Frontal System to Bring Showers, Storms to New England Through Tonight

A frontal system will cross to the north of New England, which will first lift a warm front across the region in the morning before dragging a cold front through New England later this evening into the overnight hours. This setup often results in a rather unsettled day with a couple rounds of thunderstorms and showers possible, and this system is no exception. The system's warm front will also usher in a very humid air mass, with dew points rising into the 70s for most of New England outside of Maine.

This morning's round of showers and storms will be mostly confined to northern New England with more isolated activity across southern New England. Overall, this afternoon has trended toward lower storm coverage as the cold front has slowed down, likely crossing New England in the evening and overnight hours. Still, a pre-frontal trough and energy should allow for some storms to develop earlier in the afternoon, but in general, many will likely have to wait until later in the day to see more wet weather and storms. The highest coverage of showers and storms later today will likely be in the 4pm (west)-11pm (east) time frame.

Below: HRRR showing potential weather early this afternoon (1st image) and later this evening (2nd image):

There will be a chance for some isolated strong to severe storms, but today will be far from an outbreak. The biggest severe threat will be damaging winds associated with the potential for wet microbursts to form. The other threat with these storms will be the potential for torrential downpours as the atmosphere will be very moisture-rich.

The positioning of the pre-frontal trough may support slow-moving and/or training storms through this evening and into the overnight hours, which would allow for localized flash flooding issues. Large hail and tornadoes are low concerns, but can't be completely ruled out. Should isolated discrete cells form earlier this afternoon, both hail and brief, weak tornadoes will be possible.

Looking at the ingredients for severe storms, the warm frontal passage will help set them up. First off, moisture will be very high with dew points into the 70s and precipitable water values extending to 2+ inches. Marginal effective shear up to 30 knots will be in place to help organize updrafts. The two main limiting factors will be lift and instability. The cold front will provide the main mode of lift, which has slowed down and likely won't really arrive for most of New England until after dark.

This sets up the instability issue. CAPE values will likely be 1,000-2,000+ this afternoon, which would be enough to support scattered severe storms. With that said, the greatest forcing for storms will come after this instability peaks with only isolated storms forming during this peak time.

Instability will be quickly waning toward and especially after sunset. How much instability builds this afternoon will also come down to how much clearing of the clouds can occur from this morning. With all of that said, only isolated severe weather is expected today and will be most likely across southern New England. Overall, there remains quite a bit of uncertainty with these storms given this is a same-day forecast.

The other story with this frontal system will be very high humidity and feels-like temperatures. Heat index values could reach well into the 90s toward 100° for southern and central New England. Dew point values in the low to mid 70s will make it feel rather tropical out there as well. Tonight's cold front will bring humidity levels down a notch for Wednesday and Thursday, but another cold front will sweep through New England later Thursday. This front will really bring humidity levels crashing down for the Fourth of July.

Thursday will likely see a sharper trough pass New England, with that surface cold front moving across the region later in the day. This may provide the basis for some pop-up showers and thunderstorms, especially later in the day. With that said, this system won't have much moisture to work with as moisture levels won't be very high, so unsettled weather may have a tough time forming. In general, shower activity will be more likely the farther north in New England you go.

Temperatures will likely gradually rebuild Saturday and Sunday, with each day a notch warmer than the last. Dry weather looks to be in store for Saturday with high pressure overhead ahead of a system that will be over the Great Lakes. Shower chances may begin to increase later on Sunday, especially for western New England, as a front approaches. Timing on any showers for later in the weekend remains uncertain, but overall, typical summer weather looks to hold strong for the foreseeable future.