James River State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the James River State Park clear sky chart from 2005-11-06 to 2024-02-20.

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
43%
24010
21%
79893
13%
23915
52%
23915
25%
49147

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 10thNight
25%
752
27%
3994
9%
737
44%
737
17%
2087
January11th to 20thNight
26%
759
28%
3944
10%
740
43%
740
15%
2167
January21st to endNight
24%
830
17%
4442
11%
814
44%
814
15%
2683
February1st to 10thNight
28%
760
21%
2470
11%
760
41%
760
24%
1512
February11th to 20thNight
18%
739
20%
2397
7%
738
35%
738
21%
1541
February21st to endNight
24%
592
28%
1692
11%
592
42%
592
25%
1080
March1st to 10thNight
30%
720
26%
1980
12%
720
44%
720
30%
1216
March11th to 20thNight
28%
720
20%
1980
9%
720
38%
720
23%
1333
March21st to endNight
30%
792
19%
2178
8%
792
39%
792
25%
1455
April1st to 10thNight
27%
720
21%
1850
6%
720
37%
720
30%
1202
April11th to 20thNight
39%
711
24%
1775
9%
711
46%
711
36%
1115
April21st to endNight
40%
701
22%
1781
9%
701
46%
701
31%
1179
May1st to 10thNight
40%
540
17%
1620
9%
540
46%
540
24%
1075
May11th to 20thNight
46%
531
14%
1593
9%
531
49%
531
23%
1103
May21st to endNight
60%
528
15%
1690
13%
528
63%
528
25%
1093
June1st to 10thNight
65%
360
20%
1440
23%
360
68%
360
25%
819
June11th to 20thNight
60%
360
15%
1440
17%
360
63%
360
23%
864
June21st to endNight
68%
381
19%
1461
21%
381
71%
381
28%
841
July1st to 10thNight
66%
525
14%
1575
12%
525
68%
525
27%
1037
July11th to 20thNight
74%
522
16%
1566
13%
522
75%
522
34%
937
July21st to endNight
69%
591
17%
1672
13%
558
70%
558
31%
1050
August1st to 10thNight
64%
537
16%
1600
13%
534
66%
534
25%
1063
August11th to 20thNight
63%
552
18%
1616
15%
552
64%
552
25%
1094
August21st to endNight
63%
792
16%
1980
11%
792
65%
792
29%
1376
September1st to 10thNight
65%
720
22%
1800
15%
720
66%
720
33%
1206
September11th to 20thNight
63%
720
25%
1898
21%
720
65%
720
31%
1255
September21st to endNight
47%
720
19%
2026
15%
720
52%
720
24%
1402
October1st to 10thNight
53%
720
22%
2160
20%
720
58%
720
30%
1341
October11th to 20thNight
48%
720
26%
2160
21%
720
58%
720
31%
1298
October21st to endNight
47%
792
29%
2376
21%
792
60%
792
34%
1374
November1st to 10thNight
45%
740
28%
2221
20%
740
55%
740
31%
1326
November11th to 20thNight
37%
760
26%
2434
15%
760
52%
760
29%
1408
November21st to endNight
41%
760
25%
2660
17%
760
54%
760
28%
1486
December1st to 10thNight
29%
760
22%
2660
11%
760
44%
760
20%
1678
December11th to 20thNight
34%
759
24%
3167
14%
758
49%
758
21%
1832
December21st to endNight
32%
824
15%
4595
11%
817
47%
817
13%
2619

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%5%25%5%35%5%6%8%43%
78459
Night
14%6%25%5%3445%7%45%
80725
TransparencyDay
38%7%12%22%16%4
78180
Night
38%6%11%22%18%4
80523
SeeingDay
19%11%25%25%15%6%
14047
Night
17%7%26%33%15%2
24043

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 10thDay
17%5%24424446%48%
2836
11th to 20thDay
14%7%36%5%3445%5%43%
2840
21st to endDay
20%7%36%433345%41%
3124
February1st to 10thDay
12%6%25%5%35%5%7%8%42%
1710
11th to 20thDay
19%7%245%3445%6%43%
1654
21st to endDay
19%7%35%5%25%347%39%
1559
March1st to 10thDay
14%5%25%424347%51%
1980
11th to 20thDay
17%6%35%6%35%46%7%40%
1980
21st to endDay
17%7%36%5%2445%6%39%
2178
April1st to 10thDay
10%5%24335%5%47%51%
2109
11th to 20thDay
12%5%25%42445%7%49%
2134
21st to endDay
17%5%25%5%45%45%7%42%
2194
May1st to 10thDay
14%6%26%5%35%5%6%9%39%
2340
11th to 20thDay
17%5%35%5%45%6%6%8%37%
2301
21st to endDay
14%5%25%6%35%5%6%9%39%
2577
June1st to 10thDay
11%3345%35%5%6%10%44%
2520
11th to 20thDay
10%435%5%45%6%7%11%40%
2520
21st to endDay
8%325%5%45%7%7%12%42%
2493
July1st to 10thDay
10%5%26%5%35%6%6%11%39%
2340
11th to 20thDay
5%325%6%47%7%8%11%40%
2340
21st to endDay
9%5%27%6%5%6%6%8%10%36%
2547
August1st to 10thDay
12%5%35%6%46%5%7%10%36%
2327
11th to 20thDay
12%5%36%7%5%6%7%6%9%35%
2267
21st to endDay
10%5%25%5%446%8%10%40%
2376
September1st to 10thDay
11%6%25%5%345%6%7%47%
2160
11th to 20thDay
12%5%35%5%345%6%7%45%
2059
21st to endDay
21%6%25%5%245%5%6%39%
1933
October1st to 10thDay
15%5%25%42445%6%49%
1800
11th to 20thDay
16%423324446%52%
1800
21st to endDay
14%5%24423336%52%
1980
November1st to 10thDay
13%423323445%56%
1857
11th to 20thDay
14%6%24324446%51%
1742
21st to endDay
14%42443445%7%50%
1520
December1st to 10thDay
17%7%35%3345%6%7%40%
1520
11th to 20thDay
16%5%23323345%53%
1910
21st to endDay
20%5%25%5%345%6%7%39%
2932
January1st to 10thNight
13%6%35%43445%6%48%
4109
11th to 20thNight
17%7%24323345%49%
4120
21st to endNight
20%8%35%42335%5%42%
4532
February1st to 10thNight
14%6%25%5%25%5%5%7%44%
2470
11th to 20thNight
20%8%24433445%44%
2397
21st to endNight
15%7%245%25%45%6%45%
1692
March1st to 10thNight
13%5%145%2445%7%50%
1980
11th to 20thNight
18%5%245%245%5%8%40%
1980
21st to endNight
15%7%36%4246%47%43%
2178
April1st to 10thNight
13%6%345%3446%8%45%
1850
11th to 20thNight
12%5%2442346%8%50%
1775
21st to endNight
16%5%245%35%447%45%
1781
May1st to 10thNight
15%6%26%5%35%5%7%7%40%
1620
11th to 20thNight
17%7%35%5%35%5%5%8%37%
1592
21st to endNight
13%6%24445%6%6%8%41%
1690
June1st to 10thNight
9%5%245%35%6%7%9%45%
1440
11th to 20thNight
10%6%25%6%35%6%5%9%43%
1440
21st to endNight
8%425%435%6%7%11%45%
1461
July1st to 10thNight
9%5%35%7%45%5%7%9%42%
1620
11th to 20thNight
5%315%6%35%5%8%11%47%
1620
21st to endNight
8%4245%46%7%8%11%40%
1771
August1st to 10thNight
11%427%6%45%7%6%9%39%
1611
11th to 20thNight
14%6%36%6%45%5%7%9%37%
1616
21st to endNight
10%5%27%6%36%5%7%9%39%
1980
September1st to 10thNight
12%6%35%4345%5%7%46%
1800
11th to 20thNight
12%5%345%35%6%5%7%45%
1898
21st to endNight
22%7%24435%35%6%39%
2026
October1st to 10thNight
17%5%25%334446%47%
2160
11th to 20thNight
14%6%24424447%49%
2160
21st to endNight
14%42342345%5%53%
2376
November1st to 10thNight
13%6%25%43333454%
2221
11th to 20thNight
13%5%2442445%6%51%
2434
21st to endNight
13%324434447%50%
2660
December1st to 10thNight
18%7%35%5%345%45%43%
2660
11th to 20thNight
16%6%24433446%47%
3285
21st to endNight
17%5%25%5%35%5%5%7%41%
4720

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 10thDay
36%5%8%29%16%6%
2837
11th to 20thDay
40%5%8%19%22%6%
2840
21st to endDay
46%5%8%22%16%3
3124
February1st to 10thDay
39%7%11%25%16%3
1710
11th to 20thDay
41%6%8%19%20%5%
1663
21st to endDay
47%411%15%17%6%
1559
March1st to 10thDay
35%5%9%22%23%6%
1980
11th to 20thDay
42%7%11%17%16%7%
1980
21st to endDay
46%6%9%19%15%4
2178
April1st to 10thDay
32%6%12%23%19%8%
2109
11th to 20thDay
35%5%12%22%20%6%
2134
21st to endDay
41%7%12%21%15%5%
2194
May1st to 10thDay
40%8%17%19%13%3
2340
11th to 20thDay
44%8%14%22%9%2
2305
21st to endDay
40%10%15%23%12%
2577
June1st to 10thDay
34%9%16%26%14%1
2520
11th to 20thDay
36%11%17%20%14%2
2520
21st to endDay
33%11%17%24%13%2
2493
July1st to 10thDay
37%11%14%20%15%3
2275
11th to 20thDay
32%11%19%21%15%2
2271
21st to endDay
39%11%15%22%13%1
2405
August1st to 10thDay
41%10%16%24%9%1
2314
11th to 20thDay
43%11%14%21%10%1
2267
21st to endDay
36%10%19%21%12%2
2376
September1st to 10thDay
36%8%14%18%21%4
2160
11th to 20thDay
37%7%10%24%19%4
2059
21st to endDay
45%6%11%18%18%2
1933
October1st to 10thDay
36%5%10%26%20%4
1800
11th to 20thDay
34%5%8%26%23%4
1800
21st to endDay
35%48%26%21%6%
1980
November1st to 10thDay
31%410%24%26%5%
1857
11th to 20thDay
35%5%9%22%21%8%
1742
21st to endDay
33%5%10%23%25%4
1520
December1st to 10thDay
42%7%11%20%16%4
1520
11th to 20thDay
34%49%26%18%9%
1906
21st to endDay
41%7%11%26%13%2
2932
January1st to 10thNight
36%5%9%24%22%5%
4109
11th to 20thNight
39%48%20%23%6%
4120
21st to endNight
45%46%24%15%6%
4532
February1st to 10thNight
39%6%11%24%18%3
2470
11th to 20thNight
43%48%19%19%7%
2399
21st to endNight
39%5%11%22%17%6%
1692
March1st to 10thNight
33%6%9%24%22%5%
1980
11th to 20thNight
43%6%8%20%18%4
1980
21st to endNight
42%6%11%19%17%5%
2178
April1st to 10thNight
37%6%12%17%21%6%
1850
11th to 20thNight
33%6%12%22%22%6%
1775
21st to endNight
39%6%12%22%16%5%
1781
May1st to 10thNight
41%8%14%20%13%4
1620
11th to 20thNight
44%9%13%20%12%2
1593
21st to endNight
37%11%16%24%11%1
1691
June1st to 10thNight
33%9%14%28%15%1
1440
11th to 20thNight
37%9%18%19%15%2
1440
21st to endNight
31%10%17%21%17%4
1461
July1st to 10thNight
37%10%16%18%15%4
1575
11th to 20thNight
29%10%22%24%12%2
1566
21st to endNight
34%9%19%24%13%
1672
August1st to 10thNight
39%11%17%22%11%1
1600
11th to 20thNight
42%9%15%22%12%1
1616
21st to endNight
39%10%17%21%10%3
1980
September1st to 10thNight
36%8%13%20%17%5%
1800
11th to 20thNight
37%9%11%22%19%2
1898
21st to endNight
46%6%9%19%16%3
2026
October1st to 10thNight
37%6%11%25%18%3
2160
11th to 20thNight
35%5%8%25%22%5%
2160
21st to endNight
32%5%9%23%25%7%
2376
November1st to 10thNight
36%47%21%25%7%
2221
11th to 20thNight
33%6%8%20%24%9%
2434
21st to endNight
33%5%9%25%22%6%
2660
December1st to 10thNight
44%5%7%23%17%4
2660
11th to 20thNight
39%49%21%20%7%
3288
21st to endNight
40%7%11%24%16%2
4720

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 10thDay
21%25%28%20%41
270
11th to 20thDay
27%26%34%11%1
270
21st to endDay
25%22%34%14%5%
297
February1st to 10thDay
21%23%39%12%4
270
11th to 20thDay
37%25%28%9%1
267
21st to endDay
32%19%28%17%4
330
March1st to 10thDay
24%17%33%22%4
420
11th to 20thDay
21%21%34%18%5%
420
21st to endDay
25%16%32%22%5%2
462
April1st to 10thDay
22%20%27%22%9%1
420
11th to 20thDay
20%12%32%23%10%4
412
21st to endDay
22%12%31%22%10%2
420
May1st to 10thDay
21%14%33%21%9%3
423
11th to 20thDay
20%9%27%27%13%5%
447
21st to endDay
19%420%32%19%7%
485
June1st to 10thDay
12%7%24%27%24%7%
450
11th to 20thDay
13%8%20%32%18%10%
450
21st to endDay
10%6%24%31%22%8%
450
July1st to 10thDay
13%216%28%28%13%
445
11th to 20thDay
5%215%34%31%13%
444
21st to endDay
12%319%30%23%13%
488
August1st to 10thDay
16%415%27%25%13%
446
11th to 20thDay
12%217%28%26%15%
439
21st to endDay
13%214%27%26%18%
495
September1st to 10thDay
14%314%26%24%18%
450
11th to 20thDay
16%412%30%27%11%
450
21st to endDay
28%8%16%27%16%5%
450
October1st to 10thDay
21%6%18%29%18%8%
450
11th to 20thDay
15%11%23%28%20%3
450
21st to endDay
16%10%31%29%10%3
495
November1st to 10thDay
17%9%27%29%15%4
455
11th to 20thDay
19%13%30%23%14%2
344
21st to endDay
17%14%34%23%9%2
180
December1st to 10thDay
24%14%36%19%6%1
180
11th to 20thDay
24%13%34%23%5%1
180
21st to endDay
27%14%30%19%8%1
243
January1st to 10thNight
19%12%37%28%3
760
11th to 20thNight
21%13%35%28%3
760
21st to endNight
18%10%43%26%3
836
February1st to 10thNight
17%11%40%28%3
760
11th to 20thNight
27%13%38%21%1
742
21st to endNight
21%14%37%26%2
592
March1st to 10thNight
17%13%37%29%4
720
11th to 20thNight
22%12%34%25%7%1
720
21st to endNight
19%12%35%29%5%1
792
April1st to 10thNight
16%13%39%24%7%
720
11th to 20thNight
15%10%32%32%10%1
711
21st to endNight
18%6%30%37%9%1
701
May1st to 10thNight
17%8%29%33%12%1
540
11th to 20thNight
21%5%20%36%17%2
531
21st to endNight
16%213%37%29%3
530
June1st to 10thNight
9%214%47%25%3
360
11th to 20thNight
12%316%37%29%3
360
21st to endNight
7%215%51%23%3
381
July1st to 10thNight
10%211%37%36%5%
525
11th to 20thNight
6%17%36%43%7%
522
21st to endNight
8%210%43%33%3
591
August1st to 10thNight
12%37%40%31%6%
537
11th to 20thNight
17%26%36%35%4
552
21st to endNight
13%211%34%35%5%
792
September1st to 10thNight
16%210%33%32%7%
720
11th to 20thNight
14%410%35%31%6%
720
21st to endNight
27%416%31%21%2
720
October1st to 10thNight
19%5%18%31%23%5%
720
11th to 20thNight
17%7%23%34%18%1
720
21st to endNight
16%7%26%37%14%1
792
November1st to 10thNight
16%6%26%36%13%2
740
11th to 20thNight
16%9%32%31%11%1
760
21st to endNight
15%8%31%36%9%1
760
December1st to 10thNight
22%8%33%29%7%
760
11th to 20thNight
17%8%34%34%6%
760
21st to endNight
21%9%31%35%3
836
Page generated at 2024-02-17 06:28:42. Version ac07

Copyright 2024 Attilla Danko


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