Centennial
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Centennial clear sky chart from 2005-11-06 to 2024-03-01.

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
57%
24726
28%
79918
20%
24639
65%
24639
40%
41958

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
51%
937
31%
4334
21%
926
63%
926
32%
2134
January11th to 20thNight
52%
923
32%
4262
22%
907
63%
907
34%
1884
January21st to endNight
51%
827
22%
4281
24%
814
63%
814
26%
2062
February1st to 10thNight
44%
760
28%
2470
17%
760
58%
760
39%
1299
February11th to 20thNight
43%
741
28%
2223
17%
740
54%
740
40%
1240
February21st to endNight
45%
628
35%
1884
18%
628
62%
628
45%
985
March1st to 10thNight
45%
722
28%
2166
15%
722
57%
722
43%
1144
March11th to 20thNight
54%
720
28%
2016
18%
720
60%
720
44%
1126
March21st to endNight
44%
648
29%
2034
17%
648
58%
648
37%
1123
April1st to 10thNight
42%
540
25%
1800
17%
540
55%
540
36%
954
April11th to 20thNight
43%
533
24%
1777
18%
533
54%
533
30%
1007
April21st to endNight
45%
540
22%
1800
19%
540
54%
540
30%
1044
May1st to 10thNight
49%
540
20%
1679
17%
540
56%
540
28%
1036
May11th to 20thNight
58%
531
16%
1446
14%
531
60%
531
33%
901
May21st to endNight
54%
583
19%
1552
13%
582
60%
582
39%
912
June1st to 10thNight
71%
540
24%
1440
19%
540
72%
540
51%
764
June11th to 20thNight
65%
540
26%
1440
19%
540
69%
540
51%
764
June21st to endNight
71%
540
25%
1440
21%
540
73%
540
49%
783
July1st to 10thNight
70%
525
19%
1400
18%
525
71%
525
38%
838
July11th to 20thNight
76%
522
28%
1392
24%
522
78%
522
50%
748
July21st to endNight
74%
591
23%
1521
21%
558
74%
558
39%
884
August1st to 10thNight
70%
537
15%
1614
15%
534
71%
534
34%
925
August11th to 20thNight
74%
534
27%
1778
29%
534
78%
534
41%
914
August21st to endNight
71%
594
29%
1980
32%
594
74%
594
41%
992
September1st to 10thNight
72%
540
30%
1800
31%
540
76%
540
41%
910
September11th to 20thNight
71%
540
37%
1827
36%
540
78%
540
48%
863
September21st to endNight
68%
540
32%
1980
31%
540
75%
540
43%
915
October1st to 10thNight
60%
685
29%
2125
21%
685
66%
685
42%
1118
October11th to 20thNight
63%
720
36%
2160
22%
720
72%
720
56%
1027
October21st to endNight
60%
847
34%
2431
22%
847
66%
847
46%
1299
November1st to 10thNight
63%
925
35%
2405
19%
925
70%
925
58%
1234
November11th to 20thNight
58%
950
37%
2470
21%
950
65%
950
54%
1324
November21st to endNight
57%
950
31%
2541
20%
950
63%
950
48%
1388
December1st to 10thNight
55%
950
30%
2660
18%
950
64%
950
48%
1407
December11th to 20thNight
52%
949
31%
3100
19%
948
61%
948
43%
1587
December21st to endNight
46%
1034
20%
4690
17%
1026
57%
1026
28%
2423

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
5%5%244345%6%8%54%
78554
Night
5%6%2442345%7%57%
80912
TransparencyDay
27%5%10%24%23%10%
78261
Night
26%5%10%25%25%9%
80728
SeeingDay
8%6%24%33%21%8%
14559
Night
7%325%47%16%1
24768

By Month

Percentage Cloud Cover SW (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
1436%43235%9%60%
2538
11th to 20thDay
28%35%4345%5%7%54%
2607
21st to endDay
26%3443445%7%59%
3146
February1st to 10thDay
38%46%434347%55%
1710
11th to 20thDay
1425%43445%7%59%
1842
21st to endDay
27%35%423346%59%
1570
March1st to 10thDay
46%35%42436%8%56%
1800
11th to 20thDay
6%7%35%42445%7%53%
1939
21st to endDay
6%8%24435%6%6%9%49%
2321
April1st to 10thDay
7%6%2442446%8%54%
2160
11th to 20thDay
9%7%35%435%5%5%7%48%
2131
21st to endDay
10%7%14435%46%8%47%
2160
May1st to 10thDay
10%7%35%5%35%5%6%8%41%
2278
11th to 20thDay
12%7%25%435%5%7%9%39%
2446
21st to endDay
8%5%24436%6%7%10%45%
2724
June1st to 10thDay
6%424336%6%7%9%50%
2520
11th to 20thDay
5%314436%7%7%8%52%
2520
21st to endDay
4314436%6%8%10%50%
2520
July1st to 10thDay
6%4145%35%6%9%10%47%
2520
11th to 20thDay
34235%35%6%8%10%52%
2520
21st to endDay
5%425%6%46%7%8%10%46%
2704
August1st to 10thDay
5%4245%47%8%8%10%42%
2314
11th to 20thDay
5%223335%5%7%9%55%
2123
21st to endDay
43145%35%6%7%9%54%
2376
September1st to 10thDay
5%31343445%7%61%
2160
11th to 20thDay
6%31342445%6%60%
2131
21st to endDay
6%413323346%66%
1980
October1st to 10thDay
7%413333346%62%
1832
11th to 20thDay
4413313247%68%
1800
21st to endDay
7%6%14222335%64%
1905
November1st to 10thDay
242331345%9%65%
1673
11th to 20thDay
25%2432335%7%63%
1710
21st to endDay
46%3432335%7%61%
1634
December1st to 10thDay
26%25%43436%8%59%
1520
11th to 20thDay
25%25%43345%9%58%
1926
21st to endDay
28%47%5%3445%6%52%
2794
January1st to 10thNight
19%47%5%2335%7%55%
4417
11th to 20thNight
2425%5%34447%60%
4394
21st to endNight
36%36%5%33346%57%
4521
February1st to 10thNight
38%35%5%34447%55%
2470
11th to 20thNight
28%46%5%3445%7%53%
2223
21st to endNight
38%35%323347%60%
1884
March1st to 10thNight
46%35%4245%5%7%56%
2166
11th to 20thNight
7%6%243235%46%58%
2016
21st to endNight
6%8%3442335%8%54%
2034
April1st to 10thNight
7%7%2442435%6%56%
1800
11th to 20thNight
12%8%3433445%6%50%
1777
21st to endNight
13%8%24424447%48%
1800
May1st to 10thNight
12%7%245%345%6%7%45%
1679
11th to 20thNight
15%6%233235%7%9%45%
1445
21st to endNight
8%5%2443445%9%53%
1552
June1st to 10thNight
5%21323348%11%57%
1440
11th to 20thNight
6%31332347%9%60%
1440
21st to endNight
43243345%7%9%57%
1440
July1st to 10thNight
6%3146%45%5%7%10%49%
1440
11th to 20thNight
32244346%7%10%57%
1440
21st to endNight
6%324436%6%8%11%47%
1610
August1st to 10thNight
4426%6%36%6%6%9%48%
1623
11th to 20thNight
6%3143246%6%10%55%
1778
21st to endNight
5%3244245%7%8%55%
1980
September1st to 10thNight
7%3234345%6%7%56%
1800
11th to 20thNight
6%31421336%7%63%
1827
21st to endNight
7%413323346%65%
1980
October1st to 10thNight
8%6%2332335%6%59%
2125
11th to 20thNight
4313312345%70%
2160
21st to endNight
5%8%24323336%62%
2431
November1st to 10thNight
232332335%6%68%
2405
11th to 20thNight
35%24323445%65%
2470
21st to endNight
46%24423337%61%
2541
December1st to 10thNight
26%35%423347%61%
2660
11th to 20thNight
26%3442345%9%57%
3271
21st to endNight
5%8%36%43345%6%52%
4873

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
21%49%32%25%8%
2539
11th to 20thDay
30%5%12%27%19%7%
2607
21st to endDay
24%410%31%25%6%
3146
February1st to 10thDay
30%310%27%20%9%
1710
11th to 20thDay
23%47%29%29%9%
1852
21st to endDay
26%46%23%28%14%
1570
March1st to 10thDay
27%39%24%28%10%
1800
11th to 20thDay
29%49%24%25%8%
1939
21st to endDay
31%6%12%24%20%8%
2321
April1st to 10thDay
28%5%11%25%21%11%
2160
11th to 20thDay
35%5%9%22%21%9%
2134
21st to endDay
34%6%10%24%22%5%
2160
May1st to 10thDay
39%6%11%23%17%4
2278
11th to 20thDay
39%7%14%24%12%4
2450
21st to endDay
32%8%12%25%14%8%
2724
June1st to 10thDay
26%8%14%24%18%10%
2520
11th to 20thDay
25%7%10%18%21%18%
2520
21st to endDay
26%7%10%19%25%12%
2520
July1st to 10thDay
29%8%11%19%20%13%
2451
11th to 20thDay
25%8%10%23%24%10%
2445
21st to endDay
31%9%14%24%15%7%
2554
August1st to 10thDay
31%10%15%22%14%7%
2299
11th to 20thDay
24%7%9%23%24%13%
2123
21st to endDay
24%7%9%22%27%11%
2376
September1st to 10thDay
24%47%21%24%20%
2160
11th to 20thDay
22%5%7%19%28%19%
2131
21st to endDay
20%45%19%37%14%
1980
October1st to 10thDay
24%48%21%29%14%
1832
11th to 20thDay
18%37%23%33%16%
1800
21st to endDay
24%36%27%25%16%
1905
November1st to 10thDay
17%39%25%28%18%
1673
11th to 20thDay
21%37%25%34%10%
1710
21st to endDay
24%37%21%29%16%
1634
December1st to 10thDay
23%411%29%24%9%
1520
11th to 20thDay
23%310%25%31%7%
1924
21st to endDay
31%48%22%26%9%
2794
January1st to 10thNight
27%5%8%27%28%5%
4417
11th to 20thNight
23%413%26%23%11%
4394
21st to endNight
28%5%10%32%18%6%
4521
February1st to 10thNight
28%410%27%24%7%
2470
11th to 20thNight
30%39%28%23%7%
2223
21st to endNight
25%35%26%27%14%
1884
March1st to 10thNight
25%48%23%31%8%
2166
11th to 20thNight
27%49%23%31%6%
2016
21st to endNight
30%5%10%25%26%5%
2034
April1st to 10thNight
29%412%22%22%11%
1800
11th to 20thNight
35%310%25%19%8%
1777
21st to endNight
37%410%25%19%6%
1800
May1st to 10thNight
36%7%12%23%16%5%
1679
11th to 20thNight
35%6%20%21%12%4
1446
21st to endNight
28%7%17%27%13%8%
1552
June1st to 10thNight
20%6%20%31%15%9%
1440
11th to 20thNight
21%5%14%21%22%17%
1440
21st to endNight
22%6%12%25%26%10%
1440
July1st to 10thNight
28%9%15%22%19%7%
1400
11th to 20thNight
20%6%12%29%23%9%
1392
21st to endNight
28%7%19%27%16%3
1521
August1st to 10thNight
30%8%20%24%14%6%
1614
11th to 20thNight
24%6%10%27%23%10%
1778
21st to endNight
24%5%12%26%25%8%
1980
September1st to 10thNight
25%410%21%25%14%
1800
11th to 20thNight
20%49%24%26%16%
1827
21st to endNight
22%48%21%34%11%
1980
October1st to 10thNight
26%410%20%27%13%
2125
11th to 20thNight
17%49%23%30%17%
2160
21st to endNight
25%36%24%28%14%
2431
November1st to 10thNight
17%48%25%29%17%
2405
11th to 20thNight
21%36%28%32%10%
2470
21st to endNight
25%37%22%31%12%
2541
December1st to 10thNight
23%411%27%26%9%
2660
11th to 20thNight
23%49%26%33%5%
3272
21st to endNight
32%38%25%26%6%
4873

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%24%47%17%4
270
11th to 20thDay
8%7%31%43%10%1
270
21st to endDay
46%30%43%14%3
297
February1st to 10thDay
49%41%36%8%1
270
11th to 20thDay
36%41%38%11%1
270
21st to endDay
410%36%38%10%1
225
March1st to 10thDay
5%8%32%38%15%3
240
11th to 20thDay
13%7%35%32%11%2
379
21st to endDay
14%19%30%25%10%1
462
April1st to 10thDay
10%15%32%29%12%2
420
11th to 20thDay
14%22%26%26%10%2
412
21st to endDay
17%11%31%23%16%1
420
May1st to 10thDay
15%9%28%32%13%3
541
11th to 20thDay
15%7%23%28%22%5%
625
21st to endDay
10%9%22%30%21%8%
679
June1st to 10thDay
6%5%20%31%24%14%
630
11th to 20thDay
7%5%24%36%23%7%
630
21st to endDay
5%421%33%27%8%
630
July1st to 10thDay
8%214%25%36%15%
621
11th to 20thDay
4213%28%40%14%
618
21st to endDay
6%212%26%38%17%
646
August1st to 10thDay
7%217%29%28%16%
447
11th to 20thDay
5%217%35%27%15%
437
21st to endDay
5%319%32%29%12%
495
September1st to 10thDay
6%5%16%33%28%10%
450
11th to 20thDay
5%420%31%28%12%
421
21st to endDay
6%321%29%24%17%
270
October1st to 10thDay
11%320%23%26%16%
270
11th to 20thDay
25%23%40%21%9%
270
21st to endDay
10%7%22%38%19%4
297
November1st to 10thDay
49%23%39%19%7%
270
11th to 20thDay
6%422%44%20%4
270
21st to endDay
8%430%40%14%4
270
December1st to 10thDay
46%29%44%16%2
270
11th to 20thDay
6%430%45%14%
270
21st to endDay
5%5%31%48%9%3
297
January1st to 10thNight
4332%49%11%2
950
11th to 20thNight
4334%48%9%2
927
21st to endNight
5%330%51%11%1
836
February1st to 10thNight
6%439%44%7%
760
11th to 20thNight
5%337%46%8%1
744
21st to endNight
5%437%50%3
628
March1st to 10thNight
5%337%46%8%
722
11th to 20thNight
10%326%50%10%
720
21st to endNight
9%435%43%8%
648
April1st to 10thNight
10%5%37%41%6%
540
11th to 20thNight
16%8%28%39%10%
533
21st to endNight
16%5%28%39%11%
540
May1st to 10thNight
15%5%24%43%12%1
540
11th to 20thNight
18%314%44%19%1
531
21st to endNight
10%325%39%21%1
584
June1st to 10thNight
5%315%46%28%3
540
11th to 20thNight
6%322%50%19%1
540
21st to endNight
4215%49%28%1
540
July1st to 10thNight
8%29%42%36%3
525
11th to 20thNight
2111%43%39%4
522
21st to endNight
7%27%41%41%3
591
August1st to 10thNight
5%19%45%38%2
537
11th to 20thNight
7%210%53%26%2
534
21st to endNight
5%311%48%30%2
594
September1st to 10thNight
7%211%48%29%4
540
11th to 20thNight
7%114%49%26%2
540
21st to endNight
8%216%50%23%1
540
October1st to 10thNight
10%320%46%17%3
685
11th to 20thNight
5%125%48%19%1
720
21st to endNight
9%322%48%16%2
847
November1st to 10thNight
4326%52%14%1
925
11th to 20thNight
5%329%52%10%1
950
21st to endNight
6%327%49%14%1
950
December1st to 10thNight
4330%52%11%
950
11th to 20thNight
5%331%49%12%1
950
21st to endNight
7%434%46%8%1
1045
Page generated at 2024-02-27 04:30:16. Version ac07

Copyright © 2024 Attilla Danko.


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