298 PHYSIOGRAPHY 



bring with it weather similar to that which it is now giving to the 

 region where it occurs. Hence, on the 25th, the prediction might 

 be made that rain is to be expected in about 24 hours in the region 

 about the head of Lake Superior. 



On the 26th the prediction might be made that the low which 

 is central north of Lake Superior (Fig. 247) will move on to the 

 Gulf of St. Lawrence by the succeeding day, and that rain will 

 accompany it. Rain for the region about Lake Huron and the 

 area east of it may, therefore, be predicted for the 27th. The 

 chart for that day (Fig. 248) shows that the area of precipitation 

 extends far to the south. The preceding map had shown some 

 cloudiness in this region, but had afforded no warrant for the 

 prediction of such an area of precipitation as appears on the map 

 of the 27th. 



Temperature changes as well as changes in precipitation may 

 be predicted. Thus in Fig. 245 the isotherm of 40 bends south- 

 ward notably in the high central over Iowa. As the high moves 

 east, it will probably carry the low temperature with it. Hence 

 it is safe to predict that the temperature will fall in the area into 

 which the anticyclone is to move. The map of the succeeding 

 day (Fig. 246) shows that the temperature of western Virginia has 

 fallen from about 60 to about 40 along the path of the high, while 

 areas much farther north are warmer. 



Fig. 246 also shows that North Dakota and Alberta have a 

 temperature of 50, that is, a temperature of 10 warmer than that 

 of western Virginia. It will be noted, too, that the relatively high 

 temperature of Dakota, Montana and Alberta goes with a low. As 

 the cyclone moves eastward, the temperature along its path will 

 probably rise. This is shown by the map of the next day (Fig. 

 247), which shows a temperature of about 50 north of Lake Supe- 

 rior. The same map shows how the isotherm of 40 bends to the 

 southward in front of the high which is central over western Mon- 

 tana. As the high of Montana moves eastward, it will be likely 

 to carry cold temperature with it. From this map, therefore, it 

 may be predicted that the temperature in Nebraska, Kansas, Iowa, 

 and Missouri will fall. 



The time when the rain which a given storm may bring to any 



