Rancho del Rio Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rancho del Rio 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
74%
16286
28%
47032
26%
16243
75%
16243
42%
26359

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
74%
716
29%
2312
30%
716
76%
716
41%
1205
January16th to endNight
67%
768
32%
2304
31%
768
70%
768
38%
1305
February1st to 15thNight
72%
698
32%
2106
33%
698
75%
698
43%
1136
February16th to endNight
62%
632
25%
1895
29%
632
63%
632
29%
1184
March1st to 15thNight
70%
720
26%
2160
29%
720
72%
720
39%
1205
March16th to endNight
73%
768
23%
2031
22%
768
74%
768
38%
1236
April1st to 15thNight
66%
719
24%
1799
17%
719
67%
719
39%
1121
April16th to endNight
71%
720
26%
1800
17%
720
72%
720
44%
1090
May1st to 15thNight
68%
593
22%
1674
17%
593
68%
593
34%
1052
May16th to endNight
64%
561
19%
1685
16%
561
64%
561
30%
1085
June1st to 15thNight
68%
540
16%
1620
14%
540
68%
540
30%
1068
June16th to endNight
84%
540
24%
1620
22%
540
84%
540
52%
824
July1st to 15thNight
80%
510
19%
1530
17%
510
80%
510
43%
845
July16th to endNight
79%
645
22%
1668
16%
606
78%
606
40%
992
August1st to 15thNight
78%
717
25%
1790
16%
713
78%
713
50%
1010
August16th to endNight
84%
764
32%
1910
23%
764
84%
764
56%
1037
September1st to 15thNight
82%
720
31%
1866
27%
720
82%
720
53%
1006
September16th to endNight
83%
683
38%
1890
36%
683
83%
683
59%
906
October1st to 15thNight
78%
660
33%
1815
32%
660
79%
660
48%
978
October16th to endNight
74%
704
33%
2106
36%
704
75%
704
45%
1104
November1st to 15thNight
81%
700
32%
2275
37%
700
82%
700
47%
1102
November16th to endNight
79%
720
32%
2340
36%
720
80%
720
41%
1210
December1st to 15thNight
69%
720
30%
2340
34%
720
70%
720
35%
1291
December16th to endNight
65%
768
31%
2496
31%
768
69%
768
37%
1367

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
5%413323347%61%
47837
Night
6%6%23323347%54%
47239
TransparencyDay
22%48%16%24%23%
47540
Night
28%39%14%20%22%
47038
SeeingDay
7%318%40%24%5%
5959
Night
9%17%28%39%13%
16299

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
8%413413245%58%
1625
16th to endDay
10%424223345%56%
1920
February1st to 15thDay
7%32232345%6%58%
1751
16th to endDay
11%5%3442435%8%46%
1579
March1st to 15thDay
5%32422445%9%56%
1800
16th to endDay
5%32332335%9%56%
2188
April1st to 15thDay
7%414314447%55%
2149
16th to endDay
4312213247%64%
2160
May1st to 15thDay
5%5%23324346%58%
2277
16th to endDay
4423323248%60%
2429
June1st to 15thDay
5%7%23322336%59%
2340
16th to endDay
1212213235%71%
2340
July1st to 15thDay
341332445%7%60%
2340
16th to endDay
231222445%8%61%
2382
August1st to 15thDay
1312213235%71%
2160
16th to endDay
1212212446%70%
2292
September1st to 15thDay
22221345%5%69%
2093
16th to endDay
222213236%71%
1882
October1st to 15thDay
4323323345%61%
1815
16th to endDay
6%312212235%67%
1763
November1st to 15thDay
4312324446%63%
1584
16th to endDay
6%313312347%61%
1620
December1st to 15thDay
7%32332445%8%53%
1620
16th to endDay
11%423323346%55%
1728
January1st to 15thNight
6%313424347%58%
2312
16th to endNight
9%424323236%56%
2304
February1st to 15thNight
7%423313345%59%
2101
16th to endNight
12%6%25%5%24335%46%
1895
March1st to 15thNight
7%5%24323348%53%
2160
16th to endNight
6%6%3342445%8%50%
2031
April1st to 15thNight
9%7%34422347%50%
1799
16th to endNight
6%8%23314336%55%
1800
May1st to 15thNight
7%9%25%433448%44%
1673
16th to endNight
9%10%345%23346%44%
1684
June1st to 15thNight
7%13%4433446%8%39%
1620
16th to endNight
16%2433446%9%54%
1620
July1st to 15thNight
38%334345%6%10%47%
1620
16th to endNight
46%23435%6%6%10%46%
1782
August1st to 15thNight
27%23335%45%9%52%
1800
16th to endNight
26%1231345%10%59%
1910
September1st to 15thNight
2413324347%60%
1866
16th to endNight
2412213346%66%
1890
October1st to 15thNight
3413433348%60%
1815
16th to endNight
7%5%12323336%60%
2106
November1st to 15thNight
4322223345%65%
2275
16th to endNight
5%414323447%58%
2340
December1st to 15thNight
8%5%14422447%53%
2340
16th to endNight
12%413313245%56%
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
27%36%13%21%26%
1626
16th to endDay
30%37%14%15%28%
1920
February1st to 15thDay
25%48%13%21%26%
1751
16th to endDay
36%49%14%23%11%
1579
March1st to 15thDay
25%410%18%20%21%
1800
16th to endDay
25%5%11%23%20%13%
2188
April1st to 15thDay
28%49%23%24%9%
2149
16th to endDay
18%5%10%22%23%18%
2160
May1st to 15thDay
26%49%19%24%16%
2277
16th to endDay
23%49%24%29%9%
2432
June1st to 15thDay
27%38%15%26%17%
2340
16th to endDay
14%27%9%25%41%
2340
July1st to 15thDay
21%38%13%24%28%
2201
16th to endDay
19%6%12%21%26%13%
2234
August1st to 15thDay
16%26%15%32%26%
2146
16th to endDay
15%28%14%32%26%
2292
September1st to 15thDay
15%38%11%32%28%
2093
16th to endDay
14%26%13%33%29%
1882
October1st to 15thDay
24%36%16%24%24%
1815
16th to endDay
19%36%12%21%36%
1763
November1st to 15thDay
20%38%16%16%34%
1584
16th to endDay
22%37%15%18%32%
1620
December1st to 15thDay
27%5%10%15%17%24%
1620
16th to endDay
30%48%16%21%17%
1728
January1st to 15thNight
26%36%13%19%29%
2312
16th to endNight
31%38%11%14%31%
2304
February1st to 15thNight
27%39%14%19%26%
2112
16th to endNight
39%46%12%22%15%
1895
March1st to 15thNight
30%39%17%16%22%
2160
16th to endNight
31%6%12%16%19%13%
2031
April1st to 15thNight
33%48%22%20%10%
1799
16th to endNight
30%312%17%19%17%
1800
May1st to 15thNight
35%5%12%15%15%15%
1674
16th to endNight
38%5%11%17%15%10%
1685
June1st to 15thNight
39%6%13%10%19%11%
1620
16th to endNight
21%212%13%19%31%
1620
July1st to 15thNight
27%312%11%22%22%
1530
16th to endNight
29%5%13%19%22%8%
1668
August1st to 15thNight
25%212%18%25%15%
1790
16th to endNight
20%210%12%28%25%
1910
September1st to 15thNight
22%28%12%28%26%
1866
16th to endNight
17%17%13%30%28%
1890
October1st to 15thNight
23%47%18%24%21%
1815
16th to endNight
26%25%11%19%34%
2106
November1st to 15thNight
21%37%16%15%35%
2275
16th to endNight
26%48%14%15%31%
2340
December1st to 15thNight
30%48%14%18%23%
2340
16th to endNight
30%410%14%19%21%
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
24%115%38%20%
104
16th to endDay
15%5%25%40%10%3
288
February1st to 15thDay
8%425%42%17%1
266
16th to endDay
11%6%34%34%12%1
238
March1st to 15thDay
7%6%24%38%17%5%
270
16th to endDay
5%6%25%40%15%5%
288
April1st to 15thDay
9%5%32%35%12%4
269
16th to endDay
410%30%38%11%5%
270
May1st to 15thDay
11%6%25%37%15%3
288
16th to endDay
9%5%24%39%18%2
330
June1st to 15thDay
7%120%40%26%3
315
16th to endDay
36%44%36%8%
315
July1st to 15thDay
7%6%36%41%8%
305
16th to endDay
6%134%46%11%
327
August1st to 15thDay
36%46%34%7%
315
16th to endDay
3441%42%7%
332
September1st to 15thDay
410%51%28%3
315
16th to endDay
6%17%47%22%4
280
October1st to 15thDay
35%28%45%15%1
255
16th to endDay
10%21%38%23%5%
223
November1st to 15thDay
3313%34%34%11%
90
16th to endDay
11%5%15%36%28%2
90
December1st to 15thDay
3212%41%33%7%
90
16th to endDay
11%6%15%40%22%3
96
January1st to 15thNight
7%18%39%31%11%
720
16th to endNight
12%110%35%31%8%
768
February1st to 15thNight
9%19%33%36%9%
704
16th to endNight
14%111%39%27%5%
632
March1st to 15thNight
11%19%36%33%7%
720
16th to endNight
9%19%32%37%8%
768
April1st to 15thNight
11%210%37%31%6%
719
16th to endNight
11%28%33%35%9%
720
May1st to 15thNight
9%111%31%36%8%
594
16th to endNight
13%112%25%40%5%
563
June1st to 15thNight
10%11%32%38%5%
540
16th to endNight
35%23%57%8%
540
July1st to 15thNight
7%411%59%17%
510
16th to endNight
7%39%54%25%
645
August1st to 15thNight
6%314%52%22%
717
16th to endNight
5%18%51%33%
764
September1st to 15thNight
6%314%55%20%
720
16th to endNight
45%25%45%17%
683
October1st to 15thNight
5%8%32%42%10%
660
16th to endNight
10%8%26%35%18%
704
November1st to 15thNight
6%16%32%39%15%
700
16th to endNight
6%16%32%36%16%
720
December1st to 15thNight
11%19%35%31%11%
720
16th to endNight
13%211%33%27%9%
768
Page generated at 2017-09-23 03:43:47. Version ac04

Copyright 2017 A. Danko


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