Ivanhoe Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ivanhoe Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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
28%
22701
14%
74785
8%
22657
37%
22657
17%
51946

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
15%
760
11%
2649
4%
757
24%
757
8%
2046
January11th to 20thNight
16%
732
9%
2560
4%
732
23%
732
8%
1993
January21st to endNight
20%
792
13%
2578
7%
792
29%
792
12%
1912
February1st to 10thNight
13%
720
11%
2340
3%
720
23%
720
10%
1779
February11th to 20thNight
15%
703
14%
2275
4%
700
27%
700
12%
1665
February21st to endNight
17%
592
15%
1829
5%
592
30%
592
13%
1318
March1st to 10thNight
20%
720
17%
2062
7%
720
30%
720
17%
1473
March11th to 20thNight
20%
720
16%
1979
6%
720
30%
720
17%
1425
March21st to endNight
25%
792
21%
2129
7%
792
35%
792
22%
1463
April1st to 10thNight
20%
720
18%
1800
5%
720
28%
720
19%
1311
April11th to 20thNight
25%
711
17%
1775
6%
711
31%
711
21%
1275
April21st to endNight
30%
590
16%
1670
6%
590
36%
590
20%
1174
May1st to 10thNight
33%
419
16%
1499
12%
419
41%
419
18%
970
May11th to 20thNight
36%
354
23%
1416
16%
354
54%
354
22%
816
May21st to endNight
40%
388
15%
1551
14%
388
52%
388
25%
889
June1st to 10thNight
35%
360
12%
1440
8%
360
48%
360
19%
888
June11th to 20thNight
38%
360
15%
1440
15%
360
50%
360
22%
832
June21st to endNight
42%
360
11%
1440
13%
360
49%
360
22%
864
July1st to 10thNight
49%
350
16%
1400
19%
350
58%
350
28%
754
July11th to 20thNight
51%
348
17%
1392
21%
348
58%
348
27%
782
July21st to endNight
50%
394
18%
1486
16%
372
58%
372
29%
789
August1st to 10thNight
53%
534
16%
1598
12%
532
58%
532
34%
969
August11th to 20thNight
55%
534
19%
1598
12%
534
61%
534
31%
976
August21st to endNight
46%
746
20%
1934
7%
746
52%
746
33%
1224
September1st to 10thNight
45%
720
17%
1800
6%
720
50%
720
32%
1184
September11th to 20thNight
52%
720
26%
1800
14%
720
57%
720
39%
1127
September21st to endNight
44%
720
21%
2070
15%
720
48%
720
26%
1361
October1st to 10thNight
35%
720
16%
2160
11%
720
42%
720
20%
1477
October11th to 20thNight
25%
720
13%
2160
7%
720
33%
720
16%
1587
October21st to endNight
22%
792
14%
2422
6%
792
32%
792
14%
1814
November1st to 10thNight
32%
740
18%
2454
13%
740
41%
740
19%
1626
November11th to 20thNight
22%
760
16%
2660
9%
760
32%
760
15%
1837
November21st to endNight
20%
760
11%
2660
5%
760
29%
760
11%
1967
December1st to 10thNight
15%
760
9%
2660
3%
760
23%
760
9%
2056
December11th to 20thNight
15%
759
10%
3247
3%
759
24%
759
8%
2402
December21st to endNight
11%
831
5%
4852
1%
817
18%
817
4%
3921

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%9%37%6%35%5%5%7%34%
74703
Night
17%10%37%5%345%5%6%34%
75030
TransparencyDay
49%6%12%20%11%1
74409
Night
50%6%12%20%11%1
74859
SeeingDay
23%16%31%19%9%3
13344
Night
22%13%30%24%9%1
22708

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
16%17%49%6%34445%27%
1517
11th to 20thDay
19%18%5%7%6%45%335%25%
1456
21st to endDay
14%14%6%11%7%46%445%25%
1773
February1st to 10thDay
15%15%5%11%8%36%5%5%6%22%
1620
11th to 20thDay
13%14%6%10%7%4444428%
1573
21st to endDay
19%15%48%7%45%44425%
1426
March1st to 10thDay
16%11%5%8%8%345%5%5%30%
1892
11th to 20thDay
15%15%48%7%3345%5%31%
1980
21st to endDay
20%10%36%5%23445%38%
2227
April1st to 10thDay
22%12%46%5%34436%32%
2160
11th to 20thDay
22%8%25%434347%39%
2134
21st to endDay
22%10%37%6%35%345%33%
2307
May1st to 10thDay
19%7%26%5%35%5%5%7%35%
2461
11th to 20thDay
15%6%36%6%345%5%7%40%
2478
21st to endDay
14%436%6%35%5%5%7%41%
2725
June1st to 10thDay
18%6%36%6%46%5%6%7%33%
2520
11th to 20thDay
15%5%35%5%46%5%6%8%39%
2520
21st to endDay
17%6%36%5%445%6%8%36%
2520
July1st to 10thDay
12%425%6%46%6%7%8%42%
2520
11th to 20thDay
12%6%35%7%35%6%6%9%39%
2520
21st to endDay
11%5%36%6%5%6%7%7%9%37%
2744
August1st to 10thDay
11%6%25%6%45%6%7%9%39%
2327
11th to 20thDay
13%426%7%45%5%6%8%38%
2303
21st to endDay
14%6%36%5%35%6%5%9%39%
2404
September1st to 10thDay
14%5%25%5%45%5%5%8%42%
2160
11th to 20thDay
11%5%25%43445%7%49%
2160
21st to endDay
17%6%26%4345%5%8%40%
1887
October1st to 10thDay
21%8%46%5%24447%34%
1800
11th to 20thDay
23%7%37%6%445%6%6%30%
1800
21st to endDay
28%10%46%5%44346%26%
1932
November1st to 10thDay
16%7%47%6%35%5%6%6%35%
1619
11th to 20thDay
18%10%48%6%335%5%6%30%
1520
21st to endDay
22%13%5%8%6%245%5%6%25%
1520
December1st to 10thDay
20%16%6%8%7%45%445%21%
1520
11th to 20thDay
19%14%6%8%6%43445%28%
1906
21st to endDay
30%15%49%5%2433420%
2772
January1st to 10thNight
20%14%6%10%6%35%45%5%23%
2649
11th to 20thNight
19%15%5%9%6%35%445%23%
2560
21st to endNight
13%13%5%10%7%35%5%5%5%28%
2578
February1st to 10thNight
15%14%5%9%8%45%5%5%5%25%
2340
11th to 20thNight
14%14%6%8%6%45%45%6%29%
2273
21st to endNight
17%11%47%7%445%6%5%31%
1829
March1st to 10thNight
15%11%47%6%5%5%5%45%34%
2052
11th to 20thNight
17%12%48%5%33345%35%
1979
21st to endNight
18%7%36%5%345%45%40%
2129
April1st to 10thNight
20%9%36%6%3345%6%35%
1800
11th to 20thNight
18%8%37%5%35%5%45%38%
1775
21st to endNight
19%8%36%6%25%6%5%7%34%
1670
May1st to 10thNight
20%7%35%5%35%45%7%37%
1499
11th to 20thNight
14%6%26%4245%6%7%44%
1415
21st to endNight
11%5%25%5%35%5%5%6%49%
1550
June1st to 10thNight
15%5%25%6%45%6%6%8%38%
1440
11th to 20thNight
12%5%35%5%35%46%8%44%
1440
21st to endNight
14%6%35%5%445%6%9%42%
1440
July1st to 10thNight
8%3245%4446%8%50%
1440
11th to 20thNight
11%415%5%445%6%8%47%
1440
21st to endNight
11%325%435%46%9%49%
1574
August1st to 10thNight
9%5%25%5%3447%8%48%
1608
11th to 20thNight
9%5%35%445%5%6%8%46%
1598
21st to endNight
10%5%36%4345%6%8%47%
1934
September1st to 10thNight
12%6%25%4345%6%8%46%
1800
11th to 20thNight
14%3134345%5%6%52%
1800
21st to endNight
17%6%25%5%345%5%5%44%
2070
October1st to 10thNight
18%7%36%6%4445%7%38%
2160
11th to 20thNight
23%8%37%6%44446%31%
2160
21st to endNight
24%10%37%5%35%5%5%5%28%
2422
November1st to 10thNight
20%8%345%345%46%38%
2454
11th to 20thNight
19%9%46%5%45%45%7%31%
2660
21st to endNight
21%11%37%6%35%5%6%7%27%
2660
December1st to 10thNight
22%14%5%8%6%345%6%7%20%
2660
11th to 20thNight
20%15%5%8%6%3444428%
3288
21st to endNight
30%16%48%6%3444417%
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
59%5%12%17%7%1
1518
11th to 20thDay
64%5%9%11%10%1
1456
21st to endDay
61%5%9%13%9%2
1773
February1st to 10thDay
63%5%11%15%5%1
1620
11th to 20thDay
61%49%15%10%1
1582
21st to endDay
63%49%12%10%1
1426
March1st to 10thDay
54%5%14%15%9%2
1895
11th to 20thDay
55%5%12%16%11%2
1980
21st to endDay
50%5%7%19%15%5%
2227
April1st to 10thDay
55%48%20%11%3
2160
11th to 20thDay
46%5%9%23%16%1
2134
21st to endDay
54%48%18%14%2
2307
May1st to 10thDay
49%5%10%18%15%3
2461
11th to 20thDay
43%6%10%24%15%2
2482
21st to endDay
41%7%15%21%14%2
2725
June1st to 10thDay
48%8%12%18%13%1
2520
11th to 20thDay
41%7%12%25%14%2
2520
21st to endDay
44%7%15%21%12%1
2520
July1st to 10thDay
36%8%13%27%16%1
2450
11th to 20thDay
37%8%17%27%10%
2445
21st to endDay
41%9%15%24%10%1
2591
August1st to 10thDay
37%8%18%25%11%1
2314
11th to 20thDay
41%8%16%24%11%1
2303
21st to endDay
40%8%13%27%11%1
2404
September1st to 10thDay
38%7%15%27%12%1
2160
11th to 20thDay
34%5%15%30%15%1
2160
21st to endDay
43%7%13%28%9%
1887
October1st to 10thDay
49%6%12%20%12%1
1800
11th to 20thDay
53%6%16%18%6%1
1800
21st to endDay
60%5%11%16%8%
1932
November1st to 10thDay
47%6%16%20%9%1
1619
11th to 20thDay
53%6%13%17%10%1
1520
21st to endDay
60%7%13%13%7%
1520
December1st to 10thDay
64%6%13%11%5%
1520
11th to 20thDay
60%6%14%13%7%
1906
21st to endDay
68%48%15%5%
2772
January1st to 10thNight
64%410%15%7%
2649
11th to 20thNight
64%5%11%12%7%1
2560
21st to endNight
56%6%10%17%10%1
2578
February1st to 10thNight
60%6%11%17%6%1
2340
11th to 20thNight
56%5%9%20%9%1
2275
21st to endNight
53%5%12%20%9%1
1829
March1st to 10thNight
51%6%11%19%12%2
2062
11th to 20thNight
52%410%21%11%1
1980
21st to endNight
46%5%8%21%16%3
2129
April1st to 10thNight
50%5%7%22%13%3
1800
11th to 20thNight
47%6%9%19%17%1
1775
21st to endNight
47%7%11%17%15%3
1670
May1st to 10thNight
47%49%19%17%4
1499
11th to 20thNight
38%6%10%27%16%3
1416
21st to endNight
35%7%15%20%19%4
1551
June1st to 10thNight
43%6%14%22%14%1
1440
11th to 20thNight
38%6%12%21%20%3
1440
21st to endNight
39%7%15%23%14%2
1440
July1st to 10thNight
29%9%13%26%21%3
1400
11th to 20thNight
34%7%14%31%15%
1392
21st to endNight
32%6%17%32%12%1
1486
August1st to 10thNight
34%6%18%30%12%1
1598
11th to 20thNight
34%7%17%27%14%2
1598
21st to endNight
34%8%13%32%13%1
1934
September1st to 10thNight
37%7%16%26%14%1
1800
11th to 20thNight
31%6%15%31%16%1
1800
21st to endNight
40%7%12%28%12%1
2070
October1st to 10thNight
46%7%11%22%13%1
2160
11th to 20thNight
53%7%13%20%8%
2160
21st to endNight
56%7%12%15%10%
2422
November1st to 10thNight
46%6%14%23%11%1
2454
11th to 20thNight
50%6%13%20%9%2
2660
21st to endNight
55%8%16%16%6%
2660
December1st to 10thNight
61%7%13%15%5%
2660
11th to 20thNight
59%5%12%16%7%1
3288
21st to endNight
69%6%10%11%4
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
25%24%30%17%31
180
11th to 20thDay
29%21%32%15%21
164
21st to endDay
26%22%34%13%41
260
February1st to 10thDay
34%28%30%8%1
240
11th to 20thDay
30%27%38%5%1
240
21st to endDay
38%21%33%7%2
292
March1st to 10thDay
25%19%36%15%4
420
11th to 20thDay
28%21%32%15%4
420
21st to endDay
33%19%27%14%6%1
462
April1st to 10thDay
32%19%32%10%6%
420
11th to 20thDay
29%22%22%16%8%3
412
21st to endDay
31%19%31%11%6%2
420
May1st to 10thDay
25%17%28%17%7%4
423
11th to 20thDay
19%15%35%20%8%3
447
21st to endDay
16%14%37%18%11%4
485
June1st to 10thDay
21%14%36%20%7%2
450
11th to 20thDay
15%15%32%23%12%3
450
21st to endDay
22%13%30%22%11%2
450
July1st to 10thDay
11%10%29%31%16%3
445
11th to 20thDay
15%10%30%26%15%5%
444
21st to endDay
12%9%38%28%10%4
488
August1st to 10thDay
12%9%30%28%15%6%
446
11th to 20thDay
11%8%31%28%17%7%
439
21st to endDay
15%12%30%23%13%8%
495
September1st to 10thDay
13%12%32%24%11%8%
450
11th to 20thDay
12%10%29%23%16%10%
450
21st to endDay
19%12%28%23%13%6%
450
October1st to 10thDay
24%18%24%16%12%5%
450
11th to 20thDay
26%19%32%16%6%1
450
21st to endDay
31%18%27%20%3
471
November1st to 10thDay
27%17%27%20%9%1
313
11th to 20thDay
32%22%28%14%31
180
21st to endDay
28%21%32%14%31
180
December1st to 10thDay
31%18%34%14%3
180
11th to 20thDay
37%22%27%11%21
180
21st to endDay
38%18%33%9%2
198
January1st to 10thNight
27%20%29%19%4
760
11th to 20thNight
29%16%30%19%6%
732
21st to endNight
21%18%33%23%41
792
February1st to 10thNight
23%23%36%17%2
720
11th to 20thNight
23%19%36%17%4
703
21st to endNight
25%19%35%18%3
592
March1st to 10thNight
21%19%35%22%3
720
11th to 20thNight
26%18%31%20%41
720
21st to endNight
21%16%32%22%7%1
792
April1st to 10thNight
25%16%34%21%4
720
11th to 20thNight
23%20%28%20%8%1
711
21st to endNight
23%12%31%24%10%
590
May1st to 10thNight
23%10%27%27%12%2
419
11th to 20thNight
16%8%35%31%10%
354
21st to endNight
12%8%35%30%13%2
389
June1st to 10thNight
16%7%35%31%11%
360
11th to 20thNight
14%8%35%29%13%1
360
21st to endNight
16%7%26%37%13%1
360
July1st to 10thNight
6%7%31%39%17%1
350
11th to 20thNight
11%131%37%19%1
348
21st to endNight
11%330%41%14%1
394
August1st to 10thNight
11%323%36%24%2
534
11th to 20thNight
10%5%22%37%24%2
534
21st to endNight
11%5%30%33%18%2
746
September1st to 10thNight
14%6%31%30%18%3
720
11th to 20thNight
13%5%25%28%24%4
720
21st to endNight
18%10%22%28%18%3
720
October1st to 10thNight
21%13%27%23%15%2
720
11th to 20thNight
24%14%31%23%8%1
720
21st to endNight
28%15%29%23%5%
792
November1st to 10thNight
26%12%26%26%9%1
740
11th to 20thNight
24%18%31%20%6%1
760
21st to endNight
29%17%28%21%6%
760
December1st to 10thNight
31%19%28%20%3
760
11th to 20thNight
27%18%34%18%3
760
21st to endNight
35%15%33%15%2
836
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