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 2017-04-08.

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%
15370
17%
45390
11%
15329
44%
15329
23%
30683

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
14%
2506
5%
895
25%
895
15%
1912
January16th to endNight
20%
954
11%
2673
5%
954
25%
954
15%
2035
February1st to 15thNight
20%
701
11%
2112
4%
701
27%
701
16%
1532
February16th to endNight
24%
631
15%
1893
7%
631
30%
631
16%
1359
March1st to 15thNight
25%
720
14%
2160
9%
720
29%
720
17%
1531
March16th to endNight
29%
691
16%
2035
7%
691
37%
691
20%
1430
April1st to 15thNight
28%
518
17%
1727
9%
518
41%
518
21%
1130
April16th to endNight
34%
495
19%
1565
10%
495
43%
495
24%
1012
May1st to 15thNight
36%
495
15%
1485
8%
495
42%
495
20%
1056
May16th to endNight
52%
513
16%
1460
12%
513
55%
513
27%
962
June1st to 15thNight
56%
495
19%
1320
13%
495
60%
495
34%
828
June16th to endNight
57%
495
16%
1320
13%
495
60%
495
32%
871
July1st to 15thNight
63%
465
18%
1240
15%
465
65%
465
37%
770
July16th to endNight
74%
522
22%
1315
17%
489
76%
489
44%
756
August1st to 15thNight
71%
494
23%
1488
21%
491
73%
491
36%
855
August16th to endNight
68%
525
20%
1750
21%
525
72%
525
35%
965
September1st to 15thNight
61%
542
28%
1697
25%
542
66%
542
34%
979
September16th to endNight
61%
657
26%
1815
20%
657
64%
657
35%
1106
October1st to 15thNight
53%
660
28%
1823
22%
660
59%
660
35%
1103
October16th to endNight
29%
704
18%
2269
13%
704
36%
704
21%
1462
November1st to 15thNight
36%
700
26%
2276
19%
700
48%
700
28%
1352
November16th to endNight
28%
720
17%
2340
12%
720
36%
720
17%
1635
December1st to 15thNight
21%
813
11%
2433
5%
813
27%
813
13%
1878
December16th to endNight
16%
960
10%
2688
3%
960
23%
960
12%
2164

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%
45877
Night
15%8%36%5%24346%38%
45561
Cloud CoverDay
15%8%36%5%3445%7%35%
45886
Night
15%8%36%5%24446%38%
45566
TransparencyDay
47%5%12%20%12%1
45566
Night
46%411%21%13%2
45390
SeeingDay
17%5%23%24%19%8%
5166
Night
18%8%27%29%13%1
15375

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%13%48%8%3435%423%
1432
16th to endDay
13%16%7%10%5%34435%25%
1551
February1st to 15thDay
15%14%5%7%7%5%5%34426%
1750
16th to endDay
14%13%6%9%5%345%36%27%
1580
March1st to 15thDay
19%11%5%8%5%24445%27%
1790
16th to endDay
17%11%46%6%235%5%7%29%
2198
April1st to 15thDay
20%8%345%24447%35%
2060
16th to endDay
18%9%35%5%24446%35%
2065
May1st to 15thDay
20%8%36%6%25%5%46%29%
2136
16th to endDay
11%6%35%5%46%6%5%6%38%
2300
June1st to 15thDay
11%425%6%35%45%8%40%
2310
16th to endDay
10%426%5%45%5%6%10%38%
2310
July1st to 15thDay
10%5%245%25%5%6%9%40%
2310
16th to endDay
6%3245%36%6%8%12%40%
2448
August1st to 15thDay
8%425%5%345%5%8%46%
2129
16th to endDay
8%425%5%46%6%7%8%41%
2100
September1st to 15thDay
12%5%2443445%7%43%
1922
16th to endDay
13%42432445%7%46%
1815
October1st to 15thDay
15%5%2443435%6%42%
1804
16th to endDay
19%7%25%5%24445%36%
1603
November1st to 15thDay
14%6%33432246%47%
1582
16th to endDay
18%9%46%5%24347%31%
1620
December1st to 15thDay
19%13%5%9%6%23345%25%
1526
16th to endDay
22%13%5%9%5%35%435%20%
1536
January1st to 15thNight
20%12%48%5%33435%28%
2506
16th to endNight
15%13%6%9%7%34345%27%
2673
February1st to 15thNight
18%12%5%7%5%14236%31%
2110
16th to endNight
15%12%5%8%425%335%32%
1893
March1st to 15thNight
18%10%47%5%2435%6%32%
2147
16th to endNight
16%9%36%6%34447%34%
2035
April1st to 15thNight
16%6%345%25%447%37%
1727
16th to endNight
17%7%3442345%7%39%
1565
May1st to 15thNight
18%7%26%5%25%45%7%32%
1485
16th to endNight
12%425%6%345%5%8%41%
1458
June1st to 15thNight
9%5%34334448%47%
1320
16th to endNight
9%5%25%5%35%46%7%43%
1320
July1st to 15thNight
8%424425%5%7%9%46%
1320
16th to endNight
5%32343445%10%53%
1412
August1st to 15thNight
5%4244245%6%10%47%
1499
16th to endNight
7%32443445%7%52%
1750
September1st to 15thNight
11%413423447%51%
1697
16th to endNight
11%3245%34446%50%
1815
October1st to 15thNight
12%315%323446%51%
1823
16th to endNight
19%6%25%424346%40%
2269
November1st to 15thNight
13%5%24323446%47%
2276
16th to endNight
19%10%46%5%23246%34%
2340
December1st to 15thNight
19%13%5%8%6%24335%25%
2433
16th to endNight
23%13%6%8%6%34345%22%
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
19%13%48%7%3435%423%
1432
16th to endDay
13%16%7%10%6%33435%25%
1551
February1st to 15thDay
15%14%5%8%6%46%345%26%
1750
16th to endDay
15%12%5%9%5%345%35%28%
1580
March1st to 15thDay
20%10%6%7%5%33445%27%
1800
16th to endDay
17%11%46%5%2345%7%30%
2197
April1st to 15thDay
20%8%245%24337%36%
2060
16th to endDay
19%8%36%434446%36%
2065
May1st to 15thDay
20%8%36%6%25%5%5%6%29%
2136
16th to endDay
12%5%35%5%46%6%5%6%38%
2300
June1st to 15thDay
12%425%6%35%45%8%41%
2310
16th to endDay
10%426%6%35%5%5%9%38%
2310
July1st to 15thDay
11%5%24435%5%6%9%40%
2310
16th to endDay
7%3245%27%6%8%11%41%
2448
August1st to 15thDay
8%425%5%445%5%8%46%
2129
16th to endDay
9%425%5%46%6%6%8%42%
2100
September1st to 15thDay
13%5%245%3446%7%43%
1922
16th to endDay
13%42432445%7%46%
1815
October1st to 15thDay
16%42443435%6%43%
1804
16th to endDay
19%7%25%4245%46%36%
1603
November1st to 15thDay
14%6%33422246%47%
1582
16th to endDay
18%10%46%5%2435%7%32%
1620
December1st to 15thDay
19%14%5%8%6%23346%25%
1526
16th to endDay
22%14%5%9%6%24436%20%
1536
January1st to 15thNight
20%12%5%8%5%33435%28%
2506
16th to endNight
15%13%6%9%6%34345%27%
2673
February1st to 15thNight
18%12%5%7%6%23236%31%
2103
16th to endNight
15%12%5%8%434435%32%
1893
March1st to 15thNight
18%9%47%42435%6%32%
2160
16th to endNight
16%9%47%6%24346%34%
2035
April1st to 15thNight
17%6%35%5%24447%37%
1727
16th to endNight
17%7%3442345%7%39%
1565
May1st to 15thNight
19%6%36%6%25%45%7%33%
1484
16th to endNight
12%426%6%3446%7%41%
1458
June1st to 15thNight
9%6%34434448%48%
1320
16th to endNight
9%5%25%5%35%5%6%7%44%
1320
July1st to 15thNight
8%324325%5%6%9%47%
1320
16th to endNight
5%22342445%10%53%
1412
August1st to 15thNight
6%424435%5%6%10%48%
1499
16th to endNight
7%325%42445%7%52%
1750
September1st to 15thNight
11%413423447%51%
1697
16th to endNight
11%3245%3435%6%50%
1815
October1st to 15thNight
11%324422446%51%
1823
16th to endNight
19%6%25%424346%40%
2269
November1st to 15thNight
13%5%24323447%48%
2276
16th to endNight
19%10%46%5%23335%34%
2340
December1st to 15thNight
20%13%6%8%6%2433426%
2433
16th to endNight
23%13%6%7%6%3334422%
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
63%39%14%8%
1433
16th to endDay
61%412%15%5%
1551
February1st to 15thDay
61%49%15%8%
1752
16th to endDay
58%413%18%5%
1580
March1st to 15thDay
59%5%12%16%6%
1800
16th to endDay
53%5%14%20%5%1
2198
April1st to 15thDay
48%411%21%13%
2060
16th to endDay
49%412%18%10%4
2065
May1st to 15thDay
54%6%11%18%8%
2136
16th to endDay
44%7%11%19%15%2
2304
June1st to 15thDay
41%412%24%15%1
2310
16th to endDay
39%6%14%20%16%3
2310
July1st to 15thDay
40%6%10%22%17%2
2161
16th to endDay
33%7%19%26%11%1
2282
August1st to 15thDay
34%6%12%25%19%1
2116
16th to endDay
36%6%11%22%15%6%
2100
September1st to 15thDay
39%5%11%21%17%4
1922
16th to endDay
36%5%9%24%21%2
1815
October1st to 15thDay
41%410%24%17%2
1804
16th to endDay
47%5%11%23%11%
1603
November1st to 15thDay
39%211%21%18%4
1582
16th to endDay
52%411%22%8%
1620
December1st to 15thDay
61%310%17%5%
1526
16th to endDay
66%49%14%3
1536
January1st to 15thNight
58%48%17%10%
2506
16th to endNight
60%312%16%7%
2673
February1st to 15thNight
56%313%16%8%1
2112
16th to endNight
54%411%20%7%
1893
March1st to 15thNight
53%311%20%9%2
2160
16th to endNight
50%413%22%8%1
2035
April1st to 15thNight
45%5%10%22%15%1
1727
16th to endNight
43%411%20%13%6%
1565
May1st to 15thNight
49%6%11%20%10%1
1485
16th to endNight
40%7%11%20%15%4
1460
June1st to 15thNight
34%6%10%27%18%1
1320
16th to endNight
37%7%11%21%17%4
1320
July1st to 15thNight
32%5%13%23%20%3
1240
16th to endNight
25%6%15%31%18%2
1315
August1st to 15thNight
29%6%13%25%22%2
1488
16th to endNight
30%5%12%24%21%6%
1750
September1st to 15thNight
32%410%24%20%7%
1697
16th to endNight
34%48%24%25%3
1815
October1st to 15thNight
33%410%25%23%2
1823
16th to endNight
45%310%24%13%1
2269
November1st to 15thNight
37%48%22%22%4
2276
16th to endNight
52%39%22%11%
2340
December1st to 15thNight
61%39%15%8%
2433
16th to endNight
65%49%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
30%16%33%13%5%1
90
16th to endDay
27%10%39%19%3
96
February1st to 15thDay
21%16%43%16%2
90
16th to endDay
18%9%38%19%12%1
81
March1st to 15thDay
34%17%33%11%3
90
16th to endDay
26%10%32%17%11%1
287
April1st to 15thDay
26%10%28%21%10%2
240
16th to endDay
22%5%27%21%15%7%
210
May1st to 15thDay
24%7%29%20%13%4
228
16th to endDay
13%327%26%19%9%
344
June1st to 15thDay
13%5%25%31%18%6%
420
16th to endDay
13%326%29%19%8%
420
July1st to 15thDay
14%121%28%22%13%
400
16th to endDay
6%212%32%27%18%
434
August1st to 15thDay
11%7%22%33%24%
253
16th to endDay
9%110%22%38%17%
268
September1st to 15thDay
12%310%29%34%10%
255
16th to endDay
16%49%24%32%11%
254
October1st to 15thDay
14%224%28%25%4
244
16th to endDay
23%11%34%26%4
96
November1st to 15thDay
7%10%21%26%25%8%
90
16th to endDay
32%12%33%14%7%
90
December1st to 15thDay
25%10%35%23%5%
90
16th to endDay
28%19%38%11%2
96
January1st to 15thNight
24%14%37%20%3
900
16th to endNight
20%14%35%27%3
954
February1st to 15thNight
23%13%34%25%3
704
16th to endNight
22%10%35%26%5%
631
March1st to 15thNight
22%14%32%25%5%
720
16th to endNight
18%10%36%26%7%1
691
April1st to 15thNight
19%12%35%24%8%
518
16th to endNight
22%6%33%26%10%1
495
May1st to 15thNight
21%5%29%31%12%
495
16th to endNight
12%5%21%36%22%2
515
June1st to 15thNight
12%220%47%15%
495
16th to endNight
11%219%42%24%
495
July1st to 15thNight
8%216%43%26%3
465
16th to endNight
6%210%40%34%5%
522
August1st to 15thNight
6%11%43%30%6%
494
16th to endNight
6%113%31%40%7%
525
September1st to 15thNight
13%316%36%25%5%
542
16th to endNight
12%216%33%32%2
657
October1st to 15thNight
13%5%21%36%17%5%
660
16th to endNight
22%10%32%23%9%
704
November1st to 15thNight
16%9%33%27%11%1
700
16th to endNight
23%13%29%23%9%
720
December1st to 15thNight
27%12%31%22%6%
813
16th to endNight
30%10%33%21%4
960
Page generated at 2017-04-09 06:54:11. Version ac04

Copyright 2017 A. Danko


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