Grasslands National Park East Block
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grasslands National Park East Block clear sky chart from 2005-11-06 to 2024-01-12.

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
39%
24320
17%
74372
10%
24275
46%
24275
27%
46355

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
34%
946
15%
2836
6%
946
42%
946
22%
1903
January11th to 20thNight
31%
906
17%
2595
8%
906
40%
906
22%
1747
January21st to endNight
28%
990
15%
2772
7%
990
36%
990
18%
2036
February1st to 10thNight
36%
756
15%
2376
9%
756
43%
756
20%
1626
February11th to 20thNight
31%
700
15%
2273
11%
700
37%
700
20%
1562
February21st to endNight
46%
592
18%
1855
12%
592
54%
592
23%
1230
March1st to 10thNight
34%
720
14%
2160
8%
720
40%
720
22%
1485
March11th to 20thNight
36%
720
19%
1985
10%
720
44%
720
26%
1338
March21st to endNight
38%
689
15%
2075
9%
689
44%
689
21%
1437
April1st to 10thNight
39%
540
18%
1800
12%
540
48%
540
23%
1132
April11th to 20thNight
36%
533
15%
1759
10%
533
42%
533
22%
1146
April21st to endNight
36%
540
18%
1512
10%
540
44%
540
26%
1017
May1st to 10thNight
48%
540
17%
1440
10%
540
52%
540
32%
906
May11th to 20thNight
48%
531
17%
1418
10%
531
52%
531
34%
886
May21st to endNight
43%
584
9%
1552
4%
582
46%
582
26%
1058
June1st to 10thNight
46%
425
9%
1325
7%
425
49%
425
31%
782
June11th to 20thNight
45%
360
9%
1260
6%
360
51%
360
28%
721
June21st to endNight
57%
360
10%
1260
11%
360
60%
360
39%
610
July1st to 10thNight
54%
350
11%
1225
10%
350
59%
350
42%
582
July11th to 20thNight
53%
402
17%
1272
10%
402
60%
402
44%
646
July21st to endNight
59%
591
23%
1488
14%
558
64%
558
55%
763
August1st to 10thNight
59%
537
22%
1424
14%
534
65%
534
49%
789
August11th to 20thNight
65%
534
27%
1550
19%
534
71%
534
49%
806
August21st to endNight
55%
594
27%
1892
19%
594
65%
594
42%
978
September1st to 10thNight
53%
540
24%
1800
20%
540
61%
540
39%
929
September11th to 20thNight
53%
540
26%
1800
25%
540
61%
540
35%
972
September21st to endNight
49%
646
27%
2040
19%
646
58%
646
37%
1113
October1st to 10thNight
41%
720
23%
2160
13%
720
49%
720
30%
1316
October11th to 20thNight
39%
720
23%
2160
12%
720
49%
720
30%
1300
October21st to endNight
32%
958
19%
2542
7%
958
40%
958
26%
1702
November1st to 10thNight
30%
925
17%
2554
7%
925
37%
925
22%
1799
November11th to 20thNight
30%
950
19%
2660
9%
950
39%
950
25%
1779
November21st to endNight
28%
950
15%
2660
5%
950
36%
950
24%
1792
December1st to 10thNight
33%
950
12%
2660
7%
950
38%
950
20%
1944
December11th to 20thNight
30%
949
15%
3294
8%
948
38%
948
18%
2206
December21st to endNight
29%
1032
12%
4938
6%
1026
37%
1026
17%
2317

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
8%7%37%6%45%5%6%8%40%
74819
Night
7%7%37%6%45%5%6%8%41%
74892
TransparencyDay
42%415%26%12%2
74510
Night
41%415%26%13%2
74722
SeeingDay
12%8%30%30%16%4
14706
Night
11%7%33%35%12%1
24342

By Month

Percentage Cloud Cover SW (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
5%10%49%7%6%7%6%7%9%30%
1329
11th to 20thDay
5%11%5%10%8%47%5%9%10%26%
1384
21st to endDay
310%6%9%9%6%8%9%9%9%23%
1584
February1st to 10thDay
7%10%6%9%11%5%7%7%7%6%24%
1601
11th to 20thDay
5%12%5%11%10%6%6%6%8%7%24%
1575
21st to endDay
49%7%11%9%6%8%8%5%9%26%
1400
March1st to 10thDay
5%9%5%12%10%6%6%6%7%8%25%
1800
11th to 20thDay
7%9%5%9%6%45%5%6%9%35%
1972
21st to endDay
6%10%49%8%46%6%7%11%28%
2281
April1st to 10thDay
7%9%47%8%45%6%7%9%35%
2160
11th to 20thDay
12%13%5%9%7%45%5%6%7%28%
2148
21st to endDay
13%10%37%6%35%448%37%
2447
May1st to 10thDay
15%8%36%5%35%5%6%8%36%
2520
11th to 20thDay
10%7%36%6%35%5%6%8%40%
2478
21st to endDay
19%7%36%6%46%5%5%8%32%
2724
June1st to 10thDay
14%6%36%5%35%6%5%9%37%
2632
11th to 20thDay
14%6%35%6%45%5%7%8%38%
2700
21st to endDay
7%5%245%35%6%6%9%48%
2700
July1st to 10thDay
5%324435%6%7%10%52%
2700
11th to 20thDay
43244345%7%8%57%
2643
21st to endDay
5%31332445%7%62%
2742
August1st to 10thDay
7%4134245%6%9%54%
2507
11th to 20thDay
7%425%433449%55%
2348
21st to endDay
8%32442346%8%56%
2463
September1st to 10thDay
10%5%35%5%35%5%5%6%49%
2160
11th to 20thDay
11%6%25%42446%7%48%
2160
21st to endDay
13%7%2442345%7%48%
1918
October1st to 10thDay
13%8%46%5%3445%5%45%
1800
11th to 20thDay
7%7%47%6%45%5%6%8%42%
1800
21st to endDay
7%9%48%6%35%5%6%7%40%
1796
November1st to 10thDay
9%11%5%8%7%35%45%6%36%
1523
11th to 20thDay
49%5%9%9%46%46%8%36%
1520
21st to endDay
6%8%48%7%47%8%5%9%34%
1520
December1st to 10thDay
6%9%5%10%12%6%7%6%6%8%26%
1520
11th to 20thDay
39%5%13%9%47%7%8%7%29%
1822
21st to endDay
47%37%7%45%5%7%7%43%
2442
January1st to 10thNight
47%5%9%6%47%7%8%10%33%
2836
11th to 20thNight
48%5%9%8%46%6%7%9%34%
2595
21st to endNight
310%5%10%9%6%8%7%7%9%26%
2772
February1st to 10thNight
411%5%8%7%5%7%6%7%10%29%
2376
11th to 20thNight
410%5%10%9%5%6%6%7%10%29%
2272
21st to endNight
5%8%5%8%7%5%5%7%6%8%34%
1855
March1st to 10thNight
6%7%410%9%47%7%7%9%31%
2160
11th to 20thNight
5%10%49%6%35%5%7%8%37%
1985
21st to endNight
7%8%5%9%9%5%7%5%6%7%32%
2075
April1st to 10thNight
7%8%46%6%5%6%6%7%8%39%
1800
11th to 20thNight
12%9%47%4445%7%8%35%
1759
21st to endNight
9%9%37%7%45%46%7%37%
1512
May1st to 10thNight
9%9%35%4346%6%7%44%
1440
11th to 20thNight
8%6%25%5%35%5%8%9%43%
1417
21st to endNight
14%7%35%5%46%6%6%10%35%
1552
June1st to 10thNight
10%5%36%5%2447%9%45%
1325
11th to 20thNight
13%414445%5%7%8%45%
1260
21st to endNight
6%32333447%9%56%
1260
July1st to 10thNight
5%31342446%7%59%
1260
11th to 20thNight
5%3145%3347%10%56%
1314
21st to endNight
3213325%46%8%63%
1576
August1st to 10thNight
442433446%9%58%
1432
11th to 20thNight
5%31432445%9%61%
1550
21st to endNight
8%31432445%6%60%
1892
September1st to 10thNight
10%41433345%7%56%
1800
11th to 20thNight
9%5%2442446%7%53%
1800
21st to endNight
10%5%2443345%8%53%
2040
October1st to 10thNight
12%7%25%5%3446%9%45%
2160
11th to 20thNight
8%7%36%6%345%5%7%46%
2160
21st to endNight
7%11%36%6%45%5%7%8%37%
2542
November1st to 10thNight
10%11%47%8%45%5%6%7%35%
2554
11th to 20thNight
5%8%5%9%8%45%6%7%8%36%
2660
21st to endNight
48%5%9%7%46%6%6%8%37%
2660
December1st to 10thNight
5%10%49%10%6%6%7%6%7%28%
2660
11th to 20thNight
5%9%410%8%46%6%8%7%32%
3367
21st to endNight
36%36%6%345%5%6%52%
5214

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
50%5%14%24%7%
1329
11th to 20thDay
51%5%17%20%7%1
1384
21st to endDay
53%8%15%18%7%
1584
February1st to 10thDay
57%5%10%17%10%
1601
11th to 20thDay
57%414%14%9%1
1584
21st to endDay
56%413%17%10%1
1400
March1st to 10thDay
56%6%15%18%6%
1800
11th to 20thDay
46%5%17%24%7%1
1972
21st to endDay
50%5%19%19%7%
2281
April1st to 10thDay
44%416%24%11%1
2160
11th to 20thDay
56%313%19%9%
2151
21st to endDay
48%215%26%8%
2447
May1st to 10thDay
48%211%26%11%2
2520
11th to 20thDay
42%413%31%11%
2482
21st to endDay
51%314%24%8%
2724
June1st to 10thDay
44%417%24%10%
2632
11th to 20thDay
44%317%25%11%2
2700
21st to endDay
33%416%35%11%1
2700
July1st to 10thDay
25%318%35%15%4
2626
11th to 20thDay
24%315%29%24%5%
2562
21st to endDay
22%29%36%27%4
2590
August1st to 10thDay
28%214%33%19%4
2491
11th to 20thDay
28%217%32%17%3
2348
21st to endDay
27%211%34%23%3
2463
September1st to 10thDay
36%310%30%17%4
2160
11th to 20thDay
36%314%30%14%3
2160
21st to endDay
37%311%31%16%2
1918
October1st to 10thDay
43%315%27%11%1
1800
11th to 20thDay
40%215%30%11%1
1800
21st to endDay
44%318%26%9%
1796
November1st to 10thDay
49%414%21%10%1
1523
11th to 20thDay
47%5%18%22%8%1
1520
21st to endDay
46%6%21%21%6%1
1520
December1st to 10thDay
57%5%15%18%5%1
1520
11th to 20thDay
52%5%22%16%5%
1820
21st to endDay
40%39%25%16%8%
2442
January1st to 10thNight
44%7%18%22%7%1
2836
11th to 20thNight
45%5%19%24%6%1
2595
21st to endNight
53%5%15%18%8%1
2772
February1st to 10thNight
49%416%21%8%1
2376
11th to 20thNight
50%417%18%11%1
2273
21st to endNight
47%312%25%13%
1855
March1st to 10thNight
48%417%23%8%
2160
11th to 20thNight
44%5%15%27%8%1
1985
21st to endNight
51%316%21%8%1
2075
April1st to 10thNight
42%5%13%27%13%1
1800
11th to 20thNight
46%412%24%13%2
1759
21st to endNight
46%212%28%11%
1512
May1st to 10thNight
38%311%30%17%1
1440
11th to 20thNight
35%412%32%15%1
1418
21st to endNight
45%416%26%8%1
1552
June1st to 10thNight
36%320%27%12%2
1325
11th to 20thNight
35%5%16%28%14%2
1260
21st to endNight
26%321%34%15%2
1260
July1st to 10thNight
24%314%35%20%4
1225
11th to 20thNight
25%316%29%22%5%
1272
21st to endNight
19%311%33%29%6%
1488
August1st to 10thNight
25%312%34%21%4
1424
11th to 20thNight
23%311%38%22%3
1550
21st to endNight
27%210%26%30%5%
1892
September1st to 10thNight
29%211%31%21%7%
1800
11th to 20thNight
31%312%29%21%4
1800
21st to endNight
30%311%33%21%2
2040
October1st to 10thNight
38%313%28%16%2
2160
11th to 20thNight
38%313%31%15%1
2160
21st to endNight
44%315%26%10%2
2542
November1st to 10thNight
49%413%22%9%2
2554
11th to 20thNight
45%418%24%8%1
2660
21st to endNight
45%421%22%8%
2660
December1st to 10thNight
53%5%15%19%8%1
2660
11th to 20thNight
48%420%21%6%1
3368
21st to endNight
33%312%26%19%7%
5214

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
9%8%34%29%17%2
180
11th to 20thDay
12%10%31%30%15%2
214
21st to endDay
9%10%38%31%11%1
264
February1st to 10thDay
10%11%46%25%7%1
240
11th to 20thDay
8%8%36%33%12%2
240
21st to endDay
6%7%30%37%17%4
198
March1st to 10thDay
16%6%33%33%12%
240
11th to 20thDay
10%8%37%25%15%4
412
21st to endDay
11%10%32%27%15%5%
462
April1st to 10thDay
12%13%34%32%9%1
420
11th to 20thDay
20%14%32%26%7%1
412
21st to endDay
19%9%28%30%13%1
527
May1st to 10thDay
15%7%23%32%19%5%
603
11th to 20thDay
15%6%24%27%19%8%
625
21st to endDay
18%8%24%24%19%7%
679
June1st to 10thDay
14%9%27%27%19%4
630
11th to 20thDay
17%9%36%23%12%3
630
21st to endDay
10%7%24%33%22%3
630
July1st to 10thDay
7%426%38%23%2
621
11th to 20thDay
7%6%29%37%17%4
618
21st to endDay
6%5%26%34%24%5%
684
August1st to 10thDay
8%6%27%33%20%7%
626
11th to 20thDay
10%5%23%29%25%8%
486
21st to endDay
9%6%22%39%19%6%
495
September1st to 10thDay
11%9%30%33%13%4
450
11th to 20thDay
16%8%25%33%15%3
450
21st to endDay
20%6%28%29%13%4
316
October1st to 10thDay
19%7%24%30%17%4
270
11th to 20thDay
9%8%38%27%14%4
270
21st to endDay
16%10%40%24%8%2
297
November1st to 10thDay
16%13%35%28%7%1
270
11th to 20thDay
7%13%40%26%11%1
270
21st to endDay
9%9%42%28%11%1
270
December1st to 10thDay
9%9%40%29%10%4
270
11th to 20thDay
5%12%43%28%10%2
239
21st to endDay
10%6%34%34%13%3
198
January1st to 10thNight
7%9%40%31%11%1
950
11th to 20thNight
9%12%36%32%9%2
906
21st to endNight
8%11%40%31%9%1
990
February1st to 10thNight
9%8%32%35%14%1
756
11th to 20thNight
11%8%39%34%8%1
704
21st to endNight
9%5%26%37%19%4
592
March1st to 10thNight
11%8%36%32%12%2
720
11th to 20thNight
11%8%36%32%12%2
720
21st to endNight
12%6%32%36%12%2
689
April1st to 10thNight
11%9%32%38%10%
540
11th to 20thNight
19%7%34%32%8%
533
21st to endNight
16%7%33%35%9%
540
May1st to 10thNight
14%6%24%40%15%1
540
11th to 20thNight
11%5%29%34%20%2
531
21st to endNight
18%8%23%31%19%1
584
June1st to 10thNight
13%6%26%37%15%2
425
11th to 20thNight
16%5%30%37%12%1
360
21st to endNight
7%329%41%18%2
360
July1st to 10thNight
9%430%41%16%1
350
11th to 20thNight
6%431%47%11%1
402
21st to endNight
4430%45%16%1
591
August1st to 10thNight
6%228%45%16%2
537
11th to 20thNight
5%422%45%21%2
534
21st to endNight
10%5%26%40%18%1
594
September1st to 10thNight
12%326%41%16%2
540
11th to 20thNight
12%426%39%18%1
540
21st to endNight
12%430%41%11%1
646
October1st to 10thNight
15%7%29%34%14%1
720
11th to 20thNight
12%9%31%34%13%1
720
21st to endNight
12%10%39%31%7%
958
November1st to 10thNight
16%9%36%32%6%1
925
11th to 20thNight
9%11%40%29%10%1
950
21st to endNight
9%10%42%30%7%1
950
December1st to 10thNight
11%8%35%32%13%1
950
11th to 20thNight
9%9%39%33%9%1
950
21st to endNight
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1045
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