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 2016-05-11.

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
37%
14225
17%
41759
11%
14183
44%
14183
23%
28177

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%
1705
13%
4725
4%
1700
29%
1700
17%
3503
FebruaryNight
24%
1306
15%
3755
5%
1306
31%
1306
18%
2688
MarchNight
29%
1229
14%
3822
10%
1229
34%
1229
17%
2692
AprilNight
32%
989
17%
3241
11%
989
42%
989
21%
2177
MayNight
44%
949
17%
2673
10%
948
50%
948
26%
1803
JuneNight
50%
900
15%
2400
9%
900
54%
900
30%
1593
JulyNight
66%
894
19%
2297
14%
861
69%
861
40%
1384
AugustNight
73%
926
21%
2905
21%
923
76%
923
39%
1603
SeptemberNight
60%
1049
27%
3152
23%
1049
65%
1049
36%
1808
OctoberNight
38%
1240
22%
3756
15%
1240
46%
1240
26%
2376
NovemberNight
28%
1333
20%
4259
12%
1333
38%
1333
21%
2789
DecemberNight
20%
1705
11%
4774
4%
1705
26%
1705
14%
3761

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
14%7%36%5%3445%7%35%
42208
Night
15%8%35%424446%39%
41928
Cloud CoverDay
14%8%36%5%3445%7%35%
42217
Night
15%8%35%424446%39%
41933
TransparencyDay
47%6%12%20%11%1
41894
Night
45%5%12%22%13%1
41760
SeeingDay
15%7%27%26%16%7%
3998
Night
18%8%29%29%13%1
14229

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
15%14%5%8%6%24446%26%
2753
Night
14%12%5%8%6%24345%32%
4725
FebruaryDay
16%13%5%8%5%35%436%28%
2963
Night
16%11%5%6%5%2344434%
3753
MarchDay
17%11%37%6%34446%29%
3677
Night
16%9%36%5%35%436%35%
3809
AprilDay
19%8%36%5%3445%6%33%
4006
Night
18%7%35%423446%38%
3241
MayDay
17%6%35%5%35%5%6%7%33%
4267
Night
15%5%15%5%35%5%6%8%39%
2672
JuneDay
12%5%35%5%35%6%6%8%36%
4200
Night
11%4245%35%5%5%8%41%
2400
JulyDay
8%325%5%36%5%6%9%42%
4335
Night
6%3134245%7%8%51%
2473
AugustDay
8%5%25%4345%6%9%42%
3881
Night
7%31342445%9%53%
2914
SeptemberDay
11%4244245%5%7%46%
3438
Night
10%413324447%52%
3152
OctoberDay
17%6%25%433347%40%
3061
Night
16%6%24423346%44%
3756
NovemberDay
17%8%46%423346%37%
2899
Night
16%8%35%423336%41%
4259
DecemberDay
20%13%5%7%6%34435%25%
2728
Night
23%12%48%5%24335%25%
4774

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%24446%26%
2753
Night
14%12%5%7%6%24445%32%
4725
FebruaryDay
16%13%5%7%5%34446%28%
2963
Night
16%11%5%6%5%2344434%
3746
MarchDay
17%11%37%6%3445%6%29%
3686
Night
17%9%36%5%24436%34%
3822
AprilDay
19%8%36%5%2445%6%33%
4006
Night
18%7%36%423346%38%
3241
MayDay
17%6%35%5%35%5%6%7%33%
4267
Night
14%5%15%5%35%5%5%8%39%
2671
JuneDay
12%5%35%5%35%6%6%8%36%
4200
Night
11%5%245%35%5%6%8%41%
2400
JulyDay
8%325%5%36%5%6%9%42%
4335
Night
6%3144245%7%8%51%
2473
AugustDay
9%425%435%5%6%9%42%
3881
Night
7%31342346%8%53%
2914
SeptemberDay
11%424425%45%7%46%
3438
Night
10%413424447%52%
3152
OctoberDay
17%6%25%5%33347%40%
3061
Night
16%6%24423346%44%
3756
NovemberDay
17%8%46%423346%37%
2899
Night
16%8%35%423336%41%
4259
DecemberDay
20%13%5%7%6%35%335%25%
2728
Night
23%12%48%5%33335%25%
4774

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
58%413%14%7%
2754
Night
54%5%13%17%9%
4725
FebruaryDay
57%5%11%17%6%1
2965
Night
52%412%20%8%1
3755
MarchDay
54%6%12%19%5%
3687
Night
51%5%12%18%9%1
3822
AprilDay
51%5%11%17%11%2
4006
Night
47%49%22%13%3
3241
MayDay
48%7%12%20%10%1
4271
Night
41%6%13%21%14%1
2674
JuneDay
42%8%12%22%13%1
4200
Night
38%6%13%23%15%2
2400
JulyDay
36%8%14%23%13%2
4019
Night
28%7%13%27%19%3
2297
AugustDay
35%7%13%24%16%2
3866
Night
27%5%14%27%20%4
2905
SeptemberDay
35%6%10%26%18%2
3438
Night
30%5%10%28%21%3
3152
OctoberDay
43%5%12%24%12%2
3061
Night
40%410%24%17%1
3756
NovemberDay
47%412%22%10%1
2899
Night
45%312%22%13%2
4259
DecemberDay
63%411%14%6%
2728
Night
62%410%16%5%
4774

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
MonthOccurrence of each ForecastData
Points
JanuaryDay
20%10%34%26%7%
93
Night
20%12%36%25%4
1705
FebruaryDay
27%18%34%12%42
87
Night
21%11%35%25%5%
1309
MarchDay
28%7%27%24%10%1
227
Night
21%10%33%24%9%
1229
AprilDay
20%12%27%23%12%3
420
Night
22%9%32%26%8%
989
MayDay
19%7%31%23%13%4
583
Night
16%5%27%34%15%
950
JuneDay
14%5%32%26%13%6%
690
Night
12%326%39%17%
900
JulyDay
8%428%26%19%12%
690
Night
7%116%42%27%3
894
AugustDay
7%315%32%25%15%
470
Night
7%111%44%30%4
926
SeptemberDay
10%218%29%28%10%
389
Night
11%417%33%28%4
1049
OctoberDay
15%8%24%32%15%3
166
Night
19%9%28%28%13%1
1240
NovemberDay
25%14%32%14%12%1
90
Night
20%11%34%24%8%
1333
DecemberDay
25%20%34%13%41
93
Night
29%10%33%22%4
1705
Page generated at 2016-05-12 12:52:10. Version ac04

Copyright 2016 A. Danko


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