Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 230755 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 355 AM EDT Sun Jul 23 2017 .SYNOPSIS...
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Rain moves off the S-coast this morning behind which conditions improve. Partly cloudy with near-seasonable temperatures. Cooler, damp conditions are forecast for Monday and Tuesday. High pressure in control will bring dry and pleasant weather Wednesday and probably into much of Thursday. Another low pressure system will likely bring showers/isolated thunderstorms to the region Thursday night and/or Friday, perhaps lingering into Saturday. Temperatures will be below normal for most if not all of the coming week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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4 am update... An improving trend. Weak wave low is passing to our S along a quasi- stationary frontal boundary roughly W to E off the NJ coast. SW flow of sub-tropical moisture ascending along and ahead, per latest radar, a widespread area of rain that is flirting with the immediate S coast. Have adjusted PoPs according. Should see this area of rain clear out during the early morning hours. Clouds diminishing, anticipate partly cloudy conditions beneath a cooler airmass aloft resulting in highs around the upper 70s to low 80s. E onshore winds contributing to cooler conditions along the coast, perhaps gusting up around 20 to 25 kts immediately behind the aforementioned low for a brief period of time early this morning. Comfortable overall in comparison to days past. Dewpoints dropping overnight and will continue to do so with the N/E winds during the day, some places falling into the upper 40s with daytime mixing.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
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tonight through tuesday night... A prolonged period of cool, damp weather. Potent open wave H5 trough sweeps through the region Monday night into Tuesday. In advance, an interior surface low emerges Sunday night over the E Great Lakes, transferring energy towards the coast and offshore across regions of better baroclinicity Monday. Per an isallobaric response, a wedge of high pressure settles in- between brought about by stout NE flow. More stable, cooler airmass via a cold air damming setup, amplified as the interior surface low weakens across the W foothills of the Appalachains Monday night and the low offshore deepens. Reminiscent of Winter, atypical as is the amplified trough pattern for mid-Summer. An over-running setup. The kinked frontal pattern across the region with cooler, more stable air, will keep better thunderstorm chances well S/W throughout the forecast, though can`t rule out some rumbles of thunder over S/W portions of New England with possible elevated instability. Nothing strong to severe. Main concern is with torrential rainfall. Period of heavy rain given available forcing upon deepest, most pronounced column moisture is forecast Monday with collocation of sub-tropical moisture influx undergoing lift along the kinked frontal boundary beneath some weaker ascent associated with lead shortwave energy. Will need to watch closely upon low-level convergent winds to the front. The rest of the timeframe looks to be cool and damp, especially Monday night into Tuesday as the mid-level dynamics sweep the region with stronger mid- level forcing acting upon remnant, available moisture, though more continental rather than sub-tropical. Light showery weather is to be expected along with an abundance of low clouds, perhaps some patchy fog. Clearing out Tuesday night in wake of the H5 trough. Subsidence prevailing as cooler, drier air settles S brought in by N flow becoming light with increasing high pressure up to around 1025. As model solutions vary, especially with respect to the magnitude of low level convergent forcing along the frontal profile from the NE with the GEFS suggesting +3-4 standard deviation above normal and both the EC/NAM hinting at least a 30 mph inflow, will keep it conservative and keep close to the latest SREF output. Upstream convective elements transitioning along the quasi-stationary boundary S at the start of the forecast period late Sunday into Sunday night, indications of mesoscale convective systems across PA and NY, but then it would appear the pattern across the NE CONUS becomes more synoptic with energy pinwheeling. Chance to likely PoPs, highest Monday. Will hint at the chance of thunder towards SW CT Monday. No special wording just yet on heavy rain given the uncertainty and low confidence spatially as to where heavy rain will occur.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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Highlights... * Dry and pleasant Wed and probably into much of Thu afternoon * Unsettled/wet weather likely returns by Thu night and/or Fri * Temps will remain below normal through the end of the week Details... Wednesday into Thursday afternoon... High pressure will build across the region Wed and slide east of our area by Thu. The result will be dry weather Wed and probably into most of Thu afternoon. Temperatures should rebound from early in the week, but still average a bit below normal for late July. Highs should mainly be in the middle 70s to lower 80s Wed and Thu afternoons with comfortable humidity. Thursday night through Saturday... A rather impressive shortwave for late July will dive southeastward from the Great Lakes and carve out another Northeast trough. The approaching shortwave will likely bring a period of showers and perhaps isolated thunderstorms to the region. Specific timing is uncertain with most guidance currently focused on Thu night/Fri, but it is possible some activity lingers into Sat. Temps should remain below normal with highs mainly in the 70s to the lower 80s.
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&& .AVIATION /08Z SUNDAY 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 Tuesday Night/... Today...High confidence. VFR. Eroding CIGs this morning, SCT-BKN, as last of -RA clears out along the immediate S-shore. NE winds to which potentially early this morning there may be a burst of 20 to 25 kts. Tonight...High confidence. CIGs lowering SW to NE towards MVFR-IFR as -RA begins to spread across the region. Continued E flow with gusts up to 25 kts along the S-coast forecast. Monday...Moderate confidence. MVFR-IFR CIGs with -RA. Impacts to the AM push possible with RA/+RA. Potential VSBY restrictions. Continued breezy NE flow with gusts up to 25 kts. Monday Night into Tuesday...Moderate confidence. MVFR-IFR CIGs linger with -SHRA/DZ. Lower conditions possible Monday night with LIFR. NE winds continue with gusts up to 25 kts possible especially across E MA. Tuesday Night...Moderate confidence. Improving towards VFR. Winds backing N remaining breezy. KBOS Terminal...VFR. Strong E flow developing this morning. Will hold gusts up to 20 kts but not out of the question to see gusts to 25 kts for a brief period of time as has been observed N at the Isle of Shoals off NH. KBDL Terminal...VFR. Flow becoming E as CIGs become SCT-BKN. -RA will move into the terminal roughly around midnight into early Monday morning. Outlook /Wednesday and Thursday/... Wednesday and Thursday...Moderate confidence. Mainly VFR conditions into Thursday afternoon. Potential for deteriorating cigs/vsbys Thursday night but timing of showers, low clouds, and fog patches are uncertain at this time.
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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 Tuesday Night/... Today... E/NE winds to which potentially early this morning there may be a burst of 20 to 25 kts across the E waters. As of 4a, Isle of Shoals off NH was gusting to 26 kts. Seas no greater than 4 feet. Tonight... Continued E flow with gusts up around 20 kts, as high as 25 kts along the S-coast forecast. Seas no greater than 4 feet. Monday... Widespread rain with embedded heavier showers. Could be some visibility restrictions out on the waters. Continued breezy NE flow with gusts up to 25 kts. Seas building to 5 feet on the S/SE outer waters. Monday Night into Tuesday... MVFR-IFR CIGs linger with -SHRA/DZ. Lower conditions possible Monday night with LIFR. NE winds continue with gusts up to 25 kts possible especially across E MA. Seas up to 5 feet on the E outer waters. Tuesday Night... Improving towards VFR. Winds backing N remaining breezy. Seas diminishing below 5 feet. Outlook /Wednesday through Thursday/... Wednesday and Thursday...Moderate confidence. Winds and seas should remain below small craft thresholds Wed into Thu morning with high pressure in control. As the high pressure system moves east of the waters, south to southwest winds may gust to between 20 and 25 knots by Thu afternoon.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...Frank AVIATION...Frank/Sipprell MARINE...Frank/Sipprell

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