Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261745 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 145 PM EDT Fri May 26 2017 .SYNOPSIS... Low pressure over southern New England this morning then offshore this afternoon. Periods of rain will continue today but becoming less numerous this afternoon. High pressure builds into the region beginning tonight and ushers in a drier airmass that lingers through much of the holiday weekend. This high will provide mild days and cool nights to the area Sat and Sun. The next chance of rain will arrive Sun night into Mon as a trough of low pressure moves across the region. Scattered showers possible much of next week, mainly diurnal and by no means a washout. Temperatures will warm to near normal values. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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140 PM update... Comma head showers continue to rotate south into SNE, focused mainly across central/W MA into CT/RI within defined trowal signature. These showers will decrease toward evening as the low pulls away. Previous discussion... Vertically stacked low vicinity eastern MA will move into the Gulf of Maine this afternoon. Well defined comma head across northern New Eng then wrapping south into SNE where widespread rain across central and western New Eng. Nice trowal signature and deep layer moisture will persist into early afternoon so periods of rain will continue, especially interior, then gradually improving conditions expected toward mid/late afternoon as the low pulls further away. Chilly temps in the upper 40s to lower 50s but should see highs reach lower/mid 60s by late in the day in the CT Valley and near 60 south coast, but likely remaining in the 50s northern MA. Gusty north winds 20-30 mph across coastal NE MA expected to expand south along the eastern MA coast and especially the outer Cape this afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... Tonight... Upper level low will continue to move into the North Atlantic tonight. Heights will be rising as northwest flow continues. Passing shortwave on the backside of the low may trigger a few showers overnight but overall trend will be dry. Temperatures will remain steady overnight with lows in the 50s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... */ Highlights... * Mainly dry weather w/mild days and cool nights Saturday and Sunday * Risk of rain returns Sun night into Monday * Temperatures warming to near normal Tue thru Thu along with a risk for scattered showers each day, although by no means a washout Synoptic Overview... Main large scale feature this period will be a building mean ridge over western Canada which induces downstream troughing over the Great Lakes. This will yield an active/amplified northern stream with cyclonic flow into New England much of next week. This will translate to a risk of showers each day (mainly diurnal) but also temperatures warming to near seasonal levels. Daily Details... Saturday... Dry weather prevails in response to NW flow aloft and weak high pressure at the surface advecting across the area. Typically this setup supports at least some sunshine however models are depicting lots of low level moisture remaining trapped beneath the subsidence inversion. Both the NAM and GFS moisture profiles suggest BKN-OVC strato-cu much of Saturday. Thus mostly cloudy appears to be the model consensus. Although the combination of light winds (weak high pressure overhead) and temps warming into the upper 60s - low 70s will yield very pleasant conditions. Sunday... Ensembles and deterministic guidance in very good agreement that deep layer east coast ridge lingers long enough to provide mainly dry weather here. Any showers likely hold off until after sunset. Thus a fairly nice day with temps 70-75, 60s at the coast given cooling seabreezes. Moisture profiles suggest more sunshine eastward across RI and eastern MA. Monday... Still some uncertainty regarding the timing of next system. Model consensus would support risk of showers Sunday night into Monday as northern stream trough advects across the area. Cooler given cloud cover, southeast onshore winds and risk of scattered showers with highs only in the 60s. Tuesday thru Thursday... Long wave trough sets up across the Great Lakes with cyclonic flow into New England. This setup supports isolated or scattered diurnal showers each day but by no means a washout. Somewhat warmer low level flow becoming southwest. This will support highs in the 70s, 60s for the south coast of MA/RI including Cape Cod and the Islands. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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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 Saturday night/... Through 00z...Mix of VFR/MVFR cigs will trend back to mostly MVFR with pockets of IFR Cape/Islands. Showers continue across central/W MA into CT/RI before diminishing toward evening. NW gusts to 20-25 kt Cape/Islands. Tonight...Moderate confidence. Mostly MVFR cigs, improving to VFR in central and western New Eng. Diminishing NW winds. Saturday and Saturday night...Mix of VFR/MVFR cigs. Seabreezes developing late morning into the afternoon. Low risk for a brief shower late Sat/Sat evening south of the Mass Pike. KBOS TAF...Moderate confidence. KBDL TAF...Moderate confidence. Outlook /Sunday through Tuesday/...moderate confidence. Sunday...Mainly VFR. Light winds Saturday, with seabreezes at the coasts. Light S-SE winds Sunday. Sunday night through Monday...Cigs/vsbys trending to MVFR/IFR in showers. Winds from the southeast, trending from the south Monday. Tuesday...Mainly VFR, with scattered diurnal MVFR showers.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence. 950 AM update... North wind gusts 25-30 kt ME MA waters will expand south across waters adjacent and east of Cape Cod this afternoon where G25 kt expected. Expanded SCA to Cape Cod Bay and Nantucket Sound for the afternoon. Previous Discussion... Today and Tonight... Passing low pressure system will keep seas above 5 feet for most of the period. Northerly winds will switch to the northwest by tonight. A few gusts to near 25kts are possible across the near shores, but confidence is to low to extend the adv. Outlook /Saturday through Tuesday/... Saturday...light and variable winds with seabreezes at the shore. Dry weather and good vsby prevail with high pres overhead. Sunday...light southeast winds expected with high pres just offshore. Dry weather and good vsby during the daylight hours then risk of rain and fog overnight. Monday...another front sweeps across the area with the risk of scattered showers. Modest SE winds develop. Tuesday...winds becoming southwest. Low risk for a few afternoon showers. && .TIDES/COASTAL FLOODING...
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A surge of 1 foot occurred with the midnight high tide resulting in minor coastal flooding across the MA east coast. This surge remains across most of the east coast thanks to persistent easterly flow from passing low pressure system. The focus turns to the high tide for tonight. Currently a surge of 0.2 to 0.4 feet is forecast and combined with the peak of astronomical tides (Boston at 12.41 feet), should see at a minimum coastal flooding of low-lying locations notorious for becoming inundated during such tides (i.e., Morrissey Boulevard in Boston). Additional coastal flood statements may be necessary but confidence is to low. Especially as heights are beginning to rise and surface low turns to the northwest.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ231- 232-251. Small Craft Advisory until 6 AM EDT Saturday for ANZ235-237- 250-254>256.
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&& $$ SYNOPSIS...KJC/Dunten NEAR TERM...KJC SHORT TERM...Dunten LONG TERM...Nocera AVIATION...KJC/Nocera MARINE...KJC/Nocera/Dunten TIDES/COASTAL FLOODING...

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