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 2017-09-18.

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%
15385
25%
46921
23%
15349
67%
15349
36%
26753

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
63%
716
18%
2385
19%
716
66%
716
29%
1434
January16th to endNight
60%
768
24%
2496
26%
768
61%
768
26%
1550
February1st to 15thNight
57%
697
22%
2288
23%
697
61%
697
25%
1441
February16th to endNight
53%
632
22%
1898
20%
632
58%
632
28%
1228
March1st to 15thNight
54%
720
17%
2007
15%
720
57%
720
27%
1333
March16th to endNight
54%
768
20%
2088
15%
768
57%
768
29%
1371
April1st to 15thNight
54%
719
21%
1799
13%
719
57%
719
33%
1190
April16th to endNight
62%
720
24%
1800
12%
720
65%
720
46%
1058
May1st to 15thNight
68%
614
25%
1694
18%
614
69%
614
46%
911
May16th to endNight
64%
390
22%
1513
23%
390
67%
390
31%
775
June1st to 15thNight
69%
360
23%
1440
27%
360
73%
360
35%
700
June16th to endNight
83%
360
34%
1440
44%
360
85%
360
55%
540
July1st to 15thNight
84%
378
29%
1398
36%
378
84%
378
51%
587
July16th to endNight
72%
564
31%
1593
29%
531
73%
531
46%
790
August1st to 15thNight
70%
556
28%
1629
23%
553
70%
553
41%
858
August16th to endNight
77%
764
33%
1910
21%
764
77%
764
54%
1051
September1st to 15thNight
79%
720
34%
1800
25%
720
79%
720
56%
965
September16th to endNight
78%
667
37%
1829
35%
667
79%
667
54%
930
October1st to 15thNight
72%
660
29%
1980
31%
660
75%
660
44%
1039
October16th to endNight
69%
704
30%
2112
33%
704
72%
704
38%
1177
November1st to 15thNight
69%
700
27%
2184
28%
700
72%
700
37%
1209
November16th to endNight
64%
720
24%
2430
26%
720
67%
720
32%
1358
December1st to 15thNight
56%
720
20%
2520
19%
720
61%
720
23%
1575
December16th to endNight
49%
768
20%
2688
18%
768
55%
768
24%
1683

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%56%
47872
Night
9%6%24323347%51%
47108
TransparencyDay
28%38%19%23%15%
47559
Night
32%49%19%20%14%
46922
SeeingDay
10%7%22%34%19%5%
6015
Night
13%210%33%33%7%
15398

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%41441345%7%44%
1551
16th to endDay
17%6%25%5%23346%42%
1728
February1st to 15thDay
17%8%34323345%42%
1576
16th to endDay
17%7%35%42335%6%38%
1576
March1st to 15thDay
14%6%36%5%3445%9%36%
1950
16th to endDay
12%6%35%425%5%5%7%40%
2136
April1st to 15thDay
14%7%35%42335%6%42%
2149
16th to endDay
7%423313247%57%
2160
May1st to 15thDay
4413212348%63%
2253
16th to endDay
7%7%34212346%55%
2596
June1st to 15thDay
5%5%23323346%59%
2520
16th to endDay
2212112235%73%
2520
July1st to 15thDay
1413212236%71%
2476
16th to endDay
322112236%72%
2468
August1st to 15thDay
15%14212235%69%
2322
16th to endDay
423211236%72%
2292
September1st to 15thDay
1412212235%71%
2160
16th to endDay
3312211336%69%
1854
October1st to 15thDay
5%313313337%63%
1650
16th to endDay
8%413423336%59%
1760
November1st to 15thDay
9%42432445%6%51%
1672
16th to endDay
12%7%34422446%47%
1527
December1st to 15thDay
16%7%36%41344441%
1440
16th to endDay
19%6%25%423348%40%
1536
January1st to 15thNight
13%6%244235%5%8%43%
2385
16th to endNight
16%6%33323445%45%
2496
February1st to 15thNight
15%6%3433445%6%42%
2276
16th to endNight
15%8%25%423447%41%
1898
March1st to 15thNight
16%6%26%424346%41%
2007
16th to endNight
13%6%35%423345%44%
2088
April1st to 15thNight
11%5%24425%46%8%43%
1799
16th to endNight
8%32332335%7%57%
1800
May1st to 15thNight
36%34222348%58%
1694
16th to endNight
6%9%24323337%52%
1512
June1st to 15thNight
5%5%25%323348%55%
1440
16th to endNight
2412122236%71%
1440
July1st to 15thNight
1423222348%65%
1481
16th to endNight
17%35%323449%53%
1701
August1st to 15thNight
29%3442445%9%49%
1638
16th to endNight
7%2431335%9%57%
1910
September1st to 15thNight
26%23313346%63%
1800
16th to endNight
3423212347%64%
1829
October1st to 15thNight
7%314423346%59%
1980
16th to endNight
7%5%24323446%55%
2112
November1st to 15thNight
9%6%2332335%7%53%
2184
16th to endNight
9%6%24423446%51%
2430
December1st to 15thNight
16%6%25%434445%43%
2520
16th to endNight
19%6%24323345%44%
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
37%6%13%19%16%7%
1551
16th to endDay
42%5%9%12%19%10%
1728
February1st to 15thDay
42%49%18%21%3
1576
16th to endDay
44%5%8%24%13%3
1576
March1st to 15thDay
43%5%10%20%14%5%
1950
16th to endDay
40%7%14%18%16%3
2136
April1st to 15thDay
40%5%14%18%18%2
2149
16th to endDay
26%314%25%21%7%
2160
May1st to 15thDay
21%39%29%28%8%
2253
16th to endDay
29%310%29%22%5%
2600
June1st to 15thDay
25%310%21%23%14%
2520
16th to endDay
15%1417%34%26%
2520
July1st to 15thDay
16%139%24%44%
2330
16th to endDay
15%149%27%41%
2313
August1st to 15thDay
19%1311%31%31%
2306
16th to endDay
15%1314%38%25%
2292
September1st to 15thDay
17%1414%31%29%
2160
16th to endDay
18%2425%31%19%
1854
October1st to 15thDay
23%38%20%26%16%
1650
16th to endDay
27%49%23%22%13%
1760
November1st to 15thDay
31%5%11%26%16%7%
1672
16th to endDay
38%310%18%24%4
1527
December1st to 15thDay
44%5%9%16%19%3
1440
16th to endDay
44%412%16%16%4
1536
January1st to 15thNight
37%5%12%19%16%8%
2385
16th to endNight
40%49%13%16%14%
2496
February1st to 15thNight
41%49%19%17%7%
2288
16th to endNight
41%412%24%13%2
1898
March1st to 15thNight
43%312%19%14%5%
2007
16th to endNight
39%6%12%19%17%4
2088
April1st to 15thNight
36%6%14%21%18%2
1799
16th to endNight
25%5%14%26%19%8%
1800
May1st to 15thNight
24%310%23%27%10%
1695
16th to endNight
31%312%25%20%6%
1513
June1st to 15thNight
25%5%11%20%21%15%
1440
16th to endNight
14%15%17%34%26%
1440
July1st to 15thNight
19%138%22%45%
1398
16th to endNight
24%25%12%19%35%
1593
August1st to 15thNight
29%15%10%25%28%
1629
16th to endNight
22%25%13%28%27%
1910
September1st to 15thNight
21%25%10%28%32%
1800
16th to endNight
20%2422%28%21%
1829
October1st to 15thNight
26%28%22%22%17%
1980
16th to endNight
30%37%21%22%13%
2112
November1st to 15thNight
29%413%27%16%7%
2184
16th to endNight
32%410%22%21%8%
2430
December1st to 15thNight
41%5%9%16%19%7%
2520
16th to endNight
41%5%12%15%17%6%
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
20%6%22%29%16%5%
179
16th to endDay
18%5%20%29%20%5%
256
February1st to 15thDay
21%6%22%24%23%2
236
16th to endDay
22%8%23%29%13%2
237
March1st to 15thDay
18%12%25%22%15%4
270
16th to endDay
14%13%35%25%9%2
288
April1st to 15thDay
19%17%29%23%9%1
269
16th to endDay
11%20%30%27%8%2
270
May1st to 15thDay
8%11%35%33%9%1
288
16th to endDay
15%9%22%34%13%5%
330
June1st to 15thDay
6%11%30%36%11%3
315
16th to endDay
3320%43%23%6%
315
July1st to 15thDay
315%49%24%6%
305
16th to endDay
1215%42%28%9%
327
August1st to 15thDay
4115%46%23%8%
315
16th to endDay
215%43%27%9%
332
September1st to 15thDay
4215%43%27%7%
315
16th to endDay
36%18%34%26%10%
264
October1st to 15thDay
7%7%20%36%20%7%
255
16th to endDay
12%6%24%30%19%5%
272
November1st to 15thDay
10%220%26%28%11%
178
16th to endDay
9%12%21%30%26%
75
December1st to 15thDay
21%6%25%30%13%3
60
16th to endDay
15%7%23%23%23%6%
64
January1st to 15thNight
16%28%35%29%7%
720
16th to endNight
19%29%34%25%8%
768
February1st to 15thNight
16%312%34%26%5%
704
16th to endNight
17%415%35%22%4
632
March1st to 15thNight
18%413%29%29%4
720
16th to endNight
16%414%36%24%3
768
April1st to 15thNight
13%5%16%38%22%3
719
16th to endNight
10%418%35%26%5%
720
May1st to 15thNight
7%212%40%31%5%
615
16th to endNight
14%110%34%34%5%
391
June1st to 15thNight
8%10%44%33%2
360
16th to endNight
6%5%40%43%3
360
July1st to 15thNight
7%125%56%8%
378
16th to endNight
8%320%50%15%
564
August1st to 15thNight
13%326%44%10%
556
16th to endNight
6%5%29%47%9%
764
September1st to 15thNight
8%5%25%48%12%
720
16th to endNight
6%17%29%43%12%
667
October1st to 15thNight
10%17%34%36%9%
660
16th to endNight
11%18%31%33%13%
704
November1st to 15thNight
11%19%35%33%9%
700
16th to endNight
12%212%32%30%9%
720
December1st to 15thNight
20%312%33%23%7%
720
16th to endNight
21%218%32%20%3
768
Page generated at 2017-09-19 04:32:25. Version ac04

Copyright 2017 A. Danko


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