Pleiades Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pleiades Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
42%
16088
21%
47390
13%
16041
49%
16041
28%
29723

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
27%
900
18%
2485
8%
895
36%
895
25%
1651
January16th to endNight
24%
960
18%
2496
6%
960
32%
960
24%
1735
February1st to 15thNight
26%
880
13%
2288
4%
876
31%
876
22%
1639
February16th to endNight
28%
645
23%
1907
8%
645
39%
645
27%
1190
March1st to 15thNight
30%
613
19%
2053
11%
613
40%
613
22%
1314
March16th to endNight
28%
576
13%
2064
9%
576
35%
576
17%
1435
April1st to 15thNight
33%
539
19%
1797
12%
539
44%
539
26%
1075
April16th to endNight
38%
540
20%
1800
15%
540
48%
540
24%
1166
May1st to 15thNight
43%
539
19%
1580
14%
539
49%
539
25%
1046
May16th to endNight
48%
563
20%
1497
12%
561
54%
561
31%
973
June1st to 15thNight
62%
540
19%
1440
11%
540
65%
540
41%
837
June16th to endNight
58%
540
20%
1440
11%
540
62%
540
38%
892
July1st to 15thNight
68%
510
19%
1360
14%
510
70%
510
39%
820
July16th to endNight
74%
564
24%
1502
22%
531
76%
531
47%
810
August1st to 15thNight
76%
539
24%
1610
25%
536
77%
536
42%
856
August16th to endNight
75%
573
23%
1907
26%
573
78%
573
39%
1001
September1st to 15thNight
64%
540
29%
1800
30%
540
68%
540
37%
964
September16th to endNight
62%
627
30%
1950
22%
627
69%
627
38%
1051
October1st to 15thNight
48%
720
27%
2160
19%
720
54%
720
36%
1234
October16th to endNight
39%
768
27%
2304
16%
768
49%
768
31%
1360
November1st to 15thNight
39%
700
27%
2270
16%
700
52%
700
31%
1287
November16th to endNight
30%
852
20%
2472
11%
852
39%
852
27%
1601
December1st to 15thNight
27%
900
15%
2520
6%
900
35%
900
21%
1777
December16th to endNight
24%
960
15%
2688
5%
960
32%
960
17%
2009

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
12%6%35%5%3445%7%40%
48365
Night
12%6%35%424446%44%
47572
TransparencyDay
42%312%24%14%2
48051
Night
40%312%25%16%2
47392
SeeingDay
13%5%22%30%20%7%
6087
Night
16%7%27%32%14%1
16089

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%10%5%8%5%25%446%34%
1453
16th to endDay
15%12%5%8%5%3334432%
1728
February1st to 15thDay
14%9%46%5%35%46%6%33%
1575
16th to endDay
12%9%47%5%3445%6%36%
1564
March1st to 15thDay
13%9%5%6%6%3445%5%35%
1917
16th to endDay
16%9%46%5%35%446%34%
2157
April1st to 15thDay
16%9%36%5%24335%40%
2151
16th to endDay
20%7%26%42445%6%34%
2160
May1st to 15thDay
18%7%25%5%445%5%7%32%
2367
16th to endDay
14%6%35%5%445%5%7%37%
2617
June1st to 15thDay
7%436%5%35%6%6%10%39%
2520
16th to endDay
7%425%5%45%6%5%8%43%
2520
July1st to 15thDay
6%325%5%25%5%6%9%45%
2520
16th to endDay
6%3145%35%5%7%10%46%
2560
August1st to 15thDay
7%425%5%35%5%7%9%44%
2340
16th to endDay
9%4245%245%5%9%46%
2293
September1st to 15thDay
11%424424447%49%
2160
16th to endDay
8%4244235%6%7%50%
1995
October1st to 15thDay
15%6%25%423335%48%
1800
16th to endDay
14%6%25%313345%48%
1919
November1st to 15thDay
14%6%24323436%46%
1588
16th to endDay
15%9%5%6%423336%38%
1485
December1st to 15thDay
19%11%36%5%24345%32%
1440
16th to endDay
18%11%6%6%4235%35%31%
1536
January1st to 15thNight
12%9%36%5%33346%40%
2485
16th to endNight
11%10%5%8%5%34346%37%
2496
February1st to 15thNight
15%10%46%5%34446%35%
2278
16th to endNight
14%7%35%42234446%
1907
March1st to 15thNight
16%8%245%24335%42%
2053
16th to endNight
17%9%46%5%25%46%6%31%
2064
April1st to 15thNight
14%6%2442435%5%45%
1797
16th to endNight
17%6%35%444445%39%
1800
May1st to 15thNight
15%6%35%5%3345%7%39%
1580
16th to endNight
8%5%35%6%445%5%8%43%
1496
June1st to 15thNight
7%315%32445%9%51%
1440
16th to endNight
6%4145%35%5%7%8%45%
1440
July1st to 15thNight
6%4134345%5%8%51%
1440
16th to endNight
442233446%10%52%
1605
August1st to 15thNight
42135%35%45%9%54%
1620
16th to endNight
7%313424447%56%
1907
September1st to 15thNight
10%32441335%6%54%
1800
16th to endNight
6%3144335%5%6%54%
1950
October1st to 15thNight
11%414423446%52%
2160
16th to endNight
13%5%24323435%50%
2304
November1st to 15thNight
12%5%24322335%53%
2270
16th to endNight
17%7%24324445%43%
2472
December1st to 15thNight
19%9%46%5%23445%35%
2520
16th to endNight
21%11%5%7%5%2334430%
2688

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
49%311%22%12%
1454
16th to endDay
53%215%19%8%
1728
February1st to 15thDay
50%315%22%7%
1576
16th to endDay
47%313%22%12%
1564
March1st to 15thDay
50%413%22%8%1
1917
16th to endDay
52%313%20%8%1
2159
April1st to 15thDay
47%210%24%13%1
2151
16th to endDay
50%211%20%13%1
2160
May1st to 15thDay
49%411%24%8%
2367
16th to endDay
43%5%13%21%13%1
2621
June1st to 15thDay
37%5%13%25%14%2
2520
16th to endDay
35%5%14%25%16%2
2520
July1st to 15thDay
34%5%15%28%13%3
2371
16th to endDay
32%414%29%17%
2401
August1st to 15thDay
34%5%14%27%16%1
2326
16th to endDay
34%5%12%23%18%5%
2293
September1st to 15thDay
34%38%28%18%6%
2160
16th to endDay
31%311%32%18%2
1995
October1st to 15thDay
39%28%24%22%3
1800
16th to endDay
38%210%27%17%2
1919
November1st to 15thDay
40%19%23%21%3
1588
16th to endDay
48%212%25%9%1
1485
December1st to 15thDay
53%214%20%8%
1440
16th to endDay
53%213%18%9%1
1536
January1st to 15thNight
44%212%24%14%
2485
16th to endNight
47%215%21%11%
2496
February1st to 15thNight
51%212%22%10%1
2288
16th to endNight
40%312%27%14%1
1907
March1st to 15thNight
45%211%25%12%2
2053
16th to endNight
52%413%20%8%
2064
April1st to 15thNight
39%311%25%16%3
1797
16th to endNight
45%29%23%15%3
1800
May1st to 15thNight
43%5%12%23%15%
1581
16th to endNight
38%5%13%19%20%2
1498
June1st to 15thNight
29%416%29%17%2
1440
16th to endNight
34%412%24%20%3
1440
July1st to 15thNight
31%5%10%30%18%4
1360
16th to endNight
24%416%33%19%2
1502
August1st to 15thNight
26%313%33%19%2
1610
16th to endNight
27%413%25%22%6%
1907
September1st to 15thNight
31%29%25%25%6%
1800
16th to endNight
28%310%30%22%2
1950
October1st to 15thNight
32%210%25%22%5%
2160
16th to endNight
36%28%28%20%3
2304
November1st to 15thNight
34%211%24%20%5%
2270
16th to endNight
43%210%28%14%
2472
December1st to 15thNight
51%213%22%9%
2520
16th to endNight
57%210%17%9%1
2688

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
23%11%41%21%3
90
16th to endDay
16%14%38%22%7%
96
February1st to 15thDay
12%13%43%22%8%
90
16th to endDay
13%17%30%24%11%2
81
March1st to 15thDay
20%8%51%16%3
90
16th to endDay
25%12%30%21%9%
143
April1st to 15thDay
18%10%31%25%11%2
270
16th to endDay
22%227%30%12%2
270
May1st to 15thDay
17%10%30%25%12%2
423
16th to endDay
19%7%26%27%14%5%
517
June1st to 15thDay
7%320%38%20%9%
495
16th to endDay
10%5%25%33%19%6%
495
July1st to 15thDay
9%118%37%23%9%
475
16th to endDay
6%112%36%34%9%
515
August1st to 15thDay
7%17%39%32%10%
493
16th to endDay
9%110%27%37%14%
333
September1st to 15thDay
11%112%31%30%12%
315
16th to endDay
9%315%29%28%11%
251
October1st to 15thDay
19%6%25%27%13%7%
135
16th to endDay
15%7%37%25%11%1
144
November1st to 15thDay
5%426%30%20%13%
90
16th to endDay
38%16%21%11%12%
90
December1st to 15thDay
20%15%30%25%44
90
16th to endDay
29%16%41%10%2
96
January1st to 15thNight
16%11%38%25%7%
900
16th to endNight
16%11%40%27%4
960
February1st to 15thNight
19%10%37%27%4
880
16th to endNight
19%10%36%28%4
645
March1st to 15thNight
20%10%34%27%6%
613
16th to endNight
21%9%31%29%7%
576
April1st to 15thNight
16%11%34%29%7%
539
16th to endNight
19%5%30%33%10%
540
May1st to 15thNight
17%5%25%38%12%1
540
16th to endNight
11%327%37%17%2
563
June1st to 15thNight
8%217%47%22%1
540
16th to endNight
9%223%41%21%1
540
July1st to 15thNight
10%111%42%31%2
510
16th to endNight
7%17%40%38%3
564
August1st to 15thNight
5%16%44%37%4
539
16th to endNight
8%19%38%37%5%
573
September1st to 15thNight
12%212%37%30%5%
540
16th to endNight
8%317%36%27%6%
627
October1st to 15thNight
14%426%30%21%2
720
16th to endNight
18%7%32%31%10%
768
November1st to 15thNight
15%8%31%32%11%1
700
16th to endNight
21%8%35%25%8%
852
December1st to 15thNight
24%8%32%27%5%
900
16th to endNight
25%10%30%27%5%
960
Page generated at 2017-11-01 16:23:40. Version ac04

Copyright 2017 A. Danko


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