Weather for New England and the Northeast

*Area Forecast Discussion**
**National Weather Service Gray ME**
**628 AM EDT Monday June 29 2026**

## **What Has Changed**

An Extreme Heat Watch has been issued for portions of New Hampshire and southwestern Maine from Wednesday through Friday. The aviation forecast has also been updated for the 12Z TAF forecast package.

**Key Messages**

1. High pressure brings fair weather today.

2. Hot and humid conditions arrive this week, with near record breaking heat becoming increasingly likely from the middle through the end of the week. Any preparations, such as installing air conditioning units, should be completed early this week before the hottest conditions begin on Wednesday.

3. Building heat and humidity will provide fuel for thunderstorms beginning Tuesday, with chances continuing most days through the end of the week.

**Discussion**

**Key Message 1**

An upper level trough, an area of lower pressure in the atmosphere, moves east this morning while high pressure builds into the region from southeastern Canada. This will bring a pleasant day with afternoon temperatures reaching the 80s and relatively comfortable humidity. Light winds will allow a sea breeze to develop during the early afternoon, carrying cooler ocean air well inland.

**Key Message 2**

The warming trend continues Tuesday with widespread afternoon temperatures in the 80s to lower 90s across inland areas. Along the coast, winds coming in from the ocean should keep temperatures mainly in the 70s for another day. Dew points, a measure of moisture in the air, will generally be in the lower 60s, so it will not feel much hotter than the actual air temperature.

By Wednesday, significant heat is expected across much of New Hampshire and western Maine as afternoon temperatures climb into the 90s. What makes this event especially notable is the amount of moisture accompanying the heat. Dew points are expected to rise into the lower to middle 70s, pushing heat index values into the triple digits where temperatures reach the 90s. These very humid conditions are expected to continue through at least Friday.

Nighttime temperatures from Wednesday through Friday will only fall into the 70s in many locations. These unusually warm nights will limit overnight cooling, allowing heat stress to build over several days.

One factor that could affect how hot it becomes is the possibility of clusters of thunderstorms developing near the Great Lakes and moving into New England around the edge of the high pressure ridge. If they arrive during the middle of the day, they could reduce daytime heating. If they arrive at other times, they would mainly increase humidity. Forecast confidence on the exact timing of these storm complexes should improve over the next day since their impacts will vary from place to place.

Outside of any thunderstorms, the hottest weather is expected Thursday and Friday. Forecast temperatures about 5,000 feet above the ground support afternoon highs near record levels, potentially reaching 97 to 102 degrees, depending on cloud cover, thunderstorms, or cooling sea breezes. The primary concern is not whether temperatures reach 100 degrees, but that dangerous heat and humidity are becoming increasingly likely, with heat index values approaching 110 degrees by Thursday.

As a result, an Extreme Heat Watch has been issued for portions of New Hampshire and southwestern Maine from Wednesday through Friday. The watch covers the areas most likely to experience heat index values of 105 degrees or higher each afternoon. Heat Advisories may be needed for surrounding areas as the event approaches, and parts of the current watch area could eventually be changed to advisories if forecast conditions warrant.

Recent forecast guidance has also increased the possibility that this dangerous heat could continue into Friday or even Saturday. Forecast trends have steadily become hotter for Wednesday and Thursday over the past several days and now appear to be doing the same for Friday and Saturday. Forecasters will continue monitoring this trend as cooler air remains just east of New England over Atlantic Canada.

**Key Message 3**

Low pressure moving northeast across Canada will lift a warm front into the region Tuesday afternoon, with the front moving through northern Maine by Wednesday morning. This boundary will provide the focus for showers and thunderstorms.

While the greatest atmospheric instability is expected to remain west of the region, there should still be enough wind shear, changing wind speed and direction with height, near the front to support organized thunderstorms. Several forecast models suggest that a **Mesoscale Convective System (MCS)**, a large organized cluster of thunderstorms, could move southeast across the Northeast late Tuesday, followed by additional rounds of thunderstorms Tuesday night.

The **Storm Prediction Center (SPC)** currently places parts of eastern New York and Vermont under a Marginal Risk for severe thunderstorms. That risk extends toward the Connecticut River Valley and could shift farther east if newer high resolution forecast models continue the current trend.

On Wednesday, forecast models indicate the potential for unusually high amounts of **Convective Available Potential Energy (CAPE)**, which measures the amount of energy available for thunderstorms to develop. They also suggest the presence of an **Elevated Mixed Layer (EML)**, a layer of warm, dry air several thousand feet above the ground that can help thunderstorms become stronger once they develop. Although there may be limited lifting mechanisms to trigger storms, any thunderstorm complexes moving around the high pressure ridge could become severe.

Forecast confidence remains lower regarding the exact timing and coverage of thunderstorms from Wednesday through Friday, but the overall weather pattern continues to support repeated opportunities for storms. Forecast guidance from **Colorado State University (CSU)** machine learning tools also continues to indicate this potential.