Richmond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Richmond clear sky chart from 2005-11-05 to 2017-09-21.

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
36%
15742
18%
46807
11%
15699
43%
15699
21%
31352

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
17%
900
13%
2506
6%
895
23%
895
12%
1978
January16th to endNight
18%
823
13%
2551
6%
823
25%
823
11%
1938
February1st to 15thNight
18%
702
12%
2160
5%
701
24%
701
13%
1568
February16th to endNight
22%
631
14%
1893
6%
631
29%
631
13%
1385
March1st to 15thNight
25%
720
15%
2107
7%
720
31%
720
15%
1496
March16th to endNight
27%
768
16%
2112
7%
768
35%
768
20%
1489
April1st to 15thNight
30%
548
17%
1806
11%
548
40%
548
19%
1182
April16th to endNight
33%
540
20%
1653
7%
540
46%
540
22%
1064
May1st to 15thNight
30%
540
15%
1620
7%
540
37%
540
17%
1146
May16th to endNight
45%
562
17%
1684
11%
561
51%
561
25%
1050
June1st to 15thNight
50%
540
17%
1485
12%
540
55%
540
31%
898
June16th to endNight
51%
540
17%
1440
11%
540
57%
540
33%
884
July1st to 15thNight
55%
510
16%
1360
13%
510
58%
510
31%
863
July16th to endNight
64%
564
22%
1530
16%
531
73%
531
39%
856
August1st to 15thNight
64%
539
23%
1609
18%
536
67%
536
35%
921
August16th to endNight
69%
573
23%
1848
19%
573
74%
573
36%
992
September1st to 15thNight
59%
645
26%
1905
22%
645
63%
645
35%
1107
September16th to endNight
57%
681
27%
1881
19%
681
62%
681
33%
1145
October1st to 15thNight
49%
660
28%
1842
22%
660
56%
660
32%
1116
October16th to endNight
33%
704
21%
2219
14%
704
43%
704
23%
1416
November1st to 15thNight
38%
700
26%
2276
17%
700
50%
700
25%
1347
November16th to endNight
25%
720
17%
2340
10%
720
36%
720
15%
1628
December1st to 15thNight
21%
720
11%
2340
6%
720
27%
720
11%
1771
December16th to endNight
15%
912
11%
2640
4%
912
22%
912
10%
2112

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%8%36%5%3445%7%35%
48045
Night
14%8%36%5%34447%38%
46987
Cloud CoverDay
14%8%36%5%3445%7%35%
48054
Night
14%8%36%5%34447%37%
46992
TransparencyDay
47%411%21%13%1
47743
Night
45%411%22%14%2
46807
SeeingDay
16%13%21%22%17%9%
5771
Night
15%19%21%26%14%2
15745

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
21%12%5%9%6%3435%5%23%
1432
16th to endDay
13%15%6%10%6%5%5%446%21%
1671
February1st to 15thDay
16%13%7%7%6%33335%28%
1699
16th to endDay
15%12%5%10%6%34436%27%
1580
March1st to 15thDay
20%11%48%5%24446%27%
1842
16th to endDay
18%11%47%5%34446%28%
2114
April1st to 15thDay
18%8%36%423436%36%
2151
16th to endDay
18%7%35%5%24446%36%
2306
May1st to 15thDay
21%8%26%5%3445%6%30%
2331
16th to endDay
11%6%35%5%35%6%5%8%36%
2431
June1st to 15thDay
11%425%435%5%7%8%42%
2471
16th to endDay
9%5%25%5%35%6%5%8%41%
2520
July1st to 15thDay
10%426%6%36%5%7%9%35%
2520
16th to endDay
7%335%6%36%7%7%10%39%
2531
August1st to 15thDay
7%425%6%45%46%8%42%
2340
16th to endDay
6%5%25%5%35%6%6%9%42%
2351
September1st to 15thDay
12%5%25%434447%43%
2043
16th to endDay
14%6%25%5%23347%44%
1872
October1st to 15thDay
13%6%245%2445%6%43%
1787
16th to endDay
19%7%25%423446%37%
1650
November1st to 15thDay
11%6%24424447%47%
1582
16th to endDay
18%11%47%5%23445%30%
1620
December1st to 15thDay
22%13%6%9%5%23435%23%
1620
16th to endDay
22%14%5%9%5%24346%21%
1581
January1st to 15thNight
20%12%5%9%7%35%436%23%
2506
16th to endNight
16%13%6%9%5%34335%26%
2551
February1st to 15thNight
17%12%5%6%6%34346%29%
2158
16th to endNight
16%11%5%8%6%245%46%28%
1893
March1st to 15thNight
17%8%46%5%34435%34%
2094
16th to endNight
17%9%36%5%24346%35%
2112
April1st to 15thNight
15%8%35%42445%7%37%
1806
16th to endNight
14%5%246%3445%7%40%
1653
May1st to 15thNight
19%9%35%5%34346%33%
1620
16th to endNight
11%5%244345%6%9%42%
1682
June1st to 15thNight
8%425%5%2336%9%48%
1485
16th to endNight
7%314425%5%6%10%47%
1440
July1st to 15thNight
9%5%15%4345%5%7%46%
1440
16th to endNight
6%31342446%8%53%
1636
August1st to 15thNight
5%315%5%245%5%8%51%
1620
16th to endNight
43145%345%5%10%51%
1848
September1st to 15thNight
10%414323448%50%
1905
16th to endNight
13%424423347%48%
1881
October1st to 15thNight
9%5%2442445%7%49%
1842
16th to endNight
18%6%25%423346%41%
2219
November1st to 15thNight
12%6%24423446%47%
2276
16th to endNight
20%10%45%5%3445%6%31%
2340
December1st to 15thNight
22%12%49%5%24336%24%
2340
16th to endNight
24%11%5%8%6%34335%21%
2640

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
21%12%6%9%6%34345%23%
1432
16th to endDay
13%16%7%9%7%45%445%21%
1671
February1st to 15thDay
15%14%6%8%6%24435%27%
1699
16th to endDay
16%11%6%9%6%34436%27%
1580
March1st to 15thDay
21%11%47%5%34447%26%
1852
16th to endDay
19%10%47%6%34446%29%
2113
April1st to 15thDay
18%8%36%423346%36%
2151
16th to endDay
18%7%35%424446%36%
2306
May1st to 15thDay
21%8%36%6%25%45%5%30%
2331
16th to endDay
11%6%37%5%35%5%6%8%36%
2431
June1st to 15thDay
11%424435%5%6%8%41%
2471
16th to endDay
9%5%25%5%445%6%9%40%
2520
July1st to 15thDay
10%5%25%6%46%6%6%9%36%
2520
16th to endDay
7%325%5%45%6%8%9%39%
2531
August1st to 15thDay
7%425%5%45%5%6%9%42%
2340
16th to endDay
6%5%25%5%35%5%7%9%42%
2351
September1st to 15thDay
12%5%25%5%35%35%7%43%
2043
16th to endDay
14%5%35%5%23337%44%
1872
October1st to 15thDay
13%5%245%245%5%6%43%
1787
16th to endDay
18%7%26%42445%6%37%
1650
November1st to 15thDay
10%6%3443335%7%47%
1582
16th to endDay
19%11%47%6%24445%30%
1620
December1st to 15thDay
22%13%6%10%414345%22%
1620
16th to endDay
22%15%5%9%433446%20%
1581
January1st to 15thNight
19%12%5%9%7%34345%23%
2506
16th to endNight
16%13%7%9%6%34435%26%
2551
February1st to 15thNight
16%12%5%6%6%33345%30%
2151
16th to endNight
15%11%5%7%7%24446%29%
1893
March1st to 15thNight
17%8%37%6%44435%33%
2107
16th to endNight
16%10%36%5%34347%34%
2112
April1st to 15thNight
16%8%35%5%235%5%7%37%
1806
16th to endNight
14%6%16%5%3445%7%40%
1653
May1st to 15thNight
19%8%36%434346%34%
1619
16th to endNight
11%425%435%46%9%42%
1682
June1st to 15thNight
8%4245%3435%9%49%
1485
16th to endNight
7%324325%5%6%10%47%
1440
July1st to 15thNight
9%42443445%8%46%
1440
16th to endNight
6%3134245%6%9%52%
1636
August1st to 15thNight
5%315%5%245%5%9%50%
1620
16th to endNight
43245%35%45%9%51%
1848
September1st to 15thNight
10%414323448%50%
1905
16th to endNight
13%424324347%49%
1881
October1st to 15thNight
10%5%25%42445%7%48%
1842
16th to endNight
17%7%26%423336%41%
2219
November1st to 15thNight
12%7%23424447%46%
2276
16th to endNight
19%10%45%5%3435%6%31%
2340
December1st to 15thNight
22%13%5%8%5%24336%24%
2340
16th to endNight
24%12%5%8%6%34345%21%
2640

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
62%310%14%9%
1433
16th to endDay
61%412%15%5%
1671
February1st to 15thDay
58%311%16%9%
1701
16th to endDay
58%311%20%6%
1580
March1st to 15thDay
57%312%18%6%
1852
16th to endDay
56%413%19%5%
2114
April1st to 15thDay
48%311%22%12%1
2151
16th to endDay
47%410%20%12%4
2306
May1st to 15thDay
53%5%11%19%8%
2331
16th to endDay
43%6%13%21%13%1
2435
June1st to 15thDay
37%5%11%25%17%1
2471
16th to endDay
37%6%14%21%17%2
2520
July1st to 15thDay
42%6%11%20%16%2
2371
16th to endDay
35%7%16%24%12%2
2374
August1st to 15thDay
37%5%12%25%16%2
2327
16th to endDay
34%6%11%25%15%4
2351
September1st to 15thDay
39%410%22%19%4
2043
16th to endDay
41%38%21%24%1
1872
October1st to 15thDay
39%49%23%19%2
1787
16th to endDay
46%312%24%11%1
1650
November1st to 15thDay
35%5%10%24%19%4
1582
16th to endDay
54%310%19%10%
1620
December1st to 15thDay
64%210%14%7%
1620
16th to endDay
65%39%17%3
1581
January1st to 15thNight
63%36%16%8%
2506
16th to endNight
61%39%18%6%
2551
February1st to 15thNight
56%312%19%7%
2160
16th to endNight
55%411%20%8%
1893
March1st to 15thNight
52%410%21%10%1
2107
16th to endNight
49%412%24%8%1
2112
April1st to 15thNight
45%310%23%15%1
1806
16th to endNight
41%411%20%14%6%
1653
May1st to 15thNight
51%5%10%22%9%1
1620
16th to endNight
37%6%14%21%16%3
1684
June1st to 15thNight
31%5%13%25%21%2
1485
16th to endNight
29%8%17%22%18%3
1440
July1st to 15thNight
35%5%13%21%17%5%
1360
16th to endNight
26%5%15%32%17%2
1530
August1st to 15thNight
29%5%15%26%20%2
1609
16th to endNight
27%5%14%25%21%4
1848
September1st to 15thNight
30%5%11%23%22%6%
1905
16th to endNight
34%48%23%26%2
1881
October1st to 15thNight
33%49%25%23%2
1842
16th to endNight
44%29%27%13%1
2219
November1st to 15thNight
37%48%22%22%4
2276
16th to endNight
51%310%21%11%
2340
December1st to 15thNight
61%39%16%7%1
2340
16th to endNight
64%48%16%6%
2640

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
31%14%34%13%5%1
90
16th to endDay
25%17%34%19%3
96
February1st to 15thDay
17%26%41%12%2
90
16th to endDay
17%9%49%17%6%
81
March1st to 15thDay
24%17%33%20%3
142
16th to endDay
22%19%31%17%7%1
288
April1st to 15thDay
19%21%25%19%11%2
270
16th to endDay
20%19%24%15%14%5%
270
May1st to 15thDay
27%16%21%20%10%4
288
16th to endDay
17%15%25%19%11%11%
331
June1st to 15thDay
10%13%18%29%21%6%
446
16th to endDay
10%14%25%27%15%6%
495
July1st to 15thDay
13%11%18%22%20%13%
475
16th to endDay
8%11%8%23%29%17%
391
August1st to 15thDay
10%7%9%21%26%24%
313
16th to endDay
8%6%10%24%31%19%
332
September1st to 15thDay
13%8%11%21%26%17%
315
16th to endDay
19%7%9%18%27%18%
275
October1st to 15thDay
13%10%18%30%19%7%
255
16th to endDay
17%11%33%27%9%
162
November1st to 15thDay
15%8%18%22%23%11%
90
16th to endDay
26%10%36%22%4
90
December1st to 15thDay
25%14%35%14%7%2
90
16th to endDay
27%20%38%11%2
96
January1st to 15thNight
20%25%30%19%4
900
16th to endNight
19%25%27%24%3
823
February1st to 15thNight
21%25%27%23%1
704
16th to endNight
19%25%25%25%3
631
March1st to 15thNight
19%24%25%24%5%
720
16th to endNight
17%20%28%24%7%1
768
April1st to 15thNight
15%23%27%25%7%
548
16th to endNight
15%20%25%25%11%1
540
May1st to 15thNight
19%20%22%24%12%
540
16th to endNight
12%18%16%30%17%3
563
June1st to 15thNight
9%17%15%36%19%
540
16th to endNight
7%17%16%35%22%1
540
July1st to 15thNight
10%12%12%33%27%3
510
16th to endNight
6%16%7%28%35%5%
564
August1st to 15thNight
7%10%8%35%32%5%
539
16th to endNight
39%9%33%37%6%
573
September1st to 15thNight
11%11%11%29%28%7%
645
16th to endNight
13%10%12%26%32%4
681
October1st to 15thNight
11%13%18%30%20%5%
660
16th to endNight
18%15%27%25%12%
704
November1st to 15thNight
13%19%25%23%16%2
700
16th to endNight
22%25%21%22%7%
720
December1st to 15thNight
26%22%23%19%7%1
720
16th to endNight
25%24%27%18%4
912
Page generated at 2017-09-22 07:35:31. Version ac04

Copyright 2017 A. Danko


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