Cecily Tynan's Winter Weather Outlook

So, everyone's wondering: Could this winter be nearly as brutal as last year?

To investigate, the first thing I look for is the building supply of cold air to the north.

A big factor in that is the speed and amount of snow cover development through the fall.

Looking at this year's snow cover there are two alarming signs. North America had the highest snow cover on record during September. By the end of October, Siberia had its second highest snow cover on record. So, there's a vast supply of cold air. The question: where does it go? That depends on the jet stream.

Sea temperatures over the next 3 months are forecast to be above normal in the eastern Gulf of Alaska, similar to last year. But, they're also forecast above normal in the central Pacific; that means we are likely heading into a weak El Nino winter.

This combination typically creates a big ridge in the west.

But what goes up must come down, resulting in a trough here in the east.

This big dip in the jet stream will open the door for a cross polar flow that allows arctic air to stream from Siberia across the North Pole and south into our region.

Last winter this setup gave us days with highs only in the teens.

If the northern branch of the jet stream links up with moisture from the southern jet, strong nor'easters develop. Add to that an increased threat of blocking and these storms can be slow-moving, long duration storms.

Breaking down the upcoming winter, I expect to see several nor'easters, with mixed precipitation, that means an increased threat of icing, and, yes, more visits from the Polar Vortex leading to temps averaging 1 to 2 degrees below normal.

In terms of snowfall, I'm predicting around 150% of normal in Philadelphia and along the I-95 corridor giving us 30 to 36 inches.

In the Lehigh Valley, 160% of normal, 36 to 42 inches.

And at the shore, with mixing cutting down on snowfall, 140% of normal, 18 to 24 inches.