KANSAS CITY, Mo. — The water temperature off of South America’s coast brings big impacts to our winter weather in the United States.
The Pacific waters have a tendency to run either warmer than average or cooler than average every two to seven years. An El Niño phase indicates warmer-than-normal ocean temperatures, meanwhile, cooler-than-normal ocean temperatures describes a La Niña.
This naturally occurring phenomenon typically lasts nine to 12 months, but there have also been prolonged events that last a few years.
According to NOAA, we’re currently in a La Niña and it's predicted to get even stronger through the winter.
"There’s an 85 percent chance these conditions will last through Northern Hemisphere winter and 60 percent chance it lasts into the Spring of 2021," NOAA stated.
You can check out the current temperatures of the Pacific Ocean by going online.
The colder waters, shown in blue, are expanding westward from South America. The warmer waters, in red, are then pushed closer to Indonesia. This creates a very wet season there, and in turn, leaves sinking air over South America and strengthens the easterly winds over the equator.
This will then change the upper-level weather in the Northern Hemisphere.
High pressure develops over the northern Pacific Ocean, just south of Alaska, creating a blocking pattern and a strong ridge over the ocean. This will strengthen the polar jet stream, leading to an active winter in the northwest. Colder-than-normal temperatures and wetter conditions are expected here.
This large cold air mass then spills into the northern Plains and would bring in more systems throughout the winter. Following the strong polar jet eastward, it tracks over the Ohio Valley and up through New England, also bringing a wetter-than-average winter season.
It’s a different scenario for the southern half of the U.S.
Their winters tend to be drier-than-average due to the lack of a subtropical jet. And it’s no surprise that warmer winter temperatures occur in the south.
Kansas City, located right in the middle, will have some influence from the strong polar jet. Winters would typically have near to slightly above-normal precipitation in the northern Missouri River basin and temperatures will remain slightly below average in this same area. This favors a more active storm track across the northern part of the region this winter.
In years past, strong La Niñas have brought different winter scenarios to Kansas City.
The most recent strong La Niña of 2010-2011, lingering into 2012, brought way above average snowfall amounts of 36.9" and below normal temperatures.
However, before that, the strong La Niña of 1998-1999 and 1999-2000 produced below-normal snowfall amounts each year and above-average temperatures.
Clearly, no two La Niña events are alike, but more times than not, a La Niña winter for the Kansas City region produces normal or below-normal snowfall amounts and temperatures that are average, or even above normal. Although, one big storm could easily skew these numbers.
While a La Niña helps examine the climatic norms of the United States, you cannot use this data to track or forecast the intensity of any single weather event. This is just one piece of the puzzle we examine when forecasting the winter season. There's a lot to watch as the La Niña strengthens this year.
