New York Weather Bureau. 415 



below for the summer season. A marked decrease in the num- 

 ber of cyclonic storms occurs from March to April and May; and 

 the frequent showers which commonly occur during the latter 

 months appear to be, more than at any other time, the effect of 

 admixture of air currents having different temperatures. 



An inspection of pressure charts for the summer months shows 

 an area of low pressure over the northern interior of the conti- 

 nent in place of the anticyclonic area which was present there 

 during the winter. The depression over the north Atlantic has 

 decreased in intensity, while the high pressure system of the 

 central Atlantic hais become stronger, controlling the winds over 

 the ocean and on 'both the European and American coasts, be- 

 tween parallels 10 degrees and 50 degrees north. A western 

 branch of this area also covers the southern and central United 

 States as far as the Mississippi valley, and thus the southerly 

 wind system of the western Atlantic is extended well into the 

 interior of the continent, increasing to a marked degree the sum- 

 mer temperature of the northern States. (In southwestern 

 Europe the Atlantic " high " produces an oppoisite thermal effect, 

 since that region is on the eastern side of the anticyclonic center 

 and hence is subject to northerly winds.) In summer, as In 

 winter, any increaise of pressure over the southern States tends 

 to raise the temperature in the region to the northward, and 

 when such an increase occurs in conjunction with a dimunltion 

 of pressure over Canada, a " hot wave " usually occurs in the 

 northern States. The average path of cyclonic storms is more 

 northerly than in winter, and comparatively few depressions pass 

 to the southward or eastward of New York until August. 



The Gulf of Mexico and the Atlantic Ocean ooaitribute large 

 supplies of moisture to the air currents which move northward 

 over the States in summer. Hence, although cyclonic depres- 

 sions are less frequent than at any other season, the rainfall 

 accompanying each storm is apt to be heavy, and over the greater 

 part of the country the maximum total precipitation for the year 

 occurs in the summer months. The local showers and thunder- 

 storms characteristic of the season usually accompany the pas- 

 sage of low pressure areas near the State; but such a condition is 



