Grassland Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grassland Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
43%
23996
18%
74512
12%
23943
49%
23943
20%
50293

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
23%
760
16%
2459
9%
757
34%
757
13%
1737
January11th to 20thNight
23%
735
17%
2386
8%
735
35%
735
13%
1725
January21st to endNight
22%
792
20%
2574
9%
792
36%
792
16%
1739
February1st to 10thNight
27%
720
19%
2246
10%
720
37%
720
18%
1545
February11th to 20thNight
19%
702
15%
2099
6%
700
28%
700
14%
1495
February21st to endNight
17%
592
20%
1776
7%
592
30%
592
16%
1267
March1st to 10thNight
25%
720
20%
2042
10%
720
33%
720
19%
1399
March11th to 20thNight
25%
720
14%
1980
7%
720
31%
720
17%
1438
March21st to endNight
27%
792
15%
2178
6%
792
33%
792
19%
1545
April1st to 10thNight
33%
720
19%
1980
9%
720
41%
720
24%
1280
April11th to 20thNight
35%
596
22%
1758
12%
596
44%
596
25%
1128
April21st to endNight
45%
540
22%
1620
13%
540
52%
540
25%
1038
May1st to 10thNight
43%
540
15%
1620
7%
540
49%
540
23%
1072
May11th to 20thNight
49%
531
13%
1593
9%
531
52%
531
20%
1124
May21st to endNight
63%
582
15%
1744
11%
582
64%
582
23%
1189
June1st to 10thNight
65%
540
13%
1620
11%
540
66%
540
24%
1096
June11th to 20thNight
66%
540
11%
1620
8%
540
69%
540
28%
1049
June21st to endNight
67%
540
15%
1620
13%
540
69%
540
28%
1052
July1st to 10thNight
68%
525
11%
1575
10%
525
69%
525
22%
1124
July11th to 20thNight
69%
522
10%
1566
9%
522
70%
522
21%
1116
July21st to endNight
68%
591
12%
1672
11%
558
68%
558
21%
1202
August1st to 10thNight
70%
537
11%
1600
10%
534
70%
534
22%
1141
August11th to 20thNight
63%
534
15%
1598
14%
534
63%
534
21%
1152
August21st to endNight
66%
625
14%
1945
13%
625
66%
625
21%
1337
September1st to 10thNight
62%
720
17%
1980
15%
720
63%
720
25%
1365
September11th to 20thNight
56%
720
19%
1980
16%
720
58%
720
23%
1383
September21st to endNight
54%
720
24%
1980
19%
720
58%
720
28%
1285
October1st to 10thNight
49%
720
24%
1998
19%
720
54%
720
29%
1271
October11th to 20thNight
43%
720
24%
2160
17%
720
52%
720
25%
1359
October21st to endNight
44%
792
29%
2376
21%
792
56%
792
29%
1429
November1st to 10thNight
47%
740
23%
2329
20%
740
55%
740
26%
1450
November11th to 20thNight
40%
760
25%
2470
18%
760
52%
760
24%
1502
November21st to endNight
37%
760
24%
2470
15%
760
49%
760
23%
1525
December1st to 10thNight
29%
760
16%
2470
10%
760
38%
760
14%
1783
December11th to 20thNight
32%
759
20%
2988
14%
759
42%
759
15%
2032
December21st to endNight
27%
829
11%
4440
10%
817
36%
817
9%
2919

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
10%7%37%7%46%6%6%8%35%
74899
Night
10%7%47%6%45%6%6%8%38%
74865
TransparencyDay
44%10%11%18%14%3
74622
Night
41%11%12%19%14%3
74661
SeeingDay
18%15%24%21%15%7%
13877
Night
16%13%22%28%18%3
24007

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
9%8%38%7%46%6%6%6%35%
1706
11th to 20thDay
11%9%5%9%7%36%5%5%7%33%
1647
21st to endDay
9%8%47%6%35%46%7%41%
1782
February1st to 10thDay
12%7%48%8%46%6%5%6%34%
1710
11th to 20thDay
10%10%6%8%7%445%5%6%35%
1748
21st to endDay
11%10%48%6%35%6%5%6%36%
1480
March1st to 10thDay
11%7%46%6%345%6%8%41%
1916
11th to 20thDay
14%9%48%6%46%5%5%7%33%
1980
21st to endDay
12%9%5%8%6%45%5%5%7%34%
2178
April1st to 10thDay
8%6%36%6%46%5%6%8%42%
1980
11th to 20thDay
13%7%35%5%35%5%5%8%40%
2163
21st to endDay
11%6%36%6%45%6%5%6%41%
2340
May1st to 10thDay
11%5%36%7%45%6%6%8%38%
2340
11th to 20thDay
12%9%38%8%5%6%6%6%6%31%
2301
21st to endDay
11%7%26%7%5%7%7%7%10%31%
2531
June1st to 10thDay
10%6%37%8%5%8%8%7%9%29%
2340
11th to 20thDay
6%6%37%8%6%7%9%8%9%31%
2340
21st to endDay
8%5%46%8%48%7%7%11%32%
2340
July1st to 10thDay
9%6%410%10%5%8%7%9%8%24%
2340
11th to 20thDay
10%7%48%9%6%8%8%8%8%25%
2340
21st to endDay
7%7%39%10%6%8%9%8%10%24%
2547
August1st to 10thDay
9%8%48%9%6%8%9%8%11%23%
2327
11th to 20thDay
10%6%5%8%9%5%6%7%8%9%26%
2303
21st to endDay
11%7%37%8%5%6%7%8%7%31%
2388
September1st to 10thDay
10%8%38%7%5%6%6%5%8%35%
1980
11th to 20thDay
14%7%38%7%46%5%5%8%32%
1980
21st to endDay
13%6%36%6%45%5%5%6%40%
1980
October1st to 10thDay
13%6%36%5%3445%6%45%
1961
11th to 20thDay
9%6%26%5%3445%6%49%
1800
21st to endDay
11%6%26%42345%7%50%
1980
November1st to 10thDay
8%6%35%425%446%54%
1744
11th to 20thDay
9%7%35%5%245%6%6%48%
1710
21st to endDay
9%7%35%4345%48%47%
1710
December1st to 10thDay
12%10%5%8%6%35%5%5%7%35%
1710
11th to 20thDay
10%7%45%5%45%7%8%7%39%
2153
21st to endDay
14%8%37%5%46%6%6%7%34%
3124
January1st to 10thNight
10%7%48%9%45%6%6%6%34%
2459
11th to 20thNight
10%8%5%10%8%46%5%6%7%31%
2386
21st to endNight
9%8%5%8%7%35%6%5%6%39%
2574
February1st to 10thNight
10%8%5%7%5%35%6%6%8%37%
2246
11th to 20thNight
12%10%5%9%7%35%446%34%
2098
21st to endNight
11%9%5%8%7%35%5%6%7%35%
1776
March1st to 10thNight
9%8%46%6%45%6%5%5%41%
2042
11th to 20thNight
11%10%48%6%45%6%6%8%33%
1980
21st to endNight
10%8%5%6%6%47%5%5%7%37%
2178
April1st to 10thNight
9%6%36%5%35%5%6%8%45%
1980
11th to 20thNight
10%7%36%6%34448%45%
1758
21st to endNight
9%6%37%5%345%5%8%44%
1620
May1st to 10thNight
10%7%36%5%45%6%6%10%40%
1620
11th to 20thNight
10%6%37%7%36%6%7%9%35%
1592
21st to endNight
7%6%36%7%37%6%7%10%38%
1744
June1st to 10thNight
7%437%6%47%7%8%13%35%
1620
11th to 20thNight
4435%5%37%6%8%13%41%
1620
21st to endNight
6%5%36%5%45%6%7%13%40%
1620
July1st to 10thNight
8%5%36%7%46%7%9%9%35%
1620
11th to 20thNight
6%5%36%7%5%7%8%10%12%31%
1620
21st to endNight
5%438%8%48%8%9%10%33%
1771
August1st to 10thNight
7%437%7%48%6%8%12%34%
1611
11th to 20thNight
8%7%46%8%47%7%6%10%34%
1598
21st to endNight
9%5%45%7%46%7%8%9%35%
1945
September1st to 10thNight
9%5%37%6%46%6%7%9%39%
1980
11th to 20thNight
11%8%46%7%445%5%8%37%
1980
21st to endNight
11%7%37%434446%47%
1980
October1st to 10thNight
14%7%345%23446%48%
1998
11th to 20thNight
9%8%25%6%35%5%5%7%45%
2160
21st to endNight
10%8%3442445%6%51%
2376
November1st to 10thNight
10%7%35%6%345%46%48%
2329
11th to 20thNight
10%7%35%4345%5%7%47%
2470
21st to endNight
9%7%37%5%3446%6%46%
2470
December1st to 10thNight
11%10%5%9%7%35%6%6%7%30%
2470
11th to 20thNight
10%9%410%7%45%5%46%37%
3042
21st to endNight
16%7%37%7%46%6%7%8%28%
4532

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
44%10%9%17%14%4
1707
11th to 20thDay
48%10%7%16%15%4
1647
21st to endDay
41%8%9%19%19%3
1782
February1st to 10thDay
49%9%9%15%15%3
1710
11th to 20thDay
48%9%10%16%14%3
1758
21st to endDay
46%8%9%14%16%6%
1480
March1st to 10thDay
40%8%8%19%18%6%
1916
11th to 20thDay
49%10%9%15%14%4
1980
21st to endDay
48%9%10%20%11%2
2178
April1st to 10thDay
38%9%11%22%17%3
1980
11th to 20thDay
40%8%10%16%20%5%
2163
21st to endDay
40%10%10%24%13%2
2340
May1st to 10thDay
41%11%13%21%11%2
2340
11th to 20thDay
51%11%12%16%9%1
2305
21st to endDay
44%13%13%21%10%
2531
June1st to 10thDay
46%12%16%16%8%1
2340
11th to 20thDay
44%14%16%13%12%1
2340
21st to endDay
43%13%15%17%10%2
2340
July1st to 10thDay
52%13%13%14%7%1
2275
11th to 20thDay
50%13%15%11%9%1
2271
21st to endDay
48%15%15%14%7%1
2405
August1st to 10thDay
51%15%14%16%4
2314
11th to 20thDay
49%14%14%14%7%1
2303
21st to endDay
48%12%13%17%8%2
2388
September1st to 10thDay
44%10%12%18%13%4
1980
11th to 20thDay
49%8%9%17%14%2
1980
21st to endDay
43%7%11%18%16%4
1980
October1st to 10thDay
39%7%9%18%22%5%
1961
11th to 20thDay
34%8%9%21%20%8%
1800
21st to endDay
34%7%7%23%22%7%
1980
November1st to 10thDay
31%7%8%18%27%9%
1744
11th to 20thDay
35%7%7%21%25%6%
1710
21st to endDay
36%8%9%22%20%5%
1710
December1st to 10thDay
48%9%9%17%14%3
1710
11th to 20thDay
37%12%11%15%21%4
2150
21st to endDay
44%10%11%20%13%2
3124
January1st to 10thNight
47%10%9%15%15%3
2459
11th to 20thNight
50%10%9%13%15%3
2386
21st to endNight
44%9%8%19%18%2
2574
February1st to 10thNight
43%10%11%18%15%3
2246
11th to 20thNight
50%7%8%18%13%4
2099
21st to endNight
47%9%10%16%14%5%
1776
March1st to 10thNight
42%9%9%14%20%5%
2042
11th to 20thNight
48%9%11%17%13%2
1980
21st to endNight
45%10%12%20%12%2
2178
April1st to 10thNight
36%9%13%23%17%2
1980
11th to 20thNight
38%8%10%21%20%4
1758
21st to endNight
37%9%13%27%13%1
1620
May1st to 10thNight
38%11%16%23%10%2
1620
11th to 20thNight
41%15%15%22%7%
1593
21st to endNight
38%13%15%24%8%1
1745
June1st to 10thNight
37%14%20%21%8%
1620
11th to 20thNight
32%14%24%20%9%1
1620
21st to endNight
33%13%20%21%10%3
1620
July1st to 10thNight
39%16%17%18%9%1
1575
11th to 20thNight
39%17%20%15%7%2
1566
21st to endNight
38%18%18%19%6%
1672
August1st to 10thNight
39%17%20%18%6%
1600
11th to 20thNight
42%15%17%16%9%1
1598
21st to endNight
41%12%20%18%7%1
1945
September1st to 10thNight
40%11%15%19%12%3
1980
11th to 20thNight
44%9%13%17%15%1
1980
21st to endNight
38%8%11%22%18%3
1980
October1st to 10thNight
37%6%12%19%23%3
1998
11th to 20thNight
37%8%9%23%18%5%
2160
21st to endNight
33%7%7%22%24%7%
2376
November1st to 10thNight
37%8%8%19%22%6%
2329
11th to 20thNight
36%7%7%20%23%7%
2470
21st to endNight
38%7%7%24%19%5%
2470
December1st to 10thNight
49%11%10%15%11%3
2470
11th to 20thNight
43%12%7%13%20%4
3044
21st to endNight
46%11%11%18%12%1
4532

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
29%28%32%9%2
270
11th to 20thDay
30%29%25%14%2
249
21st to endDay
28%35%26%8%3
264
February1st to 10thDay
28%31%30%9%2
240
11th to 20thDay
38%33%24%5%
240
21st to endDay
40%22%30%7%2
198
March1st to 10thDay
25%24%30%14%6%
356
11th to 20thDay
28%27%24%15%5%1
420
21st to endDay
26%25%27%16%6%
462
April1st to 10thDay
21%22%27%20%9%1
420
11th to 20thDay
22%19%25%22%9%3
412
21st to endDay
19%20%24%20%13%4
420
May1st to 10thDay
19%19%28%16%13%4
423
11th to 20thDay
17%11%29%22%15%6%
447
21st to endDay
15%8%22%26%18%11%
485
June1st to 10thDay
13%8%26%26%18%9%
450
11th to 20thDay
8%8%26%22%23%13%
450
21st to endDay
12%8%30%23%16%12%
450
July1st to 10thDay
8%419%28%23%18%
445
11th to 20thDay
10%5%16%26%24%19%
444
21st to endDay
7%317%25%30%18%
488
August1st to 10thDay
13%7%22%21%20%17%
446
11th to 20thDay
10%419%26%26%15%
439
21st to endDay
12%416%25%26%16%
495
September1st to 10thDay
10%417%29%27%13%
450
11th to 20thDay
16%5%20%21%28%10%
450
21st to endDay
17%6%19%32%22%4
450
October1st to 10thDay
18%9%21%26%19%8%
450
11th to 20thDay
15%17%24%24%18%2
450
21st to endDay
19%15%25%27%12%2
495
November1st to 10thDay
17%17%29%25%11%2
342
11th to 20thDay
21%25%31%17%5%
270
21st to endDay
20%24%33%17%6%1
270
December1st to 10thDay
29%26%29%13%3
270
11th to 20thDay
19%29%32%15%5%
270
21st to endDay
24%25%35%12%4
297
January1st to 10thNight
22%24%26%23%4
760
11th to 20thNight
20%22%30%24%4
735
21st to endNight
19%26%30%23%3
792
February1st to 10thNight
18%20%32%26%4
720
11th to 20thNight
24%29%26%21%1
703
21st to endNight
22%29%29%18%2
592
March1st to 10thNight
17%23%32%24%4
720
11th to 20thNight
21%19%30%21%7%1
720
21st to endNight
19%18%31%24%7%
792
April1st to 10thNight
18%20%26%27%8%
720
11th to 20thNight
18%14%28%26%13%1
596
21st to endNight
15%12%23%35%13%1
540
May1st to 10thNight
14%12%28%29%16%1
540
11th to 20thNight
13%7%21%33%23%3
531
21st to endNight
11%314%34%32%5%
584
June1st to 10thNight
8%215%38%31%5%
540
11th to 20thNight
6%415%32%33%10%
540
21st to endNight
8%214%34%35%7%
540
July1st to 10thNight
9%212%28%40%9%
525
11th to 20thNight
8%210%27%41%12%
522
21st to endNight
5%28%28%42%14%
591
August1st to 10thNight
9%29%30%42%9%
537
11th to 20thNight
10%212%30%39%7%
534
21st to endNight
11%38%30%39%9%
625
September1st to 10thNight
12%312%31%36%8%
720
11th to 20thNight
16%414%29%31%6%
720
21st to endNight
15%417%30%29%4
720
October1st to 10thNight
17%8%19%26%24%6%
720
11th to 20thNight
14%14%23%31%16%3
720
21st to endNight
17%14%21%32%13%2
792
November1st to 10thNight
15%11%21%33%16%3
740
11th to 20thNight
19%14%23%31%11%1
760
21st to endNight
18%16%25%29%12%1
760
December1st to 10thNight
23%19%25%27%6%
760
11th to 20thNight
18%18%28%29%7%1
760
21st to endNight
20%20%28%28%4
836
Page generated at 2024-01-11 04:22:40. Version ac07

Copyright 2024 Attilla Danko


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