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 2014-06-16.

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%
11624
17%
34089
11%
11582
43%
11582
23%
23133

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
50%
765
17%
2040
10%
765
54%
765
32%
1335
JulyNight
67%
708
20%
1801
16%
675
70%
675
39%
1092
AugustNight
72%
743
23%
2331
23%
740
75%
740
40%
1270
SeptemberNight
60%
839
27%
2522
22%
839
65%
839
35%
1462
OctoberNight
39%
992
22%
3006
16%
992
45%
992
25%
1913
NovemberNight
30%
1087
19%
3473
12%
1087
39%
1087
21%
2274
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%8%36%5%3445%7%36%
34593
Night
15%8%35%424446%39%
34258
Cloud CoverDay
15%8%36%5%3445%7%36%
34602
Night
15%8%35%424446%39%
34263
TransparencyDay
47%6%12%20%11%1
34279
Night
46%5%12%21%12%1
34090
SeeingDay
13%5%25%28%18%8%
2389
Night
19%8%28%29%12%1
11628

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%435%5%35%6%6%8%38%
3571
Night
10%4245%35%5%5%8%43%
2040
JulyDay
8%325%5%35%5%7%9%41%
3467
Night
7%323415%5%8%8%50%
1977
AugustDay
9%4244345%6%9%44%
3114
Night
7%31342335%8%55%
2340
SeptemberDay
12%42442445%6%47%
2750
Night
11%313324447%52%
2522
OctoberDay
17%6%25%5%33347%40%
2448
Night
17%6%24423346%44%
3006
NovemberDay
18%8%45%413346%38%
2365
Night
17%8%35%433236%41%
3473
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
13%435%5%35%6%6%7%38%
3571
Night
10%4245%35%5%5%8%44%
2040
JulyDay
8%325%5%35%5%7%9%41%
3467
Night
6%313425%5%7%8%50%
1977
AugustDay
9%4244345%6%8%44%
3114
Night
7%31342335%8%55%
2340
SeptemberDay
12%424424446%47%
2750
Night
11%313324446%52%
2522
OctoberDay
17%6%25%5%23347%40%
2448
Night
17%6%24423346%44%
3006
NovemberDay
18%8%45%413346%38%
2365
Night
17%8%35%423236%41%
3473
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%7%12%21%14%1
3571
Night
37%6%12%23%16%3
2040
JulyDay
37%8%14%22%14%2
3151
Night
28%7%15%26%18%3
1801
AugustDay
34%7%13%23%17%3
3099
Night
27%5%12%28%21%5%
2331
SeptemberDay
35%6%10%23%20%3
2750
Night
31%410%25%22%3
2522
OctoberDay
43%5%12%23%12%2
2448
Night
41%410%25%16%1
3006
NovemberDay
47%412%25%9%
2365
Night
45%412%22%13%1
3473
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
14%433%25%14%7%
511
Night
10%328%39%16%
765
JulyDay
8%326%30%19%11%
473
Night
7%115%44%28%2
708
AugustDay
6%313%35%24%17%
304
Night
7%112%44%29%4
743
SeptemberDay
13%318%23%29%11%
239
Night
12%416%34%26%4
839
OctoberDay
10%320%36%22%6%
58
Night
20%10%26%28%13%1
992
NovemberNight
20%11%33%26%8%
1087
DecemberNight
30%9%33%22%4
1395
Page generated at 2014-06-17 02:07:46. Version ac04

Copyright 2014 A. Danko


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