Rancho Del Sol Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rancho Del Sol 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
67%
15540
28%
47806
26%
15503
71%
15503
40%
25755

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
58%
717
20%
2491
21%
716
61%
716
29%
1412
January16th to endNight
51%
768
25%
2496
21%
768
59%
768
27%
1525
February1st to 15thNight
53%
699
24%
2243
22%
696
59%
696
26%
1402
February16th to endNight
54%
632
25%
1895
23%
632
60%
632
27%
1207
March1st to 15thNight
51%
720
17%
2084
16%
720
54%
720
26%
1392
March16th to endNight
56%
768
20%
2040
15%
768
59%
768
28%
1354
April1st to 15thNight
55%
719
19%
1799
11%
719
57%
719
29%
1236
April16th to endNight
64%
720
23%
1800
13%
720
66%
720
41%
1095
May1st to 15thNight
67%
573
27%
1653
20%
573
70%
573
51%
816
May16th to endNight
75%
374
25%
1496
31%
374
76%
374
38%
681
June1st to 15thNight
79%
360
27%
1440
36%
360
82%
360
46%
597
June16th to endNight
90%
360
36%
1440
50%
360
91%
360
64%
489
July1st to 15thNight
95%
340
34%
1360
47%
340
95%
340
71%
434
July16th to endNight
92%
471
39%
1503
41%
441
93%
441
68%
566
August1st to 15thNight
90%
595
37%
1668
29%
592
90%
592
72%
727
August16th to endNight
92%
764
44%
1910
28%
764
92%
764
79%
868
September1st to 15thNight
91%
720
43%
1800
31%
720
92%
720
80%
821
September16th to endNight
83%
716
45%
1930
40%
716
87%
716
69%
891
October1st to 15thNight
73%
720
30%
2160
31%
720
77%
720
50%
1054
October16th to endNight
75%
768
38%
2304
40%
768
79%
768
50%
1146
November1st to 15thNight
67%
760
27%
2464
28%
760
71%
760
38%
1324
November16th to endNight
60%
780
27%
2594
26%
780
65%
780
33%
1453
December1st to 15thNight
52%
728
22%
2548
18%
728
60%
728
25%
1536
December16th to endNight
44%
768
22%
2688
19%
768
51%
768
21%
1729

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%412212335%61%
48638
Night
12%412212335%59%
47997
TransparencyDay
26%27%18%24%19%
48318
Night
28%37%18%23%18%
47816
SeeingDay
13%12%31%27%9%4
6102
Night
14%39%31%31%9%
15550

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
18%5%22223335%49%
1444
16th to endDay
22%8%2221333445%
1728
February1st to 15thDay
19%6%13322335%46%
1611
16th to endDay
22%10%23312336%38%
1579
March1st to 15thDay
21%8%25%323447%37%
1875
16th to endDay
19%7%24424436%40%
2184
April1st to 15thDay
18%8%24323445%41%
2149
16th to endDay
14%412313335%56%
2160
May1st to 15thDay
6%31211245%6%64%
2292
16th to endDay
9%413323346%57%
2615
June1st to 15thDay
6%313212245%65%
2520
16th to endDay
2111112383%
2520
July1st to 15thDay
11212384%
2520
16th to endDay
1111121283%
2559
August1st to 15thDay
11112284%
2283
16th to endDay
11122385%
2292
September1st to 15thDay
111122382%
2160
16th to endDay
3222222377%
2025
October1st to 15thDay
6%212213346%64%
1800
16th to endDay
8%21342433462%
1920
November1st to 15thDay
12%413423347%51%
1725
16th to endDay
15%5%24323345%50%
1693
December1st to 15thDay
19%7%23423335%44%
1448
16th to endDay
24%7%2432225%6%39%
1536
January1st to 15thNight
17%5%13323348%47%
2491
16th to endNight
19%5%1332324447%
2496
February1st to 15thNight
17%6%24323347%42%
2241
16th to endNight
20%7%14212445%44%
1895
March1st to 15thNight
20%7%24324336%41%
2084
16th to endNight
19%6%13224445%45%
2040
April1st to 15thNight
15%6%25%5%34445%42%
1799
16th to endNight
12%414212336%57%
1800
May1st to 15thNight
7%112212346%64%
1653
16th to endNight
8%313213346%62%
1496
June1st to 15thNight
5%312212235%69%
1440
16th to endNight
111212283%
1440
July1st to 15thNight
11212385%
1440
16th to endNight
11111212283%
1607
August1st to 15thNight
11111222480%
1677
16th to endNight
111222383%
1910
September1st to 15thNight
1111112286%
1800
16th to endNight
21221122379%
1930
October1st to 15thNight
6%212212235%68%
2160
16th to endNight
8%21212346%65%
2304
November1st to 15thNight
12%412213346%56%
2464
16th to endNight
14%5%13323345%52%
2594
December1st to 15thNight
20%5%13323346%45%
2548
16th to endNight
25%7%23213235%41%
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
37%39%21%19%9%
1444
16th to endDay
43%28%14%17%13%
1728
February1st to 15thDay
41%29%19%20%7%
1611
16th to endDay
47%39%23%13%2
1579
March1st to 15thDay
46%412%15%16%5%
1875
16th to endDay
45%414%17%14%3
2184
April1st to 15thDay
42%413%21%14%3
2149
16th to endDay
30%313%25%21%5%
2160
May1st to 15thDay
21%29%32%27%6%
2292
16th to endDay
29%311%29%19%6%
2619
June1st to 15thDay
22%210%22%23%18%
2520
16th to endDay
9%1315%38%32%
2520
July1st to 15thDay
7%128%26%52%
2371
16th to endDay
9%139%26%50%
2400
August1st to 15thDay
7%1210%31%45%
2267
16th to endDay
7%1110%41%37%
2292
September1st to 15thDay
8%2312%37%36%
2160
16th to endDay
13%2423%34%21%
2025
October1st to 15thDay
20%26%23%26%20%
1800
16th to endDay
26%27%21%25%17%
1920
November1st to 15thDay
32%310%21%22%9%
1725
16th to endDay
36%38%17%27%6%
1693
December1st to 15thDay
43%27%19%20%5%
1448
16th to endDay
46%29%14%16%9%
1536
January1st to 15thNight
36%210%20%18%11%
2491
16th to endNight
40%27%12%19%17%
2496
February1st to 15thNight
41%36%19%18%10%
2252
16th to endNight
41%48%24%15%4
1895
March1st to 15thNight
45%310%16%17%6%
2084
16th to endNight
40%5%10%19%17%6%
2040
April1st to 15thNight
43%412%20%13%5%
1799
16th to endNight
28%5%12%25%20%7%
1800
May1st to 15thNight
19%313%27%25%10%
1654
16th to endNight
24%314%29%21%7%
1496
June1st to 15thNight
18%311%23%23%19%
1440
16th to endNight
10%1316%33%34%
1440
July1st to 15thNight
6%226%25%56%
1360
16th to endNight
10%128%22%54%
1503
August1st to 15thNight
10%1113%26%45%
1668
16th to endNight
7%1112%33%43%
1910
September1st to 15thNight
7%1311%38%37%
1800
16th to endNight
12%1322%37%22%
1930
October1st to 15thNight
19%36%20%27%22%
2160
16th to endNight
20%35%22%28%19%
2304
November1st to 15thNight
29%311%21%21%12%
2464
16th to endNight
34%27%21%24%10%
2594
December1st to 15thNight
40%38%19%19%8%
2548
16th to endNight
46%28%13%18%10%
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
47%6%18%18%6%2
72
16th to endDay
32%9%19%24%10%3
256
February1st to 15thDay
26%10%27%25%8%1
243
16th to endDay
29%18%23%21%6%
238
March1st to 15thDay
32%18%20%16%7%4
270
16th to endDay
25%22%28%17%5%1
288
April1st to 15thDay
29%21%28%13%5%1
269
16th to endDay
17%26%28%21%5%1
270
May1st to 15thDay
11%21%37%19%7%2
288
16th to endDay
14%16%24%27%10%6%
330
June1st to 15thDay
10%18%34%25%5%5%
315
16th to endDay
29%40%32%5%8%
315
July1st to 15thDay
237%42%5%11%
305
16th to endDay
1440%37%9%6%
327
August1st to 15thDay
3445%32%7%7%
315
16th to endDay
335%40%11%7%
332
September1st to 15thDay
26%42%31%13%3
315
16th to endDay
413%35%33%10%2
315
October1st to 15thDay
6%14%35%29%10%3
315
16th to endDay
13%9%26%27%19%4
336
November1st to 15thDay
19%7%11%31%25%4
141
16th to endDay
22%5%17%32%19%2
121
December1st to 15thDay
30%11%27%16%11%3
62
16th to endDay
20%9%18%29%15%6%
64
January1st to 15thNight
19%412%33%22%8%
720
16th to endNight
23%315%28%21%7%
768
February1st to 15thNight
20%5%12%33%22%5%
704
16th to endNight
25%7%9%31%21%5%
632
March1st to 15thNight
25%411%28%23%6%
720
16th to endNight
23%5%10%30%24%5%
768
April1st to 15thNight
19%5%12%35%22%4
719
16th to endNight
13%6%11%33%25%9%
720
May1st to 15thNight
9%314%36%29%6%
574
16th to endNight
7%37%31%41%7%
375
June1st to 15thNight
6%15%35%42%8%
360
16th to endNight
2333%50%10%
360
July1st to 15thNight
28%60%9%
340
16th to endNight
2126%52%16%
471
August1st to 15thNight
1433%49%10%
595
16th to endNight
1332%51%11%
764
September1st to 15thNight
1429%51%12%
720
16th to endNight
39%33%35%16%
716
October1st to 15thNight
8%310%35%30%11%
720
16th to endNight
9%38%29%32%16%
768
November1st to 15thNight
15%210%32%28%11%
760
16th to endNight
16%5%13%33%22%8%
780
December1st to 15thNight
23%5%11%33%20%6%
728
16th to endNight
30%414%28%17%4
768
Page generated at 2017-12-03 08:16:36. Version ac04

Copyright 2017 A. Danko


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