Post on 18-Dec-2015
Cloud Seeding
Shawn Trueman, Intern
National Weather Service Forecast Office
Phoenix, AZ
overview
• What is cloud seeding?
• My experience in cloud seeding
• Synoptic conditions for Sierra Nevada summertime convection
• Cloud-seeding tools
• Cloud-seeding demonstration
Cloud-seeding definitions
The introduction of artificial substances (usually silver iodide or dry ice) into a cloud for the purpose of either modifying its development or increasing its precipitation. (Western Regional Climate Center)
Encouragement of precipitation from clouds by freezing supercooled cloud droplets and speeding the Bergeron-Findeisen Process. (www.advancedforecasting.com)
The attempt to change the amount or type of precipitation or the structure of clouds by dispersing substances into the air which allow water droplets or ice crystals to form more easily. The most common chemicals used for cloud seeding are silver iodide and dry ice. (Wikipedia)
Why use dry ice and silver iodide?
• Dry ice because it is so cold that it ice crystals form by spontaneous nucleation.
first used as seeding agent by Vincent Schaefer at General Electric in Schenectady, NY in 1946.
• Silver iodide provides nuclei that water vapor molecules can be deposited on. Its crystal structure is similar to that of water ice.
first used as seeding agent by Bernard Vonnegut at General Electric in 1947.
My cloud-seeding experience
Radar meteorologist, Atmospherics, Inc., Fresno, California
Summer 1997
Issued forecast for chance of showers/thunderstorms for western slope of the Sierra Nevada between Yosemite NP and Kings Canyon NP
California
Courtright Reservoir, western slope central Sierra Nevada
USDA Forest Service
Shaver Lake, western slope central Sierra Nevada
If suitable convection developed, I guided flight via two-way radio and operated 5-cm radar at office.
radar control (plan position indicator) at Atmospherics, Inc.
David Newsom, AI
radar dish at Atmospherics, Inc. David Newsome, AI
Thunderstorm over central Sierra Nevada
Thunderstorm clouds over Sierra Nevada from Fresno
Laurence Kramer, Fresno
500-mb chart: July 19, 12Z
500-mb chart: July 20, 00Z
500-mb chart: July 20, 12Z
500-mb chart: July 21, 00Z
500-mb chart: July 21, 12Z
Mercury, NV sounding
Reno, NV sounding
visible imagery: July 20, 2006 at 17Z
cloud-seeding flares
acetone-silver iodide generator attached to a Piper Aztec
cloud-seeding flight in Utah
Hector Vasquez, NWS Phoenix
Fog at an airport in Alaska
Hector Vasquez, NWS Phoenix
Result of cloud seeding to disperse fog at airport in Alaska
Hector Vasquez, NWS Phoenix
With thanks to…
Hector Vasquez, Senior Forecaster, NWS PhoenixDoug Green, Science Operations Officer, NWS PhoenixDavid Runyan, Warning Coordination Meteorologist, NWS
PhoenixKim Runk, Meteorologist-in-Charge, NWS Las VegasSteve Johnson and David Newsom, Meteorologists,
Atmospherics, Inc., Fresno, CAMichael Bruce, Observing Program Team Leader, NWS
PhoenixJon Skindlov, Senior Meteorologist, Salt River ProjectDr. Peter Williams, Professor of Analytical Chemistry,
Arizona State University David Brown, Information Technology Officer, NWS Phoenix