1896.] PARKER CLIMATOLOGY OF ROCHESTER. 225 



the cold of elevation. The air comes in from the West from the 

 general drift of the atmosphere from the west to the east up to about 

 the 65th parallel. 



When the cold wave is well formed the requirement for its 

 transfer to the lower latitudes in force is to have a storm of energy 

 form and pass to the east well south along the southern front of the 

 mass of cold air. The road is then open and forces well disposed 

 for its coming with speed and energy. Sometimes the storm does 

 not respond to the necessities of the hour, in which case the 

 north keeps its own until different dispositions of forces or the advance 

 of the sun have time to mix up or destroy the severity. About the 

 first of last January such a cold wave was met on the northern border of 

 the United States by a powerful tendency toward warm which held it 

 at bay for days and finally prevailed against it so that it never reached 

 farther south. It was a huge affair with pressure above 31 inches and 

 temperatures more than 50 degrees below zero. 



Effect of the Lakes. 



It is in the meeting of these cold waves that the lakes, with their 

 vast stores of heat, become so important. Always in the early winter, 

 and generally at all seasons, these cold waves split on the lakes, one 

 detachment passing to the north and the other down over the west. 

 The western detachment has so far to travel and is subjected to the 

 influence of so much country relatively warm that even if forces 

 operate exactly right for it to go south, only far enough to clear 

 the lakes, and then northeast over this section, it does not get here 

 with severity. The northern detachment is far more dangerous 

 because its journey to the eastward north of the lakes is shorter and 

 over a country so much colder ; the severest cold that reaches 

 this section is from these northern detachments, but in this case even 

 it requires a particular operation of forces not likely to work out very 

 frequently. The cold can come in a tortuous course down over the 

 Michigan peninsula, and across the Niagara strip without crossing 

 much water. Severity has reached us by that route. The other com- 

 bination is for the cold to forge eastward far enough to clear Lake 

 Ontario, then move south to a point directly east, thence be pushed 

 back over this section. This requires two changes of direction at 

 about the right time, and is improbable in any particular case, but 

 has worked out successfully. The cold of January 6, 1896, 10 degrees 

 below zero, and the lowest of the winter, came in this way. 



The lake stands always, so long as unfrozen, as a complete barrier 



