Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261602 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1202 PM EDT Wed Apr 26 2017 .SYNOPSIS... Low pressure will slowly track northeastward today, bringing areas of rain, drizzle and fog. Then low clouds, drizzle and fog are expected to linger tonight into Thursday especially along the coast. Very mild to warm afternoons should return Friday and Saturday, with a low risk for a few showers/thunderstorms. Much cooler weather follows Sunday, especially on the coast. Another cold front will likely bring more showers to the region sometime Monday into Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Weakening surface low was centered east of the New Jersey coastline, heading slowly northeast. Warm front had lifted into southeast MA, noted by a wind shift to the southeast, surface dew points 55 to 60, and gusts of 25 to 35 mph. Have updated forecast to reflect the warmer and more humid conditions south of the front, with some higher wind gusts for today. Otherwise across southern New England, patchy light rain and areas of drizzle and fog are expected to continue thru this afternoon. Continuing to moinitor reduced visibilities in fog, visbility has lowered to 1/2 mile or less in some portions of southeast MA/RI. Early morning discussion for Today... Stacked surface low pressure system near the Mid-Atlantic will move towards southern New England today. Continuous southerly flow aloft will continue to pump moisture into the region through the day. Appears that surface warm front will try to move in, or may just stall across the area. This will result in difference in temperatures. For now continued with a blend in the guidance. The main bulk of precip will lift this morning. However, still some weak lift and with a very saturated moisture profile, anticipate on and off showers late this morning and into the afternoon hours. Increasing dewpoints across the south coast could lead to patchy fog development. Low confidence on how low vsbys will go, but something to watch through the day. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... Wednesday night... Stacked low pressure system will begin to move south and east of the region. 850 mb becomes more of a open wave resulting in a more weaken system. Upper levels appear to begin to dry out as the low begins to move, however, at the surface and mid-levels, the profile is quite saturated. Anticipate a soupy mess with low clouds and fog. Will have to watch for vsbys dropping below a quarter of a mile which would result in a dense fog advisory. Confidence is low at this time, but something to watch. Continuous easterly flow overnight combined with some weak lift will result in areas of drizzle especially across eastern locations. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Low clouds/spotty drizzle Thursday with cooler temps on coast * Mild to warm afternoons Fri/Sat with a low risk for a few thunderstorms * Backdoor cold front brings much lower temperatures by Sunday * Period of showers, which may be briefly heavy, sometime Mon/Tue Details... Thursday... Still dealing with a persistent mid level low near Nantucket Thursday morning, while the surface low pressure is slightly farther northeast. This will mean light onshore flow with lots of low level moisture. Expecting cloudy skies with areas of drizzle and fog, particularly across eastern MA. As noted by the previous forecaster, MOS guidance is likely a little too high with max temperatures Thursday. Used the lower consensus of raw model 2 meter temperatures for max temperatures. Friday and Saturday...This will be a tricky portion of the forecast. An approaching cold front should become parallel to the mid level flow, stalling somewhere just west of our region. This should mean a persistent southwest flow, and much higher temperatures than the past couple of days. Expecting max temperatures in the 70s degrees away from the south coastal areas on both days. However, these higher temperatures will combine with decent mid level lapse rates to produce a low risk for thunderstorms. Right now, Friday appears to have the greater risk of these two days, as mid level dry air may be in place for Saturday. This could all change should the stalled front shift closer to southern New England. Saturday night and Sunday... A strong high pressure moves over eastern Canada, dominating the blocking high pressure to our southeast. This push from the northwest should be enough to drive the stalled front just to our south, resulting in much lower temperatures, on the order of 15-20 degrees lower Sunday afternoon. Monday and Tuesday... A stalled front to our south should return as a warm front sometime Monday into Tuesday as a low pressure moves from WI into southeast Canada. The timing is still uncertain, as a strong high pressure should be over Labrador. Should this high linger longer than currently forecast, then the precipitation timing will be also off. Still looking like another prolonged window for periodic showers. Rainfall could be moderate to heavy at times. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Today...Moderate confidence. Mainly IFR CIGS, with local MVFR CIGS, continue with areas of -RA/-DZ and patchy fog, especially across the eastern half of southern New England. Reduced VSBYS likely, down to IFR/LIFR in spots. May see areas of LIFR CIGS across the higher inland terrain and along the coast. SE winds gusting up to around 25 kt across Cape Cod and the islands. LLWS impacts for the Cape and islands during this morning. Tonight...Moderate confidence. MVFR-IFR conditions continue in areas of fog and drizzle. A few showers are possible. KBOS TAF...High confidence in TAF, moderate confidence in timing. KBDL TAF...High confidence in TAF, moderate confidence in timing. Outlook /Thursday through Sunday/... Thursday...Moderate to high confidence. IFR to even LIFR conditions likely into the morning along with some fog, drizzle and a spot shower. Lower conditions most likely on the coast. Conditions may improve to mainly MVFR by late Thu morning and afternoon. Thursday night and Friday...Moderate confidence. MVFR/IFR conditions likely in areas of low clouds and fog patches into early Friday morning. Improvement to VFR likely by Friday afternoon, with the low risk for a few showers and perhaps a thunderstorm. Saturday and Sunday...Moderate confidence. VFR conditions. && .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 Tonight/...High confidence. Gale Warning issued for the southeast coastal waters thru 4 pm, including Nantucket Sound, Vineyard Sound and Buzzards Bay, and the adjacent outer coastal waters. This portion of the coastal waters is southeast of a warm front, allowing for some mixing with the stronger winds aloft. Those stronger winds aloft are expected to weaken later this afternoon, which will allow surface gusts to lower. For the remainder of the waters, Small Craft Advisories are in effect expect for Boston Harbor and Narragansett Bay. Seas will remain above 5 feet with winds gusts near 20-25 kts into the afternoon. As a coastal low begins to move eastward, winds gusts will begin to subside and seas will relax. Small Craft Advisories will still be needed for ocean waters, but overall trend will be improvement. Visibility restrictions at times across the waters this afternoon and tonight in locally dense fog. Outlook /Thursday through Sunday/...Moderate confidence. Winds are not expected to be be a concern through this portion of the forecast, generally remaining less than 20 kt. The main issue will be how long it takes for lingering swell from the persistent low pressure near the waters to diminish. Small Craft Advisories are likely to be needed across the outer coastal waters. In addition, areas of drizzle, fog or rain will lead to some visibility restrictions on the coastal waters into Friday.
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&& .TIDES/COASTAL FLOODING... * Isolated minor coastal flooding impacts during astronomically high tides through tonight along the east and south coasts We are entering a spring tide cycle with high tides that are astronomically high. This combined with an anticipated storm surge of around 1 foot may set the stage for isolated pockets of minor coastal flooding along both south and east coasts around the time of high tide this morning, and again tonight. Went ahead an issued a new Coastal Flood Statement for potential splashover. There is also the combination of runoff from heavy rain and elevated water levels near high tide this morning, which could exacerbate drainage of fresh water in some coastal urban areas, and near the mouths of streams and small rivers. We will need to continue to monitor the tides through at least Wednesday night as there is not a significant offshore flow or pressure rises to help evacuate a lingering surge. The astronomical high tides remain very elevated through the end of the week. Due to the breadth of the fetch, we may encounter enough wave action with lengthening periods on top of an elevated tide to cause pockets of erosion tonight through tonight along the Martha`s Vineyard south coast, Nantucket south and east coasts, and the outer Cape ocean side from Truro to Chatham. Boston High Tides (flood stage at Boston 12.5 feet)... 11.47 feet / Tuesday 11:20 pm 11.15 feet / Wednesday 11:50 am 11.92 feet / Thursday 12:07 am Providence High Tides (flood stage at Providence 7 feet)... 5.98 feet / Tuesday 8:11 pm 5.53 feet / Wednesday 8:41 am 6.21 feet / Wednesday 9:00 pm && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning until 4 PM EDT this afternoon for ANZ232>234-254- 255. Small Craft Advisory until 8 PM EDT this evening for ANZ231. Small Craft Advisory until 9 AM EDT Thursday for ANZ235-237- 250-251-256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten/NMB SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten/NMB MARINE...Belk/Dunten/NMB TIDES/COASTAL FLOODING...Staff

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