Perras Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Perras Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
27%
14811
18%
46466
8%
14779
39%
14779
20%
30431

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
17%
720
20%
2506
6%
716
34%
716
17%
1582
January16th to endNight
17%
768
21%
2658
5%
768
38%
768
16%
1681
February1st to 15thNight
14%
704
17%
2192
4%
701
29%
701
16%
1463
February16th to endNight
16%
631
24%
1893
7%
631
37%
631
18%
1245
March1st to 15thNight
17%
720
17%
2160
5%
720
31%
720
16%
1467
March16th to endNight
19%
768
23%
2006
7%
768
33%
768
22%
1325
April1st to 15thNight
17%
718
16%
1796
4%
718
25%
718
21%
1282
April16th to endNight
21%
651
17%
1731
3%
651
30%
651
22%
1189
May1st to 15thNight
22%
537
16%
1617
6%
537
32%
537
16%
1131
May16th to endNight
31%
375
12%
1497
9%
374
39%
374
16%
966
June1st to 15thNight
31%
360
13%
1440
10%
360
44%
360
16%
969
June16th to endNight
42%
360
14%
1440
13%
360
53%
360
24%
845
July1st to 15thNight
42%
340
11%
1360
13%
340
47%
340
20%
855
July16th to endNight
51%
376
14%
1418
14%
354
58%
354
21%
883
August1st to 15thNight
45%
494
17%
1543
10%
492
50%
492
28%
936
August16th to endNight
52%
700
17%
1750
9%
700
55%
700
31%
1177
September1st to 15thNight
40%
660
22%
1671
10%
660
46%
660
29%
1114
September16th to endNight
46%
657
24%
1815
17%
657
51%
657
29%
1152
October1st to 15thNight
34%
660
21%
1886
11%
660
45%
660
25%
1244
October16th to endNight
24%
704
17%
2244
6%
704
38%
704
20%
1471
November1st to 15thNight
28%
700
21%
2277
9%
700
43%
700
21%
1456
November16th to endNight
24%
720
20%
2358
9%
720
38%
720
18%
1536
December1st to 15thNight
22%
720
16%
2520
6%
720
36%
720
15%
1669
December16th to endNight
16%
768
18%
2688
4%
768
34%
768
14%
1793

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
16%5%245%3445%7%39%
47514
Night
17%6%24424446%41%
46636
Cloud CoverDay
16%6%25%43445%7%39%
47524
Night
17%6%2442445%6%41%
46641
TransparencyDay
43%6%11%21%14%2
47202
Night
43%6%11%21%15%2
46466
SeeingDay
21%14%30%20%9%2
5686
Night
21%13%33%23%7%
14811

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
15%6%25%415%5%6%6%40%
1432
16th to endDay
15%7%24325%46%7%41%
1563
February1st to 15thDay
16%6%36%445%5%5%7%35%
1669
16th to endDay
17%6%245%35%445%40%
1580
March1st to 15thDay
18%6%35%434447%37%
1790
16th to endDay
17%6%345%23345%42%
2217
April1st to 15thDay
18%7%25%42345%6%39%
2152
16th to endDay
17%425%414446%44%
2229
May1st to 15thDay
23%6%245%2445%6%34%
2344
16th to endDay
18%5%25%5%2445%7%39%
2618
June1st to 15thDay
21%6%245%3445%7%33%
2520
16th to endDay
13%6%25%5%35%5%6%8%37%
2520
July1st to 15thDay
13%5%25%6%45%6%5%8%37%
2520
16th to endDay
12%435%6%45%5%6%8%38%
2654
August1st to 15thDay
12%425%5%45%6%5%8%37%
2306
16th to endDay
11%5%35%435%45%8%42%
2100
September1st to 15thDay
13%6%25%434446%44%
1958
16th to endDay
15%423323446%47%
1815
October1st to 15thDay
19%7%24423346%43%
1743
16th to endDay
17%5%245%3445%5%42%
1628
November1st to 15thDay
18%6%245%23435%44%
1581
16th to endDay
17%5%24425%347%42%
1599
December1st to 15thDay
17%5%245%24446%40%
1440
16th to endDay
20%7%2443445%6%35%
1536
January1st to 15thNight
17%6%25%42235%6%41%
2506
16th to endNight
16%7%35%323346%42%
2658
February1st to 15thNight
15%8%35%5%24346%40%
2191
16th to endNight
17%6%24424336%43%
1893
March1st to 15thNight
19%6%25%423447%39%
2147
16th to endNight
16%6%24413347%44%
2006
April1st to 15thNight
17%7%25%5%24446%39%
1796
16th to endNight
20%5%25%422345%41%
1731
May1st to 15thNight
21%6%35%4335%37%35%
1617
16th to endNight
20%5%3342436%7%38%
1495
June1st to 15thNight
22%5%243245%46%37%
1440
16th to endNight
13%415%5%23448%45%
1440
July1st to 15thNight
14%4245%25%5%8%8%38%
1440
16th to endNight
11%325%6%46%47%8%38%
1514
August1st to 15thNight
9%5%25%4245%6%7%46%
1553
16th to endNight
13%4135%35%5%5%8%44%
1750
September1st to 15thNight
14%5%24435%446%44%
1671
16th to endNight
13%5%34324435%49%
1815
October1st to 15thNight
17%5%15%5%23435%45%
1886
16th to endNight
19%5%24424445%41%
2244
November1st to 15thNight
17%6%24423345%44%
2277
16th to endNight
19%6%24425%346%40%
2358
December1st to 15thNight
20%5%3443435%6%38%
2520
16th to endNight
22%6%24423446%37%
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
15%7%25%425%5%5%6%41%
1432
16th to endDay
15%7%25%325%5%5%7%40%
1563
February1st to 15thDay
16%5%35%5%35%5%5%7%36%
1669
16th to endDay
17%6%245%35%35%5%39%
1580
March1st to 15thDay
18%6%245%35%5%46%36%
1800
16th to endDay
17%7%35%424335%42%
2217
April1st to 15thDay
19%7%25%423446%39%
2152
16th to endDay
17%424424346%44%
2229
May1st to 15thDay
23%6%3432445%6%34%
2344
16th to endDay
17%5%25%42445%7%39%
2618
June1st to 15thDay
21%6%25%43445%7%33%
2520
16th to endDay
12%6%25%5%35%5%6%9%37%
2520
July1st to 15thDay
13%5%25%6%36%5%6%7%37%
2520
16th to endDay
12%5%25%5%46%5%6%8%37%
2654
August1st to 15thDay
12%5%25%5%45%5%6%7%38%
2306
16th to endDay
11%6%26%4345%5%8%41%
2100
September1st to 15thDay
13%6%345%24446%44%
1958
16th to endDay
15%423324446%48%
1815
October1st to 15thDay
18%7%25%323336%42%
1743
16th to endDay
17%5%25%434446%41%
1628
November1st to 15thDay
17%6%245%2343444%
1581
16th to endDay
17%5%24424348%42%
1599
December1st to 15thDay
17%5%25%43335%7%39%
1440
16th to endDay
20%8%25%425%45%6%35%
1536
January1st to 15thNight
18%7%25%423446%41%
2506
16th to endNight
16%7%35%313445%42%
2658
February1st to 15thNight
14%8%34424346%40%
2184
16th to endNight
17%6%34425%336%42%
1893
March1st to 15thNight
18%6%3443345%7%38%
2160
16th to endNight
16%7%33313347%44%
2005
April1st to 15thNight
17%6%35%4335%45%39%
1796
16th to endNight
20%6%25%422435%41%
1731
May1st to 15thNight
21%6%25%433446%35%
1617
16th to endNight
19%5%3343437%7%38%
1495
June1st to 15thNight
22%5%345%23446%38%
1440
16th to endNight
12%5%245%2445%8%45%
1440
July1st to 15thNight
13%4245%35%5%7%9%38%
1440
16th to endNight
10%326%5%46%5%7%9%37%
1514
August1st to 15thNight
10%4244246%7%7%45%
1553
16th to endNight
12%5%135%4445%8%43%
1750
September1st to 15thNight
14%5%23435%35%6%44%
1671
16th to endNight
14%5%2432443449%
1815
October1st to 15thNight
16%6%15%433445%45%
1886
16th to endNight
19%6%24424445%40%
2244
November1st to 15thNight
17%5%24423345%44%
2277
16th to endNight
19%6%23434345%40%
2358
December1st to 15thNight
20%5%35%424445%38%
2520
16th to endNight
21%7%2442445%6%37%
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
42%7%12%23%11%3
1433
16th to endDay
41%5%10%25%13%2
1563
February1st to 15thDay
46%6%12%19%13%1
1672
16th to endDay
45%411%23%13%2
1580
March1st to 15thDay
46%6%12%22%9%2
1800
16th to endDay
44%410%18%17%3
2217
April1st to 15thDay
45%410%20%15%3
2152
16th to endDay
40%5%9%22%18%3
2229
May1st to 15thDay
49%6%8%19%13%2
2344
16th to endDay
42%8%13%19%13%2
2622
June1st to 15thDay
49%7%12%19%10%1
2520
16th to endDay
42%8%13%22%12%
2520
July1st to 15thDay
44%8%10%19%15%1
2371
16th to endDay
40%8%15%19%13%2
2487
August1st to 15thDay
41%8%13%20%14%
2292
16th to endDay
39%7%10%23%17%1
2100
September1st to 15thDay
39%7%11%20%19%1
1958
16th to endDay
36%6%7%22%24%2
1815
October1st to 15thDay
42%5%11%22%15%2
1743
16th to endDay
43%5%11%23%14%2
1628
November1st to 15thDay
43%412%19%17%2
1581
16th to endDay
42%410%25%14%2
1599
December1st to 15thDay
45%416%18%13%1
1440
16th to endDay
48%6%14%18%11%
1536
January1st to 15thNight
43%412%22%13%2
2506
16th to endNight
43%410%23%15%2
2658
February1st to 15thNight
45%5%13%20%12%2
2192
16th to endNight
43%49%22%16%2
1893
March1st to 15thNight
45%5%12%20%13%2
2160
16th to endNight
40%410%21%18%4
2006
April1st to 15thNight
45%7%10%20%14%2
1796
16th to endNight
44%5%8%21%17%3
1731
May1st to 15thNight
48%6%9%18%14%2
1617
16th to endNight
44%7%16%17%11%1
1497
June1st to 15thNight
48%6%12%18%12%1
1440
16th to endNight
37%6%15%25%14%
1440
July1st to 15thNight
39%9%12%22%13%1
1360
16th to endNight
40%8%15%22%11%2
1418
August1st to 15thNight
34%8%14%25%15%2
1543
16th to endNight
37%8%11%25%16%
1750
September1st to 15thNight
39%6%11%24%18%
1671
16th to endNight
37%5%5%22%26%1
1815
October1st to 15thNight
42%5%10%21%16%2
1886
16th to endNight
44%414%21%14%
2244
November1st to 15thNight
41%5%11%19%18%3
2277
16th to endNight
45%411%24%12%2
2358
December1st to 15thNight
46%6%14%20%12%
2520
16th to endNight
48%412%20%12%
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
21%31%31%13%1
60
16th to endDay
27%26%34%11%
69
February1st to 15thDay
27%21%35%14%1
185
16th to endDay
21%23%34%15%4
239
March1st to 15thDay
28%20%32%14%4
270
16th to endDay
22%25%33%12%41
288
April1st to 15thDay
26%19%32%13%7%
270
16th to endDay
22%14%34%18%8%2
270
May1st to 15thDay
36%16%22%15%7%1
288
16th to endDay
22%13%29%23%9%1
331
June1st to 15thDay
23%14%29%19%11%1
315
16th to endDay
17%14%33%24%8%
315
July1st to 15thDay
20%8%31%26%12%1
305
16th to endDay
14%6%34%27%15%2
326
August1st to 15thDay
12%7%27%32%13%6%
297
16th to endDay
11%5%27%28%16%10%
268
September1st to 15thDay
14%9%28%23%16%7%
255
16th to endDay
19%6%29%18%14%11%
254
October1st to 15thDay
22%9%27%24%11%5%
255
16th to endDay
18%20%29%24%6%
248
November1st to 15thDay
22%15%27%23%9%2
235
16th to endDay
22%19%27%20%9%
219
December1st to 15thDay
23%26%36%8%5%
60
16th to endDay
39%20%25%15%
64
January1st to 15thNight
24%18%36%16%3
720
16th to endNight
22%20%35%18%2
768
February1st to 15thNight
21%19%38%18%1
704
16th to endNight
24%19%36%16%2
631
March1st to 15thNight
25%20%33%17%2
720
16th to endNight
20%21%34%18%3
768
April1st to 15thNight
22%18%39%16%2
718
16th to endNight
23%17%32%21%4
651
May1st to 15thNight
25%13%35%20%4
537
16th to endNight
21%9%33%28%6%
375
June1st to 15thNight
24%7%30%29%8%
360
16th to endNight
15%335%36%8%
360
July1st to 15thNight
14%332%35%13%
340
16th to endNight
11%5%26%42%13%1
376
August1st to 15thNight
12%331%39%11%
494
16th to endNight
14%224%37%18%2
700
September1st to 15thNight
17%6%30%30%14%1
660
16th to endNight
16%5%26%28%20%2
657
October1st to 15thNight
21%9%31%25%10%1
660
16th to endNight
24%14%34%21%5%
704
November1st to 15thNight
22%13%31%21%8%1
700
16th to endNight
24%14%31%20%7%
720
December1st to 15thNight
24%15%33%20%5%
720
16th to endNight
27%18%35%16%2
768
Page generated at 2017-08-13 14:16:40. Version ac04

Copyright 2017 A. Danko


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