Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 282007 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 407 PM EDT Wed Sep 28 2016 .SYNOPSIS...
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Onshore winds will bring patchy drizzle and fog through tonight and into tomorrow morning with a brief break by tomorrow afternoon. A wave of low pressure passing south of the region will result in cloudy/cool weather with periods of showers Friday into Saturday, which may linger into Sunday. Some improvement in the weather is expected early next week, but still can not rule out a period of showers.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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4 PM Update... Overall trend in the forecast is on track for this afternoon. Persistent northeast flow will continue to saturate the low levels tonight and with dry mid-levels anticipate patchy drizzle to continue. Winds will continue to gust close to 15-25 mph as pressure gradient remains over the area. Tonight... Cut-off 500 mb low over the Great Lakes will begin to slide southward overnight. Offshore ridge remains across the North Atlantic while surface high pressure to the north will keep northeast flow over the region. Cross-sections show that the low levels will remain saturated during the overnight hours so anticipate drizzle to continue. Less confidence on fog potential as winds should remain a bit gusty overnight. Best area for fog is in the CT valley which could be sheltered from the wind. Drizzle could make it as far as the Worcester hills. Also kept the potential in for the east slopes of the Berkshires which could help enhance low level lift in upslope.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
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Tomorrow and tomorrow night... Interesting set-up tomorrow as 500mb cut-off low moves over the Tennessee Valley allow for upper level ridging to occur over the Northeast. In the mid-levels, appears that the high pressure will nose into northern New England with a nose of dry air intruding into northeast MA by late in the afternoon. This could result in a break from the drizzle and low clouds for a brief period. Southern New England appears to be on the edge for this dry nose so while Boston has the potential to possibly see the sun tomorrow, Hartford may struggle. This also has resulted in a temperatures spread in the forecast. If we do clear out then current temperatures will be to cool. Because of the uncertainty, did a blend in the guidance for temperatures. Cross-sections continue to show dry air moving into the area during the overnight hour. This could limit the amount of the clouds over the area. However there is also the potential for fog to develop overnight due to advection. Otherwise the focus then turns too the approaching wave rounding the upper level low. This wave will begin to spread precip into the region closer to the predawn hours of Friday.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Highlights... * Periods of showers and drizzle Fri into Sat with cool afternoons * Some showers and drizzle may linger into Sun * Drier weather Mon-Wed but a period of showers remain poss. Details... Friday and Saturday... Strong high pressure across eastern Canada will combined with a wave of low pressure emerging off the mid Atlantic coast. Although the surface low is not too strong, pressure gradient will result in a 925 mb easterly jet 2 to 3+ standard deviations above normal and gusty northeast winds along the coast. Timing uncertain, but expect periods of showers Friday into Saturday along with areas of drizzle/fog patches. While measurable rainfall will occur, its uncertain if 1+ inch amounts will make it into any of our region or remain to our south where better low level forcing resides. Onshore flow, clouds and periods of showers will keep high temps below normal for late September mainly in the upper 50s to the middle 60s. In addition, gusty northeast winds of 25 to 35 mph are expected along the coast and perhaps a bit stronger across Nantucket. Sunday... Initial wave of low pressure moves east of the region and low level jet weakens. However, surface high pressure over the Canadian Maritimes will still still generate a moist/northeast flow of air at the surface. Depending on the exact timing, some showers and drizzle will probably linger into Sunday especially along the eastern MA coast. High temps will likely remain below normal given lingering low clouds. Monday through Wednesday... Another high pressure system will build down into eastern Canada and northern New England early next week. While a shortwave may bring a period of showers, a good shot at dry weather for a decent portion of this time frame. Northeast winds at the surface much of the time will probably continue to hold high temps mainly in the 60s to perhaps near 70. We also will have to keep a close eye on what is expected to become Hurricane Matthew over the Caribbean in the next 24 hours. Most model guidance suggests this system will remain south of our region through Wednesday of next week.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
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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 Thursday Night/...Moderate confidence. 18z update... Today and Tonight. Gusty northeast flow between 20-25 kts will keep fog and drizzle across the eastern terminals through the period. Widespread MVFR cigs will continue this afternoon with areas of IFR along the coast. Conditions will fall tonight with IFR to LIFR cigs possible across most of the terminals. Vsbys restrictions are also possible in fog. Thursday into Thursday night. Northeast flow with gusts near 25-30 kts will continue into the period. Lingering IFR cigs possible with improvements during the day to MVFR. Dry air could nose into the northeast by late day improving conditions Thursday night. Still cannot rule out IFR potential along the south coast. KBOS TAF...Moderate confidence. High confidence in trends lower confidence in timing. KBDL TAF...Moderate confidence. High confidence in trends lower confidence in timing. Outlook /Friday through Monday/... Friday through Sunday...Moderate to high confidence. Mainly MVFR to IFR conditions in low clouds, periods of showers/drizzle and patchy fog. Northeast wind gusts of 20 to 30 knots expected Fri/Sat along the coast, and perhaps a bit stronger across Nantucket. Monday...Low to moderate confidence. May see improvement to mainly VFR conditions.
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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 Thursday Night/...High confidence. Northeast flow will continue across the waters well into Thursday night. Pressure gradient will continue to tighten resulting in gusts around 25 kts tonight increase to gales by tomorrow night. Gale watch has been posted where confidence is highest. Seas will slowly build in response up to 9-10 feet by tomorrow. Outlook /Friday through Monday/... Friday...Moderate to high confidence. High pressure across eastern Canada combined with a low pressure system exiting off the mid Atlantic coast. This will generate northeast wind gusts of 25 to 35 knots. Strongest of the winds across the southern waters, where Gale Watches are posted and seas are expected to build to between 8 and 11 feet. Saturday...Moderate to high confidence. Small craft headlines will be needed for all waters as pressure gradient will support northeast wind gusts of 20 to 30 knots. Sunday and Monday...Moderate confidence. Pressure gradient weakens so expect winds and seas to remain below small craft advisory thresholds.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Gale Watch from late Thursday night through Friday evening for ANZ232>234-254. Small Craft Advisory until 4 AM EDT Friday for ANZ232>234-254. Small Craft Advisory until 9 AM EDT Friday for ANZ230-231-236- 250-251. Gale Watch from late Thursday night through Friday evening for ANZ235-237-255-256. Small Craft Advisory until 2 AM EDT Friday for ANZ235-237-255- 256.
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&& $$ SYNOPSIS...Frank/Dunten NEAR TERM...Dunten SHORT TERM...Dunten LONG TERM...Frank AVIATION...Frank/Dunten MARINE...Frank/Dunten

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