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 2017-12-20.

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%
15334
18%
48025
8%
15302
39%
15302
20%
31406

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
16%
768
21%
2658
5%
768
37%
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
18%
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
38%
374
16%
966
June1st to 15thNight
33%
360
13%
1440
10%
360
45%
360
16%
969
June16th to endNight
42%
360
14%
1440
13%
360
52%
360
24%
845
July1st to 15thNight
42%
340
11%
1360
13%
340
46%
340
20%
855
July16th to endNight
50%
376
14%
1418
14%
354
57%
354
21%
883
August1st to 15thNight
44%
509
17%
1580
10%
507
49%
507
28%
965
August16th to endNight
53%
764
18%
1910
9%
764
55%
764
32%
1272
September1st to 15thNight
39%
720
21%
1823
10%
720
45%
720
30%
1204
September16th to endNight
45%
717
25%
1980
18%
717
51%
717
29%
1256
October1st to 15thNight
35%
720
21%
2058
11%
720
44%
720
25%
1359
October16th to endNight
25%
768
19%
2448
8%
768
39%
768
21%
1592
November1st to 15thNight
28%
760
20%
2472
9%
760
43%
760
21%
1588
November16th to endNight
24%
780
22%
2555
10%
780
40%
780
19%
1629
December1st to 15thNight
22%
780
16%
2730
5%
780
36%
780
15%
1821
December16th to endNight
15%
788
18%
2755
4%
788
33%
788
14%
1837

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%2443445%7%40%
48823
Night
17%6%24424446%41%
48195
Cloud CoverDay
16%6%25%43445%7%40%
48833
Night
17%6%2442445%6%41%
48200
TransparencyDay
43%6%11%21%14%2
48511
Night
43%6%11%21%15%2
48025
SeeingDay
21%14%30%20%9%2
6124
Night
21%13%33%23%7%
15334

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%5%25%5%45%6%5%8%37%
2354
16th to endDay
11%5%34435%45%7%44%
2292
September1st to 15thDay
12%5%244345%46%45%
2136
16th to endDay
14%424333446%47%
1980
October1st to 15thDay
18%7%24423346%43%
1901
16th to endDay
18%5%24434445%42%
1776
November1st to 15thDay
18%6%245%23335%43%
1716
16th to endDay
17%424424347%44%
1732
December1st to 15thDay
17%5%35%5%24446%40%
1560
16th to endDay
20%7%3443445%6%35%
1568
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
10%5%25%4245%6%7%45%
1590
16th to endNight
12%4135%35%45%8%44%
1910
September1st to 15thNight
14%5%24435%446%45%
1823
16th to endNight
12%6%34324445%49%
1980
October1st to 15thNight
16%6%15%423435%45%
2058
16th to endNight
19%5%24424445%42%
2448
November1st to 15thNight
17%6%24423345%43%
2472
16th to endNight
18%6%24424345%42%
2555
December1st to 15thNight
20%6%3443445%5%37%
2730
16th to endNight
21%6%24423446%37%
2755

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%6%45%5%6%7%37%
2354
16th to endDay
11%5%25%33445%7%43%
2292
September1st to 15thDay
12%5%345%24446%45%
2136
16th to endDay
14%424324445%48%
1980
October1st to 15thDay
18%6%25%323346%42%
1901
16th to endDay
18%5%25%434446%42%
1776
November1st to 15thDay
18%6%245%23435%43%
1716
16th to endDay
16%5%24424348%44%
1732
December1st to 15thDay
17%5%36%433346%39%
1560
16th to endDay
20%8%25%425%446%35%
1568
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%44%
1590
16th to endNight
11%5%135%4445%8%44%
1910
September1st to 15thNight
14%5%23425%346%45%
1823
16th to endNight
13%5%24424435%48%
1980
October1st to 15thNight
16%6%14433445%45%
2058
16th to endNight
19%5%24424445%41%
2448
November1st to 15thNight
17%5%24423345%44%
2472
16th to endNight
18%6%23434345%42%
2555
December1st to 15thNight
20%6%35%424445%38%
2730
16th to endNight
21%7%2442435%6%37%
2755

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
42%8%13%20%14%
2340
16th to endDay
37%7%10%24%18%1
2292
September1st to 15thDay
39%7%11%20%19%1
2136
16th to endDay
36%5%8%22%24%2
1980
October1st to 15thDay
42%5%11%22%15%2
1901
16th to endDay
43%5%10%23%15%2
1776
November1st to 15thDay
43%5%12%19%16%2
1716
16th to endDay
40%410%26%15%2
1732
December1st to 15thDay
45%416%17%14%1
1560
16th to endDay
48%6%14%18%11%
1568
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
35%8%14%25%15%1
1580
16th to endNight
36%7%12%24%17%
1910
September1st to 15thNight
38%6%10%24%19%1
1823
16th to endNight
37%5%5%23%25%2
1980
October1st to 15thNight
42%5%10%22%17%2
2058
16th to endNight
43%413%22%14%
2448
November1st to 15thNight
41%5%11%19%18%2
2472
16th to endNight
44%410%25%13%2
2555
December1st to 15thNight
46%6%13%20%12%
2730
16th to endNight
48%5%12%20%12%1
2755

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%28%31%13%6%
313
16th to endDay
11%5%32%27%14%8%
332
September1st to 15thDay
14%12%30%20%14%6%
315
16th to endDay
19%7%28%18%13%12%
314
October1st to 15thDay
21%8%28%24%13%4
315
16th to endDay
20%18%28%23%8%1
300
November1st to 15thDay
22%15%27%23%8%1
280
16th to endDay
24%19%25%20%8%
262
December1st to 15thDay
24%23%35%8%7%
90
16th to endDay
34%22%29%13%
72
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
13%331%38%11%
509
16th to endNight
14%223%38%18%2
764
September1st to 15thNight
17%6%32%29%13%1
720
16th to endNight
16%5%26%27%20%2
717
October1st to 15thNight
21%9%30%25%11%1
720
16th to endNight
24%14%33%20%6%
768
November1st to 15thNight
22%13%32%21%8%1
760
16th to endNight
23%14%32%20%7%
780
December1st to 15thNight
25%15%32%20%5%
780
16th to endNight
27%18%34%16%2
788
Page generated at 2017-12-21 07:04:56. Version ac04

Copyright 2017 A. Danko


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