`Degree-days' affect bills, power crisis

With our continued high energy bills, ``degree-days'' -- a meteorology term that doesn't usually make the regular weather forecast -- have become the hottest topic among questions I get.

And while the immediate concern is about heating degree-days (HDD), come those warm summer days, we will all be talking about cooling degree-days (CDD). Both can affect energy bills as well as the state's power crisis.

The concept originated from heating and cooling engineers who wanted a handy way to determine energy needs based upon temperature. Their supposition was that when the daily mean temperature is below 65 degrees, most buildings require heat to maintain a comfortable temperature. When it is above 65 degrees, cooling is needed.

The daily mean temperature is simply the average of the day's high and low temperature. When the mean temperature is below 65, each degree that falls below is counted as one HDD. For example, if the high temperature on a given day is 64 degrees and the low is 44 degrees, then the average would be 54 degrees and there would be 11 heating degree-days for that day.

Conversely, the cooling degree-day statistic is the warm season counterpart. When the mean is greater than 65 degrees, then CDDs accumulate. Degree-days are summed up for an entire month and can help give a picture of how much heating or cooling might have been needed. Bear in mind that degree-days are only one very basic measure of energy usage. More complex models of weather and energy consumption take into account other factors such as wind speed, hours of sunlight and precipitation. Average heating and cooling degree-day statistics for San Jose and about 300 other California sites can be found at http://nws.mbay.net/ca_hdd.html (for heating degree-days) and http://nws.mbay.net/ca_cdd.html (for cooling degree-days). I have also assembled a summary of five years of degree-day statistics for San Jose at http://ggweather.com/HDD_CDD.htm

Q  I just saw a movie on the Donner Party tragedy that said the group's disaster was so bad (rescuers couldn't get there quickly, and the group couldn't hike out to get help) because it was the worst winter ever in the Sierra. I think it was the winter of 1846-1847. Was this an El Niņo winter? Shawn Buckley - San Jose

A  The Donner Party was trapped in the Sierra Nevada from Oct. 31, 1846, until April 3, 1847, during a winter with 10 major snowstorms. But from all accounts it was not an El Niņo season. This is not surprising because some of the worst winters in California have happened during years when El Niņo was not present in the Pacific, which indicates that lots of other things go on in the atmosphere during any particular winter.

Only three of the top 10 worst flood damage years in the state have happened during an El Niņo season. For more details on El Niņo winters, see http://ggweather.com/nino/calif_flood.html

There is an excellent article about Donner Pass weather, ``The Reign of the Sierra Storm King,'' in the January/February issue of Weatherwise magazine. The publication is available at most libraries and newsstands, and the article can also be found on the author's Web site at www.thestormking.com/Articles/Donner_Pass/donner_pass.html

Q  What is haze? What is marine haze? And does Doppler radar detect it? Gary Cooper - Portola Valley

A  Some will say that haze is simply the chamber of commerce's term for smog. However it's really any tiny particles suspended in the air that reduce the visibility by scattering sunlight. These particles are things like smoke, dust and smog. The latter is more technically ``photochemical smog'' and is the result of sunlight interacting with ozone, oxides and hydrocarbons in the air.

Marine haze occurs because of tiny salt particles suspended in the air. These also scatter more of the longer wavelengths of light, leaving a bluish color. In theory, Doppler radar can see haze and other small objects in the atmosphere, even swarms of insects, birds or bats. However, the local radar is atop 3,486-foot Mount Umunhum, and its beam overshoots the haze and marine layer by a couple of thousand feet.

Weather Web Site of the Week: For anyone with a Palm-type PDA, I have developed a small weather application. This Palm OS Weather Calculator does common weather calculations and conversions, including temperature, pressure and wind, relative humidity, heat index, wind chill and standard atmosphere. It also has tables of the Fujita Tornado Scale, Saffir-Simpson Hurricane scale and the Beaufort wind scale. It is free and can be downloaded from http://ggweather.com/palm.htm

Jan Null, founder of Golden Gate Weather Services is a retired Lead Forecaster with the National Weather Service. Send questions to him c/o Weather Corner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif., 95190. You also can telephone and fax questions at (510) 315-3015 or e-mail them to weathercorner@ggweather.com.