Mossy Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mossy Creek Observatory clear sky chart from 2005-11-06 to 2024-11-11.

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
48%
24787
19%
96502
16%
24541
54%
24541
20%
61119

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
32%
753
18%
4028
12%
737
42%
737
11%
2716
January11th to 20thNight
27%
758
24%
3941
11%
740
35%
740
10%
2493
January21st to endNight
28%
826
14%
4470
13%
814
39%
814
11%
3049
February1st to 10thNight
34%
760
21%
2333
13%
760
43%
760
21%
1597
February11th to 20thNight
24%
743
17%
2219
9%
740
32%
740
18%
1582
February21st to endNight
26%
628
20%
1884
10%
628
34%
628
19%
1340
March1st to 10thNight
35%
758
19%
3568
14%
745
43%
745
14%
2448
March11th to 20thNight
33%
755
26%
3412
11%
740
39%
740
19%
1698
March21st to endNight
38%
829
14%
3679
11%
814
43%
814
17%
2177
April1st to 10thNight
41%
755
22%
2085
12%
755
49%
755
31%
1304
April11th to 20thNight
44%
563
24%
1824
17%
563
52%
563
26%
1126
April21st to endNight
52%
570
24%
1710
18%
570
57%
570
28%
1084
May1st to 10thNight
49%
564
16%
2787
10%
559
54%
559
15%
1846
May11th to 20thNight
52%
544
15%
2774
11%
541
55%
541
15%
1735
May21st to endNight
62%
601
16%
3033
13%
593
64%
593
18%
1675
June1st to 10thNight
61%
570
16%
1710
13%
570
63%
570
27%
1102
June11th to 20thNight
71%
570
15%
1710
12%
570
73%
570
33%
1021
June21st to endNight
65%
570
17%
1710
14%
570
67%
570
28%
1088
July1st to 10thNight
65%
539
11%
2735
11%
535
66%
535
14%
1711
July11th to 20thNight
72%
535
14%
2587
13%
533
74%
533
21%
1462
July21st to endNight
64%
614
10%
2965
15%
569
67%
569
13%
2196
August1st to 10thNight
67%
551
18%
2638
15%
544
68%
544
18%
1586
August11th to 20thNight
64%
549
16%
2524
17%
543
65%
543
18%
1476
August21st to endNight
69%
607
18%
2951
19%
605
70%
605
22%
1497
September1st to 10thNight
63%
750
22%
2080
20%
750
64%
750
30%
1345
September11th to 20thNight
59%
760
20%
2090
18%
760
60%
760
28%
1390
September21st to endNight
58%
760
26%
2090
22%
760
63%
760
32%
1341
October1st to 10thNight
59%
760
22%
2574
27%
740
61%
740
25%
1764
October11th to 20thNight
55%
760
25%
2340
25%
740
60%
740
30%
1449
October21st to endNight
53%
836
27%
2697
27%
814
60%
814
28%
1671
November1st to 10thNight
56%
780
27%
2518
27%
780
61%
780
30%
1479
November11th to 20thNight
47%
763
27%
2477
23%
763
55%
763
28%
1478
November21st to endNight
47%
760
26%
2470
21%
760
56%
760
28%
1496
December1st to 10thNight
35%
760
18%
2470
14%
760
41%
760
17%
1726
December11th to 20thNight
39%
759
22%
2974
17%
759
47%
759
17%
1964
December21st to endNight
33%
827
12%
4445
12%
817
41%
817
10%
3007

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
13%8%37%5%5%5%46%8%38%
101124
Night
14%8%37%5%4446%8%38%
98002
TransparencyDay
43%411%23%16%3
104905
Night
44%310%23%17%4
102360
SeeingDay
17%8%19%24%21%11%
14928
Night
17%6%19%34%21%3
24963

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
16%9%49%5%5%5%5%6%7%30%
2836
11th to 20thDay
18%9%411%7%6%4445%29%
2840
21st to endDay
19%15%37%443345%31%
3124
February1st to 10thDay
19%11%47%5%4435%5%34%
1843
11th to 20thDay
21%9%49%44335%5%33%
1848
21st to endDay
21%9%37%5%43446%34%
1570
March1st to 10thDay
22%9%37%5%4445%5%33%
3269
11th to 20thDay
13%7%26%43435%6%47%
3480
21st to endDay
15%10%37%5%5%4345%39%
3815
April1st to 10thDay
12%6%27%45%5%5%6%7%42%
2109
11th to 20thDay
14%8%26%444447%43%
2304
21st to endDay
12%7%27%5%5%436%7%41%
2470
May1st to 10thDay
14%8%38%5%5%5%5%6%8%32%
4082
11th to 20thDay
14%8%39%6%5%5%47%6%32%
4081
21st to endDay
9%6%27%45%5%5%7%10%39%
4476
June1st to 10thDay
9%6%37%7%6%6%5%7%9%37%
2470
11th to 20thDay
45%27%6%7%6%6%8%9%40%
2470
21st to endDay
7%6%26%5%6%7%5%9%10%37%
2470
July1st to 10thDay
6%5%26%6%6%6%6%9%13%36%
4120
11th to 20thDay
10%5%37%6%6%5%47%9%39%
4120
21st to endDay
16%11%410%7%7%7%5%7%7%18%
4466
August1st to 10thDay
8%6%28%6%6%6%6%8%10%34%
4104
11th to 20thDay
8%5%27%5%6%6%5%8%12%37%
4044
21st to endDay
5%425%446%47%9%49%
4166
September1st to 10thDay
10%6%27%6%5%5%45%8%43%
2090
11th to 20thDay
12%5%27%45%5%36%7%42%
2090
21st to endDay
14%6%26%43436%7%45%
2090
October1st to 10thDay
10%6%25%33345%6%53%
2090
11th to 20thDay
12%5%25%334346%52%
1914
21st to endDay
14%6%35%333346%49%
2090
November1st to 10thDay
11%6%25%33335%6%53%
1776
11th to 20thDay
12%7%25%44335%7%48%
1710
21st to endDay
14%8%36%43435%6%44%
1710
December1st to 10thDay
19%11%47%445%45%5%34%
1710
11th to 20thDay
14%12%37%435%5%6%6%34%
2153
21st to endDay
16%13%38%5%5%5%35%7%30%
3124
January1st to 10thNight
17%12%410%5%44446%30%
4109
11th to 20thNight
20%10%36%5%5%4346%36%
4120
21st to endNight
19%13%47%5%4435%6%30%
4532
February1st to 10thNight
17%9%37%445%45%6%35%
2333
11th to 20thNight
22%10%37%44435%434%
2218
21st to endNight
21%10%37%44445%6%32%
1884
March1st to 10thNight
21%9%38%6%5%435%7%30%
3583
11th to 20thNight
12%6%35%43435%7%48%
3480
21st to endNight
14%8%26%5%45%46%6%40%
3817
April1st to 10thNight
12%6%35%45%45%6%8%43%
2085
11th to 20thNight
14%7%36%43445%7%43%
1824
21st to endNight
13%6%26%5%5%446%6%43%
1710
May1st to 10thNight
14%9%49%6%5%5%46%9%31%
2813
11th to 20thNight
18%8%37%44446%8%34%
2812
21st to endNight
7%6%37%5%5%6%48%10%39%
3079
June1st to 10thNight
8%6%37%6%5%6%5%8%12%35%
1710
11th to 20thNight
45%25%5%5%5%5%8%13%42%
1710
21st to endNight
6%6%27%6%6%7%5%6%10%39%
1710
July1st to 10thNight
9%5%37%6%7%7%6%8%11%31%
2840
11th to 20thNight
8%6%26%45%5%5%8%10%42%
2840
21st to endNight
13%10%410%7%6%6%5%8%10%21%
3087
August1st to 10thNight
7%6%28%6%5%6%5%7%10%38%
2825
11th to 20thNight
8%7%26%45%5%47%9%42%
2785
21st to endNight
6%425%35%5%5%6%11%49%
3463
September1st to 10thNight
11%7%27%5%45%45%6%44%
2080
11th to 20thNight
11%7%38%6%4436%8%39%
2090
21st to endNight
12%6%26%5%4445%6%46%
2090
October1st to 10thNight
12%5%26%433246%51%
2090
11th to 20thNight
14%6%2434325%6%51%
2266
21st to endNight
13%6%26%33325%5%50%
2508
November1st to 10thNight
14%6%26%434346%49%
2518
11th to 20thNight
14%8%25%34435%6%46%
2477
21st to endNight
14%7%36%44335%7%45%
2470
December1st to 10thNight
19%11%39%6%43346%32%
2470
11th to 20thNight
16%10%39%45%4346%37%
3042
21st to endNight
16%13%39%5%5%6%47%8%25%
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
54%25%21%16%2
2837
11th to 20thDay
58%26%16%17%1
2840
21st to endDay
57%27%20%14%
3124
February1st to 10thDay
53%37%19%17%2
1843
11th to 20thDay
54%38%18%15%2
1858
21st to endDay
52%27%15%17%5%
1570
March1st to 10thDay
54%25%19%15%5%
3269
11th to 20thDay
40%27%24%23%5%
3480
21st to endDay
49%26%28%13%2
3815
April1st to 10thDay
40%410%24%19%3
2109
11th to 20thDay
42%37%20%23%6%
2304
21st to endDay
42%39%28%15%3
2470
May1st to 10thDay
50%312%23%11%2
4120
11th to 20thDay
51%310%24%10%1
4085
21st to endDay
40%413%23%17%3
4489
June1st to 10thDay
43%5%14%23%13%2
2470
11th to 20thDay
37%6%18%22%15%2
2470
21st to endDay
38%7%15%22%15%3
2470
July1st to 10thDay
36%7%23%21%11%1
4055
11th to 20thDay
40%5%19%26%8%3
4051
21st to endDay
63%6%12%14%6%1
4324
August1st to 10thDay
42%5%17%25%10%1
4091
11th to 20thDay
38%5%18%25%13%2
4083
21st to endDay
29%415%36%12%2
4166
September1st to 10thDay
39%5%11%21%17%6%
2090
11th to 20thDay
41%5%9%24%19%3
2090
21st to endDay
39%410%23%19%6%
2090
October1st to 10thDay
28%36%22%31%11%
3480
11th to 20thDay
25%26%26%29%12%
3154
21st to endDay
29%16%31%23%10%
3428
November1st to 10thDay
33%37%23%28%5%
1776
11th to 20thDay
38%26%24%25%5%
1710
21st to endDay
41%37%25%21%3
1710
December1st to 10thDay
52%48%22%11%2
1710
11th to 20thDay
48%39%20%17%2
2150
21st to endDay
55%27%26%10%1
3124
January1st to 10thNight
57%15%20%15%2
4109
11th to 20thNight
52%25%17%22%3
4120
21st to endNight
57%26%19%15%1
4532
February1st to 10thNight
49%48%21%17%2
2333
11th to 20thNight
54%37%19%14%4
2219
21st to endNight
54%37%17%15%4
1884
March1st to 10thNight
56%17%18%15%3
3583
11th to 20thNight
36%28%25%19%10%
3480
21st to endNight
44%27%28%16%3
3817
April1st to 10thNight
38%312%24%19%4
2085
11th to 20thNight
41%37%20%22%6%
1824
21st to endNight
41%410%28%15%2
1710
May1st to 10thNight
51%313%22%10%1
2840
11th to 20thNight
49%313%24%11%1
2813
21st to endNight
39%5%12%26%16%2
3087
June1st to 10thNight
40%7%16%21%14%1
1710
11th to 20thNight
31%9%20%23%15%2
1710
21st to endNight
39%6%14%22%14%5%
1710
July1st to 10thNight
44%8%20%18%9%1
2795
11th to 20thNight
35%6%22%26%8%3
2786
21st to endNight
56%7%14%16%5%
2988
August1st to 10thNight
40%6%18%27%9%1
2814
11th to 20thNight
37%5%17%28%12%1
2812
21st to endNight
29%5%15%38%12%2
3463
September1st to 10thNight
41%412%20%17%6%
2080
11th to 20thNight
43%411%20%20%2
2090
21st to endNight
40%48%22%21%5%
2090
October1st to 10thNight
34%36%20%28%9%
3480
11th to 20thNight
24%25%25%29%15%
3765
21st to endNight
27%2430%28%10%
4120
November1st to 10thNight
38%36%22%24%7%
2518
11th to 20thNight
39%35%23%24%6%
2477
21st to endNight
40%36%28%20%3
2470
December1st to 10thNight
54%38%21%12%2
2470
11th to 20thNight
50%26%21%18%2
3044
21st to endNight
57%28%19%13%1
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
23%18%31%22%41
270
11th to 20thDay
27%20%29%16%7%1
270
21st to endDay
23%17%35%19%6%
297
February1st to 10thDay
24%16%29%22%8%
270
11th to 20thDay
35%18%29%14%4
270
21st to endDay
36%21%27%14%3
225
March1st to 10thDay
25%14%28%21%10%1
354
11th to 20thDay
24%15%30%25%5%1
460
21st to endDay
24%13%26%26%10%
506
April1st to 10thDay
20%13%24%26%16%1
460
11th to 20thDay
18%13%23%25%17%3
452
21st to endDay
19%9%24%27%15%6%
460
May1st to 10thDay
16%11%29%22%16%6%
463
11th to 20thDay
16%6%20%22%25%11%
487
21st to endDay
14%6%14%26%20%20%
529
June1st to 10thDay
12%315%27%27%16%
490
11th to 20thDay
6%416%28%28%19%
490
21st to endDay
10%317%25%28%17%
490
July1st to 10thDay
13%211%19%30%26%
485
11th to 20thDay
12%37%25%29%24%
484
21st to endDay
14%27%27%30%20%
532
August1st to 10thDay
16%410%22%27%21%
486
11th to 20thDay
13%210%27%30%18%
479
21st to endDay
14%2418%31%31%
539
September1st to 10thDay
11%49%22%33%21%
490
11th to 20thDay
15%49%19%32%21%
490
21st to endDay
18%412%27%29%10%
490
October1st to 10thDay
15%315%29%25%13%
490
11th to 20thDay
13%8%21%27%25%5%
490
21st to endDay
20%5%18%29%24%4
539
November1st to 10thDay
17%7%24%28%19%5%
314
11th to 20thDay
14%14%29%27%16%1
270
21st to endDay
16%9%25%31%17%2
270
December1st to 10thDay
24%16%26%23%10%
270
11th to 20thDay
25%9%26%29%10%1
270
21st to endDay
25%11%27%27%9%1
297
January1st to 10thNight
22%14%23%35%5%
760
11th to 20thNight
27%10%28%29%5%
760
21st to endNight
21%10%32%34%3
836
February1st to 10thNight
22%9%28%37%4
760
11th to 20thNight
28%12%32%26%2
743
21st to endNight
25%11%33%28%3
628
March1st to 10thNight
23%9%26%37%6%
760
11th to 20thNight
19%8%33%30%8%1
760
21st to endNight
20%8%26%36%10%
836
April1st to 10thNight
17%8%29%33%12%1
755
11th to 20thNight
16%8%26%35%15%
563
21st to endNight
16%420%45%14%1
570
May1st to 10thNight
16%6%19%38%20%2
570
11th to 20thNight
16%415%35%26%4
561
21st to endNight
8%312%31%40%6%
617
June1st to 10thNight
10%111%36%36%5%
570
11th to 20thNight
5%212%36%37%9%
570
21st to endNight
10%210%33%36%8%
570
July1st to 10thNight
13%26%28%41%10%
555
11th to 20thNight
10%2425%47%13%
552
21st to endNight
10%35%28%42%12%
624
August1st to 10thNight
11%25%25%48%9%
567
11th to 20thNight
12%2431%44%6%
564
21st to endNight
11%2424%47%11%
627
September1st to 10thNight
13%38%29%38%8%
750
11th to 20thNight
16%38%30%36%7%
760
21st to endNight
15%312%36%32%3
760
October1st to 10thNight
14%414%33%29%6%
760
11th to 20thNight
16%5%18%39%20%2
760
21st to endNight
17%5%18%39%19%2
836
November1st to 10thNight
17%5%16%41%19%2
780
11th to 20thNight
18%7%21%42%11%1
763
21st to endNight
17%7%22%41%13%1
760
December1st to 10thNight
25%6%23%37%8%
760
11th to 20thNight
24%8%23%37%9%
760
21st to endNight
24%9%22%38%6%
836
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