Winter Storm Warning issued for Philadelphia metro area

(WTXF/AP) - The National Weather Service has upgraded the Winter Storm Watch to a Warning from 8pm Monday to 4pm Tuesday.

This is for the Philadelphia metro area including southwest New Jersey and northern Delaware - specifically Philadelphia and Delaware counties in Pennsylvania; Camden, Gloucester, Salem and northwestern Burlington counties in New Jersey; and New Castle County in Delaware.

A Winter Storm Watch will be in effect for Cumberland, Atlantic, southern Burlington and Ocean counties.

Cold air is in place and has been locked in since last Friday's snow. You may have felt it at the Philadelphia St. Patrick's parade.

Now we need to prepare for a winter storm. This could be the most significant snowfall of the season -- more than a foot -- in the early part of the week.

DOWNLOAD: FOX 29 Weather Authority App for the latest updates this winter

A Winter Storm Warning for heavy snow means severe winter weather conditions are expected or occurring.

Snow accumulation of 8-12 inches is expected in Philadelphia. So are strong winds of 15-25mph with gusts up to 40mph.

The snow should start Monday evening, becoming heavy at times late Monday night through midday Tuesday.

Then, the snow will diminish by late Tuesday afternoon.

The heavy snow will make travel difficult or impossible Monday night and Tuesday and may produce power outages due to the weight of the snow on tree limbs and power lines.

DOWNLOAD: The FOX 29 App for the latest news and weather

An area of low pressure that started in the Pacific Northwest and went to the Great Lakes will collide with a coastal storm and transfer its energy -- and strengthen -- meaning we're going to get snow.

Monday, the bitter cold continues with partly cloudy skies and high temperatures in the mid-30s. Wear layers you'll be heading out for an extended period of time.

Then, a Nor'easter is expected to bring that major snow. In fact, it's expected to be the most significant snowfall of the season with gusty winds, especially down the shore.

Monday morning will be mostly sunny. Then, in the afternoon, more clouds will move in.

Monday evening, the snow will start. It will come up from the south.

In southern Delaware and deep South Jersey, there will probably be a switchover to sleet and rain. That will lower the snow totals.

However, for southeastern Pennsylvania, it looks like this will be an all-snow event.

The storm's forecast track could still change but as of Sunday evening, FOX 29 meteorologist Scott Williams is predicting double-digit totals for much of the Philadelphia region. There will be more snow further north, and less further south.

Coastal regions even further to our north -- including New York City and surrounding areas of Long Island, Westchester County and Connecticut -- have a blizzard watch.

WEATHER ALERTS: Watches, warnings, advisories by county

Besides there's a lot of snow predicted for many of us, we should be prepared for damaging wind, possible power outages and coastal flooding. PECO told FOX 29 News that 3,000 employees and contractors are on standby for the impending storm.

The worst weather is expected Tuesday morning but this winter storm event will start Monday night and last all the way through Wednesday morning, depending where you are in our area.

Sunday, Gov. Tom Wolf assured Pennsylvanians that state agencies are taking steps to ensure they and local communities are ready to respond and prepared for the worst.

"I ask residents and commercial drivers across the commonwealth to prepare to avoid unnecessary travel on roadways during this time," he said, "as to let road crews and emergency responders do their jobs and minimize dangerous travel."

He added, travel restrictions may be put in place Monday evening into Tuesday, should they be necessary to minimize dangerous travel.

State agencies -- including the Pennsylvania Emergency Management Agency, PennDOT, State Police and the Pennsylvania National Guard -- are coordinating to ensure resource needs can be met throughout the commonwealth and formulating plans to increase resources in areas forecasted to be hit hardest by the storm.

The governor has not declared an emergency but says he's prepared to do so should agencies need one.

Click here for more from the state on how to prepare for winter storms. Click here for conditions on more than 40,000 miles of Pennsylvania roads, including color-coded winter conditions. Meanwhile, the state offers these driving tips if you have to be out during adverse weather:

-- Monitor weather forecasts and postpone travel if necessary, especially over long distances during the storm.

-- Slow down while driving when snow is falling and always wear your seat belt. Leave plenty of distance between you and the vehicles you are following.

-- During squalls or whiteouts, do not stop on the roadway. Come to a complete stop only when you can safely get as far off the road as possible or when there is a safe area to do so.

-- When encountering plows, stay at least six car lengths behind an operating plow truck and remember that the main plow is wider than the truck.

-- When a plow is approaching you, move as far from the center of the road as is safely possible and remember that snow can obscure the actual snow plow width.

After this storm, it will stay cold. The 7-day forecast doesn't have us getting up to 40 degrees until next Friday.

The average high temperature for Philadelphia is actually 50 this time of year.

DEVELOPING NEWS: Stay with the FOX 29 Weather Authority and Fox29.com for updates as this storm gets closer.