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 2017-04-25.

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%
14829
28%
45605
25%
14792
70%
14792
39%
24756

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%
700
23%
1750
13%
700
66%
700
41%
1063
May1st to 15thNight
66%
526
28%
1516
20%
526
69%
526
50%
752
May16th to endNight
73%
342
22%
1368
26%
342
75%
342
37%
633
June1st to 15thNight
79%
330
28%
1320
37%
330
82%
330
45%
550
June16th to endNight
89%
330
33%
1320
47%
330
91%
330
63%
455
July1st to 15thNight
95%
310
36%
1240
49%
310
95%
310
69%
402
July16th to endNight
92%
435
37%
1383
39%
405
93%
405
67%
522
August1st to 15thNight
91%
545
39%
1528
31%
542
91%
542
74%
657
August16th to endNight
92%
700
42%
1750
27%
700
92%
700
80%
794
September1st to 15thNight
91%
660
45%
1650
32%
660
92%
660
81%
743
September16th to endNight
84%
656
43%
1769
39%
656
87%
656
68%
822
October1st to 15thNight
71%
660
30%
1980
31%
660
75%
660
47%
993
October16th to endNight
73%
704
35%
2112
36%
704
78%
704
49%
1071
November1st to 15thNight
68%
700
29%
2269
29%
700
72%
700
40%
1197
November16th to endNight
60%
720
27%
2394
26%
720
65%
720
34%
1322
December1st to 15thNight
52%
720
22%
2520
18%
720
60%
720
25%
1523
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%
46028
Night
12%412213335%58%
45796
TransparencyDay
27%27%18%25%18%
45708
Night
28%37%18%23%17%
45615
SeeingDay
14%13%32%27%8%3
5267
Night
14%39%32%31%8%
14839

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%412313336%55%
2098
May1st to 15thDay
7%312213446%64%
2100
16th to endDay
9%413323346%55%
2391
June1st to 15thDay
5%313212245%65%
2310
16th to endDay
2111212381%
2310
July1st to 15thDay
11222383%
2310
16th to endDay
1111121283%
2371
August1st to 15thDay
11122286%
2093
16th to endDay
111112385%
2100
September1st to 15thDay
111122384%
1980
16th to endDay
3121122378%
1856
October1st to 15thDay
7%212214346%63%
1650
16th to endDay
9%21342433461%
1760
November1st to 15thDay
9%41342335%8%53%
1590
16th to endDay
14%5%24323335%51%
1563
December1st to 15thDay
19%7%23423335%44%
1440
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%
1750
May1st to 15thNight
8%212312346%63%
1516
16th to endNight
8%313213346%60%
1368
June1st to 15thNight
5%312213335%69%
1320
16th to endNight
222212282%
1320
July1st to 15thNight
11212384%
1320
16th to endNight
11121212283%
1487
August1st to 15thNight
11111122481%
1537
16th to endNight
1111212384%
1750
September1st to 15thNight
11112287%
1650
16th to endNight
21221122378%
1769
October1st to 15thNight
7%212313236%65%
1980
16th to endNight
8%21212346%64%
2112
November1st to 15thNight
11%412213346%58%
2269
16th to endNight
13%5%13323345%53%
2394
December1st to 15thNight
20%5%13323345%45%
2520
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%26%21%5%
2098
May1st to 15thDay
22%28%31%27%6%
2100
16th to endDay
30%412%28%18%6%
2395
June1st to 15thDay
21%211%21%22%20%
2310
16th to endDay
10%1314%40%28%
2310
July1st to 15thDay
7%129%28%49%
2161
16th to endDay
9%139%27%47%
2212
August1st to 15thDay
6%1210%32%47%
2077
16th to endDay
7%110%42%37%
2100
September1st to 15thDay
7%1210%38%38%
1980
16th to endDay
13%1423%34%23%
1856
October1st to 15thDay
22%27%24%27%15%
1650
16th to endDay
27%27%22%25%14%
1760
November1st to 15thDay
30%311%20%23%10%
1590
16th to endDay
36%38%17%28%6%
1563
December1st to 15thDay
43%27%18%20%5%
1440
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
29%5%12%25%19%7%
1750
May1st to 15thNight
20%312%26%26%11%
1517
16th to endNight
25%315%28%19%7%
1368
June1st to 15thNight
18%412%22%22%20%
1320
16th to endNight
10%1316%35%32%
1320
July1st to 15thNight
7%227%26%53%
1240
16th to endNight
10%129%24%51%
1383
August1st to 15thNight
9%1113%27%46%
1528
16th to endNight
7%111%34%43%
1750
September1st to 15thNight
6%139%40%38%
1650
16th to endNight
12%1321%36%24%
1769
October1st to 15thNight
21%36%22%28%16%
1980
16th to endNight
21%35%23%29%16%
2112
November1st to 15thNight
27%311%21%22%13%
2269
16th to endNight
33%27%21%24%11%
2394
December1st to 15thNight
40%38%19%19%8%
2520
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
16%26%29%20%5%1
250
May1st to 15thDay
13%22%37%20%32
228
16th to endDay
15%18%23%28%7%6%
266
June1st to 15thDay
8%18%37%25%5%4
255
16th to endDay
211%44%30%37%
255
July1st to 15thDay
338%42%49%
245
16th to endDay
1342%39%7%5%
271
August1st to 15thDay
15%47%33%6%5%
255
16th to endDay
439%41%8%6%
268
September1st to 15thDay
26%44%32%10%3
255
16th to endDay
311%35%34%10%3
255
October1st to 15thDay
7%14%36%28%9%3
255
16th to endDay
16%10%30%26%15%
272
November1st to 15thDay
9%8%10%35%30%6%
96
16th to endDay
22%8%18%33%16%1
81
December1st to 15thDay
31%11%28%15%10%3
60
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%
700
May1st to 15thNight
9%314%35%29%7%
527
16th to endNight
7%48%31%41%6%
343
June1st to 15thNight
6%25%35%42%7%
330
16th to endNight
2335%49%9%
330
July1st to 15thNight
29%61%7%
310
16th to endNight
2126%52%16%
435
August1st to 15thNight
1335%49%10%
545
16th to endNight
1333%51%9%
700
September1st to 15thNight
1429%51%13%
660
16th to endNight
38%33%35%18%
656
October1st to 15thNight
8%311%33%31%12%
660
16th to endNight
9%39%31%30%14%
704
November1st to 15thNight
13%211%31%30%11%
700
16th to endNight
15%5%14%33%22%8%
720
December1st to 15thNight
23%5%11%33%19%6%
720
16th to endNight
30%414%28%17%4
768
Page generated at 2017-04-26 14:21:47. Version ac04

Copyright 2017 A. Danko


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