Ivan's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ivan's Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
65%
25025
11%
74540
9%
24976
67%
24976
14%
57876

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
58%
757
13%
2459
10%
757
63%
757
16%
1794
January11th to 20thNight
52%
744
11%
2417
10%
744
56%
744
12%
1869
January21st to endNight
52%
792
14%
2560
11%
792
57%
792
15%
1925
February1st to 10thNight
58%
720
16%
2160
14%
720
61%
720
16%
1610
February11th to 20thNight
62%
700
17%
1980
12%
699
67%
699
19%
1452
February21st to endNight
67%
592
23%
1628
19%
592
70%
592
22%
1158
March1st to 10thNight
57%
720
19%
1980
11%
720
64%
720
23%
1399
March11th to 20thNight
65%
720
17%
1980
13%
720
69%
720
22%
1408
March21st to endNight
65%
792
19%
2178
15%
792
67%
792
22%
1552
April1st to 10thNight
72%
720
15%
1980
13%
720
74%
720
22%
1412
April11th to 20thNight
66%
711
14%
1853
9%
711
67%
711
20%
1382
April21st to endNight
67%
720
15%
1800
9%
720
69%
720
20%
1353
May1st to 10thNight
76%
720
17%
1800
12%
720
77%
720
27%
1269
May11th to 20thNight
64%
709
8%
1771
5%
709
64%
709
16%
1412
May21st to endNight
70%
582
6%
1744
6%
582
70%
582
12%
1411
June1st to 10thNight
63%
540
5%
1620
4%
540
63%
540
8%
1404
June11th to 20thNight
73%
540
8%
1620
7%
540
73%
540
12%
1286
June21st to endNight
76%
540
5%
1620
4%
540
76%
540
10%
1370
July1st to 10thNight
75%
525
3%
1575
3%
525
75%
525
8%
1352
July11th to 20thNight
76%
522
4%
1566
5%
522
76%
522
10%
1297
July21st to endNight
79%
591
5%
1672
5%
558
80%
558
13%
1347
August1st to 10thNight
78%
567
5%
1630
5%
564
78%
564
14%
1298
August11th to 20thNight
78%
710
4%
1774
3%
710
78%
710
14%
1460
August21st to endNight
67%
792
3%
2103
3%
792
67%
792
9%
1811
September1st to 10thNight
69%
720
4%
1980
4%
720
69%
720
10%
1660
September11th to 20thNight
66%
720
2%
1980
3%
720
66%
720
9%
1698
September21st to endNight
59%
720
5%
1980
5%
720
60%
720
7%
1761
October1st to 10thNight
63%
720
9%
2075
10%
720
64%
720
12%
1694
October11th to 20thNight
66%
720
10%
2160
9%
720
68%
720
14%
1693
October21st to endNight
60%
792
13%
2376
13%
792
62%
792
14%
1840
November1st to 10thNight
58%
740
13%
2221
11%
740
63%
740
15%
1684
November11th to 20thNight
60%
760
14%
2280
13%
760
62%
760
13%
1792
November21st to endNight
58%
760
11%
2280
10%
760
61%
760
14%
1769
December1st to 10thNight
63%
760
15%
2301
14%
760
66%
760
15%
1753
December11th to 20thNight
57%
758
12%
2955
10%
758
59%
758
9%
2190
December21st to endNight
59%
829
8%
4482
13%
817
63%
817
9%
3311

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%6%37%7%5%7%7%8%11%31%
74923
Night
7%5%35%6%46%6%7%10%41%
74885
TransparencyDay
28%42%10%11%7%2
74646
Night
25%41%12%12%8%2
74681
SeeingDay
7%213%27%31%19%
14870
Night
8%213%30%32%14%
25042

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
8%5%36%6%45%6%8%10%41%
1706
11th to 20thDay
11%6%46%7%46%6%7%9%36%
1671
21st to endDay
8%6%26%6%47%6%7%9%37%
1791
February1st to 10thDay
10%6%35%6%45%5%8%11%38%
1800
11th to 20thDay
7%5%245%35%5%7%10%47%
1863
21st to endDay
7%5%36%7%36%6%7%9%43%
1628
March1st to 10thDay
4426%6%47%6%7%10%44%
1980
11th to 20thDay
7%426%5%35%6%8%11%43%
1980
21st to endDay
5%4246%46%6%6%9%46%
2178
April1st to 10thDay
5%425%5%36%7%8%12%43%
1980
11th to 20thDay
7%6%26%6%47%7%8%10%37%
2052
21st to endDay
6%4246%47%7%7%12%41%
2160
May1st to 10thDay
4215%5%47%7%8%12%46%
2160
11th to 20thDay
9%7%38%8%5%7%7%7%11%29%
2136
21st to endDay
10%6%38%8%5%7%9%6%10%27%
2531
June1st to 10thDay
14%9%49%9%6%9%8%7%9%16%
2340
11th to 20thDay
7%6%39%10%6%10%9%9%11%20%
2340
21st to endDay
8%6%38%8%6%8%8%10%12%23%
2340
July1st to 10thDay
7%6%47%7%5%9%10%10%13%21%
2340
11th to 20thDay
8%6%37%8%5%8%9%10%12%24%
2340
21st to endDay
45%38%8%5%9%9%11%13%24%
2547
August1st to 10thDay
7%5%38%8%5%8%9%9%13%24%
2278
11th to 20thDay
5%5%37%7%6%8%10%11%14%24%
2126
21st to endDay
9%6%38%9%6%8%9%9%13%20%
2246
September1st to 10thDay
9%6%38%8%7%9%10%9%11%20%
1980
11th to 20thDay
7%6%38%9%8%9%9%10%11%21%
1980
21st to endDay
12%9%49%10%6%7%9%8%8%18%
1980
October1st to 10thDay
9%7%38%8%6%8%7%9%11%23%
1882
11th to 20thDay
9%5%37%8%5%9%7%7%11%28%
1800
21st to endDay
11%6%37%6%5%6%6%7%9%34%
1980
November1st to 10thDay
9%5%35%5%5%5%7%9%10%37%
1857
11th to 20thDay
11%6%37%7%48%6%7%8%31%
1900
21st to endDay
8%437%6%47%7%7%9%36%
1900
December1st to 10thDay
8%6%37%6%45%6%6%9%40%
1874
11th to 20thDay
9%7%36%6%45%5%6%9%41%
2153
21st to endDay
13%6%37%6%5%6%7%8%10%30%
3124
January1st to 10thNight
7%5%35%435%6%7%9%46%
2459
11th to 20thNight
9%5%36%6%35%7%7%10%39%
2417
21st to endNight
8%5%36%5%36%6%6%9%43%
2560
February1st to 10thNight
9%5%35%5%345%7%9%45%
2160
11th to 20thNight
6%3244345%6%7%56%
1980
21st to endNight
6%4235%245%6%9%53%
1628
March1st to 10thNight
432343447%9%57%
1980
11th to 20thNight
7%3143345%5%10%55%
1980
21st to endNight
6%3245%345%6%10%53%
2178
April1st to 10thNight
43135%345%6%11%56%
1980
11th to 20thNight
6%334445%7%7%11%47%
1853
21st to endNight
6%4245%246%7%9%50%
1800
May1st to 10thNight
4314325%5%7%11%56%
1800
11th to 20thNight
7%5%46%7%46%7%7%10%39%
1770
21st to endNight
7%6%36%5%46%6%7%12%37%
1744
June1st to 10thNight
13%6%37%9%5%6%9%8%10%24%
1620
11th to 20thNight
6%5%36%7%46%8%9%14%32%
1620
21st to endNight
5%5%25%7%5%7%7%9%14%32%
1620
July1st to 10thNight
5%5%46%6%5%8%6%9%10%36%
1620
11th to 20thNight
5%5%36%7%46%7%8%13%37%
1620
21st to endNight
3336%7%48%6%9%13%39%
1771
August1st to 10thNight
7%4245%47%8%9%13%38%
1641
11th to 20thNight
3425%6%46%9%9%14%39%
1774
21st to endNight
8%6%37%7%47%8%10%13%28%
2103
September1st to 10thNight
6%5%36%7%5%8%9%10%12%28%
1980
11th to 20thNight
8%5%27%8%5%7%8%9%12%28%
1980
21st to endNight
9%7%38%8%6%7%9%9%10%22%
1980
October1st to 10thNight
8%5%38%8%6%8%8%8%11%28%
2075
11th to 20thNight
10%5%25%6%46%7%7%12%36%
2160
21st to endNight
11%6%25%5%46%6%6%8%40%
2376
November1st to 10thNight
10%5%25%5%35%5%5%10%44%
2221
11th to 20thNight
9%6%36%6%5%6%5%6%10%38%
2280
21st to endNight
9%6%36%6%36%5%6%10%41%
2280
December1st to 10thNight
7%5%245%35%6%6%11%45%
2301
11th to 20thNight
13%6%25%5%25%5%5%8%44%
3042
21st to endNight
11%7%37%7%5%6%6%7%9%32%
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
22%42%7%13%12%5%
1707
11th to 20thDay
28%43%9%11%7%3
1671
21st to endDay
27%40%7%13%9%4
1791
February1st to 10thDay
27%39%5%14%11%4
1800
11th to 20thDay
21%40%9%18%10%3
1873
21st to endDay
21%38%9%11%17%5%
1628
March1st to 10thDay
20%39%9%17%12%3
1980
11th to 20thDay
20%39%10%17%12%3
1980
21st to endDay
19%40%8%18%12%3
2178
April1st to 10thDay
20%40%12%16%10%2
1980
11th to 20thDay
24%40%10%14%10%1
2052
21st to endDay
23%41%8%14%12%3
2160
May1st to 10thDay
15%40%10%21%13%1
2160
11th to 20thDay
29%43%10%13%5%
2140
21st to endDay
33%43%9%10%5%
2531
June1st to 10thDay
40%42%9%7%2
2340
11th to 20thDay
34%43%11%10%1
2340
21st to endDay
37%43%13%6%1
2340
July1st to 10thDay
34%48%13%5%
2275
11th to 20thDay
33%47%12%8%
2271
21st to endDay
26%49%17%8%
2405
August1st to 10thDay
30%46%17%6%1
2265
11th to 20thDay
30%45%17%7%
2126
21st to endDay
33%48%13%5%1
2246
September1st to 10thDay
32%46%13%8%1
1980
11th to 20thDay
33%49%11%6%2
1980
21st to endDay
40%44%8%5%31
1980
October1st to 10thDay
30%44%10%9%5%1
1882
11th to 20thDay
31%42%9%11%6%1
1800
21st to endDay
30%39%7%11%12%1
1980
November1st to 10thDay
23%42%6%9%14%6%
1857
11th to 20thDay
30%41%8%9%10%2
1900
21st to endDay
24%43%10%10%12%1
1900
December1st to 10thDay
23%44%8%13%11%1
1874
11th to 20thDay
32%34%8%10%12%4
2150
21st to endDay
35%29%12%10%12%2
3124
January1st to 10thNight
19%42%9%15%12%3
2459
11th to 20thNight
24%43%9%12%9%3
2417
21st to endNight
23%41%9%15%8%4
2560
February1st to 10thNight
25%37%7%16%12%3
2160
11th to 20thNight
19%39%10%19%10%2
1981
21st to endNight
17%38%9%15%18%4
1628
March1st to 10thNight
16%38%9%17%17%4
1980
11th to 20thNight
18%37%12%19%12%3
1980
21st to endNight
17%38%10%19%14%3
2178
April1st to 10thNight
16%40%14%19%10%2
1980
11th to 20thNight
20%39%12%16%12%1
1853
21st to endNight
20%40%11%14%12%3
1800
May1st to 10thNight
13%38%9%26%13%
1800
11th to 20thNight
25%42%12%15%6%
1771
21st to endNight
29%42%13%13%3
1745
June1st to 10thNight
36%43%11%7%2
1620
11th to 20thNight
26%43%16%12%2
1620
21st to endNight
31%45%15%8%1
1620
July1st to 10thNight
32%46%15%6%1
1575
11th to 20thNight
28%46%18%8%
1566
21st to endNight
22%48%19%9%2
1672
August1st to 10thNight
22%46%21%10%1
1630
11th to 20thNight
24%47%20%9%
1774
21st to endNight
30%48%15%7%1
2103
September1st to 10thNight
29%46%15%9%1
1980
11th to 20thNight
33%45%14%7%1
1980
21st to endNight
39%44%8%6%4
1980
October1st to 10thNight
30%42%11%11%5%1
2075
11th to 20thNight
27%40%13%13%6%1
2160
21st to endNight
27%39%9%12%11%2
2376
November1st to 10thNight
22%42%9%9%13%6%
2221
11th to 20thNight
26%42%8%14%9%2
2280
21st to endNight
23%43%11%10%11%2
2280
December1st to 10thNight
20%44%9%14%10%2
2301
11th to 20thNight
30%34%9%10%10%7%
3044
21st to endNight
36%30%10%9%12%2
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
8%5%29%40%17%1
270
11th to 20thDay
13%7%25%32%19%4
257
21st to endDay
11%6%33%40%10%1
264
February1st to 10thDay
8%7%20%40%23%3
240
11th to 20thDay
7%417%40%27%6%
356
21st to endDay
7%320%36%32%2
346
March1st to 10thDay
3429%43%18%3
420
11th to 20thDay
5%322%39%28%2
420
21st to endDay
4121%41%28%4
462
April1st to 10thDay
3223%42%25%5%
420
11th to 20thDay
7%222%39%24%6%
412
21st to endDay
4214%41%33%5%
420
May1st to 10thDay
318%42%36%10%
423
11th to 20thDay
10%211%31%34%12%
447
21st to endDay
11%28%15%40%24%
485
June1st to 10thDay
10%38%18%40%21%
450
11th to 20thDay
6%26%14%34%39%
450
21st to endDay
22210%34%50%
450
July1st to 10thDay
4126%34%53%
445
11th to 20thDay
6%37%36%48%
444
21st to endDay
41112%34%47%
488
August1st to 10thDay
6%410%36%43%
446
11th to 20thDay
429%37%48%
439
21st to endDay
9%6%15%35%35%
495
September1st to 10thDay
9%2410%36%39%
450
11th to 20thDay
4414%35%41%
450
21st to endDay
8%37%18%35%30%
450
October1st to 10thDay
10%18%30%40%11%
450
11th to 20thDay
10%211%32%31%13%
450
21st to endDay
11%314%31%33%9%
495
November1st to 10thDay
9%5%17%33%27%9%
455
11th to 20thDay
12%320%33%28%4
460
21st to endDay
6%220%40%30%2
460
December1st to 10thDay
10%317%39%28%3
434
11th to 20thDay
10%318%35%29%5%
270
21st to endDay
8%7%22%31%26%6%
297
January1st to 10thNight
10%5%20%38%25%2
760
11th to 20thNight
10%5%24%38%22%2
744
21st to endNight
9%5%26%43%17%
792
February1st to 10thNight
10%5%19%41%23%1
720
11th to 20thNight
7%323%40%26%1
703
21st to endNight
6%219%46%27%
592
March1st to 10thNight
5%229%41%21%2
720
11th to 20thNight
5%321%42%27%2
720
21st to endNight
6%220%46%24%1
792
April1st to 10thNight
4213%49%29%3
720
11th to 20thNight
5%317%45%28%2
711
21st to endNight
7%116%45%28%2
720
May1st to 10thNight
4111%42%38%4
720
11th to 20thNight
10%211%39%33%5%
709
21st to endNight
8%110%22%47%13%
584
June1st to 10thNight
11%15%21%45%17%
540
11th to 20thNight
5%1413%45%31%
540
21st to endNight
5%1312%36%44%
540
July1st to 10thNight
5%137%38%46%
525
11th to 20thNight
5%117%40%45%
522
21st to endNight
327%40%47%
591
August1st to 10thNight
8%118%44%38%
567
11th to 20thNight
429%45%40%
710
21st to endNight
9%1415%38%34%
792
September1st to 10thNight
7%16%12%37%38%
720
11th to 20thNight
9%2315%37%34%
720
21st to endNight
12%26%16%36%29%
720
October1st to 10thNight
10%29%28%41%11%
720
11th to 20thNight
9%211%25%43%10%
720
21st to endNight
16%112%34%30%8%
792
November1st to 10thNight
11%319%32%30%6%
740
11th to 20thNight
10%220%32%33%4
760
21st to endNight
10%218%40%27%2
760
December1st to 10thNight
9%318%36%31%4
760
11th to 20thNight
10%5%19%33%29%4
760
21st to endNight
9%421%34%29%3
836
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