Daily Press photo Leaves in Escanaba are showing their autumn colors. The long range weather forecast could mean they will be replaced with an abundance of snow in the coming weeks.

IRON MOUNTAIN — La Nina conditions have developed but there’s no clear outlook on the weather implications for the Upper Peninsula.

La Nina, the flip side of El Nino, is the periodic cooling of sea-surface temperatures in the central Pacific Ocean. Historically, La Nina favors a warmer fall in the northern Midwest, while winter may be colder and snowier.

The National Weather Service, in its long-range forecast, calls for a 38% chance of above-normal temperatures in the Upper Peninsula through the end of December and a 28% chance of below normal. Precipitation over the same period is expected to be near average.

According to the Climate Prediction Center, La Nina officially developed by early September and is forecast to continue through the winter months.

“Much of the Lower 48 is warmer than average in October and November during La Nina years, but December is often colder than average, especially in parts of the northern and eastern U.S.,” said Linda Lam, a meteorologist at weather.com.

Further ahead, the Upper Midwest could pick up above-normal snowfall this winter, said AccuWeather meteorologist Paul Pastelok. The course of the winter may depend on the strength and positioning of the polar vortex, he added.

A strong polar vortex keeps cold Arctic air locked in place over the North Pole region, potentially leading to milder weather in the northern U.S.

“We expect the polar vortex to strengthen in the middle of the (winter) season this year,” Pastelok said. There may also be a favorable storm track mid-season for the Midwest and Great Lakes, leading to a few heavy snowfalls, he said.

The Climate Prediction Center calls for a slightly elevated chance of above-normal precipitation from January through March.

September featured a wide range of weather at Iron Mountain-Kingsford. Temperatures climbed to highs of 82 degrees on Sept. 23 and 24 after a monthly low of 30 degrees Sept. 18. The average temperature for the month was 56.2 degrees, which was 1.2 degrees below normal.

It was the coolest September since 2012, when temperatures averaged 56 degrees.

The U.S. Drought Monitor shows no areas of concern in the Upper Peninsula.