1286 



FROST 



FROST 



The prediction of frost and issuance of frost-warnings. 



The prediction of frost and issuance of adequate 

 frost-warnings necessarily belong to the United States 

 Weather Bureau. It is wholly impossible accurately 

 to predict frost locally without a knowledge of general 

 weather conditions over a considerable area. However, 

 a local observer with a complete knowledge of the 

 climatology of his district and a knowledge of the air- 

 currents, humidity, maximum and minimum tempera- 

 tures, and the like, is capable of making very accurate 

 forecasts in cooperation with the United States Weather 

 Service. For careful work, a detailed mapping of the 

 climatological features of each district should be made. 

 It is known that temperatures vary greatly within any 

 district, dependent upon elevation, contour, proximity 

 to large bodies of water, and so on. 



Frosts usually occur during periods of high baro- 

 metric pressure, following a period of low pressure in 

 which there has been some precipitation. Under such 

 conditions the air is very dry and dust-free, producing 

 conditions favorable to intense radiation, and conse- 

 quently causing rapid cooling of both plants and soil. 



1587. Orchard-heating with fifty coal-heaters to the acre. Each heater 

 holds from twenty-five to thirty-five pounds of soft coal. 



It has been stated more or less empirically that the 

 temperature of the dew-point is a safe guide in the 

 local forecasting of frosts, but recent investigations 

 have shown that it is not dependable when used alone 

 and in disregard of other important factors, such as the 

 daily maximum temperature, temperature-curve, wind- 

 direction, barometer, and condition of the sky. To 

 this should be added a complete knowledge of general 

 weather conditions as obtained from the nearest Dis- 

 trict Weather Bureau Office. 



In 1882, Lieutenant (now Brigadier General) James 

 Allen published a pamphlet entitled "To Foretell Frost 

 by the Determination of the Dew-point." He said 

 that if the dew-point is above freezing in the early 

 evening the minimum temperature next morning will 

 be above freezing; if the dew-point is below freezing, 

 the minimum temperature next morning will also be 

 below freezing. If the prediction of frosts were so 

 simple, anyone with the aid of the psychrometer, or 

 wet-and-dry bulb thermometer, might easily make 

 independent forecasts. However, it has been found 

 that the dew-point is an aid only when used in com- 

 bination with a perfect knowledge of the other weather 

 factors and a knowledge of the climatology of the 

 district. The dew-point temperature is used in the 

 Rogue River Valley, Oregon, because it has been found 

 a very safe guide in combination with the above factors 



which were determined by several years of observa- 

 tion and study. From 1909 to 1913 the average 

 departure of the minimum temperature of the follow- 

 ing morning from the previous evening's dew-point 

 temperature during periods of spring frosts has been 

 0.10 F. It is possible that every district, by a careful 

 study of all the factors governing frost conditions, may 

 be able to predict accurately not only the minimum 

 temperature that will occur, but also the time when 

 the firing in the orchards must begin. This is now done 

 in the Rogue River Valley, Oregon, and has been prac- 

 tised for several years without a single error. 



The several ways of preventing fall in temperature. 



In order to prevent the fall in temperature, the fol- 

 lowing methods have been practised: (1) Direct heat- 

 ing of the air. (2) Adding water-vapor. (3) Adding 

 both heat and water-vapor. (4) Ventilation or mixing 

 the air. (5) Irrigation, or use of water. (6) Use of heated 

 water and steam. (7) Use of screens or covers to pre- 

 vent loss of heat by radiation. (8) Spraying with water. 

 In the discussion of preventing frost-injury, all 

 the methods excepting that of adding heat 

 will be omitted, as recent experiments have 

 shown that direct heating of the stratum of 

 air in contact with the trees and fruits is the 

 only practicable way of handling frost-preven- 

 tion on a large scale. All the other methods 

 have been given extensive trials, and, while 

 practicable for small gardens, cannot be used 

 over large areas on account of the large 

 amount of labor necessary, and the further 

 fact that their application cannot be made 

 general. Direct heating is not only simple, 

 but is the least costly, and has, therefore, 

 the advantage of general application. 



Methods of direct heating in frost-preven- 

 tion. As stated above, it has been demon- 

 strated beyond question that adding heat 

 directly to the air through the agency of fires 

 distributed throughout the orchard is the 

 most successful and practicable way to handle 

 the frost problem in commercial orchards. 

 A multitude of devices and many kinds of 

 fuel have been experimented with, and it is 

 now the opinion among growers who have 

 fought frost that the best heat-producing 

 material so far demonstrated is crude- 

 oil or distillate burned in some form of 

 sheet-iron receptacle or smudge-pot. In the first 

 place, oils are easy to handle, may be readily stored, 

 and, compared with other fuels, produce more heat 

 in proportion to the cost. The cost of handling and 

 igniting such fuels as coal and wood, together with 

 the disadvantage of so much bulky material dis- 

 tributed throughout the orchard which interferes with 

 cultivation, decidedly places these fuels at a disad- 

 vantage, excepting in very small tracts. No matter 

 how remote a fruit district may be from an oil-field, 

 there is no question but that oil is the best fuel to be 

 used, especially in large commercial orchards when 

 the labor problem is one of more than ordinary impor- 

 tance. There is very much difference in the oils as 

 secured in different parts of the country. For the 

 most part, eastern crude-oils have a paraffine base, 

 while those on the Pacific slope have an asphaltum base. 

 The crude-oil, or petroleum, as it comes from the wells 

 is very rich in gases and the lighter oils, such as ben- 

 zene, gasolene, kerosene, and others, and, therefore, is 

 not used as such for orchard-heating. The gases and 

 lighter oils are all removed by fractional distillation, 

 leaving behind the heavier oils and the asphaltum or 

 paraffine base, as the case may be. The fuel-oils on the 

 market are, therefore, residuals, and as such are used 

 for orchard-heating. A residual oil with a paraffine 

 base will burn in the common smudge-pot without 



