The state of California, is about to experience an atmospheric river this weekend. For readers that are not familiar with atmospheric rivers, they are long moisture plumes that originate from the tropical/subtropical regions that advect to higher latitudes. Atmospheric rivers are capable of producing large amounts of precipitation, in the forms of rain and snow and can lead to flooding in low-lying areas.
For central and northern California, precipitation will start today, 5 April 2018, and last through Saturday, 7 April 2018. Precipitation will vary depending on location, and forecasts can be seen here.
Satellite imagery products, highlighting the atmospheric river can be seen below. They consist of the Blended Total Precipitable Water (TPW), Advected Layered Precipitable Water (ALPW) and the Near-Constant Contrast (NCC) products.
At 1109Z, this morning’s SNPP overpass highlights the NCC product (at 750-m resolution) that utilizes a sun/moon reflectance model that illuminates atmospheric features, and senses emitted and reflected light sources during the nighttime. Notice the large low-pressure system, embedded with the atmospheric river, located west of the United States.
The Blended TPW product is derived from several satellite sources, and is at a spatial resolution of 16 kilometers and temporal resolution from 1-3 hours. The product is useful in identifying rich moisture plumes such as the one recognized this morning, seen below, at 0341Z, 5 April 2018. A limitation of the Blended TPW is that it determines the ‘total’ TPW throughout the atmosphere, however, does not differentiate how much TPW exists in specified layers in the atmosphere (e.g. surface-850mb).
Advected Layered Precipitable Water (ALPW)
The ALPW product, unlike its predecessor, Blended TPW, incorporates model data, in this case, the Global Forecast System (GFS) wind data. ALPW addresses where the TPW is predominately located within the atmosphere, separated by 4 layers, the surface-850mb, 850-700, 700-500mb and 500-300mb. The video below shows the atmospheric river advecting form the East Pacific to north and central California, between 4-5 April 2018.