Robson Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robson Ranch clear sky chart from 2005-11-05 to 2017-04-24.

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
53%
15168
30%
45576
21%
15124
61%
15124
40%
24736

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
42%
897
31%
2327
14%
895
52%
895
42%
1357
January16th to endNight
41%
960
34%
2496
14%
960
53%
960
44%
1419
February1st to 15thNight
37%
747
28%
2153
12%
742
48%
742
35%
1236
February16th to endNight
28%
632
31%
1894
11%
632
44%
632
37%
1033
March1st to 15thNight
36%
542
28%
1982
17%
542
50%
542
28%
1101
March16th to endNight
39%
576
24%
2112
18%
576
51%
576
31%
1137
April1st to 15thNight
34%
539
24%
1977
14%
539
50%
539
31%
1038
April16th to endNight
39%
522
27%
1635
19%
522
53%
522
37%
903
May1st to 15thNight
41%
495
24%
1485
14%
495
56%
495
32%
900
May16th to endNight
56%
514
25%
1540
22%
513
66%
513
39%
874
June1st to 15thNight
74%
495
25%
1485
26%
495
79%
495
52%
728
June16th to endNight
78%
495
24%
1485
27%
495
80%
495
47%
766
July1st to 15thNight
81%
465
25%
1395
29%
465
82%
465
47%
726
July16th to endNight
87%
522
30%
1468
37%
489
87%
489
52%
717
August1st to 15thNight
92%
494
40%
1475
47%
491
92%
491
62%
656
August16th to endNight
80%
525
30%
1732
36%
525
82%
525
41%
878
September1st to 15thNight
72%
495
24%
1815
29%
495
74%
495
32%
971
September16th to endNight
75%
492
33%
1815
35%
492
78%
492
40%
877
October1st to 15thNight
63%
555
36%
1875
29%
555
70%
555
43%
936
October16th to endNight
54%
704
37%
2112
22%
704
64%
704
48%
1037
November1st to 15thNight
54%
742
31%
2142
18%
742
62%
742
45%
1127
November16th to endNight
44%
900
33%
2340
16%
900
53%
900
40%
1375
December1st to 15thNight
43%
900
31%
2340
15%
900
52%
900
38%
1412
December16th to endNight
37%
960
29%
2496
12%
960
48%
960
37%
1532

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
8%3133233420%45%
46026
Night
7%3122122420%50%
45774
Cloud CoverDay
10%41342445%6%53%
46024
Night
9%313313347%57%
45774
TransparencyDay
31%410%23%22%7%
45724
Night
27%49%22%24%11%
45579
SeeingDay
10%318%28%28%9%
4923
Night
10%5%26%36%18%1
15172

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
10%5%12222321%48%
1611
16th to endDay
8%322233321%48%
1728
February1st to 15thDay
11%4133223319%46%
1717
16th to endDay
12%4123113220%48%
1580
March1st to 15thDay
15%4133123321%40%
1977
16th to endDay
9%423133321%45%
2112
April1st to 15thDay
9%3133222422%44%
1971
16th to endDay
10%4133123421%43%
2179
May1st to 15thDay
10%42442235%22%37%
2136
16th to endDay
8%4145%2445%25%33%
2222
June1st to 15thDay
32134235%5%25%43%
2145
16th to endDay
21242335%24%48%
2145
July1st to 15thDay
321431446%25%42%
2145
16th to endDay
32123235%6%26%43%
2284
August1st to 15thDay
2123244416%56%
2145
16th to endDay
7%213435%6%7%18%41%
2114
September1st to 15thDay
9%31341445%16%43%
1815
16th to endDay
6%31341245%16%49%
1815
October1st to 15thDay
9%3133133413%52%
1744
16th to endDay
7%331211212%62%
1760
November1st to 15thDay
8%2133222218%51%
1713
16th to endDay
10%3132112220%51%
1620
December1st to 15thDay
14%6%133122220%40%
1620
16th to endDay
12%4133223320%42%
1728
January1st to 15thNight
8%3132122221%49%
2327
16th to endNight
7%212112321%54%
2496
February1st to 15thNight
11%4132122320%47%
2145
16th to endNight
9%3122121320%51%
1894
March1st to 15thNight
13%4132122421%42%
1982
16th to endNight
6%4122122322%50%
2112
April1st to 15thNight
7%2132133322%46%
1977
16th to endNight
10%2122122322%47%
1635
May1st to 15thNight
7%4143222423%43%
1484
16th to endNight
331332235%26%44%
1539
June1st to 15thNight
2122123426%52%
1485
16th to endNight
1123123425%53%
1485
July1st to 15thNight
32221235%26%49%
1485
16th to endNight
2122123326%52%
1576
August1st to 15thNight
111225%17%64%
1485
16th to endNight
331342335%19%48%
1732
September1st to 15thNight
8%31323345%16%47%
1815
16th to endNight
5%21322335%15%51%
1815
October1st to 15thNight
8%3122122414%55%
1875
16th to endNight
7%222122312%62%
2112
November1st to 15thNight
5%3132122318%54%
2142
16th to endNight
11%3122122319%48%
2340
December1st to 15thNight
12%4132132321%43%
2340
16th to endNight
10%4132123322%42%
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
12%5%1221323457%
1611
16th to endDay
12%412323335%56%
1728
February1st to 15thDay
13%42331233455%
1717
16th to endDay
15%5%1231133456%
1580
March1st to 15thDay
17%413323436%48%
1977
16th to endDay
14%5%24324336%50%
2110
April1st to 15thDay
11%424323347%51%
1971
16th to endDay
12%42332345%5%51%
2179
May1st to 15thDay
12%6%345%2446%6%43%
2136
16th to endDay
11%5%25%5%36%46%8%40%
2222
June1st to 15thDay
42234245%6%8%54%
2145
16th to endDay
6%2244245%6%7%53%
2145
July1st to 15thDay
5%3245%25%5%7%9%48%
2145
16th to endDay
3213435%6%7%10%51%
2284
August1st to 15thDay
31333435%7%61%
2145
16th to endDay
7%213425%6%7%10%46%
2114
September1st to 15thDay
10%424425%5%6%7%47%
1815
16th to endDay
7%31341335%8%55%
1815
October1st to 15thDay
10%313313345%57%
1744
16th to endDay
7%31321223369%
1760
November1st to 15thDay
9%31333323460%
1713
16th to endDay
11%41331222462%
1620
December1st to 15thDay
15%7%1331333452%
1620
16th to endDay
15%42432334451%
1728
January1st to 15thNight
10%413213235%59%
2327
16th to endNight
11%322213336%60%
2496
February1st to 15thNight
12%423313335%57%
2145
16th to endNight
12%412312235%59%
1894
March1st to 15thNight
14%42322345%6%51%
1982
16th to endNight
9%433323247%54%
2112
April1st to 15thNight
8%324324448%53%
1977
16th to endNight
11%323322347%55%
1635
May1st to 15thNight
10%5%25%42345%6%50%
1484
16th to endNight
6%31432446%9%52%
1539
June1st to 15thNight
22231345%8%64%
1485
16th to endNight
311331435%9%60%
1485
July1st to 15thNight
421331445%11%56%
1485
16th to endNight
22133244410%62%
1576
August1st to 15thNight
111111236%9%68%
1485
16th to endNight
431442346%11%53%
1732
September1st to 15thNight
10%42323446%7%51%
1815
16th to endNight
6%21322346%7%58%
1815
October1st to 15thNight
9%312312346%61%
1875
16th to endNight
8%31221223468%
2112
November1st to 15thNight
6%312313335%64%
2142
16th to endNight
12%41231333360%
2340
December1st to 15thNight
12%413214345%54%
2340
16th to endNight
14%5%24312346%52%
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
30%37%20%29%8%
1612
16th to endDay
30%46%20%29%9%
1728
February1st to 15thDay
34%36%22%25%8%
1718
16th to endDay
33%26%21%23%12%
1580
March1st to 15thDay
39%37%18%20%9%
1977
16th to endDay
37%310%19%21%7%
2112
April1st to 15thDay
33%311%21%18%11%
1971
16th to endDay
33%49%21%23%7%
2179
May1st to 15thDay
40%5%9%19%17%8%
2136
16th to endDay
40%7%12%20%17%2
2226
June1st to 15thDay
26%6%14%28%20%3
2145
16th to endDay
27%5%13%27%20%5%
2145
July1st to 15thDay
28%7%16%29%16%2
2006
16th to endDay
22%7%18%30%19%1
2129
August1st to 15thDay
19%6%12%30%27%3
2131
16th to endDay
29%7%15%29%14%3
2114
September1st to 15thDay
33%7%12%21%17%7%
1815
16th to endDay
26%46%24%26%10%
1815
October1st to 15thDay
28%49%22%21%13%
1744
16th to endDay
21%17%21%30%16%
1760
November1st to 15thDay
28%38%22%26%9%
1713
16th to endDay
28%25%18%31%13%
1620
December1st to 15thDay
36%35%22%26%5%
1620
16th to endDay
36%36%21%24%8%
1728
January1st to 15thNight
28%26%17%31%13%
2327
16th to endNight
26%36%19%29%14%
2496
February1st to 15thNight
32%36%19%23%14%
2155
16th to endNight
29%28%21%23%14%
1894
March1st to 15thNight
34%48%18%21%13%
1982
16th to endNight
31%411%21%24%6%
2112
April1st to 15thNight
28%5%10%21%18%14%
1977
16th to endNight
28%5%9%21%24%10%
1635
May1st to 15thNight
34%5%12%18%19%9%
1485
16th to endNight
27%6%16%24%20%3
1541
June1st to 15thNight
17%5%13%32%23%6%
1485
16th to endNight
21%5%13%25%25%7%
1485
July1st to 15thNight
22%5%12%34%20%5%
1395
16th to endNight
16%6%14%32%25%3
1468
August1st to 15thNight
11%411%31%33%7%
1475
16th to endNight
24%5%12%31%22%4
1732
September1st to 15thNight
30%5%11%21%20%10%
1815
16th to endNight
23%5%8%22%26%13%
1815
October1st to 15thNight
24%310%22%21%17%
1875
16th to endNight
21%2418%30%22%
2112
November1st to 15thNight
24%36%25%25%14%
2142
16th to endNight
29%35%15%31%14%
2340
December1st to 15thNight
32%37%21%25%9%
2340
16th to endNight
33%37%21%24%9%
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
20%8%32%25%12%1
90
16th to endDay
12%6%38%27%14%1
96
February1st to 15thDay
6%5%42%36%8%
90
16th to endDay
16%9%40%24%8%
81
March1st to 15thDay
25%12%35%16%8%1
90
16th to endDay
7%11%36%28%15%1
96
April1st to 15thDay
15%13%27%24%17%1
90
16th to endDay
14%7%39%25%11%
343
May1st to 15thDay
18%8%32%30%8%2
393
16th to endDay
17%428%28%17%4
437
June1st to 15thDay
6%113%39%30%9%
420
16th to endDay
6%19%34%35%14%
420
July1st to 15thDay
5%15%40%39%7%
400
16th to endDay
4417%50%22%
445
August1st to 15thDay
3323%52%17%
418
16th to endDay
10%330%42%11%
282
September1st to 15thDay
2313%43%37%
90
16th to endDay
5%111%48%33%
90
October1st to 15thDay
112%31%41%14%
90
16th to endDay
13%217%30%29%7%
96
November1st to 15thDay
18%221%30%25%2
90
16th to endDay
21%11%38%22%33
90
December1st to 15thDay
30%221%26%12%7%
90
16th to endDay
9%9%44%28%8%
96
January1st to 15thNight
13%8%31%36%10%
900
16th to endNight
13%8%34%35%7%
960
February1st to 15thNight
14%8%36%34%5%
747
16th to endNight
15%11%43%27%3
632
March1st to 15thNight
16%8%35%34%4
542
16th to endNight
11%9%37%35%6%
576
April1st to 15thNight
8%10%43%30%6%
539
16th to endNight
13%439%33%7%
522
May1st to 15thNight
10%6%37%36%6%2
495
16th to endNight
6%229%37%21%2
515
June1st to 15thNight
3117%49%26%1
495
16th to endNight
411%44%34%4
495
July1st to 15thNight
5%7%46%37%2
465
16th to endNight
2235%53%4
522
August1st to 15thNight
1236%54%5%
494
16th to endNight
6%439%40%8%
525
September1st to 15thNight
12%8%35%38%4
495
16th to endNight
7%9%38%38%5%
492
October1st to 15thNight
10%218%39%26%2
555
16th to endNight
9%5%26%37%18%1
704
November1st to 15thNight
8%429%36%19%1
742
16th to endNight
14%7%31%34%11%
900
December1st to 15thNight
16%8%29%38%7%
900
16th to endNight
16%6%36%32%7%
960
Page generated at 2017-04-25 06:48:22. Version ac04

Copyright 2017 A. Danko


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