Ivanhoe Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ivanhoe Observatory clear sky chart from 2005-11-05 to 2019-06-02.

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%
16931
15%
53850
8%
16900
37%
16900
18%
37202

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 15thNight
15%
840
11%
2926
3%
836
25%
836
9%
2241
January16th to endNight
17%
896
11%
2985
5%
896
25%
896
10%
2266
February1st to 15thNight
13%
824
12%
2677
3%
821
24%
821
10%
2017
February16th to endNight
19%
735
14%
2316
5%
735
30%
735
14%
1670
March1st to 15thNight
19%
840
15%
2374
6%
840
28%
840
16%
1739
March16th to endNight
27%
896
21%
2426
8%
896
38%
896
24%
1624
April1st to 15thNight
21%
838
17%
2096
4%
838
28%
838
19%
1547
April16th to endNight
32%
729
17%
1975
7%
729
38%
729
23%
1342
May1st to 15thNight
34%
466
17%
1726
13%
466
44%
466
18%
1114
May16th to endNight
38%
438
16%
1753
13%
438
51%
438
23%
1027
June1st to 15thNight
36%
392
12%
1569
9%
392
48%
392
18%
987
June16th to endNight
42%
390
11%
1560
12%
390
49%
390
22%
926
July1st to 15thNight
54%
370
17%
1480
23%
370
61%
370
32%
769
July16th to endNight
51%
408
16%
1546
15%
386
58%
386
29%
823
August1st to 15thNight
54%
573
15%
1714
11%
571
59%
571
32%
1058
August16th to endNight
52%
731
22%
1973
10%
731
59%
731
36%
1180
September1st to 15thNight
47%
780
20%
1950
9%
780
52%
780
34%
1270
September16th to endNight
50%
777
23%
2146
16%
777
54%
777
31%
1357
October1st to 15thNight
34%
780
16%
2340
11%
780
41%
780
19%
1635
October16th to endNight
21%
832
13%
2530
5%
832
31%
832
13%
1889
November1st to 15thNight
30%
820
18%
2772
13%
820
39%
820
18%
1870
November16th to endNight
21%
840
12%
2940
6%
840
30%
840
11%
2157
December1st to 15thNight
15%
840
8%
2940
3%
840
23%
840
10%
2246
December16th to endNight
13%
896
9%
3136
2%
896
21%
896
9%
2448

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%8%36%5%3445%6%33%
54492
Night
17%8%36%5%3445%6%35%
54020
Cloud CoverDay
17%8%36%5%3445%6%33%
54502
Night
17%8%36%5%34446%35%
54025
TransparencyDay
50%5%12%20%10%1
54181
Night
49%5%12%20%11%1
53850
SeeingDay
23%14%30%18%9%4
7504
Night
22%12%30%23%10%1
16932

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 15thDay
19%16%48%5%24335%27%
1672
16th to endDay
14%15%6%10%6%36%44423%
1939
February1st to 15thDay
15%14%6%11%7%35%34422%
1845
16th to endDay
18%14%47%6%4433426%
1729
March1st to 15thDay
17%13%47%7%34445%27%
2232
16th to endDay
16%8%36%5%23345%40%
2502
April1st to 15thDay
24%9%35%424335%31%
2512
16th to endDay
21%8%26%423236%37%
2603
May1st to 15thDay
19%7%25%5%35%45%6%33%
2885
16th to endDay
14%425%6%3445%7%39%
3066
June1st to 15thDay
19%6%35%5%35%46%7%30%
2744
16th to endDay
15%6%35%435%5%6%8%35%
2730
July1st to 15thDay
11%4245%35%5%6%8%41%
2730
16th to endDay
11%5%35%6%46%6%6%8%35%
2878
August1st to 15thDay
11%6%36%6%45%5%7%8%35%
2487
16th to endDay
13%5%25%5%345%48%39%
2568
September1st to 15thDay
15%5%2443445%7%42%
2340
16th to endDay
14%5%25%324347%45%
2142
October1st to 15thDay
22%6%35%5%34446%32%
1950
16th to endDay
26%9%36%5%3335%5%26%
2044
November1st to 15thDay
18%6%48%5%3345%5%33%
1742
16th to endDay
23%11%48%6%23446%24%
1680
December1st to 15thDay
18%16%5%8%5%4444423%
1680
16th to endDay
21%15%5%7%7%34335%21%
1792
January1st to 15thNight
21%13%48%6%34345%24%
2926
16th to endNight
14%14%5%9%6%35%5%5%5%24%
2985
February1st to 15thNight
15%14%5%8%7%34445%25%
2675
16th to endNight
16%11%46%6%445%5%5%30%
2316
March1st to 15thNight
18%12%36%5%4444432%
2362
16th to endNight
15%6%36%433445%42%
2426
April1st to 15thNight
21%8%25%5%335%45%33%
2096
16th to endNight
18%6%244245%46%39%
1975
May1st to 15thNight
20%6%25%42445%6%37%
1726
16th to endNight
12%425%424446%46%
1751
June1st to 15thNight
16%425%5%35%45%7%38%
1569
16th to endNight
12%5%25%43346%9%41%
1560
July1st to 15thNight
7%21343446%7%53%
1560
16th to endNight
10%31433436%8%49%
1642
August1st to 15thNight
8%5%25%43446%8%45%
1724
16th to endNight
7%425%32445%8%50%
1973
September1st to 15thNight
14%5%234235%6%6%46%
1950
16th to endNight
16%413424445%49%
2146
October1st to 15thNight
20%6%26%5%33446%35%
2340
16th to endNight
23%8%27%5%35%45%5%28%
2530
November1st to 15thNight
20%7%34423447%35%
2772
16th to endNight
22%9%36%5%35%45%5%27%
2940
December1st to 15thNight
20%14%48%5%335%5%6%22%
2940
16th to endNight
21%13%5%7%7%3444422%
3136

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 15thDay
19%15%46%5%2334428%
1672
16th to endDay
13%15%5%10%7%35%44423%
1939
February1st to 15thDay
15%14%5%11%7%45%445%23%
1845
16th to endDay
18%13%5%6%7%4444426%
1729
March1st to 15thDay
18%12%37%7%34345%28%
2243
16th to endDay
16%8%36%433345%41%
2501
April1st to 15thDay
24%10%35%5%23445%32%
2512
16th to endDay
21%7%35%5%23345%38%
2603
May1st to 15thDay
19%6%35%5%345%5%6%33%
2885
16th to endDay
13%5%36%6%25%46%6%40%
3066
June1st to 15thDay
20%6%25%5%25%6%5%7%32%
2744
16th to endDay
16%5%35%435%46%9%35%
2730
July1st to 15thDay
11%4245%26%5%6%7%43%
2730
16th to endDay
10%5%26%5%46%6%7%9%35%
2878
August1st to 15thDay
11%6%26%5%35%6%7%8%36%
2487
16th to endDay
13%425%5%3445%8%41%
2568
September1st to 15thDay
14%5%244245%5%7%43%
2340
16th to endDay
15%5%25%323347%45%
2142
October1st to 15thDay
21%7%36%4335%5%5%32%
1950
16th to endDay
26%8%36%5%33346%27%
2044
November1st to 15thDay
18%7%37%6%33447%32%
1742
16th to endDay
22%12%46%6%335%45%25%
1680
December1st to 15thDay
19%15%5%8%6%3444424%
1680
16th to endDay
22%14%6%8%6%35%335%21%
1792
January1st to 15thNight
21%13%5%7%6%24335%24%
2926
16th to endNight
15%14%5%8%6%35%5%46%25%
2985
February1st to 15thNight
16%14%5%8%6%35%445%26%
2668
16th to endNight
16%11%46%5%3445%5%30%
2316
March1st to 15thNight
18%12%46%5%3434432%
2374
16th to endNight
15%7%35%5%24335%42%
2426
April1st to 15thNight
21%8%35%5%24445%33%
2096
16th to endNight
18%6%25%42345%7%39%
1975
May1st to 15thNight
19%6%25%4235%46%37%
1726
16th to endNight
12%5%24434447%45%
1751
June1st to 15thNight
17%425%5%34447%38%
1569
16th to endNight
14%4245%2446%8%42%
1560
July1st to 15thNight
7%31442446%8%52%
1560
16th to endNight
9%42433346%8%49%
1642
August1st to 15thNight
9%5%245%3435%8%46%
1724
16th to endNight
7%425%42445%8%50%
1973
September1st to 15thNight
13%5%2432345%7%45%
1950
16th to endNight
15%324324345%49%
2146
October1st to 15thNight
20%6%26%6%3345%6%35%
2340
16th to endNight
23%8%36%5%35%445%29%
2530
November1st to 15thNight
19%8%345%24447%36%
2772
16th to endNight
23%9%36%5%3445%6%27%
2940
December1st to 15thNight
20%14%47%5%345%5%6%23%
2940
16th to endNight
21%13%47%7%3444422%
3136

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 15thDay
59%411%17%6%
1673
16th to endDay
63%5%9%12%7%1
1939
February1st to 15thDay
63%410%15%5%
1847
16th to endDay
60%310%13%10%1
1729
March1st to 15thDay
58%413%16%6%1
2243
16th to endDay
46%48%21%15%4
2502
April1st to 15thDay
55%48%17%11%2
2512
16th to endDay
48%38%21%16%2
2603
May1st to 15thDay
49%5%10%20%12%2
2885
16th to endDay
42%6%14%22%13%1
3070
June1st to 15thDay
49%6%12%19%11%
2744
16th to endDay
45%6%13%20%12%1
2730
July1st to 15thDay
35%6%13%29%14%
2581
16th to endDay
42%8%15%23%8%
2711
August1st to 15thDay
42%7%17%21%10%
2474
16th to endDay
39%6%14%27%11%
2568
September1st to 15thDay
38%6%14%25%12%1
2340
16th to endDay
38%6%11%31%10%
2142
October1st to 15thDay
51%6%11%20%9%
1950
16th to endDay
58%413%16%6%
2044
November1st to 15thDay
51%6%14%18%9%
1742
16th to endDay
58%6%12%13%7%
1680
December1st to 15thDay
63%5%14%12%4
1680
16th to endDay
66%5%7%13%6%
1792
January1st to 15thNight
63%310%14%6%
2926
16th to endNight
59%6%10%15%8%
2985
February1st to 15thNight
59%5%12%17%5%
2677
16th to endNight
53%5%11%20%9%
2316
March1st to 15thNight
54%410%20%8%
2374
16th to endNight
44%39%22%16%2
2426
April1st to 15thNight
51%5%8%19%14%1
2096
16th to endNight
43%5%11%18%18%2
1975
May1st to 15thNight
46%5%9%20%15%3
1726
16th to endNight
37%6%12%23%16%2
1753
June1st to 15thNight
44%5%12%20%15%
1569
16th to endNight
38%6%14%23%15%1
1560
July1st to 15thNight
26%7%12%28%21%2
1480
16th to endNight
32%5%15%30%15%
1546
August1st to 15thNight
34%6%18%27%12%
1714
16th to endNight
30%6%14%32%14%
1973
September1st to 15thNight
36%6%16%26%14%1
1950
16th to endNight
36%5%11%31%14%
2146
October1st to 15thNight
48%6%10%22%11%
2340
16th to endNight
55%6%13%17%7%
2530
November1st to 15thNight
48%5%13%19%11%1
2772
16th to endNight
56%6%13%16%6%
2940
December1st to 15thNight
60%5%13%15%4
2940
16th to endNight
63%6%11%11%6%
3136

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 15thDay
20%30%29%15%31
120
16th to endDay
34%20%33%9%2
170
February1st to 15thDay
35%28%32%2
180
16th to endDay
37%21%31%6%2
232
March1st to 15thDay
29%15%30%19%5%
390
16th to endDay
23%19%32%15%7%1
416
April1st to 15thDay
33%19%28%10%7%1
390
16th to endDay
26%19%28%13%8%4
379
May1st to 15thDay
30%11%29%16%7%4
408
16th to endDay
15%17%38%15%9%2
459
June1st to 15thDay
23%10%34%21%9%1
379
16th to endDay
21%11%31%21%12%2
375
July1st to 15thDay
12%7%26%28%19%5%
365
16th to endDay
13%6%36%24%13%5%
390
August1st to 15thDay
11%6%28%29%15%8%
358
16th to endDay
14%6%24%26%15%12%
396
September1st to 15thDay
13%9%26%21%14%13%
375
16th to endDay
17%9%24%23%15%10%
374
October1st to 15thDay
26%13%29%17%9%4
375
16th to endDay
28%18%28%20%3
389
November1st to 15thDay
31%10%25%23%7%
216
16th to endDay
31%20%30%12%3
120
December1st to 15thDay
25%20%30%17%5%
120
16th to endDay
34%23%35%41
128
January1st to 15thNight
29%18%29%16%5%
840
16th to endNight
23%18%33%20%3
896
February1st to 15thNight
24%20%36%15%2
824
16th to endNight
22%17%35%19%4
735
March1st to 15thNight
26%16%32%21%3
840
16th to endNight
18%14%33%22%8%1
896
April1st to 15thNight
26%15%31%20%5%
838
16th to endNight
22%13%28%23%11%
729
May1st to 15thNight
22%6%29%26%12%1
466
16th to endNight
13%6%37%30%11%
439
June1st to 15thNight
17%7%31%30%13%
392
16th to endNight
14%5%30%36%12%
390
July1st to 15thNight
7%328%40%20%1
370
16th to endNight
10%32%37%18%
408
August1st to 15thNight
12%222%36%22%2
573
16th to endNight
9%427%31%24%2
731
September1st to 15thNight
15%427%27%21%3
780
16th to endNight
16%8%20%25%23%4
777
October1st to 15thNight
23%10%27%23%13%2
780
16th to endNight
27%14%30%21%6%
832
November1st to 15thNight
25%11%28%22%9%1
820
16th to endNight
29%17%25%20%7%
840
December1st to 15thNight
30%17%30%18%2
840
16th to endNight
30%14%35%17%2
896
Page generated at 2019-06-02 19:43:05. Version ac04

Copyright 2019 A. Danko


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