This page made possible by the sponsorship of: Eric Zeiner.

The New Freedom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The New Freedom 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
50%
23983
22%
74443
16%
23929
58%
23929
28%
46083

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
25%
757
23%
2459
9%
757
43%
757
23%
1492
January11th to 20thNight
35%
740
27%
2404
16%
740
50%
740
26%
1448
January21st to endNight
28%
792
26%
2488
11%
792
44%
792
25%
1548
February1st to 10thNight
33%
720
24%
2160
12%
720
45%
720
26%
1369
February11th to 20thNight
30%
703
23%
2098
10%
699
44%
699
27%
1308
February21st to endNight
29%
592
24%
1776
12%
592
40%
592
26%
1136
March1st to 10thNight
37%
720
28%
2063
15%
720
48%
720
33%
1229
March11th to 20thNight
36%
720
22%
1980
10%
720
46%
720
28%
1265
March21st to endNight
39%
792
24%
2178
11%
792
48%
792
31%
1334
April1st to 10thNight
42%
720
25%
1980
16%
720
49%
720
33%
1207
April11th to 20thNight
47%
585
26%
1827
18%
585
56%
585
33%
1058
April21st to endNight
56%
540
33%
1649
23%
540
66%
540
40%
890
May1st to 10thNight
54%
540
27%
1620
17%
540
62%
540
38%
883
May11th to 20thNight
58%
531
17%
1592
12%
531
61%
531
30%
990
May21st to endNight
67%
582
21%
1744
17%
582
69%
582
32%
1062
June1st to 10thNight
61%
540
15%
1620
12%
540
62%
540
23%
1100
June11th to 20thNight
76%
540
18%
1620
15%
540
77%
540
32%
981
June21st to endNight
68%
540
13%
1620
11%
540
69%
540
26%
1079
July1st to 10thNight
74%
525
10%
1575
9%
525
74%
525
21%
1107
July11th to 20thNight
73%
522
9%
1566
9%
522
74%
522
25%
1071
July21st to endNight
77%
591
14%
1672
13%
558
78%
558
27%
1130
August1st to 10thNight
72%
537
12%
1600
13%
534
72%
534
26%
1076
August11th to 20thNight
69%
534
15%
1735
16%
534
69%
534
24%
1147
August21st to endNight
63%
619
15%
2005
17%
619
63%
619
20%
1375
September1st to 10thNight
64%
720
16%
1980
15%
720
65%
720
27%
1358
September11th to 20thNight
64%
720
19%
1980
16%
720
66%
720
27%
1334
September21st to endNight
61%
720
24%
1980
21%
720
65%
720
30%
1285
October1st to 10thNight
58%
720
28%
1980
22%
720
64%
720
37%
1188
October11th to 20thNight
55%
720
33%
2092
26%
720
65%
720
38%
1178
October21st to endNight
54%
792
32%
2376
27%
792
63%
792
36%
1338
November1st to 10thNight
52%
740
29%
2291
24%
740
62%
740
35%
1290
November11th to 20thNight
45%
760
29%
2470
21%
760
57%
760
32%
1380
November21st to endNight
41%
760
26%
2470
18%
760
51%
760
28%
1478
December1st to 10thNight
38%
760
27%
2470
16%
760
53%
760
26%
1493
December11th to 20thNight
37%
759
27%
2903
17%
758
48%
758
23%
1681
December21st to endNight
35%
830
15%
4420
16%
817
44%
817
12%
2795

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
11%5%25%6%35%5%6%8%43%
74889
Night
11%5%25%5%35%5%6%8%45%
74903
TransparencyDay
38%7%12%18%18%6%
74612
Night
37%7%11%18%20%8%
74699
SeeingDay
14%8%22%24%21%11%
13899
Night
13%7%23%31%22%4
23995

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
16%5%3443445%6%46%
1706
11th to 20thDay
12%7%345%23347%48%
1662
21st to endDay
17%6%35%4245%5%6%43%
1863
February1st to 10thDay
14%8%36%6%445%5%6%40%
1800
11th to 20thDay
17%5%35%42445%7%44%
1748
21st to endDay
16%7%25%5%3436%8%41%
1480
March1st to 10thDay
12%5%2443445%6%51%
1894
11th to 20thDay
13%6%36%5%345%47%44%
1980
21st to endDay
14%425%5%35%45%7%46%
2178
April1st to 10thDay
11%5%25%6%35%45%6%48%
1980
11th to 20thDay
13%5%2443345%7%49%
2095
21st to endDay
6%3245%435%5%8%55%
2308
May1st to 10thDay
7%424425%5%5%9%54%
2340
11th to 20thDay
7%5%36%5%35%6%7%10%42%
2301
21st to endDay
8%425%6%36%6%8%9%42%
2531
June1st to 10thDay
11%6%26%7%47%7%7%10%33%
2340
11th to 20thDay
5%425%6%46%7%8%13%40%
2340
21st to endDay
6%5%26%8%47%7%8%12%35%
2340
July1st to 10thDay
8%5%27%9%5%8%8%8%11%29%
2340
11th to 20thDay
7%6%37%7%6%8%8%8%11%29%
2340
21st to endDay
6%5%36%8%5%8%8%9%12%31%
2547
August1st to 10thDay
8%6%26%7%47%8%10%12%30%
2327
11th to 20thDay
9%6%37%7%48%7%8%11%29%
2161
21st to endDay
12%7%37%7%47%7%7%9%30%
2332
September1st to 10thDay
9%5%26%6%35%7%7%10%38%
1980
11th to 20thDay
13%5%26%5%35%6%7%9%40%
1980
21st to endDay
12%6%26%7%4446%6%43%
1980
October1st to 10thDay
12%5%235%3345%6%52%
1980
11th to 20thDay
10%32342345%8%56%
1866
21st to endDay
10%5%1442345%6%56%
1980
November1st to 10thDay
11%5%24434346%54%
1783
11th to 20thDay
12%5%2442335%6%53%
1710
21st to endDay
14%5%35%5%3445%6%47%
1710
December1st to 10thDay
16%6%345%35%45%6%43%
1710
11th to 20thDay
18%5%345%34345%46%
2153
21st to endDay
18%8%36%5%33335%43%
3124
January1st to 10thNight
16%7%345%3335%6%46%
2459
11th to 20thNight
14%6%35%42445%7%47%
2404
21st to endNight
18%6%25%434435%47%
2488
February1st to 10thNight
14%6%36%43436%5%45%
2160
11th to 20thNight
17%5%24424345%48%
2098
21st to endNight
15%6%35%5%245%5%6%44%
1776
March1st to 10thNight
11%5%15%433447%52%
2063
11th to 20thNight
13%5%25%5%35%46%8%45%
1980
21st to endNight
10%5%35%43445%7%49%
2178
April1st to 10thNight
10%5%25%43445%7%49%
1980
11th to 20thNight
11%425%4345%5%8%50%
1827
21st to endNight
6%2245%25%5%5%7%57%
1649
May1st to 10thNight
5%41443445%8%56%
1620
11th to 20thNight
7%425%5%35%7%6%8%46%
1592
21st to endNight
7%7%35%435%5%6%10%44%
1744
June1st to 10thNight
8%6%37%7%45%7%9%11%33%
1620
11th to 20thNight
4325%5%45%6%8%12%45%
1620
21st to endNight
5%5%27%6%48%7%8%13%36%
1620
July1st to 10thNight
6%5%36%6%47%9%10%13%32%
1620
11th to 20thNight
5%5%247%6%8%8%10%13%33%
1620
21st to endNight
6%435%6%46%8%10%13%35%
1771
August1st to 10thNight
5%426%7%47%7%8%13%36%
1611
11th to 20thNight
9%5%26%6%46%6%8%13%33%
1735
21st to endNight
10%6%26%7%46%7%8%9%33%
2005
September1st to 10thNight
9%5%36%8%45%7%7%10%37%
1980
11th to 20thNight
12%5%26%6%36%5%5%7%42%
1980
21st to endNight
10%6%26%6%35%5%6%6%44%
1980
October1st to 10thNight
11%5%24425%45%7%52%
1980
11th to 20thNight
12%5%23323346%58%
2092
21st to endNight
10%415%4245%45%55%
2376
November1st to 10thNight
11%5%2443334456%
2291
11th to 20thNight
13%5%24323346%55%
2470
21st to endNight
14%5%35%5%3435%6%48%
2470
December1st to 10thNight
13%6%244345%5%6%47%
2470
11th to 20thNight
15%6%25%423345%49%
3042
21st to endNight
17%9%47%5%34446%37%
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
40%47%18%25%7%
1707
11th to 20thDay
38%5%8%17%24%8%
1662
21st to endDay
42%35%16%24%9%
1863
February1st to 10thDay
45%49%15%18%9%
1800
11th to 20thDay
41%45%17%25%7%
1758
21st to endDay
42%5%8%16%19%11%
1480
March1st to 10thDay
35%47%19%22%13%
1894
11th to 20thDay
40%6%12%15%18%9%
1980
21st to endDay
38%5%11%18%22%6%
2178
April1st to 10thDay
37%6%9%20%19%10%
1980
11th to 20thDay
34%48%21%22%11%
2095
21st to endDay
27%6%9%25%26%7%
2308
May1st to 10thDay
29%6%10%22%26%6%
2340
11th to 20thDay
36%8%16%22%15%3
2305
21st to endDay
36%7%13%24%18%2
2531
June1st to 10thDay
43%9%15%19%12%2
2340
11th to 20thDay
33%9%17%24%14%2
2340
21st to endDay
39%11%18%18%12%2
2340
July1st to 10thDay
42%13%20%17%5%2
2275
11th to 20thDay
43%12%22%16%5%1
2271
21st to endDay
40%13%20%20%7%1
2405
August1st to 10thDay
42%13%21%20%4
2314
11th to 20thDay
44%12%20%16%8%
2161
21st to endDay
48%11%17%13%9%2
2332
September1st to 10thDay
38%10%16%17%15%3
1980
11th to 20thDay
39%9%10%19%18%5%
1980
21st to endDay
41%6%9%19%19%6%
1980
October1st to 10thDay
33%5%9%20%23%10%
1980
11th to 20thDay
28%48%24%27%10%
1866
21st to endDay
30%46%12%31%16%
1980
November1st to 10thDay
33%47%14%26%16%
1783
11th to 20thDay
33%46%17%25%15%
1710
21st to endDay
37%5%8%17%23%10%
1710
December1st to 10thDay
42%411%14%19%9%
1710
11th to 20thDay
42%35%15%27%8%
2150
21st to endDay
46%45%15%24%5%
3124
January1st to 10thNight
40%47%18%25%7%
2459
11th to 20thNight
38%46%17%26%8%
2404
21st to endNight
41%35%15%26%10%
2488
February1st to 10thNight
41%47%18%20%11%
2160
11th to 20thNight
40%46%16%22%12%
2099
21st to endNight
40%6%8%16%17%14%
1776
March1st to 10thNight
34%47%18%23%14%
2063
11th to 20thNight
37%6%12%16%19%10%
1980
21st to endNight
34%5%11%18%23%9%
2178
April1st to 10thNight
34%5%11%19%20%13%
1980
11th to 20thNight
33%5%7%21%23%12%
1827
21st to endNight
26%5%10%25%24%10%
1649
May1st to 10thNight
26%6%12%23%25%8%
1620
11th to 20thNight
32%11%18%19%17%4
1593
21st to endNight
35%6%13%24%18%4
1745
June1st to 10thNight
41%11%16%19%13%
1620
11th to 20thNight
30%11%18%27%13%2
1620
21st to endNight
38%11%21%15%12%3
1620
July1st to 10thNight
39%16%22%15%6%2
1575
11th to 20thNight
37%14%28%14%7%1
1566
21st to endNight
34%16%23%21%6%1
1672
August1st to 10thNight
35%14%25%21%5%
1600
11th to 20thNight
38%13%23%18%8%1
1735
21st to endNight
43%12%18%16%9%2
2005
September1st to 10thNight
39%11%17%15%13%4
1980
11th to 20thNight
40%9%13%15%19%4
1980
21st to endNight
38%7%13%15%21%6%
1980
October1st to 10thNight
32%5%8%20%23%11%
1980
11th to 20thNight
29%47%20%29%10%
2092
21st to endNight
30%5%5%16%28%16%
2376
November1st to 10thNight
32%38%14%27%16%
2291
11th to 20thNight
33%46%15%27%16%
2470
21st to endNight
38%37%18%22%11%
2470
December1st to 10thNight
37%5%10%18%23%7%
2470
11th to 20thNight
38%46%14%29%9%
3044
21st to endNight
49%45%17%21%4
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
18%19%47%13%2
270
11th to 20thDay
17%18%38%18%7%2
254
21st to endDay
24%22%40%10%4
264
February1st to 10thDay
21%24%35%15%5%
240
11th to 20thDay
28%18%34%19%1
240
21st to endDay
19%19%46%13%3
198
March1st to 10thDay
14%19%32%25%9%1
334
11th to 20thDay
16%14%36%23%9%1
420
21st to endDay
18%14%34%25%9%
462
April1st to 10thDay
18%17%25%27%12%2
420
11th to 20thDay
14%12%31%23%16%4
412
21st to endDay
10%10%24%32%19%5%
420
May1st to 10thDay
8%11%26%30%18%6%
423
11th to 20thDay
10%320%29%23%15%
447
21st to endDay
11%414%30%26%16%
485
June1st to 10thDay
13%212%30%26%17%
450
11th to 20thDay
10%212%22%27%26%
450
21st to endDay
7%215%27%29%20%
450
July1st to 10thDay
7%27%22%36%26%
445
11th to 20thDay
7%26%18%31%36%
444
21st to endDay
5%19%22%36%27%
488
August1st to 10thDay
13%18%22%33%24%
446
11th to 20thDay
9%26%20%38%25%
439
21st to endDay
13%28%23%35%19%
495
September1st to 10thDay
12%29%26%33%17%
450
11th to 20thDay
14%211%31%29%12%
450
21st to endDay
15%214%28%28%14%
450
October1st to 10thDay
17%224%28%19%10%
450
11th to 20thDay
11%7%19%32%23%8%
450
21st to endDay
11%8%28%28%22%3
495
November1st to 10thDay
19%6%23%32%17%3
381
11th to 20thDay
14%10%43%23%9%1
270
21st to endDay
12%15%33%26%13%1
270
December1st to 10thDay
21%17%36%17%7%1
270
11th to 20thDay
23%17%35%17%9%
270
21st to endDay
26%15%29%23%7%1
297
January1st to 10thNight
19%15%34%26%6%1
760
11th to 20thNight
16%13%30%29%11%
740
21st to endNight
19%13%36%27%5%
792
February1st to 10thNight
19%12%32%30%8%
720
11th to 20thNight
21%12%34%29%4
703
21st to endNight
17%12%38%29%4
592
March1st to 10thNight
13%11%35%34%8%
720
11th to 20thNight
14%13%31%29%12%1
720
21st to endNight
12%13%32%32%11%
792
April1st to 10thNight
13%10%31%32%14%
720
11th to 20thNight
14%8%29%32%16%1
585
21st to endNight
7%6%26%40%20%1
540
May1st to 10thNight
7%7%26%37%21%2
540
11th to 20thNight
8%323%34%26%6%
531
21st to endNight
10%210%39%33%6%
584
June1st to 10thNight
11%213%36%34%4
540
11th to 20thNight
4210%34%40%10%
540
21st to endNight
7%110%34%39%9%
540
July1st to 10thNight
8%18%27%40%16%
525
11th to 20thNight
7%15%21%49%17%
522
21st to endNight
7%16%28%46%12%
591
August1st to 10thNight
8%9%27%43%13%
537
11th to 20thNight
10%17%25%46%11%
534
21st to endNight
11%39%24%39%14%
619
September1st to 10thNight
10%29%28%43%9%
720
11th to 20thNight
13%211%32%38%5%
720
21st to endNight
13%213%32%38%3
720
October1st to 10thNight
13%319%34%26%6%
720
11th to 20thNight
15%5%20%31%26%3
720
21st to endNight
12%5%24%33%25%2
792
November1st to 10thNight
14%6%22%36%21%1
740
11th to 20thNight
15%9%26%34%14%1
760
21st to endNight
16%8%29%29%16%1
760
December1st to 10thNight
15%9%31%29%14%1
760
11th to 20thNight
18%8%30%31%12%1
760
21st to endNight
24%10%25%32%8%
836
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