King's Knoll Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the King's 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
37%
15729
19%
46957
12%
15687
44%
15687
22%
30827

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
17%
900
14%
2506
5%
895
25%
895
13%
1936
January16th to endNight
20%
786
15%
2514
8%
786
29%
786
12%
1847
February1st to 15thNight
18%
701
13%
2154
5%
701
26%
701
14%
1537
February16th to endNight
21%
631
15%
1893
7%
631
28%
631
14%
1368
March1st to 15thNight
24%
720
16%
2104
8%
720
31%
720
16%
1465
March16th to endNight
26%
768
16%
2112
8%
768
35%
768
20%
1469
April1st to 15thNight
28%
554
19%
1812
11%
554
39%
554
20%
1170
April16th to endNight
33%
540
21%
1658
7%
540
46%
540
22%
1044
May1st to 15thNight
28%
540
16%
1620
8%
540
37%
540
17%
1127
May16th to endNight
44%
562
18%
1684
11%
561
51%
561
25%
1025
June1st to 15thNight
53%
540
19%
1520
14%
540
59%
540
32%
891
June16th to endNight
52%
540
18%
1440
9%
540
60%
540
35%
854
July1st to 15thNight
54%
510
17%
1360
12%
510
57%
510
33%
845
July16th to endNight
61%
564
22%
1557
15%
531
70%
531
37%
884
August1st to 15thNight
64%
539
24%
1609
19%
536
68%
536
37%
912
August16th to endNight
70%
573
24%
1855
21%
573
75%
573
37%
987
September1st to 15thNight
60%
649
27%
1909
22%
649
64%
649
35%
1079
September16th to endNight
56%
717
30%
1980
21%
717
61%
717
34%
1199
October1st to 15thNight
51%
684
29%
1908
22%
684
57%
684
32%
1132
October16th to endNight
36%
704
22%
2211
16%
704
46%
704
24%
1414
November1st to 15thNight
38%
700
26%
2276
18%
700
50%
700
26%
1324
November16th to endNight
27%
720
18%
2340
10%
720
38%
720
16%
1598
December1st to 15thNight
21%
720
13%
2340
7%
720
28%
720
12%
1728
December16th to endNight
16%
867
12%
2595
5%
867
24%
867
11%
1992

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
14%7%36%5%3445%7%37%
48225
Night
14%7%35%5%2445%7%39%
47138
Cloud CoverDay
14%7%36%5%3445%7%37%
48234
Night
14%7%36%5%2445%7%39%
47143
TransparencyDay
45%411%22%13%2
47924
Night
44%311%23%14%2
46957
SeeingDay
15%13%21%21%16%10%
5780
Night
15%20%21%25%15%2
15733

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
19%11%5%8%6%2445%5%27%
1432
16th to endDay
14%13%5%10%6%33445%28%
1707
February1st to 15thDay
15%13%6%7%5%24336%31%
1707
16th to endDay
15%13%5%8%6%34336%30%
1580
March1st to 15thDay
22%10%35%42425%5%32%
1845
16th to endDay
18%9%46%5%24446%31%
2112
April1st to 15thDay
17%7%36%423447%37%
2146
16th to endDay
18%6%25%5%24347%38%
2301
May1st to 15thDay
22%7%36%5%3445%6%31%
2331
16th to endDay
11%5%26%5%45%6%7%8%36%
2431
June1st to 15thDay
10%425%4345%5%8%42%
2436
16th to endDay
8%435%5%35%5%6%8%42%
2520
July1st to 15thDay
11%5%26%6%36%5%5%8%37%
2520
16th to endDay
7%325%5%47%6%7%9%40%
2502
August1st to 15thDay
7%5%15%5%35%5%6%10%41%
2340
16th to endDay
7%4245%35%5%6%9%43%
2345
September1st to 15thDay
11%5%3443445%6%45%
2037
16th to endDay
12%5%24423346%47%
1980
October1st to 15thDay
11%5%25%5%345%47%44%
1850
16th to endDay
17%7%25%423446%41%
1658
November1st to 15thDay
8%6%35%423345%49%
1582
16th to endDay
17%9%36%5%23445%36%
1620
December1st to 15thDay
25%10%6%7%42434427%
1620
16th to endDay
21%13%6%7%424346%25%
1623
January1st to 15thNight
19%9%5%9%7%44435%25%
2506
16th to endNight
16%12%5%7%6%3433429%
2514
February1st to 15thNight
19%9%5%6%5%34445%31%
2152
16th to endNight
16%10%47%5%25%5%5%5%30%
1893
March1st to 15thNight
17%8%37%5%345%45%34%
2091
16th to endNight
16%8%37%5%2445%6%35%
2112
April1st to 15thNight
15%7%35%5%2345%7%39%
1812
16th to endNight
14%5%25%4345%5%7%41%
1658
May1st to 15thNight
19%6%26%6%25%45%6%34%
1620
16th to endNight
9%5%35%425%5%6%9%42%
1682
June1st to 15thNight
7%32343445%9%50%
1520
16th to endNight
5%323425%5%6%9%49%
1440
July1st to 15thNight
9%4145%3445%8%47%
1440
16th to endNight
6%424325%5%5%9%49%
1664
August1st to 15thNight
5%3144445%6%9%49%
1620
16th to endNight
432343446%10%52%
1855
September1st to 15thNight
10%5%1341345%6%52%
1909
16th to endNight
11%414433346%50%
1980
October1st to 15thNight
10%423334447%50%
1908
16th to endNight
16%7%25%5%23336%43%
2211
November1st to 15thNight
13%5%24323347%47%
2276
16th to endNight
18%10%45%5%24346%34%
2340
December1st to 15thNight
22%11%48%5%23345%26%
2340
16th to endNight
22%13%5%7%5%23446%24%
2595

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%11%5%7%6%24445%27%
1432
16th to endDay
14%12%5%9%6%24445%29%
1707
February1st to 15thDay
15%13%5%8%433345%32%
1707
16th to endDay
15%13%5%7%6%24336%30%
1580
March1st to 15thDay
22%9%25%434445%32%
1855
16th to endDay
18%10%45%5%35%345%31%
2111
April1st to 15thDay
17%8%35%424447%37%
2146
16th to endDay
18%6%26%5%33446%38%
2301
May1st to 15thDay
22%7%36%5%35%45%5%31%
2331
16th to endDay
12%5%35%6%35%5%6%9%35%
2431
June1st to 15thDay
10%425%5%26%5%6%8%42%
2436
16th to endDay
8%435%5%35%6%6%8%42%
2520
July1st to 15thDay
11%5%26%6%46%5%6%9%35%
2520
16th to endDay
7%3246%37%7%7%10%39%
2502
August1st to 15thDay
7%415%6%345%6%10%42%
2340
16th to endDay
6%425%5%35%6%6%9%43%
2345
September1st to 15thDay
12%5%25%42445%6%45%
2037
16th to endDay
12%6%24423346%48%
1980
October1st to 15thDay
11%5%15%6%3445%7%45%
1850
16th to endDay
17%6%25%5%23446%41%
1658
November1st to 15thDay
9%6%25%433346%49%
1582
16th to endDay
17%8%46%5%33345%36%
1620
December1st to 15thDay
24%10%5%7%5%3424426%
1620
16th to endDay
21%14%5%8%5%24445%24%
1623
January1st to 15thNight
19%10%5%9%6%44435%26%
2506
16th to endNight
17%12%5%9%6%25%33429%
2514
February1st to 15thNight
19%9%37%5%24346%32%
2145
16th to endNight
17%10%47%5%35%446%29%
1893
March1st to 15thNight
17%8%37%5%34446%34%
2104
16th to endNight
16%8%36%5%3445%7%35%
2112
April1st to 15thNight
15%7%45%5%2445%6%38%
1812
16th to endNight
13%5%25%4345%6%7%41%
1658
May1st to 15thNight
19%6%26%5%25%35%7%34%
1619
16th to endNight
9%5%245%25%5%6%9%42%
1682
June1st to 15thNight
7%41443445%10%50%
1520
16th to endNight
6%2244346%6%10%48%
1440
July1st to 15thNight
9%4245%2445%7%48%
1440
16th to endNight
5%41342446%9%50%
1664
August1st to 15thNight
5%3144445%6%10%49%
1620
16th to endNight
5%214425%46%9%52%
1855
September1st to 15thNight
11%413323347%52%
1909
16th to endNight
12%425%42435%5%50%
1980
October1st to 15thNight
9%423424446%51%
1908
16th to endNight
16%6%25%5%23435%43%
2211
November1st to 15thNight
13%424423348%47%
2276
16th to endNight
18%10%35%424446%34%
2340
December1st to 15thNight
22%11%49%5%23345%27%
2340
16th to endNight
23%12%47%5%24346%24%
2595

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
58%310%17%10%
1433
16th to endDay
57%313%20%5%
1707
February1st to 15thDay
55%311%19%9%
1709
16th to endDay
56%211%23%6%
1580
March1st to 15thDay
53%213%22%7%
1855
16th to endDay
53%412%20%7%
2112
April1st to 15thDay
46%310%24%13%1
2146
16th to endDay
46%29%22%13%4
2301
May1st to 15thDay
53%311%19%10%1
2331
16th to endDay
43%5%13%22%13%1
2435
June1st to 15thDay
38%412%25%17%1
2436
16th to endDay
37%6%13%21%17%3
2520
July1st to 15thDay
43%5%11%20%17%2
2371
16th to endDay
35%5%15%26%13%2
2346
August1st to 15thDay
34%414%25%17%2
2327
16th to endDay
34%5%13%25%16%4
2345
September1st to 15thDay
38%49%23%20%5%
2037
16th to endDay
36%39%23%25%1
1980
October1st to 15thDay
37%48%26%20%2
1850
16th to endDay
44%211%25%13%2
1658
November1st to 15thDay
36%38%25%20%4
1582
16th to endDay
51%28%23%13%
1620
December1st to 15thDay
61%110%17%7%
1620
16th to endDay
62%310%18%5%
1623
January1st to 15thNight
61%27%18%9%
2506
16th to endNight
58%210%20%7%
2514
February1st to 15thNight
53%311%21%7%1
2154
16th to endNight
54%312%21%7%
1893
March1st to 15thNight
50%310%22%11%1
2104
16th to endNight
48%313%25%7%1
2112
April1st to 15thNight
44%39%23%16%1
1812
16th to endNight
40%410%21%15%7%
1658
May1st to 15thNight
50%49%25%9%1
1620
16th to endNight
35%5%14%24%15%4
1684
June1st to 15thNight
29%5%11%29%21%2
1520
16th to endNight
28%6%19%20%20%4
1440
July1st to 15thNight
34%5%13%23%18%6%
1360
16th to endNight
28%5%14%32%17%2
1557
August1st to 15thNight
28%5%14%28%20%2
1609
16th to endNight
26%413%28%20%4
1855
September1st to 15thNight
30%311%24%22%6%
1909
16th to endNight
34%36%25%27%2
1980
October1st to 15thNight
32%47%28%22%4
1908
16th to endNight
43%28%27%14%2
2211
November1st to 15thNight
36%39%22%23%4
2276
16th to endNight
51%29%22%13%
2340
December1st to 15thNight
59%210%18%8%
2340
16th to endNight
61%310%16%7%
2595

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
33%16%36%7%5%
90
16th to endDay
21%23%40%10%3
96
February1st to 15thDay
24%23%36%12%3
90
16th to endDay
17%17%46%17%1
81
March1st to 15thDay
29%17%30%17%4
145
16th to endDay
21%20%32%16%6%2
288
April1st to 15thDay
19%21%23%20%11%2
270
16th to endDay
19%19%22%18%11%8%
270
May1st to 15thDay
23%18%22%19%10%5%
288
16th to endDay
19%14%22%19%12%11%
331
June1st to 15thDay
9%13%18%26%22%9%
411
16th to endDay
10%16%22%29%14%6%
495
July1st to 15thDay
13%11%18%26%17%13%
475
16th to endDay
8%10%9%23%27%19%
362
August1st to 15thDay
11%7%11%21%23%25%
313
16th to endDay
10%6%9%21%30%21%
332
September1st to 15thDay
12%7%14%20%27%17%
315
16th to endDay
14%7%14%16%30%16%
314
October1st to 15thDay
10%10%20%29%21%7%
278
16th to endDay
16%9%34%27%10%1
170
November1st to 15thDay
11%6%25%22%23%11%
90
16th to endDay
27%11%37%18%4
90
December1st to 15thDay
25%15%34%18%32
90
16th to endDay
29%19%39%9%2
96
January1st to 15thNight
18%26%30%19%4
900
16th to endNight
20%25%25%24%3
786
February1st to 15thNight
21%26%27%22%1
704
16th to endNight
18%26%26%24%3
631
March1st to 15thNight
17%26%28%22%4
720
16th to endNight
16%23%28%23%7%
768
April1st to 15thNight
16%22%29%23%8%
554
16th to endNight
13%22%25%23%12%1
540
May1st to 15thNight
18%20%25%23%10%1
540
16th to endNight
11%18%17%29%17%4
563
June1st to 15thNight
7%17%15%36%20%1
540
16th to endNight
5%17%19%33%22%1
540
July1st to 15thNight
11%12%14%30%27%3
510
16th to endNight
6%17%7%29%32%6%
564
August1st to 15thNight
6%9%10%33%34%5%
539
16th to endNight
49%9%32%37%7%
573
September1st to 15thNight
11%11%10%28%31%6%
649
16th to endNight
11%12%11%26%33%5%
717
October1st to 15thNight
11%13%18%30%22%4
684
16th to endNight
17%14%27%26%12%
704
November1st to 15thNight
13%20%24%23%16%1
700
16th to endNight
21%25%22%22%7%
720
December1st to 15thNight
24%23%23%20%6%1
720
16th to endNight
24%26%25%19%3
867
Page generated at 2017-10-07 14:07:47. Version ac04

Copyright 2017 A. Danko


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