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 2005-11-06 to 2024-01-15.

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
22%
22986
12%
74592
4%
22941
31%
22941
10%
57647

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
11%
760
13%
2649
2%
757
23%
757
8%
2028
January11th to 20thNight
12%
737
10%
2577
2%
737
23%
737
5%
2113
January21st to endNight
14%
792
14%
2772
5%
792
28%
792
9%
2059
February1st to 10thNight
11%
720
10%
2258
1%
720
23%
720
8%
1759
February11th to 20thNight
9%
703
12%
2100
1%
700
22%
700
7%
1647
February21st to endNight
11%
592
16%
1776
4%
592
26%
592
9%
1386
March1st to 10thNight
15%
720
15%
2160
4%
720
29%
720
10%
1638
March11th to 20thNight
14%
720
11%
2084
3%
720
23%
720
8%
1682
March21st to endNight
16%
792
15%
2028
4%
792
25%
792
11%
1606
April1st to 10thNight
15%
720
13%
1800
2%
720
22%
720
11%
1437
April11th to 20thNight
20%
711
12%
1775
2%
711
25%
711
11%
1440
April21st to endNight
15%
558
14%
1638
3%
558
23%
558
10%
1289
May1st to 10thNight
18%
540
10%
1620
4%
540
24%
540
8%
1317
May11th to 20thNight
17%
492
13%
1554
5%
492
25%
492
9%
1211
May21st to endNight
26%
389
10%
1551
8%
388
32%
388
10%
1167
June1st to 10thNight
27%
360
9%
1440
5%
360
36%
360
9%
1108
June11th to 20thNight
26%
360
9%
1440
8%
360
32%
360
9%
1118
June21st to endNight
36%
360
8%
1440
8%
360
42%
360
10%
1090
July1st to 10thNight
40%
350
7%
1400
7%
350
44%
350
9%
1102
July11th to 20thNight
41%
348
8%
1392
7%
348
46%
348
10%
1068
July21st to endNight
38%
394
11%
1486
9%
372
44%
372
11%
1129
August1st to 10thNight
39%
473
9%
1537
4%
471
44%
471
12%
1199
August11th to 20thNight
41%
601
12%
1665
5%
601
45%
601
13%
1309
August21st to endNight
45%
792
12%
1980
5%
792
48%
792
16%
1562
September1st to 10thNight
34%
720
13%
1800
4%
720
40%
720
15%
1433
September11th to 20thNight
40%
720
17%
1966
8%
720
47%
720
16%
1487
September21st to endNight
35%
720
14%
1980
8%
720
41%
720
14%
1553
October1st to 10thNight
30%
720
13%
1980
6%
720
36%
720
14%
1533
October11th to 20thNight
28%
720
13%
2196
5%
720
38%
720
11%
1695
October21st to endNight
19%
792
10%
2574
4%
792
28%
792
9%
2033
November1st to 10thNight
27%
740
13%
2407
6%
740
36%
740
12%
1802
November11th to 20thNight
18%
760
16%
2470
6%
760
31%
760
10%
1898
November21st to endNight
18%
760
13%
2470
3%
760
29%
760
9%
1898
December1st to 10thNight
15%
760
12%
2640
3%
760
25%
760
7%
2043
December11th to 20thNight
16%
760
12%
3212
1%
759
28%
759
7%
2344
December21st to endNight
11%
830
9%
4775
2%
817
23%
817
4%
3464

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%7%35%5%3445%7%40%
74821
Night
17%8%35%5%3445%6%41%
74948
TransparencyDay
30%37%7%15%10%1
74526
Night
30%37%7%15%10%1
74777
SeeingDay
24%18%32%18%7%2
13929
Night
23%16%34%21%6%
22992

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
14%8%35%6%3445%6%43%
1517
11th to 20thDay
18%8%35%5%346%5%7%36%
1472
21st to endDay
13%7%35%435%46%7%43%
1584
February1st to 10thDay
19%7%36%446%5%6%7%35%
1697
11th to 20thDay
14%7%45%5%35%5%5%7%40%
1748
21st to endDay
21%10%35%5%34346%36%
1480
March1st to 10thDay
16%9%25%43445%7%41%
1797
11th to 20thDay
17%6%25%7%45%5%48%38%
1876
21st to endDay
19%8%35%5%24345%41%
2326
April1st to 10thDay
18%8%36%5%3445%6%38%
2160
11th to 20thDay
17%5%245%345%5%8%41%
2134
21st to endDay
22%5%36%6%35%45%6%36%
2322
May1st to 10thDay
24%9%36%6%3345%7%31%
2340
11th to 20thDay
19%6%25%42436%7%41%
2354
21st to endDay
16%5%35%5%3445%6%44%
2725
June1st to 10thDay
18%7%35%5%35%5%6%8%34%
2520
11th to 20thDay
17%6%26%6%35%6%6%8%36%
2520
21st to endDay
16%5%35%6%36%5%6%9%36%
2520
July1st to 10thDay
13%6%26%6%45%5%6%7%40%
2520
11th to 20thDay
13%6%35%6%35%5%6%9%39%
2520
21st to endDay
12%6%35%5%46%6%6%8%39%
2744
August1st to 10thDay
11%6%36%7%36%6%7%9%36%
2373
11th to 20thDay
14%6%26%5%46%5%6%7%40%
2232
21st to endDay
12%435%6%45%5%6%8%43%
2376
September1st to 10thDay
15%6%25%445%45%6%44%
2160
11th to 20thDay
15%5%24323446%51%
1994
21st to endDay
17%6%24433447%44%
1980
October1st to 10thDay
23%6%345%24346%40%
1980
11th to 20thDay
15%7%245%2445%7%46%
1760
21st to endDay
19%7%35%5%3345%6%40%
1782
November1st to 10thDay
14%8%25%5%33345%48%
1671
11th to 20thDay
19%7%2442346%5%45%
1710
21st to endDay
17%6%345%25%45%6%43%
1710
December1st to 10thDay
19%8%36%5%25%5%5%5%39%
1539
11th to 20thDay
22%7%23333346%44%
1906
21st to endDay
20%11%36%5%24446%34%
2772
January1st to 10thNight
16%8%35%434446%44%
2649
11th to 20thNight
19%10%36%5%34446%36%
2577
21st to endNight
13%9%35%6%2445%6%43%
2772
February1st to 10thNight
17%9%46%5%345%46%38%
2258
11th to 20thNight
14%9%36%6%345%5%6%39%
2098
21st to endNight
18%9%36%6%33446%39%
1776
March1st to 10thNight
15%8%25%5%345%5%7%41%
2150
11th to 20thNight
14%8%45%6%45%5%47%39%
2083
21st to endNight
16%9%36%5%24446%41%
2028
April1st to 10thNight
17%8%36%5%445%6%5%37%
1800
11th to 20thNight
18%6%36%5%25%45%6%39%
1775
21st to endNight
22%7%34433446%39%
1638
May1st to 10thNight
23%9%345%44447%32%
1620
11th to 20thNight
19%5%35%5%3446%7%38%
1553
21st to endNight
17%7%35%5%45%46%7%39%
1550
June1st to 10thNight
16%8%35%6%35%45%8%38%
1440
11th to 20thNight
19%7%25%6%45%5%47%37%
1440
21st to endNight
13%6%35%4335%7%9%43%
1440
July1st to 10thNight
13%5%35%7%35%5%6%9%39%
1440
11th to 20thNight
15%6%36%6%35%5%6%8%36%
1440
21st to endNight
12%5%35%7%37%45%7%43%
1574
August1st to 10thNight
9%5%27%6%45%6%7%7%42%
1547
11th to 20thNight
11%7%25%6%5%5%7%6%8%38%
1665
21st to endNight
14%5%2342445%7%48%
1980
September1st to 10thNight
14%6%36%6%345%5%6%43%
1800
11th to 20thNight
13%7%24423346%52%
1966
21st to endNight
16%7%36%4335%5%5%44%
1980
October1st to 10thNight
21%7%3442435%7%41%
1980
11th to 20thNight
15%6%245%3445%6%46%
2196
21st to endNight
21%9%35%5%24445%38%
2574
November1st to 10thNight
14%6%25%5%3345%6%48%
2407
11th to 20thNight
18%7%34424445%46%
2470
21st to endNight
16%6%24435%5%47%45%
2470
December1st to 10thNight
19%9%35%424446%40%
2640
11th to 20thNight
20%6%25%4345%5%6%40%
3288
21st to endNight
20%11%36%433446%36%
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
28%39%7%19%7%1
1518
11th to 20thDay
32%41%8%10%7%1
1472
21st to endDay
26%37%8%19%8%2
1584
February1st to 10thDay
32%35%8%13%10%1
1697
11th to 20thDay
29%38%8%15%8%2
1757
21st to endDay
37%34%6%11%10%2
1480
March1st to 10thDay
28%36%9%15%10%2
1800
11th to 20thDay
33%36%7%16%7%2
1876
21st to endDay
30%36%5%13%14%3
2326
April1st to 10thDay
30%36%6%15%11%2
2160
11th to 20thDay
30%36%7%14%11%2
2134
21st to endDay
32%37%6%12%11%2
2322
May1st to 10thDay
34%36%6%13%10%2
2340
11th to 20thDay
28%37%6%14%12%2
2358
21st to endDay
25%38%10%16%9%2
2725
June1st to 10thDay
33%38%8%15%6%
2520
11th to 20thDay
30%39%9%12%10%1
2520
21st to endDay
33%38%10%13%6%1
2520
July1st to 10thDay
33%39%5%15%8%1
2450
11th to 20thDay
28%39%9%16%7%1
2445
21st to endDay
28%39%7%14%10%2
2591
August1st to 10thDay
31%38%9%14%8%
2359
11th to 20thDay
31%36%8%15%10%1
2232
21st to endDay
28%38%5%14%12%2
2376
September1st to 10thDay
27%38%6%15%13%1
2160
11th to 20thDay
22%37%7%16%16%2
1994
21st to endDay
29%36%414%16%1
1980
October1st to 10thDay
29%36%7%14%13%1
1980
11th to 20thDay
27%36%8%19%9%1
1760
21st to endDay
29%37%8%14%10%2
1782
November1st to 10thDay
25%40%6%15%13%1
1671
11th to 20thDay
25%40%7%16%11%1
1710
21st to endDay
28%40%7%16%7%1
1710
December1st to 10thDay
30%40%9%12%8%2
1539
11th to 20thDay
32%31%9%12%13%3
1906
21st to endDay
41%26%8%18%8%1
2772
January1st to 10thNight
28%39%8%15%9%
2649
11th to 20thNight
33%41%6%13%5%2
2577
21st to endNight
27%37%6%16%12%2
2772
February1st to 10thNight
31%36%7%15%9%1
2258
11th to 20thNight
31%37%7%15%8%2
2100
21st to endNight
33%34%6%16%9%2
1776
March1st to 10thNight
27%36%7%17%10%2
2160
11th to 20thNight
34%36%8%12%8%1
2084
21st to endNight
30%36%5%13%12%4
2028
April1st to 10thNight
30%36%7%13%11%2
1800
11th to 20thNight
33%36%5%13%12%1
1775
21st to endNight
32%35%7%14%8%4
1638
May1st to 10thNight
35%37%6%11%8%3
1620
11th to 20thNight
30%37%6%13%11%3
1554
21st to endNight
28%39%10%13%9%1
1551
June1st to 10thNight
32%38%10%14%7%
1440
11th to 20thNight
33%37%9%14%7%
1440
21st to endNight
28%39%12%13%7%
1440
July1st to 10thNight
30%40%8%14%7%
1400
11th to 20thNight
29%40%9%17%5%1
1392
21st to endNight
28%40%9%14%8%2
1486
August1st to 10thNight
31%38%9%16%7%
1537
11th to 20thNight
29%38%9%15%8%1
1665
21st to endNight
28%37%6%18%10%1
1980
September1st to 10thNight
29%37%6%13%12%2
1800
11th to 20thNight
24%38%6%15%16%1
1966
21st to endNight
28%38%5%14%12%3
1980
October1st to 10thNight
29%36%7%16%11%2
1980
11th to 20thNight
29%37%8%18%7%
2196
21st to endNight
32%37%7%13%9%1
2574
November1st to 10thNight
23%41%8%13%13%2
2407
11th to 20thNight
27%39%6%15%11%1
2470
21st to endNight
27%39%9%15%9%1
2470
December1st to 10thNight
29%40%8%14%8%1
2640
11th to 20thNight
31%33%10%13%12%2
3288
21st to endNight
40%26%6%20%9%
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
28%28%26%17%2
180
11th to 20thDay
31%31%26%8%4
168
21st to endDay
26%28%34%9%21
176
February1st to 10thDay
38%23%30%8%1
335
11th to 20thDay
30%31%30%8%
416
21st to endDay
35%22%31%9%3
346
March1st to 10thDay
31%22%34%10%2
420
11th to 20thDay
30%27%29%10%3
420
21st to endDay
29%23%32%11%42
462
April1st to 10thDay
33%25%26%11%5%1
420
11th to 20thDay
27%21%35%12%31
412
21st to endDay
32%19%32%14%22
420
May1st to 10thDay
34%21%29%11%5%1
423
11th to 20thDay
23%18%41%14%4
447
21st to endDay
20%15%34%22%8%2
485
June1st to 10thDay
20%15%35%20%8%2
450
11th to 20thDay
18%14%40%20%6%2
450
21st to endDay
18%15%34%23%8%2
450
July1st to 10thDay
15%11%32%27%13%2
445
11th to 20thDay
16%8%32%28%14%2
444
21st to endDay
14%9%38%29%9%1
488
August1st to 10thDay
12%10%33%33%11%2
446
11th to 20thDay
16%9%31%30%10%4
439
21st to endDay
13%10%36%24%14%4
495
September1st to 10thDay
21%10%28%21%16%4
450
11th to 20thDay
19%12%30%20%11%7%
450
21st to endDay
22%12%33%20%9%4
450
October1st to 10thDay
27%15%26%21%7%4
450
11th to 20thDay
20%18%34%18%8%2
414
21st to endDay
27%18%31%18%6%1
396
November1st to 10thDay
22%19%32%16%9%2
365
11th to 20thDay
30%22%26%16%41
370
21st to endDay
27%20%32%16%5%
370
December1st to 10thDay
28%28%27%12%5%
199
11th to 20thDay
39%24%29%6%2
180
21st to endDay
28%26%32%9%32
198
January1st to 10thNight
24%22%39%13%2
760
11th to 20thNight
29%21%34%14%2
737
21st to endNight
21%24%34%18%2
792
February1st to 10thNight
27%20%36%15%2
720
11th to 20thNight
25%27%36%11%1
703
21st to endNight
31%21%33%14%1
592
March1st to 10thNight
25%24%34%15%3
720
11th to 20thNight
23%25%37%14%2
720
21st to endNight
27%21%34%15%4
792
April1st to 10thNight
25%21%36%16%2
720
11th to 20thNight
22%22%34%19%3
711
21st to endNight
26%20%37%15%3
558
May1st to 10thNight
32%14%32%17%4
540
11th to 20thNight
23%17%39%17%4
492
21st to endNight
20%9%40%26%5%
389
June1st to 10thNight
19%8%38%27%7%
360
11th to 20thNight
20%9%39%26%5%
360
21st to endNight
13%6%41%34%6%
360
July1st to 10thNight
14%6%34%36%10%1
350
11th to 20thNight
17%329%39%12%
348
21st to endNight
13%5%37%37%7%
394
August1st to 10thNight
11%5%38%37%9%
473
11th to 20thNight
14%6%32%36%12%
601
21st to endNight
16%7%28%34%14%2
792
September1st to 10thNight
17%7%34%31%10%1
720
11th to 20thNight
17%9%29%28%16%2
720
21st to endNight
20%9%31%27%10%2
720
October1st to 10thNight
26%12%29%22%10%2
720
11th to 20thNight
20%15%33%21%11%1
720
21st to endNight
27%17%32%18%6%
792
November1st to 10thNight
18%17%34%23%8%1
740
11th to 20thNight
24%21%33%16%5%1
760
21st to endNight
25%20%35%16%5%
760
December1st to 10thNight
27%20%34%15%4
760
11th to 20thNight
25%23%33%18%2
760
21st to endNight
27%21%37%14%2
836
Page generated at 2024-01-11 22:33:51. Version ac07

Copyright 2024 Attilla Danko


Lake Sky Observatory Clear Sky Chart |Charts Home