This page made possible by the sponsorship of: Naperville Astronomical Association.

Riley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Riley Observatory clear sky chart from 2005-11-05 to 2013-10-19.

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
38%
10644
18%
31193
12%
10599
44%
10599
23%
21116

By Month

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
JanuaryNight
21%
1240
13%
3432
4%
1235
28%
1235
16%
2593
FebruaryNight
22%
942
13%
2711
5%
942
29%
942
16%
1987
MarchNight
31%
894
14%
2780
10%
894
36%
894
17%
1971
AprilNight
31%
719
17%
2357
11%
719
41%
719
20%
1601
MayNight
46%
724
19%
2036
12%
723
51%
723
27%
1353
JuneNight
50%
687
18%
1831
11%
687
55%
687
32%
1195
JulyNight
67%
708
20%
1801
16%
675
70%
675
39%
1092
AugustNight
72%
743
23%
2322
22%
737
75%
737
40%
1265
SeptemberNight
60%
839
27%
2520
22%
839
65%
839
35%
1462
OctoberNight
39%
944
22%
2851
17%
944
46%
944
25%
1815
NovemberNight
32%
964
19%
3080
13%
964
40%
964
21%
2026
DecemberNight
20%
1240
11%
3472
4%
1240
25%
1240
13%
2756

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
15%7%6%5%5%7%36%
31905
Night
15%7%5%6%39%
31369
Cloud CoverDay
15%7%5%5%5%7%36%
31415
Night
15%7%5%6%40%
30509
TransparencyDay
7%14%23%13%
28021
Night
5%13%25%14%
27599
SeeingDay
5%25%29%19%9%
2195
Night
8%28%31%13%
10275

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthOccurrence of each ForecastData
Points
JanuaryDay
16%14%5%9%6%5%26%
2000
Night
15%12%6%8%6%30%
3432
FebruaryDay
18%13%5%8%5%6%27%
2137
Night
19%11%5%6%33%
2709
MarchDay
17%11%7%5%7%29%
2671
Night
16%9%6%5%5%6%34%
2767
AprilDay
21%8%5%5%5%6%32%
2911
Night
20%7%5%6%37%
2357
MayDay
17%6%5%5%5%5%6%6%34%
3257
Night
14%5%5%5%5%5%8%40%
2035
JuneDay
13%5%5%5%6%6%8%38%
3205
Night
10%5%5%5%5%8%43%
1831
JulyDay
8%5%5%5%5%7%9%41%
3467
Night
7%5%5%8%8%50%
1977
AugustDay
9%5%6%8%44%
3105
Night
7%5%8%55%
2338
SeptemberDay
12%5%6%47%
2741
Night
11%7%52%
2520
OctoberDay
18%6%5%5%7%40%
2329
Night
17%6%6%44%
2851
NovemberDay
17%8%5%7%38%
2098
Night
17%8%5%6%40%
3080
DecemberDay
21%13%5%7%6%5%26%
1984
Night
24%12%5%8%5%25%
3472

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
MonthOccurrence of each ForecastData
Points
JanuaryDay
15%14%5%8%6%5%27%
1749
Night
15%12%6%8%6%30%
3001
FebruaryDay
18%13%5%8%5%6%27%
2137
Night
19%11%5%6%33%
2702
MarchDay
17%11%7%5%6%29%
2680
Night
17%9%6%5%5%6%34%
2780
AprilDay
21%8%5%5%5%6%32%
2911
Night
20%7%5%6%37%
2357
MayDay
17%6%5%5%5%5%5%6%34%
3257
Night
14%5%5%5%5%8%40%
2034
JuneDay
12%5%5%6%6%7%38%
3205
Night
10%5%5%5%5%8%43%
1831
JulyDay
8%5%5%5%5%7%9%41%
3467
Night
6%5%5%7%8%50%
1977
AugustDay
9%5%6%8%44%
3105
Night
7%5%8%55%
2338
SeptemberDay
12%6%47%
2741
Night
11%6%52%
2520
OctoberDay
17%6%5%5%6%40%
2329
Night
17%6%6%44%
2851
NovemberDay
17%8%5%6%38%
2098
Night
17%8%5%6%40%
3080
DecemberDay
20%13%5%7%5%5%5%27%
1736
Night
23%11%5%7%5%27%
3038

Transparency (when cloud cover <= 30%)
Color Meanings:
Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
5%16%18%6%
1691
Night
6%14%22%8%
2874
FebruaryDay
6%14%19%6%
1823
Night
5%15%23%7%
2337
MarchDay
7%16%23%5%
2259
Night
7%17%21%8%
2360
AprilDay
6%13%19%12%
2553
Night
5%12%22%15%
2075
MayDay
7%14%23%12%
2834
Night
7%16%24%16%
1797
JuneDay
9%14%25%16%
2832
Night
7%15%25%18%
1627
JulyDay
8%15%24%15%
2918
Night
8%16%27%20%
1688
AugustDay
7%14%25%19%
2890
Night
5%13%29%22%5%
2187
SeptemberDay
7%11%25%21%
2567
Night
5%11%27%23%
2397
OctoberDay
5%12%25%13%
2181
Night
10%27%17%
2653
NovemberDay
5%15%28%10%
1810
Night
15%26%13%
2688
DecemberDay
5%14%18%5%
1663
Night
11%21%5%
2916

Seeing (when cloud cover <= 80%)
Color Meanings:
Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthOccurrence of each ForecastData
Points
JanuaryNight
12%36%27%5%
1176
FebruaryNight
11%35%25%6%
909
MarchDay
26%29%15%
91
Night
10%34%26%10%
845
AprilDay
12%28%27%9%
232
Night
10%32%29%7%
691
MayDay
7%28%27%16%6%
364
Night
6%26%37%15%
700
JuneDay
5%34%26%15%6%
445
Night
28%41%16%
674
JulyDay
26%30%19%11%
467
Night
15%45%28%
698
AugustDay
13%35%25%16%
303
Night
13%45%29%
737
SeptemberDay
18%23%30%11%
235
Night
17%35%26%
829
OctoberDay
20%36%22%6%
58
Night
10%26%28%14%
922
NovemberNight
10%34%28%9%
919
DecemberNight
10%33%24%
1175
Page generated at 2013-10-20 22:37:00. Version ac01


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