Sunny Knoll Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunny Knoll Observatory clear sky chart from 2005-11-05 to 2017-04-30.

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%
15559
19%
45663
11%
15516
44%
15516
25%
29664

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
14%
2506
6%
895
31%
895
21%
1742
January16th to endNight
22%
960
14%
2565
4%
960
29%
960
18%
1860
February1st to 15thNight
25%
871
15%
2283
3%
871
33%
871
22%
1621
February16th to endNight
25%
631
20%
1893
7%
631
37%
631
22%
1245
March1st to 15thNight
29%
672
17%
2112
10%
672
36%
672
22%
1369
March16th to endNight
28%
576
13%
2028
9%
576
36%
576
17%
1391
April1st to 15thNight
29%
539
17%
1797
12%
539
38%
539
21%
1176
April16th to endNight
38%
537
18%
1791
14%
537
47%
537
21%
1197
May1st to 15thNight
33%
495
18%
1393
9%
495
42%
495
24%
970
May16th to endNight
47%
515
17%
1369
10%
513
52%
513
32%
900
June1st to 15thNight
50%
495
18%
1320
10%
495
54%
495
34%
823
June16th to endNight
50%
495
16%
1320
9%
495
54%
495
35%
824
July1st to 15thNight
62%
465
20%
1240
13%
465
66%
465
44%
719
July16th to endNight
67%
522
22%
1305
15%
489
69%
489
42%
751
August1st to 15thNight
73%
494
24%
1475
24%
491
75%
491
44%
780
August16th to endNight
64%
525
21%
1750
22%
525
69%
525
35%
975
September1st to 15thNight
62%
495
30%
1650
30%
495
67%
495
37%
878
September16th to endNight
55%
605
25%
1770
16%
605
63%
605
36%
1027
October1st to 15thNight
44%
660
27%
1980
19%
660
51%
660
33%
1162
October16th to endNight
32%
704
20%
2169
11%
704
42%
704
24%
1352
November1st to 15thNight
34%
700
26%
2276
17%
700
45%
700
26%
1331
November16th to endNight
26%
843
18%
2463
9%
843
35%
843
24%
1623
December1st to 15thNight
20%
900
14%
2520
4%
900
29%
900
18%
1855
December16th to endNight
20%
960
13%
2688
5%
960
27%
960
14%
2093

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%35%5%3445%7%37%
46075
Night
14%7%35%424346%41%
45831
Cloud CoverDay
14%7%35%5%3445%7%37%
46083
Night
14%7%35%424446%41%
45836
TransparencyDay
45%413%23%12%1
45760
Night
43%312%24%14%2
45664
SeeingDay
16%8%26%26%16%5%
5344
Night
18%8%29%30%12%1
15562

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%10%5%9%6%4445%5%29%
1432
16th to endDay
14%13%6%9%6%34435%27%
1657
February1st to 15thDay
15%11%47%5%34446%32%
1580
16th to endDay
15%8%46%7%3445%7%34%
1580
March1st to 15thDay
15%10%36%5%3445%6%35%
1847
16th to endDay
18%10%36%5%25%447%31%
2196
April1st to 15thDay
17%9%5%6%424436%34%
2151
16th to endDay
22%8%35%5%32446%33%
2148
May1st to 15thDay
19%7%35%6%35%5%5%8%28%
2226
16th to endDay
13%6%26%5%35%5%5%8%36%
2393
June1st to 15thDay
12%6%25%5%36%47%7%37%
2310
16th to endDay
9%4245%35%5%7%9%43%
2310
July1st to 15thDay
7%415%6%25%6%6%9%44%
2310
16th to endDay
7%325%5%35%5%7%10%43%
2459
August1st to 15thDay
6%4235%46%6%7%9%42%
2144
16th to endDay
11%42443345%8%47%
2100
September1st to 15thDay
13%41343445%6%48%
1980
16th to endDay
10%424435%5%5%7%46%
1848
October1st to 15thDay
15%6%23323346%48%
1650
16th to endDay
16%6%35%424446%41%
1702
November1st to 15thDay
12%8%25%4345%5%6%41%
1582
16th to endDay
17%11%36%423245%38%
1494
December1st to 15thDay
20%12%37%6%345%35%27%
1440
16th to endDay
20%13%6%7%5%23336%26%
1536
January1st to 15thNight
13%9%47%43435%6%36%
2506
16th to endNight
12%11%6%8%6%34446%31%
2565
February1st to 15thNight
13%10%46%5%34435%37%
2280
16th to endNight
15%10%36%423345%40%
1893
March1st to 15thNight
17%9%34424335%42%
2099
16th to endNight
17%8%46%6%25%45%6%32%
2028
April1st to 15thNight
16%8%35%424445%40%
1797
16th to endNight
19%8%45%324346%36%
1791
May1st to 15thNight
17%5%35%435%46%7%36%
1393
16th to endNight
11%5%24435%5%5%9%42%
1368
June1st to 15thNight
11%6%15%32435%7%47%
1320
16th to endNight
9%415%5%35%46%8%45%
1320
July1st to 15thNight
8%31332247%8%53%
1320
16th to endNight
5%3144345%6%12%48%
1401
August1st to 15thNight
431442435%8%56%
1484
16th to endNight
9%32442345%8%51%
1750
September1st to 15thNight
10%423423336%56%
1650
16th to endNight
7%414435%5%6%9%47%
1770
October1st to 15thNight
10%6%245%23335%52%
1980
16th to endNight
17%7%24423345%44%
2169
November1st to 15thNight
12%6%24422236%50%
2276
16th to endNight
18%7%35%423336%40%
2463
December1st to 15thNight
19%11%46%5%24345%32%
2520
16th to endNight
22%13%47%5%3433426%
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%10%5%8%7%345%46%29%
1432
16th to endDay
15%13%6%9%6%33436%27%
1657
February1st to 15thDay
15%11%47%6%24346%31%
1580
16th to endDay
15%7%36%7%3435%7%33%
1580
March1st to 15thDay
16%9%26%5%2445%7%34%
1857
16th to endDay
18%9%36%5%35%447%31%
2194
April1st to 15thDay
17%9%47%434446%33%
2151
16th to endDay
21%9%35%5%34446%33%
2148
May1st to 15thDay
19%8%36%6%35%45%8%28%
2226
16th to endDay
14%6%26%6%35%5%5%8%36%
2393
June1st to 15thDay
12%5%35%5%35%5%6%8%37%
2310
16th to endDay
9%4245%35%47%9%42%
2310
July1st to 15thDay
7%325%6%25%6%6%9%44%
2310
16th to endDay
7%325%6%35%5%7%10%43%
2459
August1st to 15thDay
6%4145%36%6%7%10%42%
2144
16th to endDay
11%42443435%8%47%
2100
September1st to 15thDay
13%41343345%6%48%
1980
16th to endDay
10%5%14435%5%5%8%46%
1848
October1st to 15thDay
14%6%23423346%48%
1650
16th to endDay
17%6%25%41445%5%41%
1702
November1st to 15thDay
12%8%35%4335%5%6%41%
1582
16th to endDay
17%11%36%422335%38%
1494
December1st to 15thDay
19%12%37%5%34445%28%
1440
16th to endDay
21%13%6%8%5%23335%26%
1536
January1st to 15thNight
13%10%47%43435%6%35%
2506
16th to endNight
12%10%6%8%5%34446%31%
2565
February1st to 15thNight
13%10%46%434445%37%
2273
16th to endNight
14%9%36%423346%40%
1893
March1st to 15thNight
17%8%35%43333441%
2112
16th to endNight
16%9%46%6%35%446%32%
2028
April1st to 15thNight
16%8%35%424435%40%
1797
16th to endNight
19%8%45%333445%36%
1791
May1st to 15thNight
16%6%245%35%5%6%7%35%
1392
16th to endNight
11%5%245%25%5%6%8%42%
1368
June1st to 15thNight
11%6%25%32435%7%47%
1320
16th to endNight
9%415%5%35%46%7%45%
1320
July1st to 15thNight
8%31322347%8%53%
1320
16th to endNight
5%2234246%6%10%48%
1401
August1st to 15thNight
421433345%8%56%
1484
16th to endNight
8%42432445%7%51%
1750
September1st to 15thNight
10%413423346%55%
1650
16th to endNight
6%4245%345%5%9%48%
1770
October1st to 15thNight
10%5%25%5%23345%51%
1980
16th to endNight
17%6%24423345%43%
2169
November1st to 15thNight
12%6%34422335%50%
2276
16th to endNight
18%8%35%424346%39%
2463
December1st to 15thNight
20%11%46%5%24345%31%
2520
16th to endNight
22%13%47%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
55%312%16%10%
1433
16th to endDay
59%312%16%8%
1657
February1st to 15thDay
53%214%23%6%
1581
16th to endDay
49%5%13%22%8%1
1580
March1st to 15thDay
49%316%21%8%
1857
16th to endDay
52%314%22%5%1
2196
April1st to 15thDay
52%210%22%11%
2151
16th to endDay
52%310%18%12%2
2148
May1st to 15thDay
54%412%20%8%
2226
16th to endDay
44%6%13%20%13%1
2397
June1st to 15thDay
43%412%25%13%
2310
16th to endDay
36%5%13%24%17%1
2310
July1st to 15thDay
36%413%27%14%2
2161
16th to endDay
35%6%16%24%14%2
2292
August1st to 15thDay
34%6%13%26%16%1
2129
16th to endDay
35%412%28%16%3
2100
September1st to 15thDay
35%38%26%21%3
1980
16th to endDay
35%311%28%18%1
1848
October1st to 15thDay
37%29%30%18%1
1650
16th to endDay
43%314%25%11%1
1702
November1st to 15thDay
41%311%26%13%2
1582
16th to endDay
48%216%23%7%
1494
December1st to 15thDay
57%315%17%6%
1440
16th to endDay
61%313%12%8%
1536
January1st to 15thNight
49%314%19%13%
2506
16th to endNight
52%316%17%9%
2565
February1st to 15thNight
49%312%23%10%
2283
16th to endNight
45%212%25%12%1
1893
March1st to 15thNight
45%214%24%10%2
2112
16th to endNight
51%412%21%8%1
2028
April1st to 15thNight
46%29%23%14%3
1797
16th to endNight
48%29%21%13%3
1791
May1st to 15thNight
46%5%12%21%13%
1393
16th to endNight
38%5%12%23%16%3
1370
June1st to 15thNight
36%313%27%17%2
1320
16th to endNight
35%413%20%20%4
1320
July1st to 15thNight
28%312%32%18%4
1240
16th to endNight
28%415%32%15%3
1305
August1st to 15thNight
24%414%34%17%3
1475
16th to endNight
31%411%27%19%5%
1750
September1st to 15thNight
30%29%26%27%3
1650
16th to endNight
31%411%29%20%3
1770
October1st to 15thNight
35%29%26%22%3
1980
16th to endNight
42%210%26%15%2
2169
November1st to 15thNight
36%310%25%19%4
2276
16th to endNight
45%212%27%11%
2463
December1st to 15thNight
55%311%21%7%
2520
16th to endNight
62%39%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
27%14%37%16%3
90
16th to endDay
23%12%38%13%10%1
96
February1st to 15thDay
20%25%34%15%4
90
16th to endDay
19%17%35%17%6%3
81
March1st to 15thDay
26%15%41%12%31
90
16th to endDay
29%16%26%18%8%1
180
April1st to 15thDay
19%12%35%20%11%1
270
16th to endDay
25%9%26%22%14%1
266
May1st to 15thDay
20%12%29%23%10%2
335
16th to endDay
18%8%27%28%12%5%
437
June1st to 15thDay
14%6%29%29%14%5%
420
16th to endDay
11%428%30%17%7%
420
July1st to 15thDay
11%323%29%22%10%
400
16th to endDay
7%121%34%24%9%
445
August1st to 15thDay
9%218%36%25%8%
403
16th to endDay
8%316%34%26%11%
268
September1st to 15thDay
12%220%30%23%10%
255
16th to endDay
8%7%21%30%24%7%
246
October1st to 15thDay
15%10%24%28%14%6%
90
16th to endDay
22%8%39%21%7%
96
November1st to 15thDay
5%14%32%25%14%7%
90
16th to endDay
45%8%28%13%21
90
December1st to 15thDay
25%15%32%20%5%1
90
16th to endDay
29%26%38%5%1
96
January1st to 15thNight
18%14%37%22%6%
900
16th to endNight
18%13%34%27%5%
960
February1st to 15thNight
20%12%34%27%5%
874
16th to endNight
20%10%38%24%4
631
March1st to 15thNight
23%9%31%28%7%
672
16th to endNight
22%8%33%27%7%
576
April1st to 15thNight
22%10%33%27%5%
539
16th to endNight
22%7%27%34%6%
537
May1st to 15thNight
19%437%27%9%1
495
16th to endNight
12%429%37%16%
515
June1st to 15thNight
12%425%42%14%
495
16th to endNight
10%227%40%17%1
495
July1st to 15thNight
10%216%39%26%3
465
16th to endNight
7%115%43%29%2
522
August1st to 15thNight
5%11%44%33%4
494
16th to endNight
10%114%39%29%4
525
September1st to 15thNight
12%216%37%25%5%
495
16th to endNight
8%423%32%27%3
605
October1st to 15thNight
12%5%30%29%20%1
660
16th to endNight
22%9%31%26%9%
704
November1st to 15thNight
17%11%32%27%9%1
700
16th to endNight
22%11%33%25%6%
843
December1st to 15thNight
24%12%34%23%5%
900
16th to endNight
29%11%29%25%4
960
Page generated at 2017-04-30 19:40:10. Version ac04

Copyright 2017 A. Danko


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