Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180007 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 707 PM EST Fri Feb 17 2017 .SYNOPSIS... Tonight will be dry and near seasonable, then milder and continued dry weather is expected through this weekend. A cold front swings through Southern New England Sunday night. Another cold front moves through on Wednesday. Otherwise, expect dry weather through the week. A brief cool down is expected early in the week, followed by milder air the rest of the week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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7 pm Update... Patches of high clouds are moving southeast across the region. additional high clouds are upstream in Ontario Canada and moving southeast. Expect off/on high clouds through the night. Dew points were adjustes 2-3F lower based on 6 pm observations. No other significant change to the forecast. Previous discussion... Surface high pressure brought abundant sunshine this afternoon, allowing for near seasonable afternoon highs in the mid and upper 30s, some areas even in the low 40s. NW winds have kept surface dew points on the low side...in the teens across much of the area, some locales saw dew points slip below 10 degrees with the 4 pm obs. Continue to anticipate some mid and high-level clouds passing through our region overnight, with a warm front approaching from the west. Looking at satellite imagery and latest guidance, thinking that cloud cover will will initially be more scattered in nature, then more considerable cloudiness late evening and on. Due to the combination of snow-covered ground, winds becoming light, low surface dew points and initial mostly clear skies this evening, this should allow temps to drop quickly after sunset. So have trended towards colder MAVMOS guidance, with lows in the teens to low 20s for much of the area, except a few degrees warmer in the Boston area, and along the south coasts of MA and RI.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday and Saturday night... Warm front lifts northward across the area in the morning. Looking at a mild day with a mix of sun and clouds. Mixing somewhat limited, however the S flow should drive warmer air across the region pushing highs well into the 40s, despite the snowpack across the region, with possible 50s in the Connecticut River Valley region in north Central CT. The combination of increasing dewpoints from the south along with snowmelt will yield a fairly moist, shallow boundary layer environment that pools beneath the building dry, subsidence inversion. Continued to go mild on forecast dewpoints. With temperatures dropping overnight, the potential exists for some areas of low clouds and fog. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Big Picture... Pattern shows northern and southern jet streams for the weekend. This breaks down a little in the Plains early next week with more of a meridional pattern which shifts into the Eastern USA midweek. As long as there is a distinct southern jet intercepting Gulf moisture our likely weather is moisture-starved. When this weakens midweek we see a brief window for measureable pcpn. Otherwise a dry period. Longwave pattern shows building ridge over the Eastern USA and digging trough over the West. Heights over New England show above normal values through the period, which suggests warmer than normal temps. One northern stream shortwave sweeps through late Sunday- Monday bringing crashing heights and brief colder temps. Ridge and building heights return Tuesday. So a brief cool-down expected early week followed by a return trend to above normal during midweek. Model mass fields are similar through Tuesday but then diverge. Differences are mostly in details rather than the general pattern. Confidence for the long term is moderate to high, with highest confidence Sunday and diminishing confidence with time. Details... For the most part, a quiet period for weather. Sunday through Tuesday... Dry weather Sunday as low pressure passes north of New England. Temps at 925 mb cool a degree or two, but nothing fantastic. Mixing to 925 mb would support max temps 40-45, mixing to 900 mb would support 45-52. Shortwave from the Canadian Prairies moves east and connects with a closed low over Newfoundland. This connection then sweeps the shortwave southeast over New England Sunday night and Monday morning. Limited low level moisture with the shortwave may bring a few clouds. High pressure builds in later Monday and moves overhead Tuesday. Winds become light and variable Tuesday, possibly some southerly flow Tuesday afternoon. Temps moderate a few degrees each day. Temps 20 to around 32 Sunday night and 15 to 25 with radiational cooling Monday night. Clouds and a southerly flow suggest milder temps Tuesday night. Wednesday... Cold front over the Great Lakes moves across New England. Not a lot of moisture available, but enough to mention a low probability of showers during the day. A southerly flow and temps at 950 mb suggest mild temps in the 40s. If the sun Thursday-Friday... High pressure builds surface and aloft Thursday bringing dry weather. Temps at 950 mb and 925 mb suggest max sfc temps in the low to mid 50s. Weather system that reaches the West Coast midweek races east across the country. Models show differences in timing with the GFS fastest, but all show a low level southwest jet ahead of the system overrunning a southeast surface flow over New England either Friday or Friday night. The uncertainty is whether this overrunning takes place over Southern New England or Northern New England. Expect dry warm sector weather if the latter. We will show slight chance pops in our eastern zones and low-end chance pops in the East Slope and CT Valley zones. Better chance of showers with the main weather system after Friday night. && .AVIATION /00Z 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 Range /through Friday night/...High confidence. Tonight...High Confidence. VFR. Winds becoming light out the W/SW. SCT-BKN mid and high level clouds. Saturday into Saturday Night...Moderate Confidence. W/SW flow becoming breezy. Potential for 25 kt gusts over the Cape and Islands. Low confidence concerning the potential presence of IFR low clouds and/or fog overnight. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Sunday through Wednesday/...Moderate confidence. Sunday through Tuesday... Generally VFR. A cold front moving through Sunday night could bring brief MVFR cigs. 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.
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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 Range /through Saturday night/...High confidence. Diminishing W/NW winds although gusts to 25 knots and seas 3 to 5 feet linger on outer coastal waters thru midnight. Expect existing Small Craft Advisories to expire during the night. Initially good boating weather Saturday morning across the waters with winds/seas below SCA thresholds. However, looking at a renewed period of SCA conditions Saturday afternoon and night. SW winds expected to increase Saturday afternoon with gusts around 25 knots, and seas on the outer waters building to 4 to 6 feet for Saturday night. Outlook /Sunday through Wednesday/... Moderate confidence. Sunday... Low pressure passes north of New England, swinging a cold front across the waters Sunday night. West-Northwest winds gust to 25 knots. As the front moves through, winds will shift from the North overnight. Sea heights overnight will climb to 5-6 feet on the outer waters. A Small Craft Advisory may be needed. Monday-Tuesday... North winds gust 25 to 30 knots Monday, diminishing Monday night and Tuesday as high pressure builds overhead. Seas east of Cape Cod and Nantucket start Monday at 5-6 feet, but diminish Monday night and Tuesday. Seas on the remaining waters should be less than 5 feet. Small Craft Advisory may be needed Monday. Wednesday... A cold front will cross the waters later Wednesday. Increasing south-southwest winds ahead of the front. Winds then shift from the west after the cold front goes through. Winds should remain at 20 knots or less, and seas less than 5 feet.
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&& .EQUIPMENT...
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7 pm update...KBOX radar is off-line again.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ231-250- 251-254-255. Small Craft Advisory until 10 PM EST this evening for ANZ256.
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&& $$ SYNOPSIS...WTB/NMB NEAR TERM...WTB/NMB SHORT TERM...NMB LONG TERM...WTB AVIATION...WTB/NMB MARINE...WTB/NMB EQUIPMENT...

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