River Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the River Ridge Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
46%
15664
26%
47077
17%
15617
55%
15617
32%
27671

By Month

MonthDays of 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
January1st to 15thNight
28%
900
29%
2327
9%
895
41%
895
29%
1460
January16th to endNight
25%
960
28%
2496
9%
960
37%
960
30%
1574
February1st to 15thNight
24%
866
21%
2273
6%
862
34%
862
28%
1486
February16th to endNight
24%
604
28%
1866
9%
604
40%
604
29%
1081
March1st to 15thNight
29%
540
23%
1980
13%
540
41%
540
22%
1208
March16th to endNight
33%
576
21%
2112
15%
576
44%
576
23%
1294
April1st to 15thNight
32%
539
25%
1801
13%
539
50%
539
30%
992
April16th to endNight
37%
540
25%
1800
17%
540
50%
540
31%
1022
May1st to 15thNight
45%
540
20%
1746
15%
540
55%
540
27%
1072
May16th to endNight
52%
563
22%
1684
17%
561
58%
561
31%
1015
June1st to 15thNight
75%
540
25%
1479
22%
540
79%
540
49%
809
June16th to endNight
72%
540
26%
1553
24%
540
75%
540
45%
839
July1st to 15thNight
73%
510
18%
1530
19%
510
76%
510
34%
892
July16th to endNight
83%
564
25%
1594
27%
531
84%
531
42%
868
August1st to 15thNight
77%
539
24%
1653
28%
536
79%
536
42%
889
August16th to endNight
77%
573
24%
1910
29%
573
78%
573
32%
1081
September1st to 15thNight
69%
540
26%
1800
30%
540
71%
540
34%
1015
September16th to endNight
65%
553
32%
1842
30%
553
70%
553
37%
974
October1st to 15thNight
58%
660
31%
1980
24%
660
63%
660
38%
1110
October16th to endNight
50%
704
35%
2112
22%
704
62%
704
40%
1137
November1st to 15thNight
48%
700
31%
2100
21%
700
57%
700
36%
1160
November16th to endNight
37%
753
29%
2345
18%
753
50%
753
29%
1373
December1st to 15thNight
33%
900
22%
2520
10%
900
42%
900
28%
1635
December16th to endNight
30%
960
24%
2574
10%
960
40%
960
27%
1685

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
12%5%25%5%3445%7%44%
47689
Night
11%424423347%51%
47275
TransparencyDay
38%5%10%22%18%4
47389
Night
33%410%23%21%6%
47080
SeeingDay
12%6%21%27%24%8%
5710
Night
13%8%26%30%18%2
15664

By Month

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
17%5%24323245%47%
1611
16th to endDay
14%5%25%413335%49%
1728
February1st to 15thDay
16%5%2342334447%
1588
16th to endDay
15%7%345%3345%5%41%
1616
March1st to 15thDay
18%5%25%424345%43%
1980
16th to endDay
16%6%35%5%33345%42%
2110
April1st to 15thDay
12%5%24423446%47%
2145
16th to endDay
14%5%25%6%34446%42%
2160
May1st to 15thDay
15%5%25%5%245%47%39%
2202
16th to endDay
9%426%6%47%6%7%8%36%
2430
June1st to 15thDay
6%425%6%35%6%6%9%44%
2475
16th to endDay
5%325%5%36%6%7%10%43%
2398
July1st to 15thDay
7%436%7%47%7%7%9%34%
2340
16th to endDay
5%325%6%37%6%7%9%42%
2466
August1st to 15thDay
8%315%6%45%7%7%9%39%
2295
16th to endDay
9%5%246%45%6%7%9%40%
2292
September1st to 15thDay
14%414425%5%5%6%45%
2160
16th to endDay
12%414324446%51%
1828
October1st to 15thDay
11%5%24423445%51%
1650
16th to endDay
14%21222223459%
1760
November1st to 15thDay
10%413322336%57%
1758
16th to endDay
14%7%24422335%49%
1610
December1st to 15thDay
16%7%2432335%5%45%
1440
16th to endDay
15%6%36%5%3443443%
1647
January1st to 15thNight
16%5%2332223452%
2327
16th to endNight
15%5%2332333451%
2496
February1st to 15thNight
16%6%35%323346%46%
2265
16th to endNight
12%5%23324245%52%
1866
March1st to 15thNight
17%6%25%42334445%
1980
16th to endNight
15%5%25%423346%44%
2112
April1st to 15thNight
10%423323447%52%
1801
16th to endNight
9%415%434447%50%
1800
May1st to 15thNight
13%42442345%8%46%
1745
16th to endNight
7%6%245%2446%9%45%
1683
June1st to 15thNight
231232445%9%58%
1479
16th to endNight
431342345%10%56%
1553
July1st to 15thNight
3325%5%26%6%7%12%44%
1620
16th to endNight
3113425%47%12%53%
1702
August1st to 15thNight
421443346%10%52%
1663
16th to endNight
5%314436%5%6%11%45%
1910
September1st to 15thNight
10%423323446%53%
1800
16th to endNight
8%32332445%7%55%
1842
October1st to 15thNight
10%313423436%56%
1980
16th to endNight
13%21232222462%
2112
November1st to 15thNight
10%314423246%56%
2100
16th to endNight
14%5%23313336%52%
2345
December1st to 15thNight
16%5%24423345%46%
2520
16th to endNight
16%6%34423335%46%
2574

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
40%36%25%19%5%
1612
16th to endDay
39%27%24%21%4
1728
February1st to 15thDay
39%310%24%17%4
1589
16th to endDay
45%46%21%17%4
1616
March1st to 15thDay
44%39%17%17%6%
1980
16th to endDay
45%410%23%14%1
2112
April1st to 15thDay
36%5%9%23%18%5%
2145
16th to endDay
42%49%20%19%3
2160
May1st to 15thDay
44%6%10%16%19%3
2202
16th to endDay
42%8%13%21%12%1
2434
June1st to 15thDay
34%7%13%25%18%1
2475
16th to endDay
33%7%12%24%18%3
2398
July1st to 15thDay
39%10%13%23%11%1
2201
16th to endDay
34%8%14%26%14%1
2311
August1st to 15thDay
36%9%13%24%14%2
2281
16th to endDay
38%8%15%19%14%3
2292
September1st to 15thDay
38%6%10%18%17%7%
2160
16th to endDay
33%410%20%24%6%
1828
October1st to 15thDay
34%48%19%24%8%
1650
16th to endDay
28%3424%29%10%
1760
November1st to 15thDay
29%28%26%23%8%
1758
16th to endDay
39%28%18%25%6%
1610
December1st to 15thDay
42%310%22%16%5%
1440
16th to endDay
45%29%20%16%4
1647
January1st to 15thNight
37%26%22%27%4
2327
16th to endNight
37%37%23%22%6%
2496
February1st to 15thNight
40%27%23%19%6%
2275
16th to endNight
35%29%25%19%7%
1866
March1st to 15thNight
42%39%16%19%7%
1980
16th to endNight
41%48%23%18%2
2112
April1st to 15thNight
30%411%22%21%8%
1801
16th to endNight
33%310%23%24%4
1800
May1st to 15thNight
37%6%9%21%18%6%
1746
16th to endNight
34%6%16%24%16%1
1685
June1st to 15thNight
21%6%13%32%24%1
1479
16th to endNight
23%6%13%27%24%5%
1553
July1st to 15thNight
28%9%17%26%14%2
1530
16th to endNight
21%10%16%31%18%2
1594
August1st to 15thNight
25%5%17%30%18%2
1653
16th to endNight
29%8%16%25%17%3
1910
September1st to 15thNight
30%5%9%24%20%8%
1800
16th to endNight
27%5%9%22%25%9%
1842
October1st to 15thNight
29%49%20%23%11%
1980
16th to endNight
28%2419%32%11%
2112
November1st to 15thNight
30%37%24%23%11%
2100
16th to endNight
35%36%20%28%6%
2345
December1st to 15thNight
41%38%21%18%6%
2520
16th to endNight
41%38%21%19%5%
2574

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
23%12%43%14%6%
90
16th to endDay
16%30%35%11%6%
96
February1st to 15thDay
16%20%47%12%21
90
16th to endDay
14%27%37%14%32
81
March1st to 15thDay
25%20%43%10%1
90
16th to endDay
14%26%25%27%7%
96
April1st to 15thDay
13%17%37%20%10%
264
16th to endDay
22%11%29%20%15%
270
May1st to 15thDay
17%8%35%21%13%2
339
16th to endDay
12%5%29%29%17%5%
517
June1st to 15thDay
8%16%36%26%10%
495
16th to endDay
6%318%34%29%8%
495
July1st to 15thDay
7%214%37%29%8%
475
16th to endDay
6%328%39%20%
515
August1st to 15thDay
10%9%30%35%13%
448
16th to endDay
15%15%25%37%15%
332
September1st to 15thDay
10%111%21%42%12%
315
16th to endDay
12%114%34%23%14%
150
October1st to 15thDay
15%428%32%13%5%
90
16th to endDay
16%5%23%36%14%3
96
November1st to 15thDay
14%7%28%24%22%2
90
16th to endDay
30%16%30%15%6%1
90
December1st to 15thDay
20%18%32%12%14%2
90
16th to endDay
16%22%44%12%3
96
January1st to 15thNight
20%16%31%24%6%
900
16th to endNight
18%14%39%24%3
960
February1st to 15thNight
18%15%37%25%2
866
16th to endNight
17%17%39%24%2
604
March1st to 15thNight
20%10%35%29%3
540
16th to endNight
16%9%35%29%8%
576
April1st to 15thNight
12%13%38%25%9%
539
16th to endNight
11%9%37%30%10%
540
May1st to 15thNight
14%5%30%35%12%1
540
16th to endNight
11%425%32%22%3
563
June1st to 15thNight
413%43%34%4
540
16th to endNight
5%11%41%36%4
540
July1st to 15thNight
410%39%40%4
510
16th to endNight
35%32%48%9%
564
August1st to 15thNight
6%7%32%44%9%
539
16th to endNight
7%16%33%44%6%
573
September1st to 15thNight
11%110%30%42%4
540
16th to endNight
9%116%30%36%4
553
October1st to 15thNight
12%320%30%27%4
660
16th to endNight
14%5%26%32%19%1
704
November1st to 15thNight
11%10%25%35%16%
700
16th to endNight
17%13%28%26%13%
753
December1st to 15thNight
20%9%32%29%7%
900
16th to endNight
21%13%31%28%5%
960
Page generated at 2017-09-19 06:32:23. Version ac04

Copyright 2017 A. Danko


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