Area Forecast Discussion
Issued by NWS Boston, MA

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579 FXUS61 KBOX 210939 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 439 AM EST Sun Jan 21 2018 .SYNOPSIS... A fast moving storm system will bring a period of heavy rain to southern New England Tuesday along with strong winds on the coast. This storm will be preceded by some mixed wintry precip Monday and a risk of light icing across the interior Monday night into early Tuesday morning. Blustery, dry and colder weather follows Wednesday through Friday, before above normal temperatures likely return next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Mid and high clouds continue to stream across the region, though noting southern edge of clouds has lifted to near or just S of the Mass Pike, with mainly clear skies in place across N CT/RI/SE Mass as seen on latest GOES-16 Nighttime Microphysics RGB composite imagery. Noting some lower clouds working east into the Berkshires as well. The overall westerly mid level wind flow remains across the region, with H5 heights slowly rising during the day. Large high pressure center will push off the mid Atlantic and SE coast during the day. The clouds across northern areas this morning should lift N during the afternoon, so will see at least some sunshine during the day. After chilly readings early this morning across some of the region, temps will recover, reaching the 40s at most locations though may hold in the upper 30s across NW Mass.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
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Tonight... Clouds will be on the increase as a warm front starts to push NE toward the region this evening as low pressure will push out of the mid Mississippi valley toward the Great Lakes overnight. Will remain in a general W flow aloft, but will start to turn to a more SW flow toward daybreak. Leading edge of the overrunning precip may approach overnight, but precip may hold off for most areas until Monday. However, could see some light precip reach into western areas and, depending upon the low level temp profile, could see a wintry mix at the onset as colder air damming sets up there. This may occur around the start of the early morning commute in the Hartford/Springfield area and along the I-91 corridor. Expect temps to fall back to the mid-upper 20s from N Mass down the CT valley, ranging to 30-35 across RI and SE Mass. Monday... With high pressure remaining across central Quebec, cold air may continue push down across the interior through the mid to late morning hours (at least). So, will see a mix of snow, sleet and possibly some freezing rain as the precip pushes NE during the morning. Some question how quickly the temps will rise above freezing, though it does look like it should be relatively quick as winds shift to SE-S by around midday or so. The high should remain well N of the region, allowing for slowly rising temps during the day. Looks like the biggest threat for a mix of snow and freezing rain for most of the day will be along the Route 2 corridor of N Mass. Expecting light QPF amounts, generally less than 0.1 inches, but the potential of lingering light freezing rain across northern areas and the higher terrain will be a big concern. May see some precip taper off across south coastal areas toward evening as the warm front lifts into central New England. Expect temps to reach near seasonal levels for highs on Monday, at least for now.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Highlights... * Light icing risk Mon night across interior MA high terrain * 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 Monday night... Main concern for Mon night continues to be a risk of light icing over portions of the interior. Precip expected to be light as some mid level drying moves in while best forcing remains to the west. In fact, ice crystal growth region is drying which suggests more in the way of drizzle. There is a cold air damming signature with sfc ridging nosing down from the NE with low level northerly ageostrophic flow. Leaned toward 3km NAM for temps as higher resolution datasets should better capture localized cold air damming and it targets higher terrain in western and northern MA for near freezing temps, possibly down to higher elevations in NW Hartford county. This is where the greatest threat of some light freezing rain/drizzle exists with potential for a light icing event. This also is supported by hi- res ECMWF temps. Icy roads and walkways certainly a possibility Mon night over the higher elevations. 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 /09Z SUNDAY THROUGH THURSDAY/...
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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/... Through 12Z...High confidence. Mainly VFR. Patchy MVFR-IFR CIGS/VSBYS develop in patchy fog in normally prone areas of the CT valley, possible across portions of interior E Mass for a few hours prior to sunrise. Today...High confidence. VFR. Any leftover MVFR-IFR conditions should improve by around 14Z. W-NW winds around 10 kt or less as pressure gradient relaxes. Tonight...Moderate confidence in general trends, lower in timing arrival of precip. Mainly VFR through midnight, then MVFR-IFR CIGS move into central and western areas. Expect mixed snow/sleet/freezing rain and patchy fog to move into the CT valley during the early morning commute. Monday...Moderate confidence. MVFR CIGS lower to IFR by around midday, with LIFR across southern areas in the afternoon. VSBYS lower to MVFR-IFR by midday. Mixed -SN/-PE/-FZRA to start, then changes to -RA near and S of the Mass Pike by midday, with mixed -RA/-SN across N Mass. May see a mix with -FZRA toward sunset along the N Mass border. Light/variable wind becomes E-SE during the day. KBOS Terminal...Moderate to high confidence in TAF. KBDL Terminal...Moderate to high confidence in TAF. Outlook /Monday Night through Thursday/... Monday Night: Mainly MVFR, with areas IFR possible. RA likely, chance FZRA interior northern MA. 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/...High confidence. Through 12Z... Leftover 5 ft seas along the southern outer waters should subside by around 7 AM. Otherwise NW winds up to around 10-15 kt. Today... W-NW winds diminish as high pressure passes S of New England today. Seas will also continue to subside. Tonight... Light and variable winds eventually shift to S-SW toward daybreak as low pressure remains well W of the waters. Seas remain below 5 ft. Some visibility restrictions across the western waters toward daybreak as light rain moves in. Monday... Expect E-SE winds to increase during the afternoon, up to 10-15 kt with some gusts to 20 kt. Seas will build up to 3 ft on the eastern outer waters late in the day. Visibility lowers to 1-3 NM by mid to late morning in rain along with a brief mix with snow on the eastern waters. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain. 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. Received new data from NERFC late Saturday night, so updated the Flood Statement to provide the latest information. Not too much change from the previous forecast. 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...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 AM EST this morning for ANZ254>256.
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&& $$ SYNOPSIS...KJC/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/EVT HYDROLOGY...Staff

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