RCH Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the RCH Observatory clear sky chart from 2005-11-06 to 2024-01-22.

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%
23904
27%
74355
19%
23845
57%
23845
35%
41889

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
34%
949
31%
2458
12%
946
46%
946
37%
1483
January11th to 20thNight
33%
950
28%
2470
10%
950
44%
950
32%
1550
January21st to endNight
33%
1000
30%
2600
12%
1000
43%
1000
33%
1628
February1st to 10thNight
28%
762
26%
2202
9%
762
40%
762
27%
1382
February11th to 20thNight
25%
704
23%
2098
8%
700
37%
700
26%
1313
February21st to endNight
19%
544
27%
1728
8%
544
36%
544
25%
1047
March1st to 10thNight
27%
540
24%
1980
12%
540
41%
540
23%
1188
March11th to 20thNight
31%
540
23%
1980
14%
540
42%
540
23%
1168
March21st to endNight
30%
594
26%
2178
14%
594
48%
594
29%
1172
April1st to 10thNight
31%
540
26%
1980
14%
540
50%
540
28%
1086
April11th to 20thNight
33%
533
24%
1880
15%
533
48%
533
27%
1063
April21st to endNight
32%
540
28%
1725
14%
540
51%
540
32%
988
May1st to 10thNight
33%
540
25%
1620
16%
540
44%
540
33%
945
May11th to 20thNight
44%
531
22%
1594
19%
531
53%
531
35%
924
May21st to endNight
52%
583
25%
1746
20%
582
63%
582
36%
1019
June1st to 10thNight
69%
540
23%
1620
22%
540
75%
540
46%
839
June11th to 20thNight
67%
540
27%
1620
27%
540
72%
540
53%
780
June21st to endNight
70%
540
25%
1620
28%
540
73%
540
43%
874
July1st to 10thNight
75%
525
21%
1575
24%
525
78%
525
41%
856
July11th to 20thNight
83%
522
28%
1566
31%
522
87%
522
55%
740
July21st to endNight
81%
591
27%
1673
28%
558
86%
558
53%
822
August1st to 10thNight
89%
537
34%
1601
37%
534
90%
534
66%
689
August11th to 20thNight
76%
534
29%
1600
32%
534
77%
534
43%
855
August21st to endNight
80%
594
25%
2104
31%
594
83%
594
40%
1061
September1st to 10thNight
73%
540
23%
1980
27%
540
76%
540
34%
1067
September11th to 20thNight
70%
540
23%
1980
26%
540
71%
540
31%
1086
September21st to endNight
74%
540
32%
1980
35%
540
77%
540
42%
944
October1st to 10thNight
74%
558
36%
1998
36%
558
77%
558
46%
908
October11th to 20thNight
57%
720
33%
2160
20%
720
65%
720
40%
1188
October21st to endNight
46%
792
34%
2376
19%
792
56%
792
39%
1302
November1st to 10thNight
52%
740
31%
2220
20%
740
59%
740
38%
1269
November11th to 20thNight
47%
812
29%
2332
16%
812
56%
812
37%
1332
November21st to endNight
39%
950
28%
2470
14%
950
47%
950
32%
1580
December1st to 10thNight
40%
950
31%
2470
14%
950
50%
950
36%
1524
December11th to 20thNight
32%
949
27%
2867
11%
948
41%
948
25%
1842
December21st to endNight
35%
1040
18%
4304
12%
1026
44%
1026
23%
2375

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%43445%7%48%
75003
Night
12%5%2442345%7%53%
74958
TransparencyDay
35%410%22%20%8%
74728
Night
31%410%22%22%11%
74753
SeeingDay
13%6%21%28%24%8%
13884
Night
14%6%27%35%17%2
23912

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
15%5%33323447%52%
1707
11th to 20thDay
18%5%2342335%6%48%
1710
21st to endDay
17%5%24323345%51%
1791
February1st to 10thDay
20%7%26%424346%44%
1773
11th to 20thDay
19%7%26%5%24435%43%
1749
21st to endDay
20%6%35%32333447%
1525
March1st to 10thDay
21%6%35%42345%7%41%
1980
11th to 20thDay
17%7%35%434445%42%
1980
21st to endDay
17%6%25%333445%47%
2178
April1st to 10thDay
14%8%35%5%2445%8%42%
1980
11th to 20thDay
14%6%35%5%35%5%5%8%40%
2026
21st to endDay
13%5%245%35%35%7%48%
2231
May1st to 10thDay
13%5%36%5%35%5%5%8%42%
2340
11th to 20thDay
13%6%36%5%35%5%5%7%42%
2302
21st to endDay
12%6%36%6%46%6%6%9%36%
2531
June1st to 10thDay
5%424435%6%7%11%50%
2340
11th to 20thDay
5%425%435%6%7%9%50%
2340
21st to endDay
6%435%5%46%5%6%10%46%
2340
July1st to 10thDay
7%6%26%5%47%7%7%9%41%
2340
11th to 20thDay
42134345%7%11%56%
2340
21st to endDay
43245%45%6%6%10%51%
2546
August1st to 10thDay
321342346%10%63%
2328
11th to 20thDay
6%4244345%6%10%53%
2301
21st to endDay
5%325%6%36%6%7%9%48%
2246
September1st to 10thDay
8%5%25%446%5%5%7%49%
1980
11th to 20thDay
11%416%6%45%46%7%45%
1980
21st to endDay
7%3245%345%5%7%55%
1980
October1st to 10thDay
7%41442345%7%59%
1942
11th to 20thDay
14%32343343457%
1800
21st to endDay
14%41432333459%
1980
November1st to 10thDay
14%6%24424346%50%
1858
11th to 20thDay
11%5%25%42335%6%54%
1843
21st to endDay
18%6%245%24446%46%
1710
December1st to 10thDay
14%7%25%424346%49%
1710
11th to 20thDay
17%7%35%423347%43%
2161
21st to endDay
16%7%25%423336%49%
3135
January1st to 10thNight
15%5%24323336%54%
2458
11th to 20thNight
18%6%23313345%52%
2470
21st to endNight
15%6%35%423336%51%
2600
February1st to 10thNight
19%6%24323345%48%
2202
11th to 20thNight
20%6%2432333449%
2098
21st to endNight
20%7%23324335%47%
1728
March1st to 10thNight
17%5%25%42346%7%43%
1980
11th to 20thNight
14%6%25%43446%7%46%
1980
21st to endNight
12%5%3432445%6%53%
2178
April1st to 10thNight
11%5%3433445%8%51%
1980
11th to 20thNight
12%5%2443446%6%49%
1880
21st to endNight
12%5%2443345%7%51%
1725
May1st to 10thNight
9%436%5%2445%9%48%
1620
11th to 20thNight
11%42442446%10%48%
1593
21st to endNight
9%4245%245%6%11%48%
1745
June1st to 10thNight
432433446%9%59%
1620
11th to 20thNight
321341346%10%63%
1620
21st to endNight
43244245%7%8%56%
1620
July1st to 10thNight
44243345%8%12%51%
1620
11th to 20thNight
311242446%9%65%
1620
21st to endNight
31234245%6%11%58%
1772
August1st to 10thNight
111121335%10%73%
1611
11th to 20thNight
7%3234235%6%9%56%
1600
21st to endNight
33145%25%5%7%12%52%
2104
September1st to 10thNight
7%4245%345%5%9%53%
1980
11th to 20thNight
10%5%245%3445%8%52%
1980
21st to endNight
7%31432345%8%60%
1980
October1st to 10thNight
6%222323446%66%
1998
11th to 20thNight
13%412323345%59%
2160
21st to endNight
14%423322345%60%
2376
November1st to 10thNight
11%424323435%57%
2220
11th to 20thNight
9%425%434346%56%
2332
21st to endNight
18%6%23324346%49%
2470
December1st to 10thNight
14%6%2441345%7%51%
2470
11th to 20thNight
15%7%36%423435%47%
3036
21st to endNight
18%7%2432223454%
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
34%36%20%25%11%
1708
11th to 20thDay
38%36%20%23%10%
1710
21st to endDay
37%35%17%25%13%
1791
February1st to 10thDay
44%35%15%21%12%
1773
11th to 20thDay
45%26%17%20%9%
1759
21st to endDay
43%2416%18%16%
1525
March1st to 10thDay
44%37%16%22%8%
1980
11th to 20thDay
45%47%13%21%10%
1980
21st to endDay
39%38%19%22%8%
2178
April1st to 10thDay
42%49%19%16%10%
1980
11th to 20thDay
42%48%17%19%10%
2026
21st to endDay
36%49%21%24%7%
2231
May1st to 10thDay
41%5%8%22%17%7%
2340
11th to 20thDay
41%5%11%22%19%2
2306
21st to endDay
43%7%12%23%14%2
2531
June1st to 10thDay
28%6%13%30%19%3
2340
11th to 20thDay
29%6%12%32%16%5%
2340
21st to endDay
32%7%13%26%19%3
2340
July1st to 10thDay
36%8%17%27%11%1
2276
11th to 20thDay
21%6%19%30%21%3
2271
21st to endDay
24%6%21%34%14%1
2405
August1st to 10thDay
17%5%17%38%22%2
2314
11th to 20thDay
27%5%19%31%15%3
2301
21st to endDay
30%7%15%30%16%3
2246
September1st to 10thDay
35%5%12%21%18%9%
1980
11th to 20thDay
38%6%13%19%18%7%
1980
21st to endDay
28%5%7%25%22%13%
1980
October1st to 10thDay
26%5%10%22%22%15%
1942
11th to 20thDay
33%35%16%25%18%
1800
21st to endDay
31%25%17%27%19%
1980
November1st to 10thDay
36%48%20%22%10%
1858
11th to 20thDay
33%48%18%24%13%
1843
21st to endDay
41%46%18%19%12%
1710
December1st to 10thDay
38%39%21%20%9%
1710
11th to 20thDay
42%37%15%24%10%
2159
21st to endDay
39%25%18%25%11%
3135
January1st to 10thNight
33%25%20%25%15%
2458
11th to 20thNight
37%35%18%24%13%
2470
21st to endNight
38%2416%23%17%
2600
February1st to 10thNight
41%26%13%21%16%
2202
11th to 20thNight
41%36%15%22%13%
2098
21st to endNight
41%28%14%17%18%
1728
March1st to 10thNight
40%5%9%14%22%11%
1980
11th to 20thNight
39%5%9%13%24%10%
1980
21st to endNight
32%410%20%23%10%
2178
April1st to 10thNight
33%5%10%21%18%14%
1980
11th to 20thNight
36%411%18%18%14%
1880
21st to endNight
34%410%18%26%8%
1725
May1st to 10thNight
34%412%22%19%9%
1620
11th to 20thNight
32%5%14%27%18%4
1594
21st to endNight
31%6%15%30%16%2
1746
June1st to 10thNight
22%5%17%32%21%3
1620
11th to 20thNight
18%415%36%20%6%
1620
21st to endNight
25%6%14%28%23%5%
1620
July1st to 10thNight
25%7%22%32%13%2
1575
11th to 20thNight
15%5%21%35%21%2
1566
21st to endNight
17%6%25%38%14%1
1673
August1st to 10thNight
10%418%40%24%3
1601
11th to 20thNight
24%6%19%31%16%5%
1600
21st to endNight
23%7%18%33%14%4
2104
September1st to 10thNight
29%6%14%23%19%9%
1980
11th to 20thNight
31%6%15%20%19%8%
1980
21st to endNight
23%411%24%23%15%
1980
October1st to 10thNight
20%410%26%22%18%
1998
11th to 20thNight
29%37%16%24%21%
2160
21st to endNight
29%36%17%23%22%
2376
November1st to 10thNight
32%37%19%25%14%
2220
11th to 20thNight
31%48%19%24%15%
2332
21st to endNight
39%28%16%21%14%
2470
December1st to 10thNight
35%38%22%21%11%
2470
11th to 20thNight
42%25%13%24%14%
3037
21st to endNight
37%2415%29%13%
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
20%13%36%24%7%1
270
11th to 20thDay
23%11%34%23%7%2
270
21st to endDay
20%13%38%22%7%
267
February1st to 10thDay
25%13%33%21%8%
240
11th to 20thDay
30%15%34%18%4
240
21st to endDay
29%18%36%15%2
198
March1st to 10thDay
25%15%37%18%5%
240
11th to 20thDay
20%19%33%20%6%1
240
21st to endDay
17%13%45%17%7%1
264
April1st to 10thDay
23%14%39%20%5%
240
11th to 20thDay
21%13%29%25%10%2
304
21st to endDay
16%13%36%24%9%1
491
May1st to 10thDay
13%13%35%30%8%1
603
11th to 20thDay
15%5%25%33%18%4
625
21st to endDay
14%5%23%35%19%4
679
June1st to 10thDay
5%216%42%26%9%
630
11th to 20thDay
5%117%42%28%7%
630
21st to endDay
6%213%32%35%13%
630
July1st to 10thDay
7%19%34%35%13%
621
11th to 20thDay
215%32%46%14%
618
21st to endDay
21427%51%15%
684
August1st to 10thDay
3429%46%17%
626
11th to 20thDay
7%1428%46%14%
615
21st to endDay
7%15%18%40%29%
365
September1st to 10thDay
10%320%37%30%
270
11th to 20thDay
417%24%42%21%
270
21st to endDay
9%35%27%36%20%
270
October1st to 10thDay
4313%33%35%11%
270
11th to 20thDay
11%7%21%31%23%7%
270
21st to endDay
23%11%23%21%16%6%
297
November1st to 10thDay
21%427%26%16%5%
270
11th to 20thDay
16%9%28%28%17%2
270
21st to endDay
24%14%26%24%9%2
270
December1st to 10thDay
17%9%29%26%13%6%
270
11th to 20thDay
26%12%32%23%7%1
270
21st to endDay
22%8%40%21%9%1
297
January1st to 10thNight
19%9%35%30%7%1
950
11th to 20thNight
22%11%30%30%7%
950
21st to endNight
18%12%32%31%7%
1000
February1st to 10thNight
23%10%34%27%5%
762
11th to 20thNight
24%10%37%24%4
704
21st to endNight
24%14%39%20%2
544
March1st to 10thNight
21%9%41%24%5%
540
11th to 20thNight
18%10%38%28%6%
540
21st to endNight
13%11%43%27%5%
594
April1st to 10thNight
12%11%44%29%5%
540
11th to 20thNight
14%11%39%27%8%
533
21st to endNight
14%8%43%25%9%1
540
May1st to 10thNight
9%10%44%30%7%1
540
11th to 20thNight
11%435%34%14%1
531
21st to endNight
9%329%42%16%1
584
June1st to 10thNight
4218%46%28%2
540
11th to 20thNight
4122%56%15%2
540
21st to endNight
5%114%44%31%4
540
July1st to 10thNight
4110%44%37%4
525
11th to 20thNight
28%50%36%3
522
21st to endNight
218%47%38%4
591
August1st to 10thNight
25%50%38%5%
537
11th to 20thNight
9%445%36%5%
534
21st to endNight
416%39%42%8%
594
September1st to 10thNight
7%27%39%39%6%
540
11th to 20thNight
11%17%35%41%5%
540
21st to endNight
8%111%37%36%6%
540
October1st to 10thNight
6%114%46%26%5%
558
11th to 20thNight
14%422%38%20%3
720
21st to endNight
15%8%29%31%16%1
792
November1st to 10thNight
12%5%27%36%19%1
740
11th to 20thNight
11%7%29%39%13%1
812
21st to endNight
21%11%26%29%13%1
950
December1st to 10thNight
17%8%32%33%9%1
950
11th to 20thNight
22%8%31%32%6%
950
21st to endNight
21%8%33%31%8%
1045
Page generated at 2024-01-19 08:28:32. Version ac07

Copyright 2024 Attilla Danko


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