Oak Tree Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Tree Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
52%
23720
23%
74300
18%
23660
58%
23660
30%
44292

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 10thNight
35%
949
26%
2458
11%
946
44%
946
31%
1589
January11th to 20thNight
35%
930
24%
2418
10%
930
42%
930
29%
1576
January21st to endNight
35%
990
26%
2574
11%
990
43%
990
29%
1689
February1st to 10thNight
30%
778
22%
2218
9%
778
38%
778
23%
1487
February11th to 20thNight
34%
704
20%
2098
9%
700
42%
700
25%
1336
February21st to endNight
23%
470
23%
1654
9%
470
37%
470
18%
1077
March1st to 10thNight
31%
540
23%
1980
12%
540
45%
540
20%
1241
March11th to 20thNight
34%
540
20%
1980
14%
540
43%
540
19%
1256
March21st to endNight
36%
594
24%
2178
16%
594
48%
594
26%
1242
April1st to 10thNight
36%
540
22%
1980
15%
540
48%
540
22%
1218
April11th to 20thNight
37%
533
22%
1852
16%
533
48%
533
25%
1131
April21st to endNight
35%
540
25%
1800
17%
540
48%
540
25%
1089
May1st to 10thNight
40%
540
21%
1685
17%
540
48%
540
25%
1073
May11th to 20thNight
51%
531
23%
1594
21%
531
57%
531
32%
949
May21st to endNight
58%
584
23%
1745
22%
582
64%
582
34%
1030
June1st to 10thNight
76%
540
22%
1620
25%
540
78%
540
44%
855
June11th to 20thNight
75%
540
22%
1620
25%
540
78%
540
45%
855
June21st to endNight
73%
540
19%
1620
21%
540
75%
540
33%
978
July1st to 10thNight
78%
525
16%
1575
18%
525
78%
525
33%
924
July11th to 20thNight
84%
522
23%
1566
26%
522
85%
522
45%
827
July21st to endNight
84%
591
20%
1673
22%
558
86%
558
41%
919
August1st to 10thNight
90%
537
26%
1601
29%
534
90%
534
59%
746
August11th to 20thNight
83%
534
23%
1642
25%
534
83%
534
41%
898
August21st to endNight
78%
594
18%
2092
20%
594
79%
594
30%
1220
September1st to 10thNight
78%
540
18%
1980
21%
540
79%
540
32%
1109
September11th to 20thNight
69%
540
21%
1980
23%
540
70%
540
26%
1187
September21st to endNight
73%
540
28%
1980
30%
540
76%
540
36%
1015
October1st to 10thNight
76%
594
33%
2034
33%
594
78%
594
45%
969
October11th to 20thNight
61%
720
32%
2160
24%
720
66%
720
40%
1190
October21st to endNight
55%
792
33%
2376
23%
792
61%
792
39%
1322
November1st to 10thNight
60%
740
28%
2220
22%
740
63%
740
36%
1271
November11th to 20thNight
50%
760
27%
2280
19%
760
57%
760
32%
1358
November21st to endNight
42%
869
26%
2389
16%
869
49%
869
29%
1561
December1st to 10thNight
42%
950
27%
2470
14%
950
48%
950
29%
1655
December11th to 20thNight
36%
949
22%
2886
11%
948
41%
948
21%
1924
December21st to endNight
36%
1040
15%
4322
11%
1026
43%
1026
19%
2526

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
12%5%35%6%35%5%6%8%42%
74961
Night
12%5%2442445%8%49%
74867
TransparencyDay
40%7%11%19%17%7%
74686
Night
35%6%12%21%17%9%
74662
SeeingDay
12%5%17%24%27%14%
13722
Night
15%5%22%34%22%2
23727

By Month

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 10thDay
18%6%344235%46%45%
1707
11th to 20thDay
20%8%25%424345%43%
1665
21st to endDay
20%7%34433347%43%
1782
February1st to 10thDay
24%7%35%5%33346%38%
1755
11th to 20thDay
22%8%36%5%33445%39%
1749
21st to endDay
21%6%46%43335%6%40%
1600
March1st to 10thDay
21%7%36%6%3445%6%34%
1980
11th to 20thDay
18%8%36%6%24346%40%
1980
21st to endDay
17%7%35%43445%6%42%
2178
April1st to 10thDay
14%8%37%6%45%5%46%37%
1980
11th to 20thDay
17%6%25%6%345%5%6%40%
2054
21st to endDay
12%6%36%6%3445%6%45%
2160
May1st to 10thDay
11%6%36%6%45%5%5%9%40%
2270
11th to 20thDay
11%6%26%5%36%5%6%8%41%
2302
21st to endDay
9%5%36%7%5%6%7%8%11%32%
2531
June1st to 10thDay
5%4346%36%6%7%10%45%
2340
11th to 20thDay
5%3245%46%7%9%10%44%
2340
21st to endDay
6%5%37%8%6%8%9%8%10%30%
2340
July1st to 10thDay
10%435%8%46%8%7%11%34%
2340
11th to 20thDay
4436%6%5%7%7%8%10%39%
2340
21st to endDay
5%325%6%37%7%9%12%40%
2546
August1st to 10thDay
32246%46%6%8%11%47%
2328
11th to 20thDay
5%325%7%37%7%8%10%43%
2257
21st to endDay
6%3248%47%7%8%11%39%
2259
September1st to 10thDay
6%5%36%6%47%7%8%10%39%
1980
11th to 20thDay
11%6%36%7%46%6%5%8%37%
1980
21st to endDay
7%5%26%5%36%6%6%8%45%
1980
October1st to 10thDay
6%3245%35%45%8%54%
1908
11th to 20thDay
11%5%25%5%345%46%51%
1800
21st to endDay
13%5%24423346%54%
1980
November1st to 10thDay
11%6%25%5%345%6%8%47%
1858
11th to 20thDay
12%6%2443446%7%49%
1900
21st to endDay
17%7%26%5%45%346%41%
1786
December1st to 10thDay
16%7%46%6%24446%41%
1710
11th to 20thDay
16%6%36%5%345%5%5%42%
2161
21st to endDay
16%7%25%5%24445%46%
3135
January1st to 10thNight
20%7%24323347%46%
2458
11th to 20thNight
20%6%34423335%48%
2418
21st to endNight
17%6%34424346%46%
2574
February1st to 10thNight
20%8%36%424346%40%
2218
11th to 20thNight
22%6%24323345%45%
2098
21st to endNight
23%7%44334435%40%
1654
March1st to 10thNight
18%8%35%42435%7%41%
1980
11th to 20thNight
17%7%36%5%35%45%6%40%
1980
21st to endNight
13%6%3442335%7%49%
2178
April1st to 10thNight
13%6%35%5%35%5%5%8%42%
1980
11th to 20thNight
16%6%35%424447%45%
1852
21st to endNight
15%6%26%5%2445%7%46%
1800
May1st to 10thNight
12%6%26%5%35%5%6%8%42%
1685
11th to 20thNight
10%5%25%4345%5%9%48%
1593
21st to endNight
7%435%5%35%46%11%48%
1745
June1st to 10thNight
6%31432447%10%56%
1620
11th to 20thNight
421342446%13%56%
1620
21st to endNight
5%4247%35%6%10%10%45%
1620
July1st to 10thNight
6%425%5%35%5%7%11%49%
1620
11th to 20thNight
3213425%5%6%12%57%
1620
21st to endNight
22135%36%47%13%54%
1772
August1st to 10thNight
211231335%12%67%
1611
11th to 20thNight
33245%345%6%12%54%
1642
21st to endNight
4225%6%46%5%7%12%47%
2092
September1st to 10thNight
5%434435%5%8%9%49%
1980
11th to 20thNight
11%5%35%6%35%5%5%8%45%
1980
21st to endNight
8%42442447%9%54%
1980
October1st to 10thNight
432342345%8%62%
2034
11th to 20thNight
11%423423336%58%
2160
21st to endNight
11%5%24323335%60%
2376
November1st to 10thNight
10%424434446%54%
2220
11th to 20thNight
13%5%2442445%6%51%
2280
21st to endNight
17%6%35%424446%46%
2389
December1st to 10thNight
19%7%25%333346%44%
2470
11th to 20thNight
18%8%36%5%34346%42%
3036
21st to endNight
17%7%25%423446%47%
4532

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 10thDay
41%47%15%22%10%
1708
11th to 20thDay
44%46%15%20%12%
1665
21st to endDay
43%36%15%20%13%
1782
February1st to 10thDay
49%36%13%16%12%
1755
11th to 20thDay
49%47%13%18%10%
1759
21st to endDay
47%39%15%15%11%
1600
March1st to 10thDay
50%5%8%12%18%7%
1980
11th to 20thDay
47%48%12%19%10%
1980
21st to endDay
43%5%8%16%21%8%
2178
April1st to 10thDay
48%5%7%17%15%8%
1980
11th to 20thDay
45%5%8%14%18%9%
2054
21st to endDay
40%5%8%20%20%7%
2160
May1st to 10thDay
41%7%10%19%15%8%
2270
11th to 20thDay
39%8%11%21%18%3
2306
21st to endDay
44%8%14%20%13%1
2531
June1st to 10thDay
32%8%16%26%16%2
2340
11th to 20thDay
31%11%15%25%16%2
2340
21st to endDay
44%10%17%20%9%
2340
July1st to 10thDay
40%10%20%23%6%1
2276
11th to 20thDay
36%10%20%22%11%
2271
21st to endDay
32%12%22%28%6%1
2405
August1st to 10thDay
28%10%19%31%11%1
2314
11th to 20thDay
33%11%22%24%10%2
2257
21st to endDay
36%12%19%22%9%2
2259
September1st to 10thDay
37%11%14%18%14%5%
1980
11th to 20thDay
43%9%12%17%16%4
1980
21st to endDay
34%8%13%17%17%11%
1980
October1st to 10thDay
28%5%10%23%21%13%
1908
11th to 20thDay
34%5%7%17%20%16%
1800
21st to endDay
33%45%16%24%17%
1980
November1st to 10thDay
35%7%9%18%22%10%
1858
11th to 20thDay
36%411%16%21%13%
1900
21st to endDay
45%5%6%16%17%11%
1786
December1st to 10thDay
45%48%18%18%7%
1710
11th to 20thDay
44%5%7%12%23%10%
2159
21st to endDay
41%45%16%23%11%
3135
January1st to 10thNight
39%37%17%21%13%
2458
11th to 20thNight
41%36%16%20%13%
2418
21st to endNight
41%35%15%19%15%
2574
February1st to 10thNight
47%37%12%17%14%
2218
11th to 20thNight
43%37%16%17%12%
2098
21st to endNight
48%47%13%14%14%
1654
March1st to 10thNight
44%5%9%16%17%9%
1980
11th to 20thNight
45%5%8%13%19%10%
1980
21st to endNight
37%412%16%21%10%
2178
April1st to 10thNight
40%7%9%19%15%9%
1980
11th to 20thNight
40%410%16%15%13%
1852
21st to endNight
39%5%8%21%19%8%
1800
May1st to 10thNight
39%7%10%18%17%9%
1685
11th to 20thNight
33%7%14%24%18%4
1594
21st to endNight
31%7%17%30%13%1
1746
June1st to 10thNight
22%7%18%33%19%1
1620
11th to 20thNight
21%8%18%31%18%4
1620
21st to endNight
31%9%20%27%12%1
1620
July1st to 10thNight
28%11%25%29%7%
1575
11th to 20thNight
19%9%29%32%11%
1566
21st to endNight
20%12%28%33%7%
1673
August1st to 10thNight
13%5%28%39%13%1
1601
11th to 20thNight
22%10%28%31%8%1
1642
21st to endNight
28%13%22%27%8%2
2092
September1st to 10thNight
28%10%22%22%13%5%
1980
11th to 20thNight
37%8%16%21%15%5%
1980
21st to endNight
26%7%16%22%19%11%
1980
October1st to 10thNight
21%5%12%29%19%14%
2034
11th to 20thNight
28%48%21%22%17%
2160
21st to endNight
29%37%16%23%21%
2376
November1st to 10thNight
31%5%10%21%22%10%
2220
11th to 20thNight
35%411%18%20%13%
2280
21st to endNight
41%48%16%19%11%
2389
December1st to 10thNight
42%48%21%15%10%
2470
11th to 20thNight
45%47%11%19%15%
3037
21st to endNight
40%46%14%28%9%
4532

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 10thDay
23%9%36%26%6%1
270
11th to 20thDay
24%7%28%30%9%1
255
21st to endDay
20%14%33%23%9%
264
February1st to 10thDay
29%14%24%25%7%1
240
11th to 20thDay
25%16%31%21%6%
240
21st to endDay
30%12%37%16%6%
198
March1st to 10thDay
23%13%34%23%7%1
240
11th to 20thDay
16%16%39%20%7%2
240
21st to endDay
21%12%30%26%10%1
264
April1st to 10thDay
15%13%40%22%10%
240
11th to 20thDay
25%10%26%27%12%1
332
21st to endDay
14%8%32%31%13%2
420
May1st to 10thDay
13%7%31%32%16%1
533
11th to 20thDay
13%422%33%24%3
625
21st to endDay
8%322%36%26%5%
679
June1st to 10thDay
6%27%32%39%15%
630
11th to 20thDay
5%18%33%37%15%
630
21st to endDay
8%28%22%37%23%
630
July1st to 10thDay
8%1421%39%27%
621
11th to 20thDay
21416%45%32%
618
21st to endDay
42416%46%28%
684
August1st to 10thDay
4215%46%32%
626
11th to 20thDay
6%214%41%36%
571
21st to endDay
9%1211%33%44%
378
September1st to 10thDay
7%1211%44%35%
270
11th to 20thDay
9%25%19%33%33%
270
21st to endDay
9%15%20%41%24%
270
October1st to 10thDay
7%17%30%41%13%
270
11th to 20thDay
11%316%30%26%14%
270
21st to endDay
20%7%23%19%24%7%
297
November1st to 10thDay
13%316%38%24%7%
270
11th to 20thDay
16%5%22%33%20%4
270
21st to endDay
20%13%27%24%11%3
270
December1st to 10thDay
17%5%31%25%15%6%
270
11th to 20thDay
23%13%27%28%8%2
270
21st to endDay
18%6%36%28%9%3
297
January1st to 10thNight
23%8%29%31%9%
950
11th to 20thNight
21%12%26%33%8%
930
21st to endNight
20%9%31%32%8%
990
February1st to 10thNight
25%10%31%29%5%
778
11th to 20thNight
25%7%29%33%5%
704
21st to endNight
28%10%36%24%2
470
March1st to 10thNight
22%9%34%30%5%
540
11th to 20thNight
21%6%34%32%7%
540
21st to endNight
17%7%36%32%7%1
594
April1st to 10thNight
15%7%38%36%5%
540
11th to 20thNight
19%7%32%32%10%
533
21st to endNight
15%8%37%30%9%
540
May1st to 10thNight
14%8%32%37%9%
540
11th to 20thNight
13%229%40%14%2
531
21st to endNight
8%224%42%22%2
584
June1st to 10thNight
6%19%46%35%3
540
11th to 20thNight
4112%49%33%1
540
21st to endNight
6%17%37%41%8%
540
July1st to 10thNight
5%2436%46%8%
525
11th to 20thNight
4332%53%7%
522
21st to endNight
21434%52%7%
591
August1st to 10thNight
21134%55%7%
537
11th to 20thNight
41231%55%7%
534
21st to endNight
6%1426%55%10%
594
September1st to 10thNight
6%1426%54%9%
540
11th to 20thNight
9%25%30%48%6%
540
21st to endNight
9%18%31%43%7%
540
October1st to 10thNight
4210%38%41%5%
594
11th to 20thNight
12%219%39%25%2
720
21st to endNight
13%6%22%36%20%3
792
November1st to 10thNight
12%419%41%24%1
740
11th to 20thNight
15%6%22%38%19%1
760
21st to endNight
19%7%27%33%14%1
869
December1st to 10thNight
21%6%25%32%15%
950
11th to 20thNight
24%9%27%32%8%1
950
21st to endNight
21%8%29%32%9%1
1045
Page generated at 2024-01-13 08:37:56. Version ac07

Copyright 2024 Attilla Danko


Oak Tree Observatory Clear Sky Chart |Charts Home