340 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



inches a day on January 12 to 13, 16, 21, and 27 to 28. Bermuda pres- 

 sures were 0.09 inch above normal in January and 0.08 above normal 

 in February, and temperatures were generally above normal through- 

 out the eastern and central United States. North of the flood belt 

 and in the northeast there were heavy snows. 



The West, as usual when the central valleys are flooded, was cold. 

 Southern California experienced the severest freeze and heaviest snow- 

 storms ever known. On January 13 snow fell generally, even at San 

 Diego, and at Riverside it was deep enough (5 inches) for sleighing 

 among the orange groves. Frost occurred on 29 days of January in 

 southern California and on 20 days of February. 



Another visitation, almost identical with that of January 1882, 

 came in December 1926, when, after wet preliminaries, a total of 

 nearly 10 inches of rain fell over the Cumberland Valley in 9 days and 

 the river at Nashville reached 56.2 feet. Bermuda pressures were 

 high during the rainy spells of the month. 



APRIL AND MAY FLOODS IN THE MISSISSIPPI VALLEY 



Middle and late spring floods, though caused in much the same 

 manner as the winter floods already discussed, have the advantage of 

 more vapor in the warmer tropical air and a greater intensity of 

 convection and therefore of local storminess. The leafing out in spring, 

 however, with increased interception and transpiration, reduces the 

 run-off. Three floods may be cited: the general flood of April-May 

 1927, a very great one, and the Missouri Valley floods of May 1903, 

 and June 1915. 



In April 1927, as in early 1937, 1913, and 1882, a standing high 

 in the southwestern Atlantic (Bermuda +0.06 inch) drove tropical 

 air over a long fetch of very warm water 21 and into the south-central 

 United States, where it met large flows of polar air in the middle and 

 lower Mississippi Basin. The severe rainstorms — 12 to 24 inches of 

 rain fell in April over eastern Oklahoma, central and northern Arkan- 

 sas, southern Missouri, and western Tennessee, while a large area 

 around had more than 8 inches — following only 2 months after a 

 midwinter flood, produced the highest stages theretofore known in the 

 Arkansas and lower Mississippi Rivers. Frankenfield computed that 

 about 55 cubic miles of water went down the Mississippi (26 percent 

 of the 213 cubic miles of precipitation January to April). 22 Melted 

 snow made a negligible contribution, as in 1937, 1922, and 1913. 



The rains in April 1927 were of greater violence than in 1937, 

 being associated frequently with thunderstorms and occasional torna- 

 does. In 5 days, April 10-14, 18 tornadoes occurred in connection 



" Note the southeast-northwest isobars across the Caribbean on the North Atlantic weather maps 

 Monthly Weather Rev., vol. 55, No. 4, charts 8-11, 1927. 



M Frankenfield, The floods of 1927, loc. cit.: for a summary see Henry, A. J., Frankenfield on the 1927 

 floods In the Mississippi Valley, Monthly Weather Rev., vol. 55, pp. 437-452, 1927. 



