661 FXUS61 KBOX 071924 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 324 PM EDT Mon Sep 7 2020 .SYNOPSIS... Increasing warmth and humidity Tuesday into Wednesday although mainly dry weather will continue. Periods of showers and embedded storms are possible on Thursday especially along and south of the Massachusetts Turnpike. Cooler temperatures, dry conditions and low humidity levels for late in the week into much of the upcoming weekend under high pressure. After Thursday, a cold front later on Sunday offers the next chance for rains. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... * Areas of Fog after midnight, which may be locally dense 315 PM Update... A weakening cold front to our west combined with strengthening upper level ridging to our east will keep our weather quite pleasant this evening. These two features will result in southerly flow and increasing low level moisture overnight. This coupled with a cooling boundary layer will allow for the formation of some low clouds and fog mainly after midnight. While the extent of the low clouds/fog remain a bit uncertain, appears they may be most extensive across portions of RI/SE MA. Some of the fog may become locally dense too, so this will need to be monitored overnight. We can not rule out some spotty drizzle developing too, but opted not to include in the forecast at this time. Winds will diminish this evening and become light overnight. This should allow temperatures to bottom out in the upper 50s to the lower 60s by daybreak. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... * Dry and warm on Tuesday, but turning more humid Tuesday... Strong upper level ridging east of our waters will result in a rather warm day and it will be turning more humid. Low clouds/fog patches should burnoff in most locations by mid morning. Partly to mostly sunny skies and 925T near +21C should allow afternoon highs to reach the middle to upper 80s in most locations, but it will be a few degrees cooler along the immediate coast/high terrain. Dewpoints in the 60s will certainly bring a return to some humidity across the region. Tuesday night... Strong upper level ridging to our east will remain in control. This will result in continued quiet weather, but we will have to watch for more low clouds and fog developing after midnight. Overnight low temps will drop into the upper 50s to middle 60s in most locations by daybreak. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Highlights... * Dry, but above normal temperatures and rising humidity levels for Wed. * Periods of showers and embedded thunderstorms, some with brief downpours for Thu - best chances along/south of the Mass Pike. * Dry conditions with cooler temperatures and low humidity levels Fri thru Sat nite. * Next chance for rain after Thu looks to be late Sunday with a cold front. Details... Wednesday through Wednesday Night: Ridge of high pressure over Southern New England will remain in control through Wed. SW flow aloft around anomalously strong upper level ridge over the North Atlantic (592 dm!) maintains mid-teens Celsius 850 mb temps. Higher moisture levels further south will support greater cloudiness further south and east, but despite this we are still looking at above-normal high temperatures in the 80s with mid to upper 60s dewpoints making it feel fairly humid. Will be be for most of the day, though a weakness in the ridge later Wed evening allows for tropical moisture (dewpoints rising into the upper 60s to lower 70s/PWATs climbing to at or around 1.5") to return to Southern New England. This will bring an increasing threat of at least showers for areas along and south of the Mass Pike for the overnight/early-AM hrs. Fairly muggy lows in the mid to upper 60s. Thursday/Thursday Night: Continued warm and humid but also fairly unsettled as weakness in the ridge and weak instability fosters periods of showers and a few embedded thunderstorms moving NE around the subtropical ridge. How far north this threat exists is still a little unclear, though most of the 12z models indicates the best chances are along and south of the Mass Pike. Soundings show tall, skinny CAPE profiles, warm cloud depths over 10000' and PWATs 1.75" supporting a risk for localized downpours. Weak flow fields and limited instability should make the thunder threat more of a garden variety type versus any credible strong/severe potential. Threat of showers/embedded storms should continue in the evening hrs before a strong ridge of high pressure over the Great Lakes shifts the precipitation offshore and allows for drying to filter into northwest into central MA. Lows will range from the mid 50 across northern parts of the interior to the upper 50s to lower 60s, highest towards Cape Cod and the Islands. Friday into the Weekend: Indications again point to another nice close to the workweek and into a good part of the weekend as aforementioned high pressure cell builds over New England with 500 mb heights on the rise thru Sat nite. Cooler high temperatures with strong diurnal ranges, much lower humidity levels and generally clear skies are anticipated to characterize sensible wx conditions at least through Saturday night. Highs Friday and Saturday mainly in the low to mid 70s, with lows in the upper 40s to the 50s. By Sunday, a closed upper low initially detached from the stronger belt of westerlies that was lingering around the Rockies becomes embedded in the stronger flow aloft, and deamplifies as it approaches the Great Lakes. This feature and its associated cold front looks to offer our next chance for precipitation after Thursday, though at the moment it doesn't appear to be too significant a rain-maker. Some variation across models in terms of timing this front through the region, though currently appears to be late in the day into the evening. A brief increase in dewpoints and humidity levels is likely to precede the front but looks to be fairly brief with drying conditions for overnight hrs. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18Z update... Tonight: Moderate confidence. VFR conditions continue this evening. Some MVFR-IFR cigs/vsbys will develop after midnight, but the areal coverage & extent remains uncertain. It does appear that it will be most extensive across portions of RI/SE based on model consensus. Gusty S winds diminish early this evening. Tuesday: High confidence. Most of the low clouds/fog patches should burnoff by mid morning. Otherwise, VFR conditions are on tap for Tuesday. S winds 5 to 10 knots, but some sea breeze component is expected onshore. Tuesday night: Moderate confidence. VFR early in the evening, but will likely see some more MVFR- IFR cigs/vsbys develop during the late evening/overnight hours. Areal extent and timing remains uncertain. Light S winds. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Wednesday through Friday/... Tuesday Night: Mainly VFR, with local MVFR possible. Patchy BR. Wednesday: VFR. Wednesday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Thursday: Mainly MVFR, with areas VFR possible. Chance SHRA, isolated TSRA. Thursday Night: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA. Friday: VFR. Breezy. && .MARINE... Tonight through Tuesday night...High confidence. Upper level ridging east of our waters will result in persistent SSE winds of 5 to 15 knots. Pressure gradient will remain weak enough to keep winds/seas below SCA thresholds. The main issue will be the potential for some overnight and early morning fog, which might be locally dense for portions of our southern waters. Outlook /Wednesday through Friday/... Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms. Friday: Winds less than 25 kt. Seas up to 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Loconto NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Loconto AVIATION...Frank/Loconto MARINE...Frank/Loconto