What are the odds it'll rain on any given day?

This chart will show how many times it has rained on any given day over the past 120 years (Jan. 1, 1893 - Dec. 31, 2012)

Combination of Seattle-Tacoma Airport and Federal Building

Day

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sept

Oct

Nov

Dec

1

74

66

62

60

54

38

28

10

31

39

56

81

2

70

65

71

61

53

37

31

13

26

47

66

71

3

77

71

67

59

48

34

32

15

30

39

68

70

4

81

69

56

59

47

39

34

9

30

41

70

72

5

73

62

64

63

47

39

26

17

35

39

66

77

6

70

67

46

60

44

43

25

19

28

45

68

67

7

73

67

60

61

35

39

26

15

31

53

77

70

8

79

60

69

45

47

39

22

11

31

44

66

67

9

78

69

69

52

49

45

19

14

28

53

79

76

10

71

70

63

52

46

39

24

13

33

56

75

75

11

70

63

69

60

50

43

25

13

26

44

74

77

12

75

62

70

58

35

43

18

14

26

46

74

68

13

80

70

67

60

43

48

22

20

33

53

76

68

14

75

75

60

55

42

37

20

19

40

55

66

75

15

71

75

65

59

40

29

19

25

28

49

82

75

16

78

78

67

59

50

41

25

22

37

52

75

70

17

76

72

67

55

48

33

16

23

36

50

73

66

18

72

54

59

60

45

38

13

27

38

46

65

68

19

60

61

66

60

48

37

15

19

39

53

89

75

20

72

68

66

48

37

37

12

16

39

53

67

70

21

68

61

66

48

44

30

11

20

29

50

66

78

22

66

68

66

51

38

35

13

25

33

55

63

70

23

74

68

71

48

36

33

13

22

29

49

77

73

24

77

67

64

48

42

36

11

23

31

57

75

70

25

70

62

61

44

51

28

16

30

37

53

70

70

26

67

59

56

42

50

30

16

25

41

55

62

65

27

62

70

61

50

50

36

11

27

35

55

66

76

28

70

68

68

53

46

34

11

25

34

60

63

75

29

69

 

68

53

39

33

11

29

38

64

80

82

30

68

 

60

43

41

31

9

25

43

64

80

64

31

65

 

62

 

42

 

 12

32

 

 65

 

66

Blue numbers --  wettest days of month
Red numbers -- driest days of the month
Green number
-- wettest day of the year
Orange number -- driest day of the year.

Information supplied by the National Weather Service Seattle

And here is the same chart, given as a percent chance instead of numerical counter for each year:

Day Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
1 62.3 54.7 52.1 48.7 44.4 29.9 23.1 8.5 26.5 33.3 46.1 68.3
2 58.1 54.7 58.1 50.4 42.7 29.0 24.8 11.1 22.2 39.3 53.8 58.9
3 64.1 58.9 56.4 47.8 39.3 28.2 26.5 12.8 25.6 32.5 57.2 58.9
4 66.6 57.2 46.1 48.7 38.4 31.6 28.2 7.7 24.8 34.2 58.1 60.6
5 59.8 51.2 53.8 51.2 38.4 32.5 22.2 13.7 29.9 32.5 54.7 64.9
6 58.1 55.5 38.4 49.5 36.7 35.9 21.4 16.2 31.6 37.6 56.4 55.5
7 60.6 54.7 50.4 50.4 29.0 30.7 21.4 12.0 25.6 44.4 64.1 58.1
8 65.8 50.4 57.2 37.6 39.3 31.6 17.9 8.5 25.6 35.9 55.5 56.4
9 64.1 58.1 57.2 43.6 41.8 37.6 15.4 12.0 22.2 43.6 66.6 63.2
10 58.9 58.1 51.2 43.6 38.4 32.5 20.5 11.1 27.3 46.1 64.1 63.2
11 58.1 52.1 57.2 50.4 41.8 35.9 21.4 11.1 22.2 36.7 60.6 63.2
12 62.3 50.4 57.2 48.7 29.9 35.0 14.5 12.0 22.2 38.4 61.5 56.4
13 66.6 57.2 54.7 49.5 36.7 40.1 17.9 17.1 28.2 44.4 62.3 56.4
14 61.5 61.5 49.5 46.1 35.0 31.6 16.2 16.2 34.2 44.4 54.7 62.3
15 58.1 62.3 53.8 48.7 33.3 23.1 15.4 21.4 23.1 41.0 69.2 61.5
16 64.1 64.1 54.7 47.8 41.8 34.2 19.6 18.8 30.7 44.4 62.3 58.1
17 62.3 59.8 55.5 44.4 40.1 28.2 12.8 19.6 29.0 42.7 59.8 55.5
18 59.8 45.3 48.7 49.5 37.6 30.7 11.1 23.1 30.7 38.4 52.9 55.5
19 47.8 52.1 55.5 50.4 40.1 29.0 12.8 16.2 31.6 44.4 74.3 62.3
20 59.8 57.2 54.7 39.3 29.9 30.7 9.4 13.7 32.5 44.4 56.4 58.1
21 56.4 50.4 53.8 40.1 35.0 25.6 9.4 16.2 24.8 41.0 53.8 64.9
22 55.5 56.4 55.5 43.6 30.7 29.0 9.4 20.5 27.3 44.4 52.1 58.1
23 61.5 56.4 60.6 40.1 29.0 26.5 11.1 18.8 23.9 41.0 64.1 59.8
24 63.2 55.5 53.8 38.4 35.9 29.9 9.4 19.6 26.5 47.0 63.2 58.1
25 58.1 52.1 50.4 35.9 41.8 22.2 12.8 25.6 30.7 44.4 58.9 57.2
26 53.8 48.7 47.0 33.3 41.0 25.6 13.7 21.4 33.3 44.4 51.2 52.9
27 52.9 58.1 50.4 40.1 41.0 30.7 9.4 23.1 28.2 46.1 54.7 62.3
28 58.9 56.4 55.5 43.6 37.6 29.0 9.4 21.4 29.0 48.7 52.1 62.3
29 56.4 0.0 55.5 44.4 32.5 27.3 9.4 24.8 32.5 52.9 65.8 67.5
30 56.4 0.0 48.7 34.2 33.3 25.6 7.7 20.5 35.9 52.1 66.6 54.7
31 53.8 0.0 50.4 0.0 33.3 0.0 10.2 26.5 0.0 53.8 0.0 56.4