damming into New England. The damming seems focussed on Northern New England, but could further expand into our area as well during Monday morning. Our temperature profiles support rain most places, but a rain/snow mix north of the Mass Pike. The GFS and ECMWF bring a front south into Southern New England or just to our south. This shows increasing lift potential, thus increasing pops. We show chance pops all areas Monday morning and likely pops in the afternoon in Western and Central Mass and adjoining CT. An east wind should be enough to keep ptype as rain, but it may be marginal in Western Mass/Northern Worcester County. Even with better lift, the focus of southerly low level winds and moisture remains to our west across New York State through the day. So we continue to expect QPF amounts up to 0.1 inches. Monday night... Evening cooling and the stalled front to our south may allow a brief period of freezing rain in Central and Western Mass, especially along and north of the Route 2 corridor. The front moves north during the night with winds shifting from the south. This will bring slowly rising temperatures overnight ending the icing risk. South-southwest winds 35-40 knots move up over the region during the late night. This transports 1 inch PW values into the area. Expect increasing chance of rain toward morning with categorical pops...75 pct or higher...over Western Mass and Western CT.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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Highlights... * Heavy rain Tue with a period of strong winds SE New Eng * Significant flooding issues are not expected Tuesday * Dry/blustery and turning colder Wed and especially Thu/Fri Tuesday... Potential for some light freezing rain lingering over higher terrain on MA early, otherwise it`s all rain. Decent heavy rain signal for Tue with PWAT anomaly +2SD and low level wind anomaly up to +3SD. In addition, elevated instability at the nose of the low level jet will likely result in some convective elements with an isold t-storm possible. An area of heavy rain along the pre-frontal low level jet will move west to east across SNE with rain exiting the coast around evening. System is progressive which should limit window of moderate to heavy rainfall to about 6 hours. Rainfall amounts of 0.75 to 1.50 inches still looks reasonable with heaviest amounts in western New Eng. Given that most of the rain will probably fall in a 6 hour window, expect typical minor urban and poor drainage street flooding, but river flooding is not anticipated. The other concern is a period of strong winds across RI and eastern MA as 65-70 kt low level jet moves up along the coastal plain. Low level lapse rates are near moist adiabatic which will allow for some mixing, especially where temps climb into the mid 50s across RI and SE MA and in the vicinity of any heavier convective elements. In addition, models indicate impressive pressure falls on the order of 9 mb in 3 hours which will enhance isallobaric component of the wind. Potential exists for wind gusts up to 50 mph for a few hours in the afternoon across RI and SE MA. CIPS analogs also support this with fairly decent probs of 40+ kts across SE MA. Wednesday through Friday... Turning colder and blustery behind the storm with brisk NW flow. Temps near normal Wed, then trending below normal Thu/Fri as core of coldest air aloft settles over the region. Decent shot of cold air with -15C at 850 mb into SNE on Thu. Highs likely in the 20s Thu and blustery winds will make it feel considerably colder. Wind chills Thu night/early Fri morning dropping into the single numbers with subzero wind chills over higher terrain. Looks mainly dry during this period. Saturday... High pres moves off the coast with SE CONUS ridge building north into New Eng leading to a moderating trend with above normal temps likely. Dry weather.
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&& .AVIATION /19Z SUNDAY 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 Monday Night/... Tonight...High confidence in general, moderate confidence in timing of lower conditions. VFR through midnight. MVFR cigs after 06Z. Low probability toward morning for rain/sleet/freezing rain in Western Mass and Hartford County CT. This could affect the morning commute, especially in the CEF-BDL-HFD area. Monday...Moderate confidence. MVFR cigs with areas of IFR cigs developing in the afternoon. Increaing chance of light rain through the day. Generally MVFR vsbys in rain and some mixed rain/snow. Light wind becomes light East-Northeast. Monday night...Moderate confidence. MVFR conditions with areas of IFR. Rain most places with a chance of freezing rain early in northern areas of Massachusetts such as vicinity of FIT and ORE. Winds turn from the Southeast and South toward morning. KBOS Terminal...Moderate to high confidence in TAF. KBDL Terminal...Moderate to high confidence in TAF. Outlook /Tuesday through Friday/... Tuesday: Mainly MVFR, with local IFR possible. Strong winds with gusts to 40 kt RI and SE MA. RA. Pockets of FZRA early interior northern MA. Tuesday Night: Mainly VFR, with local MVFR possible. Windy with gusts to 30 kt. Slight chance SHRA. Wednesday: VFR. Windy with gusts to 30 kt. Wednesday Night through Thursday: VFR. Windy with local gusts to 30 kt.
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&& .MARINE...
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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 Monday Night/...Moderate confidence. Tonight and Monday... Light winds shift from the south late at night and from the southeast Monday. Speeds remain below 15 knots. Seas 2 feet or less. Vsby lowers to 3-5 miles in rain during Monday afternoon. Monday night... Southeast to south wind increasing, but remaining below 25 knots. Seas building to 4 feet. Rain with vsbys 3-5 miles. Outlook /Tuesday through Friday/... Tuesday: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 13 ft. Rain. Tuesday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 10 ft. Chance of rain showers. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft.
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&& .HYDROLOGY...
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A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. No significant change from earlier forecasts. For details on specific area rivers, including observed and forecast river stages, please visit the Advanced Hydrologic Prediction Service (AHPS) graphs on our website.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB SHORT TERM...WTB LONG TERM...KJC AVIATION...WTB/KJC MARINE...WTB/KJC HYDROLOGY...

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