We are currently watching a complex of showers and thunderstorms in the Midwest and Ohio Valley as it swings eastward, along a stationary frontal boundary. Additionally, a mid-level trough will be working its way into the region from the north, which will allow the storm system to strengthen, as they interact with each other. The strengthening storm system will provide plenty of lifting in the atmosphere, as well as greatly increase the strength of a southerly low-level jet, which will help to pump plenty of moisture into the region. The combination of plenty of moisture in our atmosphere and the lift will lead to the threat for heavy rain and embedded thunderstorms. The primary threat is flash flooding, as some areas may pick up 1-2″ of rain in a short period of time.
However, the threat for severe thunderstorms with severe winds should only be confined to the southern third of New Jersey, and that threat will be isolated. This is because the frontal boundary that the storm will be tracking on should remain in Central New Jersey. North and northeast of the warm front is where more broad lifting is expected, thus the threat for heavy rain over the entire New York Metro region.
But south of the warm front is where the lifting for precipitation is not as widespread, but the atmosphere overall is more unstable — thus the threat for isolated severe weather. This means that southern NJ may not see widespread rain, but could have a brief localized heavy downpour, with flash flooding, and a strong wind gust. The instability overall, however, is only marginally strong for severe weather — thus the severe threat being marginal and isolated. Plus there is also the fact that the instability may not be strong enough for the complex of storms to entirely maintain itself as it crosses the Appalachian Mountains.
As far as the timing goes, the heavier rain should move into the region late tonight, probably somewhere between 3:00am and 6:00am from west to east, probably arriving in the NYC area around 4:30am. The period of rain should last for a few hours or so, creating a potentially very messy morning commute. Leave some extra time tomorrow morning.
Do not be surprised if you are awoken early by a loud rumble of thunder and heavy rain. The heavy rain should clear by the late-morning hours, so the afternoon should be primarily dry, but lingering lift could create the threat for a scattered shower or thunderstorm.
As the surface winds push easterly behind the storm system, lots of clouds and chillier air will remain, because of the Marine influence. Temperatures may not get out of the 60s tomorrow.
Moving forward to Friday, the upper-level trough will me moving out, so sunshine should dominate, but the trough may be just close enough to warrant a slight chance of an isolated shower or thunderstorm, particularly for eastern zones. Temperatures should rebound into the upper 70s.
The weekend looks terrific, as a ridge of high pressure will build in, leading to sunny skies and temperatures in the low 80s, as well as low humidity!