Sieteigeded iy S| ie 
tenement 
Wie Re Paneer ea 
Fig. 1. 
1013 
Official Thermograph Record, United States Weather Bureau, Medford, Oregon. 
April 10 to 17 inclusive. 
Note the short space of time during which low temperatures prevailed. 
the injurious temperature may not con- 
tinue for more than two hours and in 
some cases but a few minutes. 
Frost Prevention 
* High winds never occur during the 
time that the temperature may be below 
the freezing point. A slight breeze usual- 
ly comes up from the south during the 
early morning. However, this breeze is 
never sufficient to more than waft the 
smudge through the orchards and does 
not interfere to any great extent in keep- 
ing up the temperature where fires are 
built. It will be seen that the conditions 
in the valley are ideal for the prevention 
of injury from freezing. 
¥ The Rogue River valley is surrounded 
on all sides by mountains ranging from 
4,000 to 5,000 feet above sea level, and 
with many peaks much higher. During 
periods of frost it is usually calm, and 
in the several years during which careful 
observations have been made the great- 
est movement of the air recorded during 
a spring frost has been from one to three 
miles per hour. Contrast this with the 
severe freezes which have occurred in 
other districts where wind velocities 
ranging from twenty to thirty-eight miles 
per hour were recorded when the ther- 
mometer stood at fifteen degrees or more 
below the freezing point. The fruit grow- 
ers of the Rogue River valley little realize 
the wonderful climatic assets they are so 
fortunate to have. It can be truly stated 
that the only reason for losing a crop by 
frost is carelessness or neglect. 
* Farmers’ Bulletin No. 401. 
+ Office of Pathologist, Bulletin No. 5. 
YAKIMA VALLEY 
The conditions in the Yakima valley 
are described by Mr. T. R. Reed, special 
observer for that district. _ 
The conditions favorable for frost in 
the Yakima valley include the usual con- 
ditions of high barometer following a 
spell of cloudy, cold weather in which the 
soil has lost its accumulated heat, clear 
sky and very light or no wind. It is 
considered by local observers that frost 
is most likely to follow a period of bad 
weather and the shift of wind from the 
south or southwest into the northwest 
or north. It is popularly supposed that 
danger of frost is small unless the veering 
to northerly quarters has been preceded 
by quite a marked period of southerly 
wind. This of course may be a popular 
way of indicating the necessary intensity 
and duration of the cyclonic low* occupy- 
ing the Northwest; but it is worthy of 
note that judging from observations this 
season, dangerous frost is not likely except 
following protracted cloudy and cold 
weather, and that all the really serious 
frosts of the season have followed days 
on which the maximum temperature has 
been under 65 degrees and the current 
temperature under 60 degrees at the time 
of the afternoon observations. 
High barometer alone, while causing 
frost in other localities in the state, has 
repeatedly failed to bring freezing tem- 
peratures to this valley, attributable 
partly, perhaps, to active air movement 
often occurring in connection with anti- 
cyclonic weather. <A freeze may occur 
* Note—An area of low pressure at the north- 
west of a given point would be accompanied by 
southwest or south winds. 
