So far this winter though, the Miami Valley has missed out on major winter storms. Elwell said that’s due to a combination of La Nina and a weak polar vortex.
“This winter, we have seen a weaker polar vortex which has allowed the coldest, arctic air to get displaced from the poles,” Elwell said. “But the colder air has been deflected away for much of the winter away from the Ohio Valley.”
The La Nina pattern, which occurs when ocean water temperatures in the equatorial region of the Pacific Ocean are colder than normal, has been able to influence the pacific jet stream into the west coast, pounding that area with record amounts of rainfall and helping to end a decade-long drought to many areas.
However, this strong southern jet stream has also been able to keep the coldest, arctic air bottled up north into Canada and into New England. The average temperature in Dayton so far in February is running over five degrees above normal after an unseasonably mild January.
The warm air has kept most of the precipitation in our area falling as rain as opposed to snow. However, the same storm systems which have brought above normal rainfall to have run into much colder air in New England, allowing for bigger winter storms in this region.
Elwell says while ocean water temperatures in the Pacific have returned to normal and La Nina has pretty much ended, the weather pattern takes time to evolve, and so far the atmosphere is still behaving as if La Nina is still occurring. This will likely keep the Miami Valley unseasonably warm and wet through the rest of the month. It is unclear, however, if March will see a return of a colder pattern as the atmosphere adjusts with the end of La Nina.