Chanticlear Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chanticlear Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
36%
24160
18%
74523
11%
24105
44%
24105
20%
50078

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
15%
760
15%
2459
5%
757
27%
757
9%
1796
January11th to 20thNight
16%
737
18%
2393
6%
737
30%
737
9%
1757
January21st to endNight
14%
792
18%
2574
5%
792
30%
792
11%
1782
February1st to 10thNight
16%
720
16%
2340
5%
720
28%
720
13%
1611
February11th to 20thNight
9%
703
13%
2156
3%
700
21%
700
8%
1574
February21st to endNight
15%
592
19%
1768
7%
592
28%
592
11%
1283
March1st to 10thNight
19%
720
21%
1980
9%
720
29%
720
18%
1348
March11th to 20thNight
21%
720
15%
1980
6%
720
29%
720
15%
1439
March21st to endNight
21%
792
16%
2178
7%
792
28%
792
16%
1539
April1st to 10thNight
26%
720
17%
1972
6%
720
35%
720
19%
1327
April11th to 20thNight
31%
693
22%
1757
7%
693
40%
693
24%
1153
April21st to endNight
34%
540
20%
1620
10%
540
42%
540
21%
1081
May1st to 10thNight
35%
540
14%
1620
6%
540
40%
540
20%
1098
May11th to 20thNight
41%
531
13%
1592
8%
531
46%
531
20%
1112
May21st to endNight
56%
582
15%
1745
12%
582
58%
582
26%
1146
June1st to 10thNight
57%
540
15%
1620
13%
540
60%
540
28%
1020
June11th to 20thNight
57%
540
13%
1620
10%
540
60%
540
28%
1029
June21st to endNight
59%
540
18%
1620
15%
540
62%
540
30%
1026
July1st to 10thNight
63%
525
13%
1575
13%
525
63%
525
28%
1021
July11th to 20thNight
69%
522
14%
1566
11%
522
70%
522
34%
962
July21st to endNight
67%
591
16%
1672
13%
558
69%
558
29%
1071
August1st to 10thNight
62%
537
16%
1600
13%
534
63%
534
26%
1065
August11th to 20thNight
60%
534
19%
1598
15%
534
63%
534
26%
1068
August21st to endNight
64%
688
21%
1876
18%
688
65%
688
32%
1203
September1st to 10thNight
62%
720
22%
1930
17%
720
63%
720
31%
1271
September11th to 20thNight
57%
720
24%
1980
19%
720
60%
720
30%
1279
September21st to endNight
47%
720
21%
1980
15%
720
53%
720
25%
1337
October1st to 10thNight
48%
720
23%
2092
20%
720
53%
720
29%
1290
October11th to 20thNight
37%
720
24%
2160
17%
720
48%
720
25%
1354
October21st to endNight
35%
792
27%
2376
19%
792
46%
792
23%
1516
November1st to 10thNight
41%
740
26%
2262
19%
740
51%
740
27%
1384
November11th to 20thNight
32%
760
24%
2470
14%
760
45%
760
21%
1534
November21st to endNight
31%
760
25%
2470
14%
760
45%
760
20%
1548
December1st to 10thNight
18%
760
16%
2470
7%
760
30%
760
11%
1800
December11th to 20thNight
22%
759
19%
2989
9%
759
35%
759
10%
2093
December21st to endNight
19%
830
12%
4463
6%
817
31%
817
6%
3161

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
13%9%47%6%45%5%6%7%33%
74939
Night
12%9%47%6%35%5%5%7%36%
74852
TransparencyDay
48%5%11%20%13%2
74661
Night
46%5%11%21%14%3
74648
SeeingDay
24%17%24%19%11%5%
14023
Night
21%15%21%26%15%2
24169

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
12%11%411%9%35%346%31%
1706
11th to 20thDay
13%13%7%11%7%35%5%5%5%27%
1656
21st to endDay
12%12%7%8%5%4445%5%34%
1782
February1st to 10thDay
12%12%5%9%8%45%5%5%7%29%
1620
11th to 20thDay
15%10%5%10%6%45%5%5%6%29%
1687
21st to endDay
17%11%49%6%34445%31%
1488
March1st to 10thDay
13%8%5%7%5%2445%6%40%
1980
11th to 20thDay
17%11%5%7%6%45%45%7%30%
1980
21st to endDay
15%12%47%5%345%5%6%33%
2178
April1st to 10thDay
11%9%46%6%346%5%8%39%
1988
11th to 20thDay
13%9%46%6%345%5%7%39%
2167
21st to endDay
18%7%46%6%35%5%5%7%34%
2340
May1st to 10thDay
15%8%36%7%46%6%7%7%30%
2340
11th to 20thDay
17%9%48%7%46%5%6%7%28%
2301
21st to endDay
12%7%37%7%47%7%8%9%30%
2531
June1st to 10thDay
12%6%26%7%5%6%6%7%8%33%
2340
11th to 20thDay
9%7%36%8%47%6%7%9%34%
2340
21st to endDay
10%7%35%6%5%7%7%7%8%35%
2340
July1st to 10thDay
10%7%47%7%46%6%8%9%32%
2340
11th to 20thDay
9%7%37%7%5%7%6%8%10%31%
2340
21st to endDay
11%7%48%8%5%7%7%7%9%27%
2547
August1st to 10thDay
11%7%47%7%5%6%7%9%11%26%
2327
11th to 20thDay
13%7%38%8%6%7%7%7%8%26%
2303
21st to endDay
9%6%37%7%5%7%6%8%9%33%
2462
September1st to 10thDay
11%6%35%6%46%6%7%7%39%
2026
11th to 20thDay
14%8%36%6%45%5%6%8%35%
1980
21st to endDay
19%7%36%5%35%6%6%6%35%
1980
October1st to 10thDay
15%6%35%6%3345%6%44%
1868
11th to 20thDay
13%10%36%4245%5%5%43%
1800
21st to endDay
14%11%36%434446%42%
1980
November1st to 10thDay
12%6%26%5%2445%7%48%
1815
11th to 20thDay
10%10%35%5%445%5%8%40%
1710
21st to endDay
12%10%37%5%345%5%6%41%
1710
December1st to 10thDay
15%15%5%9%7%3445%6%27%
1710
11th to 20thDay
13%12%5%8%6%34448%34%
2153
21st to endDay
14%14%6%8%7%46%6%6%6%24%
3124
January1st to 10thNight
12%10%6%10%8%5%5%45%6%28%
2459
11th to 20thNight
13%12%6%11%8%35%45%6%26%
2393
21st to endNight
12%10%8%8%7%45%45%6%31%
2574
February1st to 10thNight
12%10%5%8%7%45%5%6%7%31%
2340
11th to 20thNight
16%11%5%10%6%45%5%46%28%
2155
21st to endNight
13%11%6%10%7%45%45%5%31%
1768
March1st to 10thNight
13%9%46%6%35%35%6%39%
1980
11th to 20thNight
15%11%5%8%6%35%5%5%7%30%
1980
21st to endNight
12%11%5%7%5%45%5%6%6%34%
2178
April1st to 10thNight
10%9%46%6%35%5%6%8%38%
1972
11th to 20thNight
10%8%45%5%345%5%9%42%
1757
21st to endNight
15%8%36%6%36%45%8%37%
1620
May1st to 10thNight
14%9%36%6%37%45%6%36%
1620
11th to 20thNight
12%9%48%8%45%5%5%8%33%
1592
21st to endNight
9%9%36%5%45%5%6%10%38%
1744
June1st to 10thNight
8%5%36%5%46%6%6%11%41%
1620
11th to 20thNight
8%5%35%7%35%6%7%9%42%
1620
21st to endNight
8%5%26%5%36%5%7%12%40%
1620
July1st to 10thNight
8%5%36%6%45%6%6%10%41%
1620
11th to 20thNight
7%425%5%36%5%7%13%43%
1620
21st to endNight
6%435%7%47%7%8%12%37%
1771
August1st to 10thNight
9%7%28%6%36%5%7%8%39%
1611
11th to 20thNight
12%7%25%6%45%6%8%7%39%
1598
21st to endNight
8%5%36%5%46%5%7%10%42%
1876
September1st to 10thNight
10%7%36%435%5%6%7%44%
1930
11th to 20thNight
13%8%35%4345%47%45%
1980
21st to endNight
13%10%36%5%35%446%42%
1980
October1st to 10thNight
15%7%24424346%48%
2092
11th to 20thNight
11%10%26%5%34447%45%
2160
21st to endNight
11%11%35%5%35%347%43%
2376
November1st to 10thNight
11%8%36%425%35%5%48%
2262
11th to 20thNight
11%9%46%5%345%6%6%42%
2470
21st to endNight
10%11%47%5%345%5%7%41%
2470
December1st to 10thNight
15%13%6%9%7%3445%6%28%
2470
11th to 20thNight
12%11%6%12%6%35%5%46%30%
3042
21st to endNight
14%12%9%9%6%45%6%5%7%23%
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
54%38%18%14%3
1707
11th to 20thDay
57%47%18%11%2
1656
21st to endDay
51%37%21%16%3
1782
February1st to 10thDay
53%5%7%21%13%1
1620
11th to 20thDay
54%48%19%13%3
1696
21st to endDay
54%5%8%14%14%5%
1488
March1st to 10thDay
45%47%24%17%3
1980
11th to 20thDay
55%48%18%12%3
1980
21st to endDay
52%5%8%23%9%3
2178
April1st to 10thDay
43%410%24%15%4
1988
11th to 20thDay
45%38%23%16%4
2167
21st to endDay
50%312%21%11%2
2340
May1st to 10thDay
51%5%12%18%12%1
2340
11th to 20thDay
54%5%12%20%7%1
2305
21st to endDay
48%6%16%22%8%
2531
June1st to 10thDay
46%7%14%21%13%
2340
11th to 20thDay
44%8%14%19%13%1
2340
21st to endDay
43%7%13%22%12%2
2340
July1st to 10thDay
48%5%16%18%11%2
2275
11th to 20thDay
45%7%17%18%12%1
2271
21st to endDay
49%7%15%20%8%1
2405
August1st to 10thDay
49%7%18%19%7%
2314
11th to 20thDay
53%6%13%19%9%
2303
21st to endDay
44%7%17%18%12%2
2462
September1st to 10thDay
43%6%12%21%14%4
2026
11th to 20thDay
46%5%7%24%17%1
1980
21st to endDay
49%310%20%14%2
1980
October1st to 10thDay
42%410%24%17%4
1868
11th to 20thDay
43%39%23%19%3
1800
21st to endDay
45%26%25%17%4
1980
November1st to 10thDay
38%38%22%25%5%
1815
11th to 20thDay
43%37%22%21%5%
1710
21st to endDay
43%39%22%19%4
1710
December1st to 10thDay
58%48%16%13%2
1710
11th to 20thDay
49%38%16%20%2
2150
21st to endDay
59%36%19%12%1
3124
January1st to 10thNight
56%5%8%15%13%3
2459
11th to 20thNight
57%5%6%15%14%3
2393
21st to endNight
52%38%21%13%2
2574
February1st to 10thNight
50%411%20%13%1
2340
11th to 20thNight
56%47%18%11%4
2156
21st to endNight
54%49%18%10%4
1768
March1st to 10thNight
45%5%8%20%19%3
1980
11th to 20thNight
53%49%22%11%1
1980
21st to endNight
49%5%10%21%13%2
2178
April1st to 10thNight
44%5%11%22%15%3
1972
11th to 20thNight
40%411%22%18%5%
1757
21st to endNight
45%413%24%12%2
1620
May1st to 10thNight
47%5%15%21%12%1
1620
11th to 20thNight
49%5%16%22%7%1
1593
21st to endNight
42%6%19%26%7%
1745
June1st to 10thNight
36%8%20%22%13%1
1620
11th to 20thNight
38%7%20%21%13%1
1620
21st to endNight
36%8%16%25%13%2
1620
July1st to 10thNight
39%8%17%21%13%3
1575
11th to 20thNight
32%8%22%22%12%3
1566
21st to endNight
35%9%18%27%10%
1672
August1st to 10thNight
43%6%18%23%10%
1600
11th to 20thNight
41%7%17%22%11%1
1598
21st to endNight
38%6%16%27%12%2
1876
September1st to 10thNight
38%7%14%21%16%4
1930
11th to 20thNight
40%5%10%25%19%2
1980
21st to endNight
45%49%25%15%1
1980
October1st to 10thNight
39%310%25%20%4
2092
11th to 20thNight
41%39%25%19%3
2160
21st to endNight
43%35%25%18%5%
2376
November1st to 10thNight
39%39%20%24%5%
2262
11th to 20thNight
42%38%20%21%6%
2470
21st to endNight
43%37%24%19%4
2470
December1st to 10thNight
57%48%18%11%3
2470
11th to 20thNight
52%6%7%16%16%2
3044
21st to endNight
60%37%15%13%1
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
39%30%23%7%11
270
11th to 20thDay
38%32%23%6%
252
21st to endDay
42%30%20%6%1
264
February1st to 10thDay
38%33%22%6%1
240
11th to 20thDay
50%29%18%3
240
21st to endDay
46%28%22%21
206
March1st to 10thDay
31%28%23%15%3
420
11th to 20thDay
30%30%24%11%41
420
21st to endDay
30%26%26%15%4
462
April1st to 10thDay
28%27%23%13%8%1
420
11th to 20thDay
28%21%23%17%9%3
412
21st to endDay
29%20%26%15%7%2
420
May1st to 10thDay
27%20%29%13%8%4
423
11th to 20thDay
22%15%31%18%10%4
447
21st to endDay
15%11%25%26%14%10%
485
June1st to 10thDay
14%11%28%26%15%6%
450
11th to 20thDay
12%12%27%26%16%7%
450
21st to endDay
15%11%30%24%13%7%
450
July1st to 10thDay
13%7%22%29%18%11%
445
11th to 20thDay
8%7%23%34%16%12%
444
21st to endDay
13%6%26%26%18%11%
488
August1st to 10thDay
14%9%21%26%19%12%
446
11th to 20thDay
14%7%18%28%21%13%
439
21st to endDay
10%6%23%26%20%15%
495
September1st to 10thDay
12%9%18%26%22%12%
450
11th to 20thDay
17%6%19%27%21%11%
450
21st to endDay
25%11%22%24%15%3
450
October1st to 10thDay
22%11%23%20%18%6%
450
11th to 20thDay
22%18%23%23%13%2
450
21st to endDay
25%18%27%18%9%2
495
November1st to 10thDay
21%16%29%21%10%2
413
11th to 20thDay
32%19%29%16%41
270
21st to endDay
27%23%30%16%3
270
December1st to 10thDay
38%24%26%10%1
270
11th to 20thDay
34%23%28%11%3
270
21st to endDay
34%25%26%11%4
297
January1st to 10thNight
31%28%21%15%3
760
11th to 20thNight
34%23%24%17%2
737
21st to endNight
29%28%25%16%2
792
February1st to 10thNight
31%22%27%18%1
720
11th to 20thNight
35%30%22%12%
703
21st to endNight
30%27%25%16%2
592
March1st to 10thNight
26%24%27%19%3
720
11th to 20thNight
29%22%24%17%7%1
720
21st to endNight
24%22%30%19%6%
792
April1st to 10thNight
24%21%25%23%7%
720
11th to 20thNight
21%19%24%25%10%1
693
21st to endNight
19%16%23%34%7%1
540
May1st to 10thNight
22%13%25%26%12%2
540
11th to 20thNight
18%9%21%33%18%1
531
21st to endNight
13%5%17%32%29%4
584
June1st to 10thNight
11%5%19%38%24%4
540
11th to 20thNight
10%5%19%30%30%5%
540
21st to endNight
11%417%37%28%4
540
July1st to 10thNight
10%214%37%34%4
525
11th to 20thNight
8%213%37%35%6%
522
21st to endNight
8%312%35%36%6%
591
August1st to 10thNight
12%311%37%34%4
537
11th to 20thNight
16%49%32%33%7%
534
21st to endNight
10%5%10%33%35%7%
688
September1st to 10thNight
13%5%12%30%34%6%
720
11th to 20thNight
18%414%29%30%5%
720
21st to endNight
21%10%15%31%22%2
720
October1st to 10thNight
20%9%16%26%23%5%
720
11th to 20thNight
20%15%23%26%14%1
720
21st to endNight
20%18%22%28%11%2
792
November1st to 10thNight
18%15%22%30%14%2
740
11th to 20thNight
23%20%21%27%9%1
760
21st to endNight
22%19%23%26%9%1
760
December1st to 10thNight
30%20%26%19%4
760
11th to 20thNight
23%26%23%24%4
760
21st to endNight
27%22%27%22%3
836
Page generated at 2024-01-11 22:33:48. Version ac07

Copyright 2024 Attilla Danko


Chanticlear Observatory Clear Sky Chart |Charts Home