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 2016-01-22.

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%
13822
17%
40540
11%
13780
44%
13780
23%
27333

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%
1660
13%
4601
4%
1655
29%
1655
17%
3418
FebruaryNight
23%
1182
14%
3399
6%
1182
30%
1182
18%
2443
MarchNight
30%
1118
14%
3476
10%
1118
35%
1118
18%
2434
AprilNight
31%
899
17%
2947
11%
899
41%
899
21%
1991
MayNight
44%
916
17%
2574
10%
915
50%
915
27%
1733
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%36%
41003
Night
15%8%35%424446%39%
40709
Cloud CoverDay
14%7%36%5%3445%7%35%
41012
Night
15%8%35%424446%39%
40714
TransparencyDay
46%6%12%21%11%1
40689
Night
45%5%12%22%13%1
40541
SeeingDay
14%6%26%26%17%7%
3612
Night
18%8%28%29%13%1
13826

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%
2674
Night
14%12%5%8%6%24345%32%
4601
FebruaryDay
17%12%5%8%5%35%436%28%
2681
Night
17%11%5%6%5%2344434%
3397
MarchDay
16%10%37%6%35%446%30%
3341
Night
15%9%36%5%35%436%35%
3463
AprilDay
19%8%36%5%3445%6%33%
3641
Night
19%7%35%424346%37%
2947
MayDay
17%6%35%5%35%5%6%7%33%
4124
Night
14%5%15%5%35%5%6%8%39%
2573
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%24445%27%
2674
Night
14%12%5%7%6%24445%32%
4601
FebruaryDay
17%13%5%8%5%34436%28%
2681
Night
17%11%5%6%5%2344434%
3390
MarchDay
16%10%47%6%3445%6%30%
3350
Night
16%9%36%5%35%436%35%
3476
AprilDay
19%9%35%5%2445%6%33%
3641
Night
19%7%36%423346%37%
2947
MayDay
17%6%35%5%35%5%6%7%33%
4124
Night
14%5%15%5%35%5%5%8%39%
2572
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%
2675
Night
54%5%12%17%9%
4601
FebruaryDay
58%5%12%17%6%1
2683
Night
53%412%20%8%1
3399
MarchDay
53%6%13%20%5%
3351
Night
50%5%13%19%9%1
3476
AprilDay
51%5%10%17%11%2
3641
Night
47%49%21%13%2
2947
MayDay
48%7%12%20%10%1
4128
Night
41%7%14%21%14%1
2575
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%32%28%7%
64
Night
20%12%36%25%4
1660
FebruaryNight
22%10%35%24%6%
1185
MarchDay
25%330%25%13%1
121
Night
19%10%34%25%9%
1118
AprilDay
19%12%27%26%10%3
300
Night
22%9%32%27%7%
899
MayDay
17%7%30%24%13%5%
539
Night
16%5%27%34%15%
917
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 2016-01-23 05:47:40. Version ac04

Copyright 2016 A. Danko


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