Lake Afton Public Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Afton Public Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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
42%
25409
25%
95815
15%
25138
53%
25138
30%
50707

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
36%
940
28%
4018
13%
926
49%
926
24%
2285
January11th to 20thNight
33%
948
29%
3998
11%
930
45%
930
26%
1973
January21st to endNight
34%
1039
21%
4467
12%
1023
47%
1023
23%
2618
February1st to 10thNight
28%
940
23%
2460
8%
940
38%
940
31%
1562
February11th to 20thNight
29%
744
23%
2218
9%
740
40%
740
30%
1310
February21st to endNight
29%
628
29%
1884
10%
628
43%
628
33%
1050
March1st to 10thNight
31%
634
36%
3475
14%
625
46%
625
24%
1492
March11th to 20thNight
30%
563
25%
3433
14%
550
42%
550
19%
1532
March21st to endNight
25%
619
15%
3680
9%
605
41%
605
15%
1916
April1st to 10thNight
27%
570
24%
2090
13%
570
46%
570
30%
1081
April11th to 20thNight
25%
563
24%
1788
11%
563
42%
563
30%
1034
April21st to endNight
31%
570
23%
1710
13%
570
46%
570
27%
1026
May1st to 10thNight
32%
566
25%
2808
13%
559
44%
559
17%
1598
May11th to 20thNight
45%
546
18%
2760
20%
541
53%
541
23%
1414
May21st to endNight
43%
609
12%
3065
13%
593
52%
593
25%
1379
June1st to 10thNight
57%
570
20%
1710
14%
570
63%
570
40%
926
June11th to 20thNight
51%
570
21%
1710
12%
570
60%
570
44%
900
June21st to endNight
54%
570
24%
1710
16%
570
60%
570
47%
883
July1st to 10thNight
68%
545
21%
2584
18%
535
71%
535
27%
1283
July11th to 20thNight
71%
539
22%
2412
23%
533
77%
533
37%
1088
July21st to endNight
69%
613
19%
2742
23%
569
73%
569
29%
1309
August1st to 10thNight
68%
552
29%
2522
25%
544
73%
544
30%
1228
August11th to 20thNight
67%
550
20%
2567
31%
543
72%
543
26%
1375
August21st to endNight
73%
607
24%
2902
31%
605
76%
605
36%
1219
September1st to 10thNight
59%
570
28%
2090
29%
570
68%
570
37%
1049
September11th to 20thNight
55%
570
28%
2090
24%
570
65%
570
35%
1079
September21st to endNight
55%
570
32%
2090
29%
570
64%
570
40%
1005
October1st to 10thNight
50%
598
30%
2140
27%
578
58%
578
32%
1168
October11th to 20thNight
40%
760
31%
2387
15%
740
54%
740
42%
1232
October21st to endNight
39%
836
27%
2769
14%
814
52%
814
32%
1568
November1st to 10thNight
42%
942
32%
2502
12%
942
54%
942
48%
1351
November11th to 20thNight
35%
1000
30%
2600
10%
1000
48%
1000
43%
1446
November21st to endNight
41%
1000
30%
2600
13%
1000
51%
1000
40%
1525
December1st to 10thNight
38%
978
30%
2542
13%
978
50%
978
42%
1469
December11th to 20thNight
31%
948
31%
2875
11%
948
45%
948
32%
1662
December21st to endNight
33%
1042
19%
4417
12%
1026
46%
1026
21%
2672

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
9%6%25%44435%7%52%
101515
Night
9%5%25%33435%7%55%
98307
TransparencyDay
30%5%11%26%22%5%
105258
Night
28%5%11%26%24%6%
102691
SeeingDay
11%9%28%31%17%4
15647
Night
11%9%33%35%11%1
25564

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
10%7%28%5%5%435%6%46%
2847
11th to 20thDay
8%7%36%6%5%5%36%7%44%
2850
21st to endDay
11%11%48%332246%46%
3135
February1st to 10thDay
10%9%46%443347%46%
1737
11th to 20thDay
7%7%27%44435%6%52%
1849
21st to endDay
7%6%26%34436%8%51%
1570
March1st to 10thDay
9%7%24233237%58%
3333
11th to 20thDay
9%5%1333335%8%58%
3480
21st to endDay
11%7%26%45%446%7%43%
3814
April1st to 10thDay
10%5%25%33335%8%52%
2090
11th to 20thDay
12%7%26%44435%6%47%
2335
21st to endDay
16%5%25%44435%6%46%
2470
May1st to 10thDay
18%10%36%43335%5%40%
4082
11th to 20thDay
10%6%26%43435%7%50%
4082
21st to endDay
11%7%26%44446%7%45%
4477
June1st to 10thDay
5%315%435%46%10%53%
2470
11th to 20thDay
6%41444447%8%54%
2470
21st to endDay
6%313335%46%9%58%
2470
July1st to 10thDay
9%5%25%44446%7%51%
4120
11th to 20thDay
6%32433447%9%56%
4120
21st to endDay
5%314345%48%11%52%
4465
August1st to 10thDay
6%5%25%445%46%9%51%
4104
11th to 20thDay
8%325%34436%9%53%
4041
21st to endDay
431433436%9%62%
4358
September1st to 10thDay
8%5%25%334347%56%
2090
11th to 20thDay
9%425%43445%6%54%
2090
21st to endDay
8%415%33435%7%57%
2090
October1st to 10thDay
11%42333435%5%58%
2043
11th to 20thDay
10%41323323465%
1900
21st to endDay
11%6%2433323458%
2090
November1st to 10thDay
8%423223347%62%
1792
11th to 20thDay
8%5%25%333345%60%
1800
21st to endDay
11%423332345%61%
1800
December1st to 10thDay
8%6%35%33335%7%56%
1755
11th to 20thDay
9%7%36%43435%6%51%
2161
21st to endDay
11%10%49%5%4445%6%38%
3135
January1st to 10thNight
9%6%38%444346%49%
4108
11th to 20thNight
5%5%26%5%44446%56%
4120
21st to endNight
15%10%3432333450%
4532
February1st to 10thNight
10%8%36%43336%6%48%
2460
11th to 20thNight
10%8%35%433346%51%
2218
21st to endNight
8%6%26%333345%56%
1884
March1st to 10thNight
7%6%25%32336%6%58%
3524
11th to 20thNight
8%5%25%44435%6%55%
3480
21st to endNight
11%7%26%44435%6%49%
3817
April1st to 10thNight
11%41334335%7%54%
2090
11th to 20thNight
14%5%2443446%8%48%
1788
21st to endNight
14%6%25%34435%6%49%
1710
May1st to 10thNight
17%7%24343346%47%
2823
11th to 20thNight
11%416%23436%10%50%
2823
21st to endNight
8%42433446%9%56%
3090
June1st to 10thNight
4425%335%47%11%53%
1710
11th to 20thNight
5%31334448%11%54%
1710
21st to endNight
6%22433436%8%61%
1710
July1st to 10thNight
6%425%34447%9%52%
2850
11th to 20thNight
232433447%11%57%
2850
21st to endNight
5%415%34438%11%51%
3098
August1st to 10thNight
5%324435%46%9%57%
2836
11th to 20thNight
6%425%45%5%47%8%52%
2798
21st to endNight
331433435%8%65%
3290
September1st to 10thNight
8%424433346%60%
2090
11th to 20thNight
7%425%33345%8%56%
2090
21st to endNight
6%31433335%6%61%
2090
October1st to 10thNight
9%5%24344247%58%
2118
11th to 20thNight
8%414222245%67%
2280
21st to endNight
10%5%13323235%62%
2508
November1st to 10thNight
9%324322245%64%
2502
11th to 20thNight
8%423333446%62%
2600
21st to endNight
12%5%14233336%58%
2600
December1st to 10thNight
7%6%2433335%7%57%
2542
11th to 20thNight
9%6%25%333346%55%
3036
21st to endNight
13%8%37%44335%6%44%
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
39%411%25%19%2
2848
11th to 20thDay
38%5%16%24%13%5%
2850
21st to endDay
42%310%24%18%2
3135
February1st to 10thDay
39%5%11%24%16%5%
1737
11th to 20thDay
33%5%13%27%17%5%
1859
21st to endDay
31%410%25%22%8%
1570
March1st to 10thDay
28%38%20%28%12%
3333
11th to 20thDay
25%5%13%25%28%4
3480
21st to endDay
37%8%12%28%12%3
3814
April1st to 10thDay
30%5%12%25%20%7%
2090
11th to 20thDay
38%5%10%24%17%5%
2335
21st to endDay
39%5%11%28%15%2
2470
May1st to 10thDay
46%6%8%18%18%4
4120
11th to 20thDay
33%7%11%26%22%1
4086
21st to endDay
37%7%11%24%15%6%
4489
June1st to 10thDay
25%9%17%30%15%4
2470
11th to 20thDay
26%6%13%28%22%5%
2470
21st to endDay
21%7%15%27%24%6%
2470
July1st to 10thDay
31%5%13%24%21%6%
4056
11th to 20thDay
23%6%12%32%22%4
4051
21st to endDay
22%8%15%31%22%1
4325
August1st to 10thDay
29%6%13%26%23%3
4090
11th to 20thDay
28%6%18%26%19%3
4080
21st to endDay
19%6%14%36%19%5%
4357
September1st to 10thDay
29%5%9%26%22%9%
2090
11th to 20thDay
31%5%9%27%24%5%
2090
21st to endDay
26%5%10%26%26%8%
2090
October1st to 10thDay
20%36%18%44%9%
3394
11th to 20thDay
17%37%27%36%10%
3140
21st to endDay
25%37%26%29%9%
3428
November1st to 10thDay
23%49%29%27%8%
1792
11th to 20thDay
27%48%27%28%7%
1800
21st to endDay
27%310%29%26%5%
1800
December1st to 10thDay
29%5%11%34%19%3
1755
11th to 20thDay
34%5%7%28%21%4
2159
21st to endDay
45%49%26%14%2
3135
January1st to 10thNight
36%49%31%17%3
4108
11th to 20thNight
29%5%16%25%22%3
4120
21st to endNight
39%310%24%21%2
4532
February1st to 10thNight
37%5%12%24%18%5%
2460
11th to 20thNight
34%5%11%25%19%5%
2218
21st to endNight
31%39%22%24%11%
1884
March1st to 10thNight
27%48%23%27%12%
3524
11th to 20thNight
30%5%9%24%29%4
3480
21st to endNight
35%7%11%32%12%3
3817
April1st to 10thNight
29%5%11%23%24%8%
2090
11th to 20thNight
32%6%14%24%19%5%
1788
21st to endNight
36%5%11%23%21%4
1710
May1st to 10thNight
38%7%11%18%18%7%
2850
11th to 20thNight
30%8%17%30%15%1
2824
21st to endNight
26%7%17%23%24%3
3099
June1st to 10thNight
25%7%20%30%16%3
1710
11th to 20thNight
23%6%16%29%21%5%
1710
21st to endNight
21%6%12%29%23%8%
1710
July1st to 10thNight
26%7%15%22%25%5%
2805
11th to 20thNight
20%5%12%33%27%4
2796
21st to endNight
25%6%16%32%20%1
2999
August1st to 10thNight
24%6%12%27%23%8%
2826
11th to 20thNight
28%7%15%24%21%4
2825
21st to endNight
18%6%16%37%19%5%
3290
September1st to 10thNight
27%49%25%24%12%
2090
11th to 20thNight
28%5%10%25%27%6%
2090
21st to endNight
23%5%9%23%30%9%
2090
October1st to 10thNight
20%36%14%46%13%
3534
11th to 20thNight
16%27%26%35%15%
3779
21st to endNight
22%37%24%38%7%
4120
November1st to 10thNight
23%311%26%28%9%
2502
11th to 20thNight
25%48%28%29%7%
2600
21st to endNight
28%48%26%25%8%
2600
December1st to 10thNight
26%5%13%31%21%4
2542
11th to 20thNight
30%5%8%30%22%5%
3037
21st to endNight
40%5%11%26%13%4
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
13%13%38%24%10%1
270
11th to 20thDay
17%15%40%24%4
270
21st to endDay
10%12%47%26%5%
297
February1st to 10thDay
17%18%41%20%31
270
11th to 20thDay
14%16%47%17%7%
270
21st to endDay
12%19%46%18%4
225
March1st to 10thDay
11%19%43%23%5%
270
11th to 20thDay
17%16%39%23%5%
270
21st to endDay
19%19%39%20%31
297
April1st to 10thDay
16%20%36%23%5%
270
11th to 20thDay
16%17%41%22%4
533
21st to endDay
20%16%36%19%8%2
650
May1st to 10thDay
17%10%38%26%8%1
653
11th to 20thDay
16%10%28%28%15%3
675
21st to endDay
15%10%30%28%15%3
734
June1st to 10thDay
6%424%36%24%7%
680
11th to 20thDay
7%329%39%19%3
680
21st to endDay
6%426%44%16%3
680
July1st to 10thDay
7%214%35%33%9%
671
11th to 20thDay
3314%41%31%7%
668
21st to endDay
6%212%37%33%10%
739
August1st to 10thDay
8%214%42%28%5%
676
11th to 20thDay
7%216%40%31%5%
665
21st to endDay
4316%35%34%8%
652
September1st to 10thDay
10%210%37%32%9%
300
11th to 20thDay
5%119%42%27%5%
300
21st to endDay
14%5%26%30%19%6%
300
October1st to 10thDay
12%8%25%28%20%6%
300
11th to 20thDay
9%10%44%25%12%1
300
21st to endDay
18%15%30%23%11%3
330
November1st to 10thDay
12%10%32%32%10%3
300
11th to 20thDay
14%17%37%19%13%1
300
21st to endDay
16%14%33%28%8%1
300
December1st to 10thDay
8%12%40%28%9%3
285
11th to 20thDay
12%14%34%30%10%1
270
21st to endDay
16%18%40%22%3
297
January1st to 10thNight
9%12%37%34%7%
950
11th to 20thNight
12%13%37%29%7%1
950
21st to endNight
12%11%37%33%6%
1045
February1st to 10thNight
14%14%39%29%3
940
11th to 20thNight
15%13%38%29%4
744
21st to endNight
12%15%38%30%4
628
March1st to 10thNight
11%13%41%32%4
641
11th to 20thNight
17%12%39%28%5%
570
21st to endNight
16%17%38%24%5%
627
April1st to 10thNight
15%13%43%22%7%
570
11th to 20thNight
16%15%40%24%4
563
21st to endNight
17%15%35%27%6%1
570
May1st to 10thNight
16%10%37%30%6%
570
11th to 20thNight
13%7%30%36%13%1
561
21st to endNight
11%7%32%34%14%2
617
June1st to 10thNight
5%5%27%39%22%2
570
11th to 20thNight
6%336%41%14%
570
21st to endNight
6%432%45%13%1
570
July1st to 10thNight
6%217%48%25%2
555
11th to 20thNight
3117%55%21%3
552
21st to endNight
7%215%46%29%1
624
August1st to 10thNight
4118%50%26%1
567
11th to 20thNight
7%313%53%23%1
564
21st to endNight
4114%48%30%2
627
September1st to 10thNight
9%224%41%22%2
570
11th to 20thNight
9%227%41%19%2
570
21st to endNight
8%5%28%40%18%1
570
October1st to 10thNight
11%5%30%33%19%2
598
11th to 20thNight
11%7%40%34%8%
760
21st to endNight
13%12%34%30%11%
836
November1st to 10thNight
11%6%38%34%11%
942
11th to 20thNight
10%13%39%29%9%
1000
21st to endNight
14%11%30%35%9%
1000
December1st to 10thNight
11%10%37%34%8%1
978
11th to 20thNight
15%11%38%32%4
950
21st to endNight
13%13%36%33%5%
1045
Page generated at 2024-12-03 05:45:13. Version ac07

Copyright © 2024 Attilla Danko.


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