Kew York Weather Bureau. 485 



tively light rainfall during September is chaipaeteristic of the 

 State at large, whterea® in the Upper Lake region the general 

 autumn maximum occuiPs during that month. Erie, Pa., shows 

 a November maximum, which feature also prevail'S in the Ohio 

 valley. ' 



Over the greater part of the interior of New York the precipita- 

 tion during the winter is the least of the year. Block Island on 

 the contrary has its annual maximum at that season, while the 

 coast stations generally appear to be aibout equally subject to 

 continental and maritime influences, showing but slight seasonal 

 variations. This is also true, in even a greater degree, of the 

 region bordering the Lower Lakes, and Rochester may be taken 

 as an example in which an annual fluctuation is almost' wholly 

 lacking. Oswego has a principal maximum in June, and a 

 secondary in autumn and early winter, but the latter becomes 

 predominent at Palermo a few miles to the eastward, and attains 

 a remarkable intensity along the ridge running parallel to the 

 lake in Lewis county. 



In the spring a March maximum is very pronounced at the 

 Atlantic coast stations, and is also observable inland in a lesser 

 degree. A diminution again occurs in April, after which the 

 curves of the continental type rise towards their summer maxi- 

 mum, corresponding to the change of prevailing winds from 

 northerly to southerly which occurs in May. 



The distinction between a continental and maritime rainfall 

 may admit of the fallowing summary statement: Since precipita- 

 tion is largely the result of an upward motion and consequent 

 cooling of air masses, it will occur on the continents in summer 

 when a high temperature renders diurnal convectional priocesses 

 most active, and the prevailing winds also are such as to afford 

 an abundant supply of vapor. Over or near large bodies of water, 

 on the other hand, the daily convectiional process is weak, and 

 hence such regions are mainly dependent for their rainfall upon 

 the powerful updraught of air within cyclonic storms, which are 

 most numerous in winter. These conditions are suflflciently illus- 

 trated by the accompanying figures in which Cooperstown repre- 



