SARANAC LAKE — A winter weather advisory is scheduled to remain in effect throughout the Tri-Lakes region until 1 p.m. today, according to the National Weather Service’s Burlington, Vermont, office, which serves northern New York.

The advisory was issued due to the threat of freezing rain. While accumulations are forecasted to be limited — under one-tenth of 1 inch — meteorologists advise people to budget extra time around their morning commute.

“There’s not a particular amount (of additional time) we advise since everyone’s morning commute looks different, but we want folks to definitely give themselves enough extra time to get where they need to while taking it slow on the roads or sidewalks,” said Adriana Kremer, a meteorologist with the National Weather Service’s Burlington, Vermont office.

She said that even though the forecasted accumulation isn’t large, it doesn’t take much to cause trouble.

“Any ice accumulation, even just a glaze, can be really hazardous and lead to things like slick roads — especially on elevated surfaces like bridges and overpasses, which can cool off faster than the ground,” she said.

While, as of press time Monday, the winter weather advisory was scheduled to last until 1 p.m., Kremer said the most likely time for slick conditions across the Tri-Lakes is between 5 and 8 a.m., before temperatures climb above freezing. She noted that there is the possibility of freezing rain extending beyond that early morning window — hence the longer advisory time.

Kremer said that forecasting a freezing rain events are tricky for meteorologists, as a tiny change in the temperature can make a vast difference in the hazard commuters face.

“Just the difference of a degree or two can change whether it’s just a liquid rain event with no real impacts or if the precipitation starts to freeze on contact, which can lead to those slick conditions,” she said.

The forecast becomes even more complicated for mountainous regions, such as the Tri-Lakes. The large variations in elevation across the area can lead to different temperature zones, and therefore, different amounts of ice accumulation, even between locations relatively close to each other in distance. For example, the village of Lake Placid is nearly 1,000 feet higher than the hamlet of Keene. The two locations are less than 15 miles apart along state Route 73.

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Precipitation terminology

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There is a spectrum of different frozen precipitation types. They vary based on temperatures at different levels, or elevations, within the atmosphere. Snowfall occurs when the temperature is uniformly below freezing between the clouds — where the precipitation forms — and the ground.

Sleet occurs if there is a layer of above-freezing air in the atmosphere but the air closer to Earth’s surface is below freezing. As the precipitation falls, it becomes a liquid rain droplet for a time before refreezing — in the air — and making contact with the surface as an ice pellet.

Freezing rain, which is what was forecasted for a portion of this morning, occurs when the air is above freezing for a larger window of the atmosphere, but there is a shallow layer of below-freezing air very close to Earth’s surface. This does not give the precipitation enough time to re-freeze as it falls — meaning that it would feel like liquid raindrops for someone standing outside — but does act to keep the surface itself below freezing. Once the liquid makes contact with the below-freezing ground surface, it re-freezes and forms a coat of ice.

Unlike sleet, which is still slippery, freezing rain is uniquely perilous because the sheet of ice that coats surfaces can be much harder to remove than sleet, which retains its pellet form and does not adhere as readily to ground surfaces.

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Looking ahead

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As of press time on Monday, there was uncertainty regarding a possible nor’easter that could impact the Tri-Lakes area Thursday afternoon into Friday, leading to possible travel disruptions around the Thanksgiving Holiday.

There is disagreement among computer models that meteorologists use in part to determine a forecast. Some suggest a sizeable nor’easter that could produce snowfall accumulation in excess of 6 inches throughout the Tri-Lakes.

Other models show a storm that is weaker, quicker to depart and tracking further away from the area — to the south and east — with most of the snow missing the Tri-Lakes area. That scenario would result in little snowfall accumulation — likely under 2 inches or less and minimal travel disruption for the Tri-Lakes.

It remains too early to say which scenario will play out, although model trends throughout Monday appeared to lean toward the lower snowfall scenario. A clearer picture will likely emerge by Wednesday.

Regardless of whether or not the nor’easter comes to fruition for the Tri-Lakes area at the end of this week, below-average temperatures are likely in store for the Tri-Lakes area next week, with additional chances for lake-effect snow showers.