Daniel Swain: Record summer heat across much of state retreats; some deeper thoughts on El Niño

Record summer heat (in many spots, except SF) fades

Sept. 19, 2018 – After a truly searing start to summer across most of California, especially in the south, the last several weeks have felt rather mild by comparison. The record-breaking heatwaves of July, followed by record warm ocean temperatures later in the summer in SoCal, made for very uncomfortable conditions across some of California’s most densely populated regions for much of the summer. Meanwhile, in interior NorCal, record daytime highs were few and far between–but relentless overnight warmth and persistently above-average daytime temperatures again combined to produce record or near-record summer temperatures. Indeed: across many parts of southern and interior California, 2018 was the warmest summer on record.

Wildfire activity moderates (for now), but autumn resurgence plausible

Following an extraordinarily bad start to the fire 2018 fire season, which included the devastating Carr Fire (and incredible “fire tornado” in Redding) and the now-largest wildfire in California history (the Ranch Fire, which exceeded the previous acreage record set by the Thomas Fire just last December), fire activity has moderated somewhat in recent days as temperatures have cooled. Fire risk is still extremely high in many areas, and the traditional peak of fire season in California (which coincides with the often warm and dry autumn offshore winds) has only just begun. At the moment, there are no severe wind events on the horizon, which is good news–but Santa Ana wind season extends through December (as last year’s late-season firestorms vividly illustrated). So after the present reprieve, I would not be surprised to see a renewed surge in heat, wind, and fire activity before the winter rains arrive. I’ll keep my fingers crossed that we get a break this year, though. It’s already been a rough few years as far as California wildfires go.

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(As of this writing, there are actually some fire weather watches in effect for the higher elevations surrounding the northern Sacramento Valley due to warm temperatures, low humidity, and gusty winds. While this is not expected to be an especially extreme event, it’s still worth noting given the number of large (but mostly-contained) fires still burning in NorCal and the near record-dry state of vegetation in this region).

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