Extreme Precipitation

Spatial coherence of extreme precipitation across the Northwestern United States

Sept292013_griddedExtreme precipitation events across the Northwest, although rare, impact the region by causing increased runoff, flooding, damages to infrastructure and loss of life and property. These impacts may be enhanced if an extreme event is synchronous across a basin or region as opposed to being a localized occurrence. Understanding the spatial nature of these extremes may provide additional insight into their potential impacts and their generating processes.

This research examined the spatial coherence and relationships to two contrasting atmospheric phenomena of the top 5% of 3-day accumulated precipitation at stations across the Northwest (Washington, Oregon, Idaho, and western Montana). Results show a general e-folding spatial coherence of ~120km, with distinct geographic variability. Additionally, illustrative patterns of coherence were seen with respect to synoptic regimes; atmospheric rivers favored broadly coherent extremes (primarily in the western portion of the region), while closed lows favored more localized extremes in the lee of the Northern Rockies. The geographic variability in spatial coherence, direction of maximum coherence, and seasonality of extremes suggests moderate extremes in the Northwest result from the interaction of synoptic factors and the region’s complex topography.

For the 2015 paper published in International Journal of Climatologyclick here.

For the poster from the 2014 PNW Climate Science Conference, click here.