Persephone Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Persephone 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
35%
15208
19%
47121
10%
15168
45%
15168
22%
30463

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
19%
717
16%
2422
7%
716
31%
716
12%
1704
January16th to endNight
16%
768
18%
2496
4%
768
32%
768
15%
1687
February1st to 15thNight
18%
704
15%
2287
4%
701
32%
701
14%
1559
February16th to endNight
18%
631
18%
1961
5%
631
34%
631
14%
1313
March1st to 15thNight
21%
720
19%
1980
7%
720
33%
720
18%
1369
March16th to endNight
23%
768
18%
2107
7%
768
32%
768
21%
1406
April1st to 15thNight
21%
718
15%
1796
5%
718
27%
718
20%
1296
April16th to endNight
37%
693
19%
1773
7%
693
43%
693
27%
1182
May1st to 15thNight
38%
525
17%
1605
10%
525
44%
525
21%
1101
May16th to endNight
48%
374
17%
1497
17%
374
55%
374
21%
903
June1st to 15thNight
48%
360
17%
1440
17%
360
57%
360
24%
841
June16th to endNight
55%
360
18%
1440
20%
360
62%
360
28%
779
July1st to 15thNight
55%
340
13%
1360
16%
340
58%
340
22%
803
July16th to endNight
64%
547
17%
1578
13%
514
68%
514
36%
887
August1st to 15thNight
65%
539
19%
1609
13%
536
68%
536
35%
947
August16th to endNight
62%
711
24%
1857
15%
711
63%
711
38%
1130
September1st to 15thNight
53%
720
25%
1800
14%
720
57%
720
34%
1156
September16th to endNight
53%
717
26%
1992
19%
717
57%
717
32%
1230
October1st to 15thNight
46%
684
22%
2051
18%
684
53%
684
28%
1280
October16th to endNight
33%
704
24%
2112
12%
704
48%
704
24%
1331
November1st to 15thNight
36%
700
23%
2230
17%
700
47%
700
25%
1360
November16th to endNight
26%
720
19%
2520
10%
720
39%
720
15%
1642
December1st to 15thNight
24%
720
14%
2520
6%
720
35%
720
12%
1741
December16th to endNight
20%
768
16%
2688
5%
768
34%
768
14%
1816

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
14%7%36%5%35%5%5%7%35%
48075
Night
14%6%35%5%3445%7%39%
47303
Cloud CoverDay
14%7%36%5%35%5%5%7%35%
48085
Night
14%6%35%5%2445%7%39%
47307
TransparencyDay
46%5%11%21%13%1
47775
Night
42%412%23%14%1
47121
SeeingDay
19%13%23%22%14%6%
5648
Night
18%14%24%28%12%1
15212

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
14%7%5%10%7%45%5%45%28%
1514
16th to endDay
13%12%5%9%7%45%445%26%
1728
February1st to 15thDay
14%13%49%6%34345%29%
1575
16th to endDay
13%9%5%11%6%2435%6%30%
1512
March1st to 15thDay
16%8%46%6%345%5%5%33%
1966
16th to endDay
16%10%36%5%34447%33%
2115
April1st to 15thDay
16%9%45%5%24346%35%
2152
16th to endDay
19%6%35%5%2444439%
2198
May1st to 15thDay
20%7%345%35%5%5%6%31%
2346
16th to endDay
16%436%5%35%45%6%37%
2618
June1st to 15thDay
12%6%35%5%36%5%6%9%36%
2520
16th to endDay
12%425%5%46%6%7%9%36%
2520
July1st to 15thDay
10%436%6%36%6%6%9%35%
2520
16th to endDay
8%436%7%47%7%7%8%35%
2481
August1st to 15thDay
10%5%35%7%37%7%6%10%31%
2340
16th to endDay
12%5%24435%5%7%8%40%
2333
September1st to 15thDay
16%5%2442445%6%42%
2160
16th to endDay
13%6%245%335%47%43%
1966
October1st to 15thDay
19%5%24433436%42%
1707
16th to endDay
17%5%35%43345%6%38%
1760
November1st to 15thDay
11%6%26%43435%7%43%
1628
16th to endDay
19%10%35%424446%34%
1440
December1st to 15thDay
17%8%48%6%36%45%6%28%
1440
16th to endDay
17%8%47%7%5%6%5%36%26%
1536
January1st to 15thNight
16%8%38%6%46%5%46%29%
2422
16th to endNight
14%8%36%5%45%5%6%7%32%
2496
February1st to 15thNight
13%8%5%6%6%35%46%8%31%
2285
16th to endNight
11%8%38%6%35%5%5%7%34%
1961
March1st to 15thNight
16%6%36%43445%6%37%
1968
16th to endNight
16%7%35%424446%40%
2107
April1st to 15thNight
15%9%37%5%2445%6%35%
1796
16th to endNight
16%5%145%24448%42%
1773
May1st to 15thNight
18%7%25%32445%8%35%
1605
16th to endNight
11%7%245%35%45%7%42%
1495
June1st to 15thNight
12%4234245%6%7%44%
1440
16th to endNight
11%313425%46%9%44%
1440
July1st to 15thNight
9%425%5%35%46%9%42%
1440
16th to endNight
6%4244245%6%11%46%
1685
August1st to 15thNight
7%315%5%245%6%10%45%
1620
16th to endNight
10%42432445%8%49%
1857
September1st to 15thNight
13%425%5%23346%48%
1800
16th to endNight
12%5%34423347%48%
1992
October1st to 15thNight
16%5%2342336%5%44%
2051
16th to endNight
17%5%2431445%7%42%
2112
November1st to 15thNight
12%7%25%5%23436%46%
2230
16th to endNight
17%7%25%435%46%6%34%
2520
December1st to 15thNight
17%8%47%6%35%5%6%5%30%
2520
16th to endNight
15%9%35%5%35%45%8%31%
2688

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
13%8%410%7%46%45%429%
1514
16th to endDay
13%12%5%7%8%45%35%5%27%
1728
February1st to 15thDay
14%12%48%6%44345%30%
1575
16th to endDay
13%9%5%9%7%245%46%30%
1512
March1st to 15thDay
17%8%46%5%345%5%6%33%
1977
16th to endDay
16%9%46%5%33446%33%
2114
April1st to 15thDay
17%9%45%5%24346%36%
2152
16th to endDay
18%6%26%5%2444439%
2198
May1st to 15thDay
20%6%25%5%36%446%32%
2346
16th to endDay
16%6%25%5%345%5%6%37%
2618
June1st to 15thDay
13%5%25%5%35%6%6%9%36%
2520
16th to endDay
12%425%5%35%6%7%9%36%
2520
July1st to 15thDay
9%5%26%6%46%6%6%9%35%
2520
16th to endDay
8%436%6%47%6%8%8%35%
2481
August1st to 15thDay
9%6%36%6%5%6%6%7%9%32%
2340
16th to endDay
12%425%425%6%6%8%40%
2333
September1st to 15thDay
16%6%24424447%42%
2160
16th to endDay
14%6%25%434446%43%
1966
October1st to 15thDay
18%5%14424446%42%
1707
16th to endDay
16%7%26%5%24447%38%
1760
November1st to 15thDay
11%7%35%43445%7%43%
1628
16th to endDay
18%9%44425%435%35%
1440
December1st to 15thDay
17%8%48%6%35%5%6%6%28%
1440
16th to endDay
17%8%48%6%5%5%5%36%27%
1536
January1st to 15thNight
16%8%47%6%36%5%46%30%
2422
16th to endNight
14%8%46%5%45%6%5%6%32%
2496
February1st to 15thNight
13%8%46%6%35%5%5%8%32%
2278
16th to endNight
11%7%37%6%345%5%7%34%
1961
March1st to 15thNight
16%6%35%425%45%5%38%
1980
16th to endNight
16%6%35%5%24446%39%
2107
April1st to 15thNight
16%9%37%5%24346%35%
1796
16th to endNight
16%5%24424448%42%
1773
May1st to 15thNight
18%8%344245%6%7%35%
1604
16th to endNight
12%6%35%5%35%45%7%42%
1495
June1st to 15thNight
12%5%244246%5%7%44%
1440
16th to endNight
10%3145%3446%9%45%
1440
July1st to 15thNight
10%425%435%5%7%8%42%
1440
16th to endNight
6%4144345%7%10%46%
1685
August1st to 15thNight
7%415%5%345%7%10%45%
1620
16th to endNight
10%415%32345%8%49%
1857
September1st to 15thNight
13%425%5%23346%47%
1800
16th to endNight
12%5%24424347%48%
1992
October1st to 15thNight
16%5%24333346%44%
2051
16th to endNight
16%5%243235%5%6%42%
2112
November1st to 15thNight
12%8%245%23446%46%
2230
16th to endNight
18%7%25%5%25%5%6%7%35%
2520
December1st to 15thNight
16%8%46%6%35%5%5%6%30%
2520
16th to endNight
15%10%35%435%5%5%8%31%
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
55%5%12%17%7%1
1515
16th to endDay
57%411%17%7%1
1728
February1st to 15thDay
57%311%19%7%1
1577
16th to endDay
52%412%19%9%1
1512
March1st to 15thDay
50%5%12%20%9%1
1977
16th to endDay
50%411%20%11%1
2115
April1st to 15thDay
48%410%19%15%1
2152
16th to endDay
47%36%20%17%3
2198
May1st to 15thDay
50%5%10%19%12%
2346
16th to endDay
46%5%14%19%12%2
2622
June1st to 15thDay
41%6%13%22%14%
2520
16th to endDay
41%6%15%22%13%1
2520
July1st to 15thDay
43%6%11%21%14%2
2371
16th to endDay
39%6%13%22%15%1
2325
August1st to 15thDay
43%7%12%22%13%
2327
16th to endDay
37%6%11%26%14%2
2333
September1st to 15thDay
40%5%10%23%18%2
2160
16th to endDay
40%39%22%21%2
1966
October1st to 15thDay
42%411%24%14%2
1707
16th to endDay
44%411%25%13%
1760
November1st to 15thDay
39%411%22%16%4
1628
16th to endDay
50%39%25%10%
1440
December1st to 15thDay
54%5%15%17%7%
1440
16th to endDay
57%5%11%18%6%
1536
January1st to 15thNight
53%411%18%10%2
2422
16th to endNight
48%413%23%9%
2496
February1st to 15thNight
47%5%14%20%10%
2287
16th to endNight
47%312%22%12%1
1961
March1st to 15thNight
45%5%11%25%10%1
1980
16th to endNight
44%314%21%14%2
2107
April1st to 15thNight
49%49%20%14%1
1796
16th to endNight
40%5%9%22%16%5%
1773
May1st to 15thNight
46%6%9%21%14%1
1605
16th to endNight
39%6%14%21%14%2
1497
June1st to 15thNight
36%6%11%29%14%
1440
16th to endNight
33%416%28%15%1
1440
July1st to 15thNight
38%7%14%22%14%3
1360
16th to endNight
28%6%18%25%17%2
1578
August1st to 15thNight
32%5%17%25%17%
1609
16th to endNight
32%412%27%19%3
1857
September1st to 15thNight
37%311%23%20%2
1800
16th to endNight
36%48%29%19%2
1992
October1st to 15thNight
40%311%26%16%1
2051
16th to endNight
40%39%30%14%
2112
November1st to 15thNight
39%39%25%15%6%
2230
16th to endNight
46%49%22%14%1
2520
December1st to 15thNight
52%413%19%9%
2520
16th to endNight
48%5%16%21%7%
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
22%40%21%12%11
74
16th to endDay
33%23%30%10%2
96
February1st to 15thDay
35%31%27%5%
90
16th to endDay
22%26%30%18%1
171
March1st to 15thDay
24%21%22%26%4
270
16th to endDay
21%22%30%14%7%3
288
April1st to 15thDay
22%21%27%18%7%2
270
16th to endDay
24%11%24%17%15%6%
270
May1st to 15thDay
30%18%18%15%11%5%
288
16th to endDay
20%13%22%20%14%8%
331
June1st to 15thDay
17%13%23%25%15%4
315
16th to endDay
16%10%29%23%13%5%
315
July1st to 15thDay
14%6%23%29%19%6%
305
16th to endDay
8%5%22%28%24%11%
326
August1st to 15thDay
12%419%27%21%14%
313
16th to endDay
12%314%28%22%18%
332
September1st to 15thDay
18%8%15%22%22%11%
315
16th to endDay
19%7%14%21%21%14%
314
October1st to 15thDay
24%419%24%23%5%
278
16th to endDay
17%16%31%21%11%1
272
November1st to 15thDay
17%9%28%22%18%2
231
16th to endDay
23%20%33%15%5%3
60
December1st to 15thDay
23%30%20%11%11%3
60
16th to endDay
28%20%31%20%
64
January1st to 15thNight
21%23%30%21%3
720
16th to endNight
20%22%33%21%1
768
February1st to 15thNight
21%23%29%23%2
704
16th to endNight
22%23%29%21%2
631
March1st to 15thNight
25%18%30%21%3
720
16th to endNight
21%20%30%20%6%
768
April1st to 15thNight
22%18%32%21%4
718
16th to endNight
18%14%24%30%12%
693
May1st to 15thNight
22%8%23%30%14%
525
16th to endNight
14%7%21%34%19%2
375
June1st to 15thNight
13%6%24%32%21%1
360
16th to endNight
11%321%44%18%
360
July1st to 15thNight
13%217%43%20%2
340
16th to endNight
7%215%40%29%4
547
August1st to 15thNight
9%213%45%25%3
539
16th to endNight
12%311%36%31%3
711
September1st to 15thNight
15%5%16%31%27%3
720
16th to endNight
15%5%18%23%30%6%
717
October1st to 15thNight
19%8%20%28%20%3
684
16th to endNight
22%14%25%29%7%
704
November1st to 15thNight
16%13%27%29%10%1
700
16th to endNight
23%23%23%21%7%1
720
December1st to 15thNight
23%18%26%25%6%
720
16th to endNight
22%19%31%25%1
768
Page generated at 2017-10-07 14:07:50. Version ac04

Copyright 2017 A. Danko


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