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 2024-02-15.

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
46%
23816
22%
79515
16%
23709
54%
23709
25%
49103

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
24%
754
22%
4006
9%
737
39%
737
12%
2407
January11th to 20thNight
27%
759
26%
3947
10%
740
41%
740
13%
2237
January21st to endNight
23%
831
18%
4232
11%
814
40%
814
13%
2770
February1st to 10thNight
31%
760
24%
2280
13%
760
41%
760
24%
1482
February11th to 20thNight
22%
722
19%
2153
7%
718
32%
718
20%
1437
February21st to endNight
19%
592
20%
1776
8%
592
31%
592
20%
1201
March1st to 10thNight
29%
720
23%
2160
12%
720
39%
720
27%
1340
March11th to 20thNight
29%
720
20%
1980
8%
720
38%
720
25%
1309
March21st to endNight
33%
792
22%
2178
12%
792
40%
792
26%
1435
April1st to 10thNight
37%
593
25%
1853
16%
593
47%
593
30%
1082
April11th to 20thNight
37%
533
27%
1775
16%
533
51%
533
30%
1026
April21st to endNight
50%
540
28%
1710
21%
540
58%
540
34%
965
May1st to 10thNight
51%
540
24%
1620
15%
540
60%
540
35%
945
May11th to 20thNight
53%
531
18%
1592
13%
531
57%
531
28%
1002
May21st to endNight
67%
582
21%
1744
18%
582
69%
582
32%
1073
June1st to 10thNight
68%
540
17%
1620
16%
540
69%
540
30%
1030
June11th to 20thNight
74%
540
18%
1620
15%
540
77%
540
39%
915
June21st to endNight
70%
540
17%
1620
13%
540
72%
540
33%
977
July1st to 10thNight
71%
525
15%
1575
13%
525
72%
525
26%
1034
July11th to 20thNight
73%
522
13%
1566
12%
522
74%
522
29%
996
July21st to endNight
68%
591
16%
1672
15%
558
69%
558
25%
1133
August1st to 10thNight
75%
537
17%
1641
18%
534
75%
534
28%
1062
August11th to 20thNight
70%
534
17%
1776
19%
534
70%
534
24%
1160
August21st to endNight
64%
594
19%
1980
21%
594
65%
594
23%
1303
September1st to 10thNight
69%
643
20%
1903
19%
643
69%
643
29%
1215
September11th to 20thNight
61%
720
22%
1980
18%
720
63%
720
29%
1297
September21st to endNight
63%
720
29%
1980
21%
720
69%
720
38%
1173
October1st to 10thNight
57%
720
31%
1980
24%
720
63%
720
41%
1133
October11th to 20thNight
49%
720
32%
2024
23%
720
59%
720
36%
1197
October21st to endNight
50%
792
31%
2434
25%
792
59%
792
33%
1400
November1st to 10thNight
51%
740
27%
2406
24%
740
58%
740
33%
1338
November11th to 20thNight
41%
760
29%
2470
19%
760
57%
760
32%
1385
November21st to endNight
40%
760
24%
2470
18%
760
50%
760
27%
1493
December1st to 10thNight
28%
760
22%
2470
13%
760
40%
760
19%
1640
December11th to 20thNight
32%
759
25%
2909
16%
758
42%
758
21%
1723
December21st to endNight
29%
830
13%
4413
12%
817
38%
817
12%
2788

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
13%6%35%5%35%5%6%7%41%
78767
Night
13%6%35%5%3445%7%44%
80319
TransparencyDay
41%7%11%19%18%4
78490
Night
38%6%10%20%20%5%
80115
SeeingDay
16%10%23%23%18%9%
13723
Night
16%9%23%29%20%3
23837

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
17%12%35%5%35%5%5%6%36%
2836
11th to 20thDay
15%7%46%5%3333447%
2840
21st to endDay
23%11%35%424335%38%
3352
February1st to 10thDay
19%9%35%444447%38%
1900
11th to 20thDay
22%8%345%4334440%
1788
21st to endDay
22%7%37%5%33445%38%
1480
March1st to 10thDay
16%5%26%5%35%45%7%43%
1800
11th to 20thDay
19%7%46%5%2445%6%38%
1980
21st to endDay
15%7%26%6%35%5%6%8%37%
2178
April1st to 10thDay
13%6%24435%45%7%46%
2121
11th to 20thDay
13%7%25%5%4445%5%47%
2134
21st to endDay
11%4245%35%5%6%7%48%
2248
May1st to 10thDay
11%5%35%435%46%8%47%
2340
11th to 20thDay
10%6%36%6%45%6%5%6%43%
2301
21st to endDay
8%5%35%6%35%6%7%10%42%
2531
June1st to 10thDay
10%6%36%7%45%7%8%10%35%
2340
11th to 20thDay
5%335%6%46%6%8%10%44%
2340
21st to endDay
7%5%35%7%47%6%7%10%38%
2340
July1st to 10thDay
9%5%36%8%5%7%8%8%10%31%
2340
11th to 20thDay
8%5%36%7%5%8%8%8%12%30%
2340
21st to endDay
6%5%36%8%5%8%7%9%11%32%
2547
August1st to 10thDay
7%425%7%49%9%10%12%31%
2281
11th to 20thDay
9%6%26%8%48%6%8%11%32%
2125
21st to endDay
12%7%37%7%47%6%6%8%32%
2376
September1st to 10thDay
9%5%27%6%37%6%7%10%38%
2039
11th to 20thDay
14%6%25%6%45%46%7%41%
1980
21st to endDay
13%5%2443445%5%49%
1980
October1st to 10thDay
11%4245%33446%54%
1980
11th to 20thDay
10%6%2443345%6%53%
1933
21st to endDay
14%5%24423445%54%
1918
November1st to 10thDay
12%5%24423235%56%
1672
11th to 20thDay
13%6%24423446%51%
1710
21st to endDay
14%6%25%43446%7%45%
1710
December1st to 10thDay
20%7%36%4345%47%38%
1710
11th to 20thDay
18%8%35%5%34435%42%
2153
21st to endDay
19%8%37%5%35%447%34%
3124
January1st to 10thNight
18%10%35%424446%39%
4109
11th to 20thNight
15%9%35%433445%45%
4120
21st to endNight
22%13%35%42333438%
4299
February1st to 10thNight
16%8%345%3445%6%43%
2280
11th to 20thNight
22%7%35%33434442%
2153
21st to endNight
21%7%25%5%3445%6%37%
1776
March1st to 10thNight
14%7%25%424446%46%
2160
11th to 20thNight
15%7%35%5%3346%7%42%
1980
21st to endNight
14%7%35%6%345%5%5%44%
2178
April1st to 10thNight
12%4244346%6%9%47%
1853
11th to 20thNight
12%6%35%5%24346%51%
1775
21st to endNight
9%5%3443445%7%53%
1710
May1st to 10thNight
9%5%245%245%5%8%51%
1620
11th to 20thNight
9%6%27%5%35%6%7%9%43%
1592
21st to endNight
8%5%246%35%5%6%9%46%
1744
June1st to 10thNight
5%436%6%36%7%7%13%39%
1620
11th to 20thNight
32246%45%5%7%11%51%
1620
21st to endNight
5%5%245%35%6%6%13%45%
1620
July1st to 10thNight
8%5%35%6%45%7%10%12%36%
1620
11th to 20thNight
6%425%6%46%6%9%13%39%
1620
21st to endNight
5%5%37%7%47%6%8%11%37%
1771
August1st to 10thNight
5%426%7%5%6%6%7%13%39%
1652
11th to 20thNight
10%435%6%46%7%6%9%40%
1776
21st to endNight
13%7%36%5%345%6%10%38%
1980
September1st to 10thNight
8%5%35%6%46%5%6%9%44%
1903
11th to 20thNight
12%5%25%5%45%45%8%44%
1980
21st to endNight
10%5%2442336%8%53%
1980
October1st to 10thNight
9%5%14423346%59%
1980
11th to 20thNight
12%5%24424346%54%
2024
21st to endNight
13%5%2443344455%
2434
November1st to 10thNight
11%5%14324346%55%
2406
11th to 20thNight
12%6%24423346%54%
2470
21st to endNight
15%5%245%3445%6%46%
2470
December1st to 10thNight
18%6%46%5%3445%6%38%
2470
11th to 20thNight
17%8%34423445%47%
3042
21st to endNight
18%9%47%5%35%5%5%8%32%
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
47%5%8%15%22%4
2837
11th to 20thDay
42%46%22%23%3
2840
21st to endDay
50%36%17%20%4
3352
February1st to 10thDay
47%47%18%21%3
1900
11th to 20thDay
49%35%19%19%5%
1798
21st to endDay
48%49%12%21%6%
1480
March1st to 10thDay
41%49%15%23%8%
1800
11th to 20thDay
47%6%10%15%18%5%
1980
21st to endDay
44%6%11%20%16%3
2178
April1st to 10thDay
37%5%11%21%20%6%
2121
11th to 20thDay
40%46%18%25%7%
2134
21st to endDay
33%6%11%25%21%3
2248
May1st to 10thDay
35%6%12%24%19%4
2340
11th to 20thDay
40%9%14%21%15%1
2305
21st to endDay
35%9%13%23%16%3
2531
June1st to 10thDay
41%12%14%20%12%1
2340
11th to 20thDay
31%9%19%25%14%2
2340
21st to endDay
38%11%17%21%11%2
2340
July1st to 10thDay
41%14%18%17%10%2
2275
11th to 20thDay
41%14%19%15%9%3
2271
21st to endDay
40%13%20%18%8%
2405
August1st to 10thDay
39%15%18%21%7%
2268
11th to 20thDay
42%13%16%18%9%2
2125
21st to endDay
48%11%13%15%10%4
2376
September1st to 10thDay
40%10%14%15%15%5%
2039
11th to 20thDay
41%9%10%20%18%3
1980
21st to endDay
36%6%9%17%24%8%
1980
October1st to 10thDay
32%7%9%17%27%8%
1980
11th to 20thDay
31%5%9%23%24%8%
1933
21st to endDay
33%5%6%18%29%9%
1918
November1st to 10thDay
32%37%18%31%9%
1672
11th to 20thDay
34%48%17%27%10%
1710
21st to endDay
38%5%7%17%26%6%
1710
December1st to 10thDay
46%5%8%17%19%5%
1710
11th to 20thDay
45%37%18%22%5%
2150
21st to endDay
49%48%19%18%2
3124
January1st to 10thNight
45%46%18%23%3
4109
11th to 20thNight
42%47%22%19%6%
4120
21st to endNight
51%35%14%23%4
4299
February1st to 10thNight
43%5%6%20%20%7%
2280
11th to 20thNight
47%36%18%19%7%
2154
21st to endNight
47%5%8%16%17%7%
1776
March1st to 10thNight
39%48%18%21%10%
2160
11th to 20thNight
41%6%11%18%19%5%
1980
21st to endNight
41%5%7%24%19%3
2178
April1st to 10thNight
33%6%13%21%21%7%
1853
11th to 20thNight
35%47%21%23%9%
1775
21st to endNight
31%5%11%28%21%5%
1710
May1st to 10thNight
31%6%12%23%24%4
1620
11th to 20thNight
36%9%18%21%16%1
1593
21st to endNight
33%8%13%25%17%3
1745
June1st to 10thNight
34%11%18%21%14%2
1620
11th to 20thNight
25%9%22%27%16%2
1620
21st to endNight
29%11%20%21%15%4
1620
July1st to 10thNight
35%13%17%21%12%2
1575
11th to 20thNight
31%14%23%19%10%3
1566
21st to endNight
37%13%18%21%9%2
1672
August1st to 10thNight
33%13%20%24%9%1
1641
11th to 20thNight
37%12%19%16%14%2
1776
21st to endNight
40%10%16%17%13%3
1980
September1st to 10thNight
35%10%17%18%15%6%
1903
11th to 20thNight
37%8%11%21%20%2
1980
21st to endNight
29%7%11%20%24%9%
1980
October1st to 10thNight
28%5%9%22%28%9%
1980
11th to 20thNight
32%5%7%21%25%10%
2024
21st to endNight
33%35%18%30%11%
2434
November1st to 10thNight
31%48%19%26%12%
2406
11th to 20thNight
32%46%20%27%11%
2470
21st to endNight
38%47%20%25%6%
2470
December1st to 10thNight
46%6%8%18%19%3
2470
11th to 20thNight
39%47%17%28%4
3044
21st to endNight
49%48%20%16%2
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
24%27%35%11%2
270
11th to 20thDay
29%22%29%15%5%
270
21st to endDay
24%28%37%8%31
297
February1st to 10thDay
29%20%35%14%2
270
11th to 20thDay
37%23%31%9%1
252
21st to endDay
31%23%37%8%1
198
March1st to 10thDay
25%20%34%16%31
240
11th to 20thDay
25%20%30%18%7%1
420
21st to endDay
21%19%35%18%6%
462
April1st to 10thDay
21%15%31%17%13%2
420
11th to 20thDay
18%18%29%22%12%2
412
21st to endDay
17%11%29%27%13%3
420
May1st to 10thDay
15%11%29%25%15%5%
423
11th to 20thDay
11%5%22%35%16%11%
447
21st to endDay
12%5%18%30%23%13%
485
June1st to 10thDay
12%421%30%20%13%
450
11th to 20thDay
8%317%26%24%22%
450
21st to endDay
10%5%17%26%25%18%
450
July1st to 10thDay
8%311%27%29%21%
445
11th to 20thDay
7%28%25%31%27%
444
21st to endDay
8%111%24%36%20%
488
August1st to 10thDay
11%213%25%30%20%
446
11th to 20thDay
10%39%31%28%18%
439
21st to endDay
16%210%25%29%19%
495
September1st to 10thDay
9%413%28%29%17%
450
11th to 20thDay
16%5%13%26%28%12%
450
21st to endDay
14%419%26%28%9%
450
October1st to 10thDay
14%5%22%29%21%9%
450
11th to 20thDay
12%11%26%26%21%3
450
21st to endDay
17%12%24%28%18%2
433
November1st to 10thDay
19%10%31%26%11%3
270
11th to 20thDay
19%17%38%19%7%1
270
21st to endDay
13%18%39%21%7%1
270
December1st to 10thDay
28%20%30%17%41
270
11th to 20thDay
24%16%32%21%5%1
270
21st to endDay
30%18%30%16%6%
297
January1st to 10thNight
23%19%31%23%5%
760
11th to 20thNight
24%15%31%24%6%
760
21st to endNight
22%17%35%23%3
836
February1st to 10thNight
21%15%31%29%5%
760
11th to 20thNight
27%16%32%23%2
722
21st to endNight
24%18%35%19%3
592
March1st to 10thNight
20%15%33%27%5%
720
11th to 20thNight
18%14%33%24%9%1
720
21st to endNight
18%14%30%29%9%
792
April1st to 10thNight
14%13%33%27%12%1
593
11th to 20thNight
15%12%31%29%12%1
533
21st to endNight
11%9%26%37%16%1
540
May1st to 10thNight
11%7%26%35%20%2
540
11th to 20thNight
11%7%20%32%26%4
531
21st to endNight
9%313%35%34%6%
584
June1st to 10thNight
7%112%41%33%6%
540
11th to 20thNight
3212%30%39%14%
540
21st to endNight
7%210%32%42%7%
540
July1st to 10thNight
9%38%23%45%13%
525
11th to 20thNight
7%16%27%45%14%
522
21st to endNight
7%29%28%44%10%
591
August1st to 10thNight
7%5%31%46%11%
537
11th to 20thNight
10%17%30%41%10%
534
21st to endNight
14%37%27%38%10%
594
September1st to 10thNight
9%38%27%42%10%
643
11th to 20thNight
14%214%29%36%4
720
21st to endNight
12%314%34%33%3
720
October1st to 10thNight
12%422%33%24%6%
720
11th to 20thNight
14%6%25%31%22%2
720
21st to endNight
15%9%21%36%17%2
792
November1st to 10thNight
14%8%23%33%20%2
740
11th to 20thNight
15%12%29%31%12%1
760
21st to endNight
18%11%27%32%11%1
760
December1st to 10thNight
22%15%29%26%8%
760
11th to 20thNight
23%11%30%27%8%1
760
21st to endNight
25%13%29%26%7%
836
Page generated at 2024-02-12 06:35:37. Version ac07

Copyright 2024 Attilla Danko


Bishop Observatory Clear Sky Chart |Charts Home