Although Hawaii and California are two thousand, four hundred, and eighty miles apart, they are occasionally connected by a large swatch of moisture that extends across the Pacific. Called the “Pineapple Express”, this is the phenomenon responsible for epic storms along the entire West Coast and Nevada, although California generally is the state hardest hit.

In meteorological nomenclature, this pattern is caused by the Madden-Julian Oscillation. In layman’s terms, normal rainfall patterns at the equator transfer north. Storms that usually occur over the Indian and east Pacific oceans move higher on the globe, and moisture which usually stays over the Philippines moves eastward. As this stream passes over the tropics, it picks up more moisture. Usually, oceanic storms are weakened by hitting great land masses, but aside from the Hawaiian Islands, there are few in this part of the Pacific; thus, when the tempest reaches the West Coast, it’s still filled with primordial fury – or at least it seems so to the inhabitants of this usually dry land. These storms may be warm or cold, depending on how far north the flow of moisture reached before extending east.

The effects of the Pineapple Express extend beyond the storms that batter the state. When they come in as cold storms, the snowpack in the Sierra Nevadas grows higher; this is particular beneficial after a prolonged period of drought, when the storms help to replenish the water supply. The reverse is true when these deluges occur from a southern sky river, when they melt the snowpack. Thus, this weather pattern can either improve or worsen a drought situation.

California’s rivers are often low and slow, but that changes when the Pineapple Express hits. Because of the drought patterns, the hard, dry soil saturates very easily; recent fires also weaken the land’s ability to hold onto water. Thus, the Pineapple Express is also associated with localized and generalized flooding. The winter of 1861-62 is remembered as California’s “Great Flood;” Sacramento, Napa, and parts of Los Angeles were forced to evacuate because of high water – water which didn’t recede in Sacramento for eighteen months! This phenomenon was also responsible for flooding in various parts of the state in 1952, 2005, and 2010.

At the beginning of January, 2017, the Pineapple Express returned to California with a vengeance, bringing blizzards to the Sierra Nevadas, extra water in the form of higher snowpack, and heavy rains in the flatlands. Concerns over flooding related to areas burned in recent fires remained high, and the state took measures to open floodgates and use reservoirs formerly dry for many years. As of this writing, the full impact of the 2017 Pineapple Express remains to be seen.