Bishop Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bishop 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
65%
23662
34%
74485
26%
23625
75%
23625
59%
32441

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
54%
756
28%
2646
20%
756
68%
756
48%
1156
January11th to 20thNight
57%
728
30%
2526
21%
728
72%
728
57%
1029
January21st to endNight
57%
792
34%
2574
26%
792
69%
792
47%
1228
February1st to 10thNight
56%
720
34%
2168
25%
720
69%
720
55%
994
February11th to 20thNight
56%
700
35%
2098
26%
700
70%
700
54%
980
February21st to endNight
48%
592
33%
1776
22%
592
65%
592
55%
827
March1st to 10thNight
51%
720
30%
2160
20%
720
66%
720
55%
1004
March11th to 20thNight
58%
720
28%
2105
19%
720
70%
720
56%
992
March21st to endNight
49%
792
32%
1980
12%
792
64%
792
56%
1041
April1st to 10thNight
53%
720
31%
1800
13%
720
63%
720
54%
971
April11th to 20thNight
54%
711
34%
1779
13%
711
64%
711
61%
884
April21st to endNight
57%
720
32%
1800
13%
720
64%
720
66%
877
May1st to 10thNight
53%
576
31%
1656
18%
576
60%
576
53%
791
May11th to 20thNight
61%
531
33%
1595
23%
531
68%
531
59%
704
May21st to endNight
59%
467
28%
1631
21%
467
69%
467
47%
705
June1st to 10thNight
75%
360
33%
1440
34%
360
84%
360
53%
547
June11th to 20thNight
76%
360
36%
1440
38%
360
85%
360
67%
471
June21st to endNight
78%
360
37%
1440
39%
360
89%
360
72%
451
July1st to 10thNight
88%
350
36%
1400
42%
350
93%
350
69%
459
July11th to 20thNight
88%
348
34%
1392
40%
348
91%
348
58%
502
July21st to endNight
89%
422
36%
1515
41%
399
89%
399
51%
624
August1st to 10thNight
79%
716
34%
1780
22%
712
81%
712
66%
878
August11th to 20thNight
85%
712
38%
1780
22%
712
88%
712
78%
811
August21st to endNight
86%
792
42%
1980
27%
792
87%
792
80%
893
September1st to 10thNight
84%
720
44%
1800
29%
720
88%
720
82%
788
September11th to 20thNight
79%
720
45%
1902
33%
720
87%
720
76%
832
September21st to endNight
77%
720
44%
1980
35%
720
87%
720
77%
842
October1st to 10thNight
72%
720
40%
1989
31%
720
83%
720
69%
893
October11th to 20thNight
75%
720
42%
2160
38%
720
84%
720
70%
891
October21st to endNight
72%
792
44%
2468
40%
792
83%
792
72%
947
November1st to 10thNight
71%
740
39%
2405
36%
740
81%
740
75%
889
November11th to 20thNight
69%
760
40%
2470
33%
760
82%
760
69%
958
November21st to endNight
64%
760
37%
2470
30%
760
76%
760
60%
1026
December1st to 10thNight
59%
760
30%
2489
21%
760
71%
760
54%
1102
December11th to 20thNight
54%
758
29%
3139
22%
758
68%
758
40%
1380
December21st to endNight
46%
827
19%
4752
20%
817
62%
817
28%
2074

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
1212223347%73%
74817
Night
1112223347%74%
74918
TransparencyDay
12%7%12%20%27%23%
74524
Night
10%7%12%23%29%20%
74733
SeeingDay
412%30%32%17%6%
14026
Night
1427%37%25%5%
23683

By Month

Percentage Cloud Cover SW (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
111222325%12%69%
1519
11th to 20thDay
1222346%8%71%
1469
21st to endDay
122332245%8%69%
1782
February1st to 10thDay
212223339%74%
1789
11th to 20thDay
12122234410%67%
1750
21st to endDay
21322335%7%71%
1480
March1st to 10thDay
21322447%9%68%
1800
11th to 20thDay
11232447%9%67%
1852
21st to endDay
121222245%7%72%
2376
April1st to 10thDay
111222335%9%70%
2160
11th to 20thDay
121222335%6%74%
2129
21st to endDay
111221235%7%75%
2160
May1st to 10thDay
1212223346%74%
2304
11th to 20thDay
2213213346%73%
2301
21st to endDay
231342445%6%67%
2640
June1st to 10thDay
221332445%7%68%
2520
11th to 20thDay
111212235%81%
2520
21st to endDay
111222234478%
2520
July1st to 10thDay
1112333445%72%
2520
11th to 20thDay
2113335%5%5%6%67%
2520
21st to endDay
23144245%6%7%62%
2706
August1st to 10thDay
2213323445%72%
2149
11th to 20thDay
1112323345%74%
2122
21st to endDay
111221333478%
2376
September1st to 10thDay
111221233478%
2160
11th to 20thDay
1112212225%82%
2057
21st to endDay
11111235%85%
1980
October1st to 10thDay
1112112345%80%
1967
11th to 20thDay
112112245%81%
1800
21st to endDay
11112346%83%
1886
November1st to 10thDay
11113248%79%
1674
11th to 20thDay
11112335%84%
1710
21st to endDay
1112213347%76%
1710
December1st to 10thDay
1111212348%76%
1687
11th to 20thDay
131342446%11%61%
1928
21st to endDay
13145%3445%10%60%
2794
January1st to 10thNight
21232345%10%67%
2646
11th to 20thNight
112223348%75%
2526
21st to endNight
13133235%5%9%66%
2574
February1st to 10thNight
22324348%72%
2168
11th to 20thNight
1112424447%70%
2098
21st to endNight
1213322337%73%
1776
March1st to 10thNight
11333345%9%69%
2160
11th to 20thNight
11322336%9%70%
2105
21st to endNight
1213323347%71%
1980
April1st to 10thNight
1213222447%73%
1800
11th to 20thNight
1112212346%77%
1779
21st to endNight
112222246%78%
1800
May1st to 10thNight
111222245%7%72%
1656
11th to 20thNight
111122336%5%76%
1594
21st to endNight
2213223436%72%
1631
June1st to 10thNight
111222335%7%74%
1440
11th to 20thNight
1111112235%82%
1440
21st to endNight
111212235%83%
1440
July1st to 10thNight
11113335%81%
1440
11th to 20thNight
1112324335%75%
1440
21st to endNight
211322345%6%71%
1604
August1st to 10thNight
121232334476%
1790
11th to 20thNight
11111233482%
1780
21st to endNight
11111333482%
1980
September1st to 10thNight
11111122487%
1800
11th to 20thNight
11121121485%
1902
21st to endNight
11111213486%
1980
October1st to 10thNight
111211123483%
1989
11th to 20thNight
121111246%82%
2160
21st to endNight
111112235%85%
2468
November1st to 10thNight
1112235%84%
2405
11th to 20thNight
11112246%81%
2470
21st to endNight
1112212338%75%
2470
December1st to 10thNight
213223448%71%
2489
11th to 20thNight
41332346%11%62%
3276
21st to endNight
12245%35%6%8%11%54%
4862

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
9%11%20%30%24%5%
1519
11th to 20thDay
11%10%17%25%26%11%
1469
21st to endDay
16%9%14%25%27%9%
1782
February1st to 10thDay
12%7%15%23%29%14%
1789
11th to 20thDay
15%8%10%27%29%11%
1760
21st to endDay
12%9%16%28%25%9%
1480
March1st to 10thDay
14%8%16%28%26%9%
1800
11th to 20thDay
13%11%18%22%27%10%
1852
21st to endDay
11%8%19%29%25%7%
2376
April1st to 10thDay
13%9%17%29%19%13%
2160
11th to 20thDay
11%8%13%24%29%14%
2132
21st to endDay
11%7%15%31%28%8%
2160
May1st to 10thDay
12%8%12%24%34%11%
2304
11th to 20thDay
14%7%11%25%34%10%
2304
21st to endDay
18%8%13%24%28%9%
2640
June1st to 10thDay
14%9%11%18%30%18%
2520
11th to 20thDay
8%5%7%15%31%35%
2520
21st to endDay
10%46%10%27%43%
2520
July1st to 10thDay
14%5%6%9%17%49%
2451
11th to 20thDay
16%6%8%12%20%37%
2445
21st to endDay
20%7%10%15%15%34%
2555
August1st to 10thDay
14%5%7%11%18%45%
2135
11th to 20thDay
11%5%8%11%21%44%
2122
21st to endDay
11%36%10%27%44%
2376
September1st to 10thDay
11%47%11%20%47%
2160
11th to 20thDay
9%36%13%31%37%
2057
21st to endDay
5%48%16%34%34%
1980
October1st to 10thDay
9%5%7%15%35%29%
1967
11th to 20thDay
9%46%17%36%28%
1800
21st to endDay
449%21%38%23%
1886
November1st to 10thDay
7%411%27%31%19%
1674
11th to 20thDay
5%412%24%40%15%
1710
21st to endDay
10%5%14%24%30%17%
1710
December1st to 10thDay
8%8%15%28%26%15%
1687
11th to 20thDay
13%14%16%29%20%9%
1928
21st to endDay
18%9%20%23%21%8%
2794
January1st to 10thNight
13%9%18%29%24%8%
2646
11th to 20thNight
9%8%18%28%26%11%
2526
21st to endNight
16%9%15%22%27%11%
2574
February1st to 10thNight
13%6%14%26%27%14%
2168
11th to 20thNight
13%7%12%26%28%14%
2099
21st to endNight
12%8%15%27%29%9%
1776
March1st to 10thNight
12%8%14%28%28%11%
2160
11th to 20thNight
11%9%18%24%29%9%
2105
21st to endNight
12%9%16%35%23%6%
1980
April1st to 10thNight
13%10%12%30%23%12%
1800
11th to 20thNight
10%6%15%26%30%13%
1779
21st to endNight
10%5%14%37%25%9%
1800
May1st to 10thNight
12%9%10%27%32%10%
1656
11th to 20thNight
11%6%11%32%31%9%
1595
21st to endNight
14%7%11%26%33%8%
1631
June1st to 10thNight
10%7%11%20%36%16%
1440
11th to 20thNight
5%5%9%16%33%31%
1440
21st to endNight
6%25%12%31%43%
1440
July1st to 10thNight
6%47%11%22%50%
1400
11th to 20thNight
10%5%9%14%23%40%
1392
21st to endNight
13%7%10%16%21%33%
1515
August1st to 10thNight
12%5%6%11%20%47%
1780
11th to 20thNight
5%46%14%27%44%
1780
21st to endNight
6%36%12%30%43%
1980
September1st to 10thNight
5%2411%31%47%
1800
11th to 20thNight
7%35%15%33%36%
1902
21st to endNight
6%45%16%35%35%
1980
October1st to 10thNight
8%5%8%17%34%28%
1989
11th to 20thNight
7%46%17%38%27%
2160
21st to endNight
5%47%19%41%23%
2468
November1st to 10thNight
5%411%26%35%19%
2405
11th to 20thNight
6%5%12%24%34%18%
2470
21st to endNight
11%5%12%23%34%16%
2470
December1st to 10thNight
12%7%15%27%24%15%
2489
11th to 20thNight
13%11%16%28%23%8%
3276
21st to endNight
17%13%17%21%25%7%
4862

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
39%43%29%12%3
180
11th to 20thDay
110%36%28%18%7%
181
21st to endDay
313%22%36%21%6%
374
February1st to 10thDay
113%36%29%13%7%
416
11th to 20thDay
7%13%33%31%13%4
415
21st to endDay
5%12%40%31%10%1
346
March1st to 10thDay
416%39%29%8%4
420
11th to 20thDay
418%34%26%16%2
420
21st to endDay
5%20%35%30%10%1
462
April1st to 10thDay
5%20%33%24%16%2
420
11th to 20thDay
10%21%31%25%11%2
412
21st to endDay
6%20%30%25%12%6%
420
May1st to 10thDay
6%21%32%26%11%4
423
11th to 20thDay
6%18%29%29%13%5%
448
21st to endDay
7%15%27%30%17%5%
485
June1st to 10thDay
5%14%28%28%18%8%
450
11th to 20thDay
317%29%29%16%6%
450
21st to endDay
114%26%35%18%6%
450
July1st to 10thDay
27%27%37%19%7%
446
11th to 20thDay
26%21%38%20%13%
444
21st to endDay
3426%36%18%12%
487
August1st to 10thDay
37%32%33%15%9%
447
11th to 20thDay
38%24%36%17%12%
437
21st to endDay
3425%38%21%9%
495
September1st to 10thDay
37%28%33%20%8%
450
11th to 20thDay
311%31%34%16%4
450
21st to endDay
110%25%40%19%4
450
October1st to 10thDay
212%30%31%20%5%
450
11th to 20thDay
210%24%37%23%3
450
21st to endDay
211%28%34%20%5%
401
November1st to 10thDay
27%33%27%27%4
270
11th to 20thDay
110%26%33%22%8%
270
21st to endDay
17%28%33%27%4
270
December1st to 10thDay
25%35%35%20%4
259
11th to 20thDay
213%29%31%17%8%
180
21st to endDay
313%34%29%17%5%
198
January1st to 10thNight
26%34%30%20%8%
760
11th to 20thNight
1237%34%19%7%
728
21st to endNight
25%33%35%17%7%
792
February1st to 10thNight
16%35%34%20%5%
720
11th to 20thNight
26%34%32%22%4
704
21st to endNight
35%41%35%13%3
592
March1st to 10thNight
1440%36%13%6%
720
11th to 20thNight
1434%35%20%5%
720
21st to endNight
18%39%34%15%2
792
April1st to 10thNight
35%37%34%19%2
720
11th to 20thNight
110%33%35%16%5%
711
21st to endNight
16%35%33%21%4
720
May1st to 10thNight
26%35%38%15%3
576
11th to 20thNight
25%30%41%21%2
531
21st to endNight
47%26%38%23%2
469
June1st to 10thNight
1319%42%33%3
360
11th to 20thNight
320%46%28%3
360
21st to endNight
118%46%33%2
360
July1st to 10thNight
8%44%45%3
350
11th to 20thNight
116%44%45%3
348
21st to endNight
21441%48%5%
422
August1st to 10thNight
2114%44%35%4
716
11th to 20thNight
1110%44%40%5%
712
21st to endNight
19%42%44%4
792
September1st to 10thNight
1211%40%41%6%
720
11th to 20thNight
1215%42%34%6%
720
21st to endNight
1119%35%35%9%
720
October1st to 10thNight
1223%38%29%7%
720
11th to 20thNight
2320%39%29%8%
720
21st to endNight
15%21%34%27%12%
792
November1st to 10thNight
226%34%29%9%
740
11th to 20thNight
1227%41%24%5%
760
21st to endNight
1427%36%25%6%
760
December1st to 10thNight
1333%39%17%6%
760
11th to 20thNight
2338%36%18%4
760
21st to endNight
25%44%29%18%3
836
Page generated at 2024-01-09 13:24:26. Version ac07

Copyright 2024 Attilla Danko


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