California and Great Basin
With September and October normally one of the driest months in California, any significant rain (more than 0.5 inches) that falls during this time will usually produce large percentages. This was the case this week when a strong upper-air trough (low pressure) affected the West Coast, drawing in Pacific moisture to most of California and the Great Basin. Unseasonably heavy precipitation (0.5 to 1 inch, locally to 2 inches) was observed in extreme southwestern California (near San Diego vicinity), the Sierra Nevada, and most of northern and western Nevada including the Las Vegas area. Although the rains were welcome and aided in the suppression of wild fire conditions and increased topsoil moisture, it did little for the long-term drought and reservoir storages, thus no changes were made to the drought map. At the end of September, the water conservation efforts in California were noticeable when compared to last year. The amount of water saved came to about 705 KAF – so that this year’s major reservoir storage was only slightly below the storage from a year ago when there were no mandatory water restrictions.
Source: The National Drought Mitigation Center