The Philadelphia area is bracing for a major winter storm that is expected to bring snow and rain to the region over the weekend before an arctic blast arrives with a potentially dangerous deep freeze that will turn any standing water and lingering moisture into ice.

In what was considered a mild prelude to the storm, snow blanketed the region early Friday, with an inch measured at Philadelphia International Airport, but caused few problems. Drivers and pedestrians encountered a light coating of snow Friday, and some schools opened late.

But what the National Weather Service is calling a “significant storm system” will bring snow, mixed precipitation, and heavy rain Saturday and Sunday. Areas north and west of Philadelphia, including western Montgomery County and northern Bucks County, are expected to be harder hit and have been placed under a winter storm watch.

Pennsylvania Gov. Tom Wolf and New Jersey Gov. Phil Murphy both declared states of emergency ahead of the storm. In Pennsylvania, the declaration included banning commercial vehicles from the Pennsylvania Turnpike and all interstate highways, except I-95 in Southeastern Pennsylvania, from noon Saturday until noon Sunday.

The National Weather Service, in its hazardous weather outlook for Southeastern Pennsylvania and South Jersey, offered this timeline of the storm’s expected progress.

Snow will develop Saturday afternoon with some accumulation possible before a change to heavy rain from south to north Saturday night. There may also be a period of freezing rain and sleet during this transition. The rain could be heavy enough to lead to urban and small stream flooding issues Saturday night into early Sunday with river flooding possible by late day Sunday.
Rain will come to an end by late day Sunday as a strong cold front moves through with strong [northwest] winds and rapidly falling temperatures as arctic air rapidly moves in. This will lead to quick refreezing of wet and slushy surfaces causing very ice conditions. Dangerous wind chills Sunday night through Tuesday.

Hundreds of trucks are on standby to treat highways and motorists should expect speed restrictions as the storm progresses or changes its shape, officials said.

The storm also is expected to affect air travel on the East Coast, including Philadelphia International Airport, and Amtrak announced it was preemptively cancelling a number of trains on Sunday, including Keystone Service (New York-Philadelphia-Harrisburg) and Pennsylvanian Service (New York-Philadelphia-Harrisburg-Pittsburgh) trains. Trains between between New York and Boston and New York and St. Albans, Vt., also are canceled Sunday. The details are on Amtrak’s website.

Here is the projected snowfall map for the weekend storm issued Friday by the weather service.

Snow accumulation projections for the weekend of Jan. 19-20, 2019.
National Weather Service
Snow accumulation projections for the weekend of Jan. 19-20, 2019.

Jeff Jumper, the Pennsylvania state meteorologist, in the meantime proposed a 24-hour-stay-at-home challenge during the peak of of the weekend storm.