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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 2020-06-03.

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%
19550
18%
57764
11%
19509
44%
19509
23%
39048

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%
1125
14%
3136
5%
1120
26%
1120
15%
2380
January16th to endNight
18%
1192
11%
3341
4%
1192
24%
1192
14%
2596
February1st to 15thNight
19%
881
11%
2652
4%
881
25%
881
14%
1979
February16th to endNight
22%
791
16%
2373
7%
791
29%
791
15%
1738
March1st to 15thNight
25%
900
15%
2700
9%
900
30%
900
18%
1893
March16th to endNight
28%
864
17%
2544
7%
864
38%
864
21%
1775
April1st to 15thNight
28%
674
16%
2247
8%
674
39%
674
20%
1502
April16th to endNight
33%
669
19%
2112
11%
669
42%
669
23%
1382
May1st to 15thNight
36%
675
15%
2025
8%
675
41%
675
22%
1406
May16th to endNight
49%
705
16%
2007
11%
705
53%
705
27%
1332
June1st to 15thNight
57%
637
18%
1700
13%
637
61%
637
35%
1056
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
61%
837
27%
2310
21%
837
65%
837
38%
1367
October1st to 15thNight
51%
840
27%
2321
20%
840
56%
840
33%
1435
October16th to endNight
30%
896
19%
2887
14%
896
38%
896
22%
1841
November1st to 15thNight
33%
880
24%
2861
16%
880
44%
880
25%
1774
November16th to endNight
26%
900
18%
2925
11%
900
36%
900
17%
2058
December1st to 15thNight
21%
1016
12%
3041
5%
1016
28%
1016
15%
2280
December16th to endNight
19%
1200
12%
3360
5%
1200
26%
1200
13%
2661

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%35%
58657
Night
14%8%36%5%24346%38%
57935
Cloud CoverDay
15%8%36%5%3445%7%35%
58666
Night
15%8%36%5%24346%38%
57940
TransparencyDay
47%5%12%20%12%1
58346
Night
46%411%21%14%2
57764
SeeingDay
18%7%25%24%17%7%
9490
Night
18%8%28%29%13%1
19555

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%7%3445%421%
1792
16th to endDay
14%16%6%10%5%44435%23%
1938
February1st to 15thDay
17%14%5%8%7%45%34423%
2200
16th to endDay
17%13%5%8%5%335%35%27%
1980
March1st to 15thDay
18%13%5%7%5%34445%27%
2240
16th to endDay
19%11%46%5%2445%6%28%
2748
April1st to 15thDay
18%9%35%5%34447%33%
2691
16th to endDay
19%9%36%5%24446%34%
2783
May1st to 15thDay
19%8%36%6%25%5%5%6%31%
2916
16th to endDay
13%6%36%5%45%6%5%7%36%
3160
June1st to 15thDay
11%425%6%345%5%7%43%
2969
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
11%42442445%7%47%
2310
October1st to 15thDay
16%5%24435%45%6%41%
2296
16th to endDay
19%8%25%424445%37%
2041
November1st to 15thDay
15%7%34432346%44%
1987
16th to endDay
18%10%5%7%423447%30%
2025
December1st to 15thDay
18%13%5%9%6%24345%25%
1907
16th to endDay
20%13%5%9%5%25%336%23%
1920
January1st to 15thNight
19%12%5%8%5%33335%29%
3136
16th to endNight
14%14%6%10%7%3433425%
3341
February1st to 15thNight
20%12%5%8%5%13235%29%
2650
16th to endNight
17%12%5%8%424335%30%
2373
March1st to 15thNight
16%10%47%5%2435%6%33%
2687
16th to endNight
17%9%36%5%23346%35%
2544
April1st to 15thNight
16%7%35%5%35%45%7%35%
2247
16th to endNight
16%7%35%423447%39%
2112
May1st to 15thNight
17%7%25%5%2445%8%35%
2025
16th to endNight
11%426%6%3446%8%40%
2005
June1st to 15thNight
8%5%34434448%49%
1700
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
9%32442445%6%52%
2310
October1st to 15thNight
12%425%32445%6%48%
2321
16th to endNight
17%7%25%424346%41%
2887
November1st to 15thNight
15%6%25%32345%6%43%
2861
16th to endNight
18%12%46%5%33245%33%
2925
December1st to 15thNight
18%13%5%9%6%24335%28%
3041
16th to endNight
21%12%6%8%6%34335%24%
3360

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
18%14%5%8%7%3445%421%
1792
16th to endDay
14%16%7%10%6%44435%23%
1938
February1st to 15thDay
17%14%5%8%7%45%34423%
2200
16th to endDay
17%14%5%9%4335%35%27%
1980
March1st to 15thDay
19%12%5%7%5%3345%5%27%
2250
16th to endDay
19%11%46%5%2445%6%29%
2747
April1st to 15thDay
18%9%25%5%24447%33%
2691
16th to endDay
19%8%36%424446%34%
2783
May1st to 15thDay
19%7%36%6%25%5%5%6%31%
2916
16th to endDay
13%5%35%5%35%6%6%7%36%
3160
June1st to 15thDay
11%425%6%3445%7%43%
2969
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%243245%5%7%47%
2310
October1st to 15thDay
17%5%2443446%6%41%
2296
16th to endDay
19%8%25%424445%37%
2041
November1st to 15thDay
15%8%34422346%43%
1987
16th to endDay
18%11%5%7%42345%6%30%
2025
December1st to 15thDay
18%13%5%9%6%23445%25%
1907
16th to endDay
21%13%5%8%5%24336%23%
1920
January1st to 15thNight
19%12%5%8%5%33335%29%
3136
16th to endNight
15%14%7%10%7%3433425%
3341
February1st to 15thNight
20%12%5%8%5%23235%29%
2643
16th to endNight
17%12%5%8%434435%30%
2373
March1st to 15thNight
17%10%47%42435%6%33%
2700
16th to endNight
17%9%36%5%23346%35%
2544
April1st to 15thNight
16%7%35%5%2445%7%35%
2247
16th to endNight
16%7%35%423447%39%
2112
May1st to 15thNight
18%6%25%5%2445%8%35%
2024
16th to endNight
12%426%5%3446%8%40%
2005
June1st to 15thNight
7%5%34434447%49%
1700
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%31442435%7%52%
2310
October1st to 15thNight
12%425%32345%6%49%
2321
16th to endNight
17%7%25%424346%42%
2887
November1st to 15thNight
15%6%25%323346%43%
2861
16th to endNight
18%11%46%5%23335%33%
2925
December1st to 15thNight
18%13%5%9%6%24335%28%
3041
16th to endNight
22%12%6%7%6%34335%24%
3360

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%
1793
16th to endDay
63%411%14%5%
1938
February1st to 15thDay
64%39%14%6%1
2202
16th to endDay
59%411%16%6%1
1980
March1st to 15thDay
59%411%17%7%
2250
16th to endDay
55%412%20%5%
2748
April1st to 15thDay
49%5%13%20%11%
2691
16th to endDay
50%412%16%11%4
2783
May1st to 15thDay
52%6%12%19%8%
2916
16th to endDay
45%7%12%19%13%2
3164
June1st to 15thDay
39%412%24%17%1
2969
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
34%6%11%24%20%2
2310
October1st to 15thDay
41%411%23%16%2
2296
16th to endDay
47%410%22%14%
2041
November1st to 15thDay
42%312%21%16%3
1987
16th to endDay
54%410%21%8%1
2025
December1st to 15thDay
61%49%17%6%
1907
16th to endDay
63%49%16%5%
1920
January1st to 15thNight
58%37%17%11%1
3136
16th to endNight
62%310%15%7%
3341
February1st to 15thNight
59%312%14%8%1
2652
16th to endNight
56%410%18%9%1
2373
March1st to 15thNight
51%411%20%10%2
2700
16th to endNight
50%412%22%9%1
2544
April1st to 15thNight
46%5%11%21%12%1
2247
16th to endNight
44%411%19%13%6%
2112
May1st to 15thNight
47%6%12%20%11%1
2025
16th to endNight
39%8%12%21%14%3
2007
June1st to 15thNight
32%6%11%26%20%2
1700
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
31%5%10%25%24%2
2310
October1st to 15thNight
35%410%25%21%2
2321
16th to endNight
44%310%24%15%1
2887
November1st to 15thNight
41%49%21%19%3
2861
16th to endNight
53%39%22%9%
2925
December1st to 15thNight
59%39%17%9%
3041
16th to endNight
63%49%15%6%
3360

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
27%15%33%18%41
225
16th to endDay
27%12%30%21%5%1
240
February1st to 15thDay
31%16%31%17%3
225
16th to endDay
29%10%36%15%6%
201
March1st to 15thDay
30%18%35%12%4
225
16th to endDay
30%9%31%17%10%1
479
April1st to 15thDay
23%13%30%20%10%1
450
16th to endDay
26%10%26%20%11%4
439
May1st to 15thDay
22%9%29%22%12%3
468
16th to endDay
16%329%25%16%7%
628
June1st to 15thDay
12%426%30%20%6%
656
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
14%414%23%29%12%
434
October1st to 15thDay
16%426%29%19%3
421
16th to endDay
27%11%32%20%8%
240
November1st to 15thDay
19%11%30%20%14%3
225
16th to endDay
28%9%36%18%7%
225
December1st to 15thDay
20%16%34%21%5%1
225
16th to endDay
26%14%37%18%2
240
January1st to 15thNight
24%13%36%19%4
1125
16th to endNight
21%14%35%25%3
1192
February1st to 15thNight
26%12%33%23%3
884
16th to endNight
24%11%34%25%4
791
March1st to 15thNight
21%13%33%26%5%
900
16th to endNight
20%9%35%26%7%
864
April1st to 15thNight
19%11%35%24%7%
674
16th to endNight
21%6%34%26%9%1
669
May1st to 15thNight
21%430%30%12%
675
16th to endNight
12%424%35%20%2
707
June1st to 15thNight
11%220%46%18%
637
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%217%33%32%2
837
October1st to 15thNight
14%5%22%36%16%4
840
16th to endNight
21%11%32%24%10%
896
November1st to 15thNight
19%8%33%26%10%1
880
16th to endNight
23%12%30%24%8%
900
December1st to 15thNight
25%12%32%22%6%
1016
16th to endNight
28%10%33%23%4
1200
Page generated at 2020-06-04 03:18:56. Version ac04

Copyright 2020 A. Danko


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