Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260823 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 423 AM EDT Wed Apr 26 2017 .SYNOPSIS...
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Low pressure will slowly track up the east coast this morning bringing periods of rain. Low clouds along with some 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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 400 AM Update.... Overall trend in the forecast remains on track for early this morning. Next batch of precip is beginning to make its way onto the south coast as of 330 AM. This bulk of precip could drop near a half of an inch of QPF. Many areas across RI have already seen over 1.5 inches of rain so this will just continue to add. Will have to closely watch for nuisance flooding in the typically prone regions of Cranston/Warwick and eventually Fall River and New Bedford. Cannot rule out a rumble of thunder with the rain as models continue to show elevated instability with showalters dropping to below 0. However haven`t seen a bolt on the lightning tracker for quite some time, so confidence is low in a rumble of thunder. If convection does develop early this morning, then this will enhance the rainfall amounts for the morning commute. 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/...
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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.
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&& .AVIATION /08Z 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 Tonight/... Before 12z...High confidence. Mainly IFR conditions persist in widespread rain showers. Heaviest rain and greatest risk for isolated t-storms will be now through 12z Wednesday. LLWS will be a concern especially across the Cape and Islands. Today...Moderate confidence. MVFR-IFR CIGS continue with areas of - RA/RA and patchy fog, especially across the eastern half of southern New England. Reduced VSBYS likely, down to IFR 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, and possibly as far north as BOS, during the morning hours. 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.
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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 Tonight/...High confidence. Small Craft Advisories are in effect for all waters expect Boston Harbor and Narragansett Bay. Seas will remain above 5 feet with winds gusts near 20-25 kts into the afternoon. As the coastal low begins to move eastward, winds gusts will begin to subside and seas will relax. SCA will still be needed for ocean waters, but overall trend will be improvement. Could see vsbys restrictions across the waters tonight in 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 for 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...Small Craft Advisory until 3 PM EDT this afternoon for ANZ231>234. Small Craft Advisory until 9 AM EDT Thursday for ANZ235-237- 250-251-254>256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten MARINE...Belk/Dunten TIDES/COASTAL FLOODING...Staff

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