Grand Cosmic Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Cosmic Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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%
16105
16%
47775
14%
16065
52%
16065
24%
31737

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
38%
816
10%
2450
8%
814
40%
814
14%
1900
January16th to endNight
40%
768
12%
2496
11%
768
43%
768
16%
1826
February1st to 15thNight
34%
699
8%
2288
8%
698
36%
698
12%
1783
February16th to endNight
33%
632
9%
1989
9%
632
34%
632
13%
1522
March1st to 15thNight
42%
720
10%
2003
8%
720
44%
720
18%
1495
March16th to endNight
39%
768
10%
2112
7%
768
41%
768
18%
1590
April1st to 15thNight
42%
596
10%
1828
7%
596
45%
596
19%
1284
April16th to endNight
46%
540
16%
1620
12%
540
48%
540
25%
1059
May1st to 15thNight
55%
539
15%
1620
13%
539
57%
539
28%
1009
May16th to endNight
52%
562
13%
1509
10%
561
54%
561
25%
1036
June1st to 15thNight
52%
489
13%
1389
9%
489
55%
489
30%
875
June16th to endNight
76%
360
28%
1260
30%
360
81%
360
52%
532
July1st to 15thNight
82%
368
23%
1218
24%
368
88%
368
53%
536
July16th to endNight
78%
564
26%
1590
27%
531
80%
531
60%
717
August1st to 15thNight
77%
539
27%
1611
25%
536
78%
536
48%
807
August16th to endNight
76%
573
36%
1737
31%
573
79%
573
53%
826
September1st to 15thNight
71%
606
29%
1866
26%
606
75%
606
46%
956
September16th to endNight
67%
716
29%
1980
23%
716
70%
716
43%
1111
October1st to 15thNight
53%
720
20%
2139
16%
720
55%
720
29%
1346
October16th to endNight
59%
768
23%
2317
20%
768
63%
768
32%
1404
November1st to 15thNight
43%
828
16%
2538
14%
828
45%
828
21%
1754
November16th to endNight
40%
975
13%
2730
9%
975
43%
975
21%
1951
December1st to 15thNight
34%
975
6%
2730
5%
975
35%
975
13%
2181
December16th to endNight
32%
984
8%
2755
6%
984
34%
984
12%
2237

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
5%9%48%6%35%45%6%39%
49033
Night
5%9%47%6%3445%6%42%
47950
TransparencyDay
43%7%12%18%13%5%
48709
Night
41%7%14%20%12%4
47775
SeeingDay
11%16%31%25%12%2
6181
Night
10%8%24%36%18%1
16115

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
216%7%10%10%46%445%26%
1465
16th to endDay
215%7%11%7%34346%32%
1728
February1st to 15thDay
418%9%11%7%44346%27%
1575
16th to endDay
218%8%15%8%45%5%35%20%
1482
March1st to 15thDay
312%7%12%7%35%45%7%29%
1956
16th to endDay
5%18%7%11%6%5%5%45%6%23%
2112
April1st to 15thDay
7%14%6%9%7%46%5%48%24%
2118
16th to endDay
7%14%5%10%7%345%5%7%29%
2340
May1st to 15thDay
8%9%47%6%45%5%6%7%35%
2331
16th to endDay
13%9%49%8%46%5%5%6%25%
2605
June1st to 15thDay
11%6%36%5%35%46%7%38%
2568
16th to endDay
2213334347%62%
2700
July1st to 15thDay
2213325%5%6%9%57%
2667
16th to endDay
3213425%5%5%6%57%
2469
August1st to 15thDay
3214435%5%6%7%54%
2340
16th to endDay
331343446%6%58%
2465
September1st to 15thDay
5%4245%34445%56%
2091
16th to endDay
7%5%15%424437%52%
1980
October1st to 15thDay
9%9%36%444345%42%
1821
16th to endDay
7%8%36%5%3445%6%44%
1905
November1st to 15thDay
8%11%6%9%5%33346%37%
1638
16th to endDay
313%6%11%6%35%335%36%
1560
December1st to 15thDay
5%13%6%12%10%6%6%6%3423%
1560
16th to endDay
5%15%7%16%10%4444422%
1557
January1st to 15thNight
316%6%11%8%45%445%29%
2450
16th to endNight
214%7%12%7%35%345%34%
2496
February1st to 15thNight
316%7%13%8%44445%27%
2277
16th to endNight
311%8%14%9%35%45%5%26%
1989
March1st to 15thNight
212%5%11%6%36%5%5%6%33%
2003
16th to endNight
5%12%6%8%7%46%5%6%6%31%
2112
April1st to 15thNight
5%12%46%6%35%6%5%9%33%
1828
16th to endNight
5%9%5%5%5%34448%42%
1620
May1st to 15thNight
6%8%145%245%6%8%45%
1619
16th to endNight
10%9%247%3446%8%38%
1508
June1st to 15thNight
9%5%25%42446%8%45%
1389
16th to endNight
312212436%70%
1260
July1st to 15thNight
1121448%11%63%
1290
16th to endNight
111221345%7%68%
1697
August1st to 15thNight
221332336%9%61%
1620
16th to endNight
222223346%68%
1737
September1st to 15thNight
421332345%7%61%
1866
16th to endNight
7%412323246%59%
1980
October1st to 15thNight
8%8%26%433345%47%
2139
16th to endNight
7%7%15%42335%6%51%
2317
November1st to 15thNight
7%11%48%6%2445%7%37%
2538
16th to endNight
411%5%9%6%345%5%6%37%
2730
December1st to 15thNight
5%15%6%11%9%5%6%445%26%
2730
16th to endNight
417%5%14%9%45%5%4423%
2755

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
58%9%14%10%6%1
1465
16th to endDay
52%8%15%15%6%1
1728
February1st to 15thDay
59%8%13%13%4
1575
16th to endDay
65%7%10%12%31
1482
March1st to 15thDay
54%10%15%14%4
1956
16th to endDay
60%7%12%14%4
2112
April1st to 15thDay
57%9%13%14%5%
2118
16th to endDay
53%8%13%19%5%
2340
May1st to 15thDay
46%7%12%25%7%
2331
16th to endDay
56%9%12%16%5%
2609
June1st to 15thDay
42%7%13%22%10%2
2568
16th to endDay
20%5%8%23%31%11%
2700
July1st to 15thDay
21%6%9%20%27%14%
2510
16th to endDay
23%5%7%13%23%26%
2313
August1st to 15thDay
25%7%9%16%26%15%
2325
16th to endDay
23%5%8%19%28%13%
2465
September1st to 15thDay
29%48%17%31%8%
2091
16th to endDay
31%6%11%26%19%4
1980
October1st to 15thDay
43%7%13%24%8%2
1821
16th to endDay
39%7%17%24%9%1
1905
November1st to 15thDay
48%7%15%19%6%2
1638
16th to endDay
51%7%17%17%5%
1560
December1st to 15thDay
63%8%10%10%6%
1560
16th to endDay
64%6%13%10%4
1557
January1st to 15thNight
56%9%13%12%6%1
2450
16th to endNight
53%7%14%16%5%2
2496
February1st to 15thNight
59%8%13%13%5%
2288
16th to endNight
58%7%14%14%41
1989
March1st to 15thNight
48%12%15%17%5%
2003
16th to endNight
50%10%14%19%3
2112
April1st to 15thNight
44%10%18%18%6%
1828
16th to endNight
40%7%18%26%5%
1620
May1st to 15thNight
33%10%15%31%9%
1620
16th to endNight
41%8%17%23%8%
1509
June1st to 15thNight
35%8%17%26%11%1
1389
16th to endNight
15%48%25%33%12%
1260
July1st to 15thNight
12%7%11%25%27%15%
1218
16th to endNight
12%48%16%30%25%
1590
August1st to 15thNight
19%6%8%21%25%18%
1611
16th to endNight
17%48%21%32%15%
1737
September1st to 15thNight
21%6%9%21%31%10%
1866
16th to endNight
26%412%28%22%5%
1980
October1st to 15thNight
38%5%16%26%10%2
2139
16th to endNight
32%8%15%29%12%1
2317
November1st to 15thNight
46%7%13%22%7%2
2538
16th to endNight
46%8%17%18%7%1
2730
December1st to 15thNight
60%8%15%10%4
2730
16th to endNight
62%7%13%11%31
2755

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
9%13%23%37%9%6%
81
16th to endDay
5%9%33%37%12%2
96
February1st to 15thDay
23%25%17%23%10%
90
16th to endDay
15%23%34%18%8%
141
March1st to 15thDay
15%35%31%15%1
270
16th to endDay
18%30%35%14%1
288
April1st to 15thDay
15%30%30%17%41
269
16th to endDay
18%25%36%11%7%
270
May1st to 15thDay
15%20%31%23%6%1
288
16th to endDay
19%10%27%24%15%2
506
June1st to 15thDay
12%14%26%29%13%2
495
16th to endDay
5%12%31%28%19%2
495
July1st to 15thDay
46%27%33%25%2
475
16th to endDay
412%40%32%7%1
328
August1st to 15thDay
6%10%39%29%12%1
315
16th to endDay
5%11%31%30%15%5%
332
September1st to 15thDay
8%16%33%23%13%4
315
16th to endDay
11%15%33%22%13%3
315
October1st to 15thDay
10%16%35%24%11%1
156
16th to endDay
12%13%28%34%6%4
144
November1st to 15thDay
11%16%28%21%14%8%
135
16th to endDay
10%12%47%23%5%
135
December1st to 15thDay
13%14%29%28%13%
135
16th to endDay
8%14%35%28%9%3
107
January1st to 15thNight
10%11%29%36%10%1
819
16th to endNight
10%7%33%34%12%1
768
February1st to 15thNight
11%10%30%36%9%
704
16th to endNight
9%11%35%31%10%1
632
March1st to 15thNight
8%14%28%36%11%1
720
16th to endNight
12%11%30%33%11%
768
April1st to 15thNight
11%12%27%33%12%1
596
16th to endNight
12%8%27%33%17%1
540
May1st to 15thNight
11%6%22%36%21%1
540
16th to endNight
16%6%17%35%23%1
563
June1st to 15thNight
12%6%23%36%20%1
489
16th to endNight
4213%46%29%2
360
July1st to 15thNight
2110%43%40%1
368
16th to endNight
1114%44%36%1
564
August1st to 15thNight
312%46%34%1
539
16th to endNight
4214%38%36%4
573
September1st to 15thNight
7%115%38%32%4
606
16th to endNight
10%215%34%30%6%
716
October1st to 15thNight
14%5%22%35%19%3
720
16th to endNight
11%5%19%42%17%3
768
November1st to 15thNight
14%10%26%36%10%1
828
16th to endNight
12%12%31%33%9%1
975
December1st to 15thNight
15%10%30%36%6%
975
16th to endNight
13%13%29%32%10%1
984
Page generated at 2017-12-21 05:04:47. Version ac04

Copyright 2017 A. Danko


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