Bishop Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bishop Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
48%
15701
23%
47865
16%
15658
56%
15658
28%
29455

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 15thNight
26%
720
22%
2327
10%
716
41%
716
21%
1471
January16th to endNight
24%
768
25%
2406
10%
768
40%
768
22%
1573
February1st to 15thNight
29%
704
24%
2112
10%
701
42%
701
25%
1315
February16th to endNight
24%
631
23%
1893
9%
631
37%
631
23%
1208
March1st to 15thNight
29%
720
22%
2100
11%
720
39%
720
25%
1344
March16th to endNight
36%
768
22%
2112
14%
768
42%
768
29%
1345
April1st to 15thNight
40%
573
25%
1831
16%
573
51%
573
33%
1028
April16th to endNight
46%
540
26%
1740
18%
540
56%
540
33%
995
May1st to 15thNight
49%
540
21%
1620
12%
540
57%
540
30%
994
May16th to endNight
67%
561
22%
1682
18%
561
70%
561
35%
997
June1st to 15thNight
73%
540
18%
1620
16%
540
74%
540
35%
975
June16th to endNight
76%
540
17%
1620
15%
540
77%
540
36%
951
July1st to 15thNight
74%
510
14%
1530
13%
510
75%
510
31%
952
July16th to endNight
71%
564
17%
1595
15%
531
72%
531
27%
1045
August1st to 15thNight
76%
539
20%
1698
21%
536
76%
536
29%
1057
August16th to endNight
67%
573
19%
1910
20%
573
68%
573
23%
1246
September1st to 15thNight
65%
669
17%
1929
16%
669
67%
669
27%
1282
September16th to endNight
64%
717
28%
1980
21%
717
68%
717
35%
1203
October1st to 15thNight
55%
720
33%
1980
25%
720
62%
720
39%
1151
October16th to endNight
50%
768
34%
2313
27%
768
61%
768
36%
1304
November1st to 15thNight
51%
760
28%
2471
24%
760
61%
760
34%
1370
November16th to endNight
42%
780
29%
2535
20%
780
55%
780
31%
1447
December1st to 15thNight
32%
728
22%
2365
15%
728
44%
728
23%
1494
December16th to endNight
29%
768
19%
2496
13%
768
38%
768
18%
1708

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%5%25%5%35%5%5%7%41%
48577
Night
11%5%2442445%7%46%
48064
TransparencyDay
40%7%11%18%17%4
48278
Night
36%6%11%20%20%5%
47867
SeeingDay
15%6%20%23%20%12%
5558
Night
14%7%23%28%21%3
15703

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 15thDay
16%8%34323345%42%
1611
16th to endDay
17%5%24424435%44%
1815
February1st to 15thDay
16%7%24433346%41%
1750
16th to endDay
19%6%245%3334441%
1580
March1st to 15thDay
17%5%25%42435%7%39%
1860
16th to endDay
15%6%25%425%45%7%40%
2111
April1st to 15thDay
12%6%2443445%6%45%
2126
16th to endDay
11%5%24435%45%5%46%
2220
May1st to 15thDay
11%6%25%4345%5%6%43%
2331
16th to endDay
8%426%6%346%5%8%42%
2431
June1st to 15thDay
8%436%7%36%6%7%10%35%
2340
16th to endDay
5%3245%36%5%7%11%43%
2340
July1st to 15thDay
10%436%7%47%6%6%10%31%
2340
16th to endDay
7%425%7%5%8%8%8%10%30%
2465
August1st to 15thDay
7%4246%49%7%9%11%32%
2248
16th to endDay
11%5%36%8%47%6%6%9%29%
2292
September1st to 15thDay
12%5%26%6%36%6%6%9%34%
2019
16th to endDay
15%5%1432445%5%46%
1980
October1st to 15thDay
11%42442335%5%53%
1980
16th to endDay
13%42331333358%
1906
November1st to 15thDay
13%5%24313245%52%
1717
16th to endDay
13%6%2432335%6%50%
1755
December1st to 15thDay
18%6%25%433446%40%
1632
16th to endDay
23%9%35%5%23335%34%
1728
January1st to 15thNight
18%6%24424446%42%
2327
16th to endNight
17%7%35%423345%41%
2406
February1st to 15thNight
14%6%23423346%47%
2103
16th to endNight
16%5%34433345%44%
1893
March1st to 15thNight
14%6%245%24447%44%
2100
16th to endNight
12%6%24424345%48%
2112
April1st to 15thNight
12%41332345%8%50%
1831
16th to endNight
9%5%23424446%52%
1740
May1st to 15thNight
9%5%25%5%2446%7%45%
1619
16th to endNight
6%414425%46%10%48%
1682
June1st to 15thNight
3325%5%446%7%11%45%
1620
16th to endNight
33235%35%6%7%12%46%
1620
July1st to 15thNight
6%3246%35%6%10%11%39%
1620
16th to endNight
4326%6%47%6%8%11%38%
1703
August1st to 15thNight
5%3246%46%6%6%11%42%
1709
16th to endNight
12%6%25%5%25%5%6%9%38%
1910
September1st to 15thNight
9%435%5%46%5%6%8%41%
1929
16th to endNight
10%41432335%7%51%
1980
October1st to 15thNight
10%413323336%56%
1980
16th to endNight
10%41442233359%
2313
November1st to 15thNight
11%414323246%54%
2471
16th to endNight
12%5%13414346%51%
2535
December1st to 15thNight
15%6%36%42335%6%42%
2365
16th to endNight
20%8%34424446%35%
2496

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 15thDay
43%5%7%16%22%4
1612
16th to endDay
42%46%20%20%5%
1815
February1st to 15thDay
43%38%21%20%2
1752
16th to endDay
45%37%17%21%4
1580
March1st to 15thDay
45%49%15%20%4
1860
16th to endDay
43%5%11%20%15%2
2112
April1st to 15thDay
39%5%9%19%20%5%
2126
16th to endDay
37%5%9%20%22%4
2220
May1st to 15thDay
39%6%11%21%17%3
2331
16th to endDay
37%8%15%22%13%3
2435
June1st to 15thDay
40%11%16%21%9%1
2340
16th to endDay
31%9%17%23%15%2
2340
July1st to 15thDay
41%11%18%16%9%2
2201
16th to endDay
42%11%19%17%8%1
2310
August1st to 15thDay
38%13%16%19%10%1
2235
16th to endDay
49%11%11%14%10%2
2292
September1st to 15thDay
43%9%13%16%12%4
2019
16th to endDay
39%6%10%19%20%4
1980
October1st to 15thDay
32%6%7%18%26%8%
1980
16th to endDay
30%45%17%30%10%
1906
November1st to 15thDay
34%36%16%31%7%
1717
16th to endDay
35%47%16%28%7%
1755
December1st to 15thDay
44%49%20%16%5%
1632
16th to endDay
53%47%16%14%3
1728
January1st to 15thNight
41%5%8%18%21%4
2327
16th to endNight
44%35%18%20%6%
2406
February1st to 15thNight
39%46%22%19%8%
2112
16th to endNight
42%46%20%22%3
1893
March1st to 15thNight
39%5%9%20%18%6%
2100
16th to endNight
38%49%26%18%3
2112
April1st to 15thNight
31%411%23%21%7%
1831
16th to endNight
32%5%10%23%21%6%
1740
May1st to 15thNight
35%6%13%18%23%2
1620
16th to endNight
30%7%16%26%15%3
1684
June1st to 15thNight
30%8%20%26%13%1
1620
16th to endNight
27%10%19%20%17%3
1620
July1st to 15thNight
31%10%19%23%11%3
1530
16th to endNight
34%12%18%20%11%2
1595
August1st to 15thNight
32%11%17%22%14%2
1698
16th to endNight
39%10%17%16%14%2
1910
September1st to 15thNight
39%9%16%17%13%4
1929
16th to endNight
31%7%10%22%22%5%
1980
October1st to 15thNight
29%5%8%22%24%9%
1980
16th to endNight
30%3315%33%13%
2313
November1st to 15thNight
31%47%19%26%11%
2471
16th to endNight
33%47%18%27%9%
2535
December1st to 15thNight
42%49%18%19%5%
2365
16th to endNight
49%5%8%17%16%3
2496

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 15thDay
16%24%34%18%41
90
16th to endDay
19%28%46%23
96
February1st to 15thDay
17%26%45%7%2
90
16th to endDay
32%11%40%16%
81
March1st to 15thDay
23%17%30%22%42
150
16th to endDay
18%10%35%21%13%
288
April1st to 15thDay
20%12%27%18%18%1
270
16th to endDay
14%7%27%27%18%5%
270
May1st to 15thDay
14%6%30%20%15%13%
288
16th to endDay
12%319%29%20%15%
331
June1st to 15thDay
12%112%25%22%25%
315
16th to endDay
11%15%21%22%27%
315
July1st to 15thDay
8%111%25%24%27%
305
16th to endDay
9%6%22%34%26%
326
August1st to 15thDay
13%19%27%29%19%
313
16th to endDay
14%17%27%29%20%
332
September1st to 15thDay
13%313%21%27%20%
315
16th to endDay
16%214%27%28%9%
314
October1st to 15thDay
14%421%24%27%6%
315
16th to endDay
14%7%21%25%26%4
294
November1st to 15thDay
25%9%25%28%8%1
135
16th to endDay
12%12%33%27%10%3
135
December1st to 15thDay
20%17%37%21%4
94
16th to endDay
34%15%28%15%6%
96
January1st to 15thNight
22%15%30%23%6%
720
16th to endNight
21%14%36%24%3
768
February1st to 15thNight
19%14%33%28%3
704
16th to endNight
20%16%36%22%3
631
March1st to 15thNight
19%14%34%25%6%
720
16th to endNight
15%12%30%27%13%
768
April1st to 15thNight
15%9%33%27%13%
573
16th to endNight
11%7%30%32%16%1
540
May1st to 15thNight
10%6%25%30%23%3
540
16th to endNight
7%215%35%32%6%
563
June1st to 15thNight
5%11%34%37%10%
540
16th to endNight
5%8%30%43%11%
540
July1st to 15thNight
7%17%26%44%11%
510
16th to endNight
5%16%27%45%13%
564
August1st to 15thNight
6%5%32%46%9%
539
16th to endNight
12%16%27%41%10%
573
September1st to 15thNight
12%19%26%40%9%
669
16th to endNight
12%113%34%33%3
717
October1st to 15thNight
13%322%29%26%4
720
16th to endNight
12%8%22%31%22%2
768
November1st to 15thNight
13%7%23%31%21%2
760
16th to endNight
15%12%27%30%14%
780
December1st to 15thNight
19%11%29%28%9%
728
16th to endNight
25%12%29%24%7%
768
Page generated at 2017-12-03 11:16:48. Version ac04

Copyright 2017 A. Danko


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