Observatoire POLARIS
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire POLARIS clear sky chart from 2005-11-06 to 2024-03-28.

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%
22739
14%
81032
7%
22650
36%
22650
15%
56820

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 10thNight
15%
754
10%
4394
2%
737
26%
737
6%
3138
January11th to 20thNight
18%
758
12%
4384
3%
740
28%
740
6%
3054
January21st to endNight
21%
829
9%
4860
7%
814
33%
814
8%
3618
February1st to 10thNight
19%
760
14%
2552
5%
760
31%
760
13%
1885
February11th to 20thNight
18%
743
14%
2307
3%
740
31%
740
14%
1684
February21st to endNight
21%
628
16%
1884
6%
628
33%
628
15%
1347
March1st to 10thNight
21%
760
15%
2280
9%
760
30%
760
14%
1683
March11th to 20thNight
20%
760
15%
2219
5%
760
30%
760
13%
1661
March21st to endNight
24%
821
19%
2051
5%
821
34%
821
20%
1469
April1st to 10thNight
24%
720
14%
1800
5%
720
29%
720
17%
1377
April11th to 20thNight
26%
711
17%
1775
5%
711
33%
711
23%
1253
April21st to endNight
23%
545
17%
1625
6%
545
32%
545
17%
1139
May1st to 10thNight
27%
403
15%
1483
10%
403
38%
403
16%
992
May11th to 20thNight
29%
354
19%
1416
15%
354
44%
354
17%
905
May21st to endNight
26%
389
12%
1551
7%
388
40%
388
17%
990
June1st to 10thNight
33%
360
8%
1440
7%
360
43%
360
17%
949
June11th to 20thNight
36%
360
9%
1440
9%
360
43%
360
16%
930
June21st to endNight
36%
360
9%
1440
10%
360
42%
360
16%
966
July1st to 10thNight
45%
350
10%
1400
13%
350
53%
350
22%
837
July11th to 20thNight
46%
348
12%
1392
17%
348
51%
348
21%
854
July21st to endNight
48%
394
13%
1486
15%
372
54%
372
22%
895
August1st to 10thNight
55%
358
14%
1422
14%
356
62%
356
21%
862
August11th to 20thNight
49%
483
15%
1547
11%
483
53%
483
26%
973
August21st to endNight
44%
792
19%
1980
9%
792
48%
792
31%
1314
September1st to 10thNight
45%
720
15%
1800
6%
720
49%
720
34%
1182
September11th to 20thNight
42%
720
19%
1885
10%
720
48%
720
33%
1199
September21st to endNight
38%
720
22%
1980
13%
720
44%
720
28%
1302
October1st to 10thNight
32%
720
21%
2088
11%
720
42%
720
21%
1416
October11th to 20thNight
27%
720
15%
2223
7%
720
37%
720
18%
1566
October21st to endNight
23%
792
12%
2574
6%
792
31%
792
15%
1867
November1st to 10thNight
25%
740
16%
2407
7%
740
37%
740
17%
1658
November11th to 20thNight
24%
760
17%
2558
10%
760
33%
760
14%
1800
November21st to endNight
20%
760
13%
2660
6%
760
30%
760
11%
1955
December1st to 10thNight
20%
760
10%
2660
4%
760
27%
760
10%
2050
December11th to 20thNight
17%
760
13%
3244
4%
759
29%
759
8%
2417
December21st to endNight
14%
827
8%
4825
3%
817
23%
817
5%
3633

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
17%10%47%6%35%5%5%6%32%
78573
Night
17%10%47%6%3445%6%34%
81422
TransparencyDay
51%8%11%19%10%1
78278
Night
51%7%12%19%10%1
81251
SeeingDay
22%17%32%20%8%2
13656
Night
22%12%31%26%8%1
22763

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 10thDay
14%13%6%10%8%44445%28%
2517
11th to 20thDay
13%14%7%11%10%3433428%
2520
21st to endDay
11%12%7%11%9%45%45%6%26%
2772
February1st to 10thDay
11%18%5%9%9%35%446%26%
1624
11th to 20thDay
12%15%6%10%6%35%445%29%
1760
21st to endDay
15%16%7%8%7%3445%5%27%
1570
March1st to 10thDay
14%12%5%9%8%4445%5%30%
1897
11th to 20thDay
14%13%5%7%7%45%445%32%
1957
21st to endDay
17%12%36%6%35%445%34%
2460
April1st to 10thDay
20%12%5%7%6%34346%30%
2160
11th to 20thDay
21%7%36%6%34445%36%
2134
21st to endDay
20%11%47%5%35%45%5%31%
2335
May1st to 10thDay
21%8%46%5%44445%35%
2492
11th to 20thDay
19%7%47%6%35%45%7%34%
2478
21st to endDay
19%7%36%6%35%5%5%7%34%
2725
June1st to 10thDay
22%8%36%6%45%6%6%7%28%
2520
11th to 20thDay
17%6%36%6%45%5%6%8%34%
2520
21st to endDay
22%8%37%7%45%5%6%7%26%
2520
July1st to 10thDay
14%5%36%7%46%6%6%8%35%
2520
11th to 20thDay
15%6%35%6%46%7%7%8%33%
2520
21st to endDay
13%6%36%6%47%6%8%9%32%
2744
August1st to 10thDay
14%7%36%6%48%7%7%9%30%
2506
11th to 20thDay
13%5%26%6%46%6%7%9%35%
2334
21st to endDay
14%6%25%5%35%5%6%8%40%
2376
September1st to 10thDay
15%5%25%5%3446%8%43%
2160
11th to 20thDay
15%6%235%25%45%6%45%
2075
21st to endDay
21%7%35%42345%6%41%
1980
October1st to 10thDay
23%6%36%5%2445%7%35%
1870
11th to 20thDay
22%10%38%5%45%446%27%
1736
21st to endDay
26%12%35%6%33445%29%
1782
November1st to 10thDay
15%11%36%5%45%45%6%34%
1671
11th to 20thDay
20%10%5%8%5%35%5%47%28%
1620
21st to endDay
20%15%46%5%36%45%6%27%
1520
December1st to 10thDay
24%15%5%8%6%34445%23%
1520
11th to 20thDay
21%14%5%8%6%24346%27%
1906
21st to endDay
22%17%6%9%5%33335%24%
2772
January1st to 10thNight
15%15%6%9%7%3445%5%27%
4429
11th to 20thNight
10%12%6%10%10%45%5%5%429%
4440
21st to endNight
10%13%6%11%9%5%5%5%5%5%25%
4884
February1st to 10thNight
12%12%7%9%8%36%5%5%5%29%
2552
11th to 20thNight
11%11%5%10%8%45%5%45%31%
2305
21st to endNight
14%12%48%6%35%45%6%32%
1884
March1st to 10thNight
15%13%5%8%6%45%446%31%
2270
11th to 20thNight
15%14%5%9%5%45%45%431%
2219
21st to endNight
14%9%47%5%345%5%5%38%
2051
April1st to 10thNight
21%11%5%7%5%3445%6%30%
1800
11th to 20thNight
18%6%36%5%3445%6%40%
1775
21st to endNight
21%10%36%42445%6%35%
1625
May1st to 10thNight
22%9%45%43435%6%37%
1483
11th to 20thNight
20%6%36%5%245%6%6%39%
1415
21st to endNight
19%6%245%45%5%46%40%
1550
June1st to 10thNight
20%6%26%5%345%6%7%35%
1440
11th to 20thNight
19%6%36%5%35%6%5%7%37%
1440
21st to endNight
19%6%45%5%45%5%48%35%
1440
July1st to 10thNight
12%5%25%6%35%6%6%8%43%
1440
11th to 20thNight
12%435%6%36%5%6%8%42%
1440
21st to endNight
13%6%35%5%25%5%6%9%43%
1574
August1st to 10thNight
11%5%346%445%6%8%43%
1432
11th to 20thNight
14%425%6%345%5%6%44%
1547
21st to endNight
15%6%2443445%7%45%
1980
September1st to 10thNight
13%5%25%435%5%6%6%47%
1800
11th to 20thNight
16%5%24424346%50%
1885
21st to endNight
19%5%25%5%23446%47%
1980
October1st to 10thNight
18%8%36%5%34345%41%
2088
11th to 20thNight
23%8%36%43445%7%35%
2223
21st to endNight
24%9%36%6%3445%6%30%
2574
November1st to 10thNight
17%9%47%5%3445%6%35%
2407
11th to 20thNight
18%11%45%6%3445%6%32%
2558
21st to endNight
21%13%48%6%34446%29%
2660
December1st to 10thNight
19%15%5%9%6%4445%5%23%
2660
11th to 20thNight
22%12%6%8%6%3444428%
3288
21st to endNight
22%16%6%9%5%3333425%
4884

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 10thDay
56%10%12%17%5%1
2518
11th to 20thDay
57%9%9%17%7%1
2520
21st to endDay
58%8%9%17%7%1
2772
February1st to 10thDay
60%48%17%9%2
1624
11th to 20thDay
57%6%11%14%11%1
1769
21st to endDay
59%6%7%16%9%3
1570
March1st to 10thDay
55%7%8%16%12%2
1900
11th to 20thDay
53%6%10%14%14%3
1957
21st to endDay
52%5%9%17%13%4
2460
April1st to 10thDay
56%6%9%15%11%3
2160
11th to 20thDay
50%6%9%21%13%3
2134
21st to endDay
54%7%8%16%12%3
2335
May1st to 10thDay
51%410%19%13%3
2492
11th to 20thDay
49%7%9%18%15%3
2482
21st to endDay
49%8%11%17%14%2
2725
June1st to 10thDay
52%10%11%17%9%2
2520
11th to 20thDay
45%8%12%21%11%2
2520
21st to endDay
56%8%11%15%9%1
2520
July1st to 10thDay
42%10%14%23%10%
2450
11th to 20thDay
43%10%15%22%9%
2445
21st to endDay
45%12%15%20%8%
2591
August1st to 10thDay
47%12%17%20%5%
2492
11th to 20thDay
40%13%16%22%9%
2334
21st to endDay
39%9%15%24%12%
2376
September1st to 10thDay
39%8%16%24%13%1
2160
11th to 20thDay
38%8%14%27%11%1
2075
21st to endDay
44%6%14%26%11%
1980
October1st to 10thDay
49%6%12%23%9%1
1870
11th to 20thDay
57%7%13%18%5%
1736
21st to endDay
58%6%11%15%9%1
1782
November1st to 10thDay
50%8%13%19%9%1
1671
11th to 20thDay
55%7%12%16%10%
1620
21st to endDay
59%8%12%15%7%1
1520
December1st to 10thDay
64%5%10%15%6%
1520
11th to 20thDay
59%5%10%18%9%
1906
21st to endDay
64%5%8%14%8%
2772
January1st to 10thNight
57%9%14%14%6%
4429
11th to 20thNight
55%8%12%19%5%1
4440
21st to endNight
57%10%10%14%8%1
4884
February1st to 10thNight
57%6%9%18%9%1
2552
11th to 20thNight
53%6%10%18%11%1
2307
21st to endNight
52%6%10%18%13%2
1884
March1st to 10thNight
55%6%9%17%11%2
2280
11th to 20thNight
56%6%7%15%13%3
2220
21st to endNight
48%5%9%20%14%4
2051
April1st to 10thNight
55%6%9%15%14%2
1800
11th to 20thNight
44%6%10%23%14%3
1775
21st to endNight
50%6%8%19%15%2
1625
May1st to 10thNight
49%5%9%19%14%4
1483
11th to 20thNight
45%6%10%20%14%4
1416
21st to endNight
43%8%12%19%15%2
1551
June1st to 10thNight
45%8%14%20%12%1
1440
11th to 20thNight
45%8%12%19%13%3
1440
21st to endNight
48%8%13%19%12%
1440
July1st to 10thNight
37%9%18%24%12%1
1400
11th to 20thNight
39%9%16%26%10%1
1392
21st to endNight
37%9%18%26%10%
1486
August1st to 10thNight
38%9%18%27%8%
1422
11th to 20thNight
38%8%19%24%11%
1547
21st to endNight
38%7%16%28%11%
1980
September1st to 10thNight
35%7%17%26%14%1
1800
11th to 20thNight
35%6%15%32%10%1
1885
21st to endNight
39%6%12%29%13%
1980
October1st to 10thNight
46%6%10%25%13%1
2088
11th to 20thNight
49%7%14%23%7%
2223
21st to endNight
54%6%12%18%9%1
2574
November1st to 10thNight
49%6%14%21%8%1
2407
11th to 20thNight
52%6%13%17%10%1
2558
21st to endNight
58%5%12%16%8%1
2660
December1st to 10thNight
62%6%12%15%5%
2660
11th to 20thNight
59%7%8%17%9%1
3288
21st to endNight
63%6%7%16%6%1
4884

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 10thDay
21%20%34%20%4
180
11th to 20thDay
24%16%37%17%41
180
21st to endDay
16%17%45%18%31
198
February1st to 10thDay
28%26%37%8%1
229
11th to 20thDay
22%23%40%13%2
367
21st to endDay
25%24%32%15%4
382
March1st to 10thDay
23%20%35%17%5%
460
11th to 20thDay
22%21%36%15%4
460
21st to endDay
27%23%28%14%7%2
490
April1st to 10thDay
27%18%32%17%6%
420
11th to 20thDay
28%21%25%16%8%2
412
21st to endDay
29%19%33%12%5%1
420
May1st to 10thDay
27%18%33%15%41
423
11th to 20thDay
20%19%34%19%6%2
447
21st to endDay
21%21%35%16%5%2
485
June1st to 10thDay
22%16%39%16%8%
450
11th to 20thDay
18%18%32%20%10%1
450
21st to endDay
23%13%28%25%9%2
450
July1st to 10thDay
14%9%36%27%11%2
445
11th to 20thDay
15%11%35%29%8%2
444
21st to endDay
14%9%32%31%13%2
488
August1st to 10thDay
14%11%30%30%13%2
446
11th to 20thDay
14%8%29%29%14%6%
439
21st to endDay
16%15%27%23%15%4
495
September1st to 10thDay
15%11%33%23%11%6%
450
11th to 20thDay
15%12%30%24%13%6%
450
21st to endDay
22%12%29%20%12%5%
450
October1st to 10thDay
24%16%25%23%10%2
450
11th to 20thDay
24%19%30%17%9%1
417
21st to endDay
32%17%26%19%5%
396
November1st to 10thDay
22%20%30%19%8%1
365
11th to 20thDay
23%22%31%18%6%
280
21st to endDay
25%28%27%17%3
180
December1st to 10thDay
29%16%29%19%6%2
180
11th to 20thDay
30%23%32%12%3
180
21st to endDay
32%20%28%16%41
198
January1st to 10thNight
24%12%38%23%4
760
11th to 20thNight
24%14%35%21%6%
760
21st to endNight
15%12%39%27%6%
836
February1st to 10thNight
18%14%38%24%6%
760
11th to 20thNight
20%17%36%22%5%
743
21st to endNight
21%15%37%23%4
628
March1st to 10thNight
24%15%33%24%4
760
11th to 20thNight
22%19%33%19%5%1
760
21st to endNight
20%17%33%24%6%
821
April1st to 10thNight
28%14%28%24%6%
720
11th to 20thNight
22%15%32%23%6%
711
21st to endNight
27%15%30%21%6%1
545
May1st to 10thNight
25%14%30%23%7%1
403
11th to 20thNight
21%14%31%28%6%
354
21st to endNight
21%8%41%21%8%
389
June1st to 10thNight
22%9%30%31%8%
360
11th to 20thNight
19%8%29%31%13%1
360
21st to endNight
19%6%29%31%14%
360
July1st to 10thNight
13%5%32%35%14%1
350
11th to 20thNight
12%329%40%15%1
348
21st to endNight
15%5%25%39%14%1
394
August1st to 10thNight
12%323%45%16%1
358
11th to 20thNight
14%424%37%19%2
483
21st to endNight
16%6%27%31%18%2
792
September1st to 10thNight
14%6%31%35%14%1
720
11th to 20thNight
18%7%28%27%18%1
720
21st to endNight
21%9%29%24%15%2
720
October1st to 10thNight
22%11%30%26%11%1
720
11th to 20thNight
25%12%30%25%8%1
720
21st to endNight
29%12%30%23%6%
792
November1st to 10thNight
24%13%29%25%8%1
740
11th to 20thNight
23%15%32%20%9%1
760
21st to endNight
27%17%27%23%6%1
760
December1st to 10thNight
28%13%30%23%6%
760
11th to 20thNight
25%15%32%21%5%
760
21st to endNight
29%15%31%21%4
836
Page generated at 2024-03-24 23:37:02. Version ac07

Copyright © 2024 Attilla Danko.


Observatoire POLARIS Clear Sky Chart |Charts Home