Hundred Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hundred Oaks Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
40%
15413
21%
46990
12%
15377
50%
15377
26%
29596

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%
716
23%
2339
8%
716
41%
716
20%
1470
January16th to endNight
22%
768
23%
2496
9%
768
41%
768
23%
1539
February1st to 15thNight
22%
701
22%
2287
8%
701
40%
701
23%
1385
February16th to endNight
21%
631
26%
1913
10%
631
40%
631
23%
1182
March1st to 15thNight
26%
720
23%
1980
10%
720
40%
720
27%
1277
March16th to endNight
27%
768
20%
2112
9%
768
38%
768
25%
1403
April1st to 15thNight
28%
718
21%
1799
5%
718
38%
718
31%
1147
April16th to endNight
40%
720
21%
1800
8%
720
45%
720
32%
1180
May1st to 15thNight
38%
564
15%
1644
7%
564
43%
564
23%
1130
May16th to endNight
55%
436
17%
1558
14%
436
60%
436
24%
953
June1st to 15thNight
63%
360
19%
1440
23%
360
67%
360
25%
826
June16th to endNight
60%
360
17%
1440
17%
360
66%
360
24%
831
July1st to 15thNight
60%
423
13%
1443
14%
423
62%
423
24%
925
July16th to endNight
69%
564
16%
1595
11%
531
74%
531
31%
992
August1st to 15thNight
68%
539
17%
1609
14%
536
68%
536
29%
1053
August16th to endNight
62%
744
18%
1890
11%
744
64%
744
28%
1295
September1st to 15thNight
61%
720
24%
1800
16%
720
63%
720
33%
1193
September16th to endNight
50%
689
20%
1912
17%
689
52%
689
25%
1314
October1st to 15thNight
47%
660
25%
1980
22%
660
54%
660
27%
1270
October16th to endNight
40%
704
30%
2112
20%
704
55%
704
32%
1232
November1st to 15thNight
40%
700
27%
2158
17%
700
53%
700
29%
1292
November16th to endNight
35%
720
22%
2475
14%
720
48%
720
25%
1432
December1st to 15thNight
29%
720
20%
2520
10%
720
42%
720
20%
1603
December16th to endNight
30%
768
23%
2688
12%
768
45%
768
21%
1672

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%5%25%5%3445%7%42%
47898
Night
14%5%2442445%7%44%
47181
Cloud CoverDay
14%5%245%3445%7%42%
47908
Night
14%5%2442445%7%44%
47185
TransparencyDay
40%6%11%22%16%3
47606
Night
39%5%10%22%17%4
46991
SeeingDay
18%7%25%25%16%6%
5701
Night
17%8%27%30%14%1
15422

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
16%6%34424446%43%
1597
16th to endDay
15%7%24324446%43%
1728
February1st to 15thDay
13%7%26%5%34446%42%
1575
16th to endDay
14%5%36%5%34447%41%
1558
March1st to 15thDay
15%5%25%423346%46%
1969
16th to endDay
17%5%26%5%34446%40%
2112
April1st to 15thDay
12%425%323346%50%
2147
16th to endDay
17%5%2443345%5%43%
2160
May1st to 15thDay
18%7%23435%5%5%7%37%
2316
16th to endDay
14%3145%35%5%5%8%41%
2556
June1st to 15thDay
11%314425%5%6%10%42%
2520
16th to endDay
8%3246%35%6%6%11%41%
2520
July1st to 15thDay
11%425%6%35%6%7%9%37%
2427
16th to endDay
6%326%6%36%7%7%11%36%
2465
August1st to 15thDay
12%436%7%46%5%6%9%33%
2340
16th to endDay
12%425%5%45%6%6%9%37%
2300
September1st to 15thDay
12%325%6%35%5%5%6%45%
2160
16th to endDay
18%6%25%5%35%45%7%35%
1881
October1st to 15thDay
18%5%24423345%47%
1650
16th to endDay
14%5%24423325%50%
1760
November1st to 15thDay
13%5%24324335%50%
1699
16th to endDay
16%413223446%48%
1482
December1st to 15thDay
15%6%2432345%6%45%
1440
16th to endDay
19%6%35%42334441%
1536
January1st to 15thNight
17%4335%24346%44%
2339
16th to endNight
16%6%24424445%45%
2496
February1st to 15thNight
14%6%25%324445%46%
2285
16th to endNight
13%7%24423336%46%
1913
March1st to 15thNight
16%4233235%47%45%
1968
16th to endNight
18%5%35%413346%43%
2112
April1st to 15thNight
11%5%245%2345%7%47%
1799
16th to endNight
13%5%23323448%46%
1800
May1st to 15thNight
17%6%35%4235%5%7%37%
1644
16th to endNight
12%4144245%6%10%41%
1557
June1st to 15thNight
9%3235%345%7%10%44%
1440
16th to endNight
7%4245%35%6%6%9%43%
1440
July1st to 15thNight
9%6%25%435%5%7%10%40%
1530
16th to endNight
5%324446%6%8%10%42%
1703
August1st to 15thNight
9%325%5%36%5%6%9%41%
1620
16th to endNight
11%5%25%6%36%5%6%10%36%
1890
September1st to 15thNight
12%4245%235%5%8%45%
1800
16th to endNight
17%7%26%324435%40%
1912
October1st to 15thNight
19%5%13424345%45%
1980
16th to endNight
15%313413345%52%
2112
November1st to 15thNight
13%5%24323435%51%
2158
16th to endNight
15%41442445%5%48%
2475
December1st to 15thNight
16%5%35%5%24446%41%
2520
16th to endNight
17%7%2442335%6%41%
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
16%6%34423446%42%
1597
16th to endDay
15%7%25%324446%42%
1728
February1st to 15thDay
13%7%25%5%25%346%42%
1575
16th to endDay
14%5%36%5%24447%41%
1558
March1st to 15thDay
15%5%24434445%46%
1980
16th to endDay
17%5%25%5%34336%40%
2111
April1st to 15thDay
12%325%42335%6%50%
2147
16th to endDay
17%5%2443345%5%43%
2160
May1st to 15thDay
18%6%244345%5%7%37%
2316
16th to endDay
14%4145%35%45%8%41%
2556
June1st to 15thDay
11%324435%5%6%9%42%
2520
16th to endDay
8%3146%35%6%6%11%41%
2520
July1st to 15thDay
11%425%6%36%5%7%9%37%
2427
16th to endDay
6%326%6%46%8%7%11%36%
2465
August1st to 15thDay
12%5%26%7%46%6%5%9%33%
2340
16th to endDay
12%425%6%45%6%6%9%36%
2300
September1st to 15thDay
12%4246%35%5%46%45%
2160
16th to endDay
18%6%245%3446%7%35%
1881
October1st to 15thDay
17%424422345%47%
1650
16th to endDay
14%5%14423335%50%
1760
November1st to 15thDay
13%423424335%51%
1699
16th to endDay
16%41322445%6%48%
1482
December1st to 15thDay
15%6%23323446%45%
1440
16th to endDay
19%6%26%42434441%
1536
January1st to 15thNight
17%5%24433345%43%
2339
16th to endNight
16%5%24324445%45%
2496
February1st to 15thNight
14%6%24324446%46%
2278
16th to endNight
13%7%25%424346%46%
1913
March1st to 15thNight
16%4243235%5%7%45%
1980
16th to endNight
17%5%35%423337%43%
2112
April1st to 15thNight
12%5%2442335%7%47%
1799
16th to endNight
13%5%3332345%8%46%
1800
May1st to 15thNight
17%6%25%4345%47%37%
1643
16th to endNight
12%4144346%6%10%41%
1557
June1st to 15thNight
8%4245%25%47%10%43%
1440
16th to endNight
7%425%5%35%6%6%9%43%
1440
July1st to 15thNight
9%5%35%425%5%6%9%40%
1530
16th to endNight
5%3245%47%6%7%10%42%
1703
August1st to 15thNight
9%325%5%36%5%6%9%41%
1620
16th to endNight
11%5%26%6%36%5%6%10%36%
1890
September1st to 15thNight
12%5%2442445%7%45%
1800
16th to endNight
17%6%36%424436%40%
1912
October1st to 15thNight
18%5%14423345%45%
1980
16th to endNight
15%31331345%5%52%
2112
November1st to 15thNight
13%5%24323445%51%
2158
16th to endNight
15%41442445%6%48%
2475
December1st to 15thNight
16%6%35%5%24446%41%
2520
16th to endNight
17%7%3442335%6%41%
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
42%410%21%16%4
1598
16th to endDay
41%410%22%16%4
1728
February1st to 15thDay
42%38%25%16%3
1577
16th to endDay
43%49%21%19%2
1558
March1st to 15thDay
39%410%22%16%5%
1980
16th to endDay
45%49%19%16%4
2112
April1st to 15thDay
35%310%26%18%6%
2147
16th to endDay
41%410%18%17%6%
2160
May1st to 15thDay
44%7%13%18%15%1
2316
16th to endDay
39%7%14%24%12%
2560
June1st to 15thDay
35%8%17%24%13%1
2520
16th to endDay
34%9%16%22%15%2
2520
July1st to 15thDay
41%7%13%19%13%3
2285
16th to endDay
36%9%14%22%15%1
2310
August1st to 15thDay
45%8%11%20%12%1
2327
16th to endDay
40%9%14%21%12%1
2300
September1st to 15thDay
37%7%11%18%21%3
2160
16th to endDay
45%6%9%19%18%1
1881
October1st to 15thDay
40%37%25%19%3
1650
16th to endDay
37%35%26%21%5%
1760
November1st to 15thDay
36%39%21%22%6%
1699
16th to endDay
35%410%22%22%4
1482
December1st to 15thDay
39%311%23%16%5%
1440
16th to endDay
45%49%22%16%1
1536
January1st to 15thNight
42%49%18%19%6%
2339
16th to endNight
40%49%24%17%3
2496
February1st to 15thNight
39%37%25%19%4
2287
16th to endNight
39%37%25%19%4
1913
March1st to 15thNight
39%49%26%16%3
1980
16th to endNight
42%49%22%18%2
2112
April1st to 15thNight
35%410%20%22%6%
1799
16th to endNight
36%6%11%19%18%8%
1800
May1st to 15thNight
44%6%12%18%14%2
1644
16th to endNight
35%10%14%24%11%2
1559
June1st to 15thNight
34%8%13%26%15%1
1440
16th to endNight
35%8%15%19%18%2
1440
July1st to 15thNight
38%9%15%18%14%3
1443
16th to endNight
32%9%16%24%15%1
1595
August1st to 15thNight
37%8%14%22%15%1
1609
16th to endNight
40%7%13%24%12%1
1890
September1st to 15thNight
35%8%13%20%17%4
1800
16th to endNight
44%5%8%17%19%3
1912
October1st to 15thNight
41%48%23%18%4
1980
16th to endNight
33%47%26%23%5%
2112
November1st to 15thNight
35%46%20%24%8%
2158
16th to endNight
36%49%23%21%4
2475
December1st to 15thNight
43%5%9%21%16%3
2520
16th to endNight
42%411%22%15%3
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%21%39%6%1
88
16th to endDay
27%25%34%11%2
96
February1st to 15thDay
24%23%45%42
90
16th to endDay
21%16%33%27%2
198
March1st to 15thDay
18%12%36%25%6%
270
16th to endDay
20%15%35%19%6%2
288
April1st to 15thDay
19%12%28%24%12%2
270
16th to endDay
21%6%28%24%12%5%
270
May1st to 15thDay
27%11%29%17%9%4
288
16th to endDay
20%327%23%20%5%
331
June1st to 15thDay
13%323%27%23%8%
315
16th to endDay
8%6%27%31%21%5%
315
July1st to 15thDay
13%22%36%21%5%
305
16th to endDay
7%18%31%26%15%
326
August1st to 15thDay
11%217%27%27%12%
313
16th to endDay
13%211%29%27%15%
332
September1st to 15thDay
13%220%24%21%17%
315
16th to endDay
28%216%22%15%14%
283
October1st to 15thDay
23%5%19%25%19%7%
255
16th to endDay
14%10%27%27%18%1
272
November1st to 15thDay
19%7%25%26%15%5%
255
16th to endDay
19%12%34%18%12%1
102
December1st to 15thDay
21%13%35%15%13%1
60
16th to endDay
31%18%23%25%1
64
January1st to 15thNight
21%15%34%23%5%
720
16th to endNight
20%13%40%23%1
768
February1st to 15thNight
20%12%40%25%1
704
16th to endNight
19%17%37%23%2
631
March1st to 15thNight
20%13%36%25%4
720
16th to endNight
20%11%35%23%7%
768
April1st to 15thNight
14%15%39%23%6%
718
16th to endNight
16%8%30%32%10%
720
May1st to 15thNight
20%6%29%29%13%
564
16th to endNight
12%221%38%22%2
438
June1st to 15thNight
8%117%42%28%1
360
16th to endNight
8%320%45%22%
360
July1st to 15thNight
12%216%38%29%1
423
16th to endNight
6%112%39%33%6%
564
August1st to 15thNight
11%19%43%31%2
539
16th to endNight
12%111%37%31%4
744
September1st to 15thNight
13%116%34%31%3
720
16th to endNight
19%416%30%25%3
689
October1st to 15thNight
23%419%30%19%3
660
16th to endNight
16%8%30%28%15%
704
November1st to 15thNight
14%11%28%29%14%1
700
16th to endNight
16%11%33%26%10%1
720
December1st to 15thNight
20%9%34%25%9%
720
16th to endNight
21%10%32%31%3
768
Page generated at 2017-09-24 09:15:55. Version ac04

Copyright 2017 A. Danko


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