FLOODS BROOKS AND THIESSEN 



335 



fair weather for a day. Owing apparently to the major thrust of 

 polar air into low latitudes along the eastern seaboard of the United 

 States, a large return of tropical air on the 20th brought renewed heavy 

 precipitation, which continued in the form of instability showers, even 

 thunderstorm rains, until the 24th. (Figure 9 is a north-south cross- 

 section of the air masses, Jan. 22.) The rainfall in this 5-day period 

 was of the order of 10 inches in a narrow central belt from Louisville 

 to Little Rock. The day of greatest rainfall in the Ohio Valley was 

 the 21st (see fig. 7). The winds at the surface were mostly northerly 

 during these heavy rains; the tropical front was to the south. The 

 temperatures of this remarkable week are shown in figure 1. The 

 rainfall for January 1-25, half to two-thirds of which fell in the 5 



Figure 10.— Successive daily positions (8 a. m.) of Figure 11.— Rainfall in the Ohio and Lower Missis- 



the front between tropical and polar air masses sippi basins between January 1 and 25, 1937. 



from January 14 to 25, 1937. (From U. S. Weather (Courtesy U. 8. Weather Bureau.) 

 Bureau Ms. Maps.) 



days, January 20-25, is shown in figure 11. J. B. Kincer computed 

 that in the belt of heaviest rainfall about 100 miles wide and 550 miles 

 long the 16 inches of rainfall amounted to more than 60 billion tons of 

 water. 13 This precipitation was four times the normal amount. 



Table 3 shows the flood stages produced throughout the length of 

 the Ohio River, which, except at Pittsburgh, reached the highest 

 stages ever known. One of the meteorological hazards in a great 

 flood, when the waters are lapping the tops of the levees at the edge 

 of a moving lake miles wide, is the wind. Not only does the wind 

 raise erosive waves, but it also raises the stage of the water. Thus 

 at Memphis after an apparent crest had been reached, a 25-mile wind 



» Record-breaking January drought, floods, freezes, and early blooms, Information for the Press, U. S. 

 Dept. of Agriculture, January 30, 1937. 



