Moisture returns to the US West Coast

October 22nd, 2021 |
MIMIC Total Precipitable water, rocking animation from 0000 UTC on 11 October to 2300 UTC on 21 October (click to enlarge)

A sequence of two intense storms in the north Pacific Ocean, noted in the GOES-17 airmass RGB below, has drawn moisture into the northwestern United States. A MIMIC (Morphed Integrated Microwave Imagery at CIMSS) Total Precipitable Water rocking animation, above (rocking animation from this site), shows the development of a ribbon of moisture that moved into the northwestern United States.

GOES-17 Airmass RGB with/without 0900 UTC analysis of fronts/pressure (Click to enlarge)

Advected Layer Precipitable Water (ALPW, from this website), differentiates the moisture into layers. At 1200 UTC, one moisture axis was right across the Bay Area of California, with 20-24 mm of moisture in the sfc-850 mb layer, 10-12 mm of moisture in the 850-700 mb layer, and 5 or 6 mm in the 700-500 mb layer.

Microwave estimates of total precipitable water in layers: Surface-850 mb, 850-700 mb, 700-500 mb, 500-300 mb, ca. 1200 UTC on 22 October 2021 (Click to enlarge)

Accumulated 1-hour precipitation (estimated with CMORPH-2) for the hour ending at 1200 UTC on 22 October, below, shows a ribbon of rain from just north of the Bay Area to central Oregon; largest amounts over northern California are 6-8 mm for the one hour. CMORPH-2 estimates of precipitation are available at RealEarth.

CMORPH estimates of 1-hour rainfall ending at 1200 UTC on 22 October 2021 (Click to enlarge)