A maturing upper-level low bringing widespread severe thunderstorms to parts of the Midwest Tuesday will trek across the Northeast Wednesday and Thursday, prompting the development of heavy rain and thunderstorms. Fortunately for the Northeast, most of these storms are not expected to be severe.
Clouds and light rain showers will move into western Pennsylvania and New York Wednesday morning, with increasing cloud coverage ahead of them. This initial round of rain will be most intense and greatest in coverage in northwest Pennsylvania and Western New York, with lesser coverage and intensity in the showers further south and east. The shield of rain will broaden and travel northeastwards, approaching Albany by sunset. Thunder is not expected with this first round of rain, since instability will be weak. Besides a few isolated showers in the evening, Wednesday should be dry south and east of I-87.
Just trailing the shield of showers, a vigorous low-level jet will supply ample moisture and lift to support heavy downpours and embedded thunderstorms overnight Wednesday into Thursday morning. These heavy showers and thunderstorms will approach the I-81 corridor after midnight and the I-95 and I-87 corridors before rush hour Thursday morning. Some of these storms may produce strong gusts of wind given the strong low-level winds. Rain chances will decrease further south and east Thursday morning so that South Jersey and eastern Long Island may not receive much rain.
Clearing will ensue Thursday afternoon for areas that received rain Thursday night. Despite the passage of a cold front, the environment will quickly warm as a ridging of high pressure expands. Thus, enough instability will remain Thursday afternoon for few thunderstorms may develop through the early evening hours in the northern Mid-Atlantic and western New England.
Further east, the weak cold frontal boundary will get left behind by the upper-level low Thursday morning, triggering discrete but widespread downpours in eastern New England throughout the day. Rain will linger in Boston until late afternoon and eastern Maine until Thursday night.
A general 1-2 inch swath of rain will fall over northern Pennsylvania, New York, and western and northern New England where the initial rain shield will overspread Wednesday into Wednesday night. Much lower rainfall totals of up to a half inch with locally higher amounts will fall over New Jersey and southeastern New York, where downpours will be less widespread.
Following these storms, the Northeast will warm and dry out Friday, which will mark the start of a heatwave for many. The region will remain mostly dry until a cold front ends the heat between Monday and the July 4th Holiday.