Clower Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clower 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
49%
23979
27%
74225
19%
23921
58%
23921
35%
41453

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%
948
30%
2458
12%
946
46%
946
38%
1474
January11th to 20thNight
33%
918
28%
2386
9%
918
44%
918
32%
1488
January21st to endNight
33%
990
30%
2574
11%
990
43%
990
34%
1602
February1st to 10thNight
31%
850
25%
2290
9%
850
41%
850
31%
1431
February11th to 20thNight
24%
704
23%
2098
9%
700
35%
700
27%
1311
February21st to endNight
20%
525
27%
1709
8%
525
37%
525
24%
1028
March1st to 10thNight
30%
540
24%
1980
12%
540
45%
540
24%
1168
March11th to 20thNight
31%
540
23%
1980
15%
540
43%
540
24%
1163
March21st to endNight
32%
594
25%
2178
14%
594
47%
594
27%
1204
April1st to 10thNight
31%
540
26%
1980
14%
540
49%
540
29%
1041
April11th to 20thNight
33%
533
24%
1825
15%
533
47%
533
28%
1044
April21st to endNight
35%
540
27%
1738
16%
540
53%
540
33%
972
May1st to 10thNight
39%
540
25%
1620
18%
540
51%
540
31%
972
May11th to 20thNight
46%
531
21%
1594
19%
531
53%
531
34%
933
May21st to endNight
52%
584
24%
1745
19%
582
62%
582
35%
1006
June1st to 10thNight
71%
540
23%
1620
24%
540
75%
540
44%
861
June11th to 20thNight
68%
540
27%
1620
28%
540
73%
540
50%
798
June21st to endNight
73%
540
27%
1620
28%
540
77%
540
46%
848
July1st to 10thNight
77%
525
22%
1575
24%
525
81%
525
42%
855
July11th to 20thNight
86%
522
31%
1566
37%
522
89%
522
62%
698
July21st to endNight
86%
591
30%
1673
35%
558
88%
558
54%
811
August1st to 10thNight
89%
537
35%
1601
40%
534
90%
534
65%
695
August11th to 20thNight
78%
534
31%
1600
34%
534
79%
534
42%
871
August21st to endNight
83%
594
27%
2006
33%
594
84%
594
43%
999
September1st to 10thNight
74%
540
25%
1980
30%
540
75%
540
38%
990
September11th to 20thNight
71%
540
26%
1980
30%
540
73%
540
34%
1048
September21st to endNight
75%
540
35%
1980
37%
540
79%
540
43%
927
October1st to 10thNight
70%
602
35%
2042
32%
602
75%
602
48%
950
October11th to 20thNight
54%
720
34%
2160
19%
720
64%
720
42%
1158
October21st to endNight
45%
792
33%
2376
20%
792
54%
792
37%
1325
November1st to 10thNight
52%
740
32%
2220
20%
740
61%
740
41%
1204
November11th to 20thNight
47%
817
31%
2337
16%
817
57%
817
39%
1313
November21st to endNight
35%
950
29%
2470
12%
950
46%
950
33%
1559
December1st to 10thNight
38%
950
30%
2470
13%
950
49%
950
35%
1533
December11th to 20thNight
35%
948
30%
2863
13%
948
44%
948
28%
1784
December21st to endNight
34%
1040
17%
4311
11%
1026
44%
1026
23%
2389

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
11%5%2443445%7%49%
74956
Night
11%5%24323447%55%
74826
TransparencyDay
34%6%11%22%21%7%
74681
Night
30%5%10%22%23%10%
74621
SeeingDay
12%7%21%28%24%8%
14002
Night
13%7%27%34%17%2
23988

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
13%7%34432246%53%
1707
11th to 20thDay
16%5%34423345%50%
1647
21st to endDay
18%6%24223237%51%
1782
February1st to 10thDay
19%7%37%423345%44%
1683
11th to 20thDay
20%8%34424235%44%
1749
21st to endDay
23%6%2432323448%
1546
March1st to 10thDay
18%7%3442345%7%44%
1980
11th to 20thDay
18%6%35%424446%44%
1980
21st to endDay
14%7%46%434445%46%
2178
April1st to 10thDay
14%6%36%335%45%7%45%
1980
11th to 20thDay
13%6%36%5%34447%44%
2084
21st to endDay
11%5%35%5%35%5%6%7%46%
2218
May1st to 10thDay
13%6%35%5%35%45%7%45%
2340
11th to 20thDay
12%6%35%6%45%5%5%7%42%
2302
21st to endDay
11%5%36%7%35%6%8%10%36%
2531
June1st to 10thDay
6%3245%46%5%6%9%50%
2340
11th to 20thDay
5%325%445%6%7%9%51%
2340
21st to endDay
5%3245%345%6%9%54%
2340
July1st to 10thDay
6%426%7%37%7%9%10%39%
2340
11th to 20thDay
3223425%6%6%9%58%
2340
21st to endDay
4324445%7%8%11%49%
2546
August1st to 10thDay
321242446%11%61%
2328
11th to 20thDay
7%423435%6%7%11%48%
2301
21st to endDay
44245%45%6%7%10%47%
2343
September1st to 10thDay
8%4245%45%35%8%52%
1980
11th to 20thDay
9%5%26%5%35%5%6%8%46%
1980
21st to endDay
8%32443445%7%57%
1980
October1st to 10thDay
6%414433447%60%
1898
11th to 20thDay
13%423323346%57%
1800
21st to endDay
15%5%24322235%57%
1980
November1st to 10thDay
12%424424346%55%
1858
11th to 20thDay
8%425%43335%6%57%
1839
21st to endDay
17%7%2442333451%
1710
December1st to 10thDay
15%5%1443445%6%49%
1710
11th to 20thDay
15%8%25%5%34346%44%
2161
21st to endDay
16%8%35%323346%47%
3135
January1st to 10thNight
13%5%24323345%55%
2458
11th to 20thNight
15%6%24333445%52%
2386
21st to endNight
15%6%2342423454%
2574
February1st to 10thNight
17%5%24423335%51%
2290
11th to 20thNight
17%7%35%323336%48%
2098
21st to endNight
19%5%34423345%49%
1709
March1st to 10thNight
17%6%25%42345%7%45%
1980
11th to 20thNight
14%5%35%424446%48%
1980
21st to endNight
11%6%25%423447%52%
2178
April1st to 10thNight
9%4244235%6%8%53%
1980
11th to 20thNight
13%4245%2445%7%49%
1825
21st to endNight
11%43332445%8%53%
1738
May1st to 10thNight
9%6%35%4345%6%8%49%
1620
11th to 20thNight
9%5%244245%6%10%49%
1593
21st to endNight
8%4244245%6%9%51%
1745
June1st to 10thNight
5%31332446%9%59%
1620
11th to 20thNight
3313323448%65%
1620
21st to endNight
42233345%5%9%60%
1620
July1st to 10thNight
4424335%6%7%10%52%
1620
11th to 20thNight
311131245%10%68%
1620
21st to endNight
11143245%7%12%60%
1772
August1st to 10thNight
211211235%12%69%
1611
11th to 20thNight
6%32443445%9%56%
1600
21st to endNight
33134345%7%10%56%
2006
September1st to 10thNight
6%424423449%57%
1980
11th to 20thNight
10%423435%447%54%
1980
21st to endNight
7%31332345%7%62%
1980
October1st to 10thNight
6%312322448%64%
2042
11th to 20thNight
13%313323236%61%
2160
21st to endNight
16%5%2422222460%
2376
November1st to 10thNight
9%6%24323235%61%
2220
11th to 20thNight
8%5%24423446%57%
2337
21st to endNight
15%6%24422345%53%
2470
December1st to 10thNight
14%5%24323347%53%
2470
11th to 20thNight
13%6%34434345%51%
3036
21st to endNight
16%6%24323335%53%
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
34%48%19%29%7%
1708
11th to 20thDay
37%48%22%24%6%
1647
21st to endDay
37%26%17%28%10%
1782
February1st to 10thDay
46%45%17%19%9%
1683
11th to 20thDay
45%46%19%19%8%
1759
21st to endDay
42%35%15%22%12%
1546
March1st to 10thDay
40%5%7%16%20%11%
1980
11th to 20thDay
42%5%9%17%22%5%
1980
21st to endDay
40%5%9%19%21%7%
2178
April1st to 10thDay
39%6%9%20%17%9%
1980
11th to 20thDay
39%6%9%17%21%8%
2084
21st to endDay
37%6%9%21%23%4
2218
May1st to 10thDay
38%6%10%22%19%6%
2340
11th to 20thDay
41%6%12%22%17%2
2306
21st to endDay
40%9%14%20%14%2
2531
June1st to 10thDay
27%9%16%29%16%2
2340
11th to 20thDay
26%9%15%28%18%4
2340
21st to endDay
26%7%13%28%22%3
2340
July1st to 10thDay
33%12%19%24%12%
2276
11th to 20thDay
19%8%17%35%19%3
2271
21st to endDay
23%10%18%36%12%1
2405
August1st to 10thDay
16%6%17%36%22%2
2314
11th to 20thDay
28%7%17%27%18%3
2301
21st to endDay
29%8%15%30%15%3
2343
September1st to 10thDay
30%6%11%23%20%9%
1980
11th to 20thDay
34%8%12%17%21%7%
1980
21st to endDay
26%6%9%22%25%12%
1980
October1st to 10thDay
25%5%12%22%22%14%
1898
11th to 20thDay
30%36%18%27%16%
1800
21st to endDay
31%47%18%26%15%
1980
November1st to 10thDay
32%48%23%25%9%
1858
11th to 20thDay
29%49%18%29%10%
1839
21st to endDay
38%36%20%24%9%
1710
December1st to 10thDay
37%410%19%23%7%
1710
11th to 20thDay
41%46%16%24%8%
2159
21st to endDay
40%46%23%21%7%
3135
January1st to 10thNight
32%37%20%26%12%
2458
11th to 20thNight
35%47%20%25%10%
2386
21st to endNight
36%35%15%28%13%
2574
February1st to 10thNight
37%38%18%22%12%
2290
11th to 20thNight
40%47%16%24%10%
2098
21st to endNight
39%48%14%19%16%
1709
March1st to 10thNight
39%5%9%15%20%13%
1980
11th to 20thNight
38%5%9%15%25%8%
1980
21st to endNight
34%5%11%19%25%7%
2178
April1st to 10thNight
29%6%11%22%18%13%
1980
11th to 20thNight
34%5%10%19%18%13%
1825
21st to endNight
29%7%10%22%27%5%
1738
May1st to 10thNight
34%7%10%21%20%8%
1620
11th to 20thNight
30%8%17%25%18%3
1594
21st to endNight
29%7%17%25%19%2
1746
June1st to 10thNight
21%8%16%31%20%4
1620
11th to 20thNight
18%7%14%36%19%6%
1620
21st to endNight
20%8%13%28%25%6%
1620
July1st to 10thNight
24%8%21%32%14%2
1575
11th to 20thNight
11%5%17%37%26%4
1566
21st to endNight
14%8%20%40%17%1
1673
August1st to 10thNight
10%416%37%28%4
1601
11th to 20thNight
26%6%15%28%20%6%
1600
21st to endNight
21%7%15%32%20%4
2006
September1st to 10thNight
26%5%12%25%22%10%
1980
11th to 20thNight
30%5%13%22%20%10%
1980
21st to endNight
22%5%9%21%28%16%
1980
October1st to 10thNight
19%411%26%21%19%
2042
11th to 20thNight
28%28%16%24%22%
2160
21st to endNight
31%3417%25%20%
2376
November1st to 10thNight
28%38%21%27%13%
2220
11th to 20thNight
28%47%19%28%14%
2337
21st to endNight
36%47%16%26%11%
2470
December1st to 10thNight
33%5%9%19%22%11%
2470
11th to 20thNight
38%46%16%26%12%
3037
21st to endNight
36%46%18%26%11%
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
17%15%36%26%6%
270
11th to 20thDay
20%16%37%18%7%1
249
21st to endDay
22%15%34%22%6%1
264
February1st to 10thDay
25%11%38%20%7%
240
11th to 20thDay
28%16%39%14%3
240
21st to endDay
33%15%38%12%2
198
March1st to 10thDay
26%13%36%22%3
240
11th to 20thDay
24%16%34%20%5%1
240
21st to endDay
16%15%42%20%5%1
264
April1st to 10thDay
23%13%36%22%5%
240
11th to 20thDay
17%14%34%27%8%1
362
21st to endDay
14%17%34%24%9%2
478
May1st to 10thDay
13%11%34%31%10%1
603
11th to 20thDay
17%5%27%31%17%3
625
21st to endDay
12%5%25%35%19%4
679
June1st to 10thDay
7%214%36%32%9%
630
11th to 20thDay
5%216%43%29%5%
630
21st to endDay
4211%35%35%12%
630
July1st to 10thDay
5%110%32%39%14%
621
11th to 20thDay
215%31%47%14%
618
21st to endDay
35%31%44%16%
684
August1st to 10thDay
315%29%50%13%
626
11th to 20thDay
8%15%31%43%12%
615
21st to endDay
7%15%20%43%23%
462
September1st to 10thDay
7%416%44%28%
270
11th to 20thDay
447%23%39%23%
270
21st to endDay
12%27%23%36%19%
270
October1st to 10thDay
3116%33%34%12%
270
11th to 20thDay
12%5%26%31%19%7%
270
21st to endDay
26%9%22%24%16%3
297
November1st to 10thDay
18%334%26%14%5%
270
11th to 20thDay
13%9%30%33%14%3
270
21st to endDay
19%13%32%25%10%1
270
December1st to 10thDay
17%11%33%26%11%2
270
11th to 20thDay
23%14%37%21%5%
270
21st to endDay
23%12%37%21%7%1
297
January1st to 10thNight
16%11%35%30%8%
950
11th to 20thNight
18%14%32%30%6%1
918
21st to endNight
17%10%36%30%6%
990
February1st to 10thNight
20%11%35%29%4
850
11th to 20thNight
21%13%39%25%2
704
21st to endNight
22%16%40%19%3
525
March1st to 10thNight
20%11%36%27%6%
540
11th to 20thNight
16%11%38%29%6%
540
21st to endNight
14%12%40%28%6%
594
April1st to 10thNight
9%12%44%28%5%
540
11th to 20thNight
15%11%38%27%8%1
533
21st to endNight
14%8%41%27%9%1
540
May1st to 10thNight
11%7%40%33%8%1
540
11th to 20thNight
10%433%35%16%2
531
21st to endNight
9%429%36%19%3
584
June1st to 10thNight
6%216%44%28%4
540
11th to 20thNight
4123%50%21%1
540
21st to endNight
4214%39%35%6%
540
July1st to 10thNight
4110%41%39%5%
525
11th to 20thNight
37%42%44%4
522
21st to endNight
115%44%45%4
591
August1st to 10thNight
3446%42%5%
537
11th to 20thNight
7%5%38%43%6%
534
21st to endNight
41438%46%7%
594
September1st to 10thNight
8%19%36%42%5%
540
11th to 20thNight
12%27%35%41%4
540
21st to endNight
8%111%38%36%6%
540
October1st to 10thNight
7%117%44%26%4
602
11th to 20thNight
14%425%37%18%2
720
21st to endNight
17%7%29%29%16%2
792
November1st to 10thNight
11%429%40%14%1
740
11th to 20thNight
10%9%30%38%12%1
817
21st to endNight
19%11%32%27%11%1
950
December1st to 10thNight
17%9%33%33%8%
950
11th to 20thNight
21%8%31%35%5%
950
21st to endNight
20%11%33%31%6%
1045
Page generated at 2024-01-11 03:22:38. Version ac07

Copyright 2024 Attilla Danko


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