Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 160605 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 205 AM EDT Wed Aug 16 2017 .SYNOPSIS...
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Dry weather which will linger today and Thursday along with plenty of sunshine. A weather system from the Plains will bring showers and scattered thunder with locally heavy rainfall possible Friday and Saturday. A drying trend likely follows for Sunday into early next week along with seasonable temperatures.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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200 AM Update... Longwave trough over the region as surface cold front pushes through the flow. Still plenty of low level moisture around with very light winds which suggests the front is still west of the region. Thus several sheltered, low lying locations will decouple tonight resulting in fog development. While dense fog is not anticipated to be widespread, still expect changing vsbys within a short amount of time. Model cross sections suggest that the low level moisture will hang around over the next several hours until the front approaches the region. When the front moves through, winds will switch to the west scouring any moisture as dry air pushes into the region. Feel that this will be closer to sunrise. Aside from pesky stratus and fog, overnight temps will remain a bit milder as stratus will limit true radiational cooling.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Tomorrow... Gert makes its closest pass during the early AM hours, just as it swings more to the E about 400sm S of Nantucket, captured by the weak front as it shifts offshore. The usurping of moisture and net gradient will yield NW flow across New England and, aside from some remnant wisps of CI. Although H85 temps will be dropping through the day, as well as mixing out of sfc dwpts, temps are likely to actually be above seasonal normals especially where the downsloping W component of the flow can be maximized. There for, looking at highs around 80 in the coolest spots to the upper 80s elsewhere. Leaned most heavily on the bias-corrected guidance which provided these warmer numbers. The main impacts from Gert will be felt on some area beaches... Beach Forecast: We still expect areas of high surf along with a high risk for rip currents along primarily south facing beaches which are open to the ocean. This extends from Watch Hill all the way across to the outer arm of Cape Cod and includes all Islands. A building swell into tomorrow morning, from Gert, will reach a 14 second period and nearly 8 ft offshore. This will create a potentially life-threatening situation due to high seas and rip currents. Will maintain the current High Surf Advisory as it stands. Tomorrow night... Pleasant sleeping weather as sfc dwpts will continue to drop even after mixing diminishes through the overnight hours. Weak gradient and mainly SKC conditions should promote some radiational cooling suggesting some min temps could dip into the low 50s. In fact, where radiational cooling is typically maximized, would not be surprised to see a few upper 40s for min temps, in the coldest valleys. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Very pleasant Thu with dry weather and low humidity * Scattered showers/T-storms with locally heavy rain Fri-Sat * Drying trend Sunday into early next week w/seasonable temps Synoptic Overview... Active northern stream jet along the Canadian/US border continues this period and will result in the risk for scattered showers/T- storms Fri and Sat. Although with the upper air pattern progressive there will also be dry weather days as well including Thu followed by a drying trend Sun into early next week. This active northern stream jet will also suppress the subtropical ridge and its excessive heat and humidity to the southern states this period. Temperatures... Residual post frontal airmass combined with 1018 mb surface high overhead will provide seasonable temperatures (U70s-L80s) and very pleasant humidity across the region Thu. Cooler Fri (70s) with overcast conditions and scattered showers/T-storms and warm sector airmass remaining west of New England. Saturday will be a warm and muggy day ahead of an approaching cold front with highs in the low 80s and dew pts in the low 70s. Behind the frontal passage, trending less humid Sunday into early next week but temperatures will be seasonably warm (highs low to mid 80s). Precipitation... Dry pleasant weather lingers into Thu. Then an airmass change Fri ahead of next short wave trough with PWATs jumping up to 2+ inches Friday. Warm sector remains west of New England so any instability will be elevated. Nonetheless scattered showers and T-storms with locally heavy rainfall possible Fri/Fri night. By Saturday cold front is over or entering the region. Cyclonic flow aloft, frontal convergence and at least marginal instability should be sufficient for another round of scattered showers/T-storms. Drier air begins to work in from the best so the highest risk for storms may be across RI and eastern MA. Instability and wind fields aloft appear marginal for severe weather so heavy rain/downpours may be the main concern. Trailing short wave trough arrives Sunday but less moisture and instability to work with per ensembles and deterministic guidance. Thus shower/T-storm coverage likely less than Sat. So not expecting a washout Sunday. Short wave ridging and associated dry weather appears to arrive early next as trough exits later Sunday. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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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 Thursday/... Before 12z...Moderate confidence. Mix of VFR to MVFR from cigs will continue early this morning. Low-lying regions will see vsbys drop to 1SM or less resulting in IFR conditions. Cigs and vsbys will improve closer to sunrise from west to east as dry air pushes into the region. Today...High confidence. Fog will burn off within a few hours after sunrise. Mainly VFR with NW winds. Gusts to around 15 kt at times through the daylight hours. Tonight and tomorrow...High confidence. VFR with light winds through the period. Sea breezes along the coast. KBOS Terminal...High confidence in TAF. Passing MVFR cigs possible early this morning. Low confidence on sea breeze development this afternoon. KBDL Terminal...Moderate confidence in TAF. A period of MVFR fog may impact the terminal over the next few hours. Outlook /Thursday Night through Sunday/... Friday...VFR to start but trending toward MVFR/IFR as showers and isolated T-storms overspread the region from west to east. High confidence on trends but lower on details. Saturday...MVFR/IFR in morning fog/low clouds likely improves to VFR- MVFR during the day however scattered afternoon showers/T-storms possible esp eastern MA/RI. High confidence on trends but lower on details. Sunday...low risk of IFR/MVFR in morning fog/low clouds but then improving to VFR by midday. Spot shower/T-storm possible. Moderate confidence.
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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 Thursday/...High confidence. Through tomorrow night... Building southerly swell overnight. Reaching as high as 7-9 ft in the open ocean waters well south of Nantucket, meanwhile seas could reach 5-7 ft in nearer to the shore as this long period swell peaks toward the morning hours Wed. Small Craft Advisories will continue, and have been hoisted even for some of the area bays and sounds (Buzzards Bay, Nantucket and Vineyard Sounds) as some near 5 ft seas are possible on the periphery of these zones, especially thanks to some tidal influences. These seas will gradually subside tomorrow night. Meanwhile, an area of rain/fog will linger through the overnight hours tonight mainly across the S waters, leading to visibility restrictions. Outlook /Thursday Night through Sunday/... Thursday...fine boating weather with high pres over the region. Southerly swells from Gert may linger across the ocean waters. Dry weather and good vsby. High forecast confidence. Friday...a warm front lifts across the area with SE winds becoming SW late. Showers and TSTMS limit vsby. Moderate confidence. Saturday...southwest winds ahead of an approaching cold front along with scattered showers/T-storms. Vsby will be restrict in fog in the morning and showers/T-storms much of the day. Moderate confidence. Sunday...main cold front pushes offshore providing an improving trend in vsby and drier conditions. However a secondary front may trigger an isolated shower/T-storm in the afternoon near shore. Moderate confidence.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...High Surf Advisory from 9 AM this morning to 8 PM EDT this evening for MAZ020-022>024. RI...High Surf Advisory from 9 AM this morning to 8 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory for hazardous seas from 5 AM early this morning to 8 PM EDT this evening for ANZ232>234. Small Craft Advisory for hazardous seas until midnight EDT tonight for ANZ235-237. Small Craft Advisory for hazardous seas until 5 AM EDT Thursday for ANZ254>256.
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&& $$ SYNOPSIS...Nocera/Doody NEAR TERM...Dunten SHORT TERM...Doody LONG TERM...Nocera AVIATION...Nocera/Dunten MARINE...Nocera/Doody

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