Observatoire POLARIS
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire POLARIS 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
28%
14441
14%
46474
7%
14409
36%
14409
17%
32856

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
11%
2506
3%
716
27%
716
11%
1896
January16th to endNight
21%
768
12%
2688
6%
768
30%
768
12%
1984
February1st to 15thNight
21%
704
11%
2336
4%
701
31%
701
12%
1757
February16th to endNight
22%
631
15%
1893
6%
631
34%
631
15%
1390
March1st to 15thNight
20%
720
14%
2159
8%
720
28%
720
13%
1620
March16th to endNight
27%
768
20%
2001
7%
768
36%
768
21%
1403
April1st to 15thNight
24%
718
17%
1796
6%
718
30%
718
18%
1351
April16th to endNight
25%
603
16%
1683
4%
603
34%
603
20%
1172
May1st to 15thNight
29%
388
15%
1468
11%
388
39%
388
16%
1004
May16th to endNight
27%
375
12%
1497
10%
374
39%
374
16%
992
June1st to 15thNight
32%
360
7%
1440
5%
360
39%
360
14%
992
June16th to endNight
38%
360
7%
1440
8%
360
41%
360
16%
975
July1st to 15thNight
47%
340
10%
1360
15%
340
52%
340
23%
811
July16th to endNight
47%
376
12%
1418
13%
354
52%
354
21%
874
August1st to 15thNight
56%
351
14%
1400
15%
349
60%
349
20%
872
August16th to endNight
49%
670
17%
1720
9%
670
52%
670
33%
1108
September1st to 15thNight
43%
660
13%
1650
6%
660
45%
660
29%
1136
September16th to endNight
41%
657
20%
1812
12%
657
46%
657
30%
1155
October1st to 15thNight
28%
660
19%
1936
9%
660
39%
660
19%
1324
October16th to endNight
24%
704
12%
2271
6%
704
32%
704
16%
1631
November1st to 15thNight
28%
700
17%
2277
10%
700
39%
700
17%
1594
November16th to endNight
22%
720
14%
2515
7%
720
31%
720
12%
1837
December1st to 15thNight
20%
720
10%
2520
4%
720
28%
720
11%
1887
December16th to endNight
14%
768
12%
2688
3%
768
25%
768
8%
2091

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
18%9%36%6%3445%6%31%
47506
Night
18%9%46%5%24445%34%
46644
TransparencyDay
52%6%11%18%9%1
47193
Night
51%5%11%19%10%1
46475
SeeingDay
22%12%30%22%10%2
5418
Night
22%10%30%26%9%
14441

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
19%12%5%7%8%34435%24%
1432
16th to endDay
12%13%6%7%8%35%345%28%
1536
February1st to 15thDay
10%16%5%8%8%46%445%26%
1523
16th to endDay
15%15%6%9%6%2433426%
1580
March1st to 15thDay
15%12%48%7%34445%28%
1790
16th to endDay
15%9%46%5%34335%38%
2220
April1st to 15thDay
21%10%35%5%2434433%
2152
16th to endDay
20%8%36%424445%36%
2277
May1st to 15thDay
22%7%37%5%34445%30%
2493
16th to endDay
22%7%36%6%34446%30%
2618
June1st to 15thDay
22%6%26%5%345%6%7%28%
2520
16th to endDay
20%7%36%7%45%5%6%7%26%
2520
July1st to 15thDay
15%5%36%6%46%5%6%8%31%
2520
16th to endDay
14%6%26%6%46%6%6%8%31%
2654
August1st to 15thDay
15%6%26%6%47%6%7%8%27%
2453
16th to endDay
11%425%5%35%5%6%9%38%
2129
September1st to 15thDay
17%7%245%3445%6%39%
1980
16th to endDay
18%5%2441335%5%44%
1818
October1st to 15thDay
23%7%36%42435%6%31%
1692
16th to endDay
25%11%36%6%34335%26%
1599
November1st to 15thDay
17%9%37%5%35%347%31%
1581
16th to endDay
22%12%35%424435%30%
1443
December1st to 15thDay
26%13%46%5%23335%25%
1440
16th to endDay
24%13%5%7%5%23235%25%
1536
January1st to 15thNight
17%14%6%8%5%3444426%
2506
16th to endNight
12%12%5%9%7%44445%28%
2688
February1st to 15thNight
10%11%6%9%9%35%5%3428%
2334
16th to endNight
16%11%48%5%25%345%30%
1893
March1st to 15thNight
18%12%47%435%345%29%
2147
16th to endNight
11%10%46%42444440%
2001
April1st to 15thNight
22%9%46%5%23445%32%
1796
16th to endNight
19%7%2442335%6%37%
1683
May1st to 15thNight
21%8%35%424445%35%
1468
16th to endNight
24%5%24424445%36%
1495
June1st to 15thNight
22%7%35%5%2445%6%32%
1440
16th to endNight
19%5%35%5%35%5%47%33%
1440
July1st to 15thNight
12%4146%245%5%7%44%
1440
16th to endNight
12%5%345%25%45%7%42%
1514
August1st to 15thNight
12%4246%35%5%6%7%40%
1410
16th to endNight
13%414434446%48%
1720
September1st to 15thNight
16%5%25%43445%6%43%
1650
16th to endNight
19%413313345%49%
1812
October1st to 15thNight
19%6%26%424346%38%
1936
16th to endNight
26%8%35%42335%5%32%
2271
November1st to 15thNight
20%7%36%5%24446%35%
2277
16th to endNight
21%12%46%5%2334430%
2515
December1st to 15thNight
21%13%5%7%42345%427%
2520
16th to endNight
21%15%6%7%5%2343424%
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
62%6%8%14%7%
1433
16th to endDay
58%48%18%8%1
1536
February1st to 15thDay
60%49%17%7%
1525
16th to endDay
60%5%6%16%9%1
1580
March1st to 15thDay
57%5%9%13%12%1
1800
16th to endDay
48%49%17%15%4
2220
April1st to 15thDay
54%47%18%11%3
2152
16th to endDay
50%5%8%18%14%3
2277
May1st to 15thDay
54%5%9%17%11%2
2493
16th to endDay
54%7%10%16%10%1
2622
June1st to 15thDay
51%9%11%16%9%1
2520
16th to endDay
54%8%10%18%7%
2520
July1st to 15thDay
46%9%13%20%9%
2371
16th to endDay
48%9%14%18%7%
2487
August1st to 15thDay
49%11%16%17%4
2439
16th to endDay
38%10%18%22%9%
2129
September1st to 15thDay
44%6%15%22%10%
1980
16th to endDay
41%6%12%28%10%
1818
October1st to 15thDay
52%5%11%21%8%
1692
16th to endDay
59%5%12%16%6%
1599
November1st to 15thDay
53%6%12%17%9%
1581
16th to endDay
56%5%11%18%8%
1443
December1st to 15thDay
62%412%16%4
1440
16th to endDay
63%5%8%12%9%
1536
January1st to 15thNight
60%5%10%16%6%
2506
16th to endNight
57%5%10%16%8%1
2688
February1st to 15thNight
58%6%9%17%7%
2336
16th to endNight
54%5%9%17%12%1
1893
March1st to 15thNight
56%5%8%17%10%1
2160
16th to endNight
46%5%8%19%16%3
2001
April1st to 15thNight
53%5%6%19%14%2
1796
16th to endNight
46%6%8%19%15%3
1683
May1st to 15thNight
50%5%10%17%13%3
1468
16th to endNight
47%6%11%20%11%1
1497
June1st to 15thNight
50%7%13%17%10%
1440
16th to endNight
49%7%11%18%12%
1440
July1st to 15thNight
37%7%17%23%12%
1360
16th to endNight
39%8%16%24%10%
1418
August1st to 15thNight
41%8%17%25%7%
1400
16th to endNight
35%6%17%28%11%
1720
September1st to 15thNight
41%6%15%24%11%
1650
16th to endNight
37%413%32%11%
1812
October1st to 15thNight
47%5%11%23%12%
1936
16th to endNight
52%5%13%20%8%
2271
November1st to 15thNight
51%5%13%19%9%1
2277
16th to endNight
57%411%18%7%
2515
December1st to 15thNight
59%5%12%17%5%
2520
16th to endNight
63%5%7%14%7%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
16%20%33%25%5%
60
16th to endDay
20%17%37%17%43
64
February1st to 15thDay
24%22%37%10%4
83
16th to endDay
26%15%31%20%6%
239
March1st to 15thDay
22%18%30%23%4
270
16th to endDay
19%15%33%18%10%3
288
April1st to 15thDay
28%17%25%19%7%1
270
16th to endDay
23%16%34%12%10%1
270
May1st to 15thDay
31%14%26%19%5%2
288
16th to endDay
22%17%32%17%7%1
331
June1st to 15thDay
25%12%33%20%8%
315
16th to endDay
21%11%32%25%8%1
315
July1st to 15thDay
16%6%35%26%10%3
305
16th to endDay
15%429%34%13%2
326
August1st to 15thDay
17%6%26%30%15%4
297
16th to endDay
11%7%26%27%20%7%
268
September1st to 15thDay
16%7%25%24%15%9%
255
16th to endDay
19%9%27%20%14%7%
254
October1st to 15thDay
24%12%27%21%11%2
255
16th to endDay
29%11%27%22%8%
243
November1st to 15thDay
17%15%28%24%13%1
235
16th to endDay
33%20%23%15%6%
63
December1st to 15thDay
35%6%30%23%13
60
16th to endDay
37%20%32%9%
64
January1st to 15thNight
23%11%38%20%5%
720
16th to endNight
19%11%35%25%6%
768
February1st to 15thNight
16%12%36%26%7%
704
16th to endNight
21%12%35%25%5%
631
March1st to 15thNight
24%14%33%22%4
720
16th to endNight
16%16%32%24%8%1
768
April1st to 15thNight
27%12%28%25%5%
718
16th to endNight
24%14%32%21%6%
603
May1st to 15thNight
24%8%32%25%7%1
388
16th to endNight
25%8%35%22%7%
375
June1st to 15thNight
24%8%28%30%8%
360
16th to endNight
19%430%33%12%
360
July1st to 15thNight
13%429%33%18%1
340
16th to endNight
15%327%36%16%
376
August1st to 15thNight
12%220%42%20%1
351
16th to endNight
14%324%35%18%1
670
September1st to 15thNight
18%428%32%14%1
660
16th to endNight
21%8%26%25%15%1
657
October1st to 15thNight
22%10%31%25%9%1
660
16th to endNight
31%10%29%21%7%
704
November1st to 15thNight
25%9%29%24%10%1
700
16th to endNight
26%14%27%21%7%2
720
December1st to 15thNight
29%10%31%22%4
720
16th to endNight
30%13%30%21%4
768
Page generated at 2017-08-13 14:16:18. Version ac04

Copyright 2017 A. Danko


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