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CLIMATOLOGICAL, NOTE NUMBER 40
SEPTEMBER I960
FREQUENCIES OF DAILY EXTREMES IN TEMPERATURE AT
SEXTON SUMMIT, OREGON
Question: "During a given 10-day period at Sexton Summit, 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 Sexton Summit 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 50 days in 100 days. During the same period, daily
maximum temperatures from 40 F to 49 F occurred at the rate of 28 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 50+28, which is 78 days in 100 days, or 78 per cent of the days.
Similar combinations of data may be made with respect to other maximum
temperatures and other periods of the year.
Question: "During a given 10-day period at Sexton Summit, what is the likelihood the min
imum 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 ques
tion 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, 3+7+49; that is, 59 days in 100 days, or 59 per cent of the time. The
likelihood that minimum temperature will be above 29 F during this period,
therefore, is 100-59, which is 41 per cent, or about 4 chances in 10.
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, 10 days in 100 days, or 10 per cent of the time.
The likelihood of minima above 19 F, therefore, would be 100-10, or 90 per
cent.
As with maximum temperatures, similar combinations of data for other
temperatures and other periods of the year may be made to answer other specific
questions OREGON
•REST
LANDS
RESEARCH
FOREST
RESEARCH
CENTER
CORVALLIS
Table 1. Frequency of Daily Maximum Temperatures at Sexton Summit, Oregon,
as Days in 100 Days.
Temperature , degrees F
30-39
40-49
50-59
50
28
8
11 - 20
16
39
37
7
21 -
17
38
36
9
10
4
41
36
14
5
11 - 20
8
37
40
13
2
21 - 29
4
36
34
26
19
2
4
1 Jan.
1 -
Feb.
Mar.
10
31
10
5
40
11 -
20
1
41
44
10
25
44
27
4
2
10
18
30
25
25
11-20
9
23
35
19
14
21 - 30
7
35
28
27
3
5
23
33
28
11
19
8
1 -
July
11 - 20
2
17
29
21 - 31
2
11
26
27
32
2
10
10
25
28
27
9
11-20
5
25
38
27
5
21 -
30
2
14
37
32
14
1
1 -
10
1
6
25
46
19
3
32
2
Sept.
Oct.
11-20
3
11
21 - 31
1
15
44
38
2
10
1
24
48
25
2
11-20
1
19
28
3
24
2
4
21 -
31
2
8
28
49
36
1 -
10
1
5
18
39
33
19
11-20
3
16
32
30
21 -
30
5
26
30
27
12
1 -
10
18
29
27
17
6
3
1 -
Dec.
23
43
19
15
6
29
31
30
4
7
27
36
27
3
27
45
17
7
30
10
4
11-20
21 - 31
tfov.
1
52
1 -
Aug.
10
90-99
25
1 -
June
80-89
1
1 -
1 -
May
70-79
34
21 - 31
Apr.
60-69
20-29
14
Period
10
11-20
4
21 -
30
13
47
1 -
10
5
50
34
7
11 - 20
6
28
41
23
2
10
4
21 - 31
5
52
29
2
Table 2. Frequency of Daily Minimum Temperatures at Sexton Summit,
Oregon, as Days in 100 Days.
,'.'''•
i• ' '' i
* i
"'"^
Temperature, degrees F
0-9
10-19
20-29
30-39
40-49
3
7
49
35
6
1 1-20
5
48
38
9
2 1-31
17
37
41
5
1-10
6
38
40
14
5
38
43
Period
I - 10
Jan.
Feb.
1 1-20
1
50-59
60-69
70-79
2
13
•
2 1-29
48
39
12
I - 10
1
5
47
37
10
Mar. 1 1-20
2
64
29
5
2 I - 31
45
47
8
I - 10
36
43
20
1
- 20
19
54
18
9
2 1 - 30
24
55
19
2
Apr. 1 I
May
1 - 10
12
50
33
5
1 I - 20
5
48
29
14
2 1 - 31
2
44
41
13
34
47
14
5
I - 10
June
July
25
58
14
2
16
54
25
5
1 - 10
5
48
35
11
1
41
43
14
2
2 1 - 31
2
40
43
14
1
I - 10
2
42
47
9
- 20
1
45
42
12
2 L - 31
1
50
42
7
I - 10
2
40
34
21
10
48
25
17
2 1 - 30
16
50
24
10
I - 10
27
54
12
7
33
46
13
4
1 1 - 20
1I
Sept. 1 I
Nov.
1
- 20
- 20
1 I - 20
4
2 I - 31
6
37
44
13
I - 10
8
30
46
16
19
61
11
6
13
46
38
3
2
1 1-20
3
2 1 - 30
Dec.
4
2 I - 30
Aug. 1 I
Oct.
1
L - 10
4
46
41
7
1 1-20
2
26
46
26
2 1-31
3
48
38
11
3
,
Table 3. Occurrence of Extremes in High and Low Temperatures at Sexton Summit.
Frequency
Jan
Feb
Mar
Days with maximuni temperatures 90
Apr
F
May
June
July
Aug
Sept
Oct
Nov
Dec
or above
Most in a year
0
0
0
0
0
1
4
3
2
0
0
0
Mean
0
0
0
0
0
0
1
1
0
0
0
0
Fewest in a yeai
0
0
0
0
0
0
0
0
0
0
0
0
2
0
0
2
9
19
30
Days with minimurri temperatur es 32 F or below
Most in a year
30
24
24
24
13
Mean
23
16
22
12
6
1
0
0
0
4
9
18
Fewest in a yeai•
11
9
16
3
1
0
0
0
0
0
2
6
Question: "In a given month at Sexton Summit, what is the greatest frequency of high daily
temperature maxima observed, and how does it compare with the average fre
quency?"
Table 3:
To give the reader an idea of the variability of temperature 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 summarized in
these Tables were made about five feet above a grassy plot in the official U.S.
Weather Bureau instrument shelter at the top of Sexton Mountain. 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
shelter.
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 Sexton Summit 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