Weather for New England and the Northeast

**Area Forecast Discussion**
**National Weather Service Gray ME**
**238 AM EDT Sun Jun 21 2026**

**What Has Changed**

No significant changes with this forecast package.

**Key Messages**

1. Scattered showers and thunderstorms today.

2. Low pressure moves in late Monday, exiting east Tuesday morning. This will bring a soaking rain to the southern half of the forecast area, with lighter rain elsewhere. Locations that see rainfall from slow-moving showers this weekend will need to be monitored for repeat moderate to heavy rainfall Monday and Tuesday.

**Discussion**

**Key Message 1 Description**

A weak upper-level disturbance, known as a shortwave trough, will move through the region during the early afternoon today. Cold air aloft will help create steep lapse rates, meaning temperatures cool rapidly with height, which supports rising air and thunderstorm development. Combined with increasing surface moisture, this should allow atmospheric instability to build quickly by midday, with forecast values reaching around 1000 J/kg of surface-based CAPE, a measure of thunderstorm fuel.

Despite the increasing instability, wind shear will be very limited, with winds less than 20 mph through much of the atmosphere. Wind shear refers to changes in wind speed and direction with height and is often needed for storms to become organized and long-lived.

A weak surface trough, combined with the approaching upper-level disturbance, will help trigger scattered showers and thunderstorms beginning around midday. With little atmospheric inhibition present, storms should develop fairly easily. A few stronger cells may produce small hail and gusty surface winds. However, because wind shear is so weak, storms are not expected to organize. Most will remain short-lived, with collapsing storm cores producing outflow winds that may trigger additional nearby showers and thunderstorms.

Shower and thunderstorm coverage will decrease rapidly later this afternoon and evening as daytime heating fades and the upper-level disturbance moves east.

Winds will be much lighter than on Saturday. High temperatures are expected to climb well into the 70s across most lower elevations.

**Key Message 2 Description**

Forecast confidence continues to improve regarding rainfall expected Monday through Monday night. Low pressure moving out of the Ohio Valley will push a warm front toward southern New England. A fast-moving weather disturbance will ride along this boundary, although forecast models still differ somewhat on how broad the rainfall coverage will be.

Recent European ensemble guidance has shifted slightly farther south and now represents the favored solution among major forecast models. The primary rainfall mechanism appears to be frontogenetic banding, often called fgen banding in meteorology. This occurs when temperature contrasts strengthen and force air upward, producing concentrated areas of heavier rain. The setup resembles the tightly wrapped precipitation shield often seen with winter storms.

As the developing low pressure system moves across southern New England and then northeast through the Gulf of Maine, the rainfall shield will move with it. This should keep rain chances elevated Monday evening across much of southern New Hampshire, coastal Maine, and portions of interior Maine before tapering off early Tuesday morning.

The atmosphere will contain abundant moisture, with precipitable water values, known as PWATs, near the 90th percentile for this time of year. Warm cloud depths of roughly 11,000 to 12,000 feet and high relative humidity below about 18,000 feet will support efficient rainfall production. In simple terms, much of the moisture available in the atmosphere will be converted into rainfall where the strongest lift occurs.

The heaviest rainfall corridor is becoming more focused on southern New Hampshire and the southern Maine coast, although any additional shift in the storm track could move that axis farther north. Because some locations may receive slow-moving showers or thunderstorms today before the main rainfall event arrives, forecasters will be monitoring for localized flooding concerns Monday and Tuesday.

Wednesday should bring a break from widespread rainfall. However, lingering low-level moisture will support afternoon cloud development and scattered showers, especially across the mountains and interior areas. Thursday may follow a similar pattern, with warmer temperatures and isolated to scattered showers. Another larger-scale weather system could arrive late in the week with additional rainfall and thunderstorms, but forecast confidence remains too low to determine specific impacts at this time.