Developing nor'easter to bring late week rain, wind and snow potential to Northeast

PHILADELPHIA - Philadelphia is starting Wednesday with sunny skies and above-average temperatures, but big changes are coming to the forecast as a strengthening storm is expected to bring periods of rain Thursday into Friday, followed by the coldest air of the season this weekend.

Sunny Wednesday Before Storm Moves In

What we know:

Sunny weather will last through daylight hours Wednesday, with Philadelphia temperatures reaching 65 degrees. Weak high pressure is keeping the region dry and mild, and skies will be clear through the day.

Later Wednesday, high clouds are expected to increase, and rain will move in after midnight in western higher elevations, forecasters said. 

Rain will become more widespread across the area Thursday, with periods of on-and-off showers and possibly a thunderstorm. The core of the developing storm will organize off the New Jersey coast Thursday into Friday and deepen as it shifts north-northeast, according to the National Weather Service.

Timeline:

Rain begins late Wednesday into early Thursday in Pennsylvania’s mountains, expanding to the wider Philadelphia area Thursday and Friday. 

The strongest winds are expected as the storm moves farther away, with peak gusts to about 35 mph on Saturday. 

Temperatures Friday and Saturday are forecast to remain in the 40s during the day, with nighttime lows dipping into the 20s and low 30s. 

Rain could mix with or change to snow in the higher elevations, especially in the southern Poconos Friday, but no significant accumulation is expected in Philadelphia.

Storm Brings Colder Air and Snow Potential

Dig deeper:

A large storm system moving out of the Ohio Valley is set to strengthen as it reaches the Mid-Atlantic region late this week. The system will evolve into a nor’easter along the coast, bringing widespread rain to the Interstate 95 corridor and the first notable snowfall to higher elevations in the Northeast and New England, according to the National Weather Service. 

The weather pattern is being influenced by colder Canadian air pushing south and a dip in the polar jet stream, helping low pressure develop between the Great Lakes and Ohio Valley before heading toward the East Coast. 

Strong winds and colder air will funnel into the region late Friday through the weekend as the storm moves away.

What we don't know:

The exact track and timing of the storm system are still uncertain and will determine how much rain falls, the possibility of thunderstorms, and how far south snowflakes could reach, especially in higher elevations. 

Coastal impacts, including tidal flooding and wind strength, depend on where the low-pressure system moves offshore.