September Fire Outlook

The significant wildland fire potential forecasts included in this outlook represent the cumulative forecasts of the ten Geographic Area Predictive Services units and the National Predictive Services unit. This will focus on the Northwest. This story is courtesy of NIFC.

The potential for significant fires remains above normal in central and southwest Oregon and central Washington for September.
Temperature varied significantly across the region through August. A cooling trend arrived during the first week of the month that pushed temperatures below normal everywhere except southern Oregon. A significant warming and drying trend followed that pushed temperatures to record values for the middle of August. Another cooldown occurred during the last half of the month with below average temperatures.

Rainfall varied across the region during August. The western two thirds of Oregon and much of southwest Washington received well below
normal amounts. However, the eastern third of Oregon and the northeastern third of Washington observed well above normal rainfall from thunderstorms associated with Normal fire season progression across the contiguous U.S. and Alaska shown by monthly fire density (number of fires per unit area). Fire size and fire severity cannot be inferred from this analysis. (Based on 1999- 2010 FPA Data) a surge of monsoonal moisture. Rainfall was also boosted by the arrival of incoming troughs from the Pacific, which enhanced precipitation.
However, precipitation observed during August over eastern Washington and eastern Oregon was insufficient to affect the severity of the exceptional drought depicted in the US Drought Monitor.

The weather events that produced new ignitions also resulted in growth on existing large fires in some areas where favorable terrain and wind conditions aligned. Following the second round of new large fires in the geographic area in mid-August, a cooling trend slowed initial attack and perimeter growth on the large fires. Over the latter half of the month, significant rainfall was observed over north-central Washington, the Olympics, the north Cascades, and the Blue Mountains. While lightning also was observed with the storms, rainfall kept initial attack light and helped suppress growth on existing large fires. Significant rain did not fall over western and south-central Oregon where dry fuels continued to result in growth on large fires through the end of the month. Cloudy conditions along with local and regional smoke production also lowered fire behavior over the Oregon fires temporarily and to a lesser extent on the Washington fires.

The hot and dry trend in early August continued to impact live and dead fuels. Heavy dead fuel moisture was well below average for most PSAs through mid-August with a few locations near record low fuel moisture values. Fire danger indices also reached maxima in several areas. Drought deepened through the central part of the geographic area with extreme and exceptional drought over many areas. Lightning ignition efficiency was very high as thunderstorms moved through and holdovers plagued resources in areas that received light rainfall in western Oregon. The very dry fuels were evident as fires exhibited a high resistance to control. By the middle of the month, overnight humidity recovery began to return to normal levels as marine air began to reach east of the Cascades and monsoon moisture occasionally traversed the eastern part of the geographic area.

With cooler and more moist conditions at the end of the month, fuel moistures began to return to more seasonal values and new ignitions decreased. Despite the cooldown, south-central Oregon had a fuels and fire behavior advisory extended for the third time with another new large fire starting during the middle of August. Live fuels are now cured in the geographic area at lower and middle elevations, while high elevations have not fully cured, with fires exhibiting some resistance to spread on north slopes and through riparian areas.
Long range outlooks from NOAA and other sources suggest September will be warmer and drier than typical for the Northwest Geographic Area. For October through December, outlooks are mixed but suggest wetter than normal conditions are most likely for much of the geographic area.

The potential for significant fires remains elevated in central and southwest Oregon and central Washington for September. For October through December, significant fire potential is forecast to be normal across the entire geographic area. It is important to note that it is rare for significant new fire starts after September, even during dry falls.

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