A cold and active pattern emerges, but will it mean snow for Lehigh Valley?

The front half of December is trending colder for the Lehigh Valley, according to the latest outlooks issued from the National Weather Service’s Climate Prediction Center.

Temperatures are expected to be near or somewhat cooler than average through Dec. 14, with models hinting at some of the chilliest air of the season thus far, but having a difference of opinion on precipitation.

While there appears to be high potential for a second storm this week, a progressive system possible Saturday into Sunday remains a question mark at this point, the National Weather Service said.

“Model agreement goes off the rails Friday through the weekend, with run-to-run and modelto-model consistency seemingly absent for the past 48 hours,” the Mount Holly forecast discussion said Monday.

Meteorologists said one model shoves any storm system south of the area, while others bring precipitation into the Lehigh Valley as early as Friday night, possibly beginning as a wintry mix.

Empire Weather, which provides localized forecasts for

The Morning Call, said it won’t rule out the possibility of some snow for the weekend.

“If [the system] consolidates, then a solid rain storm — with an outside chance of a change to snow — could occur on Saturday into Sunday. If it does not consolidate, then this system would just be a glancing blow, or we could just remain completely dry,” its forecast discussion said.

What’s shaping the atmospheric pattern?

Heading into the winter solstice, which is now less than three weeks away, a strengthening La Nina is expected to last through spring. This cooling of sea surface temperatures in the equatorial Pacific Ocean has the power to influence weather across the globe and often delivers warm and dry conditions to the East.

As we kick off December, forecasters say La Nina’s influence is being hampered by a northward bulge of the jet stream over the western U.S. and Canada, bringing a southward plunge over the southern and eastern U.S., and cold air along with it.

This pattern brings cooler, wet weather to the South and East and is known as a driver of wintry precipitation to the East Coast.

A stormy stretch ahead

If the upcoming weekend storm fails to come together, the Lehigh Valley’s next shot at wintry precipitation might come the following week, though it’s simply too early to tell.

This stormy stretch needs one key ingredient to turn rain to snow, and the Climate Prediction Center doesn’t seem to indicate that cold air will hang around. Without it, we get a heavy soaking of rain rather than snow.

Like any wintry season, cold air needs to remain established and entrenched in the eastern U.S., meteorologists say. That way, as storms track closer to the coast, it opens to the door to the possibility of frozen precipitation. The way the pattern looks now, the cold air in place may only be sufficient for snow in the far interior and rain in the Lehigh Valley.

The average date of the first snowfall in the area is typically around Dec. 18.