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 2015-05-26.

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%
12917
17%
37907
11%
12875
43%
12875
23%
25643

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%
1550
13%
4294
4%
1545
29%
1545
17%
3197
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%
901
17%
2534
10%
900
50%
900
27%
1705
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
29%
1210
18%
3866
12%
1210
37%
1210
21%
2552
DecemberNight
20%
1550
10%
4340
3%
1550
25%
1550
14%
3425

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%35%
38360
Night
15%8%35%424446%39%
38076
Cloud CoverDay
15%7%36%5%3445%7%35%
38369
Night
15%8%35%424446%39%
38081
TransparencyDay
47%6%12%20%11%1
38046
Night
45%5%12%22%12%1
37908
SeeingDay
13%5%26%27%18%8%
2685
Night
18%8%29%29%12%1
12921

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%
2502
Night
15%12%5%8%6%24345%31%
4294
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%
4051
Night
14%5%15%5%35%5%6%8%39%
2533
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%46%423346%36%
2632
Night
16%8%35%433346%40%
3866
DecemberDay
20%13%5%7%6%35%435%25%
2480
Night
23%12%48%5%34335%25%
4340

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%9%6%24445%26%
2502
Night
15%12%5%7%6%24345%31%
4294
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%
4051
Night
14%5%15%5%35%5%5%8%39%
2532
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%46%5%23346%36%
2632
Night
16%8%36%433346%40%
3866
DecemberDay
20%13%5%7%6%34435%25%
2480
Night
23%12%48%5%33335%25%
4340

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%414%14%6%
2503
Night
54%5%12%18%8%
4294
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
47%7%12%20%10%1
4055
Night
41%7%14%21%14%1
2535
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
48%412%23%9%
2632
Night
46%412%22%12%1
3866
DecemberDay
63%411%14%5%
2480
Night
62%410%16%5%
4340

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
20%12%35%25%4
1550
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%14%5%
513
Night
16%5%27%34%15%
902
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%35%24%8%
1210
DecemberNight
29%9%33%22%4
1550
Page generated at 2015-05-27 11:02:46. Version ac04

Copyright 2015 A. Danko


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