Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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621 FXUS61 KBOX 070210 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1010 PM EDT Sat Jul 6 2024 .SYNOPSIS... Aside from a lone shower or thunderstorm, warm and muggy conditions will persist tonight. Summertime heat and humidity should prevail next week, along with scattered showers and thunderstorms, especially Wednesday through Saturday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 1000 PM Update: Updated the forecast to nowcast the developing areas of thunderstorms mainly north of the Mass Pike, carrying scattered t-storms for those locations thru 2 AM. These storms appear to be blossoming in response to a sagging sfc trough that trails from Berkshire County MA into western NH. Mixed-layer CAPE values still have about 1000-1500 J/kg according to SPC mesoanalyses, and the forecast suggests this axis of instability only slowly weakens. Considerable convective inhibition exists per SPC`s mesoanalysis, and while PSF did measure a 44 mph gust associated with these storms, it likely will not get worse than that in any of these storms as they move toward the E/ENE. Lightning and brief heavy downpours are the main risks associated with this activity and severe weather is not expected. It still is unclear what the shower/t-storm risk looks like for the remainder of the overnight into early morning; there are some hints that the boundary sags southeast into the fog/stratus-blanketed southeastern MA and RI and a few guidance sources show re-developing showers for those locations. This will need to be carefully evaluated overnight; wouldn`t entirely rule out thunderstorms for SE MA and RI since it is so muggy out, but the odds aren`t especially favoring that outcome. Should be trending drier the further northwest one goes, with a drop in dewpoints from the mid 70s to the mid to upper 60s. The next issue is expanding stratus and fog over at least eastern CT and areas near and southeast of I-95. It`s a favorable setting for continued expanding stratus at least trapped under the inversion, and while we`ve been seeing more sites report visbys in the 1 to 3 SM range tonight then prior nights, visby guidance the last couple nights has also overforecast fog. Will monitor this and if visbys do drop as low as guidance suggests, we`d consider fog statements for these. Otherwise, quite muggy out with lows in the mid 70s. Previous discussion: Still have a good amount of instability across interior this evening with MLCAPE as high as 2000 J/kg but airmass shows more inhibition (CIN) farther east into central/eastern MA, eastern CT, and RI. Storms have been firing to our west and north and we are starting to see some new activity developing near Berkshires. This should be the area to focus on early tonight where instability is collocated with strong 0-6km shear, but mid level lapse rates are meager at best which will prevent activity from becoming more organized. Minor flooding from brief downpours is main threat but storms are moving along quickly. High-res guidance continues to struggle with both timing and location in weakly forced environment. Otherwise, low cloud bank was spreading inland from RI and SE MA and should expand farther inland tonight, most likely into Worcester Hills and more of Merrimack Valley. Patches of dense fog also expected with persistent SW flow, mainly along and SE of Providence to Plymouth line. Warm and muggy night is in store with lows in upper 60s and 70s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... A front slowly sags into southern New England late tonight into Sunday. Not much push behind this front, so thinking this front is still lingering nearby into Sunday night, most likely toward the coast. Very humid conditions and above normal temperatures continue. That said, a subtle intrusion of drier air in the mid levels aloft should provide more of a cap on showers and thunderstorms during this time. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights: * Summertime heat and humidity most of next week - potential Heat Advisory for some Mon/Tue * Scattered showers/storms mainly Wed-Fri Ensembles are in good agreement next week and feature persistent subtropical ridge over the western Atlantic and upper trough near Great Lakes. This pattern favors typical summertime heat and humidity as SW flow aloft transports very warm and humid air up the East Coast. Core of heat and humidity looks to be Mon/Tue. We could reach Heat Advisory criteria (heat index 95-99F for 2 or more hours on consecutive days) away from coast and especially in the Connecticut and Merrimack Valleys as well as interior eastern MA. For rest of next week, presence of more cloud cover should keep highs in 80s, but overnight lows will probably stay in 70s, especially in urban areas. As we`ve seen over the past week, there probably won`t be a lot of larger scale forcing present to result in organized showers or thunderstorms. Rather, we should see weaker short waves from Great Lakes dampen out as they run into upper ridge offshore. Timing of these short waves is always a problem in the model world, especially at longer time ranges, but it does appear our better chances of showers/storms will be in the Wed-Sat timeframe (afternoon and evening) as we also have weak surface fronts nearby. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 00z TAFs: Moderate confidence (60%). Trend will be for conditions to lower to MVFR in western MA/CT and to IFR/LIFR across much of eastern CT, RI, and central/ eastern MA overnight. TS should be confined to western MA early tonight but another passing shower or storm is possible overnight. Slow improvement to VFR from NW to SE Sunday morning, but went more pessimistic near Cape Cod and Islands where persistent SW flow should keep IFR ceilings locked in all day, although visibility should improve by midday. Expecting LIFR to return there around sunset Sunday with VFR elsewhere. KBOS TAF...High confidence (70%). Timing of improvement Sunday may be a couple of hours too slow. KBDL TAF...High confidence (80%). Outlook /Monday through Thursday/... Monday through Monday Night: VFR. Tuesday: VFR. Slight chance SHRA, isolated TSRA. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. Wednesday: VFR. Breezy. Chance SHRA, isolated TSRA. Wednesday Night: VFR. Chance SHRA. Thursday: VFR. Chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Sunday Night: S to SW flow continues as a front slowly approaches the waters tonight, then likely stalls across the waters Sunday into Sunday night. A few gusts up to 25 kt, along with marginal 5-foot seas across the southern coastal waters, so continued the Small Craft Advisories into Sunday. Areas of fog may reduce visibility below 1 mile late tonight. Visibility expected to improve Sunday. Outlook /Monday through Thursday/... Monday through Tuesday: Winds less than 25 kt. Tuesday Night: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Wednesday: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms. Wednesday Night through Thursday: Winds less than 25 kt. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Sunday for ANZ254. Small Craft Advisory until 11 AM EDT Sunday for ANZ255-256. && $$ SYNOPSIS...Belk/JWD NEAR TERM...Belk/Loconto/JWD SHORT TERM...Belk LONG TERM...JWD AVIATION...Belk/Loconto/JWD MARINE...Belk/Loconto/JWD