In general, cool and unsettled weather will prevail for the upcoming week as a large low pressure gyre aloft (around 10,000-20,000 feet) over Ontario early Sunday morning settles south across the Northeast and stalls.
The jet stream pattern across North America and the adjacent north Atlantic will become contorted as a “block” or impediment to the normal west-to-east flow of the jet stream, sets up over interior Canada. The block, called an “Omega block” due to its shape in the form of the Greek letter Omega, has the characteristic of “what you see is what you get” such that if a region is in a part of the jet stream prone to having “bad” weather (an upper level low pressure gyre), that region tends to stay in that pattern for an extended period.
Another characteristic of the upcoming week’s weather pattern is that daytimes (especially afternoons and early evenings) will tend to be wetter (more showery) than late overnights and mornings. This will be the case this week, as there is a high likelihood that it will shower each and every afternoon from Sunday through Friday.
In addition, the pool of chilly air aloft combined with the limited amount of solar heating received will render the atmosphere “unstable” and prone to producing stray thundershowers…. this will be especially true over the interior (away from the cooling effect of the Atlantic Ocean). This “blocky” pattern will break down next weekend as the upper-level low pressure gyre shifts to the east and a large ridge of high pressure builds over the Northeast, yielding noticeably brighter and warmer conditions!
SUNDAY: Morning sun yields to clouds and scattered showers and probably a t-storm in the afternoon. Temps will rise rapidly through the 70s Sunday morning, peaking in the upper 70s before the showers arrive and cool the air back down to near 70.
SUNDAY NIGHT: Lingering early evening showers/t-showers dissipate, then drier by later in the evening.