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 2018-04-23.

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%
16234
24%
49574
20%
16196
63%
16196
31%
29333

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
55%
778
17%
2571
15%
776
60%
776
25%
1603
January16th to endNight
56%
832
23%
2704
23%
832
60%
832
26%
1673
February1st to 15thNight
53%
760
24%
2483
22%
760
61%
760
26%
1509
February16th to endNight
46%
684
23%
2076
17%
684
55%
684
26%
1319
March1st to 15thNight
47%
780
17%
2155
14%
780
51%
780
24%
1474
March16th to endNight
44%
832
20%
2276
13%
832
51%
832
29%
1459
April1st to 15thNight
44%
779
23%
1949
11%
779
49%
779
30%
1263
April16th to endNight
51%
744
26%
1860
11%
744
57%
744
41%
1089
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%
720
32%
1800
21%
720
78%
720
47%
1046
September16th to endNight
70%
716
36%
1974
29%
716
76%
716
49%
1042
October1st to 15thNight
65%
720
28%
2160
26%
720
72%
720
44%
1125
October16th to endNight
67%
768
32%
2304
32%
768
71%
768
38%
1285
November1st to 15thNight
64%
760
26%
2355
24%
760
69%
760
36%
1335
November16th to endNight
58%
780
23%
2665
25%
780
62%
780
30%
1512
December1st to 15thNight
54%
780
21%
2730
19%
780
59%
780
23%
1673
December16th to endNight
47%
832
21%
2912
18%
832
54%
832
22%
1800

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%
49942
Night
8%42432345%8%51%
49763
TransparencyDay
30%5%9%18%22%13%
49631
Night
34%49%18%19%12%
49575
SeeingDay
10%12%28%31%13%3
6749
Night
12%5%16%30%28%6%
16242

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
16%7%35%42345%6%40%
1695
16th to endDay
14%6%25%5%3445%6%42%
1872
February1st to 15thDay
14%6%245%2445%6%44%
1711
16th to endDay
15%5%25%4345%5%6%40%
1684
March1st to 15thDay
14%6%25%6%3445%9%36%
2134
16th to endDay
12%415%5%3446%8%41%
2298
April1st to 15thDay
12%5%24425%46%7%44%
2329
16th to endDay
5%313323348%59%
2214
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%
2160
16th to endDay
2312112235%71%
1982
October1st to 15thDay
6%323313336%62%
1800
16th to endDay
7%5%13223347%57%
1920
November1st to 15thDay
8%42442445%7%51%
1834
16th to endDay
12%8%24423346%47%
1623
December1st to 15thDay
16%7%44323336%42%
1560
16th to endDay
17%6%36%5%23347%39%
1664
January1st to 15thNight
15%6%2442445%7%42%
2571
16th to endNight
15%5%23323446%47%
2704
February1st to 15thNight
13%5%25%424346%47%
2471
16th to endNight
14%42333245%6%47%
2076
March1st to 15thNight
14%7%25%5%3445%7%40%
2155
16th to endNight
13%424424446%49%
2276
April1st to 15thNight
9%42442445%6%49%
1949
16th to endNight
5%213313347%61%
1860
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%
1800
16th to endNight
2214313347%64%
1974
October1st to 15thNight
4413212347%62%
2160
16th to endNight
6%32332335%7%57%
2304
November1st to 15thNight
7%423323348%56%
2355
16th to endNight
9%435%423345%52%
2665
December1st to 15thNight
18%5%14323446%45%
2730
16th to endNight
16%6%2442345%6%45%
2912

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
44%5%11%16%15%6%
1695
16th to endDay
42%6%9%13%16%10%
1872
February1st to 15thDay
40%5%7%19%21%5%
1711
16th to endDay
41%6%9%24%13%3
1684
March1st to 15thDay
44%7%11%19%12%4
2134
16th to endDay
39%8%13%19%15%2
2298
April1st to 15thDay
38%6%15%20%17%2
2329
16th to endDay
25%5%15%25%23%5%
2214
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
20%35%13%29%26%
2160
16th to endDay
18%25%24%30%17%
1982
October1st to 15thDay
25%47%17%25%19%
1800
16th to endDay
29%49%22%22%12%
1920
November1st to 15thDay
32%5%12%28%13%7%
1834
16th to endDay
39%5%10%18%20%5%
1623
December1st to 15thDay
43%5%9%16%18%6%
1560
16th to endDay
44%6%11%16%15%5%
1664
January1st to 15thNight
40%5%12%19%14%7%
2571
16th to endNight
39%5%10%14%16%13%
2704
February1st to 15thNight
38%49%18%19%9%
2483
16th to endNight
37%7%11%23%16%3
2076
March1st to 15thNight
44%5%11%18%14%5%
2155
16th to endNight
38%5%11%19%20%4
2276
April1st to 15thNight
35%5%13%22%19%3
1949
16th to endNight
25%5%11%26%22%9%
1860
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%28%
1800
16th to endNight
24%15%23%25%19%
1974
October1st to 15thNight
24%37%19%22%22%
2160
16th to endNight
29%48%20%20%16%
2304
November1st to 15thNight
30%5%11%29%16%6%
2355
16th to endNight
33%5%10%22%20%7%
2665
December1st to 15thNight
40%48%16%19%9%
2730
16th to endNight
40%6%11%17%17%7%
2912

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
24%9%23%27%13%1
233
16th to endDay
14%10%26%30%16%1
304
February1st to 15thDay
17%9%26%29%14%2
281
16th to endDay
17%16%29%20%13%1
284
March1st to 15thDay
21%15%26%20%12%3
330
16th to endDay
14%20%32%21%9%1
352
April1st to 15thDay
17%23%29%21%6%1
329
16th to endDay
8%27%27%25%7%3
288
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%6%
315
16th to endDay
410%25%32%21%6%
315
October1st to 15thDay
7%8%26%33%18%4
315
16th to endDay
11%8%26%28%19%5%
336
November1st to 15thDay
12%10%21%26%22%7%
250
16th to endDay
17%8%30%30%10%1
104
December1st to 15thDay
18%16%16%22%24%1
90
16th to endDay
11%18%19%31%17%1
96
January1st to 15thNight
19%5%12%29%27%6%
780
16th to endNight
18%5%12%29%27%6%
832
February1st to 15thNight
15%6%14%31%27%4
764
16th to endNight
16%9%21%27%20%4
684
March1st to 15thNight
19%7%16%26%25%4
780
16th to endNight
15%8%25%28%20%2
832
April1st to 15thNight
13%11%25%29%16%3
779
16th to endNight
6%13%24%26%25%4
744
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%
720
16th to endNight
4314%30%37%10%
716
October1st to 15thNight
8%414%30%33%7%
720
16th to endNight
11%213%23%35%13%
768
November1st to 15thNight
10%216%29%34%7%
760
16th to endNight
13%5%13%31%28%7%
780
December1st to 15thNight
20%6%12%28%24%6%
780
16th to endNight
20%9%16%29%22%1
832
Page generated at 2018-04-24 07:03:03. Version ac04

Copyright 2018 A. Danko


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