Area Forecast Discussion
Issued by NWS Boston, MA

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373 FXUS61 KBOX 182042 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 342 PM EST Sat Feb 18 2017 .SYNOPSIS...
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Unseasonably mild temperatures will prevail Sunday. A dry cold front swings through Southern New England Sunday night, bringing a return to chilly weather into Tuesday. Milder weather returns the middle of next week. However, another pair of fronts may be accompanied by some precipitation sometime Tuesday night into Wednesday. At this point, Thursday appears to be the warmest day of the week.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Mid level shortwave passing to the north tonight will result in a weak cold front dropping south from northern New Eng late tonight. Decent low level jet will maintain a modest W/SW breeze and mild temps ahead of the front with min temps remaining mostly in the 30s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... Another shortwave passes to the north and this will help to drive the cold front south across the region during the late morning into the afternoon with a wind shift to W/NW and gusts to 20-25 mph. Cross sections indicate increasing low level moisture which will result in fair amount of clouds in the afternoon, especially interior but dry conditions. Colder air lagging well behind the front and 925 mb temps still 4-8C at 18z. This supports highs into the 50s in the coastal plain and interior valleys and may even see a few locations in interior E MA top out in the upper 50s with sufficient sun. Cooler 40s over the higher elevations. Sunday night... Mid level trof amplifies east of New Eng with closed low developing in the Maritimes. Another shortwave rotating around the low will bring a surge of coastal NW wind gusts and colder temperatures into SNE. Dry weather continues, although there is a low risk for a few snow showers along the east slopes of the Berkshires. Lows will settle back into the 20s, except lower 30s along the immediate coast. && .LONG TERM /MONDAY THROUGH SATURDAY/...
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Highlights... * Seasonably cool Mon and Tue. * Light rain/pockets of FZ rain possible Tue night - Wed. * Thu looks to be our warmest day. * More widespread rain Fri night into Sun. Overview and model preferences... The pseudo-Rex Block which has been a dominating feature across mainly the plains and portions of the CONUS just E of the Continental Divide begins a gradual slip to the E through the long term. This is thanks in part to a sharpening of the trof currently residing over the SW, which will allow warm advection into the upstream ridge to assist with its building as it moves E. Therefore, although generally shy of record-breaking warmth will move in through the end of the week, following the brief cool down Sun-Mon. This occurs even as the ridge itself breaks down late in the weak in response to longwave trof/cutoff shifting SSE through Manitoba/Saskatchewan. The resulting flow, although nearly zonal, have a slightly more SW-NE tilt through the northeast rather than W-E. This suggest the continued advection of warmer air will linger even as the ridge itself flattens and moves E of the region. A consensus blend will be used through at least mid week, given there is reasonably good agreement on the primary pattern drivers, will add more weight to ensembles for the latter half of the week to smooth out the more significant uncertainties regarding the aforementioned longwave trof/cutoff placement and it`s impact on the zonal flow downstream. Details... Mon and Tue... The last vestiges of an opening cutoff across the Maritimes will begin to slide E of the region allowing an initially cool high pres to slide E. H92 temps start around -8C at 12C but warm to an average of -5C by evening, suggesting highs will mainly stay in the upper 30s to around 40, cooler than Sun. By Tue the early onset of warm advection allows these same H92 temps to rebound back into the positive numbers, mainly around +2C. Therefore, more widespread mid 40s are expected. Dry wx prevails as high pres leads to predominant subsidence across S New England. Wed... Modest warm front will cross the region, along with more moistened profile in the lowest 400mb. This added moisture combined with overruning along the front should yield a period of light precipitation, likely only culminating in about 0.1-0.2 inches of QPF total. This occurs mainly during the late night hours Tue night into Wed morning, as the front remains progressive, perpendicular to the steering flow. Although winds remain southerly and temps aloft near or above freezing, sfc temps may be allowed to dip below freezing in some spots before or during precipitation. Therefore, can`t rule out the possibility of some patchy freezing rain (as rain will be the dominant p-type through the column), especially where some snowpack remains. This will have to be monitored for potential headlines. By mid-late day on Wed, conditions improve with warming allowing temps to rebound back into the 40s, ending any risk for further freezing. Thu and Fri... One weak trof will push through N New England with attendant clipper, however climatologically, the current track generally yields only clouds, and less in the way of precipitation, given peak forcing also remains well the N. Therefore, will continue to highlight the current dry forecast. Low-mid lvl warming continues, with H92 temps reaching +7C to +10C Thu and potentially +9C to +12C by Fri. 50s are likely here, with at least a modest probability of a few spots reaching the 60s if all conditions can turn out right and the bulk of the snowpack has melted/sublimated. Will need to watch a more significant system with attendant warm front moving in late Fri. This feature has much more moisture potential (already ensembles suggests PWATs nearly 2-3 std deviations above normal). Precipitation could begin as early as Fri evening. Next weekend... Already moderate agreement that a strong low pres will impact the region, allowing us first into the warm sector, followed by a robust cold frontal passage. Initial indications suggest that warm sector/pre cold frontal precipitation could be heavy with high PWATs/K-values. Can`t even rule out the potential for isolated TS given very high TT values and modestly steep mid lvl lapse rates. A lot to work out here, but given many ensembles agree with the deterministic counterparts for a very amplified inside runner, this is worth at least a mention now.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 00z...VFR. SW gusts to 25-30 kt, especially across southern RI and SE MA. Tonight through Sunday night...Moderate confidence. VFR, but patchy MVFR cigs possible Sun afternoon and night, especially interior. SW gusts diminishing tonight, but areas of LLWS through the first half of tonight. NW gusts to 25 kt developing Sun night along the coast. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday through Thursday/...Moderate confidence. Monday through Tuesday... Generally VFR. West winds ahead of the cold front turn from the North overnight and Monday with gusts to 30 knots possible. Winds diminish Monday night and Tuesday as high pressure moves overhead. Wednesday... Cold front sweeps through with Southwest winds leading the front, then shifting from the West after passage. CIGs and Vsbys lower to MVFR in showers, then improve to VFR after the front moves through. && .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 Night/...High confidence. Through tonight...SW gusts 25-30 kt, strongest over eastern waters, will gradually diminish overnight. SCA all waters into the evening. Sunday...Mainly west winds up to 20 kt, but W/NW gusts to 25 kt may develop by late afternoon over NE MA waters. Sunday night...A surge of NW winds with gusts 25-30 developing, strongest eastern waters. Outlook /Monday through Thursday/... Mon and Tue...High confidence. Mainly VFR. W-NW winds may gust 20-25 kt at times on Mon, lighter by Tue out of the S. Tue night into Wed...Moderate confidence. Mixed MVFR/VFR although a few spots of IFR not out of the question. Light rain, may mix with snow at times toward NE MA, but rain dominates. Some light freezing rain in the higher terrain of Central and W MA. Conditions improve through the daylight hours Wed. Thu...High confidence. VFR. W-SW winds.
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&& .EQUIPMENT... 2 PM update...KBOX radar is back in service. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ230>237-250-251-254>256. && $$ SYNOPSIS...KJC/Doody NEAR TERM...KJC SHORT TERM...KJC LONG TERM...Doody AVIATION...KJC/Doody MARINE...KJC/Doody EQUIPMENT...staff

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