Young's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Young's Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
77%
15603
36%
46922
32%
15564
81%
15564
55%
22206

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
69%
719
32%
2327
32%
716
74%
716
47%
1123
January16th to endNight
65%
768
35%
2496
33%
768
73%
768
42%
1264
February1st to 15thNight
70%
700
35%
2202
33%
700
78%
700
52%
1033
February16th to endNight
67%
632
36%
1860
35%
632
72%
632
48%
955
March1st to 15thNight
69%
720
39%
1980
32%
720
76%
720
58%
973
March16th to endNight
77%
768
38%
2112
30%
768
82%
768
63%
988
April1st to 15thNight
72%
692
34%
1951
26%
692
78%
692
58%
938
April16th to endNight
75%
540
45%
1737
40%
540
83%
540
72%
658
May1st to 15thNight
78%
539
40%
1619
34%
539
83%
539
69%
675
May16th to endNight
82%
561
40%
1684
33%
561
85%
561
73%
679
June1st to 15thNight
87%
540
35%
1620
31%
540
88%
540
71%
661
June16th to endNight
91%
540
34%
1620
31%
540
91%
540
71%
670
July1st to 15thNight
84%
510
23%
1530
20%
510
84%
510
45%
803
July16th to endNight
81%
564
24%
1593
20%
531
81%
531
37%
910
August1st to 15thNight
86%
539
28%
1611
25%
536
86%
536
44%
838
August16th to endNight
84%
612
31%
1862
30%
612
84%
612
43%
1002
September1st to 15thNight
80%
720
31%
1980
27%
720
81%
720
49%
1069
September16th to endNight
83%
667
42%
1847
34%
667
86%
667
66%
849
October1st to 15thNight
77%
660
40%
1906
34%
660
82%
660
63%
869
October16th to endNight
85%
704
44%
2112
39%
704
89%
704
70%
880
November1st to 15thNight
79%
700
42%
2100
37%
700
84%
700
65%
903
November16th to endNight
74%
720
39%
2337
37%
720
80%
720
55%
1047
December1st to 15thNight
71%
720
37%
2340
38%
720
75%
720
48%
1125
December16th to endNight
68%
768
35%
2496
35%
768
72%
768
41%
1294

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
3212213346%68%
47869
Night
4212213346%67%
47118
TransparencyDay
17%25%12%24%37%
47564
Night
18%25%12%23%37%
46924
SeeingDay
5%417%34%29%9%
5425
Night
5%111%39%36%5%
15611

By Month

Percentage Cloud Cover SW (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
6%31231333466%
1611
16th to endDay
8%312213246%63%
1728
February1st to 15thDay
4313212245%67%
1659
16th to endDay
8%413223336%61%
1612
March1st to 15thDay
5%212212245%67%
1980
16th to endDay
3212213235%70%
2112
April1st to 15thDay
212312236%72%
1997
16th to endDay
21111122481%
2220
May1st to 15thDay
11112235%78%
2331
16th to endDay
11111112282%
2429
June1st to 15thDay
11111222480%
2340
16th to endDay
11111223480%
2340
July1st to 15thDay
2213435%5%5%9%56%
2340
16th to endDay
4325%5%45%6%9%12%41%
2467
August1st to 15thDay
3224325%6%6%9%53%
2340
16th to endDay
2213425%5%6%8%56%
2336
September1st to 15thDay
421232435%7%62%
1980
16th to endDay
31111223477%
1838
October1st to 15thDay
212213245%73%
1722
16th to endDay
11212225%79%
1760
November1st to 15thDay
1111112236%76%
1759
16th to endDay
42321113472%
1620
December1st to 15thDay
7%32223436%63%
1620
16th to endDay
8%313313246%60%
1728
January1st to 15thNight
6%212313345%63%
2327
16th to endNight
9%31322334461%
2496
February1st to 15thNight
4312212236%67%
2191
16th to endNight
7%23322446%60%
1860
March1st to 15thNight
6%212212335%69%
1980
16th to endNight
3111212246%71%
2112
April1st to 15thNight
4112312345%69%
1951
16th to endNight
11111112283%
1737
May1st to 15thNight
111112235%77%
1619
16th to endNight
1111122382%
1684
June1st to 15thNight
1112111135%79%
1620
16th to endNight
1112235%80%
1620
July1st to 15thNight
22134246%7%10%55%
1620
16th to endNight
32235%447%8%13%43%
1701
August1st to 15thNight
13134246%7%9%54%
1620
16th to endNight
13135%27%6%6%8%53%
1862
September1st to 15thNight
321342445%9%58%
1980
16th to endNight
21221224474%
1847
October1st to 15thNight
311212235%74%
1906
16th to endNight
11111122479%
2112
November1st to 15thNight
2212211235%75%
2100
16th to endNight
421221223471%
2337
December1st to 15thNight
8%212212336%64%
2340
16th to endNight
9%323323335%58%
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
22%26%12%27%28%
1612
16th to endDay
23%25%15%24%29%
1728
February1st to 15thDay
19%25%16%25%30%
1659
16th to endDay
24%2315%28%25%
1612
March1st to 15thDay
18%227%31%37%
1980
16th to endDay
17%248%30%37%
2112
April1st to 15thDay
14%129%35%37%
1997
16th to endDay
9%29%23%53%
2220
May1st to 15thDay
10%138%24%52%
2331
16th to endDay
10%25%23%56%
2432
June1st to 15thDay
10%11416%66%
2340
16th to endDay
9%135%13%66%
2340
July1st to 15thDay
23%5%9%15%18%27%
2201
16th to endDay
31%7%17%22%14%6%
2312
August1st to 15thDay
25%5%10%17%16%23%
2325
16th to endDay
22%5%10%17%24%20%
2336
September1st to 15thDay
21%39%15%23%26%
1980
16th to endDay
12%136%28%47%
1838
October1st to 15thDay
14%2410%25%43%
1722
16th to endDay
10%148%26%48%
1760
November1st to 15thDay
10%1211%33%39%
1759
16th to endDay
17%1311%24%41%
1620
December1st to 15thDay
23%25%16%29%23%
1620
16th to endDay
26%25%19%29%16%
1728
January1st to 15thNight
22%2411%26%31%
2327
16th to endNight
26%25%11%25%28%
2496
February1st to 15thNight
20%15%14%24%32%
2202
16th to endNight
24%2414%26%27%
1860
March1st to 15thNight
17%238%26%42%
1980
16th to endNight
14%1410%32%36%
2112
April1st to 15thNight
17%128%32%36%
1951
16th to endNight
8%27%23%56%
1737
May1st to 15thNight
10%127%28%49%
1620
16th to endNight
9%127%18%61%
1685
June1st to 15thNight
10%2414%67%
1620
16th to endNight
9%13412%68%
1620
July1st to 15thNight
21%6%12%16%15%27%
1530
16th to endNight
27%7%16%21%19%6%
1593
August1st to 15thNight
22%6%13%19%13%25%
1611
16th to endNight
23%6%11%16%21%20%
1862
September1st to 15thNight
22%49%19%20%23%
1980
16th to endNight
12%237%26%47%
1847
October1st to 15thNight
14%2312%21%45%
1906
16th to endNight
10%139%22%51%
2112
November1st to 15thNight
13%1211%29%42%
2100
16th to endNight
18%1310%22%43%
2337
December1st to 15thNight
22%1414%29%27%
2340
16th to endNight
27%26%16%27%19%
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%221%37%17%
90
16th to endDay
11%315%39%19%10%
96
February1st to 15thDay
5%223%40%25%2
174
16th to endDay
12%6%26%37%16%
238
March1st to 15thDay
6%9%28%31%17%6%
270
16th to endDay
310%29%30%22%3
288
April1st to 15thDay
412%27%33%15%7%
269
16th to endDay
315%34%30%11%4
270
May1st to 15thDay
311%29%30%20%3
288
16th to endDay
15%28%35%24%3
330
June1st to 15thDay
4222%39%26%5%
315
16th to endDay
217%42%34%10%
315
July1st to 15thDay
46%36%38%13%
305
16th to endDay
5%327%38%24%
327
August1st to 15thDay
2329%46%19%
315
16th to endDay
1326%46%20%
332
September1st to 15thDay
7%27%35%34%12%
315
16th to endDay
7%114%40%29%5%
264
October1st to 15thDay
4414%32%36%7%
162
16th to endDay
5%434%45%10%
96
November1st to 15thDay
3415%40%26%10%
90
16th to endDay
10%320%44%22%
90
December1st to 15thDay
10%6%38%40%4
90
16th to endDay
21%223%31%19%1
96
January1st to 15thNight
7%115%51%20%3
720
16th to endNight
11%116%42%23%4
768
February1st to 15thNight
6%115%45%26%3
704
16th to endNight
8%118%47%21%2
632
March1st to 15thNight
5%218%41%27%4
720
16th to endNight
3113%42%33%4
768
April1st to 15thNight
4215%50%25%2
692
16th to endNight
2217%44%29%3
540
May1st to 15thNight
2215%45%31%4
540
16th to endNight
2111%42%36%4
563
June1st to 15thNight
115%45%44%1
540
16th to endNight
5%32%55%4
540
July1st to 15thNight
2425%59%7%
510
16th to endNight
4314%65%12%
564
August1st to 15thNight
2217%65%12%
539
16th to endNight
4220%62%10%
612
September1st to 15thNight
317%28%50%8%
720
16th to endNight
218%39%41%7%
667
October1st to 15thNight
4112%40%36%4
660
16th to endNight
28%41%37%8%
704
November1st to 15thNight
4111%44%32%5%
700
16th to endNight
5%15%44%29%3
720
December1st to 15thNight
9%112%43%31%2
720
16th to endNight
11%112%49%22%3
768
Page generated at 2017-09-19 04:32:26. Version ac04

Copyright 2017 A. Danko


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