ARkStorm Fears Recede in California Despite Flooding; Anomalous Lack of Rain-Shadowing Explained by Weather West

Fears of an impending ARkStorm in California have receded, although much of the state has been receiving prodigious amounts of rainfall and the forecast remains wet for the next 10 days. In the most recent storm, the heaviest rains have fallen in the Santa Barbara and Ventura areas, northwest of Los Angeles. The map posted below shows total precipitation amounts of up to 14 inches in a 24-hour period; other reports indicate that a few areas have received more than 18 inches. As would be expected, floods and mudslides have hit the region, causing considerable damage and taking several lives. For the state as a whole, however, the damage has been less than has been reported in many sensational news articles. I have read stories and seen videos that describe California as being “devastated,” “drowned,” and “underwater.” Despite the localized destruction, which should not be minimized, the recent storms have been beneficial for the state as a whole, washing away a devastating drought, at least temporarily. Even in some of the hardest hit locations, some rain enthusiasts posting on the Weather West blog are joyful for what they have received.

From a climatological perspective, the most interesting feature of the map posted above is not the torrential rain in places like San Marcos Pass, which periodically receive heavy and extended downpours. More unusual are the relatively high figures in inland areas that are rain-shadowed by mountains, such as the Cuyama Valley. Cuyama is extremely dry, receiving only 8 inches of precipitation a year on average. As bands of rain typically move from the south or southwest to the north and east, they dump most of their moisture over the coastal highlands as the air rises and cools; as the air descends and warms on the lee side, precipitation rates plummet. This dynamic is especially noted under conditions of an atmospheric river, which brings a relatively shallow but extremely wet airmass streaming in from the subtropics. As the recent flooding rains in the Santa Barbara area came from a stalled atmospheric river, the relatively high level of rainfall in Cuyama was unexpected.

A more pronounced precipitation anomaly was found further to the north, just to the east of the Sierra Nevada crest in east-central California. A high range, the Sierra rings most of the water out of winter storms. And as result, the Owens Valley, lying just to east of the southern Sierra, is extremely dry. The town of Bishop in the northern valley receives less than 5 inches of precipitation in the average year. Yet over the course of a mere 24-hour period on January 9th and 10th, 2023 – under conditions of an atmospheric river – Bishop received over 3 inches. And the downpour continues; just 11 minutes ago, commentator Unbiased Observer noted in Weather West that Bishop is closing in on 4 inches. This oddity demands an explanation.

Fortunately, such an explanation was made available, again by Unbiased Observer, on the Weather West blog, run by meteorologist Daniel Swain. I have posted the pertinent information below from the blog’s discussion forum. Such sharing of information among a devoted community of weather watchers is one of the many reasons why Weather West is such a valuable resource.