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Atmospheric Rivers, what are they?

It is time for winter weather and we tend to get some rain. 

The big buzzword is "Atmospheric River"... 

What are they? 

Atmospheric rivers (AR) are long, narrow streams of water vapor in the sky, moving moisture from the tropics. When the AR makes landfall, it releases rain or snow. The AR is a key factor in our water cycle.

AR are not uncommon or necessarily devastating.  

Many potentially come to California during these winter months. They can produce large amounts of rain or moderate to small amounts. 

So, not every one is a powerful storm. 

A strong AR is called The "Pineapple Express," which brings moisture from Hawaii to the U.S. West Coast. It begins as a warm water storm over the Pacific Ocean, and then prevailing winds give AR its shape and velocity.

During El Nino weather cycles the warming effects of the water can produce these powerful AR. 

El Nino and La Nina weather patterns occur every 2 - 7 years, but not on a regular schedule. 

According to NASA, atmospheric rivers off California's coast form regularly during winter months, and usually deliver up to 50% of the region's annual rain and snow. 

Atmospheric rivers are present somewhere on Earth at any given time. They are a primary feature in the entire global water cycle.

Forecasting the weather can be difficult since these systems tend to move or change course. 

KCRA 3 says the forecasting of weather skills is more challenging the farther out they try to forecast. Here is their timetable:

  • 1-2 days out, the timing, particulars, and totals are very good.

  • 2-5 days out, the potential impacts are fair to moderate to determine.

  • 5-7 days out of a storm could be possible to predict, but the outcome could change, making forecasting poor.

  • 10+ days out, the broad patterns that could easily dissipate or change make forecasting very poor.

So don't get mad at the weather person when the forecast is off. Ultimately, it is all up to Mother Nature. 

Just relax and enjoy what she brings, but be prepared. 

Atmospheric river
Atmospheric river


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