Updated Significant Weather Weekly Outlook
Excessive Heat Mid to Late Week
NWS has Issued an Excessive Heat Warning for Most of Southern New England
The weather message issued Monday June 29 describing the heat dome building over the eastern United States remains more or less valid. The main adjustment in this update is to extend the likelihood of the excessive heat into Saturday. A few temperature records may be broken – most likely on Thursday or Friday. Note that the National Weather Service Excessive Heat Watch has now been upgraded to an Excessive Heat Warning for most of southern New England.
Excessive Heat
Confidence is high that southern New England will experience excessive heat conditions Wednesday through Saturday with daytime temperatures rising to the upper 90s to around 100 degrees (except 85 to 90 across the Cape and Islands and very immediate south coast). Dewpoints are expected to be in the 65 to 70-degree range. Daytime heat indices will reach 100 to 110 across most of southern New England Wednesday through Saturday. Overnight temperatures will likely not drop below the 70s and may even not go below 80 degrees in major urban core areas such as Boston. The greatest change from yesterday’s message is that it looks as though this excessive heat episode will persist into Saturday (4th of July). This will be a prolonged and dangerous heat episode. It’s important to take precautions and check on those who could be more vulnerable (elderly, very young, medically compromised, etc.). Some relief in the heat and humidity is expected by Sunday as a cold front finally makes its way through New England.
Thunderstorms
There is much less confidence on the thunderstorm forecast. The heat and humidity (as well as possibly an elevated mixed layer) will set the stage for an unstable atmosphere over the next several days but probably with a lack of broad triggering ascent until a cold front approaches Saturday afternoon/evening. Although a series of shortwave troughs may move about the northeast side of the upper-level ridge, the deep high pressure area itself could cap convections due to subsidence aloft. A cluster of thunderstorms (embedded in the northwest flow about the large high pressure ridge aloft) may produce severe weather in Vermont late this afternoon/evening but also may weaken as they move into northwest or north central MA. Nevertheless, there is a low risk of damaging wind gusts over northwest or north central MA. Still another cluster of thunderstorms may approach southern New England from the northwest Wednesday evening or night, but it’s very uncertain how that might evolve, if at all. Cannot totally disregard the thunderstorm risk given that New England’s climatology contains several cases of strong thunderstorms in such northwest flow environments. However, a greater risk of thunderstorms, some possibly strong to severe, exists for Saturday afternoon/evening as a cold front approaches. Will continue to monitor that risk since some July 4 activities may be impacted.
As a reminder, this blog doesn’t attempt to “chase” thunderstorm development. People engaged in outdoor activities should monitor National Weather Service forecast updates as well as any warnings or statements.
Summary
In summary, expect dangerous heat Wednesday now through Saturday. Also, one or more episodes of thunderstorms may occur anytime this week with the best chance for more widespread thunderstorms Saturday afternoon/evening when a cold front and upper trough approaches. At this point confidence remains low on timing, coverage, and intensity.
Next Message
More weather blogs may be issued this week due to the excessive heat or if a significant risk for severe thunderstorms should become more apparent. The next significant weather weekly outlook is scheduled for Monday July 6.
Be safe. Wish all of you a Happy 4th of July and 250th birthday of our nation.
About this Blog and Disclaimer
The National Weather Service monitors the weather 24/7 and updates forecasts, watches, and warnings as necessary. For most of southern New England, refer to your local Weather Forecast Office for the latest forecast/warning information at weather.gov/box. For information from other Weather Forecast Offices, go to weather.gov and click on the location of interest on the map.
The frequency of this blog will depend upon the nature of the weather threat and availability of the author. Thus, for the latest information on weather forecasts and warnings, refer to the National Weather Service, which monitors and forecasts the weather 24/7.
Blue Hill Observatory and Science Center (BHOSC)
The BHOSC maintains a continuous daily observation record that dates from February 1, 1885 without interruption and provides educational information on weather and climate to area students and the community at large. Your support of BHOSC is much appreciated and enables this nonprofit organization to maintain the long-term climate record at the Blue Hill Observatory (longest continuous record in North America) and provide valuable educational resources on weather and climate via outreach to schools, site visits/tours, webinars, and conferences. For more information on the Blue Hill Observatory and Science Center, explore bluehill.org.
Message issued June 30, 2026 by:
Bob Thompson
Retired National Weather Service Meteorologist
Blue Hill Observatory and Science Center Board member
