Orion Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orion Ranch Observatory clear sky chart from 2005-11-05 to 2019-06-19.

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
49%
17791
26%
54003
18%
17744
57%
17744
34%
30999

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
37%
1049
28%
2717
12%
1045
47%
1045
35%
1677
January16th to endNight
35%
1053
29%
2845
11%
1053
47%
1053
34%
1743
February1st to 15thNight
32%
824
27%
2466
12%
818
44%
818
29%
1467
February16th to endNight
22%
736
26%
2206
8%
736
36%
736
28%
1335
March1st to 15thNight
32%
654
27%
2334
14%
654
46%
654
25%
1375
March16th to endNight
32%
672
24%
2464
14%
672
46%
672
27%
1388
April1st to 15thNight
29%
629
25%
2307
13%
629
47%
629
27%
1292
April16th to endNight
30%
624
25%
2014
13%
624
47%
624
29%
1202
May1st to 15thNight
35%
629
24%
1890
17%
629
47%
629
30%
1150
May16th to endNight
46%
658
24%
1972
17%
657
58%
657
36%
1140
June1st to 15thNight
66%
630
24%
1890
23%
630
73%
630
51%
933
June16th to endNight
70%
597
22%
1791
24%
597
73%
597
40%
1005
July1st to 15thNight
79%
555
22%
1665
24%
555
81%
555
46%
871
July16th to endNight
83%
612
28%
1738
30%
579
86%
579
50%
865
August1st to 15thNight
88%
575
31%
1759
36%
572
90%
572
57%
809
August16th to endNight
78%
621
20%
2133
25%
621
79%
621
34%
1162
September1st to 15thNight
73%
585
19%
2145
24%
585
74%
585
28%
1252
September16th to endNight
67%
582
26%
2145
26%
582
70%
582
29%
1211
October1st to 15thNight
69%
600
33%
2160
31%
600
73%
600
38%
1085
October16th to endNight
55%
832
34%
2496
21%
832
63%
832
43%
1310
November1st to 15thNight
51%
854
29%
2494
18%
854
57%
854
35%
1464
November16th to endNight
46%
1050
31%
2730
15%
1050
54%
1050
39%
1624
December1st to 15thNight
38%
1050
29%
2730
15%
1050
46%
1050
33%
1745
December16th to endNight
35%
1120
23%
2912
9%
1120
44%
1120
30%
1894

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
11%5%24424447%48%
54709
Night
10%423323347%53%
54205
Cloud CoverDay
11%5%24424447%48%
54707
Night
10%423323347%53%
54205
TransparencyDay
35%5%10%19%19%8%
54407
Night
31%5%11%20%19%11%
54010
SeeingDay
13%5%21%31%22%5%
7672
Night
13%6%27%36%15%1
17794

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
15%423413335%51%
1881
16th to endDay
13%5%23323345%52%
2096
February1st to 15thDay
14%5%25%222346%50%
2050
16th to endDay
18%5%23323345%47%
1840
March1st to 15thDay
16%6%25%423246%44%
2285
16th to endDay
13%6%24423345%49%
2464
April1st to 15thDay
11%6%25%423346%47%
2301
16th to endDay
13%5%25%423436%47%
2546
May1st to 15thDay
14%7%25%5%34448%38%
2721
16th to endDay
11%6%245%45%5%6%7%38%
2846
June1st to 15thDay
5%312345%5%6%9%53%
2730
16th to endDay
8%4345%35%6%6%9%42%
2577
July1st to 15thDay
6%3246%36%6%5%9%45%
2535
16th to endDay
6%3234345%6%11%49%
2674
August1st to 15thDay
11134245%5%10%59%
2441
16th to endDay
6%415%6%46%5%6%8%43%
2419
September1st to 15thDay
9%6%35%6%35%5%5%6%41%
2145
16th to endDay
9%4245%35%5%6%7%44%
2145
October1st to 15thDay
10%5%13423445%53%
2116
16th to endDay
10%31221223463%
2080
November1st to 15thDay
12%5%25%424335%49%
2021
16th to endDay
11%423222435%56%
1890
December1st to 15thDay
16%7%23422346%47%
1890
16th to endDay
16%6%24423435%44%
2016
January1st to 15thNight
15%414213335%53%
2717
16th to endNight
14%5%13323336%52%
2845
February1st to 15thNight
14%7%24212225%52%
2462
16th to endNight
15%5%23413245%49%
2206
March1st to 15thNight
15%5%24313447%46%
2334
16th to endNight
10%423324447%50%
2464
April1st to 15thNight
9%5%245%2335%7%51%
2307
16th to endNight
12%5%2432345%6%48%
2014
May1st to 15thNight
9%6%2442345%8%47%
1889
16th to endNight
8%42333447%9%50%
1971
June1st to 15thNight
221221345%9%62%
1890
16th to endNight
5%323225%47%8%54%
1791
July1st to 15thNight
42232346%10%57%
1755
16th to endNight
211232345%13%59%
1846
August1st to 15thNight
21122245%9%68%
1769
16th to endNight
6%314425%46%10%50%
2133
September1st to 15thNight
10%4244345%5%8%46%
2145
16th to endNight
8%5%245%2435%7%49%
2145
October1st to 15thNight
8%31332335%6%58%
2160
16th to endNight
11%312213335%62%
2496
November1st to 15thNight
9%5%24323246%54%
2494
16th to endNight
11%5%13313335%57%
2730
December1st to 15thNight
15%6%24313346%49%
2730
16th to endNight
16%7%2342333448%
2912

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
15%413413345%50%
1881
16th to endDay
14%424313346%52%
2096
February1st to 15thDay
15%424312237%50%
2050
16th to endDay
18%5%23323345%47%
1840
March1st to 15thDay
16%7%25%423236%43%
2285
16th to endDay
13%6%23423346%49%
2462
April1st to 15thDay
11%7%24424347%46%
2301
16th to endDay
12%5%25%424335%48%
2546
May1st to 15thDay
14%7%26%5%34447%38%
2721
16th to endDay
11%6%245%35%6%6%6%39%
2846
June1st to 15thDay
4213335%5%6%8%53%
2730
16th to endDay
8%435%5%36%5%6%9%42%
2577
July1st to 15thDay
7%3246%36%5%6%8%45%
2535
16th to endDay
6%314435%5%6%10%49%
2674
August1st to 15thDay
111242445%10%59%
2441
16th to endDay
6%415%6%36%6%6%8%43%
2419
September1st to 15thDay
9%6%26%6%45%45%6%41%
2145
16th to endDay
9%4245%346%6%8%44%
2145
October1st to 15thDay
9%5%13423346%53%
2116
16th to endDay
11%31221223463%
2080
November1st to 15thDay
12%6%25%423335%49%
2021
16th to endDay
11%5%14213435%56%
1890
December1st to 15thDay
16%7%14332345%47%
1890
16th to endDay
16%6%34423435%45%
2016
January1st to 15thNight
15%423213335%53%
2717
16th to endNight
14%5%13323335%52%
2845
February1st to 15thNight
14%6%24312225%53%
2462
16th to endNight
15%5%23413245%49%
2206
March1st to 15thNight
15%5%24313347%46%
2334
16th to endNight
10%423424447%51%
2464
April1st to 15thNight
9%5%2442335%6%51%
2307
16th to endNight
12%5%24323446%49%
2014
May1st to 15thNight
8%6%3442345%8%48%
1889
16th to endNight
7%42333447%8%50%
1971
June1st to 15thNight
231231345%9%63%
1890
16th to endNight
5%323325%47%8%55%
1791
July1st to 15thNight
42331346%10%57%
1755
16th to endNight
311231336%12%59%
1846
August1st to 15thNight
211213449%67%
1769
16th to endNight
6%414425%46%10%50%
2133
September1st to 15thNight
10%424435%45%8%47%
2145
16th to endNight
8%5%245%3335%7%49%
2145
October1st to 15thNight
8%31332235%7%58%
2160
16th to endNight
10%312213235%62%
2496
November1st to 15thNight
9%5%24323336%55%
2494
16th to endNight
11%413323335%57%
2730
December1st to 15thNight
15%6%23313246%49%
2730
16th to endNight
15%7%2342333448%
2912

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
36%37%18%22%12%
1882
16th to endDay
35%26%13%27%15%
2096
February1st to 15thDay
37%47%14%20%16%
2051
16th to endDay
39%36%17%19%13%
1840
March1st to 15thDay
43%47%12%20%12%
2285
16th to endDay
36%5%9%17%22%9%
2464
April1st to 15thDay
37%47%18%18%12%
2301
16th to endDay
39%46%19%20%9%
2546
May1st to 15thDay
44%6%9%14%17%7%
2721
16th to endDay
41%8%10%18%17%3
2850
June1st to 15thDay
26%7%13%25%21%4
2730
16th to endDay
36%8%13%21%16%3
2577
July1st to 15thDay
33%8%17%24%14%2
2396
16th to endDay
25%7%18%30%15%1
2519
August1st to 15thDay
19%6%16%35%19%2
2427
16th to endDay
34%9%16%23%12%3
2419
September1st to 15thDay
42%6%11%20%14%5%
2145
16th to endDay
35%7%10%18%18%8%
2145
October1st to 15thDay
32%5%10%20%17%13%
2116
16th to endDay
26%25%15%29%20%
2080
November1st to 15thDay
38%47%21%17%9%
2021
16th to endDay
31%36%15%22%19%
1890
December1st to 15thDay
40%38%16%21%10%
1890
16th to endDay
41%48%15%20%9%
2016
January1st to 15thNight
34%36%17%21%17%
2717
16th to endNight
34%35%14%24%18%
2845
February1st to 15thNight
36%36%14%20%18%
2472
16th to endNight
37%37%15%19%15%
2206
March1st to 15thNight
38%48%13%22%13%
2334
16th to endNight
33%6%11%18%21%9%
2464
April1st to 15thNight
33%5%8%16%19%15%
2307
16th to endNight
36%5%10%18%20%10%
2014
May1st to 15thNight
34%7%11%22%16%7%
1890
16th to endNight
29%6%16%29%15%3
1973
June1st to 15thNight
17%6%17%29%25%4
1890
16th to endNight
24%8%15%28%18%3
1791
July1st to 15thNight
20%7%23%30%16%1
1665
16th to endNight
16%7%22%36%15%1
1738
August1st to 15thNight
13%5%20%36%20%2
1759
16th to endNight
27%7%22%27%11%3
2133
September1st to 15thNight
32%8%15%22%14%6%
2145
16th to endNight
33%6%13%21%16%8%
2145
October1st to 15thNight
25%5%13%23%18%13%
2160
16th to endNight
24%36%15%26%23%
2496
November1st to 15thNight
32%49%21%20%12%
2494
16th to endNight
30%36%16%23%19%
2730
December1st to 15thNight
37%38%17%21%11%
2730
16th to endNight
40%36%14%22%12%
2912

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%8%33%30%6%
180
16th to endDay
18%13%36%22%7%1
192
February1st to 15thDay
22%15%34%23%3
180
16th to endDay
30%11%38%18%
159
March1st to 15thDay
22%16%40%16%4
180
16th to endDay
10%9%43%29%6%
192
April1st to 15thDay
16%13%42%24%3
180
16th to endDay
14%11%42%21%10%
438
May1st to 15thDay
17%9%35%28%9%
618
16th to endDay
16%5%29%32%13%1
677
June1st to 15thDay
7%14%48%24%4
645
16th to endDay
9%211%43%27%6%
587
July1st to 15thDay
5%18%38%35%11%
550
16th to endDay
4331%47%11%
595
August1st to 15thDay
3435%45%11%
504
16th to endDay
8%434%35%15%
331
September1st to 15thDay
10%5%23%41%19%
180
16th to endDay
10%17%30%36%14%
180
October1st to 15thDay
7%115%25%37%12%
180
16th to endDay
22%421%24%23%3
192
November1st to 15thDay
25%7%25%31%7%2
180
16th to endDay
16%12%32%22%12%3
180
December1st to 15thDay
22%7%33%20%10%5%
180
16th to endDay
29%12%33%19%4
192
January1st to 15thNight
17%9%30%32%8%
1050
16th to endNight
17%9%34%31%6%
1053
February1st to 15thNight
19%12%33%29%4
824
16th to endNight
19%11%44%22%1
736
March1st to 15thNight
16%10%36%31%4
654
16th to endNight
12%9%43%30%4
672
April1st to 15thNight
13%9%45%29%1
629
16th to endNight
13%8%45%24%7%
624
May1st to 15thNight
13%8%40%31%6%
630
16th to endNight
10%336%35%13%
659
June1st to 15thNight
424%49%19%1
630
16th to endNight
5%117%52%20%2
597
July1st to 15thNight
410%50%31%3
555
16th to endNight
36%54%31%3
612
August1st to 15thNight
3449%37%4
575
16th to endNight
7%446%37%4
621
September1st to 15thNight
11%16%40%35%5%
585
16th to endNight
11%110%34%39%3
582
October1st to 15thNight
9%115%42%25%5%
600
16th to endNight
11%5%24%32%23%2
832
November1st to 15thNight
12%427%37%16%1
854
16th to endNight
14%7%28%33%14%1
1050
December1st to 15thNight
20%8%29%31%9%
1050
16th to endNight
21%8%30%31%7%
1120
Page generated at 2019-06-20 07:02:32. Version ac04

Copyright 2019 A. Danko


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