Longest, warmest days of summer rarely match up

WEATHER CORNER

BY JAN NULL
Special to the Mercury News

Summer will begin officially on Thursday with the summer solstice at 38 minutes past midnight. However, the solstice is more of an astronomical event than a meteorological one.

Anyone who has watched weather in the Bay Area will tell you that nature doesn't always follow the calendar.

Even though the summer solstice is the day with the most hours of daylight and when the sun's rays are nearly perpendicular to the Earth's surface in the northern hemisphere, it is not the warmest day of the year. The atmosphere warms slowly, so there is a lag between the longest day and the warmest day of the year.

For example, July and August are the warmest months in San Jose. July 17 has the year's highest average maximum temperature of 84 degrees.

In San Francisco, where there is a greater lag because of the persistent summertime sea breeze from May into August, the warmest months are September and October.

Q  It was recently reported that Californians had used 11 percent less energy this May than in May 2000. This gives a lie to Vice President Dick Cheney's lack of faith in conservation, and all those who participated in conserving energy should be proud of their efforts. I believe that even more energy savings could have been accomplished if California's weather in May hadn't been so warm.

How much above normal were temperatures around the state? How did this year's temperatures compare with May 2000? Have the powers that be in the energy hierarchy calculated the amount of additional energy needed if average temperatures are above normal?  John Quadros - Fremont

A  May was indeed very warm throughout the Golden State, which is split into seven climate divisions. Four of them -- Northwest, Sacramento, Northeast and San Joaquin -- were the warmest since 1895. The Central Coast division, which includes the Bay Area, and Southeast Desert had the second warmest May, behind only 1997.

The South Coast -- Los Angeles and San Diego -- was milder with the 15th warmest May on record. But across the state, May 2001 saw the warmest average temperature since at least 1895. The overall average reading of 66.2 surpassed the 1997 record of 66 degrees.

Actually, the 11 percent reduction announced by the California Energy Commission did take into account much warmer than normal weather and the population and economic growth in the state. The unadjusted decrease in megawatts used was about 3 percent.

Q  I have a couple of questions on the sun's position and arc depending on the season. I have a house in the Sierra where landmarks make it easy to visually measure how far north the sun rises and sets on the summer solstice, the midpoint for the equinoxes and how far south for the winter solstice.

In the summer, the sun rises pretty far north and completely exposes my deck, which faces almost due north. Yet it arcs southward such that, by noon, there is still a shadow on my deck. By sunset, the deck is completely exposed again. I cannot visualize the sun and the Earth and explain that arc. What is the swing in degrees from the equinoxes to the summer and winter solstices? Are they exactly equal?

A  We all take for granted that the sun rises in the east and sets in the west but seldom think about these subtleties through the year. On the equinoxes, the sun rises from due east and sets to due west, and at noon reaches a maximum elevation of 53 degrees in the southern sky.

As Earth tilts toward the sun during the spring, the sun rises farther and farther north on the eastern horizon, sets farther north on the western horizon and is higher in the southern sky at noon.

By the summer solstice at San Jose's latitude, the sun rises from the east-northeast (azimuth 60 degrees), sets to the west-northwest (azimuth 300 degrees) and climbs to 76 degrees above the southern horizon at noon. These angles would allow the sun to shine on the north side of your cabin during the early morning and late afternoon. Conversely, in the winter, the sun rises about 30 degrees south of due east, sets about 30 degrees south of due west and rises only to 30 degrees above the southern horizon.

I have posted a graphic on my Web site that illustrates the path of the sun at various times of the year. See http://ggweather.com/solar.gif.

Q  Can you recommend a monitoring system for me? We have a vacation house at Mammoth Lakes, elevation 8,300 feet. I want to monitor the weather conditions remotely from my PC in Santa Cruz. My top priority is the temperature inside the house. If the furnace fails while we are gone, the pipes could freeze. I also want to monitor temperature outside the house, visually assess the snow depth on the front deck and street (a still picture will do; I don't need live video) and wind velocity.

A simple system that just gives me the inside temperature would be acceptable, although I'd love to figure out how to get the other readings as well. A cost of a few hundred dollars is acceptable.  Ralph Kimball - Boulder Creek

A  There are probably a number of ways to solve this problem, though staying within a budget of a few hundred dollars may be tough.

I would begin with a weather station as I described in my Nov. 21, 2000, column at http://ggweather.com/archive/weacornernov21.htm. In addition to measuring outdoor conditions, most systems will give you the inside temperature. These weather systems have software available that dumps their data into a personal computer. A small video camera could also be connected to give you a look at the snow on the deck. I would use a program such as PC Anywhere to access the computer remotely or transfer the data to an online Web site.

Now, a caveat. The winter environment at 8,300 feet is very hard on meteorological equipment, especially wind-measuring equipment that will ice up and fail. An option in the Mammoth Lakes area is a Web site at http://www.mammothweather.com/index.htm that will give you all the outside conditions