May 22, 2015 – A fuels and fire behavior advisory has been issued for the Tanana Valley, Upper Yukon Valley and Copper River Basin. Early unseasonably warm and very dry weather have combined with dry pre-green fuels across a portion of southern and eastern Interior Alaska. High pressure will keep out moisure and keep relative humidities dangerously low.
An unusually persistent upper level ridge over Canada and eastern Alaska is keeping the eastern half of the state extremely dry. This pattern is expected to dominate for the next 7 days, keeping an extremely dry air mass across the eastern Interior. Widespread RH values in the teens have been occurring for a week and are expected to continue for another week in the Tanana Valley, Upper Yukon Valleys and the Copper River Basin. Some areas along the Alaska Range have also seen RH in the single digits. Poor humidity has also been wide spread over the advisory area.
Conditions are still transitioning from pre-green to green with abundant dead fuel that is easily dried and available for ignition. With Fine Fuel Moisture Code (FFMC) values in the extreme range across broad portions in the Interior, ignition potential for human caused starts and any lightning that may occur highlights a very real risk. The current and forecast position of the upper level ridge is likely to bring a chinook pattern to the Alaska Range with periods of gusty winds in several of these critical areas. With that combination, very rapid spread rates and intense burning of surface fuels will cause torching and crown fire. This was seen on the Seaton Road House fire May 20, 2015. No relief is anticipated within the next week.
Difference from normal conditions: Above normal temperatures and extremely low relative humidities are producing very hazardous potential for the start and spread of wildfires across eastern Interior of Alaska. While these conditions do occur in the spring this is an unusually strong and persistent pattern with very warm temperatures, low RH, poor overnight RH recovery and no rain in the last 10 days. This has brought Duff Moisture Codes (DMCs) well above seasonal records. Fuels have been snow free for three weeks, and green-up is still progressing northward. These very dry conditions are expected to continue for the next week, and periods of gusty winds will contribute to what can be fast moving and intensely burning wildfires.
Concerns to Firefighters and the Public:
• Windy conditions that can produce very high rates of spread, reducing time for escape to safe areas.
• Intense burning at the fire-front that can render escape into the black, or burned areas, unavailable.
• Potential for crown fire and extreme fire behavior under these extremely dry conditions.
• Keep updated weather forecasts in hand and in mind when attacking fires.
• Ensure that briefings highlight the unusually warm and dry weather that is creating very low fine fuel moisture.
• Alert initial attack personnel to the need for effective anchor points, and accessible safety zones.
• Escape into the black should be a primary consideration with rapidly spreading surface fires.
• Warn the public to anticipate surprisingly easy ignition of fuels around their houses and the difficulty of stopping them once they start.
Area of Concern: Tanana Valley, Upper Yukon Valley and Copper River Basin
For a PDF of the advisory click here: 2015_05_22_FuelsAdvisory