2:05 PM | *Late week powerful and slow-moving ocean storm to produce rain, wind and accumulating snow in some areas*
The overall weather pattern across North America will soon feature strong high-latitude blocking over Greenland and northern Canada and this transition period in the atmosphere will result in a slow-moving and powerful storm over the western Atlantic Ocean by the end of the week. Strong low pressure will head towards the Ohio Valley on Thursday, but then it will become overshadowed by intensifying low pressure over the western Atlantic Ocean and it is this system which will run into a brick wall in the atmosphere as it tries to push to the north. As a result of the blocking pattern setting up in the atmosphere to our north, this strong ocean storm will be forced to the southeast - perhaps in a "looping" fashion - and this will prolong impacts from the immediate I-95 corridor to the coastline. Rain and wind will increase from later Thursday into Thursday night and, as colder air wraps into the system on Friday, there is the chance that some areas generally to the north of the PA/MD border see a mixing with or changeover to ice and/or snow before the precipitation winds down.
One strong upper-level wave will head towards the northern Ohio Valley on Thursday while a second wave takes a more southern route on its way to the Mid-Atlantic coastline. The details on exactly how and when these two systems phase together still need to be ironed, but eventually, the main player will be a strong storm over the western Atlantic Ocean. The exact track of the upper-level low will also be critical as strong upward motion just to its north could lead to "dynamical cooling" and accumulating snow for some areas.
Rain should break out in the DC-to-Philly-to-NYC corridor during the day on Thursday as these two waves begin to consolidate and it'll continue into the day on Friday. While this system will have little cold air to work with, there is still a chance that the rain mixes with or changes to ice and/or snow later Friday in areas generally to the north of the Mason-Dixon Line; especially, in higher elevation locations. In fact, accumulating snow is quite likely in such higher elevation locations as the Poconos (PA) and Catskills (NY) and can't be ruled out in areas farther to the south like the Philly metro region.
In addition to the threat for rain and snow, this unfolding storm will feature strong winds; especially, in areas near the coastline from the Delmarva Peninsula to southern New England. As the storm intensifies over the western Atlantic Ocean, the pressure gradient will tighten dramatically and winds may gust past 40 mph in the entire DC-to-Philly-to-NYC corridor later Friday and Friday night. Coastal flooding may also become a concern at times of high tide (e.g., Friday morning) and this threat will have to be monitored as well.
Stay tuned...complex storm unfolding and many small-scale details need to be ironed out.
Meteorologist Paul Dorian