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 2005-11-06 to 2024-01-14.

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
49%
23560
22%
74585
16%
23501
56%
23501
27%
45837

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
28%
950
24%
2458
8%
946
40%
946
27%
1594
January11th to 20thNight
30%
920
24%
2392
10%
920
39%
920
26%
1623
January21st to endNight
26%
886
24%
2470
9%
886
37%
886
24%
1640
February1st to 10thNight
26%
720
23%
2160
9%
720
36%
720
23%
1423
February11th to 20thNight
28%
703
20%
2099
8%
700
38%
700
22%
1385
February21st to endNight
19%
592
19%
1776
7%
592
29%
592
17%
1257
March1st to 10thNight
29%
640
24%
2080
13%
640
40%
640
24%
1284
March11th to 20thNight
32%
540
19%
1980
12%
540
42%
540
19%
1285
March21st to endNight
34%
594
24%
2084
15%
594
47%
594
28%
1173
April1st to 10thNight
35%
540
24%
1800
16%
540
45%
540
23%
1110
April11th to 20thNight
38%
533
24%
1775
17%
533
49%
533
26%
1060
April21st to endNight
49%
540
29%
1800
22%
540
61%
540
35%
964
May1st to 10thNight
53%
540
25%
1800
20%
540
64%
540
36%
966
May11th to 20thNight
56%
531
19%
1769
20%
531
60%
531
31%
1025
May21st to endNight
65%
584
19%
1938
17%
582
70%
582
32%
1120
June1st to 10thNight
67%
540
15%
1645
15%
540
68%
540
28%
1061
June11th to 20thNight
75%
540
19%
1522
19%
540
76%
540
38%
909
June21st to endNight
72%
540
15%
1620
17%
540
72%
540
28%
1042
July1st to 10thNight
77%
525
12%
1575
14%
525
77%
525
25%
1044
July11th to 20thNight
77%
522
13%
1566
14%
522
77%
522
25%
1043
July21st to endNight
77%
591
13%
1803
16%
558
78%
558
27%
1144
August1st to 10thNight
83%
537
11%
1778
14%
534
84%
534
32%
1038
August11th to 20thNight
75%
534
15%
1776
17%
534
75%
534
22%
1173
August21st to endNight
70%
594
16%
1980
19%
594
70%
594
24%
1293
September1st to 10thNight
71%
540
21%
1800
23%
540
72%
540
28%
1117
September11th to 20thNight
67%
562
24%
1822
24%
562
68%
562
29%
1117
September21st to endNight
66%
720
29%
1980
23%
720
68%
720
37%
1183
October1st to 10thNight
65%
720
29%
2088
23%
720
68%
720
42%
1150
October11th to 20thNight
57%
720
34%
2160
25%
720
67%
720
40%
1179
October21st to endNight
52%
792
32%
2376
26%
792
58%
792
35%
1348
November1st to 10thNight
54%
740
31%
2220
24%
740
62%
740
37%
1245
November11th to 20thNight
45%
760
30%
2379
21%
760
56%
760
34%
1318
November21st to endNight
42%
760
28%
2470
19%
760
53%
760
27%
1480
December1st to 10thNight
36%
760
26%
2470
17%
760
48%
760
25%
1535
December11th to 20thNight
33%
759
23%
2907
14%
758
42%
758
19%
1850
December21st to endNight
30%
991
13%
4267
9%
978
36%
978
14%
2659

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
12%6%36%6%45%5%6%7%40%
74579
Night
12%6%25%5%3445%8%46%
75116
TransparencyDay
41%8%10%17%18%6%
74312
Night
36%7%12%18%19%8%
74904
SeeingDay
15%9%20%24%22%11%
13753
Night
15%8%22%29%21%5%
23567

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 10thDay
19%7%25%424446%43%
1707
11th to 20thDay
19%7%35%424336%43%
1647
21st to endDay
18%8%34434345%44%
1881
February1st to 10thDay
19%7%36%43445%6%38%
1800
11th to 20thDay
19%7%35%42445%7%40%
1748
21st to endDay
16%10%47%6%3345%7%35%
1480
March1st to 10thDay
17%7%37%5%345%46%40%
1894
11th to 20thDay
16%8%37%6%3445%6%39%
1980
21st to endDay
11%6%36%5%45%5%6%7%42%
2272
April1st to 10thDay
11%6%25%6%36%5%6%7%42%
2160
11th to 20thDay
16%6%35%6%35%5%6%7%40%
2134
21st to endDay
9%5%35%5%35%5%6%8%46%
2160
May1st to 10thDay
12%5%36%5%35%48%8%42%
2160
11th to 20thDay
10%6%26%6%46%6%6%8%40%
2124
21st to endDay
8%436%7%5%7%6%9%9%36%
2337
June1st to 10thDay
9%6%37%7%5%7%7%8%10%31%
2284
11th to 20thDay
5%427%7%49%7%9%10%36%
2410
21st to endDay
7%5%37%9%49%8%8%11%30%
2340
July1st to 10thDay
8%6%48%9%6%8%8%8%9%25%
2340
11th to 20thDay
8%6%37%8%5%8%9%8%10%26%
2340
21st to endDay
8%5%47%8%5%7%7%8%10%31%
2406
August1st to 10thDay
5%5%37%8%6%7%7%8%9%34%
2148
11th to 20thDay
10%6%38%7%5%6%7%6%8%33%
2125
21st to endDay
13%427%7%47%7%6%9%33%
2376
September1st to 10thDay
9%6%37%7%5%7%6%6%8%35%
2160
11th to 20thDay
12%6%26%6%35%5%6%7%41%
2120
21st to endDay
10%5%25%5%2446%7%50%
1980
October1st to 10thDay
6%425%5%345%5%6%55%
1868
11th to 20thDay
9%426%43435%7%53%
1800
21st to endDay
11%5%24433446%55%
1980
November1st to 10thDay
11%6%235%25%45%5%53%
1858
11th to 20thDay
11%6%25%434346%52%
1796
21st to endDay
15%6%245%2445%6%46%
1710
December1st to 10thDay
16%6%35%43445%6%43%
1710
11th to 20thDay
16%9%36%6%3344441%
2153
21st to endDay
16%7%35%435%5%5%7%40%
3191
January1st to 10thNight
19%7%34323347%46%
2458
11th to 20thNight
18%7%35%423445%45%
2392
21st to endNight
20%7%35%32434443%
2470
February1st to 10thNight
18%7%34434446%41%
2160
11th to 20thNight
20%7%35%423346%42%
2098
21st to endNight
20%8%46%6%35%45%6%36%
1776
March1st to 10thNight
14%7%26%43445%7%45%
2080
11th to 20thNight
15%7%35%6%35%5%5%7%39%
1980
21st to endNight
12%5%3443435%7%50%
2084
April1st to 10thNight
13%6%25%5%35%45%7%46%
1800
11th to 20thNight
14%6%245%345%5%7%46%
1775
21st to endNight
9%42342345%8%55%
1800
May1st to 10thNight
9%414325%45%8%55%
1800
11th to 20thNight
8%426%5%345%6%9%47%
1769
21st to endNight
6%425%6%35%47%11%46%
1938
June1st to 10thNight
7%5%26%6%46%6%7%10%40%
1645
11th to 20thNight
4325%435%6%8%10%50%
1522
21st to endNight
5%5%36%6%35%8%8%13%39%
1620
July1st to 10thNight
6%5%25%6%47%6%10%13%36%
1620
11th to 20thNight
6%425%6%47%8%9%13%37%
1620
21st to endNight
5%4246%47%5%10%13%40%
1909
August1st to 10thNight
3325%5%46%8%8%13%45%
1790
11th to 20thNight
6%5%25%6%5%7%7%8%11%37%
1776
21st to endNight
10%6%26%5%36%6%8%11%38%
1980
September1st to 10thNight
8%426%6%35%6%8%10%43%
1800
11th to 20thNight
9%6%25%5%35%6%6%9%45%
1822
21st to endNight
8%5%25%5%2445%8%52%
1980
October1st to 10thNight
6%424424447%59%
2088
11th to 20thNight
8%424324446%57%
2160
21st to endNight
11%6%24323345%56%
2376
November1st to 10thNight
11%424424345%58%
2220
11th to 20thNight
12%5%2332345%6%55%
2379
21st to endNight
14%6%345%3345%5%48%
2470
December1st to 10thNight
17%7%35%42435%6%47%
2470
11th to 20thNight
15%9%35%435%345%43%
3042
21st to endNight
19%10%36%423345%42%
4447

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
42%46%17%23%8%
1708
11th to 20thDay
44%4313%26%9%
1647
21st to endDay
44%35%14%24%10%
1881
February1st to 10thDay
47%47%14%17%10%
1800
11th to 20thDay
45%46%14%22%9%
1758
21st to endDay
49%5%6%14%16%10%
1480
March1st to 10thDay
45%5%6%16%19%9%
1894
11th to 20thDay
47%5%9%12%20%7%
1980
21st to endDay
39%6%10%17%22%6%
2272
April1st to 10thDay
40%8%9%17%19%8%
2160
11th to 20thDay
44%5%7%17%19%7%
2134
21st to endDay
34%7%10%21%24%3
2160
May1st to 10thDay
38%7%10%19%20%5%
2160
11th to 20thDay
40%8%12%24%15%2
2128
21st to endDay
40%10%13%22%14%1
2337
June1st to 10thDay
44%10%14%21%10%1
2284
11th to 20thDay
38%11%16%21%12%2
2410
21st to endDay
44%12%15%21%7%1
2340
July1st to 10thDay
50%14%16%14%6%1
2276
11th to 20thDay
46%15%18%16%42
2271
21st to endDay
44%12%18%18%7%1
2272
August1st to 10thDay
41%12%19%18%9%
2136
11th to 20thDay
47%12%16%17%7%2
2125
21st to endDay
44%12%15%17%10%3
2376
September1st to 10thDay
44%10%12%16%14%4
2160
11th to 20thDay
41%8%10%18%16%7%
2120
21st to endDay
33%7%11%21%19%9%
1980
October1st to 10thDay
29%7%10%18%24%12%
1868
11th to 20thDay
31%47%15%30%14%
1800
21st to endDay
31%46%16%29%15%
1980
November1st to 10thDay
32%47%16%27%13%
1858
11th to 20thDay
34%46%15%28%12%
1796
21st to endDay
39%5%7%17%22%11%
1710
December1st to 10thDay
42%5%8%18%18%8%
1710
11th to 20thDay
47%46%11%24%8%
2150
21st to endDay
42%6%7%19%22%3
3191
January1st to 10thNight
40%37%15%26%8%
2458
11th to 20thNight
43%5%417%22%9%
2392
21st to endNight
45%35%13%24%10%
2470
February1st to 10thNight
44%48%16%19%10%
2160
11th to 20thNight
45%45%15%21%11%
2099
21st to endNight
50%7%5%13%13%12%
1776
March1st to 10thNight
39%5%8%15%22%10%
2080
11th to 20thNight
45%6%10%13%18%7%
1980
21st to endNight
34%5%12%19%24%7%
2084
April1st to 10thNight
39%6%9%17%18%10%
1800
11th to 20thNight
37%5%11%20%18%9%
1775
21st to endNight
28%6%10%22%27%7%
1800
May1st to 10thNight
28%6%10%27%22%7%
1800
11th to 20thNight
32%8%16%23%19%2
1770
21st to endNight
31%8%18%25%17%2
1939
June1st to 10thNight
37%10%17%23%13%1
1645
11th to 20thNight
28%9%19%28%13%2
1522
21st to endNight
33%13%20%21%12%1
1620
July1st to 10thNight
35%15%23%18%7%2
1575
11th to 20thNight
32%17%27%19%42
1566
21st to endNight
31%15%25%20%7%1
1803
August1st to 10thNight
26%13%32%19%10%
1778
11th to 20thNight
35%16%21%18%9%2
1776
21st to endNight
36%13%21%16%10%3
1980
September1st to 10thNight
34%10%18%18%14%6%
1800
11th to 20thNight
34%9%15%17%15%9%
1822
21st to endNight
31%6%12%23%18%10%
1980
October1st to 10thNight
26%6%10%18%25%15%
2088
11th to 20thNight
26%6%7%20%27%15%
2160
21st to endNight
32%36%16%25%18%
2376
November1st to 10thNight
30%47%19%24%16%
2220
11th to 20thNight
31%47%15%28%15%
2379
21st to endNight
39%36%19%21%12%
2470
December1st to 10thNight
40%5%8%21%20%7%
2470
11th to 20thNight
45%46%11%22%12%
3044
21st to endNight
46%46%17%20%7%
4447

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
25%20%34%17%31
270
11th to 20thDay
25%18%32%18%7%1
249
21st to endDay
24%26%37%9%3
264
February1st to 10thDay
30%22%29%14%5%
240
11th to 20thDay
34%19%28%17%3
240
21st to endDay
23%30%34%12%2
198
March1st to 10thDay
25%19%32%21%3
240
11th to 20thDay
24%23%35%15%3
240
21st to endDay
19%19%30%23%8%1
358
April1st to 10thDay
17%15%32%25%10%
420
11th to 20thDay
24%13%28%23%11%1
412
21st to endDay
11%12%29%33%13%2
420
May1st to 10thDay
13%10%28%29%17%4
423
11th to 20thDay
15%321%32%19%9%
447
21st to endDay
7%320%29%28%13%
485
June1st to 10thDay
13%212%28%29%15%
522
11th to 20thDay
7%314%30%35%11%
630
21st to endDay
10%312%26%30%18%
630
July1st to 10thDay
7%29%22%42%18%
621
11th to 20thDay
8%16%22%37%25%
618
21st to endDay
10%17%24%35%22%
544
August1st to 10thDay
5%27%21%35%31%
446
11th to 20thDay
13%25%17%38%26%
439
21st to endDay
13%37%20%31%26%
495
September1st to 10thDay
9%110%24%36%20%
450
11th to 20thDay
12%49%25%37%12%
450
21st to endDay
12%212%31%33%10%
450
October1st to 10thDay
7%7%21%35%22%9%
338
11th to 20thDay
10%6%23%31%22%7%
270
21st to endDay
20%11%20%30%14%4
297
November1st to 10thDay
18%7%27%31%16%2
270
11th to 20thDay
15%14%35%24%12%
270
21st to endDay
17%19%32%19%9%3
270
December1st to 10thDay
22%11%33%24%8%1
270
11th to 20thDay
23%16%36%19%5%1
270
21st to endDay
25%19%28%21%6%1
297
January1st to 10thNight
24%15%31%25%6%
950
11th to 20thNight
23%11%33%26%7%
920
21st to endNight
25%13%32%26%4
886
February1st to 10thNight
22%13%36%24%5%
720
11th to 20thNight
28%15%27%26%5%
703
21st to endNight
26%17%35%20%2
592
March1st to 10thNight
20%13%34%27%6%
640
11th to 20thNight
18%12%34%28%8%1
540
21st to endNight
16%11%36%29%9%
594
April1st to 10thNight
16%10%36%27%10%1
540
11th to 20thNight
17%11%31%27%14%1
533
21st to endNight
10%8%29%37%15%1
540
May1st to 10thNight
11%428%39%16%1
540
11th to 20thNight
9%322%39%24%3
531
21st to endNight
6%219%35%30%7%
584
June1st to 10thNight
9%111%37%35%7%
540
11th to 20thNight
4111%31%43%10%
540
21st to endNight
7%29%28%41%14%
540
July1st to 10thNight
6%2426%46%17%
525
11th to 20thNight
6%1321%48%20%
522
21st to endNight
6%16%24%47%16%
591
August1st to 10thNight
31320%48%24%
537
11th to 20thNight
7%1420%51%18%
534
21st to endNight
11%35%22%40%20%
594
September1st to 10thNight
8%26%26%44%13%
540
11th to 20thNight
10%48%29%40%8%
562
21st to endNight
11%211%32%39%6%
720
October1st to 10thNight
8%317%35%33%3
720
11th to 20thNight
9%5%23%34%24%4
720
21st to endNight
15%9%20%33%21%2
792
November1st to 10thNight
13%6%21%35%21%3
740
11th to 20thNight
15%8%27%34%15%1
760
21st to endNight
18%9%26%30%14%1
760
December1st to 10thNight
21%11%28%28%11%
760
11th to 20thNight
23%8%32%29%9%
760
21st to endNight
28%12%26%28%6%
997
Page generated at 2024-01-11 12:32:01. Version ac07

Copyright 2024 Attilla Danko


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