Operational cloud-seeding project target areas for enhancement of winter snowpack in the mountains of the western United States in 2015 (colored green). No projects occurred in the states that are colored blue. (Source: North American Weather Modification Council.)
Locations of major research projects in the western United States that were designed to evaluate the feasibility of orographic enhancement of snowpack through cloud seeding over the period 1960–2019.
Examples of (left) WRF-simulated and (right) HYSPLIT-simulated AgI number concentrations using a logarithmic scale [log(m−3)] at three vertical levels: (a) 2500, (b) 3000, and (c) 3500 m MSL. The ground-based AgI generators are at the southern edge of the plume indicated by the stars on the HYSPLIT maps. The WRF maps include terrain contours (1500 and 2500 m) and state lines for Idaho.
Three-dimensional depictions of the topography of the Medicine Bow Range in Wyoming, AgI aerosol number concentration (>100 L−1 for visible plumes), and wind vectors at three levels [~2800 (yellow), ~3600 m (blue), and ~4400 (purple) m MSL] at three times separated by 90 min, shown as a (left) bird’s-eye view from the south and (right) side views from the southeast. (Adapted from Xue et al. (2014).]
Example of seeding lines observed during the 2017 SNOWIE campaign. Shown, from a single pass by the Wyoming King Air, are in situ measured (a) hydrometeor concentration for liquid droplets (blue; from Cloud Droplet Probe) and ice particles (red; only particles >50 μm in diameter, from 2DS probe) and (b) bulk condensed water content for liquid (blue) and ice (red), both from the deep-cone Nevzorov probe. (c) The vertical cross-section of W-band reflectivity during the same pass. The horizontal dotted line is the flight track. The locations of echoes resulting from seeding plumes are highlighted (green line). (d) A time-coincident 0.5° plan-position indicator scan using a ground-based X-band Doppler on Wheels, with the horizontal extent of the echo resulting from the seeding plume also highlighted. Also shown are 2DS probe particle size distributions (e) measured inside the plumes (black) and just upwind of the plumes (blue) and (f) corresponding two-dimensional hydrometeor shadows (left) outside the plumes and (right) inside the plumes.
Monthly time series of accumulative precipitation (mm) for (a) 2001–02, (b) 2003–04, (c) 2005–06, and (d) 2007–08. Solid line is simulated precipitation with the WRF Model at SNOTEL mountain site locations. Dashed lines are SNOTEL measurements, with gray shades representing 1 standard deviation from the average daily precipitation totals at SNOTEL sites. The dots are Parameter–Elevation Regressions on Independent Slopes Model (PRISM) monthly averaged snowfall estimates. [From Rasmussen et al. (2011).]
Schematic of the AgI–cloud interactions that are simulated in the seeding parameterization. [Adapted from Xue et al. (2013a), with additional parameterizations now included in the scheme.]
