From Wunderground's Weather Historian blog:
Crunch Time for California Drought
The most dangerous month of the year for wild fires is underway in California and starting off with a significant heat wave. Last week’s rainfall had little impact on the overall drought conditions but was a welcome respite nevertheless and hopefully a harbinger of some drought relief as the rainy season approaches.
Welcome rainfall of 0.30” to over 3” brought relief to the northern half of California on September 24-26 and helped squelch the massive King Wild Fire but, unfortunately, they hardly made a dent to the state’s overall drought situation and ground moisture conditions, let alone reservoir levels.
A comparison of the Drought Monitor maps at the beginning of the dry season in May and the latest map issued. The latest drought map (top) released on October 2nd shows only an imperceptible improvement in conditions (in the far northwestern county of Del Norte) following the rainfall during the last week of September. Map from NOAA/NCDC et al.
As the U.S. Drought Monitor reported in their Western Regional text summary, ”The rains had little impact on the ongoing drought, especially in California, where deficits are huge and the normal annual precipitation in parts of the northern coastal areas can reach 75-100 inches. Topsoil in a few areas benefited, wildfires were hindered, and stream flow increased, but the stream flow recovery was short-lived as streams rapidly returned to the low flows they had prior to the rain event, and reservoir levels did not improve. Statewide, California soil moisture conditions were the same as last week, with 80% of topsoil and 85% of subsoil rated short or very short of moisture by the USDA.”
To make matters worse, a significant heat wave has now engulfed the state and raised the specter of more wild fires to come.....MORE
...The cause for the October warmth is when the first outbreaks of cold air from Canada invade the Rocky Mountain states which causes a high pressure ridge to build over California and strong offshore flow winds to form at the surface. These are the same winds (known as the Santa Ana and Diablo winds) that have caused some of California’s worst wild fires on record. Fortunately, during the current heat wave, very strong offshore winds are not forecast to develop. In any case, the heat wave is expected to last through the weekend with even hotter temperatures expected at most locations on Friday and Saturday (I will update the numbers and new records this weekend).
Needless to say, the hot dry conditions have completely eliminated the beneficial effects of the September rainfall, and conditions have set the stage for a critical month, both in terms of the drought and potential wild fires. Reservoir capacities continue to shrink: Lake Oroville, one of the state’s most important water storage facilities, is now down to 30% capacity, approaching its all-time record low of 26% set in 1977 during the state’s worst drought on record.
Lake Oroville when at full capacity in 2011 (top) and in August, 2014 (bottom) when it had shrunk to 32% capacity. Since August it has declined to 30% capacity. Photos by Paul Hames, California Department of Water Resources and Justin Sullican, Getty Images....MUCH MORE
