Nirvana
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nirvana clear sky chart from 2005-11-06 to 2024-03-23.

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
25%
22882
13%
81034
7%
22795
33%
22795
14%
58465

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
12%
753
7%
4415
2%
737
20%
737
4%
3479
January11th to 20thNight
13%
755
6%
4424
2%
740
20%
740
4%
3502
January21st to endNight
16%
830
7%
4609
6%
814
24%
814
6%
3749
February1st to 10thNight
13%
760
10%
2470
3%
760
21%
760
10%
1886
February11th to 20thNight
13%
742
14%
2405
3%
740
26%
740
12%
1763
February21st to endNight
15%
628
13%
1940
4%
628
27%
628
13%
1420
March1st to 10thNight
16%
760
16%
2195
7%
760
25%
760
14%
1614
March11th to 20thNight
19%
760
15%
2089
6%
760
28%
760
16%
1520
March21st to endNight
23%
801
20%
2142
7%
801
33%
801
21%
1496
April1st to 10thNight
18%
720
16%
1800
5%
720
25%
720
19%
1345
April11th to 20thNight
23%
711
18%
1775
6%
711
29%
711
21%
1269
April21st to endNight
29%
585
15%
1665
6%
585
35%
585
18%
1213
May1st to 10thNight
36%
391
18%
1471
14%
391
44%
391
18%
944
May11th to 20thNight
32%
354
21%
1416
14%
354
49%
354
20%
850
May21st to endNight
35%
389
15%
1551
11%
388
48%
388
23%
888
June1st to 10thNight
31%
360
10%
1440
7%
360
43%
360
17%
921
June11th to 20thNight
37%
360
14%
1440
15%
360
47%
360
22%
844
June21st to endNight
39%
360
10%
1440
12%
360
47%
360
18%
907
July1st to 10thNight
45%
350
15%
1400
17%
350
54%
350
26%
790
July11th to 20thNight
46%
348
16%
1392
19%
348
53%
348
24%
794
July21st to endNight
47%
394
16%
1486
14%
372
55%
372
27%
834
August1st to 10thNight
50%
494
16%
1558
12%
492
55%
492
28%
975
August11th to 20thNight
55%
534
17%
1598
10%
534
60%
534
29%
1012
August21st to endNight
42%
742
19%
1930
7%
742
48%
742
31%
1254
September1st to 10thNight
41%
720
17%
1800
6%
720
47%
720
33%
1178
September11th to 20thNight
47%
720
22%
1800
12%
720
51%
720
35%
1174
September21st to endNight
40%
720
20%
2067
15%
720
44%
720
24%
1379
October1st to 10thNight
30%
720
16%
2160
11%
720
37%
720
19%
1507
October11th to 20thNight
20%
720
11%
2160
5%
720
29%
720
14%
1616
October21st to endNight
19%
792
13%
2448
5%
792
29%
792
12%
1876
November1st to 10thNight
25%
740
16%
2464
11%
740
34%
740
16%
1708
November11th to 20thNight
19%
760
14%
2660
9%
760
27%
760
12%
1942
November21st to endNight
18%
760
10%
2660
5%
760
25%
760
9%
2076
December1st to 10thNight
12%
760
7%
2660
2%
760
18%
760
6%
2187
December11th to 20thNight
12%
760
9%
3252
4%
759
21%
759
7%
2504
December21st to endNight
8%
829
5%
4852
1%
817
14%
817
3%
4049

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
17%11%48%6%35%45%6%30%
78575
Night
16%11%5%8%6%35%45%6%31%
81309
TransparencyDay
53%6%11%18%10%1
78280
Night
53%7%12%18%9%1
81138
SeeingDay
23%18%32%18%7%2
13536
Night
22%15%32%22%8%1
22908

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 10thDay
15%17%6%14%9%4433420%
2517
11th to 20thDay
13%15%9%15%8%46%45%417%
2520
21st to endDay
18%21%7%14%8%3333417%
3039
February1st to 10thDay
14%16%6%11%10%45%5%5%5%20%
1710
11th to 20thDay
12%16%7%10%7%4445%5%27%
1663
21st to endDay
18%15%5%7%7%35%6%45%25%
1513
March1st to 10thDay
15%12%5%10%7%5%5%445%27%
1981
11th to 20thDay
12%15%6%8%8%44446%28%
2090
21st to endDay
18%12%46%424335%38%
2258
April1st to 10thDay
20%12%5%6%6%45%335%30%
2160
11th to 20thDay
21%9%36%434445%37%
2134
21st to endDay
22%10%48%5%34445%33%
2311
May1st to 10thDay
19%9%36%5%25%5%5%5%35%
2488
11th to 20thDay
17%8%37%6%345%46%37%
2478
21st to endDay
14%5%36%7%45%46%8%38%
2725
June1st to 10thDay
22%9%36%5%45%5%5%7%30%
2520
11th to 20thDay
16%5%35%5%46%6%6%9%36%
2520
21st to endDay
18%6%37%6%35%5%6%6%34%
2520
July1st to 10thDay
12%6%35%6%46%5%6%9%38%
2520
11th to 20thDay
12%7%36%5%35%6%6%9%36%
2520
21st to endDay
12%7%26%6%36%6%7%10%35%
2744
August1st to 10thDay
11%7%37%7%46%5%6%8%36%
2367
11th to 20thDay
13%7%47%6%35%6%6%7%37%
2303
21st to endDay
14%7%36%6%445%6%8%36%
2407
September1st to 10thDay
16%6%26%6%45%45%7%39%
2160
11th to 20thDay
13%6%35%5%3445%7%45%
2160
21st to endDay
19%6%36%6%3445%8%36%
1891
October1st to 10thDay
22%9%37%6%2345%6%33%
1800
11th to 20thDay
24%11%5%7%5%45%35%6%25%
1800
21st to endDay
28%12%37%6%445%5%423%
1908
November1st to 10thDay
15%11%37%6%45%45%7%33%
1610
11th to 20thDay
16%15%5%8%7%45%445%26%
1520
21st to endDay
22%16%6%9%8%345%35%19%
1520
December1st to 10thDay
21%19%5%11%7%4445%415%
1520
11th to 20thDay
18%15%7%9%7%33445%25%
1906
21st to endDay
25%19%6%12%7%2222318%
2772
January1st to 10thNight
17%15%9%11%8%45%445%17%
4429
11th to 20thNight
11%15%6%13%11%5%7%5%5%6%16%
4440
21st to endNight
17%17%8%11%8%45%34419%
4614
February1st to 10thNight
13%15%6%10%7%36%5%6%7%22%
2470
11th to 20thNight
13%12%6%10%6%35%5%5%6%29%
2403
21st to endNight
13%14%6%7%6%36%5%5%7%28%
1940
March1st to 10thNight
15%11%5%9%8%34445%32%
2185
11th to 20thNight
14%13%6%7%7%3435%6%32%
2089
21st to endNight
15%9%47%5%35%446%38%
2142
April1st to 10thNight
20%11%46%6%2445%5%33%
1800
11th to 20thNight
18%8%45%6%34446%38%
1775
21st to endNight
19%9%27%5%35%5%5%6%33%
1665
May1st to 10thNight
19%8%35%5%35%446%38%
1471
11th to 20thNight
16%6%35%4445%5%7%42%
1415
21st to endNight
12%5%25%5%345%6%8%46%
1550
June1st to 10thNight
16%6%35%5%446%6%8%35%
1440
11th to 20thNight
12%6%36%6%2446%7%44%
1440
21st to endNight
16%7%25%6%35%5%6%7%37%
1440
July1st to 10thNight
9%436%445%5%5%7%47%
1440
11th to 20thNight
11%5%36%5%3446%8%45%
1440
21st to endNight
9%4345%35%5%5%10%46%
1574
August1st to 10thNight
10%5%25%5%45%5%6%9%45%
1568
11th to 20thNight
9%5%36%5%35%6%6%8%44%
1598
21st to endNight
12%5%35%4345%5%7%47%
1930
September1st to 10thNight
11%5%25%6%35%36%8%46%
1800
11th to 20thNight
14%5%25%4245%46%49%
1800
21st to endNight
17%7%245%235%6%5%43%
2067
October1st to 10thNight
19%8%36%435%45%5%37%
2160
11th to 20thNight
21%9%48%7%345%45%29%
2160
21st to endNight
22%13%47%6%35%447%26%
2448
November1st to 10thNight
16%12%46%5%3445%6%34%
2464
11th to 20thNight
18%11%5%8%6%35%5%5%5%28%
2660
21st to endNight
19%15%5%7%7%45%5%5%6%22%
2660
December1st to 10thNight
19%19%6%9%7%45%5%5%6%16%
2660
11th to 20thNight
19%16%6%9%7%34345%24%
3288
21st to endNight
27%19%6%11%7%3333415%
4884

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
66%7%11%8%6%1
2518
11th to 20thDay
68%7%9%9%6%1
2520
21st to endDay
73%46%9%6%1
3039
February1st to 10thDay
64%6%9%15%5%1
1710
11th to 20thDay
58%6%10%15%10%1
1672
21st to endDay
60%5%11%12%10%1
1513
March1st to 10thDay
58%5%12%14%10%2
1984
11th to 20thDay
57%6%10%15%10%2
2090
21st to endDay
51%48%19%14%6%
2258
April1st to 10thDay
57%47%17%12%3
2160
11th to 20thDay
49%5%8%21%15%1
2134
21st to endDay
55%5%7%15%14%4
2311
May1st to 10thDay
49%7%9%17%14%4
2488
11th to 20thDay
48%6%9%20%15%3
2482
21st to endDay
44%7%13%19%14%3
2725
June1st to 10thDay
53%7%10%18%12%1
2520
11th to 20thDay
44%7%12%22%13%2
2520
21st to endDay
48%8%12%19%12%1
2520
July1st to 10thDay
41%7%12%26%13%1
2450
11th to 20thDay
41%8%16%24%11%1
2445
21st to endDay
42%9%15%24%10%
2591
August1st to 10thDay
44%8%15%22%11%
2353
11th to 20thDay
44%8%17%22%8%1
2303
21st to endDay
44%8%14%24%10%1
2407
September1st to 10thDay
41%7%12%27%11%1
2160
11th to 20thDay
39%7%12%28%14%
2160
21st to endDay
47%7%14%23%10%
1891
October1st to 10thDay
52%6%11%20%11%1
1800
11th to 20thDay
59%6%13%15%6%1
1800
21st to endDay
63%6%9%14%7%1
1908
November1st to 10thDay
49%8%16%20%7%1
1610
11th to 20thDay
59%6%12%14%9%1
1520
21st to endDay
67%7%9%9%7%1
1520
December1st to 10thDay
71%6%9%10%3
1520
11th to 20thDay
62%6%13%11%7%
1906
21st to endDay
73%46%13%4
2772
January1st to 10thNight
68%7%11%11%3
4429
11th to 20thNight
64%10%12%9%5%1
4440
21st to endNight
70%5%9%8%7%1
4614
February1st to 10thNight
60%6%12%15%6%1
2470
11th to 20thNight
56%5%11%19%8%1
2405
21st to endNight
53%7%11%18%10%1
1940
March1st to 10thNight
54%5%10%16%12%2
2195
11th to 20thNight
52%5%12%19%11%2
2090
21st to endNight
47%5%8%21%16%3
2142
April1st to 10thNight
52%5%8%20%13%2
1800
11th to 20thNight
47%5%9%22%16%1
1775
21st to endNight
51%8%8%15%16%2
1665
May1st to 10thNight
46%5%8%21%16%4
1471
11th to 20thNight
40%6%11%23%17%3
1416
21st to endNight
36%7%16%20%19%3
1551
June1st to 10thNight
44%8%14%22%11%1
1440
11th to 20thNight
38%7%12%25%17%2
1440
21st to endNight
42%8%16%21%12%1
1440
July1st to 10thNight
33%8%13%24%19%2
1400
11th to 20thNight
36%6%14%30%13%
1392
21st to endNight
32%8%19%28%12%1
1486
August1st to 10thNight
35%9%18%26%11%1
1558
11th to 20thNight
35%9%17%27%10%1
1598
21st to endNight
36%8%15%30%11%1
1930
September1st to 10thNight
35%7%16%27%14%1
1800
11th to 20thNight
34%8%14%33%11%1
1800
21st to endNight
41%7%12%30%9%1
2067
October1st to 10thNight
48%7%12%19%14%
2160
11th to 20thNight
54%8%13%17%7%
2160
21st to endNight
58%7%12%14%9%
2448
November1st to 10thNight
49%7%14%21%9%1
2464
11th to 20thNight
55%7%12%16%9%1
2660
21st to endNight
62%7%12%15%4
2660
December1st to 10thNight
67%8%10%11%3
2660
11th to 20thNight
63%6%10%14%7%1
3288
21st to endNight
74%5%7%11%3
4884

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
23%23%36%14%31
180
11th to 20thDay
29%19%35%13%4
180
21st to endDay
26%24%35%12%4
276
February1st to 10thDay
29%30%29%9%2
270
11th to 20thDay
29%29%37%5%
270
21st to endDay
35%22%33%9%1
325
March1st to 10thDay
25%24%35%14%3
460
11th to 20thDay
27%21%34%14%41
460
21st to endDay
33%20%29%14%4
470
April1st to 10thDay
27%24%32%11%6%
420
11th to 20thDay
32%21%22%17%7%1
412
21st to endDay
28%21%32%12%5%1
420
May1st to 10thDay
26%17%32%17%44
423
11th to 20thDay
23%17%34%17%7%2
447
21st to endDay
19%16%36%17%9%3
485
June1st to 10thDay
23%15%38%17%7%
450
11th to 20thDay
16%19%32%22%10%2
450
21st to endDay
18%13%36%20%10%3
450
July1st to 10thDay
12%9%32%34%11%2
445
11th to 20thDay
15%13%31%23%16%2
444
21st to endDay
16%10%37%27%8%3
488
August1st to 10thDay
14%8%33%29%13%4
446
11th to 20thDay
11%9%30%30%14%6%
439
21st to endDay
15%13%32%25%10%6%
495
September1st to 10thDay
16%13%32%20%14%5%
450
11th to 20thDay
13%12%28%23%15%9%
450
21st to endDay
19%16%29%19%11%6%
450
October1st to 10thDay
27%16%24%18%11%3
450
11th to 20thDay
29%22%30%14%41
450
21st to endDay
32%19%31%15%4
459
November1st to 10thDay
26%18%34%16%6%
304
11th to 20thDay
28%25%28%13%41
180
21st to endDay
28%28%32%9%21
180
December1st to 10thDay
30%22%36%9%21
180
11th to 20thDay
37%24%27%11%11
180
21st to endDay
35%24%29%10%21
198
January1st to 10thNight
28%21%32%15%4
760
11th to 20thNight
28%20%31%16%5%1
760
21st to endNight
19%19%36%20%6%
836
February1st to 10thNight
22%22%38%17%2
760
11th to 20thNight
19%24%41%13%3
743
21st to endNight
22%23%36%17%2
628
March1st to 10thNight
22%22%35%19%2
760
11th to 20thNight
24%21%32%18%31
760
21st to endNight
22%16%35%19%8%1
801
April1st to 10thNight
26%17%34%19%4
720
11th to 20thNight
23%21%30%19%7%
711
21st to endNight
24%13%30%24%9%1
585
May1st to 10thNight
23%9%28%30%9%1
391
11th to 20thNight
18%11%35%28%7%
354
21st to endNight
14%9%38%27%12%
389
June1st to 10thNight
16%11%36%29%9%
360
11th to 20thNight
14%12%32%31%9%1
360
21st to endNight
19%9%29%30%13%
360
July1st to 10thNight
6%7%35%37%15%1
350
11th to 20thNight
12%5%30%39%15%
348
21st to endNight
10%432%42%12%
394
August1st to 10thNight
10%6%25%37%20%1
494
11th to 20thNight
10%424%38%21%3
534
21st to endNight
13%8%32%27%18%2
742
September1st to 10thNight
12%7%35%27%17%2
720
11th to 20thNight
15%8%26%28%19%3
720
21st to endNight
21%11%24%24%18%2
720
October1st to 10thNight
23%13%29%21%12%2
720
11th to 20thNight
28%15%31%18%7%1
720
21st to endNight
29%17%29%20%4
792
November1st to 10thNight
24%17%29%23%6%1
740
11th to 20thNight
26%18%33%15%8%1
760
21st to endNight
29%19%27%19%4
760
December1st to 10thNight
30%19%33%15%3
760
11th to 20thNight
27%20%35%16%21
760
21st to endNight
34%16%33%14%2
836
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