Lake Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Sky 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
23%
14954
18%
46902
7%
14922
36%
14922
19%
30726

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
12%
720
20%
2506
5%
716
30%
716
14%
1609
January16th to endNight
11%
768
20%
2688
3%
768
32%
768
13%
1742
February1st to 15thNight
11%
704
17%
2177
3%
701
28%
701
15%
1455
February16th to endNight
13%
631
23%
1893
5%
631
34%
631
16%
1237
March1st to 15thNight
15%
720
17%
2160
6%
720
29%
720
16%
1471
March16th to endNight
17%
768
23%
2020
6%
768
31%
768
19%
1358
April1st to 15thNight
16%
718
17%
1796
3%
718
25%
718
18%
1292
April16th to endNight
19%
611
18%
1691
3%
611
30%
611
20%
1169
May1st to 15thNight
19%
540
16%
1620
6%
540
29%
540
16%
1126
May16th to endNight
22%
405
11%
1527
6%
404
30%
404
15%
1010
June1st to 15thNight
26%
360
12%
1440
7%
360
39%
360
16%
951
June16th to endNight
32%
360
12%
1440
11%
360
42%
360
22%
868
July1st to 15thNight
38%
340
12%
1360
12%
340
45%
340
21%
847
July16th to endNight
39%
376
15%
1418
14%
354
47%
354
20%
883
August1st to 15thNight
39%
497
17%
1568
10%
495
46%
495
26%
991
August16th to endNight
48%
751
21%
1897
11%
751
52%
751
34%
1213
September1st to 15thNight
34%
720
19%
1851
8%
720
41%
720
29%
1233
September16th to endNight
41%
693
25%
1913
16%
693
48%
693
31%
1202
October1st to 15thNight
29%
660
23%
1848
10%
660
42%
660
24%
1214
October16th to endNight
22%
704
17%
2277
5%
704
36%
704
18%
1497
November1st to 15thNight
25%
700
21%
2277
8%
700
41%
700
20%
1449
November16th to endNight
20%
720
20%
2340
7%
720
36%
720
17%
1495
December1st to 15thNight
17%
720
17%
2507
5%
720
33%
720
14%
1634
December16th to endNight
12%
768
19%
2688
3%
768
31%
768
13%
1780

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%6%25%5%3445%6%39%
48034
Night
16%7%25%424446%40%
47072
Cloud CoverDay
17%6%25%42445%6%39%
48044
Night
16%7%25%424446%41%
47077
TransparencyDay
44%411%21%14%2
47722
Night
44%411%21%15%2
46902
SeeingDay
22%15%31%19%8%2
5911
Night
22%15%34%20%6%
14954

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
15%6%345%245%5%6%40%
1432
16th to endDay
13%6%25%42445%7%42%
1536
February1st to 15thDay
16%6%35%445%5%5%7%35%
1681
16th to endDay
16%8%35%5%33345%40%
1580
March1st to 15thDay
20%7%25%333446%37%
1790
16th to endDay
17%6%345%23335%43%
2202
April1st to 15thDay
19%6%35%434346%38%
2152
16th to endDay
18%4245%2445%6%40%
2268
May1st to 15thDay
25%7%25%423345%33%
2332
16th to endDay
18%5%25%5%2445%6%39%
2596
June1st to 15thDay
24%6%35%423348%33%
2520
16th to endDay
14%5%25%5%36%6%6%8%35%
2520
July1st to 15thDay
12%5%25%6%35%6%6%8%36%
2520
16th to endDay
12%6%25%5%36%5%5%8%37%
2654
August1st to 15thDay
13%6%25%6%35%5%5%8%36%
2370
16th to endDay
11%5%25%5%3445%6%44%
2303
September1st to 15thDay
14%5%2443445%446%
2109
16th to endDay
15%5%23323345%49%
1906
October1st to 15thDay
20%6%135%14347%42%
1779
16th to endDay
15%6%345%33446%43%
1595
November1st to 15thDay
19%8%23423335%43%
1581
16th to endDay
16%6%234245%5%6%42%
1620
December1st to 15thDay
18%6%25%424446%40%
1452
16th to endDay
20%7%244245%46%35%
1536
January1st to 15thNight
17%8%35%424345%41%
2506
16th to endNight
15%9%35%5%23346%40%
2688
February1st to 15thNight
14%8%35%5%24446%39%
2176
16th to endNight
16%8%25%5%23345%41%
1893
March1st to 15thNight
17%7%25%5%34447%37%
2147
16th to endNight
14%8%35%423435%42%
2020
April1st to 15thNight
16%8%36%5%35%45%5%36%
1796
16th to endNight
20%6%245%23336%40%
1691
May1st to 15thNight
22%7%24433246%36%
1620
16th to endNight
18%6%35%44436%8%35%
1525
June1st to 15thNight
22%5%2443435%7%35%
1440
16th to endNight
14%5%25%43446%7%41%
1440
July1st to 15thNight
13%5%25%6%245%6%8%38%
1440
16th to endNight
12%5%35%6%36%45%7%40%
1514
August1st to 15thNight
9%5%26%5%446%6%7%43%
1578
16th to endNight
12%413435%448%46%
1897
September1st to 15thNight
14%5%25%5%24445%44%
1851
16th to endNight
13%6%24412445%50%
1913
October1st to 15thNight
18%7%24314246%43%
1848
16th to endNight
17%6%245%24445%40%
2277
November1st to 15thNight
16%7%24423345%44%
2277
16th to endNight
19%6%24324445%41%
2340
December1st to 15thNight
18%7%34324445%39%
2507
16th to endNight
18%9%25%423446%37%
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
14%7%34425%45%5%40%
1432
16th to endDay
14%6%36%425%346%43%
1536
February1st to 15thDay
16%7%25%445%5%5%7%35%
1681
16th to endDay
15%9%35%424345%40%
1580
March1st to 15thDay
20%6%25%424346%37%
1800
16th to endDay
17%7%345%23345%42%
2202
April1st to 15thDay
19%6%35%434446%38%
2152
16th to endDay
18%4145%35%446%41%
2268
May1st to 15thDay
25%8%25%423345%33%
2332
16th to endDay
18%5%25%434446%40%
2596
June1st to 15thDay
24%6%3442435%7%33%
2520
16th to endDay
15%425%435%6%6%9%35%
2520
July1st to 15thDay
13%5%345%46%5%6%7%36%
2520
16th to endDay
12%5%25%6%36%5%6%8%37%
2654
August1st to 15thDay
14%5%25%6%35%5%6%7%37%
2370
16th to endDay
11%5%25%5%345%47%43%
2303
September1st to 15thDay
14%5%2442444447%
2109
16th to endDay
15%5%24423345%49%
1906
October1st to 15thDay
20%6%14323336%43%
1779
16th to endDay
15%6%25%5%24445%44%
1595
November1st to 15thDay
20%7%23324345%43%
1581
16th to endDay
16%6%244245%5%6%42%
1620
December1st to 15thDay
18%7%25%323447%40%
1452
16th to endDay
20%8%245%2435%6%35%
1536
January1st to 15thNight
17%8%35%423335%41%
2506
16th to endNight
15%9%36%423335%41%
2688
February1st to 15thNight
14%8%36%434447%38%
2169
16th to endNight
16%8%25%5%23345%42%
1893
March1st to 15thNight
17%7%25%5%34447%36%
2160
16th to endNight
15%8%35%423336%42%
2019
April1st to 15thNight
16%8%35%5%35%447%35%
1796
16th to endNight
20%6%25%433425%40%
1691
May1st to 15thNight
22%7%35%433246%37%
1620
16th to endNight
18%6%25%42445%8%35%
1525
June1st to 15thNight
22%5%2442445%6%37%
1440
16th to endNight
14%426%4335%6%8%40%
1440
July1st to 15thNight
12%5%35%4245%6%8%38%
1440
16th to endNight
11%5%26%5%36%45%7%39%
1514
August1st to 15thNight
10%416%5%345%5%8%43%
1578
16th to endNight
12%424425%36%7%47%
1897
September1st to 15thNight
14%4245%2445%5%44%
1851
16th to endNight
15%6%14323345%49%
1913
October1st to 15thNight
19%6%24423336%44%
1848
16th to endNight
17%6%25%424345%41%
2277
November1st to 15thNight
16%7%24423345%44%
2277
16th to endNight
19%6%24423445%41%
2340
December1st to 15thNight
18%8%25%424345%40%
2507
16th to endNight
18%8%35%424446%36%
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
43%412%24%11%3
1433
16th to endDay
42%311%26%13%1
1536
February1st to 15thDay
47%413%20%12%1
1684
16th to endDay
47%210%22%13%3
1580
March1st to 15thDay
48%312%22%10%3
1800
16th to endDay
44%310%21%15%5%
2202
April1st to 15thDay
47%310%19%15%2
2152
16th to endDay
43%49%21%18%3
2268
May1st to 15thDay
53%47%18%13%2
2332
16th to endDay
44%6%13%21%12%2
2600
June1st to 15thDay
50%5%12%20%10%1
2520
16th to endDay
43%7%14%20%13%
2520
July1st to 15thDay
45%6%10%21%13%1
2371
16th to endDay
42%6%13%20%12%3
2487
August1st to 15thDay
44%6%13%20%13%
2356
16th to endDay
38%6%9%25%18%1
2303
September1st to 15thDay
39%5%11%21%19%2
2109
16th to endDay
37%36%22%26%2
1906
October1st to 15thDay
42%311%22%16%3
1779
16th to endDay
42%412%23%15%2
1595
November1st to 15thDay
45%412%19%16%2
1581
16th to endDay
40%5%11%23%16%2
1620
December1st to 15thDay
44%316%18%15%
1452
16th to endDay
50%414%18%11%
1536
January1st to 15thNight
46%312%22%13%2
2506
16th to endNight
46%49%22%14%2
2688
February1st to 15thNight
46%412%20%12%2
2177
16th to endNight
45%310%21%17%2
1893
March1st to 15thNight
47%411%20%13%2
2160
16th to endNight
44%29%18%18%5%
2020
April1st to 15thNight
48%49%18%16%2
1796
16th to endNight
47%38%19%15%5%
1691
May1st to 15thNight
49%410%18%14%2
1620
16th to endNight
47%7%15%18%9%1
1527
June1st to 15thNight
47%6%13%20%11%
1440
16th to endNight
40%5%14%22%14%
1440
July1st to 15thNight
41%7%12%24%14%
1360
16th to endNight
42%6%13%24%11%2
1418
August1st to 15thNight
38%7%13%23%14%2
1568
16th to endNight
35%6%11%28%17%
1897
September1st to 15thNight
40%5%10%22%19%1
1851
16th to endNight
37%47%21%26%2
1913
October1st to 15thNight
43%311%21%16%4
1848
16th to endNight
45%411%22%14%
2277
November1st to 15thNight
42%410%20%18%3
2277
16th to endNight
45%313%21%14%2
2340
December1st to 15thNight
46%413%21%12%
2507
16th to endNight
48%411%22%12%
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
25%31%26%15%1
60
16th to endDay
29%17%42%10%
64
February1st to 15thDay
27%25%33%10%2
215
16th to endDay
23%27%30%14%3
239
March1st to 15thDay
32%20%31%11%4
270
16th to endDay
22%26%31%12%5%1
288
April1st to 15thDay
25%21%34%12%5%
270
16th to endDay
22%15%35%20%23
270
May1st to 15thDay
38%15%23%14%6%1
288
16th to endDay
21%13%36%20%7%
331
June1st to 15thDay
25%14%30%21%7%1
315
16th to endDay
17%12%37%23%6%1
315
July1st to 15thDay
20%9%32%25%11%
305
16th to endDay
12%8%32%29%14%2
326
August1st to 15thDay
15%9%29%30%12%2
313
16th to endDay
13%6%33%25%14%6%
332
September1st to 15thDay
17%10%30%21%16%3
315
16th to endDay
22%6%27%21%10%12%
287
October1st to 15thDay
23%10%30%19%10%6%
255
16th to endDay
19%21%30%23%6%
242
November1st to 15thDay
25%15%31%15%9%1
235
16th to endDay
25%17%31%16%7%1
240
December1st to 15thDay
29%29%27%8%5%
72
16th to endDay
35%26%26%10%
64
January1st to 15thNight
24%22%38%12%2
720
16th to endNight
25%21%35%15%1
768
February1st to 15thNight
21%23%38%14%1
704
16th to endNight
26%23%33%15%1
631
March1st to 15thNight
24%23%34%14%2
720
16th to endNight
23%22%33%16%3
768
April1st to 15thNight
22%20%37%16%2
718
16th to endNight
24%18%35%17%3
611
May1st to 15thNight
29%15%32%17%4
540
16th to endNight
20%10%41%22%4
405
June1st to 15thNight
24%8%35%25%5%
360
16th to endNight
13%5%43%31%5%
360
July1st to 15thNight
13%6%34%34%10%
340
16th to endNight
13%334%38%9%
376
August1st to 15thNight
13%436%35%9%
497
16th to endNight
14%327%38%14%1
751
September1st to 15thNight
17%6%35%28%11%
720
16th to endNight
18%7%28%25%16%4
693
October1st to 15thNight
23%12%30%21%10%1
660
16th to endNight
24%19%31%19%5%
704
November1st to 15thNight
20%17%31%20%8%1
700
16th to endNight
26%17%30%17%7%
720
December1st to 15thNight
25%20%33%16%4
720
16th to endNight
26%22%36%13%1
768
Page generated at 2017-09-25 09:02:21. Version ac04

Copyright 2017 A. Danko


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