Cluny
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cluny clear sky chart from 2005-11-05 to 2017-09-17.

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
42%
15250
13%
46788
8%
15223
47%
15223
21%
31741

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
34%
895
10%
2685
6%
895
37%
895
15%
2031
January16th to endNight
36%
850
17%
2770
10%
850
45%
850
20%
1879
February1st to 15thNight
42%
698
12%
2381
11%
696
46%
696
16%
1644
February16th to endNight
42%
632
12%
2008
12%
632
45%
632
18%
1429
March1st to 15thNight
36%
720
13%
2091
8%
720
41%
720
19%
1511
March16th to endNight
36%
768
9%
2112
3%
768
41%
768
17%
1591
April1st to 15thNight
36%
602
10%
1694
5%
602
39%
602
18%
1260
April16th to endNight
42%
540
14%
1620
10%
540
46%
540
22%
1104
May1st to 15thNight
45%
461
11%
1425
9%
461
48%
461
23%
929
May16th to endNight
41%
375
5%
1309
4%
374
43%
374
16%
909
June1st to 15thNight
45%
360
1%
1260
0%
360
45%
360
16%
885
June16th to endNight
52%
360
1%
1260
0%
360
52%
360
24%
783
July1st to 15thNight
60%
340
2%
1190
0%
340
61%
340
26%
714
July16th to endNight
61%
376
11%
1245
10%
354
65%
354
33%
666
August1st to 15thNight
63%
435
11%
1507
13%
433
65%
433
28%
874
August16th to endNight
60%
573
22%
1719
17%
573
64%
573
39%
944
September1st to 15thNight
56%
627
17%
1803
12%
627
59%
627
33%
1114
September16th to endNight
52%
664
20%
1837
13%
664
57%
664
37%
1097
October1st to 15thNight
43%
660
17%
1939
9%
660
50%
660
23%
1312
October16th to endNight
44%
704
17%
2282
11%
704
53%
704
23%
1454
November1st to 15thNight
37%
850
18%
2425
10%
850
44%
850
24%
1627
November16th to endNight
33%
900
13%
2646
8%
900
39%
900
20%
1881
December1st to 15thNight
33%
900
10%
2700
6%
900
37%
900
15%
2016
December16th to endNight
35%
960
13%
2880
7%
960
41%
960
17%
2087

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
9%8%36%5%35%5%6%8%36%
48023
Night
7%8%47%6%35%5%6%8%35%
46935
Cloud CoverDay
9%8%36%5%35%5%6%8%36%
48024
Night
7%8%47%6%35%5%6%8%35%
46938
TransparencyDay
43%8%16%21%8%1
47674
Night
44%7%16%20%9%1
46788
SeeingDay
13%6%25%30%18%5%
6042
Night
11%5%29%34%15%2
15262

By Month

Percentage Cloud Cover NW (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
8%11%5%8%8%45%5%5%8%27%
1253
16th to endDay
7%9%6%9%6%45%5%7%8%28%
1464
February1st to 15thDay
9%11%48%7%46%5%47%29%
1482
16th to endDay
5%13%7%10%8%5%6%6%5%7%23%
1464
March1st to 15thDay
6%10%5%11%8%36%45%7%29%
1869
16th to endDay
10%13%5%8%7%345%6%8%25%
2111
April1st to 15thDay
11%11%5%8%7%446%5%7%28%
2251
16th to endDay
13%9%46%7%45%5%5%7%31%
2340
May1st to 15thDay
11%8%36%5%35%5%5%7%37%
2523
16th to endDay
18%7%36%5%35%5%5%8%29%
2802
June1st to 15thDay
14%7%36%5%36%6%7%8%31%
2700
16th to endDay
11%5%25%436%5%6%8%37%
2700
July1st to 15thDay
7%424435%5%6%11%44%
2700
16th to endDay
5%213325%5%6%9%53%
2837
August1st to 15thDay
8%5%244345%6%9%44%
2445
16th to endDay
7%213435%45%9%51%
2483
September1st to 15thDay
12%6%24333345%50%
2156
16th to endDay
9%5%2442335%10%46%
1828
October1st to 15thDay
11%8%37%6%35%347%37%
1691
16th to endDay
8%7%36%5%46%5%6%6%39%
1587
November1st to 15thDay
8%11%5%7%6%35%46%7%32%
1422
16th to endDay
6%13%5%7%6%35%46%6%33%
1311
December1st to 15thDay
7%14%6%12%9%35%45%7%22%
1260
16th to endDay
49%6%10%7%47%6%6%8%27%
1344
January1st to 15thNight
5%12%5%9%9%5%7%6%6%7%24%
2685
16th to endNight
5%11%48%7%35%5%6%8%32%
2770
February1st to 15thNight
7%9%49%7%45%5%5%7%32%
2370
16th to endNight
5%10%6%11%7%35%5%7%7%30%
2008
March1st to 15thNight
5%10%5%9%7%45%5%6%9%29%
2091
16th to endNight
8%13%49%6%46%6%6%8%25%
2109
April1st to 15thNight
9%10%5%8%8%36%5%6%7%28%
1694
16th to endNight
10%8%36%6%36%5%6%8%33%
1620
May1st to 15thNight
10%9%36%4245%5%7%38%
1424
16th to endNight
18%7%45%435%5%6%9%30%
1309
June1st to 15thNight
14%7%36%6%36%6%8%6%30%
1260
16th to endNight
8%5%247%5%5%5%7%8%39%
1260
July1st to 15thNight
7%4245%5%5%6%6%10%42%
1260
16th to endNight
43134246%6%11%51%
1329
August1st to 15thNight
5%325%5%35%6%5%9%46%
1515
16th to endNight
6%41442346%9%52%
1719
September1st to 15thNight
12%5%15%324446%50%
1803
16th to endNight
8%41342445%9%50%
1837
October1st to 15thNight
10%8%35%6%35%5%5%7%37%
1939
16th to endNight
9%7%26%5%25%5%7%10%38%
2282
November1st to 15thNight
6%9%35%6%35%5%6%8%37%
2425
16th to endNight
6%11%48%7%45%6%6%8%31%
2646
December1st to 15thNight
6%11%6%12%8%45%5%5%7%26%
2700
16th to endNight
5%11%5%10%9%45%5%5%8%28%
2880

Percentage Cloud Cover SW (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
8%11%48%9%46%5%6%8%27%
1253
16th to endDay
8%9%49%7%36%5%8%9%28%
1464
February1st to 15thDay
9%12%48%7%45%5%6%7%28%
1482
16th to endDay
5%13%7%11%7%45%7%5%7%23%
1464
March1st to 15thDay
6%10%6%10%9%45%45%6%28%
1869
16th to endDay
10%13%5%8%7%35%5%6%8%24%
2112
April1st to 15thDay
10%11%5%7%7%35%5%5%7%28%
2251
16th to endDay
13%9%46%6%35%45%7%31%
2340
May1st to 15thDay
11%8%36%5%45%5%5%8%36%
2523
16th to endDay
18%7%27%5%35%5%6%8%29%
2802
June1st to 15thDay
14%8%36%5%36%6%6%8%31%
2700
16th to endDay
11%6%35%5%35%5%7%9%37%
2700
July1st to 15thDay
7%324435%6%7%10%44%
2700
16th to endDay
5%213325%5%6%9%53%
2837
August1st to 15thDay
8%5%244345%6%9%44%
2445
16th to endDay
6%31442446%8%52%
2483
September1st to 15thDay
11%5%35%32433450%
2156
16th to endDay
9%6%2442345%10%46%
1828
October1st to 15thDay
11%7%38%5%34447%38%
1691
16th to endDay
8%7%36%445%5%6%7%38%
1587
November1st to 15thDay
8%11%5%6%6%45%45%8%32%
1422
16th to endDay
6%13%5%7%6%35%46%7%33%
1311
December1st to 15thDay
7%13%6%13%10%3445%8%22%
1260
16th to endDay
410%6%10%7%38%6%7%8%26%
1344
January1st to 15thNight
5%11%5%9%9%5%7%6%6%8%23%
2685
16th to endNight
5%11%5%8%6%35%46%9%32%
2770
February1st to 15thNight
7%9%49%8%445%5%7%32%
2370
16th to endNight
5%9%6%12%7%35%5%6%8%29%
2008
March1st to 15thNight
5%10%5%9%7%45%5%7%9%29%
2091
16th to endNight
8%12%5%9%7%36%5%6%7%25%
2112
April1st to 15thNight
9%11%49%6%47%46%8%28%
1694
16th to endNight
10%8%26%6%35%6%6%9%32%
1620
May1st to 15thNight
9%10%35%5%25%5%5%8%38%
1424
16th to endNight
17%7%45%435%5%6%8%31%
1309
June1st to 15thNight
13%7%35%6%46%6%7%8%30%
1260
16th to endNight
7%5%25%7%46%6%6%8%39%
1260
July1st to 15thNight
7%415%5%36%6%6%10%42%
1260
16th to endNight
4314415%5%7%10%51%
1329
August1st to 15thNight
4325%5%345%6%10%47%
1515
16th to endNight
5%415%31346%8%53%
1719
September1st to 15thNight
11%5%23424446%50%
1803
16th to endNight
8%41443335%9%50%
1837
October1st to 15thNight
10%8%35%5%35%5%6%7%37%
1939
16th to endNight
8%6%26%5%346%6%10%38%
2282
November1st to 15thNight
6%8%45%6%35%5%6%8%38%
2425
16th to endNight
6%11%47%7%45%5%6%8%31%
2646
December1st to 15thNight
6%11%5%12%8%45%45%7%26%
2700
16th to endNight
5%11%5%10%8%45%5%6%8%28%
2880

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
52%8%14%19%41
1253
16th to endDay
48%9%15%17%7%2
1464
February1st to 15thDay
52%7%15%16%7%
1482
16th to endDay
54%9%14%15%5%
1464
March1st to 15thDay
52%7%17%15%5%
1869
16th to endDay
54%8%15%16%4
2112
April1st to 15thDay
52%8%13%16%7%
2251
16th to endDay
50%6%14%18%8%1
2340
May1st to 15thDay
44%7%14%22%11%
2523
16th to endDay
50%8%15%18%6%
2807
June1st to 15thDay
47%9%16%18%6%1
2700
16th to endDay
40%9%18%24%6%
2700
July1st to 15thDay
31%10%21%27%8%
2541
16th to endDay
25%9%22%29%12%1
2658
August1st to 15thDay
33%9%21%26%7%1
2428
16th to endDay
27%6%20%30%13%1
2483
September1st to 15thDay
36%5%12%24%15%4
2156
16th to endDay
33%7%14%29%11%3
1828
October1st to 15thDay
45%6%15%24%8%
1691
16th to endDay
41%8%17%24%8%
1587
November1st to 15thDay
48%7%15%20%7%
1422
16th to endDay
48%7%16%19%7%1
1311
December1st to 15thDay
60%7%13%14%4
1260
16th to endDay
50%7%16%17%6%
1344
January1st to 15thNight
54%8%14%15%41
2685
16th to endNight
46%6%15%18%10%2
2770
February1st to 15thNight
49%6%14%18%9%1
2381
16th to endNight
50%7%13%18%9%
2008
March1st to 15thNight
48%8%17%18%5%
2091
16th to endNight
53%7%14%17%5%
2112
April1st to 15thNight
51%7%14%16%8%
1694
16th to endNight
45%7%14%22%8%2
1620
May1st to 15thNight
42%7%12%23%12%1
1425
16th to endNight
48%9%16%17%7%1
1309
June1st to 15thNight
48%9%15%17%7%1
1260
16th to endNight
37%9%22%23%7%
1260
July1st to 15thNight
34%9%19%26%9%
1190
16th to endNight
24%10%20%29%12%1
1245
August1st to 15thNight
30%10%21%26%9%1
1507
16th to endNight
26%5%15%31%16%4
1719
September1st to 15thNight
34%6%12%23%17%6%
1803
16th to endNight
30%6%17%26%14%4
1837
October1st to 15thNight
44%6%15%19%11%2
1939
16th to endNight
38%8%18%25%8%
2282
November1st to 15thNight
41%7%16%21%11%1
2425
16th to endNight
47%8%17%16%8%1
2646
December1st to 15thNight
55%7%15%17%3
2700
16th to endNight
51%7%16%18%5%
2880

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
13%21%21%23%20%
60
16th to endDay
12%6%26%21%23%9%
64
February1st to 15thDay
20%9%20%29%17%4
75
16th to endDay
18%5%23%33%16%2
123
March1st to 15thDay
12%8%38%33%5%1
270
16th to endDay
10%10%40%23%11%3
288
April1st to 15thDay
13%13%31%25%14%1
269
16th to endDay
20%7%25%28%15%2
270
May1st to 15thDay
14%7%25%27%19%5%
403
16th to endDay
20%5%19%27%21%5%
517
June1st to 15thDay
15%6%28%29%17%3
495
16th to endDay
12%5%27%33%17%4
495
July1st to 15thDay
8%419%35%24%7%
475
16th to endDay
7%425%36%20%5%
506
August1st to 15thDay
9%317%35%26%8%
315
16th to endDay
9%6%17%32%25%9%
332
September1st to 15thDay
18%6%20%27%20%6%
315
16th to endDay
11%11%26%30%15%4
260
October1st to 15thDay
14%8%28%28%16%3
131
16th to endDay
10%423%32%23%5%
96
November1st to 15thDay
15%11%34%24%12%2
90
16th to endDay
13%5%30%30%8%11%
69
December1st to 15thDay
16%343%23%10%3
60
16th to endDay
14%326%28%25%3
64
January1st to 15thNight
11%7%32%32%14%2
900
16th to endNight
11%6%33%34%12%1
850
February1st to 15thNight
9%8%25%33%18%4
704
16th to endNight
9%426%37%17%3
632
March1st to 15thNight
8%437%34%12%1
720
16th to endNight
13%6%31%34%13%
768
April1st to 15thNight
14%7%31%33%12%1
602
16th to endNight
15%6%27%35%13%1
540
May1st to 15thNight
12%6%27%35%16%1
462
16th to endNight
21%5%24%27%20%1
375
June1st to 15thNight
19%425%34%14%1
360
16th to endNight
9%326%39%20%
360
July1st to 15thNight
8%121%41%25%1
340
16th to endNight
7%223%43%21%1
376
August1st to 15thNight
6%320%38%28%2
435
16th to endNight
8%421%41%22%1
573
September1st to 15thNight
13%419%36%23%2
627
16th to endNight
9%5%28%35%17%3
664
October1st to 15thNight
15%5%26%34%15%3
660
16th to endNight
11%5%30%37%13%1
704
November1st to 15thNight
10%9%36%30%10%2
850
16th to endNight
11%7%35%31%11%2
900
December1st to 15thNight
11%6%31%31%16%1
900
16th to endNight
10%5%33%33%13%3
960
Page generated at 2017-09-18 06:38:27. Version ac04

Copyright 2017 A. Danko


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