Fred's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred's Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
38%
23926
16%
74636
11%
23872
44%
23872
20%
51474

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
16%
760
12%
2459
5%
757
25%
757
10%
1936
January11th to 20thNight
15%
744
10%
2417
4%
744
22%
744
9%
1932
January21st to endNight
18%
792
12%
2574
7%
792
26%
792
11%
2008
February1st to 10thNight
21%
720
11%
2340
6%
720
27%
720
12%
1793
February11th to 20thNight
18%
700
11%
2144
5%
700
24%
700
12%
1620
February21st to endNight
15%
592
13%
1776
5%
592
23%
592
12%
1377
March1st to 10thNight
24%
720
17%
2056
8%
720
32%
720
18%
1464
March11th to 20thNight
26%
720
18%
1980
9%
720
34%
720
21%
1383
March21st to endNight
27%
792
17%
2178
9%
792
34%
792
19%
1567
April1st to 10thNight
28%
720
15%
1980
7%
720
35%
720
23%
1342
April11th to 20thNight
33%
547
20%
1630
10%
547
41%
547
24%
1080
April21st to endNight
31%
540
18%
1620
7%
540
39%
540
23%
1083
May1st to 10thNight
36%
540
13%
1620
7%
540
41%
540
19%
1159
May11th to 20thNight
40%
531
16%
1593
10%
531
45%
531
22%
1105
May21st to endNight
58%
583
15%
1745
12%
582
61%
582
30%
1078
June1st to 10thNight
55%
540
16%
1620
13%
540
59%
540
30%
1009
June11th to 20thNight
58%
540
17%
1620
13%
540
63%
540
31%
993
June21st to endNight
57%
540
17%
1620
14%
540
62%
540
32%
998
July1st to 10thNight
62%
525
15%
1575
14%
525
64%
525
31%
978
July11th to 20thNight
67%
522
17%
1566
15%
522
69%
522
32%
949
July21st to endNight
64%
591
16%
1672
14%
558
66%
558
29%
1064
August1st to 10thNight
67%
537
19%
1600
15%
534
68%
534
32%
967
August11th to 20thNight
67%
534
21%
1598
18%
534
69%
534
30%
1011
August21st to endNight
68%
594
26%
1782
21%
594
71%
594
38%
1012
September1st to 10thNight
60%
720
23%
1980
17%
720
63%
720
36%
1203
September11th to 20thNight
66%
720
29%
1980
23%
720
70%
720
40%
1156
September21st to endNight
50%
720
25%
1980
18%
720
56%
720
32%
1260
October1st to 10thNight
52%
720
23%
2052
20%
720
58%
720
33%
1265
October11th to 20thNight
38%
720
21%
2160
15%
720
47%
720
25%
1390
October21st to endNight
34%
792
21%
2389
16%
792
41%
792
21%
1638
November1st to 10thNight
41%
740
23%
2406
18%
740
49%
740
27%
1445
November11th to 20thNight
30%
760
20%
2470
12%
760
40%
760
18%
1671
November21st to endNight
28%
760
16%
2470
11%
760
35%
760
16%
1774
December1st to 10thNight
20%
760
11%
2470
7%
760
25%
760
11%
1920
December11th to 20thNight
24%
759
13%
3006
8%
759
30%
759
11%
2184
December21st to endNight
17%
831
6%
4508
5%
817
24%
817
5%
3660

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
16%9%47%6%35%5%6%7%33%
74918
Night
15%9%46%5%3445%7%36%
74902
TransparencyDay
49%7%12%19%11%1
74641
Night
47%7%11%20%13%2
74698
SeeingDay
21%12%26%21%14%6%
13780
Night
20%10%26%29%14%2
23936

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
18%15%7%10%7%445%46%19%
1706
11th to 20thDay
20%18%7%12%7%44345%19%
1665
21st to endDay
18%17%7%10%6%45%345%19%
1782
February1st to 10thDay
23%13%5%9%7%33445%23%
1620
11th to 20thDay
17%13%7%11%6%44446%24%
1702
21st to endDay
19%14%6%8%5%33345%29%
1480
March1st to 10thDay
18%10%5%6%6%345%5%7%32%
1903
11th to 20thDay
19%12%48%6%35%45%6%29%
1980
21st to endDay
22%9%47%5%3445%6%30%
2178
April1st to 10thDay
14%12%48%6%345%46%34%
1982
11th to 20thDay
17%9%36%5%35%45%7%35%
2291
21st to endDay
19%7%37%6%45%5%6%7%32%
2340
May1st to 10thDay
19%9%47%6%45%46%8%30%
2340
11th to 20thDay
22%6%36%5%35%5%5%8%31%
2301
21st to endDay
9%436%6%46%7%7%11%37%
2531
June1st to 10thDay
13%5%36%5%35%6%7%10%37%
2340
11th to 20thDay
11%7%26%6%45%6%6%10%36%
2340
21st to endDay
12%5%35%5%46%6%7%10%36%
2340
July1st to 10thDay
12%6%36%6%46%6%5%10%36%
2340
11th to 20thDay
10%6%36%6%46%6%7%9%39%
2340
21st to endDay
11%5%25%6%46%6%7%10%37%
2547
August1st to 10thDay
10%5%26%6%35%7%9%10%37%
2327
11th to 20thDay
10%6%27%6%36%6%8%11%34%
2303
21st to endDay
8%6%26%5%46%6%7%9%43%
2551
September1st to 10thDay
15%5%15%5%2445%7%46%
1980
11th to 20thDay
10%5%25%6%3446%7%48%
1980
21st to endDay
17%8%36%43345%6%42%
1980
October1st to 10thDay
14%6%36%5%345%6%7%42%
1908
11th to 20thDay
16%6%26%6%3446%7%40%
1800
21st to endDay
22%9%36%6%34345%35%
1962
November1st to 10thDay
10%7%36%43345%6%49%
1672
11th to 20thDay
17%12%46%5%34446%36%
1710
21st to endDay
20%11%47%5%345%47%31%
1710
December1st to 10thDay
22%16%7%10%6%25%44420%
1710
11th to 20thDay
19%16%6%10%7%335%5%5%22%
2153
21st to endDay
21%22%6%10%6%35%445%13%
3124
January1st to 10thNight
17%14%8%9%8%45%44423%
2459
11th to 20thNight
19%15%6%10%7%45%35%5%22%
2417
21st to endNight
18%14%6%11%7%35%435%24%
2574
February1st to 10thNight
22%14%48%6%44445%27%
2340
11th to 20thNight
20%11%48%7%45%5%5%5%26%
2143
21st to endNight
21%14%6%8%5%3443427%
1776
March1st to 10thNight
17%9%37%6%34445%36%
2056
11th to 20thNight
18%10%45%5%3445%7%35%
1980
21st to endNight
21%9%46%5%2435%6%34%
2178
April1st to 10thNight
16%8%35%43445%7%39%
1980
11th to 20thNight
15%7%27%4445%5%9%37%
1630
21st to endNight
16%8%27%5%4446%8%37%
1620
May1st to 10thNight
17%8%46%445%6%5%7%33%
1620
11th to 20thNight
16%8%46%5%345%5%7%38%
1592
21st to endNight
7%5%35%6%35%5%8%11%42%
1744
June1st to 10thNight
9%5%25%5%35%5%5%9%46%
1620
11th to 20thNight
10%435%5%35%5%6%10%45%
1620
21st to endNight
11%5%243346%7%10%45%
1620
July1st to 10thNight
9%5%35%5%245%6%8%48%
1620
11th to 20thNight
7%5%245%35%5%7%9%46%
1620
21st to endNight
8%5%35%6%45%6%7%9%42%
1771
August1st to 10thNight
5%5%26%6%36%5%7%11%44%
1611
11th to 20thNight
7%6%36%5%36%5%7%8%45%
1598
21st to endNight
8%4235%35%5%6%9%51%
1782
September1st to 10thNight
13%4235%2445%7%51%
1980
11th to 20thNight
10%32433445%7%55%
1980
21st to endNight
14%6%35%42335%6%48%
1980
October1st to 10thNight
10%5%35%5%3446%7%48%
2052
11th to 20thNight
16%7%36%42445%8%42%
2160
21st to endNight
21%8%35%43345%6%37%
2389
November1st to 10thNight
14%7%25%43335%5%49%
2406
11th to 20thNight
17%9%46%6%3445%6%36%
2470
21st to endNight
19%12%47%435%5%5%6%30%
2470
December1st to 10thNight
22%14%6%9%6%34445%23%
2470
11th to 20thNight
18%13%7%7%6%2445%6%27%
3042
21st to endNight
22%20%7%9%6%34346%16%
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
66%6%9%13%5%
1707
11th to 20thDay
69%5%11%12%2
1665
21st to endDay
68%5%10%12%5%1
1782
February1st to 10thDay
64%412%12%7%
1620
11th to 20thDay
62%6%9%16%8%
1712
21st to endDay
59%5%11%17%8%2
1480
March1st to 10thDay
52%5%11%23%7%1
1903
11th to 20thDay
56%6%11%18%9%1
1980
21st to endDay
56%6%10%19%9%
2178
April1st to 10thDay
50%7%10%20%11%2
1982
11th to 20thDay
47%7%12%17%14%3
2291
21st to endDay
50%7%10%20%10%2
2340
May1st to 10thDay
52%6%12%19%9%2
2340
11th to 20thDay
51%8%12%17%11%1
2305
21st to endDay
37%12%16%22%12%1
2531
June1st to 10thDay
40%9%12%23%14%2
2340
11th to 20thDay
41%10%14%20%14%1
2340
21st to endDay
41%9%15%20%14%2
2340
July1st to 10thDay
42%10%13%20%14%1
2275
11th to 20thDay
39%9%13%23%14%1
2271
21st to endDay
39%9%15%22%13%2
2405
August1st to 10thDay
37%12%14%25%12%1
2314
11th to 20thDay
39%9%16%25%10%1
2303
21st to endDay
34%9%15%22%15%5%
2551
September1st to 10thDay
38%6%12%21%20%3
1980
11th to 20thDay
34%6%13%26%20%2
1980
21st to endDay
43%410%23%20%1
1980
October1st to 10thDay
40%7%11%22%19%1
1908
11th to 20thDay
42%5%12%23%17%1
1800
21st to endDay
51%5%11%22%10%1
1962
November1st to 10thDay
36%6%10%28%17%3
1672
11th to 20thDay
50%6%9%20%12%3
1710
21st to endDay
54%6%11%18%11%1
1710
December1st to 10thDay
67%5%10%14%3
1710
11th to 20thDay
62%5%10%16%7%
2150
21st to endDay
72%7%9%8%3
3124
January1st to 10thNight
64%5%9%14%7%1
2459
11th to 20thNight
66%5%12%12%41
2417
21st to endNight
63%5%10%15%6%1
2574
February1st to 10thNight
60%6%10%17%6%1
2340
11th to 20thNight
60%5%10%16%8%1
2144
21st to endNight
61%5%9%15%8%2
1776
March1st to 10thNight
50%6%8%23%12%1
2056
11th to 20thNight
48%6%12%23%10%2
1980
21st to endNight
51%6%8%21%13%2
2178
April1st to 10thNight
44%6%13%21%14%2
1980
11th to 20thNight
43%6%12%17%19%4
1630
21st to endNight
44%7%12%21%14%2
1620
May1st to 10thNight
48%9%12%18%10%3
1620
11th to 20thNight
45%8%11%21%12%3
1593
21st to endNight
33%9%18%25%13%2
1745
June1st to 10thNight
34%9%12%23%20%2
1620
11th to 20thNight
32%10%15%24%16%3
1620
21st to endNight
32%9%14%25%17%3
1620
July1st to 10thNight
33%9%13%22%20%3
1575
11th to 20thNight
31%10%14%25%17%3
1566
21st to endNight
35%10%15%24%15%2
1672
August1st to 10thNight
31%9%16%27%16%1
1600
11th to 20thNight
34%9%14%23%18%1
1598
21st to endNight
27%8%14%27%19%5%
1782
September1st to 10thNight
33%5%13%22%20%6%
1980
11th to 20thNight
28%7%12%26%25%3
1980
21st to endNight
37%6%11%21%25%1
1980
October1st to 10thNight
34%7%11%25%20%3
2052
11th to 20thNight
41%6%10%24%17%2
2160
21st to endNight
47%6%10%22%13%2
2389
November1st to 10thNight
37%5%11%24%19%3
2406
11th to 20thNight
48%5%10%19%15%2
2470
21st to endNight
54%5%13%19%9%1
2470
December1st to 10thNight
63%5%9%17%6%
2470
11th to 20thNight
57%6%12%19%6%
3044
21st to endNight
69%7%9%12%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
29%21%33%11%6%
270
11th to 20thDay
29%21%38%9%2
255
21st to endDay
31%23%30%13%3
264
February1st to 10thDay
37%23%28%11%1
240
11th to 20thDay
34%28%28%8%1
240
21st to endDay
32%25%37%5%1
198
March1st to 10thDay
27%22%31%16%4
343
11th to 20thDay
30%14%34%15%6%
420
21st to endDay
31%15%32%18%4
462
April1st to 10thDay
24%15%31%19%8%3
420
11th to 20thDay
27%15%28%17%10%4
412
21st to endDay
26%15%34%16%6%2
420
May1st to 10thDay
26%15%30%15%9%4
423
11th to 20thDay
21%10%28%26%10%4
447
21st to endDay
13%8%22%27%22%7%
485
June1st to 10thDay
15%6%27%29%17%6%
450
11th to 20thDay
16%8%22%28%18%7%
450
21st to endDay
13%6%27%28%18%7%
450
July1st to 10thDay
16%414%23%23%20%
445
11th to 20thDay
12%5%19%26%26%12%
444
21st to endDay
15%5%19%26%21%14%
488
August1st to 10thDay
15%214%26%28%15%
446
11th to 20thDay
13%5%20%30%20%12%
439
21st to endDay
9%6%17%28%28%13%
495
September1st to 10thDay
15%5%16%26%26%13%
450
11th to 20thDay
11%414%24%32%14%
450
21st to endDay
21%9%19%26%19%6%
450
October1st to 10thDay
12%8%27%29%16%7%
450
11th to 20thDay
18%13%31%24%11%2
450
21st to endDay
29%14%29%19%9%1
477
November1st to 10thDay
16%19%33%22%9%2
270
11th to 20thDay
29%19%27%19%7%1
270
21st to endDay
26%19%34%18%3
270
December1st to 10thDay
30%19%33%13%41
270
11th to 20thDay
27%23%36%11%21
270
21st to endDay
35%16%32%13%3
297
January1st to 10thNight
25%19%31%20%4
760
11th to 20thNight
28%17%31%20%3
744
21st to endNight
27%15%33%22%3
792
February1st to 10thNight
29%14%31%24%2
720
11th to 20thNight
28%17%34%20%2
703
21st to endNight
28%14%36%20%2
592
March1st to 10thNight
23%14%33%24%5%
720
11th to 20thNight
22%15%32%22%8%1
720
21st to endNight
24%11%31%25%7%1
792
April1st to 10thNight
21%13%34%25%7%
720
11th to 20thNight
18%11%34%24%12%1
547
21st to endNight
20%7%37%29%7%
540
May1st to 10thNight
20%9%29%29%12%1
540
11th to 20thNight
19%7%27%31%14%2
531
21st to endNight
9%5%21%36%26%3
584
June1st to 10thNight
12%223%41%22%1
540
11th to 20thNight
11%418%41%24%2
540
21st to endNight
13%221%37%24%3
540
July1st to 10thNight
12%213%37%30%7%
525
11th to 20thNight
7%316%35%34%6%
522
21st to endNight
11%313%35%35%3
591
August1st to 10thNight
7%210%40%36%4
537
11th to 20thNight
10%410%39%33%5%
534
21st to endNight
10%215%31%35%8%
594
September1st to 10thNight
15%414%33%29%5%
720
11th to 20thNight
11%313%35%34%5%
720
21st to endNight
17%5%21%32%22%3
720
October1st to 10thNight
13%5%24%34%21%3
720
11th to 20thNight
20%10%29%29%12%1
720
21st to endNight
24%11%27%27%10%1
792
November1st to 10thNight
19%10%26%29%16%1
740
11th to 20thNight
21%15%27%27%8%1
760
21st to endNight
26%13%28%26%7%1
760
December1st to 10thNight
31%14%28%22%5%
760
11th to 20thNight
25%15%30%25%5%
760
21st to endNight
31%14%28%24%2
836
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