MARYLAND GEOLOGICAL SURVEY 191 



The foregoing table shows the stations from which meteorological 

 data are included in the present discussion. 



Temperature Conditions. 



The average temperature conditions for Prince George's County 

 are given in the following tables. 



The average for the year is about 54 degrees and the range in the 

 monthly mean temperatures is about 42 degrees. January, as a rule, 

 is the coldest and July the warmest month of the year. The extreme 

 maximum temperature (tlie highest ever recorded at any station in 

 the county) as shown in the following tables is 105 degrees, recorded 

 at College Park in July, 1808, and the e^itreme minimum temper- 

 ature is 18 degrees, recorded at Lalirel in February, 1809, indicating 

 an extreme range for the county of 123 degrees. 



It will be of interest to compare these temperatures with simihir 

 data for Garrett, the coldest county in ]\rarvland : 



Annual Warmest Coldest 



County Mean Month Month 



Garrett 47.0° 68.0° in July 24.0° in February. 



Prince George's 54.5° 76.8° In July 33.3° in January. 



Garrett County is much colder chiefly on account of its far greater 

 elevation above sea level. 



Tlie average date of the last killing frost in the Sju'ing is April 

 7 for Washington, April 16 for Cheltenham, and April 20 for 

 T^aurel. The latest date recorded for a killing frost is May 11, lOOG. 

 The average date of the earliest killing frost in the Fall is October 

 22 for Washington, October 21 for Cheltenham, and October 18 for 

 Laurel. The earliest dates recorded for a killing frost are October 

 2 for Washington, October for Cheltenham, and October 1 for 

 Ijanrel. 



Precipitation. 



As Mr. Von Herrmann correctly points out, precipitation is an 

 extremely variable element of climate, and very great differences 

 jnay be found at stations not widely separated ; no corrections can be 



