California wildfires rage amidst remarkably inactive summer monsoon; ridiculously resilient ridge to return this winter in CA? Daniel Swain on August 23, 2016 • 13 Comments

Just how warm this summer has felt in California depends largely upon who you ask. Residents of immediate coastal Northern California–including most of the Bay Area–have benefited from nature’s air conditioning so far this season. Relatively cool ocean temperatures just offshore (a product of increased coastal upwelling this year) have resulted in a robust marine layer, and the traditional “June Gloom” associated with California’s marine stratus has persisted into August in some spots.

….Meanwhile, across all of Southern California and even more inland parts of Northern California, this summer has been yet another hot one–and several heatwaves have occurred since June. Unusually warm ocean conditions have persisted along the SoCal coastline, keeping the marine influence in check and allowing for very hot conditions at times just a few miles inland from the immediate coastline….

….During a typical summer, pulses of moist and relatively unstable air can move from east to west across the Desert Southwest in the clockwise flow around the 4-Corners High–sometimes triggering mountain and desert thunderstorms during the warm season. So far during summer 2016, though, this high pressure area has been centered almost directly over California. As a result, there have been remarkably few convectively active periods so far this season (although a handful of locations did fare a bit better over the past week).

…..The 4-Corners High has been stronger and more westward-shifted than usual this summer. (Daniel Swain via ESRL Plotter)…

….Interestingly (and somewhat disconcertingly), many of these fires have occurred despite the absence of strong and dry offshore wind events that often drive California’s most destructive fires. Instead, most of the current fires in California appear to be preferentially favoring those regions hardest hit in California’s ongoing, multi-year drought. Vegetation fuel moistures and “energy release components” (measures of flammability and potential combustion intensity, respectively) in these regions have reached or exceed record values this summer. While there is an increasing amount of evidence that California’s astonishing drought-related recent tree mortality may not directly increase wildfire intensity in the long run, it’s pretty clear that California’s severe drought has been exerting a strong influence upon fire risk and behavior across California over the past couple of years in other ways…..

….Is the probable lack of a moderate or strong La Niña during 2016-2017 good news for California? Well, it’s certainly true that a strong La Niña would probably be bad news for Southern California–which fared quite poorly precipitation-wise even during one of the strongest El Niño events on record last year. But as Californians have become painfully aware in recent years, La Niña is not the only possible cause of dry conditions and drought in California. The latest seasonal predictions–which are based upon simulations of an ensemble of ocean-atmosphere models that take into account the present state of the atmosphere, global oceans, and sea ice–do not inspire a great deal of hope that the coming winter will bring widespread drought relief. At the moment, these simulations depict a pattern characterized by persistent West Coast winter ridging. This setup looks a fair bit like the Ridiculously Resilient Ridge, and is similar to the kind of atmospheric ridge patterns we’ve started to see more frequently in recent decades…..


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