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 2017-09-19.

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
67%
15388
33%
46868
25%
15360
76%
15360
58%
20975

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
61%
716
27%
2506
21%
716
73%
716
52%
1076
January16th to endNight
60%
768
30%
2541
25%
768
69%
768
47%
1195
February1st to 15thNight
60%
700
31%
2116
26%
699
69%
699
54%
987
February16th to endNight
55%
632
30%
1895
24%
632
67%
632
50%
932
March1st to 15thNight
59%
720
28%
2160
21%
720
72%
720
57%
995
March16th to endNight
56%
768
29%
2002
14%
768
68%
768
56%
1027
April1st to 15thNight
53%
719
28%
1799
12%
719
62%
719
53%
977
April16th to endNight
58%
720
30%
1800
14%
720
64%
720
62%
890
May1st to 15thNight
60%
562
31%
1642
20%
562
65%
562
56%
769
May16th to endNight
63%
483
28%
1607
22%
483
70%
483
50%
712
June1st to 15thNight
73%
360
31%
1440
30%
360
84%
360
56%
530
June16th to endNight
83%
360
37%
1440
43%
360
91%
360
74%
442
July1st to 15thNight
89%
340
31%
1360
38%
340
92%
340
57%
502
July16th to endNight
88%
396
36%
1435
41%
373
90%
373
53%
573
August1st to 15thNight
82%
717
35%
1790
22%
713
84%
713
70%
856
August16th to endNight
88%
764
42%
1910
27%
764
89%
764
79%
868
September1st to 15thNight
87%
720
42%
1809
28%
720
90%
720
77%
822
September16th to endNight
79%
671
42%
1856
34%
671
86%
671
73%
808
October1st to 15thNight
72%
660
36%
1876
31%
660
79%
660
62%
867
October16th to endNight
73%
704
41%
2169
38%
704
83%
704
67%
889
November1st to 15thNight
72%
700
36%
2275
33%
700
81%
700
66%
913
November16th to endNight
65%
720
37%
2340
30%
720
78%
720
61%
963
December1st to 15thNight
60%
720
27%
2412
19%
720
72%
720
49%
1105
December16th to endNight
51%
768
29%
2688
21%
768
65%
768
42%
1277

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
112212346%72%
47957
Night
11112236%75%
47045
TransparencyDay
13%6%12%20%26%20%
47631
Night
10%6%12%24%28%16%
46871
SeeingDay
415%33%29%12%4
5768
Night
1325%34%28%6%
15399

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 15thDay
1111215%9%74%
1432
16th to endDay
111231235%7%67%
1680
February1st to 15thDay
111212339%71%
1743
16th to endDay
21321235%8%67%
1579
March1st to 15thDay
1111235%9%71%
1800
16th to endDay
11111236%8%70%
2220
April1st to 15thDay
111222335%8%68%
2149
16th to endDay
111212236%75%
2160
May1st to 15thDay
112212336%73%
2307
16th to endDay
221331335%6%66%
2504
June1st to 15thDay
112213347%71%
2520
16th to endDay
1111123381%
2520
July1st to 15thDay
1112325%45%6%65%
2520
16th to endDay
1213324446%64%
2632
August1st to 15thDay
111212445%73%
2160
16th to endDay
111221334475%
2292
September1st to 15thDay
1112212335%74%
2151
16th to endDay
111235%82%
1849
October1st to 15thDay
111112345%76%
1752
16th to endDay
11336%79%
1702
November1st to 15thDay
1112236%79%
1584
16th to endDay
12236%79%
1620
December1st to 15thDay
11212349%72%
1545
16th to endDay
13312349%69%
1536
January1st to 15thNight
112212238%72%
2506
16th to endNight
1212322348%68%
2541
February1st to 15thNight
112133310%70%
2107
16th to endNight
1212322337%70%
1895
March1st to 15thNight
1112247%74%
2160
16th to endNight
11113348%73%
2002
April1st to 15thNight
113222336%72%
1799
16th to endNight
1112236%78%
1800
May1st to 15thNight
111111346%75%
1642
16th to endNight
1111112336%73%
1606
June1st to 15thNight
1113246%76%
1440
16th to endNight
1112486%
1440
July1st to 15thNight
1213335%75%
1440
16th to endNight
1221234474%
1532
August1st to 15thNight
1111222381%
1800
16th to endNight
1223481%
1910
September1st to 15thNight
11112483%
1809
16th to endNight
1111125%83%
1856
October1st to 15thNight
11111235%78%
1876
16th to endNight
11235%81%
2169
November1st to 15thNight
112225%82%
2275
16th to endNight
11111237%77%
2340
December1st to 15thNight
2211235%8%69%
2412
16th to endNight
1222345%10%65%
2688

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
9%9%18%29%28%5%
1432
16th to endDay
16%10%16%24%20%11%
1680
February1st to 15thDay
13%8%17%26%24%10%
1743
16th to endDay
16%9%15%28%24%6%
1579
March1st to 15thDay
11%8%18%26%26%8%
1800
16th to endDay
12%10%21%26%24%5%
2220
April1st to 15thDay
15%8%16%28%21%10%
2149
16th to endDay
12%7%15%29%27%8%
2160
May1st to 15thDay
13%8%12%24%33%7%
2307
16th to endDay
19%8%12%21%28%10%
2507
June1st to 15thDay
14%7%10%17%28%21%
2520
16th to endDay
9%35%9%26%45%
2520
July1st to 15thDay
18%5%7%9%16%43%
2371
16th to endDay
21%5%7%11%16%37%
2466
August1st to 15thDay
12%47%10%19%45%
2146
16th to endDay
13%36%10%28%37%
2292
September1st to 15thDay
14%47%11%23%38%
2151
16th to endDay
6%48%18%34%26%
1849
October1st to 15thDay
11%6%6%19%40%15%
1752
16th to endDay
9%49%21%39%16%
1702
November1st to 15thDay
8%5%13%30%29%11%
1584
16th to endDay
8%416%26%35%9%
1620
December1st to 15thDay
10%10%17%29%24%6%
1545
16th to endDay
15%11%18%25%21%8%
1536
January1st to 15thNight
12%7%17%27%28%6%
2506
16th to endNight
15%8%16%24%23%11%
2541
February1st to 15thNight
13%7%16%30%21%11%
2118
16th to endNight
14%8%16%27%27%4
1895
March1st to 15thNight
11%7%16%28%25%10%
2160
16th to endNight
11%9%20%30%24%4
2002
April1st to 15thNight
14%8%14%29%25%7%
1799
16th to endNight
10%5%17%33%24%8%
1800
May1st to 15thNight
10%8%10%31%30%7%
1643
16th to endNight
13%7%11%27%31%9%
1607
June1st to 15thNight
9%6%11%22%31%18%
1440
16th to endNight
5%1411%35%40%
1440
July1st to 15thNight
9%5%7%12%21%42%
1360
16th to endNight
12%5%7%12%22%38%
1435
August1st to 15thNight
9%4412%23%46%
1790
16th to endNight
5%36%15%31%36%
1910
September1st to 15thNight
7%26%13%34%35%
1809
16th to endNight
7%46%21%32%28%
1856
October1st to 15thNight
10%6%9%21%38%13%
1876
16th to endNight
7%5%8%23%40%14%
2169
November1st to 15thNight
7%6%14%28%30%13%
2275
16th to endNight
9%5%12%25%36%10%
2340
December1st to 15thNight
13%9%18%29%23%5%
2412
16th to endNight
14%11%17%25%23%8%
2688

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
18%60%16%5%8%
60
16th to endDay
312%27%31%16%8%
208
February1st to 15thDay
211%33%27%16%8%
265
16th to endDay
414%38%29%10%1
238
March1st to 15thDay
219%37%18%12%8%
270
16th to endDay
5%22%36%24%10%
288
April1st to 15thDay
7%27%35%17%10%1
269
16th to endDay
9%31%34%19%41
270
May1st to 15thDay
6%23%33%25%8%2
288
16th to endDay
6%17%29%30%11%3
330
June1st to 15thDay
7%19%33%27%10%2
315
16th to endDay
18%28%31%13%6%
315
July1st to 15thDay
47%28%38%14%6%
305
16th to endDay
37%34%34%11%7%
327
August1st to 15thDay
411%39%27%12%5%
315
16th to endDay
36%28%39%15%7%
332
September1st to 15thDay
5%9%35%30%15%3
315
16th to endDay
313%25%42%13%1
268
October1st to 15thDay
316%35%30%12%1
255
16th to endDay
214%34%35%12%
214
November1st to 15thDay
1221%15%45%14%
90
16th to endDay
111%35%34%17%
90
December1st to 15thDay
10%46%28%14%
77
16th to endDay
16%34%32%15%9%
64
January1st to 15thNight
1130%30%25%10%
720
16th to endNight
1232%33%18%10%
768
February1st to 15thNight
1332%33%22%6%
704
16th to endNight
25%35%33%19%4
632
March1st to 15thNight
1234%34%17%9%
720
16th to endNight
16%34%33%21%3
768
April1st to 15thNight
25%36%32%20%3
719
16th to endNight
8%30%32%21%5%
720
May1st to 15thNight
15%30%38%20%3
563
16th to endNight
26%26%36%25%2
485
June1st to 15thNight
222%40%32%1
360
16th to endNight
14%48%32%3
360
July1st to 15thNight
5%39%49%4
340
16th to endNight
15%39%49%4
396
August1st to 15thNight
113%40%39%4
717
16th to endNight
8%35%48%6%
764
September1st to 15thNight
8%36%44%7%
720
16th to endNight
1116%32%36%12%
671
October1st to 15thNight
1321%33%29%10%
660
16th to endNight
1321%33%28%12%
704
November1st to 15thNight
124%33%28%11%
700
16th to endNight
327%33%25%7%
720
December1st to 15thNight
2332%37%17%7%
720
16th to endNight
1341%29%20%3
768
Page generated at 2017-09-20 01:49:51. Version ac04

Copyright 2017 A. Danko


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