Castro Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Castro Valley clear sky chart from 2005-11-05 to 2018-10-08.

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
65%
16753
25%
51088
23%
16717
68%
16717
36%
29077

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
61%
776
18%
2585
18%
776
64%
776
27%
1595
January16th to endNight
60%
832
23%
2704
25%
832
61%
832
26%
1689
February1st to 15thNight
59%
757
25%
2483
25%
757
64%
757
27%
1512
February16th to endNight
53%
684
23%
2054
21%
684
59%
684
29%
1300
March1st to 15thNight
53%
780
17%
2174
15%
780
56%
780
26%
1467
March16th to endNight
54%
832
19%
2262
15%
832
57%
832
29%
1485
April1st to 15thNight
54%
779
22%
1949
13%
779
57%
779
33%
1285
April16th to endNight
62%
772
24%
1930
12%
772
65%
772
46%
1130
May1st to 15thNight
67%
665
25%
1835
18%
665
68%
665
45%
999
May16th to endNight
62%
424
21%
1643
22%
424
65%
424
29%
874
June1st to 15thNight
71%
390
24%
1560
29%
390
74%
390
36%
745
June16th to endNight
83%
390
32%
1560
43%
390
85%
390
54%
594
July1st to 15thNight
83%
411
30%
1521
37%
411
84%
411
50%
648
July16th to endNight
73%
612
30%
1737
28%
579
74%
579
46%
854
August1st to 15thNight
71%
593
29%
1738
24%
590
71%
590
42%
906
August16th to endNight
77%
828
32%
2070
20%
828
77%
828
53%
1149
September1st to 15thNight
78%
780
35%
1950
26%
780
79%
780
55%
1056
September16th to endNight
78%
776
37%
2127
34%
776
80%
776
56%
1069
October1st to 15thNight
72%
752
29%
2256
30%
752
76%
752
46%
1160
October16th to endNight
70%
768
32%
2304
35%
768
73%
768
40%
1267
November1st to 15thNight
68%
760
25%
2371
27%
760
71%
760
36%
1333
November16th to endNight
63%
780
24%
2633
26%
780
66%
780
31%
1494
December1st to 15thNight
58%
780
21%
2730
21%
780
63%
780
25%
1652
December16th to endNight
50%
832
20%
2912
18%
832
56%
832
24%
1814

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%5%24323346%57%
52043
Night
9%6%24323347%51%
51275
TransparencyDay
28%38%19%24%15%
51730
Night
31%49%18%21%14%
51089
SeeingDay
10%7%22%33%19%6%
7385
Night
13%210%33%33%7%
16766

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
17%5%15%41345%7%42%
1681
16th to endDay
16%6%25%5%33446%41%
1872
February1st to 15thDay
16%7%3432335%6%44%
1711
16th to endDay
16%7%35%42335%6%40%
1706
March1st to 15thDay
15%6%36%5%3445%8%35%
2113
16th to endDay
12%6%35%425%5%5%8%39%
2314
April1st to 15thDay
14%7%35%42335%6%42%
2329
16th to endDay
7%423314247%57%
2305
May1st to 15thDay
3413212348%63%
2441
16th to endDay
7%7%34213347%55%
2818
June1st to 15thDay
45%23323336%61%
2730
16th to endDay
2312112235%74%
2730
July1st to 15thDay
1413212236%71%
2682
16th to endDay
323112236%72%
2676
August1st to 15thDay
15%13212235%70%
2465
16th to endDay
423211235%71%
2484
September1st to 15thDay
2312212235%71%
2340
16th to endDay
3312212236%70%
2160
October1st to 15thDay
4313313336%64%
1873
16th to endDay
7%413423346%59%
1920
November1st to 15thDay
9%5%25%3245%5%6%50%
1815
16th to endDay
13%8%34323446%46%
1654
December1st to 15thDay
15%7%36%41344443%
1560
16th to endDay
18%6%25%423347%40%
1664
January1st to 15thNight
14%6%25%4235%6%8%41%
2585
16th to endNight
15%6%34324446%44%
2704
February1st to 15thNight
14%6%24434446%45%
2471
16th to endNight
14%7%25%413447%43%
2054
March1st to 15thNight
16%7%26%424346%39%
2174
16th to endNight
14%6%35%423345%45%
2262
April1st to 15thNight
11%6%2442446%8%43%
1949
16th to endNight
7%31332335%7%57%
1930
May1st to 15thNight
36%34323348%56%
1835
16th to endNight
7%11%24423337%50%
1642
June1st to 15thNight
45%25%313348%56%
1560
16th to endNight
1412122236%70%
1560
July1st to 15thNight
1423222348%64%
1604
16th to endNight
17%25%32445%10%52%
1845
August1st to 15thNight
29%34423449%50%
1747
16th to endNight
7%2431335%9%56%
2070
September1st to 15thNight
26%23213347%62%
1950
16th to endNight
2423212347%64%
2127
October1st to 15thNight
6%314313346%61%
2256
16th to endNight
7%5%24223446%55%
2304
November1st to 15thNight
9%5%2332335%7%52%
2371
16th to endNight
11%5%24423446%50%
2633
December1st to 15thNight
14%6%25%424346%45%
2730
16th to endNight
18%7%24323345%43%
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
39%6%12%18%15%7%
1681
16th to endDay
42%6%10%12%18%9%
1872
February1st to 15thDay
40%48%18%23%4
1711
16th to endDay
42%5%9%23%15%3
1706
March1st to 15thDay
44%5%10%20%13%5%
2113
16th to endDay
40%6%14%19%16%2
2314
April1st to 15thDay
40%5%13%19%18%2
2329
16th to endDay
27%313%26%22%6%
2305
May1st to 15thDay
21%38%30%27%8%
2441
16th to endDay
30%410%28%21%5%
2822
June1st to 15thDay
24%39%22%25%14%
2730
16th to endDay
14%1417%34%27%
2730
July1st to 15thDay
16%139%25%43%
2536
16th to endDay
15%1411%27%39%
2521
August1st to 15thDay
19%1311%32%31%
2449
16th to endDay
16%1414%38%24%
2484
September1st to 15thDay
17%1414%31%30%
2340
16th to endDay
17%2424%30%20%
2160
October1st to 15thDay
22%38%19%25%21%
1873
16th to endDay
26%39%22%22%14%
1920
November1st to 15thDay
31%5%11%27%16%7%
1815
16th to endDay
38%310%19%23%4
1654
December1st to 15thDay
42%5%8%15%19%7%
1560
16th to endDay
43%5%12%16%17%4
1664
January1st to 15thNight
39%5%12%19%15%8%
2585
16th to endNight
40%5%10%13%16%13%
2704
February1st to 15thNight
38%48%18%19%8%
2483
16th to endNight
39%413%24%15%2
2054
March1st to 15thNight
45%411%19%14%5%
2174
16th to endNight
39%5%11%20%18%4
2262
April1st to 15thNight
36%6%14%21%18%2
1949
16th to endNight
25%5%14%27%20%8%
1930
May1st to 15thNight
25%310%23%26%10%
1836
16th to endNight
33%312%24%19%5%
1643
June1st to 15thNight
25%5%10%20%23%15%
1560
16th to endNight
15%15%17%32%26%
1560
July1st to 15thNight
19%148%23%42%
1521
16th to endNight
23%27%12%20%33%
1737
August1st to 15thNight
28%15%10%26%28%
1738
16th to endNight
23%25%14%28%26%
2070
September1st to 15thNight
22%25%10%28%31%
1950
16th to endNight
19%25%21%28%22%
2127
October1st to 15thNight
24%38%20%21%21%
2256
16th to endNight
29%37%20%22%16%
2304
November1st to 15thNight
30%5%13%26%16%7%
2371
16th to endNight
33%410%22%21%7%
2633
December1st to 15thNight
39%5%8%15%19%11%
2730
16th to endNight
41%5%12%16%17%6%
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%5%21%26%17%4
219
16th to endDay
18%421%28%21%5%
304
February1st to 15thDay
18%5%23%25%23%3
281
16th to endDay
20%9%26%28%13%2
289
March1st to 15thDay
20%12%25%22%15%3
330
16th to endDay
14%12%33%26%10%2
352
April1st to 15thDay
19%17%29%21%9%2
329
16th to endDay
11%19%28%27%9%4
318
May1st to 15thDay
8%12%34%32%10%1
348
16th to endDay
16%9%23%32%13%5%
394
June1st to 15thDay
5%10%28%36%14%4
375
16th to endDay
2221%42%23%6%
375
July1st to 15thDay
315%48%24%6%
365
16th to endDay
2114%40%29%11%
391
August1st to 15thDay
5%115%43%24%9%
359
16th to endDay
315%42%26%11%
396
September1st to 15thDay
4315%43%25%7%
375
16th to endDay
36%19%34%26%10%
375
October1st to 15thDay
6%7%25%33%19%7%
345
16th to endDay
10%6%22%29%22%9%
336
November1st to 15thDay
11%320%28%26%9%
231
16th to endDay
12%8%18%32%28%
112
December1st to 15thDay
14%6%21%25%21%11%
90
16th to endDay
15%9%18%18%29%8%
96
January1st to 15thNight
17%28%34%29%7%
780
16th to endNight
18%29%34%26%7%
832
February1st to 15thNight
15%312%34%27%5%
764
16th to endNight
16%415%35%22%4
684
March1st to 15thNight
19%413%29%28%4
780
16th to endNight
17%414%37%23%3
832
April1st to 15thNight
14%5%16%38%22%3
779
16th to endNight
9%418%35%26%6%
772
May1st to 15thNight
8%212%40%30%5%
666
16th to endNight
17%110%33%32%5%
425
June1st to 15thNight
8%9%42%35%3
390
16th to endNight
6%5%40%43%3
390
July1st to 15thNight
7%225%56%8%
411
16th to endNight
7%320%51%15%
612
August1st to 15thNight
13%326%44%11%
593
16th to endNight
7%430%46%10%
828
September1st to 15thNight
8%5%28%45%11%
780
16th to endNight
6%17%30%42%12%
776
October1st to 15thNight
9%19%35%35%8%
752
16th to endNight
11%18%29%35%14%
768
November1st to 15thNight
11%18%36%32%8%
760
16th to endNight
13%211%32%30%8%
780
December1st to 15thNight
18%312%33%25%7%
780
16th to endNight
21%218%31%22%3
832
Page generated at 2018-10-09 07:39:11. Version ac04

Copyright 2018 A. Danko


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