Cygnus Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cygnus Hill Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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%
14873
14%
47384
8%
14844
35%
14844
16%
33528

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
14%
720
7%
2506
2%
716
20%
716
6%
2012
January16th to endNight
18%
768
11%
2604
5%
768
26%
768
11%
1978
February1st to 15thNight
15%
702
9%
2287
3%
701
23%
701
10%
1760
February16th to endNight
18%
631
14%
1964
5%
631
29%
631
13%
1430
March1st to 15thNight
18%
720
13%
2071
6%
720
25%
720
15%
1529
March16th to endNight
29%
768
20%
2052
8%
768
38%
768
23%
1410
April1st to 15thNight
20%
718
16%
1796
5%
718
26%
718
18%
1311
April16th to endNight
28%
662
17%
1742
7%
662
34%
662
22%
1232
May1st to 15thNight
31%
360
17%
1440
13%
360
43%
360
18%
927
May16th to endNight
32%
374
14%
1497
10%
374
46%
374
19%
913
June1st to 15thNight
33%
360
10%
1440
8%
360
42%
360
15%
960
June16th to endNight
41%
360
9%
1440
10%
360
47%
360
17%
941
July1st to 15thNight
48%
340
15%
1360
20%
340
54%
340
27%
746
July16th to endNight
53%
376
14%
1418
16%
354
58%
354
28%
803
August1st to 15thNight
48%
485
15%
1556
11%
483
53%
483
26%
954
August16th to endNight
50%
696
21%
1842
10%
696
55%
696
37%
1121
September1st to 15thNight
45%
720
18%
1800
8%
720
49%
720
31%
1207
September16th to endNight
47%
717
24%
1968
15%
717
53%
717
31%
1252
October1st to 15thNight
32%
720
16%
2160
11%
720
40%
720
20%
1504
October16th to endNight
21%
768
12%
2370
5%
768
30%
768
12%
1805
November1st to 15thNight
25%
700
18%
2343
13%
700
34%
700
16%
1635
November16th to endNight
20%
720
12%
2520
7%
720
28%
720
10%
1919
December1st to 15thNight
14%
720
6%
2520
2%
720
19%
720
7%
2009
December16th to endNight
12%
768
8%
2688
3%
768
18%
768
7%
2170

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%9%36%5%34446%32%
48375
Night
17%9%36%5%34446%33%
47554
Cloud CoverDay
17%8%36%5%34446%33%
48385
Night
17%9%36%5%34446%34%
47559
TransparencyDay
51%6%11%19%10%1
48063
Night
50%6%11%19%10%1
47384
SeeingDay
23%13%29%19%9%4
5633
Night
22%13%30%23%9%
14876

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
20%16%5%7%5%3434424%
1432
16th to endDay
14%15%6%10%9%4433423%
1619
February1st to 15thDay
14%13%5%11%8%35%5%45%22%
1575
16th to endDay
18%14%5%6%7%35%33426%
1509
March1st to 15thDay
16%12%5%8%8%5%5%32327%
1876
16th to endDay
15%9%36%43333441%
2171
April1st to 15thDay
23%10%35%423345%33%
2152
16th to endDay
20%8%35%423445%37%
2229
May1st to 15thDay
18%8%36%6%24446%34%
2511
16th to endDay
15%5%36%5%35%5%47%37%
2618
June1st to 15thDay
22%7%35%4245%5%7%30%
2520
16th to endDay
17%5%26%6%35%5%6%8%32%
2520
July1st to 15thDay
13%5%25%5%35%5%6%8%36%
2520
16th to endDay
12%6%36%436%6%6%9%34%
2654
August1st to 15thDay
12%6%35%6%35%5%5%7%37%
2391
16th to endDay
13%5%16%5%35%5%6%8%39%
2346
September1st to 15thDay
16%6%2442345%7%42%
2160
16th to endDay
15%5%245%24336%46%
1992
October1st to 15thDay
22%7%36%42435%6%34%
1800
16th to endDay
25%9%46%6%35%335%25%
1851
November1st to 15thDay
15%9%46%6%345%46%34%
1513
16th to endDay
22%12%5%6%5%34345%25%
1440
December1st to 15thDay
22%13%5%9%6%34435%20%
1440
16th to endDay
23%15%5%8%6%24335%20%
1536
January1st to 15thNight
19%14%6%9%8%3443420%
2506
16th to endNight
13%14%5%9%6%35%445%26%
2604
February1st to 15thNight
13%15%6%9%7%3445%6%23%
2285
16th to endNight
14%13%46%6%34346%30%
1964
March1st to 15thNight
18%11%47%5%3434432%
2059
16th to endNight
15%8%45%5%2334442%
2052
April1st to 15thNight
22%7%45%433345%35%
1796
16th to endNight
18%7%25%5%24446%38%
1742
May1st to 15thNight
20%8%244225%5%5%38%
1440
16th to endNight
14%5%25%5%2345%8%40%
1495
June1st to 15thNight
16%7%46%5%4445%7%34%
1440
16th to endNight
15%5%25%5%46%46%8%35%
1440
July1st to 15thNight
9%423425%5%49%46%
1440
16th to endNight
9%4134345%6%9%47%
1514
August1st to 15thNight
9%5%344335%6%8%43%
1566
16th to endNight
8%5%2442345%8%51%
1842
September1st to 15thNight
13%5%14424447%45%
1800
16th to endNight
15%424323346%49%
1968
October1st to 15thNight
20%6%35%5%24336%36%
2160
16th to endNight
24%9%37%6%23446%27%
2370
November1st to 15thNight
16%10%36%4345%46%33%
2343
16th to endNight
22%10%47%6%35%345%25%
2520
December1st to 15thNight
20%15%5%9%5%34445%22%
2520
16th to endNight
23%14%48%6%35%335%20%
2688

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
20%16%5%7%5%2435%424%
1432
16th to endDay
14%15%6%10%8%3443423%
1619
February1st to 15thDay
14%13%5%11%7%46%445%23%
1575
16th to endDay
19%14%5%7%7%35%23426%
1509
March1st to 15thDay
18%11%5%8%9%45%32327%
1887
16th to endDay
15%9%46%43433441%
2170
April1st to 15thDay
23%9%44423345%33%
2152
16th to endDay
20%8%26%423345%37%
2229
May1st to 15thDay
19%7%36%5%34346%34%
2511
16th to endDay
15%5%36%5%2445%7%37%
2618
June1st to 15thDay
22%6%45%43445%7%31%
2520
16th to endDay
17%5%26%6%25%46%7%33%
2520
July1st to 15thDay
13%435%5%35%5%5%9%37%
2520
16th to endDay
12%6%25%5%36%5%7%9%35%
2654
August1st to 15thDay
13%6%35%6%35%5%6%8%36%
2391
16th to endDay
13%5%15%5%345%5%9%40%
2346
September1st to 15thDay
16%5%34424447%42%
2160
16th to endDay
16%5%24424345%46%
1992
October1st to 15thDay
21%8%26%5%2335%6%34%
1800
16th to endDay
26%8%37%6%44435%25%
1851
November1st to 15thDay
14%10%27%5%35%446%34%
1513
16th to endDay
22%12%5%7%434435%26%
1440
December1st to 15thDay
23%14%49%7%33435%21%
1440
16th to endDay
23%15%5%8%5%3334421%
1536
January1st to 15thNight
19%15%5%10%7%45%33420%
2506
16th to endNight
14%13%5%9%7%35%445%26%
2604
February1st to 15thNight
13%15%6%8%6%445%5%6%23%
2278
16th to endNight
15%13%46%7%33345%31%
1964
March1st to 15thNight
19%11%37%6%23335%32%
2071
16th to endNight
16%7%5%5%423346%41%
2052
April1st to 15thNight
22%7%36%42433435%
1796
16th to endNight
18%7%35%42435%6%38%
1742
May1st to 15thNight
21%8%25%42245%5%37%
1440
16th to endNight
14%5%35%43345%7%41%
1495
June1st to 15thNight
17%6%46%6%3445%6%34%
1440
16th to endNight
15%5%25%5%46%47%8%35%
1440
July1st to 15thNight
9%425%5%2445%8%47%
1440
16th to endNight
9%41343347%8%48%
1514
August1st to 15thNight
9%5%25%5%346%6%8%42%
1566
16th to endNight
9%42442246%8%50%
1842
September1st to 15thNight
14%5%14424447%45%
1800
16th to endNight
16%424323346%49%
1968
October1st to 15thNight
21%7%25%424346%36%
2160
16th to endNight
24%9%37%5%3345%5%27%
2370
November1st to 15thNight
18%10%35%434446%33%
2343
16th to endNight
22%11%37%5%35%445%25%
2520
December1st to 15thNight
20%15%5%9%6%34435%22%
2520
16th to endNight
24%14%5%8%6%25%335%20%
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
63%5%10%13%6%
1433
16th to endDay
65%5%8%11%8%
1619
February1st to 15thDay
62%6%10%15%4
1577
16th to endDay
62%39%11%10%1
1509
March1st to 15thDay
62%410%14%6%1
1887
16th to endDay
47%49%19%14%5%
2171
April1st to 15thDay
53%5%7%18%13%2
2152
16th to endDay
48%48%19%15%3
2229
May1st to 15thDay
50%5%10%17%13%2
2511
16th to endDay
44%8%13%20%11%2
2622
June1st to 15thDay
51%6%11%19%9%
2520
16th to endDay
48%7%11%20%11%
2520
July1st to 15thDay
39%8%13%26%11%
2371
16th to endDay
44%9%15%21%9%
2487
August1st to 15thDay
43%9%14%21%10%
2377
16th to endDay
38%7%16%25%10%
2346
September1st to 15thDay
40%6%13%26%12%
2160
16th to endDay
39%6%10%30%11%
1992
October1st to 15thDay
49%5%12%21%9%
1800
16th to endDay
60%7%10%15%4
1851
November1st to 15thDay
48%8%14%17%9%
1513
16th to endDay
60%7%10%12%7%1
1440
December1st to 15thDay
66%7%12%10%3
1440
16th to endDay
67%6%10%10%5%
1536
January1st to 15thNight
67%5%10%11%4
2506
16th to endNight
59%6%10%15%8%
2604
February1st to 15thNight
59%7%12%15%5%
2287
16th to endNight
54%412%17%9%
1964
March1st to 15thNight
55%5%11%18%8%
2071
16th to endNight
45%410%20%16%3
2052
April1st to 15thNight
50%47%20%15%1
1796
16th to endNight
46%6%8%18%17%3
1742
May1st to 15thNight
46%5%10%18%14%4
1440
16th to endNight
40%7%14%20%14%2
1497
June1st to 15thNight
48%6%13%19%11%1
1440
16th to endNight
44%9%12%19%13%
1440
July1st to 15thNight
32%6%13%28%17%1
1360
16th to endNight
32%8%16%27%14%
1418
August1st to 15thNight
36%8%17%24%13%
1556
16th to endNight
30%6%17%31%13%
1842
September1st to 15thNight
36%8%12%29%11%1
1800
16th to endNight
35%6%11%33%12%
1968
October1st to 15thNight
49%5%11%21%12%
2160
16th to endNight
58%5%12%16%6%
2370
November1st to 15thNight
49%6%13%17%11%1
2343
16th to endNight
60%6%10%17%5%
2520
December1st to 15thNight
64%6%12%12%3
2520
16th to endNight
67%5%9%11%5%
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
31%26%20%13%8%
60
16th to endDay
46%11%25%12%3
78
February1st to 15thDay
35%25%35%3
90
16th to endDay
33%19%28%13%4
168
March1st to 15thDay
26%18%31%19%4
270
16th to endDay
25%17%33%14%8%1
288
April1st to 15thDay
28%23%25%12%8%
270
16th to endDay
24%19%27%16%7%5%
270
May1st to 15thDay
29%12%28%17%7%3
288
16th to endDay
19%14%35%18%9%3
331
June1st to 15thDay
24%10%33%21%7%2
315
16th to endDay
19%13%30%22%11%2
315
July1st to 15thDay
17%8%28%26%14%5%
305
16th to endDay
15%7%33%24%13%6%
326
August1st to 15thDay
14%5%31%30%12%6%
313
16th to endDay
15%6%27%25%13%11%
332
September1st to 15thDay
16%11%25%20%13%12%
315
16th to endDay
18%8%24%19%19%9%
314
October1st to 15thDay
27%13%28%17%8%4
315
16th to endDay
29%20%26%18%5%
319
November1st to 15thDay
19%12%32%24%8%1
167
16th to endDay
35%11%26%20%6%
60
December1st to 15thDay
30%18%31%16%3
60
16th to endDay
45%29%23%1
64
January1st to 15thNight
29%19%29%16%3
720
16th to endNight
21%15%35%22%4
768
February1st to 15thNight
20%22%33%19%2
704
16th to endNight
22%16%37%18%4
631
March1st to 15thNight
28%16%32%20%1
720
16th to endNight
21%15%30%22%9%1
768
April1st to 15thNight
26%18%30%20%3
718
16th to endNight
22%15%30%20%9%
662
May1st to 15thNight
22%10%29%28%7%2
360
16th to endNight
15%8%38%25%11%
375
June1st to 15thNight
18%8%31%31%8%1
360
16th to endNight
16%333%31%13%
360
July1st to 15thNight
10%230%38%16%
340
16th to endNight
9%229%42%15%
376
August1st to 15thNight
13%5%24%35%20%1
485
16th to endNight
10%428%34%19%2
696
September1st to 15thNight
16%5%29%27%19%2
720
16th to endNight
17%8%22%25%22%3
717
October1st to 15thNight
25%10%27%21%12%1
720
16th to endNight
30%14%28%21%5%
768
November1st to 15thNight
25%11%32%19%9%
700
16th to endNight
30%17%26%17%7%
720
December1st to 15thNight
29%19%30%16%3
720
16th to endNight
33%14%32%16%1
768
Page generated at 2017-11-01 17:23:31. Version ac04

Copyright 2017 A. Danko


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