SCIENCE ROOM
CLIMATOLOGICAL NOTE NUMBER 6
April 1959
FREQUENCIES OF VARIOUS FORMS OF PRECIPITATION AND RESTRICTIONS
TO VISIBILITY AT PENDLETON, OREGON
Question: "During a given 10-day period at Pendleton, what is the likelihood
that visibility will be restricted by smoke and/or haze some time
during the day?"
Table:
As an example of how to read the table, look at the row of figures for
the period 1-10 January. The figures tabulated are based on the
actual observations made at Pendleton during the years 1948-58 and
are presented on the basis of "days per 100 days".
That is, during
the first third of January smoke and/or haze has been observed at
the rate of 5 days per 100 days, or 5%. The likelihood that smoke
and/or haze will be observed during this period on a given day in the
future, therefore, is about 1 chance in 20.
Similar interpretations can be placed on the data for other periods
and for the other weather variables shown.
The data:
One must keep in mind that the data in the table summarize obser
vations made at the U. S. Weather Bureau Station at Pendleton Field.
This means that, for example, sleet in the general vicinity of
Pendleton would not necessarily have been counted as a day of sleet
in these records.
The sleet must actually have been observed to
fall at the station itself. Similarly, an observer may not have heard
the roll of distant thunder even though it did occur.
These circum
stances, therefore, must be kept in mind when drawing conclusions
from or applying the data presented. Even so, the tabulations pre
sented will give the user a good idea of roughly when and to what
degree various weather variables may be expected to occur in the
Pendleton area.
William P. Lowry
Research Meteorologist
OREGON jFOREST LANDS RESEARCH CENTER
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