Castro Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Castro Valley clear sky chart from 2005-11-06 to 2024-01-12.

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
61%
23671
25%
74773
23%
23625
65%
23625
33%
43610

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 10thNight
54%
756
17%
2549
17%
756
57%
756
23%
1649
January11th to 20thNight
58%
726
21%
2358
18%
726
63%
726
25%
1472
January21st to endNight
55%
792
23%
2574
24%
792
58%
792
24%
1644
February1st to 10thNight
58%
720
25%
2340
25%
720
63%
720
29%
1394
February11th to 20thNight
52%
700
24%
2189
21%
700
59%
700
28%
1340
February21st to endNight
56%
592
24%
1776
23%
592
61%
592
32%
1072
March1st to 10thNight
47%
720
17%
2021
13%
720
52%
720
24%
1382
March11th to 20thNight
51%
720
23%
1980
20%
720
54%
720
27%
1316
March21st to endNight
52%
792
18%
2142
12%
792
56%
792
29%
1396
April1st to 10thNight
54%
720
20%
1800
13%
720
56%
720
32%
1194
April11th to 20thNight
51%
711
25%
1779
12%
711
55%
711
38%
1114
April21st to endNight
62%
720
26%
1800
14%
720
65%
720
46%
1052
May1st to 10thNight
61%
653
25%
1733
16%
653
63%
653
41%
1008
May11th to 20thNight
60%
470
21%
1533
19%
470
61%
470
32%
858
May21st to endNight
57%
388
22%
1552
22%
388
62%
388
25%
851
June1st to 10thNight
65%
360
22%
1440
26%
360
69%
360
32%
722
June11th to 20thNight
75%
360
31%
1440
37%
360
79%
360
46%
600
June21st to endNight
72%
360
30%
1440
38%
360
75%
360
43%
623
July1st to 10thNight
75%
350
26%
1400
34%
350
76%
350
44%
611
July11th to 20thNight
73%
494
30%
1538
30%
494
74%
494
47%
743
July21st to endNight
65%
591
28%
1674
26%
558
67%
558
42%
853
August1st to 10thNight
60%
537
25%
1602
21%
534
60%
534
33%
906
August11th to 20thNight
73%
649
30%
1717
20%
649
73%
649
50%
919
August21st to endNight
71%
792
30%
1980
19%
792
71%
792
48%
1146
September1st to 10thNight
77%
720
36%
1800
26%
720
78%
720
56%
967
September11th to 20thNight
64%
720
32%
1800
24%
720
66%
720
43%
1084
September21st to endNight
77%
720
37%
2044
35%
720
80%
720
56%
1002
October1st to 10thNight
72%
720
29%
2160
31%
720
77%
720
47%
1093
October11th to 20thNight
67%
720
32%
2160
34%
720
71%
720
39%
1180
October21st to endNight
69%
792
34%
2376
35%
792
73%
792
42%
1274
November1st to 10thNight
66%
740
28%
2259
28%
740
70%
740
36%
1287
November11th to 20thNight
63%
760
26%
2470
27%
760
67%
760
31%
1413
November21st to endNight
65%
760
27%
2614
29%
760
70%
760
36%
1374
December1st to 10thNight
57%
760
21%
2660
21%
760
62%
760
25%
1625
December11th to 20thNight
52%
760
17%
3238
20%
759
56%
759
15%
2274
December21st to endNight
45%
826
12%
4835
17%
817
52%
817
13%
3172

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%6%24423347%57%
74687
Night
10%7%35%43445%7%50%
75035
TransparencyDay
28%48%19%24%16%
74406
Night
34%5%9%19%20%14%
74838
SeeingDay
10%9%25%32%19%5%
14254
Night
13%313%35%30%6%
23690

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 10thDay
19%6%36%6%245%6%8%35%
1613
11th to 20thDay
14%5%25%5%24447%48%
1630
21st to endDay
14%8%25%6%3346%8%40%
1782
February1st to 10thDay
16%6%3442345%6%46%
1620
11th to 20thDay
13%8%45%43345%7%45%
1660
21st to endDay
14%6%35%5%34446%47%
1480
March1st to 10thDay
15%8%47%5%35%5%5%8%36%
1936
11th to 20thDay
16%6%37%5%35%5%5%8%37%
1980
21st to endDay
12%7%25%5%35%5%6%8%43%
2212
April1st to 10thDay
13%7%35%5%34448%44%
2160
11th to 20thDay
10%6%2443435%6%55%
2129
21st to endDay
6%5%2432446%8%57%
2160
May1st to 10thDay
5%5%2431345%8%60%
2222
11th to 20thDay
6%5%34223348%59%
2357
21st to endDay
6%7%34323347%58%
2723
June1st to 10thDay
5%6%33323448%59%
2520
11th to 20thDay
2323222346%73%
2520
21st to endDay
3423222236%71%
2520
July1st to 10thDay
15%23212336%70%
2520
11th to 20thDay
1423323347%68%
2365
21st to endDay
1323223346%72%
2546
August1st to 10thDay
26%25%323236%66%
2328
11th to 20thDay
1313322346%72%
2183
21st to endDay
15%23222245%72%
2376
September1st to 10thDay
232331222476%
2160
11th to 20thDay
36%2443335%7%62%
2160
21st to endDay
3313212236%74%
1913
October1st to 10thDay
3313323336%69%
1800
11th to 20thDay
6%423323346%63%
1800
21st to endDay
7%5%14423336%62%
1980
November1st to 10thDay
8%4243245%5%9%54%
1817
11th to 20thDay
9%8%36%433447%50%
1710
21st to endDay
11%5%243235%5%7%53%
1563
December1st to 10thDay
13%6%36%4245%5%6%45%
1520
11th to 20thDay
23%9%47%5%3445%5%31%
1928
21st to endDay
16%11%36%6%345%5%8%34%
2794
January1st to 10thNight
16%8%36%4345%6%8%38%
2549
11th to 20thNight
12%7%36%435%45%7%44%
2358
21st to endNight
16%7%35%42445%6%43%
2574
February1st to 10thNight
16%6%2432435%5%49%
2340
11th to 20thNight
11%7%35%5%3445%7%45%
2187
21st to endNight
12%7%25%423447%50%
1776
March1st to 10thNight
17%8%36%5%35%5%5%6%39%
2021
11th to 20thNight
15%8%36%5%3435%8%40%
1980
21st to endNight
14%7%35%5%34345%47%
2142
April1st to 10thNight
10%9%36%43346%8%44%
1800
11th to 20thNight
11%7%33324447%53%
1779
21st to endNight
6%42442446%8%57%
1800
May1st to 10thNight
6%9%35%323346%55%
1733
11th to 20thNight
6%10%45%42445%7%48%
1532
21st to endNight
7%14%34423437%49%
1552
June1st to 10thNight
6%8%35%42335%7%53%
1440
11th to 20thNight
2425%22335%7%66%
1440
21st to endNight
29%25%233235%63%
1440
July1st to 10thNight
19%44323337%61%
1440
11th to 20thNight
26%45%423448%57%
1590
21st to endNight
28%5%7%43447%9%48%
1773
August1st to 10thNight
314%5%6%5%34448%44%
1611
11th to 20thNight
17%45%42446%9%54%
1717
21st to endNight
110%46%32335%7%55%
1980
September1st to 10thNight
17%43323346%64%
1800
11th to 20thNight
410%46%424346%52%
1800
21st to endNight
35%24222347%67%
2044
October1st to 10thNight
5%5%15%323345%63%
2160
11th to 20thNight
6%6%26%43325%6%57%
2160
21st to endNight
7%5%3432335%6%59%
2376
November1st to 10thNight
9%6%24425%45%7%53%
2259
11th to 20thNight
10%7%25%42436%8%50%
2470
21st to endNight
9%5%24423447%56%
2614
December1st to 10thNight
14%7%35%433446%47%
2660
11th to 20thNight
26%10%35%42435%6%32%
3276
21st to endNight
17%9%36%6%45%5%5%6%34%
4862

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 10thDay
45%7%14%21%10%4
1613
11th to 20thDay
36%6%12%16%18%12%
1630
21st to endDay
41%6%10%14%21%7%
1782
February1st to 10thDay
39%48%20%21%8%
1620
11th to 20thDay
39%5%10%18%22%7%
1669
21st to endDay
37%6%9%24%19%6%
1480
March1st to 10thDay
45%6%10%20%15%4
1936
11th to 20thDay
44%6%9%21%17%4
1980
21st to endDay
37%7%15%21%17%4
2212
April1st to 10thDay
39%6%13%19%19%4
2160
11th to 20thDay
30%5%14%25%21%5%
2132
21st to endDay
25%414%29%24%5%
2160
May1st to 10thDay
24%5%9%26%29%7%
2222
11th to 20thDay
24%48%31%25%8%
2360
21st to endDay
28%411%30%23%3
2724
June1st to 10thDay
25%411%26%24%9%
2520
11th to 20thDay
14%38%22%36%16%
2520
21st to endDay
18%1414%33%30%
2520
July1st to 10thDay
18%2310%25%43%
2451
11th to 20thDay
18%26%10%23%41%
2294
21st to endDay
14%2411%29%41%
2405
August1st to 10thDay
22%2413%30%29%
2312
11th to 20thDay
15%2411%36%32%
2183
21st to endDay
17%2314%33%31%
2376
September1st to 10thDay
16%139%32%40%
2160
11th to 20thDay
23%35%22%30%16%
2160
21st to endDay
14%35%23%33%23%
1913
October1st to 10thDay
19%47%17%29%24%
1800
11th to 20thDay
22%49%18%23%23%
1800
21st to endDay
25%47%20%23%19%
1980
November1st to 10thDay
28%5%10%24%21%12%
1817
11th to 20thDay
35%5%9%22%22%6%
1710
21st to endDay
31%410%19%27%9%
1563
December1st to 10thDay
38%7%9%19%18%9%
1520
11th to 20thDay
53%6%9%14%14%4
1928
21st to endDay
48%7%12%19%12%3
2794
January1st to 10thNight
42%7%13%21%11%5%
2549
11th to 20thNight
39%7%11%16%14%13%
2358
21st to endNight
41%6%10%13%19%10%
2574
February1st to 10thNight
38%48%21%19%11%
2340
11th to 20thNight
38%5%9%18%21%8%
2189
21st to endNight
35%5%12%27%17%4
1776
March1st to 10thNight
45%5%12%18%15%4
2021
11th to 20thNight
43%47%23%18%5%
1980
21st to endNight
39%6%13%21%17%5%
2142
April1st to 10thNight
37%7%14%21%17%4
1800
11th to 20thNight
32%5%12%25%19%7%
1779
21st to endNight
24%6%13%31%21%5%
1800
May1st to 10thNight
29%48%25%23%9%
1733
11th to 20thNight
32%5%10%24%22%6%
1533
21st to endNight
35%5%13%23%21%3
1552
June1st to 10thNight
28%6%10%25%22%9%
1440
11th to 20thNight
18%49%19%32%17%
1440
21st to endNight
23%15%15%30%25%
1440
July1st to 10thNight
23%15%8%24%39%
1400
11th to 20thNight
24%26%12%21%36%
1538
21st to endNight
27%26%12%22%30%
1674
August1st to 10thNight
36%26%10%23%23%
1602
11th to 20thNight
25%26%12%26%30%
1717
21st to endNight
28%2414%26%27%
1980
September1st to 10thNight
21%247%27%39%
1800
11th to 20thNight
31%37%19%25%15%
1800
21st to endNight
18%35%21%30%23%
2044
October1st to 10thNight
23%38%18%24%23%
2160
11th to 20thNight
29%37%18%21%22%
2160
21st to endNight
27%47%21%21%20%
2376
November1st to 10thNight
31%5%11%23%18%13%
2259
11th to 20thNight
33%6%10%24%19%8%
2470
21st to endNight
29%411%21%24%11%
2614
December1st to 10thNight
38%7%9%18%16%12%
2660
11th to 20thNight
53%5%9%14%15%3
3276
21st to endNight
47%9%14%15%11%4
4862

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 10thDay
24%11%26%22%13%4
274
11th to 20thDay
19%7%22%28%21%3
344
21st to endDay
15%6%24%31%20%4
374
February1st to 10thDay
18%9%21%25%22%4
340
11th to 20thDay
19%13%28%25%14%2
373
21st to endDay
14%13%27%34%12%1
346
March1st to 10thDay
20%15%30%23%10%3
420
11th to 20thDay
19%17%23%24%13%4
420
21st to endDay
16%14%34%23%12%1
462
April1st to 10thDay
18%15%31%24%10%3
420
11th to 20thDay
15%17%32%25%8%4
412
21st to endDay
8%19%30%28%10%5%
420
May1st to 10thDay
10%14%32%30%12%3
423
11th to 20thDay
12%13%30%29%13%2
448
21st to endDay
13%11%27%31%13%5%
485
June1st to 10thDay
7%11%29%32%17%4
450
11th to 20thDay
310%28%40%15%4
450
21st to endDay
47%26%39%19%5%
450
July1st to 10thDay
45%20%47%19%5%
446
11th to 20thDay
1220%44%29%4
444
21st to endDay
3120%44%25%8%
487
August1st to 10thDay
6%5%21%40%21%6%
447
11th to 20thDay
3220%44%22%9%
437
21st to endDay
4320%39%27%7%
495
September1st to 10thDay
4416%42%26%9%
450
11th to 20thDay
5%8%24%36%20%7%
450
21st to endDay
47%21%33%28%7%
450
October1st to 10thDay
48%26%32%21%9%
450
11th to 20thDay
8%8%18%32%26%8%
450
21st to endDay
8%7%24%31%21%9%
495
November1st to 10thDay
8%10%22%25%27%8%
413
11th to 20thDay
7%9%15%34%26%10%
270
21st to endDay
10%5%23%30%28%3
201
December1st to 10thDay
16%12%20%22%23%7%
180
11th to 20thDay
16%11%20%26%23%5%
180
21st to endDay
22%10%25%21%19%3
198
January1st to 10thNight
19%5%12%34%22%7%
760
11th to 20thNight
15%5%12%36%26%5%
726
21st to endNight
20%312%37%23%5%
792
February1st to 10thNight
18%413%36%25%4
720
11th to 20thNight
13%5%19%36%23%5%
704
21st to endNight
15%7%16%40%19%3
592
March1st to 10thNight
20%6%18%31%23%3
720
11th to 20thNight
20%5%13%34%24%4
720
21st to endNight
17%7%17%38%19%2
792
April1st to 10thNight
14%5%17%40%22%2
720
11th to 20thNight
14%6%21%32%22%5%
711
21st to endNight
8%5%19%39%23%5%
720
May1st to 10thNight
11%416%40%25%5%
653
11th to 20thNight
13%212%37%31%5%
470
21st to endNight
15%5%14%35%26%5%
389
June1st to 10thNight
11%212%42%30%3
360
11th to 20thNight
6%111%49%31%2
360
21st to endNight
6%410%36%41%3
360
July1st to 10thNight
7%25%32%51%3
350
11th to 20thNight
6%436%42%12%
494
21st to endNight
8%18%25%47%12%
591
August1st to 10thNight
15%18%28%39%9%
537
11th to 20thNight
8%19%34%41%8%
649
21st to endNight
7%18%34%42%9%
792
September1st to 10thNight
7%17%32%43%10%
720
11th to 20thNight
10%212%33%35%7%
720
21st to endNight
5%210%30%41%12%
720
October1st to 10thNight
8%29%37%36%8%
720
11th to 20thNight
10%210%31%38%9%
720
21st to endNight
10%310%33%32%12%
792
November1st to 10thNight
10%312%33%33%9%
740
11th to 20thNight
13%211%36%31%7%
760
21st to endNight
12%214%38%27%6%
760
December1st to 10thNight
17%414%36%24%5%
760
11th to 20thNight
25%412%35%20%5%
760
21st to endNight
21%5%21%32%19%2
836
Page generated at 2024-01-09 04:14:40. Version ac07

Copyright 2024 Attilla Danko


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