What is an atmospheric river? Weather event behind California floods, record snow

Storms related to atmospheric rivers have dumped document quantities of rain and snow in California this winter, leading to flooding and different hazards.

The large image: Atmospheric rivers direct tropical moisture, typically from greater than 1,500 miles away, towards the Golden State, the place it’s wrung out within the type of heavy precipitation.

• Atmospheric rivers are lengthy, slender highways of moisture, sometimes situated at about 10,000 to fifteen,000 ft above the floor. They’ll journey hundreds of miles and are accountable for 30-50% of the moist season precipitation alongside the West Coast of the U.S., in keeping with NOAA.
• A robust atmospheric river can transport an quantity of water vapor that’s “roughly equal to 7.5–15 instances the common movement of liquid water on the mouth of the Mississippi River,” NOAA has discovered.
• Scientists have solely just lately gained a larger understanding of the function that atmospheric rivers play in West Coast storm occasions, and noticed them affecting different areas of the world as properly.

• Through the previous few months, hurricane hunters operated by the Air Pressure and NOAA have been investigating atmospheric rivers over the Pacific Ocean and offering added information for laptop fashions to refine their projections.

‘Menace stage: This winter, California has been hit by greater than a dozen atmospheric river occasions, lots of them sturdy ones which have dumped upwards of 100 inches of snow at a time within the Sierra Nevada mountains, and a few foot of rain at decrease elevations.

• Whereas all this precipitation has helped ease, although not eradicate, the document drought affecting the state, there could be an excessive amount of of a superb factor.
• With an epic snowpack 200 inches deep in some locations, reservoirs which are rising towards full ranges and rivers working excessive, any further atmospheric river occasions might trigger critical flooding.
• That is significantly the case for heat atmospheric rivers, which might increase snow ranges and trigger rain to fall on high of the present snow, releasing a few of its water content material.
• Damaging flooding has already occurred in Central and Northern California throughout mid-March from atmospheric river occasions, and extra could also be on the way in which.

Between the traces: Local weather change is including much more moisture to atmospheric rivers, enabling them to dump larger rain and snow totals.

• That is occurring as a result of ocean temperatures are growing, inflicting extra warmth and moisture to be transferred into the ambiance and made accessible to storm methods.
• As well as, with every 1°C (1.8°F) enhance in air temperatures, a selected air mass can maintain a minimum of 7% extra moisture.
• Particular person storms related to atmospheric rivers can pull in much more water vapor than this, making damaging rain and snowfall extra seemingly.
• California remains to be in a long-term extreme drought, significantly given its depleted groundwater provides.

The underside line: Research additionally present that local weather change raises the percentages of climate whiplash occasions from drought to flooding and again once more.

• That is noteworthy since California was already recognized for its feast or famine precipitation regime.

Go deeper: Subsequent in parade of atmospheric rivers set to slam storm-hit California