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 2014-11-08.

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%
12116
17%
35544
11%
12074
44%
12074
23%
24018

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%
1395
13%
3863
4%
1390
28%
1390
16%
2897
FebruaryNight
23%
1062
13%
3055
5%
1062
29%
1062
17%
2221
MarchNight
31%
1006
13%
3128
10%
1006
35%
1006
17%
2215
AprilNight
30%
809
16%
2652
10%
809
40%
809
20%
1819
MayNight
45%
823
18%
2312
11%
822
51%
822
27%
1548
JuneNight
51%
810
16%
2160
10%
810
54%
810
31%
1423
JulyNight
66%
801
18%
2049
14%
768
68%
768
40%
1240
AugustNight
73%
836
22%
2624
21%
833
75%
833
39%
1449
SeptemberNight
59%
944
27%
2837
22%
944
64%
944
36%
1633
OctoberNight
38%
1116
22%
3381
16%
1116
45%
1116
26%
2151
NovemberNight
30%
1119
19%
3577
12%
1119
39%
1119
21%
2335
DecemberNight
19%
1395
11%
3906
3%
1395
25%
1395
13%
3087

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%36%5%3445%7%36%
36347
Night
15%7%35%424446%39%
35713
Cloud CoverDay
15%7%36%5%3445%7%36%
36356
Night
15%7%35%424446%39%
35718
TransparencyDay
47%6%12%21%11%1
36033
Night
45%5%12%22%12%1
35545
SeeingDay
13%5%25%27%18%9%
2555
Night
18%8%28%29%13%1
12120

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%15%5%9%6%24445%26%
2251
Night
15%12%5%8%5%24345%31%
3863
FebruaryDay
18%12%5%8%5%24436%28%
2409
Night
18%11%5%6%5%2334434%
3053
MarchDay
17%11%47%5%34447%29%
3006
Night
16%9%36%5%35%436%34%
3115
AprilDay
20%9%35%5%3445%6%32%
3276
Night
20%7%35%424446%35%
2652
MayDay
17%6%35%5%35%5%6%7%34%
3704
Night
14%5%14435%5%6%8%40%
2311
JuneDay
13%5%35%5%35%6%6%8%37%
3780
Night
10%4245%36%5%5%8%42%
2160
JulyDay
8%325%5%35%5%6%9%42%
3901
Night
6%313415%5%8%7%50%
2225
AugustDay
9%425%435%5%6%9%42%
3503
Night
7%31342446%9%53%
2633
SeptemberDay
12%42442445%6%47%
3094
Night
11%413324447%52%
2837
OctoberDay
17%7%25%5%33347%39%
2754
Night
17%6%24423346%44%
3381
NovemberDay
17%8%45%423346%38%
2437
Night
16%8%35%433236%41%
3577
DecemberDay
20%13%5%7%6%25%43425%
2232
Night
24%12%5%8%5%24335%25%
3906

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
16%15%5%9%6%24445%26%
2251
Night
15%12%6%8%6%24345%31%
3863
FebruaryDay
18%12%5%8%5%24436%28%
2409
Night
18%12%5%6%5%2344434%
3046
MarchDay
17%11%47%6%3445%6%29%
3015
Night
17%9%36%5%35%436%34%
3128
AprilDay
20%9%35%5%3445%5%31%
3276
Night
20%7%36%423446%36%
2652
MayDay
17%6%35%5%35%5%6%7%34%
3704
Night
14%5%24435%5%5%8%40%
2310
JuneDay
12%5%35%5%35%6%6%8%37%
3780
Night
10%4245%36%5%6%8%42%
2160
JulyDay
8%325%5%45%5%7%9%42%
3901
Night
6%3234245%7%8%51%
2225
AugustDay
9%425%435%5%6%9%42%
3503
Night
7%31342446%8%53%
2633
SeptemberDay
12%42442445%6%47%
3094
Night
11%413324447%52%
2837
OctoberDay
17%7%25%5%33347%39%
2754
Night
17%6%24423346%44%
3381
NovemberDay
17%8%45%423347%37%
2437
Night
16%8%35%423336%41%
3577
DecemberDay
20%13%5%7%6%35%435%25%
2232
Night
24%12%48%5%23335%25%
3906

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
59%413%15%6%
2252
Night
55%5%12%18%7%
3863
FebruaryDay
58%5%12%17%6%
2411
Night
54%412%20%7%
3055
MarchDay
54%6%13%20%4
3016
Night
51%5%14%19%7%1
3128
AprilDay
52%6%11%17%10%2
3276
Night
49%410%20%12%2
2652
MayDay
47%7%13%20%10%1
3708
Night
41%6%14%21%14%1
2313
JuneDay
41%8%12%22%13%1
3780
Night
37%7%13%22%15%2
2160
JulyDay
36%8%14%23%13%2
3585
Night
28%7%14%27%18%3
2049
AugustDay
35%7%14%23%16%2
3488
Night
27%5%14%27%19%4
2624
SeptemberDay
35%6%9%25%19%2
3094
Night
31%5%10%27%21%3
2837
OctoberDay
44%5%11%23%12%2
2754
Night
41%410%25%16%1
3381
NovemberDay
47%413%24%9%
2437
Night
45%412%23%13%1
3577
DecemberDay
63%412%15%4
2232
Night
62%410%17%4
3906

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
JanuaryNight
21%12%35%25%4
1395
FebruaryNight
23%11%34%24%6%
1065
MarchDay
27%227%26%13%1
109
Night
20%10%33%25%9%
1006
AprilDay
20%11%27%26%10%3
270
Night
23%10%31%27%7%
809
MayDay
16%6%26%27%16%6%
425
Night
16%5%27%34%16%
824
JuneDay
13%5%33%26%14%7%
540
Night
10%327%39%16%
810
JulyDay
8%426%28%19%11%
535
Night
7%116%43%27%2
801
AugustDay
6%212%33%26%17%
342
Night
7%11%43%30%4
836
SeptemberDay
12%318%23%30%11%
269
Night
12%417%32%27%4
944
OctoberDay
13%323%33%20%6%
65
Night
20%9%27%27%13%1
1116
NovemberNight
19%11%34%25%8%
1119
DecemberNight
30%9%33%22%4
1395
Page generated at 2014-11-09 03:43:30. Version ac04

Copyright 2014 A. Danko


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