METEOEOLOGY CLIMATOLOGY. 27 



"A larpre amount of ice formed on the lakes during the winter of 1898-99, but 

 winter navigation on Lake Michigan was not suspended except during the severe 

 cold in the early part of February. . . . 



" Tliunderstorms. — The greatest number of thunderstorms occurs in the South 

 Atlantic and Gulf States and the Mississippi Valley. The number diminishes 

 toward the northward and westward, although there seems to be a second region of 

 maximum frequency along the eastern foothills of the Rocky Mountains in Colorado, 

 Wyoming, and northern New Mexico. West of the Rockies, except possibly in 

 Idaho, the number diminishes to less than 20 per annum. In California, Oregon, 

 and AVashington they rarely occur on the immediate coast, but are not infrequent 

 in the interior valleys and mountains back of the coast range. In Arizona they are 

 most frequent in July and August, the rainy season in the mountainous part of that 

 Territory. 



"There seem to have been more thunderstorms in 1899 than in the preceding year, 

 although the difference is not very great. The greatest increase in the number of 

 thunderstorms in 1899, as compared with 1898, occtirred in the States of Florida, 

 Michigan, Wisconsin, Minnesota, Iowa, and Nebraska. In a number of States, 

 particularly those bordering on the Gulf of Mexico, there were fewer thunderstorms 

 in 1899 than in 1898." 



The climate of San Francisco, Cal., A. G. McAdie and G. H. 



WiLLSON {[/. iS. Dept. Agr., Weather Bureau Bui. 28, pj). 30, charts 

 4). — Data relating- especially to temperature and rainfall, accumulated 

 at the San Francisco Station during the last 30 years, are reported in 

 detail. 



"The mean annual temperature, as determined from the records of the Weather 

 Bureau for 28 years, is 56.2°. May and November have practically the same 

 temperature. The warmest month is September, 60.9°; the coldest January, 

 50.1°; the other months have mean temperatures as follows: February, 52°; March, 

 54°; April, 55°; May, 57°; June, 59°; August, 59°; October, 60°; November, 56°; 

 December, 52°. 



"The highest temperature ever recorded in San Francisco was 100° on June 29, 

 1891, and the lowest 29° on January 15, 1888. Abnormally warm and cold periods 

 last, as a rule, about 3 days. The mean of the 3 consecutive warmest days at San 

 Francisco has never exceeded 76.3°. A period of warm weather during the summer 

 months is, as a rule, brought to a close about the evening of the third day with 

 strong west winds, dense fog, and temperatures ranging from 49 to 54°. The mean 

 of the 3 consecutive coldest days was 40.7°. The greatest daily range of temperature 

 was 43°, on June 29, 1891. . . . 



"July and August are practically without rain, while December and January 

 together have nearly 10 in. The annual rainfall is 23 in. 



" By comparing tlie seasonal rainfall with the crop yield it would appear that in 

 years when the rain falls generously in March and April the yield is largest, other 

 things ])eing equal. In other words, it is the time distribution of the rain, more 

 than the intensity or total rainfall, which benefits vegetation. . . . 



"The summer fogs of San Francisco result from a chilling of the upper warm air, 

 descending to the ocean surface, and particularly over the cold current close to the 

 shore. There is a great difference of temperature between the valley and the ocean, 

 often 50° within as many miles, and this is probably the prime factor in establishing 

 a marked air movement, shown by the strong indraft through the Gate on summer 

 afternoons." 



The meteorology of Ben Nevis in clear and in foggy weather, 



J. Y. Buchanan {Trans. Boy. Soc. Edlnhurgh, SO {1899), pt. 3, JVo.31, 

 pp. 48, pis. 8). — In this paper observations ou pressure, temperature, 

 3809— No. 1 3 



