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FOR THE
.
FOREST INDUSTRY
SEPTEMBER I960
CLIMATOLOGICAL. NOTE NUMBER 39
FREQUENCIES OF DAILY EXTREMES IN TEMPERATURE AT MEDFORD, OREGON
Question: "During a given 10-day period at Medford, what is the likelihood the maximum
temperature observed during the day will be a certain value?"
Table 1:
As an example of how to read Table 1, which presents data on daily maximum
temperatures, look at the top row of numbers for the period 1-10 January.
Values tabulated are based on actual observations made at Medford during the
years 1948-58, and are presented on the basis of "days in 100 days". That is,
during the first third of January, daily maximum temperatures from 30 F to
39 F occurred at the rate of 32 days in 100 days. During the same period,
daily maximum temperatures from 40 F to 49 F occurred at the rate of 45 days
in 100 days. Combining these two statements, one may compute that during the
first third of January daily maximum temperatures from 30 F to 49 F occurred
at the rate of 32+45, which is 77 days in 100 days, or 77 per cent of the days.
Similar combinations of data may be made with respect to other maximum tem
peratures and other periods of the year.
Question: "During a given 10-day period at Medford, what is the likelihood the minimum
temperature observed during the day will be below a certain value?"
Table 2:
Table 2 is similar to Table 1, except it presents data on daily minimum tem
peratures. As an example of how to read this Table, look again at the row of
values for the first third of January. Suppose we are interested, in the
question above, in minima below 30 F. For this period, we may compute the
answer by adding all the numbers to the left of the column headed "30-39 F";
that is 2+5+38; that is, 45 days in 100 days, or 45 per cent of the time. The
likelihood that minimum temperature will be above 29 F during this period,
therefore, is 100-45, which is 55 per cent, or about 11 chances in 20.
If we had been interested in minima below 20 F in the question above, the
answer would have been the sum of the numbers lying to the left of the column
headed "20-29 F"; that is, 7 days in 100 days, or 7 per cent of the time. The
likelihood of minima above 19 F, therefore, would be 100-7, or 93 per cent.
As with maximum temperatures, similar combinations of data for other tem
peratures and other periods of the year may be made to answer other specific
questions
OREGON
\forest lands research
FOREST
RESEARCH
CENTER
CORVALLIS
Table 1. Frequency of Daily Maximum Temperatures at Medford, Oregon,
as Days in 100 Days.
Temperature, degr ees F
20-29
Period
Jan.
Feb.
Mar.
Apr.
May
July
Aug.
Sept.
Oct.
Nov.
50-59
60-69
70-79
80-89
90-99
10
1
32
45
19
1 L -
20
2
16
59
24
2. L -
31
1
21
54
24
L -
10
7
43
35
15
1" L -
20
5
39
47
8
2 L -
29
4
30
35
31
L -
10
4
28
43
20
5
1. L -
20
25
49
22
4
2] L -
31
10
49
32
9
L -
10
6
37
24
28
5
1] L -
20
4
19
34
30
13
2]L -
30
4
28
30
31
6
18
34
24
23
15
24
29
24
7
26
26
31
9
I -
10
1] I -
20
2] L -
31
1
1
99 +
3
1
1
8
1
10
5
24
25
31
14
1] I - 20
2
20
36
31
11
6
36
35
21
2
3
18
38
37
3
6
35
53
6
6
35
52
6
21 L -
30
I -
10
1] I -
20
2] I -
31
1
1
L -
10
9
43
44
4
1] I -
20
7
50
37
6
21 i -
31
6
17
41
34
2
L -
10
3
14
42
35
6
1] I -
20
15
27
32
23
3
21 I -
30
15
34
31
15
1
1 -
10
6
4
1
1]t - 20
11
30
29
18
16
46
26
12
1
21 . -
31
9
25
45
20
. -
10
10
41
41
8
36
43
12
9
1]. - 20
9
21. - 30
Dec.
40-49
L -
L -
June
30-39
9
37
45
. -
10
18
59
20
3
1]. -
20
28
42
27
3
21 . -
31
28
60
9
1
2
•
Table 2. Frequency of Daily Minimum Temperatures at Medford,
Oregon, as Days in 100 Days.
Temperature, degrees
0-9 | 10-19
Peri od
Jan.
Feb.
30-39
40-49
1 - 10
2
5
38
50
5
1 1 - 20
2
6
37
45
10
2 1 -
31
2
8
34
46
10
L - 10
3
3
45
35
14
3
32
50
14
28
56
16
L - 10
1
35
49
15
1 L - 20
2
25
59
14
10
71
19
1 L - 20
2 L - 29
Mar.
20-29
F
50-59
60-69
1
•
2 L - 31
L -
Apr. 1
May
10
10
67
23
L - 20
3
44
52
1
1
2'L -
30
1
59
39
L -
10
1
32
62
5
17
61
22
31
12
64
24
L - 10
5
43
50
I! L
- 20
2] L -
June
July
1! L - 20
5
46
44
5
21L -
30
1
42
53
4
I -
10
21
72
7
- 20
10
74
16
1 ]I
2] t - 31
12
71
17
10
15
70
15
- 20
14
76
10
2] i - 31
32
63
5
4
56
3
53
41
1
L -
Aug. 11L
. -
10
Sept. 1. i - 20
Oct.
Nov.
5
21. -
30
1
19
58
22
. -
10
1
28
56
15
11 i - 20
3
26
53
8
2]. -
31
13
60
26
1
. -
10
19
56
24
1
11. - 20
24
54
21
1
1]. - 30
5
28
48
17
10
1
29
24
61
9
59
17
45
46
5
. -
Dec.
2
1] - 20
21
- 31
4
2
.
Table 3. Occurrence of Extremes in High and Low Temperatures at Medford.
Frequency
Jan
Feb
Mar
Days with maximum temperatures 90
Most in a year
0
0
0
Apr
F
May
June
Aug
Sept
26
27
16
6
0
0
8
1
0
0
July
Oct
Nov
Dec
or iibove
1
4
9
Mean
0
0
0
0
2
5
17
13
Fewest in a yeai
0
0
0
0
0
0
9
3
4
0
0
0
Days with minimum temperatures 32
F o r t»elow
Most in a year
28
23
20
8
2
1
0
1
2
18
24
30
Mean
20
16
13
4
0
0
0
0
0
5
13
16
8
3
4
1
0
0
0
0
0
1
2
1
Fewest in a yeai
Question: "In a given month at Medford, what is the greatest frequency of high daily tem
perature maxima observed, and how does it compare with the average frequency?"
Table 3:
To give the reader an idea of the variability of teinperature extremes in a given
period from one year to another, data on the range of frequencies of high and
low temperatures together with average frequencies are presented in Table 3.
This Table is developed from the same observations as the other Tables of this
Note, but presents them differently. Interpretation of data such as in Table 3 is
considered in some detail on page 15 of Note 22, "Putting Weather Records to
Work."
The data: One must keep in mind that the observations of temperature suinmarized in
these Tables were made about five feet above a grassy plot in the official U.S.
Weather Bureau instrument shelter at Medford Municipal Airport. Not only
will temperatures vary from place to place at a given time, but also they will
be different nearer the earth's surface or farther from it than in the official shel
ter.
In short, values presented here cannot be considered more than a suggestion
of the patterns in time and space of temperature occurring on a given day.
Even with these various restrictions on interpreting the data, they will give the
reader a rough idea of the levels of temperature extreme likely at different
times of the year in the Medford area.
For detailed information on dates of last freeze in the spring and first freeze in
the fall at various locations in Oregon, the reader may wish to refer to a publi
cation soon to be made available by the Oregon Agricultural Experiment Station,
Corvallis.
William P. Lowry,
In Charge, Forest Meteorology