La Nina has started in the Pacific Ocean and will likely persist through this upcoming winter and into 2021. The phenomenon is a natural occurring oceanic-atmospheric connection marked by cooler than normal sea surface temperatures over the central and eastern Pacific Ocean near the Equator. The opposite is, of course, El Nino which features warmer than normal sea surface temperatures in the same region. As La Nina started to take shape this past summer, it likely played a role in the tropical season of 2020.
Last September saw a very active Atlantic basin filled with up to 5 named storms at once. While September is usually active in the tropics given the time of year (very warm waters), last year was extremely busy. La Nina years can lead to an increase in Atlantic tropical cyclone activity because wind shear (changing of wind speed with height) is weaker over the Caribbean and Atlantic Basin. If wind shear is high, it rips storms apart and doesn’t allow them to reach their full potential. With a lack of shear, storms can blossom over warm waters and continue to grow into major hurricanes. The developing La Nina could have certainly played a role in the very high count of tropical systems last year.
Meteorologists at the national level believe La Nina will be in place through at least February 2021. What does this mean for the U.S. weather and our local forecast? Typically, La Nina brings above-average precipitation and colder than normal temperatures for the northern part of the country with drier weather and warmer conditions for the southern U.S. The last time La Nina occurred was during the winter of 2017-2018. That winter locally featured nothing impressive. Looking back, the mean temperature was 1° above normal and our snowfall was below normal by almost 7”. That certainly bucked the typical La Nina signals for northern parts of the country.
But given the hot summer last season and the active tropics from last fall, perhaps this La Nina is going to be stronger than the previous one. We also had almost no snow locally last winter, so perhaps we are due to stay busy this year. Time will tell!
2021 ABC27 Weather Almanac
- Most extreme temperatures in the history of Pennsylvania
- What is the Polar Vortex and how does it affect Central Pa.?
- La Nina brings the possibility of lower temps and above-average precipitation to the Midstate in Feb.
- How the ABC27 Weather Team adjusted in the era of COVID-19 to deliver your Most Accurate Weather Forecast
- June and July are the most active months for severe weather in the Midstate
- What is precipitable water?
- How tropical storms get their names
- July 2020 was the hottest summer on record for Central Pa.
- Feast or famine in the Midstate
- Despite a record tropical season, summer drought worsened for much of Pa.
- Hyperactive tropics of 2020
- Understanding the Jetstream and how it affects bigger storm systems