Feather River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Feather River 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
68%
15185
28%
46942
26%
15150
72%
15150
42%
24863

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%
2476
20%
716
65%
716
29%
1429
January16th to endNight
56%
768
26%
2496
26%
768
60%
768
29%
1517
February1st to 15thNight
59%
697
23%
2288
24%
696
63%
696
27%
1412
February16th to endNight
56%
632
26%
1900
25%
632
61%
632
30%
1174
March1st to 15thNight
54%
720
17%
2049
16%
720
56%
720
27%
1359
March16th to endNight
50%
768
21%
2064
15%
768
54%
768
31%
1331
April1st to 15thNight
55%
719
22%
1799
13%
719
58%
719
34%
1181
April16th to endNight
65%
720
26%
1800
13%
720
68%
720
48%
1024
May1st to 15thNight
66%
529
30%
1609
21%
529
71%
529
53%
761
May16th to endNight
72%
374
27%
1496
31%
374
76%
374
40%
659
June1st to 15thNight
73%
360
25%
1440
32%
360
78%
360
46%
609
June16th to endNight
81%
360
35%
1440
45%
360
87%
360
63%
487
July1st to 15thNight
92%
340
34%
1360
47%
340
94%
340
76%
415
July16th to endNight
92%
491
41%
1522
41%
460
95%
460
84%
516
August1st to 15thNight
90%
547
39%
1620
32%
544
91%
544
73%
657
August16th to endNight
93%
764
45%
1910
29%
764
94%
764
85%
835
September1st to 15thNight
90%
720
43%
1800
29%
720
92%
720
81%
816
September16th to endNight
83%
688
43%
1871
38%
688
86%
688
74%
810
October1st to 15thNight
73%
660
32%
1980
32%
660
78%
660
52%
967
October16th to endNight
74%
704
35%
2112
36%
704
77%
704
48%
1060
November1st to 15thNight
71%
700
27%
2247
29%
700
74%
700
40%
1196
November16th to endNight
63%
720
24%
2455
26%
720
65%
720
32%
1378
December1st to 15thNight
57%
720
21%
2520
22%
720
61%
720
25%
1536
December16th to endNight
50%
768
21%
2688
20%
768
54%
768
22%
1734

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
10%312212235%63%
47967
Night
12%312212335%60%
47124
TransparencyDay
23%37%18%24%21%
47649
Night
26%38%18%22%20%
46943
SeeingDay
11%6%18%28%27%8%
5876
Night
12%211%32%34%6%
15198

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
20%413424245%46%
1459
16th to endDay
23%5%13223346%44%
1728
February1st to 15thDay
23%413213336%45%
1576
16th to endDay
22%6%12213447%42%
1574
March1st to 15thDay
22%314424346%40%
1909
16th to endDay
20%5%13413348%42%
2158
April1st to 15thDay
17%5%2432335%7%44%
2149
16th to endDay
9%412212436%60%
2160
May1st to 15thDay
5%32212347%66%
2337
16th to endDay
6%313312446%63%
2615
June1st to 15thDay
5%31321324466%
2520
16th to endDay
211112384%
2520
July1st to 15thDay
112287%
2520
16th to endDay
111288%
2539
August1st to 15thDay
111111287%
2330
16th to endDay
112289%
2292
September1st to 15thDay
1111111384%
2160
16th to endDay
311111135%77%
1923
October1st to 15thDay
6%2221343467%
1650
16th to endDay
11%312313346%57%
1760
November1st to 15thDay
12%312324448%51%
1609
16th to endDay
19%412312325%51%
1503
December1st to 15thDay
22%424323445%42%
1440
16th to endDay
26%5%24223335%40%
1536
January1st to 15thNight
18%413322347%48%
2476
16th to endNight
21%42332232449%
2496
February1st to 15thNight
20%5%13233447%43%
2276
16th to endNight
21%42231335%5%46%
1900
March1st to 15thNight
22%423323447%39%
2049
16th to endNight
18%5%24313346%46%
2064
April1st to 15thNight
12%5%2443345%8%44%
1799
16th to endNight
9%312213337%61%
1800
May1st to 15thNight
5%212212335%68%
1609
16th to endNight
5%21232245%6%63%
1496
June1st to 15thNight
432212346%67%
1440
16th to endNight
2111222380%
1440
July1st to 15thNight
111111187%
1440
16th to endNight
121289%
1627
August1st to 15thNight
11111112283%
1629
16th to endNight
1122386%
1910
September1st to 15thNight
1111112385%
1800
16th to endNight
2111123480%
1871
October1st to 15thNight
7%212212335%67%
1980
16th to endNight
8%31221225%6%63%
2112
November1st to 15thNight
12%31221335%7%56%
2247
16th to endNight
15%413323346%51%
2455
December1st to 15thNight
24%313313336%45%
2520
16th to endNight
27%412313445%41%
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
40%49%19%17%7%
1459
16th to endDay
42%47%14%18%13%
1728
February1st to 15thDay
40%311%19%19%5%
1576
16th to endDay
40%49%28%14%2
1574
March1st to 15thDay
43%5%10%18%14%7%
1909
16th to endDay
41%6%12%19%16%4
2158
April1st to 15thDay
38%410%23%18%4
2149
16th to endDay
24%410%25%26%8%
2160
May1st to 15thDay
17%39%26%31%12%
2337
16th to endDay
21%412%27%24%9%
2619
June1st to 15thDay
20%5%9%20%22%22%
2520
16th to endDay
7%1414%35%36%
2520
July1st to 15thDay
5%129%28%52%
2371
16th to endDay
5%1210%23%57%
2382
August1st to 15thDay
6%1210%32%46%
2314
16th to endDay
4111%38%42%
2292
September1st to 15thDay
7%1312%33%41%
2160
16th to endDay
11%25%22%33%24%
1923
October1st to 15thDay
17%48%21%28%19%
1650
16th to endDay
26%5%6%21%24%15%
1760
November1st to 15thDay
29%5%12%27%16%9%
1609
16th to endDay
36%48%22%19%8%
1503
December1st to 15thDay
43%48%16%21%4
1440
16th to endDay
45%47%16%18%6%
1536
January1st to 15thNight
36%412%19%18%9%
2476
16th to endNight
39%38%14%18%16%
2496
February1st to 15thNight
40%49%18%17%10%
2288
16th to endNight
37%5%8%25%19%4
1900
March1st to 15thNight
43%410%16%16%7%
2049
16th to endNight
38%5%10%20%17%7%
2064
April1st to 15thNight
35%6%12%21%15%8%
1799
16th to endNight
23%412%22%26%11%
1800
May1st to 15thNight
17%49%24%28%15%
1610
16th to endNight
20%5%12%28%22%10%
1496
June1st to 15thNight
16%6%12%21%22%21%
1440
16th to endNight
9%2414%29%40%
1440
July1st to 15thNight
6%29%24%56%
1360
16th to endNight
4211%20%60%
1522
August1st to 15thNight
8%1212%30%44%
1620
16th to endNight
5%312%32%46%
1910
September1st to 15thNight
7%139%34%43%
1800
16th to endNight
8%25%17%35%31%
1871
October1st to 15thNight
19%36%19%27%23%
1980
16th to endNight
21%37%21%26%19%
2112
November1st to 15thNight
26%5%13%26%17%10%
2247
16th to endNight
33%47%23%20%11%
2455
December1st to 15thNight
40%49%17%19%7%
2520
16th to endNight
44%5%8%13%19%8%
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
40%413%27%12%1
87
16th to endDay
23%9%16%24%20%6%
256
February1st to 15thDay
25%5%17%25%23%3
236
16th to endDay
26%9%18%24%16%5%
237
March1st to 15thDay
28%10%21%17%16%5%
270
16th to endDay
22%11%22%25%15%2
288
April1st to 15thDay
18%10%27%25%13%4
269
16th to endDay
12%16%25%25%15%4
270
May1st to 15thDay
7%9%29%30%19%4
288
16th to endDay
6%9%17%24%32%10%
330
June1st to 15thDay
6%6%21%32%24%7%
315
16th to endDay
1316%36%30%10%
315
July1st to 15thDay
119%36%41%8%
305
16th to endDay
13%32%43%10%
327
August1st to 15thDay
1114%28%41%12%
315
16th to endDay
12%29%40%16%
332
September1st to 15thDay
1112%34%36%13%
315
16th to endDay
36%19%27%30%13%
284
October1st to 15thDay
6%7%24%22%26%12%
255
16th to endDay
16%418%27%27%5%
272
November1st to 15thDay
15%11%22%35%14%
115
16th to endDay
22%118%35%22%
71
December1st to 15thDay
36%10%20%25%8%
60
16th to endDay
18%320%23%29%4
64
January1st to 15thNight
20%18%33%28%7%
720
16th to endNight
22%211%33%23%7%
768
February1st to 15thNight
20%38%34%28%4
704
16th to endNight
20%412%33%23%5%
632
March1st to 15thNight
22%412%29%25%5%
720
16th to endNight
19%418%29%25%2
768
April1st to 15thNight
13%6%17%35%23%4
719
16th to endNight
10%415%33%29%6%
720
May1st to 15thNight
7%119%34%31%4
530
16th to endNight
4413%33%41%3
375
June1st to 15thNight
5%116%36%36%4
360
16th to endNight
212%33%46%4
360
July1st to 15thNight
336%53%5%
340
16th to endNight
426%61%6%
491
August1st to 15thNight
1333%53%7%
547
16th to endNight
429%58%6%
764
September1st to 15thNight
15%24%57%9%
720
16th to endNight
318%31%39%15%
688
October1st to 15thNight
8%211%33%33%10%
660
16th to endNight
9%29%31%35%11%
704
November1st to 15thNight
13%110%32%34%8%
700
16th to endNight
15%212%33%29%7%
720
December1st to 15thNight
24%211%32%21%7%
720
16th to endNight
27%213%32%22%1
768
Page generated at 2017-09-24 06:15:56. Version ac04

Copyright 2017 A. Danko


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