Want to know when the next hot spell is coming? It might help to look at the weather forecasts — a few thousand miles away. Summer heat waves in California’s Central Valley are almost always preceded by heavy rainfall over the tropical Indian and Pacific oceans, scientists at UC Davis and in South Korea determined in a recently published research effort. Researchers identified 24 heat waves that took place in California’s Central Valley during summer months from 1979 to 2010, and compared those heat waves to a weather pattern called the Madden-Julian Oscillation (MJO) that brings heavy rain to the tropical Indian and Pacific oceans.

There’s no weekend reprieve in store for Northern California after a wet start to the week. In fact, it should only get wetter. National Weather Service says Friday and Saturday will see a “stronger, wetter” storm than the one passing through Monday and Tuesday, with as much as 1 to 2 feet of snow possible near summit passes this weekend. Rain and snowfall were expected to be light during this week’s first storm, but Caltrans and sheriff’s departments have reported a snow slide incident Monday afternoon and an avalanche Tuesday morning, both of which closed stretches of highways.

The heaviest rain, heaviest snow and highest probability of thunderstorms accompanying the current storm will pass through Northern California at varying times Wednesday. Early morning showers were scattered, dropping heavier precipitation in the northern half of the Sacramento Valley while Sacramento stayed mostly dry as of 6 a.m., as National Weather Service radar images show. Rain in Sacramento will likely begin later Wednesday morning.