Cearley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cearley Observatory clear sky chart from 2005-11-05 to 2017-04-28.

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
46%
15030
23%
45633
15%
14987
55%
14987
27%
28182

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
24%
720
23%
2327
8%
716
41%
716
20%
1460
January16th to endNight
25%
768
25%
2439
11%
768
41%
768
21%
1560
February1st to 15thNight
28%
704
25%
2112
9%
701
44%
701
25%
1302
February16th to endNight
22%
631
24%
1893
8%
631
37%
631
23%
1198
March1st to 15thNight
28%
720
22%
2076
10%
720
39%
720
25%
1323
March16th to endNight
37%
768
21%
2112
13%
768
44%
768
29%
1319
April1st to 15thNight
42%
617
25%
1875
16%
617
53%
617
32%
1078
April16th to endNight
49%
534
26%
1693
18%
534
58%
534
32%
970
May1st to 15thNight
48%
495
21%
1485
12%
495
57%
495
28%
932
May16th to endNight
62%
513
20%
1538
13%
513
67%
513
33%
922
June1st to 15thNight
73%
495
17%
1485
16%
495
74%
495
31%
927
June16th to endNight
77%
495
17%
1485
15%
495
79%
495
37%
861
July1st to 15thNight
69%
465
15%
1395
13%
465
70%
465
27%
923
July16th to endNight
71%
522
15%
1469
14%
489
73%
489
28%
951
August1st to 15thNight
74%
494
21%
1515
22%
491
75%
491
30%
933
August16th to endNight
64%
525
17%
1750
19%
525
65%
525
21%
1178
September1st to 15thNight
64%
635
20%
1790
19%
635
64%
635
27%
1212
September16th to endNight
57%
657
24%
1815
16%
657
63%
657
30%
1170
October1st to 15thNight
53%
660
34%
1815
25%
660
60%
660
39%
1060
October16th to endNight
50%
704
33%
2112
26%
704
61%
704
37%
1179
November1st to 15thNight
48%
700
30%
2276
24%
700
60%
700
35%
1217
November16th to endNight
37%
720
27%
2340
17%
720
51%
720
28%
1366
December1st to 15thNight
31%
720
23%
2340
13%
720
44%
720
23%
1450
December16th to endNight
29%
768
20%
2496
14%
768
39%
768
18%
1691

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
13%5%245%35%5%5%7%41%
46058
Night
12%5%2442445%7%45%
45832
TransparencyDay
40%6%11%19%17%4
45759
Night
37%5%10%20%19%5%
45635
SeeingDay
16%6%19%22%22%13%
4786
Night
14%8%23%27%21%3
15032

By Month

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
17%8%24324446%41%
1611
16th to endDay
18%6%34323445%42%
1783
February1st to 15thDay
17%6%24323448%41%
1750
16th to endDay
19%5%24424446%41%
1580
March1st to 15thDay
16%6%25%5%2345%7%39%
1884
16th to endDay
16%4245%35%447%41%
2111
April1st to 15thDay
12%6%25%5%235%5%6%45%
2082
16th to endDay
11%4144345%47%47%
2212
May1st to 15thDay
11%5%344345%6%7%41%
2136
16th to endDay
9%425%5%35%5%6%8%42%
2223
June1st to 15thDay
8%435%5%36%7%8%10%35%
2145
16th to endDay
32135%36%6%8%12%44%
2145
July1st to 15thDay
11%426%6%5%8%8%7%10%29%
2145
16th to endDay
8%5%25%6%48%8%9%10%30%
2283
August1st to 15thDay
7%425%6%47%7%9%11%34%
2101
16th to endDay
13%6%36%7%5%7%7%7%9%25%
2100
September1st to 15thDay
13%5%25%6%36%5%7%8%36%
1829
16th to endDay
16%5%1443445%7%41%
1815
October1st to 15thDay
13%413423335%54%
1815
16th to endDay
12%42331333357%
1758
November1st to 15thDay
13%5%13213345%54%
1582
16th to endDay
15%5%25%423345%48%
1620
December1st to 15thDay
19%6%2442345%6%39%
1620
16th to endDay
25%8%25%32434435%
1728
January1st to 15thNight
19%6%24323446%42%
2327
16th to endNight
18%6%35%424345%42%
2439
February1st to 15thNight
15%6%14323446%46%
2103
16th to endNight
17%5%34424445%44%
1893
March1st to 15thNight
14%6%25%5%23346%44%
2076
16th to endNight
11%5%25%424446%47%
2112
April1st to 15thNight
12%41432345%8%49%
1875
16th to endNight
8%42442346%7%50%
1693
May1st to 15thNight
10%4245%35%6%47%44%
1484
16th to endNight
6%4245%25%46%9%47%
1538
June1st to 15thNight
5%3236%25%6%7%12%43%
1485
16th to endNight
32135%346%10%12%46%
1485
July1st to 15thNight
6%436%6%47%6%7%10%36%
1485
16th to endNight
5%426%6%36%6%8%12%37%
1577
August1st to 15thNight
6%425%5%25%6%7%12%42%
1526
16th to endNight
11%6%25%6%35%5%6%10%35%
1750
September1st to 15thNight
10%5%26%6%346%5%9%38%
1790
16th to endNight
14%4145%3446%6%45%
1815
October1st to 15thNight
10%423213246%56%
1815
16th to endNight
10%41442322458%
2112
November1st to 15thNight
10%5%22223335%57%
2276
16th to endNight
14%6%23413445%50%
2340
December1st to 15thNight
15%7%25%323346%43%
2340
16th to endNight
22%7%25%433346%35%
2496

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
43%48%15%23%4
1612
16th to endDay
42%36%19%21%5%
1783
February1st to 15thDay
40%48%21%21%3
1752
16th to endDay
44%37%19%19%5%
1580
March1st to 15thDay
43%410%18%19%5%
1884
16th to endDay
41%5%12%20%16%3
2112
April1st to 15thDay
38%5%9%21%19%4
2082
16th to endDay
34%6%9%22%21%4
2212
May1st to 15thDay
39%6%13%20%16%3
2136
16th to endDay
36%8%14%23%14%2
2227
June1st to 15thDay
38%9%17%23%8%1
2145
16th to endDay
27%9%18%26%14%2
2145
July1st to 15thDay
43%12%17%16%8%1
2006
16th to endDay
42%12%18%17%7%1
2128
August1st to 15thDay
38%11%17%21%9%1
2088
16th to endDay
50%10%14%15%9%1
2100
September1st to 15thDay
42%8%14%17%13%3
1829
16th to endDay
40%6%11%17%20%4
1815
October1st to 15thDay
32%49%17%26%9%
1815
16th to endDay
31%26%17%30%10%
1758
November1st to 15thDay
32%35%16%33%9%
1582
16th to endDay
38%37%16%26%7%
1620
December1st to 15thDay
44%48%20%15%6%
1620
16th to endDay
52%37%16%14%4
1728
January1st to 15thNight
42%38%18%22%4
2327
16th to endNight
43%35%19%21%6%
2439
February1st to 15thNight
39%37%20%20%8%
2112
16th to endNight
41%36%21%23%4
1893
March1st to 15thNight
39%49%19%18%8%
2076
16th to endNight
36%410%25%18%3
2112
April1st to 15thNight
33%39%24%22%6%
1875
16th to endNight
32%410%23%20%7%
1693
May1st to 15thNight
36%7%13%20%19%2
1485
16th to endNight
31%8%15%26%15%3
1540
June1st to 15thNight
31%11%20%25%10%1
1485
16th to endNight
26%9%20%23%16%3
1485
July1st to 15thNight
38%9%19%20%9%2
1395
16th to endNight
34%11%20%20%10%1
1469
August1st to 15thNight
32%10%16%25%13%1
1515
16th to endNight
42%10%16%16%13%1
1750
September1st to 15thNight
40%8%15%18%12%4
1790
16th to endNight
37%7%10%21%18%5%
1815
October1st to 15thNight
30%410%17%27%8%
1815
16th to endNight
31%2417%31%13%
2112
November1st to 15thNight
30%35%16%31%12%
2276
16th to endNight
35%36%17%27%9%
2340
December1st to 15thNight
41%39%20%18%7%
2340
16th to endNight
49%37%16%17%4
2496

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
22%14%40%16%6%
90
16th to endDay
20%31%38%5%4
96
February1st to 15thDay
25%20%41%11%2
90
16th to endDay
30%16%43%9%
81
March1st to 15thDay
26%14%31%20%6%
174
16th to endDay
18%10%32%24%12%2
288
April1st to 15thDay
18%11%29%21%17%1
270
16th to endDay
15%324%27%24%5%
259
May1st to 15thDay
13%6%30%18%17%14%
228
16th to endDay
14%113%26%27%15%
267
June1st to 15thDay
11%18%26%26%25%
255
16th to endDay
2110%27%27%30%
255
July1st to 15thDay
14%7%20%27%28%
245
16th to endDay
10%414%38%31%
270
August1st to 15thDay
13%15%18%33%26%
253
16th to endDay
17%15%25%27%22%
268
September1st to 15thDay
13%5%7%20%30%22%
255
16th to endDay
17%415%29%25%7%
254
October1st to 15thDay
17%322%23%26%5%
255
16th to endDay
17%6%17%24%26%6%
267
November1st to 15thDay
30%16%18%17%14%2
90
16th to endDay
12%13%37%23%11%2
90
December1st to 15thDay
23%17%35%18%4
90
16th to endDay
37%14%30%14%3
96
January1st to 15thNight
24%16%30%21%7%
720
16th to endNight
22%16%32%25%3
768
February1st to 15thNight
20%14%32%27%4
704
16th to endNight
19%18%35%23%3
631
March1st to 15thNight
17%15%35%24%6%
720
16th to endNight
15%10%30%29%13%
768
April1st to 15thNight
15%11%28%27%16%
617
16th to endNight
11%6%26%35%16%1
534
May1st to 15thNight
10%6%27%29%23%2
495
16th to endNight
9%215%31%33%7%
515
June1st to 15thNight
6%111%33%36%10%
495
16th to endNight
38%32%42%11%
495
July1st to 15thNight
6%17%26%45%12%
465
16th to endNight
6%16%22%50%12%
522
August1st to 15thNight
6%17%28%45%11%
494
16th to endNight
13%18%24%41%10%
525
September1st to 15thNight
12%28%28%37%10%
635
16th to endNight
15%117%33%29%1
657
October1st to 15thNight
12%5%24%28%23%5%
660
16th to endNight
11%8%24%31%20%3
704
November1st to 15thNight
13%8%26%27%23%1
700
16th to endNight
17%14%27%26%13%
720
December1st to 15thNight
18%14%30%26%9%
720
16th to endNight
26%12%28%25%7%
768
Page generated at 2017-04-29 09:45:06. Version ac04

Copyright 2017 A. Danko


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