A Strong Windstorm on December 10, 1906

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Wolf Read

On December 10, 1906, a deep low raced northward just off the Pacific coast, perhaps along 126ºW longitude, and landing in southern Vancouver Island before turning in a more northeasterly direction. This interpretation is based on a somewhat questionable map of the storm's track in the December 1906 Monthly Weather Review (MWR). A section of the official Weather Bureau surface conditions map appears above, and shows a strong low off of southwest Oregon. Whatever the exact path was, this cyclone lashed the coast with a potent gale that stretched from San Francisco northward into British Columbia, as evidenced by official wind measurements and damage reports, a clear signature of a classic event.

As if the great earthquake of April 18, 1906 wasn't enough, powerful winds tore through the San Francisco Bay Area just eight months later. According to the National Park Service's documentation on the Presidio's history, the windstorm toppled a barracks at Fort Miley, and disrupted slate roofs, windows and fences at the Presidio.

A Forecaster for the Weather Bureau's "San Francisco Forecast District," summarized the windstorm in the December 1906 Monthly Weather Review:

"The most severe storm of the winter occurred on the 10th, covering the entire coast. At San Francisco a maximum wind velocity of 53 miles occurred; at Southeast Farallon, 72 miles, and at Point Reyes Light, 92 miles from the south. The storm did considerable damage thruout the southern portion of the Sate, and especially in the San Francisco Bay district. Warnings were given a few hours in advance of the storm."

This statement was made by a Forecaster from the "Portland, Oreg., Forecast District," also in the December 1906 MWR:

"Two severe storms swept this district during the month of December. The first was noted as approaching the Washington coast the morning of the 6th and warnings were at once sent to all seaports and inland stations were at once notified of the expected high winds. Fifteen hours later the winds had increased to a whole gale along the coast, and within twenty-four hours high winds were blowing at inland stations. The Oregonian editorially commended the work of the Weather Bureau in connection with this warning, saying that 'with a warning so well in advance of the storm, there was plenty of time to make everything snug, and as a result, very little damage was reported'.

"The second storm was first noted as approaching the Oregon coast the morning of the 10th at which time there was some doubt as to weather (sic) it would move directly east or advance northeastward. It was finally decided that it would move northeastward and warnings were promptly issued. This storm proved to be as severe as the former one and the warnings were just as timely."

The following storm track map is at best a rough estimation based on available information from the December 1906 MWR.

Storm Data

Offical wind measurements from the time period of this storm are widely spread and are of a different character than modern records. Data and summary tables of monthly weather data in the December 1906 MWR provide some of the details about this strong windstorm. The data generally point toward a storm path similar to other big sou'westers, as depicted in the above map.

Note on wind readings from the pre-1928 time period: Four-cup anemometers made out of brass and weighing 550 grams, with cups four inches in diameter, were employed by the Weather Bureau pre-1928. Due to the unique inertial response of the anemometers, readings from a 4-cup system tended to be high when compared to the actual wind velocity. This physical reality was carefully studied in the late 19th century with the results reported in the MWR. What this means is that the 4-cup readings, as reported in the MWR and other sources, need to be adjusted downwards to be comparable to the 3-cup anemometers that were employed from 1928 to approximately 2006 (from about 2003 to 2007, many official cup anemometers were replaced with sonic anemometers). In general, a 4-cup system reads about 9.0% high when indicating 25 mph, 22.5% high when indicating 50 mph, 27.7% high when reading 75 mph and 30% high when reading 90 mph [3]. Original 4-cup figures are shown in the data below, with corrected readings in parenthesis. Correction factors are based on a table provided in early issues of the MWR, and the table accessed appeared in January 1894, Vol. XXII, No. 1, pp 28-29.

Table of Peak Wind and Estimated Gust

Location Official Peak
5-minute Wind
mph		 Adjusted Peak
5-minute Wind
mph		 Estimated
Peak 1-second
Gust*
mph		 Anemometer
Height
feet AGL
San Francisco SW 53 43 56 204
Mt. Tamalpias SE 69 55 72 18
Sacramento SE 52 42 55 117
Point Reyes Light S 92 71 92 18
Red Bluff SE 34 29 38 57
Eureka SW 45 37 48 80
Roseburg SW 24 21 27 57
Portland S 38 32 42 106
North Head SE 94 72 94 56
Tatoosh Island SW 72 57 74 57
Tacoma SW 46 38 49 120
Seattle S 63 50 65 224

* Peak gust is conservatively estimated using a standard 1.3 gust factor; this gust factor is normally applied to 1-minute winds, and is likely higher for 5-minute readings.

Note that many of these anemometers were well above the standard 10-meter (~33 feet) height officially employed in the modern ASOS era, which means that the maximum 5-minute winds could be revised downward for a more accurate comparison to recent storms. The readings at both Seattle and San Francisco would be the most strongly effected.

Last Modified: November 29, 2007
Page Created: December 11, 2002

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