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 2018-04-23.

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
41%
15383
9%
49485
8%
15354
43%
15354
14%
37310

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%
825
9%
2911
8%
821
29%
821
9%
2381
January16th to endNight
29%
848
6%
2966
6%
848
30%
848
8%
2430
February1st to 15thNight
27%
759
6%
2483
4%
759
30%
759
9%
2053
February16th to endNight
32%
684
12%
2210
9%
684
37%
684
13%
1690
March1st to 15thNight
27%
780
5%
2231
4%
780
27%
780
10%
1876
March16th to endNight
31%
832
6%
2247
4%
832
31%
832
10%
1918
April1st to 15thNight
34%
778
7%
1948
3%
778
36%
778
14%
1596
April16th to endNight
40%
522
8%
1638
7%
522
40%
522
12%
1289
May1st to 15thNight
55%
359
12%
1439
18%
359
58%
359
19%
914
May16th to endNight
58%
375
6%
1463
10%
374
60%
374
16%
989
June1st to 15thNight
54%
360
2%
1260
1%
360
54%
360
17%
889
June16th to endNight
56%
360
5%
1260
2%
360
56%
360
18%
867
July1st to 15thNight
74%
340
10%
1190
9%
340
75%
340
34%
638
July16th to endNight
78%
376
15%
1329
22%
354
80%
354
40%
631
August1st to 15thNight
79%
432
17%
1504
23%
430
79%
430
39%
744
August16th to endNight
72%
612
19%
1758
17%
612
73%
612
37%
1028
September1st to 15thNight
77%
720
21%
1800
13%
720
77%
720
45%
1067
September16th to endNight
49%
716
17%
1976
14%
716
50%
716
21%
1418
October1st to 15thNight
49%
720
10%
2160
10%
720
50%
720
20%
1525
October16th to endNight
35%
768
7%
2400
7%
768
37%
768
11%
1914
November1st to 15thNight
23%
760
5%
2660
5%
760
25%
760
6%
2272
November16th to endNight
26%
780
5%
2730
3%
780
28%
780
7%
2274
December1st to 15thNight
30%
797
7%
2802
6%
797
33%
797
9%
2267
December16th to endNight
20%
880
7%
3120
4%
880
24%
880
7%
2640

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
24%7%35%5%24445%31%
50059
Night
27%7%35%424345%30%
49639
Cloud CoverDay
25%8%35%5%24445%29%
50059
Night
29%8%35%423345%29%
49642
TransparencyDay
55%7%13%15%6%1
49716
Night
57%6%12%15%6%1
49486
SeeingDay
26%417%26%20%4
6776
Night
33%313%23%21%5%
15389

By Month

Percentage Cloud Cover NW (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
42%8%37%425%33314%
1358
16th to endDay
39%9%37%5%25%34415%
1606
February1st to 15thDay
36%9%46%6%33345%15%
1711
16th to endDay
25%10%37%5%34446%23%
1549
March1st to 15thDay
36%10%46%6%3433415%
2057
16th to endDay
29%10%48%6%3444419%
2328
April1st to 15thDay
26%9%46%5%46%6%5%6%20%
2329
16th to endDay
22%9%37%6%345%5%6%25%
2435
May1st to 15thDay
16%7%36%425%5%46%36%
2511
16th to endDay
18%7%36%5%35%5%5%7%30%
2645
June1st to 15thDay
19%6%36%6%35%5%5%6%32%
2700
16th to endDay
17%7%25%5%3446%7%34%
2700
July1st to 15thDay
9%424323446%54%
2700
16th to endDay
9%31322335%5%59%
2745
August1st to 15thDay
9%423323346%56%
2446
16th to endDay
10%41442345%8%49%
2444
September1st to 15thDay
12%5%24423346%50%
2160
16th to endDay
25%6%26%434446%31%
1982
October1st to 15thDay
25%7%36%4245%5%6%28%
1800
16th to endDay
35%8%47%5%23446%18%
1824
November1st to 15thDay
46%7%25%33333416%
1528
16th to endDay
39%9%36%5%3434316%
1560
December1st to 15thDay
31%12%45%5%3333321%
1485
16th to endDay
43%10%36%41342216%
1456
January1st to 15thNight
41%9%25%42323421%
2911
16th to endNight
36%9%36%5%25%346%18%
2966
February1st to 15thNight
36%8%36%433335%19%
2471
16th to endNight
28%9%35%423345%29%
2210
March1st to 15thNight
37%9%35%5%2333420%
2231
16th to endNight
31%9%46%6%2434419%
2243
April1st to 15thNight
26%8%47%6%34446%23%
1948
16th to endNight
24%8%37%6%35%45%5%25%
1638
May1st to 15thNight
16%5%35%43347%6%39%
1439
16th to endNight
15%6%26%5%36%5%5%7%34%
1463
June1st to 15thNight
19%8%25%5%24336%36%
1260
16th to endNight
13%6%47%6%35%5%5%6%35%
1260
July1st to 15thNight
6%323313336%60%
1260
16th to endNight
5%214313345%64%
1421
August1st to 15thNight
6%313323346%62%
1512
16th to endNight
8%31433346%8%52%
1758
September1st to 15thNight
8%212313336%61%
1800
16th to endNight
21%6%36%6%23346%37%
1976
October1st to 15thNight
22%6%245%24335%39%
2160
16th to endNight
33%8%34424446%23%
2400
November1st to 15thNight
41%8%35%5%3333316%
2660
16th to endNight
37%9%45%5%3332420%
2730
December1st to 15thNight
33%9%36%5%34335%21%
2802
16th to endNight
41%11%35%42322319%
3120

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
42%9%46%5%2432415%
1358
16th to endDay
39%9%36%5%2334416%
1606
February1st to 15thDay
38%9%36%5%34345%15%
1711
16th to endDay
26%11%36%5%34347%22%
1549
March1st to 15thDay
39%11%27%5%3333414%
2057
16th to endDay
32%10%38%6%3444316%
2328
April1st to 15thDay
29%8%47%6%45%6%45%17%
2329
16th to endDay
24%10%37%6%345%5%5%22%
2435
May1st to 15thDay
19%7%36%435%45%6%32%
2511
16th to endDay
19%9%35%6%35%45%7%27%
2645
June1st to 15thDay
21%8%46%6%35%5%46%28%
2700
16th to endDay
18%8%36%6%35%45%7%30%
2700
July1st to 15thDay
11%32442345%5%52%
2700
16th to endDay
10%423323345%56%
2745
August1st to 15thDay
10%424323346%53%
2446
16th to endDay
11%5%1442445%7%47%
2444
September1st to 15thDay
13%6%25%323236%50%
2160
16th to endDay
26%6%26%434435%30%
1982
October1st to 15thDay
26%8%25%5%2445%6%29%
1800
16th to endDay
37%7%47%5%23445%17%
1824
November1st to 15thDay
48%8%2441333413%
1528
16th to endDay
41%9%45%424335%15%
1560
December1st to 15thDay
33%11%46%43443319%
1485
16th to endDay
43%13%37%3323216%
1456
January1st to 15thNight
42%9%2432323421%
2910
16th to endNight
37%9%26%424336%19%
2966
February1st to 15thNight
37%10%36%433345%19%
2471
16th to endNight
29%9%35%423335%28%
2210
March1st to 15thNight
39%9%35%42433319%
2231
16th to endNight
33%9%36%6%25%445%18%
2247
April1st to 15thNight
27%10%37%6%24446%22%
1948
16th to endNight
26%9%37%6%35%45%5%23%
1638
May1st to 15thNight
18%5%35%5%235%5%6%38%
1439
16th to endNight
15%8%25%5%45%5%6%8%33%
1463
June1st to 15thNight
21%8%3443435%6%34%
1260
16th to endNight
15%7%36%6%35%5%6%5%34%
1260
July1st to 15thNight
7%413423247%58%
1260
16th to endNight
6%214322345%63%
1421
August1st to 15thNight
8%313223335%62%
1512
16th to endNight
8%31332345%9%52%
1758
September1st to 15thNight
8%223214435%60%
1800
16th to endNight
22%7%26%5%23335%37%
1976
October1st to 15thNight
22%6%25%5%2434438%
2160
16th to endNight
35%7%345%23346%22%
2400
November1st to 15thNight
43%8%36%5%3432415%
2660
16th to endNight
38%8%46%5%2332319%
2730
December1st to 15thNight
34%10%35%5%24345%20%
2802
16th to endNight
43%12%35%41222318%
3120

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
73%7%6%7%4
1358
16th to endDay
71%6%8%9%2
1606
February1st to 15thDay
72%5%8%6%42
1711
16th to endDay
62%7%11%12%5%
1549
March1st to 15thDay
72%6%9%9%1
2057
16th to endDay
70%7%9%10%1
2328
April1st to 15thDay
65%9%12%10%1
2329
16th to endDay
61%8%12%12%4
2435
May1st to 15thDay
50%8%15%17%7%
2511
16th to endDay
54%9%17%15%3
2649
June1st to 15thDay
53%8%18%14%41
2700
16th to endDay
50%9%18%15%4
2700
July1st to 15thDay
32%8%17%26%12%3
2541
16th to endDay
27%9%19%28%13%1
2574
August1st to 15thDay
31%8%18%29%10%2
2429
16th to endDay
34%9%20%26%7%1
2444
September1st to 15thDay
36%6%15%21%16%2
2160
16th to endDay
55%7%11%15%7%
1982
October1st to 15thDay
55%8%14%13%7%
1800
16th to endDay
68%7%10%9%4
1824
November1st to 15thDay
74%6%7%7%21
1528
16th to endDay
71%6%6%8%5%
1560
December1st to 15thDay
69%6%5%9%7%1
1485
16th to endDay
75%47%8%21
1456
January1st to 15thNight
67%6%6%14%4
2911
16th to endNight
67%7%8%11%31
2966
February1st to 15thNight
68%6%10%8%32
2483
16th to endNight
58%6%10%16%6%1
2210
March1st to 15thNight
69%6%10%11%3
2231
16th to endNight
68%7%10%10%2
2247
April1st to 15thNight
63%6%12%14%3
1948
16th to endNight
61%7%12%13%5%
1638
May1st to 15thNight
44%6%17%18%10%1
1440
16th to endNight
46%9%21%16%4
1463
June1st to 15thNight
50%7%20%15%42
1260
16th to endNight
48%7%17%18%5%2
1260
July1st to 15thNight
28%6%14%31%15%3
1190
16th to endNight
22%5%19%33%15%3
1329
August1st to 15thNight
24%5%21%31%13%3
1504
16th to endNight
29%7%20%28%10%3
1758
September1st to 15thNight
25%6%17%25%20%4
1800
16th to endNight
49%6%11%22%7%2
1976
October1st to 15thNight
50%5%14%19%9%
2160
16th to endNight
62%8%12%11%5%
2400
November1st to 15thNight
73%5%9%6%21
2660
16th to endNight
70%6%8%7%6%
2730
December1st to 15thNight
66%5%9%9%6%1
2802
16th to endNight
72%5%7%8%41
3120

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%212%16%17%20%
90
16th to endDay
62%7%9%9%8%1
112
February1st to 15thDay
47%6%9%18%15%2
281
16th to endDay
35%7%20%19%13%3
253
March1st to 15thDay
45%6%18%15%10%3
330
16th to endDay
40%7%17%20%10%2
352
April1st to 15thDay
33%7%20%21%13%2
329
16th to endDay
25%6%27%24%13%2
288
May1st to 15thDay
22%322%30%19%1
288
16th to endDay
20%220%24%24%7%
360
June1st to 15thDay
19%323%30%19%4
495
16th to endDay
18%323%30%21%3
495
July1st to 15thDay
10%213%37%32%3
475
16th to endDay
8%114%38%32%5%
414
August1st to 15thDay
13%18%35%28%12%
315
16th to endDay
10%116%33%29%8%
332
September1st to 15thDay
18%218%28%26%6%
315
16th to endDay
26%216%25%20%7%
315
October1st to 15thDay
32%219%24%17%4
315
16th to endDay
41%5%13%20%15%3
256
November1st to 15thDay
54%6%17%15%41
90
16th to endDay
48%6%12%13%7%11%
90
December1st to 15thDay
48%211%8%16%12%
90
16th to endDay
51%5%8%22%9%3
96
January1st to 15thNight
46%414%15%15%3
825
16th to endNight
44%413%21%13%2
848
February1st to 15thNight
42%416%22%13%1
764
16th to endNight
34%5%19%23%14%2
684
March1st to 15thNight
42%6%15%19%13%1
780
16th to endNight
39%415%22%13%4
832
April1st to 15thNight
34%5%14%26%16%3
778
16th to endNight
31%413%29%16%4
522
May1st to 15thNight
19%210%31%32%4
360
16th to endNight
18%26%29%37%5%
375
June1st to 15thNight
22%311%26%30%5%
360
16th to endNight
16%213%29%32%4
360
July1st to 15thNight
9%27%27%45%7%
340
16th to endNight
7%6%27%48%9%
376
August1st to 15thNight
10%319%45%19%
432
16th to endNight
12%6%22%44%13%
612
September1st to 15thNight
10%15%27%40%14%
720
16th to endNight
26%112%24%26%8%
716
October1st to 15thNight
27%115%25%23%5%
720
16th to endNight
39%313%23%17%3
768
November1st to 15thNight
48%416%22%6%
760
16th to endNight
42%5%16%19%12%4
780
December1st to 15thNight
39%415%23%13%2
797
16th to endNight
50%5%18%18%6%
880
Page generated at 2018-04-24 07:02:59. Version ac04

Copyright 2018 A. Danko


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