000 FXUS61 KBOX 202325 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 725 PM EDT Fri Sep 20 2019 .SYNOPSIS... High pressure remains in control into Monday with summer-like temperatures and dry weather. A cold front will bring a period of showers late Monday and Monday night followed by cooler but seasonably warm weather through the rest of the week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 7 pm update... Forecast remains in great shape with no significant changes needed attm. While current temps are outpacing forecast values by a few degrees, expectation of good radiational cooling commencing with sundown should bring temperatures more in line. Essentially a modified persistence forecast to last night with high pressure in control; the main exception being that temperatures should be several degrees warmer than the last couple nights as low-level temps have moderated to some extent. Still looking at development of radiation fog in the CT River Valley. Lows mainly upper 40s across western MA/Pioneer Valley and into the low-mid 50s elsewhere. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... Mid level ridge builds across New Eng with warming temps aloft. Expect lots of sunshine and warmer temps. 925 mb temps 20-21C so we should see highs into the low/mid 80s, except upper 70s along the immediate coast as sea breezes develop. While the swell from Hurricane Humberto will be subsiding, it will not be entirely gone. Still an elevated risk for rip currents Saturday. If going to the beach this weekend, be especially cautious if there are no lifeguards present. Saturday night... Mainly clear skies with some high clouds spilling into the region as mid level shortwave approaches. Lows ranging through the 50s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... * Continued dry weather with mild daytime temperatures Sunday. * Rain/brief downpours associated with cold front Monday night- Tuesday. Possible embedded thunder. * Brief cooldown Tuesday, turning warmer by late week/weekend. Details... Sunday... Upper-level ridge crests and shifts eastward into the Gulf of Maine by early Sunday. Continued mild and dry weather looks to continue into Sunday under surface high pressure and highs into the 80s. Will also see some southwesterly breezes, strongest toward the south coast (nearing 25 mph). Later Sunday into the overnight, geopotential heights start to fall and ribbon of mid-high level moisture on increasing west-southwest flow should lead to an increase in clouds. Combination of clouds and southwesterly winds should keep temperatures from falling too far - into the 60s most areas. Monday - Tuesday... First part of Monday now looking to be dry, though cloud cover will be steadily filling/lowering from west to east in advance of a cold front. Guidance still keying on frontal passing timing beginning mainly after sundown (12z NAM is a few hours earlier) through the first half of the evening across interior MA/CT and RI and not until the overnight toward the Boston-Providence/I-95 corridor, and into early Tuesday on the Cape, Islands and coastal waters. Ahead of and along the front, deep layer moisture quality improves with PWAT values rising to 1.5-1.75" and warm cloud depths are between 10-12kft. These values argue for brief downpours along what would likely be a strongly-forced band of frontal rain, perhaps embedded with rumbles of thunder driven mainly from favorable dynamics versus convective instability. Any embedded thunder would only serve to enhance rainfall rates, and while wind fields are strong with straight hodographs, strong storms aren't anticipated in light of the meager instability progged given unfavorable time of day and weak mid-level lapse rates. Even the faster NAM only generates about 500 J/kg or less of CAPE from a most-unstable parcel ascent. Still some leftover showers into Tuesday on the Cape, but across the interior looking at variable clouds with cold advection bringing temps closer to seasonal values. With cooler thermal profiles aloft, may still be enough moisture and shallow instability to produce some spotty daytime convective showers in northern MA mainly near and north of Route 2. Still some lingering clouds but dry weather anticipated by Tuesday night. Wednesday thru Friday: By Wednesday, the 500 mb pattern across the eastern roughly two thirds of CONUS transitions to one of quasi-zonal flow - governed by a prominent upper low over Hudson Bay with mean troughing into the northern Plains and northern Rockies, a closed low over the Desert Southwest, and a subtropical ridge over the Deep South into the northern Gulf of Mexico. Wednesday's looking largely dry, with temperatures moderating amid 850 mb temperatures rising to the 10-12C range supporting 70s to near 80s. Still some level of uncertainty on a potential frontal passage Thursday - with the GFS/Canadian indicating a wetter frontal passage than the ECMWF is, though limited moisture from the Gulf of Mexico could lend support to the drier FROPA indicated by the EC. Looking ahead, another period of above-normal temps looks to be in the offing for late next week into next weekend per most models and teleconnection forecasts centered in the 6-10 day period. It also jives with CPC's 6-10 day temperature outlook showing a significant tilt in the odds toward above-normal temperatures across southern New England. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. 7 pm update: VFR to continue though the 00z TAF valid period, with generally light winds. Sea breezes developing by midday Saturday to affect BOS with northeast- easterlies under 10 kts. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Sunday through Wednesday/... Saturday Night: VFR. Sunday through Sunday Night: VFR. Breezy. Monday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Monday Night: Mainly MVFR, with areas VFR possible. Breezy. Chance SHRA. Tuesday: Mainly VFR, with areas MVFR possible. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/...High confidence. 7 pm update: Forecast still on track. Still have high surf advisories in effect till 9 PM tonight, and small craft advisories through Saturday due to rough seas due to swell from Humberto. Should see the peak of the swell occur by this evening, with receding trends into Saturday night. Light winds through the period. Outlook /Sunday through Wednesday/...Moderate confidence. Saturday Night through Sunday: Winds less than 25 kt. Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain showers likely. Tuesday: Winds less than 25 kt. Local rough seas. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Surf Advisory until 9 PM EDT this evening for MAZ007-019- 020-022>024. RI...High Surf Advisory until 9 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 2 PM EDT Saturday for ANZ250-254. Small Craft Advisory until 8 AM EDT Saturday for ANZ251. Small Craft Advisory until 11 AM EDT Saturday for ANZ255. Small Craft Advisory until 6 AM EDT Saturday for ANZ256. && $$ SYNOPSIS...KJC/Loconto NEAR TERM...KJC/Loconto SHORT TERM...KJC LONG TERM...Loconto AVIATION...KJC/Loconto MARINE...KJC/Loconto