Shady Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shady Oaks 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
23%
14927
19%
46859
7%
14895
37%
14895
19%
30245

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
10%
720
20%
2506
5%
716
29%
716
14%
1583
January16th to endNight
11%
768
21%
2688
4%
768
33%
768
13%
1699
February1st to 15thNight
10%
704
18%
2183
3%
701
27%
701
14%
1439
February16th to endNight
13%
631
23%
1893
5%
631
34%
631
15%
1237
March1st to 15thNight
14%
720
17%
2160
5%
720
30%
720
15%
1464
March16th to endNight
18%
768
23%
2017
6%
768
32%
768
19%
1337
April1st to 15thNight
15%
718
17%
1796
3%
718
25%
718
19%
1289
April16th to endNight
19%
615
18%
1695
3%
615
30%
615
20%
1157
May1st to 15thNight
20%
540
16%
1620
6%
540
29%
540
17%
1108
May16th to endNight
25%
394
12%
1516
8%
393
34%
393
17%
975
June1st to 15thNight
26%
360
13%
1440
7%
360
40%
360
16%
932
June16th to endNight
34%
360
12%
1440
10%
360
44%
360
22%
859
July1st to 15thNight
42%
340
12%
1360
13%
340
49%
340
22%
821
July16th to endNight
42%
376
15%
1418
14%
354
49%
354
22%
859
August1st to 15thNight
40%
488
17%
1559
11%
486
47%
486
29%
932
August16th to endNight
49%
756
22%
1902
11%
756
52%
756
35%
1216
September1st to 15thNight
35%
720
20%
1845
8%
720
41%
720
30%
1217
September16th to endNight
42%
677
26%
1869
16%
677
50%
677
34%
1132
October1st to 15thNight
29%
660
23%
1856
10%
660
42%
660
25%
1211
October16th to endNight
21%
704
17%
2274
5%
704
36%
704
18%
1484
November1st to 15thNight
24%
700
22%
2277
7%
700
42%
700
20%
1432
November16th to endNight
20%
720
20%
2340
7%
720
36%
720
17%
1503
December1st to 15thNight
17%
720
17%
2517
4%
720
33%
720
15%
1607
December16th to endNight
12%
768
20%
2688
4%
768
32%
768
13%
1752

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
17%6%25%5%3445%6%39%
47984
Night
16%7%2442445%6%40%
47029
Cloud CoverDay
16%6%25%5%3445%7%39%
47994
Night
16%7%35%42445%6%40%
47034
TransparencyDay
44%311%23%14%2
47672
Night
44%311%23%15%2
46859
SeeingDay
22%14%31%20%8%2
5874
Night
22%16%33%21%6%
14927

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
14%7%24435%45%6%39%
1432
16th to endDay
13%6%35%5%245%5%6%41%
1536
February1st to 15thDay
15%6%35%6%36%5%5%6%34%
1675
16th to endDay
15%8%26%6%33345%39%
1580
March1st to 15thDay
20%7%36%325%35%6%36%
1790
16th to endDay
17%6%25%5%23346%42%
2202
April1st to 15thDay
18%7%25%5%34445%38%
2152
16th to endDay
18%4145%24447%40%
2265
May1st to 15thDay
25%7%25%425%346%32%
2332
16th to endDay
18%5%35%5%2335%7%39%
2607
June1st to 15thDay
24%6%3342445%7%32%
2520
16th to endDay
15%5%25%5%36%6%6%9%34%
2520
July1st to 15thDay
13%5%25%6%45%6%5%8%36%
2520
16th to endDay
12%5%25%5%36%5%6%8%37%
2654
August1st to 15thDay
13%5%26%5%45%5%6%7%37%
2379
16th to endDay
11%5%35%5%35%448%43%
2297
September1st to 15thDay
14%5%15%424446%45%
2114
16th to endDay
15%5%14323336%49%
1860
October1st to 15thDay
18%7%2442335%6%41%
1774
16th to endDay
15%5%35%433446%42%
1598
November1st to 15thDay
17%8%2442333443%
1581
16th to endDay
17%5%2442345%5%42%
1620
December1st to 15thDay
19%5%245%2445%7%39%
1440
16th to endDay
20%8%245%245%5%5%34%
1536
January1st to 15thNight
17%8%35%5%23345%40%
2506
16th to endNight
15%8%345%2335%5%40%
2688
February1st to 15thNight
15%8%35%42445%6%38%
2182
16th to endNight
16%8%345%23445%40%
1893
March1st to 15thNight
17%8%24436%45%7%35%
2147
16th to endNight
14%8%35%424346%42%
2017
April1st to 15thNight
17%7%35%5%345%45%35%
1796
16th to endNight
20%6%35%433335%41%
1695
May1st to 15thNight
21%7%25%423445%36%
1620
16th to endNight
18%7%3443435%8%35%
1514
June1st to 15thNight
22%5%245%3445%7%35%
1440
16th to endNight
16%42442445%7%41%
1440
July1st to 15thNight
14%6%23425%5%6%9%38%
1440
16th to endNight
11%5%35%6%35%6%5%6%40%
1514
August1st to 15thNight
9%416%5%35%45%8%44%
1569
16th to endNight
12%4144345%5%8%45%
1902
September1st to 15thNight
13%5%25%42435%6%44%
1845
16th to endNight
13%5%2441335%450%
1869
October1st to 15thNight
18%7%23323335%44%
1856
16th to endNight
18%5%35%434446%39%
2274
November1st to 15thNight
17%7%23423345%44%
2277
16th to endNight
18%6%24424445%40%
2340
December1st to 15thNight
19%7%3432345%6%38%
2517
16th to endNight
18%8%35%42445%6%37%
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
14%7%25%435%5%5%6%39%
1432
16th to endDay
13%6%35%5%245%5%6%41%
1536
February1st to 15thDay
15%6%26%6%45%6%5%7%34%
1675
16th to endDay
15%8%36%6%23345%39%
1580
March1st to 15thDay
20%7%25%424446%36%
1800
16th to endDay
16%6%25%5%24346%42%
2202
April1st to 15thDay
18%7%25%434445%38%
2152
16th to endDay
18%4245%24447%40%
2265
May1st to 15thDay
25%7%25%424346%32%
2332
16th to endDay
18%5%25%5%23447%39%
2607
June1st to 15thDay
24%6%3443345%7%32%
2520
16th to endDay
15%425%5%36%6%6%9%34%
2520
July1st to 15thDay
13%5%26%6%35%5%6%8%36%
2520
16th to endDay
11%5%35%5%46%5%6%7%38%
2654
August1st to 15thDay
13%5%26%5%46%5%6%8%36%
2379
16th to endDay
10%5%26%5%3445%6%43%
2297
September1st to 15thDay
14%5%245%24446%45%
2114
16th to endDay
15%5%24323336%50%
1860
October1st to 15thDay
18%6%2432335%6%41%
1774
16th to endDay
15%5%35%5%23446%42%
1598
November1st to 15thDay
17%8%2442334443%
1581
16th to endDay
17%5%135%3445%6%41%
1620
December1st to 15thDay
19%5%245%2445%7%39%
1440
16th to endDay
21%8%24425%5%46%34%
1536
January1st to 15thNight
17%7%35%423346%40%
2506
16th to endNight
14%9%35%5%2435%5%40%
2688
February1st to 15thNight
14%8%36%43445%6%38%
2175
16th to endNight
15%8%345%23345%41%
1893
March1st to 15thNight
17%8%345%35%447%35%
2160
16th to endNight
14%8%35%424436%42%
2016
April1st to 15thNight
16%7%36%5%345%5%5%36%
1796
16th to endNight
20%6%25%424335%40%
1695
May1st to 15thNight
21%7%345%24345%36%
1620
16th to endNight
18%6%3443446%8%34%
1514
June1st to 15thNight
22%5%25%43445%7%35%
1440
16th to endNight
15%5%245%3436%7%41%
1440
July1st to 15thNight
13%6%34435%5%5%9%38%
1440
16th to endNight
11%5%27%5%35%5%5%6%40%
1514
August1st to 15thNight
9%425%5%35%5%6%8%43%
1569
16th to endNight
11%5%144345%5%7%46%
1902
September1st to 15thNight
13%6%26%424445%45%
1845
16th to endNight
13%5%24313445%50%
1869
October1st to 15thNight
18%7%24323335%44%
1856
16th to endNight
18%5%35%5%34346%39%
2274
November1st to 15thNight
16%8%23424445%44%
2277
16th to endNight
19%6%2442435%5%40%
2340
December1st to 15thNight
18%8%3442435%6%38%
2517
16th to endNight
18%8%35%42435%6%37%
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
43%413%24%11%2
1433
16th to endDay
42%312%26%13%1
1536
February1st to 15thDay
48%411%21%12%
1678
16th to endDay
47%28%23%14%2
1580
March1st to 15thDay
48%310%23%10%3
1800
16th to endDay
44%29%22%16%4
2202
April1st to 15thDay
47%210%21%15%2
2152
16th to endDay
42%39%21%18%3
2265
May1st to 15thDay
53%36%21%12%2
2332
16th to endDay
44%313%22%12%2
2611
June1st to 15thDay
50%411%22%10%
2520
16th to endDay
44%6%12%21%13%
2520
July1st to 15thDay
44%410%23%14%1
2371
16th to endDay
42%414%21%13%2
2487
August1st to 15thDay
44%412%24%12%1
2365
16th to endDay
39%38%28%17%1
2297
September1st to 15thDay
40%410%23%19%2
2114
16th to endDay
36%26%26%25%2
1860
October1st to 15thDay
43%39%25%14%3
1774
16th to endDay
42%312%24%14%2
1598
November1st to 15thDay
44%311%22%15%1
1581
16th to endDay
42%310%24%16%2
1620
December1st to 15thDay
44%316%20%14%
1440
16th to endDay
50%414%18%11%
1536
January1st to 15thNight
46%212%23%12%2
2506
16th to endNight
45%210%23%14%2
2688
February1st to 15thNight
46%312%22%12%2
2183
16th to endNight
45%29%22%16%2
1893
March1st to 15thNight
48%210%20%14%2
2160
16th to endNight
43%28%21%18%5%
2017
April1st to 15thNight
50%28%19%16%2
1796
16th to endNight
47%37%21%16%4
1695
May1st to 15thNight
50%29%19%14%2
1620
16th to endNight
46%5%17%20%9%1
1516
June1st to 15thNight
47%5%13%21%11%
1440
16th to endNight
41%5%13%24%14%
1440
July1st to 15thNight
41%5%13%26%13%
1360
16th to endNight
42%414%25%11%2
1418
August1st to 15thNight
36%415%26%14%2
1559
16th to endNight
36%411%30%17%
1902
September1st to 15thNight
40%410%25%19%
1845
16th to endNight
35%27%25%25%2
1869
October1st to 15thNight
42%311%23%15%4
1856
16th to endNight
46%312%23%14%
2274
November1st to 15thNight
42%310%21%18%3
2277
16th to endNight
45%312%22%14%2
2340
December1st to 15thNight
46%314%22%12%
2517
16th to endNight
47%311%23%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
20%31%28%15%5%
60
16th to endDay
29%20%39%10%
64
February1st to 15thDay
25%27%33%11%2
206
16th to endDay
23%26%32%12%3
239
March1st to 15thDay
33%17%32%13%2
270
16th to endDay
21%28%30%12%5%1
288
April1st to 15thDay
25%18%35%13%5%1
270
16th to endDay
24%14%31%21%43
270
May1st to 15thDay
36%14%26%14%6%1
288
16th to endDay
20%12%34%23%7%1
331
June1st to 15thDay
25%13%29%23%8%1
315
16th to endDay
17%12%39%20%8%2
315
July1st to 15thDay
20%9%29%26%11%1
305
16th to endDay
15%6%30%31%12%3
326
August1st to 15thDay
14%5%30%31%12%4
313
16th to endDay
12%7%31%25%15%7%
332
September1st to 15thDay
18%9%29%24%12%6%
315
16th to endDay
17%7%25%23%11%13%
270
October1st to 15thDay
21%11%28%19%12%5%
255
16th to endDay
16%24%31%21%5%
243
November1st to 15thDay
24%12%34%17%9%1
235
16th to endDay
25%18%28%17%8%1
240
December1st to 15thDay
28%25%35%6%5%
60
16th to endDay
37%31%21%7%1
64
January1st to 15thNight
25%23%36%12%2
720
16th to endNight
26%21%34%14%1
768
February1st to 15thNight
23%23%37%13%1
704
16th to endNight
26%22%33%14%1
631
March1st to 15thNight
26%23%33%14%1
720
16th to endNight
22%23%32%17%3
768
April1st to 15thNight
23%19%38%16%2
718
16th to endNight
24%20%33%17%5%
615
May1st to 15thNight
26%17%33%18%3
540
16th to endNight
22%10%37%24%5%
394
June1st to 15thNight
24%7%35%26%6%
360
16th to endNight
15%440%32%6%
360
July1st to 15thNight
15%5%29%38%10%
340
16th to endNight
13%232%38%12%
376
August1st to 15thNight
11%336%36%11%
488
16th to endNight
14%426%36%15%2
756
September1st to 15thNight
17%7%33%29%11%1
720
16th to endNight
16%6%28%26%18%3
677
October1st to 15thNight
24%11%31%21%9%1
660
16th to endNight
24%20%30%18%5%
704
November1st to 15thNight
21%18%31%20%7%1
700
16th to endNight
25%18%31%16%7%
720
December1st to 15thNight
26%20%31%16%4
720
16th to endNight
25%24%34%13%1
768
Page generated at 2017-09-21 07:18:15. Version ac04

Copyright 2017 A. Danko


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