it does not form into sneets or bands, and that it does not show, in 

 any part of the sky, any tendency to pass into cirrostratus. 



2. Cirrus, Delicate, not Increasing, Abundant but not Forming a 



Continuous Layer (42). 



The definition of tliis type is precisely the same as the preceding 

 with the exception tliat in this type the cirrus is more abundant 

 over tlie whole sky, but without any tendency to increase in any 

 particular direction. 



Cirrus of this type is the forerunner of a disturbance either on its 

 front or on its borders. 



3. Cirrus of Anvil Clouds, Usually Dense (43, 44). 



In this type the cirrus either actually proceeds from the anvil of 

 a cumulonimbus, in which case one sees cirriform masses attached to 

 the remains of cumulus, or it has probably so originated, being still 

 anvil-like in shape, or else remarkable for its density and frayed-out 

 appearance, generally showing virga in places. 



Originating in cumulonimbus, this type of cirrus is met with either 

 in the rear of typical disturbances or else around thunderstorms. 



In the first case the cloud is hybrid cirrus; in the second it is dense 

 cirrus, in which case the cumulonimbus stage may have ended some 

 time previously. 



4. Cirrus, Increasing, Generally in the Form of Hooks Ending in a 



Point or in a Small Tuft (45). 



This type of cirrus which is often in the form of streaks ending in a 

 little upturned point or in a small tuft, increases in amount both in 

 time and in a certain direction. In this direction it reaches the 

 horizon where there is a tendency for the cloud elements to fuse 

 together, but the clouds do not pass into cirrostratus. 



This type often occurs on the front of a typical disturbance. 



If the cirrus increases in time and in a certain direction tending 

 also to pass into cirrostratus in this direction it should be coded as C^=6 

 or C„ = b according as to whether the front of the cirrus sheet, formed 

 out of the scattered cirrus is at a greater or lesser altitude than 45° 

 above the horizon. 



5. Cirrus (Often in Polar Bands), or Cirrostratus Advancing Over the 



Sky, but not More Than 45° Above the Horizon (46). 



A sheet of fibrous cirrus partly uniting into cirrostratus, especially 

 toward the horizon in the direction where the cirrus strands tend to 

 fuse together; the cirrus is often in a herring-bone formation, or is 

 in great bands converging more or less to a point on the horizon. In 

 this class is also included a sheet of cirrostratus without any cirrus. 

 In either case the front of the sheet is not more than 45° above the 

 horizon. 



This type occurs in the front of a typical disturbance. 



The varieties included in this definition are "herring-bone cirrus" 

 and "polar bands." What is termed the front of the sheet means 

 the front either of the cirrostratus sheet, if this cloud exists without 

 cirrus, or of that part of the sky where the cirrus fibers are close enough 

 to each other to appear welded together, instead of beiug discrete 

 masses like the cirrus which precedes this sheet. 



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