Owl Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Owl Ridge Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
39%
16311
19%
47823
11%
16267
46%
16267
25%
31266

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
28%
900
13%
2506
5%
895
35%
895
20%
1770
January16th to endNight
24%
960
15%
2517
5%
960
32%
960
19%
1862
February1st to 15thNight
24%
877
15%
2288
3%
876
31%
876
21%
1647
February16th to endNight
29%
673
19%
1935
7%
673
40%
673
25%
1289
March1st to 15thNight
32%
618
19%
2058
12%
618
41%
618
23%
1292
March16th to endNight
27%
576
11%
2064
7%
576
33%
576
15%
1451
April1st to 15thNight
27%
539
17%
1797
12%
539
36%
539
21%
1180
April16th to endNight
35%
540
18%
1794
15%
540
45%
540
20%
1224
May1st to 15thNight
34%
540
17%
1505
8%
540
43%
540
25%
1031
May16th to endNight
44%
563
19%
1497
9%
561
51%
561
30%
1000
June1st to 15thNight
53%
540
16%
1440
8%
540
57%
540
34%
913
June16th to endNight
52%
540
18%
1440
8%
540
56%
540
37%
881
July1st to 15thNight
68%
510
19%
1360
12%
510
69%
510
44%
784
July16th to endNight
70%
564
22%
1457
17%
531
73%
531
44%
843
August1st to 15thNight
68%
539
22%
1610
23%
536
70%
536
39%
900
August16th to endNight
64%
573
22%
1878
25%
573
68%
573
33%
1069
September1st to 15thNight
65%
540
27%
1800
27%
540
70%
540
36%
964
September16th to endNight
55%
623
27%
1956
20%
623
64%
623
36%
1099
October1st to 15thNight
43%
720
24%
2160
17%
720
49%
720
30%
1327
October16th to endNight
35%
768
21%
2322
12%
768
44%
768
26%
1453
November1st to 15thNight
34%
763
24%
2474
15%
763
45%
763
27%
1484
November16th to endNight
28%
975
19%
2730
8%
975
37%
975
25%
1820
December1st to 15thNight
22%
910
13%
2547
4%
910
29%
910
17%
1911
December16th to endNight
24%
960
14%
2688
5%
960
32%
960
14%
2072

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%38%
48623
Night
12%7%35%5%24446%42%
47996
Cloud CoverDay
14%7%35%5%3445%7%37%
48632
Night
12%7%35%5%24446%42%
48000
TransparencyDay
44%6%12%22%12%1
48313
Night
41%5%12%23%14%2
47824
SeeingDay
15%6%27%28%17%4
6251
Night
16%7%30%31%12%1
16314

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
11%10%6%6%6%6%5%447%30%
1432
16th to endDay
13%14%6%8%6%35%5%46%25%
1704
February1st to 15thDay
12%11%5%7%6%25%446%31%
1575
16th to endDay
14%7%46%5%25%5%5%7%35%
1536
March1st to 15thDay
16%8%37%42345%7%35%
1900
16th to endDay
19%11%46%435%35%6%29%
2159
April1st to 15thDay
18%9%36%6%2445%5%33%
2151
16th to endDay
24%9%25%423346%32%
2163
May1st to 15thDay
18%9%35%6%345%5%6%30%
2445
16th to endDay
14%6%26%5%35%5%5%7%36%
2617
June1st to 15thDay
13%435%435%5%5%8%40%
2520
16th to endDay
9%425%5%35%5%6%8%43%
2520
July1st to 15thDay
6%4245%25%5%8%8%44%
2520
16th to endDay
7%4245%35%6%7%9%43%
2610
August1st to 15thDay
6%5%245%35%6%6%9%42%
2340
16th to endDay
11%5%245%35%45%7%44%
2324
September1st to 15thDay
12%323423347%52%
2160
16th to endDay
9%425%6%245%5%7%46%
1989
October1st to 15thDay
17%6%245%2333445%
1800
16th to endDay
16%7%25%433446%41%
1902
November1st to 15thDay
12%8%345%2435%6%41%
1710
16th to endDay
17%7%34423337%41%
1560
December1st to 15thDay
19%13%38%5%25%346%26%
1450
16th to endDay
19%16%5%7%7%3334424%
1536
January1st to 15thNight
11%9%5%7%6%45%446%35%
2506
16th to endNight
11%11%5%7%6%345%4434%
2517
February1st to 15thNight
12%12%5%6%5%33345%36%
2285
16th to endNight
13%7%36%5%33445%42%
1935
March1st to 15thNight
16%6%25%433346%43%
2046
16th to endNight
16%9%47%6%45%445%32%
2064
April1st to 15thNight
16%8%35%5%2335%5%39%
1797
16th to endNight
20%7%24423447%37%
1794
May1st to 15thNight
15%5%26%5%245%5%6%40%
1505
16th to endNight
10%435%6%35%45%7%42%
1496
June1st to 15thNight
10%42442446%7%46%
1440
16th to endNight
8%314325%5%6%9%48%
1440
July1st to 15thNight
5%21432347%9%55%
1440
16th to endNight
4313435%48%10%51%
1556
August1st to 15thNight
44145%2445%8%54%
1620
16th to endNight
9%32443335%7%51%
1878
September1st to 15thNight
9%31332335%6%56%
1800
16th to endNight
7%424424347%53%
1956
October1st to 15thNight
13%5%24424335%50%
2160
16th to endNight
13%7%25%423345%47%
2322
November1st to 15thNight
12%6%25%423346%48%
2474
16th to endNight
16%8%24424345%43%
2730
December1st to 15thNight
17%12%46%6%24345%31%
2547
16th to endNight
21%13%5%6%5%24335%27%
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
11%10%6%5%7%5%5%45%7%29%
1432
16th to endDay
13%13%6%9%6%35%446%25%
1704
February1st to 15thDay
13%10%5%7%7%2445%6%31%
1575
16th to endDay
14%8%46%5%25%45%8%35%
1536
March1st to 15thDay
16%8%46%42435%7%35%
1911
16th to endDay
19%10%46%5%34346%30%
2157
April1st to 15thDay
18%9%37%5%3445%5%33%
2151
16th to endDay
24%8%35%423346%32%
2163
May1st to 15thDay
18%9%35%6%35%45%7%30%
2445
16th to endDay
14%7%25%6%35%5%5%7%35%
2617
June1st to 15thDay
13%5%25%435%5%5%8%40%
2520
16th to endDay
9%425%435%5%6%8%43%
2520
July1st to 15thDay
6%425%5%25%5%7%10%44%
2520
16th to endDay
7%3245%45%6%7%9%42%
2610
August1st to 15thDay
6%425%5%35%7%7%8%42%
2340
16th to endDay
11%5%245%35%447%44%
2324
September1st to 15thDay
12%313323438%52%
2160
16th to endDay
9%425%6%345%5%7%46%
1989
October1st to 15thDay
17%6%245%2333445%
1800
16th to endDay
16%7%24434346%41%
1902
November1st to 15thDay
12%8%345%3445%7%41%
1710
16th to endDay
17%8%34323337%40%
1560
December1st to 15thDay
20%13%39%425%336%27%
1450
16th to endDay
19%16%5%7%7%2334424%
1536
January1st to 15thNight
10%9%5%7%6%35%45%5%35%
2506
16th to endNight
11%11%5%7%6%3444434%
2517
February1st to 15thNight
12%11%5%6%5%34345%36%
2278
16th to endNight
13%7%37%5%33445%42%
1935
March1st to 15thNight
16%6%25%423336%43%
2058
16th to endNight
16%9%46%6%445%46%31%
2064
April1st to 15thNight
16%8%36%5%23445%40%
1797
16th to endNight
20%7%3442345%6%36%
1794
May1st to 15thNight
14%6%35%425%45%6%40%
1504
16th to endNight
10%425%5%45%45%7%42%
1496
June1st to 15thNight
10%435%42436%8%45%
1440
16th to endNight
7%314425%6%6%9%47%
1440
July1st to 15thNight
5%31342246%9%55%
1440
16th to endNight
43134346%7%10%50%
1556
August1st to 15thNight
43245%2446%7%54%
1620
16th to endNight
9%41443335%8%50%
1878
September1st to 15thNight
9%31342335%6%56%
1800
16th to endNight
6%424423447%53%
1956
October1st to 15thNight
13%6%23423345%49%
2160
16th to endNight
13%7%25%423345%46%
2322
November1st to 15thNight
12%5%26%423346%48%
2474
16th to endNight
16%7%24424335%43%
2730
December1st to 15thNight
17%12%46%6%24435%31%
2547
16th to endNight
21%14%5%6%5%24335%28%
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
53%6%12%17%9%
1433
16th to endDay
59%5%12%14%7%
1704
February1st to 15thDay
52%5%15%20%5%
1576
16th to endDay
46%8%14%20%8%1
1536
March1st to 15thDay
48%416%21%9%
1911
16th to endDay
54%5%12%19%6%1
2159
April1st to 15thDay
52%410%23%9%
2151
16th to endDay
52%6%9%19%11%1
2163
May1st to 15thDay
53%6%12%20%8%
2445
16th to endDay
45%8%12%19%12%1
2621
June1st to 15thDay
40%7%12%23%14%1
2520
16th to endDay
36%8%12%23%17%1
2520
July1st to 15thDay
33%9%13%27%13%2
2371
16th to endDay
33%8%17%22%16%1
2446
August1st to 15thDay
34%8%15%25%14%1
2326
16th to endDay
37%7%12%25%15%2
2324
September1st to 15thDay
31%5%10%28%22%2
2160
16th to endDay
35%6%11%29%15%1
1989
October1st to 15thDay
41%49%23%19%1
1800
16th to endDay
43%5%12%23%13%1
1902
November1st to 15thDay
41%411%25%14%1
1710
16th to endDay
44%417%23%8%
1560
December1st to 15thDay
59%412%17%6%
1450
16th to endDay
63%411%12%7%
1536
January1st to 15thNight
48%5%14%16%13%
2506
16th to endNight
51%6%14%17%10%
2517
February1st to 15thNight
48%5%11%23%9%
2288
16th to endNight
43%413%24%11%1
1935
March1st to 15thNight
41%412%26%12%1
2058
16th to endNight
53%413%17%8%
2064
April1st to 15thNight
45%49%24%13%2
1797
16th to endNight
47%5%9%20%13%3
1794
May1st to 15thNight
42%7%13%23%12%
1505
16th to endNight
39%6%11%21%17%2
1498
June1st to 15thNight
35%5%13%25%15%3
1440
16th to endNight
30%7%13%24%19%4
1440
July1st to 15thNight
24%6%15%31%17%4
1360
16th to endNight
24%7%16%32%17%1
1457
August1st to 15thNight
26%7%13%31%17%3
1610
16th to endNight
32%5%10%27%19%5%
1878
September1st to 15thNight
27%5%9%28%25%2
1800
16th to endNight
29%5%10%32%19%1
1956
October1st to 15thNight
36%48%23%22%3
2160
16th to endNight
39%412%24%16%2
2322
November1st to 15thNight
37%411%25%17%3
2474
16th to endNight
43%412%28%10%
2730
December1st to 15thNight
55%5%11%20%7%
2547
16th to endNight
60%410%15%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
28%7%36%21%32
90
16th to endDay
21%8%32%26%9%2
96
February1st to 15thDay
12%18%40%21%7%
90
16th to endDay
23%9%35%16%14%
81
March1st to 15thDay
24%18%40%13%3
90
16th to endDay
34%7%27%20%6%1
143
April1st to 15thDay
20%11%32%25%10%
270
16th to endDay
28%8%30%20%11%
273
May1st to 15thDay
21%11%32%23%8%1
468
16th to endDay
16%9%28%28%13%3
517
June1st to 15thDay
11%5%27%30%21%3
495
16th to endDay
9%6%31%31%16%5%
495
July1st to 15thDay
6%126%33%21%10%
475
16th to endDay
8%121%35%26%6%
515
August1st to 15thDay
8%122%34%27%6%
493
16th to endDay
11%314%35%24%10%
364
September1st to 15thDay
10%5%16%33%25%10%
315
16th to endDay
9%428%29%25%3
242
October1st to 15thDay
23%9%28%24%8%5%
135
16th to endDay
20%6%41%20%9%
144
November1st to 15thDay
12%11%33%22%15%4
135
16th to endDay
31%14%32%14%5%
135
December1st to 15thDay
26%18%27%19%7%1
94
16th to endDay
30%18%39%11%
96
January1st to 15thNight
15%12%36%27%7%
900
16th to endNight
16%10%37%29%5%
960
February1st to 15thNight
18%10%37%27%6%
880
16th to endNight
18%9%38%27%5%1
673
March1st to 15thNight
19%10%33%26%10%
618
16th to endNight
19%10%35%26%6%
576
April1st to 15thNight
20%11%34%29%4
539
16th to endNight
23%6%28%30%9%1
540
May1st to 15thNight
17%8%35%28%8%1
540
16th to endNight
12%432%34%15%
563
June1st to 15thNight
12%5%23%40%17%
540
16th to endNight
9%229%41%16%1
540
July1st to 15thNight
8%115%43%29%2
510
16th to endNight
4117%43%30%3
564
August1st to 15thNight
415%43%31%2
539
16th to endNight
11%114%41%27%4
573
September1st to 15thNight
10%315%38%25%5%
540
16th to endNight
8%426%34%23%2
623
October1st to 15thNight
17%6%28%29%17%1
720
16th to endNight
18%9%31%29%10%
768
November1st to 15thNight
15%9%35%28%10%
763
16th to endNight
20%10%37%24%7%
975
December1st to 15thNight
22%12%35%23%5%
910
16th to endNight
27%9%30%26%5%
960
Page generated at 2017-12-03 10:16:43. Version ac04

Copyright 2017 A. Danko


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