Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240855 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 455 AM EDT Tue Apr 24 2018 .SYNOPSIS...
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High pressure in control today will result in plenty of sunshine and another mild afternoon. Low pressure approaching from the southwest will bring a soaking rain to the region very late tonight and Wednesday with localized heavy downpours. This may result in some brief nuisance poor drainage street flooding. Seasonable temperatures follow Thursday through Saturday with mainly dry weather other than a few brief showers possible. A brief cool down expected on Sunday, but this will be short lived as unseasonably warm temperatures are possible by the middle of next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Bands of high clouds continue to stream across the region early this morning, though noting some breaks in the bands across W Mass into N CT on latest GOES-East night fog satellite imagery. With light S-SW or calm winds, quite a range in temps at 08Z, with 26 degrees reported at KMVY, 31 at KTAN ranging up to 46 degrees at KFIT. High pressure S of Nova Scotia that noses W back across S coastal areas early this morning will shift slowly E during the day. The ridge will hold in place so expect a dry day with filtered sunshine as the high clouds continue to move across. Will see low pressure slowly shift out of the Tennessee Valley to the Carolinas by this evening. Expect temps to rebound nicely away from the S coast as S-SW winds remain in place. Expect highs to range from the lower-mid 50s along the S coast to the 60s inland, and may see a couple of places reach 70. Some question as to whether a sea breeze briefly develops late this morning through midday along E coastal locations. At this point, looks like there will be enough of a S or SW gradient to keep it from developing.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
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Tonight... As the high shifts E, low pressure will develop near Chesapeake Bay and the Delmarva peninsula. This will cause winds to back to SE and start to increase. Noting a good low level moisture feed setting up with the developing SE fetch from the western Atlantic, which will moisten up the airmass. Will see area of rain to lift NE into western areas by around midnight, then steadily shifts E overnight. Swath of PWAT moisture on the order of 1 to 1.2 inches works across the region with the onshore flow. POPs approach categorical across most areas by daybreak. Best lift remains S and W of the region, so will see light rainfall, up to 0.2 inches across the lower CT valley by 12Z. With increasing clouds and dewpoints across the region, will see temps only bottom out in the 40s. Wednesday... Low pressure will hug the NJ/DE coast during the day, keeping a steady SE moisture feed working across the region. All models signal a good slug of rainfall moving across, especially across central and western areas. May see up to 0.5 to 1 inches of rainfall, with a good shot of a bit more across the eastern slopes of the Berkshires and Worcester Hills with a good upslope feed. Also noting very good instability axis crossing the region during the day as the low approaches with K indices to the lower 30s, LI values of zero to -1 and Total Totals around 50. Have continued to mention isolated thunder. With the convection, could see locally heavy downpours that may produce urban and poor drainage flooding. Rather strong SE low level jet, on order of 55-60 kt, but some question how much of this will mix down. May see some of this mix down along the S coast Wed afternoon, with gusts up to 25-35 kt possible.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Highlights... * Scattered showers Wed night with an isolated t-storm possible * Mainly dry+seasonable Thu/Fri/Sat other than a few brief showers * Dry and a bit cooler Sun with moderating temperatures by Mon * Unseasonably warm temps may arrive by the middle of next week Details... Wednesday night... The deeper moisture and forcing will push east of the region Wednesday evening, bringing an end to the widespread rain. However, upper level energy remaining west of the region coupled with surface boundary will result in scattered showers persisting well into the night. In fact...there is enough elevated instability for an isolated thunderstorm or two. Low temps will drop mainly into the upper 40s to around 50 and areas of fog are also anticipated. Thursday... Drier mid level air will be working into the region from the west allowing for partial sunshine. Given the mild start high temps should reach well into the 60s in most locales. Mainly dry weather anticipated...but shortwave/cold pool aloft will move across central and northern New England. We should be on the southern fringe of its main impacts...but given cold pool aloft a few brief showers are possible with the greatest risk north of MA turnpike. Friday and Saturday... Overall...seasonable weather continues for late April. While most of this period will feature dry weather, it is possible a wave of low pressure brings a brief period of showers late Friday if it tracks close enough to the coast. Greatest risk for this will be across southeast New England. As for Sat...while most of the time will be dry a cold front may bring a few passing showers Sat afternoon and evening. Highs Fri and Sat will mainly be in the 60s. Sunday and Monday... Dry weather behind the cold front with somewhat cooler weather Sun. Still a pleasant day though with highs mainly in the 50s to perhaps a few locales near 60 across southeast New England. After a cool start early Monday morning with many locales dipping down into the 30s...highs should recover into the 60s Monday afternoon as rising height fields begin the warming trend. In fact...much of our long range guidance is showing the potential for unseasonable warmth by the middle of next week with upper level ridging building over the eastern U.S.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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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 Wednesday/...High confidence. Through 12Z...VFR with SCT-BKN high clouds streaming in. Light S-SW or calm winds. Low to moderate risk of MVFR-IFR CIGS/VSBYS in patchy fog across outer Cape Cod, KMVY and KACK. Today...VFR. Prevailing wind from the S-SW, increasing to around 10 kt by midday. Tonight...Mainly VFR. Patches of MVFR conditions after midnight, with local IFR possible towards daybreak across CT valley. -RA moving across the area by around midnight across the CT valley, then shifting E after midnight. Wednesday...Conditions lower to IFR from W-E by midday, with local LIFR possible along S coastal terminals. SE wind gusts up to 25-30 kt across Cape Cod and the islands Wed afternoon. Isolated TSRA. LLWS along S coast Wed afternoon. KBOS Terminal...High confidence in TAF. Low risk for possible brief sea breeze late morning to midday today before S-SW winds increase. KBDL Terminal...High confidence in TAF. Outlook /Wednesday Night through Saturday/...Moderate to High confidence. Wednesday Night: MVFR/IFR conditions possible. Windy with local gusts to 30 kt across southeast New England coast during the evening with some LLWS. SCT SHRA, areas BR, isolated TSRA. Thursday: VFR. Slight chance SHRA. Thursday Night: VFR. Friday: VFR. Slight chance SHRA. Friday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Saturday: VFR. Breezy. Slight chance SHRA.
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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 Wednesday/... Through 12Z...High confidence. High pressure across the waters with S-SW winds 10 kt or less. Seas 1 to 2 feet. Good visibility. Today...High confidence. S-SW wind increasing with gusts to 20 kt. Seas 3 feet or less. Tonight...High confidence. Winds shift to SE and gusts up to 25 kt. Small craft advisories have been issued. Seas build to 5 ft on the southern outer coastal waters late. Visibility restrictions in patchy fog. Rain developing after midnight from W-E. Wednesday...Moderate confidence. SE winds gusting to 25-30 kt. Low risk of Gale force gusts on the eastern outer waters Wed afternoon. Seas build to 6 to 12 feet, highest on the southern outer waters. Visibility restrictions in areas of rain and fog. Isolated thunderstorms. Outlook /Wednesday Night through Saturday/...Moderate to High confidence. Wednesday Night: Small Craft Advisory winds with gusts up to 30 kt and a low risk for a few 35 knot gusts early in the evening across the southeast waters. Rough seas up to 13 ft. Chance of rain showers, areas fog, isolated thunderstorms. Visibility 1 to 3 nm. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Slight chance of rain showers. Thursday Night: Winds less than 25 kt. Rough seas up to 9 ft. Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Friday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers. Saturday: Winds less than 25 kt. Seas up to 5 ft.
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&& .FIRE WEATHER...
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Dry conditions with minimum RH values of 15 to 25 percent away from the immediate coast are expected today. South to southwest winds will gust up to 15 to 20 mph with some brief gusts up to 25 mph possible this afternoon.
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&& .EQUIPMENT... The NOAA Weather Radio transmitter serving Providence is out of service due to phone line problems. The phone company has prioritized the issues and is working to get the weather broadcast back on the air as soon as possible. The transmitter serving Hyannis is back in service. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 4 AM to 6 PM EDT Wednesday for ANZ231-232-235-237-254. Small Craft Advisory from 7 AM to 6 PM EDT Wednesday for ANZ233-234. Small Craft Advisory from 9 AM to 6 PM EDT Wednesday for ANZ236. Small Craft Advisory from 8 AM to 6 PM EDT Wednesday for ANZ250. Small Craft Advisory from 3 AM to 6 PM EDT Wednesday for ANZ255-256.
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&& $$ SYNOPSIS...Frank/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/EVT MARINE...Frank/EVT FIRE WEATHER...EVT EQUIPMENT...Staff

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