Super Hot Dangerous Heat Event Developing in California

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An Excessive Heat Warning is issued for the southern half of California and an upgrade from a watch to a warning for the northern half of California is due by tomorrow. Excessive heat warnings are the highest state of alert for the California electricity markets. The projected population weight CDD for Sep. 4-10 for the Pacific region is 104 which is slightly higher than the 102 observed Aug. 14-20.

Highlight: Incoming Pacific Region Hot Event Exceeds August Event. This is a dangerous episode – record heat and fire risk!

Discussion: An Excessive Heat Warning is issued for the southern half of California and an upgrade from a watch to a warning for the northern half of California is due by tomorrow. Excessive heat warnings are the highest state of alert for the California electricity markets. The projected population weight CDD for Sep. 4-10 for the Pacific region is 104 which is slightly higher than the 102 observed Aug. 14-20 AND much warmer than normal compared to the August event (+70 vs. +59). The peak of the heat event is Sunday/Monday of next week.

Fig. 1: The population weight CDD weekly observations in August and 4-week forecast in September compared to last year and the 30-year normal.

The character of this heat wave is much different from the August episode. First, there are no thunderstorms associated with this event. Lightning strikes caused fires during the previous heat wave as residual moisture arriving from the south (former tropical systems) provided the catalyst for daily convection mostly over mountain areas. The air mass is much drier this time.

Second, a strong east wind is likely to occur across the Interior Northwest early next week surging southward through California Tuesday/Wednesday. The high wind will maintain the hot weather and as important provide the catalyst to an extremely dangerous fire risk.

The mega-cluster ensemble indicates the heat may ease but not end later next week followed by conditions that sustain the heat into the extended-range.

The northern half of California is most susceptible to record heat centered on early next week. The dry soil/drought condition there supports the call on record heat. Temperatures will be well into the 110’s across favored areas of Interior Northern California.