Robson Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robson Ranch clear sky chart from 2005-11-06 to 2024-02-05.

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%
24122
29%
79218
20%
24021
59%
24021
37%
42099

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 10thNight
39%
943
35%
3961
14%
926
51%
926
31%
1925
January11th to 20thNight
37%
946
33%
3911
11%
930
48%
930
32%
1753
January21st to endNight
38%
1036
22%
4457
13%
1023
51%
1023
23%
2599
February1st to 10thNight
32%
806
28%
2282
10%
806
44%
806
32%
1369
February11th to 20thNight
28%
704
24%
2098
9%
700
39%
700
31%
1245
February21st to endNight
24%
592
29%
1776
9%
592
40%
592
29%
1037
March1st to 10thNight
32%
542
27%
1982
14%
542
46%
542
27%
1125
March11th to 20thNight
32%
540
25%
1980
14%
540
46%
540
28%
1103
March21st to endNight
33%
594
27%
2178
16%
594
50%
594
30%
1151
April1st to 10thNight
32%
540
26%
1980
15%
540
49%
540
31%
1031
April11th to 20thNight
31%
533
25%
1879
16%
533
47%
533
30%
1019
April21st to endNight
35%
540
29%
1620
16%
540
53%
540
37%
906
May1st to 10thNight
40%
540
27%
1620
17%
540
55%
540
34%
939
May11th to 20thNight
45%
531
20%
1594
17%
531
53%
531
34%
948
May21st to endNight
52%
583
24%
1745
18%
582
63%
582
38%
993
June1st to 10thNight
71%
540
23%
1620
24%
540
76%
540
46%
837
June11th to 20thNight
70%
540
27%
1620
29%
540
75%
540
53%
783
June21st to endNight
73%
540
27%
1620
28%
540
77%
540
51%
807
July1st to 10thNight
77%
525
24%
1575
26%
525
79%
525
44%
828
July11th to 20thNight
84%
522
32%
1566
37%
522
88%
522
63%
700
July21st to endNight
86%
591
33%
1673
40%
558
87%
558
54%
800
August1st to 10thNight
86%
537
38%
1601
41%
534
89%
534
65%
697
August11th to 20thNight
79%
534
36%
1600
39%
534
82%
534
47%
820
August21st to endNight
84%
594
30%
2037
36%
594
85%
594
47%
947
September1st to 10thNight
78%
540
26%
1980
32%
540
79%
540
38%
981
September11th to 20thNight
71%
540
26%
1980
30%
540
72%
540
31%
1082
September21st to endNight
73%
540
36%
1980
37%
540
78%
540
47%
889
October1st to 10thNight
66%
548
38%
1988
34%
548
73%
548
44%
925
October11th to 20thNight
53%
720
35%
2160
20%
720
64%
720
45%
1117
October21st to endNight
45%
792
34%
2376
20%
792
54%
792
39%
1278
November1st to 10thNight
52%
740
32%
2220
18%
740
62%
740
43%
1179
November11th to 20thNight
48%
921
31%
2441
16%
921
57%
921
47%
1331
November21st to endNight
37%
950
30%
2470
13%
950
48%
950
35%
1512
December1st to 10thNight
40%
950
33%
2470
15%
950
52%
950
40%
1455
December11th to 20thNight
35%
949
32%
2860
14%
948
45%
948
31%
1708
December21st to endNight
34%
1039
19%
4318
11%
1026
45%
1026
26%
2280

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%42442445%7%53%
78665
Night
10%423323347%58%
80246
TransparencyDay
31%5%10%23%23%8%
78390
Night
28%49%22%25%11%
80041
SeeingDay
12%6%22%28%24%8%
14096
Night
11%6%28%36%17%1
24150

By Month

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 10thDay
11%6%245%23346%56%
2847
11th to 20thDay
9%5%13212335%64%
2850
21st to endDay
21%8%3432333448%
3135
February1st to 10thDay
15%6%25%423445%50%
1787
11th to 20thDay
16%7%3443344449%
1749
21st to endDay
20%6%2332232453%
1480
March1st to 10thDay
17%5%234245%47%47%
1976
11th to 20thDay
16%5%25%423346%50%
1980
21st to endDay
13%6%244345%5%6%49%
2178
April1st to 10thDay
11%5%25%43445%6%51%
1980
11th to 20thDay
12%7%3443345%7%48%
2027
21st to endDay
12%5%244345%5%6%50%
2335
May1st to 10thDay
11%6%3443445%7%50%
2340
11th to 20thDay
12%5%346%35%46%7%45%
2302
21st to endDay
11%6%25%6%36%5%7%9%40%
2531
June1st to 10thDay
5%324425%5%8%10%52%
2340
11th to 20thDay
5%3245%345%6%8%56%
2340
21st to endDay
5%2245%346%6%8%56%
2340
July1st to 10thDay
5%325%6%45%6%9%10%45%
2340
11th to 20thDay
321232446%9%64%
2340
21st to endDay
33235%45%6%8%10%52%
2546
August1st to 10thDay
2213335%45%8%64%
2328
11th to 20thDay
8%3145%35%5%6%8%52%
2301
21st to endDay
4224425%6%7%10%54%
2311
September1st to 10thDay
8%423335%5%5%7%56%
1980
11th to 20thDay
10%426%5%345%6%7%48%
1980
21st to endDay
8%313424347%60%
1980
October1st to 10thDay
6%31332445%6%61%
1954
11th to 20thDay
10%5%2332334463%
1800
21st to endDay
14%42422323362%
1980
November1st to 10thDay
12%423334236%59%
1858
11th to 20thDay
7%313333336%64%
1734
21st to endDay
14%5%24323335%56%
1710
December1st to 10thDay
13%6%24424445%53%
1710
11th to 20thDay
14%6%35%5%2344448%
2161
21st to endDay
17%6%2442334451%
3135
January1st to 10thNight
13%413313346%59%
4108
11th to 20thNight
10%423212235%65%
4120
21st to endNight
18%6%2432334450%
4532
February1st to 10thNight
15%5%24423335%54%
2282
11th to 20thNight
14%7%24323346%51%
2098
21st to endNight
17%5%23423345%54%
1776
March1st to 10thNight
14%5%25%4335%6%7%48%
1982
11th to 20thNight
13%6%3332435%6%52%
1980
21st to endNight
10%5%3342335%7%56%
2178
April1st to 10thNight
9%4243245%5%8%54%
1980
11th to 20thNight
11%5%24423347%53%
1879
21st to endNight
10%433324348%56%
1620
May1st to 10thNight
10%42442346%7%53%
1620
11th to 20thNight
9%435%4345%6%8%50%
1593
21st to endNight
8%4244335%6%10%52%
1745
June1st to 10thNight
43134245%6%9%60%
1620
11th to 20thNight
322341346%9%64%
1620
21st to endNight
2113325%45%10%64%
1620
July1st to 10thNight
42145%25%45%12%56%
1620
11th to 20thNight
2112213349%71%
1620
21st to endNight
121342445%10%63%
1772
August1st to 10thNight
211221236%10%69%
1611
11th to 20thNight
5%41333446%10%58%
1600
21st to endNight
331342446%10%60%
2037
September1st to 10thNight
8%32333445%6%60%
1980
11th to 20thNight
9%5%3443446%7%51%
1980
21st to endNight
6%21332345%7%64%
1980
October1st to 10thNight
6%313323347%64%
1988
11th to 20thNight
10%322322345%64%
2160
21st to endNight
15%5%1321223462%
2376
November1st to 10thNight
9%32332234463%
2220
11th to 20thNight
6%423324446%63%
2441
21st to endNight
15%5%2332444455%
2470
December1st to 10thNight
11%5%23424345%58%
2470
11th to 20thNight
12%6%2432435%6%52%
3036
21st to endNight
15%6%24322235%55%
4532

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 10thDay
30%38%21%32%6%
2848
11th to 20thDay
25%39%22%33%8%
2850
21st to endDay
42%3420%22%8%
3135
February1st to 10thDay
39%46%20%21%9%
1787
11th to 20thDay
39%38%20%20%9%
1759
21st to endDay
38%3416%24%15%
1480
March1st to 10thDay
38%47%18%21%12%
1976
11th to 20thDay
39%49%18%23%7%
1980
21st to endDay
36%410%21%21%8%
2178
April1st to 10thDay
35%5%10%21%19%11%
1980
11th to 20thDay
36%5%10%19%19%10%
2027
21st to endDay
34%5%10%23%24%5%
2335
May1st to 10thDay
34%5%10%24%20%8%
2340
11th to 20thDay
38%6%11%23%19%2
2306
21st to endDay
40%7%12%23%15%2
2531
June1st to 10thDay
25%9%17%28%17%3
2340
11th to 20thDay
25%6%13%30%20%5%
2340
21st to endDay
24%6%13%26%26%5%
2340
July1st to 10thDay
29%8%20%26%15%1
2276
11th to 20thDay
16%6%14%35%24%4
2271
21st to endDay
21%8%17%34%18%1
2405
August1st to 10thDay
17%6%15%33%26%3
2314
11th to 20thDay
28%8%14%27%21%2
2301
21st to endDay
23%7%14%32%19%5%
2311
September1st to 10thDay
27%6%9%23%25%10%
1980
11th to 20thDay
35%7%11%19%21%7%
1980
21st to endDay
24%5%8%23%29%12%
1980
October1st to 10thDay
23%5%10%24%22%16%
1954
11th to 20thDay
27%37%17%28%18%
1800
21st to endDay
29%27%19%27%16%
1980
November1st to 10thDay
29%47%22%27%10%
1858
11th to 20thDay
24%410%21%31%11%
1734
21st to endDay
33%35%21%26%11%
1710
December1st to 10thDay
34%47%24%24%7%
1710
11th to 20thDay
40%37%14%27%9%
2159
21st to endDay
37%36%23%23%8%
3135
January1st to 10thNight
28%36%21%32%10%
4108
11th to 20thNight
25%29%20%31%13%
4120
21st to endNight
38%46%17%26%10%
4532
February1st to 10thNight
35%37%19%22%13%
2282
11th to 20thNight
36%38%18%24%11%
2098
21st to endNight
36%27%16%21%17%
1776
March1st to 10thNight
36%5%7%17%21%15%
1982
11th to 20thNight
34%410%18%25%9%
1980
21st to endNight
31%411%22%24%8%
2178
April1st to 10thNight
28%6%10%22%20%14%
1980
11th to 20thNight
31%5%10%20%19%15%
1879
21st to endNight
29%5%10%23%26%6%
1620
May1st to 10thNight
31%6%10%23%21%9%
1620
11th to 20thNight
32%7%16%23%20%3
1594
21st to endNight
27%7%17%27%19%2
1746
June1st to 10thNight
20%7%16%31%21%5%
1620
11th to 20thNight
17%5%14%33%22%8%
1620
21st to endNight
17%7%14%26%29%7%
1620
July1st to 10thNight
23%6%17%32%19%3
1575
11th to 20thNight
12%5%12%34%30%8%
1566
21st to endNight
15%6%13%38%25%2
1673
August1st to 10thNight
11%411%36%32%6%
1601
11th to 20thNight
22%5%13%30%26%5%
1600
21st to endNight
19%5%14%31%26%5%
2037
September1st to 10thNight
25%5%10%23%27%10%
1980
11th to 20thNight
31%6%10%19%22%11%
1980
21st to endNight
20%49%23%28%17%
1980
October1st to 10thNight
22%49%25%23%18%
1988
11th to 20thNight
24%38%15%27%22%
2160
21st to endNight
29%25%18%28%19%
2376
November1st to 10thNight
26%47%21%27%15%
2220
11th to 20thNight
23%48%22%29%15%
2441
21st to endNight
34%46%16%28%12%
2470
December1st to 10thNight
30%38%23%25%12%
2470
11th to 20thNight
34%45%17%28%12%
3037
21st to endNight
33%36%19%27%12%
4532

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 10thDay
18%14%32%29%6%
270
11th to 20thDay
20%14%33%24%7%2
270
21st to endDay
20%10%37%24%8%1
297
February1st to 10thDay
19%12%39%23%7%
252
11th to 20thDay
25%13%38%19%4
240
21st to endDay
32%12%37%15%4
198
March1st to 10thDay
23%17%33%19%7%
240
11th to 20thDay
25%14%35%19%5%1
240
21st to endDay
15%16%44%18%8%
264
April1st to 10thDay
16%15%40%22%7%1
240
11th to 20thDay
18%11%38%26%8%
305
21st to endDay
15%12%40%23%9%1
595
May1st to 10thDay
13%10%33%34%8%1
603
11th to 20thDay
17%5%28%32%14%4
625
21st to endDay
14%5%26%32%18%4
679
June1st to 10thDay
6%213%41%30%8%
630
11th to 20thDay
5%115%41%30%7%
630
21st to endDay
4114%33%35%13%
630
July1st to 10thDay
5%15%33%38%18%
621
11th to 20thDay
21428%46%18%
618
21st to endDay
315%26%48%19%
684
August1st to 10thDay
216%28%47%15%
626
11th to 20thDay
8%2427%45%14%
615
21st to endDay
415%24%43%23%
430
September1st to 10thDay
42218%44%29%
270
11th to 20thDay
6%17%25%41%20%
270
21st to endDay
13%18%25%34%18%
270
October1st to 10thDay
3118%30%36%11%
270
11th to 20thDay
11%6%32%26%22%3
270
21st to endDay
24%9%23%23%17%4
297
November1st to 10thDay
19%334%24%17%3
270
11th to 20thDay
11%7%34%28%14%4
270
21st to endDay
17%14%36%21%11%1
270
December1st to 10thDay
18%12%30%26%9%4
270
11th to 20thDay
17%9%37%27%10%
270
21st to endDay
21%12%33%26%7%
297
January1st to 10thNight
13%8%37%33%9%1
950
11th to 20thNight
15%12%32%34%6%
950
21st to endNight
14%10%33%35%7%
1045
February1st to 10thNight
17%9%38%31%5%
806
11th to 20thNight
18%11%39%27%5%
704
21st to endNight
21%13%41%23%3
592
March1st to 10thNight
16%10%39%31%5%
542
11th to 20thNight
17%8%39%32%4
540
21st to endNight
11%12%41%32%4
594
April1st to 10thNight
9%13%43%29%6%
540
11th to 20thNight
13%11%41%30%5%
533
21st to endNight
13%9%42%29%7%1
540
May1st to 10thNight
11%6%39%36%7%1
540
11th to 20thNight
10%6%34%36%13%1
531
21st to endNight
8%331%40%16%2
584
June1st to 10thNight
4215%50%27%2
540
11th to 20thNight
3120%55%20%1
540
21st to endNight
2117%44%32%4
540
July1st to 10thNight
3110%41%38%5%
525
11th to 20thNight
38%42%43%4
522
21st to endNight
11444%47%3
591
August1st to 10thNight
27%45%42%3
537
11th to 20thNight
6%16%41%41%5%
534
21st to endNight
31443%42%7%
594
September1st to 10thNight
7%17%39%41%5%
540
11th to 20thNight
11%27%41%36%4
540
21st to endNight
5%116%42%33%4
540
October1st to 10thNight
7%121%41%27%3
548
11th to 20thNight
10%5%26%41%16%2
720
21st to endNight
18%7%28%32%15%1
792
November1st to 10thNight
10%430%39%16%1
740
11th to 20thNight
8%7%33%39%12%1
921
21st to endNight
18%10%33%29%11%
950
December1st to 10thNight
14%9%34%37%7%
950
11th to 20thNight
18%8%33%34%6%
950
21st to endNight
16%9%37%31%6%
1045
Page generated at 2024-02-02 04:20:30. Version ac07

Copyright 2024 Attilla Danko


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