After a brief ridge of high pressure brought heat (to some) and mostly dry conditions, New England will be slipping right back into a pattern dominated by low pressure and stormy conditions. This transition back to low pressure will begin Thursday as a cutoff low south of New England slowly starts working north.
This cutoff low has been suppressed to the south due to a Rex Block (high pressure north of low pressure), however, this block is now beginning to break down. While the center of this low will not make it to New England until late this weekend, energy associated with the system will begin to arrive on Friday as an associated warm front lifts through New England.
THUNDERSTORMS & DOWNPOURS
It needs to be emphasized right off the bat that the downpours and thunderstorms will be scattered throughout the day. The overall setup is unlikely to lead to an all day rain event. Many areas will see plenty of dry times and some peaks of sun will be possible between the storms.
First image showing where the storms are likely to develop, second image showing the true nature of the event (i.e. more scattered, meaning an all day washout is unlikely):
On Friday, showers will be isolated and confined mainly to areas south of Boston and Springfield, Massachusetts. Clouds will increase across the region as will dew points. Humidity levels will be noticeably higher on Friday afternoon than what New England has seen so far this season, this will support high shower and storm activity.
Saturday is when thunderstorms and downpours will become widespread across the region. While the entire region will have the chance for downpours, the highest chance for thunder and lightning will be concentrated to areas away from the coastal plain.
The biggest threat, by far, with these storms will be the possibility of very heavy rainfall rates due to such high dew points. The Weather Prediction Center has parts of New England in the "marginal" risk of excessive rainfall for Saturday and Sunday (and Tuesday of next week as well). These areas are concentrated in western and northern New England.
Along with intense rainfall rates, storm training will be possible. This occurs when storms move very slowly, causing a localized area to get into a prolonged period of rain. Due to the scattered nature of the storms, any flooding (and flooding is looking isolated over the weekend) should remain localized.
At this time, it does not appear that a widespread severe thunderstorm outbreak will occur. Despite this, some isolated strong storms are possible with the threat of localized high winds and hail.
Sunday will be very similar to Saturday, although it currently looks like Sunday will feature less storms, leading to more and longer stretches of dry weather. Sunday is looking like the better of the two weekend days for most.
HUMIDITY & TEMPERATURES
Humidity will be on the rise big time from Friday afternoon right through early next week. By the weekend, dew points will be in the mid 60s north to low 70s south. These high humidity rates will hold through the early part of next week. This will really make it feel like summer as humidity levels like this have not been seen since last August.
Dew point levels on Saturday, expect the same on Sunday:
Thankfully, temperatures will not be soaring really high along with these oppressive dew points. Temperatures will be around seasonable levels, upper 70s to low 80s for southern New England and low to upper 70s for northern New England. Temperatures are mainly limited by thick clouds and rain.
BEYOND THIS WEEKEND
This unsettled pattern will continue until further notice, with daily chances for storms and showers through next week and potentially beyond next week as a parade of low pressure systems makes their way through the region.
Humidity will likely last through at least Tuesday. There are early indications of a cold front coming through in the middle of next week. This would knock out the high humidity and potentially bring a widespread rainfall event. This is an early indication and much can change, but should this hold up, flooding and rivers could become a concern as rain continues to fall.
Surface map for Wednesday, June 28 showing a cold front being dragged across New England, bringing more rain with it:
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