Many may wonder exactly why it has been so warm these past few months. It seems out of place to have leaves turning color while wearing shorts. If we remember last October we had an ice storm, while this fall, Norman has only dropped below freezing a few times. Based on climatology, this fall is not record-breaking, but looking at the daily temperature chart it has been close. Especially this past November, we have trended above the average.
Would you believe that this is caused in part by what is happening in the Pacific Ocean?
Observations suggest we transitioned into La Niña this past September-October, and it will continue through the upcoming winter months. La Niña is part of the El Niño Southern Oscillation which impacts the seasonal conditions in North America. Due to strengthening easterly winds across the Pacific Ocean, colder ocean water can rise up along the South American coast, in a process called upwelling. Upwelling is very beneficial for fisherman as fish populations boom with colder, nutrient-dense water. In the atmosphere, cooler Pacific Ocean temperatures cause the polar jet stream to shift northward. The polar jet stream is a very fast current of air high in the atmosphere, around 12 km (7.5 mi) above the ground. It acts almost as a barrier, steering the low-pressure systems more northward. As a result, the southern states experience weaker and drier cold front passages than the Northern Plains and Ohio River Valley. La Niña typically lasts for 9-12 months, so it is likely these conditions will persist throughout the rest of winter. Although, it is always possible that we have a few strong systems bringing more winter weather. At least for now, I am thankful we do not have to scrape ice off of my car in the morning.
By Francesca Lappin
World Meteorological Organization:
NOAA National Ocean Service: https://oceanservice.noaa.gov/facts/ninonina.html
Norman Weather Forecasting Office: https://www.weather.gov/oun/climate-records