San Rafael
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Rafael clear sky chart from 2005-11-05 to 2017-09-15.

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
58%
15361
24%
46900
19%
15323
63%
15323
31%
27829

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
56%
718
18%
2372
15%
716
62%
716
26%
1447
January16th to endNight
56%
768
24%
2496
24%
768
59%
768
26%
1538
February1st to 15thNight
52%
700
22%
2288
20%
700
58%
700
24%
1441
February16th to endNight
45%
632
22%
1918
16%
632
54%
632
24%
1250
March1st to 15thNight
49%
720
17%
1989
14%
720
52%
720
25%
1333
March16th to endNight
44%
768
21%
2101
13%
768
51%
768
29%
1347
April1st to 15thNight
44%
719
23%
1799
11%
719
49%
719
30%
1166
April16th to endNight
51%
720
25%
1800
11%
720
56%
720
40%
1061
May1st to 15thNight
59%
584
25%
1664
14%
584
65%
584
42%
914
May16th to endNight
55%
408
22%
1531
17%
408
64%
408
29%
832
June1st to 15thNight
61%
360
21%
1440
20%
360
70%
360
28%
763
June16th to endNight
74%
360
30%
1440
36%
360
79%
360
45%
602
July1st to 15thNight
74%
395
22%
1415
24%
395
77%
395
34%
729
July16th to endNight
63%
564
20%
1593
17%
531
65%
531
22%
1053
August1st to 15thNight
60%
538
21%
1611
16%
535
62%
535
26%
1012
August16th to endNight
69%
760
25%
1906
15%
760
70%
760
37%
1221
September1st to 15thNight
76%
719
32%
1799
21%
719
78%
719
47%
1045
September16th to endNight
70%
656
33%
1809
27%
656
75%
656
47%
979
October1st to 15thNight
64%
660
28%
1980
26%
660
71%
660
41%
1065
October16th to endNight
66%
704
30%
2112
30%
704
70%
704
37%
1183
November1st to 15thNight
64%
700
27%
2169
25%
700
69%
700
37%
1209
November16th to endNight
58%
720
23%
2460
25%
720
62%
720
31%
1375
December1st to 15thNight
51%
720
20%
2520
17%
720
57%
720
21%
1596
December16th to endNight
46%
768
20%
2688
17%
768
53%
768
21%
1668

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
7%424323347%55%
47827
Night
8%42432345%8%51%
47089
TransparencyDay
30%5%9%18%22%13%
47516
Night
34%49%18%19%12%
46901
SeeingDay
9%12%29%32%13%3
6025
Night
12%5%16%30%28%6%
15369

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
15%6%35%42345%6%42%
1564
16th to endDay
14%5%25%43445%5%43%
1728
February1st to 15thDay
15%6%245%2445%5%43%
1576
16th to endDay
17%6%25%4345%5%7%37%
1556
March1st to 15thDay
15%6%25%5%3436%9%37%
1970
16th to endDay
12%415%5%3445%8%41%
2121
April1st to 15thDay
12%5%24425%47%7%44%
2149
16th to endDay
4314323348%59%
2160
May1st to 15thDay
3323213348%63%
2284
16th to endDay
4423313348%59%
2578
June1st to 15thDay
5%323312347%61%
2520
16th to endDay
1212212247%71%
2520
July1st to 15thDay
1313213238%67%
2457
16th to endDay
1323212249%65%
2468
August1st to 15thDay
1314312338%64%
2340
16th to endDay
424212348%65%
2295
September1st to 15thDay
1313312337%67%
2150
16th to endDay
3313212235%70%
1817
October1st to 15thDay
6%324313336%60%
1650
16th to endDay
8%5%13323347%56%
1760
November1st to 15thDay
8%42442445%7%52%
1690
16th to endDay
12%8%24423346%48%
1498
December1st to 15thDay
17%8%44334345%40%
1440
16th to endDay
18%6%35%413347%39%
1536
January1st to 15thNight
14%5%2432445%7%44%
2372
16th to endNight
16%5%23313346%47%
2496
February1st to 15thNight
14%5%25%424446%44%
2276
16th to endNight
15%4244325%6%7%44%
1918
March1st to 15thNight
14%6%15%434447%42%
1989
16th to endNight
12%424424446%48%
2101
April1st to 15thNight
9%42442446%6%50%
1799
16th to endNight
5%213324347%61%
1800
May1st to 15thNight
322432235%8%61%
1664
16th to endNight
431331445%10%57%
1530
June1st to 15thNight
22133245%6%10%55%
1440
16th to endNight
112213249%69%
1440
July1st to 15thNight
13234245%6%12%54%
1500
16th to endNight
15%35%5%25%8%7%12%40%
1701
August1st to 15thNight
25%36%5%246%7%14%42%
1620
16th to endNight
15%25%32446%10%52%
1906
September1st to 15thNight
131432445%10%59%
1799
16th to endNight
2224413348%62%
1809
October1st to 15thNight
5%424312347%59%
1980
16th to endNight
6%42332345%7%56%
2112
November1st to 15thNight
7%423322348%57%
2169
16th to endNight
9%435%423245%54%
2460
December1st to 15thNight
19%6%14323436%43%
2520
16th to endNight
17%5%24313446%45%
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
41%5%12%17%16%7%
1564
16th to endDay
42%6%9%12%17%11%
1728
February1st to 15thDay
43%6%7%18%19%4
1576
16th to endDay
43%6%9%24%11%3
1556
March1st to 15thDay
43%7%11%18%13%4
1970
16th to endDay
40%8%13%19%14%3
2121
April1st to 15thDay
38%6%15%19%17%2
2149
16th to endDay
25%5%15%25%22%5%
2160
May1st to 15thDay
21%5%8%28%27%7%
2284
16th to endDay
27%6%12%26%21%5%
2582
June1st to 15thDay
26%5%10%21%23%12%
2520
16th to endDay
16%37%17%33%22%
2520
July1st to 15thDay
21%25%9%23%37%
2313
16th to endDay
22%45%8%24%34%
2313
August1st to 15thDay
24%36%12%28%25%
2324
16th to endDay
23%16%14%31%21%
2295
September1st to 15thDay
21%35%13%29%26%
2150
16th to endDay
19%2423%29%19%
1817
October1st to 15thDay
26%47%19%26%14%
1650
16th to endDay
29%49%23%21%10%
1760
November1st to 15thDay
31%5%12%28%13%7%
1690
16th to endDay
38%5%10%18%21%5%
1498
December1st to 15thDay
45%5%9%17%17%3
1440
16th to endDay
44%6%12%16%14%5%
1536
January1st to 15thNight
38%5%12%19%15%8%
2372
16th to endNight
39%5%9%13%17%14%
2496
February1st to 15thNight
41%5%10%18%17%7%
2288
16th to endNight
39%7%11%23%15%2
1918
March1st to 15thNight
42%5%12%18%15%5%
1989
16th to endNight
38%5%12%19%19%4
2101
April1st to 15thNight
35%5%13%21%19%3
1799
16th to endNight
25%5%11%25%22%8%
1800
May1st to 15thNight
25%49%21%26%11%
1665
16th to endNight
30%6%11%24%19%6%
1531
June1st to 15thNight
31%6%10%18%21%12%
1440
16th to endNight
19%25%13%33%24%
1440
July1st to 15thNight
31%15%7%20%32%
1415
16th to endNight
47%36%6%11%25%
1593
August1st to 15thNight
43%248%20%20%
1611
16th to endNight
36%36%10%21%22%
1906
September1st to 15thNight
27%35%12%23%27%
1799
16th to endNight
26%15%21%25%20%
1809
October1st to 15thNight
26%38%20%22%17%
1980
16th to endNight
30%48%21%21%14%
2112
November1st to 15thNight
29%5%11%29%16%7%
2169
16th to endNight
32%5%10%23%20%8%
2460
December1st to 15thNight
43%5%8%17%18%6%
2520
16th to endNight
40%6%11%16%17%7%
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
22%10%23%26%15%1
192
16th to endDay
14%11%26%30%15%1
256
February1st to 15thDay
20%10%26%28%13%1
236
16th to endDay
19%15%27%21%13%1
234
March1st to 15thDay
20%16%28%17%13%3
270
16th to endDay
14%21%33%20%8%1
288
April1st to 15thDay
17%24%30%20%6%
269
16th to endDay
8%28%29%24%5%2
270
May1st to 15thDay
6%23%34%28%7%
288
16th to endDay
7%18%32%26%11%3
330
June1st to 15thDay
7%16%40%26%6%1
315
16th to endDay
16%34%42%12%1
315
July1st to 15thDay
1329%51%13%1
305
16th to endDay
2228%48%13%4
327
August1st to 15thDay
5%5%30%44%11%2
315
16th to endDay
3128%43%16%5%
332
September1st to 15thDay
5%326%40%16%7%
312
16th to endDay
49%25%31%22%6%
255
October1st to 15thDay
9%9%25%34%16%5%
255
16th to endDay
13%9%29%27%16%3
272
November1st to 15thDay
9%11%20%24%26%8%
196
16th to endDay
15%11%33%30%8%
69
December1st to 15thDay
28%20%23%15%11%1
60
16th to endDay
12%21%21%32%9%1
64
January1st to 15thNight
17%5%12%30%27%6%
720
16th to endNight
19%5%12%29%26%6%
768
February1st to 15thNight
16%6%14%31%26%4
704
16th to endNight
17%8%21%26%20%5%
632
March1st to 15thNight
18%8%16%26%25%4
720
16th to endNight
15%8%25%27%20%2
768
April1st to 15thNight
12%12%25%28%16%3
719
16th to endNight
7%13%24%26%24%4
720
May1st to 15thNight
4324%33%30%4
585
16th to endNight
8%6%26%31%22%4
409
June1st to 15thNight
4424%41%23%2
360
16th to endNight
3116%44%30%3
360
July1st to 15thNight
5%10%39%37%6%
395
16th to endNight
13%10%28%39%8%
564
August1st to 15thNight
12%15%29%34%6%
538
16th to endNight
8%15%35%34%6%
760
September1st to 15thNight
5%10%30%41%10%
719
16th to endNight
5%214%29%37%11%
656
October1st to 15thNight
9%414%29%33%8%
660
16th to endNight
11%213%24%33%13%
704
November1st to 15thNight
10%216%27%35%7%
700
16th to endNight
12%5%14%30%28%7%
720
December1st to 15thNight
21%6%13%28%22%6%
720
16th to endNight
20%9%16%30%21%1
768
Page generated at 2017-09-15 21:58:31. Version ac04

Copyright 2017 A. Danko


San Rafael Clear Sky Chart | Charts Home