FXUS61 KBOX 021443 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1043 AM EDT Fri May 2 2025 .SYNOPSIS... The last of the scattered showers and embedded thunderstorms were already departing the Cape and Islands very early this morning. Otherwise...low clouds this morning should give way to a partly sunny and warm afternoon away from the south coast with mainly dry weather outside the risk of an isolated shower/t-storm or two. Another warm day is on tap for Saturday with scattered showers and thunderstorms developing during the afternoon...a few of which may become strong to severe. The weather pattern will remain unsettled at times for the first half of next week but with cooler temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10AM Update: 12z Guidance came in a bit more robust for afternoon thunderstorm coverage, but the question that remains is how well will the environment recover from thunderstorms last night and low cloud cover this morning. Thinking there is a short window this afternoon between 3-7pm where up to 1000 J/kg of CAPE could build and break the CAP. However, BUFKIT soundings show a significant dry layer around 500mb which could act against the updraft causing evaporative cooling aloft. With modest 0-6km shear, any convection that does form may become organized and produce lightning and strong wind gusts. Key Messages... * Clouds give way to partial sunshine later today with a warm afternoon & highs in the upper 70s/lower 80s NW of I-95 * Once the early AM activity departs much of today will be dry, but an isolated PM shower/t-storm or two is possible NW of I-95 Details... The elevated instability burst that brought the fast moving showers and embedded t-storms very early this morning was already departing the Cape/Islands. Otherwise...the main issue this morning will be low clouds and fog patches with the increase in low level moisture. Enough subsidence and mixing behind this early morning shortwave/warm front should be enough to allow for partial sunshine to develop away from the south coast by afternoon. The low clouds and fog patches may flirt with parts of the immediate south coast, Cape and Islands all day with increasing low level moisture. A warmer and a somewhat humid airmass will work into much of the region. The expected partial clearing and southwest flow should be enough to push highs into the upper 70s to the lower 80s northwest of I-95...but the southwest modified marine airmass will result in temps somewhat cooler southeast of this region and especially across the Cape/Islands. We do expect some instability to develop given decent ML lapse rates coupled with the warmer temps and increasing dewpoints. We are thinking we will see 500-1000 J/KG of Cape to develop northwest of I- 95 this afternoon. The limiting factor though appears to be subsidence and some mid level dry air behind the early morning shortwave. Therefore...we think much of today will be dry but enough instability is present for an isolated shower/t-storm or two this afternoon northwest of I-95. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Key Messages... * Unseasonably mild tonight with overnight lows in the 50s/near 60 * Warm Sat with highs in the lower 80s away from the south coast * A few strong to severe t-storms possible Sat PM near & NW of I-95 Details... Tonight... High pressure well off the mid Atlantic coast will combined with a vigorous shortwave over the central Plains to keep our region in an unseasonably mild southwest flow of air. Increasing low level moisture will result in overnight low temps only in the 50s to near 60. We also expect to see low clouds and fog patches develop across parts of RI/SE MA especially the near the south coast given the higher dewpoint air advecting in over the relatively cool ocean. Generally expect the weather to remain dry tonight...other than perhaps some drizzle/mist possible on the south coast given the low clouds and fog patches. Saturday... Partly sunny skies and southwest flow will result in another warm day for Sat along with a bit of humidity too. Given the unseasonably mild start and 925T near +20C...thinking high temps may reach the lower 80s away in many locations away from the modified marine airmass near the south coast. In fact...would not be surprised to see a few spots even reach the middle 80s. The biggest concern though will be for the convective risk Sat afternoon...mainly near and northwest of the I-95 corridor. The atmosphere will become somewhat unstable with surface Capes on the order of 1000 J/KG. The deep closed low over the central Plains should eject a piece of shortwave energy that will combined with the instability. Expect scattered showers & t-storms to develop Sat afternoon mainly near and northwest of the I-95 corridor. There also will be about 35 to 45 knots of effective shear. Putting this all together...the risk for a few strong to severe thunderstorms will be possible. The latest HREF indicates some modest 2-5 KM updraft helicity swaths and this is also supported by the CSU/NSSL machine learning probs. This all seems reasonable given modest amounts of effective shear and instability. While the instability probably will not be high enough for a widespread severe weather outbreak...isolated strong to severe t-storms with locally strong/damaging wind gusts, hail and brief torrential rainfall will be possible. We have included some enhanced wording in the forecast near and especially northwest of I-95. The marine layer should prevent convection towards the south coast, Cape and Islands. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Key Messages: * Frontal boundary near southern New England Sunday, bringing good chances for showers across the area. * Closed mid-level low slowly moves to the northeast next week and promotes unsettled/rain conditions. Saturday Night and Sunday: Guidance seems to finally be coming together for the late weekend, with the latest run of the GFS bringing that quasi-stationary front further south into New England... still further north than ECMWF/GEM, but a good indication that Sunday will remain wet for at least a decent portion of the day, especially across interior southern New England. Afternoon temperatures still a little tricky to nail down, but roughly in the upper 50s for the Islands, low 60s across the immediate coast and Cape, and upper 60s to possibly low 70s for the interior. Monday through Thursday: Stacked low over the southern Great Lakes region slowly moves northeast this coming week as ridging builds across the center of the country. This upper-level pattern and VORT maxes rotating about the mid-level low continues the unsettled and rainy conditions into next week, have opt'd to keep NBM POPs through next week as rain remains possible, though confidence in exact timing is low. Temperatures should remain in the mid to upper 60s for Tuesday, with a decent chance (roughly 50 percent on the ensembles) the interior could rise above 70F for Wednesday. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12z TAF Update... Today...Moderate Confidence. The last of the showers and isolated t-storms were already quickly exiting the Cape/Islands through 12z. Otherwise...MVFR- IFR conditions in mainly low clouds this morning should give way to mainly VFR levels by mid afternoon away from the south coast. However...low clouds and fog patches may continue to flirt with the immediate south coast, Cape and Islands through the day. Generally dry weather is on tap for much of today...but we can not rule out an isolated shower/t-storm during the afternoon across the interior. Winds becoming SW 5 to 15 knots. Tonight...Moderate Confidence. Moist low level southwest flow coupled with a cooling boundary layer will result in IFR-LIFR conditions in low clouds and fog across parts of RI/SE MA especially near the south coast. Given the winds are SW at the surface do not think the low clouds make it too much further northwest of I-95...but may see some localized patchy ground fog. Light SSW generally less than 10 knots. Saturday...High Confidence. VFR conditions will dominate much of the day except towards the Cape and Islands where low clouds and fog patches may impact the region. Otherwise...the main concern will be for scattered showers and thunderstorms Sat afternoon mainly near and northwest of the I-95 corridor. A few of these storms may be strong and produce brief heavy rainfall & localized strong wind gusts. The marine layer should result in little if any convection making it too far southeast of the I-95 corridor. KBOS TAF...Moderate Confidence in TAF. KBDL TAF...Moderate Confidence in TAF. Outlook /Saturday Night through Tuesday/... Saturday Night: MVFR/IFR conditions possible. Breezy. SHRA likely. Sunday: Mainly VFR, with local IFR possible. Chance SHRA. Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA likely. Monday: MVFR/IFR conditions possible. Breezy. Chance SHRA. Monday Night: MVFR/IFR conditions possible. Chance SHRA. Tuesday: MVFR/IFR conditions possible. Breezy. SHRA likely. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Saturday...High Confidence. A brief round of scattered showers and t-storms will impact the waters though daybreak...but depart not too long after sunrise. Otherwise...high pressure off the mid-Atlantic coast combined with shortwave energy passing to the northwest of the waters will result in a continued southwest flow of air across the region. SW winds may gust to 20+ knots at times...but overall thinking the inversion should keep winds/seas generally below small craft advisory thresholds. We still may see some choppy seas at times with brief marginal small craft conditions. Areas of fog may reduce vsbys for mariners at times especially this morning and again tonight over our southern waters. Outlook /Saturday Night through Tuesday/... Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Local visibility 1 to 3 nm. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Sunday Night: Winds less than 25 kt. Chance of rain showers. Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/McMinn NEAR TERM...Frank/KP SHORT TERM...Frank LONG TERM...McMinn AVIATION...Frank/McMinn MARINE...Frank/McMinn