Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200515 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 115 AM EDT Sun Jun 20 2021 .SYNOPSIS... A round of showers and thunderstorms is possible late this afternoon and evening ahead of a cold front, especially across CT, RI and south of the Massachusetts Turnpike. Dry, very warm but less humid conditions (away from the south coast) follow Sunday. Hot and very humid conditions arrive Monday which will be followed by more showers and thunderstorms Monday night into Tuesday. The heat and humidity break late Tuesday into Wed, with much more seasonable and less humid weather. Warmer and more humid return Fri into next weekend. && .NEAR TERM /UNTIL 9 AM THIS MORNING/... 1245 AM update... Short-wave aloft still slowly moving over southern New England. KBOX radar still displaying light showers scattered across southern New England. Light showers will continue over the next couple of hours as the short-wave begins to make its way east of southern New England. Adjusted PoPs to reflect latest radar trends, but otherwise the forecast for the rest of the night is on track. && .SHORT TERM /9 AM THIS MORNING THROUGH 6 PM MONDAY/... 400 PM Update: Sunday: Zonal flow aloft but with rising 500 mb heights for most of Father`s Day. Southerly flow should bring in warmer low-level temps (850 mb temps rise to around +15 to +17C) with mostly full sun. Dewpoints in the mid 60s should make it feel fairly muggy out but not looking at oppressive humidity levels. Surface-based CAPEs given the strong insolation and the higher dewpoints are progged around 800-1500 J/kg, highest west towards the Berkshires. That said, given background weak subsidence and lack of lifting/triggering sources most of the area should be dry. Some guidance offer some weak upslope flow that could pop off a shower or thunderstorm in the Berkshires but kept PoPs at 15-20% as most should be dry. Given the more humid air mass, do also have to watch for some lower stratus/fog near the South Coast and the Islands. Highs should reach well into the 80s with lower 90s in the interior. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... 226 PM update... Highlights... * Hot and very humid Monday * Scattered T-storms & heavy downpours late Mon/Tuesday * More seasonable & less humid Mid Week * Warmer & more humid Fri into next weekend Sunday night/Monday...short wave ridging ahead of remnants of TS Claudette should provide mainly dry weather, other than an isolated shower/T-storm western MA/CT late Monday. SSW flow provides hot and very humid conditions, with 850 mb temps warming to +18C to +19C (+22C to +24C inland at 925 mb!) by late Mon along with dew pts rising into the low 70s! Thus, low 90s likely away from the south coast along with heat indices (apparent temp) 95-100! Mon night/Tuesday...12z guidance has trended remnants of Claudette farther offshore. Subsidence on NW side of system may yield mainly dry weather here Monday night. However, by Tue remnants of Claudette exiting off to the northeast and with mid level trough and surface front approaching from the west, Tue likely the greatest risk of showers and storms. It`s far out there in time, but some favorable parameters for severe weather Tue including robust CAPE/Shear profiles. Although timing of front will be critical. Tue night/Wed/Thu...FROPA late Tue/Tue night ushering in drier/less humid air across the region. 1030 mb high (impressive by late June standards) will provide mild to warm days Wed and Thu with comfortable humidity, along with cool nights. Friday/Saturday...return flow, in response to mid level trough digging into the High Plains and Great Lakes, yields a warming trend here Fri/Sat along with increasing humidity. Increasing chance of scattered storms by Sat. && .AVIATION /06Z 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. Through 12Z...High Confidence VCSH taper off by about 09Z for the eastern terminals. Today...High Confidence VFR with light westerly winds. Cape Terminals could see gustier westerly winds greater than 15 knots by mid-afternoon. Tonight...High Confidence VFR conditions continue at all terminals minus ACK. May see some fog develop after midnight at ACK resulting in IFR visibilities. ===================================================================== Tonight: Moderate confidence. Generally VFR, though brief periods MVFR-LIFR visbys mainly south of the Mass Pike 01-07z west to east as rains and embedded thunder move eastward from southern NY/PA. Clearing from west to east around 05-10z with VFR. WSW to W winds 3-6 kt. Sunday: High confidence. VFR. Can`t rule out an isolated TSRA near the Berkshires by afternoon but stays away from the TAFs. Do have to watch for lower clouds/possible FG towards Cape Cod/Islands late in the day as moisture levels start to rise. SW winds 5-10 kt, strongest Cape Cod/Islands. Sunday Night: Moderate/high confidence. Generally VFR; somewhat better chance for stratus/fog and associated IFR/lower categories for South Coast/Cape and Islands. KBOS TAF...High Confidence in TAF. KBDL TAF...High Confidence in TAF. Possible TSRA 18-22z but lower probability. Outlook /Monday Night through Thursday/... Monday: VFR. Breezy. Slight chance SHRA. Monday Night: MVFR/IFR conditions possible. Breezy. Chance SHRA, chance TSRA, patchy FG. Tuesday: Mainly MVFR, with local IFR possible. Breezy. Chance SHRA, chance TSRA, patchy FG. Tuesday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Wednesday through Thursday: VFR.
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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 Monday/...High Confidence. * Small Craft Advisory remains in effect for the outer waters through Sunday morning; expiring for the near-shore waters at 6 PM. Gusty SW winds across most waters (20-25 kt) should subside early tonight, then shift to W and ease to 10-20 kt. Seas to remain in the 4-6 ft range especially outer waters. Potential for thunder and lightning particularly for the southern waters later this evening and into the overnight. For Sunday/Sunday night: Winds become SW again but at sub-SCA levels. Seas begin to subside on all waters to 2-4 ft. Patchy fog and stratus could lead to lower visibilities, particularly Sunday night. Outlook /Monday Night through Thursday/... Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Patchy fog. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers, chance of thunderstorms, patchy fog. Areas of visibility 1 to 3 nm. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, chance of thunderstorms, patchy fog. Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ254>256. && $$ SYNOPSIS...Nocera/Loconto NEAR TERM...RM SHORT TERM...Loconto LONG TERM...Nocera AVIATION...RM MARINE...Nocera/Loconto/RM is the U.S. government's official web portal to all federal, state and local government web resources and services.