Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261813 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 213 PM EDT Wed Apr 26 2017 .SYNOPSIS... Low pressure will slowly track northeastward this afternoon, 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/... 18Z Update... Weakening stacked low pressure center was centered south of Long Island at 18Z, drifting northeastward. Warm front extended from approximately Westerly RI to Marshfield MA, with a coastal front component that pushed thru Boston and Beverly. On the warm side of the front, surface dewpoints were 55 to 60, with an ESE/SE wind. HRRR shows this front should remain nearly stationary late this afternoon before becoming less discernible this evening. Moisture convergence along the front will allow for continued chances for showers this afternoon and into this evening, especially within RI and eastern MA. Abundant low level moisture will also allow for areas of fog and drizzle. Fog will be locally dense this afternoon and into this evening along east coastal MA and coastal RI, with visibility below 1/2 mile at times. Winds have diminished somewhat on the southeast side of the front. Gusts 20 to 30 mph still possible Cape/Islands thru mid afternoon, gradually diminishing. && .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 /18Z WEDNESDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... This afternoon...Moderate confidence. Mainly IFR/LIFR CIGS/VSBYS in low clouds, drizzle, areas of light rain and fog. Exception may be BDL/BAF and vicinity, with MVFR conditions for a period of time this afternoon. Fog may be locally dense this afternoon within east coastal MA and south coastal RI, with localized vsbys 1/2 mile or less at times. Tonight...Moderate confidence. IFR/LIFR conditions continue in areas of fog and drizzle. A few showers are possible. KBOS TAF...Moderate confidence in TAF, moderate confidence in timing. KBDL TAF...Moderate confidence in TAF, moderate confidence in timing. Outlook /Thursday through Sunday/... Thursday...Moderate confidence. IFR/LIFR conditions likely into the morning hours with areas of fog, patchy drizzle and a spot shower. Lower conditions most likely along 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... 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. && .TIDES/COASTAL FLOODING... * Isolated minor coastal flooding impacts during astronomically high tide tonight along the east and south coasts We are in 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 tonight. 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 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)... 11.92 feet / Thursday 12:07 am Providence High Tides (flood stage at Providence 7 feet)... 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 is the U.S. government's official web portal to all federal, state and local government web resources and services.