Frontal Boundary to Bring Storms, Showers to New England Through Saturday

Upper-level ridging remains in control for many in New England, though it will slowly break down as a slow-moving frontal boundary pushes into northern New England. This boundary will push its way into northern New England from Canada this afternoon, but won't make too much progress southward. This front will provide the basis for multiple rounds of thunderstorms and showers across New England over the coming days.

As far as the storm potential goes for Thursday, there will be ample shear and moisture to fuel and drive thunderstorm development. Instability will present with CAPE values building toward 1,500-2,000 joules/kilogram across the region, which is plenty to allow for storms. The big issue, which will likely greatly limit storm coverage, especially across southern and central New England, will be a lack of lift and weak forcing.

The window for thunderstorms will be rather narrow for northernmost New England as the front will likely cross into the area from Canada early in the afternoon. Storms will likely fire up in greater numbers across the mountains and foothills by mid-afternoon and last through the evening.

Storms will likely be most numerous in a band across northern New England where the boundary sets up in the afternoon; this is where forcing will be strongest. With that said, the amount of instability and moisture alone could allow for an isolated storm or two to pop up anywhere in the region, including southern New England.

Below: HRRR showing potential weather late this afternoon:

The threat for strong to severe storms is on the lower end, but muted ingredients are in place with instability and moisture building. Shear will be strongest near the Canadian border and lift will be strongest along the cold front, as stated before. Large hail across northernmost New England will be a threat in any strong storm as well as the potential for damaging winds within potential downbursts.

As the frontal boundary slowly pushes farther south on Friday, the threat of scattered storms will push south as well. By Friday, the boundary will likely be draped over southern New England, near the southern Massachusetts border. A wave of low pressure will likely ride along the front, providing stronger forcing for showers and storms as opposed to Thursday. This wave will eventually lift the front back north as a warm front.

Overall conditions for storms will be similar to Thursday, with ample instability and moisture in place. There should also be enough shear to help storms maintain themselves after forming. The greatest chance for storms and showers will be on the north side of the frontal boundary. This is where lift and forcing will be stronger.

This is the case since the boundary will likely be lifting back northward later in the day. Southernmost and northernmost New England will likely see much more limited to no activity. There will be more isolated chances for showers or even a couple thunderstorms Friday morning before the main round later in the afternoon.

Below: HRRR showing potential weather mid-morning Friday (1st image) and late Friday afternoon (2nd image):

The threat for strong to severe storms will be at a similar level to Thursday, just shifted south. The overall threat is on the lower end, but enough will be in place for some storms to get juicy. CAPE values will once again rise into the 1,500 to 2,000 j/kg range. Moisture will still be ample and forcing will generally be stronger. Shear levels, while sufficient for thunderstorms, are on the lower end for severe storms, which will be the main limiting factor. The main threat will be gusty winds with a lesser chance for large hail compared to Thursday.

By Saturday, an area of low pressure will likely move just to the north of New England and into northern Maine as the frontal boundary continues to waffle over the region. This low will eventually drag a cold front across New England as it exits. This will allow for continued rounds of showers and storms into Saturday, with the wettest weather occurring across northern New England.

At this point, it looks like Saturday will be wettest across northern New England, closer to the actual area of low pressure. Moving south, away from the low, showers look to become more scattered in nature with less forcing. Showers across southern New England will likely erupt along the cold front while a period of longer-lasting rain may develop across northern New England. A half inch to inch of rain is possible for northern New England with much less across southern New England amid more widely scattered showers.

Below: RGEM showing potential weather early Saturday afternoon:

After a few days and many rounds of showers and storms later, the boundary looks to clear out by Sunday, setting up a drying trend. New England's next system looks to approach around next Tuesday. After cooling off this weekend and into early next week, signals point toward another round of summer heat late next week. Whether that manages to develop or not will remain to be seen.