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 2019-06-24.

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
66%
17504
29%
54025
25%
17466
71%
17466
43%
28228

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
59%
836
19%
2870
19%
836
63%
836
27%
1730
January16th to endNight
57%
896
23%
2912
22%
896
61%
896
27%
1788
February1st to 15thNight
56%
817
24%
2678
23%
816
63%
816
27%
1635
February16th to endNight
53%
736
26%
2212
22%
736
61%
736
32%
1326
March1st to 15thNight
54%
840
17%
2380
16%
840
56%
840
26%
1596
March16th to endNight
51%
896
20%
2416
14%
896
56%
896
33%
1512
April1st to 15thNight
52%
839
23%
2099
10%
839
58%
839
34%
1374
April16th to endNight
64%
832
27%
2080
13%
832
68%
832
52%
1123
May1st to 15thNight
68%
641
32%
1901
22%
641
74%
641
58%
882
May16th to endNight
69%
439
25%
1752
27%
438
75%
438
43%
751
June1st to 15thNight
70%
420
30%
1680
31%
420
81%
420
52%
644
June16th to endNight
80%
406
35%
1624
42%
406
87%
406
71%
510
July1st to 15thNight
87%
370
36%
1480
46%
370
91%
370
74%
455
July16th to endNight
88%
557
40%
1682
37%
524
92%
524
84%
583
August1st to 15thNight
83%
587
41%
1732
31%
584
86%
584
74%
702
August16th to endNight
91%
828
44%
2070
27%
828
93%
828
85%
904
September1st to 15thNight
87%
780
44%
1950
29%
780
90%
780
81%
874
September16th to endNight
82%
776
44%
2117
37%
776
87%
776
76%
903
October1st to 15thNight
72%
780
34%
2340
32%
780
79%
780
55%
1080
October16th to endNight
77%
832
37%
2496
38%
832
81%
832
53%
1196
November1st to 15thNight
66%
820
30%
2619
29%
820
73%
820
41%
1374
November16th to endNight
61%
840
23%
2859
23%
840
65%
840
31%
1611
December1st to 15thNight
56%
840
23%
2940
22%
840
62%
840
28%
1730
December16th to endNight
50%
896
22%
3136
18%
896
58%
896
23%
1945

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%
54797
Night
10%312213346%61%
54209
TransparencyDay
23%38%19%24%19%
54480
Night
25%49%19%23%19%
54026
SeeingDay
10%414%23%28%17%
8123
Night
11%214%35%31%4
17516

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
19%6%25%424446%39%
1725
16th to endDay
19%6%35%324346%41%
2016
February1st to 15thDay
18%6%14313346%45%
1846
16th to endDay
17%424323446%45%
1833
March1st to 15thDay
18%5%24424347%40%
2237
16th to endDay
15%5%2442345%7%44%
2512
April1st to 15thDay
13%5%345%24447%44%
2509
16th to endDay
5%312212247%64%
2485
May1st to 15thDay
321212247%71%
2706
16th to endDay
5%21322335%7%63%
3063
June1st to 15thDay
4212211246%71%
2940
16th to endDay
1112385%
2844
July1st to 15thDay
11112387%
2730
16th to endDay
1111387%
2729
August1st to 15thDay
11111386%
2471
16th to endDay
12388%
2484
September1st to 15thDay
1111112483%
2340
16th to endDay
211111125%79%
2169
October1st to 15thDay
412212345%71%
1950
16th to endDay
8%312323347%61%
2080
November1st to 15thDay
9%31332345%7%53%
1898
16th to endDay
15%5%15%423345%49%
1758
December1st to 15thDay
17%6%36%5%23246%42%
1680
16th to endDay
19%6%35%324346%40%
1792
January1st to 15thNight
17%5%14323338%45%
2870
16th to endNight
17%5%14423345%47%
2912
February1st to 15thNight
16%5%13324347%45%
2666
16th to endNight
16%31331245%6%50%
2212
March1st to 15thNight
17%5%25%425%438%41%
2380
16th to endNight
16%413224446%49%
2416
April1st to 15thNight
10%425%425%45%7%47%
2099
16th to endNight
6%212212237%66%
2080
May1st to 15thNight
411213237%70%
1901
16th to endNight
321231245%7%64%
1752
June1st to 15thNight
311113235%73%
1680
16th to endNight
11112384%
1624
July1st to 15thNight
111111288%
1560
16th to endNight
12389%
1789
August1st to 15thNight
11111111284%
1741
16th to endNight
1111387%
2070
September1st to 15thNight
1111112485%
1950
16th to endNight
111225%81%
2117
October1st to 15thNight
4222234471%
2340
16th to endNight
5%22212336%68%
2496
November1st to 15thNight
9%21232335%7%58%
2619
16th to endNight
13%313323446%52%
2859
December1st to 15thNight
19%41321235%7%47%
2940
16th to endNight
20%42332345%6%43%
3136

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
45%5%12%15%16%4
1725
16th to endDay
44%5%9%14%16%9%
2016
February1st to 15thDay
40%411%18%19%6%
1846
16th to endDay
39%5%10%25%15%3
1833
March1st to 15thDay
44%5%12%17%12%7%
2237
16th to endDay
40%5%12%19%17%3
2512
April1st to 15thDay
39%6%10%23%16%4
2509
16th to endDay
21%412%25%27%7%
2485
May1st to 15thDay
14%310%28%30%12%
2706
16th to endDay
21%5%14%29%21%9%
3067
June1st to 15thDay
15%310%24%24%20%
2940
16th to endDay
6%1415%36%35%
2844
July1st to 15thDay
5%138%30%50%
2581
16th to endDay
5%1312%24%52%
2573
August1st to 15thDay
7%1211%32%44%
2455
16th to endDay
41314%36%39%
2484
September1st to 15thDay
7%1412%33%40%
2340
16th to endDay
11%15%21%33%26%
2169
October1st to 15thDay
15%47%21%27%24%
1950
16th to endDay
24%38%23%26%14%
2080
November1st to 15thDay
29%412%26%18%8%
1898
16th to endDay
37%6%10%21%17%6%
1758
December1st to 15thDay
43%39%19%17%5%
1680
16th to endDay
45%5%10%17%16%4
1792
January1st to 15thNight
38%5%12%21%14%7%
2870
16th to endNight
39%5%9%15%16%13%
2912
February1st to 15thNight
38%5%9%18%18%9%
2678
16th to endNight
34%5%10%23%21%5%
2212
March1st to 15thNight
42%6%10%17%16%6%
2380
16th to endNight
35%5%12%21%19%6%
2416
April1st to 15thNight
34%7%12%20%18%6%
2099
16th to endNight
20%413%25%27%9%
2080
May1st to 15thNight
14%49%27%28%16%
1902
16th to endNight
18%415%28%21%11%
1752
June1st to 15thNight
14%311%24%25%21%
1680
16th to endNight
7%1415%31%40%
1624
July1st to 15thNight
6%118%28%53%
1480
16th to endNight
4211%24%56%
1682
August1st to 15thNight
9%1112%29%46%
1732
16th to endNight
5%1211%36%43%
2070
September1st to 15thNight
7%1311%35%41%
1950
16th to endNight
7%25%18%32%33%
2117
October1st to 15thNight
16%37%17%26%27%
2340
16th to endNight
18%37%21%26%22%
2496
November1st to 15thNight
25%412%26%19%11%
2619
16th to endNight
32%5%9%21%21%9%
2859
December1st to 15thNight
37%411%19%18%8%
2940
16th to endNight
40%6%10%18%18%6%
3136

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
33%318%20%19%5%
173
16th to endDay
21%5%15%24%19%13%
352
February1st to 15thDay
24%7%16%19%21%10%
326
16th to endDay
21%10%18%23%17%8%
340
March1st to 15thDay
22%10%23%18%16%8%
390
16th to endDay
20%11%17%22%19%8%
416
April1st to 15thDay
19%10%25%23%14%7%
389
16th to endDay
8%9%18%24%20%17%
378
May1st to 15thDay
5%420%30%25%12%
408
16th to endDay
8%417%22%26%20%
458
June1st to 15thDay
3316%24%32%18%
435
16th to endDay
1210%28%37%20%
408
July1st to 15thDay
1329%38%25%
365
16th to endDay
425%38%30%
391
August1st to 15thDay
15%21%44%26%
359
16th to endDay
5%18%42%32%
396
September1st to 15thDay
218%22%38%26%
375
16th to endDay
3213%25%28%26%
375
October1st to 15thDay
5%9%18%24%25%16%
375
16th to endDay
9%313%19%32%22%
400
November1st to 15thDay
12%312%20%36%15%
224
16th to endDay
20%16%28%23%9%
142
December1st to 15thDay
25%5%15%21%16%15%
120
16th to endDay
17%7%15%25%30%3
128
January1st to 15thNight
19%211%34%27%5%
840
16th to endNight
19%412%32%25%5%
896
February1st to 15thNight
17%415%32%26%3
824
16th to endNight
18%419%32%20%3
736
March1st to 15thNight
18%5%16%30%26%3
840
16th to endNight
17%421%31%23%1
896
April1st to 15thNight
12%424%33%22%2
839
16th to endNight
8%5%18%33%29%4
832
May1st to 15thNight
5%221%39%27%2
642
16th to endNight
4318%42%28%1
439
June1st to 15thNight
4121%41%29%1
420
16th to endNight
115%44%37%
406
July1st to 15thNight
19%50%37%1
370
16th to endNight
17%42%45%1
557
August1st to 15thNight
211%42%40%2
587
16th to endNight
6%39%49%2
828
September1st to 15thNight
18%32%52%4
780
16th to endNight
2112%32%40%10%
776
October1st to 15thNight
5%315%37%31%6%
780
16th to endNight
6%39%32%38%10%
832
November1st to 15thNight
10%115%33%33%5%
820
16th to endNight
14%215%34%27%4
840
December1st to 15thNight
21%214%31%22%7%
840
16th to endNight
23%316%29%24%1
896
Page generated at 2019-06-24 17:41:29. Version ac04

Copyright 2019 A. Danko


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