Miller Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Miller 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
64%
23639
32%
74507
25%
23591
72%
23591
44%
37511

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%
756
39%
2268
25%
756
70%
756
46%
1150
January11th to 20thNight
61%
744
36%
2232
25%
744
72%
744
46%
1127
January21st to endNight
54%
792
38%
2376
25%
792
67%
792
42%
1242
February1st to 10thNight
60%
720
37%
2160
24%
720
72%
720
48%
1066
February11th to 20thNight
54%
703
27%
2098
17%
700
64%
700
42%
1112
February21st to endNight
46%
592
35%
1776
18%
592
61%
592
44%
894
March1st to 10thNight
50%
720
32%
2160
16%
720
63%
720
42%
1141
March11th to 20thNight
48%
720
29%
2078
16%
720
58%
720
40%
1130
March21st to endNight
48%
594
42%
1980
26%
594
66%
594
48%
889
April1st to 10thNight
49%
540
39%
1800
25%
540
66%
540
42%
874
April11th to 20thNight
46%
533
35%
1777
23%
533
65%
533
48%
814
April21st to endNight
51%
540
37%
1800
27%
540
69%
540
49%
802
May1st to 10thNight
59%
540
30%
1800
25%
540
73%
540
49%
830
May11th to 20thNight
53%
531
26%
1770
25%
531
62%
531
37%
931
May21st to endNight
59%
582
28%
1781
25%
582
69%
582
43%
938
June1st to 10thNight
69%
540
26%
1620
25%
540
73%
540
50%
803
June11th to 20thNight
75%
540
27%
1620
26%
540
78%
540
45%
854
June21st to endNight
74%
540
28%
1620
27%
540
77%
540
47%
831
July1st to 10thNight
76%
525
17%
1750
19%
525
77%
525
33%
981
July11th to 20thNight
83%
522
29%
1740
33%
522
86%
522
51%
803
July21st to endNight
80%
591
28%
1859
33%
558
83%
558
44%
921
August1st to 10thNight
87%
537
29%
1779
35%
534
89%
534
50%
816
August11th to 20thNight
80%
534
25%
1778
29%
534
82%
534
38%
954
August21st to endNight
78%
594
21%
1980
23%
594
80%
594
32%
1140
September1st to 10thNight
77%
540
24%
1800
26%
540
78%
540
36%
999
September11th to 20thNight
75%
540
25%
1930
29%
540
76%
540
30%
1083
September21st to endNight
74%
540
28%
1980
29%
540
77%
540
34%
1040
October1st to 10thNight
78%
540
32%
1980
34%
540
81%
540
44%
913
October11th to 20thNight
69%
602
37%
2042
31%
602
75%
602
42%
1011
October21st to endNight
71%
792
40%
2376
28%
792
77%
792
55%
1112
November1st to 10thNight
75%
783
38%
2263
25%
783
80%
783
58%
1065
November11th to 20thNight
68%
950
34%
2470
21%
950
72%
950
56%
1284
November21st to endNight
59%
950
36%
2470
19%
950
67%
950
50%
1337
December1st to 10thNight
66%
950
38%
2470
25%
950
71%
950
50%
1360
December11th to 20thNight
58%
948
35%
2898
21%
948
66%
948
44%
1516
December21st to endNight
60%
974
26%
4226
24%
965
69%
965
39%
1748

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
431342445%7%62%
74752
Night
431342446%8%61%
75082
TransparencyDay
21%5%9%19%25%21%
74502
Night
21%6%9%19%23%21%
74854
SeeingDay
5%7%22%32%26%9%
13407
Night
5%421%44%24%2
23658

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
6%323322346%65%
1897
11th to 20thDay
6%313313346%65%
1850
21st to endDay
42245%23335%67%
1980
February1st to 10thDay
332343335%5%66%
1800
11th to 20thDay
5%423324347%63%
1749
21st to endDay
421232336%7%66%
1480
March1st to 10thDay
35%23435%35%9%58%
1800
11th to 20thDay
6%4244345%45%60%
1877
21st to endDay
231332335%7%69%
2376
April1st to 10thDay
241332346%8%65%
2160
11th to 20thDay
231331435%5%70%
2131
21st to endDay
4213223346%70%
2160
May1st to 10thDay
3223324446%69%
2160
11th to 20thDay
221343445%7%65%
2125
21st to endDay
321231345%7%69%
2487
June1st to 10thDay
11332446%9%68%
2340
11th to 20thDay
321342345%8%65%
2340
21st to endDay
42234235%6%10%59%
2333
July1st to 10thDay
6%3246%47%7%7%9%45%
2160
11th to 20thDay
33134245%6%8%60%
2160
21st to endDay
32134346%8%11%54%
2349
August1st to 10thDay
32123245%7%11%60%
2149
11th to 20thDay
5%425%6%46%6%8%11%43%
2123
21st to endDay
43145%45%7%7%10%50%
2376
September1st to 10thDay
6%426%5%45%5%6%9%48%
2160
11th to 20thDay
7%5%245%35%5%6%8%50%
2030
21st to endDay
5%3244345%6%7%59%
1980
October1st to 10thDay
221232346%9%66%
1980
11th to 20thDay
6%323423346%64%
1913
21st to endDay
5%212212236%73%
1980
November1st to 10thDay
5%212212336%74%
1793
11th to 20thDay
4312323345%70%
1710
21st to endDay
5%424334345%64%
1710
December1st to 10thDay
6%413423347%62%
1710
11th to 20thDay
2424435%5%6%6%60%
2161
21st to endDay
421332345%7%67%
3263
January1st to 10thNight
5%324334347%63%
2268
11th to 20thNight
7%22332335%7%63%
2232
21st to endNight
5%32442445%6%61%
2376
February1st to 10thNight
3323424347%64%
2160
11th to 20thNight
5%413425%45%8%58%
2098
21st to endNight
4323325%45%6%64%
1776
March1st to 10thNight
44143345%5%8%59%
2160
11th to 20thNight
6%5%2432445%6%60%
2078
21st to endNight
3323223347%69%
1980
April1st to 10thNight
34134345%5%8%62%
1800
11th to 20thNight
222323435%7%67%
1777
21st to endNight
321232445%6%69%
1800
May1st to 10thNight
4322324447%66%
1800
11th to 20thNight
4324435%45%6%60%
1770
21st to endNight
32134345%7%10%58%
1781
June1st to 10thNight
2213425%5%8%12%57%
1620
11th to 20thNight
2213435%6%7%10%54%
1620
21st to endNight
3223325%5%7%9%58%
1620
July1st to 10thNight
3225%5%46%6%9%12%47%
1800
11th to 20thNight
211233346%9%65%
1800
21st to endNight
2223435%5%7%12%56%
1969
August1st to 10thNight
2111325%6%7%12%60%
1790
11th to 20thNight
3215%425%7%8%13%50%
1778
21st to endNight
43235%46%6%9%10%48%
1980
September1st to 10thNight
5%3246%345%7%10%51%
1800
11th to 20thNight
6%325%5%36%6%9%10%46%
1930
21st to endNight
4323435%6%7%10%52%
1980
October1st to 10thNight
3112425%5%6%9%62%
1980
11th to 20thNight
6%314324346%62%
2042
21st to endNight
4313323325%73%
2376
November1st to 10thNight
4212222335%73%
2263
11th to 20thNight
431332335%6%68%
2470
21st to endNight
5%31332335%6%64%
2470
December1st to 10thNight
5%32332445%8%61%
2470
11th to 20thNight
24245%24447%62%
3036
21st to endNight
331342336%8%64%
4432

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
22%4417%33%20%
1898
11th to 20thDay
22%35%16%33%21%
1850
21st to endDay
23%36%14%36%19%
1980
February1st to 10thDay
21%35%14%26%31%
1800
11th to 20thDay
24%47%13%24%29%
1759
21st to endDay
16%45%12%27%36%
1480
March1st to 10thDay
24%46%16%24%26%
1800
11th to 20thDay
26%5%5%12%22%31%
1877
21st to endDay
17%3412%27%36%
2376
April1st to 10thDay
18%46%12%25%36%
2160
11th to 20thDay
16%46%12%24%38%
2134
21st to endDay
17%3412%25%38%
2160
May1st to 10thDay
16%46%11%25%37%
2160
11th to 20thDay
18%5%8%19%25%26%
2128
21st to endDay
15%6%8%21%25%25%
2487
June1st to 10thDay
12%6%11%24%28%19%
2340
11th to 20thDay
17%5%8%18%30%21%
2340
21st to endDay
21%6%13%22%23%15%
2333
July1st to 10thDay
32%10%18%23%14%4
2101
11th to 20thDay
20%7%12%28%24%10%
2097
21st to endDay
19%9%19%32%19%3
2219
August1st to 10thDay
16%7%14%34%23%5%
2136
11th to 20thDay
31%9%17%24%16%3
2123
21st to endDay
26%10%17%23%16%7%
2376
September1st to 10thDay
31%9%16%20%15%9%
2160
11th to 20thDay
30%8%13%18%23%7%
2030
21st to endDay
25%6%11%19%26%13%
1980
October1st to 10thDay
15%7%13%25%21%19%
1980
11th to 20thDay
21%6%8%19%21%25%
1913
21st to endDay
16%3415%33%30%
1980
November1st to 10thDay
15%37%19%31%24%
1793
11th to 20thDay
17%49%20%29%22%
1710
21st to endDay
24%36%18%27%22%
1710
December1st to 10thDay
24%37%19%28%17%
1710
11th to 20thDay
24%5%6%19%30%17%
2159
21st to endDay
16%45%14%36%25%
3263
January1st to 10thNight
22%4414%32%24%
2268
11th to 20thNight
22%46%15%29%25%
2232
21st to endNight
25%45%14%31%21%
2376
February1st to 10thNight
21%36%13%26%31%
2160
11th to 20thNight
25%48%13%20%30%
2098
21st to endNight
20%5%5%8%26%36%
1776
March1st to 10thNight
24%5%5%17%24%25%
2160
11th to 20thNight
25%5%6%13%20%30%
2078
21st to endNight
17%46%14%24%35%
1980
April1st to 10thNight
22%5%6%14%21%33%
1800
11th to 20thNight
16%5%8%15%21%34%
1777
21st to endNight
16%48%16%23%33%
1800
May1st to 10thNight
19%49%15%20%33%
1800
11th to 20thNight
25%7%8%19%21%19%
1771
21st to endNight
22%7%13%23%16%19%
1782
June1st to 10thNight
18%6%14%28%23%11%
1620
11th to 20thNight
21%7%12%19%25%16%
1620
21st to endNight
19%7%15%22%21%15%
1620
July1st to 10thNight
26%11%20%28%13%2
1750
11th to 20thNight
17%6%14%29%26%8%
1740
21st to endNight
20%7%18%35%18%1
1859
August1st to 10thNight
15%7%15%34%25%3
1779
11th to 20thNight
23%10%21%29%15%2
1778
21st to endNight
27%12%15%24%15%6%
1980
September1st to 10thNight
28%8%18%24%14%8%
1800
11th to 20thNight
29%10%18%20%17%6%
1930
21st to endNight
26%9%12%23%18%13%
1980
October1st to 10thNight
19%7%16%23%18%17%
1980
11th to 20thNight
23%5%8%21%19%24%
2042
21st to endNight
17%3416%28%32%
2376
November1st to 10thNight
15%46%17%32%25%
2263
11th to 20thNight
17%47%20%26%25%
2470
21st to endNight
21%48%16%24%26%
2470
December1st to 10thNight
22%5%7%21%25%21%
2470
11th to 20thNight
22%5%6%18%27%22%
3037
21st to endNight
19%45%13%35%24%
4432

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%9%34%30%16%1
270
11th to 20thDay
7%11%30%33%18%1
255
21st to endDay
5%17%30%30%16%1
264
February1st to 10thDay
6%11%25%35%18%5%
240
11th to 20thDay
12%11%30%33%13%2
240
21st to endDay
8%14%37%30%9%2
198
March1st to 10thDay
8%9%34%33%14%3
240
11th to 20thDay
9%15%37%24%11%4
317
21st to endDay
6%18%36%28%9%2
462
April1st to 10thDay
5%14%43%27%10%1
420
11th to 20thDay
5%15%44%23%12%
412
21st to endDay
6%15%40%31%7%1
420
May1st to 10thDay
410%41%29%13%4
423
11th to 20thDay
38%34%39%14%3
448
21st to endDay
26%24%42%25%1
635
June1st to 10thDay
2117%35%36%8%
630
11th to 20thDay
3113%37%41%6%
630
21st to endDay
3213%29%44%9%
623
July1st to 10thDay
429%28%36%22%
446
11th to 20thDay
27%35%39%18%
444
21st to endDay
228%37%37%15%
487
August1st to 10thDay
315%29%40%23%
447
11th to 20thDay
5%38%31%32%22%
437
21st to endDay
417%30%36%22%
495
September1st to 10thDay
5%19%38%31%16%
450
11th to 20thDay
7%1426%40%23%
320
21st to endDay
7%29%21%38%23%
270
October1st to 10thDay
4311%32%36%14%
270
11th to 20thDay
9%316%31%30%11%
270
21st to endDay
8%5%18%29%28%12%
297
November1st to 10thDay
8%416%34%30%9%
270
11th to 20thDay
8%9%17%31%27%8%
270
21st to endDay
9%13%24%31%20%3
270
December1st to 10thDay
8%6%21%34%26%5%
270
11th to 20thDay
7%7%33%33%18%1
270
21st to endDay
5%8%35%37%15%1
297
January1st to 10thNight
7%426%45%17%1
760
11th to 20thNight
8%5%20%45%20%1
744
21st to endNight
7%7%26%45%15%1
792
February1st to 10thNight
5%8%23%45%18%1
720
11th to 20thNight
7%5%29%46%12%1
704
21st to endNight
6%12%31%43%8%
592
March1st to 10thNight
8%8%31%42%12%1
720
11th to 20thNight
9%8%31%38%14%1
720
21st to endNight
5%9%34%38%12%1
594
April1st to 10thNight
49%34%43%9%
540
11th to 20thNight
28%40%42%8%
533
21st to endNight
39%34%45%9%
540
May1st to 10thNight
4428%51%11%1
540
11th to 20thNight
6%5%30%47%10%1
531
21st to endNight
2428%49%16%
584
June1st to 10thNight
3222%50%22%1
540
11th to 20thNight
315%50%31%1
540
21st to endNight
3115%46%33%1
540
July1st to 10thNight
4110%43%41%2
525
11th to 20thNight
28%40%49%1
522
21st to endNight
219%42%43%3
591
August1st to 10thNight
21438%53%2
537
11th to 20thNight
316%31%52%7%
534
21st to endNight
6%15%36%50%2
594
September1st to 10thNight
5%16%39%45%3
540
11th to 20thNight
6%17%42%42%2
540
21st to endNight
5%312%41%37%3
540
October1st to 10thNight
3113%48%34%2
540
11th to 20thNight
8%114%50%24%2
602
21st to endNight
6%314%41%30%6%
792
November1st to 10thNight
6%213%43%31%4
783
11th to 20thNight
5%419%44%26%2
950
21st to endNight
7%5%25%41%20%3
950
December1st to 10thNight
6%417%49%21%2
950
11th to 20thNight
45%27%48%15%1
950
21st to endNight
47%23%50%16%1
984
Page generated at 2024-01-13 08:37:56. Version ac07

Copyright 2024 Attilla Danko


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