Weather for New England and the Northeast

**Area Forecast Discussion**
**National Weather Service Gray ME**
**234 PM EDT Monday June 29 2026**

**What Has Changed**

A slight expansion of the Extreme Heat Watch now includes parts of southern Grafton County, including the Lebanon area. Forecast trends also indicate Saturday will likely be hotter than previously expected.

**Key Messages**

1. Heat builds into the region by Wednesday and continues through at least Friday. Saturday is also trending hotter. High humidity combined with the heat will create hazardous conditions from Wednesday through at least Friday. Air conditioning installations and other heat preparations should be completed by Tuesday.

2. Showers and thunderstorms will be possible most days through the holiday weekend. With abundant heat and humidity, any of these days could also produce strong to severe thunderstorms.

**Discussion**

**Key Message 1 Description**

Temperatures on Tuesday will climb into the upper 80s to lower 90s away from the coastline. Dew points remain in the lower 60s, so it will feel close to the actual air temperature, keeping heat index values below advisory criteria.

The significant heat arrives Wednesday, especially across New Hampshire and western Maine. Afternoon temperatures will climb into the middle to upper 90s, while other areas reach the middle 80s to lower 90s. A sea breeze should help keep the immediate Maine coastline cooler, with highs remaining in the 80s.

Dew points are expected to rise into the lower to middle 70s, pushing heat index values between 105 and 110 degrees across much of New Hampshire and western Maine. Forecasters expect some afternoon mixing of the atmosphere in the Merrimack River Valley, which could slightly lower humidity and reduce heat index values by a few degrees compared to the National Blend of Models, or NBM. Even so, conditions are still expected to reach warning level heat. An Extreme Heat Watch remains in effect because thunderstorms could still influence how hot it ultimately becomes.

Thursday continues to appear to be the hottest day of the week. Temperatures about one mile above the ground, known as the 850 millibar level, are forecast to reach around 72 degrees, a strong indicator of an exceptionally hot air mass. Afternoon highs near or above 100 degrees appear likely across much of the interior, especially southern New Hampshire. Whether the coast experiences a cooling sea breeze remains uncertain and will also depend on thunderstorm development.

Dew points will once again climb into the lower to middle 70s. Any rainfall Wednesday night would only add more moisture to the atmosphere, allowing heat index values to approach 110 degrees where afternoon temperatures reach the upper 90s or lower 100s.

Friday looks very similar, with widespread upper 90s to near 100 degrees expected once again. Humidity may ease slightly, but dew points should still remain in the upper 60s to lower 70s.

Saturday is increasingly expected to remain very hot, particularly across New Hampshire. Recent forecast trends suggest the upper level ridge of high pressure will remain in place for at least one more day. While it is still too early to know exactly how hot every location will become for the Fourth of July, planning for another day with highs in the middle to upper 90s across much of the interior is a good idea.

Sunday should finally bring some relief, although temperatures are still expected to remain above normal. Highs in the 80s to lower 90s currently appear most likely.

Overnight temperatures from Tuesday night through Friday night remain uncertain because thunderstorms could develop. Without storms, many locations across southern and central areas may only cool into the middle to upper 70s, with some parts of the Merrimack River Valley remaining close to 80 degrees Wednesday and Thursday nights. If thunderstorms develop, temperatures could briefly fall into the upper 60s to lower 70s.

All daytime temperature forecasts assume thunderstorms do not develop. If storms form during the afternoon, they could temporarily reduce temperatures and limit the overall heat.

**Key Message 2 Description**

Forecasting thunderstorms later this week will be challenging.

The atmosphere will contain plenty of energy for storm development because of the combination of extreme heat and increasing humidity. Meteorologists measure this available energy using CAPE, which stands for Convective Available Potential Energy. Forecasts indicate CAPE values will be more than sufficient to support strong thunderstorms.

Wind shear, the change in wind speed and direction with height, is also expected to remain favorable. Forecast guidance indicates bulk shear of at least 25 knots through much of the week, enough to help thunderstorms organize and persist rather than quickly collapse.

The European Centre for Medium Range Weather Forecasts Extreme Forecast Index, or ECMWF EFI, also continues to indicate that the combination of atmospheric instability and wind shear will remain unusually favorable for this time of year through the holiday weekend.

The remaining ingredient is a trigger to initiate thunderstorms.

Several possibilities exist. A disturbance in the upper atmosphere, known as a shortwave, could move through and produce more widespread thunderstorms. However, forecast guidance does not strongly support that scenario until at least Friday. Smaller disturbances generated by previous thunderstorms could also spark new development, but those are very difficult to predict more than about 24 hours in advance. Local features, such as mountain heating or sea breeze boundaries, may also initiate storms.

Because of these factors, isolated severe thunderstorms are possible nearly every day. If a stronger upper level disturbance develops later in the week, thunderstorm coverage and severity could become more widespread.

The primary hazard with any thunderstorm will be damaging straight line winds. Large hail is also possible, although the unusually warm atmosphere makes that threat somewhat lower than normal. The tornado threat also appears lower than average because of the lack of a strong large scale weather system. However, any thunderstorm will be capable of producing torrential precipitation, frequent lightning, and localized flooding.

Both afternoon and overnight thunderstorms remain possible through the work week. High resolution forecast models, known as CAMs, or Convective Allowing Models, continue to suggest that Mesoscale Convective Systems, or MCSs, clusters of organized thunderstorms, could develop to the west and gradually weaken as they move into the region Tuesday and Wednesday.
As the week progresses, the focus for these thunderstorm complexes is expected to gradually shift farther south.