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.
To make matters worse, a significant heat wave has now engulfed the state and raised the specter of more wild fires to come. Temperatures on Thursday, October 2nd, broke records in southwestern California where Santee, Ventura, and Fullerton all hit 102°F (38.9°C), the warmest places in the nation. Santa Maria, on the normally cool coastline hit 100°F (37.8°C) breaking its previous daily record of 96°F (35.6°C) set in 1945. Long Beach (in the Los Angeles area) had a record 98°F (36.7°C) beating out the former record for the date of 96°F (35.6°C) also set in 1945. The San Francisco Bay Area was also hot, but not in record territory. Salinas was the warm spot reaching 97°F (36.1°C) and San Francisco (airport location) reached 91°F (32.8°C), its 2nd hottest day of the year so far (following a 92°F/33.3°C reading on May 13th). Although impressive, October often registers the hottest temperatures of the year for coastal locations in the state. Monterey’s hottest temperature on record occurred on October 5, 1987 when a scorching 104°F (40°C) was observed. Eureka’s all-time heat record happened even later in the month, on October 26, 1993 with an 87°F (30.6°C) reading. San Francisco has seen several occasions of 100°F+ temperatures during October. UPDATE: On Friday, October 3rd, record temperatures continued. San Francisco Airport reached 95°F and San Francisco Downtown 92°F, both figures represent the warmest temperatures observed so far this year. Pacifica, right on the coast, reached 96°F. A little further south, Gilroy peaked at 105°F, the hottest place in the nation on Friday. Monterey measured a daily record high of 96°F. Santa Cruz was 99°F.
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.
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