January will continue to be dry in Southern California as the jet stream settles into a stable or zonal pattern, which means it flows more directly from west to east with little fluctuation. A wavy or undulating jet stream is the pattern that brings storms from the north Pacific into California. “When the winter jet stream calms down, Southern California stays dry,” says Bill Patzert, former climatologist at NASA’s Jet Propulsion Laboratory. When the jet stream is unstable, it meanders from north to south and back again. Cold air sinks farther south and warm air is carried into higher latitudes.