Rayville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rayville Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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
52%
23873
24%
74629
19%
23813
58%
23813
31%
44030

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%
950
25%
2458
11%
946
43%
946
32%
1581
January11th to 20thNight
31%
935
25%
2431
10%
935
40%
935
28%
1633
January21st to endNight
30%
990
26%
2574
9%
990
40%
990
29%
1712
February1st to 10thNight
30%
832
23%
2272
9%
832
39%
832
27%
1495
February11th to 20thNight
28%
703
20%
2099
9%
700
36%
700
24%
1373
February21st to endNight
24%
579
23%
1763
7%
579
36%
579
21%
1195
March1st to 10thNight
37%
540
25%
1980
17%
540
48%
540
24%
1169
March11th to 20thNight
35%
540
20%
1980
13%
540
45%
540
21%
1215
March21st to endNight
39%
594
23%
2156
17%
594
49%
594
26%
1256
April1st to 10thNight
41%
540
27%
1800
18%
540
54%
540
31%
1027
April11th to 20thNight
40%
533
25%
1775
18%
533
52%
533
29%
1031
April21st to endNight
45%
540
28%
1800
23%
540
57%
540
33%
1015
May1st to 10thNight
54%
540
23%
1800
21%
540
62%
540
33%
1005
May11th to 20thNight
59%
531
22%
1769
24%
531
63%
531
33%
1008
May21st to endNight
67%
584
23%
1782
22%
582
71%
582
38%
1001
June1st to 10thNight
71%
540
18%
1620
19%
540
74%
540
34%
952
June11th to 20thNight
77%
540
22%
1620
23%
540
78%
540
46%
836
June21st to endNight
75%
540
23%
1620
24%
540
76%
540
38%
919
July1st to 10thNight
79%
525
16%
1575
18%
525
80%
525
35%
938
July11th to 20thNight
81%
522
19%
1566
21%
522
81%
522
40%
861
July21st to endNight
83%
591
22%
1673
25%
558
84%
558
40%
926
August1st to 10thNight
83%
537
19%
1714
24%
534
84%
534
44%
884
August11th to 20thNight
80%
534
21%
1776
27%
534
80%
534
35%
993
August21st to endNight
73%
594
21%
1980
25%
594
74%
594
32%
1147
September1st to 10thNight
74%
540
24%
1800
27%
540
75%
540
33%
1030
September11th to 20thNight
68%
540
27%
1800
28%
540
70%
540
32%
1041
September21st to endNight
73%
666
32%
2019
29%
666
75%
666
42%
1084
October1st to 10thNight
69%
720
30%
2160
25%
720
72%
720
44%
1134
October11th to 20thNight
54%
720
34%
2160
24%
720
62%
720
38%
1214
October21st to endNight
53%
792
32%
2376
25%
792
60%
792
38%
1334
November1st to 10thNight
59%
740
32%
2220
25%
740
65%
740
40%
1233
November11th to 20thNight
48%
760
30%
2280
23%
760
56%
760
36%
1292
November21st to endNight
43%
760
27%
2434
19%
760
52%
760
29%
1452
December1st to 10thNight
40%
792
25%
2502
17%
792
50%
792
26%
1556
December11th to 20thNight
37%
949
24%
2967
12%
948
44%
948
25%
1892
December21st to endNight
33%
1040
15%
4328
10%
1026
40%
1026
18%
2596

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%8%44%
74641
Night
12%5%2443445%7%49%
75191
TransparencyDay
38%6%12%20%19%5%
74366
Night
34%5%11%20%21%8%
74987
SeeingDay
13%6%19%24%25%13%
13989
Night
14%6%22%32%22%4
23879

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
18%8%34424346%44%
1707
11th to 20thDay
20%9%26%423335%42%
1674
21st to endDay
19%7%25%323335%47%
1782
February1st to 10thDay
18%9%35%434345%41%
1685
11th to 20thDay
22%7%35%5%33345%40%
1748
21st to endDay
21%8%36%6%33345%36%
1506
March1st to 10thDay
18%6%36%5%3445%7%41%
1980
11th to 20thDay
16%7%35%6%45%45%6%39%
1980
21st to endDay
11%6%27%5%345%5%7%45%
2200
April1st to 10thDay
13%425%5%35%5%5%7%44%
2160
11th to 20thDay
16%6%36%5%345%47%43%
2134
21st to endDay
11%5%36%5%35%5%5%7%46%
2160
May1st to 10thDay
13%5%37%6%35%5%5%7%42%
2160
11th to 20thDay
11%5%26%445%6%5%10%43%
2124
21st to endDay
8%325%446%7%8%10%42%
2489
June1st to 10thDay
9%4345%46%7%8%10%41%
2340
11th to 20thDay
4425%6%46%5%8%9%46%
2340
21st to endDay
6%425%5%46%6%8%11%44%
2340
July1st to 10thDay
6%435%6%5%7%8%9%10%38%
2340
11th to 20thDay
7%425%5%47%6%7%12%40%
2340
21st to endDay
8%425%6%47%7%8%11%38%
2546
August1st to 10thDay
5%415%6%47%6%7%10%45%
2212
11th to 20thDay
8%5%25%5%46%7%8%10%41%
2125
21st to endDay
12%425%5%35%5%6%9%43%
2376
September1st to 10thDay
7%5%15%6%46%6%7%8%45%
2160
11th to 20thDay
12%5%36%5%45%5%5%7%44%
2160
21st to endDay
10%41443445%6%54%
1919
October1st to 10thDay
7%32442445%6%59%
1800
11th to 20thDay
12%415%433346%56%
1800
21st to endDay
15%5%2442343454%
1980
November1st to 10thDay
11%5%34432346%56%
1858
11th to 20thDay
10%5%35%324346%54%
1900
21st to endDay
16%6%26%5%3435%6%44%
1739
December1st to 10thDay
18%7%3443445%6%41%
1673
11th to 20thDay
16%8%36%5%34445%42%
2069
21st to endDay
15%7%25%5%34447%43%
3135
January1st to 10thNight
18%5%2432345%449%
2458
11th to 20thNight
19%7%26%433345%46%
2431
21st to endNight
19%6%25%424345%46%
2574
February1st to 10thNight
16%8%35%433446%44%
2272
11th to 20thNight
20%7%345%34345%43%
2098
21st to endNight
22%7%3442344442%
1763
March1st to 10thNight
15%6%245%34449%44%
1980
11th to 20thNight
14%7%25%5%35%5%6%6%42%
1980
21st to endNight
13%5%35%43445%7%48%
2156
April1st to 10thNight
11%425%5%245%6%7%50%
1800
11th to 20thNight
14%5%2443445%6%49%
1775
21st to endNight
9%5%245%2445%7%52%
1800
May1st to 10thNight
10%425%435%5%5%9%50%
1800
11th to 20thNight
8%5%245%345%7%11%46%
1769
21st to endNight
7%324435%5%6%11%50%
1782
June1st to 10thNight
6%326%5%346%7%12%45%
1620
11th to 20thNight
43234245%7%10%56%
1620
21st to endNight
6%4245%35%5%7%10%51%
1620
July1st to 10thNight
5%424437%5%8%13%44%
1620
11th to 20thNight
6%313435%6%8%12%49%
1620
21st to endNight
43143247%8%12%51%
1772
August1st to 10thNight
32234246%7%12%55%
1724
11th to 20thNight
7%313435%6%8%12%47%
1776
21st to endNight
9%4244345%7%9%49%
1980
September1st to 10thNight
6%425%5%345%7%9%49%
1800
11th to 20thNight
8%5%35%5%3445%7%51%
1800
21st to endNight
9%41432335%7%59%
2019
October1st to 10thNight
7%31442445%6%61%
2160
11th to 20thNight
10%5%24423346%57%
2160
21st to endNight
13%5%1342333458%
2376
November1st to 10thNight
11%423323335%59%
2220
11th to 20thNight
12%424423446%55%
2280
21st to endNight
15%5%345%3335%6%48%
2434
December1st to 10thNight
17%6%35%433446%46%
2502
11th to 20thNight
16%6%26%5%34345%47%
3118
21st to endNight
17%8%35%423445%45%
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
43%37%21%20%6%
1708
11th to 20thDay
48%35%17%22%6%
1674
21st to endDay
42%3419%25%7%
1782
February1st to 10thDay
46%47%16%17%10%
1685
11th to 20thDay
49%45%17%18%7%
1758
21st to endDay
51%46%11%20%7%
1506
March1st to 10thDay
45%49%16%18%8%
1980
11th to 20thDay
46%6%9%17%17%5%
1980
21st to endDay
38%6%11%20%22%3
2200
April1st to 10thDay
39%5%9%22%17%7%
2160
11th to 20thDay
42%5%9%18%19%7%
2134
21st to endDay
37%410%23%23%3
2160
May1st to 10thDay
41%5%11%20%18%5%
2160
11th to 20thDay
36%5%17%26%15%1
2128
21st to endDay
33%8%16%28%15%1
2489
June1st to 10thDay
35%8%17%25%14%1
2340
11th to 20thDay
31%8%17%25%17%2
2340
21st to endDay
31%9%16%24%16%3
2340
July1st to 10thDay
37%10%22%22%8%1
2276
11th to 20thDay
33%10%23%23%10%1
2271
21st to endDay
36%9%21%22%10%1
2405
August1st to 10thDay
32%9%21%27%11%
2198
11th to 20thDay
35%10%17%24%12%2
2125
21st to endDay
38%7%18%21%13%3
2376
September1st to 10thDay
35%8%14%21%18%5%
2160
11th to 20thDay
38%7%11%18%20%7%
2160
21st to endDay
30%5%10%22%22%10%
1919
October1st to 10thDay
27%5%9%21%24%14%
1800
11th to 20thDay
30%45%18%29%14%
1800
21st to endDay
35%35%17%29%12%
1980
November1st to 10thDay
31%47%18%30%10%
1858
11th to 20thDay
33%36%18%28%12%
1900
21st to endDay
42%46%18%23%7%
1739
December1st to 10thDay
44%5%9%19%16%8%
1673
11th to 20thDay
46%35%16%25%5%
2067
21st to endDay
43%36%17%28%3
3135
January1st to 10thNight
38%47%18%27%7%
2458
11th to 20thNight
43%46%18%21%8%
2431
21st to endNight
43%3416%25%9%
2574
February1st to 10thNight
43%46%18%22%8%
2272
11th to 20thNight
45%45%17%21%9%
2099
21st to endNight
48%46%12%17%13%
1763
March1st to 10thNight
39%48%17%21%10%
1980
11th to 20thNight
41%6%12%15%18%8%
1980
21st to endNight
36%6%9%19%25%6%
2156
April1st to 10thNight
32%6%11%21%20%10%
1800
11th to 20thNight
36%410%19%21%11%
1775
21st to endNight
32%5%8%23%27%5%
1800
May1st to 10thNight
31%7%10%23%21%8%
1800
11th to 20thNight
32%6%13%28%19%2
1770
21st to endNight
28%7%16%27%21%1
1783
June1st to 10thNight
30%8%17%27%17%1
1620
11th to 20thNight
22%6%19%32%18%4
1620
21st to endNight
27%8%17%25%19%4
1620
July1st to 10thNight
28%10%27%23%10%2
1575
11th to 20thNight
24%9%27%25%13%2
1566
21st to endNight
22%11%25%29%11%2
1673
August1st to 10thNight
21%7%28%29%12%1
1714
11th to 20thNight
27%9%23%21%16%3
1776
21st to endNight
31%9%19%21%17%5%
1980
September1st to 10thNight
30%8%14%25%15%8%
1800
11th to 20thNight
32%7%14%16%21%10%
1800
21st to endNight
26%410%23%23%13%
2019
October1st to 10thNight
24%5%9%20%25%17%
2160
11th to 20thNight
30%46%16%28%16%
2160
21st to endNight
31%37%16%28%15%
2376
November1st to 10thNight
29%47%19%27%14%
2220
11th to 20thNight
32%48%16%28%13%
2280
21st to endNight
37%46%18%24%11%
2434
December1st to 10thNight
41%49%20%20%7%
2502
11th to 20thNight
42%36%13%26%10%
3119
21st to endNight
42%36%20%23%6%
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
23%15%37%17%6%1
270
11th to 20thDay
23%16%33%19%9%2
258
21st to endDay
22%14%36%25%4
264
February1st to 10thDay
23%11%38%21%6%1
240
11th to 20thDay
33%16%31%16%4
240
21st to endDay
30%19%30%17%41
198
March1st to 10thDay
22%15%31%23%9%
240
11th to 20thDay
20%19%38%18%5%1
240
21st to endDay
16%16%38%18%12%
286
April1st to 10thDay
15%9%35%28%12%1
420
11th to 20thDay
22%12%26%25%14%2
412
21st to endDay
13%11%26%31%18%1
420
May1st to 10thDay
15%7%27%29%20%2
423
11th to 20thDay
12%319%32%24%10%
447
21st to endDay
7%316%32%28%14%
637
June1st to 10thDay
10%212%25%33%17%
630
11th to 20thDay
4212%30%40%12%
630
21st to endDay
7%29%25%34%22%
630
July1st to 10thDay
5%16%25%39%24%
621
11th to 20thDay
5%15%21%37%31%
618
21st to endDay
7%1420%41%25%
684
August1st to 10thDay
7%15%17%41%30%
510
11th to 20thDay
10%1316%42%28%
439
21st to endDay
14%1415%31%36%
495
September1st to 10thDay
6%16%24%40%23%
450
11th to 20thDay
10%28%20%33%27%
450
21st to endDay
13%27%25%36%18%
353
October1st to 10thDay
8%216%32%27%14%
270
11th to 20thDay
9%5%24%30%23%9%
270
21st to endDay
16%10%28%24%14%7%
297
November1st to 10thDay
16%7%22%33%18%5%
270
11th to 20thDay
11%10%31%31%13%4
270
21st to endDay
19%13%30%24%10%4
270
December1st to 10thDay
19%9%38%23%9%2
270
11th to 20thDay
23%13%34%20%10%1
270
21st to endDay
20%16%34%23%5%3
297
January1st to 10thNight
20%11%32%32%6%
950
11th to 20thNight
24%9%31%27%8%
935
21st to endNight
22%7%36%29%5%
990
February1st to 10thNight
21%10%35%29%5%
832
11th to 20thNight
23%10%35%28%4
703
21st to endNight
24%12%36%26%2
579
March1st to 10thNight
18%10%32%33%7%
540
11th to 20thNight
16%8%35%33%7%
540
21st to endNight
16%9%33%30%11%
594
April1st to 10thNight
12%7%37%33%10%
540
11th to 20thNight
14%9%32%33%11%1
533
21st to endNight
10%8%33%35%14%1
540
May1st to 10thNight
10%425%45%15%1
540
11th to 20thNight
8%324%40%24%2
531
21st to endNight
6%315%38%33%6%
584
June1st to 10thNight
6%210%37%41%4
540
11th to 20thNight
229%35%47%5%
540
21st to endNight
7%17%31%42%12%
540
July1st to 10thNight
5%2331%49%11%
525
11th to 20thNight
5%15%25%51%13%
522
21st to endNight
41426%52%12%
591
August1st to 10thNight
31426%50%16%
537
11th to 20thNight
8%1228%50%11%
534
21st to endNight
10%25%23%47%14%
594
September1st to 10thNight
6%26%32%46%7%
540
11th to 20thNight
9%19%31%42%7%
540
21st to endNight
10%28%37%38%5%
666
October1st to 10thNight
8%213%36%34%7%
720
11th to 20thNight
11%422%38%21%3
720
21st to endNight
15%5%22%34%21%3
792
November1st to 10thNight
12%421%39%21%3
740
11th to 20thNight
14%6%27%38%15%1
760
21st to endNight
17%7%28%32%14%2
760
December1st to 10thNight
19%9%28%34%9%
792
11th to 20thNight
21%8%29%32%9%
950
21st to endNight
23%10%29%31%7%
1045
Page generated at 2024-01-14 08:55:00. Version ac07

Copyright 2024 Attilla Danko


Rayville Observatory Clear Sky Chart |Charts Home