192 THE CLIMATE OF PRINCE GEOKGE S COUNTY 



applied to short records of rainfall, the averages for the various 

 stations in the county are given in the accompanying tables. 



Prince George's County receives about 42 inches of rain per 

 annum. While this amount is slightly less than that for most other 

 counties farther north, it is not the lov^est value in Maryland, which 

 appears to obtain in Allegany County, where the annual rainfall is 

 approximately 34 inches per annum. As in all other counties of 

 Maryland the precipitation is quite uniformly distributed through- 

 out the year. 



The records at Washington covering 90 years show an annual 

 rainfall of 43.5 inches. The greatest average occurs in July with 

 4.65 inches, or more than 10 per cent, of the annual total; and the 

 least occurs in JSTovember with 2,71 inches, or about 6 per cent, of 

 the annual amount. 



One of the most significant things revealed by an inspection of 

 the precipitation tables is the remarkably even distribution of the 

 precipitation through the year. It is also interesting to note that 

 during the entire period covered by these records — back to 1824 — 

 there is not a single month when no precipitation was recorded. On 

 the average, precipitation to the amount of .01 of an inch or more 

 occurs on 10 days out of each month. The fall is now and then 

 excessive, but as a general thing it is moderate. There is probably 

 no very material difference in the fall in the eastern as compared 

 with the western portion of the county, but the records seem to 

 indicate a slightly greater fall in the Patuxent valley than in that 

 of the Potomac. Snow occurs every year, although in some years 

 the amount is very small, amounting to between 15 and 20 inches. 



Thunderstorms, not infrequently accompanied by hail, occur, 

 especially during the summer months, being most frequent in ]May 

 and August. The prevailing winds of winter are from the nortli- 

 west and of summer from a southerly direction. The humidity of 

 the air is not excessive, being probably less than 70 per cent, for the 

 year. The percentage is highest, as a rule, in September and lowest 

 in April and May. The percentage of sunshine and cloudiness dur- 

 ing the year is about equal, the former possibly exceeding the latter 

 by a small margin. 



