#234 TAKING CALIFORNIA'S TEMPERATURE

TAHOE NUGGET #234: TAKING CALIFORNIA’S TEMPERATURE

Working as a forecaster for the National Weather Service is not a job for the meek, especially if your zone of responsibility includes a region like the volatile Central Sierra. But there have never been so many tools in the arsenal of a professional meteorologist: satellites, buoys, radar, and complex computer modeling all feed into the mix before forecasts are issued.

When predicting high and low temperatures days in advance, weather professionals use climate averages to help base their forecast. Building up and maintaining databases of daily measurements for thousands of locations requires a complex network of automated sensors, official weather stations, and an extensive web of volunteer observers.

In the far western United States, with its challenging topography and myriad microclimates, it’s a vital network that took a century and a half to develop. The very first scientific records of weather, water and climate in the western United States were collected during the Lewis and Clark Expedition.

That epic journey by the “Corp of Discovery” vastly increased the knowledge of flora, fauna, geography, geology, native peoples, trade possibilities and routes of the western wilderness. Reports from that expedition also informed politicians, scientists, and the general public that the land and weather “out west” were substantially different than what most of contemporary Americans knew at the time.

In California there is no evidence that Spanish, Mexican, or indigenous peoples attempted to accurately measure temperature or precipitation. The Spanish missions in California left no thermometer readings, but they kept track of annual wheat harvest production and how much seed was planted, which can help indicate abnormal wet or dry seasons.

It appears that the first instrumental weather observations in California were taken by Captain Frederick W. Beechey during a visit to Yerba Buena (San Francisco) in November and December 1826. Beechey, a British naval officer, anchored in San Francisco Bay during his four year exploration of the Pacific and Bering Strait. Capt. Beechey kept a detailed diary during his stay in Yerba Buena that not only included temperature and rainfall, but also atmospheric pressure, tides, and even magnetic variations.

British naval officer Captain Beechey among the first to document California weather.

During his 1826 reconnaissance of San Francisco Bay, Capt. Beechey and his crew experienced early winter weather. In his Dec. 3 diary entry, the captain noted “As we left the harbor of San Francisco, the shore of which, being newly clothed with snow, had a very wintry appearance.”

In 1812, the Russians had established two settlements along the California coast north of San Francisco Bay. From 1836 to 1840, weather diaries were kept at Fort Ross, with temperature observations made three times a day, as well as air pressure, cloud cover, rain, hail and fog.

Fort Ross is now a California State Park

In the politically charged six years leading up to the 1846 Mexican-American War, no regular weather observations were recorded in California. American sailors conducted detailed weather observations for a time during the fight against Mexico, but the record ended when U.S. warships and troops stationed in Monterey and San Francisco bays were deployed to San Diego and points south.

Several American warships anchored in Monterey and San Francisco bays briefly kept weather records during the 1846-1848 Mexican-American War.

The first temperature reading published in a California newspaper appeared in San Francisco’s California Star in September 1847, noting “a week of hot and calm weather; 92 degrees in the shade.”

After the establishment of a U.S. military base at the Presidio in San Francisco in 1847, the post’s Army Surgeon was required to maintain a “Diary of the Weather” using a thermometer and rain gauge. These scattered and intermittent attempts at taking California’s temperature were of limited value for understanding day to day weather for agricultural and mining purposes.

Ultimately, continuous, long-term weather observations got started with the first wave of forty-niners as they invaded San Francisco in the Gold Rush. Medical doctors played a prominent role when they arrived with delicate instruments and the knowledge of how to use them.

Trained men of science like Dr. G.H. Gibbons and Dr. T.M. Logan would compile reliable observations, but it’s Thomas Tennent who’s recognized as the first person in California to establish a record of daily weather measurements shortly after his arrival in San Francisco.

Sergeant James A. Barwick was an observer with the U.S. Signal Corps in Sacramento, Director of the California Weather Service and Meteorologist to the State Board of Agriculture. In 1892 Barwick was concerned about improper weather station and instrument siting among cooperative observers that could skew weather statistics. The same issues crop up today among climate change skeptics.  

Tennent was a skilled craftsman from Philadelphia who made nautical and mathematical instruments for sea-faring ships. It had taken him 95 days to journey from Philadelphia to San Francisco via the Panama Canal — he walked the last 110 miles from Monterey.

Upon arrival, Tennent ordered weather instruments from the East and began his official observations in August 1849, and maintained daily measurements until February 1871, an impressive 22 year effort. He supplied his meteorological data to local newspapers, which were eventually published in Tennent’s Nautical Almanac.

U.S. Signal Service Station and Sacramento headquarters of the Meteorological Department of the State Agricultural Society. Note weather instruments on roof. Not surprisingly, average wind speeds dropped in many cities, including the "Windy City" Chicago, Illinois, when anemometers were removed from the tops of buildings.

Along with Sacramento and San Diego, San Francisco is among California cities with the longest weather records. Appropriate for a town where its beloved San Francisco Chronicle columnist Herb Caen once wrote, “A city where you can get a sunburn in the fog and pneumonia in the sun, freeze during baseball season and swelter during football, and read any morning that ‘it was the coldest day since last August.’”

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1 comment (Add your own)

1. chris burt wrote:
Fantastic blog! Very interesting to hear on Dec. 3 1812 the SF peninsula was blanketed in snow. Wow. Since the long-term weather records for San Francisco began in 1850 there have been only a handful of occasions that measurable snow has been recorded in San Francisco, and none of them occurred prior to December 31, 1882 when 3.5" accumulated.

Tue, May 1, 2012 @ 11:56 PM

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