Storms may return late Thursday into Friday

Enjoy the pleasant, warm weather over the next 24 hours: Unsettled weather is likely to return over the days that follow as  disturbances begin moving into the Northeast and Mid-Atlantic from the west on Thursday. There’s now an increasing likelihood of a period of heavy rainfall with some thunderstorms in the parts of the region later Thursday night into Friday morning.

Some mid-level warm air advection and sheared vorticity will cause cloud cover to increase throughout the Northeast tomorrow. A few showers are possible over the interior during the afternoon or evening, though high pressure offshore will likely provide enough subsidence (sinking air) to keep most of the region dry. Temperatures tomorrow will reach the mid to upper 70s near the coast and lower 80s inland, with more cloud cover along the coast and an onshore flow.

A wave of low pressure will likely develop tomorrow night over the Mid-Atlantic, in response to well defined northern and southern stream disturbances (shortwaves)  interacting with each other along a broad trough. These disturbances aren’t likely to phase, but model guidance suggest enough divergence from the upper-level jet and a strong thermal gradient along a baroclinic zone — aiding in surface low pressure developing and intensifying slowly as moves further northward near the coast.

Model guidance suggests the potential for a 30-40kt southwesterly jet, enhancing moisture convergence and elevated instability near and south of the surface low track. This could lead to an area of moderate to heavy rainfall with some embedded thunderstorms. Precipitable water values will be approaching and possibly exceeding 2.00″ in many areas as a southerly plume of subtropical moisture moves up the Mid-Atlantic coast. At this this time, we aren’t anticipating any organized severe weather, as any surface-based instability will likely remain weak during the overnight hours.

Some details remain uncertain in regards to the exact track and timing of this system moving through the region. It isn’t likely that everyone will see heavy rainfall out this system, due to the compact and perhaps convective nature of system. This suggests sporadic nature of heavy rains as instability and forcing is locally juxtaposed,While other areas will get more subsidence from this amount of dynamic lift.

By Friday afternoon, the storm system is likely to move northeast of the region, as the pattern remains somewhat progressive with a lack of high-latitude blocking. Subsidence between the disturbances could help skies clear for more sunshine in parts of the region Friday afternoon. This will help warm temperatures up well into the 80s, with southwest winds continuing as well.

A frontal boundary will then shift back towards the Northeast states Friday afternoon and into Friday evening. The sunshine will help destabilize the atmosphere again —  so there is the possibility a few more scattered showers and thunderstorms develop. High precipitable water values could again support localized very heavy rainfall and localized flash flooding.

This cold/occluded frontal boundary will move eastward during Saturday morning, with any lingering scattered showers coming to end. Drier west-northwest downslope winds behind this frontal boundary will allow clouds to clear for sunshine with temperatures rising into the lower to mid 80s by Saturday afternoon. Some cold air moving in aloft could cause the atmosphere to become unstable enough (again!) for a few isolated showers to pop over the Interior — but most regions should remain rather pleasant in terms of sensible weather conditions..

So stay tuned for more premium updates on the potential for t-storms with heavy rainfall later Thursday night into Friday.