Robert Clyde Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert Clyde Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
61%
16059
20%
47026
16%
16019
66%
16019
30%
29759

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
51%
717
19%
2327
15%
716
59%
716
27%
1423
January16th to endNight
49%
768
25%
2439
19%
768
58%
768
30%
1450
February1st to 15thNight
49%
701
24%
2103
17%
698
57%
698
33%
1279
February16th to endNight
51%
631
28%
1803
17%
631
61%
631
39%
1016
March1st to 15thNight
55%
720
31%
1980
18%
720
65%
720
43%
1104
March16th to endNight
59%
768
27%
2112
21%
768
64%
768
43%
1184
April1st to 15thNight
63%
718
23%
1976
19%
718
67%
718
44%
1090
April16th to endNight
60%
720
28%
1842
17%
720
66%
720
44%
1077
May1st to 15thNight
68%
627
27%
1707
19%
627
72%
627
42%
992
May16th to endNight
77%
561
20%
1682
17%
561
79%
561
34%
1035
June1st to 15thNight
70%
540
9%
1620
8%
540
70%
540
20%
1182
June16th to endNight
70%
540
7%
1620
7%
540
70%
540
21%
1205
July1st to 15thNight
72%
510
6%
1530
6%
510
72%
510
20%
1170
July16th to endNight
75%
564
6%
1595
7%
531
75%
531
21%
1183
August1st to 15thNight
76%
539
6%
1609
5%
536
76%
536
24%
1110
August16th to endNight
63%
750
6%
2076
5%
750
63%
750
18%
1565
September1st to 15thNight
62%
720
5%
1980
5%
720
62%
720
17%
1505
September16th to endNight
59%
693
11%
1914
11%
693
59%
693
18%
1411
October1st to 15thNight
67%
660
23%
1884
24%
660
69%
660
32%
1180
October16th to endNight
61%
704
25%
2112
24%
704
66%
704
32%
1280
November1st to 15thNight
63%
700
31%
2101
28%
700
69%
700
38%
1171
November16th to endNight
56%
720
31%
2178
26%
720
64%
720
34%
1275
December1st to 15thNight
57%
720
26%
2340
25%
720
63%
720
29%
1411
December16th to endNight
59%
768
23%
2496
22%
768
64%
768
31%
1461

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%5%36%7%46%6%6%8%35%
47883
Night
7%425%5%35%5%6%9%43%
47235
TransparencyDay
44%7%14%16%12%5%
47584
Night
35%8%16%20%14%5%
47038
SeeingDay
9%210%20%25%31%
5897
Night
8%215%33%29%10%
16068

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
10%6%25%5%36%5%7%9%36%
1611
16th to endDay
9%4245%25%46%8%44%
1782
February1st to 15thDay
10%5%25%5%345%47%45%
1750
16th to endDay
6%5%25%5%35%5%6%7%46%
1667
March1st to 15thDay
43145%446%5%8%51%
1980
16th to endDay
7%3245%35%5%5%8%48%
2111
April1st to 15thDay
5%425%7%46%6%7%8%43%
1972
16th to endDay
5%5%246%46%6%6%8%44%
2118
May1st to 15thDay
4425%6%36%5%5%8%46%
2252
16th to endDay
7%5%37%9%5%7%5%7%8%32%
2431
June1st to 15thDay
11%9%5%9%8%6%7%6%7%7%20%
2340
16th to endDay
9%7%48%10%5%8%7%7%10%21%
2340
July1st to 15thDay
10%6%410%9%6%8%8%6%8%19%
2340
16th to endDay
8%5%410%9%6%9%8%6%9%20%
2465
August1st to 15thDay
7%5%48%8%5%9%7%8%11%22%
2340
16th to endDay
12%8%37%9%5%7%8%7%8%20%
2108
September1st to 15thDay
8%6%49%11%5%8%6%7%9%23%
1980
16th to endDay
12%8%49%8%5%7%7%7%9%20%
1905
October1st to 15thDay
8%5%26%7%46%7%6%8%36%
1746
16th to endDay
9%5%25%6%36%5%6%8%41%
1760
November1st to 15thDay
5%436%5%35%5%5%8%45%
1757
16th to endDay
7%435%5%35%6%5%7%44%
1780
December1st to 15thDay
10%5%35%6%45%5%5%7%40%
1620
16th to endDay
6%425%6%35%5%6%7%45%
1728
January1st to 15thNight
8%5%26%6%35%5%6%9%40%
2327
16th to endNight
10%5%24335%5%6%8%44%
2439
February1st to 15thNight
10%5%245%24448%46%
2103
16th to endNight
5%32442446%8%52%
1803
March1st to 15thNight
422443445%8%56%
1980
16th to endNight
432431445%7%55%
2112
April1st to 15thNight
322432445%9%55%
1976
16th to endNight
5%31433445%8%54%
1842
May1st to 15thNight
4314425%448%55%
1707
16th to endNight
6%214436%6%7%10%44%
1682
June1st to 15thNight
8%6%37%7%47%7%8%12%26%
1620
16th to endNight
7%5%37%8%47%6%7%10%30%
1620
July1st to 15thNight
8%6%36%7%47%6%8%11%29%
1620
16th to endNight
5%5%37%7%5%8%7%8%12%28%
1703
August1st to 15thNight
5%5%25%6%36%6%9%12%34%
1620
16th to endNight
11%5%36%6%36%6%8%12%29%
2076
September1st to 15thNight
8%5%38%7%47%8%7%11%26%
1980
16th to endNight
9%7%38%7%46%6%8%9%28%
1914
October1st to 15thNight
8%5%245%445%6%8%44%
1884
16th to endNight
9%6%2442345%7%47%
2112
November1st to 15thNight
5%4245%24448%52%
2101
16th to endNight
7%4245%2446%9%48%
2178
December1st to 15thNight
8%5%35%425%5%5%7%46%
2340
16th to endNight
5%5%245%36%5%6%8%45%
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
40%6%9%19%19%4
1612
16th to endDay
36%47%21%21%9%
1782
February1st to 15thDay
37%37%17%20%13%
1752
16th to endDay
34%5%9%18%20%11%
1667
March1st to 15thDay
29%5%10%25%20%8%
1980
16th to endDay
33%5%9%21%21%8%
2112
April1st to 15thDay
35%6%13%20%19%5%
1972
16th to endDay
35%6%10%16%22%7%
2118
May1st to 15thDay
34%5%11%19%20%7%
2252
16th to endDay
46%7%12%19%12%1
2435
June1st to 15thDay
58%7%16%13%3
2340
16th to endDay
55%10%19%12%2
2340
July1st to 15thDay
60%10%19%7%1
2201
16th to endDay
56%11%20%10%1
2310
August1st to 15thDay
49%12%27%9%
2327
16th to endDay
56%13%20%7%1
2108
September1st to 15thDay
54%11%21%9%2
1980
16th to endDay
57%11%16%9%31
1905
October1st to 15thDay
42%7%11%16%15%6%
1746
16th to endDay
40%49%14%21%10%
1760
November1st to 15thDay
35%38%21%20%10%
1757
16th to endDay
37%5%9%18%16%12%
1780
December1st to 15thDay
42%5%12%17%16%5%
1620
16th to endDay
34%5%12%21%17%7%
1728
January1st to 15thNight
37%5%13%22%15%5%
2327
16th to endNight
35%5%9%24%17%7%
2439
February1st to 15thNight
35%47%18%20%12%
2112
16th to endNight
27%5%13%23%21%8%
1803
March1st to 15thNight
25%410%31%20%7%
1980
16th to endNight
26%5%13%25%20%8%
2112
April1st to 15thNight
24%5%16%26%19%6%
1976
16th to endNight
26%5%13%24%23%6%
1842
May1st to 15thNight
26%6%12%27%19%6%
1708
16th to endNight
30%9%18%23%16%
1684
June1st to 15thNight
46%11%22%15%4
1620
16th to endNight
44%13%23%13%4
1620
July1st to 15thNight
45%15%25%11%2
1530
16th to endNight
43%15%28%12%
1595
August1st to 15thNight
37%15%37%9%
1609
16th to endNight
44%16%27%9%1
2076
September1st to 15thNight
47%15%23%10%2
1980
16th to endNight
47%12%18%16%4
1914
October1st to 15thNight
35%6%14%18%19%4
1884
16th to endNight
35%5%10%15%22%9%
2112
November1st to 15thNight
30%39%25%22%8%
2101
16th to endNight
32%5%7%24%18%11%
2178
December1st to 15thNight
36%5%10%25%14%6%
2340
16th to endNight
33%6%14%21%17%7%
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
17%436%21%13%6%
90
16th to endDay
12%11%32%23%16%3
96
February1st to 15thDay
8%10%24%30%17%8%
90
16th to endDay
11%426%38%17%
168
March1st to 15thDay
5%324%37%24%4
270
16th to endDay
7%321%28%31%7%
288
April1st to 15thDay
3220%33%30%9%
270
16th to endDay
6%311%31%26%20%
270
May1st to 15thDay
5%19%22%36%24%
288
16th to endDay
5%17%17%32%36%
331
June1st to 15thDay
17%16%10%20%43%
315
16th to endDay
7%116%20%61%
315
July1st to 15thDay
6%417%70%
305
16th to endDay
9%119%17%60%
326
August1st to 15thDay
7%16%19%63%
313
16th to endDay
12%119%19%55%
332
September1st to 15thDay
11%329%21%51%
315
16th to endDay
12%8%34%43%
287
October1st to 15thDay
10%15%28%34%18%
255
16th to endDay
11%117%23%32%12%
272
November1st to 15thDay
8%111%33%30%14%
265
16th to endDay
8%218%35%30%5%
250
December1st to 15thDay
8%231%42%14%1
90
16th to endDay
4313%35%36%7%
96
January1st to 15thNight
10%5%22%40%20%1
720
16th to endNight
11%5%27%40%14%
768
February1st to 15thNight
12%426%42%13%
704
16th to endNight
7%328%45%13%
631
March1st to 15thNight
5%429%43%16%1
720
16th to endNight
6%224%46%19%
768
April1st to 15thNight
3322%47%21%1
718
16th to endNight
7%221%43%24%
720
May1st to 15thNight
6%114%47%27%2
628
16th to endNight
6%6%36%41%7%
563
June1st to 15thNight
10%322%48%15%
540
16th to endNight
7%1212%46%31%
540
July1st to 15thNight
8%16%48%34%
510
16th to endNight
6%17%43%39%
564
August1st to 15thNight
6%16%45%39%
539
16th to endNight
12%2314%35%30%
750
September1st to 15thNight
9%1314%40%28%
720
16th to endNight
11%2320%45%17%
693
October1st to 15thNight
11%15%35%37%7%
660
16th to endNight
13%114%35%30%4
704
November1st to 15thNight
6%118%43%27%3
700
16th to endNight
9%122%42%21%1
720
December1st to 15thNight
10%318%39%25%1
720
16th to endNight
6%321%38%27%2
768
Page generated at 2017-09-25 09:02:28. Version ac04

Copyright 2017 A. Danko


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