Anderson University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anderson University Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
40%
15881
17%
47009
12%
15839
45%
15839
23%
31709

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 15thNight
17%
900
12%
2506
5%
895
24%
895
13%
1978
January16th to endNight
19%
892
11%
2620
5%
892
25%
892
13%
2041
February1st to 15thNight
23%
701
10%
2136
5%
701
28%
701
16%
1557
February16th to endNight
24%
631
15%
1893
7%
631
31%
631
17%
1390
March1st to 15thNight
27%
720
14%
2132
9%
720
32%
720
18%
1507
March16th to endNight
30%
738
15%
2082
8%
738
38%
738
20%
1479
April1st to 15thNight
31%
539
17%
1797
10%
539
42%
539
22%
1194
April16th to endNight
35%
540
20%
1677
11%
540
44%
540
24%
1087
May1st to 15thNight
36%
540
14%
1620
9%
540
41%
540
19%
1141
May16th to endNight
53%
562
17%
1663
13%
561
58%
561
30%
1057
June1st to 15thNight
61%
540
18%
1440
13%
540
64%
540
37%
877
June16th to endNight
58%
540
18%
1440
14%
540
61%
540
36%
896
July1st to 15thNight
64%
510
15%
1360
13%
510
65%
510
35%
863
July16th to endNight
75%
564
23%
1478
18%
531
78%
531
43%
847
August1st to 15thNight
71%
539
22%
1609
20%
536
73%
536
36%
929
August16th to endNight
72%
573
22%
1882
22%
573
76%
573
36%
1022
September1st to 15thNight
64%
620
27%
1880
23%
620
69%
620
36%
1090
September16th to endNight
61%
717
28%
1980
21%
717
65%
717
35%
1193
October1st to 15thNight
50%
684
27%
1888
21%
684
56%
684
35%
1136
October16th to endNight
32%
704
20%
2255
14%
704
41%
704
23%
1442
November1st to 15thNight
39%
700
25%
2276
18%
700
50%
700
27%
1358
November16th to endNight
29%
720
17%
2340
12%
720
37%
720
17%
1626
December1st to 15thNight
22%
747
11%
2367
6%
747
28%
747
13%
1829
December16th to endNight
18%
960
10%
2688
3%
960
24%
960
11%
2170

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
15%8%36%5%3445%7%36%
48189
Night
15%8%36%5%34446%38%
47184
Cloud CoverDay
15%8%36%5%3445%7%35%
48198
Night
15%8%36%5%34446%38%
47189
TransparencyDay
47%412%21%12%1
47882
Night
46%411%21%13%2
47009
SeeingDay
16%5%23%24%19%9%
5895
Night
18%7%26%29%15%1
15885

By Month

Percentage Cloud Cover NE (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 15thDay
21%15%48%6%3434423%
1432
16th to endDay
14%15%8%9%5%35%5%5%5%22%
1602
February1st to 15thDay
15%13%6%10%6%34345%26%
1726
16th to endDay
15%13%5%9%6%34345%28%
1580
March1st to 15thDay
21%10%5%8%5%3335%5%28%
1817
16th to endDay
18%10%46%5%2335%6%30%
2154
April1st to 15thDay
19%9%35%5%3345%5%36%
2151
16th to endDay
19%6%37%5%34337%35%
2283
May1st to 15thDay
20%8%35%6%3445%6%30%
2331
16th to endDay
13%5%35%5%36%5%5%8%37%
2449
June1st to 15thDay
11%425%436%5%6%8%41%
2520
16th to endDay
10%5%25%5%45%5%6%9%40%
2520
July1st to 15thDay
11%325%6%35%5%6%10%39%
2520
16th to endDay
8%325%5%36%6%7%10%42%
2587
August1st to 15thDay
9%4245%25%5%6%9%45%
2340
16th to endDay
8%5%25%5%35%6%6%9%42%
2318
September1st to 15thDay
12%5%245%245%6%6%43%
2067
16th to endDay
12%5%24423347%48%
1980
October1st to 15thDay
14%6%25%5%23446%44%
1869
16th to endDay
18%7%25%43345%7%36%
1614
November1st to 15thDay
12%6%2442425%6%47%
1582
16th to endDay
19%10%5%7%5%2345%7%29%
1620
December1st to 15thDay
22%15%49%5%24335%23%
1591
16th to endDay
21%16%5%9%5%3444420%
1536
January1st to 15thNight
20%13%5%8%6%3333326%
2506
16th to endNight
16%15%7%8%6%3434425%
2620
February1st to 15thNight
16%13%6%7%6%3324430%
2134
16th to endNight
15%10%6%9%5%34435%29%
1893
March1st to 15thNight
16%10%37%5%24346%33%
2119
16th to endNight
16%10%36%5%34346%34%
2082
April1st to 15thNight
16%7%25%5%3445%6%38%
1797
16th to endNight
17%5%144235%5%7%40%
1677
May1st to 15thNight
20%8%26%5%245%46%32%
1620
16th to endNight
13%5%25%5%2447%9%41%
1661
June1st to 15thNight
8%5%14434438%50%
1440
16th to endNight
8%425%425%5%6%8%46%
1440
July1st to 15thNight
7%425%5%35%46%7%46%
1440
16th to endNight
5%323424448%54%
1579
August1st to 15thNight
5%315%435%46%9%50%
1620
16th to endNight
6%31443446%7%52%
1882
September1st to 15thNight
10%42442235%9%50%
1880
16th to endNight
11%4234235%46%50%
1980
October1st to 15thNight
11%415%423446%50%
1888
16th to endNight
19%6%145%23346%41%
2255
November1st to 15thNight
13%7%24323346%47%
2276
16th to endNight
20%9%36%5%23336%33%
2340
December1st to 15thNight
21%12%6%8%6%2433425%
2367
16th to endNight
23%14%5%8%6%34335%21%
2688

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 15thDay
21%15%5%8%6%34335%23%
1432
16th to endDay
13%16%9%8%5%35%5%5%5%21%
1602
February1st to 15thDay
15%13%7%9%7%25%345%25%
1726
16th to endDay
15%13%5%9%5%43345%28%
1580
March1st to 15thDay
21%11%48%5%23346%27%
1827
16th to endDay
18%10%46%5%3335%6%31%
2153
April1st to 15thDay
19%10%245%3335%5%36%
2151
16th to endDay
19%6%37%5%34347%35%
2283
May1st to 15thDay
21%8%36%6%3445%6%30%
2331
16th to endDay
13%5%36%5%26%46%7%37%
2449
June1st to 15thDay
11%425%5%35%46%7%41%
2520
16th to endDay
10%5%25%5%35%6%6%9%40%
2520
July1st to 15thDay
11%425%5%26%5%5%10%38%
2520
16th to endDay
8%4245%35%6%6%10%42%
2587
August1st to 15thDay
9%5%245%345%5%10%44%
2340
16th to endDay
8%425%5%35%5%6%9%42%
2318
September1st to 15thDay
12%5%34425%5%5%7%43%
2067
16th to endDay
13%5%14433347%48%
1980
October1st to 15thDay
13%6%25%423446%44%
1869
16th to endDay
18%8%25%43435%7%37%
1614
November1st to 15thDay
12%6%2442335%7%46%
1582
16th to endDay
18%11%5%6%6%2345%7%28%
1620
December1st to 15thDay
22%15%49%5%24235%22%
1591
16th to endDay
21%15%5%9%5%2435%5%19%
1536
January1st to 15thNight
20%13%5%8%6%3433425%
2506
16th to endNight
16%14%7%8%6%3334425%
2620
February1st to 15thNight
16%13%5%7%5%2424430%
2127
16th to endNight
14%11%5%10%6%34435%29%
1893
March1st to 15thNight
17%10%46%6%24346%33%
2132
16th to endNight
16%9%46%5%34447%34%
2082
April1st to 15thNight
16%7%25%5%35%45%6%38%
1797
16th to endNight
16%6%2443445%7%39%
1677
May1st to 15thNight
20%8%36%5%335%5%6%32%
1619
16th to endNight
12%6%145%3347%9%40%
1661
June1st to 15thNight
8%5%145%35%348%50%
1440
16th to endNight
8%3244245%7%8%46%
1440
July1st to 15thNight
7%4245%25%46%7%47%
1440
16th to endNight
5%3144235%6%8%54%
1579
August1st to 15thNight
6%3144345%5%8%50%
1620
16th to endNight
6%313435%46%7%52%
1882
September1st to 15thNight
10%425%32345%8%50%
1880
16th to endNight
11%41442445%6%51%
1980
October1st to 15thNight
11%425%423446%50%
1888
16th to endNight
19%5%145%23346%41%
2255
November1st to 15thNight
12%7%24423346%47%
2276
16th to endNight
20%10%36%5%23336%33%
2340
December1st to 15thNight
21%12%6%8%5%2433425%
2367
16th to endNight
23%14%6%9%5%34335%21%
2688

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 15thDay
64%29%15%7%
1433
16th to endDay
62%414%13%4
1602
February1st to 15thDay
60%311%14%9%
1728
16th to endDay
58%313%19%5%
1580
March1st to 15thDay
58%312%18%6%
1827
16th to endDay
54%415%20%41
2154
April1st to 15thDay
48%411%22%11%
2151
16th to endDay
49%410%20%10%4
2283
May1st to 15thDay
53%6%12%18%8%
2331
16th to endDay
43%7%12%21%14%1
2453
June1st to 15thDay
39%412%24%17%1
2520
16th to endDay
37%6%15%21%16%2
2520
July1st to 15thDay
40%5%12%20%17%2
2371
16th to endDay
32%7%19%25%12%2
2425
August1st to 15thDay
34%6%12%26%17%1
2327
16th to endDay
36%6%10%25%15%5%
2318
September1st to 15thDay
38%5%11%21%19%3
2067
16th to endDay
36%49%24%24%1
1980
October1st to 15thDay
40%310%26%16%2
1869
16th to endDay
47%312%24%11%
1614
November1st to 15thDay
37%410%24%19%4
1582
16th to endDay
55%312%20%7%
1620
December1st to 15thDay
64%210%15%5%
1591
16th to endDay
66%311%15%3
1536
January1st to 15thNight
62%47%16%8%
2506
16th to endNight
62%310%16%7%
2620
February1st to 15thNight
57%314%17%7%
2136
16th to endNight
56%311%19%7%
1893
March1st to 15thNight
51%412%21%8%2
2132
16th to endNight
51%413%22%7%1
2082
April1st to 15thNight
46%49%23%14%1
1797
16th to endNight
43%5%10%20%13%7%
1677
May1st to 15thNight
52%312%21%8%1
1620
16th to endNight
38%5%14%22%14%4
1663
June1st to 15thNight
32%412%26%21%2
1440
16th to endNight
32%7%14%23%18%3
1440
July1st to 15thNight
34%6%14%20%18%5%
1360
16th to endNight
26%5%14%32%17%3
1478
August1st to 15thNight
29%6%13%24%21%2
1609
16th to endNight
28%5%13%25%22%5%
1882
September1st to 15thNight
32%410%24%22%5%
1880
16th to endNight
33%5%7%25%25%3
1980
October1st to 15thNight
34%310%24%23%2
1888
16th to endNight
44%310%27%12%1
2255
November1st to 15thNight
38%37%23%21%4
2276
16th to endNight
52%211%21%10%
2340
December1st to 15thNight
63%39%16%7%
2367
16th to endNight
66%39%14%5%
2688

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 15thDay
31%17%32%11%6%1
90
16th to endDay
21%19%38%15%4
96
February1st to 15thDay
21%17%41%18%1
90
16th to endDay
14%11%48%17%8%
81
March1st to 15thDay
32%13%33%16%4
117
16th to endDay
25%9%32%18%12%1
288
April1st to 15thDay
21%12%29%23%11%2
270
16th to endDay
21%8%27%22%11%7%
270
May1st to 15thDay
27%9%25%22%10%5%
288
16th to endDay
19%227%23%17%9%
349
June1st to 15thDay
11%322%34%21%7%
495
16th to endDay
12%427%28%19%7%
495
July1st to 15thDay
14%122%28%20%13%
475
16th to endDay
8%113%27%31%18%
447
August1st to 15thDay
13%8%22%30%23%
313
16th to endDay
11%112%23%31%20%
332
September1st to 15thDay
13%311%24%33%14%
315
16th to endDay
15%314%19%30%17%
314
October1st to 15thDay
13%6%20%30%21%7%
278
16th to endDay
22%5%41%26%3
126
November1st to 15thDay
12%10%21%18%28%8%
90
16th to endDay
31%8%37%16%5%
90
December1st to 15thDay
25%13%37%16%6%
90
16th to endDay
25%21%42%9%1
96
January1st to 15thNight
25%14%36%19%4
900
16th to endNight
24%13%34%24%4
892
February1st to 15thNight
23%9%35%27%3
704
16th to endNight
22%8%37%26%4
631
March1st to 15thNight
21%13%31%28%5%
720
16th to endNight
22%8%33%28%6%1
738
April1st to 15thNight
17%9%36%27%8%
539
16th to endNight
20%6%34%25%12%2
540
May1st to 15thNight
24%427%32%11%
540
16th to endNight
12%323%35%21%3
563
June1st to 15thNight
8%319%47%19%
540
16th to endNight
10%120%41%25%1
540
July1st to 15thNight
9%213%41%30%3
510
16th to endNight
6%18%40%37%5%
564
August1st to 15thNight
7%12%38%34%6%
539
16th to endNight
7%110%34%42%5%
573
September1st to 15thNight
12%213%34%30%6%
620
16th to endNight
12%215%31%31%5%
717
October1st to 15thNight
14%6%22%33%18%5%
684
16th to endNight
22%8%33%24%9%
704
November1st to 15thNight
16%9%30%26%14%1
700
16th to endNight
25%11%27%25%9%
720
December1st to 15thNight
28%10%30%23%6%
747
16th to endNight
31%10%33%20%4
960
Page generated at 2017-10-07 14:07:49. Version ac04

Copyright 2017 A. Danko


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