Weather for New England and the Northeast

**Area Forecast Discussion, National Weather Service Gray ME**
**230 PM EDT
Thursday, September 17, 2026**

**What Has Changed**

High-resolution models have become a little more optimistic about pockets of heavier rain this evening across portions of southern New Hampshire and southwestern Maine.

**Key Messages**

1. A quick-moving low-pressure system and cold front will lead to increasing rain chances this afternoon through the first part of tonight. Expect some gusty winds behind the front on Friday afternoon.

2. Another rainy Sunday will be followed by mostly dry weather through much of next week, with temperatures running near to slightly below normal.

**Discussion**

**Key Message 1 Description**

As an upper-level shortwave, an area of lower pressure and rising motion higher in the atmosphere, approaches, a weak surface low will move from eastern New York early this afternoon to the southern New Hampshire and Maine border by this evening. These features will lead to increasing rain chances later this afternoon, with rain expanding north and east into western Maine through the first part of tonight.

The highest rain chances, 60 to 90 percent, will be along the track of the low and trailing cold front. The front should move across southern New Hampshire and into portions of the western Maine Foothills, the Interior, and the coast.

CAMs, or convection-allowing models designed to better resolve individual showers and thunderstorms, have come into fairly solid agreement on the track of the heavier showers. RAP, the Rapid Refresh weather model, soundings, which provide a vertical profile of the atmosphere, suggest there could be some MUCAPE around 100 J/kg. MUCAPE, or most unstable convective available potential energy, is a measure of how much energy is available for thunderstorms and stronger showers.

This means there will likely be a convective element to the rain, which could produce a few brief, heavier downpours. A rumble of thunder or two cannot be ruled out.

The best estimate is for higher rainfall totals in the 0.5 to 1 inch range, which matches well with what the **8 AM EDT HREF mean** is advertising. HREF, or High-Resolution Ensemble Forecast, is a model system that uses multiple forecasts to estimate the range of possible outcomes. The HREF 24-hour maximum precipitation output does suggest the potential for some 1.5 to 2 inch totals. Locally higher amounts will therefore be possible, depending on how the heavier showers develop.

Rain will then move out quickly overnight as the low moves into the Gulf of Maine.

Behind the cold front, Friday should bring plenty of sunshine and a stiff breeze. While pressure rises are not especially strong, we will see some decent cold air advection, meaning colder air moving into the region, along with steep low-level lapse rates. Lapse rates describe how quickly temperatures decrease with height in the atmosphere, and steeper lapse rates can help stronger winds mix down to the surface.

Forecast NAM and GFS soundings suggest winds of 30 to 35 knots near the top of the mixed layer. With the favorable atmospheric conditions, widespread wind gusts of 25 to 35 mph appear reasonable. The strongest winds are most likely across Maine.

Gusty winds could create a limited power outage threat if branches are brought down. Winds should diminish rather quickly around and after sunset Friday evening, becoming calm overnight.

While some lingering high clouds are possible, conditions should become favorable in many areas for radiational cooling, which occurs when the ground loses heat efficiently under relatively clear and calm conditions. Overnight lows may fall into the low to mid 30s along and north of the mountains, with temperatures in the upper 30s to mid 40s elsewhere. Some areas of frost will be possible across northern areas.

**Key Message 2 Description**

High pressure will slide through the region Saturday, making it the pick of the weekend. Upper-level troughing, or a dip in the jet-stream pattern that typically brings cooler air, will lower temperatures several thousand feet above the ground. The 850 millibar temperatures are expected to be around 36 to 41 degrees, which will support a cooler day with highs generally in the low to mid 60s.

Clouds will increase Saturday night as another shortwave moves through the broader upper-level trough toward the region and high pressure begins to move offshore. Temperatures will fall into the mid to upper 30s north of the mountains and into the low to mid 40s farther south.

High pressure will remain in place through Sunday morning, but rain will move into New Hampshire by Sunday afternoon as a wave of low pressure tracks through southern New England. There is some uncertainty regarding how far north the rain will extend, but the upward motion associated with the shortwave should be enough to produce measurable rainfall across most of the area.

The higher rainfall totals are likely to occur south of Concord, where stronger atmospheric forcing will overlap with higher moisture. NBM, or National Blend of Models, is currently showing a 40 to 50 percent probability of at least one-half inch of rain in that area.

Rain will taper off overnight, and by late Monday morning most of the area should be back under mostly sunny skies.

Global forecast models are in good agreement that strong high pressure will build and then settle over the region through much of next week. This should bring mostly dry conditions, with daytime temperatures generally in the 60s.

Nighttime temperatures should also be seasonable, ranging from the upper 30s in the north to the 40s in the south. With high pressure overhead, conditions will often be favorable for radiational cooling, and frost could develop in northern areas more than once.