SUMMER HOT WINDS ON THE GREAT PLAINS. 341 
The low pressure area accompanying twenty-six of these 
periods was of an elongated or elliptical form and extended 
south from Northwest Territory, generally to the thirty-fifth 
parallel of latitude and in some instances to western Texas. 
These may be described as V shaped. In nine of these there 
were secon lary depressions in the vicinity of the hot winds. 
In the other nine periods of hot winds (not included in the 
above) there was a general low pressure area along the east¬ 
ern slope, and this sometimes extended eastward to the lakes 
and central valleys. In four of these there was a general 
well defined cyclonic movement, while in the other five 
there was a well defined secondary low pressure in the local¬ 
ity in which the hot winds occurred. During the devel¬ 
opment and progress of all these low pressure areas the 
barometer was generally about 30 inches or above along 
the western coast of the United States between the thirty- 
fifth and forty-eighth parallels of latitude. The eastward 
movement of the atmosphere from the Pacific slope across 
the divide toward the low pressure area was generally well 
defined, and cloudiness, with more or less rain, prevailed 
from the Pacific coast to the summit of the Rocky Mountain 
divide. The hot winds are generally found near the inner¬ 
most or the second isobar of the low-pressure area which 
they accompany, and their direction, like that of the surface 
winds, conforms to the trend of the isobars. 
The existence of a particular class of winds in summer 
over the eastern slope of the Rocky mountains or any part 
of it has been denied by some who have studied the subject 
and who claim that the term “ hot winds ” as used by the 
inhabitants of that section applies to winds which occur 
under the same conditions and are of the same generic 
character as the warm wave or heated term of the eastern 
States, and that their dryness and heat are caused by drouth 
and insolation * at the earth’s surface. This view is strongly 
* The word ‘ ‘ insolation ” is used to imply local heating at and near the 
earth’s surface by the rays of the sun, including absorption, radiation, 
and convection. 
44—Bull. Phil. Soc., Wash., Vol. 12. 
