Land-o-Clouds Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Land-o-Clouds 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
34%
24751
16%
74682
9%
24697
41%
24697
21%
51212

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
20%
950
13%
2648
4%
946
28%
946
17%
1956
January11th to 20thNight
18%
921
12%
2577
4%
921
25%
921
13%
2013
January21st to endNight
20%
990
12%
2772
3%
990
28%
990
15%
2133
February1st to 10thNight
20%
900
13%
2344
2%
900
27%
900
17%
1745
February11th to 20thNight
25%
726
19%
2125
7%
726
35%
726
18%
1482
February21st to endNight
20%
592
16%
1776
4%
592
31%
592
17%
1259
March1st to 10thNight
30%
720
16%
2160
7%
720
37%
720
20%
1483
March11th to 20thNight
32%
691
20%
2118
11%
691
40%
691
24%
1367
March21st to endNight
35%
594
19%
1980
15%
594
42%
594
18%
1375
April1st to 10thNight
25%
540
13%
1800
7%
540
35%
540
18%
1241
April11th to 20thNight
31%
533
18%
1775
14%
533
39%
533
20%
1193
April21st to endNight
33%
540
16%
1670
9%
540
40%
540
22%
1142
May1st to 10thNight
33%
540
15%
1578
9%
540
38%
540
21%
1105
May11th to 20thNight
35%
531
19%
1416
9%
531
44%
531
25%
995
May21st to endNight
48%
583
14%
1552
8%
582
52%
582
31%
1019
June1st to 10thNight
51%
540
16%
1440
8%
540
56%
540
35%
909
June11th to 20thNight
43%
540
17%
1440
10%
540
48%
540
33%
906
June21st to endNight
54%
540
16%
1440
9%
540
58%
540
37%
895
July1st to 10thNight
68%
525
17%
1400
10%
525
70%
525
44%
810
July11th to 20thNight
59%
522
20%
1392
12%
522
63%
522
40%
822
July21st to endNight
64%
591
23%
1487
15%
558
68%
558
42%
857
August1st to 10thNight
66%
537
22%
1423
18%
534
68%
534
39%
858
August11th to 20thNight
65%
534
22%
1688
19%
534
70%
534
34%
978
August21st to endNight
60%
594
22%
1980
21%
594
66%
594
33%
1134
September1st to 10thNight
56%
540
22%
1800
21%
540
62%
540
31%
1041
September11th to 20thNight
56%
619
29%
1879
23%
619
62%
619
34%
1097
September21st to endNight
44%
720
22%
1980
15%
720
49%
720
30%
1264
October1st to 10thNight
43%
720
21%
2060
14%
720
49%
720
28%
1305
October11th to 20thNight
28%
720
17%
2191
8%
720
38%
720
19%
1513
October21st to endNight
30%
792
14%
2574
9%
792
37%
792
17%
1790
November1st to 10thNight
32%
740
23%
2406
14%
740
44%
740
24%
1500
November11th to 20thNight
20%
760
15%
2470
7%
760
29%
760
14%
1804
November21st to endNight
21%
929
16%
2639
7%
929
30%
929
19%
1893
December1st to 10thNight
18%
950
10%
2660
2%
950
24%
950
13%
2045
December11th to 20thNight
16%
950
11%
3214
2%
948
24%
948
10%
2458
December21st to endNight
15%
1037
7%
4828
2%
1026
22%
1026
7%
3825

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%37%
74813
Night
13%10%47%6%35%45%7%37%
74986
TransparencyDay
46%7%12%23%11%1
74514
Night
46%6%11%22%13%1
74806
SeeingDay
16%11%29%26%14%4
14762
Night
17%10%32%29%11%1
24763

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
11%12%6%9%7%5%5%6%5%6%28%
1517
11th to 20thDay
13%15%8%11%8%45%5%5%6%19%
1472
21st to endDay
11%15%7%11%8%45%5%46%24%
1584
February1st to 10thDay
11%12%7%9%5%46%5%5%6%30%
1615
11th to 20thDay
13%11%46%5%35%45%6%36%
1721
21st to endDay
13%14%6%8%6%36%45%6%30%
1480
March1st to 10thDay
13%11%5%7%6%35%45%6%36%
1800
11th to 20thDay
12%11%5%7%6%3445%5%38%
1857
21st to endDay
17%11%47%6%35%45%7%31%
2376
April1st to 10thDay
15%12%47%6%35%46%6%31%
2160
11th to 20thDay
19%11%35%5%345%5%5%35%
2134
21st to endDay
19%9%37%7%345%5%6%32%
2288
May1st to 10thDay
15%8%46%5%36%5%6%7%34%
2380
11th to 20thDay
15%5%36%5%35%45%8%39%
2479
21st to endDay
12%5%26%7%45%5%6%8%40%
2725
June1st to 10thDay
10%5%36%435%5%6%10%44%
2520
11th to 20thDay
11%6%25%5%35%5%6%8%43%
2520
21st to endDay
9%5%25%5%35%5%6%10%44%
2520
July1st to 10thDay
6%424435%6%7%11%49%
2520
11th to 20thDay
9%4245%35%5%6%10%46%
2520
21st to endDay
7%4245%35%5%6%9%49%
2743
August1st to 10thDay
7%425%5%446%8%11%44%
2507
11th to 20thDay
11%6%25%4346%7%8%42%
2208
21st to endDay
11%6%35%435%5%5%8%45%
2376
September1st to 10thDay
12%6%35%6%345%5%8%43%
2160
11th to 20thDay
13%5%2443445%9%48%
2062
21st to endDay
13%8%35%5%3446%8%40%
1980
October1st to 10thDay
16%7%25%43445%7%42%
1896
11th to 20thDay
21%11%37%5%35%5%5%6%28%
1769
21st to endDay
17%12%47%5%35%346%34%
1782
November1st to 10thDay
13%9%37%5%345%5%7%40%
1672
11th to 20thDay
11%12%6%10%8%46%5%5%6%27%
1710
21st to endDay
16%12%5%8%6%33446%33%
1539
December1st to 10thDay
13%11%6%11%8%5%5%6%6%6%23%
1520
11th to 20thDay
12%14%5%11%7%5%6%5%5%6%24%
1918
21st to endDay
18%18%8%12%8%4444415%
2783
January1st to 10thNight
12%12%6%10%8%45%345%33%
2648
11th to 20thNight
14%14%6%11%7%35%445%26%
2577
21st to endNight
12%13%6%10%8%45%45%6%26%
2772
February1st to 10thNight
11%14%6%9%7%44445%33%
2344
11th to 20thNight
10%9%410%6%45%5%45%38%
2124
21st to endNight
17%12%46%5%34445%35%
1776
March1st to 10thNight
15%10%35%5%45%5%5%7%36%
2160
11th to 20thNight
12%9%36%5%35%5%5%8%41%
2118
21st to endNight
17%9%37%5%35%5%5%6%35%
1980
April1st to 10thNight
18%11%46%435%447%34%
1800
11th to 20thNight
19%10%36%5%3445%5%37%
1775
21st to endNight
17%9%36%6%3445%6%36%
1670
May1st to 10thNight
15%9%27%6%446%5%8%34%
1578
11th to 20thNight
15%7%27%6%45%46%7%37%
1416
21st to endNight
11%5%35%5%35%6%5%10%41%
1551
June1st to 10thNight
11%425%435%46%9%47%
1440
11th to 20thNight
10%6%35%5%345%6%9%45%
1440
21st to endNight
8%5%25%43445%9%51%
1440
July1st to 10thNight
6%323335%35%9%57%
1440
11th to 20thNight
6%4245%35%6%6%10%51%
1440
21st to endNight
6%325%4345%7%9%54%
1575
August1st to 10thNight
7%4245%345%8%10%48%
1432
11th to 20thNight
8%5%25%4245%5%9%51%
1688
21st to endNight
9%6%235%3445%8%51%
1980
September1st to 10thNight
10%6%35%43445%7%50%
1800
11th to 20thNight
13%425%423446%53%
1879
21st to endNight
12%7%36%5%2345%6%47%
1980
October1st to 10thNight
11%6%36%5%3445%6%46%
2060
11th to 20thNight
17%10%36%5%345%47%36%
2191
21st to endNight
18%12%36%4345%6%7%33%
2574
November1st to 10thNight
12%8%36%5%2445%6%44%
2406
11th to 20thNight
13%12%5%10%8%44446%30%
2470
21st to endNight
15%11%48%6%3445%6%34%
2639
December1st to 10thNight
13%13%5%10%7%37%5%5%7%26%
2660
11th to 20thNight
12%14%7%10%7%45%5%45%27%
3279
21st to endNight
18%17%6%10%7%44445%20%
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
54%7%13%18%8%
1518
11th to 20thDay
64%6%8%14%8%
1472
21st to endDay
61%6%10%15%7%1
1584
February1st to 10thDay
54%5%11%20%9%1
1615
11th to 20thDay
48%5%11%23%11%2
1731
21st to endDay
55%6%9%18%10%2
1480
March1st to 10thDay
48%7%13%21%9%2
1800
11th to 20thDay
46%5%11%20%14%2
1857
21st to endDay
53%5%13%20%7%1
2376
April1st to 10thDay
53%6%12%19%10%
2160
11th to 20thDay
50%6%9%20%13%2
2134
21st to endDay
51%7%10%19%11%1
2288
May1st to 10thDay
48%6%14%22%10%1
2380
11th to 20thDay
44%6%13%24%12%2
2483
21st to endDay
41%7%12%24%13%2
2725
June1st to 10thDay
36%7%12%28%15%2
2520
11th to 20thDay
38%7%13%25%16%1
2520
21st to endDay
35%8%14%27%15%1
2520
July1st to 10thDay
27%9%14%32%15%3
2451
11th to 20thDay
32%8%15%28%16%2
2445
21st to endDay
29%8%16%28%16%4
2591
August1st to 10thDay
32%9%16%29%12%2
2492
11th to 20thDay
37%8%13%30%11%1
2208
21st to endDay
36%7%12%26%17%2
2376
September1st to 10thDay
39%7%12%26%16%1
2160
11th to 20thDay
36%5%14%32%13%1
2062
21st to endDay
42%5%12%29%10%
1980
October1st to 10thDay
41%7%10%27%15%1
1896
11th to 20thDay
54%6%12%19%8%1
1769
21st to endDay
53%5%12%19%11%
1782
November1st to 10thDay
43%5%13%24%13%1
1672
11th to 20thDay
56%6%13%17%6%1
1710
21st to endDay
52%6%14%21%7%1
1539
December1st to 10thDay
59%10%11%14%6%1
1520
11th to 20thDay
59%6%14%14%5%2
1915
21st to endDay
73%5%7%10%5%
2783
January1st to 10thNight
55%410%18%12%1
2648
11th to 20thNight
61%5%10%16%7%1
2577
21st to endNight
59%5%10%16%9%1
2772
February1st to 10thNight
54%48%20%12%2
2344
11th to 20thNight
49%5%9%22%13%2
2125
21st to endNight
52%412%19%11%2
1776
March1st to 10thNight
47%6%13%20%11%2
2160
11th to 20thNight
41%6%13%23%15%2
2118
21st to endNight
50%6%9%22%11%1
1980
April1st to 10thNight
50%5%10%17%17%2
1800
11th to 20thNight
49%49%19%16%3
1775
21st to endNight
47%5%12%21%14%1
1670
May1st to 10thNight
48%7%12%21%11%1
1578
11th to 20thNight
45%6%10%23%13%2
1417
21st to endNight
37%7%14%24%15%2
1552
June1st to 10thNight
33%8%12%29%17%1
1440
11th to 20thNight
35%7%11%28%18%2
1440
21st to endNight
31%8%16%26%16%3
1440
July1st to 10thNight
25%7%14%32%19%4
1400
11th to 20thNight
27%7%14%29%19%3
1392
21st to endNight
26%7%15%31%17%4
1487
August1st to 10thNight
28%8%17%29%15%3
1423
11th to 20thNight
30%8%14%32%16%
1688
21st to endNight
31%7%11%28%20%3
1980
September1st to 10thNight
33%7%11%24%24%2
1800
11th to 20thNight
33%5%11%34%16%1
1879
21st to endNight
37%6%10%30%16%1
1980
October1st to 10thNight
38%6%9%29%17%2
2060
11th to 20thNight
48%6%12%20%13%1
2191
21st to endNight
50%6%13%20%11%
2574
November1st to 10thNight
40%5%11%25%16%2
2406
11th to 20thNight
55%5%11%17%10%1
2470
21st to endNight
51%5%15%21%6%1
2639
December1st to 10thNight
56%9%11%17%7%1
2660
11th to 20thNight
59%5%11%16%8%1
3281
21st to endNight
66%6%9%13%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
16%15%34%27%7%1
270
11th to 20thDay
20%14%35%23%7%
252
21st to endDay
19%12%38%23%7%1
264
February1st to 10thDay
14%18%44%19%6%
240
11th to 20thDay
19%23%35%18%5%
240
21st to endDay
22%20%42%14%21
198
March1st to 10thDay
18%18%43%16%5%
240
11th to 20thDay
21%17%30%23%44
253
21st to endDay
25%13%30%24%7%2
462
April1st to 10thDay
24%11%37%22%5%
420
11th to 20thDay
25%17%27%19%9%3
412
21st to endDay
22%12%28%24%12%1
420
May1st to 10thDay
21%10%32%26%9%2
463
11th to 20thDay
16%11%32%25%11%4
625
21st to endDay
14%9%29%27%15%5%
679
June1st to 10thDay
10%6%31%33%15%4
630
11th to 20thDay
13%8%30%28%15%5%
630
21st to endDay
13%9%26%32%16%4
630
July1st to 10thDay
7%420%32%27%11%
621
11th to 20thDay
10%6%24%34%19%7%
618
21st to endDay
7%429%33%21%7%
684
August1st to 10thDay
8%422%35%23%9%
626
11th to 20thDay
14%415%28%25%13%
460
21st to endDay
13%7%20%28%21%10%
495
September1st to 10thDay
15%6%20%29%21%9%
450
11th to 20thDay
12%420%35%20%9%
450
21st to endDay
16%11%27%23%19%4
450
October1st to 10thDay
18%12%23%25%16%5%
366
11th to 20thDay
22%19%31%20%7%1
270
21st to endDay
26%12%39%15%6%2
297
November1st to 10thDay
16%15%35%23%10%1
270
11th to 20thDay
16%17%40%22%5%
270
21st to endDay
23%17%36%20%4
270
December1st to 10thDay
20%20%40%15%5%
270
11th to 20thDay
22%16%39%16%6%1
270
21st to endDay
23%21%36%16%4
297
January1st to 10thNight
17%13%38%24%7%
950
11th to 20thNight
20%12%38%23%6%1
921
21st to endNight
19%11%39%26%6%
990
February1st to 10thNight
20%12%38%25%5%
900
11th to 20thNight
15%15%39%24%6%
729
21st to endNight
24%13%36%21%6%
592
March1st to 10thNight
21%11%33%25%9%1
720
11th to 20thNight
17%12%36%28%7%1
691
21st to endNight
23%7%27%32%9%1
594
April1st to 10thNight
23%10%36%25%6%
540
11th to 20thNight
24%10%30%29%6%1
533
21st to endNight
20%9%32%30%8%1
540
May1st to 10thNight
19%8%34%30%7%1
540
11th to 20thNight
17%8%35%30%10%1
531
21st to endNight
12%5%28%38%15%1
584
June1st to 10thNight
12%427%39%18%1
540
11th to 20thNight
14%5%32%36%13%1
540
21st to endNight
9%426%41%19%1
540
July1st to 10thNight
8%217%42%28%2
525
11th to 20thNight
7%324%41%23%2
522
21st to endNight
7%221%44%25%1
591
August1st to 10thNight
8%117%46%26%3
537
11th to 20thNight
10%316%40%28%3
534
21st to endNight
11%320%42%22%3
594
September1st to 10thNight
11%423%35%22%5%
540
11th to 20thNight
14%5%21%35%21%5%
619
21st to endNight
15%7%26%29%19%3
720
October1st to 10thNight
15%8%28%30%18%2
720
11th to 20thNight
22%14%32%24%8%
720
21st to endNight
24%11%29%27%9%1
792
November1st to 10thNight
16%12%35%26%9%1
740
11th to 20thNight
20%17%37%21%6%
760
21st to endNight
21%15%37%21%7%
929
December1st to 10thNight
19%16%38%20%6%
950
11th to 20thNight
21%15%37%21%6%1
950
21st to endNight
24%14%37%22%3
1045
Page generated at 2024-01-11 21:33:49. Version ac07

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