Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 301408 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1008 AM EDT Fri Sep 30 2016 .SYNOPSIS... While high pressure remains across Quebec, low pressure will move along a nearly stationary front south of New England to bring cloudy, cool conditions with showers and patchy fog through this weekend. Another low moves east from the Great Lakes across New England early next week. High pressure then brings dry weather midweek. Attention then turns to Hurricane Matthew. Still uncertain what impacts our region will see, if any at all. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10am update... Inverted ridging and dry air aloft continues to keep band of overruning precip well offshore. However, noting new band forming along nose of LLJ E of the DELMARVA. This should be enough to increase overall column moisture such that rain can overspread the entire region from S-N by the afternoon and evening hours. Given these factors, the primary changes made with this morning`s update were to delay POPs until the afternoon. Previous discussion... First slug of precip working slowly NNW, heading toward central and eastern areas as seen on latest KBOX 88D radar loop. The precip is running into drier air across the region and higher pressure across northern New England in Quebec. Current radar trends suggest that the leading edge of the rain will reach the S coast by around 12Z, then move steadily across most of the region through midday. With drier air aloft across central and northern areas, will take a while for the rain to reach the ground. The area of showers is associated with PWAT plume as seen on short range models, on the order of 2 to 2.2 inches. So, once the airmass becomes saturated, may see some brief heavy downpours. Models are showing this plume will slowly move N as it pushes against the strong Quebec high. Strong E-NE pressure gradient in place with wind gusts up to 25-35 mph expected south of Boston down to Cape Cod and the islands where the highest gusts are forecast. Will be a cool, raw day with the E-NE winds in place. Highs will only reach the upper 50s to lower 60s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Tonight and Saturday...Weak low pressure will move along the front stalled south of New England, which will enhance the rainfall tonight into early Saturday. PWAT plume will remain just offshore, but will also help to enhance the rainfall especially across central and eastern areas. Current QPF amounts suggest rainfall of 0.5 to 1 inch may fall during this timeframe, with some locally higher amounts possible across E Mass into RI with the moisture rich airmass there. This will put a small dent into the long term drought across the region. Depending upon timing, could see the showers start to taper off across the CT valley late in the day, but low confidence on this timing with the blocking pattern in place. Temps will bottom out in the upper 40s across the higher inland terrain to the mid-upper 50s along the coast tonight. Highs Saturday will be mainly in the 50s to around 60 inland, ranging to the lower-mid 60s along the immediate coast. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Big Picture... Latest guidance remains in decent agreement with overall themes, and even some details through Tuesday. Beyond Tuesday though, have above normal uncertainty with the details, largely due to the large spread of model solutions for Hurricane Matthew. Still looking at a potent high pressure over the western Atlantic, with a cutoff low over the Great Lakes region this weekend. This cutoff low slowly lifts northeast into the Maritimes, while the high moves farther offshore toward the middle of next week. This leaves Hurricane Matthew in a position where it could make a run toward the East Coast late next week. At this time, favor a model consensus through Tuesday to smooth over the minor differences. Beyond Tuesday, favor a solution closest to the 00Z GFS, which is more in line with the official forecast for Hurricane Matthew. This is a storm which will bear watching over the next several days. Details... Saturday night into Sunday... We should still be dealing with a close upper low over the Great Lakes for much of this time. All signs still point to a significant onshore flow with abundant moisture. This should result in widespread showers during this time. Some of these showers could be locally heavy. Even when it`s not raining, we likely will not see any sunshine late this weekend. Rainfall chances slowly diminish Sunday. Monday into Tuesday... Upper low and cold pool moves overhead late Monday and Tuesday. This will generate some instability, but not enough for thunderstorms. Thinking scattered showers continue Monday, then slowly diminish Tuesday with the cold pool moving offshore. Surface wind flow will maintain a northeast direction, meaning near to below normal temperatures continue. Wednesday into Thursday... High pressure builds over our region from the Maritimes with dry weather and partly sunny skies. Northeast flow continues. As noted above, will need to keep an eye on Matthew for possible impacts late next week. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/... Today...High confidence. Will see mainly VFR VSBYS through midday across the region, then will lower to MVFR in showers and patchy fog moving from S-N, though will likely hold off across central and N Mass until tonight. MVFR CIGS running from near KLWM-KIJD southward with the low level moisture in place, which will lower to areas of IFR from S-N across the entire region by midday or early afternoon. Gusty NE winds to 25-30 kt continue along the east coast. Tonight...Moderate confidence. CIGS lower to IFR this evening, though timing may be later across N Mass. May see periods of LIFR CIGS across N CT/RI/SE Mass. Mainly MVFR VSBYS this evening, with areas of IFR moving across central and southern areas after 06Z- 08Z when steadiest rain moves in. NE wind gusts up to 25-30 kt continue along the coast. Saturday...Low to moderate confidence due to timing. MVFR-IFR CIGS/VSBYS, lowest across RI/E and central MA. May see areas of LIFR CIGS across higher terrain at times. NE winds continue to gust to around 25 kt. KBOS TAF...High confidence in trends, moderate confidence in timing. KBDL TAF...High confidence in trends, moderate confidence in timing. Outlook /Saturday Night through Tuesday/... Saturday Night into Sunday...Moderate confidence. MVFR/IFR cigs and vsbys in showers and fog. Northeast flow diminishing. Monday into Tuesday...Low confidence. Mainly VFR with areas of MVFR in scattered showers. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/... High confidence. Marine headlines continue, with gale warnings extended across RI sound and the outer waters S of Nantucket and the Vineyard with gusts up to 35-40 kt this afternoon and early tonight. Otherwise, small crafts continue through Saturday, but winds will gradually diminish. Seas remain high, up to 8-12 feet, highest across the southern outer waters today into tonight then will slowly subside from N-S but remain AOA 5 feet. Outlook /Saturday Night through Tuesday/... Persistent northeast winds through this portion of the forecast. Speeds diminishing Saturday night into Sunday, then increasing again toward Tuesday. Rough seas across the outer coastal waters diminish Sunday into Sunday night. Seas likely to build again Tuesday as winds increase. Small Craft Advisories will likely be needed at times during this time. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 PM EDT Saturday for ANZ232. Small Craft Advisory until noon EDT Saturday for ANZ233-234. Small Craft Advisory from 10 PM this evening to 8 AM EDT Saturday for ANZ230. Small Craft Advisory until 8 PM EDT Saturday for ANZ231-250- 251-254. Small Craft Advisory until 11 AM EDT Saturday for ANZ236. Gale Warning until 2 AM EDT Saturday for ANZ235-237. Gale Warning until midnight EDT tonight for ANZ255. Gale Warning until 5 AM EDT Saturday for ANZ256. && $$ SYNOPSIS...Belk/EVT NEAR TERM...Doody/EVT SHORT TERM...EVT LONG TERM...Belk AVIATION...Belk/EVT MARINE...Belk/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.