Twin Lakes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Lakes Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
45%
23851
22%
74449
14%
23795
53%
23795
25%
46645

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
21%
760
21%
2459
7%
757
37%
757
19%
1563
January11th to 20thNight
25%
737
22%
2393
9%
737
42%
737
18%
1573
January21st to endNight
23%
792
28%
2511
11%
792
41%
792
22%
1548
February1st to 10thNight
29%
720
23%
2160
11%
720
41%
720
23%
1382
February11th to 20thNight
21%
703
20%
2098
6%
699
35%
699
20%
1390
February21st to endNight
20%
592
21%
1776
8%
592
33%
592
19%
1202
March1st to 10thNight
29%
720
25%
2104
12%
720
40%
720
27%
1292
March11th to 20thNight
29%
720
19%
1980
8%
720
39%
720
24%
1322
March21st to endNight
34%
792
21%
2178
11%
792
42%
792
26%
1411
April1st to 10thNight
39%
689
24%
1949
14%
689
48%
689
30%
1180
April11th to 20thNight
41%
533
26%
1775
17%
533
54%
533
30%
1007
April21st to endNight
49%
540
29%
1648
19%
540
58%
540
34%
938
May1st to 10thNight
51%
540
22%
1620
12%
540
59%
540
31%
968
May11th to 20thNight
50%
531
16%
1593
10%
531
55%
531
26%
1025
May21st to endNight
62%
582
19%
1744
14%
582
65%
582
29%
1107
June1st to 10thNight
65%
540
15%
1620
14%
540
66%
540
25%
1085
June11th to 20thNight
69%
540
15%
1620
12%
540
71%
540
33%
976
June21st to endNight
71%
540
16%
1620
13%
540
73%
540
31%
1018
July1st to 10thNight
66%
525
13%
1575
12%
525
66%
525
24%
1055
July11th to 20thNight
68%
522
11%
1566
10%
522
69%
522
24%
1050
July21st to endNight
69%
591
14%
1672
11%
558
70%
558
24%
1139
August1st to 10thNight
67%
537
13%
1600
13%
534
67%
534
24%
1090
August11th to 20thNight
66%
534
18%
1720
20%
534
66%
534
23%
1148
August21st to endNight
60%
594
17%
1980
19%
594
60%
594
20%
1356
September1st to 10thNight
65%
697
19%
1957
18%
697
66%
697
29%
1288
September11th to 20thNight
60%
720
22%
1980
18%
720
63%
720
29%
1304
September21st to endNight
60%
720
26%
1980
19%
720
66%
720
33%
1238
October1st to 10thNight
57%
720
29%
1980
22%
720
63%
720
39%
1156
October11th to 20thNight
47%
720
31%
2084
22%
720
58%
720
35%
1213
October21st to endNight
49%
792
32%
2376
24%
792
60%
792
35%
1337
November1st to 10thNight
48%
740
28%
2385
23%
740
59%
740
33%
1313
November11th to 20thNight
38%
760
29%
2470
18%
760
53%
760
31%
1381
November21st to endNight
38%
760
25%
2470
17%
760
49%
760
25%
1501
December1st to 10thNight
27%
760
23%
2470
10%
760
43%
760
20%
1615
December11th to 20thNight
32%
759
25%
2925
15%
758
44%
758
21%
1672
December21st to endNight
26%
829
14%
4411
11%
817
37%
817
11%
2802

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%25%5%35%5%6%8%41%
74886
Night
14%6%35%5%345%5%7%44%
74895
TransparencyDay
39%8%12%19%17%5%
74609
Night
38%7%11%19%19%6%
74691
SeeingDay
16%11%23%23%19%9%
13764
Night
16%9%23%28%20%4
23861

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
20%7%35%42335%6%42%
1706
11th to 20thDay
20%7%24423445%43%
1656
21st to endDay
19%7%35%43335%5%45%
1840
February1st to 10thDay
18%8%26%5%345%6%6%38%
1800
11th to 20thDay
23%6%25%324346%42%
1748
21st to endDay
24%6%35%433446%39%
1480
March1st to 10thDay
15%425%43445%7%45%
1854
11th to 20thDay
20%6%25%5%345%5%6%39%
1980
21st to endDay
17%5%35%6%345%5%7%40%
2178
April1st to 10thDay
13%5%25%5%35%5%6%7%45%
2024
11th to 20thDay
14%6%25%5%35%447%46%
2134
21st to endDay
11%4144346%5%7%50%
2312
May1st to 10thDay
11%5%25%43445%9%48%
2340
11th to 20thDay
12%6%26%6%35%5%7%8%41%
2301
21st to endDay
10%6%35%5%35%5%6%10%40%
2531
June1st to 10thDay
10%6%36%7%45%6%9%10%34%
2340
11th to 20thDay
7%3246%47%7%8%12%41%
2340
21st to endDay
8%426%6%47%7%8%11%37%
2340
July1st to 10thDay
10%6%26%7%5%7%8%8%11%29%
2340
11th to 20thDay
10%5%36%6%6%8%8%9%12%27%
2340
21st to endDay
7%5%36%8%5%10%8%8%11%29%
2547
August1st to 10thDay
9%6%26%8%5%8%8%9%10%30%
2327
11th to 20thDay
13%6%27%7%47%6%8%9%31%
2177
21st to endDay
13%6%38%8%5%6%6%8%9%29%
2376
September1st to 10thDay
12%6%36%5%45%5%6%8%39%
1985
11th to 20thDay
14%7%25%5%25%6%6%7%41%
1980
21st to endDay
13%5%25%5%33446%49%
1980
October1st to 10thDay
13%5%24424345%55%
1980
11th to 20thDay
12%5%2432335%6%55%
1873
21st to endDay
14%5%24323345%54%
1980
November1st to 10thDay
13%5%23323345%57%
1690
11th to 20thDay
14%42433445%5%53%
1710
21st to endDay
15%5%3442445%7%46%
1710
December1st to 10thDay
23%6%345%3345%6%38%
1710
11th to 20thDay
18%6%26%434445%44%
2153
21st to endDay
24%7%4443446%6%36%
3124
January1st to 10thNight
20%6%34424445%43%
2459
11th to 20thNight
18%8%45%43445%6%39%
2393
21st to endNight
18%6%35%433345%46%
2511
February1st to 10thNight
17%6%35%43445%7%43%
2160
11th to 20thNight
22%6%35%42433443%
2098
21st to endNight
22%6%26%43435%5%39%
1776
March1st to 10thNight
15%6%2442335%5%49%
2104
11th to 20thNight
17%5%25%425%5%6%7%42%
1980
21st to endNight
14%6%35%43445%7%45%
2178
April1st to 10thNight
12%5%23435%5%5%7%49%
1949
11th to 20thNight
14%6%15%3235%46%50%
1775
21st to endNight
9%5%2442445%8%51%
1648
May1st to 10thNight
9%425%435%5%6%7%50%
1620
11th to 20thNight
10%7%35%6%36%45%7%44%
1592
21st to endNight
10%6%246%345%6%9%45%
1744
June1st to 10thNight
8%435%7%5%6%8%8%11%36%
1620
11th to 20thNight
5%436%5%36%5%9%11%45%
1620
21st to endNight
7%4245%36%6%8%11%43%
1620
July1st to 10thNight
9%5%36%6%46%6%8%9%38%
1620
11th to 20thNight
8%436%7%37%7%9%12%34%
1620
21st to endNight
7%5%26%6%47%8%8%12%35%
1771
August1st to 10thNight
9%6%25%6%447%8%12%36%
1611
11th to 20thNight
11%5%36%7%445%7%10%39%
1720
21st to endNight
13%7%35%6%46%6%7%9%34%
1980
September1st to 10thNight
11%5%26%5%45%5%6%8%42%
1957
11th to 20thNight
13%5%25%5%35%5%5%9%43%
1980
21st to endNight
12%5%144345%5%7%49%
1980
October1st to 10thNight
12%5%1332336%5%56%
1980
11th to 20thNight
11%425%423345%56%
2084
21st to endNight
13%5%23423346%55%
2376
November1st to 10thNight
13%423423346%57%
2385
11th to 20thNight
15%5%23323346%54%
2470
21st to endNight
16%5%244335%5%5%46%
2470
December1st to 10thNight
19%7%36%5%34446%39%
2470
11th to 20thNight
18%7%24423445%47%
3042
21st to endNight
21%8%46%5%2445%7%34%
4532

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%6%9%18%21%5%
1707
11th to 20thDay
43%48%19%21%5%
1656
21st to endDay
42%46%20%21%7%
1840
February1st to 10thDay
46%49%17%19%4
1800
11th to 20thDay
44%5%7%19%19%6%
1758
21st to endDay
47%5%8%14%19%8%
1480
March1st to 10thDay
38%5%11%17%21%9%
1854
11th to 20thDay
46%6%10%15%17%6%
1980
21st to endDay
43%7%11%21%16%3
2178
April1st to 10thDay
37%6%11%21%20%5%
2024
11th to 20thDay
37%6%8%18%23%8%
2134
21st to endDay
31%7%12%27%20%4
2312
May1st to 10thDay
32%7%14%21%22%4
2340
11th to 20thDay
39%10%15%21%14%2
2305
21st to endDay
36%9%14%23%16%2
2531
June1st to 10thDay
40%11%18%19%9%2
2340
11th to 20thDay
31%12%21%25%10%1
2340
21st to endDay
36%12%18%20%11%2
2340
July1st to 10thDay
42%14%19%16%8%2
2275
11th to 20thDay
42%14%20%14%7%3
2271
21st to endDay
40%16%19%17%8%
2405
August1st to 10thDay
42%14%19%20%5%1
2314
11th to 20thDay
44%12%17%16%8%2
2177
21st to endDay
48%12%14%15%9%2
2376
September1st to 10thDay
40%10%15%15%17%4
1985
11th to 20thDay
40%9%12%18%20%2
1980
21st to endDay
36%5%11%18%22%7%
1980
October1st to 10thDay
32%6%10%17%29%8%
1980
11th to 20thDay
29%5%11%22%25%9%
1873
21st to endDay
34%37%18%28%10%
1980
November1st to 10thDay
31%47%16%32%11%
1690
11th to 20thDay
34%38%18%27%10%
1710
21st to endDay
37%6%8%18%25%6%
1710
December1st to 10thDay
47%6%7%18%16%6%
1710
11th to 20thDay
43%47%16%23%7%
2150
21st to endDay
45%6%11%18%17%3
3124
January1st to 10thNight
43%5%8%17%23%5%
2459
11th to 20thNight
45%5%8%17%20%5%
2393
21st to endNight
40%36%20%25%5%
2511
February1st to 10thNight
40%6%9%19%19%7%
2160
11th to 20thNight
45%46%18%20%7%
2099
21st to endNight
46%5%8%16%18%8%
1776
March1st to 10thNight
37%49%18%21%11%
2104
11th to 20thNight
39%8%11%16%20%6%
1980
21st to endNight
39%6%10%22%19%4
2178
April1st to 10thNight
33%6%11%20%24%6%
1949
11th to 20thNight
33%5%8%22%22%10%
1775
21st to endNight
30%6%12%27%20%5%
1648
May1st to 10thNight
32%8%14%21%22%4
1620
11th to 20thNight
37%10%16%22%14%1
1593
21st to endNight
35%9%12%24%16%3
1745
June1st to 10thNight
37%12%18%19%11%2
1620
11th to 20thNight
30%10%22%25%12%1
1620
21st to endNight
31%12%20%21%13%3
1620
July1st to 10thNight
39%12%19%19%10%1
1575
11th to 20thNight
35%16%23%16%8%3
1566
21st to endNight
36%16%21%19%7%2
1672
August1st to 10thNight
37%14%20%22%6%1
1600
11th to 20thNight
39%12%18%16%14%1
1720
21st to endNight
43%12%16%17%10%2
1980
September1st to 10thNight
37%9%15%18%17%4
1957
11th to 20thNight
37%9%12%19%20%3
1980
21st to endNight
34%8%11%19%20%8%
1980
October1st to 10thNight
30%5%12%17%28%7%
1980
11th to 20thNight
32%5%9%20%25%9%
2084
21st to endNight
30%47%19%28%12%
2376
November1st to 10thNight
30%5%7%18%27%12%
2385
11th to 20thNight
32%47%18%27%12%
2470
21st to endNight
37%6%7%19%24%7%
2470
December1st to 10thNight
45%5%9%18%17%5%
2470
11th to 20thNight
38%410%16%27%6%
3044
21st to endNight
47%7%8%20%15%3
4532

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%26%36%10%2
270
11th to 20thDay
27%21%28%18%5%
252
21st to endDay
23%26%38%11%21
264
February1st to 10thDay
25%24%33%16%3
240
11th to 20thDay
37%25%27%11%
240
21st to endDay
32%23%34%9%2
198
March1st to 10thDay
21%18%35%20%5%
294
11th to 20thDay
21%22%30%20%6%1
420
21st to endDay
19%18%35%20%7%1
462
April1st to 10thDay
18%17%29%25%10%2
420
11th to 20thDay
14%17%33%21%14%1
412
21st to endDay
16%11%27%25%16%4
420
May1st to 10thDay
13%13%30%25%13%5%
423
11th to 20thDay
15%422%30%18%11%
447
21st to endDay
14%6%15%28%25%12%
485
June1st to 10thDay
13%316%28%26%13%
450
11th to 20thDay
6%5%14%28%26%20%
450
21st to endDay
11%417%27%26%16%
450
July1st to 10thDay
11%29%25%31%22%
445
11th to 20thDay
9%210%21%33%25%
444
21st to endDay
6%9%23%39%23%
488
August1st to 10thDay
11%414%23%26%22%
446
11th to 20thDay
13%111%25%34%15%
439
21st to endDay
15%212%23%27%20%
495
September1st to 10thDay
11%5%11%29%29%16%
450
11th to 20thDay
14%5%14%24%32%11%
450
21st to endDay
13%419%25%27%11%
450
October1st to 10thDay
15%5%23%29%19%10%
450
11th to 20thDay
14%12%23%25%22%4
450
21st to endDay
17%10%25%27%17%3
495
November1st to 10thDay
20%8%28%26%16%2
288
11th to 20thDay
17%20%34%21%7%1
270
21st to endDay
12%18%37%21%10%1
270
December1st to 10thDay
30%20%29%16%41
270
11th to 20thDay
21%20%33%20%5%1
270
21st to endDay
32%18%30%17%41
297
January1st to 10thNight
24%19%32%20%5%
760
11th to 20thNight
22%17%31%23%7%
737
21st to endNight
21%19%34%23%3
792
February1st to 10thNight
19%16%34%26%5%
720
11th to 20thNight
25%18%33%22%2
703
21st to endNight
24%18%35%21%3
592
March1st to 10thNight
18%16%34%28%4
720
11th to 20thNight
19%13%34%24%9%
720
21st to endNight
17%15%29%30%8%1
792
April1st to 10thNight
14%15%29%31%11%
689
11th to 20thNight
16%10%28%32%14%1
533
21st to endNight
11%8%27%34%19%1
540
May1st to 10thNight
11%8%25%32%22%1
540
11th to 20thNight
12%423%33%23%5%
531
21st to endNight
14%313%31%33%7%
584
June1st to 10thNight
9%112%40%33%6%
540
11th to 20thNight
5%314%31%34%14%
540
21st to endNight
7%111%39%34%9%
540
July1st to 10thNight
10%28%25%43%12%
525
11th to 20thNight
9%19%19%48%13%
522
21st to endNight
6%28%27%46%11%
591
August1st to 10thNight
11%29%27%42%10%
537
11th to 20thNight
11%39%28%40%9%
534
21st to endNight
15%310%26%37%10%
594
September1st to 10thNight
11%210%30%36%10%
697
11th to 20thNight
15%213%30%36%3
720
21st to endNight
14%316%34%31%2
720
October1st to 10thNight
13%321%32%24%7%
720
11th to 20thNight
13%7%27%31%20%3
720
21st to endNight
15%9%22%33%18%2
792
November1st to 10thNight
15%8%24%32%19%1
740
11th to 20thNight
16%13%30%27%13%1
760
21st to endNight
19%13%27%28%13%1
760
December1st to 10thNight
21%15%31%25%7%
760
11th to 20thNight
23%12%30%25%9%
760
21st to endNight
28%15%27%26%5%
836
Page generated at 2024-01-11 22:33:51. Version ac07

Copyright 2024 Attilla Danko


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