Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 230809 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 409 AM EDT Wed Aug 23 2017 .SYNOPSIS...
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A cold front crosses most of the region this morning bringing beautiful weather today an end to the oppressive humidity, except for the Cape and Islands where low clouds and muggy conditions will persist into this afternoon. Otherwise, high pressure brings dry weather with very comfortable humidity levels Thursday through early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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***Much lower humidity will bring beautiful weather today except across the Cape/Islands where low clouds and muggy conditions linger into the afternoon*** Isolated spot showers early this morning will be coming to an end across most areas by daybreak as drier air works into the region. However, will have to watch for an area of showers and perhaps an isolated thunderstorm or two that may clip the far southeast New England coast into mid morning but it may also remain just offshore. Otherwise, much drier air will work into most of the region behind this morning/s cold frontal passage. Skies will become partly to mostly sunny from northwest to southeast as highs top out between 80 and 85, with much more comfortable humidity. The exception to this will be across the Cape/Islands, where the cold front will get hung up. While we do expect any left over showers to come to an end by late morning, an abundance of clouds will likely remain in place into the afternoon along with muggy conditions persisting.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
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Tonight... Much drier air along with mainly clear skies/diminishing wind will result in a much cooler night. The cold front will also finally clear Cape/Islands this evening, allowing any left over low clouds to exit the region. Low temps across much of the region will bottom out well down into the 50s by daybreak Thursday. Patchy fog may develop late in the typically prone locations, but not expecting anything widespread.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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The persistence of low pressure across the Gulf of Alaska rebuilds the monsoonal high over the 4-corners region of the CONUS. The flux of milder, Pacific air into Central Canada enhances the shearing flow equatorward across SE Canada and NE CONUS with reinforcing shots of cooler, drier air. Keeping the tropical-moist axis at bay, well S/E of the region draped E off the Mid-Atlantic, looking at slightly cooler than average conditions with comfortable conditions under a continual influence of 1025 surface high pressure and light winds. While the atmosphere devoid of moisture, will need to watch two periods in particular of spot shower activity given stronger mid- level ascent across the region as individual shortwaves rotate through towards the rear of the prevailing H5 troughing pattern across SE Canada into early next week. This in addition to steep lapse rates via a maintained cold pool aloft with H85 temperatures hovering around +6-8C beginning roughly Friday and continuing into early next week as well. However restrained, agree with the prior forecaster that within the upper level jet axis with predominant confluent flow, in the left entrance region which, ageostrophically, is a region more so of subsidence. Consensus of forecast guidance through 12z Monday, then forecast guidance diverges on mid-upper level features and will thus focus on ensemble means between the GEFS and ECens. Overall, similar thinking as earlier, looking like a prolonged period of dry weather with low humidity, low dewpoints, making for comfortable conditions. Highs around the mid to low 70s with lows down into the 50s. Scattered cloud decks at times. Dewpoints ranging in the upper 40s to low 50s.
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&& .AVIATION /08Z 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 Tonight/... Today...High confidence in TAFS except moderate confidence across the Cape and Islands. VFR conditions as much drier air works into most locations. The exception will be the Cape/Islands, where low clouds may linger through the morning and perhaps well into the afternoon especially across Nantucket. Tonight...High confidence. Mainly VFR except for perhaps some lingering fog and low clouds during the evening across Nantucket. May also see some patchy ground fog develop in the typically prone locations toward daybreak, but nothing widespread is expected. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Thursday through Sunday/... VFR. Daytime SCT low-end VFR CIGs 4-5 kft agl. N/W winds throughout, light at times to allow onshore E sea-breezes.
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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 Tonight/...High confidence. Today and Tonight...Southwest low level jet weakens through 12z allowing small craft wind gusts to come to an end. However, seas will be slower to diminish but should drop below criteria across all waters by mid afternoon. Winds and seas will remain below small craft advisory thresholds tonight as cold front clears the entire region this evening. Outlook /Thursday through Sunday/... Good boating weather throughout. N winds persisting. Reinforcing shots of cool, dry weather as high pressure builds into the region. Subsequent slight enhancement in winds, gusts remaining below 20 kts with seas 4 feet or less.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ231>234-251. Small Craft Advisory until 2 PM EDT this afternoon for ANZ235- 237-250-254>256.
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&& $$ SYNOPSIS...Frank/Sipprell NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Sipprell AVIATION...Frank/Sipprell MARINE...Frank/Sipprell

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