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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 2005-11-05 to 2019-09-17.

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
38%
18526
18%
54711
12%
18485
44%
18485
23%
36834

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
18%
1050
14%
2926
5%
1045
27%
1045
16%
2217
January16th to endNight
19%
1112
12%
3117
4%
1112
25%
1112
15%
2383
February1st to 15thNight
20%
821
11%
2472
4%
821
26%
821
15%
1823
February16th to endNight
22%
735
14%
2205
6%
735
28%
735
15%
1623
March1st to 15thNight
25%
840
15%
2520
9%
840
30%
840
17%
1765
March16th to endNight
29%
807
17%
2375
8%
807
38%
807
21%
1657
April1st to 15thNight
28%
629
16%
2097
9%
629
40%
629
20%
1397
April16th to endNight
34%
624
18%
1970
11%
624
42%
624
24%
1280
May1st to 15thNight
37%
630
15%
1890
9%
630
42%
630
22%
1314
May16th to endNight
50%
657
17%
1871
11%
657
54%
657
28%
1223
June1st to 15thNight
57%
630
18%
1680
13%
630
61%
630
35%
1043
June16th to endNight
57%
630
17%
1680
13%
630
61%
630
33%
1095
July1st to 15thNight
65%
600
18%
1600
15%
600
67%
600
37%
987
July16th to endNight
73%
660
23%
1686
18%
627
76%
627
44%
972
August1st to 15thNight
72%
620
24%
1867
22%
617
74%
617
38%
1058
August16th to endNight
66%
669
21%
2230
21%
669
70%
669
33%
1244
September1st to 15thNight
63%
689
26%
2159
24%
689
67%
689
34%
1237
September16th to endNight
62%
782
27%
2159
21%
782
65%
782
37%
1287
October1st to 15thNight
51%
780
27%
2155
20%
780
57%
780
33%
1341
October16th to endNight
30%
832
19%
2681
14%
832
38%
832
23%
1701
November1st to 15thNight
34%
820
25%
2666
18%
820
45%
820
25%
1640
November16th to endNight
26%
840
18%
2730
11%
840
36%
840
17%
1904
December1st to 15thNight
22%
949
12%
2839
5%
949
28%
949
14%
2139
December16th to endNight
17%
1120
11%
3136
3%
1120
24%
1120
12%
2504

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%8%36%5%3445%7%36%
55989
Night
14%8%36%5%24346%38%
54882
Cloud CoverDay
15%8%36%5%3445%7%36%
55998
Night
14%8%36%5%24346%38%
54887
TransparencyDay
47%5%12%20%12%1
55678
Night
45%411%21%14%2
54711
SeeingDay
18%6%24%24%18%7%
8593
Night
18%8%27%29%14%1
18531

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
19%14%5%8%8%4445%421%
1672
16th to endDay
14%15%6%10%5%44435%24%
1810
February1st to 15thDay
17%14%5%8%7%5%5%34424%
2050
16th to endDay
16%14%6%9%5%345%35%26%
1840
March1st to 15thDay
18%12%5%8%5%34445%27%
2090
16th to endDay
18%11%46%5%2345%6%30%
2564
April1st to 15thDay
19%8%35%5%24447%33%
2511
16th to endDay
19%9%36%424446%35%
2595
May1st to 15thDay
19%8%36%6%25%5%5%6%30%
2721
16th to endDay
12%5%35%5%45%6%5%7%37%
2945
June1st to 15thDay
11%425%6%345%5%7%43%
2940
16th to endDay
11%425%5%35%5%6%9%38%
2940
July1st to 15thDay
9%5%245%35%5%6%9%42%
2940
16th to endDay
7%324436%6%7%10%42%
3089
August1st to 15thDay
7%3145%345%6%9%47%
2662
16th to endDay
8%5%25%5%45%5%7%8%42%
2676
September1st to 15thDay
12%5%2443445%7%45%
2447
16th to endDay
12%5%2442445%6%47%
2156
October1st to 15thDay
17%5%24435%45%6%40%
2132
16th to endDay
19%7%25%424445%38%
1895
November1st to 15thDay
16%7%34432346%44%
1852
16th to endDay
17%10%5%7%5%2335%6%31%
1890
December1st to 15thDay
19%13%5%9%6%24445%25%
1780
16th to endDay
21%13%5%9%5%34436%22%
1792
January1st to 15thNight
19%12%48%6%33335%29%
2926
16th to endNight
14%13%6%9%7%34335%27%
3117
February1st to 15thNight
20%12%5%8%5%13235%29%
2470
16th to endNight
17%12%5%8%424335%30%
2205
March1st to 15thNight
16%10%47%5%2435%6%33%
2507
16th to endNight
17%9%36%5%23346%35%
2375
April1st to 15thNight
16%7%35%5%25%45%7%35%
2097
16th to endNight
16%7%35%42345%7%39%
1970
May1st to 15thNight
18%6%25%5%2445%7%35%
1890
16th to endNight
11%425%5%2446%8%41%
1869
June1st to 15thNight
7%5%34434448%49%
1680
16th to endNight
9%5%25%5%25%46%8%44%
1680
July1st to 15thNight
6%4244245%6%9%48%
1680
16th to endNight
5%313434449%54%
1783
August1st to 15thNight
44244245%6%10%50%
1878
16th to endNight
7%3245%2445%7%51%
2230
September1st to 15thNight
11%413423447%51%
2159
16th to endNight
10%324424446%52%
2159
October1st to 15thNight
13%425%32445%7%48%
2155
16th to endNight
17%6%25%424346%42%
2681
November1st to 15thNight
15%6%24323446%44%
2666
16th to endNight
18%11%46%5%23235%34%
2730
December1st to 15thNight
18%13%5%8%6%24345%27%
2839
16th to endNight
22%13%6%8%6%34345%23%
3136

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
19%14%5%8%8%3445%421%
1672
16th to endDay
14%16%6%9%6%34435%24%
1810
February1st to 15thDay
17%14%5%8%7%46%34424%
2050
16th to endDay
16%14%5%9%5%345%35%26%
1840
March1st to 15thDay
19%11%5%7%5%3345%5%27%
2100
16th to endDay
19%11%46%5%2345%6%30%
2563
April1st to 15thDay
19%9%25%5%24447%33%
2511
16th to endDay
19%8%36%433446%35%
2595
May1st to 15thDay
20%8%36%6%25%5%5%6%30%
2721
16th to endDay
13%5%35%5%35%6%5%6%37%
2945
June1st to 15thDay
11%425%6%35%45%7%43%
2940
16th to endDay
11%425%6%35%5%5%9%39%
2940
July1st to 15thDay
9%4245%35%5%6%9%42%
2940
16th to endDay
8%3245%26%6%7%10%43%
3089
August1st to 15thDay
7%3245%345%5%9%47%
2662
16th to endDay
9%425%5%45%5%6%8%42%
2676
September1st to 15thDay
13%5%2443445%6%45%
2447
16th to endDay
12%5%2432445%6%47%
2156
October1st to 15thDay
17%5%2443446%6%40%
2132
16th to endDay
19%7%25%424445%38%
1895
November1st to 15thDay
16%7%34422346%43%
1852
16th to endDay
17%10%47%42335%6%32%
1890
December1st to 15thDay
18%13%5%9%6%23445%25%
1780
16th to endDay
22%13%5%8%6%34436%21%
1792
January1st to 15thNight
19%12%5%8%6%33435%28%
2926
16th to endNight
15%13%6%9%6%34345%27%
3117
February1st to 15thNight
20%12%5%7%6%23236%30%
2463
16th to endNight
17%12%5%8%434435%30%
2205
March1st to 15thNight
17%9%47%5%2435%6%33%
2520
16th to endNight
17%9%36%5%23346%35%
2375
April1st to 15thNight
17%7%35%5%2445%7%35%
2097
16th to endNight
16%7%3442345%7%39%
1970
May1st to 15thNight
18%6%25%5%2445%8%34%
1889
16th to endNight
12%426%5%3446%8%41%
1869
June1st to 15thNight
7%5%344345%47%49%
1680
16th to endNight
9%5%25%5%35%47%7%44%
1680
July1st to 15thNight
7%324425%5%6%9%48%
1680
16th to endNight
5%32332445%9%54%
1783
August1st to 15thNight
5%4244245%6%10%50%
1878
16th to endNight
7%325%43445%7%51%
2230
September1st to 15thNight
11%413423447%51%
2159
16th to endNight
10%32442435%6%52%
2159
October1st to 15thNight
13%425%323446%48%
2155
16th to endNight
18%6%25%424346%42%
2681
November1st to 15thNight
15%6%24323346%44%
2666
16th to endNight
18%11%46%5%23335%34%
2730
December1st to 15thNight
18%13%5%8%6%24335%27%
2839
16th to endNight
22%13%6%7%6%3434423%
3136

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%38%14%8%
1673
16th to endDay
61%411%15%5%
1810
February1st to 15thDay
63%39%15%7%
2052
16th to endDay
60%412%16%6%
1840
March1st to 15thDay
59%411%16%7%
2100
16th to endDay
53%412%21%6%
2564
April1st to 15thDay
49%5%12%20%11%
2511
16th to endDay
50%412%16%11%4
2595
May1st to 15thDay
53%6%12%19%8%
2721
16th to endDay
44%7%12%19%14%2
2949
June1st to 15thDay
39%412%24%17%1
2940
16th to endDay
39%6%14%22%14%2
2940
July1st to 15thDay
37%7%12%22%16%3
2791
16th to endDay
33%7%16%25%14%2
2923
August1st to 15thDay
31%7%13%27%18%1
2649
16th to endDay
36%6%12%23%15%5%
2676
September1st to 15thDay
38%5%12%22%17%4
2447
16th to endDay
35%5%10%24%21%2
2156
October1st to 15thDay
43%411%23%15%2
2132
16th to endDay
46%410%22%13%
1895
November1st to 15thDay
42%312%20%17%4
1852
16th to endDay
53%410%22%8%1
1890
December1st to 15thDay
61%49%17%6%
1780
16th to endDay
65%410%15%4
1792
January1st to 15thNight
57%48%17%10%1
2926
16th to endNight
60%311%16%7%
3117
February1st to 15thNight
58%313%15%8%1
2472
16th to endNight
57%410%18%8%
2205
March1st to 15thNight
51%411%20%10%2
2520
16th to endNight
50%412%22%9%1
2375
April1st to 15thNight
46%5%11%21%13%1
2097
16th to endNight
44%411%19%13%6%
1970
May1st to 15thNight
47%6%12%21%10%1
1890
16th to endNight
38%7%13%21%14%3
1871
June1st to 15thNight
32%6%11%26%19%2
1680
16th to endNight
35%7%13%22%16%3
1680
July1st to 15thNight
30%7%14%23%19%4
1600
16th to endNight
25%5%14%30%19%4
1686
August1st to 15thNight
28%6%13%27%22%1
1867
16th to endNight
30%5%12%24%20%5%
2230
September1st to 15thNight
31%5%11%24%20%5%
2159
16th to endNight
32%49%25%25%3
2159
October1st to 15thNight
35%410%25%21%2
2155
16th to endNight
43%310%25%15%1
2681
November1st to 15thNight
40%38%22%20%4
2666
16th to endNight
52%39%23%10%
2730
December1st to 15thNight
59%39%17%9%
2839
16th to endNight
64%49%15%6%
3136

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
28%12%33%18%42
180
16th to endDay
27%12%35%22%2
192
February1st to 15thDay
29%16%32%18%2
180
16th to endDay
28%12%35%16%6%
159
March1st to 15thDay
31%18%32%14%3
180
16th to endDay
28%8%33%16%11%1
415
April1st to 15thDay
25%12%29%20%10%1
390
16th to endDay
26%9%26%20%12%5%
379
May1st to 15thDay
23%9%26%22%14%4
408
16th to endDay
15%329%25%16%8%
557
June1st to 15thDay
12%425%29%20%6%
645
16th to endDay
13%426%28%19%8%
645
July1st to 15thDay
11%17%26%26%17%
625
16th to endDay
9%213%32%27%15%
661
August1st to 15thDay
8%11%23%36%18%
418
16th to endDay
10%216%26%31%12%
460
September1st to 15thDay
14%210%30%32%10%
435
16th to endDay
15%311%22%32%12%
378
October1st to 15thDay
18%424%29%20%3
362
16th to endDay
25%11%33%21%7%
192
November1st to 15thDay
21%11%24%22%16%4
180
16th to endDay
24%10%38%19%7%
180
December1st to 15thDay
22%17%31%20%6%1
180
16th to endDay
28%16%35%15%21
192
January1st to 15thNight
24%13%36%20%5%
1050
16th to endNight
20%14%36%25%2
1112
February1st to 15thNight
26%12%33%24%3
824
16th to endNight
24%11%34%25%4
735
March1st to 15thNight
21%14%33%25%5%
840
16th to endNight
19%9%35%25%7%
807
April1st to 15thNight
20%11%35%24%7%
629
16th to endNight
21%6%33%27%10%1
624
May1st to 15thNight
21%429%30%13%
630
16th to endNight
12%423%35%21%2
659
June1st to 15thNight
11%220%46%18%
630
16th to endNight
11%220%39%25%
630
July1st to 15thNight
8%114%40%30%5%
600
16th to endNight
7%110%41%33%5%
660
August1st to 15thNight
6%10%44%32%6%
620
16th to endNight
7%115%33%35%6%
669
September1st to 15thNight
12%315%36%26%5%
689
16th to endNight
11%216%32%33%2
782
October1st to 15thNight
14%5%21%36%16%4
780
16th to endNight
21%10%32%23%10%
832
November1st to 15thNight
19%8%32%26%11%1
820
16th to endNight
23%12%30%24%8%
840
December1st to 15thNight
25%12%32%22%6%
949
16th to endNight
28%10%34%21%4
1120
Page generated at 2019-09-17 21:12:19. Version ac04

Copyright 2019 A. Danko


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