Cedar Knoll Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cedar Knoll Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
47%
15762
22%
47032
16%
15719
53%
15719
28%
29471

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
28%
899
20%
2506
10%
895
37%
895
21%
1740
January16th to endNight
26%
915
19%
2526
8%
915
34%
915
23%
1735
February1st to 15thNight
24%
704
17%
2112
8%
701
32%
701
19%
1479
February16th to endNight
25%
631
19%
1893
8%
631
35%
631
21%
1277
March1st to 15thNight
30%
720
18%
2160
9%
720
37%
720
22%
1438
March16th to endNight
38%
651
16%
2022
11%
651
44%
651
22%
1348
April1st to 15thNight
42%
539
24%
1797
16%
539
54%
539
29%
1045
April16th to endNight
45%
540
22%
1785
18%
540
53%
540
27%
1098
May1st to 15thNight
46%
539
19%
1619
12%
539
52%
539
26%
1054
May16th to endNight
62%
561
20%
1661
16%
561
65%
561
32%
1024
June1st to 15thNight
67%
540
22%
1440
17%
540
70%
540
41%
842
June16th to endNight
75%
540
24%
1440
19%
540
77%
540
43%
834
July1st to 15thNight
74%
510
20%
1360
17%
510
74%
510
38%
837
July16th to endNight
75%
564
24%
1465
21%
531
77%
531
41%
857
August1st to 15thNight
75%
539
24%
1749
26%
536
76%
536
37%
951
August16th to endNight
76%
573
26%
1910
30%
573
78%
573
37%
1013
September1st to 15thNight
66%
574
27%
1834
27%
574
67%
574
33%
1043
September16th to endNight
61%
717
30%
1980
24%
717
64%
717
37%
1182
October1st to 15thNight
58%
684
33%
1900
25%
684
63%
684
38%
1113
October16th to endNight
46%
704
27%
2211
22%
704
55%
704
29%
1343
November1st to 15thNight
48%
700
30%
2276
25%
700
58%
700
34%
1263
November16th to endNight
37%
720
24%
2340
17%
720
47%
720
27%
1405
December1st to 15thNight
32%
738
16%
2358
12%
738
38%
738
19%
1621
December16th to endNight
28%
960
18%
2688
8%
960
37%
960
20%
1929

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
12%6%25%5%3445%7%41%
48164
Night
13%6%24423447%44%
47213
TransparencyDay
40%411%24%15%2
47847
Night
39%410%23%17%3
47034
SeeingDay
13%419%23%24%14%
5803
Night
17%6%22%30%20%2
15766

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
19%7%38%43435%5%33%
1432
16th to endDay
12%9%46%5%24446%38%
1692
February1st to 15thDay
15%10%46%423346%37%
1750
16th to endDay
13%10%36%6%3445%6%35%
1580
March1st to 15thDay
21%8%25%5%23445%37%
1800
16th to endDay
17%8%35%6%2445%6%34%
2210
April1st to 15thDay
12%7%345%2445%7%42%
2151
16th to endDay
15%6%35%42445%6%41%
2173
May1st to 15thDay
16%6%35%6%345%6%7%34%
2331
16th to endDay
9%5%26%6%35%5%6%8%38%
2449
June1st to 15thDay
7%3145%35%5%7%9%46%
2520
16th to endDay
5%3146%35%7%6%10%44%
2520
July1st to 15thDay
9%5%25%6%36%5%6%8%40%
2520
16th to endDay
5%2145%36%7%8%12%39%
2601
August1st to 15thDay
5%5%25%435%5%7%9%43%
2198
16th to endDay
7%5%245%345%6%9%44%
2292
September1st to 15thDay
11%5%25%5%3446%7%42%
2112
16th to endDay
11%5%14424347%50%
1980
October1st to 15thDay
12%424313337%51%
1855
16th to endDay
16%413422335%51%
1661
November1st to 15thDay
11%425%5%23336%52%
1582
16th to endDay
19%5%1332445%5%43%
1620
December1st to 15thDay
19%9%36%5%23436%35%
1599
16th to endDay
18%9%45%5%23335%36%
1536
January1st to 15thNight
17%9%36%5%23345%37%
2506
16th to endNight
16%8%46%42445%6%38%
2526
February1st to 15thNight
19%9%45%5%2333437%
2103
16th to endNight
15%8%36%434445%38%
1893
March1st to 15thNight
16%8%45%323336%40%
2160
16th to endNight
16%8%345%2445%7%37%
2022
April1st to 15thNight
13%6%1332345%6%48%
1797
16th to endNight
15%5%35%5%23447%43%
1785
May1st to 15thNight
16%6%35%42445%7%40%
1619
16th to endNight
6%226%5%25%47%10%44%
1660
June1st to 15thNight
7%3234245%6%10%50%
1440
16th to endNight
3114426%47%12%49%
1440
July1st to 15thNight
7%4234345%410%48%
1440
16th to endNight
7%3134445%5%9%50%
1565
August1st to 15thNight
5%3144245%5%9%52%
1760
16th to endNight
6%41442445%9%51%
1910
September1st to 15thNight
12%423323446%50%
1834
16th to endNight
10%5%23332336%53%
1980
October1st to 15thNight
11%423323446%53%
1900
16th to endNight
16%6%2432323449%
2211
November1st to 15thNight
12%424313345%53%
2276
16th to endNight
17%423323346%47%
2340
December1st to 15thNight
21%10%35%423345%34%
2358
16th to endNight
23%8%35%423335%35%
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
52%39%22%11%
1433
16th to endDay
47%310%28%8%
1692
February1st to 15thDay
48%39%26%11%1
1752
16th to endDay
49%313%20%11%1
1580
March1st to 15thDay
49%48%22%12%1
1800
16th to endDay
50%412%24%7%
2211
April1st to 15thDay
41%410%23%18%1
2151
16th to endDay
42%410%27%12%1
2173
May1st to 15thDay
46%6%12%20%11%
2331
16th to endDay
40%6%15%20%13%2
2453
June1st to 15thDay
31%7%12%26%19%2
2520
16th to endDay
32%6%13%22%20%3
2520
July1st to 15thDay
40%5%11%23%13%4
2371
16th to endDay
32%7%20%24%12%2
2438
August1st to 15thDay
34%6%12%27%16%2
2185
16th to endDay
35%5%11%24%18%4
2292
September1st to 15thDay
39%5%9%23%17%4
2112
16th to endDay
35%47%23%24%4
1980
October1st to 15thDay
32%39%26%23%4
1855
16th to endDay
36%35%28%21%4
1661
November1st to 15thDay
35%28%22%23%7%
1582
16th to endDay
41%27%28%16%2
1620
December1st to 15thDay
51%311%20%11%1
1599
16th to endDay
50%311%23%9%1
1536
January1st to 15thNight
49%37%22%16%1
2506
16th to endNight
47%311%22%12%1
2526
February1st to 15thNight
52%37%23%11%1
2112
16th to endNight
47%410%22%13%1
1893
March1st to 15thNight
46%310%20%14%4
2160
16th to endNight
46%413%22%11%1
2022
April1st to 15thNight
34%410%25%19%5%
1797
16th to endNight
40%37%25%17%4
1785
May1st to 15thNight
42%411%24%14%1
1620
16th to endNight
32%9%13%24%16%3
1662
June1st to 15thNight
28%6%14%26%21%3
1440
16th to endNight
25%7%16%23%22%5%
1440
July1st to 15thNight
32%5%12%27%16%5%
1360
16th to endNight
29%5%15%29%17%2
1465
August1st to 15thNight
26%7%14%25%23%2
1749
16th to endNight
28%412%29%20%4
1910
September1st to 15thNight
34%37%27%20%5%
1834
16th to endNight
33%37%21%26%7%
1980
October1st to 15thNight
31%37%22%28%6%
1900
16th to endNight
39%25%25%20%6%
2211
November1st to 15thNight
32%27%23%25%8%
2276
16th to endNight
39%28%25%19%3
2340
December1st to 15thNight
51%311%18%12%2
2358
16th to endNight
52%29%21%11%1
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
30%13%35%11%6%3
90
16th to endDay
15%11%48%19%4
96
February1st to 15thDay
20%18%41%15%4
90
16th to endDay
23%12%35%18%9%
81
March1st to 15thDay
30%10%38%15%5%
90
16th to endDay
20%7%31%27%10%1
261
April1st to 15thDay
16%10%29%25%14%2
270
16th to endDay
18%5%25%25%18%6%
270
May1st to 15thDay
18%9%22%27%14%7%
288
16th to endDay
14%219%26%22%13%
349
June1st to 15thDay
8%216%22%31%18%
495
16th to endDay
6%317%32%26%13%
495
July1st to 15thDay
13%114%28%26%14%
475
16th to endDay
5%18%20%34%30%
461
August1st to 15thDay
10%17%20%33%26%
313
16th to endDay
13%6%19%40%20%
332
September1st to 15thDay
13%17%18%31%27%
315
16th to endDay
14%11%18%34%21%
314
October1st to 15thDay
12%118%25%29%12%
256
16th to endDay
16%223%30%21%5%
96
November1st to 15thDay
3327%27%25%12%
90
16th to endDay
26%8%28%23%11%1
90
December1st to 15thDay
13%8%41%21%11%4
90
16th to endDay
23%12%41%19%2
96
January1st to 15thNight
22%13%31%27%4
900
16th to endNight
21%11%35%27%3
915
February1st to 15thNight
24%12%33%26%2
704
16th to endNight
20%12%37%27%2
631
March1st to 15thNight
21%11%31%30%4
720
16th to endNight
20%6%27%32%11%
651
April1st to 15thNight
17%9%28%31%11%
539
16th to endNight
16%5%26%34%15%
540
May1st to 15thNight
21%321%33%17%1
540
16th to endNight
7%118%36%32%4
563
June1st to 15thNight
8%112%37%35%3
540
16th to endNight
4110%40%39%3
540
July1st to 15thNight
9%15%34%43%5%
510
16th to endNight
9%6%29%42%11%
564
August1st to 15thNight
7%6%28%46%10%
539
16th to endNight
8%6%29%49%6%
573
September1st to 15thNight
15%27%26%38%9%
574
16th to endNight
12%213%25%37%8%
717
October1st to 15thNight
13%316%32%28%6%
684
16th to endNight
20%5%23%32%17%1
704
November1st to 15thNight
13%8%24%33%18%1
700
16th to endNight
21%8%28%27%12%
720
December1st to 15thNight
27%9%25%28%8%
738
16th to endNight
27%9%30%27%5%
960
Page generated at 2017-10-07 13:07:49. Version ac04

Copyright 2017 A. Danko


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