Scattered Thunderstorms Likely Today Across New England, Some Strong

Yesterday's frontal boundary has slowly pushed farther south and is now draped across southern New England. With that, the threat of scattered storms has pushed south as well. A wave of low pressure will likely ride along the front, providing stronger forcing for showers and storms as opposed to Thursday. This low will eventually lift the front back north as a warm front this afternoon and evening.

After a couple rounds of isolated showers and storms through the morning, the main round of storms will likely begin to fire up early this afternoon across western New England. It may take some time for storms to begin to fill in this afternoon, so while numerous storms are expected, some may not see much activity until late in the afternoon or evening, especially across eastern Massachusetts and southeast New Hampshire.

Below: HRRR showing potential weather late this afternoon:

Conditions for storms will be more favorable than what was seen on Thursday. There will be 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 to the north and along the frontal boundary.

This is where lift and forcing will be strongest. This is the case since the boundary will likely be lifting back northward through the day. Southernmost and northernmost New England will likely see more limited activity. Central New England (northern MA, southern NH & VT) look to be in the best placement for storms given the boundary’s position.

Below: Weather map this afternoon, showing the boundary as a warm front lifting north:

There is a moderate chance of strong to severe storms across interior Massachusetts, southern New Hampshire and southern Vermont. The main threat will be gusty winds with a lesser chance for large hail compared to Thursday. With weak wind fields, the threat for tornadoes is nil. Elevated moisture and the potential for multiple rounds of convection will also lead to the potential for some localized flash flooding.

Looking at the ingredients in place for severe thunderstorms, lift and moisture will be abundant given a frontal boundary draped over the region and an attending wave of low pressure. Moisture remains elevated with high humidity and dew points, which will remain in place as the boundary lifts northward, placing southern New England within the warm sector.

Ample instability looks to build with CAPE values climbing into the 2,000 to 2,500+ joules/kilogram range. The biggest limiting factor today will be weaker shear. While enough shear is likely for scattered thunderstorm development, it will be on the weaker side for storms to become severe. Should strong to severe storms generally fail to develop, and if storm coverage ends up on the lower end, it will be because of marginal shear.

The other area to watch out for with these showers and storms will be the potential for torrential downpours and localized flash flooding. Precipitable water values (which measures the amount of water vapor in the atmosphere) are highly elevated, with values in excess of 1.5 inches. This indicates a moisture-rich atmosphere that will be primed for downpours within storms. With weak wind fields, storms could also be slow-moving.

Guidance is pointing to potentially 2-3 inches of rain falling within storms this afternoon and evening, which would be enough to exceed the flash flooding threshold, which currently sits at 2-3 inches of rain within three hours. Rainfall amounts will be highly varied and these high amounts will be localized. A flood watch has been posted for interior Massachusetts and much of New Hampshire given this threat.

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.

Below: HRRR showing potential weather Saturday morning (1st image) and Saturday afternoon (2nd image):