C.J. Observatory & Retreat
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C.J. Observatory & Retreat 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
61%
23455
35%
74203
25%
23406
73%
23406
48%
35604

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
58%
756
36%
2457
29%
756
70%
756
47%
1173
January11th to 20thNight
58%
734
37%
2385
29%
734
72%
734
51%
1082
January21st to endNight
54%
792
39%
2574
28%
792
72%
792
46%
1220
February1st to 10thNight
57%
720
38%
2340
28%
720
74%
720
54%
1038
February11th to 20thNight
47%
700
35%
2133
21%
700
64%
700
48%
1034
February21st to endNight
39%
592
43%
1655
20%
592
61%
592
54%
804
March1st to 10thNight
42%
720
40%
1980
16%
720
63%
720
51%
980
March11th to 20thNight
52%
720
38%
1980
19%
720
67%
720
55%
968
March21st to endNight
47%
792
39%
2178
16%
792
65%
792
56%
1054
April1st to 10thNight
45%
586
41%
1846
19%
586
70%
586
59%
776
April11th to 20thNight
43%
533
40%
1777
22%
533
68%
533
54%
747
April21st to endNight
42%
540
44%
1800
22%
540
72%
540
55%
720
May1st to 10thNight
50%
540
38%
1800
25%
540
70%
540
60%
732
May11th to 20thNight
55%
531
35%
1681
25%
531
69%
531
56%
740
May21st to endNight
54%
584
38%
1746
24%
582
69%
582
62%
749
June1st to 10thNight
65%
540
33%
1620
26%
540
72%
540
53%
771
June11th to 20thNight
67%
540
34%
1620
26%
540
74%
540
60%
725
June21st to endNight
72%
540
22%
1620
20%
540
74%
540
41%
888
July1st to 10thNight
73%
525
22%
1575
18%
525
74%
525
39%
874
July11th to 20thNight
77%
522
20%
1566
18%
522
77%
522
29%
985
July21st to endNight
74%
591
19%
1674
19%
558
74%
558
31%
1025
August1st to 10thNight
78%
537
18%
1619
18%
534
78%
534
31%
982
August11th to 20thNight
75%
534
23%
1778
24%
534
77%
534
29%
1058
August21st to endNight
77%
594
25%
1980
29%
594
77%
594
32%
1127
September1st to 10thNight
75%
540
27%
1800
31%
540
76%
540
34%
1017
September11th to 20thNight
80%
593
36%
1853
35%
593
82%
593
45%
950
September21st to endNight
77%
720
36%
2038
26%
720
82%
720
57%
1000
October1st to 10thNight
70%
720
34%
2160
25%
720
76%
720
52%
1053
October11th to 20thNight
73%
720
42%
2160
30%
720
81%
720
62%
958
October21st to endNight
72%
792
45%
2376
31%
792
82%
792
67%
1005
November1st to 10thNight
74%
740
45%
2220
32%
740
83%
740
65%
940
November11th to 20thNight
70%
760
43%
2280
30%
760
80%
760
62%
1012
November21st to endNight
57%
760
42%
2280
28%
760
70%
760
48%
1137
December1st to 10thNight
61%
760
40%
2432
31%
760
73%
760
49%
1163
December11th to 20thNight
55%
759
35%
2907
26%
759
69%
759
38%
1419
December21st to endNight
54%
828
25%
4313
30%
817
66%
817
34%
1698

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
431332445%7%63%
75044
Night
431332445%7%64%
74752
TransparencyDay
21%25%15%28%29%
74771
Night
21%25%16%28%27%
74546
SeeingDay
6%8%21%30%24%11%
13367
Night
5%423%40%24%4
23472

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
5%31332345%6%64%
1708
11th to 20thDay
5%212223446%68%
1647
21st to endDay
6%423323345%65%
1782
February1st to 10thDay
3314323347%69%
1620
11th to 20thDay
6%213423446%65%
1713
21st to endDay
441232334471%
1596
March1st to 10thDay
441442345%6%63%
1980
11th to 20thDay
4323323445%69%
1980
21st to endDay
221232345%7%69%
2178
April1st to 10thDay
211322225%6%74%
2113
11th to 20thDay
221211223479%
2131
21st to endDay
2112111246%79%
2160
May1st to 10thDay
212213335%77%
2160
11th to 20thDay
2213313345%72%
2210
21st to endDay
211111233480%
2530
June1st to 10thDay
2213323448%68%
2340
11th to 20thDay
2212223346%74%
2340
21st to endDay
3414435%5%6%8%57%
2340
July1st to 10thDay
5%3246%36%7%7%10%46%
2340
11th to 20thDay
5%415%7%47%7%8%11%41%
2340
21st to endDay
6%426%7%6%9%9%8%11%32%
2545
August1st to 10thDay
5%335%6%46%7%8%10%42%
2311
11th to 20thDay
5%325%7%47%7%7%10%43%
2123
21st to endDay
5%325%5%45%7%8%9%47%
2376
September1st to 10thDay
8%4245%36%5%7%9%47%
2160
11th to 20thDay
5%31332446%8%60%
2103
21st to endDay
321332335%7%68%
1920
October1st to 10thDay
422331435%6%67%
1800
11th to 20thDay
3313322335%73%
1800
21st to endDay
211221233479%
1980
November1st to 10thDay
2212222336%74%
1859
11th to 20thDay
2312323346%71%
1900
21st to endDay
5%413423447%62%
1900
December1st to 10thDay
5%312423447%64%
1744
11th to 20thDay
5%6%345%24337%58%
2169
21st to endDay
231332345%8%65%
3146
January1st to 10thNight
5%41242345%7%63%
2457
11th to 20thNight
4313323336%69%
2385
21st to endNight
6%423323346%65%
2574
February1st to 10thNight
2212324448%68%
2340
11th to 20thNight
5%423323335%67%
2133
21st to endNight
341232345%5%69%
1655
March1st to 10thNight
43123235%5%8%65%
1980
11th to 20thNight
4212323335%71%
1980
21st to endNight
2313223445%71%
2178
April1st to 10thNight
1212213346%74%
1846
11th to 20thNight
2313312245%74%
1777
21st to endNight
1112223345%77%
1800
May1st to 10thNight
3212212336%76%
1800
11th to 20thNight
32332335%7%70%
1681
21st to endNight
2112222235%77%
1746
June1st to 10thNight
3213424446%67%
1620
11th to 20thNight
221332435%5%72%
1620
21st to endNight
43245%45%6%7%9%51%
1620
July1st to 10thNight
45%345%45%6%9%12%44%
1620
11th to 20thNight
3325%7%6%9%9%9%13%33%
1620
21st to endNight
4446%7%46%8%8%15%35%
1773
August1st to 10thNight
3435%6%47%9%10%12%37%
1628
11th to 20thNight
5%4246%5%7%8%8%12%37%
1778
21st to endNight
5%425%6%46%8%9%12%40%
1980
September1st to 10thNight
5%425%6%36%6%6%9%48%
1800
11th to 20thNight
5%3134345%6%8%58%
1853
21st to endNight
3313323347%68%
2038
October1st to 10thNight
5%313323446%66%
2160
11th to 20thNight
3212222235%76%
2160
21st to endNight
222212235%79%
2376
November1st to 10thNight
212213445%76%
2220
11th to 20thNight
3212222346%73%
2280
21st to endNight
6%324323346%65%
2280
December1st to 10thNight
5%32332445%7%64%
2432
11th to 20thNight
43244345%6%7%58%
3041
21st to endNight
5%423323345%65%
4521

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
22%25%16%37%18%
1709
11th to 20thDay
17%2414%39%24%
1647
21st to endDay
23%2113%36%24%
1782
February1st to 10thDay
18%1416%25%35%
1620
11th to 20thDay
23%2314%30%29%
1723
21st to endDay
19%119%30%39%
1596
March1st to 10thDay
23%2311%31%32%
1980
11th to 20thDay
19%2212%27%37%
1980
21st to endDay
16%2310%37%33%
2178
April1st to 10thDay
13%1210%37%37%
2113
11th to 20thDay
13%117%29%49%
2134
21st to endDay
10%1110%32%45%
2160
May1st to 10thDay
12%1110%25%51%
2160
11th to 20thDay
16%25%11%28%38%
2213
21st to endDay
10%129%24%54%
2530
June1st to 10thDay
18%129%28%42%
2340
11th to 20thDay
13%116%21%58%
2340
21st to endDay
25%35%14%21%33%
2340
July1st to 10thDay
31%410%16%19%20%
2276
11th to 20thDay
33%5%12%25%16%8%
2271
21st to endDay
40%6%18%21%12%3
2404
August1st to 10thDay
33%5%14%25%17%7%
2296
11th to 20thDay
33%6%12%21%20%8%
2123
21st to endDay
30%5%12%23%20%10%
2376
September1st to 10thDay
32%38%20%22%16%
2160
11th to 20thDay
23%36%17%29%21%
2103
21st to endDay
18%2416%36%25%
1920
October1st to 10thDay
19%27%16%24%32%
1800
11th to 20thDay
17%1211%29%40%
1800
21st to endDay
12%1216%35%33%
1980
November1st to 10thDay
14%1416%36%28%
1859
11th to 20thDay
17%2317%30%31%
1900
21st to endDay
24%2317%32%22%
1900
December1st to 10thDay
22%2421%32%20%
1744
11th to 20thDay
30%2421%28%16%
2168
21st to endDay
20%15%16%38%21%
3146
January1st to 10thNight
22%2417%36%19%
2457
11th to 20thNight
19%2315%39%22%
2385
21st to endNight
22%2216%36%21%
2574
February1st to 10thNight
17%2318%27%33%
2340
11th to 20thNight
22%2216%31%28%
2133
21st to endNight
18%2212%31%35%
1655
March1st to 10thNight
20%2316%28%32%
1980
11th to 20thNight
18%1213%28%37%
1980
21st to endNight
17%2313%35%30%
2178
April1st to 10thNight
13%2212%37%34%
1846
11th to 20thNight
16%118%30%44%
1777
21st to endNight
13%2112%32%41%
1800
May1st to 10thNight
14%118%25%50%
1800
11th to 20thNight
16%25%12%25%40%
1682
21st to endNight
13%228%24%51%
1746
June1st to 10thNight
20%2211%25%40%
1620
11th to 20thNight
16%127%22%53%
1620
21st to endNight
28%47%13%16%32%
1620
July1st to 10thNight
30%413%20%17%17%
1575
11th to 20thNight
38%7%15%21%13%6%
1566
21st to endNight
37%5%23%21%11%3
1674
August1st to 10thNight
35%6%16%26%11%6%
1619
11th to 20thNight
35%7%16%17%17%8%
1778
21st to endNight
34%5%15%24%16%7%
1980
September1st to 10thNight
33%5%10%19%17%17%
1800
11th to 20thNight
24%48%18%25%20%
1853
21st to endNight
18%36%17%33%23%
2038
October1st to 10thNight
21%27%15%26%29%
2160
11th to 20thNight
14%2114%28%41%
2160
21st to endNight
12%1217%32%36%
2376
November1st to 10thNight
12%2315%36%31%
2220
11th to 20thNight
15%1217%33%31%
2280
21st to endNight
23%1317%32%23%
2280
December1st to 10thNight
22%2423%28%22%
2432
11th to 20thNight
26%17%20%30%15%
3041
21st to endNight
23%1317%35%21%
4521

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
12%7%27%37%13%3
270
11th to 20thDay
7%8%28%34%19%4
249
21st to endDay
5%8%29%36%15%8%
264
February1st to 10thDay
39%25%35%23%5%
240
11th to 20thDay
13%9%31%35%10%2
240
21st to endDay
9%27%33%22%7%1
314
March1st to 10thDay
10%21%31%27%10%1
420
11th to 20thDay
10%16%28%31%12%3
420
21st to endDay
8%23%34%25%9%2
462
April1st to 10thDay
5%15%36%27%12%4
420
11th to 20thDay
7%19%34%26%12%2
412
21st to endDay
5%15%37%26%16%2
420
May1st to 10thDay
413%35%30%15%3
423
11th to 20thDay
39%29%34%21%4
448
21st to endDay
28%32%36%18%3
485
June1st to 10thDay
45%22%38%25%6%
450
11th to 20thDay
3422%38%26%8%
450
21st to endDay
4210%42%30%12%
450
July1st to 10thDay
7%15%29%34%25%
446
11th to 20thDay
7%1221%39%30%
444
21st to endDay
5%1316%45%30%
487
August1st to 10thDay
5%2218%39%33%
447
11th to 20thDay
5%35%24%40%23%
437
21st to endDay
426%21%39%28%
495
September1st to 10thDay
10%25%30%36%16%
450
11th to 20thDay
5%110%32%36%16%
450
21st to endDay
4414%38%31%10%
390
October1st to 10thDay
7%416%33%27%14%
270
11th to 20thDay
8%5%16%33%30%8%
270
21st to endDay
46%17%32%28%14%
297
November1st to 10thDay
6%427%36%21%6%
270
11th to 20thDay
35%17%39%29%7%
270
21st to endDay
9%11%23%35%18%4
270
December1st to 10thDay
6%6%23%36%24%5%
270
11th to 20thDay
9%7%30%33%17%3
270
21st to endDay
8%10%30%35%14%3
297
January1st to 10thNight
6%5%27%41%17%4
760
11th to 20thNight
6%428%40%18%4
734
21st to endNight
9%6%27%41%15%3
792
February1st to 10thNight
35%32%39%17%4
720
11th to 20thNight
8%7%34%38%12%2
704
21st to endNight
5%8%45%32%9%1
592
March1st to 10thNight
6%9%40%34%10%1
720
11th to 20thNight
7%7%30%39%14%2
720
21st to endNight
5%9%36%38%11%1
792
April1st to 10thNight
28%42%39%9%1
586
11th to 20thNight
49%42%33%11%1
533
21st to endNight
113%40%35%10%1
540
May1st to 10thNight
46%38%45%7%1
540
11th to 20thNight
4431%45%15%1
531
21st to endNight
35%34%47%12%1
584
June1st to 10thNight
5%223%51%18%1
540
11th to 20thNight
2423%53%17%1
540
21st to endNight
5%213%46%33%1
540
July1st to 10thNight
7%26%38%43%5%
525
11th to 20thNight
32330%54%8%
522
21st to endNight
6%1225%56%10%
591
August1st to 10thNight
42224%56%12%
537
11th to 20thNight
5%25%30%49%9%
534
21st to endNight
5%1327%56%8%
594
September1st to 10thNight
6%2435%51%3
540
11th to 20thNight
7%16%43%39%5%
593
21st to endNight
4112%45%33%5%
720
October1st to 10thNight
6%217%47%25%3
720
11th to 20thNight
4218%50%22%4
720
21st to endNight
3319%42%25%8%
792
November1st to 10thNight
4219%43%26%7%
740
11th to 20thNight
3320%45%25%3
760
21st to endNight
8%424%39%19%5%
760
December1st to 10thNight
6%325%43%19%4
760
11th to 20thNight
6%428%45%14%3
760
21st to endNight
8%6%26%41%16%3
836
Page generated at 2024-01-11 02:22:43. Version ac07

Copyright 2024 Attilla Danko


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