556 FXUS61 KBOX 291904 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 304 PM EDT Mon Jun 29 2026 .WHAT HAS CHANGED... No significant changes. && .KEY MESSAGES... - Dangerously high heat indices are looking likely Wednesday through Friday and possibly lingering into the Fourth of July. - Showers and thunderstorms possible later this week. && .DISCUSSION... KEY MESSAGE 1...Dangerously high heat indices are looking likely Wednesday through Friday and possibly lingering into the Fourth of July. An anomalously strong upper level ridge will be centered over the lower Ohio Valley through the northern mid-Atlantic through the rest of the workweek, then beginning to flatten into the Fourth of July holiday. The presence of this ridge will advect the warmest airmass we've seen to this point in the summer by a large margin, with 850 mb temps running around +22 to +24C Wednesday through Friday. These values are similar/only slightly cooler on the Fourth of July, running around +18 to +21C. We've opted to extend the Extreme Heat Watch into the Fourth of July with this forecast package. This is not without uncertainty though, as the ridge starts to flatten on the Fourth of July, which opens the door for cloud cover and possible thunderstorm opportunities to cool us down. Still, with a number of outdoor activities ahead given the holiday, we didn't want to give the impression that the dangerously high heat indices are totally out of the question. Latest ensembles seem to be tilting in favor of a continuation of high heat and humidity on the Fourth of July. Peak of the heat and humidity falls on Wednesday through Friday, and the most oppressive of the days currently looks to be Thursday. Air temperatures in the mid 90s to around 100 with elevated dewpoints leading to high humidity levels, will favor heat indices in the 105 to 110 degree range with potential for even higher values. What is important to keep in mind is that this isn't just for one day: that we'll be dealing with this level of heat and humidity for 3 to potentially as many as 4 days, with muggy nighttime lows in the mid 70s adding to the accumulation of heat stress justifies the Watch. Even if heat indices fall short of extreme heat warning criterion on the Fourth of July, heat indices should still be enough to cause potential for heat- related illnesses. KEY MESSAGE 2...Showers and thunderstorms possible later this week. Southern New England is expected to remain east of a mid level ridge axis into the middle part of this week. This will keep us in a relative northwest flow aloft. Meanwhile, the increasing heat and humidity closer to the ground will result in some modest potential for showers and thunderstorms at times. Current thinking for Tuesday is that showers and thunderstorms should arrive from the northwest late in the day. This could be close to sunset, which will dampen the risk for stronger thunderstorms. Most unstable CAPE values of 500-800 J/kg are anticipated with 40+ kt of effective shear. Thus, thinking the greatest risk for the strongest convection will be to our northwest. Any showers should move off to our east or north by Wednesday as a warm front moves into northern New England and a high pressure over the central Appalachians takes more control of our weather. Cannot dismiss the idea of a few pop-up afternoon or evening showers and thunderstorms Wednesday through Friday, but most of this time should be dry. A front sagging south later Friday into Saturday should be our next chance for showers and thunderstorms. Those details will come into better focus with later forecasts this week. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 00Z Today...High confidence. VFR with light winds. Seabreezes continue through sunset. Tonight...High confidence. IFR likely to return with fog overnight across portions of SE MA, RI, CT, and the Cape and Islands. Winds mostly S, remaining light and going calm from time to time. Tuesday...High confidence. VFR. Winds pick up in the afternoon from the SSW, gusting to 20 kt across much of SE MA, RI, and CT. Showers possible towards the late evening hours. Tuesday Night...High Confidence. VFR. Light southwest winds. KBOS Terminal...High Confidence in TAF. KBDL Terminal...High Confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday through Thursday Night: VFR. Breezy. Friday: VFR. Breezy. Slight chance SHRA, slight chance TSRA. Friday Night: VFR. Slight chance SHRA. Independence Day: VFR. Chance SHRA, chance TSRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Tuesday Night: High confidence. Relatively light winds and seas expected through at least Tuesday morning. Increasing southwest winds ahead of a cold front could result in some gusts near 25 kt Tuesday afternoon into Tuesday night. Areas of fog return tonight, resulting in poor visibility less than 1 mile at times. Outlook /Wednesday through Saturday/... Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday: Winds less than 25 kt. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms. Independence Day: Winds less than 25 kt. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert from 11 AM to 11 PM EDT Tuesday for CTZ002. Extreme Heat Watch from Wednesday morning through Saturday evening for CTZ002>004. MA...Extreme Heat Watch from Wednesday morning through Saturday evening for MAZ002>021-026. RI...Extreme Heat Watch from Wednesday morning through Saturday evening for RIZ001>007. MARINE...None. && $$ DISCUSSION...Belk/Loconto AVIATION...Belk/Loconto MARINE...Belk/Loconto