Freeman Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Freeman Lake Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
47%
15875
21%
47677
16%
15832
53%
15832
28%
30319

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
26%
899
16%
2506
7%
895
34%
895
20%
1810
January16th to endNight
25%
788
19%
2480
11%
788
35%
788
20%
1691
February1st to 15thNight
23%
704
16%
2112
7%
701
32%
701
20%
1483
February16th to endNight
22%
631
18%
1893
8%
631
30%
631
20%
1309
March1st to 15thNight
28%
720
17%
2133
10%
720
33%
720
21%
1489
March16th to endNight
36%
739
16%
2083
10%
739
41%
739
22%
1435
April1st to 15thNight
39%
539
23%
1797
15%
539
51%
539
28%
1067
April16th to endNight
44%
540
21%
1715
15%
540
50%
540
25%
1095
May1st to 15thNight
44%
539
17%
1619
11%
539
50%
539
23%
1108
May16th to endNight
63%
561
20%
1684
16%
561
66%
561
31%
1050
June1st to 15thNight
70%
540
21%
1531
17%
540
72%
540
41%
874
June16th to endNight
74%
540
22%
1440
17%
540
75%
540
40%
858
July1st to 15thNight
65%
510
17%
1360
14%
510
66%
510
34%
869
July16th to endNight
76%
564
23%
1557
20%
531
79%
531
40%
877
August1st to 15thNight
78%
539
25%
1645
25%
536
79%
536
39%
918
August16th to endNight
79%
573
23%
1910
27%
573
79%
573
37%
1018
September1st to 15thNight
67%
627
25%
1887
24%
627
69%
627
33%
1124
September16th to endNight
63%
717
30%
1980
25%
717
65%
717
38%
1181
October1st to 15thNight
60%
720
33%
1980
27%
720
64%
720
40%
1148
October16th to endNight
45%
768
28%
2417
23%
768
55%
768
31%
1438
November1st to 15thNight
46%
760
28%
2471
24%
760
55%
760
31%
1439
November16th to endNight
40%
780
25%
2535
20%
780
49%
780
27%
1559
December1st to 15thNight
33%
728
16%
2365
11%
728
39%
728
19%
1653
December16th to endNight
28%
849
18%
2577
11%
849
36%
849
18%
1826

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
14%6%35%5%3445%7%39%
48761
Night
13%6%35%42445%6%42%
47864
TransparencyDay
43%411%23%15%2
48451
Night
41%310%23%17%3
47678
SeeingDay
15%5%19%24%21%12%
5901
Night
16%5%23%31%20%2
15879

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 15thDay
21%8%38%5%33445%32%
1432
16th to endDay
15%8%45%5%2345%6%37%
1737
February1st to 15thDay
17%10%5%7%5%23445%34%
1750
16th to endDay
14%8%48%6%3445%6%32%
1580
March1st to 15thDay
21%9%35%42434436%
1827
16th to endDay
17%9%36%5%25%447%32%
2150
April1st to 15thDay
14%6%25%435%5%46%40%
2151
16th to endDay
16%6%25%5%2445%7%39%
2244
May1st to 15thDay
19%6%35%5%35%45%7%33%
2331
16th to endDay
10%6%35%5%46%5%5%8%37%
2431
June1st to 15thDay
8%326%5%46%5%6%8%42%
2424
16th to endDay
6%4245%45%6%7%9%42%
2520
July1st to 15thDay
12%6%25%5%35%5%7%9%34%
2520
16th to endDay
8%3245%47%6%7%9%39%
2501
August1st to 15thDay
8%6%15%435%5%7%10%40%
2302
16th to endDay
8%425%5%35%5%6%8%43%
2292
September1st to 15thDay
14%6%24435%5%5%7%40%
2061
16th to endDay
13%425%42345%7%47%
1980
October1st to 15thDay
13%423313337%51%
1980
16th to endDay
16%4245%1333448%
1803
November1st to 15thDay
14%5%24434345%47%
1717
16th to endDay
16%7%24314345%44%
1755
December1st to 15thDay
22%10%45%42334432%
1632
16th to endDay
19%11%45%423336%35%
1641
January1st to 15thNight
17%8%5%9%6%34345%32%
2506
16th to endNight
17%10%36%43435%5%35%
2480
February1st to 15thNight
19%9%46%5%24445%33%
2103
16th to endNight
17%9%47%5%34345%34%
1893
March1st to 15thNight
17%9%36%5%34335%36%
2133
16th to endNight
14%9%46%5%35%446%35%
2083
April1st to 15thNight
12%5%35%42445%8%44%
1797
16th to endNight
13%6%35%5%35%447%41%
1715
May1st to 15thNight
16%5%36%6%35%45%6%36%
1619
16th to endNight
6%326%7%45%6%7%9%42%
1682
June1st to 15thNight
6%4243235%6%9%51%
1531
16th to endNight
5%223435%6%7%12%46%
1440
July1st to 15thNight
11%5%244245%5%8%45%
1440
16th to endNight
6%214425%47%10%48%
1664
August1st to 15thNight
5%2144245%7%9%52%
1656
16th to endNight
5%224425%5%6%9%51%
1910
September1st to 15thNight
12%424235%35%7%48%
1887
16th to endNight
9%424424445%52%
1980
October1st to 15thNight
10%424323446%53%
1980
16th to endNight
15%5%14423335%49%
2417
November1st to 15thNight
13%5%2442334450%
2471
16th to endNight
16%6%34323445%44%
2535
December1st to 15thNight
21%9%46%434345%32%
2365
16th to endNight
23%10%45%324345%32%
2577

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
54%38%21%11%
1433
16th to endDay
48%110%28%8%1
1737
February1st to 15thDay
52%37%24%9%1
1752
16th to endDay
51%311%21%10%1
1580
March1st to 15thDay
50%39%19%14%1
1827
16th to endDay
51%311%24%8%
2151
April1st to 15thDay
42%410%22%17%1
2151
16th to endDay
44%410%24%14%2
2244
May1st to 15thDay
48%413%21%11%
2331
16th to endDay
43%5%14%21%13%2
2435
June1st to 15thDay
37%5%12%25%16%1
2424
16th to endDay
34%6%13%21%20%3
2520
July1st to 15thDay
43%5%14%18%13%4
2371
16th to endDay
35%7%17%23%12%2
2345
August1st to 15thDay
36%7%13%22%16%2
2289
16th to endDay
36%5%11%23%17%4
2292
September1st to 15thDay
42%5%10%19%16%4
2061
16th to endDay
36%39%23%24%3
1980
October1st to 15thDay
33%28%26%24%3
1980
16th to endDay
38%27%26%22%2
1803
November1st to 15thDay
39%27%24%19%6%
1717
16th to endDay
40%26%27%20%1
1755
December1st to 15thDay
54%210%19%10%2
1632
16th to endDay
51%213%23%8%1
1641
January1st to 15thNight
53%28%19%14%1
2506
16th to endNight
50%29%24%10%1
2480
February1st to 15thNight
52%29%22%10%1
2112
16th to endNight
51%212%21%10%1
1893
March1st to 15thNight
50%39%19%13%3
2133
16th to endNight
48%412%23%9%1
2083
April1st to 15thNight
37%411%21%21%3
1797
16th to endNight
43%37%25%14%4
1715
May1st to 15thNight
47%410%24%11%1
1620
16th to endNight
35%7%14%21%16%3
1684
June1st to 15thNight
28%5%16%26%20%3
1531
16th to endNight
27%7%15%22%21%5%
1440
July1st to 15thNight
36%5%14%23%16%4
1360
16th to endNight
25%7%17%28%17%2
1557
August1st to 15thNight
27%6%14%26%20%4
1645
16th to endNight
26%6%15%25%21%4
1910
September1st to 15thNight
34%49%23%21%5%
1887
16th to endNight
33%38%23%25%5%
1980
October1st to 15thNight
31%37%25%27%4
1980
16th to endNight
38%26%26%22%4
2417
November1st to 15thNight
36%26%23%23%6%
2471
16th to endNight
41%37%25%20%2
2535
December1st to 15thNight
53%210%19%11%1
2365
16th to endNight
54%210%21%9%1
2577

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
33%18%30%8%6%2
90
16th to endDay
18%23%42%11%3
96
February1st to 15thDay
22%23%38%13%2
90
16th to endDay
17%17%39%20%4
81
March1st to 15thDay
27%11%36%21%2
117
16th to endDay
21%10%32%24%9%1
288
April1st to 15thDay
16%12%27%26%15%2
270
16th to endDay
19%6%23%25%17%7%
270
May1st to 15thDay
22%8%26%23%11%8%
288
16th to endDay
16%319%27%18%15%
331
June1st to 15thDay
9%113%28%31%15%
399
16th to endDay
6%419%30%25%13%
495
July1st to 15thDay
16%113%28%26%13%
475
16th to endDay
8%26%23%29%28%
361
August1st to 15thDay
11%7%19%33%26%
313
16th to endDay
12%15%24%34%22%
332
September1st to 15thDay
16%19%18%34%19%
315
16th to endDay
14%11%24%29%19%
314
October1st to 15thDay
14%120%27%24%11%
315
16th to endDay
16%8%26%25%17%4
201
November1st to 15thDay
20%6%23%31%12%5%
135
16th to endDay
20%11%28%27%11%1
135
December1st to 15thDay
18%13%34%22%8%3
94
16th to endDay
23%20%38%14%2
96
January1st to 15thNight
21%10%36%27%5%
900
16th to endNight
22%8%38%27%3
788
February1st to 15thNight
24%7%36%28%1
704
16th to endNight
23%7%39%25%3
631
March1st to 15thNight
21%8%34%28%6%
720
16th to endNight
18%7%29%32%10%
739
April1st to 15thNight
14%6%34%30%13%
539
16th to endNight
14%7%26%34%15%1
540
May1st to 15thNight
19%422%33%17%2
540
16th to endNight
6%116%39%28%7%
563
June1st to 15thNight
7%211%40%34%4
540
16th to endNight
5%19%40%38%3
540
July1st to 15thNight
13%17%30%43%2
510
16th to endNight
7%5%31%43%11%
564
August1st to 15thNight
5%1431%47%10%
539
16th to endNight
6%433%48%6%
573
September1st to 15thNight
14%17%30%39%6%
627
16th to endNight
10%213%28%38%7%
717
October1st to 15thNight
12%317%32%28%6%
720
16th to endNight
17%428%31%17%1
768
November1st to 15thNight
13%7%26%30%20%1
760
16th to endNight
19%5%30%30%12%
780
December1st to 15thNight
25%5%28%29%10%1
728
16th to endNight
28%9%27%29%5%
849
Page generated at 2017-12-03 11:16:48. Version ac04

Copyright 2017 A. Danko


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