Area Forecast Discussion
Issued by NWS Boston, MA

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416 FXUS61 KBOX 290303 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1103 PM EDT Wed Sep 28 2016 .SYNOPSIS... Onshore winds will bring patchy drizzle and fog across southeast New England into Thursday morning with a brief break by the 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. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 1045 PM Update... Low clouds and patchy fog and drizzle continues across the region Noting somewhat drier air trying to work SW down the Maine coast into Cape Ann at 02Z. Gusty NE winds continue across E Mass into coastal RI as well, with strong high pressure across Quebec, combining with low pressure over the Ohio valley. Will continue to see cool, raw conditions overnight with the persistent onshore wind, especially across eastern areas. Some question as to whether drier air will push into N Mass after 06Z which may bring partial clearing and cooler temps. Have updated near term forecast to bring conditions current. Previous Discussion... Large/strong high pressure will continue to build south from eastern Canada tonight. Mid levels of the atmosphere are quite dry, so not expecting more than patchy drizzle tonight mainly across RI/SE MA where low levels are quite saturated. Given an abundance of low clouds and northeast winds, temps will only fall a few degrees from their current readings. Lows should bottom out mainly in the upper 40s to the middle 50s. Pressure gradient will allow for gusty northeast winds between 20 and 30 mph along the coast tonight. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... 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. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... 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. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... 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. Overnight...MVFR Cigs will remain across the region, but some IFR conditions expected across southeast MA/RI as well as the Worcester Hills. Northeast wind gusts of 20 to 25 knots expected along the coast. 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 to high confidence in TAF. KBDL TAF...Moderate to high confidence in TAF. 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. && .MARINE... 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 between 25 and 30 kts overnight, increasing to gales by Thursday night across the southern waters. Gale watch has been posted where confidence is highest. Seas will have already increased to around 10 feet across the eastern waters, mainly in swells. 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. && .BOX WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...Frank/Dunten NEAR TERM...Frank/EVT SHORT TERM...Dunten LONG TERM...Frank AVIATION...Frank/Dunten/EVT MARINE...Frank/Dunten/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.