While it was record winter and spring season in Utah, Nevada, and Hawaii; the potential for significant wildland fire to occur remains high in Hawaii and Southern Nevada.
Great Basin (Includes Utah and Nevada): Normal significant large fire potential is expected across the region during the outlook period except across the southern portion of the region in May and June when Above Normal significant wildland fire potential is expected and across the higher mountains of eastern Idaho and Utah where Below Normal significant large fire potential is expected May through July. Below Normal significant wildland fire potential is also expected across the eastern portions of the Sierras in May and June. The majority of the Great Basin is at or above average for precipitation over the past two to three months. However, over the last 30 days, the southern portion of the Great Basin has seen much drier conditions than previously observed as the storm track shifted north, with little to no precipitation received over the last 30 days. Snowpack is 140-200% of average in the higher elevations of Nevada and Utah into eastern Idaho. Even though conditions have not been as wet further north, snowpack across Idaho and Wyoming is just above average for the time of year. There have been several cold, low elevations snowfalls this winter and spring across the northern half of Nevada into Utah. This likely will compact some of the carryover fuels we have seen from the last two years, which in turn could reduce fuel loading going into fire season. However, wet weather has occurred off and on across the northern two thirds of the Great Basin much of the spring. Forecast data continues to show wet conditions are expected across the northern two thirds of the Great Basin for the next several months, which potentially could last into the summer. This has already allowed for new fine fuel growth, which may be continuous, albeit short in some areas. A potential also exists for multiple crops of fine fuel through June, depending on the length and amount of wet weather and the ensuing dry periods. This expected weather pattern, and reduced carryover fuels may keep things fairly quiet early in the fire season across many areas of the Great Basin that have seen well above normal fire activity the last few years. However, smaller fires will continue to increase during drier periods. Southern areas of the Great Basin will likely see more fine fuel compared to the last 2 years due to the wet winter and spring. This may raise fire concerns early in the season across southern areas.
The unusually wet winter is expected to lead to an above average grass crop across southern Nevada, southern Utah and parts of the Arizona Strip. With the shift to warmer and drier conditions in April and likely heading into May especially for southern Nevada, southwestern Utah and parts of the Arizona Strip, vegetation will begin to dry and cure, with above average fuel loading expected to be available by May and June. With this in mind, Above Normal significant large fire potential is expected across these areas through May, then expanding east across southern areas of the Great Basin by June, which may also extend into July depending upon the monsoon. The length of the drier conditions will likely determine the potential for fire activity in the south. Further north, an early fire season is not anticipated with wet weather expected to continue to affect the northern two thirds of the Great Basin through at least May periodically. Small fires can be expected to increase during periods of dry and warm weather in May and June in the fine fuels, however storm systems will likely still move across the Great Basin every week or so and bring some periods of cooling and wet weather. The passage of systems may continue into June and July, which could further limit the fire potential in the north. The deep snowpack will also delay fire season in the higher elevations of the Sierra into Nevada, Utah, and eastern Idaho. The highest mountain ranges of the Sierra and Central through Northern Utah into Eastern Idaho will likely see Below Normal large fire potential through at least June, and possibly into July. Currently, we are keeping normal conditions for fire potential in the lower elevations of northern and western Nevada into northern Utah, but if drier weather resumes by June and July, depending on the fine fuel loading and continuity, a reevaluation may be needed.
Northern California and Hawaii: Normal significant large fire potential is expected across mainland portions of the region in May. Above Normal significant fore potential is expected across the mountains and forests surrounding the Bay Area and in the Sacramento Valley and surrounding foothills June through August. The Above Normal fire potential will expand north to the Oregon state line in August. Below Normal significant fire potential is expected in July across the high Sierras and across portions of the Northwestern Mountains. Above Normal significant fire potential is expected across the lee side of the Hawaiian Islands during the outlook period. Areas not mentioned above can expect Normal significant large fire potential during the outlook period. The region has received well above average precipitation since January 1. Most of the winter storms this season have been accompanied by average to lower than average snow levels, and this has led to snow pack water content readings that reached more than 160% of the average seasonal peak. Temperatures were cooler than average in early April, but warmer and drier than average weather in place since the middle of April has allowed led to robust growth of fine fuels and brush at elevations below 3000 ft. Periods of cool wet weather are expected into June, and perhaps even into late June. This will allow an already heavier than average fine fuel crop to increase before reaching its curing phase, which will take place later than usual. The snow pack is expected to melt off more slowly. This will lead to very quiet fire activity at elevations above 6500 feet through July. The above average fine fuel crop will likely cure out between late May and mid-June in the lower elevations of the Bay Area, Sacramento Valley, and Mid Coast areas. It bears to mention that in mid-February a significant heavy snow event in the northern Sacramento Valley. The event caused extensive damage to plants and trees of all sizes, leading to a large amount of dead and down fuels that will enhance the potential of significant wildfires starting in June.
Typically, wildfire activity is minimal through May. Although low elevation grass fires increase in May, they do not typically grow to significant sizes. Significant fire potential will remain Normal, or minimal, through May. Due to the down and dead fuel loading in the northern Sacramento Valley and the expected curing of a robust fine fuel and brush crop at lower elevations, the Bay Area, Sacramento Valley, and Mid Coast areas (except the Mendocino NF) have Above Normal Significant Fire Potential in June and July. All other areas will continue to have normal Significant Fire Potential in June. However, the higher elevations will likely be on the quiet side of the Normal fire potential range in June, and that will continue into July due to the time it takes for the snow pack to melt. Since it is typical for large fire activity to increase at higher elevations in July, the northwestern mountains and northern Sierra have Below Normal significant fire potential in July. All other areas will remain Normal in July. In August, elevations above 6500 feet, especially the Northern Sierra, will be move to the Normal significant fire potential category, but likely lean toward the quiet side of the Normal range. Most areas below 5000 feet in the region will be Above Normal in August, with the exception of the North Coast, which will be Normal.
Sea surface temperatures (SSTs) surrounding the Hawaiian Islands have been near to slightly cooler than average until recently, and are near to slightly above average as April ends. Rainfall was below average throughout much of the region in April, which is typical during an El Niño event. El Niño conditions are now expected to continue in the equatorial Pacific through the summer, and this will likely lead to a continuation of dry conditions. Fuel loading remains above average, and wildfire activity has been above average over the winter and into the early part of spring, especially on the lee sides of the islands. Weather outlooks suggest that warmer and drier than average conditions will continue through the rest of spring and summer. Therefore, Significant Fire Potential will remain Above Normal through August on the lee sides of the islands. On the windward sides, significant fire potential will remain Normal through August.