Bixby Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bixby Creek Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
50%
24197
26%
74288
19%
24137
58%
24137
35%
42478

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
35%
949
28%
2458
12%
946
45%
946
36%
1499
January11th to 20thNight
31%
910
27%
2366
11%
910
41%
910
34%
1475
January21st to endNight
36%
990
32%
2574
12%
990
47%
990
39%
1528
February1st to 10thNight
31%
900
22%
2340
7%
900
40%
900
31%
1518
February11th to 20thNight
28%
787
20%
2182
7%
783
37%
783
29%
1380
February21st to endNight
26%
512
27%
1696
12%
512
40%
512
25%
1008
March1st to 10thNight
36%
540
25%
1980
15%
540
47%
540
25%
1139
March11th to 20thNight
36%
540
22%
1980
16%
540
47%
540
24%
1166
March21st to endNight
33%
594
23%
2178
14%
594
47%
594
25%
1280
April1st to 10thNight
34%
540
23%
1950
16%
540
48%
540
27%
1088
April11th to 20thNight
39%
533
25%
1775
19%
533
52%
533
30%
1005
April21st to endNight
40%
540
24%
1725
16%
540
54%
540
31%
1017
May1st to 10thNight
49%
540
23%
1620
19%
540
57%
540
32%
964
May11th to 20thNight
54%
531
23%
1594
22%
531
60%
531
32%
961
May21st to endNight
57%
584
21%
1745
18%
582
63%
582
33%
1038
June1st to 10thNight
75%
540
24%
1620
24%
540
79%
540
44%
849
June11th to 20thNight
73%
540
25%
1620
25%
540
76%
540
47%
838
June21st to endNight
79%
540
29%
1620
28%
540
81%
540
55%
768
July1st to 10thNight
82%
525
21%
1575
24%
525
83%
525
42%
870
July11th to 20thNight
86%
522
27%
1566
32%
522
87%
522
56%
734
July21st to endNight
82%
591
27%
1673
33%
558
82%
558
46%
878
August1st to 10thNight
83%
537
26%
1601
29%
534
83%
534
44%
851
August11th to 20thNight
80%
534
31%
1600
35%
534
81%
534
42%
869
August21st to endNight
81%
594
28%
1952
33%
594
82%
594
42%
996
September1st to 10thNight
75%
540
28%
1890
33%
540
77%
540
38%
967
September11th to 20thNight
70%
540
27%
1980
30%
540
72%
540
32%
1069
September21st to endNight
67%
540
34%
1980
33%
540
73%
540
40%
951
October1st to 10thNight
67%
664
32%
2104
27%
664
71%
664
43%
1078
October11th to 20thNight
51%
720
33%
2160
20%
720
61%
720
41%
1171
October21st to endNight
46%
792
29%
2376
19%
792
54%
792
34%
1388
November1st to 10thNight
50%
740
33%
2220
19%
740
62%
740
43%
1182
November11th to 20thNight
44%
859
30%
2379
16%
859
54%
859
41%
1343
November21st to endNight
40%
950
29%
2470
15%
950
48%
950
36%
1522
December1st to 10thNight
36%
950
28%
2470
12%
950
47%
950
34%
1540
December11th to 20thNight
34%
949
28%
2884
13%
948
43%
948
27%
1809
December21st to endNight
33%
1040
17%
4385
11%
1026
44%
1026
19%
2739

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
12%6%25%5%3445%7%48%
74955
Night
11%5%2442345%7%53%
74793
TransparencyDay
36%6%10%24%20%5%
74679
Night
31%5%10%24%23%7%
74589
SeeingDay
13%7%22%28%24%8%
14234
Night
13%7%25%35%18%2
24204

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%8%36%424347%49%
1707
11th to 20thDay
12%8%36%424346%49%
1634
21st to endDay
15%7%24423336%51%
1782
February1st to 10thDay
18%9%36%5%3343443%
1620
11th to 20thDay
16%7%46%5%2435%7%43%
1680
21st to endDay
20%7%35%434345%41%
1558
March1st to 10thDay
15%7%25%424346%48%
1980
11th to 20thDay
18%7%36%5%2444443%
1980
21st to endDay
17%8%37%5%24447%38%
2178
April1st to 10thDay
12%425%5%35%45%7%47%
2008
11th to 20thDay
16%6%26%5%2445%6%45%
2134
21st to endDay
18%7%36%5%34445%42%
2232
May1st to 10thDay
14%7%36%5%345%46%43%
2340
11th to 20thDay
13%6%35%6%35%45%7%42%
2302
21st to endDay
11%5%35%6%46%5%6%10%39%
2531
June1st to 10thDay
8%5%35%5%445%6%9%46%
2340
11th to 20thDay
7%425%5%445%6%9%49%
2340
21st to endDay
43245%3446%8%58%
2340
July1st to 10thDay
7%4346%46%6%8%10%42%
2340
11th to 20thDay
4214435%5%6%10%57%
2340
21st to endDay
6%3245%35%6%7%11%48%
2546
August1st to 10thDay
43246%35%6%7%9%50%
2328
11th to 20thDay
9%5%345%35%46%8%49%
2301
21st to endDay
5%324435%6%7%9%52%
2401
September1st to 10thDay
10%5%2442446%7%53%
2066
11th to 20thDay
11%5%25%4345%6%7%48%
1980
21st to endDay
8%3235%35%5%6%5%57%
1980
October1st to 10thDay
8%425%424446%58%
1836
11th to 20thDay
11%424322335%61%
1800
21st to endDay
18%5%24322345%51%
1980
November1st to 10thDay
10%5%2333335%7%57%
1858
11th to 20thDay
11%5%23323236%60%
1797
21st to endDay
15%6%24323346%52%
1710
December1st to 10thDay
13%7%34424337%49%
1710
11th to 20thDay
15%8%35%434346%44%
2161
21st to endDay
18%11%47%5%34446%35%
3135
January1st to 10thNight
12%6%14423447%53%
2458
11th to 20thNight
14%7%24323336%52%
2366
21st to endNight
12%6%24313335%57%
2574
February1st to 10thNight
16%9%34333346%47%
2340
11th to 20thNight
15%7%36%422346%48%
2181
21st to endNight
15%7%26%5%23345%47%
1696
March1st to 10thNight
15%5%345%24445%48%
1980
11th to 20thNight
18%5%33424346%48%
1980
21st to endNight
14%6%25%42435%6%48%
2178
April1st to 10thNight
12%5%2443445%6%51%
1950
11th to 20thNight
12%5%2442345%7%52%
1775
21st to endNight
12%5%35%5%3335%7%49%
1725
May1st to 10thNight
11%5%23435%46%8%49%
1620
11th to 20thNight
11%5%245%335%6%8%48%
1593
21st to endNight
8%5%35%5%35%46%11%46%
1745
June1st to 10thNight
5%32443446%10%58%
1620
11th to 20thNight
5%32332347%9%59%
1620
21st to endNight
312332445%8%66%
1620
July1st to 10thNight
33145%35%6%7%12%51%
1620
11th to 20thNight
121242346%12%63%
1620
21st to endNight
4314435%46%10%57%
1772
August1st to 10thNight
2224435%7%6%9%57%
1611
11th to 20thNight
5%313425%6%8%9%55%
1600
21st to endNight
33234345%7%9%58%
1952
September1st to 10thNight
8%42332445%7%59%
1890
11th to 20thNight
10%425%425%5%5%7%51%
1980
21st to endNight
6%42432345%6%61%
1980
October1st to 10thNight
8%42332345%6%62%
2104
11th to 20thNight
13%42232333461%
2160
21st to endNight
17%5%24322335%55%
2376
November1st to 10thNight
10%423422245%62%
2220
11th to 20thNight
8%5%24423345%59%
2379
21st to endNight
15%5%23422345%54%
2470
December1st to 10thNight
13%6%24423446%51%
2470
11th to 20thNight
14%7%35%433445%49%
3036
21st to endNight
16%8%46%434445%43%
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%49%23%23%4
1708
11th to 20thDay
38%49%23%23%3
1634
21st to endDay
37%47%27%21%4
1782
February1st to 10thDay
47%310%20%16%3
1620
11th to 20thDay
43%39%22%18%5%
1689
21st to endDay
47%37%17%20%7%
1558
March1st to 10thDay
38%47%22%17%12%
1980
11th to 20thDay
45%48%22%15%6%
1980
21st to endDay
47%5%9%24%13%2
2178
April1st to 10thDay
36%6%11%22%18%5%
2008
11th to 20thDay
40%6%10%23%16%5%
2134
21st to endDay
45%6%8%22%17%2
2232
May1st to 10thDay
43%5%9%22%18%2
2340
11th to 20thDay
40%7%13%24%15%1
2306
21st to endDay
39%9%13%25%13%1
2531
June1st to 10thDay
33%7%15%28%15%3
2340
11th to 20thDay
31%7%15%27%18%3
2340
21st to endDay
24%7%13%29%23%5%
2340
July1st to 10thDay
32%10%16%25%16%1
2276
11th to 20thDay
22%7%14%30%23%4
2271
21st to endDay
28%8%17%32%15%1
2405
August1st to 10thDay
28%10%14%27%18%3
2314
11th to 20thDay
33%6%12%25%21%3
2301
21st to endDay
27%9%14%29%18%4
2401
September1st to 10thDay
30%6%9%24%23%9%
2066
11th to 20thDay
33%6%10%22%22%6%
1980
21st to endDay
27%6%9%21%29%8%
1980
October1st to 10thDay
28%6%10%21%27%9%
1836
11th to 20thDay
29%36%19%32%11%
1800
21st to endDay
37%48%23%19%9%
1980
November1st to 10thDay
27%49%26%28%7%
1858
11th to 20thDay
28%38%28%25%9%
1797
21st to endDay
34%49%20%27%6%
1710
December1st to 10thDay
37%49%27%20%3
1710
11th to 20thDay
43%35%21%23%5%
2159
21st to endDay
49%6%7%20%14%3
3135
January1st to 10thNight
33%49%24%25%5%
2458
11th to 20thNight
36%39%24%23%5%
2366
21st to endNight
31%36%27%26%7%
2574
February1st to 10thNight
40%311%24%17%5%
2340
11th to 20thNight
40%37%25%19%6%
2182
21st to endNight
40%38%18%22%9%
1696
March1st to 10thNight
38%48%18%20%12%
1980
11th to 20thNight
38%6%10%21%18%7%
1980
21st to endNight
37%5%9%25%18%4
2178
April1st to 10thNight
33%6%9%21%21%9%
1950
11th to 20thNight
32%6%9%25%18%10%
1775
21st to endNight
35%5%10%25%23%2
1725
May1st to 10thNight
34%6%12%24%20%5%
1620
11th to 20thNight
33%7%13%27%18%2
1594
21st to endNight
31%8%17%26%15%2
1746
June1st to 10thNight
22%6%15%31%21%3
1620
11th to 20thNight
21%6%13%32%24%4
1620
21st to endNight
16%5%13%30%29%7%
1620
July1st to 10thNight
23%9%16%27%23%2
1575
11th to 20thNight
15%5%15%34%25%6%
1566
21st to endNight
23%6%15%32%23%1
1673
August1st to 10thNight
21%9%15%31%22%3
1601
11th to 20thNight
24%7%13%24%28%4
1600
21st to endNight
22%8%13%28%24%6%
1952
September1st to 10thNight
25%7%8%26%22%11%
1890
11th to 20thNight
31%6%10%21%25%8%
1980
21st to endNight
23%5%8%24%31%9%
1980
October1st to 10thNight
24%5%11%23%26%11%
2104
11th to 20thNight
28%36%18%31%15%
2160
21st to endNight
34%36%21%24%12%
2376
November1st to 10thNight
26%38%24%28%10%
2220
11th to 20thNight
28%38%24%27%10%
2379
21st to endNight
35%37%21%28%7%
2470
December1st to 10thNight
35%5%10%22%22%7%
2470
11th to 20thNight
39%37%21%24%6%
3037
21st to endNight
42%5%8%22%17%6%
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
18%14%33%27%7%1
270
11th to 20thDay
19%15%38%23%4
245
21st to endDay
16%14%39%23%8%
264
February1st to 10thDay
26%14%33%22%5%
240
11th to 20thDay
23%16%40%17%3
240
21st to endDay
31%16%34%16%3
198
March1st to 10thDay
20%16%33%23%8%
240
11th to 20thDay
23%18%32%22%6%
240
21st to endDay
25%14%39%16%5%1
264
April1st to 10thDay
12%13%42%23%8%2
268
11th to 20thDay
20%13%33%27%6%1
412
21st to endDay
20%13%32%24%10%2
492
May1st to 10thDay
14%8%33%32%12%
603
11th to 20thDay
15%426%33%16%5%
625
21st to endDay
14%425%31%21%6%
679
June1st to 10thDay
9%312%30%35%10%
630
11th to 20thDay
7%213%37%33%8%
630
21st to endDay
3215%37%33%10%
630
July1st to 10thDay
8%110%26%37%18%
621
11th to 20thDay
316%31%43%15%
618
21st to endDay
5%25%25%44%19%
684
August1st to 10thDay
5%27%32%45%9%
626
11th to 20thDay
10%27%30%41%11%
615
21st to endDay
5%1423%47%20%
520
September1st to 10thDay
8%25%20%42%24%
356
11th to 20thDay
46%34%36%20%
270
21st to endDay
10%314%26%30%16%
270
October1st to 10thDay
6%5%23%31%23%12%
270
11th to 20thDay
10%9%29%34%17%1
270
21st to endDay
25%11%23%28%11%3
297
November1st to 10thDay
15%6%32%31%13%3
270
11th to 20thDay
15%9%34%27%14%1
270
21st to endDay
21%13%30%27%8%1
270
December1st to 10thDay
16%11%35%25%11%2
270
11th to 20thDay
23%11%35%25%6%
270
21st to endDay
18%17%38%23%5%
297
January1st to 10thNight
17%10%35%31%7%1
950
11th to 20thNight
18%12%35%29%5%
910
21st to endNight
15%9%37%34%4
990
February1st to 10thNight
21%12%33%30%4
900
11th to 20thNight
20%11%38%28%3
787
21st to endNight
20%12%38%28%3
512
March1st to 10thNight
17%9%34%35%4
540
11th to 20thNight
21%9%31%34%5%
540
21st to endNight
15%9%39%29%7%1
594
April1st to 10thNight
14%9%37%33%7%
540
11th to 20thNight
14%10%33%33%10%
533
21st to endNight
16%8%33%33%9%1
540
May1st to 10thNight
12%6%29%43%10%
540
11th to 20thNight
13%5%22%41%16%2
531
21st to endNight
9%323%39%24%2
584
June1st to 10thNight
5%211%43%36%3
540
11th to 20thNight
6%213%53%25%2
540
21st to endNight
2212%44%36%4
540
July1st to 10thNight
415%39%44%6%
525
11th to 20thNight
216%37%50%5%
522
21st to endNight
5%1338%47%6%
591
August1st to 10thNight
215%41%45%4
537
11th to 20thNight
6%16%39%44%4
534
21st to endNight
426%36%47%6%
594
September1st to 10thNight
10%18%36%43%3
540
11th to 20thNight
11%28%38%36%4
540
21st to endNight
9%216%35%33%5%
540
October1st to 10thNight
9%217%39%30%4
664
11th to 20thNight
15%426%40%14%1
720
21st to endNight
18%7%26%33%15%1
792
November1st to 10thNight
13%429%39%13%1
740
11th to 20thNight
10%10%32%35%11%
859
21st to endNight
19%9%30%34%9%
950
December1st to 10thNight
17%9%33%34%7%
950
11th to 20thNight
22%7%32%33%5%
950
21st to endNight
18%11%35%31%6%
1045
Page generated at 2024-01-09 15:24:23. Version ac07

Copyright 2024 Attilla Danko


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