• Abatzoglou, J. T., A. P. Williams, L. Boschetti, M. Zubkova, and C. A. Kolden, 2018: Global patterns of interannual climate–fire relationships. Global Change Biol., 24, 51645175, https://doi.org/10.1111/gcb.14405.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bentley A. M., L. F. Bosart, and D. Keyser, 2019: A climatology of extratropical cyclones leading to extreme weather events over central and eastern North America. Mon. Wea. Rev., 147, 14711490, https://doi.org/10.1175/MWR-D-18-0453.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Conrick, R., C. F. Mass, K. P. Boomgard-Zagrodnik, and D. Ovens, 2021: The influence of wildfire smoke on cloud microphysics during the September 2020 Pacific Northwest wildfires. Wea. Forecasting, 36, 15191536, https://doi.org/10.1175/WAF-D-21-0044.1.

    • Search Google Scholar
    • Export Citation
  • Dague, C. I., 1930: Disastrous fire weather of September 1929. Mon. Wea. Rev., 58, 368370, https://doi.org/10.1175/1520-0493(1930)58<368:DFWOS>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Dague, C. I., 1934: The weather of the great Tillamook, Oregon fire of August 1933. Mon. Wea. Rev., 62, 227231, https://doi.org/10.1175/1520-0493(1934)62<227:TWOTGT>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Keeley, J. E., and C. J. Fotheringham, 2003: Impact of past, present, and future fire regimes on North American Mediterranean shrub lands. Ecol. Stud., 160, 218262, https://doi.org/10.1007/0-387-21710-X_8.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Keeley, J. E., and A. D. Syphard, 2016: Climate change and future fire regimes: Examples from California. Geosciences, 6, 37, https://doi.org/10.3390/geosciences6030037.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Keeley, J. E., and A. D. Syphard, 2017: Different historical fire-climate patterns in California. Int. J. Wildland Fire, 26, 253268, https://doi.org/10.1071/WF16102.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Keeley, J. E., and A. D. Syphard, 2019: Twenty-first century California, USA, wildfires: Fuel-dominated vs. wind-dominated fires. Fire Ecol., 15, 24, https://doi.org/10.1186/s42408-019-0041-0.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Marlon, J. R., and et al. , 2012: Long-term perspective on wildfires in the western USA. Proc. Natl. Acad. Sci. USA, 109, E535E543, https://doi.org/10.1073/pnas.1112839109.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McDonald, J. M., A. F. Srock, and J. J. Charney, 2018: Development and application of a Hot-Dry-Windy index (HDW) climatology. Atmosphere, 9, 285, https://doi.org/10.3390/atmos9070285.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • National Wildfire Coordinating Group, 2002: Gaining an understanding of the National Fire Danger Rating System. Rep. PMS 732, 82 pp., https://www.nwcg.gov/sites/default/files/products/pms932.pdf.

  • Oregon Forest Research Institute, 2014: Fire in Oregon’s Forests. Oregon Forest Research Institute, 16 pp., https://oregonforests.org/sites/default/files/2017-05/OFRI_2014_Fire_Report_0.pdf.

  • Srock, A. F., L. J. Charney, B. E. Potter, and S. L. Goodrick, 2018: The hot-dry-windy index: A new Fire Weather Index. Atmosphere, 9, 279, https://doi.org/10.3390/atmos9070279.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Weise, D. R., R. A. Hartford, and L. Mahaffey, 1998: Assessing live fuel moisture for fire management applications. Fire in Ecosystem Management: Shifting the Paradigm from Suppression to Prescription, T. L. Pruden and L. A. Brennan, Eds., Tall Timbers Research Station, 49–55.

  • Williams, A. P., J. T. Abatzoglou, A. Gershunov, J. Guzman-Morales, D. A. Bishop, J. K. Balch, and D. P. Lettenmaier, 2019: Observed impacts of anthropogenic climate change on wildfire in California. Earth’s Future, 7, 892910, https://doi.org/10.1029/2019EF001210.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zyback, B., 2003: The Great Fires: Indian burning and catastrophic forest fire patterns of the Oregon Coast Range, 1491–1951. Ph.D. thesis, Oregon State University, 451 pp., http://www.nwmapsco.com/ZybachB/Thesis/Zybach_PhD_2003.pdf.

All Time Past Year Past 30 Days
Abstract Views 57 57 57
Full Text Views 43 43 43
PDF Downloads 55 55 55

The September 2020 Wildfires over the Pacific Northwest

View More View Less
  • 1 a Department of Atmospheric Sciences, University of Washington, Seattle, Washington
  • | 2 b U.S. Fish and Wildlife Service Predictive Services, Northwest Coordination Center, Portland, Oregon
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

A series of major fires spread across eastern Washington and western Oregon starting on 7 September 2020, driven by strong easterly and northeasterly winds gusting to ~70 kt (1 kt ≈ 0.51 m s−1) at exposed locations. This event was associated with a high-amplitude upper-level ridge over the eastern Pacific and a mobile trough that moved southward on its eastern flank. The synoptic environment during the event was highly unusual, with the easterly 925-hPa wind speeds at Salem, Oregon, being unprecedented for the August–September period. The September 2020 wildfires produced dense smoke that initially moved westward over the Willamette Valley and eventually covered the region. As a result, air quality rapidly degraded to hazardous levels, representing the worst air quality period of recent decades. High-resolution numerical simulations using the WRF Model indicated the importance of a high-amplitude mountain wave in producing strong easterly winds over western Oregon. The dead fuel moisture levels over eastern Washington before the fires were typical for that time of the year. Along the western slopes of the Oregon Cascades, where the fuels largely comprise a dense conifer forest with understory vegetation, fire weather indices were lower (moister) than normal during the early part of the summer, but transitioned to above-normal (drier) values during August, with a spike to record values in early September coincident with the strong easterly winds. Forecast guidance was highly accurate for both the Washington and Oregon wildfire events. Analyses of climatological data and fuel indices did not suggest that unusual preexisting climatic conditions were major drivers of the September 2020 Northwest wildfires.

Significance Statement

This paper describes the meteorological conditions associated with major wildfires in eastern Washington and western Oregon during September 2020. It was found that unusual, extreme winds from the north and east played a critical role in initiating and supporting the fires.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Clifford Mass, cmass@uw.edu

Abstract

A series of major fires spread across eastern Washington and western Oregon starting on 7 September 2020, driven by strong easterly and northeasterly winds gusting to ~70 kt (1 kt ≈ 0.51 m s−1) at exposed locations. This event was associated with a high-amplitude upper-level ridge over the eastern Pacific and a mobile trough that moved southward on its eastern flank. The synoptic environment during the event was highly unusual, with the easterly 925-hPa wind speeds at Salem, Oregon, being unprecedented for the August–September period. The September 2020 wildfires produced dense smoke that initially moved westward over the Willamette Valley and eventually covered the region. As a result, air quality rapidly degraded to hazardous levels, representing the worst air quality period of recent decades. High-resolution numerical simulations using the WRF Model indicated the importance of a high-amplitude mountain wave in producing strong easterly winds over western Oregon. The dead fuel moisture levels over eastern Washington before the fires were typical for that time of the year. Along the western slopes of the Oregon Cascades, where the fuels largely comprise a dense conifer forest with understory vegetation, fire weather indices were lower (moister) than normal during the early part of the summer, but transitioned to above-normal (drier) values during August, with a spike to record values in early September coincident with the strong easterly winds. Forecast guidance was highly accurate for both the Washington and Oregon wildfire events. Analyses of climatological data and fuel indices did not suggest that unusual preexisting climatic conditions were major drivers of the September 2020 Northwest wildfires.

Significance Statement

This paper describes the meteorological conditions associated with major wildfires in eastern Washington and western Oregon during September 2020. It was found that unusual, extreme winds from the north and east played a critical role in initiating and supporting the fires.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Clifford Mass, cmass@uw.edu
Save