By Reginald Stanley. Posted December 31, 2021, 5:01 AM.

A cutoff low situated off the coast southwest of Southern California this week was slated to produce heavy rainfall and mountain snow across most of the region between Wednesday and Thursday, however only Ventura and Los Angeles counties were affected, while the rest of the region remained mostly dry.

A stationary band of heavy rain targeted Ventura and Los Angeles counties late Wednesday and Thursday, producing very high rainfall rates and localized flooding in its path. However the cutoff low did not move into the anticipated path, which was to spread that heavy precipitation eastward over the rest of Southern California over Thursday and Friday. WeatherCurrents' stations in Simi Valley and Pinon Hills were in the path of the storm, the only two WeatherCurrents stations to record significant rainfall by Friday, while all other locations saw mostly cloudy skies with very little, if any measurable precipitation throughout this period. Simi Valley recorded 3.10 inches over Wednesday and Thursday, most of it falling on the latter day - leading all other WeatherCurrents stations by a very large margin. The normally rainshadowed Pinon Hills recorded the only other notable total, with 0.85 inches by Friday morning.

The remainder of the WeatherCurrents network only experienced patchy light showers and drizzle over the two days, with occasional sunshine. Some parts of the Temecula Valley had a slight benefit from precipitation coming off the Santa Ana Mountains, however totals were still low. The eastern valleys were exceptionally dry, where less than 0.1 inch was recorded in Hemet and San Jacinto. In East Highland, a total of 0.42 inches was reported (courtesy of Peter Michas). In Temecula Valley's Wine Country, 0.25 inches was reported (courtesy of Jim Sappington). Earlier in the week, precipitation projections for the inland valleys originally ranged from between 1.5 and 4 inches between Wednesday and Friday. Needless to say, due to the selective storm track of the cutoff low, the predictions were not even remotely close for these areas. Much of San Diego County received totals of less than 0.1 inch as well.

By Thursday night, the low had moved southeast of Southern California, taking any remaining moisture with it. According to the National Weather Service, a small chance of showers remains for Friday, mainly in the western mountain slopes as a shortwave trough affects the region. A cold, dry airmass will be left in its wake by Friday night, leading to near-freezing temperatures overnight inland. A ridge will dry the region out over next week, while temperatures are expected to remaining between below-normal and near-normal.

Here are the rain totals for the WeatherCurrents network and associates: