Area Forecast Discussion
Issued by NWS Boston, MA

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141 FXUS61 KBOX 212327 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 727 PM EDT Fri Apr 21 2017 .SYNOPSIS... Low pressure tracks through southern Quebec tonight, with a secondary low pressure passing south of New England. Onshore winds will keep low clouds, fog, and patchy rain and drizzle in the area tonight. Drying Saturday as low pressure south of Nantucket moves out to sea. Weak high pressure provides dry weather Sunday into Monday. A coastal low may bring more rain Monday night into Wednesday of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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7 pm update... No significant changes with this evening`s update. WV imagery showing large extent of mid lvl dry air and subsidence across the region meanwhile a fair amount of moisture remains trapped especially at or below H7. This will lead to the continuation of a mix of low clouds/fog and drizzle mixing with SHRA overnight even as a secondary front washes out with energy transfer from the N New England low to offshore triple point low. Therefore another soupy night for S New England, although with the likelihood of some breaks forming by the morning hours as drier air gets pushed in behind the newly deepening low and begins to scour out the low-lvl moisture. Previous discussion follows... Radar indicated very light rain and drizzle lingered across eastern MA and RI, with surface obs showing light rain as far west as ORH, and drizzle in the Springfield to Hartford corridor. This light precipitation will persist thru the remainder of today. Models show area of low pressure passing west to east through southern Quebec late this afternoon and tonight. A secondary low pressure passes south of New England late this afternoon and tonight, eventually becoming somewhat deeper than the Quebec low. Between the two systems, an occluded front approaches our area from the west. Although mid level moisture is lacking, abundant low level moisture remains in place tonight. Low clouds and areas of fog are expected to persist. An east/northeast onshore flow continues through midnight, then as the occluded front moves thru the winds transition to north and possibly northwest. Models continue to advertise the potential for light rain/showers in our area this evening, hence keeping chance to low likely pops for tonight, mainly before midnight and ahead of the occluded front. The slight wind shift from east to north behind the front should help to lower precip chances. Temps remain nearly steady in the 40s.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... Weak low pressure southeast of Nantucket slowly moves out to sea with mid level dry air overspreading the region. There may be a weak secondary circulation that passes south of our region. Model soundings show that it may take some time for the low level moisture to erode during the day, so initially on Saturday low clouds and patchy fog should remain in place. Then some brightening, but partly to mostly cloudy skies persist with diurnal stratocumulus taking the place of the low stratus. Can`t rule out a shower or two but overall looks to be a dry day. High temps mainly in the 50s to low 60s. Saturday night... Anticipating high pressure moving into the area allowing for partial clearing overnight. With light northwest winds, temperatures expected to fall into the upper 30s to low 40s, with some mid 30s possible in the far interior. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Big Picture... A coastal storm moves up the Atlantic seaboard early next week, bringing periods of heavy rain to the region for Tuesday and Wednesday. Above normal temperatures return late next week. Details... Sunday... Sunday will be mostly dry with broken skies throughout the day. Winds will be predominately southwesterly, as temperatures range from the mid 50s to mid 60s across the region. Winds will begin to shift as a cold front approaches from the northwest and a low pressure system strengthens over the Carolinas. Temperatures will drop into the 40s overnight as the cold front sweeps down from the Great Lakes and across Southern New England. Monday... The cold front will make its way across the region by 15z Monday, keeping temperatures in the 50s. The approaching low pressure storm strengthens along the Atlantic coast, causing winds to become northerly over New England. With cold air advecting from the north, overnight temperatures will drop into the upper 30s and lower 40s. The chance for rain showers increases along the southern coast Monday night as the coastal low moves north towards the region. Winds will also pick up ahead of the coastal low Monday night, producing wind gusts up to 25 mph through Tuesday morning. Tuesday... Tuesday will start out with strong wind gusts along the southeastern coast of New England as the coastal low approaches from the south. Northeasterly winds may gust up to 30mph at times along the coast Tuesday, gusting up to 20 mph inland as well late that morning. These strong winds will pull colder air from Canada over New England, making for unseasonably cool temperatures throughout the day. Afternoon temperatures are only expected to reach into the low 50s Tuesday. Rain showers become likely Tuesday afternoon, especially along the Eastern coast of Massachusetts. Rain and gusty winds will continue through the night Wednesday... The coastal low will be just south of Long Island early Wednesday morning as rain continues across most of the region. Winds will become northeasterly and continue to gust up to 30 mph along the coast, but slowly diminish inland. Skies will be cloudy throughout the day and temperatures may reach into the low 60s Wednesday afternoon. As the coastal low continues to move northeast along the Atlantic coast, winds and rain showers begin to diminish along the coasts. One key note for the Tue-Wed timeframe will be tides. With new moon approaching, tides will be astronomically high, reaching 11.5 ft Tue night and 11.9 ft by Wed for Boston. E-NE flow and building seas related to the slow coastal system could yield some coastal flooding issues. Still time to refine details, but this will need to be watched. Thursday and Friday... Rain showers may linger early Thursday morning along the eastern coast as the coastal low continues north along the coast. Skies will slowly begin to clear behind the system as dry weather and warmer temperatures return. Temperatures will be above normal for much of Thursday and Friday as winds become southwesterly once more. && .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 Term /through Saturday Night/... Overnight...High confidence. No significant changes with 00Z taf update. Expecting mainly a mix of IFR/LIFR across all terminals through early AM hours. This will be in a mix of low CIGS as well as occasional fog/drizzle reducing vsbys. Some improvement from W-E mainly after 09Z. Saturday...Moderate confidence. Mix IFR gradually trends toward MVFR W-E early with low risk of spotty light rain...then trending upward to VFR during the afternoon along with dry weather likely, may take until late afternoon/evening for portions of E MA to reach VFR. KBOS TAF...Continued high confidence in trends, but moderate confidence on exact details including timing, especially in regards to visibility. Steady -RA transitioning -RA after 16Z. For much of today into tonight, IFR-LIFR prevails. KBDL TAF...Moderate confidence in timing and trends. MVFR cigs with improved vsbys probable thru 18Z, then should see a return to IFR conditions later in the day. Saturday night...Moderate confidence. Ceilings clearing as winds initially shift out of the W. Lingering low-end VFR / MVFR. Outlook /Sunday through Wednesday/... Sunday...High confidence Higher cigs with VFR. Light southerly winds and broken skies throughout the day. Dry conditions throughout the day. Monday...Moderate confidence VFR starts. Lowering cigs towards MVFR/IFR by evening with increasing chances of -RA. Increasing easterly flow with potential for gusts around 20 kts. Tuesday...Moderate confidence MVFR/IFR conditions along the eastern coast as heavy rain approaches from the south. Strong northeasterly winds gusting up to 30 knots along the coast, and 20 knots inland. Wednesday...Moderate confidence. Conditions will gradually improve Wed out of the IFR/MVFR. Remaining in lower categories longest across E MA/RI.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. Tonight... Winds initially gusting around 25 knots on the waters with the exception of Boston Harbor and Narragansett Bay. Winds should diminish nearshore by midnight. However rough seas will linger on the waters with a weak low pressure passing south of New England. Thus SCA headlines continue for the outer coastal waters and Mass Bay during the overnight. Areas of rain, drizzle and fog expected tonight. Saturday... Low pres passes southeast of Nantucket and exits seaward with improving visibility during the day. However SCA headlines continue for the outer coastal waters due to rough seas associated with the low. Saturday night...Moderate confidence. High pressure in control. Light winds overall across the waters. Lingering swell may occur on the eastern outer coastal waters, SCA headlines may need to be continued. Outlook /Sunday through Wednesday/... Sunday...High confidence High pressure in control. Light winds overall across the waters. Wave heights generally below 3 feet. Monday...Moderate confidence Coastal low tracking N along the E coast. Wind gusts up to 20 kts in the southern waters. Increasing winds could result in seas building up around 4 feet. Tuesday...Moderate confidence Strong northeasterly winds gusting up to 30 knots and wave heights reaching up to 7 feet on the outer waters. Small craft advisories are likely with a low risk for Gales. Wednesday...High confidence. Improving weather on the waters. Seas gradually diminish as they shift to the N, dropping below small craft thresholds by afternoon. Seas, although diminishing will remain at or above 5ft through the day, so advisories may linger due to the seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ231>235- 237. Small Craft Advisory until 8 PM EDT Saturday for ANZ250-254- 255. Small Craft Advisory until noon EDT Saturday for ANZ251. Small Craft Advisory until 3 AM EDT Saturday for ANZ256. && $$ SYNOPSIS...Doody/Correia/NMB NEAR TERM...Doody/NMB SHORT TERM...NMB LONG TERM...Doody/Correia AVIATION...Doody/Correia/NMB MARINE...Doody/Correia/NMB

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