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Joseph B. Pollina, Brian A. Colle, and Joseph J. Charney

1. Introduction a. Motivation Wildfires are an important forecast problem with significant societal impacts. Across the United States, ~4.7 million (~500 000) acres burn on average each year from wildfires west (east) of the Mississippi River (NIFC 2008 ). [This is equivalent to ~1.9 million (~202 430) ha, where 1 ha = 2.47 acre.] Wildfires in the northeast United States ( Fig. 1 ) have resulted in 13 633 acres burned on average annually, which is 0.27% of the total acres burned within the

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Neil P. Lareau and Craig B. Clements

1. Introduction Smoke dispersion is strongly affected by the structure and evolution of wildfire convective plumes. When wildfire plumes penetrate into the free troposphere they inject smoke aloft, causing regional- to global-scale impacts such as reduced insolation ( Penner et al. 1992 ) and modified cloud microphysics ( Andreae et al. 2004 ). On the other hand, when plumes remain confined within the atmospheric boundary layer, the smoke can more directly impact human populations, posing

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Clifford F. Mass, David Ovens, Robert Conrick, and John Saltenberger

1. Introduction On 7–8 September 2020, strong northerly/northeasterly winds, gusting to 40–70 kt (1 kt ≈ 0.51 m s −1 ) in exposed locations, pushed southward across eastern Washington and then westward across the Oregon Cascades, initiating and spreading multiple large fires in both states ( Fig. 1 ). In eastern Washington, the wildfires were mainly limited to grass and range vegetation within the Columbia basin, with total burned area reaching 529 000 acres. Less than 10% of the total burned

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Robert Conrick, Clifford F. Mass, Joseph P. Boomgard-Zagrodnik, and David Ovens

1. Introduction Wildfire smoke has many impacts on the meteorological environment. Through the aerosol direct effect, solar radiation is scattered by smoke particles which typically exhibit submicron sizes (e.g., Rissler et al. 2006 ). Such scattering of solar radiation reduces solar heating at the surface and results in a reduction in air temperatures in the lower troposphere, as described in several studies (e.g., Robock 1988 , 1991 ; Eck et al. 1998 ; Treffeisen et al. 2007 ; Stone et

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Taylor B. Aydell and Craig B. Clements

1. Introduction Wildfires are high-impact societal problems for the western United States and other fire-prone regions that can result in loss of life, property, and natural resources as well as degraded human health through the release of smoke and by-combustion products ( Dempsey 2013 ; McRae et al. 2015 ; Clements et al. 2018 ). Wildfires can cause regional- to global-scale impacts through smoke injection into the atmosphere such as reduced solar radiation ( Penner et al. 1992 ; Price et

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Piyush Jain and Mike Flannigan

ridging associated with drought events in California. Nakamura and Huang (2018) considered a mathematical analogy to traffic congestion to relate the onset of blocking with jet stream dynamics. Quinting and Vitart (2019) further explored the relationship of Rossby wave packets (RWPs) and blocking and found the decay of RWPs is associated with the onset of blocking in the European-Atlantic sector. a. Synoptic weather and wildfires At the landscape scale, wildland fire activity is determined by a

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A. Park Williams, Richard Seager, Max Berkelhammer, Alison K. Macalady, Michael A. Crimmins, Thomas W. Swetnam, Anna T. Trugman, Nikolaus Buenning, Natalia Hryniw, Nate G. McDowell, David Noone, Claudia I. Mora, and Thom Rahn

1. Introduction The southwestern United States (SW) experienced extreme drought in 2011, related at least in part to a La Niña event in the tropical Pacific Ocean ( Rupp et al. 2012 ; Hoerling et al. 2013 ; Seager et al. 2014a ). The 2011 SW drought event was accompanied by record-breaking total burned area ( Williams et al. 2014 ) and record-size “megafires” in the forests of eastern Arizona and northern New Mexico. Extreme drought and wildfire conditions prompted widespread concern as to

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Ted M. Uecker, Susan D. Kaspari, Keith N. Musselman, and S. McKenzie Skiles

increase the solar radiation absorbed by the snowpack ( Hansen and Nazarenko 2004 ; Andreae and Gelencsér 2006 ; Painter et al. 2012 ). Slight reductions in snow albedo can increase melt rates and alter the timing and magnitude of seasonal streamflow ( Hall 2004 ; Flanner et al. 2009 ; Skiles et al. 2012 ). Warming temperatures and less persistent snow cover have led to increases in wildfire frequency, magnitude, severity, and duration in the western United States ( Westerling et al. 2006

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Timothy J. Lang, Steven A. Rutledge, Brenda Dolan, Paul Krehbiel, William Rison, and Daniel T. Lindsey

1. Introduction Pyrocumulus clouds frequently occur over wildfires, often growing to high altitudes and impacting chemical composition and aerosol concentrations in the upper troposphere ( Fromm et al. 2010 ). On occasion, these clouds also have been observed to electrify and produce lightning ( Latham 1991 ; Rosenfeld et al. 2007 ). Interestingly, observed cloud-to-ground (CG) lightning flashes from these clouds, or other thunderstorms ingesting smoke, will often transfer a predominantly

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Min Deng, Zhien Wang, Rainer Volkamer, Jefferson R. Snider, Larry Oolman, David M. Plummer, Natalie Kille, Kyle J. Zarzana, Christopher F. Lee, Teresa Campos, Nicholas Ryan Mahon, Brent Glover, Matthew D. Burkhart, and Austin Morgan

1. Introduction Wildfire in the western United States has a strong annual cycle, which maximizes around May–September, as the prolonged drought and extreme heat wave in the summer tend to trigger more frequent and intense wildfire activity. According to the wildfire statistics of National Interagency Coordination Center, the number of annual wildfires has decreased slightly over the last 5 years, but the number of acres impacted generally has increased, which indicates that the wildfire

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