The trade-off between high pressure and low pressure continues through this weekend for New England. High pressure will be overhead of New England for Friday before shifting offshore late today. This high will steadily slide away on Saturday as the next disturbance approaches. As this system makes its way from the Great Lakes, it will try to produce showers across northern Vermont and New Hampshire in the morning, but dry air may initially be able to keep much of the wet weather at bay initially.
By Saturday afternoon, scattered showers will begin to fill in across northern New England in the afternoon. These showers will continue to slide eastward through the evening. For southern New England, showers should hold off until after dark on Saturday, though clouds will begin to build in the afternoon.
HRRR showing potential weather Saturday mid-afternoon:
Showers will continue through the overnight hours, eventually pushing into all of New England as the system's warm front is pulled through the region. This front will provide the forcing for these showers Saturday afternoon through Sunday morning. During the afternoon Saturday, as the warm front lifts into New England, it will bring back a southerly flow, which will, in turn, bring a tropical-like air mass into New England.
This will bring higher humidity and a moisture-rich atmosphere. This will allow for a swath of heavy downpours to develop within the wider shower coverage. Placing where exactly the downpours set up is a challenge, but it looks to be most likely across northern and western New England, particularly Vermont.
HRRR showing potential weather late Saturday night:
With that said, any shower will have the chance to become a downpour in New England, but there will likely be more numerous showers across northern New England. These downpours may result in localized flooding issues. The Weather Prediction Center currently has Vermont, northern and western New Hampshire and northwest Maine in the "marginal" category (level 1 of 4) for excessive rainfall through Sunday morning.
There will also likely be gusty winds at times along with the showers as a rather strong (for summer) low-level jet crosses the region. This jet will be strongest over northern New England, particularly Vermont. This will help transport the southern moisture into the region, aiding in downpour development. Any thunder development could help mix these gusty winds to the ground, leading to gusty winds within the downpours.
Low-level jet winds (about 5,000 feet above sea level) around Saturday evening, showing 55-65mph winds across Vermont. This wind will generally stay aloft, but any storm/downpour could help bring some of the winds down to the ground for a time:
The bulk of this rain will be during the overnight hours with some lingering activity around in the morning. By Sunday morning, much of New England will be in the system’s warm sector. With showers ending and clouds potentially breaking, temperatures will climb into the 80s, and well into the 80s for some, along with high humidity.
This Sunday afternoon may feel a lot like last Sunday afternoon with humidity potentially spiking. This will help set the stage for afternoon thunderstorms to develop. This will come as the system’s cold front gets dragged across the region. As usual, the timing of this front will determine the extent of storm coverage and how strong storms can get.
Areas that see the front cross in the morning (i.e. western and northern New England) will have a lower storm and strong storm threat. As of now, the Storm Prediction Center has southern New England and the northern New England coastal plain in the “slight” category (level 2 of 5) for severe weather. This will hinge on the timing of the cold front and could change in later updates.
Current Storm Prediction Center thunderstorm outlook for Sunday:
After this weekend, the general weather pattern we’ve been in this week continues, with cooler and less humid weather behind this front for Monday as high pressure returns. Humidity will once again fall behind the front as well. Heat and humidity are looking to rebound heading toward the middle of next week (fourth of July), but nothing notable is popping up in guidance at this point.
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