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 2018-02-14.

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%
16510
18%
48751
12%
16469
44%
16469
23%
32776

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%
975
14%
2716
6%
970
26%
970
15%
2052
January16th to endNight
20%
1033
12%
2895
5%
1033
26%
1033
15%
2193
February1st to 15thNight
20%
757
11%
2280
4%
757
27%
757
15%
1661
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
29%
539
17%
1797
8%
539
41%
539
21%
1173
April16th to endNight
35%
540
20%
1707
12%
540
44%
540
25%
1095
May1st to 15thNight
36%
540
14%
1620
8%
540
42%
540
20%
1144
May16th to endNight
50%
561
17%
1597
11%
561
54%
561
27%
1049
June1st to 15thNight
58%
540
18%
1440
13%
540
62%
540
36%
885
June16th to endNight
57%
540
18%
1440
13%
540
61%
540
33%
938
July1st to 15thNight
63%
510
17%
1360
14%
510
65%
510
37%
846
July16th to endNight
74%
564
24%
1428
19%
531
76%
531
45%
813
August1st to 15thNight
71%
539
22%
1624
20%
536
73%
536
37%
931
August16th to endNight
68%
573
22%
1910
23%
573
72%
573
35%
1053
September1st to 15thNight
61%
591
26%
1851
24%
591
65%
591
34%
1067
September16th to endNight
62%
717
28%
1980
22%
717
65%
717
37%
1180
October1st to 15thNight
52%
720
27%
1989
21%
720
57%
720
34%
1220
October16th to endNight
30%
768
20%
2475
14%
768
37%
768
22%
1591
November1st to 15thNight
35%
760
25%
2471
18%
760
46%
760
26%
1495
November16th to endNight
27%
780
19%
2535
12%
780
38%
780
18%
1742
December1st to 15thNight
22%
881
11%
2636
5%
881
28%
881
14%
1994
December16th to endNight
16%
1040
11%
2912
3%
1040
24%
1040
12%
2334

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%
49334
Night
14%8%36%5%24346%38%
48922
Cloud CoverDay
14%7%36%5%3445%7%36%
49343
Night
15%8%36%5%24346%39%
48927
TransparencyDay
47%5%12%20%12%2
49023
Night
45%411%21%14%2
48751
SeeingDay
16%6%24%24%19%7%
6348
Night
18%8%27%29%13%1
16515

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%5%8%7%3445%422%
1552
16th to endDay
13%16%6%10%5%34435%25%
1681
February1st to 15thDay
15%14%5%8%7%5%5%34425%
1883
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
19%7%345%24447%35%
2151
16th to endDay
18%9%36%5%24446%35%
2253
May1st to 15thDay
20%8%36%6%25%5%46%30%
2331
16th to endDay
12%6%35%5%46%6%5%6%38%
2515
June1st to 15thDay
10%425%6%3445%8%43%
2520
16th to endDay
10%426%5%45%5%6%10%39%
2520
July1st to 15thDay
10%5%25%5%35%5%6%10%40%
2520
16th to endDay
6%324436%6%8%11%41%
2643
August1st to 15thDay
8%425%5%345%5%8%46%
2322
16th to endDay
8%425%5%45%5%7%8%42%
2292
September1st to 15thDay
12%6%24434447%44%
2097
16th to endDay
12%42432445%7%47%
1980
October1st to 15thDay
17%5%2443445%6%41%
1968
16th to endDay
19%7%25%5%245%45%37%
1749
November1st to 15thDay
15%7%34432246%45%
1717
16th to endDay
17%9%46%42335%7%33%
1755
December1st to 15thDay
18%13%5%9%6%23445%26%
1653
16th to endDay
21%13%5%9%5%35%435%21%
1664
January1st to 15thNight
19%12%47%6%33435%29%
2716
16th to endNight
14%13%6%9%7%34345%28%
2895
February1st to 15thNight
19%12%5%8%5%13236%30%
2278
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%45%7%37%
1797
16th to endNight
16%7%2442345%7%40%
1707
May1st to 15thNight
19%7%26%5%25%45%7%34%
1620
16th to endNight
12%425%5%345%6%8%41%
1595
June1st to 15thNight
8%5%34334348%50%
1440
16th to endNight
8%425%5%35%46%7%44%
1440
July1st to 15thNight
7%4244245%7%9%46%
1440
16th to endNight
432343445%10%54%
1525
August1st to 15thNight
5%4244245%6%10%48%
1635
16th to endNight
7%32443445%7%53%
1910
September1st to 15thNight
10%5%23423447%51%
1851
16th to endNight
10%224424346%52%
1980
October1st to 15thNight
13%425%323446%49%
1989
16th to endNight
18%6%25%424346%40%
2475
November1st to 15thNight
14%6%24323446%46%
2471
16th to endNight
18%10%46%5%23345%35%
2535
December1st to 15thNight
18%13%5%8%6%24335%27%
2636
16th to endNight
22%13%6%8%6%34345%22%
2912

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%48%7%3445%422%
1552
16th to endDay
13%16%6%9%6%33435%25%
1681
February1st to 15thDay
15%14%5%8%7%46%335%25%
1883
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
19%8%245%24447%35%
2151
16th to endDay
18%8%36%434446%35%
2253
May1st to 15thDay
20%8%36%6%25%5%46%30%
2331
16th to endDay
13%5%35%5%45%5%5%6%38%
2515
June1st to 15thDay
11%425%6%35%45%7%44%
2520
16th to endDay
10%425%6%35%5%6%9%39%
2520
July1st to 15thDay
10%5%25%5%35%5%6%10%40%
2520
16th to endDay
6%3145%26%6%8%11%42%
2643
August1st to 15thDay
8%325%5%445%5%8%46%
2322
16th to endDay
8%425%445%5%6%8%42%
2292
September1st to 15thDay
13%5%245%3445%6%44%
2097
16th to endDay
13%4233235%5%7%47%
1980
October1st to 15thDay
17%5%2443435%6%41%
1968
16th to endDay
19%7%25%4245%45%37%
1749
November1st to 15thDay
15%7%33422246%45%
1717
16th to endDay
17%9%46%5%2335%7%33%
1755
December1st to 15thDay
18%13%5%8%6%23445%26%
1653
16th to endDay
22%14%5%9%6%34436%20%
1664
January1st to 15thNight
19%11%5%7%5%33435%29%
2716
16th to endNight
14%13%6%9%6%34345%28%
2895
February1st to 15thNight
19%12%5%7%5%23236%30%
2271
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
16%6%25%5%2445%7%37%
1797
16th to endNight
17%7%2442335%7%40%
1707
May1st to 15thNight
19%6%26%6%2445%7%33%
1619
16th to endNight
12%426%5%2446%7%41%
1595
June1st to 15thNight
8%5%24324448%50%
1440
16th to endNight
8%5%25%5%35%46%7%44%
1440
July1st to 15thNight
8%324425%5%6%9%47%
1440
16th to endNight
5%22342445%10%54%
1525
August1st to 15thNight
5%4244245%6%10%48%
1635
16th to endNight
7%325%42445%7%53%
1910
September1st to 15thNight
11%5%13423447%51%
1851
16th to endNight
10%32443435%6%52%
1980
October1st to 15thNight
13%324323446%50%
1989
16th to endNight
18%6%25%424346%41%
2475
November1st to 15thNight
14%6%24324447%46%
2471
16th to endNight
18%10%45%5%23335%36%
2535
December1st to 15thNight
18%13%5%8%6%24335%28%
2636
16th to endNight
22%13%6%7%6%3334423%
2912

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%
1553
16th to endDay
60%412%15%5%
1681
February1st to 15thDay
61%49%15%7%
1885
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%412%21%12%
2151
16th to endDay
49%413%17%10%4
2253
May1st to 15thDay
54%6%11%19%8%
2331
16th to endDay
44%7%11%19%15%2
2519
June1st to 15thDay
38%412%24%18%1
2520
16th to endDay
38%6%14%20%15%3
2520
July1st to 15thDay
40%6%11%22%17%2
2371
16th to endDay
33%7%18%26%12%2
2477
August1st to 15thDay
33%6%13%25%19%1
2309
16th to endDay
36%6%12%23%15%5%
2292
September1st to 15thDay
38%5%11%22%17%4
2097
16th to endDay
34%6%9%25%21%2
1980
October1st to 15thDay
43%410%23%16%2
1968
16th to endDay
47%5%10%23%12%
1749
November1st to 15thDay
41%212%20%17%4
1717
16th to endDay
50%410%23%9%1
1755
December1st to 15thDay
60%410%18%6%
1653
16th to endDay
66%49%14%4
1664
January1st to 15thNight
57%47%17%11%1
2716
16th to endNight
59%312%17%7%
2895
February1st to 15thNight
56%313%16%9%1
2280
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%14%1
1797
16th to endNight
43%411%20%13%6%
1707
May1st to 15thNight
49%6%11%20%10%1
1620
16th to endNight
39%7%12%20%16%4
1597
June1st to 15thNight
32%6%10%27%21%2
1440
16th to endNight
35%7%12%21%17%4
1440
July1st to 15thNight
32%6%14%22%20%3
1360
16th to endNight
25%5%15%31%19%3
1428
August1st to 15thNight
29%6%14%25%22%2
1624
16th to endNight
29%5%11%25%21%5%
1910
September1st to 15thNight
32%410%25%20%6%
1851
16th to endNight
32%48%25%25%2
1980
October1st to 15thNight
34%410%25%22%2
1989
16th to endNight
45%310%25%14%1
2475
November1st to 15thNight
39%38%22%20%4
2471
16th to endNight
51%39%24%11%
2535
December1st to 15thNight
59%39%17%9%
2636
16th to endNight
65%49%14%6%
2912

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
26%13%35%17%5%1
135
16th to endDay
27%11%39%20%2
144
February1st to 15thDay
23%15%41%16%2
130
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
24%10%31%20%11%2
270
16th to endDay
22%6%27%24%12%6%
270
May1st to 15thDay
25%9%26%21%13%3
288
16th to endDay
15%330%25%17%7%
415
June1st to 15thDay
11%424%31%21%6%
495
16th to endDay
12%430%27%17%7%
495
July1st to 15thDay
13%122%29%21%12%
475
16th to endDay
7%212%31%28%17%
503
August1st to 15thDay
10%10%22%33%21%
313
16th to endDay
8%112%23%38%15%
332
September1st to 15thDay
13%310%29%32%10%
315
16th to endDay
14%310%23%33%14%
314
October1st to 15thDay
17%322%28%22%3
303
16th to endDay
22%9%34%26%6%
144
November1st to 15thDay
17%10%22%23%20%5%
135
16th to endDay
24%11%39%15%8%
135
December1st to 15thDay
20%20%33%20%5%
135
16th to endDay
27%20%38%12%1
144
January1st to 15thNight
24%13%36%20%4
975
16th to endNight
19%14%36%26%2
1033
February1st to 15thNight
25%12%33%24%3
760
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
18%12%35%24%8%
539
16th to endNight
21%5%33%28%9%1
540
May1st to 15thNight
22%428%30%12%
540
16th to endNight
12%5%23%35%20%2
563
June1st to 15thNight
11%220%47%17%
540
16th to endNight
10%221%41%22%
540
July1st to 15thNight
8%216%43%25%3
510
16th to endNight
6%210%40%35%5%
564
August1st to 15thNight
6%11%44%30%7%
539
16th to endNight
6%113%31%39%6%
573
September1st to 15thNight
12%316%37%24%5%
591
16th to endNight
11%216%32%33%3
717
October1st to 15thNight
14%5%21%36%17%5%
720
16th to endNight
22%10%32%23%10%
768
November1st to 15thNight
17%8%33%27%11%1
760
16th to endNight
22%13%30%23%9%
780
December1st to 15thNight
25%12%32%22%6%
881
16th to endNight
29%10%33%21%4
1040
Page generated at 2018-02-15 10:58:45. Version ac04

Copyright 2018 A. Danko


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