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 2005-11-05 to 2017-10-06.

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
64%
16349
16%
47143
14%
16312
67%
16312
26%
31528

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
55%
716
15%
2327
12%
716
61%
716
22%
1525
January16th to endNight
55%
768
22%
2487
19%
768
62%
768
28%
1508
February1st to 15thNight
55%
701
24%
2092
21%
700
61%
700
33%
1250
February16th to endNight
61%
631
26%
1735
20%
631
67%
631
36%
1045
March1st to 15thNight
59%
720
24%
1980
17%
720
65%
720
37%
1190
March16th to endNight
64%
768
23%
2112
20%
768
67%
768
37%
1272
April1st to 15thNight
74%
718
23%
1967
20%
718
76%
718
43%
1103
April16th to endNight
66%
720
21%
1800
13%
720
69%
720
36%
1137
May1st to 15thNight
75%
719
23%
1799
15%
719
77%
719
44%
1065
May16th to endNight
68%
617
14%
1739
11%
617
68%
617
25%
1214
June1st to 15thNight
64%
540
9%
1620
8%
540
64%
540
16%
1236
June16th to endNight
79%
540
9%
1620
8%
540
79%
540
21%
1147
July1st to 15thNight
70%
510
5%
1530
6%
510
70%
510
16%
1150
July16th to endNight
79%
564
9%
1595
9%
531
79%
531
26%
1068
August1st to 15thNight
76%
620
7%
1690
7%
617
76%
617
27%
1160
August16th to endNight
68%
764
6%
1992
5%
764
68%
764
19%
1520
September1st to 15thNight
66%
720
4%
1980
4%
720
66%
720
15%
1552
September16th to endNight
61%
717
6%
1980
6%
717
61%
717
13%
1618
October1st to 15thNight
66%
684
14%
1996
16%
684
66%
684
21%
1440
October16th to endNight
54%
704
16%
2112
17%
704
56%
704
21%
1482
November1st to 15thNight
62%
700
21%
2101
21%
700
66%
700
30%
1320
November16th to endNight
53%
720
19%
2160
17%
720
58%
720
23%
1486
December1st to 15thNight
56%
720
18%
2233
17%
720
59%
720
22%
1499
December16th to endNight
63%
768
20%
2496
21%
768
67%
768
26%
1541

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%47%7%8%10%27%
48040
Night
7%425%5%36%6%7%10%38%
47345
TransparencyDay
44%13%15%14%9%2
47741
Night
37%11%18%18%10%2
47147
SeeingDay
9%110%22%29%26%
6158
Night
9%112%29%32%14%
16359

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 15thDay
11%6%37%6%45%7%7%9%30%
1611
16th to endDay
8%6%36%6%46%6%7%8%35%
1734
February1st to 15thDay
10%7%35%5%35%46%10%36%
1765
16th to endDay
7%5%25%6%35%5%6%8%42%
1738
March1st to 15thDay
5%426%7%36%6%8%11%36%
1980
16th to endDay
6%426%7%46%6%7%10%36%
2111
April1st to 15thDay
6%5%25%5%36%7%8%12%36%
1978
16th to endDay
7%5%25%7%38%6%7%11%35%
2160
May1st to 15thDay
4316%5%47%7%7%10%41%
2152
16th to endDay
9%7%38%8%5%7%9%6%10%23%
2384
June1st to 15thDay
12%8%49%9%6%9%8%8%8%15%
2340
16th to endDay
8%6%39%8%5%9%9%9%10%18%
2340
July1st to 15thDay
8%6%48%7%5%9%9%10%11%17%
2340
16th to endDay
6%5%38%9%48%8%10%11%20%
2465
August1st to 15thDay
7%6%38%8%48%9%9%13%19%
2247
16th to endDay
9%6%38%8%5%8%9%9%11%18%
2205
September1st to 15thDay
8%7%38%9%7%10%9%9%9%15%
1980
16th to endDay
12%10%410%10%6%7%8%7%7%13%
1980
October1st to 15thDay
8%7%38%8%6%8%7%9%10%20%
1761
16th to endDay
14%6%38%7%46%6%6%8%26%
1760
November1st to 15thDay
8%6%36%6%5%6%6%8%7%34%
1757
16th to endDay
10%5%38%7%48%6%6%6%32%
1800
December1st to 15thDay
9%8%47%7%46%5%6%7%31%
1724
16th to endDay
7%5%36%6%46%7%6%11%34%
1728
January1st to 15thNight
9%5%36%5%36%6%8%10%35%
2327
16th to endNight
6%325%5%26%6%6%10%43%
2487
February1st to 15thNight
9%42442346%8%47%
2086
16th to endNight
43235%25%5%6%9%50%
1735
March1st to 15thNight
5%424335%5%7%9%49%
1980
16th to endNight
5%3145%345%5%10%48%
2112
April1st to 15thNight
32134235%6%11%54%
1967
16th to endNight
5%4244247%7%9%46%
1800
May1st to 15thNight
3314315%5%6%10%54%
1799
16th to endNight
7%5%36%5%46%6%7%12%33%
1738
June1st to 15thNight
11%5%36%8%46%9%9%10%24%
1620
16th to endNight
5%4246%5%7%8%9%14%31%
1620
July1st to 15thNight
5%5%48%6%47%6%8%10%31%
1620
16th to endNight
3335%6%47%6%7%12%39%
1703
August1st to 15thNight
5%3145%37%7%8%13%38%
1701
16th to endNight
7%5%26%6%47%8%9%12%29%
1992
September1st to 15thNight
6%6%37%7%5%7%9%10%12%23%
1980
16th to endNight
9%6%28%9%6%7%9%9%10%21%
1980
October1st to 15thNight
7%5%36%7%48%7%8%12%28%
1996
16th to endNight
14%7%26%5%446%6%8%33%
2112
November1st to 15thNight
6%5%25%5%35%5%6%10%42%
2101
16th to endNight
9%6%35%5%36%5%5%9%37%
2160
December1st to 15thNight
8%5%25%6%36%6%7%10%36%
2233
16th to endNight
6%424436%6%7%9%44%
2496

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
44%10%13%14%12%4
1612
16th to endDay
42%7%10%18%14%5%
1734
February1st to 15thDay
39%7%10%21%16%5%
1767
16th to endDay
35%7%14%21%15%5%
1738
March1st to 15thDay
36%8%15%22%13%2
1980
16th to endDay
35%10%14%20%14%5%
2112
April1st to 15thDay
33%9%17%21%15%2
1978
16th to endDay
37%10%11%19%17%3
2160
May1st to 15thDay
32%9%14%23%14%5%
2152
16th to endDay
47%14%14%17%6%
2388
June1st to 15thDay
57%15%12%10%3
2340
16th to endDay
49%19%19%10%
2340
July1st to 15thDay
50%20%21%8%
2201
16th to endDay
45%20%23%10%
2310
August1st to 15thDay
45%19%23%10%1
2234
16th to endDay
51%18%20%9%
2205
September1st to 15thDay
53%21%17%6%1
1980
16th to endDay
61%17%11%6%3
1980
October1st to 15thDay
50%13%14%12%7%1
1761
16th to endDay
50%8%10%13%13%4
1760
November1st to 15thDay
41%8%12%15%16%4
1757
16th to endDay
47%7%10%11%16%6%
1800
December1st to 15thDay
45%9%12%15%13%2
1724
16th to endDay
39%8%14%18%15%3
1728
January1st to 15thNight
40%9%15%20%11%2
2327
16th to endNight
33%8%15%22%13%5%
2487
February1st to 15thNight
34%5%11%26%16%6%
2094
16th to endNight
29%8%15%25%16%5%
1735
March1st to 15thNight
29%7%15%23%18%4
1980
16th to endNight
30%7%16%25%16%4
2112
April1st to 15thNight
22%8%19%30%15%2
1967
16th to endNight
30%9%16%20%18%4
1800
May1st to 15thNight
25%7%14%32%15%5%
1800
16th to endNight
40%11%18%23%6%
1740
June1st to 15thNight
48%15%18%13%4
1620
16th to endNight
39%16%29%13%1
1620
July1st to 15thNight
44%17%25%11%
1530
16th to endNight
32%17%33%15%1
1595
August1st to 15thNight
33%16%31%17%1
1690
16th to endNight
41%19%25%11%1
1992
September1st to 15thNight
47%19%22%9%1
1980
16th to endNight
52%18%16%9%3
1980
October1st to 15thNight
44%12%16%15%9%1
1996
16th to endNight
48%6%12%16%11%3
2112
November1st to 15thNight
37%5%15%17%18%5%
2101
16th to endNight
45%7%11%13%15%6%
2160
December1st to 15thNight
40%10%13%16%15%2
2233
16th to endNight
35%9%12%21%17%3
2496

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
21%324%28%22%
90
16th to endDay
14%8%21%36%12%6%
96
February1st to 15thDay
9%118%41%21%6%
106
16th to endDay
9%223%39%23%1
239
March1st to 15thDay
5%124%42%22%3
270
16th to endDay
6%120%38%27%5%
288
April1st to 15thDay
4117%35%31%9%
270
16th to endDay
6%11%36%36%8%
270
May1st to 15thDay
317%29%42%15%
288
16th to endDay
8%15%16%36%31%
331
June1st to 15thDay
12%6%13%33%33%
315
16th to endDay
3137%27%56%
315
July1st to 15thDay
6%1329%58%
305
16th to endDay
416%28%57%
326
August1st to 15thDay
7%27%29%52%
313
16th to endDay
13%5%9%23%48%
332
September1st to 15thDay
9%310%24%51%
315
16th to endDay
12%213%28%42%
314
October1st to 15thDay
12%16%25%37%16%
278
16th to endDay
15%213%29%24%13%
272
November1st to 15thDay
12%110%32%30%12%
265
16th to endDay
10%122%35%30%
270
December1st to 15thDay
19%314%28%29%4
194
16th to endDay
10%37%28%41%9%
96
January1st to 15thNight
11%418%36%26%3
720
16th to endNight
8%323%40%22%1
768
February1st to 15thNight
10%322%41%20%1
704
16th to endNight
6%123%45%22%
631
March1st to 15thNight
6%225%38%23%2
720
16th to endNight
6%119%45%25%1
768
April1st to 15thNight
412%46%32%3
718
16th to endNight
8%14%44%29%1
720
May1st to 15thNight
5%18%41%38%3
720
16th to endNight
9%9%26%39%13%
619
June1st to 15thNight
10%15%16%41%24%
540
16th to endNight
5%210%41%40%
540
July1st to 15thNight
7%17%41%40%
510
16th to endNight
416%35%51%
564
August1st to 15thNight
8%16%45%38%
620
16th to endNight
10%39%36%38%
764
September1st to 15thNight
8%5%11%34%39%
720
16th to endNight
14%313%34%34%
717
October1st to 15thNight
11%17%26%41%13%
684
16th to endNight
19%112%27%29%10%
704
November1st to 15thNight
10%116%33%31%6%
700
16th to endNight
14%119%34%26%3
720
December1st to 15thNight
11%318%35%27%2
720
16th to endNight
8%218%30%34%5%
768
Page generated at 2017-10-07 14:07:50. Version ac04

Copyright 2017 A. Danko


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