Charles Nicholas Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charles Nicholas Memorial Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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
45%
24859
33%
98065
17%
24611
62%
24611
36%
41007

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%
759
43%
3970
15%
736
61%
736
32%
1335
January11th to 20thNight
32%
756
43%
3904
16%
740
55%
740
30%
1239
January21st to endNight
35%
830
25%
4231
17%
814
60%
814
27%
1674
February1st to 10thNight
30%
760
39%
2295
13%
760
57%
760
40%
1029
February11th to 20thNight
23%
743
36%
2218
11%
740
48%
740
39%
1008
February21st to endNight
17%
628
38%
1884
7%
628
48%
628
36%
786
March1st to 10thNight
27%
759
44%
3477
10%
744
52%
744
30%
1235
March11th to 20thNight
33%
759
34%
3444
13%
740
52%
740
24%
1730
March21st to endNight
23%
737
29%
3441
10%
716
53%
716
35%
1139
April1st to 10thNight
23%
570
42%
1900
12%
570
58%
570
42%
763
April11th to 20thNight
26%
563
38%
1877
11%
563
60%
563
43%
754
April21st to endNight
30%
570
40%
1900
15%
570
63%
570
42%
771
May1st to 10thNight
30%
568
46%
2918
16%
559
61%
559
42%
873
May11th to 20thNight
45%
553
26%
2995
19%
541
62%
541
38%
971
May21st to endNight
39%
612
27%
3088
15%
593
62%
593
51%
806
June1st to 10thNight
55%
570
29%
1520
17%
570
66%
570
46%
829
June11th to 20thNight
56%
570
37%
1520
23%
570
68%
570
62%
723
June21st to endNight
63%
570
21%
1533
16%
570
66%
570
38%
918
July1st to 10thNight
74%
539
19%
2587
18%
535
76%
535
24%
1358
July11th to 20thNight
79%
538
21%
2346
22%
533
80%
533
29%
1203
July21st to endNight
80%
608
14%
2739
18%
569
82%
569
24%
1543
August1st to 10thNight
79%
553
25%
2630
22%
545
79%
545
29%
1216
August11th to 20thNight
77%
544
20%
2572
24%
543
79%
543
31%
1149
August21st to endNight
79%
608
15%
3205
23%
605
81%
605
25%
1585
September1st to 10thNight
74%
570
25%
1900
28%
570
76%
570
36%
1027
September11th to 20thNight
73%
570
33%
1909
32%
570
78%
570
43%
965
September21st to endNight
68%
570
36%
2090
35%
570
76%
570
48%
907
October1st to 10thNight
56%
705
49%
3287
21%
704
67%
704
44%
1103
October11th to 20thNight
51%
748
29%
3417
19%
740
66%
740
38%
1362
October21st to endNight
48%
823
48%
3749
20%
813
64%
813
51%
1109
November1st to 10thNight
45%
780
43%
2340
18%
780
64%
780
50%
1035
November11th to 20thNight
48%
970
38%
2570
17%
970
61%
970
55%
1205
November21st to endNight
36%
986
38%
2562
13%
986
52%
986
41%
1334
December1st to 10thNight
36%
950
40%
2470
14%
950
55%
950
43%
1242
December11th to 20thNight
28%
950
36%
3044
11%
949
50%
949
32%
1467
December21st to endNight
27%
970
24%
4533
12%
955
49%
955
29%
1614

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
441433446%7%60%
104585
Night
331323335%7%67%
103653
TransparencyDay
21%5%9%18%25%22%
104351
Night
17%49%19%27%23%
103477
SeeingDay
12%16%27%26%16%4
14830
Night
9%15%26%29%17%3
25036

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
412223347%70%
2858
11th to 20thDay
1112223236%78%
2860
21st to endDay
2425%33446%9%58%
3146
February1st to 10thDay
1423223346%70%
1883
11th to 20thDay
2314333246%69%
1849
21st to endDay
312332246%74%
1570
March1st to 10thDay
17%25%333346%63%
3273
11th to 20thDay
310%2333435%6%57%
3490
21st to endDay
131333346%8%65%
3979
April1st to 10thDay
1313332246%73%
2280
11th to 20thDay
3313223346%70%
2251
21st to endDay
2312212236%76%
2280
May1st to 10thDay
2112121245%79%
3800
11th to 20thDay
4313345%46%7%61%
3765
21st to endDay
1112222246%78%
4417
June1st to 10thDay
1314445%48%10%57%
2660
11th to 20thDay
221332446%7%66%
2660
21st to endDay
8%425%5%5%7%7%8%7%43%
2638
July1st to 10thDay
7%5%27%6%6%7%6%9%10%35%
4110
11th to 20thDay
5%416%5%5%7%6%7%8%45%
4110
21st to endDay
9%5%26%6%7%7%7%11%10%30%
4404
August1st to 10thDay
5%425%46%7%6%7%11%43%
3784
11th to 20thDay
7%426%5%5%6%5%7%9%45%
3726
21st to endDay
7%5%26%7%6%8%6%8%10%35%
4180
September1st to 10thDay
11%6%26%5%45%47%7%43%
2280
11th to 20thDay
9%5%25%45%435%7%51%
2269
21st to endDay
6%315%333246%64%
2090
October1st to 10thDay
6%31323324469%
3214
11th to 20thDay
5%313223345%68%
3150
21st to endDay
12211112386%
3438
November1st to 10thDay
2212223236%76%
1959
11th to 20thDay
121312225%7%72%
1807
21st to endDay
331222345%7%67%
1773
December1st to 10thDay
331423335%7%66%
1710
11th to 20thDay
1436%23346%8%61%
1991
21st to endDay
131322236%6%72%
2931
January1st to 10thNight
1213233347%72%
4097
11th to 20thNight
1212223245%75%
4110
21st to endNight
242433347%10%59%
4521
February1st to 10thNight
31322335%8%70%
2295
11th to 20thNight
221223235%7%72%
2218
21st to endNight
1212212346%75%
1884
March1st to 10thNight
323223347%71%
3592
11th to 20thNight
314%34223235%58%
3490
21st to endNight
11222236%9%71%
3653
April1st to 10thNight
121222335%8%71%
1900
11th to 20thNight
2211123247%74%
1877
21st to endNight
1311223246%76%
1900
May1st to 10thNight
2211112145%80%
3170
11th to 20thNight
3312223245%73%
3140
21st to endNight
21111223483%
3146
June1st to 10thNight
2415%45%437%9%57%
1520
11th to 20thNight
321222335%6%72%
1520
21st to endNight
6%42445%6%46%8%49%
1533
July1st to 10thNight
8%5%24345%5%8%11%46%
2860
11th to 20thNight
331445%6%6%8%10%53%
2860
21st to endNight
8%6%24445%5%10%15%38%
3159
August1st to 10thNight
3213445%49%15%50%
3155
11th to 20thNight
431333446%12%58%
3113
21st to endNight
5%3144445%9%14%47%
3487
September1st to 10thNight
8%41433447%9%52%
1900
11th to 20thNight
8%31322336%7%61%
1909
21st to endNight
5%313223247%68%
2090
October1st to 10thNight
322222235%78%
3751
11th to 20thNight
241322334472%
3778
21st to endNight
211211212483%
4120
November1st to 10thNight
3313222235%74%
2340
11th to 20thNight
121222335%7%73%
2570
21st to endNight
25%13333346%67%
2562
December1st to 10thNight
3313123347%69%
2470
11th to 20thNight
131333446%7%65%
3200
21st to endNight
131422235%5%72%
4763

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
15%3421%31%26%
2859
11th to 20thDay
10%27%21%37%23%
2860
21st to endDay
22%212%20%29%15%
3146
February1st to 10thDay
16%45%18%30%27%
1883
11th to 20thDay
18%45%18%27%28%
1859
21st to endDay
15%16%12%29%37%
1570
March1st to 10thDay
22%46%12%22%35%
3273
11th to 20thDay
22%9%6%14%32%16%
3490
21st to endDay
17%47%22%31%20%
3979
April1st to 10thDay
14%35%17%36%26%
2280
11th to 20thDay
16%2414%30%34%
2254
21st to endDay
13%25%18%34%28%
2280
May1st to 10thDay
9%1412%25%49%
3800
11th to 20thDay
18%9%6%14%24%29%
3768
21st to endDay
9%3412%17%55%
4417
June1st to 10thDay
19%6%11%19%25%19%
2660
11th to 20thDay
15%45%16%23%36%
2660
21st to endDay
32%8%12%16%18%14%
2638
July1st to 10thDay
38%11%17%15%12%7%
4046
11th to 20thDay
32%8%13%21%23%4
4041
21st to endDay
39%9%19%23%9%1
4265
August1st to 10thDay
30%8%12%32%15%2
3772
11th to 20thDay
33%7%13%21%24%2
3762
21st to endDay
36%10%18%25%9%1
4179
September1st to 10thDay
36%6%13%17%18%10%
2280
11th to 20thDay
33%5%8%18%26%10%
2269
21st to endDay
22%37%23%31%14%
2090
October1st to 10thDay
19%27%11%31%30%
3214
11th to 20thDay
18%38%18%30%22%
3150
21st to endDay
8%1314%40%34%
3438
November1st to 10thDay
13%2422%33%25%
1959
11th to 20thDay
14%17%21%31%26%
1807
21st to endDay
17%38%18%26%28%
1773
December1st to 10thDay
18%37%24%32%17%
1710
11th to 20thDay
20%310%18%30%19%
1989
21st to endDay
13%28%16%30%32%
2931
January1st to 10thNight
15%35%19%31%26%
4097
11th to 20thNight
13%38%17%35%24%
4110
21st to endNight
20%212%21%29%15%
4521
February1st to 10thNight
14%48%18%27%29%
2295
11th to 20thNight
14%46%18%29%28%
2218
21st to endNight
11%19%16%28%35%
1884
March1st to 10thNight
14%36%14%29%34%
3592
11th to 20thNight
26%7%6%14%31%16%
3490
21st to endNight
12%27%26%34%19%
3653
April1st to 10thNight
11%36%18%36%26%
1900
11th to 20thNight
12%27%17%30%32%
1877
21st to endNight
11%45%19%35%25%
1900
May1st to 10thNight
8%439%23%52%
3170
11th to 20thNight
14%37%18%26%32%
3141
21st to endNight
8%2410%20%56%
3147
June1st to 10thNight
21%6%10%19%23%21%
1520
11th to 20thNight
14%25%17%22%40%
1520
21st to endNight
31%5%15%17%14%17%
1533
July1st to 10thNight
29%7%20%21%15%7%
2815
11th to 20thNight
23%7%15%30%21%4
2806
21st to endNight
31%7%24%27%11%1
3060
August1st to 10thNight
21%6%19%35%17%2
3144
11th to 20thNight
20%5%16%30%27%2
3143
21st to endNight
26%8%23%27%15%1
3487
September1st to 10thNight
29%6%16%18%19%13%
1900
11th to 20thNight
23%6%12%20%27%12%
1909
21st to endNight
19%310%22%33%13%
2090
October1st to 10thNight
13%26%11%34%33%
3751
11th to 20thNight
17%38%14%33%25%
3778
21st to endNight
9%2314%37%35%
4120
November1st to 10thNight
14%2419%31%29%
2340
11th to 20thNight
12%45%21%31%28%
2570
21st to endNight
19%37%18%29%24%
2562
December1st to 10thNight
16%39%21%28%23%
2470
11th to 20thNight
19%29%22%26%22%
3201
21st to endNight
15%27%19%28%29%
4763

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
16%28%34%18%4
270
11th to 20thDay
21%21%32%18%7%1
270
21st to endDay
11%26%31%22%10%1
297
February1st to 10thDay
16%25%30%22%6%1
270
11th to 20thDay
22%26%33%15%31
270
21st to endDay
32%28%25%10%4
225
March1st to 10thDay
20%29%35%11%4
348
11th to 20thDay
22%25%33%13%6%1
460
21st to endDay
25%31%33%8%31
506
April1st to 10thDay
14%32%37%13%31
460
11th to 20thDay
17%33%33%15%3
452
21st to endDay
16%30%35%16%3
460
May1st to 10thDay
8%30%40%19%3
463
11th to 20thDay
9%21%38%22%8%2
488
21st to endDay
7%18%43%22%9%1
642
June1st to 10thDay
38%32%35%19%3
680
11th to 20thDay
39%32%38%15%3
680
21st to endDay
8%419%34%28%7%
658
July1st to 10thDay
7%114%36%33%10%
486
11th to 20thDay
418%39%35%12%
484
21st to endDay
5%18%31%40%15%
531
August1st to 10thDay
5%28%32%39%16%
487
11th to 20thDay
9%212%34%32%11%
477
21st to endDay
8%39%37%33%11%
539
September1st to 10thDay
12%317%38%23%7%
490
11th to 20thDay
5%419%45%22%5%
479
21st to endDay
6%7%30%32%21%4
300
October1st to 10thDay
11%10%27%33%16%4
300
11th to 20thDay
12%11%34%23%17%4
300
21st to endDay
13%16%29%25%11%6%
330
November1st to 10thDay
17%22%32%17%10%1
300
11th to 20thDay
14%16%31%20%15%4
300
21st to endDay
19%26%27%16%12%1
291
December1st to 10thDay
20%19%31%23%6%1
270
11th to 20thDay
17%26%32%21%5%
270
21st to endDay
22%27%32%14%5%
297
January1st to 10thNight
9%22%32%23%11%3
760
11th to 20thNight
11%23%30%24%9%3
760
21st to endNight
12%22%28%26%10%2
836
February1st to 10thNight
9%23%35%21%8%3
760
11th to 20thNight
12%22%41%19%5%1
744
21st to endNight
17%30%35%14%31
628
March1st to 10thNight
14%27%29%23%6%1
760
11th to 20thNight
13%20%30%27%9%1
760
21st to endNight
12%25%38%19%6%
738
April1st to 10thNight
11%23%42%19%5%
570
11th to 20thNight
11%22%38%23%5%
563
21st to endNight
9%24%34%27%6%
570
May1st to 10thNight
5%20%43%28%4
570
11th to 20thNight
7%13%32%35%11%2
561
21st to endNight
7%13%38%31%11%
617
June1st to 10thNight
35%29%44%18%1
570
11th to 20thNight
45%31%41%17%2
570
21st to endNight
6%317%42%29%2
570
July1st to 10thNight
8%26%40%41%3
555
11th to 20thNight
415%35%46%8%
552
21st to endNight
6%2328%50%11%
624
August1st to 10thNight
6%1330%47%13%
567
11th to 20thNight
5%25%32%43%13%
564
21st to endNight
5%16%29%50%9%
627
September1st to 10thNight
7%37%37%38%7%
570
11th to 20thNight
9%112%43%30%4
570
21st to endNight
7%416%43%27%3
570
October1st to 10thNight
7%8%23%39%20%3
724
11th to 20thNight
8%10%28%35%16%3
760
21st to endNight
9%13%27%28%16%7%
836
November1st to 10thNight
9%14%30%28%14%5%
780
11th to 20thNight
7%14%29%34%13%3
970
21st to endNight
12%20%29%23%13%3
986
December1st to 10thNight
13%20%28%27%10%2
950
11th to 20thNight
12%25%31%23%8%1
950
21st to endNight
15%25%31%22%5%2
974
Page generated at 2024-11-24 22:22:19. Version ac07

Copyright © 2024 Attilla Danko.


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