09/02/2024
From Dr. Daniel Swain at weatherwest.com
A mix of various local setups will broadly increase wildfire risk across most of West in early September
By next weekend or early next week, offshore troughing may increase southwesterly flow aloft over northern CA and the Pacific NW. This could bring a few showers to the PacNW, but mainly cooler and at times windy conditions over NorCal.
Today (Labor Day), elevated fire weather risk is present across far eastern and interior Northern CA as well as the Great Basin/eastern OR region (including Reno/Tahoe) as a combination of dry/windy conditions, plus isolated dry lightning, increases both the likelihood of new ignitions and potential behavior on fires. Although winds will die down in the coming days, temperatures will rise and humidity will drop–further drying out the landscape at a time when many regions are already nearing peak seasonal dryness. This will be true across a broad region from Southern California northward into central Washington/Oregon and eastward across the Great Basin and Rockies. In fact, it’s probably simpler to list the areas that I think will not see substantially increased wildfire activity in the coming days: the North Coast of CA (too damp and cool this summer!), far western OR/WA (not hot enough during this event and too damp as of late) and perhaps portions of the Four Corners vicinity (where Monsoon 2024 has been very active). Numerous large and active fires are already burning in Idaho, Montana, and western Wyoming, and this activity will likely expand and intensity considerably over the next 1-2 weeks as widespread heat and generally below average precipitation persists.
There are a couple of additional wrinkles. A handful of weaker troughs and possibly associated low pressure systems will pass through the upper portion of the ridge over the next 2 weeks. These will bring periods of cooler weather (especially along the coast) as well as occasionally breezy to windy conditions. Because this will occur in the broader context of hotter than average temperatures, and amid generally dry fuel conditions, these periods of occasional onshore winds will likely feature windows of increased wildfire risk across a broad zone.
Also, there are some weak hints that one of two of these modest low pressure systems could generate a few showers or thunderstorms (possibly containing little precipitation) at times from NorCal northward (mainly over mountains), and that could lead to some scattered new lightning ignitions as they would occur immediately following another major heatwave and drying event. For now, I don’t foresee this as a huge risk but collectively it does appear the pieces are coming together in a way that will be favorable for a major surge in wildfire activity across a broad region, with localized episodes of more extreme fire weather possible due to a combination of heat, stronger winds, and lightning. It’s unlikely that most locations will see all three of these, but I think there’s a pretty good chance of a robust “second season” from a wildfire perspective this year (following the initial July surge, there may well be another in Sep into Oct in some regions).
