Oak Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Hills 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
71%
15966
35%
46863
28%
15924
77%
15924
53%
22519

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
55%
717
29%
2327
24%
716
64%
716
39%
1187
January16th to endNight
55%
768
33%
2319
23%
768
67%
768
38%
1253
February1st to 15thNight
59%
699
33%
2107
28%
698
68%
698
42%
1100
February16th to endNight
55%
632
29%
1895
27%
632
62%
632
34%
1104
March1st to 15thNight
60%
720
29%
2160
25%
720
69%
720
44%
1125
March16th to endNight
64%
768
31%
2025
23%
768
71%
768
48%
1105
April1st to 15thNight
59%
719
30%
1799
17%
719
65%
719
49%
996
April16th to endNight
65%
720
35%
1800
17%
720
71%
720
58%
935
May1st to 15thNight
72%
572
34%
1652
23%
572
75%
572
60%
756
May16th to endNight
68%
561
33%
1685
25%
561
73%
561
62%
746
June1st to 15thNight
78%
540
34%
1620
29%
540
80%
540
71%
666
June16th to endNight
93%
363
42%
1443
49%
363
95%
363
81%
422
July1st to 15thNight
93%
365
35%
1385
41%
365
93%
365
69%
470
July16th to endNight
86%
609
32%
1635
25%
573
87%
573
61%
769
August1st to 15thNight
91%
717
38%
1790
25%
713
92%
713
80%
804
August16th to endNight
94%
764
43%
1910
30%
764
94%
764
80%
864
September1st to 15thNight
90%
720
39%
1854
31%
720
91%
720
73%
854
September16th to endNight
87%
716
47%
1980
43%
716
91%
716
79%
817
October1st to 15thNight
74%
684
38%
1881
33%
684
80%
684
59%
913
October16th to endNight
74%
704
40%
2145
38%
704
81%
704
57%
956
November1st to 15thNight
72%
700
35%
2275
34%
700
81%
700
55%
985
November16th to endNight
70%
720
36%
2340
35%
720
77%
720
46%
1117
December1st to 15thNight
60%
720
32%
2340
28%
720
70%
720
37%
1225
December16th to endNight
51%
768
32%
2496
25%
768
62%
768
32%
1350

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
1112212346%72%
48325
Night
1112212346%70%
47059
TransparencyDay
15%36%15%27%31%
48017
Night
17%37%15%27%28%
46869
SeeingDay
316%37%29%9%3
5974
Night
25%16%33%31%9%
15977

By Month

Percentage Cloud Cover SW (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
23233235%46%62%
1611
16th to endDay
3425%323446%59%
1902
February1st to 15thDay
1225%213447%63%
1751
16th to endDay
3325%5%23448%55%
1579
March1st to 15thDay
121222345%9%63%
1800
16th to endDay
122222446%7%65%
2196
April1st to 15thDay
222322335%7%66%
2149
16th to endDay
11211237%75%
2160
May1st to 15thDay
1111125%8%75%
2297
16th to endDay
111112236%78%
2429
June1st to 15thDay
1111125%81%
2340
16th to endDay
111289%
2511
July1st to 15thDay
11212345%76%
2490
16th to endDay
11221235%7%71%
2419
August1st to 15thDay
111222482%
2160
16th to endDay
11112236%79%
2292
September1st to 15thDay
1111236%79%
2106
16th to endDay
111122383%
1980
October1st to 15thDay
1321323473%
1876
16th to endDay
111212336%75%
1725
November1st to 15thDay
112213345%71%
1584
16th to endDay
2213323446%66%
1620
December1st to 15thDay
211232347%11%59%
1620
16th to endDay
4325%41335%7%57%
1728
January1st to 15thNight
242332445%6%60%
2327
16th to endNight
4225%32335%7%59%
2319
February1st to 15thNight
231442445%5%62%
2101
16th to endNight
2335%5%2446%8%52%
1895
March1st to 15thNight
121342447%7%61%
2160
16th to endNight
11432335%8%63%
2025
April1st to 15thNight
121331435%9%63%
1799
16th to endNight
1222225%7%72%
1800
May1st to 15thNight
1236%7%74%
1652
16th to endNight
121235%7%75%
1684
June1st to 15thNight
12123481%
1620
16th to endNight
112289%
1443
July1st to 15thNight
112122480%
1467
16th to endNight
213222235%72%
1746
August1st to 15thNight
111222384%
1800
16th to endNight
111122484%
1910
September1st to 15thNight
111222480%
1854
16th to endNight
1122385%
1980
October1st to 15thNight
1112212246%72%
1881
16th to endNight
12211245%74%
2145
November1st to 15thNight
112212345%73%
2275
16th to endNight
22331335%7%65%
2340
December1st to 15thNight
321432246%9%58%
2340
16th to endNight
4325%41346%6%58%
2496

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
23%48%17%26%20%
1612
16th to endDay
28%37%16%22%21%
1902
February1st to 15thDay
22%45%18%25%22%
1751
16th to endDay
31%38%15%27%13%
1579
March1st to 15thDay
19%39%22%24%20%
1800
16th to endDay
21%49%23%25%16%
2196
April1st to 15thDay
21%36%23%29%14%
2149
16th to endDay
13%39%22%30%20%
2160
May1st to 15thDay
12%38%20%31%23%
2297
16th to endDay
11%26%20%40%18%
2432
June1st to 15thDay
10%15%10%32%39%
2340
16th to endDay
5%3420%63%
2511
July1st to 15thDay
10%25%7%20%52%
2343
16th to endDay
13%48%16%22%34%
2268
August1st to 15thDay
6%249%22%54%
2146
16th to endDay
9%15%9%29%43%
2292
September1st to 15thDay
8%26%10%27%44%
2106
16th to endDay
8%1310%31%45%
1980
October1st to 15thDay
16%2414%30%31%
1876
16th to endDay
14%35%11%27%38%
1725
November1st to 15thDay
16%37%14%32%25%
1584
16th to endDay
20%37%14%25%27%
1620
December1st to 15thDay
23%5%11%19%22%17%
1620
16th to endDay
29%5%8%19%20%15%
1728
January1st to 15thNight
24%48%14%25%22%
2327
16th to endNight
27%49%14%20%23%
2319
February1st to 15thNight
25%38%16%23%22%
2112
16th to endNight
30%6%6%16%24%14%
1895
March1st to 15thNight
22%49%18%23%20%
2160
16th to endNight
21%5%8%23%26%14%
2025
April1st to 15thNight
22%39%24%24%15%
1799
16th to endNight
16%37%23%31%18%
1800
May1st to 15thNight
12%47%22%32%20%
1653
16th to endNight
13%210%20%36%16%
1685
June1st to 15thNight
10%15%13%30%38%
1620
16th to endNight
4145%22%62%
1443
July1st to 15thNight
8%15%9%16%58%
1385
16th to endNight
14%37%12%26%34%
1635
August1st to 15thNight
6%2310%27%49%
1790
16th to endNight
6%249%32%45%
1910
September1st to 15thNight
9%26%6%32%42%
1854
16th to endNight
6%1310%34%42%
1980
October1st to 15thNight
16%2414%33%29%
1881
16th to endNight
15%25%9%28%38%
2145
November1st to 15thNight
15%26%15%32%27%
2275
16th to endNight
20%47%15%24%27%
2340
December1st to 15thNight
26%47%15%24%20%
2340
16th to endNight
28%49%16%24%15%
2496

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
8%23%33%28%5%
90
16th to endDay
9%29%29%22%8%
270
February1st to 15thDay
323%36%26%7%1
266
16th to endDay
8%32%30%21%5%
238
March1st to 15thDay
7%23%35%21%11%1
270
16th to endDay
5%22%41%21%7%1
288
April1st to 15thDay
7%26%39%14%10%1
269
16th to endDay
237%33%19%42
270
May1st to 15thDay
120%42%26%5%3
288
16th to endDay
315%46%25%5%3
330
June1st to 15thDay
17%42%27%7%3
315
16th to endDay
16%40%37%6%7%
315
July1st to 15thDay
5%34%40%12%6%
305
16th to endDay
1133%40%14%7%
327
August1st to 15thDay
2444%30%10%8%
315
16th to endDay
2234%38%12%10%
332
September1st to 15thDay
1345%35%11%2
315
16th to endDay
112%34%35%13%2
315
October1st to 15thDay
317%40%28%10%
278
16th to endDay
312%37%29%16%
212
November1st to 15thDay
16%21%25%25%11%
90
16th to endDay
324%30%30%12%
90
December1st to 15thDay
418%21%42%11%2
90
16th to endDay
12%15%33%27%11%
96
January1st to 15thNight
5%9%24%33%20%6%
720
16th to endNight
8%9%22%31%22%5%
768
February1st to 15thNight
47%21%35%23%6%
704
16th to endNight
5%11%25%33%19%5%
632
March1st to 15thNight
28%23%36%23%5%
720
16th to endNight
18%22%36%26%5%
768
April1st to 15thNight
310%23%34%22%6%
719
16th to endNight
27%24%34%24%7%
720
May1st to 15thNight
5%20%40%26%6%
573
16th to endNight
1324%34%28%7%
563
June1st to 15thNight
217%41%34%4
540
16th to endNight
438%48%7%
363
July1st to 15thNight
1221%61%13%
365
16th to endNight
1430%50%12%
609
August1st to 15thNight
1426%49%17%
717
16th to endNight
1120%52%24%
764
September1st to 15thNight
5%26%46%19%
720
16th to endNight
18%30%41%16%
716
October1st to 15thNight
25%15%36%31%8%
684
16th to endNight
1414%32%30%15%
704
November1st to 15thNight
25%17%33%31%10%
700
16th to endNight
36%16%36%27%10%
720
December1st to 15thNight
5%9%19%35%24%6%
720
16th to endNight
6%13%23%34%19%3
768
Page generated at 2017-10-07 11:07:56. Version ac04

Copyright 2017 A. Danko


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