What is the 'Pineapple Express,' and how is it connected to an atmospheric river?

What does the term 'pineapple express' mean and what impacts does the weather phenomenon create?

Weather systems that affect the West Coast of the United States often have their origins in the northern Pacific Ocean. This is because the jet stream usually flows in a general west-to-east fashion. Sometimes, however, this is not the case.

When the jet stream dips far to the south in the central Pacific Ocean, abundant moisture from the tropics can be transported toward the West Coast. Oftentimes, the ripple in the jet stream occurs near Hawaii.

Since pineapples are one thing that Hawaii is known for, this flow of moisture is referred to as "the Pineapple Express." In fact, Hawaii is home to one of the world's largest and most diverse pineapple collections, according to the United States Department of Agriculture.

"The Pineapple Express is an atmospheric river which has its origin in the tropical Pacific," said AccuWeather Senior Meteorologist Alex Sosnowski.

Since the pineapple express starts thousands of miles to the west of Washington, Oregon and California, there is plenty of time for excessive moisture to gather. Impacts when an atmospheric river moves ashore can range from beneficial rainfall in drought-stricken areas to significant travel disruptions, flooding, mudslides and excessive snowfall. In the mountains where the precipitation falls as snow, yards of snow can pile up in a short period of time.

There can be several instances of a Pineapple Express in any given year, but they are most common during the stormier fall and winter months along the West Coast.

While impacts may be negative in the short term, the longer-term benefits are often welcomed. Despite the extreme amounts of rain and snow that these can produce, the Pineapple Express and other atmospheric river events can sometimes go a long way in replenishing water supplies of lakes, rivers and reservoirs.

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