Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 140534 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1234 AM EST Sat Jan 14 2017 .SYNOPSIS... High pressure slowly builds over the region into Saturday, with a return of colder, more wintry temperatures. Surge of colder air continues over the weekend with a perhaps snow flurries or a brief period of light snow Saturday night across the Islands with a passing offshore low. High pressure maintains dry and seasonable conditions Monday, then milder temperatures return for the rest of the week with a wet period around midweek. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 10pm update... Slight breezes and some CI have limited early radiational cooling and sfc dwpts are higher than previously forecast. Therefore, have tempered radiational cooling for the rest of the night by a bit. Lows are now a few degrees warmer than previously forecast. Still a chilly night. Otherwise, forecast remains on track so no other changes are needed. Previous discussion... Northern stream short wave moving across southeast Quebec this evening providing strong post frontal cold air advection with 925 mb temps over southern New England falling from about -4C this afternoon to -12C by 12z Sat! Hasn`t been as windy today on the Cape and Islands and this is due to shallow nature of this cold airmass with 850 temps warmer than at 925 mb across this region. However as cold air gets deeper this evening winds low level lapse rates will increase and winds will pickup over the Cape and islands. Thus cold wind chills this evening. However as the 1040 mb high builds over the region the pres gradient relaxes so expecting winds to slacken toward daybreak. Given many locations will see winds go light/variable or calm leaned toward the colder MOS guid temps for tonight. This results in min temps ranging from +5F to +15F most locations. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... Saturday... Cold start to the day with 1040 mb high over the region. Not much airmass modification as surface high remains across the area. Thus below normal cold Saturday with only 25-30...perhaps briefly cracking the freezing mark along the immediate south coast and islands. The only good news is that winds will be light so not much of a wind chill tomorrow. Sunshine will be filtered by mid and high clouds most of the day. Saturday night... Another northern stream trough approaches from the northwest with surface wave tracking well south of the 40N/70W benchmark. All model guidance has deep layer moisture just clipping the immediate south coast and islands. Thus any steady/accumulating snow will remain offshore with just some flurries or a brief period of very light snow clipping the immediate south coast and islands. Otherwise remainder of the region stays dry and cold with lows mainly in the teens...low 20s for the heat urban centers including Cape Cod and Islands. Good news is that there won`t be much wind so wind chills not an issue. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Dry and seasonable Monday * Milder period the rest of the week * Wet weather likely around midweek Overview... While the extended period will start out seasonably cold, active Pacific jet coming onshore in the west combined with building SE CONUS ridge suggests a period of mild weather next week with main storm track west of New Eng. There are differences in the timing of mid level system moving into the NE but general agreement on a period of rain around the midweek period, then mainly dry and mild through the end of the week. Details... Sunday into Monday... Strong high pres builds into the region from the west providing mostly sunny skies and seasonably cold conditions. Modest NW winds expected Sun, light Sun night then gradually shifting to SW Mon afternoon as the high shifts south of New Eng. Excellent radiational cooling Sun night will result in low temps dropping into the single numbers and teens. Tuesday... This will be transition day as the high moves offshore and moisture begins to move into the region in developing warm advection pattern. Clouds should increase during the day. GFS is a fast outlier and leaned toward slower timing which suggests dry weather may hold on for much of the day with just a low risk for some light rain in the west before days end. If timing is quicker and precip were to move in during the morning there would be a low risk for some icing at the onset in western MA but this is unlikely. Tuesday night into Thursday... A period of rain is likely sometime during this timeframe as next system moves into the region but given the differences among the models, forecast confidence in timing is low. GFS and bulk of the GEFS members have bulk of rain Tue night into early Wed then dry Wed night/Thu. ECMWF has some rain Tue night into Wed then a slug of heavier rain Wed night which may also linger into early Thu. EPS has highest probs for rainfall in the Wed/Wed night period and we generally followed this scenario with gradual improvement Thu. GFS is an outlier with the strength of the mid level low and cooling on Wed and we discarded this solution. Mild temps well above normal likely Wed/Thu and EPS has fairly high probs of 50 degrees in the coastal plain. Friday... Deterministic and ensemble guidance suggesting mainly dry and mild weather. Once again, EPS probs have a fairly strong signal for 50 degrees in the coastal plain. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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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 Sunday/... Through 18Z...High confidence. VFR. Winds NW, shift mainly to SW this afternoon, but remain light. This evening and overnight...Moderate confidence. VFR remains N of a line along the MA border with CT/RI into SE MA. S of this line, light snowfall is possible, with some light accumulations (less than an inch) possible especially near the coast and over the Islands. This could yield a period of MVFR conditions in lowered vsbys and CIGS. Conditions clear during the early morning hours Sun. Winds S-SW, but shift back to the NW after snows end. Sun...High confidence. VFR. NW flow, mainly 10 kt or less. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF overall. Low risk for very light snowfall this evening, but VFR likely to dominate. Outlook /Sunday Night through Wednesday/... Sunday and Monday...High confidence. VFR. Tuesday...Moderate confidence. Cigs may lower to MVFR with a chance of rain moving in from the west. Tuesday night and Wednesday...Moderate confidence. Areas of MVFR/IFR possible in periods of rain and fog.
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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 Sunday/... Tonight...High confidence. WNW winds actually increase early this evening across the southern waters as cold air advection increases. WNW winds 20-30kt then slowly decreasing late tonight and especially toward morning. Dry weather and good vsby. Low risk of some light freezing spray along the eastern MA near shore waters especially vicinity of Cape Ann waters. Could have a few ocean effect snow showers well offshore. Saturday...High confidence. High pres will yield a period of quiet boating wx through the day. Winds will remain light, but shift from NW to S-SW by afternoon. Saturday night...high confidence. Weak wave of low pressure tracks south of 40N/70W with its precip shield just clipping the southern waters in the form of very light snow or flurries. Otherwise light winds and fairly tranquil conditions for mid Jan. Outlook /Sunday Night through Wednesday/... Sunday...High confidence. NW wind gusts to 20-25 kt eastern waters where SCA conditions likely. Winds becoming light Sun night. Monday...High confidence. Light winds becoming SW 10-20 kt in the afternoon. Tuesday and Wednesday...Low confidence wind forecast. Winds will depend on timing, track and intensity of sfc low tracking west of New Eng. A period of SCA S/SW gusts possible sometime during this period. Vsbys may be reduced in rain and fog at times Tue night and Wed.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EST early this morning for ANZ231>234-251. Small Craft Advisory until 10 AM EST this morning for ANZ250- 254. Small Craft Advisory until 5 AM EST early this morning for ANZ255-256.
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&& $$ SYNOPSIS...KJC/Nocera NEAR TERM...Nocera/Doody SHORT TERM...Nocera LONG TERM...KJC AVIATION...KJC/Doody MARINE...KJC/Nocera

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