The Looking Glass Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Looking Glass Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
43%
23874
19%
79924
14%
23762
50%
23762
22%
51984

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%
755
16%
4039
9%
737
32%
737
10%
2675
January11th to 20thNight
18%
759
20%
3987
9%
740
27%
740
8%
2649
January21st to endNight
19%
834
13%
4406
8%
814
31%
814
10%
2993
February1st to 10thNight
23%
760
18%
2280
9%
760
31%
760
18%
1606
February11th to 20thNight
16%
743
16%
2218
6%
739
25%
739
15%
1608
February21st to endNight
18%
611
18%
1831
9%
611
26%
611
14%
1352
March1st to 10thNight
24%
720
18%
2148
8%
720
33%
720
21%
1447
March11th to 20thNight
25%
720
17%
1980
8%
720
32%
720
19%
1415
March21st to endNight
30%
792
15%
2178
8%
792
35%
792
20%
1528
April1st to 10thNight
36%
604
23%
1864
13%
604
48%
604
27%
1132
April11th to 20thNight
40%
533
25%
1775
16%
533
52%
533
27%
1056
April21st to endNight
41%
540
23%
1643
13%
540
49%
540
27%
1031
May1st to 10thNight
43%
540
19%
1620
11%
540
51%
540
27%
1036
May11th to 20thNight
53%
531
16%
1593
11%
531
56%
531
26%
1042
May21st to endNight
60%
582
16%
1745
11%
582
63%
582
26%
1142
June1st to 10thNight
65%
540
17%
1620
14%
540
67%
540
29%
1030
June11th to 20thNight
71%
540
18%
1620
14%
540
74%
540
39%
914
June21st to endNight
66%
540
17%
1620
15%
540
67%
540
29%
1021
July1st to 10thNight
68%
525
11%
1575
11%
525
69%
525
24%
1062
July11th to 20thNight
72%
522
16%
1566
13%
522
73%
522
30%
976
July21st to endNight
69%
591
16%
1672
15%
558
71%
558
27%
1084
August1st to 10thNight
69%
537
17%
1600
15%
534
70%
534
29%
1025
August11th to 20thNight
70%
534
16%
1705
16%
534
70%
534
27%
1079
August21st to endNight
70%
594
19%
1980
22%
594
70%
594
27%
1216
September1st to 10thNight
64%
644
20%
1904
18%
644
65%
644
28%
1203
September11th to 20thNight
62%
720
23%
1980
19%
720
64%
720
31%
1271
September21st to endNight
59%
720
28%
1980
20%
720
64%
720
35%
1214
October1st to 10thNight
58%
720
30%
1980
25%
720
62%
720
41%
1134
October11th to 20thNight
44%
720
26%
2076
18%
720
52%
720
30%
1272
October21st to endNight
43%
792
29%
2456
22%
792
53%
792
29%
1475
November1st to 10thNight
50%
740
27%
2406
25%
740
58%
740
30%
1373
November11th to 20thNight
37%
760
26%
2470
18%
760
50%
760
26%
1471
November21st to endNight
36%
760
24%
2470
17%
760
46%
760
23%
1557
December1st to 10thNight
27%
760
17%
2470
10%
760
35%
760
15%
1768
December11th to 20thNight
31%
759
20%
2987
15%
759
40%
759
16%
2005
December21st to endNight
24%
832
10%
4480
9%
817
33%
817
8%
3122

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%8%36%6%35%5%6%7%36%
78802
Night
12%7%36%5%35%5%5%7%40%
80503
TransparencyDay
45%8%11%19%14%3
78525
Night
42%7%11%20%16%3
80299
SeeingDay
18%13%24%22%15%7%
13740
Night
16%12%23%28%18%3
23889

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
15%13%6%9%6%35%5%5%6%28%
2836
11th to 20thDay
18%9%5%13%6%35%34430%
2840
21st to endDay
20%14%7%5%424345%32%
3186
February1st to 10thDay
17%11%5%7%5%34446%34%
1900
11th to 20thDay
20%9%5%8%5%3445%5%32%
1848
21st to endDay
20%9%49%5%24445%35%
1520
March1st to 10thDay
14%9%36%6%4445%7%37%
1810
11th to 20thDay
21%10%47%6%34446%31%
1980
21st to endDay
16%10%47%6%35%5%5%7%32%
2178
April1st to 10thDay
12%7%35%6%35%45%7%43%
2110
11th to 20thDay
14%8%36%5%34447%43%
2134
21st to endDay
13%6%36%6%35%6%6%6%40%
2314
May1st to 10thDay
15%6%36%5%35%5%6%8%38%
2340
11th to 20thDay
13%9%37%6%45%5%6%7%34%
2301
21st to endDay
9%7%27%5%35%6%7%10%37%
2531
June1st to 10thDay
9%6%35%6%46%7%7%9%36%
2340
11th to 20thDay
5%426%7%46%6%7%10%41%
2340
21st to endDay
7%426%6%5%6%7%8%12%38%
2340
July1st to 10thDay
9%6%36%9%5%8%7%8%9%30%
2340
11th to 20thDay
10%5%37%8%5%7%8%7%9%30%
2340
21st to endDay
10%5%47%7%5%8%7%8%11%29%
2547
August1st to 10thDay
9%6%38%7%48%7%9%9%30%
2327
11th to 20thDay
10%6%36%7%5%7%6%9%9%32%
2192
21st to endDay
10%7%36%6%5%6%7%8%9%32%
2376
September1st to 10thDay
15%6%35%6%46%5%6%8%36%
2036
11th to 20thDay
12%8%36%5%46%5%5%7%38%
1980
21st to endDay
13%5%25%4445%5%7%45%
1980
October1st to 10thDay
11%5%25%5%3445%6%51%
1980
11th to 20thDay
12%6%2442445%7%50%
1882
21st to endDay
14%8%2432345%7%46%
1895
November1st to 10thDay
10%6%2442445%6%54%
1672
11th to 20thDay
13%6%35%5%2445%6%47%
1710
21st to endDay
15%8%45%5%34346%44%
1710
December1st to 10thDay
18%11%48%6%34435%34%
1710
11th to 20thDay
14%12%5%6%6%36%5%6%6%34%
2153
21st to endDay
16%14%5%6%5%35%45%8%30%
3124
January1st to 10thNight
15%13%5%8%6%34446%32%
4109
11th to 20thNight
18%10%5%7%6%44345%34%
4120
21st to endNight
18%14%5%6%5%34345%32%
4468
February1st to 10thNight
16%9%37%6%35%46%6%35%
2280
11th to 20thNight
22%8%48%6%3435%5%33%
2218
21st to endNight
21%9%47%6%345%47%31%
1831
March1st to 10thNight
14%8%46%6%35%5%5%6%39%
2148
11th to 20thNight
16%8%37%6%35%45%6%36%
1980
21st to endNight
14%9%37%6%45%46%7%36%
2178
April1st to 10thNight
11%5%24435%6%6%8%47%
1864
11th to 20thNight
12%6%25%435%45%7%48%
1775
21st to endNight
11%6%35%5%45%45%8%44%
1643
May1st to 10thNight
9%7%35%5%345%6%8%45%
1620
11th to 20thNight
10%6%35%5%45%5%7%8%42%
1592
21st to endNight
5%5%36%7%45%6%8%10%41%
1744
June1st to 10thNight
6%5%36%5%46%6%7%8%44%
1620
11th to 20thNight
32145%35%5%7%12%53%
1620
21st to endNight
5%325%5%45%7%7%12%43%
1620
July1st to 10thNight
9%5%25%7%47%6%8%11%37%
1620
11th to 20thNight
7%425%5%46%6%7%12%44%
1620
21st to endNight
6%5%36%6%46%7%7%12%38%
1771
August1st to 10thNight
7%435%6%46%6%7%10%44%
1611
11th to 20thNight
7%5%26%6%446%7%9%44%
1705
21st to endNight
9%5%25%5%35%5%7%10%44%
1980
September1st to 10thNight
10%6%36%5%35%45%8%44%
1904
11th to 20thNight
11%5%26%5%245%5%8%46%
1980
21st to endNight
10%435%434446%53%
1980
October1st to 10thNight
10%424313447%58%
1980
11th to 20thNight
13%5%25%424446%51%
2076
21st to endNight
12%8%26%434346%49%
2456
November1st to 10thNight
11%5%35%43435%6%53%
2406
11th to 20thNight
12%6%36%43445%7%47%
2470
21st to endNight
13%9%46%433447%43%
2470
December1st to 10thNight
17%11%5%7%6%3445%5%32%
2470
11th to 20thNight
14%11%5%9%5%3345%5%36%
3042
21st to endNight
14%10%6%8%7%5%7%6%6%7%25%
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
53%5%10%17%13%2
2837
11th to 20thDay
57%6%6%15%16%1
2840
21st to endDay
54%5%8%20%12%1
3186
February1st to 10thDay
53%5%8%16%16%2
1900
11th to 20thDay
54%5%7%18%13%3
1858
21st to endDay
52%5%9%13%15%5%
1520
March1st to 10thDay
47%6%8%18%17%5%
1810
11th to 20thDay
54%5%9%16%12%3
1980
21st to endDay
51%8%10%19%11%1
2178
April1st to 10thDay
40%7%12%22%16%3
2110
11th to 20thDay
42%6%8%18%24%3
2134
21st to endDay
42%8%11%24%13%1
2314
May1st to 10thDay
43%8%12%24%11%2
2340
11th to 20thDay
47%11%13%19%11%1
2305
21st to endDay
39%12%15%21%10%2
2531
June1st to 10thDay
41%11%15%19%12%1
2340
11th to 20thDay
36%11%17%20%14%2
2340
21st to endDay
36%13%17%19%12%4
2340
July1st to 10thDay
45%14%13%16%10%2
2275
11th to 20thDay
45%12%16%14%10%3
2271
21st to endDay
44%13%15%19%8%1
2405
August1st to 10thDay
45%14%16%17%7%
2314
11th to 20thDay
44%12%15%16%12%1
2192
21st to endDay
42%13%15%16%11%3
2376
September1st to 10thDay
43%9%12%18%15%4
2036
11th to 20thDay
42%9%12%19%16%2
1980
21st to endDay
37%7%11%22%19%5%
1980
October1st to 10thDay
33%6%11%21%25%5%
1980
11th to 20thDay
33%6%10%20%24%7%
1882
21st to endDay
36%6%9%24%20%5%
1895
November1st to 10thDay
31%5%9%23%27%5%
1672
11th to 20thDay
38%5%7%22%22%6%
1710
21st to endDay
42%5%8%20%21%3
1710
December1st to 10thDay
54%5%6%20%13%2
1710
11th to 20thDay
49%7%9%17%16%2
2150
21st to endDay
51%5%12%19%10%2
3124
January1st to 10thNight
49%8%10%18%14%2
4109
11th to 20thNight
52%5%7%14%17%5%
4120
21st to endNight
55%48%14%18%1
4468
February1st to 10thNight
49%6%10%18%15%2
2280
11th to 20thNight
53%5%7%18%13%5%
2219
21st to endNight
54%6%7%14%15%4
1831
March1st to 10thNight
45%6%10%14%19%6%
2148
11th to 20thNight
48%7%9%19%14%2
1980
21st to endNight
46%7%12%22%12%2
2178
April1st to 10thNight
34%7%12%25%19%3
1864
11th to 20thNight
36%6%10%20%22%6%
1775
21st to endNight
38%7%12%28%13%1
1643
May1st to 10thNight
37%9%12%27%13%3
1620
11th to 20thNight
37%11%17%22%12%1
1593
21st to endNight
35%12%17%22%12%1
1745
June1st to 10thNight
34%11%15%25%13%2
1620
11th to 20thNight
24%10%23%28%14%2
1620
21st to endNight
33%12%16%24%12%4
1620
July1st to 10thNight
37%14%17%19%12%2
1575
11th to 20thNight
31%12%20%18%14%4
1566
21st to endNight
33%14%19%22%10%2
1672
August1st to 10thNight
33%12%18%26%11%1
1600
11th to 20thNight
34%11%20%18%14%2
1705
21st to endNight
34%10%17%24%13%2
1980
September1st to 10thNight
37%8%15%19%16%5%
1904
11th to 20thNight
36%8%13%20%21%2
1980
21st to endNight
32%7%9%23%24%4
1980
October1st to 10thNight
28%5%12%22%27%7%
1980
11th to 20thNight
35%6%9%21%21%8%
2076
21st to endNight
37%46%22%24%7%
2456
November1st to 10thNight
34%5%8%21%25%8%
2406
11th to 20thNight
36%5%7%20%23%8%
2470
21st to endNight
42%47%23%19%4
2470
December1st to 10thNight
53%6%8%18%12%3
2470
11th to 20thNight
48%6%8%17%18%3
3044
21st to endNight
53%9%13%14%11%1
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
28%29%30%12%1
270
11th to 20thDay
35%29%22%11%21
270
21st to endDay
25%31%33%8%2
297
February1st to 10thDay
31%25%30%11%1
270
11th to 20thDay
41%27%26%411
270
21st to endDay
42%26%28%41
210
March1st to 10thDay
28%24%37%10%1
250
11th to 20thDay
26%28%26%15%4
420
21st to endDay
25%23%30%16%6%
462
April1st to 10thDay
23%20%25%21%10%1
420
11th to 20thDay
20%18%31%19%10%1
412
21st to endDay
21%15%32%17%13%1
420
May1st to 10thDay
19%16%34%18%9%4
423
11th to 20thDay
14%11%27%26%14%7%
447
21st to endDay
14%8%21%28%17%12%
485
June1st to 10thDay
12%7%22%28%18%13%
450
11th to 20thDay
5%5%18%30%28%14%
450
21st to endDay
8%5%24%30%21%12%
450
July1st to 10thDay
9%415%27%24%20%
445
11th to 20thDay
9%7%15%26%25%18%
444
21st to endDay
11%5%13%26%30%15%
488
August1st to 10thDay
14%417%26%22%15%
446
11th to 20thDay
11%317%32%26%11%
439
21st to endDay
12%5%11%26%30%16%
495
September1st to 10thDay
11%5%15%27%30%13%
450
11th to 20thDay
15%414%27%29%12%
450
21st to endDay
16%5%18%29%25%8%
450
October1st to 10thDay
12%9%22%25%23%8%
450
11th to 20thDay
16%14%28%24%14%3
450
21st to endDay
21%13%30%22%12%2
410
November1st to 10thDay
16%13%36%26%7%2
270
11th to 20thDay
19%17%40%21%3
270
21st to endDay
18%21%37%17%6%1
270
December1st to 10thDay
31%21%31%12%4
270
11th to 20thDay
25%24%27%17%6%
270
21st to endDay
31%23%33%11%21
297
January1st to 10thNight
21%24%31%20%4
760
11th to 20thNight
27%23%27%18%4
760
21st to endNight
21%19%37%21%2
836
February1st to 10thNight
22%17%35%23%3
760
11th to 20thNight
28%20%32%18%1
743
21st to endNight
28%23%29%19%1
611
March1st to 10thNight
20%17%34%25%3
720
11th to 20thNight
20%20%30%23%6%1
720
21st to endNight
23%15%28%26%8%
792
April1st to 10thNight
15%17%29%28%11%
604
11th to 20thNight
16%12%30%29%13%1
533
21st to endNight
13%10%31%34%11%1
540
May1st to 10thNight
13%11%28%32%15%2
540
11th to 20thNight
11%8%21%35%21%4
531
21st to endNight
7%417%33%33%6%
584
June1st to 10thNight
7%5%14%38%31%5%
540
11th to 20thNight
3215%36%37%7%
540
21st to endNight
6%312%39%31%8%
540
July1st to 10thNight
11%26%31%40%10%
525
11th to 20thNight
7%48%27%43%11%
522
21st to endNight
7%29%31%42%10%
591
August1st to 10thNight
9%38%28%44%8%
537
11th to 20thNight
8%310%33%41%5%
534
21st to endNight
10%37%29%40%11%
594
September1st to 10thNight
9%311%31%37%8%
644
11th to 20thNight
13%212%31%35%8%
720
21st to endNight
13%417%31%32%4
720
October1st to 10thNight
13%7%18%26%30%7%
720
11th to 20thNight
16%9%25%30%18%2
720
21st to endNight
15%12%26%31%14%2
792
November1st to 10thNight
12%11%21%36%17%3
740
11th to 20thNight
14%18%29%27%11%1
760
21st to endNight
18%17%25%29%10%
760
December1st to 10thNight
24%20%27%24%6%
760
11th to 20thNight
20%17%28%28%6%1
760
21st to endNight
27%17%27%25%4
836
Page generated at 2024-02-22 06:05:47. Version ac07

Copyright 2024 Attilla Danko


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