![]() Once the high pressure backs out of the Western U.S. that shields it from storms coming out of the Pacific. This creates a barrier around the Western U.S. ![]() It captures how much a high-pressure system in the northeast Pacific wobbles between the West Coast and the middle of the ocean.Ī positive PNA phase indicates that the high pressure that normally sits in the middle of the Pacific Ocean is shifting toward the West Coast. The PNA signals a change in pressure patterns between weather systems in the middle of the Pacific Ocean and the West Coast of the U.S. These systems act like barriers for moisture, making it difficult for storms from the western Pacific Ocean to make it over to the eastern side of the ocean.īut there’s another weather phenomenon that might be a boon for drought - the Pacific North American Oscillation. Generally, we can expect dry high-pressure systems to form over the West Coast for most of the winter. That doesn’t mean we haven’t seen wet La Niña winters, and variability between average and above average rainfall can occur when La Niña is disturbed by other patterns. On the other side of the ocean, warmer and more humid air stays off the coast of East Asia. This means that waters off the coast of the Americas will be running cooler than average, and high-pressure systems can form more easily over the West Coast. Instead, most of the models - including the European, American and Canadian models - are signaling this being a La Niña winter. These storms then carry all that moisture off toward the West Coast, bringing periods of beneficial rains to a parched California. This promotes evaporation in the tropics that can spawn storms over Hawaii. During El Niño phases, the waters off the coast of the Americas run warmer than average, while the opposite happens off the coast of East Asia. These phases spread out over the entire Pacific basin. The El Niño-Southern Oscillation comes in two flavors, or phases: El Niño and La Niña. It will be going up against the PNA, which can sometimes interrupt what ENSO brings to the table. These patterns have such a large reach that they oscillate over the entire Northern Hemisphere, and changes to water temperatures in the tropics thousands of miles away can influence the severity of drought in California.ĮNSO is likely to be the biggest weather pattern to influence California’s rain chances over the course of October and the wet season. The air circulation patterns hover over the earth some 30,000 feet above us, thousands of miles away from California. Two very different large-scale weather patterns, the El Niño-Southern Oscillation(ENSO) and Pacific North American Oscillation(PNA), are the main players dictating October weather. But another weather pattern could shake up our chances of seeing at least one more storm roll into California before the end of the month. A quiet, mostly dry pattern looks to be taking center stage for October as California is set to enter its third consecutive year of La Niña. This roller coaster of temperatures and intense back-and-forth between extreme heat and strong rains has come to a halt, though.
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