Prairie Grass Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prairie Grass 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
37%
24434
18%
74657
12%
24379
44%
24379
22%
50746

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
18%
950
13%
2648
5%
946
25%
946
14%
2039
January11th to 20thNight
17%
926
12%
2591
4%
926
24%
926
14%
2048
January21st to endNight
20%
979
11%
2747
4%
979
25%
979
13%
2119
February1st to 10thNight
18%
720
10%
2160
4%
720
24%
720
13%
1656
February11th to 20thNight
22%
700
15%
2099
7%
700
29%
700
16%
1522
February21st to endNight
18%
592
15%
1776
4%
592
27%
592
15%
1307
March1st to 10thNight
25%
720
15%
2160
9%
720
30%
720
17%
1521
March11th to 20thNight
27%
720
19%
2071
9%
720
35%
720
23%
1393
March21st to endNight
26%
679
15%
2065
7%
679
35%
679
18%
1474
April1st to 10thNight
28%
540
18%
1800
9%
540
40%
540
22%
1163
April11th to 20thNight
33%
533
21%
1775
14%
533
43%
533
22%
1134
April21st to endNight
28%
540
16%
1661
6%
540
38%
540
21%
1138
May1st to 10thNight
31%
540
14%
1620
7%
540
38%
540
20%
1144
May11th to 20thNight
42%
531
16%
1593
11%
531
47%
531
24%
1078
May21st to endNight
52%
582
18%
1618
10%
582
57%
582
29%
1060
June1st to 10thNight
57%
540
19%
1440
13%
540
61%
540
35%
892
June11th to 20thNight
56%
540
21%
1440
15%
540
60%
540
34%
897
June21st to endNight
55%
540
18%
1440
14%
540
60%
540
33%
945
July1st to 10thNight
65%
525
17%
1400
14%
525
67%
525
34%
889
July11th to 20thNight
70%
522
23%
1392
18%
522
72%
522
45%
808
July21st to endNight
70%
591
25%
1504
18%
558
73%
558
41%
885
August1st to 10thNight
69%
537
22%
1600
20%
534
71%
534
36%
924
August11th to 20thNight
68%
534
22%
1710
22%
534
71%
534
32%
1012
August21st to endNight
65%
594
24%
1980
24%
594
70%
594
36%
1060
September1st to 10thNight
63%
540
23%
1800
24%
540
66%
540
30%
1049
September11th to 20thNight
65%
706
32%
1966
26%
706
69%
706
42%
1110
September21st to endNight
56%
720
27%
1980
19%
720
60%
720
35%
1202
October1st to 10thNight
53%
720
27%
1980
21%
720
57%
720
36%
1202
October11th to 20thNight
36%
720
22%
2142
14%
720
46%
720
25%
1364
October21st to endNight
26%
792
19%
2574
12%
792
35%
792
19%
1719
November1st to 10thNight
34%
740
25%
2406
17%
740
46%
740
28%
1421
November11th to 20thNight
30%
760
23%
2470
14%
760
43%
760
21%
1604
November21st to endNight
25%
760
18%
2470
11%
760
35%
760
16%
1764
December1st to 10thNight
21%
812
13%
2522
5%
812
29%
812
15%
1855
December11th to 20thNight
23%
950
15%
3197
6%
948
30%
948
14%
2320
December21st to endNight
16%
1039
6%
4860
3%
1026
22%
1026
6%
4028

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
14%9%46%5%35%5%5%7%36%
74871
Night
15%9%47%5%3445%7%38%
74947
TransparencyDay
47%6%12%21%13%2
74575
Night
47%5%11%21%14%2
74765
SeeingDay
18%7%26%25%17%7%
14489
Night
19%8%28%30%14%2
24445

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
17%14%5%10%8%445%6%422%
1517
11th to 20thDay
17%17%8%11%7%4444420%
1480
21st to endDay
15%18%7%10%6%445%36%22%
1607
February1st to 10thDay
17%15%7%9%8%46%345%23%
1800
11th to 20thDay
17%11%49%7%35%5%5%6%28%
1748
21st to endDay
17%15%6%9%5%335%35%29%
1480
March1st to 10thDay
17%12%6%7%5%5%445%5%30%
1800
11th to 20thDay
17%10%47%5%345%6%7%32%
1888
21st to endDay
21%13%5%7%6%3445%6%26%
2307
April1st to 10thDay
16%9%47%6%35%447%35%
2160
11th to 20thDay
18%9%35%5%35%45%7%37%
2134
21st to endDay
21%9%37%5%3445%7%33%
2299
May1st to 10thDay
18%9%36%6%36%5%5%7%32%
2340
11th to 20thDay
20%7%46%6%35%5%5%6%33%
2301
21st to endDay
11%6%36%6%46%6%6%8%38%
2655
June1st to 10thDay
11%5%26%6%36%5%6%8%43%
2520
11th to 20thDay
10%425%6%35%5%6%9%46%
2520
21st to endDay
11%5%35%6%35%6%6%9%40%
2520
July1st to 10thDay
10%5%35%5%35%6%7%10%41%
2520
11th to 20thDay
8%4245%35%6%7%11%46%
2520
21st to endDay
9%425%6%36%6%7%9%44%
2725
August1st to 10thDay
8%425%5%445%6%10%48%
2327
11th to 20thDay
9%5%25%5%46%6%6%9%42%
2187
21st to endDay
7%425%445%5%6%9%48%
2376
September1st to 10thDay
12%6%35%5%3445%7%46%
2156
11th to 20thDay
11%4245%345%6%7%48%
1980
21st to endDay
13%6%244345%6%7%47%
1980
October1st to 10thDay
14%5%25%5%3446%7%46%
1980
11th to 20thDay
18%7%25%4345%5%6%41%
1814
21st to endDay
20%9%37%5%35%45%6%32%
1782
November1st to 10thDay
12%7%2443345%7%50%
1672
11th to 20thDay
18%11%5%6%5%3335%6%36%
1710
21st to endDay
18%10%48%5%3445%7%33%
1710
December1st to 10thDay
18%14%6%9%6%34345%27%
1655
11th to 20thDay
14%13%7%12%7%34446%27%
1918
21st to endDay
23%21%8%12%5%3433414%
2783
January1st to 10thNight
17%14%5%10%6%44445%27%
2648
11th to 20thNight
17%15%6%10%7%44335%25%
2591
21st to endNight
16%13%7%11%7%34445%26%
2747
February1st to 10thNight
20%14%6%9%7%34345%25%
2160
11th to 20thNight
15%12%5%10%7%34436%32%
2098
21st to endNight
20%12%5%9%434445%31%
1776
March1st to 10thNight
16%10%5%7%6%35%446%34%
2160
11th to 20thNight
15%9%47%5%35%45%7%38%
2071
21st to endNight
21%10%47%5%3335%6%33%
2065
April1st to 10thNight
14%7%45%6%445%6%8%39%
1800
11th to 20thNight
18%8%35%42445%8%39%
1775
21st to endNight
18%7%46%5%45%45%6%36%
1661
May1st to 10thNight
18%8%46%6%345%49%33%
1620
11th to 20thNight
18%6%25%5%345%7%7%38%
1592
21st to endNight
10%327%6%36%6%7%9%42%
1617
June1st to 10thNight
8%6%26%5%35%5%5%7%50%
1440
11th to 20thNight
8%6%345%345%5%8%49%
1440
21st to endNight
9%5%35%5%35%5%7%9%43%
1440
July1st to 10thNight
8%435%5%35%5%5%11%46%
1440
11th to 20thNight
7%3244245%6%10%54%
1440
21st to endNight
7%424335%45%8%54%
1592
August1st to 10thNight
7%425%435%5%6%8%51%
1611
11th to 20thNight
6%5%26%6%35%5%6%8%48%
1710
21st to endNight
8%325%42445%8%55%
1980
September1st to 10thNight
12%5%25%43445%7%49%
1800
11th to 20thNight
9%42342435%8%57%
1966
21st to endNight
12%42443445%7%51%
1980
October1st to 10thNight
11%5%25%4235%46%52%
1980
11th to 20thNight
18%6%25%433446%45%
2142
21st to endNight
19%9%35%5%25%45%6%37%
2574
November1st to 10thNight
13%6%35%42445%6%49%
2406
11th to 20thNight
15%10%36%43445%7%40%
2470
21st to endNight
19%12%5%7%6%34345%32%
2470
December1st to 10thNight
17%13%5%9%7%25%446%29%
2522
11th to 20thNight
16%14%5%9%6%34446%31%
3279
21st to endNight
22%19%7%9%6%4444416%
4884

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
63%47%16%8%1
1518
11th to 20thDay
68%411%11%5%
1480
21st to endDay
64%410%14%6%1
1607
February1st to 10thDay
66%39%14%7%1
1800
11th to 20thDay
56%5%10%20%8%1
1758
21st to endDay
59%411%17%7%2
1480
March1st to 10thDay
57%5%10%20%8%
1800
11th to 20thDay
52%5%13%18%10%1
1888
21st to endDay
59%411%20%5%1
2307
April1st to 10thDay
49%5%13%19%14%1
2160
11th to 20thDay
47%6%11%22%10%3
2134
21st to endDay
51%5%11%18%11%3
2299
May1st to 10thDay
51%6%12%21%9%
2340
11th to 20thDay
51%6%11%18%12%1
2305
21st to endDay
42%8%12%20%15%2
2655
June1st to 10thDay
39%6%12%25%16%3
2520
11th to 20thDay
35%5%12%24%21%3
2520
21st to endDay
39%8%15%19%15%4
2520
July1st to 10thDay
37%8%14%23%15%3
2451
11th to 20thDay
31%7%16%28%16%2
2445
21st to endDay
35%8%15%24%15%3
2574
August1st to 10thDay
32%8%15%30%14%1
2314
11th to 20thDay
36%7%14%26%16%1
2187
21st to endDay
32%7%13%25%18%6%
2376
September1st to 10thDay
37%6%13%24%16%5%
2156
11th to 20thDay
34%6%11%25%21%3
1980
21st to endDay
36%6%9%25%22%2
1980
October1st to 10thDay
38%5%12%25%18%3
1980
11th to 20thDay
43%6%10%23%18%1
1814
21st to endDay
53%5%9%20%12%1
1782
November1st to 10thDay
35%5%14%25%18%4
1672
11th to 20thDay
51%210%22%12%3
1710
21st to endDay
52%5%10%22%10%1
1710
December1st to 10thDay
60%410%18%8%
1655
11th to 20thDay
61%47%24%41
1915
21st to endDay
75%48%9%4
2783
January1st to 10thNight
59%5%7%18%10%1
2648
11th to 20thNight
64%310%15%7%1
2591
21st to endNight
61%410%16%8%1
2747
February1st to 10thNight
62%412%14%7%1
2160
11th to 20thNight
55%410%18%11%2
2099
21st to endNight
57%410%18%9%2
1776
March1st to 10thNight
52%410%20%12%1
2160
11th to 20thNight
46%412%23%12%3
2071
21st to endNight
53%412%21%9%1
2065
April1st to 10thNight
43%6%12%23%14%2
1800
11th to 20thNight
43%5%9%22%16%5%
1775
21st to endNight
47%6%11%19%13%4
1661
May1st to 10thNight
50%6%11%20%11%2
1620
11th to 20thNight
44%7%12%22%13%2
1593
21st to endNight
37%9%13%21%15%5%
1618
June1st to 10thNight
33%7%10%27%20%3
1440
11th to 20thNight
34%7%10%24%22%4
1440
21st to endNight
35%9%14%23%15%5%
1440
July1st to 10thNight
33%8%14%23%17%5%
1400
11th to 20thNight
25%7%14%31%22%2
1392
21st to endNight
28%7%14%28%19%5%
1504
August1st to 10thNight
29%7%14%29%18%2
1600
11th to 20thNight
32%8%13%26%20%2
1710
21st to endNight
28%6%12%25%22%6%
1980
September1st to 10thNight
34%6%12%24%18%6%
1800
11th to 20thNight
27%5%11%29%26%3
1966
21st to endNight
33%6%10%24%24%3
1980
October1st to 10thNight
32%6%10%27%22%3
1980
11th to 20thNight
42%48%24%20%2
2142
21st to endNight
48%5%9%22%15%2
2574
November1st to 10thNight
37%5%9%25%21%3
2406
11th to 20thNight
45%49%23%16%3
2470
21st to endNight
56%38%23%10%
2470
December1st to 10thNight
57%410%19%9%1
2522
11th to 20thNight
56%49%20%11%1
3281
21st to endNight
71%5%9%10%5%
4884

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
24%13%34%23%41
270
11th to 20thDay
25%14%35%20%32
255
21st to endDay
28%12%33%21%5%
264
February1st to 10thDay
30%11%39%18%3
240
11th to 20thDay
27%18%33%14%7%1
240
21st to endDay
28%14%43%12%3
198
March1st to 10thDay
22%20%38%17%4
240
11th to 20thDay
29%11%33%20%6%1
328
21st to endDay
33%12%31%16%7%1
462
April1st to 10thDay
22%12%32%23%8%3
420
11th to 20thDay
24%11%31%19%12%3
412
21st to endDay
27%12%31%18%9%3
420
May1st to 10thDay
21%11%32%22%11%3
423
11th to 20thDay
22%5%27%28%14%5%
447
21st to endDay
12%328%28%18%11%
609
June1st to 10thDay
11%426%32%21%7%
630
11th to 20thDay
13%326%30%22%6%
630
21st to endDay
15%329%27%18%9%
630
July1st to 10thDay
12%114%27%29%17%
621
11th to 20thDay
9%117%36%22%15%
618
21st to endDay
11%215%32%27%13%
666
August1st to 10thDay
8%112%29%31%19%
446
11th to 20thDay
13%214%30%28%14%
439
21st to endDay
7%214%29%34%14%
495
September1st to 10thDay
15%312%29%31%10%
450
11th to 20thDay
12%112%30%28%17%
450
21st to endDay
14%7%21%24%25%10%
450
October1st to 10thDay
15%324%31%20%6%
450
11th to 20thDay
16%14%34%24%11%
342
21st to endDay
33%8%37%18%4
297
November1st to 10thDay
13%12%34%24%13%4
270
11th to 20thDay
23%17%29%20%10%1
270
21st to endDay
26%10%36%23%5%
270
December1st to 10thDay
23%17%32%20%7%1
270
11th to 20thDay
22%13%38%21%5%1
270
21st to endDay
30%15%32%20%3
297
January1st to 10thNight
23%13%37%23%5%
950
11th to 20thNight
25%12%36%22%4
926
21st to endNight
22%12%35%27%3
979
February1st to 10thNight
28%9%36%24%3
720
11th to 20thNight
22%15%35%24%5%
703
21st to endNight
28%11%37%21%4
592
March1st to 10thNight
21%13%33%27%6%
720
11th to 20thNight
18%10%38%27%5%1
720
21st to endNight
26%8%33%27%6%1
679
April1st to 10thNight
17%11%37%26%7%1
540
11th to 20thNight
23%8%32%27%9%
533
21st to endNight
23%5%38%24%8%1
540
May1st to 10thNight
21%6%35%29%9%
540
11th to 20thNight
21%323%34%16%2
531
21st to endNight
11%324%38%22%2
584
June1st to 10thNight
12%219%47%20%
540
11th to 20thNight
11%219%46%20%1
540
21st to endNight
11%223%38%25%1
540
July1st to 10thNight
9%112%40%31%7%
525
11th to 20thNight
7%115%40%31%6%
522
21st to endNight
10%112%43%33%2
591
August1st to 10thNight
8%110%44%33%5%
537
11th to 20thNight
7%110%41%35%6%
534
21st to endNight
10%114%32%38%6%
594
September1st to 10thNight
15%112%39%27%5%
540
11th to 20thNight
11%313%37%32%3
706
21st to endNight
13%320%36%26%3
720
October1st to 10thNight
12%423%38%18%5%
720
11th to 20thNight
22%9%28%30%11%1
720
21st to endNight
24%10%34%24%7%
792
November1st to 10thNight
17%6%37%28%10%1
740
11th to 20thNight
20%13%31%28%7%1
760
21st to endNight
25%12%30%26%7%
760
December1st to 10thNight
23%12%35%25%5%
812
11th to 20thNight
26%9%33%26%7%
950
21st to endNight
30%12%31%24%3
1045
Page generated at 2024-01-13 01:38:08. Version ac07

Copyright 2024 Attilla Danko


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