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Philadelphia Weather: Winter Storm Warning In Place As Region Braces For Possibility Of Several Inches Of Snow

PHILADELPHIA (CBS) -- As we all start to prepare for the threat of winter weather to end the weekend and start the next work week, the National Weather Service in Mount Holly is doing the same. The NWS has upgraded its Winter Storm Watch to a Winter Storm Warning for Philadelphia and its surrounding counties, Berks County and the Lehigh Valley.

It will still go into effect on Sunday and last through Tuesday.

At this time, periods of snow, some of which will likely be heavy, is set to plow across the region during the day on Monday. The threat for significant snow accumulation is high with this system, hence why the Winter Storm Watch was issued.

A Winter Storm Watch means that significant winter weather is on the horizon. A Winter Storm Watch is usually issued 36-48 hours prior to an event occurring. A Watch is used to signify that we need to be on alert for the impending significant or hazardous winter weather. In the Philadelphia region, significant snowfall is defined by the NWS as 7 inches of snow in a 24-hour period.

Once the winter weather begins, if the snow and hazardous weather either stays in the significant range or even picks up in intensity, a Winter Storm Warning will be issued. A Warning is issued when significant or hazardous weather is imminent, six to 18 hours away, or already occurring.

While a Watch does not have to be issued prior to a Warning, it is very common for a Winter Storm Watch to be upgraded to a Warning as we get closer to the event.

The biggest changes in the forecast from Friday to Saturday come in the form of precipitation type, especially on Sunday night and where and how much snow falls across the region.

The timing of the storm is holding steady with flakes starting on Sunday evening as the atmosphere becomes more saturated, with the bulk of the heaviest precipitation developing overnight Sunday and falling during the day on Monday, before tapering off through the day on Tuesday.

When it comes to the type of precipitation we will see there is still a bit of a mixed bag, no pun intended. Snow will be the primary mode of precipitation across all areas as the event begins on Sunday afternoon and evening. We are likely to see the snow last into the early nighttime hours as well.

During Sunday night though mid-level warm air will start to intrude into the region. How far inland the warm air gets will make a huge difference is the type of precipitation we receive. Right now it looks as though warm air will get far enough inland what we see a change from snow to sleet/snow along and south of a line roughly from West Chester down to Atlantic City.

North of that line, we should remain cold enough for all snow. There is even a chance for a brief period of all rain along the immediate Jersey Shore. As we progress then into and through Monday morning, cold air will quickly wrap back in and transition the areas where mix took over, back to all snow.

Once we transition back to snow it should stay that way for the rest of the event.

Snow totals for this system are looking significant for much of the region, especially in Southeastern Pennsylvania. The lowest totals will be near the Shore the mix or rain will limit snow amounts, expect 1-3 inches at most. A thin ribbon of 3-6 inches will be possible then from the Shore to Eastern Camden and Gloucester Counties. A widespread swath of 6-8 inches then is possible for a majority of the region, basically from inland New Jersey to the Poconos.

Then within that larger area, we are likely to see the heaviest bands of snow set up, mainly in southeastern Pennsylvania, where 8-10 inches-plus of snow could fall. Adding to the situation on Monday will be strong winds that develop. Wind gusts on Monday will be widespread in the 30-40mph range with gusts as high as 50 mph at the coastline. This will lead to lots of blowing snow and hazardous travel conditions.

It will be advised to stay off the roads Monday if at all possible. Conditions should improve on the roadways by Tuesday.

Stay with the Eyewitness Weather Team as we continue to update you on the evolving winter storm.


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