Cors Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cors Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
27%
22879
19%
74571
8%
22834
39%
22834
20%
48122

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
14%
760
21%
2649
5%
757
34%
757
17%
1636
January11th to 20thNight
15%
736
16%
2574
3%
736
30%
736
12%
1729
January21st to endNight
14%
792
20%
2772
5%
792
33%
792
16%
1754
February1st to 10thNight
15%
720
16%
2306
4%
720
30%
720
15%
1569
February11th to 20thNight
15%
703
21%
2100
4%
700
34%
700
17%
1384
February21st to endNight
18%
592
24%
1776
7%
592
38%
592
18%
1152
March1st to 10thNight
15%
720
21%
2160
6%
720
34%
720
18%
1419
March11th to 20thNight
16%
720
18%
2056
4%
720
30%
720
17%
1405
March21st to endNight
19%
792
21%
2067
5%
792
32%
792
20%
1410
April1st to 10thNight
21%
720
18%
1800
4%
720
30%
720
21%
1274
April11th to 20thNight
22%
681
19%
1745
5%
681
30%
681
23%
1201
April21st to endNight
22%
540
19%
1620
5%
540
33%
540
17%
1101
May1st to 10thNight
23%
540
14%
1620
6%
540
30%
540
17%
1136
May11th to 20thNight
23%
497
16%
1559
7%
497
33%
497
17%
1044
May21st to endNight
36%
389
13%
1551
12%
388
45%
388
17%
980
June1st to 10thNight
33%
360
14%
1440
11%
360
46%
360
15%
936
June11th to 20thNight
36%
360
13%
1440
13%
360
47%
360
19%
916
June21st to endNight
38%
360
12%
1440
11%
360
47%
360
19%
908
July1st to 10thNight
44%
350
12%
1400
13%
350
51%
350
19%
866
July11th to 20thNight
51%
348
13%
1392
15%
348
55%
348
23%
807
July21st to endNight
51%
394
20%
1486
20%
372
59%
372
25%
854
August1st to 10thNight
51%
483
17%
1547
13%
481
55%
481
29%
925
August11th to 20thNight
43%
532
18%
1596
12%
532
48%
532
23%
1060
August21st to endNight
48%
789
21%
1977
10%
789
53%
789
36%
1264
September1st to 10thNight
42%
720
21%
1808
8%
720
50%
720
35%
1159
September11th to 20thNight
42%
720
24%
1980
13%
720
49%
720
35%
1196
September21st to endNight
40%
720
25%
1980
14%
720
49%
720
31%
1249
October1st to 10thNight
33%
720
17%
1980
9%
720
40%
720
23%
1357
October11th to 20thNight
32%
720
22%
2209
10%
720
47%
720
24%
1371
October21st to endNight
23%
792
16%
2574
6%
792
35%
792
17%
1707
November1st to 10thNight
29%
740
23%
2407
11%
740
45%
740
23%
1473
November11th to 20thNight
23%
760
25%
2470
8%
760
43%
760
21%
1531
November21st to endNight
20%
760
23%
2470
6%
760
39%
760
19%
1523
December1st to 10thNight
17%
760
19%
2640
5%
760
35%
760
15%
1745
December11th to 20thNight
20%
760
19%
3188
4%
758
37%
758
13%
1975
December21st to endNight
15%
829
14%
4792
3%
817
34%
817
9%
3106

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
17%6%25%5%345%5%7%40%
74822
Night
17%7%35%5%3445%6%40%
74935
TransparencyDay
44%5%11%22%16%3
74527
Night
44%411%23%15%2
74764
SeeingDay
22%16%32%20%8%2
13890
Night
21%14%32%24%8%1
22886

By Month

Percentage Cloud Cover NE (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%8%36%5%3445%6%42%
1517
11th to 20thDay
19%7%25%6%3446%6%38%
1464
21st to endDay
13%8%25%6%45%5%46%42%
1584
February1st to 10thDay
19%7%45%5%36%5%6%6%34%
1648
11th to 20thDay
14%7%26%6%25%45%7%40%
1748
21st to endDay
18%10%46%6%3445%5%36%
1480
March1st to 10thDay
16%9%35%5%3446%8%36%
1797
11th to 20thDay
17%7%36%5%345%5%7%39%
1902
21st to endDay
18%8%36%6%34435%40%
2286
April1st to 10thDay
19%9%36%5%34446%39%
2160
11th to 20thDay
17%6%25%5%45%45%8%39%
2164
21st to endDay
22%6%36%6%34446%35%
2340
May1st to 10thDay
24%8%25%5%34447%33%
2340
11th to 20thDay
18%5%36%5%3445%7%39%
2349
21st to endDay
15%5%25%5%35%5%5%9%42%
2725
June1st to 10thDay
20%6%25%6%36%5%6%7%32%
2520
11th to 20thDay
17%5%35%5%345%5%8%39%
2520
21st to endDay
18%6%26%6%45%5%5%8%33%
2520
July1st to 10thDay
14%5%35%5%35%5%6%8%40%
2520
11th to 20thDay
13%6%25%5%36%5%7%10%38%
2520
21st to endDay
13%5%25%5%36%6%7%8%39%
2744
August1st to 10thDay
11%6%26%6%36%6%7%8%38%
2363
11th to 20thDay
13%6%26%5%45%6%7%8%39%
2304
21st to endDay
13%424335%6%6%9%46%
2376
September1st to 10thDay
13%5%25%435%5%5%6%46%
2152
11th to 20thDay
15%5%25%423336%51%
1980
21st to endDay
16%6%25%434346%47%
1980
October1st to 10thDay
23%6%245%34346%40%
1980
11th to 20thDay
15%5%15%44446%6%45%
1749
21st to endDay
23%7%25%5%3445%5%38%
1782
November1st to 10thDay
16%6%245%32445%49%
1671
11th to 20thDay
20%5%24424346%46%
1710
21st to endDay
20%6%35%4235%46%43%
1710
December1st to 10thDay
19%7%36%5%25%447%37%
1539
11th to 20thDay
22%7%25%324445%42%
1906
21st to endDay
23%10%36%5%24446%33%
2772
January1st to 10thNight
15%9%35%43445%6%42%
2649
11th to 20thNight
18%9%35%5%45%5%5%6%35%
2574
21st to endNight
13%8%35%6%36%5%46%40%
2772
February1st to 10thNight
16%9%36%6%35%45%6%37%
2306
11th to 20thNight
14%9%45%5%3445%7%39%
2098
21st to endNight
18%8%3443446%7%41%
1776
March1st to 10thNight
15%9%35%4345%5%6%41%
2150
11th to 20thNight
17%7%46%435%5%5%6%38%
2056
21st to endNight
18%9%35%423445%42%
2067
April1st to 10thNight
18%8%36%5%35%447%37%
1800
11th to 20thNight
21%7%24434446%40%
1745
21st to endNight
21%6%36%5%25%446%37%
1620
May1st to 10thNight
22%8%36%5%35%5%5%7%32%
1620
11th to 20thNight
18%6%35%6%35%5%5%7%36%
1558
21st to endNight
17%6%45%5%345%6%6%39%
1550
June1st to 10thNight
19%8%36%6%35%446%36%
1440
11th to 20thNight
21%6%244345%5%8%38%
1440
21st to endNight
17%7%345%345%6%9%38%
1440
July1st to 10thNight
15%6%25%6%36%5%5%9%38%
1440
11th to 20thNight
13%5%35%5%446%8%9%39%
1440
21st to endNight
14%5%25%4446%6%8%44%
1574
August1st to 10thNight
10%6%25%435%5%6%8%45%
1557
11th to 20thNight
13%7%26%6%46%5%7%8%36%
1596
21st to endNight
14%5%2442446%8%47%
1977
September1st to 10thNight
13%6%25%42445%7%48%
1808
11th to 20thNight
14%5%24424447%52%
1980
21st to endNight
15%5%245%34447%47%
1980
October1st to 10thNight
21%7%35%5%3435%5%40%
1980
11th to 20thNight
16%5%245%35%5%5%5%45%
2209
21st to endNight
23%7%26%43445%6%38%
2574
November1st to 10thNight
15%5%25%425%5%46%46%
2407
11th to 20thNight
18%6%25%434446%46%
2470
21st to endNight
16%6%35%4345%47%44%
2470
December1st to 10thNight
19%7%36%5%34446%38%
2640
11th to 20thNight
20%5%25%435%46%6%41%
3288
21st to endNight
22%9%36%5%24446%36%
4884

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%410%26%15%2
1518
11th to 20thDay
47%5%14%19%12%3
1464
21st to endDay
42%410%25%15%3
1584
February1st to 10thDay
48%5%13%19%12%2
1648
11th to 20thDay
43%5%11%22%14%4
1757
21st to endDay
50%49%20%15%3
1480
March1st to 10thDay
46%5%12%19%14%5%
1800
11th to 20thDay
44%49%20%17%6%
1902
21st to endDay
47%47%18%16%8%
2286
April1st to 10thDay
48%37%19%18%5%
2160
11th to 20thDay
44%5%10%21%17%3
2164
21st to endDay
50%5%7%17%18%3
2340
May1st to 10thDay
52%48%19%14%2
2340
11th to 20thDay
43%5%10%20%18%3
2353
21st to endDay
40%6%15%23%14%3
2725
June1st to 10thDay
49%7%12%21%11%1
2520
11th to 20thDay
43%5%12%20%17%3
2520
21st to endDay
49%6%10%21%12%1
2520
July1st to 10thDay
40%6%12%23%17%2
2450
11th to 20thDay
40%6%13%27%13%1
2445
21st to endDay
39%8%13%24%13%3
2591
August1st to 10thDay
41%7%15%23%13%1
2349
11th to 20thDay
40%6%14%25%13%1
2304
21st to endDay
34%6%13%24%20%3
2376
September1st to 10thDay
36%6%12%25%19%2
2152
11th to 20thDay
36%47%27%24%3
1980
21st to endDay
39%49%24%22%2
1980
October1st to 10thDay
47%49%23%14%4
1980
11th to 20thDay
38%411%31%14%2
1749
21st to endDay
48%410%21%14%3
1782
November1st to 10thDay
39%313%26%17%2
1671
11th to 20thDay
40%48%24%21%3
1710
21st to endDay
43%416%22%15%2
1710
December1st to 10thDay
47%414%17%16%2
1539
11th to 20thDay
46%311%18%17%5%
1906
21st to endDay
54%312%19%10%2
2772
January1st to 10thNight
43%412%24%15%3
2649
11th to 20thNight
49%6%13%21%9%2
2574
21st to endNight
44%410%20%19%3
2772
February1st to 10thNight
49%5%11%19%14%3
2306
11th to 20thNight
45%410%22%15%3
2100
21st to endNight
44%410%23%15%4
1776
March1st to 10thNight
45%49%22%16%5%
2160
11th to 20thNight
47%411%17%17%4
2057
21st to endNight
46%39%16%21%5%
2067
April1st to 10thNight
48%49%19%17%3
1800
11th to 20thNight
45%48%22%19%3
1745
21st to endNight
48%5%10%19%15%4
1620
May1st to 10thNight
52%39%20%13%3
1620
11th to 20thNight
47%5%11%19%14%4
1559
21st to endNight
46%5%13%21%12%2
1551
June1st to 10thNight
49%410%23%12%1
1440
11th to 20thNight
44%6%12%20%15%3
1440
21st to endNight
43%7%13%23%13%1
1440
July1st to 10thNight
42%7%13%22%14%2
1400
11th to 20thNight
38%6%17%28%11%
1392
21st to endNight
36%7%14%30%12%2
1486
August1st to 10thNight
35%7%16%25%15%2
1547
11th to 20thNight
43%7%15%21%13%1
1596
21st to endNight
36%5%12%26%21%1
1977
September1st to 10thNight
36%412%27%19%1
1808
11th to 20thNight
34%410%26%25%2
1980
21st to endNight
37%49%27%20%2
1980
October1st to 10thNight
46%411%22%13%3
1980
11th to 20thNight
39%5%12%29%14%1
2209
21st to endNight
48%311%22%13%2
2574
November1st to 10thNight
40%410%24%19%3
2407
11th to 20thNight
41%39%24%20%3
2470
21st to endNight
41%313%26%14%1
2470
December1st to 10thNight
49%411%23%12%1
2640
11th to 20thNight
44%413%19%19%1
3288
21st to endNight
52%49%24%11%1
4884

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
27%23%29%19%2
180
11th to 20thDay
25%25%35%11%21
166
21st to endDay
18%28%38%13%31
176
February1st to 10thDay
29%27%30%12%2
320
11th to 20thDay
27%28%31%11%3
416
21st to endDay
27%23%34%14%2
346
March1st to 10thDay
27%19%39%12%3
420
11th to 20thDay
25%27%34%11%21
420
21st to endDay
28%20%34%11%5%2
462
April1st to 10thDay
29%22%30%12%6%1
420
11th to 20thDay
26%24%29%14%6%1
412
21st to endDay
29%16%33%15%5%1
420
May1st to 10thDay
32%20%31%10%5%1
423
11th to 20thDay
19%18%39%19%42
447
21st to endDay
19%14%34%25%7%1
485
June1st to 10thDay
22%11%36%20%10%1
450
11th to 20thDay
18%16%34%25%5%2
450
21st to endDay
18%11%38%22%8%2
450
July1st to 10thDay
18%5%33%27%13%3
445
11th to 20thDay
18%5%32%29%12%3
444
21st to endDay
13%8%34%34%9%2
488
August1st to 10thDay
14%8%28%33%16%2
446
11th to 20thDay
17%9%29%26%15%4
439
21st to endDay
15%8%33%28%12%5%
495
September1st to 10thDay
18%8%29%25%14%6%
450
11th to 20thDay
20%12%30%18%15%6%
450
21st to endDay
18%11%34%22%10%6%
450
October1st to 10thDay
27%12%28%21%9%3
450
11th to 20thDay
18%14%33%23%10%2
392
21st to endDay
30%13%30%20%6%
396
November1st to 10thDay
16%21%32%21%8%2
365
11th to 20thDay
28%22%27%18%5%1
370
21st to endDay
28%20%29%16%6%1
370
December1st to 10thDay
20%27%31%16%6%
199
11th to 20thDay
29%25%32%13%1
180
21st to endDay
26%27%26%14%6%1
198
January1st to 10thNight
21%23%36%18%3
760
11th to 20thNight
26%19%34%19%3
736
21st to endNight
20%23%36%18%3
792
February1st to 10thNight
24%19%36%19%2
720
11th to 20thNight
23%20%37%16%3
703
21st to endNight
24%19%34%20%3
592
March1st to 10thNight
25%19%37%16%3
720
11th to 20thNight
21%21%36%15%5%
720
21st to endNight
24%18%34%20%4
792
April1st to 10thNight
24%18%33%21%4
720
11th to 20thNight
25%17%33%19%6%
681
21st to endNight
23%16%33%23%5%
540
May1st to 10thNight
26%13%32%23%6%
540
11th to 20thNight
22%12%35%24%6%1
497
21st to endNight
20%8%29%32%10%
389
June1st to 10thNight
21%8%30%30%9%2
360
11th to 20thNight
22%6%29%34%8%1
360
21st to endNight
21%431%34%11%
360
July1st to 10thNight
17%424%42%12%1
350
11th to 20thNight
14%224%44%17%1
348
21st to endNight
16%326%41%14%1
394
August1st to 10thNight
13%225%41%17%1
483
11th to 20thNight
15%6%27%33%16%2
532
21st to endNight
15%425%37%18%2
789
September1st to 10thNight
15%5%32%30%17%1
720
11th to 20thNight
17%6%29%27%18%3
720
21st to endNight
18%7%30%28%16%3
720
October1st to 10thNight
24%9%28%25%13%1
720
11th to 20thNight
20%13%29%27%10%1
720
21st to endNight
28%13%30%23%6%
792
November1st to 10thNight
18%13%36%25%8%1
740
11th to 20thNight
22%19%31%21%7%1
760
21st to endNight
21%22%31%20%5%1
760
December1st to 10thNight
24%17%37%19%3
760
11th to 20thNight
23%21%32%21%3
760
21st to endNight
25%19%34%19%1
836
Page generated at 2024-01-11 13:31:59. Version ac07

Copyright 2024 Attilla Danko


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