Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 300852 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 452 AM EDT Fri Sep 30 2016 .SYNOPSIS... A low pressure will pass south of the region, bringing cloudy, cool conditions with showers at times today through Saturday, which may linger into Sunday, too. Another low pressure 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/... 1045 PM Update... Latest NE regional 88D mosaic radar loop showing leading edge of showers moving into SW CT at 02Z, moving just N-NW rotating around the periphery of the cutoff H5 low pres over the Ohio valley. Some precip has reached into SW CT, but have tended to weaken with drier air aloft further inland. Noting a relatively dry layer between H9 and H6 on the 00Z KOKX upper air sounding, with a very dry layer from around H95 upward on the 00Z KCHH sounding. Another area of showers working toward Long Island into S CT, should push into W RI by 05Z-06Z but should be light as air aloft becomes more saturated. Low clouds remain from about the Mass Pike southward. Noting colder cloud tops wrapping toward the S coast around the cutoff low as far E as Cape Cod and the islands, though they are tending to warm as they shift N-NW. Have updated the timing of the precip into W RI and N CT to bring in CHC POPs from about 08Z onward, though do expect precip to be light there. Elsewhere, should remain dry overnight though some showers might reach as far E as Providence to Nantucket by daybreak. 02Z temps running ranging from around 50 across N Mass to around 60 along the E coast from Boston southward. Expect readings to fall back to the upper 40s across the higher inland terrain, but holding in the mid-upper 50s along the south coast to around Plymouth with the steady and gradually freshening onshore winds. Previous Discussion... Northeast flow continues through the night with gusts 25 to 30 mph along the coast. Mid and high clouds are already streaming overhead, and expect lower clouds to move in with the onshore flow. So the trend will be to cloudy skies. Extrapolation off radar shows pcpn arriving a couple of hours slower than forecast, so we adjusted pops to be a little slower, but same trend with a few showers to the south coast by daybreak. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Friday and Friday night...A strong pressure gradient between the high pressure to the north and a weak low pressure to the south will result in a strong low level jet and periods of showers. There will be plenty of moisture with a plume of higher PWAT (1.5-2 inches) air moving into the region at this same time. Periods of heavy rain are possible, particularly where collocated with the anomalous low level jet along the south coast. That said, the drought continues, with only up to around an inch of rain expected for most places. In addition, gusty northeasterly winds will continue. Expect similar temperatures to today with highs in the upper 50s to lower 60s and lows in the upper 40s to mid 50s. && .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 /08Z 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/... Overnight...High confidence. Expect MVFR-IFR CIGS from KBOS-KORH- KIJD south and east with onshore flow keeping low level moisture feeding in. Elsewhere, expect mainly VFR conditions. CIGS may start to lower to MVFR further inland after 06Z-08Z as low level moisture starts to encroach. Gusty NE winds to 25-30 kt continue along the east coast. Friday and Friday night...Low confidence, mainly for timing. Will see MVFR- IFR CIGS and/or VSBYS as -SHRA and patchy fog move in from S-N during the day. NE wind gusts up to 25 kt continue along the coast. 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. Small craft advisories and gale warnings continue on the waters for much of the period with gusty NE winds continuing through Friday night. These winds will allow seas to build as well. Therefore, added about 30 percent to the SWANNAM wave heights to bring the waves more in line with what we`re seeing now and what we`re expecting over the next 36 to 48 hours. 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 8 AM EDT Saturday for ANZ231>236- 250-251-254-255. Gale Warning until 8 PM EDT this evening for ANZ237-256. && $$ SYNOPSIS...Belk/RLG NEAR TERM...EVT SHORT TERM...RLG LONG TERM...Belk AVIATION...Belk/RLG MARINE...Belk/RLG is the U.S. government's official web portal to all federal, state and local government web resources and services.