Area Forecast Discussion
Issued by NWS Boston, MA

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724 FXUS61 KBOX 170532 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 132 AM EDT Thu Aug 17 2017 .SYNOPSIS... Dry and pleasant conditions continue into tomorrow. A weather system moving through the Great Lakes Region towards the end of the workweek will bring showers and scattered thunderstorms to southern New England during Friday and Saturday. High pressure returns with fair seasonable weather Sunday and Monday. A cold front approaches from the west Tuesday and Wednesday, bringing our next chance of showers. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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200 AM Update... Forecast remains on track for the overnight hours. Weak wave moving through the northwest flow this morning has trigger some strato cu per latest IR imagery. Dewpoints continue to drop with a few locations across northeast MA in the 40s. Surface temps are radiating out with some locations in the low to mid 60s. Metro regions are hanging tough with temps in the 70s, but with the cooler dewpoints anticipate them to drop over the next few hours. OVerall a very pleasant night across southern New England.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... Tomorrow... High pres crests over the region providing stout subsidence. Despite the mostly sunny conditions this suggests, the combination of suppressed mixing and a cooler start to the day will lead to overall high temps a few degrees cooler than yesterday. This is also in spite of generally W flow. Mainly upper 70s and low 80s in the warmest spots where the downsloping can be maximized. Overall a pleasant day especially with dwpts remaining in the 50s. Will still need to watch mainly exposed beaches across Cape Cod and Nantucket, as the remnants of Gert continue to shift east, a lingering swell could maintain a moderate risk for rip currents through the day in these areas. Tomorrow night... A pleasant evening to start, however upper lvl wave will be tilting and lifting through Ontario and Quebec with sfc wave pushing a warm front toward New England. PWATs increase through the overnight hours, such that by 12Z Fri, they near 2.00 inches (or nearly 2 std deviations above normal). Initial overruning is weak and this moisture load is from the top of the column to the sfc. Therefore, expecting only building clouds through the evening, with the risk for any precipitation holding off until the early morning hours. Indeed, timing of measurable QPF has slowed on regional models due to this initial lack of lift and dry column. Still could see some wetting rainfall by sunrise mainly W of the Worcester hills in MA and Thames river region of CT. Noting some QPF bullseyes, but these are mostly likely some convective feedback. Column remains relatively stable through 12Z. The increased moisture from W-E will limit diurnal cooling in spite of the weak pres gradient to start. Coolest areas will likely be across E MA/RI, where some radiational cooling can occur initially. Overnight mins range from the upper 50s in these cooler spots to the low 60s elsewhere due to the increased cloud cover. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Details... Friday and Saturday... Moderate confidence. During Friday and Saturday short waves move eastward thru our area, with the upper ridge axis shifting offshore and upper trough moving into the Great Lakes region, gradually approaching our area. Surface high pressure slides further offshore while surface low churns thru northern Great Lakes Region, heading towards southern Quebec. On Friday a warm front associated with the Great Lakes surface low lifts northward into our area. Southerly flow will bring deep moisture to southern New England, with precipitable water values increasing to around 2 inches by midday. This in conjunction with short waves will allow for rain/showers Friday-Fri night. Lack of surface-based CAPE on Friday, but surface LIs drop to 0 to -2 and K indices mid 30s. Should be primarily showers but can`t rule out rumbles of thunder. Could see brief heavy downpours. During Saturday the surface low`s associated cold front advances eastward through our region, while upper trough approaches from the west. Models also indicate a zone of upper difluence affecting our area. While deeper moisture axis shifts offshore, we still start the day with precipitable water 1.5 inches or so across the eastern half of the area, somewhat less later in the day. Cape values 500-1000 J/Kg. Expecting scattered showers with a chance of thunderstorms. Max temps are expected to be mainly in the 70s on Friday. Airmass warms several degrees Saturday with highs ranging from the upper 70s to mid 80s. High dew points should contribute to areas of fog each night/early morning. Anticipating a drying trend Saturday night, however models hint at potential for a weak surface low developing along the front in northern New England as the upper trough passes thru New England, so this could keep some clouds and a chance for light rain in our area at least early. Patchy fog possible. Sunday through Wednesday... Upper trough lifts out during the Sunday with surface high pressure building east into the area during Sunday and Monday. So anticipating a period of mainly dry weather. Then the high moves offshore Monday night and Tuesday, with increasing moisture later Tuesday as another short wave and cold front approach from the west. This could bring our next round of showers for late Tuesday-Tue night and Wednesday. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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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 Friday/... Before 00z...High confidence. VFR except some very patchy ground fog early AM mainly at typically prone terminals. Today...High confidence. VFR. Winds shift lightly W during the day except sea breezes along coast. Tonight and tomorrow...Moderate confidence in trends, lower confidence on timing. VFR to start with deteriorating conditions after 09z as widespread rain approaches. Conditions will fall to MVFR/IFR through the day as rain moves from west to east and could be heavy at times restricting vsbys. Iso -TSRA is also possible on Friday. Southerly winds with gusts near 15 kts by the afternoon. KBOS Terminal...High confidence in TAF. Sea breeze development expected for Thu. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Monday/... Friday through Monday... Moderate confidence. Saturday...MVFR/IFR to start. Improving to VFR, except for possibly the Cape and Islands where MVFR/IFR could linger thru the day. Then localized MVFR/IFR Saturday night in patchy fog possible. Sunday and Monday...VFR.
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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 Friday/...High confidence. Noting seas have reached 8-9 ft along the open ocean waters S of S New England as hurricane Gert begins its E shift. This will allow these seas to gradually recede through the overnight hours. Small craft advisories continue, but will be able to be dropped as the night progresses. Otherwise, mainly quiet boating weather continued into tomorrow night after these seas recede. Outlook /Friday Night through Monday/... Friday... Winds/seas below SCA thresholds to start, however during late Friday/Fri night may see some southerly wind gusts to 25 kts. Seas building to 3-5 feet Friday night. Increasing chance of showers west to east during Friday. A Small Craft Advisory may be needed. Showers and scattered thunderstorms Friday night and reduced visibility in areas of fog. Saturday... Lingering showers and scattered thunderstorms Saturday, with reduced visibility in patchy fog. Seas 3 to 6 feet on the outer waters, and possibly the exposed portions of the southern waters, subsiding during Sat night. Southerly winds Saturday turn to the west Saturday night with gusts to 25 kts possible. A Small Craft Advisory may be needed. Sunday and Monday... High pressure builds over the waters. Winds and seas expected to be below SCA thresholds. Isolated showers possible early Sunday, but these move off to the east during the morning.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 8 AM EDT this morning for ANZ254-255.
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&& $$ SYNOPSIS...Doody/NMB NEAR TERM...Dunten SHORT TERM...Doody LONG TERM...NMB AVIATION...Dunten/NMB MARINE...Doody/NMB

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