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 2018-02-22.

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%
15210
14%
48914
7%
15178
37%
15178
17%
34530

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
18%
780
11%
2716
3%
776
28%
776
11%
2040
January16th to endNight
21%
832
12%
2912
5%
832
30%
832
12%
2146
February1st to 15thNight
21%
764
11%
2535
4%
761
31%
761
12%
1907
February16th to endNight
22%
659
15%
1976
6%
659
34%
659
15%
1450
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
55%
359
13%
1430
15%
357
59%
357
19%
893
August16th to endNight
48%
731
19%
1877
10%
731
52%
731
34%
1207
September1st to 15thNight
43%
720
14%
1800
6%
720
46%
720
30%
1229
September16th to endNight
44%
717
21%
1977
13%
717
49%
717
31%
1250
October1st to 15thNight
30%
720
19%
2112
9%
720
41%
720
21%
1427
October16th to endNight
24%
768
13%
2478
7%
768
33%
768
16%
1775
November1st to 15thNight
28%
760
17%
2472
9%
760
38%
760
17%
1732
November16th to endNight
22%
780
14%
2725
8%
780
31%
780
12%
1988
December1st to 15thNight
20%
780
10%
2730
4%
780
28%
780
11%
2048
December16th to endNight
14%
832
13%
2912
3%
832
26%
832
9%
2244

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%
49346
Night
17%9%46%5%24445%34%
49084
TransparencyDay
52%6%11%18%9%1
49033
Night
51%5%11%19%10%1
48915
SeeingDay
21%12%30%22%10%2
5993
Night
22%10%30%26%9%
15210

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%13%5%7%7%34435%23%
1552
16th to endDay
12%13%6%8%8%35%345%28%
1664
February1st to 15thDay
11%16%5%8%8%45%445%25%
1654
16th to endDay
15%15%6%9%6%2443427%
1644
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%
2508
16th to endDay
11%425%5%35%5%6%9%39%
2324
September1st to 15thDay
17%6%245%3445%6%39%
2160
16th to endDay
17%5%2442335%5%46%
1983
October1st to 15thDay
23%7%36%42435%6%32%
1846
16th to endDay
25%10%36%6%34335%27%
1744
November1st to 15thDay
17%10%47%5%35%347%30%
1716
16th to endDay
22%12%35%424436%29%
1563
December1st to 15thDay
24%14%45%5%23335%24%
1560
16th to endDay
22%13%5%8%5%23236%25%
1664
January1st to 15thNight
17%14%6%8%5%3445%426%
2716
16th to endNight
12%12%5%9%7%44445%28%
2912
February1st to 15thNight
10%11%6%9%9%36%5%3428%
2533
16th to endNight
16%11%47%6%25%35%5%30%
1976
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%45%5%6%7%39%
1440
16th to endNight
13%414434446%48%
1877
September1st to 15thNight
16%5%1443445%6%43%
1800
16th to endNight
17%414313345%49%
1977
October1st to 15thNight
18%6%26%424346%40%
2112
16th to endNight
26%8%35%42335%6%32%
2478
November1st to 15thNight
20%7%36%5%24346%35%
2472
16th to endNight
21%12%46%5%23345%30%
2725
December1st to 15thNight
21%13%5%7%42335%427%
2730
16th to endNight
20%15%6%8%5%2343425%
2912

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
63%6%8%14%7%
1553
16th to endDay
57%49%18%8%1
1664
February1st to 15thDay
60%49%16%7%1
1656
16th to endDay
60%47%16%9%1
1644
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
2494
16th to endDay
37%10%17%24%9%
2324
September1st to 15thDay
44%6%15%22%11%
2160
16th to endDay
39%6%13%29%11%
1983
October1st to 15thDay
51%5%11%22%7%
1846
16th to endDay
59%5%13%16%5%
1744
November1st to 15thDay
53%6%12%17%8%
1716
16th to endDay
56%5%10%17%8%
1563
December1st to 15thDay
62%411%16%4
1560
16th to endDay
62%5%8%12%10%
1664
January1st to 15thNight
60%5%10%16%7%
2716
16th to endNight
57%5%10%15%9%1
2912
February1st to 15thNight
58%5%9%18%7%
2535
16th to endNight
54%5%9%17%11%1
1976
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%
1430
16th to endNight
35%6%17%29%10%
1877
September1st to 15thNight
40%6%15%25%12%
1800
16th to endNight
36%5%14%31%11%
1977
October1st to 15thNight
46%5%11%24%12%
2112
16th to endNight
52%5%13%20%7%
2478
November1st to 15thNight
51%5%13%19%9%1
2472
16th to endNight
57%411%18%7%
2725
December1st to 15thNight
59%5%12%17%5%
2730
16th to endNight
62%5%7%14%8%1
2912

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%16%34%22%5%
90
16th to endDay
17%21%37%17%32
96
February1st to 15thDay
25%23%37%10%3
124
16th to endDay
27%15%32%19%5%
265
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%5%27%30%14%3
313
16th to endDay
11%8%25%26%19%7%
332
September1st to 15thDay
16%7%27%24%16%7%
315
16th to endDay
16%9%24%25%16%7%
314
October1st to 15thDay
24%12%26%22%12%1
315
16th to endDay
29%12%27%21%7%
292
November1st to 15thDay
18%15%29%22%12%1
280
16th to endDay
33%22%25%13%4
93
December1st to 15thDay
31%8%34%21%22
90
16th to endDay
29%21%35%10%3
96
January1st to 15thNight
24%11%37%21%5%
780
16th to endNight
19%12%35%25%6%
832
February1st to 15thNight
16%12%37%26%6%
764
16th to endNight
22%12%35%24%5%
659
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
13%220%42%19%1
359
16th to endNight
14%325%34%19%1
731
September1st to 15thNight
18%428%32%14%1
720
16th to endNight
20%8%25%26%18%1
717
October1st to 15thNight
21%10%31%26%10%1
720
16th to endNight
31%10%29%21%7%
768
November1st to 15thNight
25%9%28%24%10%1
760
16th to endNight
26%13%28%21%7%2
780
December1st to 15thNight
29%11%31%22%4
780
16th to endNight
28%12%31%21%4
832
Page generated at 2018-02-23 11:21:37. Version ac04

Copyright 2018 A. Danko


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