Tainter Lake Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tainter Lake Skies Observatory clear sky chart from 2005-11-06 to 2024-03-23.

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
36%
25122
15%
80809
9%
25027
42%
25027
20%
55109

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
29%
939
11%
4386
6%
926
36%
926
11%
3199
January11th to 20thNight
23%
947
9%
4372
5%
930
28%
930
8%
3354
January21st to endNight
24%
1033
7%
4597
3%
1023
29%
1023
8%
3503
February1st to 10thNight
27%
950
15%
2470
4%
950
34%
950
21%
1784
February11th to 20thNight
26%
929
18%
2404
5%
925
34%
925
23%
1667
February21st to endNight
26%
662
16%
1918
4%
662
36%
662
19%
1336
March1st to 10thNight
31%
717
17%
2237
10%
717
37%
717
20%
1495
March11th to 20thNight
33%
570
20%
2090
13%
570
43%
570
18%
1317
March21st to endNight
34%
600
17%
2124
15%
600
40%
600
17%
1448
April1st to 10thNight
27%
540
15%
1800
9%
540
36%
540
18%
1224
April11th to 20thNight
32%
533
16%
1775
11%
533
41%
533
17%
1239
April21st to endNight
31%
540
16%
1689
10%
540
40%
540
21%
1155
May1st to 10thNight
31%
540
14%
1450
7%
540
36%
540
22%
1048
May11th to 20thNight
39%
531
19%
1417
10%
531
44%
531
28%
960
May21st to endNight
46%
584
14%
1551
6%
582
50%
582
26%
1055
June1st to 10thNight
49%
540
15%
1440
6%
540
54%
540
34%
910
June11th to 20thNight
47%
540
14%
1440
6%
540
51%
540
32%
924
June21st to endNight
57%
540
16%
1440
8%
540
60%
540
37%
884
July1st to 10thNight
62%
525
18%
1400
9%
525
64%
525
46%
784
July11th to 20thNight
60%
522
19%
1392
10%
522
63%
522
41%
821
July21st to endNight
68%
591
22%
1487
13%
558
72%
558
48%
818
August1st to 10thNight
67%
537
22%
1534
18%
534
69%
534
36%
931
August11th to 20thNight
58%
534
22%
1600
20%
534
63%
534
33%
962
August21st to endNight
55%
594
21%
1951
21%
594
60%
594
33%
1109
September1st to 10thNight
55%
540
22%
1800
21%
540
61%
540
32%
1017
September11th to 20thNight
51%
540
26%
1800
21%
540
61%
540
34%
1012
September21st to endNight
41%
662
20%
2038
12%
662
48%
662
29%
1228
October1st to 10thNight
42%
720
21%
2160
15%
720
48%
720
30%
1324
October11th to 20thNight
31%
720
20%
2160
10%
720
40%
720
22%
1426
October21st to endNight
34%
792
16%
2466
10%
792
40%
792
19%
1687
November1st to 10thNight
32%
773
22%
2439
13%
773
43%
773
23%
1572
November11th to 20thNight
25%
950
15%
2660
6%
950
32%
950
18%
1928
November21st to endNight
27%
950
16%
2660
8%
950
34%
950
20%
1867
December1st to 10thNight
25%
950
11%
2660
4%
950
31%
950
17%
1969
December11th to 20thNight
21%
948
12%
3205
3%
948
28%
948
12%
2400
December21st to endNight
18%
1039
7%
4797
3%
1026
25%
1026
7%
3752

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
13%9%47%6%35%5%5%7%36%
78628
Night
13%9%47%6%3445%6%37%
81313
TransparencyDay
47%6%13%23%10%1
78328
Night
47%6%12%23%11%1
81133
SeeingDay
17%10%30%26%14%4
15046
Night
17%9%31%32%11%1
25156

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
10%17%9%12%7%34435%24%
2527
11th to 20thDay
6%11%5%12%10%7%10%10%45%19%
2530
21st to endDay
11%17%7%12%7%3445%6%23%
3016
February1st to 10thDay
9%10%5%9%7%45%6%6%7%32%
1710
11th to 20thDay
10%9%5%9%6%445%5%8%35%
1664
21st to endDay
11%11%5%8%6%25%5%6%8%32%
1535
March1st to 10thDay
14%10%47%7%35%5%47%35%
1961
11th to 20thDay
13%9%46%7%445%48%36%
2090
21st to endDay
19%10%46%6%35%45%7%31%
2276
April1st to 10thDay
16%10%46%6%35%45%7%33%
2160
11th to 20thDay
21%9%47%5%35%45%6%31%
2134
21st to endDay
21%10%36%6%45%5%5%6%28%
2268
May1st to 10thDay
18%7%36%6%35%5%5%6%34%
2510
11th to 20thDay
16%8%36%5%35%5%5%6%36%
2479
21st to endDay
15%7%35%6%46%5%6%8%37%
2725
June1st to 10thDay
13%5%35%5%345%5%9%44%
2520
11th to 20thDay
12%7%26%7%46%5%6%9%37%
2520
21st to endDay
10%5%25%5%36%6%7%10%40%
2520
July1st to 10thDay
8%3245%45%6%6%10%47%
2520
11th to 20thDay
9%425%5%345%7%10%46%
2520
21st to endDay
7%3245%36%6%7%9%48%
2743
August1st to 10thDay
9%5%36%5%46%6%7%9%41%
2392
11th to 20thDay
12%6%26%6%35%5%6%8%42%
2301
21st to endDay
10%5%244345%5%8%49%
2404
September1st to 10thDay
11%6%26%5%2445%9%46%
2160
11th to 20thDay
13%5%245%345%5%8%45%
2160
21st to endDay
17%6%35%43445%8%41%
1899
October1st to 10thDay
16%7%36%43446%6%41%
1800
11th to 20thDay
16%10%46%6%44447%35%
1800
21st to endDay
19%11%47%5%2345%5%35%
1889
November1st to 10thDay
13%9%47%5%3445%7%38%
1634
11th to 20thDay
14%13%6%8%8%345%7%5%28%
1520
21st to endDay
15%11%5%5%6%3445%5%37%
1520
December1st to 10thDay
11%13%6%11%10%5%6%5%45%24%
1520
11th to 20thDay
11%14%7%10%9%45%5%4427%
1918
21st to endDay
21%16%8%13%7%3433418%
2783
January1st to 10thNight
9%15%9%12%6%34445%29%
4428
11th to 20thNight
8%11%6%12%10%6%7%8%6%5%21%
4440
21st to endNight
11%19%8%12%6%34445%23%
4647
February1st to 10thNight
7%11%6%10%7%45%45%6%35%
2470
11th to 20thNight
8%9%5%8%6%45%5%6%6%39%
2403
21st to endNight
13%9%47%7%45%5%5%6%36%
1918
March1st to 10thNight
12%8%46%6%45%45%6%39%
2237
11th to 20thNight
11%9%47%7%3445%6%40%
2090
21st to endNight
18%9%47%6%34346%36%
2124
April1st to 10thNight
17%10%46%5%2446%7%35%
1800
11th to 20thNight
23%9%35%4345%5%5%34%
1775
21st to endNight
20%8%36%435%45%7%36%
1689
May1st to 10thNight
21%8%36%5%34446%36%
1450
11th to 20thNight
18%6%36%42445%7%41%
1416
21st to endNight
13%6%36%6%3446%7%42%
1551
June1st to 10thNight
10%5%25%435%5%6%9%46%
1440
11th to 20thNight
11%5%25%5%25%5%6%8%46%
1440
21st to endNight
7%4245%36%5%7%9%48%
1440
July1st to 10thNight
6%3234245%6%10%55%
1440
11th to 20thNight
7%4244345%5%10%52%
1440
21st to endNight
43224345%6%9%58%
1575
August1st to 10thNight
6%425%5%46%5%7%7%49%
1543
11th to 20thNight
13%5%245%235%5%7%49%
1600
21st to endNight
11%5%34433445%54%
1951
September1st to 10thNight
10%5%25%4245%47%51%
1800
11th to 20thNight
11%5%2442346%7%52%
1800
21st to endNight
15%5%3442345%7%48%
2038
October1st to 10thNight
14%6%25%433446%48%
2160
11th to 20thNight
17%7%36%5%44447%40%
2160
21st to endNight
17%11%36%5%3445%7%36%
2466
November1st to 10thNight
13%9%5%5%424448%41%
2439
11th to 20thNight
14%9%5%9%7%45%45%6%33%
2660
21st to endNight
15%10%47%5%245%5%6%37%
2660
December1st to 10thNight
11%12%5%11%8%35%5%47%31%
2660
11th to 20thNight
12%14%5%9%8%45%5%5%6%26%
3279
21st to endNight
24%15%6%10%7%33445%21%
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
63%5%11%17%4
2528
11th to 20thDay
65%6%9%15%6%
2530
21st to endDay
61%5%15%15%4
3016
February1st to 10thDay
50%6%13%19%10%1
1710
11th to 20thDay
47%6%13%24%9%1
1673
21st to endDay
50%6%13%19%10%2
1535
March1st to 10thDay
50%5%14%20%9%1
1961
11th to 20thDay
48%5%13%23%10%1
2090
21st to endDay
53%6%11%21%8%1
2276
April1st to 10thDay
50%5%12%20%12%1
2160
11th to 20thDay
54%5%10%18%12%2
2134
21st to endDay
55%6%11%18%9%1
2268
May1st to 10thDay
49%6%13%22%9%1
2510
11th to 20thDay
47%7%14%20%12%1
2483
21st to endDay
45%8%10%24%12%2
2725
June1st to 10thDay
36%7%13%30%12%2
2520
11th to 20thDay
43%9%12%23%13%1
2520
21st to endDay
37%9%16%28%10%1
2520
July1st to 10thDay
31%9%15%31%14%1
2451
11th to 20thDay
32%6%15%27%18%3
2445
21st to endDay
29%9%17%29%15%2
2591
August1st to 10thDay
37%9%15%29%9%2
2377
11th to 20thDay
39%8%14%27%12%
2301
21st to endDay
32%7%13%30%17%1
2404
September1st to 10thDay
35%7%14%30%14%
2160
11th to 20thDay
37%7%16%32%8%1
2160
21st to endDay
41%6%13%30%9%
1899
October1st to 10thDay
42%6%13%30%10%
1800
11th to 20thDay
50%413%21%11%1
1800
21st to endDay
51%5%13%22%9%
1889
November1st to 10thDay
46%6%13%20%13%2
1634
11th to 20thDay
57%6%13%16%8%1
1520
21st to endDay
48%5%17%21%7%2
1520
December1st to 10thDay
61%6%13%15%5%
1520
11th to 20thDay
60%5%14%15%5%1
1915
21st to endDay
71%5%8%12%5%
2783
January1st to 10thNight
58%5%12%18%6%1
4428
11th to 20thNight
62%6%11%13%7%
4440
21st to endNight
63%5%9%18%5%1
4647
February1st to 10thNight
50%5%12%21%10%2
2470
11th to 20thNight
44%6%13%26%9%2
2404
21st to endNight
48%6%11%22%10%2
1918
March1st to 10thNight
45%6%14%24%10%1
2237
11th to 20thNight
45%5%11%23%15%2
2090
21st to endNight
50%5%10%22%12%1
2124
April1st to 10thNight
48%6%9%19%17%2
1800
11th to 20thNight
52%5%8%18%14%2
1775
21st to endNight
48%5%10%21%15%2
1689
May1st to 10thNight
49%6%12%18%13%1
1450
11th to 20thNight
41%6%11%25%14%3
1417
21st to endNight
41%8%11%21%18%2
1552
June1st to 10thNight
33%8%13%29%17%2
1440
11th to 20thNight
34%8%14%24%18%2
1440
21st to endNight
29%9%15%32%12%3
1440
July1st to 10thNight
25%5%15%33%21%2
1400
11th to 20thNight
27%7%15%29%20%3
1392
21st to endNight
21%8%18%31%18%5%
1487
August1st to 10thNight
32%7%14%29%16%3
1534
11th to 20thNight
32%7%15%28%16%2
1600
21st to endNight
32%5%12%29%17%3
1951
September1st to 10thNight
31%7%12%33%16%1
1800
11th to 20thNight
31%6%15%32%16%
1800
21st to endNight
35%6%14%31%13%1
2038
October1st to 10thNight
37%5%10%32%14%2
2160
11th to 20thNight
44%6%12%24%14%1
2160
21st to endNight
48%6%13%22%11%1
2466
November1st to 10thNight
43%5%11%26%14%1
2439
11th to 20thNight
52%6%13%17%12%1
2660
21st to endNight
48%6%15%23%7%1
2660
December1st to 10thNight
54%6%15%20%6%
2660
11th to 20thNight
58%5%13%18%6%1
3281
21st to endNight
67%410%15%5%
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
15%12%34%26%10%3
270
11th to 20thDay
17%12%37%26%7%1
270
21st to endDay
15%9%39%25%10%1
297
February1st to 10thDay
15%13%44%19%8%2
270
11th to 20thDay
15%19%38%19%9%
270
21st to endDay
18%12%46%22%2
225
March1st to 10thDay
16%14%39%20%11%1
270
11th to 20thDay
19%13%35%24%7%3
270
21st to endDay
23%15%29%19%10%3
346
April1st to 10thDay
24%14%34%21%6%1
420
11th to 20thDay
30%11%26%23%8%1
412
21st to endDay
26%15%27%20%10%2
528
May1st to 10thDay
20%14%30%26%8%2
603
11th to 20thDay
20%13%28%24%13%4
625
21st to endDay
18%10%25%25%17%5%
679
June1st to 10thDay
10%7%26%33%19%4
630
11th to 20thDay
14%10%33%28%13%3
630
21st to endDay
13%6%29%29%17%6%
630
July1st to 10thDay
8%5%21%29%26%11%
621
11th to 20thDay
10%5%28%30%19%9%
618
21st to endDay
6%425%35%20%8%
684
August1st to 10thDay
12%421%33%23%7%
626
11th to 20thDay
14%420%28%27%7%
615
21st to endDay
13%6%23%29%24%5%
523
September1st to 10thDay
14%6%27%30%19%5%
450
11th to 20thDay
12%6%28%30%21%4
450
21st to endDay
23%14%22%26%13%3
330
October1st to 10thDay
20%9%33%21%16%3
270
11th to 20thDay
22%17%32%23%6%
270
21st to endDay
26%18%33%15%6%2
297
November1st to 10thDay
20%11%34%24%10%1
270
11th to 20thDay
22%14%38%20%6%1
270
21st to endDay
24%12%41%15%7%
270
December1st to 10thDay
17%13%37%23%9%1
270
11th to 20thDay
18%16%37%21%7%1
270
21st to endDay
28%13%37%20%21
297
January1st to 10thNight
13%12%33%32%9%1
950
11th to 20thNight
18%10%35%30%6%1
950
21st to endNight
18%10%33%31%7%
1045
February1st to 10thNight
13%12%37%30%7%1
950
11th to 20thNight
13%12%40%27%8%
929
21st to endNight
18%13%33%29%7%
662
March1st to 10thNight
15%11%37%30%7%1
717
11th to 20thNight
17%9%35%32%6%
570
21st to endNight
22%9%30%26%11%2
600
April1st to 10thNight
24%12%33%25%6%1
540
11th to 20thNight
28%8%28%28%7%1
533
21st to endNight
24%7%33%26%8%1
540
May1st to 10thNight
22%9%31%31%6%
540
11th to 20thNight
20%8%28%32%11%1
531
21st to endNight
15%6%25%39%15%1
584
June1st to 10thNight
10%6%28%41%14%1
540
11th to 20thNight
12%5%31%40%11%
540
21st to endNight
8%425%45%18%1
540
July1st to 10thNight
8%222%38%28%2
525
11th to 20thNight
7%5%23%42%21%2
522
21st to endNight
6%219%47%23%3
591
August1st to 10thNight
7%315%48%26%1
537
11th to 20thNight
14%219%35%26%4
534
21st to endNight
14%223%34%25%2
594
September1st to 10thNight
12%423%38%18%5%
540
11th to 20thNight
12%427%36%19%2
540
21st to endNight
16%11%30%29%14%1
662
October1st to 10thNight
18%8%28%31%14%2
720
11th to 20thNight
21%10%33%29%7%
720
21st to endNight
22%11%29%30%8%
792
November1st to 10thNight
18%10%34%29%8%1
773
11th to 20thNight
19%13%35%25%8%
950
21st to endNight
20%13%34%27%6%
950
December1st to 10thNight
17%11%35%29%7%1
950
11th to 20thNight
21%9%35%25%7%2
950
21st to endNight
26%9%34%25%5%
1045
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