August – November 2024 North Ops Highlights
An alignment of critically dry dead and live fuels is likely to occur for extended periods during August & September with some moisture intrusions across the north during October & November.
A mix of Heat-Wind & Lightning concerns is expected during August then more Wind driven fire concerns during September.
Herbaceous fuel loading is above to well above normal thus increasing the potential for large fire development, even under less than gusty scenarios.
Significant Fire Potential is above normal during August & September across most of the area excluding some Coastal areas due to Marine influences, then returns back to Normal for October & November when large fire activity is historically less.
Editor’s note: During August, 2 to 5 large fires occur per Predictive Service Area (PSA) with the exception of less than 1 large fire in the Bay Area PSAs. During September most PSAs average 1 to 3 large fires excluding the Bay Area and Far Eastside PSAs which is less than 1.
North Ops Fire Business & Trends
Fire business continued to increase during July with 23 fires on average per day. Large, costly fires occurred throughout the month, starting with the Thompson fire near Oroville and ending with the Park fire near Chico. Large fires burned through all fuel types including grass, shrub and timber. Complex incident management teams and/or Type 1 teams were requested to help manage the Thompson, Shelly, Hill, Gold Complex and Park incidents. The Park fire ignited during the afternoon of the 24th and had grown to a little over 350,000 acres in oak woodland and timber by the evening of the 27th. Very few prescribed burn projects were carried out during July due to the lack of resources and pre-existing very flammable conditions.
Flash drought has likely set in across the area and moderate drought is likely to expand across the north and east during the next 2 months. Woody fuels will continue to cure and become more receptive further up the slopes. Critically flammable alignments in both the dead and live fuels will likely occur for extended periods during August and to a lesser extent September due to possible moisture relief across the north. Impactful lightning events should peak during August and will be less likely September into the fall. Enhanced summer wind events should continue during the next 4 months. The offshore wind season will be largely dependent on how the Pacific Ridge builds and alters the expected active storm track across the Pacific NW. It is too early to say with confidence right now but will be monitoring model and analog year trends since abundant dead grass will be a likely contributor until a series of widespread wetting events can occur.
The significant fire potential outlook has been altered to increase the potential during August and September due to the expectation of continued heat, enhanced wind and lightning signals on top of a flammable fuel bed. The unusual amounts of dead grasses help tip the scale, especially during September when wind events will be more common. Normal significant fire potential has been designated for October and November when large fire potential typically decreases although may need some above normal in future outlooks if better clarity occurs with the offshore wind season.
Fuels Discussion
The previously mentioned historic heat wave event set the stage for an extended period of critically dry dead fuels across most of the area during July. Some PSAs neared all time dead fuel dryness records. Live woody fuels became more flammable across the low and mid elevations due to intense herbaceous and shrub curing. This set the stage for an all fuel stratum flammable alignment driven by abundant cured out grass, historically dry dead fuels and increasingly stressed live fuels. Shrub and native grasses were a bit more moist, and less resistant to fire spread across the higher elevations, generally above 6000-6500 feet.
The blue line found on the North Ops 1000-hour dead fuel moisture chart illustrates the historic drying that took place during July with the majority of the line spent below or along the record minimum red line. The grey line is the historical average based on 23 years of data. The dashed lines represent various flammable percentile thresholds from the 40th to the 3rd.
Above to well above normal herbaceous fuel loading continues to aid the rapid fire growth observed during July. Most of the herbaceous fuels are in some sort of cured or curing phase with the exception of less exposed +7000 ft elevations. Woody live fuels continue to cure across the low & mid elevations and have reached or are nearing a critically flammable stage. Chamise found in the PG&E live fuel moisture chart is one such fuel. Sage is another. Many of the live fuel moisture readings are starting to trend near to below normal versus near to above normal observed previously.
Moderate drought has also returned to northern CA. Late July 2-month EDDI graphic illustrates a flash drying effect with significantly high drought categories across the south & east, likely putting stresses on the live fuels.
Weather Discussion
The weather pattern during July comprised of dominant ridging with occasional weakening of the ridge periods due to Pacific Trough or coastal disturbance passages. A historical 2-week heat wave event helped set the stage for above to well above normal average temperatures across most of the area although near normal was found across some of the Coastal areas. Precipitation was generally below normal although a couple of multi-day Monsoon thunderstorm events brought some patchy above normal areas to the east. Around 2900 lightning strikes were recorded during the month which fell well short of the 2012-2022 July average of around 7500 strikes. A dry-gusty northerly wind event occurred on the 2nd and3rd, otherwise the wind induced RedFlag Warning and High Risk issuances were due to warm-dry westerly southerly winds events.
The outlook forecasts have been shaky the past couple of months in terms of determining ridge vs trough impacts.This is maybe partially due to a delay in the ENSO transition from Neutral to LaNina as well as other climate factors such as stratospheric influences. August is expected to have similar pattern characteristics to July with generally warmer than normal temperatures, away from the Coastal influences, and a mix of lightning and enhanced summer wind periods. Troughing is expected to be more dominant than ridging during September which means some Jet induced moisture intrusions are likely but probably favor the northern tier.Some guidance suggest impacts from the moist side of the Jet during October and November although confidence is less and Predictive Services will be monitoring the trends.