Knox College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Knox College Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
38%
15958
19%
46898
12%
15914
46%
15914
26%
30282

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
23%
900
16%
2506
5%
895
32%
895
21%
1751
January16th to endNight
22%
960
15%
2546
4%
960
30%
960
20%
1833
February1st to 15thNight
25%
864
14%
2275
3%
863
33%
863
21%
1626
February16th to endNight
25%
631
21%
1893
7%
631
37%
631
23%
1222
March1st to 15thNight
27%
669
18%
2109
10%
669
35%
669
21%
1400
March16th to endNight
28%
576
13%
2029
8%
576
36%
576
16%
1399
April1st to 15thNight
29%
539
17%
1797
13%
539
39%
539
22%
1149
April16th to endNight
36%
540
18%
1800
14%
540
45%
540
21%
1186
May1st to 15thNight
35%
540
17%
1550
10%
540
42%
540
23%
1064
May16th to endNight
46%
563
19%
1497
11%
561
52%
561
32%
968
June1st to 15thNight
56%
540
18%
1440
11%
540
60%
540
36%
890
June16th to endNight
50%
540
18%
1440
9%
540
54%
540
35%
902
July1st to 15thNight
67%
510
18%
1360
12%
510
69%
510
39%
831
July16th to endNight
73%
564
24%
1423
18%
531
76%
531
44%
804
August1st to 15thNight
71%
539
22%
1636
23%
536
73%
536
40%
879
August16th to endNight
69%
573
22%
1910
24%
573
74%
573
36%
1061
September1st to 15thNight
62%
540
29%
1800
30%
540
66%
540
37%
956
September16th to endNight
57%
620
28%
1818
20%
620
65%
620
37%
1037
October1st to 15thNight
47%
660
28%
1980
20%
660
54%
660
35%
1135
October16th to endNight
34%
704
20%
2159
12%
704
43%
704
26%
1341
November1st to 15thNight
33%
700
25%
2276
16%
700
45%
700
27%
1347
November16th to endNight
26%
826
19%
2446
9%
826
37%
826
23%
1600
December1st to 15thNight
22%
900
14%
2520
5%
900
30%
900
19%
1823
December16th to endNight
20%
960
13%
2688
4%
960
28%
960
14%
2078

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%7%35%5%3445%7%38%
47951
Night
13%7%35%424446%42%
47067
Cloud CoverDay
13%7%35%5%3445%7%38%
47959
Night
13%7%35%424446%42%
47072
TransparencyDay
44%5%12%22%12%1
47637
Night
41%412%23%15%2
46899
SeeingDay
14%6%25%27%19%5%
5978
Night
16%8%29%30%13%1
15960

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
13%12%5%9%6%45%436%28%
1432
16th to endDay
14%15%48%7%35%345%25%
1677
February1st to 15thDay
14%11%5%7%6%25%436%31%
1588
16th to endDay
13%10%46%7%3435%6%33%
1580
March1st to 15thDay
15%10%45%6%24446%34%
1852
16th to endDay
17%10%37%5%3446%7%28%
2193
April1st to 15thDay
16%10%45%424346%36%
2151
16th to endDay
20%7%26%6%34445%34%
2160
May1st to 15thDay
19%7%35%6%25%5%5%7%31%
2400
16th to endDay
15%6%25%5%35%45%8%35%
2617
June1st to 15thDay
11%5%36%5%35%45%7%41%
2520
16th to endDay
8%5%25%5%35%5%6%9%41%
2520
July1st to 15thDay
7%3245%35%6%7%9%43%
2520
16th to endDay
5%325%5%36%5%7%10%44%
2647
August1st to 15thDay
6%5%245%346%7%9%41%
2313
16th to endDay
9%416%5%35%5%5%7%45%
2292
September1st to 15thDay
11%323424446%50%
2160
16th to endDay
8%5%2443446%7%47%
1896
October1st to 15thDay
15%5%24323335%48%
1650
16th to endDay
17%7%25%32445%5%41%
1713
November1st to 15thDay
14%8%245%2335%5%43%
1582
16th to endDay
17%9%45%424346%37%
1512
December1st to 15thDay
18%13%47%6%34446%27%
1440
16th to endDay
19%14%5%7%6%23346%26%
1536
January1st to 15thNight
13%9%47%5%34445%37%
2506
16th to endNight
11%11%5%7%6%35%445%33%
2546
February1st to 15thNight
14%9%46%5%35%45%6%34%
2272
16th to endNight
13%8%46%424346%41%
1893
March1st to 15thNight
15%8%45%5%23445%40%
2096
16th to endNight
16%9%45%6%3435%6%32%
2029
April1st to 15thNight
14%8%26%433446%40%
1797
16th to endNight
18%6%36%5%23446%38%
1800
May1st to 15thNight
17%6%36%5%34447%37%
1550
16th to endNight
9%4346%3446%8%43%
1496
June1st to 15thNight
10%5%2343445%7%49%
1440
16th to endNight
8%3346%35%5%6%8%45%
1440
July1st to 15thNight
7%213435%5%6%10%50%
1440
16th to endNight
4214326%5%6%10%52%
1519
August1st to 15thNight
332443445%8%55%
1646
16th to endNight
8%3135%2335%7%53%
1910
September1st to 15thNight
12%413323346%56%
1800
16th to endNight
7%424435%46%7%50%
1818
October1st to 15thNight
9%6%2441335%5%53%
1980
16th to endNight
15%6%2442345%5%45%
2159
November1st to 15thNight
12%7%25%313236%50%
2276
16th to endNight
17%8%25%5%23446%40%
2446
December1st to 15thNight
18%11%47%434345%33%
2520
16th to endNight
20%13%5%7%5%2433427%
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
13%12%5%8%7%45%436%28%
1432
16th to endDay
14%15%5%8%7%44345%25%
1677
February1st to 15thDay
14%11%5%7%5%35%446%31%
1588
16th to endDay
13%10%46%7%3435%6%33%
1580
March1st to 15thDay
15%10%46%6%24447%33%
1862
16th to endDay
17%11%46%6%345%5%7%29%
2191
April1st to 15thDay
16%10%46%433346%36%
2151
16th to endDay
19%8%26%6%34345%34%
2160
May1st to 15thDay
19%7%36%5%35%46%7%30%
2400
16th to endDay
15%7%245%445%5%8%35%
2617
June1st to 15thDay
11%6%26%435%5%5%7%42%
2520
16th to endDay
9%5%25%435%5%6%9%41%
2520
July1st to 15thDay
6%415%5%36%5%7%9%43%
2520
16th to endDay
5%4246%35%5%7%11%43%
2647
August1st to 15thDay
6%5%25%5%347%7%9%42%
2313
16th to endDay
9%5%25%5%25%5%5%8%44%
2292
September1st to 15thDay
11%324324446%50%
2160
16th to endDay
9%5%244345%5%8%46%
1896
October1st to 15thDay
15%5%14423345%49%
1650
16th to endDay
16%7%34324446%41%
1713
November1st to 15thDay
14%8%3442445%5%43%
1582
16th to endDay
17%9%45%423345%37%
1512
December1st to 15thDay
18%12%37%5%34445%28%
1440
16th to endDay
19%13%6%6%6%23346%26%
1536
January1st to 15thNight
13%9%5%7%5%34345%37%
2506
16th to endNight
12%11%5%8%5%25%445%33%
2546
February1st to 15thNight
14%9%45%5%35%45%6%34%
2265
16th to endNight
13%8%45%423346%41%
1893
March1st to 15thNight
16%9%45%42444439%
2109
16th to endNight
16%9%46%5%34447%32%
2029
April1st to 15thNight
14%8%36%434346%40%
1797
16th to endNight
18%6%26%5%23446%38%
1800
May1st to 15thNight
17%5%36%5%34446%37%
1549
16th to endNight
9%4246%3447%8%42%
1496
June1st to 15thNight
10%423434448%48%
1440
16th to endNight
8%425%5%35%46%8%45%
1440
July1st to 15thNight
6%212435%5%6%10%50%
1440
16th to endNight
4224336%5%6%10%52%
1519
August1st to 15thNight
332442445%8%55%
1646
16th to endNight
8%3135%2445%7%53%
1910
September1st to 15thNight
12%313323346%56%
1800
16th to endNight
7%324425%5%5%7%50%
1818
October1st to 15thNight
10%6%2442335%5%53%
1980
16th to endNight
16%5%24424346%45%
2159
November1st to 15thNight
13%7%24313236%50%
2276
16th to endNight
17%7%25%423446%40%
2446
December1st to 15thNight
18%11%37%434345%33%
2520
16th to endNight
20%13%5%7%5%3433427%
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
57%411%15%10%
1433
16th to endDay
60%313%15%7%
1677
February1st to 15thDay
53%316%19%5%
1589
16th to endDay
50%413%21%9%
1580
March1st to 15thDay
49%415%22%7%
1862
16th to endDay
53%414%20%5%
2193
April1st to 15thDay
49%311%23%11%
2151
16th to endDay
51%49%19%12%1
2160
May1st to 15thDay
51%5%12%21%8%
2400
16th to endDay
45%7%12%19%14%1
2621
June1st to 15thDay
39%5%12%24%15%1
2520
16th to endDay
36%7%13%23%16%2
2520
July1st to 15thDay
34%6%14%26%14%3
2371
16th to endDay
33%6%16%26%14%2
2480
August1st to 15thDay
34%7%14%26%16%1
2299
16th to endDay
35%6%12%25%17%3
2292
September1st to 15thDay
32%49%26%21%5%
2160
16th to endDay
34%412%27%19%1
1896
October1st to 15thDay
37%39%28%19%1
1650
16th to endDay
42%312%24%13%2
1713
November1st to 15thDay
41%312%25%14%2
1582
16th to endDay
48%315%23%8%1
1512
December1st to 15thDay
57%314%17%6%
1440
16th to endDay
59%411%14%8%1
1536
January1st to 15thNight
48%312%19%13%
2506
16th to endNight
51%315%19%9%
2546
February1st to 15thNight
50%313%20%10%1
2275
16th to endNight
44%312%26%11%
1893
March1st to 15thNight
46%412%23%10%1
2109
16th to endNight
52%413%20%8%1
2029
April1st to 15thNight
44%310%24%14%2
1797
16th to endNight
47%310%19%14%3
1800
May1st to 15thNight
47%412%22%13%
1550
16th to endNight
37%5%14%20%19%2
1498
June1st to 15thNight
33%5%12%25%18%4
1440
16th to endNight
34%6%13%21%21%4
1440
July1st to 15thNight
29%7%12%29%18%3
1360
16th to endNight
25%5%16%30%18%2
1423
August1st to 15thNight
25%6%15%31%17%3
1636
16th to endNight
28%6%11%27%20%5%
1910
September1st to 15thNight
29%39%28%24%5%
1800
16th to endNight
30%411%29%21%3
1818
October1st to 15thNight
32%39%26%22%4
1980
16th to endNight
40%311%25%17%1
2159
November1st to 15thNight
37%310%24%19%4
2276
16th to endNight
43%411%27%12%
2446
December1st to 15thNight
53%313%21%8%
2520
16th to endNight
60%310%16%8%
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%15%27%22%3
90
16th to endDay
21%15%37%14%9%1
96
February1st to 15thDay
18%13%43%17%5%1
90
16th to endDay
17%13%38%22%6%2
81
March1st to 15thDay
24%20%35%15%4
90
16th to endDay
27%14%28%18%10%1
177
April1st to 15thDay
20%13%30%23%12%
270
16th to endDay
24%7%27%22%14%4
270
May1st to 15thDay
20%11%28%25%10%3
390
16th to endDay
17%7%29%25%14%4
517
June1st to 15thDay
12%5%26%29%21%5%
495
16th to endDay
11%6%31%28%17%5%
495
July1st to 15thDay
12%220%34%20%10%
475
16th to endDay
6%118%32%31%8%
515
August1st to 15thDay
6%117%34%30%10%
466
16th to endDay
8%314%30%30%13%
332
September1st to 15thDay
10%312%31%34%7%
315
16th to endDay
8%419%29%30%8%
262
October1st to 15thDay
12%6%23%28%18%10%
90
16th to endDay
20%8%31%28%11%
96
November1st to 15thDay
48%33%25%21%6%
90
16th to endDay
45%12%26%10%41
90
December1st to 15thDay
22%16%32%20%7%1
90
16th to endDay
30%14%47%5%2
96
January1st to 15thNight
17%14%40%19%7%
900
16th to endNight
17%13%39%26%3
960
February1st to 15thNight
20%11%35%25%6%
866
16th to endNight
18%13%39%22%5%
631
March1st to 15thNight
21%10%35%25%6%
669
16th to endNight
22%12%31%27%6%
576
April1st to 15thNight
19%13%34%26%5%
539
16th to endNight
20%9%27%33%8%
540
May1st to 15thNight
19%6%31%31%9%1
540
16th to endNight
11%429%39%15%
563
June1st to 15thNight
12%421%42%17%
540
16th to endNight
10%230%37%18%
540
July1st to 15thNight
9%115%43%28%2
510
16th to endNight
5%112%44%32%2
564
August1st to 15thNight
4111%44%32%5%
539
16th to endNight
9%111%41%32%3
573
September1st to 15thNight
13%413%37%27%4
540
16th to endNight
9%5%21%33%26%4
620
October1st to 15thNight
11%6%29%31%19%2
660
16th to endNight
21%9%32%27%9%
704
November1st to 15thNight
17%10%34%27%9%1
700
16th to endNight
22%11%35%22%7%
826
December1st to 15thNight
24%12%35%23%5%
900
16th to endNight
27%13%32%22%4
960
Page generated at 2017-09-21 06:18:19. Version ac04

Copyright 2017 A. Danko


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