Redding Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Redding Observatory clear sky chart from 2005-11-06 to 2024-12-09.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
56%
25593
17%
99447
15%
25361
61%
25361
22%
61415

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
40%
754
21%
4018
15%
737
53%
737
16%
2360
January11th to 20thNight
45%
755
20%
4058
19%
740
58%
740
16%
2629
January21st to endNight
34%
829
16%
4416
13%
814
47%
814
15%
2581
February1st to 10thNight
41%
760
23%
2280
15%
760
50%
760
27%
1440
February11th to 20thNight
41%
740
22%
2218
12%
739
52%
739
31%
1320
February21st to endNight
44%
628
26%
1765
17%
628
53%
628
37%
1042
March1st to 10thNight
46%
759
19%
3416
19%
745
56%
745
21%
2285
March11th to 20thNight
47%
750
24%
3436
17%
740
54%
740
26%
1663
March21st to endNight
46%
828
18%
3737
16%
814
54%
814
22%
2166
April1st to 10thNight
46%
760
24%
2090
16%
760
52%
760
37%
1211
April11th to 20thNight
46%
751
22%
1996
15%
751
51%
751
35%
1225
April21st to endNight
56%
760
27%
1900
16%
760
60%
760
43%
1128
May1st to 10thNight
66%
629
29%
2891
19%
628
70%
628
34%
1271
May11th to 20thNight
66%
554
13%
2768
13%
541
69%
541
21%
1531
May21st to endNight
71%
595
17%
3023
15%
593
72%
593
28%
1238
June1st to 10thNight
64%
570
14%
1710
10%
570
66%
570
23%
1173
June11th to 20thNight
69%
570
13%
1710
11%
570
69%
570
24%
1170
June21st to endNight
69%
570
9%
1710
7%
570
69%
570
22%
1212
July1st to 10thNight
69%
537
7%
2698
7%
535
69%
535
13%
1778
July11th to 20thNight
72%
534
4%
2784
6%
533
72%
533
12%
1861
July21st to endNight
72%
605
6%
2977
10%
569
74%
569
13%
2037
August1st to 10thNight
74%
555
7%
2774
7%
545
76%
545
15%
1765
August11th to 20thNight
74%
582
6%
2628
8%
581
75%
581
18%
1596
August21st to endNight
61%
814
8%
3668
9%
814
61%
814
13%
2381
September1st to 10thNight
64%
760
9%
2090
8%
760
64%
760
18%
1563
September11th to 20thNight
60%
760
8%
2090
8%
760
61%
760
18%
1573
September21st to endNight
64%
760
17%
2090
17%
760
65%
760
24%
1455
October1st to 10thNight
57%
760
12%
3441
18%
740
60%
740
13%
2631
October11th to 20thNight
67%
760
22%
2821
29%
740
71%
740
26%
1774
October21st to endNight
63%
836
21%
3007
26%
814
69%
814
26%
1903
November1st to 10thNight
55%
780
24%
2341
20%
780
62%
780
31%
1427
November11th to 20thNight
54%
800
25%
2400
21%
800
60%
800
29%
1475
November21st to endNight
48%
800
24%
2505
19%
800
57%
800
29%
1537
December1st to 10thNight
51%
795
28%
2581
21%
795
63%
795
31%
1474
December11th to 20thNight
48%
759
23%
2950
21%
758
55%
758
23%
1751
December21st to endNight
48%
834
15%
4460
20%
817
56%
817
15%
2789

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
9%6%27%6%6%6%5%7%9%37%
101230
Night
9%6%26%5%5%5%47%9%42%
98486
TransparencyDay
39%10%16%18%12%4
104971
Night
36%9%17%19%13%5%
102885
SeeingDay
9%7%22%25%21%15%
15705
Night
10%5%20%33%26%7%
25784

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
13%7%27%5%45%45%6%43%
2836
11th to 20thDay
21%9%46%5%35%35%6%33%
2840
21st to endDay
12%7%27%445%45%7%44%
3136
February1st to 10thDay
13%7%26%445%46%7%40%
1900
11th to 20thDay
9%5%27%443346%52%
1848
21st to endDay
10%6%26%45%5%5%6%6%45%
1686
March1st to 10thDay
8%8%39%6%5%5%46%10%36%
3435
11th to 20thDay
6%426%44447%9%50%
3480
21st to endDay
11%6%26%5%4446%6%46%
3815
April1st to 10thDay
7%426%45%6%46%9%47%
2090
11th to 20thDay
10%5%26%6%5%6%5%8%8%39%
2130
21st to endDay
6%416%44447%8%51%
2280
May1st to 10thDay
432445%5%47%10%53%
4002
11th to 20thDay
11%5%28%5%6%6%5%7%9%36%
4081
21st to endDay
5%415%5%5%5%5%7%10%49%
4476
June1st to 10thDay
12%7%39%6%8%7%5%7%10%25%
2470
11th to 20thDay
7%6%39%8%8%9%7%8%9%28%
2470
21st to endDay
10%7%310%7%6%7%6%8%9%27%
2470
July1st to 10thDay
7%6%38%7%7%8%7%11%12%24%
4120
11th to 20thDay
5%5%38%8%7%7%6%10%15%25%
4120
21st to endDay
5%6%39%8%8%8%7%10%13%25%
4466
August1st to 10thDay
7%7%39%6%7%7%6%9%12%26%
4104
11th to 20thDay
4427%6%7%7%7%9%14%33%
3931
21st to endDay
8%6%310%7%8%8%7%9%12%23%
3835
September1st to 10thDay
8%7%310%8%8%8%7%10%9%21%
2090
11th to 20thDay
11%8%310%8%8%7%6%8%9%21%
2090
21st to endDay
12%6%310%7%7%7%5%7%7%30%
2090
October1st to 10thDay
15%6%38%6%6%6%5%5%8%32%
2043
11th to 20thDay
7%5%26%5%5%5%5%7%7%46%
1900
21st to endDay
8%5%27%45%5%46%7%47%
2090
November1st to 10thDay
8%5%27%6%5%6%47%7%43%
1957
11th to 20thDay
11%6%28%6%5%5%5%6%7%40%
2000
21st to endDay
12%6%26%45%446%7%44%
1890
December1st to 10thDay
8%6%26%44446%9%46%
1782
11th to 20thDay
13%7%27%6%45%46%7%39%
2153
21st to endDay
12%8%37%5%5%5%45%6%40%
3124
January1st to 10thNight
14%7%36%5%5%445%7%42%
4109
11th to 20thNight
17%10%37%44436%7%35%
4120
21st to endNight
12%7%37%44436%7%42%
4503
February1st to 10thNight
11%8%25%5%5%5%36%7%45%
2280
11th to 20thNight
10%6%25%44436%7%49%
2218
21st to endNight
8%435%5%4435%7%53%
1765
March1st to 10thNight
16%9%48%434346%40%
3418
11th to 20thNight
6%415%445%47%11%48%
3480
21st to endNight
11%6%27%44435%6%47%
3817
April1st to 10thNight
8%425%33446%8%53%
2090
11th to 20thNight
8%5%26%5%3446%7%50%
1996
21st to endNight
6%41444445%9%55%
1900
May1st to 10thNight
421433446%9%59%
2919
11th to 20thNight
8%5%26%445%48%10%43%
2812
21st to endNight
431433436%9%60%
3079
June1st to 10thNight
11%5%27%5%5%6%5%8%12%35%
1710
11th to 20thNight
5%6%28%6%5%7%6%9%12%34%
1710
21st to endNight
7%7%38%6%6%6%6%8%10%34%
1710
July1st to 10thNight
6%7%38%6%6%7%6%9%12%31%
2840
11th to 20thNight
45%27%6%7%9%7%11%13%29%
2840
21st to endNight
6%7%39%7%7%7%6%9%13%26%
3087
August1st to 10thNight
5%5%39%6%6%6%5%9%13%34%
2825
11th to 20thNight
4327%6%5%6%5%9%15%39%
2849
21st to endNight
8%6%37%5%5%6%5%9%12%34%
3815
September1st to 10thNight
9%7%37%6%5%7%5%10%11%29%
2090
11th to 20thNight
10%8%37%7%6%7%6%8%10%28%
2090
21st to endNight
11%6%28%5%5%6%5%6%9%37%
2090
October1st to 10thNight
11%7%27%5%5%6%5%6%9%37%
2135
11th to 20thNight
5%426%43446%8%52%
2280
21st to endNight
8%5%25%45%445%7%51%
2508
November1st to 10thNight
9%5%26%6%4446%7%47%
2341
11th to 20thNight
9%6%36%5%5%446%8%45%
2400
21st to endNight
10%5%26%5%5%45%7%7%44%
2505
December1st to 10thNight
8%425%5%4446%9%49%
2581
11th to 20thNight
14%7%25%444345%49%
3042
21st to endNight
15%8%37%5%4446%6%37%
4532

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
41%6%8%16%21%9%
2837
11th to 20thDay
51%46%15%15%9%
2840
21st to endDay
38%7%9%18%18%10%
3136
February1st to 10thDay
40%7%10%14%20%9%
1900
11th to 20thDay
33%5%9%20%22%12%
1858
21st to endDay
37%6%10%15%22%10%
1686
March1st to 10thDay
41%9%12%19%14%5%
3435
11th to 20thDay
29%6%14%24%22%5%
3480
21st to endDay
36%6%11%26%14%8%
3815
April1st to 10thDay
32%8%14%21%18%9%
2090
11th to 20thDay
38%9%10%20%18%6%
2130
21st to endDay
28%7%14%22%22%8%
2280
May1st to 10thDay
21%9%19%29%17%5%
4039
11th to 20thDay
39%11%17%21%10%2
4085
21st to endDay
26%9%16%33%16%1
4489
June1st to 10thDay
49%12%18%16%5%
2470
11th to 20thDay
47%13%18%19%2
2470
21st to endDay
48%14%21%13%3
2470
July1st to 10thDay
43%17%25%13%1
4055
11th to 20thDay
42%18%33%7%
4051
21st to endDay
42%18%29%9%1
4324
August1st to 10thDay
44%16%28%10%2
4091
11th to 20thDay
34%17%24%20%5%
3970
21st to endDay
47%16%21%15%1
3835
September1st to 10thDay
51%18%17%10%4
2090
11th to 20thDay
53%14%17%12%3
2090
21st to endDay
47%11%14%14%10%3
2090
October1st to 10thDay
55%9%13%11%7%4
3394
11th to 20thDay
29%6%9%21%27%7%
3140
21st to endDay
26%6%7%23%32%6%
3428
November1st to 10thDay
36%8%13%17%19%8%
1957
11th to 20thDay
41%7%9%18%19%8%
2000
21st to endDay
38%6%9%20%19%7%
1890
December1st to 10thDay
33%7%14%24%16%6%
1782
11th to 20thDay
42%7%9%14%18%9%
2150
21st to endDay
44%6%10%18%15%7%
3124
January1st to 10thNight
42%6%8%16%21%8%
4109
11th to 20thNight
48%5%8%20%14%5%
4120
21st to endNight
40%7%11%16%16%10%
4503
February1st to 10thNight
38%6%10%17%16%13%
2280
11th to 20thNight
33%7%12%19%20%11%
2219
21st to endNight
30%6%14%19%22%9%
1765
March1st to 10thNight
45%7%13%17%14%5%
3418
11th to 20thNight
27%8%19%26%15%5%
3480
21st to endNight
36%7%10%20%21%6%
3817
April1st to 10thNight
27%7%18%23%15%9%
2090
11th to 20thNight
32%6%12%26%18%7%
1996
21st to endNight
26%7%14%27%20%7%
1900
May1st to 10thNight
18%10%21%32%15%4
2948
11th to 20thNight
32%11%23%24%9%1
2813
21st to endNight
21%8%17%36%18%1
3087
June1st to 10thNight
39%13%21%22%4
1710
11th to 20thNight
37%15%23%23%3
1710
21st to endNight
41%13%23%15%6%1
1710
July1st to 10thNight
39%16%29%15%1
2795
11th to 20thNight
38%20%34%7%1
2786
21st to endNight
44%15%30%10%1
2988
August1st to 10thNight
39%14%35%11%1
2814
11th to 20thNight
30%15%29%21%6%
2876
21st to endNight
40%14%28%16%2
3815
September1st to 10thNight
44%17%20%13%5%
2090
11th to 20thNight
46%15%19%15%4
2090
21st to endNight
41%11%17%20%9%2
2090
October1st to 10thNight
54%10%12%13%7%4
3564
11th to 20thNight
28%6%9%24%29%5%
3779
21st to endNight
28%6%10%22%28%6%
4120
November1st to 10thNight
34%8%13%20%18%9%
2341
11th to 20thNight
36%7%11%19%20%8%
2400
21st to endNight
36%7%12%19%19%7%
2505
December1st to 10thNight
31%7%16%27%13%6%
2581
11th to 20thNight
38%5%10%19%19%9%
3044
21st to endNight
44%7%12%18%14%5%
4532

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
15%13%47%19%5%1
270
11th to 20thDay
10%14%39%26%8%3
270
21st to endDay
18%21%46%11%4
297
February1st to 10thDay
14%17%40%19%8%2
270
11th to 20thDay
10%16%40%24%9%1
270
21st to endDay
9%14%36%25%15%1
341
March1st to 10thDay
6%15%38%28%12%1
460
11th to 20thDay
10%15%31%27%16%3
460
21st to endDay
10%13%31%27%16%2
506
April1st to 10thDay
9%13%34%27%13%4
460
11th to 20thDay
12%11%31%25%16%5%
452
21st to endDay
7%9%27%29%17%11%
460
May1st to 10thDay
6%8%24%29%21%12%
463
11th to 20thDay
9%422%31%21%14%
487
21st to endDay
7%212%27%32%19%
529
June1st to 10thDay
11%413%30%22%20%
490
11th to 20thDay
8%313%25%24%26%
490
21st to endDay
6%310%19%29%33%
490
July1st to 10thDay
8%25%15%30%40%
485
11th to 20thDay
5%2416%32%41%
484
21st to endDay
7%25%20%31%35%
532
August1st to 10thDay
8%39%18%30%34%
486
11th to 20thDay
41417%31%42%
479
21st to endDay
9%37%23%27%32%
539
September1st to 10thDay
11%47%19%31%29%
490
11th to 20thDay
10%410%25%29%22%
490
21st to endDay
9%412%25%28%23%
490
October1st to 10thDay
17%5%22%28%20%8%
490
11th to 20thDay
5%6%20%37%24%7%
490
21st to endDay
8%5%25%36%21%5%
539
November1st to 10thDay
9%8%24%30%24%4
495
11th to 20thDay
12%9%27%32%15%4
500
21st to endDay
11%11%33%31%13%2
390
December1st to 10thDay
7%12%41%27%12%2
294
11th to 20thDay
12%14%36%26%12%1
270
21st to endDay
10%12%30%38%8%2
297
January1st to 10thNight
14%9%31%34%11%1
760
11th to 20thNight
11%9%28%36%14%1
760
21st to endNight
15%11%35%31%8%
836
February1st to 10thNight
15%7%32%33%12%1
760
11th to 20thNight
11%8%33%37%10%1
743
21st to endNight
9%7%35%41%7%
628
March1st to 10thNight
6%10%34%38%11%
760
11th to 20thNight
9%8%31%37%14%1
760
21st to endNight
8%7%33%38%13%1
836
April1st to 10thNight
9%9%31%38%13%
760
11th to 20thNight
9%8%32%34%16%1
751
21st to endNight
7%428%43%18%1
760
May1st to 10thNight
6%317%50%23%1
639
11th to 20thNight
7%216%40%32%3
561
21st to endNight
7%210%35%40%6%
617
June1st to 10thNight
11%210%31%41%6%
570
11th to 20thNight
6%28%25%41%18%
570
21st to endNight
8%2424%44%18%
570
July1st to 10thNight
9%2416%46%23%
555
11th to 20thNight
5%1314%49%28%
552
21st to endNight
5%2419%48%21%
624
August1st to 10thNight
7%1319%50%20%
567
11th to 20thNight
5%1215%51%26%
602
21st to endNight
12%27%19%42%18%
836
September1st to 10thNight
10%36%22%40%19%
760
11th to 20thNight
12%38%27%38%11%
760
21st to endNight
13%27%27%41%11%
760
October1st to 10thNight
14%414%36%27%5%
760
11th to 20thNight
6%314%37%35%4
760
21st to endNight
10%317%41%26%4
836
November1st to 10thNight
10%421%37%25%2
780
11th to 20thNight
10%6%22%41%20%2
800
21st to endNight
11%5%28%40%15%1
800
December1st to 10thNight
9%5%27%36%22%2
795
11th to 20thNight
13%7%25%36%18%1
760
21st to endNight
13%7%25%36%17%1
836
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