Far Horizons Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Far Horizons 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
45%
24947
19%
74511
13%
24905
51%
24905
28%
46763

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
37%
946
17%
2647
10%
946
43%
946
25%
1797
January11th to 20thNight
34%
920
18%
2575
8%
920
42%
920
24%
1767
January21st to endNight
32%
931
17%
2713
9%
931
40%
931
21%
1882
February1st to 10thNight
34%
720
12%
2340
9%
720
38%
720
15%
1703
February11th to 20thNight
33%
700
12%
2273
9%
700
38%
700
19%
1548
February21st to endNight
41%
592
17%
1808
13%
592
46%
592
23%
1217
March1st to 10thNight
40%
720
16%
2150
9%
720
45%
720
28%
1368
March11th to 20thNight
44%
720
19%
1980
12%
720
48%
720
29%
1301
March21st to endNight
40%
694
14%
2080
10%
694
44%
694
20%
1456
April1st to 10thNight
39%
540
14%
1800
11%
540
45%
540
19%
1208
April11th to 20thNight
37%
533
15%
1777
13%
533
42%
533
18%
1240
April21st to endNight
46%
540
16%
1643
13%
540
50%
540
23%
1106
May1st to 10thNight
50%
540
17%
1440
13%
540
53%
540
29%
952
May11th to 20thNight
50%
531
16%
1418
11%
531
52%
531
27%
959
May21st to endNight
48%
584
11%
1552
7%
582
49%
582
25%
1081
June1st to 10thNight
50%
540
13%
1440
7%
540
52%
540
30%
961
June11th to 20thNight
41%
540
12%
1440
5%
540
45%
540
32%
935
June21st to endNight
60%
540
15%
1440
8%
540
63%
540
40%
844
July1st to 10thNight
62%
525
15%
1400
10%
525
63%
525
44%
807
July11th to 20thNight
55%
522
20%
1392
11%
522
61%
522
46%
783
July21st to endNight
70%
591
26%
1488
19%
558
74%
558
52%
803
August1st to 10thNight
63%
537
24%
1467
19%
534
68%
534
45%
819
August11th to 20thNight
67%
534
26%
1602
22%
534
71%
534
48%
807
August21st to endNight
64%
594
27%
1948
27%
594
67%
594
40%
1013
September1st to 10thNight
62%
540
28%
1800
27%
540
70%
540
42%
907
September11th to 20thNight
61%
540
29%
1800
28%
540
67%
540
36%
964
September21st to endNight
54%
634
27%
2033
25%
634
59%
634
36%
1120
October1st to 10thNight
50%
720
22%
2160
17%
720
54%
720
30%
1350
October11th to 20thNight
47%
720
28%
2160
18%
720
54%
720
32%
1272
October21st to endNight
44%
906
23%
2490
12%
906
51%
906
33%
1550
November1st to 10thNight
45%
925
22%
2454
12%
925
52%
925
32%
1599
November11th to 20thNight
38%
950
23%
2660
11%
950
47%
950
27%
1725
November21st to endNight
39%
950
24%
2660
12%
950
49%
950
31%
1660
December1st to 10thNight
37%
950
17%
2660
9%
950
43%
950
24%
1826
December11th to 20thNight
37%
948
21%
3150
11%
948
45%
948
23%
1971
December21st to endNight
34%
1030
13%
4671
8%
1026
41%
1026
17%
2462

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
9%6%35%5%345%6%8%47%
74775
Night
8%7%36%5%35%5%6%8%44%
75016
TransparencyDay
34%6%14%25%16%4
74478
Night
37%7%13%24%15%4
74835
SeeingDay
12%8%26%31%18%5%
14809
Night
12%7%29%38%13%1
24972

By Month

Percentage Cloud Cover SW (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
9%10%47%7%46%5%7%7%36%
1518
11th to 20thDay
9%12%46%6%45%45%6%39%
1464
21st to endDay
5%10%5%10%7%45%5%6%8%35%
1660
February1st to 10thDay
9%13%6%9%7%45%5%5%7%31%
1620
11th to 20thDay
7%15%5%10%5%345%5%6%34%
1575
21st to endDay
5%10%5%8%7%46%6%6%8%35%
1448
March1st to 10thDay
7%8%5%8%6%445%6%9%39%
1808
11th to 20thDay
8%7%36%5%45%5%6%10%41%
1980
21st to endDay
11%8%46%6%45%6%7%9%35%
2275
April1st to 10thDay
14%8%35%5%35%46%7%40%
2160
11th to 20thDay
13%11%37%6%45%5%7%8%31%
2131
21st to endDay
17%8%36%5%35%5%5%6%37%
2315
May1st to 10thDay
12%8%35%4345%6%8%42%
2520
11th to 20thDay
13%5%26%5%35%46%11%41%
2478
21st to endDay
18%6%35%5%45%6%7%9%33%
2724
June1st to 10thDay
11%5%25%4346%6%9%46%
2520
11th to 20thDay
9%4246%346%6%9%46%
2520
21st to endDay
42133235%6%9%61%
2520
July1st to 10thDay
431332346%9%61%
2520
11th to 20thDay
221333345%8%67%
2520
21st to endDay
321232346%7%66%
2742
August1st to 10thDay
5%4134235%5%8%60%
2460
11th to 20thDay
7%31332346%7%61%
2299
21st to endDay
5%31332335%8%63%
2407
September1st to 10thDay
6%41332335%6%63%
2160
11th to 20thDay
9%31442345%7%59%
2160
21st to endDay
13%313423348%56%
1923
October1st to 10thDay
16%7%25%423346%47%
1800
11th to 20thDay
13%7%25%42446%7%46%
1800
21st to endDay
10%7%26%4345%5%8%45%
1847
November1st to 10thDay
10%6%36%5%245%6%8%44%
1621
11th to 20thDay
7%10%38%7%3446%7%42%
1520
21st to endDay
49%46%5%35%6%6%9%43%
1520
December1st to 10thDay
6%10%5%9%5%35%6%5%8%37%
1520
11th to 20thDay
5%8%47%5%345%5%9%44%
1926
21st to endDay
6%7%36%5%36%5%6%7%45%
2794
January1st to 10thNight
7%9%47%7%45%6%6%7%37%
2647
11th to 20thNight
8%10%37%7%45%5%6%6%38%
2575
21st to endNight
6%10%5%8%7%45%6%7%8%34%
2713
February1st to 10thNight
8%12%6%11%8%46%5%5%7%28%
2340
11th to 20thNight
6%11%5%9%7%46%5%6%8%33%
2272
21st to endNight
6%11%48%6%35%5%6%8%38%
1808
March1st to 10thNight
7%9%36%5%35%5%6%8%42%
2150
11th to 20thNight
8%7%37%6%35%5%6%9%42%
1980
21st to endNight
11%10%48%6%45%5%7%7%33%
2080
April1st to 10thNight
12%11%5%6%6%35%5%5%7%36%
1800
11th to 20thNight
13%9%5%8%6%36%6%6%8%31%
1777
21st to endNight
13%8%36%6%36%45%8%38%
1643
May1st to 10thNight
13%6%346%35%45%10%42%
1440
11th to 20thNight
13%7%35%6%35%46%9%38%
1417
21st to endNight
16%5%25%4445%7%8%38%
1552
June1st to 10thNight
9%6%25%6%36%6%7%10%40%
1440
11th to 20thNight
9%426%6%35%6%7%9%44%
1440
21st to endNight
8%313435%48%8%53%
1440
July1st to 10thNight
7%4135%3447%10%53%
1440
11th to 20thNight
42144345%6%9%57%
1440
21st to endNight
5%2134345%6%10%59%
1576
August1st to 10thNight
5%414435%5%7%8%54%
1475
11th to 20thNight
6%21342445%9%59%
1602
21st to endNight
6%323435%46%10%54%
1948
September1st to 10thNight
7%41342345%7%59%
1800
11th to 20thNight
11%414424446%57%
1800
21st to endNight
11%6%1432345%7%53%
2033
October1st to 10thNight
15%7%35%324446%48%
2160
11th to 20thNight
10%7%2442445%7%50%
2160
21st to endNight
7%7%25%5%35%5%6%9%46%
2490
November1st to 10thNight
9%8%36%6%35%46%7%44%
2454
11th to 20thNight
7%8%36%7%35%6%5%7%43%
2660
21st to endNight
5%8%36%6%25%46%8%45%
2660
December1st to 10thNight
7%9%47%7%46%5%7%8%36%
2660
11th to 20thNight
6%7%47%6%35%5%6%7%43%
3271
21st to endNight
5%9%36%5%345%6%7%45%
4873

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
45%8%15%25%6%1
1519
11th to 20thDay
46%6%13%24%8%2
1464
21st to endDay
45%7%14%23%9%2
1660
February1st to 10thDay
52%6%14%20%9%1
1620
11th to 20thDay
50%5%16%17%10%1
1584
21st to endDay
44%7%15%20%13%2
1448
March1st to 10thDay
41%7%18%22%12%
1808
11th to 20thDay
39%6%16%27%11%1
1980
21st to endDay
44%7%18%23%6%1
2275
April1st to 10thDay
43%6%16%24%10%1
2160
11th to 20thDay
48%9%15%20%8%
2134
21st to endDay
47%6%14%21%11%1
2315
May1st to 10thDay
38%7%14%28%13%1
2520
11th to 20thDay
37%7%17%25%12%2
2482
21st to endDay
45%10%17%21%7%
2724
June1st to 10thDay
33%8%18%27%12%1
2520
11th to 20thDay
33%8%18%25%13%3
2520
21st to endDay
19%7%14%29%24%7%
2520
July1st to 10thDay
18%5%11%32%25%8%
2451
11th to 20thDay
15%5%9%26%33%12%
2445
21st to endDay
16%49%21%35%14%
2590
August1st to 10thDay
22%410%26%26%12%
2444
11th to 20thDay
22%5%9%26%30%9%
2299
21st to endDay
21%49%24%30%12%
2407
September1st to 10thDay
22%48%25%29%12%
2160
11th to 20thDay
25%5%12%29%22%7%
2160
21st to endDay
28%410%31%23%3
1923
October1st to 10thDay
39%410%26%17%4
1800
11th to 20thDay
37%5%13%28%14%4
1800
21st to endDay
36%6%15%26%14%2
1847
November1st to 10thDay
37%6%11%26%16%4
1621
11th to 20thDay
41%6%15%24%13%2
1520
21st to endDay
36%6%18%24%15%1
1520
December1st to 10thDay
44%7%14%24%11%1
1520
11th to 20thDay
36%8%22%28%6%1
1924
21st to endDay
36%6%10%31%14%2
2794
January1st to 10thNight
43%7%16%24%8%1
2647
11th to 20thNight
44%7%16%22%9%2
2575
21st to endNight
46%8%15%20%11%1
2713
February1st to 10thNight
54%7%12%17%9%1
2340
11th to 20thNight
47%7%15%22%8%1
2273
21st to endNight
44%7%14%20%13%2
1808
March1st to 10thNight
37%8%19%23%11%1
2150
11th to 20thNight
38%8%13%25%14%2
1980
21st to endNight
48%7%15%20%10%1
2080
April1st to 10thNight
47%7%13%19%12%2
1800
11th to 20thNight
49%8%12%23%8%1
1777
21st to endNight
44%7%12%24%13%
1643
May1st to 10thNight
39%7%12%29%13%1
1440
11th to 20thNight
41%8%13%24%12%2
1418
21st to endNight
41%10%19%22%7%1
1552
June1st to 10thNight
36%10%17%27%9%1
1440
11th to 20thNight
33%10%19%21%14%3
1440
21st to endNight
25%9%14%24%22%5%
1440
July1st to 10thNight
26%6%11%32%20%5%
1400
11th to 20thNight
22%7%11%21%25%14%
1392
21st to endNight
19%6%9%24%31%11%
1488
August1st to 10thNight
24%6%11%23%24%11%
1467
11th to 20thNight
21%412%25%29%9%
1602
21st to endNight
25%5%11%20%25%13%
1948
September1st to 10thNight
24%5%7%24%27%14%
1800
11th to 20thNight
28%6%10%25%24%8%
1800
21st to endNight
29%5%10%25%25%5%
2033
October1st to 10thNight
38%6%11%22%20%4
2160
11th to 20thNight
33%6%11%28%18%4
2160
21st to endNight
33%8%16%26%14%4
2490
November1st to 10thNight
38%6%14%23%16%4
2454
11th to 20thNight
39%7%12%27%13%2
2660
21st to endNight
35%7%14%28%15%2
2660
December1st to 10thNight
43%8%14%22%11%1
2660
11th to 20thNight
38%7%16%30%9%
3272
21st to endNight
36%5%11%32%13%4
4873

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%7%34%23%15%6%
270
11th to 20thDay
12%14%21%31%18%4
249
21st to endDay
13%13%37%29%7%2
264
February1st to 10thDay
17%12%36%31%4
240
11th to 20thDay
15%13%34%27%9%2
240
21st to endDay
13%8%33%31%14%1
198
March1st to 10thDay
13%11%29%31%13%3
248
11th to 20thDay
14%8%27%32%15%4
420
21st to endDay
18%9%26%29%16%3
462
April1st to 10thDay
20%10%27%31%10%1
420
11th to 20thDay
20%18%33%21%7%1
412
21st to endDay
24%8%23%27%15%3
460
May1st to 10thDay
13%10%24%28%18%6%
603
11th to 20thDay
18%6%20%31%20%5%
625
21st to endDay
17%8%22%27%18%8%
679
June1st to 10thDay
10%6%23%29%24%8%
630
11th to 20thDay
13%8%36%27%15%2
630
21st to endDay
6%6%25%36%22%6%
630
July1st to 10thDay
6%321%39%26%6%
621
11th to 20thDay
3428%41%23%2
618
21st to endDay
4420%40%28%6%
684
August1st to 10thDay
7%322%42%20%6%
579
11th to 20thDay
7%320%33%24%12%
437
21st to endDay
46%21%32%29%8%
495
September1st to 10thDay
7%6%22%33%24%8%
450
11th to 20thDay
10%321%30%26%9%
450
21st to endDay
16%5%24%23%24%7%
311
October1st to 10thDay
19%7%18%27%18%11%
270
11th to 20thDay
19%8%21%31%14%7%
270
21st to endDay
12%14%35%24%12%3
297
November1st to 10thDay
15%13%28%26%14%4
270
11th to 20thDay
11%11%34%27%14%3
270
21st to endDay
7%11%36%34%10%1
270
December1st to 10thDay
10%11%39%29%10%2
270
11th to 20thDay
13%11%32%33%9%1
270
21st to endDay
10%10%28%33%16%3
297
January1st to 10thNight
11%8%33%34%13%1
950
11th to 20thNight
13%9%34%31%11%1
920
21st to endNight
11%11%35%33%9%1
931
February1st to 10thNight
13%9%31%33%13%1
720
11th to 20thNight
11%9%35%36%8%1
704
21st to endNight
12%7%30%34%14%2
592
March1st to 10thNight
12%7%34%37%10%1
720
11th to 20thNight
11%5%32%40%10%1
720
21st to endNight
16%7%27%36%14%1
694
April1st to 10thNight
18%7%26%40%8%1
540
11th to 20thNight
16%7%31%35%10%
533
21st to endNight
18%5%23%40%13%1
540
May1st to 10thNight
16%6%21%40%16%1
540
11th to 20thNight
18%421%36%19%2
531
21st to endNight
18%427%33%18%1
584
June1st to 10thNight
11%7%26%37%18%2
540
11th to 20thNight
10%8%35%35%11%
540
21st to endNight
8%5%23%48%16%1
540
July1st to 10thNight
7%324%45%21%
525
11th to 20thNight
5%333%47%12%
522
21st to endNight
5%320%52%20%1
591
August1st to 10thNight
6%223%50%18%
537
11th to 20thNight
6%220%51%21%1
534
21st to endNight
7%420%48%21%1
594
September1st to 10thNight
8%422%46%19%1
540
11th to 20thNight
12%5%19%44%17%2
540
21st to endNight
13%5%23%38%18%2
634
October1st to 10thNight
18%422%36%18%2
720
11th to 20thNight
14%7%26%36%17%1
720
21st to endNight
11%9%30%36%13%1
906
November1st to 10thNight
13%7%28%40%11%1
925
11th to 20thNight
10%10%35%35%10%1
950
21st to endNight
10%9%35%38%8%
950
December1st to 10thNight
11%10%34%36%10%1
950
11th to 20thNight
10%8%34%36%11%1
950
21st to endNight
14%9%31%33%11%1
1045
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