Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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202 FXUS61 KBOX 200646 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 246 AM EDT Sat Jul 20 2024 .SYNOPSIS... High pressure will build southeastward early today. While this will bring a modest increase in cloud cover, mostly dry weather, seasonably warm temperatures and lower humidity levels are expected through the weekend. The pattern turns more active again next week with increasing humidity and periods of wet weather with heavy rain possible. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The main change today will be increasing cloudcover as mid and high clouds advect in on southwest flow around the high to our east. A layer of moisture around 800 mb also allows for some diurnal clouds to pop up late morning/afternoon as well, so expect a mix of clouds and sun much of the day. Dewpoints initially in the 50s will increase to the low 60s by the day`s end on increasingly moist SW flow, but comfortable humidity continues for much of the day accompanying high temperatures in the mid 80s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... While SNE remains under the influence of cyclonic flow aloft through the weekend a weak disturbance will rotate around the trough with potential to kick off an isolated shower later Saturday given PWATs briefly rising back to 1.5" and a weak warm front moving north. However, limited forcing should keep any pop-up showers isolated and most locations remain dry. Sunday looks to be more of the same, with mostly dry conditions but increasing lapse rates with diurnal heating beneath -10C temps at 500mb may allow for a few isolated diurnal showers. Less cloudcover will allow for temps a few degrees warmer, in the upper 80s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Key Points * Seasonable temps with increasing humidity next week. * Unsettled weather pattern returns with daily chances for rain and thunderstorms Monday - Friday. A more active pattern will set in again next week as deep SW flow aloft kicks back in bringing increased moisture and humidity. Temperatures this time wont be nearly as hot with highs peaking in the upper 80s Monday, then falling into the upper 70s to mid 80s by Wednesday and Thursday. Dewpoints on the other hand will rise into the upper 60s to low 70s again Monday and stay there through the week. As for rain chances this week, exact timing of features remains messy with several weak shortwaves traversing through the SW flow. Monday at this time appears the driest day with only isolated thunderstorms possible. Not expecting any severe thunderstorms with less then 500 J/kg of MLCAPE. A stronger shortwave and associated surface low looks to exit the Ohio River Valley mid week. Guidance was in good agreement on timing of this feature bringing it through late Tuesday into early Wednesday, but has since become more spread on the timing bringing it in as early as Tuesday afternoon to as late as Thursday afternoon. Guidance is also in significant disagreement on exact track of the low. PWATS ahead of this low increase upwards of 1.5 to 2.0+ inches which could bring heavy rain concerns to SNE. WPC has highlighted much of New England in a marginal risk for excessive rain on Wednesday. 24 hour Ensemble mean QPF for Wed and Thur are showing a wide spread 1/4 to 1/2 inch of rain, with 99th percentile still showing localized areas of 2 - 3 inches. Will also need to watch for severe weather in this time period with CSU machine learning guidance showing 5% probs for severe thunderstorms on Wednesday and Thursday. Looking way ahead to next weekend, the pattern appears to bring back drier conditions with an upper level ridge building in. This could bring back excessive heat concerns with CPC highlighting SNE in a slight risk for excessive heat. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 06z update... Today...High confidence. VFR, with increasing mid to high clouds today. Light and variable winds early this morning increast to 5-10 kts from the SW today. Tonight...High confidence. VFR. SW winds around 5 kt. Sunday...High confidence. VFR. W winds 5-10 kts. KBOS TAF...High confidence in TAF. VFR thru the period. SE seabreezes to shift to light S winds by 00-01Z, then increasing to around 5-10 kt on Sat and shifting to SW. KBDL TAF...High confidence in TAF. VFR thru the period. Variable winds shift to SW at 5-10 kts by Sat afternoon. Outlook /Sunday Night through Wednesday/... Sunday Night through Monday: VFR. Monday Night: VFR. Slight chance SHRA, isolated TSRA. Tuesday through Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. Wednesday: MVFR/IFR conditions possible. 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: High confidence. W/SW winds becoming breezing today especially over the nearshore waters, with speeds around 15-20 kt during the daytime hrs; decreasing to 10 kt or less this evening. Seas 2-3 feet or less all waters. Mostly dry weather to prevail though an isolated shower is possible. Dry weather continues for Sunday with SW winds continuing. Seas 2-3 feet. Outlook /Sunday Night through Wednesday/... Sunday Night through Monday Night: Winds less than 25 kt. Tuesday: Winds less than 25 kt. Slight chance of rain showers. Tuesday Night: Winds less than 25 kt. Chance of rain showers. Wednesday: Winds less than 25 kt. Chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...BL/KP NEAR TERM...BW SHORT TERM...BW LONG TERM...KP AVIATION...BW/KP MARINE...BW/KP