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 2017-10-31.

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%
15754
30%
47427
21%
15710
61%
15710
40%
25633

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
52%
960
44%
1419
February1st to 15thNight
36%
747
28%
2153
12%
742
47%
742
35%
1236
February16th to endNight
28%
632
31%
1894
11%
632
44%
632
37%
1033
March1st to 15thNight
35%
542
28%
1982
17%
542
49%
542
28%
1101
March16th to endNight
39%
576
24%
2112
18%
576
50%
576
31%
1137
April1st to 15thNight
34%
539
24%
1977
14%
539
49%
539
31%
1038
April16th to endNight
37%
540
28%
1689
19%
540
52%
540
37%
933
May1st to 15thNight
41%
540
24%
1620
14%
540
56%
540
34%
950
May16th to endNight
53%
562
26%
1684
22%
561
64%
561
40%
946
June1st to 15thNight
72%
540
24%
1620
24%
540
78%
540
51%
799
June16th to endNight
77%
540
26%
1620
29%
540
79%
540
48%
828
July1st to 15thNight
79%
510
24%
1530
28%
510
80%
510
48%
787
July16th to endNight
86%
564
32%
1594
39%
531
87%
531
53%
768
August1st to 15thNight
89%
539
38%
1610
44%
536
89%
536
59%
737
August16th to endNight
80%
573
30%
1891
36%
573
81%
573
40%
972
September1st to 15thNight
73%
540
24%
1980
28%
540
75%
540
34%
1032
September16th to endNight
74%
537
34%
1980
36%
537
77%
537
39%
968
October1st to 15thNight
63%
606
34%
2046
28%
606
70%
606
43%
1020
October16th to endNight
54%
768
38%
2304
23%
768
64%
768
49%
1126
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
42%
900
31%
2340
15%
900
51%
900
38%
1412
December16th to endNight
37%
960
29%
2496
12%
960
47%
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%46%
48318
Night
7%3132122420%50%
47625
Cloud CoverDay
10%41342445%6%53%
48316
Night
8%313313347%58%
47625
TransparencyDay
30%5%10%23%22%7%
48016
Night
26%49%23%25%11%
47430
SeeingDay
10%318%28%29%10%
5729
Night
10%5%26%36%18%1
15758

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%
2266
May1st to 15thDay
9%4234222421%40%
2331
16th to endDay
7%4145%2435%24%35%
2430
June1st to 15thDay
43134235%5%23%43%
2340
16th to endDay
211342335%23%48%
2340
July1st to 15thDay
321432446%23%44%
2340
16th to endDay
2223235%6%25%44%
2466
August1st to 15thDay
21232445%16%54%
2340
16th to endDay
7%213435%6%6%17%41%
2307
September1st to 15thDay
9%3134144416%46%
1980
16th to endDay
7%31341345%15%49%
1980
October1st to 15thDay
8%3133133412%54%
1902
16th to endDay
7%231221211%63%
1919
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%2122222322%48%
1689
May1st to 15thNight
6%4143212421%47%
1619
16th to endNight
321322235%25%45%
1683
June1st to 15thNight
2122123424%52%
1620
16th to endNight
1123123424%54%
1620
July1st to 15thNight
32221235%25%50%
1620
16th to endNight
1122223325%54%
1702
August1st to 15thNight
1112235%16%62%
1620
16th to endNight
331343335%18%47%
1891
September1st to 15thNight
7%31322345%15%50%
1980
16th to endNight
6%21332335%15%52%
1980
October1st to 15thNight
8%3122123414%56%
2046
16th to endNight
7%222122212%63%
2304
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%6%51%
2266
May1st to 15thDay
11%5%345%2435%6%46%
2331
16th to endDay
10%5%245%36%46%8%41%
2430
June1st to 15thDay
5%2234245%6%8%53%
2340
16th to endDay
6%2144245%6%7%53%
2340
July1st to 15thDay
5%3245%25%5%7%9%49%
2340
16th to endDay
3213435%6%7%10%52%
2466
August1st to 15thDay
3113435%45%7%59%
2340
16th to endDay
7%314425%6%7%9%46%
2307
September1st to 15thDay
10%3233245%5%7%50%
1980
16th to endDay
8%41441335%7%54%
1980
October1st to 15thDay
9%313313345%59%
1902
16th to endDay
7%31321223369%
1919
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%323323347%55%
1689
May1st to 15thNight
9%42432345%6%53%
1619
16th to endNight
6%21432346%9%53%
1683
June1st to 15thNight
32231345%8%63%
1620
16th to endNight
311331435%10%60%
1620
July1st to 15thNight
421331445%11%57%
1620
16th to endNight
2133243410%63%
1702
August1st to 15thNight
111221336%9%66%
1620
16th to endNight
431442346%11%52%
1891
September1st to 15thNight
9%32322445%7%53%
1980
16th to endNight
7%21332346%7%57%
1980
October1st to 15thNight
9%312312346%61%
2046
16th to endNight
8%21221222469%
2304
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%
2266
May1st to 15thDay
38%5%9%18%20%8%
2331
16th to endDay
38%6%11%21%18%2
2434
June1st to 15thDay
26%6%13%27%21%3
2340
16th to endDay
27%5%12%27%21%5%
2340
July1st to 15thDay
27%7%15%30%16%2
2201
16th to endDay
21%7%18%31%19%1
2311
August1st to 15thDay
21%6%13%29%25%3
2326
16th to endDay
29%8%15%29%13%3
2307
September1st to 15thDay
31%7%11%22%19%7%
1980
16th to endDay
27%5%7%25%24%9%
1980
October1st to 15thDay
27%410%22%20%14%
1902
16th to endDay
21%27%19%30%18%
1919
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%10%21%24%10%
1689
May1st to 15thNight
32%5%12%18%21%10%
1620
16th to endNight
26%6%16%25%21%3
1685
June1st to 15thNight
17%5%13%33%23%6%
1620
16th to endNight
20%5%13%26%27%7%
1620
July1st to 15thNight
21%5%12%34%20%4
1530
16th to endNight
16%5%14%33%25%3
1594
August1st to 15thNight
13%412%31%31%6%
1610
16th to endNight
25%5%12%30%21%5%
1891
September1st to 15thNight
28%5%11%22%22%10%
1980
16th to endNight
24%5%9%23%25%12%
1980
October1st to 15thNight
24%310%23%20%16%
2046
16th to endNight
21%2417%31%23%
2304
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%9%40%23%10%
376
May1st to 15thDay
16%8%32%30%8%3
468
16th to endDay
15%5%30%29%16%3
517
June1st to 15thDay
7%111%40%29%9%
495
16th to endDay
6%19%33%36%13%
495
July1st to 15thDay
5%5%36%41%10%
475
16th to endDay
3418%50%23%
515
August1st to 15thDay
4323%50%17%
493
16th to endDay
10%429%40%14%
347
September1st to 15thDay
2214%47%33%
135
16th to endDay
8%217%48%23%
135
October1st to 15thDay
16%25%43%12%
135
16th to endDay
11%320%31%25%6%
144
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%5%40%32%7%
540
May1st to 15thNight
10%5%37%36%8%1
540
16th to endNight
6%330%37%20%1
563
June1st to 15thNight
3117%49%26%1
540
16th to endNight
311%45%34%4
540
July1st to 15thNight
47%45%37%3
510
16th to endNight
2235%53%5%
564
August1st to 15thNight
1236%53%5%
539
16th to endNight
6%439%41%7%
573
September1st to 15thNight
11%8%35%40%4
540
16th to endNight
7%9%40%36%4
537
October1st to 15thNight
9%218%38%27%3
606
16th to endNight
8%6%27%37%18%1
768
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 2017-11-01 16:23:40. Version ac04

Copyright 2017 A. Danko


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