Area Forecast Discussion
Issued by NWS Boston, MA

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284 FXUS61 KBOX 252319 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 719 PM EDT Sat Mar 25 2017 .SYNOPSIS... A cold front lingers offshore well south of New England tonight. The front will then push northward as a warm front Sunday. A weather system lifts through the Great Lakes Sunday and Monday bringing a wintry mix inland and wet weather near the coast. Another low pressure area will move across southern New England Tuesday bringing some rain showers. High pressure brings dry but cooler weather Wednesday and Thursday. Then more precipitation possible late Friday into Saturday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 715 PM update... Skies had begun to rapidly clear across northern MA early this evening. This trend should continue across our area by midnight. Per composite guidance, the cloud shield motion stalls over SW CT and Long Island between midnight and 3 AM, then slowly builds north again. Shortwave ridge aloft builds east into our area tonight. This turns our upper flow from the northwest. This allows surface high pressure centered over Quebec to build south into New England. So expect clearing or partial clearing most places. A northeast marine wind will not carry any low dew points, but we should see a small lowering trend through early tonight. Min temps expected to be a little above dew point, in the mid 20s to lower 30s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... High pressure shifts east into the Maritimes. The pressure builds southwest through New England with a typical cold air damming signal. Ageostrophic winds at 1000 mb turn from north Sunday morning at 10-15 knots...would like to see that a little higher, but the direction is good. The GGEM is most aggressive in bringing precip north into New England...and even that is west of Hartford at 12Z Sunday. Most of the others are not even in New England. The strongest low level winds and resulting lift will be in NY/PA, with little wind over here. Expect most of the precip to be to our west, with light QPF in Western New England...about 0 to 0.03 inches. Temperature profiles suggest that if there is any precip, it would involve rain or a rain/sleet mix and mainly for the western and central hills. Consensus timing would bring any chance for the precip into Western New England late morning. If anything reaches farther east it would be in the afternoon/evening, by which point temperatures should be above freezing. Model high temps show upper 30s in the hills and low-mid 40s lower down. With clouds, cold air damming, and the chance of pcpn, we opted to undercut this by 2-4F. Forecast max temps will be in the mid 30s to low 40s. Sunday night... The stronger low level south winds shift farther east Sunday evening and bring a greater potential for lift and precip production. The upper ridge also shifts east at this time, bringing under the influence of the approaching Great Lakes shortwave and associated upper jet. This will mean an increasing chance of precip during the night. Temperature profiles show a layer of above-freezing air between 800-900 mb with max temps around 3C. This indicates a sleet potential, especially overnight as cooling surface temps may allow the precip to refreeze below the warm layer. A 3C temperature is on the low side for freezing rain production, but close enough to consider the possibility. Precip amounts start the evening light, but will build up overnight as the shortwave and low level lift increase. This will be a concern just as the early Monday morning commute gets started. We are anticipating the need for winter weather headlines starting sometime during the night. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Rain Monday and showery on Tuesday * Sunshine mid-week * More precipitation late Friday into Saturday Upper level pattern overview... Several short wave troughs moving through our region through the upcoming week. The first is weak and moves through on Mon. The next is stronger and closes off an upper low as it moves through northern New England on Wed. Then large model differences occur, with the ECMWF much more amplified with a ridge over our region Thu and a sharp trough approaching by Sat. Other models have a more benign west-southwest flow aloft over the region in that time frame. Details... Monday...Moderate confidence. Southerly low level jet of 30-40 kt will usher warmer air into the region Monday morning, changing any leftover freezing rain in the hilly terrain of western and north-Central MA over to all rain by mid to late morning. A weak surface warm front will become stationary over southern parts of the region while a weak wave of low pressure develops along the front. Due to cold air damming, areas north of the Mass Pike will take longer to reach the lower 40s but in northern CT, RI, and southeast MA we are forecasting highs to reach the upper 40s. Rain is likely across the region...and it could be briefly moderate to heavy at times...with generally about one-half inch of rainfall expected in most places. Mon. afternoon Total Totals reach 50 and K reaches 25-30 but with no CAPE, have not mentioned any thunder. Monday night into Tuesday night... Moderate confidence. As the upper level shortwaves trough moves away from our region, it will be replaced by a weak mid-level ridge Monday night. There will be a lull or complete break in the precipitation Monday night. Skies will remain cloudy with perhaps some drizzle, which will keep low temperatures in the upper 30s and lower 40s. Another weak low pressure area will be moving through on Tuesday, accompanied by PVA with the upper shortwave trough axis late in the day. There is a chance of showers anywhere during the day. Model high temperatures have come way up, due to 925 mb temperatures possibly nearing 8C to 9C. Have split the difference between the warm GFS and the cooler ECMWF and am forecasting highs mainly in the 55 to 60 range...cooler along the coast. That system departs Tuesday night with shower chances diminishing. Lows mainly 35 to 40. Wednesday through Friday morning... Cold air aloft will overspread southern New England as strong high pressure over Hudson Bay Wednesday morning builds across the New England region by Friday morning. Late March sunshine, however, will allow high temperatures to still reach into the lower 50s Wednesday and mid 40s to lower 50s Thursday and Friday. Mostly clear skies could allow nighttime lows to dip well into the 20s in northern and western areas each night, with the coldest being Thursday night. Friday afternoon into Saturday...Low confidence. All models agree on an increase in cloudiness Friday afternoon. But there is much uncertainty as to whether low pressure will track across the region or skirt the area to the south. Currently, we have a chance of showers in the forecast. However, depending on timing, there is a low chance that northwest hills of MA could have a touch of freezing rain early on Saturday morning - April foolin`. Again confidence is low that far out. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/...Moderate confidence. This evening...MVFR conditions... with isolated IFR at ORH... will become VFR with patches of MVFR. Tonight...High pressure builds from the north. This will bring clearing skies between 8 pm and midnight, as well as an improvement to VFR. Light East-Northeast flow through the night. Areas of MVFR may redevelop after midnight in CT. GFS implies an area of low ceilings moving onshore of eastern MA overnight, too. Will need to watch for that. Sunday... Mainly VFR. Areas of MVFR cigs/vsbys in possible precipitation, especially in CT and Western MA. Some sleet or freezing rain possible Sunday morning. Sunday night... Conditions lower to MVFR, with IFR in the Central Hills and the Berkshires. Increasing chance of precipitation with time. Increasing chance of sleet or freezing rain in areas north and west of Boston-Providence. Best chance of precipitation will be late at night, as the Monday morning push starts to gear up. KBOS TAF...High confidence in TAF trends. Moderate confidence in timing. KBDL TAF...High confidence in TAF trends. Moderate confidence in timing. Outlook /Monday through Thursday/... Monday-Monday night...Moderate confidence. Any leftover -FZRA/-PL Monday morning will end across higher terrain by mid to late morning. Otherwise MVFR-IFR CIGS in rain. Tuesday and Tuesday night...Moderate confidence. MVFR conditions within any passing rain showers. Wednesday through Thursday...High confidence. VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... This evening... High confidence. Area of light rain moves southeast across the waters early this evening. Northeast winds less than 20 knots. Lingering 5 foot seas on the southern outer waters. A Small Craft Advisory continues there. Seas less than 5 feet all other waters. Tonight... High confidence. East-Northeast winds less than 20 knots. Seas will remain less than 5 feet. Sunday... High confidence. East winds less than 20 knots. Seas less than 5 feet. Sunday night... Moderate-High confidence. Approaching weather system from the west will spread rain across the waters from west to east. Winds will remain below 20 knots and seas below 5 feet through the period. Outlook /Monday through Thursday/... Monday...Moderate confidence. Warm front with weak low pressure along it may kick up southeast to south winds to near 25 kt gusts and seas could build to 5-6 ft over the outer waters. SCA may be needed. Monday night...Winds diminishing to below SCA gusts but seas will only slowly subside. Tuesday/Tuesday night...Expecting winds and seas below SCA levels. Wednesday and Thursday...SCA likely. NW winds ahead of advancing strong high pressure, along with cold air aloft over the relatively warmer waters, will lead to good momentum transfer over the waters. Should see gusts to at least 25-30 kt over the outer waters, especially off of eastern MA. Seas building to 5-8 ft over the eastern waters and 5-6 ft over the southern waters, south of the islands. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ254>256. && $$ SYNOPSIS...WTB/GAF NEAR TERM...WTB/GAF SHORT TERM...WTB LONG TERM...GAF AVIATION...WTB/GAF MARINE...WTB/GAF is the U.S. government's official web portal to all federal, state and local government web resources and services.