River's Astronomy Pad
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the River's Astronomy Pad clear sky chart from 2005-11-05 to 2017-09-16.

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%
16012
20%
46917
11%
15965
46%
15965
29%
28987

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
26%
900
18%
2377
7%
895
35%
895
27%
1567
January16th to endNight
21%
960
20%
2496
5%
960
32%
960
23%
1736
February1st to 15thNight
25%
880
12%
2288
4%
876
31%
876
21%
1656
February16th to endNight
27%
723
23%
1985
6%
723
39%
723
29%
1266
March1st to 15thNight
35%
540
21%
1980
15%
540
45%
540
24%
1162
March16th to endNight
25%
576
14%
2112
8%
576
35%
576
17%
1398
April1st to 15thNight
29%
539
19%
1845
13%
539
42%
539
24%
1124
April16th to endNight
29%
540
18%
1647
12%
540
40%
540
21%
1109
May1st to 15thNight
39%
540
18%
1620
12%
540
47%
540
27%
1018
May16th to endNight
40%
563
16%
1537
7%
561
47%
561
31%
976
June1st to 15thNight
52%
540
17%
1440
7%
540
55%
540
37%
878
June16th to endNight
53%
540
21%
1440
9%
540
57%
540
49%
780
July1st to 15thNight
70%
510
16%
1396
9%
510
72%
510
50%
747
July16th to endNight
76%
564
24%
1594
21%
531
79%
531
51%
774
August1st to 15thNight
65%
539
21%
1610
22%
536
67%
536
40%
894
August16th to endNight
60%
573
23%
1773
24%
573
65%
573
36%
1009
September1st to 15thNight
59%
540
25%
1848
24%
540
66%
540
38%
943
September16th to endNight
50%
495
27%
1826
23%
495
61%
495
34%
935
October1st to 15thNight
37%
652
27%
1972
17%
652
46%
652
33%
1137
October16th to endNight
34%
704
22%
2112
11%
704
43%
704
31%
1251
November1st to 15thNight
34%
834
26%
2291
11%
834
46%
834
36%
1332
November16th to endNight
28%
900
20%
2520
9%
900
38%
900
28%
1582
December1st to 15thNight
22%
900
15%
2520
4%
900
32%
900
21%
1772
December16th to endNight
22%
960
18%
2688
6%
960
32%
960
19%
1941

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%7%35%5%3445%7%40%
47838
Night
10%6%35%423447%45%
47101
Cloud CoverDay
10%6%25%423346%49%
47849
Night
8%6%24423346%54%
47105
Cloud CoverDay
12%7%35%5%3445%7%40%
47847
Night
10%6%35%424447%45%
47105
TransparencyDay
42%313%24%12%1
47540
Night
38%313%26%15%2
46917
SeeingDay
14%7%29%29%15%3
6021
Night
14%8%33%31%11%
16012

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
8%9%46%7%4445%6%37%
1558
16th to endDay
11%12%5%9%6%25%45%7%30%
1728
February1st to 15thDay
12%11%5%9%6%34347%31%
1575
16th to endDay
11%9%38%7%3435%6%35%
1499
March1st to 15thDay
11%9%47%5%3436%7%36%
1969
16th to endDay
18%12%46%5%34445%31%
2112
April1st to 15thDay
16%8%46%424345%37%
2101
16th to endDay
23%9%35%434346%31%
2312
May1st to 15thDay
17%6%35%435%5%46%35%
2331
16th to endDay
16%7%25%5%345%5%7%36%
2577
June1st to 15thDay
13%5%25%5%35%45%8%40%
2520
16th to endDay
6%314435%6%6%8%49%
2520
July1st to 15thDay
7%4145%345%6%9%47%
2478
16th to endDay
5%324425%5%5%10%50%
2466
August1st to 15thDay
7%5%245%36%6%6%9%42%
2340
16th to endDay
11%5%245%3445%7%46%
2429
September1st to 15thDay
10%5%2442345%7%50%
2110
16th to endDay
10%31231346%7%54%
1820
October1st to 15thDay
14%5%24323236%51%
1650
16th to endDay
13%9%25%423345%44%
1760
November1st to 15thDay
9%5%15%424337%51%
1567
16th to endDay
13%10%35%424347%40%
1440
December1st to 15thDay
14%10%49%7%34436%31%
1440
16th to endDay
14%11%5%11%6%35%446%25%
1536
January1st to 15thNight
7%8%47%6%3435%8%39%
2377
16th to endNight
10%9%5%7%6%34446%37%
2496
February1st to 15thNight
13%10%47%6%44446%33%
2285
16th to endNight
9%7%26%5%34346%46%
1985
March1st to 15thNight
11%7%35%324247%46%
1968
16th to endNight
15%10%35%5%3446%6%34%
2112
April1st to 15thNight
12%7%26%423337%44%
1845
16th to endNight
17%9%35%5%3335%6%36%
1647
May1st to 15thNight
14%42442346%8%43%
1620
16th to endNight
10%6%26%5%2435%7%45%
1535
June1st to 15thNight
7%425%5%245%5%8%47%
1440
16th to endNight
31134235%5%9%58%
1440
July1st to 15thNight
411332446%8%59%
1479
16th to endNight
311232346%8%61%
1702
August1st to 15thNight
5%4244235%5%10%51%
1620
16th to endNight
9%424433337%53%
1773
September1st to 15thNight
9%413322437%56%
1848
16th to endNight
10%41332335%6%55%
1826
October1st to 15thNight
14%424312335%53%
1972
16th to endNight
14%7%24312335%51%
2112
November1st to 15thNight
8%5%24323447%53%
2291
16th to endNight
11%7%35%323446%47%
2520
December1st to 15thNight
12%11%47%5%2445%5%35%
2520
16th to endNight
14%9%6%8%6%34346%32%
2688

Percentage Cloud Cover SW (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
6%7%35%7%44435%47%
1558
16th to endDay
9%11%38%5%24345%41%
1728
February1st to 15thDay
9%9%48%5%33236%42%
1575
16th to endDay
9%9%27%6%3334445%
1499
March1st to 15thDay
8%8%36%423345%48%
1980
16th to endDay
13%9%35%42343444%
2112
April1st to 15thDay
13%7%35%423335%48%
2101
16th to endDay
19%9%24423336%40%
2312
May1st to 15thDay
14%6%24423335%47%
2331
16th to endDay
13%6%245%2435%5%46%
2577
June1st to 15thDay
12%425%433346%49%
2520
16th to endDay
5%3133245%5%7%58%
2520
July1st to 15thDay
6%3135%2445%7%55%
2478
16th to endDay
431342445%7%58%
2466
August1st to 15thDay
6%4144345%6%8%49%
2340
16th to endDay
9%424323446%52%
2429
September1st to 15thDay
8%414313346%56%
2110
16th to endDay
9%21232345%6%59%
1820
October1st to 15thDay
12%5%24422235%56%
1650
16th to endDay
11%8%24423335%49%
1760
November1st to 15thDay
7%415%413325%59%
1567
16th to endDay
10%8%24312245%52%
1440
December1st to 15thDay
11%8%49%6%3233442%
1440
16th to endDay
11%10%49%5%23345%39%
1536
January1st to 15thNight
5%7%26%6%33246%51%
2377
16th to endNight
8%8%36%5%33345%46%
2496
February1st to 15thNight
10%8%26%5%33335%45%
2278
16th to endNight
7%6%26%423335%53%
1985
March1st to 15thNight
9%7%24313235%55%
1980
16th to endNight
11%9%24423446%46%
2112
April1st to 15thNight
10%7%15%312236%54%
1845
16th to endNight
14%8%25%5%23345%44%
1647
May1st to 15thNight
10%5%23322346%54%
1619
16th to endNight
9%5%25%423346%53%
1535
June1st to 15thNight
7%41442345%6%55%
1440
16th to endNight
2113313446%67%
1440
July1st to 15thNight
312323347%66%
1479
16th to endNight
2221335%7%68%
1702
August1st to 15thNight
5%313423449%58%
1620
16th to endNight
7%413422335%59%
1773
September1st to 15thNight
8%313322346%60%
1848
16th to endNight
8%412322346%60%
1826
October1st to 15thNight
13%314312235%58%
1972
16th to endNight
12%5%14322235%56%
2112
November1st to 15thNight
7%423323335%61%
2291
16th to endNight
9%7%13312335%57%
2520
December1st to 15thNight
10%10%26%42434445%
2520
16th to endNight
11%8%47%5%2223445%
2688

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
8%9%46%7%45%45%6%36%
1558
16th to endDay
11%12%5%9%6%3435%7%30%
1728
February1st to 15thDay
12%11%5%9%6%34347%31%
1575
16th to endDay
12%9%37%6%3435%6%35%
1499
March1st to 15thDay
11%9%5%6%6%3435%6%36%
1980
16th to endDay
18%11%46%434445%30%
2110
April1st to 15thDay
16%8%36%424346%37%
2101
16th to endDay
23%10%35%424446%30%
2312
May1st to 15thDay
17%7%35%5%35%446%35%
2331
16th to endDay
15%7%25%5%3446%7%35%
2577
June1st to 15thDay
13%5%25%43445%9%40%
2520
16th to endDay
6%324436%5%6%8%48%
2520
July1st to 15thDay
8%3145%245%6%9%47%
2478
16th to endDay
5%314425%6%6%9%50%
2466
August1st to 15thDay
8%5%24436%6%6%9%42%
2340
16th to endDay
11%5%244245%5%7%46%
2429
September1st to 15thDay
10%5%24323447%50%
2110
16th to endDay
10%21332346%7%54%
1820
October1st to 15thDay
14%5%24413235%51%
1650
16th to endDay
13%9%25%414336%43%
1760
November1st to 15thDay
9%5%25%424437%50%
1567
16th to endDay
13%9%35%42335%7%40%
1440
December1st to 15thDay
13%10%5%9%7%23436%31%
1440
16th to endDay
14%11%5%11%6%25%35%6%25%
1536
January1st to 15thNight
6%9%47%6%34448%40%
2377
16th to endNight
11%9%47%6%3445%6%37%
2496
February1st to 15thNight
13%10%47%6%45%446%33%
2278
16th to endNight
9%7%26%5%34446%45%
1985
March1st to 15thNight
11%7%35%314347%45%
1980
16th to endNight
15%11%35%5%345%5%7%34%
2112
April1st to 15thNight
12%7%26%424337%44%
1845
16th to endNight
17%8%36%5%33446%36%
1647
May1st to 15thNight
13%5%2443345%8%43%
1619
16th to endNight
10%5%35%5%33438%45%
1535
June1st to 15thNight
8%425%4245%6%8%47%
1440
16th to endNight
3114425%5%5%9%58%
1440
July1st to 15thNight
31342436%8%59%
1479
16th to endNight
311232346%9%61%
1702
August1st to 15thNight
6%41442445%10%52%
1620
16th to endNight
8%4235%23336%54%
1773
September1st to 15thNight
9%313323447%56%
1848
16th to endNight
10%423323346%55%
1826
October1st to 15thNight
15%324312246%52%
1972
16th to endNight
15%6%24312325%51%
2112
November1st to 15thNight
8%5%24323346%53%
2291
16th to endNight
11%8%35%323446%46%
2520
December1st to 15thNight
12%11%47%6%2445%5%35%
2520
16th to endNight
14%9%6%7%7%34345%32%
2688

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
46%316%21%11%
1559
16th to endDay
53%215%19%8%
1728
February1st to 15thDay
53%214%21%7%
1576
16th to endDay
49%313%20%11%2
1499
March1st to 15thDay
47%314%22%11%1
1980
16th to endDay
55%315%19%5%1
2112
April1st to 15thDay
48%311%26%8%1
2101
16th to endDay
54%311%20%9%
2312
May1st to 15thDay
47%413%23%9%
2331
16th to endDay
47%413%22%10%1
2581
June1st to 15thDay
41%416%24%12%1
2520
16th to endDay
31%5%15%30%13%2
2520
July1st to 15thDay
32%5%17%27%12%4
2332
16th to endDay
27%417%31%17%1
2311
August1st to 15thDay
36%6%15%26%14%1
2326
16th to endDay
36%5%10%26%17%3
2429
September1st to 15thDay
34%312%30%17%2
2110
16th to endDay
28%313%32%20%
1820
October1st to 15thDay
36%29%30%19%2
1650
16th to endDay
42%211%25%16%1
1760
November1st to 15thDay
34%113%25%22%1
1567
16th to endDay
44%314%26%10%
1440
December1st to 15thDay
54%413%19%7%1
1440
16th to endDay
59%312%16%6%1
1536
January1st to 15thNight
43%216%22%15%
2377
16th to endNight
48%215%22%10%
2496
February1st to 15thNight
52%212%22%7%1
2288
16th to endNight
39%213%25%16%2
1985
March1st to 15thNight
39%212%27%14%2
1980
16th to endNight
49%413%23%7%1
2112
April1st to 15thNight
40%310%28%15%1
1845
16th to endNight
48%213%21%11%1
1647
May1st to 15thNight
38%5%14%24%15%1
1620
16th to endNight
38%417%24%13%2
1537
June1st to 15thNight
33%315%29%14%2
1440
16th to endNight
22%416%29%22%4
1440
July1st to 15thNight
22%321%32%16%4
1396
16th to endNight
18%417%36%20%3
1594
August1st to 15thNight
28%416%30%17%2
1610
16th to endNight
32%312%23%20%7%
1773
September1st to 15thNight
27%312%30%21%4
1848
16th to endNight
30%310%34%19%2
1826
October1st to 15thNight
34%29%26%22%3
1972
16th to endNight
37%113%26%18%1
2112
November1st to 15thNight
31%213%26%22%3
2291
16th to endNight
38%314%28%13%1
2520
December1st to 15thNight
50%313%24%8%
2520
16th to endNight
53%312%20%9%1
2688

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
12%14%45%24%3
90
16th to endDay
21%5%43%22%42
96
February1st to 15thDay
16%17%38%21%5%
90
16th to endDay
20%6%34%28%7%2
81
March1st to 15thDay
14%15%47%20%11
90
16th to endDay
29%15%30%21%3
96
April1st to 15thDay
18%12%35%25%6%
220
16th to endDay
30%10%28%19%9%
422
May1st to 15thDay
20%14%29%25%10%
468
16th to endDay
18%7%35%24%13%1
517
June1st to 15thDay
12%429%33%17%1
495
16th to endDay
6%5%37%31%14%3
495
July1st to 15thDay
8%127%33%21%8%
475
16th to endDay
6%120%40%25%5%
515
August1st to 15thDay
9%317%40%26%3
493
16th to endDay
15%219%32%23%7%
469
September1st to 15thDay
8%328%31%22%4
265
16th to endDay
6%6%32%34%16%3
92
October1st to 15thDay
10%10%32%31%11%5%
90
16th to endDay
14%6%45%27%6%
96
November1st to 15thDay
6%6%33%37%11%4
90
16th to endDay
34%15%33%14%2
90
December1st to 15thDay
15%25%36%17%31
90
16th to endDay
28%23%38%8%1
96
January1st to 15thNight
12%14%39%25%7%
900
16th to endNight
17%12%41%23%5%
960
February1st to 15thNight
18%9%38%26%6%
880
16th to endNight
13%11%43%24%6%1
723
March1st to 15thNight
15%10%34%28%10%
540
16th to endNight
22%9%38%23%6%
576
April1st to 15thNight
16%11%37%29%4
539
16th to endNight
20%9%35%25%9%
540
May1st to 15thNight
17%8%32%31%10%
540
16th to endNight
12%6%34%36%10%
563
June1st to 15thNight
11%427%43%13%
540
16th to endNight
4234%43%13%
540
July1st to 15thNight
5%19%46%26%1
510
16th to endNight
3112%54%26%2
564
August1st to 15thNight
7%117%46%25%1
539
16th to endNight
11%318%39%23%3
573
September1st to 15thNight
10%222%35%23%4
540
16th to endNight
11%5%29%33%18%1
495
October1st to 15thNight
16%7%34%29%10%1
652
16th to endNight
19%9%32%28%9%
704
November1st to 15thNight
12%11%38%27%9%
834
16th to endNight
16%13%38%24%6%
900
December1st to 15thNight
18%12%40%23%4
900
16th to endNight
20%10%36%26%6%
960
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Copyright 2017 A. Danko


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