Late week storm/late weekend threat
A cold frontal system slipped through the Mid-Atlantic in the overnight hours and today has turned out to be a windy and cold day despite plenty of sunshine. High pressure will be in control of the weather at mid-week and then another cold front will works its way through the region later on Thursday. A chilly air mass will follow the frontal passage during Thursday night and will be supported by building high pressure across southeastern Canada. This cold air mass will be somewhat slow to give up its ground on Friday as a large area of moisture heads to the Mid-Atlantic region from the Tennessee Valley – and this may set the stage for a period of sleet and/or freezing rain in at least parts of the area.
On Friday, surface low pressure will pull out of the south-central states and head towards the Great Lakes – well to the west of the I-95 corridor. At the same time, high pressure will be parked over southeastern Canada and it will be somewhat slow to retreat as will some low-level cold air entrenched in the Mid-Atlantic. As a result, there can be a period of sleet and/or freezing rain on Friday as an area of moisture associated with low pressure over the Midwest reaches us from the Tennessee Valley. While there can be some sleet and/or freezing rain at the onset of this late week storm system in suburban locations well to the north and west of Washington, D.C., a better chance for something frozen will take place north of the PA/MD border including in the northern and western suburbs of Philadelphia and New York City. Eventually, enough milder air will push in at the lower levels of the atmosphere for plain rain to be the dominate precipitation type later on Friday across the Mid-Atlantic while accumulating snow falls along a path from the central Plains to the Great Lakes.
Once this late week system departs to Canada on early Saturday, it will actually turn quite mild in the Mid-Atlantic to begin the upcoming weekend. However, another cold frontal system is likely to push through by the middle stages of the weekend and it’ll turn colder on Sunday. A lingering area of short-wave upper-level energy is then going to wrap around a large scale upper-level trough and it should help to spawn the formation of a second low pressure system later in the weekend over the southeastern part of the US. This system would likely intensify near or over the Mid-Atlantic coastline on Sunday and there will be a colder air mass moving into the region following the passage of the cold frontal system. Consequently, there is a chance that some snow could result on Sunday in the I-95 corridor should this second storm system materialize in time for an impact – something we’ll have to monitor in coming days.