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 2024-01-16.

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%
24571
20%
74517
16%
24514
61%
24514
28%
47325

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
41%
759
23%
2459
15%
757
53%
757
26%
1488
January11th to 20thNight
46%
744
26%
2417
19%
744
58%
744
30%
1387
January21st to endNight
35%
792
23%
2559
13%
792
48%
792
24%
1617
February1st to 10thNight
41%
720
22%
2160
15%
720
50%
720
27%
1372
February11th to 20thNight
42%
700
23%
2098
12%
699
53%
699
32%
1227
February21st to endNight
44%
592
28%
1664
18%
592
53%
592
35%
997
March1st to 10thNight
48%
720
31%
1980
19%
720
58%
720
44%
1088
March11th to 20thNight
48%
720
26%
1980
17%
720
55%
720
36%
1180
March21st to endNight
47%
792
26%
2178
16%
792
55%
792
37%
1289
April1st to 10thNight
46%
720
24%
1980
16%
720
53%
720
38%
1148
April11th to 20thNight
46%
711
22%
1890
15%
711
50%
711
34%
1175
April21st to endNight
57%
720
28%
1800
17%
720
61%
720
43%
1075
May1st to 10thNight
66%
606
28%
1686
20%
606
71%
606
46%
914
May11th to 20thNight
68%
531
17%
1592
13%
531
70%
531
32%
967
May21st to endNight
71%
582
19%
1744
16%
582
72%
582
30%
1111
June1st to 10thNight
63%
540
13%
1620
10%
540
64%
540
22%
1131
June11th to 20thNight
70%
540
13%
1620
11%
540
71%
540
24%
1103
June21st to endNight
70%
540
9%
1620
7%
540
70%
540
23%
1138
July1st to 10thNight
69%
525
7%
1575
6%
525
69%
525
20%
1158
July11th to 20thNight
72%
522
7%
1566
6%
522
72%
522
20%
1138
July21st to endNight
74%
591
10%
1672
10%
558
75%
558
23%
1178
August1st to 10thNight
76%
537
7%
1600
7%
534
76%
534
23%
1125
August11th to 20thNight
75%
570
9%
1634
8%
570
75%
570
25%
1140
August21st to endNight
61%
792
10%
2165
9%
792
61%
792
19%
1609
September1st to 10thNight
66%
720
10%
1980
9%
720
66%
720
18%
1464
September11th to 20thNight
61%
720
8%
1980
8%
720
61%
720
18%
1488
September21st to endNight
64%
720
16%
1980
17%
720
64%
720
23%
1398
October1st to 10thNight
58%
720
20%
2022
19%
720
61%
720
25%
1368
October11th to 20thNight
68%
720
29%
2160
30%
720
72%
720
37%
1231
October21st to endNight
63%
792
27%
2376
25%
792
68%
792
34%
1402
November1st to 10thNight
55%
740
24%
2221
20%
740
61%
740
31%
1355
November11th to 20thNight
54%
760
26%
2280
22%
760
60%
760
29%
1401
November21st to endNight
47%
760
23%
2379
18%
760
56%
760
27%
1487
December1st to 10thNight
52%
760
26%
2470
21%
760
62%
760
30%
1436
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
10%6%37%7%46%6%7%9%37%
74922
Night
9%5%35%5%35%5%6%9%44%
74890
TransparencyDay
41%10%14%17%13%5%
74645
Night
36%9%16%20%14%5%
74686
SeeingDay
9%7%21%26%21%16%
14447
Night
10%5%20%33%26%7%
24580

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
12%5%25%435%5%5%8%45%
1706
11th to 20thDay
9%5%25%6%345%5%9%47%
1671
21st to endDay
12%6%36%5%25%5%5%8%43%
1794
February1st to 10thDay
14%7%35%5%35%5%6%8%40%
1800
11th to 20thDay
8%436%5%34447%53%
1748
21st to endDay
10%6%35%445%6%5%7%44%
1589
March1st to 10thDay
5%425%5%35%448%54%
1980
11th to 20thDay
9%426%5%45%5%6%8%47%
1980
21st to endDay
9%5%25%6%35%45%6%49%
2178
April1st to 10thDay
7%426%5%36%5%6%8%48%
1980
11th to 20thDay
11%435%6%47%7%7%9%37%
2016
21st to endDay
6%425%4345%7%9%51%
2160
May1st to 10thDay
6%424435%5%6%9%52%
2287
11th to 20thDay
10%426%6%37%7%6%9%39%
2301
21st to endDay
8%6%26%7%5%7%8%8%8%35%
2531
June1st to 10thDay
13%6%38%8%5%8%6%7%10%24%
2340
11th to 20thDay
7%5%38%9%6%9%8%7%9%28%
2340
21st to endDay
10%6%38%8%5%7%8%8%9%28%
2340
July1st to 10thDay
10%7%38%9%5%9%8%8%9%24%
2340
11th to 20thDay
8%7%48%10%7%8%8%7%10%23%
2340
21st to endDay
8%6%49%9%6%8%7%9%9%24%
2547
August1st to 10thDay
7%5%39%9%6%8%8%9%12%24%
2327
11th to 20thDay
7%6%37%9%7%8%9%9%12%23%
2246
21st to endDay
12%8%39%8%5%9%7%7%10%22%
2185
September1st to 10thDay
8%6%38%9%6%9%9%10%9%22%
1980
11th to 20thDay
11%7%38%9%7%8%7%8%9%22%
1980
21st to endDay
12%6%39%8%47%8%7%7%29%
1980
October1st to 10thDay
13%6%37%7%5%6%7%5%7%33%
1936
11th to 20thDay
8%426%6%45%6%7%8%45%
1800
21st to endDay
8%5%26%5%45%6%6%7%46%
1980
November1st to 10thDay
8%436%7%37%5%6%7%43%
1857
11th to 20thDay
11%6%37%6%35%6%6%7%40%
1900
21st to endDay
13%6%27%4445%6%7%43%
1796
December1st to 10thDay
9%5%26%5%35%5%7%10%45%
1710
11th to 20thDay
13%7%37%7%35%5%6%7%39%
2153
21st to endDay
13%8%36%6%45%5%5%6%40%
3124
January1st to 10thNight
13%5%35%43446%7%46%
2459
11th to 20thNight
9%5%25%43446%8%48%
2417
21st to endNight
14%6%36%5%25%46%7%43%
2559
February1st to 10thNight
12%7%346%35%45%7%44%
2160
11th to 20thNight
9%5%25%5%3446%7%51%
2098
21st to endNight
8%435%5%35%35%8%51%
1664
March1st to 10thNight
4325%42345%7%60%
1980
11th to 20thNight
9%4234346%5%9%50%
1980
21st to endNight
8%425%5%3445%6%55%
2178
April1st to 10thNight
9%32442446%8%54%
1980
11th to 20thNight
8%5%36%5%345%5%8%49%
1890
21st to endNight
6%414435%5%5%9%55%
1800
May1st to 10thNight
5%212325%45%8%61%
1686
11th to 20thNight
6%425%445%6%6%10%48%
1592
21st to endNight
7%425%6%37%6%7%10%44%
1744
June1st to 10thNight
11%5%26%6%36%6%8%12%34%
1620
11th to 20thNight
5%5%37%6%47%7%9%12%35%
1620
21st to endNight
7%6%47%7%46%7%8%11%34%
1620
July1st to 10thNight
8%6%37%7%47%6%7%12%33%
1620
11th to 20thNight
5%6%47%7%48%8%8%10%33%
1620
21st to endNight
6%5%27%7%5%7%7%7%11%35%
1771
August1st to 10thNight
6%5%37%7%46%6%10%13%34%
1611
11th to 20thNight
6%437%8%46%6%9%14%35%
1634
21st to endNight
10%7%37%7%45%7%8%11%31%
2165
September1st to 10thNight
9%6%36%7%46%7%10%12%31%
1980
11th to 20thNight
10%7%46%8%47%8%7%10%28%
1980
21st to endNight
11%6%27%6%46%7%7%9%36%
1980
October1st to 10thNight
10%6%36%6%35%6%6%9%39%
2022
11th to 20thNight
6%425%4245%6%9%53%
2160
21st to endNight
9%5%25%435%5%5%7%51%
2376
November1st to 10thNight
10%5%25%5%35%5%6%6%48%
2221
11th to 20thNight
9%6%36%5%445%5%8%45%
2280
21st to endNight
10%5%36%6%35%6%7%8%42%
2379
December1st to 10thNight
8%425%6%345%6%9%48%
2470
11th to 20thNight
14%6%25%5%34445%49%
3042
21st to endNight
15%8%36%6%345%6%7%38%
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
37%7%11%17%19%10%
1707
11th to 20thDay
34%6%7%22%22%8%
1671
21st to endDay
39%6%10%16%19%10%
1794
February1st to 10thDay
41%8%10%14%20%9%
1800
11th to 20thDay
32%49%20%23%12%
1758
21st to endDay
38%6%11%15%21%9%
1589
March1st to 10thDay
29%5%11%23%24%8%
1980
11th to 20thDay
34%7%13%22%15%9%
1980
21st to endDay
34%7%10%20%19%9%
2178
April1st to 10thDay
32%8%14%21%18%8%
1980
11th to 20thDay
39%9%10%19%17%5%
2016
21st to endDay
28%7%14%23%21%8%
2160
May1st to 10thDay
27%6%12%21%24%9%
2287
11th to 20thDay
38%9%17%20%13%3
2305
21st to endDay
41%10%14%18%15%2
2531
June1st to 10thDay
51%12%17%15%5%
2340
11th to 20thDay
48%13%19%19%2
2340
21st to endDay
48%13%21%14%4
2340
July1st to 10thDay
51%17%18%12%2
2275
11th to 20thDay
53%14%20%12%1
2271
21st to endDay
48%15%21%14%2
2405
August1st to 10thDay
46%17%25%11%1
2314
11th to 20thDay
46%18%24%11%1
2246
21st to endDay
53%14%19%12%2
2185
September1st to 10thDay
50%18%18%10%4
1980
11th to 20thDay
53%14%17%12%3
1980
21st to endDay
48%12%14%14%10%3
1980
October1st to 10thDay
47%9%10%14%13%8%
1936
11th to 20thDay
34%7%11%22%21%6%
1800
21st to endDay
34%7%10%17%23%10%
1980
November1st to 10thDay
36%8%13%16%19%8%
1857
11th to 20thDay
42%7%9%17%19%7%
1900
21st to endDay
40%7%9%20%19%6%
1796
December1st to 10thDay
34%7%14%24%15%5%
1710
11th to 20thDay
42%7%9%14%18%9%
2150
21st to endDay
44%6%10%18%15%7%
3124
January1st to 10thNight
37%6%10%18%20%9%
2459
11th to 20thNight
33%5%10%23%21%8%
2417
21st to endNight
41%5%9%18%18%9%
2559
February1st to 10thNight
39%6%10%16%16%13%
2160
11th to 20thNight
32%6%12%20%20%11%
2099
21st to endNight
31%6%14%19%22%8%
1664
March1st to 10thNight
23%6%14%27%22%8%
1980
11th to 20thNight
30%7%15%24%15%8%
1980
21st to endNight
29%7%12%26%18%9%
2178
April1st to 10thNight
27%7%18%23%15%9%
1980
11th to 20thNight
33%6%11%26%18%6%
1890
21st to endNight
26%7%13%27%20%7%
1800
May1st to 10thNight
22%7%14%26%24%7%
1686
11th to 20thNight
31%10%21%24%12%2
1593
21st to endNight
34%10%16%22%17%1
1745
June1st to 10thNight
41%13%20%22%4
1620
11th to 20thNight
37%15%23%23%3
1620
21st to endNight
40%14%23%16%6%1
1620
July1st to 10thNight
43%15%26%13%2
1575
11th to 20thNight
42%16%29%12%2
1566
21st to endNight
38%16%28%16%1
1672
August1st to 10thNight
37%16%34%12%1
1600
11th to 20thNight
35%17%32%14%2
1634
21st to endNight
45%15%23%15%2
2165
September1st to 10thNight
42%18%21%14%5%
1980
11th to 20thNight
46%15%19%15%4
1980
21st to endNight
42%12%17%18%9%2
1980
October1st to 10thNight
39%11%13%18%12%7%
2022
11th to 20thNight
28%7%10%28%22%5%
2160
21st to endNight
32%7%12%18%22%10%
2376
November1st to 10thNight
34%8%13%19%18%9%
2221
11th to 20thNight
36%7%11%19%19%8%
2280
21st to endNight
37%7%12%20%18%6%
2379
December1st to 10thNight
32%7%16%27%12%6%
2470
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
9%14%39%26%9%4
257
21st to endDay
19%19%46%12%4
264
February1st to 10thDay
13%18%40%19%9%2
240
11th to 20thDay
8%13%40%27%10%2
240
21st to endDay
9%13%35%25%17%1
307
March1st to 10thDay
5%14%38%30%13%1
420
11th to 20thDay
10%15%29%26%17%3
420
21st to endDay
9%12%30%29%17%3
462
April1st to 10thDay
9%13%32%28%14%4
420
11th to 20thDay
12%11%31%25%16%6%
412
21st to endDay
8%8%27%29%17%11%
420
May1st to 10thDay
6%9%25%28%21%11%
423
11th to 20thDay
9%319%31%22%15%
447
21st to endDay
8%311%26%32%20%
485
June1st to 10thDay
11%414%28%22%20%
450
11th to 20thDay
7%311%26%25%28%
450
21st to endDay
5%39%20%28%35%
450
July1st to 10thDay
9%2414%30%42%
445
11th to 20thDay
5%1416%34%40%
444
21st to endDay
8%16%21%32%33%
488
August1st to 10thDay
7%28%17%31%35%
446
11th to 20thDay
5%1316%32%43%
439
21st to endDay
9%36%22%28%32%
495
September1st to 10thDay
11%36%20%30%31%
450
11th to 20thDay
10%411%24%28%23%
450
21st to endDay
8%411%25%28%24%
450
October1st to 10thDay
15%5%24%29%19%8%
450
11th to 20thDay
5%6%18%38%26%8%
450
21st to endDay
8%5%24%34%23%6%
495
November1st to 10thDay
10%8%25%29%24%4
455
11th to 20thDay
12%9%27%32%15%4
460
21st to endDay
12%9%33%32%12%2
356
December1st to 10thDay
7%12%39%27%12%3
270
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
12%8%28%37%14%1
744
21st to endNight
15%10%35%31%8%
792
February1st to 10thNight
15%7%32%33%13%1
720
11th to 20thNight
11%8%33%38%10%1
703
21st to endNight
9%8%34%41%8%
592
March1st to 10thNight
5%9%35%39%11%
720
11th to 20thNight
9%7%30%37%15%1
720
21st to endNight
8%7%33%39%13%1
792
April1st to 10thNight
9%9%31%38%14%
720
11th to 20thNight
9%7%32%34%17%1
711
21st to endNight
7%427%43%18%1
720
May1st to 10thNight
6%318%50%23%1
606
11th to 20thNight
7%115%40%33%3
531
21st to endNight
8%210%34%40%6%
584
June1st to 10thNight
12%210%31%40%6%
540
11th to 20thNight
6%27%24%42%19%
540
21st to endNight
8%2423%45%18%
540
July1st to 10thNight
9%2416%46%24%
525
11th to 20thNight
5%1315%48%28%
522
21st to endNight
5%2419%49%21%
591
August1st to 10thNight
6%319%51%20%
537
11th to 20thNight
5%1215%51%25%
570
21st to endNight
13%27%18%42%18%
792
September1st to 10thNight
10%36%22%41%20%
720
11th to 20thNight
12%38%27%39%12%
720
21st to endNight
13%27%26%42%11%
720
October1st to 10thNight
12%415%36%28%5%
720
11th to 20thNight
6%313%37%37%5%
720
21st to endNight
11%316%39%27%4
792
November1st to 10thNight
10%422%37%24%2
740
11th to 20thNight
10%6%22%41%20%2
760
21st to endNight
11%428%41%14%1
760
December1st to 10thNight
9%426%36%23%2
760
11th to 20thNight
13%7%25%36%18%1
760
21st to endNight
13%7%25%36%17%1
836
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