MEL Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MEL Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
46%
23808
25%
74487
17%
23750
55%
23750
30%
44101

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
37%
948
30%
2458
13%
946
47%
946
35%
1489
January11th to 20thNight
34%
950
27%
2470
11%
950
43%
950
32%
1557
January21st to endNight
32%
901
29%
2541
11%
901
45%
901
28%
1606
February1st to 10thNight
28%
720
26%
2160
10%
720
41%
720
25%
1338
February11th to 20thNight
28%
704
22%
2098
10%
700
38%
700
26%
1299
February21st to endNight
18%
592
25%
1776
6%
592
35%
592
23%
1129
March1st to 10thNight
26%
571
24%
2011
10%
571
40%
571
21%
1250
March11th to 20thNight
30%
540
22%
1980
13%
540
40%
540
20%
1213
March21st to endNight
28%
594
24%
2178
14%
594
42%
594
24%
1264
April1st to 10thNight
29%
540
24%
1980
13%
540
45%
540
23%
1167
April11th to 20thNight
27%
533
22%
1945
12%
533
44%
533
21%
1188
April21st to endNight
28%
540
27%
1668
13%
540
46%
540
26%
1048
May1st to 10thNight
32%
540
24%
1620
16%
540
42%
540
26%
1032
May11th to 20thNight
42%
531
21%
1594
19%
531
49%
531
29%
1002
May21st to endNight
45%
583
21%
1745
15%
582
55%
582
29%
1107
June1st to 10thNight
64%
540
23%
1620
22%
540
71%
540
44%
860
June11th to 20thNight
56%
540
23%
1620
20%
540
64%
540
44%
871
June21st to endNight
65%
540
22%
1620
23%
540
69%
540
36%
957
July1st to 10thNight
67%
525
15%
1575
16%
525
70%
525
32%
959
July11th to 20thNight
79%
522
26%
1566
27%
522
83%
522
46%
813
July21st to endNight
78%
591
24%
1673
25%
558
84%
558
47%
871
August1st to 10thNight
83%
537
28%
1609
30%
534
86%
534
58%
742
August11th to 20thNight
77%
534
24%
1778
27%
534
79%
534
34%
991
August21st to endNight
76%
594
19%
2070
23%
594
78%
594
33%
1166
September1st to 10thNight
71%
540
21%
1980
24%
540
73%
540
31%
1113
September11th to 20thNight
70%
540
21%
1980
23%
540
71%
540
25%
1215
September21st to endNight
66%
540
25%
1980
26%
540
69%
540
32%
1077
October1st to 10thNight
72%
540
32%
1980
34%
540
74%
540
38%
1000
October11th to 20thNight
53%
634
30%
2074
22%
634
61%
634
33%
1193
October21st to endNight
51%
792
32%
2376
19%
792
59%
792
37%
1342
November1st to 10thNight
55%
740
28%
2220
19%
740
59%
740
33%
1328
November11th to 20thNight
47%
883
26%
2403
14%
883
54%
883
35%
1462
November21st to endNight
36%
950
26%
2470
11%
950
44%
950
28%
1613
December1st to 10thNight
40%
950
30%
2470
14%
950
48%
950
34%
1560
December11th to 20thNight
33%
949
26%
2893
12%
948
40%
948
23%
1894
December21st to endNight
36%
1040
17%
4306
12%
1026
44%
1026
22%
2385

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%3445%7%47%
75008
Night
13%5%24423447%51%
75063
TransparencyDay
37%6%10%19%19%9%
74733
Night
34%6%11%20%19%11%
74858
SeeingDay
15%7%22%30%21%5%
13739
Night
16%7%25%34%16%2
23817

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
14%5%25%323346%53%
1707
11th to 20thDay
18%7%24324245%49%
1710
21st to endDay
16%6%34323336%51%
1973
February1st to 10thDay
19%7%35%423345%46%
1800
11th to 20thDay
19%7%24423347%44%
1749
21st to endDay
19%425%413345%50%
1480
March1st to 10thDay
18%7%36%5%2445%6%41%
1948
11th to 20thDay
16%6%25%434446%45%
1980
21st to endDay
15%6%24424346%49%
2178
April1st to 10thDay
15%7%36%5%3445%6%43%
1980
11th to 20thDay
20%6%34424446%44%
1960
21st to endDay
14%6%345%34446%46%
2290
May1st to 10thDay
15%7%36%5%35%5%5%6%40%
2340
11th to 20thDay
14%8%36%6%35%5%5%5%39%
2302
21st to endDay
17%6%35%5%45%6%6%9%34%
2531
June1st to 10thDay
6%4245%36%6%7%9%49%
2340
11th to 20thDay
7%4245%36%5%7%8%48%
2340
21st to endDay
8%5%36%6%46%6%7%9%39%
2340
July1st to 10thDay
10%6%35%7%5%5%7%6%9%38%
2340
11th to 20thDay
5%313447%5%7%10%51%
2340
21st to endDay
5%334435%5%7%11%51%
2546
August1st to 10thDay
22134245%5%11%62%
2315
11th to 20thDay
6%3145%45%5%6%8%52%
2123
21st to endDay
5%325%6%47%7%8%11%41%
2284
September1st to 10thDay
9%5%35%7%45%5%5%7%44%
1980
11th to 20thDay
11%7%36%6%45%6%6%8%39%
1980
21st to endDay
9%4245%35%5%7%8%49%
1980
October1st to 10thDay
8%5%24435%5%5%7%53%
1980
11th to 20thDay
13%5%2443345%7%50%
1866
21st to endDay
12%5%24423345%58%
1980
November1st to 10thDay
14%7%36%5%2346%6%45%
1858
11th to 20thDay
13%426%4335%5%5%50%
1772
21st to endDay
17%7%25%5%2434446%
1710
December1st to 10thDay
15%6%35%423346%48%
1710
11th to 20thDay
15%7%35%5%3445%445%
2161
21st to endDay
16%6%2332323455%
3135
January1st to 10thNight
17%5%23313347%53%
2458
11th to 20thNight
17%6%24323345%52%
2470
21st to endNight
18%6%35%422335%49%
2541
February1st to 10thNight
18%6%25%423245%48%
2160
11th to 20thNight
19%7%2432234450%
2098
21st to endNight
20%6%24423345%45%
1776
March1st to 10thNight
18%6%245%33447%43%
2011
11th to 20thNight
16%8%35%424445%46%
1980
21st to endNight
16%6%34333447%48%
2178
April1st to 10thNight
14%5%35%5%33448%46%
1980
11th to 20thNight
19%6%2442444446%
1945
21st to endNight
18%6%24423336%48%
1668
May1st to 10thNight
13%7%35%4345%46%47%
1620
11th to 20thNight
12%6%25%5%3435%9%46%
1593
21st to endNight
13%5%344345%6%9%43%
1745
June1st to 10thNight
5%32342346%9%59%
1620
11th to 20thNight
5%3234245%5%10%58%
1620
21st to endNight
7%4234245%7%10%51%
1620
July1st to 10thNight
10%4343345%6%12%46%
1620
11th to 20thNight
321333447%9%62%
1620
21st to endNight
5%21332446%11%59%
1772
August1st to 10thNight
11221345%9%71%
1619
11th to 20thNight
6%323435%5%6%11%52%
1778
21st to endNight
7%3235%35%5%6%11%49%
2070
September1st to 10thNight
7%5%25%5%3445%7%53%
1980
11th to 20thNight
9%7%346%35%5%6%7%46%
1980
21st to endNight
9%5%2443445%8%52%
1980
October1st to 10thNight
7%423434347%60%
1980
11th to 20thNight
14%5%24323447%52%
2074
21st to endNight
15%42322322460%
2376
November1st to 10thNight
14%6%24423335%53%
2220
11th to 20thNight
11%6%25%423446%54%
2403
21st to endNight
17%6%15%433346%46%
2470
December1st to 10thNight
15%6%23323347%51%
2470
11th to 20thNight
16%9%35%43333447%
3036
21st to endNight
19%6%23212235%54%
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
35%45%19%22%15%
1708
11th to 20thDay
39%36%15%21%16%
1710
21st to endDay
36%46%14%25%15%
1973
February1st to 10thDay
44%35%12%21%16%
1800
11th to 20thDay
42%47%17%17%13%
1759
21st to endDay
40%46%16%18%16%
1480
March1st to 10thDay
44%6%8%13%18%11%
1948
11th to 20thDay
41%5%7%12%19%15%
1980
21st to endDay
38%5%9%17%19%12%
2178
April1st to 10thDay
43%6%7%17%17%11%
1980
11th to 20thDay
43%5%7%15%19%11%
1960
21st to endDay
40%5%6%20%19%10%
2290
May1st to 10thDay
46%6%7%15%19%7%
2340
11th to 20thDay
45%7%8%18%18%4
2306
21st to endDay
47%8%11%19%14%1
2531
June1st to 10thDay
30%9%12%26%19%4
2340
11th to 20thDay
34%7%13%25%17%5%
2340
21st to endDay
41%8%11%22%14%3
2340
July1st to 10thDay
41%11%13%24%10%2
2276
11th to 20thDay
26%9%17%27%19%2
2271
21st to endDay
24%10%18%34%13%1
2405
August1st to 10thDay
19%6%17%37%20%1
2301
11th to 20thDay
29%8%17%30%13%4
2123
21st to endDay
33%10%16%25%12%3
2284
September1st to 10thDay
40%7%9%20%16%8%
1980
11th to 20thDay
40%9%11%17%17%5%
1980
21st to endDay
33%7%11%20%18%11%
1980
October1st to 10thDay
30%6%12%19%23%10%
1980
11th to 20thDay
34%6%9%14%19%17%
1866
21st to endDay
30%45%15%25%20%
1980
November1st to 10thDay
39%5%8%19%19%10%
1858
11th to 20thDay
36%5%7%17%21%13%
1772
21st to endDay
43%45%15%20%14%
1710
December1st to 10thDay
39%48%20%21%9%
1710
11th to 20thDay
41%6%7%10%21%15%
2159
21st to endDay
35%35%14%28%15%
3135
January1st to 10thNight
33%47%16%23%18%
2458
11th to 20thNight
36%36%17%22%16%
2470
21st to endNight
39%45%14%19%19%
2541
February1st to 10thNight
40%36%13%20%18%
2160
11th to 20thNight
41%35%16%19%16%
2098
21st to endNight
42%46%14%17%17%
1776
March1st to 10thNight
42%6%8%16%19%11%
2011
11th to 20thNight
42%5%8%12%17%16%
1980
21st to endNight
37%5%10%16%17%14%
2178
April1st to 10thNight
38%6%8%18%17%13%
1980
11th to 20thNight
42%5%7%14%18%15%
1945
21st to endNight
40%5%8%20%18%10%
1668
May1st to 10thNight
40%6%9%18%17%10%
1620
11th to 20thNight
37%7%11%25%17%4
1594
21st to endNight
38%7%15%25%15%1
1746
June1st to 10thNight
23%7%16%29%23%3
1620
11th to 20thNight
23%7%15%31%19%5%
1620
21st to endNight
29%9%18%27%15%3
1620
July1st to 10thNight
32%10%21%27%10%1
1575
11th to 20thNight
19%9%22%30%19%1
1566
21st to endNight
19%8%27%35%10%1
1673
August1st to 10thNight
12%7%23%39%18%1
1609
11th to 20thNight
24%12%20%30%11%3
1778
21st to endNight
28%9%21%28%11%3
2070
September1st to 10thNight
31%7%16%22%17%7%
1980
11th to 20thNight
36%9%13%22%14%5%
1980
21st to endNight
30%7%14%20%17%11%
1980
October1st to 10thNight
25%6%12%24%21%12%
1980
11th to 20thNight
34%5%9%16%18%18%
2074
21st to endNight
31%36%16%23%22%
2376
November1st to 10thNight
35%48%18%22%13%
2220
11th to 20thNight
33%5%9%19%19%16%
2403
21st to endNight
40%48%15%19%14%
2470
December1st to 10thNight
36%48%19%21%12%
2470
11th to 20thNight
43%3411%20%19%
3037
21st to endNight
36%3413%29%14%
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
22%14%36%22%5%
270
11th to 20thDay
29%15%29%20%7%
270
21st to endDay
21%16%38%20%5%
282
February1st to 10thDay
30%14%30%20%5%
240
11th to 20thDay
29%17%33%18%3
240
21st to endDay
28%19%38%14%1
198
March1st to 10thDay
25%16%40%16%3
240
11th to 20thDay
21%16%40%16%6%
240
21st to endDay
22%16%36%21%41
264
April1st to 10thDay
21%16%41%19%3
240
11th to 20thDay
24%20%29%20%7%
238
21st to endDay
20%14%38%22%7%
550
May1st to 10thDay
18%9%38%27%7%
603
11th to 20thDay
18%9%28%33%10%2
625
21st to endDay
18%7%24%34%16%1
679
June1st to 10thDay
8%217%39%29%6%
630
11th to 20thDay
8%317%45%24%3
630
21st to endDay
9%216%38%28%8%
630
July1st to 10thDay
9%211%37%32%9%
621
11th to 20thDay
5%17%36%44%7%
618
21st to endDay
41435%45%10%
684
August1st to 10thDay
315%37%42%12%
613
11th to 20thDay
7%5%37%39%11%
437
21st to endDay
5%1432%37%20%
403
September1st to 10thDay
9%17%28%40%15%
270
11th to 20thDay
8%18%26%43%14%
270
21st to endDay
11%210%24%42%11%
270
October1st to 10thDay
6%317%37%28%10%
270
11th to 20thDay
13%6%21%36%19%6%
270
21st to endDay
23%12%26%23%14%3
297
November1st to 10thDay
19%428%31%14%3
270
11th to 20thDay
21%14%24%27%10%3
270
21st to endDay
26%15%32%17%8%2
270
December1st to 10thDay
16%11%35%26%8%3
270
11th to 20thDay
23%17%29%22%9%
270
21st to endDay
24%11%36%22%6%
297
January1st to 10thNight
20%10%29%31%8%
950
11th to 20thNight
21%12%29%30%8%
950
21st to endNight
22%11%30%29%8%
901
February1st to 10thNight
23%13%31%26%6%
720
11th to 20thNight
27%12%33%26%3
704
21st to endNight
27%12%40%19%2
592
March1st to 10thNight
23%10%36%27%4
571
11th to 20thNight
23%9%34%29%5%
540
21st to endNight
18%10%40%27%41
594
April1st to 10thNight
16%12%37%29%4
540
11th to 20thNight
23%11%35%28%4
533
21st to endNight
20%10%39%23%8%
540
May1st to 10thNight
18%10%37%30%5%
540
11th to 20thNight
15%8%31%36%10%1
531
21st to endNight
16%5%30%36%13%1
584
June1st to 10thNight
7%221%46%23%1
540
11th to 20thNight
4233%46%15%1
540
21st to endNight
7%218%44%24%4
540
July1st to 10thNight
10%214%42%29%4
525
11th to 20thNight
3110%51%32%2
522
21st to endNight
5%19%50%32%3
591
August1st to 10thNight
111%50%34%3
537
11th to 20thNight
5%19%49%32%5%
534
21st to endNight
7%7%38%41%6%
594
September1st to 10thNight
9%19%37%39%5%
540
11th to 20thNight
12%18%38%39%3
540
21st to endNight
13%112%33%36%4
540
October1st to 10thNight
8%213%44%28%5%
540
11th to 20thNight
15%422%36%21%2
634
21st to endNight
18%8%21%31%20%2
792
November1st to 10thNight
14%6%21%38%20%2
740
11th to 20thNight
15%7%26%36%15%1
883
21st to endNight
21%12%27%29%11%1
950
December1st to 10thNight
21%7%29%33%9%1
950
11th to 20thNight
26%9%27%30%8%
950
21st to endNight
22%8%30%33%7%
1045
Page generated at 2024-01-24 08:37:29. Version ac07

Copyright 2024 Attilla Danko


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