CWCB Wintertime Weather Mod Report

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'" I I I I I I I I I I I I I I I I I I SUMMARY OF WEATHER AND OPERATIONAL SEEDING OPPORTUNITIES FOR THE 2002-2003 SEASON OF THE UPPER ARKANSAS RIVER BASIN CLOUD SEEDING PROGRAM November 2002 started out with a continuation of the wet weather trend started during the second half of October. Five weather systems over twelve calendar days continued to maintain the above normal snowpack left by Octobers weather systems. Early indications were that this winter might be near or slightly above normal for snowpack and precipitation and allowed for earlier openings for most of the ski areas in Colorado. The trend of frequent weather systems moving through the Western U.S. increased through December bringing with it the occurrence of eight seeding opportunities over 22 calendar days into January 1,2003. A subtle change was becoming apparent with these systems. The intensity and duration of each system was becoming slightly less as there was less southwesterly wind to bring in large amounts of moisture and most of the precipitation with these systems was occurring mainly in the higher elevations ofthe mountains. By the end of December, the snow pack in the Central Mountains had decreased to an average slightly under normal with several monitoring sites in the Seeding Area continuing to have above normal readings. ' The gradual drying trend of the weather system continued throughout January with shorter storm duration's for seeding operations. Six seeding opportunities occurred over 13 days in January. At the end of January, the high country snow pack in the Central Mountains had dropped to near 80% of normal. Most of the Seeded Area monitoring sites still indicating an additional 15% greater snowpack and precipitation Above normal precipitation and frequent weather systems with good seeding potential returned to the Central and Northern Colorado Mountains during February with 9 weather systems and 21 operational seeding days. February's snowpack increased so rapidly in the last half of February that an avalanche warning was issued. The average precipitation for the region had increased to about 90% of normal with many monitoring sites in the Seeded Areas indicating 10 to 15% more precipitation than adjacent unseeded sites. The wet weather trend continued into early March and then quickly turned very dry with warming temperatures. A very large slow-moving weather system moved into Colorado from the Southern California region in mid March and produced nearly continuous precipitation for about six days. This one system produced nearly half of the normal annual snowpack for the Eastern Slopes of Colorado and added about 10 to 15% to the snowpack in the central Rocky Mountain Region. A second weather system moved into Colorado from the northwest a few days later and continued the mountain precipitation for another four days until the 27th of March. Several avalanche warnings were issued for the Northern, Central and the East-slope Mountain Ranges in Colorado during these weather events suspending some seeding activities mainly in the Northern and Eastern portions of the Seeded Area. At the end of Marcil, the snowpack and precipitation in the Colorado Central Mountains had returned to just under normal with most monitoring sites in the seeded area indicating 8 to IS % above normal precipitation for the season. By early March 2003, all of the proposed 5,601.3 seeding hours for the Upper Arkansas had been used. A reallocation of funds from two uncompleted proposed generator site installations and supporting services and $5,000.00 of additional contract funding continued the seeding operations of the Program until March 25,2003 allowing the Program to completed 6,978.75 total seeding hours over the Program Area. The seeding operations ended for the Upper Arkansas Program on March 25, 2003. The Upper Arkansas Operational Seeding Summary is presented in two parts. The fIrst summary of seeding events is for the main Upper Arkansas Program Area. This Summary indicates the dates of all of this season's seeding operations, the number of and total seeding hours of the generators in the network that were used to seed the Program Area, the number of generators shared with the DWD Program and the Total Output of Silver Iodide for