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 2016-11-15.

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%
14851
17%
43589
11%
14809
44%
14809
24%
29228

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%
1009
17%
2835
10%
1008
50%
1008
27%
1905
JuneNight
51%
990
16%
2640
10%
990
55%
990
32%
1718
JulyNight
66%
987
19%
2545
14%
954
68%
954
40%
1533
AugustNight
73%
1019
21%
3198
21%
1016
75%
1016
38%
1777
SeptemberNight
60%
1155
27%
3468
23%
1155
65%
1155
36%
1994
OctoberNight
39%
1364
22%
4133
15%
1364
47%
1364
27%
2593
NovemberNight
29%
1393
20%
4453
13%
1393
39%
1393
22%
2887
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%36%
44511
Night
15%7%35%424446%40%
43758
Cloud CoverDay
14%7%36%5%3445%7%36%
44520
Night
15%7%35%424446%40%
43763
TransparencyDay
46%6%12%21%11%1
44197
Night
44%5%12%22%13%2
43590
SeeingDay
14%7%27%27%16%7%
4796
Night
18%8%28%30%13%1
14855

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%36%5%35%5%5%7%34%
4545
Night
14%5%145%35%5%6%8%39%
2834
JuneDay
11%5%35%5%35%6%6%8%38%
4620
Night
11%4245%35%5%5%8%43%
2640
JulyDay
7%325%5%36%5%7%9%42%
4769
Night
6%3144245%7%8%51%
2721
AugustDay
8%5%25%4345%6%9%41%
4270
Night
7%31342445%9%52%
3207
SeptemberDay
11%424435%5%5%7%46%
3781
Night
10%413424448%52%
3468
OctoberDay
17%6%25%433347%40%
3366
Night
16%6%25%423346%45%
4133
NovemberDay
16%8%46%423346%38%
3033
Night
16%8%35%423346%41%
4453
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
16%6%36%5%35%5%6%7%33%
4545
Night
14%5%145%35%5%5%8%39%
2833
JuneDay
11%5%35%5%35%6%6%8%38%
4620
Night
11%424435%5%5%8%44%
2640
JulyDay
7%325%5%46%5%7%9%41%
4769
Night
6%3144245%7%8%51%
2721
AugustDay
9%5%25%5%35%5%7%9%42%
4270
Night
7%31442446%9%52%
3207
SeptemberDay
11%424435%5%5%7%46%
3781
Night
10%413424447%52%
3468
OctoberDay
17%6%25%5%33347%40%
3366
Night
16%6%25%423346%45%
4133
NovemberDay
16%7%46%424346%38%
3033
Night
16%8%35%423346%41%
4453
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
47%7%12%20%11%1
4549
Night
41%7%13%21%14%1
2836
JuneDay
40%7%12%22%15%1
4620
Night
37%6%12%23%17%2
2640
JulyDay
36%8%14%24%13%2
4453
Night
28%7%14%27%19%3
2545
AugustDay
35%8%13%24%15%2
4255
Night
27%6%15%27%19%3
3198
SeptemberDay
35%7%10%25%18%3
3781
Night
30%5%10%28%22%3
3468
OctoberDay
43%5%12%24%12%1
3366
Night
40%410%25%17%1
4133
NovemberDay
46%412%23%11%1
3033
Night
45%311%22%14%2
4453
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
17%8%32%23%13%4
681
Night
16%428%34%15%
1010
JuneDay
12%6%32%28%14%5%
840
Night
12%326%40%16%
990
JulyDay
8%329%27%19%11%
845
Night
7%117%43%26%3
987
AugustDay
8%314%32%25%15%
601
Night
7%11%44%30%4
1019
SeptemberDay
10%318%31%27%8%
509
Night
11%417%34%28%4
1155
OctoberDay
17%8%28%28%13%3
266
Night
19%9%28%28%13%1
1364
NovemberDay
18%13%27%24%11%3
134
Night
19%11%34%24%9%
1393
DecemberDay
25%20%34%13%41
93
Night
29%10%33%22%4
1705
Page generated at 2016-11-16 11:29:41. Version ac04

Copyright 2016 A. Danko


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