La Niña Has Arrived In PA: What Forecasters Are Saying It Means

The famous and irregular climate pattern La Niña has arrived in the mid-Atlantic region, and conditions are likely to persist around Pennsylvania through the early winter, the National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center said in an October advisory.

Warmer and potentially wetter conditions, including rain and snow, typically accompany La Niña when it hits the Pennsylvania region, though that largely depends on the strength of its impact. This year's La Niña is expected to be more mild, officials said.

“A weak La Niña would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance," NOAA said.

La Niña is a recurring pattern of weather that typically arrives every three to five years. It develops when winds in the Pacific increase, pushing warm surface water to the west and causing cold, deep water to rise to the surface. The changing in the surface temperatures of the ocean has a ripple effect on atmospheric conditions and weather around the world.

The latest NOAA advisory comes after a La Niña watch was issued by NOAA in early September, with maps showing a 33-40 percent chance of above-normal temperatures in Pennsylvania for the winter.

In their Oct. 9 advisory, NOAA said La Niña conditions are favored to persist through February 2026 before transitioning to neutral conditions between the January-March timeframe.

These conditions often impact where cold air, snow and rain are likely to occur in the U.S.

When La Niña conditions are present, they must persist for five consecutive three-month periods for La Niña to be official, AccuWeather Senior Meteorologist and Long-Range Expert Paul Pastelok said.

Though La Niña is predicted to continue through early winter and affect snow, rain, and temperature trends across the country, Pastelok echoed NOAA's opinion that this year's La Niña appears to be weak.

A weaker La Niña leaves plenty of room for other oceanic factors to influence the forecast, such as a marine heat wave in the northern Pacific Ocean.

"These waters off the West Coast and extending farther out are very, very important going into our [winter] forecast this year," Pastelok said.

AccuWeather does forecast snow in Pennsylvania this winter, but overall snowfall totals may still finish below the historical average, as some storms later in the season could bring a mix of rain and snow.

Once La Niña conditions phase out, NOAA said the weather is expected to transition to ENSO-neutral in January-March, which occurs when Pacific sea surface temperatures are close to average.

La Niña is the counterpart to El Niño, which occurs when there are above-average sea temperatures in the central and eastern tropical Pacific Ocean.

Related

• New Winter Snowfall Predictions Released For PA
  
• Here's How Snowy You Can Expect This Winter To Be In PA

With reporting from Patch correspondent Sara Winick