Fox Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fox Observatory clear sky chart from 2005-11-06 to 2024-11-03.

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
64%
25872
17%
97067
16%
25738
68%
25738
25%
57792

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
59%
751
18%
4056
22%
737
68%
737
20%
2328
January11th to 20thNight
52%
752
13%
4109
17%
740
59%
740
14%
2868
January21st to endNight
48%
825
16%
4382
19%
814
58%
814
17%
2615
February1st to 10thNight
55%
760
28%
2280
23%
760
61%
760
34%
1339
February11th to 20thNight
60%
742
30%
2107
22%
739
68%
739
43%
1144
February21st to endNight
63%
628
33%
1727
26%
628
69%
628
45%
945
March1st to 10thNight
57%
754
21%
3413
20%
745
66%
745
24%
2061
March11th to 20thNight
61%
749
24%
3454
21%
740
68%
740
33%
1495
March21st to endNight
59%
827
21%
3690
24%
814
65%
814
31%
1771
April1st to 10thNight
70%
760
27%
2090
24%
760
74%
760
50%
1107
April11th to 20thNight
62%
751
21%
1975
16%
751
66%
751
43%
1154
April21st to endNight
65%
760
26%
1900
17%
760
68%
760
44%
1121
May1st to 10thNight
72%
750
35%
3100
18%
749
75%
749
44%
1204
May11th to 20thNight
64%
719
15%
3028
9%
715
65%
715
26%
1499
May21st to endNight
72%
595
13%
3041
15%
593
73%
593
23%
1497
June1st to 10thNight
64%
570
10%
1710
8%
570
64%
570
17%
1273
June11th to 20thNight
72%
570
10%
1710
9%
570
72%
570
24%
1168
June21st to endNight
75%
570
6%
1710
6%
570
75%
570
22%
1189
July1st to 10thNight
75%
536
9%
2687
6%
535
75%
535
16%
1632
July11th to 20thNight
77%
534
5%
2753
8%
533
77%
533
18%
1607
July21st to endNight
82%
604
6%
2884
9%
569
84%
569
20%
1633
August1st to 10thNight
77%
568
9%
2747
8%
563
77%
563
17%
1762
August11th to 20thNight
78%
731
6%
2991
5%
729
78%
729
19%
1839
August21st to endNight
68%
814
3%
3757
5%
814
68%
814
14%
2399
September1st to 10thNight
70%
760
6%
2090
6%
760
70%
760
20%
1523
September11th to 20thNight
64%
760
5%
2090
5%
760
64%
760
19%
1545
September21st to endNight
60%
760
10%
2090
10%
760
61%
760
17%
1580
October1st to 10thNight
63%
760
15%
2176
15%
760
65%
760
21%
1521
October11th to 20thNight
67%
760
18%
2280
19%
760
69%
760
28%
1452
October21st to endNight
61%
836
23%
2508
22%
836
65%
836
30%
1565
November1st to 10thNight
61%
749
26%
2246
24%
749
68%
749
37%
1302
November11th to 20thNight
59%
760
23%
2280
23%
760
63%
760
28%
1457
November21st to endNight
62%
760
26%
2280
24%
760
67%
760
33%
1378
December1st to 10thNight
66%
760
28%
2312
24%
760
72%
760
35%
1337
December11th to 20thNight
59%
759
24%
2936
25%
758
64%
758
27%
1669
December21st to endNight
61%
828
14%
4478
22%
817
66%
817
17%
2813

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
8%6%28%6%6%7%6%8%10%33%
100562
Night
7%5%26%5%5%5%5%7%10%42%
98341
TransparencyDay
42%9%18%19%10%2
100369
Night
35%9%20%22%11%3
98204
SeeingDay
8%315%28%25%20%
15983
Night
8%313%32%32%12%
26100

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
10%8%37%45%5%46%8%39%
2836
11th to 20thDay
16%6%39%6%5%6%6%7%9%26%
2840
21st to endDay
7%6%410%6%6%6%5%6%7%38%
3170
February1st to 10thDay
10%8%26%7%45%46%8%40%
1900
11th to 20thDay
8%415%445%46%10%50%
1958
21st to endDay
7%5%15%6%6%6%5%6%8%46%
1727
March1st to 10thDay
8%5%27%7%7%7%6%8%10%32%
3435
11th to 20thDay
5%315%45%5%5%8%8%52%
3480
21st to endDay
10%5%25%5%4445%8%47%
3815
April1st to 10thDay
5%315%6%5%6%5%7%12%45%
2090
11th to 20thDay
7%428%6%6%6%5%8%9%40%
2153
21st to endDay
7%426%5%5%6%48%10%43%
2280
May1st to 10thDay
3214445%46%9%57%
3765
11th to 20thDay
7%5%27%5%6%6%5%8%10%37%
3817
21st to endDay
7%5%26%6%5%6%5%7%9%42%
4476
June1st to 10thDay
15%10%311%9%7%8%5%7%7%17%
2470
11th to 20thDay
9%9%411%8%7%8%6%8%10%19%
2470
21st to endDay
9%7%310%9%8%9%7%9%9%19%
2470
July1st to 10thDay
6%7%39%7%7%7%6%10%13%24%
4120
11th to 20thDay
6%6%39%8%8%9%7%10%13%23%
4120
21st to endDay
5%5%28%6%7%8%7%9%14%28%
4466
August1st to 10thDay
6%5%210%8%8%9%8%11%13%19%
4024
11th to 20thDay
5%428%7%8%9%8%11%14%23%
3730
21st to endDay
6%5%29%7%8%10%8%11%15%19%
3874
September1st to 10thDay
8%6%411%8%9%9%7%8%10%19%
2090
11th to 20thDay
10%7%311%9%8%9%5%9%10%20%
2090
21st to endDay
12%9%411%9%7%8%7%7%8%20%
2090
October1st to 10thDay
9%8%310%7%8%8%7%8%10%23%
2000
11th to 20thDay
10%5%38%7%7%9%7%8%8%27%
1900
21st to endDay
13%6%28%6%5%5%5%6%9%36%
2090
November1st to 10thDay
8%6%26%6%5%6%5%7%10%39%
1877
11th to 20thDay
11%6%37%9%7%5%5%6%9%33%
1900
21st to endDay
8%6%26%5%6%7%5%7%9%39%
1900
December1st to 10thDay
8%5%36%6%5%6%47%8%42%
1862
11th to 20thDay
10%7%26%5%5%5%46%8%43%
2153
21st to endDay
13%6%27%6%5%7%5%8%9%31%
3124
January1st to 10thNight
8%6%37%6%5%5%47%10%39%
4109
11th to 20thNight
17%9%48%6%5%5%46%8%28%
4120
21st to endNight
8%6%38%6%6%6%5%6%7%40%
4468
February1st to 10thNight
8%6%25%44446%9%47%
2280
11th to 20thNight
7%313445%5%5%7%57%
2107
21st to endNight
5%21444435%8%59%
1727
March1st to 10thNight
7%5%27%5%6%5%5%7%8%42%
3418
11th to 20thNight
5%315%34446%11%55%
3480
21st to endNight
7%41443436%7%55%
3817
April1st to 10thNight
421433447%10%58%
2090
11th to 20thNight
6%315%345%47%9%53%
1975
21st to endNight
7%4244445%6%9%52%
1900
May1st to 10thNight
321332335%9%65%
3130
11th to 20thNight
6%324445%5%7%10%49%
3103
21st to endNight
6%5%25%445%48%10%47%
3079
June1st to 10thNight
11%7%39%7%7%7%7%7%10%26%
1710
11th to 20thNight
7%7%26%6%5%6%5%9%13%33%
1710
21st to endNight
6%5%17%6%5%7%5%11%14%31%
1710
July1st to 10thNight
45%27%6%5%6%6%8%12%38%
2840
11th to 20thNight
45%27%5%5%7%7%9%12%37%
2840
21st to endNight
3426%5%46%5%10%14%41%
3087
August1st to 10thNight
4427%6%6%7%6%9%14%35%
2857
11th to 20thNight
4416%5%6%7%6%10%15%35%
3097
21st to endNight
5%426%5%6%8%8%12%15%28%
3761
September1st to 10thNight
6%5%27%6%7%8%7%10%11%30%
2090
11th to 20thNight
8%6%39%7%6%6%5%8%12%30%
2090
21st to endNight
10%6%39%7%8%7%6%9%11%26%
2090
October1st to 10thNight
9%6%39%6%7%7%5%9%10%30%
2176
11th to 20thNight
8%6%37%5%5%5%5%7%11%39%
2280
21st to endNight
10%6%26%5%45%46%8%43%
2508
November1st to 10thNight
9%415%44446%8%50%
2246
11th to 20thNight
8%6%26%6%6%5%46%8%41%
2280
21st to endNight
7%5%26%5%5%45%6%9%46%
2280
December1st to 10thNight
6%425%445%46%9%50%
2312
11th to 20thNight
12%6%26%43435%9%48%
3042
21st to endNight
10%7%38%6%6%5%5%7%9%35%
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
41%5%10%24%16%5%
2837
11th to 20thDay
53%6%14%15%9%3
2840
21st to endDay
44%5%9%21%16%6%
3170
February1st to 10thDay
40%5%10%24%16%5%
1900
11th to 20thDay
29%5%9%28%22%7%
1968
21st to endDay
33%6%10%19%24%9%
1727
March1st to 10thDay
41%9%14%21%12%3
3435
11th to 20thDay
26%6%17%36%12%3
3480
21st to endDay
34%5%8%28%19%6%
3815
April1st to 10thDay
30%6%16%29%16%3
2090
11th to 20thDay
38%6%16%21%16%3
2153
21st to endDay
35%7%10%24%20%4
2280
May1st to 10thDay
21%6%14%33%22%4
3800
11th to 20thDay
37%8%21%28%6%
3821
21st to endDay
35%7%15%30%12%
4489
June1st to 10thDay
62%9%15%11%3
2470
11th to 20thDay
56%12%18%12%1
2470
21st to endDay
54%13%23%9%1
2470
July1st to 10thDay
44%13%29%14%
4055
11th to 20thDay
46%12%31%10%
4051
21st to endDay
39%14%32%15%
4324
August1st to 10thDay
49%16%25%10%1
4011
11th to 20thDay
42%15%29%14%
3766
21st to endDay
46%16%32%6%1
3874
September1st to 10thDay
54%15%19%11%1
2090
11th to 20thDay
54%12%21%9%3
2090
21st to endDay
60%10%14%11%41
2090
October1st to 10thDay
52%9%15%15%7%1
2000
11th to 20thDay
49%8%13%16%12%1
1900
21st to endDay
44%5%9%19%17%5%
2090
November1st to 10thDay
38%6%12%20%18%7%
1877
11th to 20thDay
47%6%10%18%14%5%
1900
21st to endDay
40%6%11%19%21%3
1900
December1st to 10thDay
38%6%12%24%18%2
1862
11th to 20thDay
39%5%9%20%19%7%
2150
21st to endDay
46%6%13%19%14%2
3124
January1st to 10thNight
40%5%14%23%15%3
4109
11th to 20thNight
54%5%13%16%9%2
4120
21st to endNight
41%6%10%22%15%6%
4468
February1st to 10thNight
32%5%13%29%17%4
2280
11th to 20thNight
25%6%11%28%23%7%
2108
21st to endNight
23%6%11%26%27%7%
1727
March1st to 10thNight
37%8%15%22%14%4
3418
11th to 20thNight
23%6%26%31%12%3
3480
21st to endNight
26%6%13%26%25%4
3817
April1st to 10thNight
20%6%18%37%16%3
2090
11th to 20thNight
26%6%19%26%20%3
1975
21st to endNight
26%6%15%29%20%4
1900
May1st to 10thNight
16%5%20%41%15%3
3160
11th to 20thNight
27%8%23%32%9%
3104
21st to endNight
28%9%21%34%9%
3087
June1st to 10thNight
50%11%22%14%2
1710
11th to 20thNight
39%13%28%18%3
1710
21st to endNight
38%15%35%11%1
1710
July1st to 10thNight
36%13%34%17%
2795
11th to 20thNight
35%13%41%11%
2786
21st to endNight
29%14%39%16%1
2988
August1st to 10thNight
37%14%30%16%2
2846
11th to 20thNight
31%16%34%18%
3127
21st to endNight
37%17%38%6%1
3761
September1st to 10thNight
41%17%28%13%1
2090
11th to 20thNight
45%15%26%12%2
2090
21st to endNight
48%14%18%15%5%
2090
October1st to 10thNight
45%10%19%19%6%1
2176
11th to 20thNight
38%7%19%21%13%1
2280
21st to endNight
38%6%12%24%16%5%
2508
November1st to 10thNight
31%5%14%24%19%7%
2246
11th to 20thNight
40%5%12%24%14%5%
2280
21st to endNight
34%6%14%23%19%4
2280
December1st to 10thNight
31%6%14%29%17%3
2312
11th to 20thNight
34%5%9%24%19%9%
3044
21st to endNight
43%8%15%18%14%2
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
11%8%32%36%12%2
270
11th to 20thDay
12%7%33%31%13%3
270
21st to endDay
11%6%46%27%8%1
297
February1st to 10thDay
10%7%28%39%13%3
270
11th to 20thDay
8%326%38%19%6%
381
21st to endDay
5%5%22%37%27%3
382
March1st to 10thDay
47%30%35%21%3
460
11th to 20thDay
7%5%27%37%21%3
460
21st to endDay
6%327%36%22%6%
506
April1st to 10thDay
35%31%31%23%6%
460
11th to 20thDay
8%428%32%21%8%
452
21st to endDay
7%322%34%26%9%
460
May1st to 10thDay
4118%33%29%15%
463
11th to 20thDay
9%217%32%27%14%
487
21st to endDay
11%36%27%27%25%
529
June1st to 10thDay
16%37%24%28%22%
490
11th to 20thDay
10%3420%28%34%
490
21st to endDay
6%2117%25%49%
490
July1st to 10thDay
5%2113%29%50%
485
11th to 20thDay
6%2114%31%46%
484
21st to endDay
43215%28%47%
532
August1st to 10thDay
8%2315%29%44%
486
11th to 20thDay
6%2315%28%46%
479
21st to endDay
9%3322%29%35%
539
September1st to 10thDay
8%3314%29%43%
490
11th to 20thDay
7%25%15%27%45%
490
21st to endDay
12%36%21%27%32%
490
October1st to 10thDay
12%38%34%30%13%
490
11th to 20thDay
12%115%30%28%14%
490
21st to endDay
11%317%35%26%9%
539
November1st to 10thDay
9%420%35%24%8%
463
11th to 20thDay
12%322%31%25%8%
460
21st to endDay
6%223%35%29%5%
460
December1st to 10thDay
11%318%38%25%5%
422
11th to 20thDay
9%5%24%37%19%6%
270
21st to endDay
11%6%27%35%15%6%
297
January1st to 10thNight
9%5%19%41%24%2
760
11th to 20thNight
10%5%24%41%19%1
760
21st to endNight
8%5%28%43%15%1
836
February1st to 10thNight
10%5%22%42%19%2
760
11th to 20thNight
7%424%43%22%1
743
21st to endNight
7%320%48%21%1
628
March1st to 10thNight
5%327%44%19%1
760
11th to 20thNight
7%320%46%22%1
760
21st to endNight
7%323%43%22%2
836
April1st to 10thNight
4218%50%24%2
760
11th to 20thNight
6%321%46%22%2
751
21st to endNight
8%217%46%25%3
760
May1st to 10thNight
3214%45%33%3
760
11th to 20thNight
9%211%42%32%4
735
21st to endNight
8%2430%45%10%
617
June1st to 10thNight
11%2322%46%15%
570
11th to 20thNight
7%2214%45%30%
570
21st to endNight
5%2210%44%38%
570
July1st to 10thNight
5%118%42%43%
555
11th to 20thNight
5%28%44%41%
552
21st to endNight
216%44%46%
624
August1st to 10thNight
6%219%46%37%
586
11th to 20thNight
32210%44%39%
750
21st to endNight
9%2218%41%28%
836
September1st to 10thNight
6%2412%41%35%
760
11th to 20thNight
10%3214%43%29%
760
21st to endNight
12%2418%41%24%
760
October1st to 10thNight
11%26%33%37%11%
760
11th to 20thNight
11%36%32%39%9%
760
21st to endNight
13%213%36%29%7%
836
November1st to 10thNight
10%318%35%30%4
749
11th to 20thNight
9%217%37%30%5%
760
21st to endNight
8%316%43%27%3
760
December1st to 10thNight
7%214%40%33%4
760
11th to 20thNight
10%417%38%28%3
760
21st to endNight
8%220%39%28%3
836
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