DATASTREME WES WEEK FIVE: 23-27 February 2004

• An update on the New Zealand flooding -- Last week's heavy rains that caused devastating floods on New Zealand's North Island are now considered the nation's costliest storm. [USA Today]
• Restrictions on the North Platte -- In an attempt to replenish water in two Wyoming reservoirs during the extended drought, the State Engineer's Office has placed restrictions on water taken from the North Platte River. [Casper Star Tribune]
• Ancient Inuit hunting practices aided by satellites -- The annual practice of hunting and fishing along the edge of the Arctic ice by the Inuit of northern Canada has been aided by satellite images that locate the ice type and extent obtained from the Northern View Floe Edge Information Service, which is supported by the European Space Agency (ESA). [ESA News]
• Endangered ancient desert markings seen from space -- Some of the largest Nasca Lines, which are ancient desert markings from about 400 BC on the Nasca plain between the Andes and Pacific Coast in southern Peru, are visible from an orbiting ESA satellite. However, these markings, designated a World Heritage Site, appear to be endangered because of human encroachment as well as increasingly frequent flood events. [ESA News]
• A penalty for a big-time goof -- The city of Cape Coral in southwest Florida must pay a fine because city workers mistakenly connected four homes to treated wastewater lines instead of drinking water lines. [US Water News Online]
• Improved water quality hampered by slow moving ground water -- A recent USGS study reports that slow moving ground water in the Chesapeake Bay watershed, which represent a major pathway of nitrogen to the Bay, have been a major cause of the poor water quality in this major estuary and have also hampered the efforts at implementing nutrient-reduction strategies aimed at improving water-quality conditions. [USGS]
• Snowmaking plan opposed -- Several American Indian tribes in northern Arizona are opposed to plans for more snowmaking and expanded skiing at the Arizona Snowbowl near Flagstaff based upon this increased activity would desecrate the sacred San Francisco Peaks. [US Water News Online]
• Diminishing water supplies could continue across the West -- A forecast modeler at the US Department of Energy's Pacific Northwest National Laboratory reported that according to a new climate change model, the anticipated increases in global temperature during the next 50 years could significantly reduce the amount of water stored in the snowpack of the mountains across the West. [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

The snow season is fast approaching. 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 can 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)].

• 23 February 1802...A great snowstorm raged along the New England coast producing 48 inches of snow north of Boston and 54 inches of snow piled up 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)
• 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 dollars 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)
• 28 February 1959...An accumulation of heavy snow on the roof of a Listowel, ON arena caused it to collapse during a hockey game. Several people inside were killed. (The Weather Doctor)
• 28 February 1964...A world 12-hour rainfall record was set at Belouve, La Reunion Island in the western Indian Ocean when 52.76 inches of rain fell. World records for 9 hours and 18.5 hours were also set with 42.79 and 66.49 inches, respectively. (Accord's Weather Calendar) (The Weather Doctor)

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Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2004, The American Meteorological Society.