Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 300316 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1116 PM EDT Thu Sep 29 2016 .SYNOPSIS... A wave of low pressure will pass south of the region, bringing cloudy, cool conditions with showers Friday through Saturday which may linger into Sunday. Low pressure lifts to the Great Lakes over the weekend and sweeps east across New England early next week. High pressure then brings dry weather midweek. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 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 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... 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 THROUGH THURSDAY/... Big Picture... Longwave scale shows high pressure lingering over the West Atlantic through the period while a trough remains over the Western USA. Shortwave scale shows the Atlantic ridge shifting south a little during the weekend, making room for Midwest closed low to lift a little and then eject across New England early next week. High pressure then builds over the Northeast USA midweek. Operational GFS at long ranges is showing Matthew approaching up the coast for later Thursday. The track has again moved to a western/inland path. The ECMWF is much slower with Matthew over the Bahamas, a substantial blocking ridge over the Northeast, and no trough to guide the storm north. The lack of model-to-model and run- to-run consistency leads to no confidence in any forecast bringing rain to our area Thursday. This remains a storm to watch, but at this time expect a slower solution for us than what the GFS hints. Details... Saturday-Sunday... Closed upper low over the Midwest and upper ridge over the West Atlantic provide a south-southwest channel in the upper flow. A 100- knot jet in that flow moves toward New England with our area in the right entrance region, favoring upper venting and lift. Meanwhile the low-level easterly flow remains in place with 25-30 knot winds just off the deck. Expect the moist south flow to be lifted over the low level easterlies generating showers. PW values 1.5 to 1.75 inches, so any showers may have locally heavy downpours. Expect the low level east- northeast flow to maintain clouds and fog. Monday-Tuesday... Upper low and cold pool move overhead late Monday and Tuesday. This will bring instability with totals in the upper 40s, and should maintain partly to mostly cloudy skies each day with a chance of showers. Surface wind flow will maintain a northeast direction off the ocean. This buffers temps with max values in the 60s to around 70, warmest in the CT River Valley. Wednesday-Thursday... High pressure builds over the region with dry weather and partly sunny skies. Northeast flow continues. As noted above, GFS handling of Matthew is a fast outlier and so is discounted in favor of the slower solutions. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... 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 through Tuesday/... Saturday-Sunday...Moderate confidence. MVFR/IFR cigs and vsbys in showers and fog. Northeast flow with gusts 20 to 30 knots Saturday, diminishing Sunday. Monday-Tuesday...Low confidence. 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 Friday Night/... 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 through Tuesday/... Saturday...Northeast winds gusting 25 to 30 knots. Rough seas with Eastern MA exposed waters reaching 7 to 10 feet and outer Southern waters around 5 feet. Poor vsbys in showers and fog. Small craft advisory will be needed. Sunday...Diminishing Northeast winds with gusts 20 knots or less. Seas 5 to 6 feet on the waters east of MA. A Small Craft Advisory may be needed on the eastern waters. Monday...Northeast winds less than 20 knots. Seas less than 5 feet. Tuesday...Northeast winds with gusts 20-25 knots on the outer waters. Seas build to 5-7 feet on the outer waters. Small Craft Advisory may be needed on those waters. && .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 from 2 AM to 8 PM EDT Friday for ANZ237-256. && $$ SYNOPSIS...WTB/RLG NEAR TERM...WTB/EVT SHORT TERM...RLG LONG TERM...WTB AVIATION...WTB/RLG/EVT MARINE...WTB/RLG/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.