OWN VOICE. ~ InPerspective by Gregg Dieguez —
Just a quick note to counter a dangerous piece of misinformation floating around out there on anti-Social Media. The claim is that Diablo winds are only 0.4% probability, so we don’t have to stress out about them. Yes, we do, and an understanding of probability will make this clear.
Images: Click to enlarge for improved readability in a new window.
Slightly outdated evidence is that Diablo winds, which are vigorous and blow from the E/NE during the highest fire danger parts of the year, occurred in only about 600 hours over a 15 year period (2003-2018). Given that there are 131,400 hours in a 15 year period, those winds occur only 0.46% of the hours. However, do not confuse that with the probability of Diablo winds 
NOT occurring for an extended period of time. To do a proper probability analysis we have to consider the Cumulative Probability, that is, the probability that something will keep NOT happening, again and again, and again. As you can see in the screenshot at left, and can explore for yourself in this spreadsheet: https://docs.google.com/spreadsheets/d/1LhJy9A5iDCw9QoScJ9shRO0WoZZZ_LCL/edit?usp=sharing&ouid=112260193980395249411&rtpof=true&sd=true, even with a low rate of occurrence, the probability that a Diablo wind will occur in any year is very close to 100%. And the probability that they will occur at least once during the Fall, peak wildfire season, is at least 99.9956279…%, well you get the point. In fact, we already had them during a recent COVID February, and I counted 3 dozen trees in Quarry Park felled by those winds. Of course, in February the ground was wet, which is why the shallow roots of those trees allowed them to be toppled.
This risk can be further refined by having a wind meter installed near to Quarry Park, which is a need identified in the recent El Granada Wildfire Resiliency Scoping Project. I’ll bet my car that it will show higher wind speeds, and more often, than are registered by the more distant wind gauges used today, and in the survey used for these Diablo calculations.
Of course, given our Climate Crisis, these winds are likely to occur even more frequently and more vigorously than during the period surveyed above. But Diablo winds are virtually certain to occur annually. The issue is: will someone light a fire, or set off a fireworks, or will we have lightning strike at the wrong time? How much prevention is worth paying for to ensure a wildfire doesn’t ravage our region, and blow eucalyptus over onto our limited evacuation routes? Those are matters up for debate. But let there be no debate about Diablo winds, they are here Every Single Year, at the worst possible wildfire times.
More From Gregg Dieguez ~ InPerspective
Mr. Dieguez is a native San Franciscan, longtime San Mateo County resident, and semi-retired entrepreneur who causes occasional controversy on the Coastside. He is a member of the MCC, but his opinions here are his own, and not those of the Council. In 2003 he co-founded MIT’s Clean Tech Program here in NorCal, which became MIT’s largest alumni speaker program. He lives in Montara. He loves a productive dialog in search of shared understanding.