If you're in California, put on these slippery slippers and put on these dirt boots, because the day will be muddy, windy and rainy. A weather phenomenon called the "atmospheric river" is making its way through the golden state.
An atmospheric river is a thin, transient column of condensed tropical water vapor located in the atmosphere – "like a river in the sky," according to the National Oceanic and Atmospheric Administration (NOAA). When the "river" manages to land, it usually comes in the form of heavy rain or snowfall.
This current event is also known as "Pineapple Express" because the moisture originated in Hawaii and traveled to the western United States. In general, atmospheric rivers are approximately 1,600 kilometers long and 400 to 600 kilometers wide. They can carry water vapor between 7.5 and 15 times the average water flow at the mouth of the Mississippi River.
Although it sounds catastrophic, it's not just bad news. As long as everyone is safe during the event, rainfall can provide much needed water and snow to areas such as the Sierra.
"All atmospheric rivers do not cause damage; most are weak systems that often provide beneficial rain or snow, essential to the water supply, "notes NOAA. "Atmospheric rivers are a key element of the global water cycle and are closely linked to both water supply and flood risks – especially in the western part of the world. United States."
Like most weather events, it's a double-edged sword. The atmospheric river can provide water to the regions that need it, but it can also cost lives and injuries, as it was found a few days ago when passengers on a flight between southern California and Seattle have experienced severe turbulence in making an emergency landing.
This month, a new scale for classifying atmospheric rivers was created by researchers at the University of San Diego in the US Meteorological Society Bulletin. They attributed these weather events on a scale of categories 1 to 5, from "low" to "exceptional" respectively. The criteria are based on the amount of water vapor and its duration in one place.
This storm is a category 3, according to CBS San Francisco. This is considered a "strong" event with a balance of beneficial and dangerous results. Scientists provide an example of an earlier Category 3 event: the 14 October 2016 atmospheric river, which lasted 36 hours and produced 5 to 10 inches of rain. Fortunately, it filled reservoirs after a drought. This is not very good news, some rivers have grown too much.
It should also be noted that atmospheric rivers "move with time and are present somewhere on the Earth at any time," according to NOAA.
For this event, the National Weather Service reported waves of wind and rain, with an area of the San Bernardino Mountains receiving an incredible total of 9.4 inches over 48 hours. Thousands of people in Northern California have lost electricity and flood warnings are in effect in many areas.
In other words, stay safe outside.