Chabot Space and Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chabot Space and Science Center clear sky chart from 2005-11-05 to 2017-08-12.

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
63%
15227
26%
46546
23%
15191
66%
15191
34%
26931

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%
716
19%
2383
18%
716
65%
716
28%
1427
January16th to endNight
58%
768
25%
2496
26%
768
60%
768
27%
1535
February1st to 15thNight
55%
698
23%
2288
23%
698
60%
698
25%
1424
February16th to endNight
51%
632
23%
1903
20%
632
59%
632
28%
1218
March1st to 15thNight
53%
720
18%
2004
16%
720
56%
720
27%
1326
March16th to endNight
51%
768
20%
2091
15%
768
55%
768
29%
1358
April1st to 15thNight
49%
719
22%
1799
11%
719
54%
719
32%
1169
April16th to endNight
57%
720
25%
1800
12%
720
61%
720
43%
1065
May1st to 15thNight
67%
605
26%
1685
19%
605
68%
605
44%
918
May16th to endNight
62%
393
24%
1516
24%
393
67%
393
30%
786
June1st to 15thNight
66%
360
23%
1440
25%
360
72%
360
32%
718
June16th to endNight
80%
360
33%
1440
43%
360
82%
360
47%
590
July1st to 15thNight
86%
379
29%
1399
36%
379
87%
379
45%
629
July16th to endNight
73%
564
29%
1593
28%
531
74%
531
35%
884
August1st to 15thNight
68%
537
27%
1586
21%
534
69%
534
31%
929
August16th to endNight
74%
700
29%
1750
18%
700
75%
700
45%
1045
September1st to 15thNight
79%
660
35%
1650
26%
660
79%
660
50%
941
September16th to endNight
78%
656
37%
1801
33%
656
80%
656
51%
932
October1st to 15thNight
70%
660
30%
1980
31%
660
75%
660
42%
1049
October16th to endNight
69%
704
31%
2112
33%
704
72%
704
38%
1181
November1st to 15thNight
68%
700
28%
2183
28%
700
72%
700
38%
1210
November16th to endNight
61%
720
25%
2439
27%
720
65%
720
32%
1357
December1st to 15thNight
56%
720
21%
2520
19%
720
61%
720
23%
1562
December16th to endNight
48%
768
21%
2688
19%
768
55%
768
23%
1678

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
9%423323347%57%
47430
Night
10%5%24423347%50%
46733
TransparencyDay
29%37%19%24%16%
47117
Night
33%47%18%21%14%
46547
SeeingDay
10%10%26%33%14%3
5869
Night
11%5%9%33%31%7%
15239

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%2433445%6%43%
1552
16th to endDay
18%5%24424246%43%
1728
February1st to 15thDay
18%7%24323245%42%
1576
16th to endDay
18%7%3442345%7%38%
1571
March1st to 15thDay
16%7%25%43245%9%37%
1955
16th to endDay
13%6%35%5%2445%7%40%
2133
April1st to 15thDay
15%6%35%42335%7%42%
2149
16th to endDay
7%423313347%58%
2160
May1st to 15thDay
4312213348%63%
2262
16th to endDay
7%5%24312348%57%
2596
June1st to 15thDay
5%423314346%60%
2520
16th to endDay
2112212236%73%
2520
July1st to 15thDay
1212212246%71%
2475
16th to endDay
1212212236%73%
2468
August1st to 15thDay
1313212337%68%
2280
16th to endDay
1313212137%71%
2100
September1st to 15thDay
1312211235%72%
1980
16th to endDay
3312212235%70%
1826
October1st to 15thDay
6%322222336%63%
1650
16th to endDay
9%413312336%58%
1760
November1st to 15thDay
10%5%2422445%6%52%
1675
16th to endDay
14%7%24422346%47%
1518
December1st to 15thDay
18%7%34313435%42%
1440
16th to endDay
20%6%34423347%40%
1536
January1st to 15thNight
15%5%2432445%8%43%
2383
16th to endNight
17%6%24323346%45%
2496
February1st to 15thNight
16%6%24424445%42%
2276
16th to endNight
16%6%2342435%7%42%
1903
March1st to 15thNight
17%5%2432445%7%40%
2004
16th to endNight
15%5%34423346%45%
2091
April1st to 15thNight
12%6%244235%5%7%45%
1799
16th to endNight
7%424313346%58%
1800
May1st to 15thNight
3425%32325%8%58%
1685
16th to endNight
5%6%345%14346%54%
1515
June1st to 15thNight
4425%31346%7%55%
1440
16th to endNight
1212412346%67%
1440
July1st to 15thNight
121322435%10%61%
1482
16th to endNight
1435%5%35%47%9%47%
1701
August1st to 15thNight
25%27%6%345%6%11%44%
1595
16th to endNight
427%5%3246%10%51%
1750
September1st to 15thNight
2424323349%60%
1650
16th to endNight
2223322347%63%
1801
October1st to 15thNight
8%413322347%58%
1980
16th to endNight
8%41432435%5%55%
2112
November1st to 15thNight
9%423323348%54%
2183
16th to endNight
11%5%14423345%53%
2439
December1st to 15thNight
18%6%24324345%43%
2520
16th to endNight
20%5%24423336%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
39%412%19%15%8%
1552
16th to endDay
44%39%13%18%11%
1728
February1st to 15thDay
43%28%20%21%3
1576
16th to endDay
44%38%25%13%3
1571
March1st to 15thDay
44%311%21%13%5%
1955
16th to endDay
41%5%13%18%17%3
2133
April1st to 15thDay
41%314%19%18%2
2149
16th to endDay
27%312%26%22%6%
2160
May1st to 15thDay
21%36%31%28%8%
2262
16th to endDay
27%310%29%22%6%
2600
June1st to 15thDay
25%48%22%24%15%
2520
16th to endDay
15%2217%35%26%
2520
July1st to 15thDay
16%218%25%45%
2329
16th to endDay
14%328%26%44%
2313
August1st to 15thDay
19%3110%31%33%
2264
16th to endDay
16%1213%40%26%
2100
September1st to 15thDay
16%2212%33%32%
1980
16th to endDay
18%2225%31%20%
1826
October1st to 15thDay
23%26%22%27%17%
1650
16th to endDay
28%27%24%23%13%
1760
November1st to 15thDay
32%311%28%16%8%
1675
16th to endDay
39%38%19%23%5%
1518
December1st to 15thDay
45%110%18%19%4
1440
16th to endDay
43%311%18%17%5%
1536
January1st to 15thNight
38%411%20%16%9%
2383
16th to endNight
40%38%14%16%15%
2496
February1st to 15thNight
42%28%20%17%7%
2288
16th to endNight
41%310%26%14%2
1903
March1st to 15thNight
42%410%20%15%5%
2004
16th to endNight
40%412%19%18%5%
2091
April1st to 15thNight
37%414%21%19%3
1799
16th to endNight
27%412%26%21%9%
1800
May1st to 15thNight
27%27%23%28%11%
1686
16th to endNight
31%310%25%21%7%
1516
June1st to 15thNight
27%6%8%18%23%15%
1440
16th to endNight
18%3215%33%27%
1440
July1st to 15thNight
19%46%21%46%
1399
16th to endNight
29%6%26%17%36%
1593
August1st to 15thNight
33%6%7%22%29%
1586
16th to endNight
27%5%19%28%28%
1750
September1st to 15thNight
23%417%28%34%
1650
16th to endNight
21%3222%27%22%
1801
October1st to 15thNight
26%36%22%23%17%
1980
16th to endNight
29%45%22%23%15%
2112
November1st to 15thNight
29%411%29%17%8%
2183
16th to endNight
33%28%23%23%8%
2439
December1st to 15thNight
43%38%17%19%7%
2520
16th to endNight
42%411%16%18%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%7%24%26%17%1
180
16th to endDay
19%9%22%28%16%3
256
February1st to 15thDay
21%10%21%27%18%1
236
16th to endDay
22%11%24%26%12%1
237
March1st to 15thDay
22%12%27%19%14%3
270
16th to endDay
17%18%32%21%8%1
288
April1st to 15thDay
20%22%26%20%8%1
269
16th to endDay
13%24%27%25%7%1
270
May1st to 15thDay
8%15%39%29%6%
288
16th to endDay
11%14%24%34%12%2
330
June1st to 15thDay
6%15%36%33%6%2
315
16th to endDay
15%30%41%17%3
315
July1st to 15thDay
2222%51%19%1
305
16th to endDay
1224%46%16%8%
327
August1st to 15thDay
2426%43%18%5%
300
16th to endDay
225%50%15%4
268
September1st to 15thDay
3319%47%17%8%
255
16th to endDay
29%25%33%21%7%
255
October1st to 15thDay
8%8%28%35%12%5%
255
16th to endDay
13%8%29%26%19%2
272
November1st to 15thDay
10%7%20%23%31%6%
181
16th to endDay
10%17%24%28%17%
73
December1st to 15thDay
25%15%25%25%8%1
60
16th to endDay
15%18%18%21%21%3
64
January1st to 15thNight
17%38%34%28%8%
720
16th to endNight
19%49%32%26%7%
768
February1st to 15thNight
17%6%11%33%25%5%
704
16th to endNight
18%6%15%31%23%5%
632
March1st to 15thNight
20%5%10%29%29%5%
720
16th to endNight
15%7%15%33%24%2
768
April1st to 15thNight
12%11%16%34%21%3
719
16th to endNight
9%9%17%32%26%5%
720
May1st to 15thNight
6%313%43%29%4
606
16th to endNight
7%9%10%38%29%5%
394
June1st to 15thNight
46%13%44%28%2
360
16th to endNight
137%50%35%2
360
July1st to 15thNight
22335%49%7%
379
16th to endNight
34227%49%12%
564
August1st to 15thNight
5%5%431%43%9%
537
16th to endNight
325%34%46%8%
700
September1st to 15thNight
42428%47%12%
660
16th to endNight
326%33%41%12%
656
October1st to 15thNight
9%46%35%35%8%
660
16th to endNight
10%48%29%34%13%
704
November1st to 15thNight
9%310%33%34%8%
700
16th to endNight
13%5%9%33%28%9%
720
December1st to 15thNight
20%6%8%34%22%7%
720
16th to endNight
20%6%14%32%23%2
768
Page generated at 2017-08-13 11:16:20. Version ac04

Copyright 2017 A. Danko


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