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 2018-02-22.

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%
16004
26%
48941
23%
15968
67%
15968
34%
28231

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
60%
776
18%
2583
18%
776
63%
776
27%
1583
January16th to endNight
58%
832
24%
2704
24%
832
61%
832
27%
1669
February1st to 15thNight
56%
758
26%
2483
25%
758
63%
758
28%
1493
February16th to endNight
52%
660
25%
1988
21%
660
60%
660
28%
1256
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%
550
26%
1623
21%
547
68%
547
31%
954
August16th to endNight
75%
764
31%
1910
19%
764
75%
764
44%
1143
September1st to 15thNight
78%
720
34%
1800
25%
720
78%
720
50%
1033
September16th to endNight
78%
716
39%
1965
35%
716
81%
716
53%
1000
October1st to 15thNight
71%
720
30%
2160
31%
720
76%
720
46%
1109
October16th to endNight
70%
768
33%
2304
35%
768
73%
768
39%
1273
November1st to 15thNight
68%
760
26%
2370
26%
760
72%
760
36%
1335
November16th to endNight
61%
780
25%
2642
27%
780
64%
780
31%
1491
December1st to 15thNight
58%
780
22%
2730
21%
780
63%
780
25%
1635
December16th to endNight
49%
832
22%
2912
20%
832
56%
832
23%
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%423323347%57%
49313
Night
10%5%24423347%50%
49128
TransparencyDay
29%37%19%24%16%
49000
Night
33%37%18%21%15%
48942
SeeingDay
10%10%26%32%15%4
6501
Night
11%5%9%33%32%7%
16016

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
18%5%2433445%6%41%
1682
16th to endDay
17%5%25%5%24346%42%
1872
February1st to 15thDay
17%7%2432325%6%44%
1711
16th to endDay
18%7%3442345%7%39%
1632
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%67%
2328
16th to endDay
313212137%72%
2292
September1st to 15thDay
1312211236%71%
2160
16th to endDay
3211212235%70%
1992
October1st to 15thDay
6%322212336%65%
1800
16th to endDay
8%413312336%59%
1920
November1st to 15thDay
10%5%25%22435%6%51%
1818
16th to endDay
14%7%24422346%46%
1644
December1st to 15thDay
17%7%34313435%44%
1560
16th to endDay
18%7%34423346%40%
1664
January1st to 15thNight
16%5%2432445%8%41%
2583
16th to endNight
17%6%24323346%44%
2704
February1st to 15thNight
15%5%24424446%45%
2471
16th to endNight
15%6%2442435%7%43%
1988
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%28%6%345%6%11%44%
1632
16th to endNight
327%6%335%6%10%51%
1910
September1st to 15thNight
2424323348%59%
1800
16th to endNight
2223322347%65%
1965
October1st to 15thNight
7%313212337%61%
2160
16th to endNight
8%41422435%6%55%
2304
November1st to 15thNight
9%423324348%52%
2370
16th to endNight
12%5%14423345%51%
2642
December1st to 15thNight
16%6%24224346%45%
2730
16th to endNight
19%5%24323336%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
41%412%19%15%7%
1682
16th to endDay
44%39%14%18%10%
1872
February1st to 15thDay
41%28%20%22%4
1711
16th to endDay
43%38%25%14%4
1632
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%3111%31%33%
2312
16th to endDay
15%2113%39%27%
2292
September1st to 15thDay
16%2214%32%30%
2160
16th to endDay
17%2225%32%19%
1992
October1st to 15thDay
22%25%21%25%22%
1800
16th to endDay
27%28%22%24%14%
1920
November1st to 15thDay
33%311%29%15%7%
1818
16th to endDay
39%38%20%23%4
1644
December1st to 15thDay
43%19%17%19%8%
1560
16th to endDay
44%311%17%17%5%
1664
January1st to 15thNight
39%411%20%15%8%
2583
16th to endNight
41%310%14%16%14%
2704
February1st to 15thNight
39%27%20%19%9%
2483
16th to endNight
40%310%26%15%3
1988
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
34%6%7%22%29%
1623
16th to endNight
27%5%18%27%29%
1910
September1st to 15thNight
24%418%27%33%
1800
16th to endNight
20%3223%27%22%
1965
October1st to 15thNight
24%26%21%23%22%
2160
16th to endNight
28%35%20%22%17%
2304
November1st to 15thNight
31%411%28%16%7%
2370
16th to endNight
34%28%22%22%7%
2642
December1st to 15thNight
40%38%16%19%11%
2730
16th to endNight
42%410%16%18%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
25%6%22%26%17%1
220
16th to endDay
18%9%23%28%17%3
304
February1st to 15thDay
18%9%23%27%17%2
281
16th to endDay
21%12%25%25%12%1
262
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
15%26%42%18%5%
315
16th to endDay
222%46%20%7%
332
September1st to 15thDay
4420%44%19%7%
315
16th to endDay
29%24%33%21%7%
315
October1st to 15thDay
6%8%30%34%12%5%
315
16th to endDay
11%7%26%25%21%6%
336
November1st to 15thDay
11%8%21%24%29%5%
234
16th to endDay
14%11%22%31%19%
109
December1st to 15thDay
16%12%21%23%18%7%
90
16th to endDay
13%17%16%22%26%3
96
January1st to 15thNight
17%38%33%28%7%
780
16th to endNight
18%49%33%27%7%
832
February1st to 15thNight
16%6%11%33%26%6%
764
16th to endNight
17%6%15%31%23%5%
660
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%6%431%43%9%
550
16th to endNight
22434%45%9%
764
September1st to 15thNight
5%25%29%45%12%
720
16th to endNight
326%34%40%11%
716
October1st to 15thNight
9%47%36%34%8%
720
16th to endNight
9%47%27%35%14%
768
November1st to 15thNight
9%39%36%32%8%
760
16th to endNight
14%49%33%28%9%
780
December1st to 15thNight
19%6%8%34%24%7%
780
16th to endNight
20%6%14%30%25%2
832
Page generated at 2018-02-23 08:21:35. Version ac04

Copyright 2018 A. Danko


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