Observing and Modeling Recurrent Diurnal Summertime Wind Systems in the Complex Terrain of the Columbia River Basin during the Second Wind Forecast Improvement Project

The Columbia River Basin in the arid interior of Washington and Oregon to the east of the Cascade Mountain Range is a region that experiences recurrent, thermally forced wind systems in summer. These wind systems, which reach maximum wind speeds in the lowest 400 m at midnight local time and minimum speeds at noon, result from sea-breeze forcing modified by mountains and valley winds. The winds are an important source of wind-generated electrical power during the warm season for the extensive wind farms located in this region. The Basin was the site of the Second Wind Forecast Improvement Project (WFIP-2), an 18-month field-deployment and NWP-modeling study undertaken to improve quantitative predictions of wind properties, such as speed, direction, and turbulence, for wind-energy applications. Better understanding and modeling of wind-flow patterns related to wind-energy generation were goals of this project. Detailed, precise measurements of the wind profile were available at 15-min intervals from Doppler lidars at three locations separated by 70 km, as part of a comprehensive deployment of remote-sensing and in-situ instrumentation. The diurnal recurrence of the winds due to the inland penetration of the Pacific coastal sea breeze was a striking feature of the summertime wind flow in the Columbia Basin. Summer of 2016 saw eight clear examples of this phenomenon, exhibiting significant day-to-day variability in the way in which the diurnal flow evolved. Here we form composite time-height cross sections and time series of the mean speed, standard deviation, and other properties of the winds to reveal the mean behavior and when it exhibits the most variability, and we relate these to aspects of the basic forcing such as the surface radiation and energy budget, horizontal pressure gradients, and regional cloudiness. This dataset is then used to evaluate the ability of NOAA’s HRRR forecast model to simulate these composite flows, and their day-to-day variability, by calculating model-error statistics of the winds themselves and the basic forcing mechanisms studied.