The Pineapple Express may sound like the next great train ride, but did you know it's an actual weather event and something Alaska is experiencing. Lately, Alaska has gone off the rails and tapped into the tropics, as abnormal warmth and plenty of rain has gripped a large portion of the state.

The end of October usually brings an average snow depth of nearly 2 inches for Anchorage, but all we're seeing is bare trees, brown grass, and a steady stream of moisture into the state. Cue the Pineapple Express, or an atmospheric river, which has crashed into the state bringing record temps, strong winds and heavy rain. 

The science behind atmospheric rivers

Atmospheric rivers are narrow regions in the atmosphere that transport a significant amount of moisture from the tropics to the northern latitudes. The most well-known example is the Pineapple Express when moisture builds up around Hawaii and is eventually transported to either the West Coast of the U.S. or sometimes, even Alaska.  

All across the globe, there are concentrated rivers of wind, known as a jet stream. These jet streams are responsible for carrying weather systems across the globe. Because this "river" is flowing over the entire Pacific Ocean, it has an abundance of moisture to work with. You see this on satellites as a long stretch of clouds, which stretch for several thousand miles, originating near Hawaii. It's for this reason the atmospheric river has been coined the Pineapple Express. 

Satellite imagery from Monday shows just that, as a strong southerly flow continues to pull in not only moisture but warmth for a large portion of the state. 


These atmospheric river events are typically associated with very heavy rainfall events, of which flooding is a possibility. That's something that has occurred across Southcentral, as social media posts show the extent of the rainfall on Kodiak Island, where more than 3 inches of rain has fallen since Friday. 


It's not uncommon for flooding to occur in events such as this, as atmospheric rivers can carry enough water vapor that can be equivalent to the flow of water at the mouth of the Mississippi River. Atmospheric rivers are also responsible for significant snowpack in a region, but that hasn't been a concern for Alaska due to the abnormally warm temperatures. As tropical air surges northward from Hawaii it is modifying somewhat, but high temperatures are still topping out near 50 degrees, which is roughly 15 degrees above what is normal for this time of year. Because of this warmth, Anchorage will close out the month of October as the third warmest on record. 



So what are the direct results of this seasonal derailment? While Alaska and Canada remain on the warm and wet side, parts of the Lower 48 will be dealing with temperatures dipping well below average temperatures and more snow than Anchorage and parts of the state have seen so far this season. Parts of the Midwest are expected to dip well into the 20s for overnight lows over the coming days, which is significantly colder than Anchorage's coldest low this season of 26 degrees. 

Like it or not, Alaska is feeling somewhat tropical. You might as well climb aboard the Pineapple Express and settle in because high temperatures don't look to fall into the 30s again until next week. 

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