623 FXUS61 KBOX 051111 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 711 AM EDT Thu Jun 5 2025 .SYNOPSIS... Hot and somewhat humid conditions are on tap for today with the risk of afternoon and evening isolated showers and thunderstorms...but most locations will remain dry. A much better chance of showers and thunderstorms exists Friday especially north of the Connecticut and Rhode Island border...where localized torrential rainfall and an isolated threat for severe weather will exist. A few showers and thunderstorms will remain possible Saturday but with temperatures cooling to seasonable levels. Mainly dry and seasonable weather is expected Sunday and Monday before the next chance of showers arrives by next Tuesday and/or Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Key Messages... * Hot & somewhat humid today with isolated showers/thunderstorms possible this afternoon and evening...but most locations remain dry * High temps in the 90-95 degree range away from the immediate coast Details... Upper level ridging will be in control of our weather today. The above normal height fields will result in 925T reaching around +25C this afternoon. Plenty of sunshine is expected today and while the HRRR/RAP indicate some smoke/haze in the sky today...the values are not as high as yesterday so do not expect a big impact on temperatures. Given the above...expect a hot and somewhat humid day. High temps to reach between 90 and 95 today in many locales away from the very immediate coast. Dewpoints will be in the lower to middle 60s...so heat index values will reach the lower to middle 90s in many locations. We do not meet the criteria for any heat headlines...but our experimental HeatRisk page is indicating moderate impacts to individuals who are sensitive to heat. Temperatures will be a few degrees cooler in the high terrain as well as the immediate coast with some localized sea breezes. The other issue is the risk for isolated showers/thunderstorms this afternoon and evening with modest instability developing. Upper level ridging overhead will limit forcing/upper level support...so any activity that develops should be isolated with most locations remaining dry. Some of the high resolution guidance indicates a bit better chance for isolated activity near and south of I-90... especially on any weak sea breeze front that develops or near terrain changes as a result of elevated heating. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Key Messages... * Dry/mild tonight after any isolated evening activity dissipates * Areas of showers/t-storms Fri with localized torrential rain with the focus for more widespread activity north of CT/RI/MA border * Isolated severe weather potential Fri Details... Tonight... Any isolated activity that is able to develop this afternoon will dissipate this evening with the loss of daytime heating and limited upper level support. Otherwise...mainly dry and unseasonably mild temperatures tonight. A ridge of high pressure off the mid-Atlantic coast will result in a most low level southwest flow tonight. This will hold low temps mainly in the middle to upper 60s...except a bit cooler from the modified marine airmass near the south coast. We may have some low clouds and fog patches try to develop near the south coast...but do not think any of that will make it much further north than that. Friday... A warm and humid airmass is on tap for Friday. While it will not be as hot as today...highs will still be into the 80s with dewpoints in the 60s. This will create a modest amount of instability with the HREF indicated 1500-2000 J/KG of Cape. This combined with a shortwave and a weak low level convergence boundary to ignite showers and thunderstorms. While this activity may occur just about anywhere...it looks like the primary area of concern will be north of the boundary where there is deeper moisture/forcing. So thinking that areas north of the CT/RI/MA border and especially across northern MA will see a fair amount of showers and thunderstorms developing by Friday afternoon. Pwats in excess of 1.5 inches and weak wind fields may result in torrential rainfall with any of the stronger t-storms along with very localized street flooding. Effective shear is on the lower side of what we like to see for severe weather...generally 20-30 knots but that is enough for some organized convection and perhaps an isolated severe weather risk too. The HREF is indicating fairly impressive probs of 2-5 KM UH swaths north of the CT/MA/RI border and especially in northern MA. The CSU Machine learning probs along with the HRRR Neural Network indicate an isolated severe weather risk...especially across western/central and northern MA. The main threat will be localized strong to damaging wind gusts. Given the above...we expect a fair amount of showers and thunderstorms to develop Friday. While the activity is possible anywhere...the focus or the majority of them north of the CT/RI/MA border. Main concern is pockets of torrential rainfall with the stronger slow moving storms and very localized street flooding. While shear is limited...20-30 knots north of the CT/RI border combined with the UH swaths might be enough to support an isolated severe weather threat. The main severe threat would be localized strong to damaging wind gusts the main concern. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Key Messages: * Chance that showers and thunderstorms linger into Saturday * Briefly dry Sunday into Monday before rain chances return Tuesday * Highs mostly in the upper 70s and low 80s through this period, aside from Saturday Details... Another round of showers likely throughout Saturday as a cold front moves into southern New England. While thunder can`t be ruled out as the NAM`s SBCAPE values look to be around 1000-1200 J/kg, severe storms are not likely. Guidance is hinting at a mostly dry Sunday heading into Monday as a broad high pressure starts to build over central Ontario. Rain chances and elevated surface moisture make a return Tuesday through Wednesday as a cold front sweeps through the Mid-Atlantic. Regarding temperatures... highs across southern New England are expected to remain in the upper 70s and low to mid 80s through the period. Saturday could be the exception as there is a chance some areas could remain in the lower 70s. Lows generally expected to remain in the high 50s to low 60s through the period. && .AVIATION /11Z THURSDAY THROUGH MONDAY/... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z TAF Update... Today...High confidence. VFR. SW winds 5-10 knots except for sea breeze development on portions of the immediate coast and 15-20 knots gusts over the Islands. There also will be an isolated shower/t-storm threat this afternoon into this evening...but most locations will remain dry. Tonight...High confidence. VFR outside some patchy of fog and low clouds which may develop near the south coast, Cape and Islands. Winds becoming light-calm. Friday...Moderate confidence. Varying conditions expected with VFR conditions and then times of MVFR-IFR cigs/vsbys in scattered showers and t-storms...a few of which might be strong and contain torrential rainfall resulting in brief LIFR conditions. Areal coverage will be greatest north of the CT/RI/MA border. Light and variable winds. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. Saturday: Mainly MVFR, with areas VFR possible. Chance SHRA, isolated TSRA. Saturday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Sunday: VFR. Slight chance SHRA. Sunday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Monday: Mainly VFR, with local IFR possible. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Friday...High Confidence. Pressure gradient will remain weak enough to keep winds/seas below small craft advisory thresholds through Fri. The main concern will be the risk for an isolated t-storm this afternoon/evening near shore with a better chance Fri especially across the waters adjacent to northeast MA. Lastly...areas of fog will be possible late tonight into Friday morning across the southern waters. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Slight chance of rain showers. Saturday through Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until 11 PM EDT this evening for CTZ002>004. MA...Air Quality Alert until 11 PM EDT this evening for MAZ006-007- 013-015-016. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/McMinn NEAR TERM...Frank SHORT TERM...Frank LONG TERM...McMinn AVIATION...Frank/McMinn MARINE...Frank/McMinn