Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 161103 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 703 AM EDT Wed May 16 2018 .SYNOPSIS... High pressure builds to our north Wednesday and brings cool east winds to our area, with lower temperatures. Summer returns Thursday with dry weather. Cooler weather for Friday with showers moving in by the later half of the day. Widespread heavy rainfall Friday night into Saturday followed by hit or miss showers on Sunday and Monday. Dry weather returns by Tuesday of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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700 AM Update... Overall trends are generally on track. Any radiational fog early this morning is beginning to burn off thanks to mixing and the high sun angle. Some light radar echoes are moving across the south coast, cannot rule out a sprinkle or light rain shower, but they are moving quickly so little impacted is expected. Currently there is a weak mid-level ridge over the region. This is keeping bulk of any precipitation at bay this morning as passing front yesterday remains to our south. However, water vapor imagery shows shortwave moving through the flow which is enhancing rain showers along the stalled front. These showers will make their way into southern New England late this morning into the afternoon. Locations along the south cost will have the best chance, but expect showers everywhere towards evening/overnight as the upper level wave passes across the region. Last think to note, winds are already beginning to switch from the north to the northeast as high pressure over ME slides eastward. This easterly flow will keep locations along the east coast cooler with highs well below average. Tight pressure gradient ongoing has also helped enhanced the wind gusts with BOS quickly gusting to 25 kts. These quick gusts will continue into the early morning hours, but should subside towards noon. Previous Discussion... Expecting a much more quiet day weather-wise across southern New England than Tuesday. High pressure over Quebec will veer winds over to the east by late this afternoon. Still thinking a dry day for much of our region, except for an increasing risk for showers towards the south coast of New England as a nearly stationary front tries to retreat northward, especially later this afternoon. Thinking more clouds to start out today and onshore winds will result in below normal max temperatures.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... High pressure to our north maintains a light easterly flow into our region. This will in turn slowly raise dewpoints tonight into Wednesday. A weak wave translating along the front just to our south may provide the needed lift to tap into this low level moisture and generate some showers. The greatest risk for any showers would be towards the South Coast and the islands. Drier weather should return Thursday. Temperatures expected to be near to above normal during this time. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Widespread heavy rainfall Friday night into Saturday * Hit or miss showers on Sunday and Monday with warming trend * Dry weather returns by Tuesday of next week Details... Thursday night into Monday...Moderate confidence. Building sub-tropical ridge over Bermuda will begin to push high PWAT air towards the region starting on Friday. Guidance continues to indicate low pressure from the Ohio Valley moving into the Great Lakes with a slow moving frontal system associated with the low. This front will stall south of the region on Friday thanks to passing surface high pressure associated with the northern stream. However, by Friday night and into Saturday, this front and associated low pressure systems will push into the region resulting in widespread rain showers. Several shortwave moving through the southwest flow will result in on and off showers and perhaps some thunder on Sunday with another chance on Monday with passing cold front. This system over the weekend will have tropical connections as its moisture will work northward into the region. However, latest trends suggest that the heaviest rainfall through the entire event will remain just south of the region. Keep in mind that this wavy frontal system could inch closer to the region increasing the heavy rainfall chances, or could move father south. For now continued with a blend of the guidance and ensembles. Overall flood threat is low for rivers/streams since flows are currently near or below normal for mid May, but this could present flood issues for urban/ poor drainage areas if heavier rainfall materializes. Cooler conditions on Friday and Saturday north of the front, warm and moist on Sunday and Monday as the region will be south of the front. Tuesday and beyond...Moderate confidence. Conditions should be improving as upper level trough pushes cold front through the region Monday night/early Tuesday. Surface high pressure from Canada will move into the region resulting in dry weather and seasonal conditions into Thursday. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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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/...Moderate confidence. Today...Mainly VFR, with areas MVFR possible South Coast. Breezy. Chance SHRA south of the Pike late this morning into the afternoon. Best chance for possible IFR is across the Island in heavy rain. Tonight...Low end MVFR/IFR conditions in stratus and fog developing with onshore flow. Thursday...Conditions improving to VFR early. KBOS Terminal...Moderate confidence in TAF. Need to monitor potential for brief IFR cigs or vsby once winds turn NE this morning. KBDL Terminal..High confidence in TAF. Outlook /Thursday Night through Sunday/...Moderate confidence. Thursday Night: VFR. Breezy. Slight chance SHRA. Friday: VFR. Breezy. Chance SHRA. Friday Night: Mainly MVFR, with areas VFR possible. Breezy. SHRA likely. Saturday: Mainly MVFR, with areas IFR possible. Breezy. SHRA likely. Saturday Night: MVFR/IFR conditions possible. SHRA likely. Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA.
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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 Thursday/...Moderate confidence. Winds and seas slowly diminish today, and generally remain below Small Craft Advisory thresholds tonight and Thursday. Chance of rain showers on the southern waters later today into tonight. Outlook /Thursday Night through Sunday/...Moderate confidence. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain showers likely. Saturday: Winds less than 25 kt. Seas up to 5 ft. Rain showers likely. Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Sunday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ254. Small Craft Advisory until 7 PM EDT this evening for ANZ255- 256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Belk LONG TERM...Dunten AVIATION...Belk/Dunten MARINE...Belk/Dunten

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