DATASTREME WES WEEK FIVE: 21-25 February 2005

• California threatened by more mudslides -- The heavy rain and mountain snow that has pelted California as the result of a stagnant offshore storm system has increased the threat of mudslides across southern California over the weekend. [USA Today]
• Levels on Lake Mead rising -- Following last fall's record low water levels due to the extended drought, Lake Mead, the reservoir on the Colorado River behind Hoover Dam (between Arizona and New Mexico) has been rising because of the heavy precipitation from recent winter storms of the last 6 weeks. [USA Today]
• Survivors of a tropical cyclone found -- A US Coast Guard aircraft found six survivors of Tropical Cyclone Olaf onboard their crippled fishing boat off American Samoa nearly two days after the tropical cyclone (the South Pacific counterpart of a hurricane) hit the islands. [USA Today]

• Increased nitrogen pollution found in nation's coastal waters -- Scientists from Cornell University and the University of California-Berkley reported that nitrogen pollution has increased much faster than previously thought in the watersheds and estuaries that are part of the nation's coast system because of increased fossil fuel combustion from vehicles and power plants. [EurekAlert!]
• International agreement reached on global observation network -- Representatives from the US and nearly 60 other countries along with 40 scientific organizations met at the Third Earth Observation Summit in Brussels and agreed to implement a 10-year plan for the Global Earth Observation System of Systems (GEOSS). This plan is intended to create a comprehensive linked system of environmental systems and data sets, which will be available for information and research on the global ocean and water cycle. [NOAA News] A European perspective is also available. [ESA]
• Modeling of huge waves -- A professor at Texas A&M University has created a numerical model that can be used to forecast huge waves on the Gulf of Mexico and the Gulf of Maine. [EurekAlert!]
• A new approach needed for restoration of an important estuary -- Scientists have called for a new approach to the nearly 20 years of restoration attempts that have been employed for Chesapeake Bay, the nation's largest estuary. This new approach that would involve state and federal agencies is called "adaptive management". [EurekAlert!]
• Melting ice indicates global change -- A Penn State glaciologist points to the observed melting of mountain glaciers and ice sheets as an indication of a global warming. [EurekAlert!]
• Good news from Iraq -- Success at restoring the decimated Ahwar wetlands in southern Iraq appears to be at hand due to the efforts by an international team of scientists along with local residents. [EurekAlert!]
• Global and US Hazards/Climate Extremes -- A review and analysis of the global impacts of various weather-related events, including drought, floods, and storms during the current month. [NCDC]
• Global Water News Watch -- Other water news sources can be obtained through the SAHRA Project at the University of Arizona [SAHRA Project]
• Earthweek -- Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

Concept of the Week: Artificial Snow

Snow is the essential ingredient for many winter recreational activities including downhill and cross-country skiing, snow boarding, and snowmobiling. No natural snow cover means no cross-country skiing or snowmobiling. But downhill ski hill operators have another option if weather conditions do not provide adequate snow cover—they can generate their own snow. Artificial snow is used to build a base for skiing, refresh snow surfaces, and make skiing possible even during a snow drought, significantly lengthening the ski season. Some ski areas have the equipment to spread artificial snow over 80% or more of their terrain. Whereas snowmaking offers many recreational and economic advantages, some drawbacks stem from altering the local water balance.

Artificial snow is actually tiny particles of ice. Snow makers use specially designed snow guns into which flexible hoses feed compressed air and water separately. A jet of compressed air breaks the stream of water into a fine mist of tiny droplets, which if conditions are favorable, freezes to ice crystals. Expansional cooling of the compressed air as it is emitted through the nozzle of the snow gun and into the atmosphere chills the water droplets. Artificial "snowflakes" settle onto the slopes and mechanized snow groomers then till and spread the accumulated artificial snow evenly over the ski slopes.

Many snowmakers add a special protein (commercially known as Snowmax) to the air/water mix to improve both the quality and quantity of artificial snow. A non-toxic and non-pathogenic strain of a bacterium produces the protein that attracts water and promotes ice crystal formation. Snowmax increases the amount of artificial snow produced at higher temperatures and snowflakes tend to be drier and lighter than other artificial snowflakes.

Ideal weather for snowmaking consists of low air temperature, light winds, and low humidity. Snowmaking is possible even when the air temperature is above 0ºC provided that the relative humidity is sufficiently low that the wet-bulb temperature is below 0ºC. Recall from pages 65-66 in your DataStreme WES Textbook that the wet-bulb temperature is the reading obtained through evaporative cooling when water vaporizes from the wetted bulb of a liquid-in-glass thermometer. Some droplets in the fine water spray (produced by the snow gun) evaporate, tapping latent heat from the air. With sufficient evaporative cooling, the air temperature drops to the wet-bulb reading, that is, to freezing or below, and subsequent water droplets freeze to ice crystals.

The significant water demand for snowmaking may impact the local water balance. In Vermont, for example, snowmaking uses about 2 billion gallons of water per year—equivalent to about one-seventh of the volume of the public water supply. To cover an area measuring 500 m by 60 m with 20 cm (8 in.) of artificial snow requires about 2500 cubic meters (658,000 gallons) of water. Streams are the usual source of water for snowmaking but ski areas are typically located high on hill or mountain slopes where stream flow is normally low, especially in winter. In some cases, dams or holding ponds are constructed to ensure an adequate water supply. Diversion of water for snowmaking may cut the supply of water for users downstream. Water that is stored in the winter snowpack on the ski trails runs off to streams during the spring snowmelt, adding to the normally high spring stream discharge and perhaps increasing the potential for downstream flooding.

Concept of the Week: Questions

1. If the air temperature were above 0ºC, artificial snow can be made if the wet-bulb temperature were [(above) (below)] the freezing point of water.
2. When water droplets evaporate while falling through a layer of relatively dry air, the temperature of the surrounding air [(falls) (rises)].

• 21 February 1992...Today marked the 16^th consecutive day that Sacramento, CA recorded measurable rain, breaking the old record of 15 consecutive days set back in February 1936 and again in November 1970. Total rainfall over the 16-day period was 6.41 inches. (Intellicast)
• 22 February 1986...A twelve-day siege of heavy rain and snow, which produced widespread flooding and mudslides across northern and central California, finally came to an end. The storm caused more than $400 million in property damage. Bucks Lake, located in the Sierra Nevada Range, received 49.6 in. of rain during the twelve-day period. (Storm Data)
• 22-26 February 1995...Cyclone Bobby slammed into the Western Australia coast causing widespread flooding. Some areas reported up to 12 in. of rain from the storm. (The Weather Doctor)
• 23 February 1802...A great snowstorm raged along the New England coast producing 48 inches of snow north of Boston and 54 inches at Epping, NH. Three large (indiamen) ships from Salem were wrecked along Cape Cod by strong winds. (David Ludlum) (Intellicast)
• 23 February 1991...A black rain fell on eastern Turkey as soot from the Kuwait oil field fires mixed with the precipitation. (The Weather Doctor)
• 23 February 1998 -- Another storm in the series of storms during the major El Niño episode pounded southern California with 2 to 3 inches of rain, and 3 to 4 feet of snow in the mountains above 7000 feet. A sinkhole that measured 550 feet in length, 35 feet in width, and 65 feet in depth developed near I-15 in San Diego. (Accord's Weather Guide Calendar)

• 24 February 1925...A 250,000-ton ice jam on the St. Lawrence River near Waddington, NY was removed using thermit for the first time in the U.S. Thermit is a mixture of finely divided magnesium and red iron oxide that produces hot molten iron when ignited. (Today in Science)

• 26 February 1910...Parts of Washington State were in the midst of a storm which produced 129 in. of snow at Laconia between the 24^th and the 26^th, a single storm record for the state. A series of storms, which began on the 23^rd, led to a deadly avalanche on the first of March. By late on the 28^th, the snow had changed to rain, setting the stage for disaster. (The Weather Channel)
• 26 February 1972...The "Buffalo Creek Disaster" occurred in the Buffalo Creek Hollow of Logan County in West Virginia. A coal slag dam on the Middle Fork of Buffalo Creek burst sending a fifty-foot wall of water down a narrow valley killing 125 persons and causing $51 million in damage. Three days of rain atop a six-inch snow cover prompted the dam break. (David Ludlum) (The Weather Channel)
• 27 February 1717...What was perhaps the greatest snow in New England history commenced on this date. During a ten-day period a series of four snowstorms dumped three feet of snow on Boston, and the city was snowbound for two weeks. Up to six feet of snow was reported farther to the north, and drifts covered many one-story houses. (David Ludlum)
• 27 February 1988...A major rain event occurred across Saudi Arabia's Foroson Islands in the Red Sea and on the adjacent mainland around Jizon when 1.15 in. fell. The monthly average rainfall is only 0.02 in. On the following day, flash flooding south of Riyadh killed 3 children. (Accord's Weather Calendar)

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Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2005, The American Meteorological Society.