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 2017-08-12.

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
39%
15276
21%
46554
12%
15240
49%
15240
25%
29265

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
25%
716
24%
2348
10%
716
41%
716
19%
1453
January16th to endNight
20%
768
23%
2496
8%
768
38%
768
22%
1533
February1st to 15thNight
24%
701
21%
2287
9%
701
41%
701
22%
1379
February16th to endNight
21%
631
26%
1907
9%
631
41%
631
23%
1166
March1st to 15thNight
26%
720
24%
1980
11%
720
39%
720
25%
1266
March16th to endNight
27%
768
21%
2103
9%
768
37%
768
23%
1418
April1st to 15thNight
26%
718
22%
1796
5%
718
37%
718
30%
1172
April16th to endNight
35%
720
20%
1800
7%
720
41%
720
32%
1183
May1st to 15thNight
36%
600
16%
1680
7%
600
41%
600
25%
1142
May16th to endNight
54%
422
19%
1544
15%
422
61%
422
25%
913
June1st to 15thNight
58%
360
16%
1440
17%
360
63%
360
24%
840
June16th to endNight
58%
360
17%
1440
17%
360
65%
360
24%
837
July1st to 15thNight
56%
409
14%
1429
14%
409
59%
409
23%
917
July16th to endNight
68%
564
17%
1595
12%
531
71%
531
32%
991
August1st to 15thNight
64%
530
17%
1578
12%
527
65%
527
28%
1030
August16th to endNight
60%
700
17%
1750
10%
700
60%
700
29%
1206
September1st to 15thNight
60%
660
24%
1650
16%
660
63%
660
32%
1109
September16th to endNight
47%
657
17%
1816
14%
657
50%
657
23%
1266
October1st to 15thNight
46%
660
25%
1980
21%
660
54%
660
26%
1255
October16th to endNight
38%
704
30%
2112
19%
704
53%
704
30%
1246
November1st to 15thNight
40%
700
25%
2173
16%
700
52%
700
29%
1298
November16th to endNight
36%
720
23%
2442
16%
720
49%
720
24%
1434
December1st to 15thNight
30%
720
21%
2520
11%
720
43%
720
21%
1550
December16th to endNight
28%
768
23%
2688
12%
768
44%
768
19%
1661

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
13%5%25%5%3445%7%42%
47401
Night
14%5%2442445%7%44%
46744
Cloud CoverDay
13%5%25%5%3445%7%42%
47411
Night
14%5%2442445%7%44%
46748
TransparencyDay
39%5%11%22%17%3
47108
Night
39%5%10%21%18%4
46555
SeeingDay
18%8%24%25%17%6%
5585
Night
17%10%27%30%13%1
15284

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
16%6%245%23445%44%
1587
16th to endDay
16%6%245%22345%45%
1728
February1st to 15thDay
15%6%25%5%23445%43%
1575
16th to endDay
15%5%245%35%36%6%41%
1563
March1st to 15thDay
15%424424348%46%
1969
16th to endDay
18%5%26%424346%41%
2121
April1st to 15thDay
11%424424337%51%
2152
16th to endDay
15%5%25%423446%44%
2160
May1st to 15thDay
16%5%25%43446%7%37%
2280
16th to endDay
13%4245%3446%8%41%
2570
June1st to 15thDay
12%314435%6%6%10%41%
2520
16th to endDay
7%425%5%35%6%6%11%40%
2520
July1st to 15thDay
8%5%26%6%37%6%6%10%35%
2442
16th to endDay
5%315%7%47%6%8%10%38%
2465
August1st to 15thDay
11%6%27%6%36%5%7%9%34%
2274
16th to endDay
12%426%6%45%6%7%9%35%
2100
September1st to 15thDay
11%5%245%35%46%6%44%
1980
16th to endDay
18%6%26%5%3345%6%35%
1809
October1st to 15thDay
18%5%2432332448%
1650
16th to endDay
14%414323335%52%
1760
November1st to 15thDay
15%415%324335%49%
1685
16th to endDay
14%424323345%51%
1515
December1st to 15thDay
16%6%143225%5%6%45%
1440
16th to endDay
19%6%26%323345%42%
1536
January1st to 15thNight
16%5%24324446%44%
2348
16th to endNight
17%6%2332344445%
2496
February1st to 15thNight
15%5%24423445%45%
2285
16th to endNight
14%5%25%5%23336%47%
1907
March1st to 15thNight
14%5%1442435%6%46%
1968
16th to endNight
18%5%25%424346%41%
2103
April1st to 15thNight
11%5%35%5%33348%47%
1796
16th to endNight
14%6%24424347%46%
1800
May1st to 15thNight
16%6%3443445%8%39%
1680
16th to endNight
13%4135%3346%7%45%
1543
June1st to 15thNight
8%3345%35%5%7%10%40%
1440
16th to endNight
8%325%5%35%5%6%9%43%
1440
July1st to 15thNight
8%426%6%46%45%7%41%
1515
16th to endNight
5%4245%36%6%9%9%41%
1703
August1st to 15thNight
8%426%6%35%5%7%9%38%
1589
16th to endNight
12%5%25%5%35%6%6%9%37%
1750
September1st to 15thNight
12%425%4345%6%6%44%
1650
16th to endNight
19%6%25%42436%6%37%
1816
October1st to 15thNight
17%425%5%23335%45%
1980
16th to endNight
15%413322345%52%
2112
November1st to 15thNight
13%6%14323345%50%
2173
16th to endNight
15%423324445%48%
2442
December1st to 15thNight
15%6%24424446%43%
2520
16th to endNight
18%6%25%323346%42%
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
16%6%245%2344444%
1587
16th to endDay
16%6%24422446%45%
1728
February1st to 15thDay
15%6%25%43335%5%42%
1575
16th to endDay
15%5%245%35%46%7%41%
1563
March1st to 15thDay
14%42442335%7%46%
1980
16th to endDay
18%6%26%5%23346%41%
2120
April1st to 15thDay
11%4245%23336%51%
2152
16th to endDay
15%5%26%423346%44%
2160
May1st to 15thDay
16%6%25%435%46%6%37%
2280
16th to endDay
13%4245%35%5%6%9%41%
2570
June1st to 15thDay
12%3145%35%6%6%10%41%
2520
16th to endDay
7%426%5%35%6%6%10%40%
2520
July1st to 15thDay
8%5%26%6%46%6%6%10%35%
2442
16th to endDay
5%325%7%46%6%8%11%38%
2465
August1st to 15thDay
10%5%27%6%45%6%7%9%34%
2274
16th to endDay
11%426%6%35%6%7%10%35%
2100
September1st to 15thDay
11%5%24435%46%6%44%
1980
16th to endDay
18%6%26%5%3345%6%36%
1809
October1st to 15thDay
18%5%2432332449%
1650
16th to endDay
14%414323336%52%
1760
November1st to 15thDay
15%415%314335%49%
1685
16th to endDay
13%5%24313345%51%
1515
December1st to 15thDay
15%6%143225%5%6%45%
1440
16th to endDay
19%6%35%423335%41%
1536
January1st to 15thNight
16%5%24324446%44%
2348
16th to endNight
17%6%2432344445%
2496
February1st to 15thNight
16%5%34423445%46%
2278
16th to endNight
14%425%5%23246%47%
1907
March1st to 15thNight
14%5%1442445%6%46%
1980
16th to endNight
18%5%25%5%24346%41%
2103
April1st to 15thNight
11%5%25%5%23348%46%
1796
16th to endNight
15%5%24424347%46%
1800
May1st to 15thNight
16%6%25%434448%38%
1679
16th to endNight
13%4145%345%5%8%45%
1543
June1st to 15thNight
9%3245%35%6%7%10%40%
1440
16th to endNight
8%325%5%35%5%7%9%43%
1440
July1st to 15thNight
8%426%6%36%5%5%8%41%
1515
16th to endNight
5%4245%27%6%8%9%41%
1703
August1st to 15thNight
8%436%6%35%6%7%9%38%
1589
16th to endNight
11%6%25%5%36%5%6%9%37%
1750
September1st to 15thNight
12%425%5%345%6%7%43%
1650
16th to endNight
18%7%25%5%2445%6%37%
1816
October1st to 15thNight
17%425%5%23335%45%
1980
16th to endNight
15%414312345%52%
2112
November1st to 15thNight
13%6%24424335%50%
2173
16th to endNight
15%423324446%48%
2442
December1st to 15thNight
15%7%24424446%43%
2520
16th to endNight
18%6%35%323346%42%
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
41%49%22%17%4
1588
16th to endDay
40%39%23%17%5%
1728
February1st to 15thDay
42%37%24%18%3
1577
16th to endDay
41%49%22%18%3
1563
March1st to 15thDay
37%410%23%17%5%
1980
16th to endDay
44%49%19%17%4
2121
April1st to 15thDay
34%310%24%20%6%
2152
16th to endDay
40%310%18%17%8%
2160
May1st to 15thDay
44%5%13%19%14%1
2280
16th to endDay
38%6%15%25%13%1
2574
June1st to 15thDay
35%8%15%25%13%1
2520
16th to endDay
35%8%16%21%16%2
2520
July1st to 15thDay
40%8%15%18%12%3
2299
16th to endDay
36%9%15%21%15%1
2310
August1st to 15thDay
42%8%13%21%12%1
2261
16th to endDay
42%6%14%21%12%1
2100
September1st to 15thDay
38%7%13%15%21%3
1980
16th to endDay
48%5%8%17%18%1
1809
October1st to 15thDay
40%46%24%20%3
1650
16th to endDay
33%36%25%24%5%
1760
November1st to 15thDay
37%37%21%22%6%
1685
16th to endDay
34%47%23%24%4
1515
December1st to 15thDay
38%5%9%25%16%5%
1440
16th to endDay
45%47%22%17%2
1536
January1st to 15thNight
40%49%19%19%6%
2348
16th to endNight
40%39%24%17%4
2496
February1st to 15thNight
39%37%24%20%4
2287
16th to endNight
39%37%24%19%5%
1907
March1st to 15thNight
38%5%7%27%18%3
1980
16th to endNight
44%47%22%17%3
2103
April1st to 15thNight
37%49%21%21%5%
1796
16th to endNight
38%411%19%18%7%
1800
May1st to 15thNight
43%5%14%20%13%2
1680
16th to endNight
36%7%14%26%13%1
1545
June1st to 15thNight
35%8%16%22%15%1
1440
16th to endNight
34%8%15%18%19%3
1440
July1st to 15thNight
41%8%14%19%13%3
1429
16th to endNight
32%9%17%24%14%1
1595
August1st to 15thNight
37%8%15%22%14%
1578
16th to endNight
39%8%13%21%14%1
1750
September1st to 15thNight
37%7%14%18%17%4
1650
16th to endNight
46%5%9%15%18%3
1816
October1st to 15thNight
41%48%23%19%4
1980
16th to endNight
34%37%24%24%5%
2112
November1st to 15thNight
37%38%17%25%7%
2173
16th to endNight
36%47%23%21%6%
2442
December1st to 15thNight
42%49%21%18%3
2520
16th to endNight
43%310%22%16%4
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
29%22%40%5%2
86
16th to endDay
29%29%32%8%1
96
February1st to 15thDay
24%33%34%6%1
90
16th to endDay
18%16%38%23%3
222
March1st to 15thDay
20%18%30%24%6%
270
16th to endDay
20%15%36%18%7%2
288
April1st to 15thDay
17%11%31%26%11%2
270
16th to endDay
23%8%27%26%9%4
270
May1st to 15thDay
25%12%28%19%9%4
288
16th to endDay
20%421%26%21%5%
331
June1st to 15thDay
13%6%22%28%20%9%
315
16th to endDay
11%5%24%36%17%4
315
July1st to 15thDay
11%119%37%23%6%
305
16th to endDay
7%18%30%30%12%
326
August1st to 15thDay
16%115%25%32%9%
297
16th to endDay
11%12%29%27%17%
268
September1st to 15thDay
15%314%23%25%16%
255
16th to endDay
31%217%19%17%11%
254
October1st to 15thDay
26%5%18%24%18%7%
255
16th to endDay
13%9%30%27%17%2
272
November1st to 15thDay
18%7%26%26%16%4
253
16th to endDay
17%13%31%20%14%1
135
December1st to 15thDay
25%10%41%10%11%1
60
16th to endDay
28%18%26%21%4
64
January1st to 15thNight
20%17%32%23%5%
720
16th to endNight
22%15%36%24%1
768
February1st to 15thNight
21%14%35%26%1
704
16th to endNight
19%20%35%22%2
631
March1st to 15thNight
19%16%35%24%4
720
16th to endNight
20%13%34%24%6%
768
April1st to 15thNight
14%17%38%24%4
718
16th to endNight
19%8%34%26%11%
720
May1st to 15thNight
18%9%32%30%9%
600
16th to endNight
14%419%40%18%2
423
June1st to 15thNight
10%319%40%24%2
360
16th to endNight
7%421%44%22%
360
July1st to 15thNight
9%219%38%27%1
409
16th to endNight
7%114%39%29%7%
564
August1st to 15thNight
9%112%45%28%3
530
16th to endNight
13%212%35%31%5%
700
September1st to 15thNight
15%113%35%29%3
660
16th to endNight
21%317%31%23%1
657
October1st to 15thNight
20%6%21%28%20%3
660
16th to endNight
17%12%28%26%14%
704
November1st to 15thNight
17%8%28%30%13%2
700
16th to endNight
17%14%28%29%10%
720
December1st to 15thNight
19%11%32%25%9%
720
16th to endNight
21%14%31%28%4
768
Page generated at 2017-08-13 14:16:57. Version ac04

Copyright 2017 A. Danko


Richmond Clear Sky Chart | Charts Home