Marble Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marble Lake Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
29%
14726
15%
46942
8%
14697
37%
14697
18%
32199

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 15thNight
14%
720
9%
2506
3%
716
22%
716
7%
1955
January16th to endNight
19%
768
14%
2583
6%
768
29%
768
12%
1906
February1st to 15thNight
15%
702
12%
2287
4%
701
26%
701
13%
1670
February16th to endNight
19%
631
16%
1982
6%
631
33%
631
15%
1413
March1st to 15thNight
17%
720
15%
2049
6%
720
27%
720
17%
1477
March16th to endNight
29%
768
22%
2070
10%
768
39%
768
25%
1364
April1st to 15thNight
22%
718
17%
1796
5%
718
29%
718
22%
1283
April16th to endNight
31%
636
19%
1716
8%
636
39%
636
24%
1162
May1st to 15thNight
37%
379
19%
1459
16%
379
49%
379
20%
905
May16th to endNight
36%
374
15%
1497
10%
374
50%
374
22%
889
June1st to 15thNight
33%
360
10%
1440
7%
360
44%
360
17%
912
June16th to endNight
44%
360
11%
1440
13%
360
51%
360
20%
882
July1st to 15thNight
47%
340
15%
1360
20%
340
55%
340
29%
712
July16th to endNight
54%
376
16%
1418
15%
354
61%
354
29%
762
August1st to 15thNight
52%
511
16%
1582
11%
509
57%
509
32%
948
August16th to endNight
50%
678
22%
1824
10%
678
57%
678
38%
1081
September1st to 15thNight
45%
720
19%
1800
8%
720
50%
720
33%
1183
September16th to endNight
48%
693
25%
1902
16%
693
54%
693
33%
1193
October1st to 15thNight
32%
660
18%
1980
11%
660
40%
660
20%
1365
October16th to endNight
20%
704
11%
2156
4%
704
29%
704
14%
1616
November1st to 15thNight
27%
700
19%
2367
14%
700
37%
700
18%
1593
November16th to endNight
20%
720
13%
2520
8%
720
28%
720
11%
1886
December1st to 15thNight
15%
720
7%
2520
3%
720
20%
720
9%
1934
December16th to endNight
12%
768
10%
2688
3%
768
20%
768
9%
2108

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%9%36%6%34446%31%
47994
Night
16%9%36%5%3445%6%33%
47112
Cloud CoverDay
17%9%36%6%34446%32%
48004
Night
16%9%36%5%34446%33%
47117
TransparencyDay
53%210%20%10%1
47682
Night
50%311%22%11%1
46942
SeeingDay
22%11%29%20%10%4
5453
Night
22%11%30%24%9%1
14729

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 15thDay
20%15%6%8%5%24335%22%
1432
16th to endDay
15%14%6%11%7%5%5%33421%
1640
February1st to 15thDay
13%15%6%11%8%34445%21%
1575
16th to endDay
17%16%47%6%23335%27%
1490
March1st to 15thDay
15%13%47%8%36%44427%
1899
16th to endDay
14%9%35%5%24245%39%
2154
April1st to 15thDay
22%9%35%5%24335%32%
2152
16th to endDay
19%8%35%5%24245%37%
2253
May1st to 15thDay
19%8%36%4245%45%33%
2490
16th to endDay
15%5%26%6%35%5%5%7%36%
2618
June1st to 15thDay
20%8%25%5%35%45%6%29%
2520
16th to endDay
16%5%36%5%35%5%6%8%31%
2520
July1st to 15thDay
13%6%346%35%6%7%7%36%
2520
16th to endDay
11%6%36%6%46%5%6%9%34%
2654
August1st to 15thDay
11%7%37%6%35%5%6%7%34%
2366
16th to endDay
14%6%25%5%36%5%5%7%36%
2366
September1st to 15thDay
16%6%25%5%33447%40%
2160
16th to endDay
16%5%245%24346%43%
1912
October1st to 15thDay
22%7%45%6%24447%30%
1650
16th to endDay
27%11%36%7%34335%24%
1716
November1st to 15thDay
16%7%37%6%34446%33%
1491
16th to endDay
23%13%5%7%6%35%345%22%
1440
December1st to 15thDay
20%16%8%8%7%33435%17%
1440
16th to endDay
22%17%6%7%6%33335%19%
1536
January1st to 15thNight
19%14%5%10%7%4443419%
2506
16th to endNight
12%15%5%9%7%34446%24%
2583
February1st to 15thNight
12%13%6%8%6%45%5%6%6%23%
2285
16th to endNight
14%12%46%5%345%6%6%29%
1982
March1st to 15thNight
17%11%46%5%35%335%31%
2037
16th to endNight
14%7%35%424346%42%
2070
April1st to 15thNight
20%9%45%324346%35%
1796
16th to endNight
15%7%25%5%2345%7%38%
1716
May1st to 15thNight
19%7%35%423447%38%
1459
16th to endNight
13%6%345%35%35%7%41%
1495
June1st to 15thNight
16%6%36%5%3445%8%35%
1440
16th to endNight
14%5%35%5%25%5%6%7%37%
1440
July1st to 15thNight
8%425%435%447%49%
1440
16th to endNight
9%3244345%7%8%47%
1514
August1st to 15thNight
8%5%344245%7%8%45%
1592
16th to endNight
9%42442345%7%51%
1824
September1st to 15thNight
13%42443445%7%44%
1800
16th to endNight
16%41431245%5%49%
1902
October1st to 15thNight
21%7%26%5%235%46%34%
1980
16th to endNight
24%11%27%5%2445%7%25%
2156
November1st to 15thNight
16%9%35%42445%6%34%
2367
16th to endNight
23%11%46%5%35%445%24%
2520
December1st to 15thNight
21%16%5%8%5%24446%20%
2520
16th to endNight
22%15%5%8%6%3443419%
2688

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 15thDay
20%15%6%9%5%24435%23%
1432
16th to endDay
15%15%6%10%7%5%443422%
1640
February1st to 15thDay
14%15%5%11%8%35%445%22%
1575
16th to endDay
18%15%5%7%5%23435%27%
1490
March1st to 15thDay
16%12%5%7%8%45%43427%
1910
16th to endDay
14%10%35%424346%40%
2153
April1st to 15thDay
22%10%35%5%24335%32%
2152
16th to endDay
19%8%345%2335%5%37%
2253
May1st to 15thDay
19%8%36%5%245%5%6%33%
2490
16th to endDay
14%6%35%6%445%5%7%36%
2618
June1st to 15thDay
21%6%36%5%35%5%5%7%30%
2520
16th to endDay
16%6%36%5%35%46%7%32%
2520
July1st to 15thDay
12%6%346%36%5%6%8%36%
2520
16th to endDay
12%5%35%6%36%6%6%8%34%
2654
August1st to 15thDay
12%7%37%6%36%5%5%7%35%
2366
16th to endDay
15%5%25%5%46%5%5%7%36%
2366
September1st to 15thDay
16%6%25%5%33347%41%
2160
16th to endDay
16%5%245%24346%43%
1912
October1st to 15thDay
22%8%36%5%3345%6%31%
1650
16th to endDay
27%11%36%7%34335%24%
1716
November1st to 15thDay
16%8%28%6%3435%6%33%
1491
16th to endDay
23%12%5%7%5%35%345%23%
1440
December1st to 15thDay
21%16%6%9%7%3443417%
1440
16th to endDay
22%17%5%9%5%24335%19%
1536
January1st to 15thNight
19%14%5%10%7%34435%19%
2506
16th to endNight
13%15%5%8%7%34447%25%
2583
February1st to 15thNight
12%14%5%8%6%35%5%6%6%24%
2278
16th to endNight
14%12%5%6%5%345%5%6%29%
1982
March1st to 15thNight
18%11%47%5%24346%31%
2049
16th to endNight
15%7%45%424345%42%
2070
April1st to 15thNight
20%9%45%423346%36%
1796
16th to endNight
16%7%25%5%23447%39%
1716
May1st to 15thNight
19%6%2443246%6%38%
1459
16th to endNight
13%5%35%435%45%7%42%
1495
June1st to 15thNight
17%6%27%43445%7%35%
1440
16th to endNight
13%6%35%6%246%5%8%38%
1440
July1st to 15thNight
8%325%43445%6%50%
1440
16th to endNight
9%3243345%7%8%47%
1514
August1st to 15thNight
9%5%25%5%245%6%8%45%
1592
16th to endNight
9%425%423447%51%
1824
September1st to 15thNight
13%4245%3435%7%44%
1800
16th to endNight
16%425%322345%49%
1902
October1st to 15thNight
21%7%25%5%23346%34%
1980
16th to endNight
24%10%37%5%33447%25%
2156
November1st to 15thNight
16%9%35%5%245%46%34%
2367
16th to endNight
23%10%46%5%35%445%25%
2520
December1st to 15thNight
21%15%5%8%5%24447%21%
2520
16th to endNight
22%16%5%8%5%3434420%
2688

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 15thDay
64%29%15%7%
1433
16th to endDay
66%17%13%9%1
1640
February1st to 15thDay
64%210%16%5%
1577
16th to endDay
60%29%14%12%1
1490
March1st to 15thDay
61%211%16%6%1
1910
16th to endDay
46%27%21%15%5%
2154
April1st to 15thDay
54%27%18%13%2
2152
16th to endDay
49%17%21%17%3
2253
May1st to 15thDay
51%38%18%15%2
2490
16th to endDay
46%312%21%13%1
2622
June1st to 15thDay
54%39%21%10%
2520
16th to endDay
49%312%20%13%
2520
July1st to 15thDay
42%411%29%12%
2371
16th to endDay
46%412%25%10%
2487
August1st to 15thDay
47%314%23%10%
2352
16th to endDay
45%312%27%10%
2366
September1st to 15thDay
44%111%28%13%
2160
16th to endDay
43%210%31%11%
1912
October1st to 15thDay
53%210%20%11%1
1650
16th to endDay
64%210%16%5%
1716
November1st to 15thDay
50%314%20%10%
1491
16th to endDay
64%310%13%7%1
1440
December1st to 15thDay
70%210%12%3
1440
16th to endDay
68%29%12%6%
1536
January1st to 15thNight
67%29%14%5%
2506
16th to endNight
60%28%18%9%
2583
February1st to 15thNight
58%213%18%6%
2287
16th to endNight
53%39%21%10%
1982
March1st to 15thNight
54%210%21%9%1
2049
16th to endNight
44%29%23%17%3
2070
April1st to 15thNight
50%17%22%15%2
1796
16th to endNight
44%38%21%18%2
1716
May1st to 15thNight
45%39%23%15%3
1459
16th to endNight
42%312%23%16%2
1497
June1st to 15thNight
47%314%20%13%
1440
16th to endNight
44%313%24%13%
1440
July1st to 15thNight
32%313%30%18%1
1360
16th to endNight
33%416%30%14%
1418
August1st to 15thNight
35%417%29%12%
1582
16th to endNight
32%315%34%13%
1824
September1st to 15thNight
38%314%29%12%1
1800
16th to endNight
37%311%37%9%
1902
October1st to 15thNight
51%210%22%13%
1980
16th to endNight
59%313%16%7%
2156
November1st to 15thNight
49%313%20%11%1
2367
16th to endNight
60%310%18%5%
2520
December1st to 15thNight
64%313%15%3
2520
16th to endNight
67%29%13%7%
2688

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 15thDay
35%21%20%16%6%
60
16th to endDay
41%12%35%7%2
81
February1st to 15thDay
36%24%32%5%1
90
16th to endDay
38%17%30%12%2
149
March1st to 15thDay
27%16%30%21%4
270
16th to endDay
26%15%33%13%10%1
288
April1st to 15thDay
27%20%28%14%8%
270
16th to endDay
25%17%27%15%11%3
270
May1st to 15thDay
30%9%29%17%6%5%
288
16th to endDay
19%13%34%20%9%2
331
June1st to 15thDay
24%10%33%21%9%
315
16th to endDay
17%12%32%25%10%2
315
July1st to 15thDay
13%7%28%31%16%3
305
16th to endDay
15%7%33%25%12%5%
326
August1st to 15thDay
13%427%34%13%7%
313
16th to endDay
14%428%27%15%9%
332
September1st to 15thDay
15%7%27%21%15%12%
315
16th to endDay
18%6%25%21%16%11%
287
October1st to 15thDay
24%13%27%18%11%3
255
16th to endDay
35%13%28%18%3
264
November1st to 15thDay
21%8%35%22%10%1
145
16th to endDay
31%15%30%16%5%1
60
December1st to 15thDay
28%21%31%15%3
60
16th to endDay
40%25%32%1
64
January1st to 15thNight
29%16%30%17%5%
720
16th to endNight
22%14%34%22%5%
768
February1st to 15thNight
21%17%38%18%2
704
16th to endNight
21%17%37%19%4
631
March1st to 15thNight
26%14%35%22%2
720
16th to endNight
20%12%32%22%9%2
768
April1st to 15thNight
26%14%31%22%4
718
16th to endNight
21%14%28%25%9%1
636
May1st to 15thNight
24%6%26%32%8%1
379
16th to endNight
16%6%35%28%12%1
375
June1st to 15thNight
20%8%28%31%9%1
360
16th to endNight
16%6%26%38%11%
360
July1st to 15thNight
8%430%37%17%1
340
16th to endNight
9%228%40%18%
376
August1st to 15thNight
12%224%35%22%2
511
16th to endNight
11%427%32%21%2
678
September1st to 15thNight
15%5%28%26%20%3
720
16th to endNight
19%6%21%26%21%4
693
October1st to 15thNight
27%9%25%23%12%1
660
16th to endNight
30%11%28%21%6%
704
November1st to 15thNight
23%12%31%22%9%1
700
16th to endNight
34%14%24%18%7%
720
December1st to 15thNight
31%15%30%18%3
720
16th to endNight
33%13%33%16%2
768
Page generated at 2017-09-25 09:02:30. Version ac04

Copyright 2017 A. Danko


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