Graceland University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Graceland University Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
35%
15978
21%
46990
11%
15931
44%
15931
26%
28947

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
26%
900
21%
2389
8%
895
37%
895
24%
1540
January16th to endNight
20%
960
20%
2496
6%
960
31%
960
23%
1660
February1st to 15thNight
21%
880
14%
2288
4%
876
27%
876
20%
1630
February16th to endNight
23%
710
22%
1972
6%
710
35%
710
24%
1258
March1st to 15thNight
30%
540
22%
1980
12%
540
43%
540
21%
1150
March16th to endNight
22%
576
13%
2112
7%
576
31%
576
15%
1426
April1st to 15thNight
25%
539
19%
1818
11%
539
40%
539
22%
1078
April16th to endNight
25%
540
20%
1719
10%
540
41%
540
17%
1130
May1st to 15thNight
31%
539
18%
1619
10%
539
41%
539
22%
1062
May16th to endNight
37%
563
21%
1517
8%
561
47%
561
27%
963
June1st to 15thNight
48%
540
19%
1440
7%
540
53%
540
35%
837
June16th to endNight
48%
540
20%
1440
8%
540
54%
540
40%
822
July1st to 15thNight
61%
510
18%
1382
11%
510
64%
510
41%
773
July16th to endNight
61%
564
22%
1594
17%
531
71%
531
40%
845
August1st to 15thNight
66%
539
22%
1610
23%
536
70%
536
40%
856
August16th to endNight
64%
573
24%
1821
24%
573
70%
573
35%
1004
September1st to 15thNight
56%
540
27%
1800
25%
540
64%
540
33%
970
September16th to endNight
53%
538
27%
1932
21%
538
64%
538
33%
990
October1st to 15thNight
40%
660
26%
1980
17%
660
45%
660
29%
1187
October16th to endNight
31%
704
24%
2112
11%
704
42%
704
30%
1249
November1st to 15thNight
33%
763
27%
2241
13%
763
46%
763
33%
1242
November16th to endNight
24%
900
20%
2520
8%
900
35%
900
24%
1592
December1st to 15thNight
22%
900
16%
2520
6%
900
30%
900
18%
1756
December16th to endNight
20%
960
17%
2688
5%
960
31%
960
16%
1927

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
12%7%35%5%2445%7%40%
47934
Night
11%6%35%424447%46%
47178
TransparencyDay
42%413%24%12%1
47626
Night
37%313%26%15%2
46991
SeeingDay
13%14%23%28%15%4
5999
Night
12%21%25%27%11%
15979

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 15thDay
10%9%47%6%34346%38%
1546
16th to endDay
15%10%6%8%6%34336%31%
1728
February1st to 15thDay
13%9%5%7%7%44446%32%
1575
16th to endDay
13%8%36%6%2436%6%37%
1512
March1st to 15thDay
12%10%5%7%5%2445%6%34%
1980
16th to endDay
17%12%5%6%5%34445%30%
2110
April1st to 15thDay
17%8%35%5%2335%6%38%
2129
16th to endDay
22%7%27%6%33445%32%
2238
May1st to 15thDay
16%7%47%6%3445%7%33%
2331
16th to endDay
14%6%35%5%35%45%6%38%
2595
June1st to 15thDay
10%6%25%42445%8%43%
2520
16th to endDay
6%3245%36%6%7%9%44%
2520
July1st to 15thDay
8%4145%35%5%7%9%45%
2493
16th to endDay
5%3145%25%5%7%10%49%
2466
August1st to 15thDay
6%425%5%35%6%7%10%43%
2340
16th to endDay
11%5%25%4345%47%45%
2381
September1st to 15thDay
12%424313348%50%
2160
16th to endDay
10%41442345%9%49%
1873
October1st to 15thDay
15%5%25%323246%48%
1650
16th to endDay
13%7%15%423445%45%
1760
November1st to 15thDay
9%5%24313347%52%
1611
16th to endDay
17%8%44423246%40%
1440
December1st to 15thDay
15%10%48%6%44447%31%
1440
16th to endDay
14%13%410%5%2345%7%29%
1536
January1st to 15thNight
8%6%36%6%2445%7%43%
2389
16th to endNight
9%8%47%425%35%6%41%
2496
February1st to 15thNight
13%10%48%5%24347%35%
2278
16th to endNight
11%8%35%424346%45%
1972
March1st to 15thNight
11%6%35%423345%48%
1980
16th to endNight
18%9%45%5%2445%6%32%
2112
April1st to 15thNight
14%5%24423346%47%
1818
16th to endNight
18%7%25%5%2434441%
1719
May1st to 15thNight
13%5%35%5%35%46%7%39%
1619
16th to endNight
8%424425%5%5%9%45%
1515
June1st to 15thNight
6%42332346%11%50%
1440
16th to endNight
5%223325%5%6%11%52%
1440
July1st to 15thNight
5%31232446%9%55%
1464
16th to endNight
42144245%5%9%54%
1702
August1st to 15thNight
32144335%6%9%53%
1620
16th to endNight
8%31342445%7%52%
1821
September1st to 15thNight
10%31441335%6%54%
1800
16th to endNight
8%31432345%7%54%
1932
October1st to 15thNight
12%6%25%423235%50%
1980
16th to endNight
13%6%24423235%52%
2112
November1st to 15thNight
9%424312447%55%
2241
16th to endNight
14%7%3441235%6%45%
2520
December1st to 15thNight
15%10%46%424336%37%
2520
16th to endNight
16%9%49%5%23345%34%
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
47%213%21%13%1
1547
16th to endDay
55%215%18%7%
1728
February1st to 15thDay
52%414%21%7%
1576
16th to endDay
46%313%23%11%
1512
March1st to 15thDay
49%414%21%9%1
1980
16th to endDay
54%413%18%6%1
2112
April1st to 15thDay
47%310%26%10%
2129
16th to endDay
54%312%19%9%
2238
May1st to 15thDay
50%413%21%10%
2331
16th to endDay
44%5%14%24%9%1
2599
June1st to 15thDay
38%5%15%24%13%2
2520
16th to endDay
32%6%16%27%15%1
2520
July1st to 15thDay
33%6%16%27%12%3
2346
16th to endDay
27%5%17%32%16%1
2311
August1st to 15thDay
33%6%16%27%15%
2326
16th to endDay
37%5%10%24%17%4
2381
September1st to 15thDay
32%312%29%17%3
2160
16th to endDay
32%312%32%17%1
1873
October1st to 15thDay
37%110%26%20%2
1650
16th to endDay
39%311%27%14%2
1760
November1st to 15thDay
32%213%28%20%3
1611
16th to endDay
46%214%24%12%
1440
December1st to 15thDay
53%215%19%7%
1440
16th to endDay
54%313%18%8%1
1536
January1st to 15thNight
39%414%26%15%
2389
16th to endNight
42%317%24%11%
2496
February1st to 15thNight
49%313%22%10%
2288
16th to endNight
40%212%25%16%2
1972
March1st to 15thNight
39%212%28%14%1
1980
16th to endNight
50%413%21%8%1
2112
April1st to 15thNight
38%311%28%16%2
1818
16th to endNight
45%311%23%12%2
1719
May1st to 15thNight
42%5%12%24%14%
1620
16th to endNight
35%6%13%26%13%3
1517
June1st to 15thNight
27%5%18%29%16%2
1440
16th to endNight
25%416%27%21%4
1440
July1st to 15thNight
25%418%31%14%4
1382
16th to endNight
24%414%35%19%1
1594
August1st to 15thNight
24%5%17%33%15%2
1610
16th to endNight
29%5%11%26%19%7%
1821
September1st to 15thNight
29%49%28%21%5%
1800
16th to endNight
28%312%33%19%2
1932
October1st to 15thNight
36%28%24%22%4
1980
16th to endNight
36%210%26%20%3
2112
November1st to 15thNight
28%315%25%21%5%
2241
16th to endNight
40%211%29%14%1
2520
December1st to 15thNight
49%314%23%9%
2520
16th to endNight
52%312%18%10%1
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
21%10%42%20%42
90
16th to endDay
26%8%36%23%5%
96
February1st to 15thDay
10%17%41%22%8%
90
16th to endDay
14%18%33%18%13%1
81
March1st to 15thDay
18%16%37%23%3
90
16th to endDay
32%13%36%16%1
96
April1st to 15thDay
21%19%27%21%9%
248
16th to endDay
24%21%29%16%6%1
348
May1st to 15thDay
18%21%26%22%8%2
468
16th to endDay
16%17%28%22%12%2
517
June1st to 15thDay
11%16%18%30%19%4
495
16th to endDay
5%17%28%30%14%3
495
July1st to 15thDay
10%10%17%34%18%8%
475
16th to endDay
413%13%40%24%4
515
August1st to 15thDay
8%7%13%37%26%6%
493
16th to endDay
12%8%14%31%24%8%
421
September1st to 15thDay
12%7%17%26%28%7%
315
16th to endDay
11%324%41%9%9%
114
October1st to 15thDay
12%8%27%33%10%7%
90
16th to endDay
13%10%39%31%5%
96
November1st to 15thDay
4434%34%14%7%
90
16th to endDay
41%8%35%10%4
90
December1st to 15thDay
18%23%31%17%44
90
16th to endDay
29%19%33%15%2
96
January1st to 15thNight
9%26%31%23%8%
900
16th to endNight
13%25%33%22%5%
960
February1st to 15thNight
15%25%30%23%5%
880
16th to endNight
13%25%32%20%6%1
710
March1st to 15thNight
16%24%24%25%8%
540
16th to endNight
20%23%30%20%5%
576
April1st to 15thNight
15%24%31%23%4
539
16th to endNight
19%23%27%22%6%
540
May1st to 15thNight
13%21%26%30%7%
540
16th to endNight
10%21%25%28%12%1
563
June1st to 15thNight
9%19%18%35%16%1
540
16th to endNight
419%25%37%14%
540
July1st to 15thNight
6%12%14%39%25%2
510
16th to endNight
5%17%9%40%25%1
564
August1st to 15thNight
410%11%40%29%2
539
16th to endNight
8%9%10%39%27%3
573
September1st to 15thNight
11%10%17%30%26%3
540
16th to endNight
9%11%21%32%22%2
538
October1st to 15thNight
15%15%24%30%13%2
660
16th to endNight
15%16%32%26%9%
704
November1st to 15thNight
9%24%29%26%9%
763
16th to endNight
15%27%30%19%7%
900
December1st to 15thNight
19%25%26%22%5%
900
16th to endNight
18%25%27%24%4
960
Page generated at 2017-09-25 08:02:19. Version ac04

Copyright 2017 A. Danko


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