Star Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Lake Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
51%
15313
23%
47173
17%
15267
57%
15267
29%
28829

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
32%
900
24%
2327
9%
895
42%
895
27%
1523
January16th to endNight
26%
891
24%
2427
9%
891
36%
891
25%
1609
February1st to 15thNight
32%
704
26%
2112
11%
701
43%
701
26%
1321
February16th to endNight
26%
631
24%
1893
8%
631
37%
631
23%
1217
March1st to 15thNight
29%
606
23%
2046
13%
606
40%
606
22%
1290
March16th to endNight
41%
576
23%
2049
16%
576
52%
576
30%
1126
April1st to 15thNight
39%
539
23%
1797
17%
539
49%
539
26%
1064
April16th to endNight
47%
540
26%
1800
21%
540
58%
540
32%
992
May1st to 15thNight
54%
539
22%
1800
17%
539
64%
539
33%
1015
May16th to endNight
64%
563
21%
1869
20%
561
69%
561
33%
1061
June1st to 15thNight
74%
540
15%
1574
15%
540
75%
540
33%
980
June16th to endNight
74%
540
16%
1614
17%
540
75%
540
30%
1019
July1st to 15thNight
81%
510
15%
1530
17%
510
81%
510
27%
988
July16th to endNight
76%
564
13%
1680
15%
531
76%
531
25%
1104
August1st to 15thNight
80%
539
12%
1788
15%
536
80%
536
28%
1105
August16th to endNight
70%
573
16%
1910
20%
573
70%
573
21%
1285
September1st to 15thNight
71%
540
20%
1800
23%
540
72%
540
29%
1098
September16th to endNight
68%
644
27%
1858
23%
644
70%
644
34%
1124
October1st to 15thNight
64%
660
33%
1936
26%
660
68%
660
43%
1034
October16th to endNight
55%
704
34%
2112
27%
704
62%
704
39%
1152
November1st to 15thNight
51%
700
33%
2103
24%
700
61%
700
36%
1192
November16th to endNight
46%
720
30%
2340
23%
720
56%
720
33%
1293
December1st to 15thNight
37%
720
24%
2340
16%
720
47%
720
24%
1474
December16th to endNight
31%
870
18%
2468
11%
870
37%
870
20%
1763

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
11%6%26%6%35%5%6%7%38%
47671
Night
11%5%2442445%8%46%
47380
TransparencyDay
43%7%10%16%17%5%
47381
Night
35%6%11%18%18%8%
47175
SeeingDay
13%5%15%25%26%14%
5415
Night
14%6%21%28%22%5%
15314

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
18%6%24323345%43%
1611
16th to endDay
19%6%3342433444%
1794
February1st to 15thDay
15%6%25%42345%6%42%
1750
16th to endDay
16%8%345%23347%40%
1580
March1st to 15thDay
18%7%26%423445%39%
1923
16th to endDay
11%6%36%5%35%45%6%41%
2173
April1st to 15thDay
12%5%25%5%35%46%6%40%
2151
16th to endDay
10%5%25%6%36%5%5%8%40%
2160
May1st to 15thDay
11%6%36%5%45%5%7%7%36%
2151
16th to endDay
9%436%7%46%5%7%8%35%
2244
June1st to 15thDay
6%426%7%48%7%9%11%29%
2351
16th to endDay
6%437%9%49%8%8%9%28%
2340
July1st to 15thDay
8%6%37%9%6%8%8%7%8%24%
2340
16th to endDay
8%5%48%9%6%8%7%8%9%23%
2372
August1st to 15thDay
7%6%37%8%6%7%8%7%9%28%
2160
16th to endDay
13%5%28%8%47%7%5%8%28%
2292
September1st to 15thDay
11%6%26%6%5%6%5%6%6%36%
2160
16th to endDay
11%5%26%5%25%5%5%7%41%
1927
October1st to 15thDay
6%415%43445%6%52%
1691
16th to endDay
9%324322346%56%
1760
November1st to 15thDay
9%6%24424346%51%
1752
16th to endDay
12%5%23323335%54%
1620
December1st to 15thDay
17%7%35%33435%5%40%
1620
16th to endDay
18%9%35%423446%36%
1749
January1st to 15thNight
16%6%34323336%46%
2327
16th to endNight
19%7%25%323345%43%
2427
February1st to 15thNight
15%6%24423336%46%
2103
16th to endNight
17%6%34424345%44%
1893
March1st to 15thNight
15%6%35%433347%42%
2046
16th to endNight
11%42332335%7%51%
2049
April1st to 15thNight
10%425%424447%48%
1797
16th to endNight
9%41342446%8%51%
1800
May1st to 15thNight
8%5%1432446%10%49%
1799
16th to endNight
5%325%5%2447%9%48%
1869
June1st to 15thNight
4425%6%46%5%6%11%43%
1574
16th to endNight
4325%5%35%7%7%12%41%
1614
July1st to 15thNight
5%3245%47%6%8%11%39%
1620
16th to endNight
5%3246%47%6%9%14%34%
1795
August1st to 15thNight
3315%5%46%8%8%12%39%
1800
16th to endNight
9%5%26%5%36%6%8%10%35%
1910
September1st to 15thNight
8%326%435%5%6%9%44%
1800
16th to endNight
6%5%245%2445%10%47%
1858
October1st to 15thNight
6%324324346%59%
1936
16th to endNight
10%41321323460%
2112
November1st to 15thNight
9%5%23323345%55%
2103
16th to endNight
12%423322235%55%
2340
December1st to 15thNight
15%6%34424346%44%
2340
16th to endNight
20%8%46%5%24335%35%
2468

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
42%3414%24%10%
1612
16th to endDay
44%3412%25%9%
1794
February1st to 15thDay
41%47%16%21%9%
1752
16th to endDay
44%35%16%21%8%
1580
March1st to 15thDay
46%5%5%17%19%5%
1923
16th to endDay
42%49%15%22%6%
2175
April1st to 15thDay
41%6%8%16%19%7%
2151
16th to endDay
39%6%10%20%19%3
2160
May1st to 15thDay
43%6%11%15%16%5%
2151
16th to endDay
42%8%12%21%14%
2248
June1st to 15thDay
43%10%14%20%10%
2351
16th to endDay
46%11%14%18%8%1
2340
July1st to 15thDay
51%13%14%12%6%1
2201
16th to endDay
52%11%16%14%4
2224
August1st to 15thDay
47%11%16%14%8%1
2148
16th to endDay
50%11%14%13%7%2
2292
September1st to 15thDay
45%9%12%16%11%4
2160
16th to endDay
39%6%10%16%19%6%
1927
October1st to 15thDay
31%5%8%14%25%15%
1691
16th to endDay
28%36%10%33%17%
1760
November1st to 15thDay
33%37%15%30%9%
1752
16th to endDay
32%35%14%26%16%
1620
December1st to 15thDay
46%47%18%16%7%
1620
16th to endDay
48%5%6%17%17%4
1749
January1st to 15thNight
40%36%14%25%10%
2327
16th to endNight
43%35%14%22%9%
2427
February1st to 15thNight
40%36%17%21%12%
2112
16th to endNight
42%4417%20%11%
1893
March1st to 15thNight
42%48%15%22%6%
2046
16th to endNight
32%412%19%24%6%
2049
April1st to 15thNight
36%49%20%17%10%
1797
16th to endNight
30%6%12%21%22%8%
1800
May1st to 15thNight
30%6%12%24%18%7%
1800
16th to endNight
30%7%15%26%18%1
1871
June1st to 15thNight
32%8%18%25%13%
1574
16th to endNight
31%12%21%21%12%
1614
July1st to 15thNight
32%13%23%20%7%2
1530
16th to endNight
35%14%25%20%4
1680
August1st to 15thNight
30%13%27%17%9%
1788
16th to endNight
37%14%19%16%9%2
1910
September1st to 15thNight
34%8%18%19%12%6%
1800
16th to endNight
32%6%13%19%18%9%
1858
October1st to 15thNight
25%48%18%26%17%
1936
16th to endNight
27%45%13%26%22%
2112
November1st to 15thNight
30%46%16%28%13%
2103
16th to endNight
32%25%17%23%18%
2340
December1st to 15thNight
41%48%20%19%5%
2340
16th to endNight
52%36%14%17%5%
2468

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%14%30%20%7%2
90
16th to endDay
16%32%34%13%3
96
February1st to 15thDay
17%15%36%25%4
90
16th to endDay
22%14%32%27%3
81
March1st to 15thDay
31%18%34%15%
90
16th to endDay
19%13%21%30%14%1
159
April1st to 15thDay
19%11%24%28%15%
270
16th to endDay
13%7%23%35%17%2
270
May1st to 15thDay
15%7%21%31%16%6%
288
16th to endDay
12%319%28%22%12%
331
June1st to 15thDay
11%19%29%34%13%
423
16th to endDay
9%10%27%32%18%
495
July1st to 15thDay
8%16%21%41%20%
475
16th to endDay
8%423%36%26%
421
August1st to 15thDay
11%218%36%29%
313
16th to endDay
13%1418%35%26%
332
September1st to 15thDay
10%29%20%34%21%
315
16th to endDay
11%6%27%38%14%
283
October1st to 15thDay
6%5%18%29%27%12%
131
16th to endDay
15%7%12%31%23%9%
96
November1st to 15thDay
23%434%25%11%1
90
16th to endDay
12%15%42%16%8%4
90
December1st to 15thDay
26%8%38%20%23
90
16th to endDay
27%18%25%28%1
96
January1st to 15thNight
20%13%30%26%8%
900
16th to endNight
24%11%33%25%5%
891
February1st to 15thNight
19%13%33%27%6%
704
16th to endNight
22%16%32%25%3
631
March1st to 15thNight
18%12%34%27%6%
606
16th to endNight
14%7%33%30%13%
576
April1st to 15thNight
12%10%34%28%13%
539
16th to endNight
11%7%30%34%15%
540
May1st to 15thNight
11%325%38%19%1
540
16th to endNight
6%219%38%28%5%
563
June1st to 15thNight
5%9%35%42%6%
540
16th to endNight
5%18%27%42%15%
540
July1st to 15thNight
5%226%45%19%
510
16th to endNight
6%1320%46%20%
564
August1st to 15thNight
5%318%48%24%
539
16th to endNight
11%1320%42%21%
573
September1st to 15thNight
9%26%27%39%15%
540
16th to endNight
10%19%31%40%6%
644
October1st to 15thNight
8%217%32%34%3
660
16th to endNight
12%5%22%29%26%3
704
November1st to 15thNight
12%6%24%32%19%4
700
16th to endNight
15%8%26%32%15%1
720
December1st to 15thNight
20%9%29%30%11%
720
16th to endNight
26%10%26%27%7%
870
Page generated at 2017-09-24 08:15:56. Version ac04

Copyright 2017 A. Danko


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