Yuba City Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yuba City Astronomical Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
67%
15231
29%
46950
25%
15193
72%
15193
43%
24452

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
62%
716
19%
2458
19%
716
65%
716
29%
1434
January16th to endNight
57%
768
25%
2496
24%
768
62%
768
28%
1504
February1st to 15thNight
56%
697
23%
2288
22%
696
62%
696
26%
1416
February16th to endNight
55%
632
26%
1900
22%
632
62%
632
32%
1146
March1st to 15thNight
56%
720
17%
2040
16%
720
59%
720
27%
1346
March16th to endNight
51%
768
21%
2070
14%
768
56%
768
33%
1293
April1st to 15thNight
54%
719
23%
1799
10%
719
60%
719
35%
1166
April16th to endNight
62%
720
26%
1800
12%
720
67%
720
50%
989
May1st to 15thNight
66%
549
30%
1629
21%
549
71%
549
57%
760
May16th to endNight
71%
375
28%
1496
30%
374
78%
374
48%
596
June1st to 15thNight
68%
360
27%
1440
29%
360
78%
360
50%
567
June16th to endNight
79%
360
36%
1440
44%
360
86%
360
69%
463
July1st to 15thNight
87%
340
35%
1360
45%
340
91%
340
75%
415
July16th to endNight
88%
513
41%
1542
38%
480
92%
480
84%
534
August1st to 15thNight
82%
550
39%
1623
30%
547
85%
547
73%
664
August16th to endNight
90%
764
45%
1910
28%
764
92%
764
84%
840
September1st to 15thNight
87%
720
42%
1800
28%
720
90%
720
80%
809
September16th to endNight
81%
688
45%
1872
37%
688
86%
688
76%
804
October1st to 15thNight
74%
660
33%
1980
33%
660
79%
660
54%
927
October16th to endNight
74%
704
35%
2112
35%
704
78%
704
48%
1056
November1st to 15thNight
67%
700
28%
2236
26%
700
73%
700
41%
1171
November16th to endNight
62%
720
24%
2451
24%
720
66%
720
33%
1334
December1st to 15thNight
54%
720
21%
2520
19%
720
60%
720
26%
1527
December16th to endNight
49%
768
21%
2688
18%
768
56%
768
22%
1691

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%312212235%64%
47962
Night
9%312213335%62%
47134
TransparencyDay
23%38%19%24%20%
47645
Night
24%49%19%23%19%
46951
SeeingDay
9%414%24%28%18%
5907
Night
11%214%35%31%4
15243

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%24323446%43%
1477
16th to endDay
19%5%24423346%43%
1728
February1st to 15thDay
18%5%24313346%45%
1576
16th to endDay
18%424323447%44%
1574
March1st to 15thDay
17%5%24424347%42%
1917
16th to endDay
14%5%245%2335%7%44%
2154
April1st to 15thDay
12%42442445%8%46%
2149
16th to endDay
6%322212246%64%
2160
May1st to 15thDay
322212246%71%
2319
16th to endDay
421321335%6%64%
2615
June1st to 15thDay
4212212246%69%
2520
16th to endDay
1112484%
2520
July1st to 15thDay
1111388%
2520
16th to endDay
111388%
2517
August1st to 15thDay
11111386%
2328
16th to endDay
12388%
2292
September1st to 15thDay
1111112484%
2160
16th to endDay
321111125%78%
1921
October1st to 15thDay
412213345%70%
1650
16th to endDay
9%312323336%59%
1760
November1st to 15thDay
9%31332445%7%52%
1622
16th to endDay
14%5%14313345%51%
1507
December1st to 15thDay
18%6%36%5%2323443%
1440
16th to endDay
20%6%35%324246%40%
1536
January1st to 15thNight
15%413323338%49%
2458
16th to endNight
17%5%2342333450%
2496
February1st to 15thNight
16%5%23425%45%7%43%
2276
16th to endNight
16%31331245%6%49%
1900
March1st to 15thNight
16%5%25%425%348%42%
2040
16th to endNight
15%413224447%49%
2070
April1st to 15thNight
10%414325%46%7%48%
1799
16th to endNight
7%112212237%65%
1800
May1st to 15thNight
411213337%70%
1629
16th to endNight
221221235%6%67%
1496
June1st to 15thNight
421113235%72%
1440
16th to endNight
1111123382%
1440
July1st to 15thNight
11111188%
1440
16th to endNight
11289%
1649
August1st to 15thNight
11121111284%
1632
16th to endNight
1112486%
1910
September1st to 15thNight
1111112485%
1800
16th to endNight
1111225%81%
1872
October1st to 15thNight
5%2222345%69%
1980
16th to endNight
6%22322337%65%
2112
November1st to 15thNight
9%21231335%6%58%
2236
16th to endNight
12%313313346%54%
2451
December1st to 15thNight
20%5%13212246%46%
2520
16th to endNight
22%42331345%6%43%
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
41%413%15%18%5%
1477
16th to endDay
42%5%9%14%17%11%
1728
February1st to 15thDay
39%411%18%19%5%
1576
16th to endDay
40%5%11%26%14%3
1574
March1st to 15thDay
41%5%13%18%13%7%
1917
16th to endDay
40%5%12%18%17%4
2154
April1st to 15thDay
37%5%10%22%17%5%
2149
16th to endDay
22%413%23%26%9%
2160
May1st to 15thDay
14%39%26%32%13%
2319
16th to endDay
20%5%12%28%23%10%
2619
June1st to 15thDay
17%410%22%23%21%
2520
16th to endDay
6%15%15%36%35%
2520
July1st to 15thDay
4139%30%50%
2371
16th to endDay
41311%22%55%
2361
August1st to 15thDay
7%1211%31%45%
2312
16th to endDay
41314%36%39%
2292
September1st to 15thDay
7%15%12%32%40%
2160
16th to endDay
12%26%22%33%23%
1921
October1st to 15thDay
16%47%23%28%19%
1650
16th to endDay
26%38%23%26%11%
1760
November1st to 15thDay
29%5%12%27%17%7%
1622
16th to endDay
35%6%9%23%18%6%
1507
December1st to 15thDay
45%38%20%17%3
1440
16th to endDay
45%410%16%16%5%
1536
January1st to 15thNight
35%5%12%21%16%8%
2458
16th to endNight
38%49%15%17%14%
2496
February1st to 15thNight
39%5%10%18%17%9%
2288
16th to endNight
34%5%10%24%20%4
1900
March1st to 15thNight
41%5%10%18%16%7%
2040
16th to endNight
34%5%13%20%19%7%
2070
April1st to 15thNight
33%7%12%20%17%8%
1799
16th to endNight
21%414%22%27%11%
1800
May1st to 15thNight
15%49%25%28%17%
1630
16th to endNight
15%315%28%24%12%
1496
June1st to 15thNight
15%311%24%23%21%
1440
16th to endNight
8%1414%30%40%
1440
July1st to 15thNight
6%118%28%54%
1360
16th to endNight
4210%22%58%
1542
August1st to 15thNight
9%1113%29%45%
1623
16th to endNight
5%1311%36%43%
1910
September1st to 15thNight
7%1411%34%41%
1800
16th to endNight
7%26%19%34%30%
1872
October1st to 15thNight
17%38%19%28%22%
1980
16th to endNight
21%38%22%25%18%
2112
November1st to 15thNight
25%5%13%26%20%9%
2236
16th to endNight
31%49%23%22%9%
2451
December1st to 15thNight
39%411%19%18%6%
2520
16th to endNight
41%6%9%15%19%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
35%320%17%19%4
105
16th to endDay
19%6%17%22%18%15%
256
February1st to 15thDay
23%5%16%18%23%11%
236
16th to endDay
23%8%15%21%18%11%
237
March1st to 15thDay
19%11%21%17%18%11%
270
16th to endDay
19%12%18%21%19%9%
288
April1st to 15thDay
16%9%24%26%14%8%
269
16th to endDay
10%11%20%28%18%11%
270
May1st to 15thDay
6%5%22%31%22%11%
288
16th to endDay
7%315%22%26%23%
330
June1st to 15thDay
5%317%27%30%15%
315
16th to endDay
228%26%37%21%
315
July1st to 15thDay
430%39%24%
305
16th to endDay
5%29%37%27%
327
August1st to 15thDay
16%23%44%23%
315
16th to endDay
6%18%42%31%
332
September1st to 15thDay
28%22%36%29%
315
16th to endDay
4314%25%25%27%
284
October1st to 15thDay
5%6%18%23%24%21%
255
16th to endDay
13%415%23%27%15%
272
November1st to 15thDay
11%310%17%37%18%
128
16th to endDay
15%122%33%26%
71
December1st to 15thDay
35%6%20%26%8%3
60
16th to endDay
17%315%26%35%1
64
January1st to 15thNight
17%212%34%27%5%
720
16th to endNight
19%411%31%25%6%
768
February1st to 15thNight
17%414%32%27%3
704
16th to endNight
18%418%33%21%4
632
March1st to 15thNight
17%414%31%28%3
720
16th to endNight
17%5%22%30%23%1
768
April1st to 15thNight
11%423%34%22%2
719
16th to endNight
8%5%18%35%27%3
720
May1st to 15thNight
6%222%39%26%2
550
16th to endNight
2418%43%29%1
375
June1st to 15thNight
4122%42%27%
360
16th to endNight
116%42%38%1
360
July1st to 15thNight
19%51%36%1
340
16th to endNight
18%43%44%2
513
August1st to 15thNight
211%42%39%2
550
16th to endNight
7%40%49%2
764
September1st to 15thNight
17%31%53%5%
720
16th to endNight
213%32%40%10%
688
October1st to 15thNight
6%213%37%32%6%
660
16th to endNight
7%39%33%36%8%
704
November1st to 15thNight
10%115%32%34%5%
700
16th to endNight
13%215%35%28%4
720
December1st to 15thNight
22%215%31%21%6%
720
16th to endNight
25%416%28%23%2
768
Page generated at 2017-09-24 06:15:58. Version ac04

Copyright 2017 A. Danko


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