Olmzog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Olmzog Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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
29%
22886
18%
74724
8%
22841
41%
22841
19%
48210

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
18%
760
21%
2649
6%
757
37%
757
16%
1660
January11th to 20thNight
19%
748
15%
2616
5%
748
32%
748
12%
1809
January21st to endNight
19%
792
20%
2772
7%
792
36%
792
16%
1731
February1st to 10thNight
13%
720
14%
2309
2%
720
28%
720
14%
1579
February11th to 20thNight
15%
703
20%
2100
4%
700
34%
700
15%
1414
February21st to endNight
16%
592
21%
1776
6%
592
34%
592
16%
1174
March1st to 10thNight
18%
720
22%
2160
7%
720
37%
720
18%
1397
March11th to 20thNight
19%
720
18%
2113
6%
720
32%
720
17%
1413
March21st to endNight
22%
792
23%
1980
6%
792
34%
792
21%
1371
April1st to 10thNight
20%
720
19%
1800
4%
720
29%
720
22%
1254
April11th to 20thNight
24%
711
17%
1775
4%
711
31%
711
22%
1221
April21st to endNight
22%
583
18%
1663
4%
583
31%
583
18%
1135
May1st to 10thNight
23%
540
14%
1620
6%
540
30%
540
17%
1134
May11th to 20thNight
25%
397
18%
1459
10%
397
38%
397
17%
931
May21st to endNight
40%
389
14%
1551
13%
388
49%
388
19%
951
June1st to 10thNight
35%
360
15%
1440
12%
360
48%
360
18%
898
June11th to 20thNight
37%
360
13%
1440
12%
360
47%
360
20%
878
June21st to endNight
44%
360
13%
1440
14%
360
53%
360
22%
857
July1st to 10thNight
48%
350
14%
1400
13%
350
58%
350
23%
813
July11th to 20thNight
52%
348
15%
1392
18%
348
57%
348
24%
797
July21st to endNight
54%
394
19%
1486
20%
372
62%
372
27%
804
August1st to 10thNight
54%
398
19%
1462
14%
396
61%
396
29%
817
August11th to 20thNight
50%
635
15%
1699
8%
635
52%
635
28%
1126
August21st to endNight
51%
792
21%
1980
10%
792
54%
792
35%
1261
September1st to 10thNight
48%
720
21%
1800
9%
720
54%
720
35%
1149
September11th to 20thNight
48%
720
26%
1926
15%
720
55%
720
35%
1164
September21st to endNight
43%
720
25%
1980
16%
720
51%
720
31%
1258
October1st to 10thNight
36%
720
17%
2009
9%
720
43%
720
22%
1364
October11th to 20thNight
33%
720
20%
2203
10%
720
46%
720
25%
1377
October21st to endNight
23%
792
15%
2574
7%
792
34%
792
16%
1758
November1st to 10thNight
30%
740
23%
2407
12%
740
45%
740
22%
1463
November11th to 20thNight
25%
760
22%
2470
9%
760
40%
760
18%
1577
November21st to endNight
26%
760
20%
2550
7%
760
42%
760
19%
1554
December1st to 10thNight
18%
760
17%
2660
6%
760
34%
760
14%
1776
December11th to 20thNight
20%
760
16%
3222
4%
759
34%
759
12%
2072
December21st to endNight
17%
830
13%
4841
4%
817
34%
817
7%
3273

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
16%7%36%6%35%5%6%7%38%
74812
Night
15%7%35%5%345%5%7%41%
75004
TransparencyDay
45%6%12%22%14%2
74517
Night
43%5%13%23%14%2
74833
SeeingDay
24%16%29%20%9%3
13779
Night
21%15%30%25%8%1
22892

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
11%8%46%6%5%5%6%7%7%36%
1517
11th to 20thDay
15%8%36%7%46%5%7%6%33%
1488
21st to endDay
10%9%47%7%35%5%5%8%38%
1584
February1st to 10thDay
13%9%48%7%46%5%7%7%30%
1644
11th to 20thDay
11%8%38%7%36%5%7%7%36%
1748
21st to endDay
19%10%47%6%44445%34%
1480
March1st to 10thDay
13%7%37%6%45%5%6%7%38%
1797
11th to 20thDay
15%8%37%6%45%6%5%5%37%
1842
21st to endDay
17%8%36%5%3445%6%39%
2376
April1st to 10thDay
16%9%37%6%345%5%6%37%
2160
11th to 20thDay
15%7%35%6%35%5%6%7%37%
2134
21st to endDay
20%6%37%6%35%5%5%6%34%
2295
May1st to 10thDay
22%9%36%6%345%5%6%33%
2340
11th to 20thDay
19%5%35%5%345%5%6%40%
2450
21st to endDay
15%5%25%5%25%5%5%7%42%
2725
June1st to 10thDay
18%5%25%7%46%6%6%8%33%
2520
11th to 20thDay
17%5%35%5%445%5%9%38%
2520
21st to endDay
16%6%36%6%46%6%6%9%33%
2520
July1st to 10thDay
14%425%6%45%6%6%9%39%
2520
11th to 20thDay
12%5%25%6%45%6%5%10%40%
2520
21st to endDay
14%5%25%6%36%6%6%8%39%
2744
August1st to 10thDay
11%5%26%7%45%7%8%8%39%
2449
11th to 20thDay
12%5%26%5%45%6%7%10%37%
2197
21st to endDay
13%4246%445%6%9%43%
2376
September1st to 10thDay
13%6%24445%46%9%43%
2160
11th to 20thDay
15%426%43336%7%49%
2034
21st to endDay
17%5%245%245%48%44%
1980
October1st to 10thDay
24%5%25%5%35%45%5%38%
1948
11th to 20thDay
14%6%25%5%35%5%6%7%42%
1756
21st to endDay
21%8%36%5%44447%34%
1782
November1st to 10thDay
12%7%25%6%33446%49%
1671
11th to 20thDay
17%7%35%435%5%5%6%41%
1710
21st to endDay
17%7%36%4445%6%6%39%
1627
December1st to 10thDay
16%9%38%7%45%5%5%6%30%
1520
11th to 20thDay
20%9%25%5%34345%39%
1906
21st to endDay
18%11%36%6%45%45%7%31%
2772
January1st to 10thNight
12%8%36%5%345%5%6%42%
2649
11th to 20thNight
14%9%36%6%5%5%5%6%7%33%
2616
21st to endNight
10%8%46%5%46%5%6%8%39%
2772
February1st to 10thNight
13%9%37%6%46%5%6%6%36%
2309
11th to 20thNight
10%8%45%6%5%7%6%5%7%39%
2098
21st to endNight
15%8%37%6%35%45%6%38%
1776
March1st to 10thNight
12%10%35%6%345%5%7%41%
2150
11th to 20thNight
15%8%345%45%6%6%7%39%
2112
21st to endNight
14%7%36%5%345%6%7%41%
1980
April1st to 10thNight
16%8%25%5%45%5%6%6%39%
1800
11th to 20thNight
16%6%25%4445%5%7%41%
1775
21st to endNight
20%7%35%5%2435%6%39%
1663
May1st to 10thNight
21%9%46%5%2446%6%34%
1620
11th to 20thNight
16%6%25%6%45%5%5%6%39%
1458
21st to endNight
16%5%25%5%345%6%9%41%
1550
June1st to 10thNight
17%6%35%5%35%447%40%
1440
11th to 20thNight
18%5%234345%5%9%40%
1440
21st to endNight
15%5%24435%6%6%8%44%
1440
July1st to 10thNight
13%5%24435%6%5%8%46%
1440
11th to 20thNight
13%5%144445%8%9%42%
1440
21st to endNight
11%424435%46%8%49%
1574
August1st to 10thNight
10%425%435%45%9%50%
1472
11th to 20thNight
12%5%26%6%36%46%7%42%
1699
21st to endNight
16%42342346%7%49%
1980
September1st to 10thNight
13%4244335%6%8%48%
1800
11th to 20thNight
14%423423446%54%
1926
21st to endNight
15%4245%34446%48%
1980
October1st to 10thNight
23%5%2443445%6%41%
2009
11th to 20thNight
15%5%25%5%35%46%6%44%
2203
21st to endNight
23%7%25%5%35%5%46%37%
2574
November1st to 10thNight
14%6%25%5%3445%5%47%
2407
11th to 20thNight
17%6%35%4345%5%6%42%
2470
21st to endNight
13%7%35%4245%5%6%45%
2550
December1st to 10thNight
16%8%45%6%45%5%5%7%35%
2660
11th to 20thNight
18%8%35%5%345%5%7%38%
3288
21st to endNight
21%9%5%8%5%245%5%5%31%
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
44%7%10%26%12%1
1518
11th to 20thDay
50%6%14%17%10%3
1488
21st to endDay
44%5%13%23%13%3
1584
February1st to 10thDay
51%6%13%17%11%2
1644
11th to 20thDay
47%6%11%21%13%3
1757
21st to endDay
53%49%19%14%2
1480
March1st to 10thDay
46%414%19%13%4
1800
11th to 20thDay
48%5%11%17%15%4
1842
21st to endDay
47%48%19%17%5%
2376
April1st to 10thDay
48%410%21%14%3
2160
11th to 20thDay
43%7%12%20%16%2
2134
21st to endDay
49%6%9%19%14%3
2295
May1st to 10thDay
53%48%21%13%1
2340
11th to 20thDay
45%410%21%17%3
2454
21st to endDay
40%6%16%24%12%2
2725
June1st to 10thDay
47%7%13%21%11%1
2520
11th to 20thDay
44%6%14%20%15%1
2520
21st to endDay
46%8%13%21%11%1
2520
July1st to 10thDay
41%7%12%24%15%1
2450
11th to 20thDay
39%6%16%27%11%1
2445
21st to endDay
40%8%14%24%14%1
2591
August1st to 10thDay
39%8%16%24%12%1
2435
11th to 20thDay
40%6%16%26%11%1
2197
21st to endDay
37%7%14%27%14%2
2376
September1st to 10thDay
38%6%14%26%16%1
2160
11th to 20thDay
36%5%10%24%22%2
2034
21st to endDay
39%5%10%25%17%3
1980
October1st to 10thDay
49%410%21%13%3
1948
11th to 20thDay
40%6%14%27%11%2
1756
21st to endDay
52%412%18%11%3
1782
November1st to 10thDay
38%415%26%15%2
1671
11th to 20thDay
42%6%10%21%17%2
1710
21st to endDay
44%5%17%22%10%2
1627
December1st to 10thDay
53%6%13%15%12%1
1520
11th to 20thDay
49%411%21%14%1
1906
21st to endDay
53%5%14%17%11%1
2772
January1st to 10thNight
43%412%23%15%3
2649
11th to 20thNight
50%6%14%18%8%3
2616
21st to endNight
43%5%11%21%18%3
2772
February1st to 10thNight
49%5%15%19%10%2
2309
11th to 20thNight
44%7%11%21%14%3
2100
21st to endNight
47%313%23%11%4
1776
March1st to 10thNight
43%411%26%14%2
2160
11th to 20thNight
45%5%12%20%14%3
2113
21st to endNight
44%411%18%19%5%
1980
April1st to 10thNight
45%5%12%21%16%2
1800
11th to 20thNight
43%6%10%24%16%2
1775
21st to endNight
47%5%10%20%14%4
1663
May1st to 10thNight
51%410%20%14%2
1620
11th to 20thNight
45%412%20%15%3
1459
21st to endNight
42%7%14%25%12%2
1551
June1st to 10thNight
44%6%13%25%11%1
1440
11th to 20thNight
42%6%17%22%12%1
1440
21st to endNight
37%8%16%23%14%1
1440
July1st to 10thNight
35%9%15%25%14%2
1400
11th to 20thNight
36%7%16%29%11%
1392
21st to endNight
32%7%18%28%13%2
1486
August1st to 10thNight
32%6%17%29%14%1
1462
11th to 20thNight
41%6%18%24%11%
1699
21st to endNight
36%413%29%17%1
1980
September1st to 10thNight
34%6%15%27%17%1
1800
11th to 20thNight
33%411%27%23%2
1926
21st to endNight
38%411%27%17%2
1980
October1st to 10thNight
45%5%13%22%12%3
2009
11th to 20thNight
39%5%15%27%12%1
2203
21st to endNight
49%413%20%11%1
2574
November1st to 10thNight
38%5%12%24%17%3
2407
11th to 20thNight
44%411%23%15%3
2470
21st to endNight
40%418%25%12%1
2550
December1st to 10thNight
48%5%14%21%11%1
2660
11th to 20thNight
47%414%18%14%3
3288
21st to endNight
55%411%21%9%1
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
31%19%30%15%41
180
11th to 20thDay
33%18%35%8%42
172
21st to endDay
20%28%35%10%6%1
176
February1st to 10thDay
35%28%27%10%1
269
11th to 20thDay
31%23%32%13%1
416
21st to endDay
31%22%30%14%3
346
March1st to 10thDay
29%20%33%17%2
420
11th to 20thDay
30%24%29%13%32
420
21st to endDay
30%22%29%11%5%3
462
April1st to 10thDay
34%18%28%11%6%2
420
11th to 20thDay
31%21%28%11%7%1
412
21st to endDay
32%17%29%15%5%2
420
May1st to 10thDay
33%18%26%14%6%2
423
11th to 20thDay
24%16%35%19%5%2
447
21st to endDay
20%14%32%22%10%3
485
June1st to 10thDay
20%15%32%23%8%2
450
11th to 20thDay
19%13%33%23%10%1
450
21st to endDay
19%14%34%19%10%4
450
July1st to 10thDay
16%11%29%27%14%3
445
11th to 20thDay
15%7%33%29%14%3
444
21st to endDay
14%9%37%26%11%3
488
August1st to 10thDay
10%9%27%32%16%6%
446
11th to 20thDay
15%9%28%26%15%7%
439
21st to endDay
14%12%27%27%14%7%
495
September1st to 10thDay
19%10%22%24%18%7%
450
11th to 20thDay
17%12%26%21%16%9%
450
21st to endDay
20%12%28%23%10%7%
450
October1st to 10thDay
28%13%22%19%12%6%
450
11th to 20thDay
20%19%25%24%11%2
428
21st to endDay
34%13%25%21%7%1
396
November1st to 10thDay
23%16%26%24%9%2
365
11th to 20thDay
29%21%25%20%41
370
21st to endDay
31%16%28%21%5%1
287
December1st to 10thDay
29%22%27%18%41
180
11th to 20thDay
39%17%34%8%3
180
21st to endDay
31%19%29%17%31
198
January1st to 10thNight
21%21%33%20%3
760
11th to 20thNight
26%18%32%22%21
748
21st to endNight
19%19%35%23%4
792
February1st to 10thNight
23%19%37%18%3
720
11th to 20thNight
22%22%37%18%1
703
21st to endNight
27%22%31%19%2
592
March1st to 10thNight
23%21%35%19%3
720
11th to 20thNight
24%21%32%20%4
720
21st to endNight
23%17%33%21%6%
792
April1st to 10thNight
25%18%32%20%5%
720
11th to 20thNight
21%20%31%21%7%
711
21st to endNight
27%19%27%22%5%
583
May1st to 10thNight
29%12%29%22%7%1
540
11th to 20thNight
20%13%34%27%5%
397
21st to endNight
20%7%29%31%12%2
389
June1st to 10thNight
20%9%29%29%12%
360
11th to 20thNight
18%8%31%31%11%
360
21st to endNight
16%5%28%38%11%1
360
July1st to 10thNight
13%6%26%41%13%
350
11th to 20thNight
14%324%41%15%2
348
21st to endNight
11%5%26%42%15%1
394
August1st to 10thNight
13%423%37%22%2
398
11th to 20thNight
14%6%23%37%18%3
635
21st to endNight
16%6%20%35%20%2
792
September1st to 10thNight
15%6%24%35%18%2
720
11th to 20thNight
16%8%23%31%18%5%
720
21st to endNight
19%7%25%31%16%2
720
October1st to 10thNight
26%12%21%27%12%3
720
11th to 20thNight
19%11%32%26%11%1
720
21st to endNight
27%16%28%22%6%
792
November1st to 10thNight
20%17%28%25%8%1
740
11th to 20thNight
22%17%31%22%7%1
760
21st to endNight
21%18%31%24%6%1
760
December1st to 10thNight
25%18%33%18%5%
760
11th to 20thNight
26%18%32%21%4
760
21st to endNight
26%21%31%19%3
836
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