Oak Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Lake Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
30%
14733
14%
46890
8%
14701
37%
14701
17%
32816

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%
719
8%
2506
3%
716
21%
716
7%
1986
January16th to endNight
18%
768
12%
2550
6%
768
26%
768
10%
1961
February1st to 15thNight
16%
704
10%
2287
3%
701
24%
701
11%
1753
February16th to endNight
20%
631
14%
2002
5%
631
32%
631
13%
1458
March1st to 15thNight
19%
720
14%
2019
6%
720
27%
720
15%
1495
March16th to endNight
29%
768
20%
2089
9%
768
38%
768
24%
1408
April1st to 15thNight
23%
718
15%
1796
5%
718
29%
718
19%
1323
April16th to endNight
32%
612
19%
1692
8%
612
39%
612
24%
1145
May1st to 15thNight
36%
411
17%
1491
12%
411
45%
411
19%
960
May16th to endNight
39%
374
15%
1497
12%
374
50%
374
21%
882
June1st to 15thNight
35%
360
11%
1440
8%
360
46%
360
17%
909
June16th to endNight
46%
360
10%
1440
13%
360
51%
360
20%
888
July1st to 15thNight
51%
340
15%
1360
20%
340
58%
340
31%
706
July16th to endNight
53%
388
16%
1429
14%
365
60%
365
30%
771
August1st to 15thNight
56%
539
15%
1609
10%
536
59%
536
32%
987
August16th to endNight
52%
660
21%
1806
10%
660
58%
660
36%
1093
September1st to 15thNight
46%
720
18%
1800
9%
720
50%
720
31%
1191
September16th to endNight
48%
669
22%
1850
14%
669
52%
669
30%
1185
October1st to 15thNight
33%
660
17%
1980
11%
660
41%
660
19%
1392
October16th to endNight
20%
704
11%
2131
4%
704
30%
704
11%
1651
November1st to 15thNight
31%
700
18%
2388
14%
700
38%
700
17%
1609
November16th to endNight
21%
720
11%
2520
6%
720
28%
720
10%
1915
December1st to 15thNight
14%
720
6%
2520
2%
720
19%
720
8%
1990
December16th to endNight
13%
768
8%
2688
2%
768
19%
768
7%
2158

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%5%3445%6%32%
47912
Night
17%9%36%5%34446%34%
47062
Cloud CoverDay
17%9%36%6%3445%6%32%
47922
Night
16%9%36%5%3445%6%34%
47067
TransparencyDay
51%5%11%19%10%1
47602
Night
50%6%12%20%10%
46890
SeeingDay
21%12%30%20%9%4
5398
Night
22%12%30%24%10%1
14735

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
19%16%5%7%423336%24%
1432
16th to endDay
15%15%6%10%8%45%34422%
1673
February1st to 15thDay
13%15%5%12%7%445%3421%
1575
16th to endDay
16%15%48%6%2433327%
1470
March1st to 15thDay
17%11%47%7%3435%5%28%
1927
16th to endDay
15%9%36%5%23445%39%
2134
April1st to 15thDay
23%9%35%424245%32%
2152
16th to endDay
20%8%25%423336%38%
2278
May1st to 15thDay
19%7%26%5%35%45%5%34%
2460
16th to endDay
15%5%246%35%5%5%7%38%
2618
June1st to 15thDay
21%6%25%5%35%5%47%30%
2520
16th to endDay
15%6%26%436%5%5%8%33%
2520
July1st to 15thDay
13%4146%45%5%6%9%38%
2520
16th to endDay
10%6%36%6%46%6%6%8%34%
2640
August1st to 15thDay
12%6%26%6%45%6%6%8%34%
2340
16th to endDay
14%5%25%5%25%5%6%8%38%
2384
September1st to 15thDay
16%5%245%35%45%6%41%
2160
16th to endDay
15%6%35%42345%6%43%
1832
October1st to 15thDay
22%7%26%6%34447%31%
1650
16th to endDay
29%9%35%6%33345%23%
1741
November1st to 15thDay
18%8%35%6%35%446%34%
1470
16th to endDay
23%13%47%5%2445%6%22%
1440
December1st to 15thDay
20%17%6%9%6%3434319%
1440
16th to endDay
22%17%8%7%6%34235%19%
1536
January1st to 15thNight
20%16%5%7%7%3443421%
2506
16th to endNight
15%14%5%9%8%245%35%24%
2550
February1st to 15thNight
13%14%6%8%7%35%5%45%25%
2285
16th to endNight
16%11%46%5%445%5%6%28%
2002
March1st to 15thNight
18%10%47%5%35%345%32%
2007
16th to endNight
15%7%36%5%23435%42%
2089
April1st to 15thNight
20%8%25%424446%34%
1796
16th to endNight
16%7%244235%5%6%40%
1692
May1st to 15thNight
17%6%35%42445%6%38%
1491
16th to endNight
12%4245%345%5%6%44%
1495
June1st to 15thNight
15%6%25%4345%5%8%37%
1440
16th to endNight
12%5%25%5%36%5%47%41%
1440
July1st to 15thNight
8%2144245%5%7%52%
1440
16th to endNight
9%323435%47%8%49%
1526
August1st to 15thNight
9%5%1443346%9%47%
1620
16th to endNight
7%42442446%7%50%
1806
September1st to 15thNight
14%5%245%2345%8%44%
1800
16th to endNight
16%6%23323345%48%
1850
October1st to 15thNight
21%5%35%43435%6%35%
1980
16th to endNight
24%10%36%5%3445%5%26%
2131
November1st to 15thNight
18%7%35%434347%36%
2388
16th to endNight
23%10%36%6%345%5%6%25%
2520
December1st to 15thNight
21%15%6%6%5%34446%21%
2520
16th to endNight
23%14%5%9%5%3344420%
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
19%16%5%8%5%23346%25%
1432
16th to endDay
14%14%7%10%7%35%34422%
1673
February1st to 15thDay
13%15%6%12%8%345%45%20%
1575
16th to endDay
16%15%5%8%7%3433427%
1470
March1st to 15thDay
16%12%5%7%7%34445%28%
1938
16th to endDay
15%9%36%5%23345%39%
2133
April1st to 15thDay
23%9%45%423345%32%
2152
16th to endDay
20%8%25%5%23346%38%
2278
May1st to 15thDay
19%8%25%5%35%45%5%33%
2460
16th to endDay
14%5%25%5%35%5%47%38%
2618
June1st to 15thDay
20%6%25%6%35%447%30%
2520
16th to endDay
15%6%36%5%36%5%6%8%33%
2520
July1st to 15thDay
12%4246%36%5%6%9%37%
2520
16th to endDay
10%6%26%6%46%6%5%9%34%
2640
August1st to 15thDay
11%7%36%6%45%6%6%7%34%
2340
16th to endDay
13%5%26%5%35%5%6%7%38%
2384
September1st to 15thDay
16%5%245%345%46%41%
2160
16th to endDay
15%6%35%42435%6%42%
1832
October1st to 15thDay
21%7%36%6%4445%7%30%
1650
16th to endDay
28%10%36%5%34435%23%
1741
November1st to 15thDay
17%8%35%6%34445%34%
1470
16th to endDay
23%13%47%5%3345%5%22%
1440
December1st to 15thDay
20%17%6%9%6%3434319%
1440
16th to endDay
21%17%7%8%6%2433419%
1536
January1st to 15thNight
20%15%6%8%6%3443421%
2506
16th to endNight
14%14%5%9%7%35%445%24%
2550
February1st to 15thNight
13%14%6%8%7%35%5%45%25%
2278
16th to endNight
16%12%46%5%45%5%5%6%28%
2002
March1st to 15thNight
19%9%46%5%34445%31%
2019
16th to endNight
14%7%36%423345%41%
2089
April1st to 15thNight
20%8%35%42445%6%34%
1796
16th to endNight
16%7%244335%5%6%39%
1692
May1st to 15thNight
17%7%26%42445%6%38%
1491
16th to endNight
12%4245%35%45%6%44%
1495
June1st to 15thNight
15%6%26%5%3445%8%37%
1440
16th to endNight
12%5%25%5%35%5%47%40%
1440
July1st to 15thNight
8%2244245%5%8%51%
1440
16th to endNight
9%314425%37%8%49%
1526
August1st to 15thNight
9%5%145%2346%9%46%
1620
16th to endNight
7%42442446%8%49%
1806
September1st to 15thNight
14%5%1443345%7%45%
1800
16th to endNight
16%6%1332335%5%48%
1850
October1st to 15thNight
21%6%25%5%34446%35%
1980
16th to endNight
23%10%36%5%3445%5%25%
2131
November1st to 15thNight
18%7%35%43435%7%35%
2388
16th to endNight
23%9%36%5%35%5%5%6%25%
2520
December1st to 15thNight
21%15%5%7%5%3445%6%20%
2520
16th to endNight
23%14%6%8%6%34445%19%
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
61%412%13%6%
1433
16th to endDay
65%49%11%7%1
1673
February1st to 15thDay
65%5%10%13%4
1577
16th to endDay
61%39%12%11%
1470
March1st to 15thDay
58%414%15%6%1
1938
16th to endDay
47%47%21%15%3
2134
April1st to 15thDay
54%48%18%12%2
2152
16th to endDay
48%38%22%15%2
2278
May1st to 15thDay
50%5%8%19%14%1
2460
16th to endDay
44%7%12%20%13%1
2622
June1st to 15thDay
52%5%11%19%10%
2520
16th to endDay
47%6%12%20%11%1
2520
July1st to 15thDay
38%8%12%26%13%
2371
16th to endDay
45%7%14%22%9%
2474
August1st to 15thDay
45%6%16%19%10%
2327
16th to endDay
41%6%14%26%10%1
2384
September1st to 15thDay
42%5%12%25%12%
2160
16th to endDay
41%6%12%28%10%
1832
October1st to 15thDay
53%5%11%17%10%
1650
16th to endDay
63%5%11%14%6%
1741
November1st to 15thDay
51%5%14%17%9%1
1470
16th to endDay
62%5%12%12%5%1
1440
December1st to 15thDay
69%5%12%10%3
1440
16th to endDay
69%47%12%5%
1536
January1st to 15thNight
66%410%11%5%
2506
16th to endNight
61%5%7%16%8%
2550
February1st to 15thNight
60%6%12%15%5%
2287
16th to endNight
54%5%11%19%8%
2002
March1st to 15thNight
54%5%11%18%8%
2019
16th to endNight
44%410%21%16%2
2089
April1st to 15thNight
50%6%8%19%13%2
1796
16th to endNight
43%5%11%20%17%2
1692
May1st to 15thNight
45%5%10%19%15%3
1491
16th to endNight
38%6%12%24%15%2
1497
June1st to 15thNight
44%6%12%20%14%
1440
16th to endNight
41%7%14%22%13%1
1440
July1st to 15thNight
28%6%13%31%18%1
1360
16th to endNight
31%5%17%30%14%
1429
August1st to 15thNight
33%7%19%26%12%
1609
16th to endNight
31%6%14%31%14%
1806
September1st to 15thNight
38%6%15%26%12%1
1800
16th to endNight
38%5%12%32%11%
1850
October1st to 15thNight
49%6%11%21%11%
1980
16th to endNight
59%6%11%14%7%
2131
November1st to 15thNight
47%5%13%20%10%1
2388
16th to endNight
58%7%12%15%4
2520
December1st to 15thNight
64%6%13%13%3
2520
16th to endNight
67%5%9%10%6%
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
26%26%25%16%5%
60
16th to endDay
34%17%34%12%1
87
February1st to 15thDay
30%27%38%3
90
16th to endDay
35%17%32%12%1
129
March1st to 15thDay
27%12%35%21%4
270
16th to endDay
25%15%34%13%9%1
288
April1st to 15thDay
25%20%28%15%8%1
270
16th to endDay
23%17%28%17%9%3
270
May1st to 15thDay
32%11%25%17%5%7%
288
16th to endDay
19%13%37%16%8%3
331
June1st to 15thDay
24%10%32%23%9%
315
16th to endDay
16%9%34%25%10%3
315
July1st to 15thDay
14%6%29%29%13%6%
305
16th to endDay
13%7%33%26%12%6%
326
August1st to 15thDay
10%5%29%30%15%8%
313
16th to endDay
15%426%25%14%13%
332
September1st to 15thDay
14%8%26%20%17%12%
315
16th to endDay
18%8%25%24%13%10%
262
October1st to 15thDay
21%12%31%17%12%4
255
16th to endDay
34%14%27%18%4
269
November1st to 15thDay
20%7%33%27%8%2
124
16th to endDay
28%16%30%18%6%
60
December1st to 15thDay
36%21%25%13%3
60
16th to endDay
39%29%28%3
64
January1st to 15thNight
31%19%28%15%4
720
16th to endNight
22%15%33%22%5%1
768
February1st to 15thNight
22%17%35%20%2
704
16th to endNight
22%18%33%20%5%
631
March1st to 15thNight
25%17%33%20%3
720
16th to endNight
20%13%31%22%9%1
768
April1st to 15thNight
24%14%32%21%6%
718
16th to endNight
20%12%31%23%10%
612
May1st to 15thNight
23%6%29%26%13%1
411
16th to endNight
14%6%34%32%11%
375
June1st to 15thNight
17%8%32%28%12%
360
16th to endNight
13%6%26%41%11%
360
July1st to 15thNight
7%5%30%37%19%
340
16th to endNight
9%130%38%17%1
388
August1st to 15thNight
12%222%34%25%2
539
16th to endNight
10%425%30%26%2
660
September1st to 15thNight
16%5%26%28%20%3
720
16th to endNight
18%7%22%24%22%3
669
October1st to 15thNight
24%9%27%23%12%1
660
16th to endNight
29%14%28%21%6%
704
November1st to 15thNight
21%12%30%24%10%1
700
16th to endNight
29%14%28%19%6%
720
December1st to 15thNight
30%17%33%15%2
720
16th to endNight
31%15%31%17%3
768
Page generated at 2017-09-19 07:32:32. Version ac04

Copyright 2017 A. Danko


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