Black Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Lake Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
27%
22793
14%
80707
8%
22710
36%
22710
15%
56891

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
14%
754
8%
4410
3%
737
21%
737
5%
3225
January11th to 20thNight
16%
758
8%
4411
4%
740
24%
740
5%
3397
January21st to endNight
20%
828
7%
4678
6%
814
29%
814
6%
3707
February1st to 10thNight
14%
760
11%
2470
3%
760
23%
760
10%
1881
February11th to 20thNight
16%
740
15%
2405
4%
740
29%
740
12%
1758
February21st to endNight
20%
611
15%
1838
5%
611
31%
611
13%
1365
March1st to 10thNight
20%
720
15%
2129
8%
720
29%
720
15%
1558
March11th to 20thNight
21%
720
17%
1979
6%
720
32%
720
17%
1414
March21st to endNight
25%
792
21%
2082
7%
792
34%
792
20%
1476
April1st to 10thNight
20%
720
17%
1800
4%
720
27%
720
20%
1301
April11th to 20thNight
23%
711
18%
1775
6%
711
29%
711
19%
1264
April21st to endNight
28%
640
16%
1720
7%
640
34%
640
19%
1263
May1st to 10thNight
33%
360
17%
1440
13%
360
42%
360
17%
932
May11th to 20thNight
31%
354
22%
1416
16%
354
48%
354
19%
850
May21st to endNight
34%
388
15%
1551
11%
388
47%
388
24%
875
June1st to 10thNight
35%
360
11%
1440
10%
360
46%
360
17%
935
June11th to 20thNight
38%
360
14%
1440
15%
360
48%
360
21%
850
June21st to endNight
43%
360
12%
1440
14%
360
49%
360
18%
910
July1st to 10thNight
47%
350
15%
1400
18%
350
55%
350
26%
763
July11th to 20thNight
49%
348
17%
1392
22%
348
57%
348
26%
793
July21st to endNight
50%
394
16%
1486
15%
372
56%
372
26%
828
August1st to 10thNight
48%
444
17%
1508
13%
442
55%
442
28%
892
August11th to 20thNight
53%
534
19%
1598
12%
534
58%
534
31%
977
August21st to endNight
43%
789
19%
1977
8%
789
48%
789
33%
1286
September1st to 10thNight
42%
720
18%
1800
7%
720
47%
720
34%
1194
September11th to 20thNight
49%
720
24%
1800
13%
720
54%
720
37%
1134
September21st to endNight
40%
720
23%
2045
15%
720
46%
720
28%
1320
October1st to 10thNight
33%
720
17%
2160
11%
720
41%
720
20%
1489
October11th to 20thNight
24%
720
14%
2160
8%
720
32%
720
17%
1550
October21st to endNight
23%
792
14%
2486
6%
792
33%
792
14%
1813
November1st to 10thNight
24%
740
18%
2407
10%
740
36%
740
18%
1615
November11th to 20thNight
20%
760
18%
2655
9%
760
34%
760
14%
1824
November21st to endNight
19%
760
11%
2660
6%
760
27%
760
10%
2000
December1st to 10thNight
13%
760
8%
2660
3%
760
21%
760
8%
2124
December11th to 20thNight
16%
760
11%
3244
5%
759
24%
759
8%
2406
December21st to endNight
13%
826
6%
4845
2%
817
20%
817
4%
3922

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
17%10%47%6%45%5%5%6%32%
78274
Night
17%11%48%6%3445%6%32%
81015
TransparencyDay
53%311%21%11%1
77979
Night
55%311%20%10%1
80844
SeeingDay
25%13%30%20%9%3
13498
Night
24%12%30%24%9%1
22823

By Month

Percentage Cloud Cover NE (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%6%9%7%45%44425%
2517
11th to 20thDay
14%15%7%12%8%45%445%22%
2520
21st to endDay
18%18%6%12%8%5%433417%
2971
February1st to 10thDay
16%14%411%8%35%5%5%6%23%
1710
11th to 20thDay
12%15%6%10%7%45%445%29%
1663
21st to endDay
20%13%6%9%7%345%4424%
1512
March1st to 10thDay
16%11%5%10%8%5%434429%
1825
11th to 20thDay
16%12%5%7%7%45%445%30%
1980
21st to endDay
19%12%46%42333438%
2272
April1st to 10thDay
21%12%46%5%34345%33%
2160
11th to 20thDay
21%9%36%434445%38%
2134
21st to endDay
22%10%37%5%345%5%5%32%
2256
May1st to 10thDay
19%7%46%5%44446%35%
2520
11th to 20thDay
16%6%46%5%35%45%7%39%
2478
21st to endDay
12%7%36%5%45%6%6%8%38%
2725
June1st to 10thDay
21%8%35%5%45%5%6%6%31%
2520
11th to 20thDay
16%5%26%5%35%6%6%9%38%
2520
21st to endDay
16%7%36%7%46%5%5%8%34%
2520
July1st to 10thDay
11%5%36%5%45%5%6%9%41%
2520
11th to 20thDay
12%6%35%5%45%6%6%10%38%
2520
21st to endDay
11%6%26%6%36%7%7%9%37%
2744
August1st to 10thDay
12%7%35%6%45%5%6%7%40%
2417
11th to 20thDay
12%6%26%5%26%5%7%10%38%
2286
21st to endDay
13%6%26%5%45%5%6%9%40%
2376
September1st to 10thDay
15%5%25%5%36%5%6%8%41%
2160
11th to 20thDay
13%5%25%43445%7%47%
2160
21st to endDay
18%5%35%5%44447%40%
1911
October1st to 10thDay
22%7%37%5%3345%6%36%
1800
11th to 20thDay
21%9%47%5%45%5%6%6%28%
1800
21st to endDay
27%9%47%6%345%46%26%
1868
November1st to 10thDay
15%8%46%5%5%5%5%5%7%34%
1671
11th to 20thDay
18%12%49%6%3445%5%30%
1520
21st to endDay
20%14%5%8%7%46%5%45%22%
1520
December1st to 10thDay
22%16%6%10%6%45%45%5%18%
1520
11th to 20thDay
21%13%6%9%6%35%35%5%25%
1906
21st to endDay
27%16%5%11%6%3332320%
2772
January1st to 10thNight
18%14%7%11%8%4445%5%21%
4429
11th to 20thNight
14%15%5%12%10%46%5%5%5%20%
4440
21st to endNight
19%17%7%11%7%5%443420%
4683
February1st to 10thNight
15%15%6%8%8%45%46%6%23%
2470
11th to 20thNight
13%15%6%8%7%45%446%29%
2403
21st to endNight
15%13%5%7%6%45%45%6%29%
1838
March1st to 10thNight
16%12%49%7%45%45%5%31%
2119
11th to 20thNight
17%13%47%5%33447%33%
1979
21st to endNight
17%9%47%5%33345%40%
2082
April1st to 10thNight
21%8%47%5%24445%36%
1800
11th to 20thNight
20%8%36%5%34445%37%
1775
21st to endNight
20%10%46%5%345%47%31%
1720
May1st to 10thNight
22%7%25%5%35%447%36%
1440
11th to 20thNight
15%7%36%5%3445%7%42%
1415
21st to endNight
12%5%35%4345%5%9%45%
1550
June1st to 10thNight
17%6%46%5%45%5%6%8%34%
1440
11th to 20thNight
13%7%35%435%5%5%8%41%
1440
21st to endNight
16%5%27%6%35%6%6%9%35%
1440
July1st to 10thNight
9%436%5%35%5%6%8%46%
1440
11th to 20thNight
11%5%25%435%5%6%8%43%
1440
21st to endNight
10%5%245%35%5%7%8%47%
1574
August1st to 10thNight
9%6%36%5%345%6%8%44%
1518
11th to 20thNight
9%6%26%6%35%5%7%8%43%
1598
21st to endNight
10%6%35%5%35%47%8%45%
1977
September1st to 10thNight
12%6%25%6%2446%7%45%
1800
11th to 20thNight
13%4144245%5%7%50%
1800
21st to endNight
16%6%26%43445%7%43%
2045
October1st to 10thNight
18%7%46%6%45%45%7%36%
2160
11th to 20thNight
21%9%36%7%35%46%6%31%
2160
21st to endNight
23%10%46%6%345%5%6%29%
2486
November1st to 10thNight
18%10%36%43445%6%36%
2407
11th to 20thNight
18%10%47%6%345%5%6%33%
2655
21st to endNight
21%12%48%6%45%45%6%25%
2660
December1st to 10thNight
20%17%6%10%7%44445%20%
2660
11th to 20thNight
21%14%5%8%6%34335%27%
3288
21st to endNight
30%15%410%6%3444417%
4884

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
63%215%13%6%2
2518
11th to 20thDay
68%110%12%8%
2520
21st to endDay
73%39%9%5%1
2971
February1st to 10thDay
63%38%20%5%1
1710
11th to 20thDay
59%210%18%10%1
1672
21st to endDay
66%28%12%10%1
1512
March1st to 10thDay
61%29%17%10%2
1828
11th to 20thDay
57%310%15%13%3
1980
21st to endDay
51%37%19%14%6%
2272
April1st to 10thDay
54%36%20%14%3
2160
11th to 20thDay
49%36%23%17%2
2134
21st to endDay
54%38%17%14%4
2256
May1st to 10thDay
51%39%18%17%3
2520
11th to 20thDay
46%38%25%16%2
2482
21st to endDay
44%415%22%13%3
2725
June1st to 10thDay
53%49%20%13%1
2520
11th to 20thDay
44%310%27%14%2
2520
21st to endDay
49%413%21%12%1
2520
July1st to 10thDay
38%411%30%15%1
2450
11th to 20thDay
40%415%30%10%
2445
21st to endDay
42%5%15%26%11%1
2591
August1st to 10thDay
42%315%27%11%1
2403
11th to 20thDay
41%415%27%12%1
2286
21st to endDay
41%313%28%14%1
2376
September1st to 10thDay
41%414%28%13%1
2160
11th to 20thDay
37%412%30%16%
2160
21st to endDay
45%412%28%11%
1911
October1st to 10thDay
51%211%24%12%1
1800
11th to 20thDay
56%314%19%8%1
1800
21st to endDay
61%310%19%8%1
1868
November1st to 10thDay
50%314%23%9%
1671
11th to 20thDay
56%312%17%10%2
1520
21st to endDay
64%412%12%8%
1520
December1st to 10thDay
69%312%11%41
1520
11th to 20thDay
65%414%13%5%
1906
21st to endDay
73%27%14%4
2772
January1st to 10thNight
66%215%12%4
4429
11th to 20thNight
69%211%12%5%
4440
21st to endNight
71%210%11%6%1
4683
February1st to 10thNight
63%310%17%7%1
2470
11th to 20thNight
58%39%20%9%
2405
21st to endNight
58%39%18%12%1
1838
March1st to 10thNight
57%310%17%12%1
2129
11th to 20thNight
54%211%20%12%2
1980
21st to endNight
50%36%20%17%4
2082
April1st to 10thNight
52%27%21%15%2
1800
11th to 20thNight
50%37%20%18%2
1775
21st to endNight
54%38%16%16%3
1720
May1st to 10thNight
50%37%19%17%5%
1440
11th to 20thNight
43%47%25%18%3
1416
21st to endNight
38%317%20%18%3
1551
June1st to 10thNight
47%5%12%23%12%1
1440
11th to 20thNight
42%412%22%19%2
1440
21st to endNight
45%6%13%22%13%1
1440
July1st to 10thNight
35%5%11%27%19%3
1400
11th to 20thNight
38%413%31%14%
1392
21st to endNight
36%5%16%30%14%1
1486
August1st to 10thNight
38%416%28%13%1
1508
11th to 20thNight
38%416%29%13%1
1598
21st to endNight
37%5%14%30%13%1
1977
September1st to 10thNight
38%412%30%14%1
1800
11th to 20thNight
34%414%33%13%2
1800
21st to endNight
42%211%32%11%1
2045
October1st to 10thNight
49%49%23%14%1
2160
11th to 20thNight
54%313%20%9%1
2160
21st to endNight
57%313%17%10%
2486
November1st to 10thNight
50%314%22%11%1
2407
11th to 20thNight
53%311%20%12%2
2655
21st to endNight
62%312%17%6%
2660
December1st to 10thNight
69%39%15%4
2660
11th to 20thNight
62%310%16%8%1
3288
21st to endNight
73%29%13%3
4884

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
29%17%36%13%41
180
11th to 20thDay
36%13%32%16%21
180
21st to endDay
24%18%34%18%5%
256
February1st to 10thDay
35%20%33%11%1
270
11th to 20thDay
30%24%39%7%1
270
21st to endDay
37%16%33%12%3
354
March1st to 10thDay
26%19%33%17%5%
420
11th to 20thDay
32%15%34%14%5%
420
21st to endDay
33%19%27%12%8%1
462
April1st to 10thDay
31%19%28%15%7%
420
11th to 20thDay
33%17%23%16%9%3
412
21st to endDay
30%16%34%13%5%2
420
May1st to 10thDay
26%15%31%19%7%2
423
11th to 20thDay
20%14%36%20%8%2
447
21st to endDay
19%13%33%22%11%2
485
June1st to 10thDay
25%10%32%23%8%2
450
11th to 20thDay
20%13%29%24%12%3
450
21st to endDay
21%10%29%24%12%4
450
July1st to 10thDay
15%5%28%32%15%4
445
11th to 20thDay
17%7%30%27%14%4
444
21st to endDay
14%8%33%29%12%4
488
August1st to 10thDay
16%5%28%32%14%4
446
11th to 20thDay
12%5%29%31%16%7%
439
21st to endDay
17%9%30%25%12%7%
495
September1st to 10thDay
16%10%31%24%12%8%
450
11th to 20thDay
14%9%26%25%17%10%
450
21st to endDay
21%9%29%23%14%4
450
October1st to 10thDay
27%14%26%17%12%4
450
11th to 20thDay
31%16%29%17%5%2
450
21st to endDay
32%18%27%19%4
439
November1st to 10thDay
25%17%28%21%8%
365
11th to 20thDay
31%14%34%13%6%2
180
21st to endDay
29%21%34%13%3
180
December1st to 10thDay
32%17%34%13%4
180
11th to 20thDay
36%21%31%9%41
180
21st to endDay
38%14%32%12%31
198
January1st to 10thNight
30%17%30%20%3
760
11th to 20thNight
31%15%30%20%41
760
21st to endNight
22%14%33%25%6%
836
February1st to 10thNight
24%19%34%20%2
760
11th to 20thNight
23%18%38%18%3
743
21st to endNight
25%17%35%19%4
611
March1st to 10thNight
26%15%31%24%4
720
11th to 20thNight
27%18%28%22%5%
720
21st to endNight
25%14%31%22%8%
792
April1st to 10thNight
29%13%32%22%4
720
11th to 20thNight
27%17%28%19%8%1
711
21st to endNight
27%12%28%25%8%1
640
May1st to 10thNight
25%8%26%28%11%2
360
11th to 20thNight
15%11%34%31%9%1
354
21st to endNight
12%11%38%26%13%1
389
June1st to 10thNight
16%7%31%35%10%1
360
11th to 20thNight
17%9%28%31%14%1
360
21st to endNight
18%425%38%15%1
360
July1st to 10thNight
11%430%37%17%1
350
11th to 20thNight
14%328%37%17%1
348
21st to endNight
10%429%42%14%1
394
August1st to 10thNight
13%424%36%22%1
444
11th to 20thNight
14%321%36%24%3
534
21st to endNight
13%6%29%32%18%2
789
September1st to 10thNight
15%6%30%30%17%1
720
11th to 20thNight
17%6%21%30%20%5%
720
21st to endNight
20%9%26%24%20%3
720
October1st to 10thNight
23%11%27%22%14%3
720
11th to 20thNight
27%11%31%23%7%1
720
21st to endNight
30%12%27%25%5%
792
November1st to 10thNight
28%12%29%21%8%1
740
11th to 20thNight
27%17%30%17%9%1
760
21st to endNight
32%15%27%20%6%
760
December1st to 10thNight
30%16%32%18%4
760
11th to 20thNight
28%18%32%18%31
760
21st to endNight
35%15%29%19%2
836
Page generated at 2024-02-22 06:05:46. Version ac07

Copyright 2024 Attilla Danko


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