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 2017-09-22.

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
50%
15474
27%
47002
18%
15427
58%
15427
35%
26653

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
36%
899
26%
2327
11%
895
45%
895
34%
1445
January16th to endNight
35%
903
31%
2439
12%
903
48%
903
34%
1482
February1st to 15thNight
34%
704
29%
2106
12%
698
48%
698
32%
1199
February16th to endNight
24%
632
30%
1894
9%
632
40%
632
31%
1087
March1st to 15thNight
33%
560
28%
2000
14%
560
48%
560
26%
1159
March16th to endNight
32%
576
24%
2112
15%
576
46%
576
28%
1176
April1st to 15thNight
29%
539
24%
1977
12%
539
46%
539
27%
1105
April16th to endNight
29%
540
25%
1746
13%
540
47%
540
28%
1056
May1st to 15thNight
34%
539
23%
1620
15%
539
47%
539
31%
975
May16th to endNight
46%
562
25%
1684
19%
561
58%
561
35%
992
June1st to 15thNight
67%
540
22%
1620
22%
540
73%
540
51%
799
June16th to endNight
71%
540
23%
1620
26%
540
74%
540
39%
911
July1st to 15thNight
77%
510
23%
1530
25%
510
80%
510
47%
797
July16th to endNight
83%
564
27%
1594
30%
531
86%
531
48%
808
August1st to 15thNight
89%
539
32%
1649
37%
536
90%
536
57%
759
August16th to endNight
77%
573
21%
1968
26%
573
78%
573
33%
1102
September1st to 15thNight
76%
540
20%
1980
25%
540
77%
540
32%
1107
September16th to endNight
70%
513
28%
1891
27%
513
74%
513
32%
1032
October1st to 15thNight
69%
508
34%
1828
32%
508
73%
508
39%
901
October16th to endNight
57%
704
35%
2112
22%
704
65%
704
45%
1079
November1st to 15thNight
52%
729
30%
2129
19%
729
59%
729
39%
1203
November16th to endNight
46%
900
31%
2340
15%
900
54%
900
38%
1394
December1st to 15thNight
39%
900
28%
2340
15%
900
46%
900
33%
1492
December16th to endNight
37%
960
25%
2496
10%
960
45%
960
32%
1593

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
10%5%24424447%48%
47873
Night
10%423323347%54%
47204
Cloud CoverDay
10%5%24424447%48%
47871
Night
9%423323347%54%
47204
TransparencyDay
34%5%10%19%19%9%
47571
Night
30%5%11%20%20%12%
47009
SeeingDay
11%419%33%24%6%
5437
Night
12%6%27%36%16%1
15477

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
16%413313335%52%
1611
16th to endDay
13%423323345%53%
1796
February1st to 15thDay
13%5%24222245%54%
1750
16th to endDay
15%5%32222335%52%
1580
March1st to 15thDay
17%6%25%413236%46%
1959
16th to endDay
14%6%24323335%50%
2112
April1st to 15thDay
11%6%2442435%7%46%
1971
16th to endDay
13%5%35%423436%46%
2211
May1st to 15thDay
14%7%25%5%34448%39%
2331
16th to endDay
13%7%35%5%45%5%6%7%36%
2430
June1st to 15thDay
5%312345%5%6%9%51%
2340
16th to endDay
8%4345%35%6%6%9%41%
2340
July1st to 15thDay
7%3246%36%6%5%9%44%
2340
16th to endDay
6%324435%5%6%11%46%
2466
August1st to 15thDay
12134245%5%11%59%
2298
16th to endDay
6%415%7%46%6%6%8%40%
2232
September1st to 15thDay
8%6%25%6%35%5%5%7%44%
1980
16th to endDay
8%3245%35%5%6%8%47%
1881
October1st to 15thDay
10%423323345%55%
1790
16th to endDay
8%31221223466%
1760
November1st to 15thDay
11%5%25%423235%51%
1727
16th to endDay
12%423222425%56%
1620
December1st to 15thDay
16%7%13412336%47%
1620
16th to endDay
14%6%34423435%47%
1728
January1st to 15thNight
15%414313335%53%
2327
16th to endNight
14%5%13223336%52%
2439
February1st to 15thNight
12%6%23212225%57%
2102
16th to endNight
13%5%23423245%53%
1894
March1st to 15thNight
14%5%24313347%48%
2000
16th to endNight
11%423324337%52%
2112
April1st to 15thNight
10%5%2442335%6%51%
1977
16th to endNight
13%5%2432345%6%48%
1746
May1st to 15thNight
9%6%24423449%48%
1619
16th to endNight
9%4233345%7%9%48%
1683
June1st to 15thNight
231221345%8%62%
1620
16th to endNight
5%323225%47%8%54%
1620
July1st to 15thNight
42332346%11%57%
1620
16th to endNight
211232346%13%57%
1702
August1st to 15thNight
21122245%9%68%
1659
16th to endNight
6%424425%46%9%48%
1968
September1st to 15thNight
7%4144345%6%8%49%
1980
16th to endNight
7%5%235%2435%7%51%
1891
October1st to 15thNight
8%312223346%61%
1828
16th to endNight
8%312213235%64%
2112
November1st to 15thNight
8%424223246%57%
2129
16th to endNight
12%5%1331222458%
2340
December1st to 15thNight
14%6%23313336%50%
2340
16th to endNight
14%6%2341333351%
2496

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
16%413313335%52%
1611
16th to endDay
14%424313346%52%
1796
February1st to 15thDay
13%5%24212236%54%
1750
16th to endDay
15%5%23223335%52%
1580
March1st to 15thDay
17%6%25%323236%46%
1959
16th to endDay
14%6%23413335%50%
2110
April1st to 15thDay
11%7%24424347%46%
1971
16th to endDay
12%5%35%424345%47%
2211
May1st to 15thDay
14%6%26%5%34447%39%
2331
16th to endDay
13%7%345%35%6%6%6%37%
2430
June1st to 15thDay
5%313335%5%6%8%51%
2340
16th to endDay
8%4345%36%5%6%9%41%
2340
July1st to 15thDay
7%3246%36%5%5%8%44%
2340
16th to endDay
6%324435%5%6%11%46%
2466
August1st to 15thDay
1112425%45%10%59%
2298
16th to endDay
7%426%6%36%6%6%8%40%
2232
September1st to 15thDay
8%6%25%6%35%5%5%6%44%
1980
16th to endDay
8%3145%345%6%8%47%
1881
October1st to 15thDay
9%5%13423336%55%
1790
16th to endDay
8%312212225%66%
1760
November1st to 15thDay
11%6%25%433335%51%
1727
16th to endDay
12%42321243456%
1620
December1st to 15thDay
16%7%14332335%47%
1620
16th to endDay
14%6%34423435%47%
1728
January1st to 15thNight
15%423313335%53%
2327
16th to endNight
15%5%13323335%53%
2439
February1st to 15thNight
12%6%24212225%57%
2102
16th to endNight
13%423423245%54%
1894
March1st to 15thNight
14%5%24313347%48%
2000
16th to endNight
11%423324336%53%
2112
April1st to 15thNight
10%5%2442335%6%51%
1977
16th to endNight
12%5%2432345%6%48%
1746
May1st to 15thNight
9%5%3432345%8%48%
1619
16th to endNight
8%42333347%8%49%
1683
June1st to 15thNight
231231345%8%63%
1620
16th to endNight
4323325%47%8%55%
1620
July1st to 15thNight
5%2332346%11%57%
1620
16th to endNight
311231436%13%57%
1702
August1st to 15thNight
211212449%68%
1659
16th to endNight
6%414425%45%10%48%
1968
September1st to 15thNight
7%31443445%8%49%
1980
16th to endNight
7%4235%3335%7%51%
1891
October1st to 15thNight
8%312222346%61%
1828
16th to endNight
8%312213235%64%
2112
November1st to 15thNight
8%423323336%58%
2129
16th to endNight
11%5%13322235%58%
2340
December1st to 15thNight
14%6%23313246%50%
2340
16th to endNight
14%7%2342333450%
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
35%36%18%23%12%
1612
16th to endDay
34%26%13%26%16%
1796
February1st to 15thDay
33%37%14%23%17%
1751
16th to endDay
35%35%18%21%14%
1580
March1st to 15thDay
41%47%12%21%13%
1959
16th to endDay
37%5%8%16%22%10%
2112
April1st to 15thDay
37%5%8%17%17%13%
1971
16th to endDay
39%47%18%19%10%
2211
May1st to 15thDay
44%6%9%13%18%8%
2331
16th to endDay
43%8%10%16%16%3
2434
June1st to 15thDay
27%8%12%23%22%5%
2340
16th to endDay
36%8%13%20%16%3
2340
July1st to 15thDay
33%8%16%25%13%2
2201
16th to endDay
27%8%18%29%13%1
2311
August1st to 15thDay
19%6%17%35%19%2
2284
16th to endDay
36%9%16%22%11%3
2232
September1st to 15thDay
38%6%12%21%15%5%
1980
16th to endDay
32%7%10%18%19%9%
1881
October1st to 15thDay
30%48%21%18%15%
1790
16th to endDay
23%25%16%31%20%
1760
November1st to 15thDay
36%46%21%19%11%
1727
16th to endDay
32%36%13%21%22%
1620
December1st to 15thDay
40%38%17%21%9%
1620
16th to endDay
39%49%15%20%10%
1728
January1st to 15thNight
34%36%16%20%17%
2327
16th to endNight
34%35%14%23%19%
2439
February1st to 15thNight
32%36%13%22%21%
2112
16th to endNight
33%37%16%21%17%
1894
March1st to 15thNight
36%48%13%23%14%
2000
16th to endNight
33%5%10%16%23%11%
2112
April1st to 15thNight
34%5%8%15%19%16%
1977
16th to endNight
37%5%10%16%19%11%
1746
May1st to 15thNight
33%7%11%21%17%9%
1620
16th to endNight
30%7%16%26%15%4
1685
June1st to 15thNight
17%6%16%27%26%5%
1620
16th to endNight
24%9%15%27%18%4
1620
July1st to 15thNight
19%7%23%32%15%1
1530
16th to endNight
17%8%23%35%13%1
1594
August1st to 15thNight
13%5%20%37%20%2
1649
16th to endNight
29%7%21%26%11%3
1968
September1st to 15thNight
29%8%15%23%15%6%
1980
16th to endNight
30%6%13%22%17%10%
1891
October1st to 15thNight
24%411%23%19%15%
1828
16th to endNight
22%36%16%26%23%
2112
November1st to 15thNight
29%48%21%21%13%
2129
16th to endNight
31%36%14%21%22%
2340
December1st to 15thNight
37%38%17%21%11%
2340
16th to endNight
37%37%14%23%13%
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
22%7%31%34%4
90
16th to endDay
13%13%42%21%6%2
96
February1st to 15thDay
10%17%33%33%5%
90
16th to endDay
13%13%45%25%1
81
March1st to 15thDay
25%10%35%20%8%
90
16th to endDay
8%7%45%32%6%
96
April1st to 15thDay
14%15%37%27%4
90
16th to endDay
13%12%43%20%10%
321
May1st to 15thDay
17%10%36%26%8%
468
16th to endDay
19%6%28%31%12%1
517
June1st to 15thDay
6%114%45%27%4
495
16th to endDay
9%211%41%27%7%
495
July1st to 15thDay
5%19%42%32%8%
475
16th to endDay
4332%46%11%
515
August1st to 15thDay
3333%46%12%
451
16th to endDay
10%15%38%31%13%
272
September1st to 15thDay
2228%48%18%
135
16th to endDay
4327%47%15%
108
October1st to 15thDay
38%36%41%10%
90
16th to endDay
20%116%27%31%3
96
November1st to 15thDay
31%5%24%26%7%4
90
16th to endDay
26%12%30%18%10%2
90
December1st to 15thDay
24%425%23%13%8%
90
16th to endDay
20%15%39%17%5%1
96
January1st to 15thNight
17%10%31%31%8%
900
16th to endNight
17%9%34%32%6%
903
February1st to 15thNight
15%13%33%32%4
704
16th to endNight
16%12%45%24%1
632
March1st to 15thNight
16%10%35%33%4
560
16th to endNight
12%10%43%29%4
576
April1st to 15thNight
13%7%46%30%1
539
16th to endNight
14%8%44%23%7%
540
May1st to 15thNight
12%9%41%30%6%
540
16th to endNight
10%335%33%15%
563
June1st to 15thNight
423%49%20%1
540
16th to endNight
5%117%51%22%2
540
July1st to 15thNight
410%51%29%2
510
16th to endNight
36%53%32%3
564
August1st to 15thNight
3348%39%5%
539
16th to endNight
8%5%43%39%3
573
September1st to 15thNight
8%6%42%36%5%
540
16th to endNight
9%110%35%39%3
513
October1st to 15thNight
9%116%44%23%4
508
16th to endNight
9%5%25%32%24%2
704
November1st to 15thNight
10%428%37%17%1
729
16th to endNight
15%7%28%33%13%1
900
December1st to 15thNight
19%8%30%31%9%
900
16th to endNight
19%8%31%32%8%
960
Page generated at 2017-09-23 05:43:42. Version ac04

Copyright 2017 A. Danko


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