John Bryan State Park Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the John Bryan State Park Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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
39%
25126
15%
106808
12%
24757
45%
24757
16%
71516

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
17%
935
8%
6127
5%
907
24%
907
5%
4833
January11th to 20thNight
16%
795
7%
5701
5%
760
23%
760
4%
4527
January21st to endNight
18%
871
12%
6216
8%
836
25%
836
5%
4533
February1st to 10thNight
21%
781
13%
2489
7%
781
28%
781
14%
1870
February11th to 20thNight
21%
740
14%
2219
7%
740
29%
740
15%
1608
February21st to endNight
17%
628
12%
1884
4%
628
24%
628
13%
1419
March1st to 10thNight
27%
758
17%
3618
9%
745
34%
745
12%
2418
March11th to 20thNight
28%
757
21%
3434
8%
740
36%
740
15%
1978
March21st to endNight
28%
832
10%
3693
8%
814
36%
814
14%
2313
April1st to 10thNight
30%
661
17%
1991
9%
661
38%
661
23%
1326
April11th to 20thNight
36%
563
20%
1782
13%
563
44%
563
24%
1153
April21st to endNight
29%
570
17%
1710
7%
570
39%
570
23%
1157
May1st to 10thNight
33%
565
13%
2778
7%
559
38%
559
11%
2013
May11th to 20thNight
44%
550
15%
2768
10%
541
50%
541
16%
1662
May21st to endNight
57%
604
13%
3040
13%
593
62%
593
22%
1565
June1st to 10thNight
56%
570
16%
1710
13%
570
60%
570
32%
1036
June11th to 20thNight
62%
570
19%
1544
14%
570
66%
570
37%
944
June21st to endNight
59%
570
18%
1520
13%
570
64%
570
37%
934
July1st to 10thNight
65%
546
21%
2333
16%
535
68%
535
23%
1366
July11th to 20thNight
68%
539
18%
2374
17%
533
71%
533
27%
1246
July21st to endNight
66%
607
15%
2815
17%
569
69%
569
20%
1666
August1st to 10thNight
69%
557
19%
2631
19%
544
71%
544
21%
1582
August11th to 20thNight
67%
548
19%
2508
19%
543
70%
543
21%
1535
August21st to endNight
69%
606
18%
2944
21%
605
72%
605
26%
1483
September1st to 10thNight
62%
689
24%
2019
20%
689
66%
689
35%
1200
September11th to 20thNight
70%
760
31%
2090
25%
760
72%
760
43%
1181
September21st to endNight
51%
760
26%
2090
20%
760
56%
760
32%
1329
October1st to 10thNight
53%
760
23%
2223
20%
740
59%
740
31%
1402
October11th to 20thNight
40%
760
17%
2624
16%
740
47%
740
22%
1672
October21st to endNight
33%
836
18%
2953
16%
814
41%
814
18%
2036
November1st to 10thNight
41%
780
24%
2536
20%
780
49%
780
28%
1513
November11th to 20thNight
30%
800
21%
2600
12%
800
41%
800
20%
1706
November21st to endNight
27%
800
16%
2600
11%
800
35%
800
15%
1907
December1st to 10thNight
19%
794
17%
4112
7%
780
26%
780
9%
2726
December11th to 20thNight
22%
796
9%
4726
7%
778
30%
778
7%
3535
December21st to endNight
18%
868
6%
6406
6%
839
25%
839
4%
5142

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
14%9%48%5%5%5%46%7%34%
109300
Night
15%10%48%5%4435%6%35%
108904
TransparencyDay
47%6%11%21%13%1
112971
Night
47%5%11%22%14%2
113359
SeeingDay
18%9%26%24%16%7%
15611
Night
18%8%27%30%15%2
25305

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
15%16%9%15%5%5%434420%
3682
11th to 20thDay
13%16%7%14%7%7%6%33321%
4060
21st to endDay
21%14%8%10%6%5%5%44418%
4466
February1st to 10thDay
19%13%6%11%6%44446%24%
1800
11th to 20thDay
15%13%5%12%7%5%5%335%26%
1848
21st to endDay
18%15%49%5%43446%28%
1570
March1st to 10thDay
21%16%6%10%5%43345%23%
3184
11th to 20thDay
14%9%38%445%35%8%38%
3480
21st to endDay
18%10%48%5%4435%7%32%
3815
April1st to 10thDay
14%12%49%44435%7%32%
2204
11th to 20thDay
15%10%38%5%44347%38%
2346
21st to endDay
17%8%38%5%5%5%46%6%33%
2470
May1st to 10thDay
21%10%38%5%4435%7%29%
4082
11th to 20thDay
20%9%36%44445%7%35%
4081
21st to endDay
11%6%37%5%5%5%5%8%10%34%
4476
June1st to 10thDay
12%7%27%5%5%5%5%6%10%37%
2470
11th to 20thDay
10%5%26%5%5%5%5%7%9%40%
2630
21st to endDay
10%5%26%5%5%6%5%7%10%38%
2660
July1st to 10thDay
11%7%38%5%6%5%5%7%9%35%
4440
11th to 20thDay
8%426%45%5%47%10%45%
4227
21st to endDay
10%6%37%5%6%6%5%7%9%35%
4466
August1st to 10thDay
8%5%26%5%46%5%8%10%41%
4104
11th to 20thDay
8%5%26%5%47%5%7%10%40%
4044
21st to endDay
6%425%445%46%9%49%
4317
September1st to 10thDay
12%5%25%44346%7%49%
2140
11th to 20thDay
9%5%26%44436%9%49%
2090
21st to endDay
16%7%25%43435%7%44%
2090
October1st to 10thDay
11%7%26%44445%7%47%
2085
11th to 20thDay
14%7%35%44435%7%45%
1900
21st to endDay
20%9%37%44435%7%35%
1972
November1st to 10thDay
10%7%36%44435%6%49%
1762
11th to 20thDay
15%12%49%5%4435%6%34%
1800
21st to endDay
18%12%5%9%6%5%3246%31%
1800
December1st to 10thDay
18%10%48%5%4435%6%33%
2930
11th to 20thDay
21%15%6%11%5%4434423%
3373
21st to endDay
23%20%6%10%5%44345%15%
4436
January1st to 10thNight
14%17%7%15%8%5%435%418%
6221
11th to 20thNight
12%16%8%14%7%7%5%445%18%
5900
21st to endNight
21%14%6%9%5%5%334426%
6490
February1st to 10thNight
21%13%49%5%45%445%28%
2489
11th to 20thNight
15%13%49%6%5%445%6%30%
2218
21st to endNight
20%15%5%10%444335%28%
1884
March1st to 10thNight
22%12%36%5%43346%33%
3655
11th to 20thNight
13%8%37%45%5%35%7%41%
3480
21st to endNight
19%9%37%443346%40%
3817
April1st to 10thNight
15%9%36%5%4436%7%38%
1991
11th to 20thNight
15%8%26%44445%8%39%
1782
21st to endNight
17%7%36%44446%6%38%
1710
May1st to 10thNight
24%10%38%5%4446%6%28%
2813
11th to 20thNight
19%7%25%44336%8%39%
2812
21st to endNight
9%426%445%5%7%9%44%
3079
June1st to 10thNight
8%5%25%5%45%45%8%48%
1710
11th to 20thNight
8%5%26%45%447%12%46%
1544
21st to endNight
6%5%25%5%45%5%7%11%46%
1520
July1st to 10thNight
11%6%25%4445%5%7%47%
2530
11th to 20thNight
7%42444446%9%52%
2732
21st to endNight
10%6%37%5%5%5%47%9%40%
3087
August1st to 10thNight
9%6%37%5%5%5%5%6%9%41%
2825
11th to 20thNight
8%8%36%44445%7%46%
2785
21st to endNight
4316%45%5%47%10%53%
3336
September1st to 10thNight
12%6%2443436%7%51%
2019
11th to 20thNight
8%5%1443335%6%57%
2090
21st to endNight
15%6%26%433346%48%
2090
October1st to 10thNight
8%5%37%43335%7%51%
2095
11th to 20thNight
16%7%26%5%34346%44%
2280
21st to endNight
18%9%36%43435%6%39%
2622
November1st to 10thNight
14%7%25%34435%7%47%
2536
11th to 20thNight
17%10%37%33435%6%37%
2600
21st to endNight
18%14%47%6%4435%7%27%
2600
December1st to 10thNight
17%11%48%5%4435%5%33%
4250
11th to 20thNight
19%16%7%10%5%44345%23%
4822
21st to endNight
24%19%7%10%5%43345%16%
6490

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
68%46%15%6%
3683
11th to 20thDay
69%5%7%10%9%1
4060
21st to endDay
68%5%10%9%6%1
4466
February1st to 10thDay
63%410%12%9%1
1800
11th to 20thDay
62%5%9%16%8%1
1858
21st to endDay
59%5%9%18%8%1
1570
March1st to 10thDay
64%49%17%5%1
3184
11th to 20thDay
44%7%10%26%13%1
3480
21st to endDay
50%7%13%21%9%
3815
April1st to 10thDay
50%6%12%20%12%1
2204
11th to 20thDay
47%5%12%21%13%3
2346
21st to endDay
49%5%12%20%11%2
2470
May1st to 10thDay
53%7%10%22%7%1
4120
11th to 20thDay
47%7%13%24%9%1
4085
21st to endDay
39%10%15%21%12%3
4489
June1st to 10thDay
41%7%11%24%14%2
2470
11th to 20thDay
37%7%15%23%16%1
2630
21st to endDay
38%8%15%21%15%3
2660
July1st to 10thDay
43%7%11%20%16%2
4371
11th to 20thDay
31%7%12%29%19%1
4154
21st to endDay
41%9%14%18%15%4
4324
August1st to 10thDay
33%10%16%28%12%1
4091
11th to 20thDay
34%7%13%30%15%1
4083
21st to endDay
30%7%13%29%18%3
4316
September1st to 10thDay
33%6%12%24%21%4
2140
11th to 20thDay
32%5%13%25%22%3
2090
21st to endDay
41%49%23%22%1
2090
October1st to 10thDay
25%410%31%28%1
3462
11th to 20thDay
31%410%29%24%2
3140
21st to endDay
38%411%24%21%2
3222
November1st to 10thDay
36%411%27%19%3
1762
11th to 20thDay
51%410%20%13%2
1800
21st to endDay
56%5%10%19%9%1
1800
December1st to 10thDay
53%412%24%7%
2930
11th to 20thDay
65%49%16%6%
3370
21st to endDay
72%5%8%10%4
4436
January1st to 10thNight
68%5%8%13%6%
6221
11th to 20thNight
68%5%8%11%7%1
5900
21st to endNight
62%410%16%7%2
6490
February1st to 10thNight
59%410%17%8%1
2489
11th to 20thNight
55%5%9%19%11%1
2219
21st to endNight
60%410%15%9%2
1884
March1st to 10thNight
52%5%8%23%11%1
3655
11th to 20thNight
40%7%11%27%12%2
3480
21st to endNight
46%5%9%27%11%1
3817
April1st to 10thNight
44%6%12%23%13%2
1991
11th to 20thNight
42%6%12%18%18%4
1782
21st to endNight
44%7%11%23%12%3
1710
May1st to 10thNight
55%7%9%20%7%2
2840
11th to 20thNight
42%7%13%27%9%1
2813
21st to endNight
31%9%15%28%14%4
3087
June1st to 10thNight
34%7%12%24%21%2
1710
11th to 20thNight
30%8%17%24%18%4
1544
21st to endNight
30%8%17%24%17%3
1520
July1st to 10thNight
36%6%11%24%17%5%
2490
11th to 20thNight
28%6%13%32%20%1
2682
21st to endNight
37%7%14%22%16%4
2988
August1st to 10thNight
37%7%16%26%13%1
2814
11th to 20thNight
36%7%10%27%20%
2812
21st to endNight
26%7%16%28%21%3
3336
September1st to 10thNight
32%6%12%25%19%6%
2019
11th to 20thNight
27%5%10%26%28%4
2090
21st to endNight
37%6%9%22%24%2
2090
October1st to 10thNight
23%48%29%34%2
3498
11th to 20thNight
30%410%26%28%3
3779
21st to endNight
34%47%25%25%5%
4309
November1st to 10thNight
38%412%23%21%3
2536
11th to 20thNight
47%48%23%16%3
2600
21st to endNight
57%410%19%9%1
2600
December1st to 10thNight
53%5%11%23%7%
4250
11th to 20thNight
63%5%10%16%6%
4824
21st to endNight
71%48%13%3
6490

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
24%16%36%19%41
300
11th to 20thDay
24%18%40%14%4
300
21st to endDay
29%15%35%16%5%
330
February1st to 10thDay
28%15%36%18%3
285
11th to 20thDay
24%23%36%13%4
270
21st to endDay
27%14%43%14%3
225
March1st to 10thDay
25%16%36%19%4
308
11th to 20thDay
23%15%34%19%7%1
460
21st to endDay
28%12%35%19%6%
506
April1st to 10thDay
18%13%36%21%9%2
460
11th to 20thDay
20%15%30%21%10%4
452
21st to endDay
22%11%37%19%10%2
460
May1st to 10thDay
27%12%27%22%8%4
463
11th to 20thDay
22%7%25%26%14%7%
487
21st to endDay
13%6%25%27%17%12%
529
June1st to 10thDay
14%5%20%30%22%9%
490
11th to 20thDay
12%423%30%23%8%
650
21st to endDay
12%6%27%28%19%9%
680
July1st to 10thDay
14%215%27%22%19%
671
11th to 20thDay
11%321%24%27%15%
548
21st to endDay
11%214%30%27%16%
532
August1st to 10thDay
12%213%25%29%20%
486
11th to 20thDay
13%315%30%26%13%
479
21st to endDay
9%212%29%31%18%
539
September1st to 10thDay
12%5%12%24%33%13%
490
11th to 20thDay
10%212%27%30%18%
490
21st to endDay
21%8%16%24%24%8%
490
October1st to 10thDay
11%6%22%31%21%9%
490
11th to 20thDay
17%11%31%23%14%4
490
21st to endDay
23%9%34%26%6%1
421
November1st to 10thDay
16%10%35%25%9%5%
300
11th to 20thDay
20%15%33%19%11%2
300
21st to endDay
26%12%37%21%4
300
December1st to 10thDay
21%18%35%18%8%
300
11th to 20thDay
25%13%40%17%4
300
21st to endDay
34%14%32%16%4
330
January1st to 10thNight
23%16%35%22%5%1
951
11th to 20thNight
25%15%35%22%4
800
21st to endNight
24%12%35%25%4
880
February1st to 10thNight
27%9%36%26%2
781
11th to 20thNight
24%14%36%24%2
743
21st to endNight
26%11%39%21%3
628
March1st to 10thNight
21%11%35%27%6%1
760
11th to 20thNight
22%12%34%25%7%1
760
21st to endNight
25%10%31%26%8%
836
April1st to 10thNight
19%11%35%29%6%
661
11th to 20thNight
18%10%32%27%11%1
563
21st to endNight
18%7%40%25%8%2
570
May1st to 10thNight
22%6%32%27%12%1
570
11th to 20thNight
20%5%25%33%16%2
561
21st to endNight
9%222%38%24%4
617
June1st to 10thNight
10%222%43%22%1
570
11th to 20thNight
9%418%43%24%2
570
21st to endNight
8%322%39%27%2
570
July1st to 10thNight
12%111%35%33%8%
555
11th to 20thNight
8%114%40%32%5%
552
21st to endNight
10%111%40%35%3
624
August1st to 10thNight
7%210%40%36%4
567
11th to 20thNight
9%212%40%32%5%
564
21st to endNight
7%211%36%37%7%
627
September1st to 10thNight
15%313%33%31%5%
689
11th to 20thNight
11%112%36%36%5%
760
21st to endNight
16%5%19%36%21%3
760
October1st to 10thNight
12%424%34%21%4
760
11th to 20thNight
20%7%28%31%13%1
760
21st to endNight
22%9%32%28%10%
836
November1st to 10thNight
18%8%30%28%16%1
780
11th to 20thNight
21%13%32%25%9%1
800
21st to endNight
25%11%30%27%7%
800
December1st to 10thNight
26%12%35%23%5%
800
11th to 20thNight
25%11%35%25%5%1
800
21st to endNight
29%14%30%23%4
880
Page generated at 2025-02-03 03:05:49. Version ac07

Copyright © 2025 Attilla Danko.


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