Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201947 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 347 PM EDT SAT AUG 20 2016 .SYNOPSIS...
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Isolated showers are expected at times through Sunday afternoon, but the vast majority of the time will be dry with increasing humidity. More widespread showers and thunderstorms with locally heavy rain will move through the region Sunday night with a cold front. A few strong thunderstorms are possible. After a cold front moves east on Monday, a prolonged period of mainly dry weather will accompany high pressure for most of next week.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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4 PM Update...Showers have come to an end for the most part, though one or two still linger over western MA/northern CT. Expect these off and on pop up showers to continue through the afternoon/evening in weak warm advection. Otherwise, a nice afternoon with mostly sunny conditions and warm temperatures is expected. Tonight...Any isolated showers that are ongoing should come to an end fairly quickly after sunset. With continued SE surface winds, and increasing moisture, expect areas of low clouds and fog to develop during the overnight hours. Low temperatures will drop into the low to mid 60s for most locations, with a few readings in the upper 70s in the normally warmer locations.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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Sunday...A shortwave in the eastern Great Lakes will move slowly eastward, approaching southern New England Sunday night. This will result in an increase in clouds through the day as southerly winds continue to draw in moisture. Most of the day should be dry, with the increasing clouds mainly across western MA/northern CT. However,a few isolated showers may develop in the warm advection in these same areas. There is little instability to draw on so expect that like today, these will be mainly showers. High temperatures will be a couple of degrees cooler thanks to the increase in cloud cover, but will remain in the upper 70s to mid 80s. In addition, increasing low level moisture and humidity will result in it feeling a bit warmer. Sunday night...This period actually holds the best chance for rain in the forecast. Low pressure moving through Quebec ahead of the shortwave will bring a cold front through southern New England. Ahead of this front, tropical moisture, drawn in on the southerly winds, will bring a line of showers and thunderstorms across the region. The tropical moisture will keep the chance for heavy rain in the forecast, which could lead to some urban/poor drainage street flooding but the storms are expected to progress quickly across the area, which will limit flood risk. Models are still hinting at developing a surface wave on the front but differ on where exactly this wave would develop. This, coupled with an increase in low level wind shear and instability, could produce a few strong storms. In addition, in this low CAPE, high shear environment, we have to watch storms carefully for the possibility of a brief tornado. However, this is a very mesoscale situation and many things need to come together for this to actually occur.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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Highlights... * A touch of fall Mon and Tue * Warming later in the week * No rainfall expected through most of the work week. Overview and model preferences... 20.12Z model update shows little change from previous runs. Therefore, no major changes to the forecast are expected with this update, so will be using a consensus blend along with persistence. The shortwave expected to deliver some rainfall Sun night will shift north into Labrador early in the week. The remnant longwave trof will deliver some of the driest air we have seen in some time this summer from central Canada. The trof lingers early in the week also yielding some cooler temps, however the subtropical ridge will regain control late thanks to a shifting PNA with trof digging across the W CONUS. Details... Mon... As mentioned by the previous forecaster, deep layer moisture should already be sliding offshore by 12Z Mon morning, leaving the remaining rainfall mainly across the Cape and Islands. Gusty W-NW winds fill follow thanks to deepening offshore low pres moving into the maritimes leading to strong isallobaric flow. Drier air expected as dwpts drop rapidly into the 50s and even 40s thanks to PBL mixing. H85 temps will be a bit slower to decline until upper lvl reinforcing shortwave moves through. Therefore, with sunshine still expecting widespread low-mid 80s. Mon night into Wed... The dry wx prevails with dwpts remaining in the upper 40s and low 50s (lowest in the afternoon) through mid week. Strong high pres (about 1025hpa) will be slowly building across the NE during this time. With H85 temps dipping first to around +8C early Tue then warming back to near +12C by Wed afternoon. Looking at one of the cooler nights of late Mon night thanks to the low dwpts and weakening pres gradient, expect a lot of low 50s with even an isolated upper 40 not out of the question. Tue looks to be mainly in the 70s and very pleasant thanks to the low dwpts. A bit warmer by Wed, above/near seasonal normals for late August, low-mid 80s. Thu and Fri... The high pres remains in control but shifts E allowing for low and mid lvl return flow. This suggests a warming trend along with a rise in overall moisture and dwpts back into the 60s. H85 temps warm back to near +15C or slightly warmer. Therefore, a return to more humid and summer heat (mainly mid-upper 80s) by late week. Fri night into Sat... Slow moving front currently well agreed upon, moving through late Fri night into Sat. Risk for some rain/thunder possible, but given the it is late week won`t get too deep into the details just yet.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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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 Sunday Night/... Through 00Z...High confidence. Mainly VFR conditions expected with isolated showers perhaps resulting in brief MVFR conditions. Tonight...Moderate confidence. Cooling boundary layer and increasing low level moisture should allow areas of low clouds and patchy fog to develop resulting in MVFR/IFR conditions at times. Timing and areal extent remain uncertain, but highest risk for low clouds and fog will be across western MA/northern CT. Sunday...Moderate confidence. CIGS/VSBYS improve some by late morning, but still expect MVFR cigs at times for much of the region and even a low risk for localized IFR conditions across the Cape/Islands. Isolated to widely scattered showers expected with focus across western MA/Northern CT. Sunday night...Moderate confidence. Conditions lower to MVFR/IFR from west to east as SCT SHRA/TSRA develop and move into the west between 00-06Z and into the east 06-12Z. Heavy rain is likely with a few strong storms possible. Quick improvement to VFR from west to east between 06-12Z. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday through Thursday/... High confidence in a stretch of mainly VFR weather. Sea breezes most likely mid-late week.
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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 Sunday Night/...High confidence. Quiet boating weather is expected through the period, with a slight rise in winds and seas ahead of a cold front Sunday night. Otherwise, isolated showers through tomorrow and a chance of showers and thunderstorms Sunday night will be the main hazard to boaters. Keep an eye on the weather especially Sunday night and remember that lightning and gusty winds are always a possibility in any thunderstorm. Outlook /Monday through Thursday/...Moderate confidence. Monday...Moderate Confidence. Winds will be shifting to the W-NW behind an exiting front early. Gusts may reach close to small craft thresholds, along with some building seas (which should remain below small craft levels). Rain/fog early, clearing all waters by mid day. Tuesday through Thursday...High confidence. Quiet boating weather as slow moving high pressure builds over the waters.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Doody/RLG NEAR TERM...RLG SHORT TERM...RLG LONG TERM...Doody AVIATION...Doody/RLG MARINE...Doody/RLG

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