A Note on the Possibility of Long-Range Weather Forecasts. 19 
In six of the given years the rainfall of the second half of May was 
above the average of the period, and in eight years it was below. Table II 
epitomises the June temperatures in two groups for these same six and eight 
years respectively. 
Table II. — Showing the Dependence of June Temperatures wpon May 
Rainfall. 
June averages of — 
For rainfall of 
May 16-31 
above the 
average. 
For rainfall of 
May 16-31 
beloA^' the 
average. 
Degrees 
Degrees 
Fahr. 
Fahr. 
Mean miniinuni temperature .... 
36-4 
35-6 
Lowest „ ,, .... 
27-6 
26-4 
Mean temperature on grass .... 
27-1 
24-3 
Lowest „ „ .... 
17-3 
14 2 
Mean maximum temperature .... 
63-9 
64-7 
Number of times the temperatures fell below 30°F. : 
Air temperatures ..... 
2-50 
3-75 
Grass „ ..... 
21-83 
25 00 
The meaning of Table II will be best understood from an example : The 
average for the whole fourteen years of the lowest June temperatures on 
grass was IS'S^F. ; for the six years in which the May lG-31 rainfall was 
above the average rainfall the average of the lowest June temperatures on 
grass was 17'3°F. ; for the eight years in which the May 16-31 rainfall was 
below the average rainfall the average of the lowest June temperatures on 
grass was 14*2° F. 
It follows from Table II that when the second half of May is wet, the 
following June days tend to be cooler and the nights warmer than when the 
second half of May is dry. It appears, moreover, that heavier rains towards 
the end of May determine fewer cold June nights. As it happens, a good 
many of the cold June nights following a wet May come near the end of the 
month. 
The physical significance of these results is, of course, that dry ground 
will cool faster by radiation than wet ground will by evaporation and radia- 
tion combined. By the same token, because the specific heat of wet ground 
is greater than that of dry ground, June days following a wet May are 
cooler than those following a dry May. '* 
* For information about long-range weather fore«asting see W. N. Shaw^ ' Fore- 
casting Weather/ 1911, p. 356; also E. B. Garriott, Long-Range Weather Forecasts,' 
1904. The remarks of R. de C. Ward on changes of climate in ' Climate,' 1908, p. 338 
are worth attention. ' 
