Rayville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rayville Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
54%
15654
25%
47627
19%
15608
60%
15608
33%
27988

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
38%
900
25%
2327
12%
895
46%
895
32%
1499
January16th to endNight
31%
960
25%
2496
10%
960
40%
960
29%
1658
February1st to 15thNight
34%
779
24%
2186
10%
776
43%
776
29%
1386
February16th to endNight
29%
622
26%
1884
10%
622
41%
622
27%
1188
March1st to 15thNight
38%
540
23%
1980
17%
540
49%
540
23%
1189
March16th to endNight
46%
576
22%
2097
18%
576
53%
576
29%
1185
April1st to 15thNight
44%
539
26%
1797
18%
539
56%
539
34%
989
April16th to endNight
49%
540
26%
1800
22%
540
58%
540
31%
1037
May1st to 15thNight
55%
540
22%
1800
20%
540
62%
540
30%
1053
May16th to endNight
66%
563
24%
1763
24%
561
70%
561
38%
972
June1st to 15thNight
78%
540
19%
1620
19%
540
81%
540
41%
889
June16th to endNight
74%
540
22%
1620
24%
540
75%
540
38%
916
July1st to 15thNight
80%
510
18%
1530
20%
510
80%
510
38%
868
July16th to endNight
84%
564
21%
1594
25%
531
85%
531
40%
885
August1st to 15thNight
83%
539
20%
1748
26%
536
83%
536
40%
930
August16th to endNight
73%
573
20%
1910
25%
573
73%
573
29%
1165
September1st to 15thNight
73%
540
23%
1800
26%
540
73%
540
33%
1032
September16th to endNight
75%
621
32%
1947
31%
621
76%
621
40%
1051
October1st to 15thNight
66%
720
30%
2160
26%
720
69%
720
42%
1169
October16th to endNight
60%
768
37%
2304
29%
768
67%
768
43%
1225
November1st to 15thNight
56%
700
31%
2100
25%
700
62%
700
38%
1168
November16th to endNight
45%
720
31%
2257
22%
720
55%
720
33%
1301
December1st to 15thNight
40%
800
24%
2411
16%
800
48%
800
27%
1521
December16th to endNight
36%
960
20%
2496
11%
960
42%
960
27%
1712

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
12%5%25%5%35%5%5%7%43%
48104
Night
11%42442345%7%49%
47826
TransparencyDay
38%5%11%20%18%5%
47805
Night
33%5%11%20%21%8%
47630
SeeingDay
11%213%23%30%17%
5695
Night
13%421%32%24%4
15654

By Month

Percentage Cloud Cover SE (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%6%24324335%44%
1611
16th to endDay
21%7%25%31233444%
1728
February1st to 15thDay
16%7%24423335%44%
1672
16th to endDay
18%6%25%5%22335%42%
1598
March1st to 15thDay
18%6%35%424445%41%
1980
16th to endDay
11%5%26%5%24447%44%
2125
April1st to 15thDay
13%325%434446%45%
2151
16th to endDay
12%5%25%4345%5%6%43%
2160
May1st to 15thDay
13%5%37%5%45%5%47%39%
2151
16th to endDay
7%325%446%7%6%9%40%
2347
June1st to 15thDay
6%4245%36%6%8%10%40%
2340
16th to endDay
6%3245%36%7%9%10%39%
2340
July1st to 15thDay
8%3246%46%6%7%11%36%
2340
16th to endDay
8%415%6%47%6%7%10%35%
2466
August1st to 15thDay
7%4145%46%6%6%10%42%
2202
16th to endDay
12%5%25%5%36%6%6%8%36%
2292
September1st to 15thDay
9%5%145%36%6%7%7%41%
2160
16th to endDay
10%3245%35%45%6%48%
1998
October1st to 15thDay
8%31342445%6%55%
1800
16th to endDay
14%31321223459%
1919
November1st to 15thDay
9%424423335%56%
1758
16th to endDay
15%5%25%32333449%
1698
December1st to 15thDay
20%7%245%3434438%
1540
16th to endDay
18%7%36%5%33336%38%
1728
January1st to 15thNight
16%5%25%32334449%
2327
16th to endNight
19%5%24423235%45%
2496
February1st to 15thNight
14%7%34423336%46%
2178
16th to endNight
18%5%3332334446%
1884
March1st to 15thNight
16%424424447%43%
1980
16th to endNight
13%5%23424345%50%
2097
April1st to 15thNight
9%22432445%7%53%
1797
16th to endNight
9%5%24425%35%6%50%
1800
May1st to 15thNight
9%425%435%5%5%9%45%
1799
16th to endNight
7%32342445%10%50%
1763
June1st to 15thNight
32144246%7%11%51%
1620
16th to endNight
5%3145%25%5%6%10%50%
1620
July1st to 15thNight
6%313426%47%13%46%
1620
16th to endNight
42132146%8%11%50%
1702
August1st to 15thNight
42133245%6%12%51%
1758
16th to endNight
9%4144346%8%10%41%
1910
September1st to 15thNight
8%3244345%6%8%49%
1800
16th to endNight
8%313313347%56%
1947
October1st to 15thNight
6%31342435%6%58%
2160
16th to endNight
11%31321233462%
2304
November1st to 15thNight
9%323323346%56%
2100
16th to endNight
14%424412235%53%
2257
December1st to 15thNight
18%6%25%322236%45%
2411
16th to endNight
18%7%35%42344442%
2496

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
42%36%19%21%7%
1612
16th to endDay
43%3417%22%7%
1728
February1st to 15thDay
43%36%18%20%7%
1674
16th to endDay
45%36%17%21%6%
1598
March1st to 15thDay
46%48%18%18%5%
1980
16th to endDay
39%5%11%19%21%2
2127
April1st to 15thDay
38%5%9%21%19%6%
2151
16th to endDay
39%5%10%20%20%4
2160
May1st to 15thDay
43%411%16%17%5%
2151
16th to endDay
35%6%16%26%13%1
2351
June1st to 15thDay
34%7%17%25%14%
2340
16th to endDay
34%10%15%21%16%2
2340
July1st to 15thDay
35%8%21%23%8%1
2201
16th to endDay
39%9%18%20%11%
2311
August1st to 15thDay
35%8%18%24%12%1
2188
16th to endDay
41%8%16%18%12%2
2292
September1st to 15thDay
38%7%13%19%15%5%
2160
16th to endDay
33%6%10%20%21%8%
1998
October1st to 15thDay
29%49%19%22%15%
1800
16th to endDay
29%2415%33%14%
1919
November1st to 15thDay
30%27%20%30%8%
1758
16th to endDay
38%25%15%27%9%
1698
December1st to 15thDay
48%37%17%15%6%
1540
16th to endDay
47%38%19%17%4
1728
January1st to 15thNight
38%36%15%26%8%
2327
16th to endNight
42%35%18%21%8%
2496
February1st to 15thNight
40%26%18%23%8%
2187
16th to endNight
41%35%18%21%10%
1884
March1st to 15thNight
40%49%17%20%7%
1980
16th to endNight
35%411%20%23%5%
2097
April1st to 15thNight
30%5%10%23%20%9%
1797
16th to endNight
33%5%9%20%24%6%
1800
May1st to 15thNight
34%6%10%19%21%7%
1800
16th to endNight
27%5%16%27%19%2
1765
June1st to 15thNight
24%7%17%31%17%1
1620
16th to endNight
27%7%17%24%19%4
1620
July1st to 15thNight
26%8%25%25%11%2
1530
16th to endNight
22%10%24%27%12%1
1594
August1st to 15thNight
23%7%24%25%15%3
1748
16th to endNight
33%9%19%18%14%4
1910
September1st to 15thNight
31%6%15%24%14%8%
1800
16th to endNight
26%5%11%19%25%12%
1947
October1st to 15thNight
26%49%18%24%16%
2160
16th to endNight
26%3414%31%20%
2304
November1st to 15thNight
29%48%18%27%11%
2100
16th to endNight
34%25%14%27%14%
2257
December1st to 15thNight
42%28%19%20%6%
2411
16th to endNight
45%27%17%19%5%
2496

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
20%6%32%22%17%1
90
16th to endDay
18%7%52%16%5%
96
February1st to 15thDay
13%10%42%27%6%
90
16th to endDay
13%9%39%29%6%1
81
March1st to 15thDay
26%8%37%23%3
90
16th to endDay
8%13%28%28%18%1
111
April1st to 15thDay
14%5%30%30%16%3
270
16th to endDay
14%7%21%30%24%1
270
May1st to 15thDay
13%420%35%22%4
288
16th to endDay
9%416%28%29%12%
434
June1st to 15thDay
9%15%25%41%16%
495
16th to endDay
7%5%26%37%22%
495
July1st to 15thDay
5%422%41%25%
475
16th to endDay
8%214%39%34%
515
August1st to 15thDay
10%111%42%33%
355
16th to endDay
15%311%34%34%
332
September1st to 15thDay
9%6%17%37%29%
315
16th to endDay
10%320%38%27%
248
October1st to 15thDay
214%27%36%17%
135
16th to endDay
13%225%20%24%13%
144
November1st to 15thDay
18%25%36%16%2
90
16th to endDay
18%333%23%12%8%
90
December1st to 15thDay
24%5%33%17%17%1
90
16th to endDay
15%17%33%20%9%3
96
January1st to 15thNight
18%7%30%33%9%
900
16th to endNight
23%6%34%30%5%
960
February1st to 15thNight
18%8%33%32%6%
779
16th to endNight
18%9%38%31%2
622
March1st to 15thNight
16%7%32%36%7%
540
16th to endNight
15%5%28%35%14%
576
April1st to 15thNight
9%6%37%32%12%1
539
16th to endNight
10%6%30%37%15%1
540
May1st to 15thNight
9%423%44%17%1
540
16th to endNight
8%114%38%31%4
563
June1st to 15thNight
27%36%47%4
540
16th to endNight
416%26%48%11%
540
July1st to 15thNight
6%228%50%11%
510
16th to endNight
4218%57%15%
564
August1st to 15thNight
5%220%48%21%
539
16th to endNight
11%1222%48%13%
573
September1st to 15thNight
9%16%30%42%8%
540
16th to endNight
9%15%33%43%6%
621
October1st to 15thNight
8%114%33%34%6%
720
16th to endNight
12%319%34%25%4
768
November1st to 15thNight
10%423%36%22%3
700
16th to endNight
16%5%28%31%16%2
720
December1st to 15thNight
21%7%27%33%10%
800
16th to endNight
22%8%27%30%9%
960
Page generated at 2017-11-01 16:23:40. Version ac04

Copyright 2017 A. Danko


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