Charlottesville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charlottesville clear sky chart from 2005-11-06 to 2024-03-28.

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%
24003
21%
80297
14%
23910
52%
23910
25%
49272

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
28%
751
27%
3994
10%
737
46%
737
18%
2056
January11th to 20thNight
28%
759
28%
3933
12%
740
44%
740
16%
2145
January21st to endNight
28%
828
17%
4437
11%
814
46%
814
15%
2672
February1st to 10thNight
32%
760
21%
2470
12%
760
44%
760
24%
1537
February11th to 20thNight
20%
741
20%
2403
7%
739
38%
739
20%
1524
February21st to endNight
25%
628
25%
1815
9%
628
41%
628
24%
1182
March1st to 10thNight
30%
760
26%
2090
12%
760
43%
760
30%
1297
March11th to 20thNight
29%
760
22%
2090
12%
760
39%
760
26%
1359
March21st to endNight
32%
821
19%
2256
9%
821
40%
821
26%
1477
April1st to 10thNight
31%
720
21%
1832
7%
720
40%
720
30%
1199
April11th to 20thNight
38%
711
23%
1775
8%
711
46%
711
36%
1117
April21st to endNight
41%
713
21%
1793
10%
713
46%
713
33%
1169
May1st to 10thNight
41%
540
18%
1620
8%
540
47%
540
24%
1049
May11th to 20thNight
47%
531
14%
1592
9%
531
51%
531
22%
1090
May21st to endNight
58%
450
16%
1612
14%
450
62%
450
24%
1016
June1st to 10thNight
65%
360
20%
1440
23%
360
69%
360
26%
816
June11th to 20thNight
60%
360
15%
1440
16%
360
63%
360
23%
874
June21st to endNight
60%
360
19%
1440
20%
360
66%
360
25%
840
July1st to 10thNight
63%
452
14%
1502
14%
452
65%
452
25%
962
July11th to 20thNight
73%
522
15%
1566
13%
522
74%
522
31%
955
July21st to endNight
70%
591
16%
1672
14%
558
71%
558
29%
1067
August1st to 10thNight
66%
537
16%
1600
13%
534
66%
534
26%
1078
August11th to 20thNight
61%
560
17%
1624
13%
560
62%
560
25%
1100
August21st to endNight
61%
792
16%
1980
10%
792
62%
792
28%
1394
September1st to 10thNight
61%
720
22%
1800
15%
720
63%
720
31%
1222
September11th to 20thNight
61%
720
26%
1867
21%
720
63%
720
33%
1208
September21st to endNight
48%
720
19%
2042
16%
720
52%
720
25%
1388
October1st to 10thNight
52%
720
21%
2160
21%
720
57%
720
29%
1348
October11th to 20thNight
47%
720
26%
2160
20%
720
57%
720
29%
1316
October21st to endNight
47%
792
29%
2376
22%
792
57%
792
34%
1396
November1st to 10thNight
44%
740
28%
2221
19%
740
55%
740
32%
1316
November11th to 20thNight
39%
760
25%
2483
16%
760
53%
760
29%
1450
November21st to endNight
42%
760
25%
2660
18%
760
54%
760
29%
1491
December1st to 10thNight
31%
760
21%
2660
11%
760
45%
760
21%
1658
December11th to 20thNight
37%
759
24%
3171
15%
759
51%
759
22%
1839
December21st to endNight
35%
825
15%
4721
13%
817
47%
817
14%
2665

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%7%43%
78858
Night
15%5%25%43445%7%45%
81135
TransparencyDay
38%7%12%22%16%4
78579
Night
38%6%11%22%18%4
80933
SeeingDay
18%10%24%26%16%6%
14151
Night
17%7%26%34%15%2
24037

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
18%5%25%423445%48%
2836
11th to 20thDay
14%7%36%5%35%45%5%44%
2840
21st to endDay
18%8%35%5%34445%41%
3124
February1st to 10thDay
12%7%36%5%45%5%5%6%42%
1710
11th to 20thDay
19%6%25%43345%6%43%
1663
21st to endDay
18%7%36%435%5%46%38%
1635
March1st to 10thDay
14%5%34434347%49%
2090
11th to 20thDay
16%6%35%44445%7%42%
2090
21st to endDay
15%7%37%7%3445%6%39%
2255
April1st to 10thDay
11%425%425%45%7%51%
2128
11th to 20thDay
13%425%43445%7%48%
2134
21st to endDay
17%5%25%6%35%45%6%42%
2182
May1st to 10thDay
14%6%25%5%45%6%6%9%39%
2340
11th to 20thDay
17%6%35%5%35%5%6%9%37%
2301
21st to endDay
15%5%25%5%35%5%6%10%39%
2659
June1st to 10thDay
10%425%5%36%5%6%10%44%
2520
11th to 20thDay
11%5%25%5%46%6%7%9%39%
2520
21st to endDay
8%3245%46%6%7%10%44%
2520
July1st to 10thDay
10%425%6%47%5%7%9%39%
2408
11th to 20thDay
6%326%6%47%8%8%11%40%
2340
21st to endDay
10%5%26%6%47%7%7%11%36%
2547
August1st to 10thDay
10%5%36%6%46%6%9%9%35%
2327
11th to 20thDay
12%5%26%6%46%7%7%9%35%
2259
21st to endDay
10%6%25%6%35%6%6%9%41%
2376
September1st to 10thDay
13%5%245%35%45%7%47%
2160
11th to 20thDay
11%6%245%25%5%5%7%46%
2089
21st to endDay
21%6%245%35%5%5%6%38%
1917
October1st to 10thDay
15%425%433447%49%
1800
11th to 20thDay
16%423424445%52%
1800
21st to endDay
14%6%24424336%53%
1980
November1st to 10thDay
13%41342435%6%55%
1857
11th to 20thDay
15%41432445%5%51%
1689
21st to endDay
15%42442435%6%52%
1520
December1st to 10thDay
16%6%345%35%45%8%42%
1520
11th to 20thDay
16%5%24333345%52%
1910
21st to endDay
20%6%25%5%345%5%7%38%
2812
January1st to 10thNight
13%6%25%324446%50%
4109
11th to 20thNight
19%7%24323345%49%
4120
21st to endNight
20%8%35%424335%43%
4532
February1st to 10thNight
14%6%245%35%5%6%6%43%
2470
11th to 20thNight
20%6%24424345%44%
2403
21st to endNight
15%6%25%5%3435%7%44%
1815
March1st to 10thNight
14%4245%2446%6%50%
2090
11th to 20thNight
17%5%245%2445%7%45%
2090
21st to endNight
15%6%35%5%34346%46%
2256
April1st to 10thNight
13%6%25%43445%6%46%
1832
11th to 20thNight
12%425%42435%9%49%
1775
21st to endNight
16%5%14435%45%7%46%
1793
May1st to 10thNight
17%5%25%5%345%5%9%42%
1620
11th to 20thNight
19%5%245%35%6%6%8%36%
1592
21st to endNight
15%5%25%5%45%5%5%8%41%
1612
June1st to 10thNight
11%3245%35%6%7%10%45%
1440
11th to 20thNight
11%5%35%5%35%7%6%9%42%
1440
21st to endNight
9%325%5%45%5%7%10%44%
1440
July1st to 10thNight
11%5%346%35%5%8%9%42%
1547
11th to 20thNight
6%4245%45%7%8%11%44%
1620
21st to endNight
8%426%448%7%8%11%38%
1771
August1st to 10thNight
10%5%36%6%46%6%8%8%38%
1611
11th to 20thNight
13%6%35%6%35%6%6%9%37%
1624
21st to endNight
11%5%36%6%46%6%6%9%37%
1980
September1st to 10thNight
14%5%25%5%35%46%7%45%
1800
11th to 20thNight
13%5%25%43345%7%47%
1867
21st to endNight
22%6%25%43445%6%40%
2042
October1st to 10thNight
17%5%2442445%6%47%
2160
11th to 20thNight
16%5%25%43345%6%48%
2160
21st to endNight
15%42442445%6%52%
2376
November1st to 10thNight
12%6%34433335%53%
2221
11th to 20thNight
13%5%25%424346%51%
2483
21st to endNight
13%324435%447%51%
2660
December1st to 10thNight
15%8%25%5%345%45%43%
2660
11th to 20thNight
17%6%24424346%48%
3285
21st to endNight
17%5%25%5%35%5%5%7%42%
4839

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
37%7%7%29%14%6%
2837
11th to 20thDay
41%6%8%19%19%7%
2840
21st to endDay
45%5%10%21%16%3
3124
February1st to 10thDay
42%5%11%24%15%3
1710
11th to 20thDay
42%5%8%21%19%5%
1672
21st to endDay
46%6%10%16%17%5%
1635
March1st to 10thDay
36%5%10%23%21%6%
2090
11th to 20thDay
41%7%10%18%17%7%
2090
21st to endDay
46%6%9%18%15%5%
2255
April1st to 10thDay
33%6%11%23%19%9%
2128
11th to 20thDay
35%5%12%19%22%6%
2134
21st to endDay
42%7%11%22%14%5%
2182
May1st to 10thDay
39%9%15%19%15%3
2340
11th to 20thDay
43%10%13%21%11%2
2305
21st to endDay
40%8%15%24%12%
2659
June1st to 10thDay
34%9%16%25%15%1
2520
11th to 20thDay
38%11%15%19%15%2
2520
21st to endDay
32%11%15%25%15%1
2520
July1st to 10thDay
39%10%13%20%15%3
2343
11th to 20thDay
32%12%16%24%14%2
2271
21st to endDay
38%12%13%23%13%1
2405
August1st to 10thDay
41%10%17%22%9%1
2314
11th to 20thDay
41%10%15%20%12%1
2259
21st to endDay
37%9%18%21%12%3
2376
September1st to 10thDay
37%8%14%17%20%4
2160
11th to 20thDay
35%7%9%26%19%4
2089
21st to endDay
46%6%10%18%17%3
1917
October1st to 10thDay
37%5%9%26%19%4
1800
11th to 20thDay
35%5%10%25%23%4
1800
21st to endDay
34%48%25%23%5%
1980
November1st to 10thDay
31%5%9%23%28%5%
1857
11th to 20thDay
35%410%21%22%8%
1689
21st to endDay
33%5%11%24%23%4
1520
December1st to 10thDay
42%6%11%23%13%4
1520
11th to 20thDay
34%5%9%30%15%7%
1906
21st to endDay
43%7%10%26%12%2
2812
January1st to 10thNight
35%5%9%24%23%5%
4109
11th to 20thNight
39%48%21%23%6%
4120
21st to endNight
45%47%24%17%4
4532
February1st to 10thNight
39%6%10%24%17%3
2470
11th to 20thNight
44%38%20%19%7%
2405
21st to endNight
42%5%10%20%17%6%
1815
March1st to 10thNight
35%5%10%24%21%5%
2090
11th to 20thNight
38%6%9%20%21%5%
2090
21st to endNight
41%6%10%20%17%6%
2256
April1st to 10thNight
38%5%11%18%21%7%
1832
11th to 20thNight
32%5%13%20%23%6%
1775
21st to endNight
37%5%13%24%15%6%
1793
May1st to 10thNight
40%8%14%22%13%5%
1620
11th to 20thNight
43%10%12%20%12%2
1593
21st to endNight
40%8%15%23%13%1
1613
June1st to 10thNight
32%10%13%29%14%1
1440
11th to 20thNight
36%10%18%20%13%2
1440
21st to endNight
33%10%16%20%17%4
1440
July1st to 10thNight
37%11%17%16%15%4
1502
11th to 20thNight
31%11%20%25%10%2
1566
21st to endNight
34%11%18%24%12%1
1672
August1st to 10thNight
39%11%16%22%11%1
1600
11th to 20thNight
42%9%15%21%12%1
1624
21st to endNight
41%10%15%22%10%3
1980
September1st to 10thNight
39%8%12%22%15%6%
1800
11th to 20thNight
37%7%12%22%20%3
1867
21st to endNight
44%6%10%20%17%3
2042
October1st to 10thNight
39%5%10%24%18%3
2160
11th to 20thNight
37%5%8%24%21%5%
2160
21st to endNight
33%410%24%24%5%
2376
November1st to 10thNight
35%5%8%21%24%7%
2221
11th to 20thNight
36%48%21%24%7%
2483
21st to endNight
35%49%25%22%6%
2660
December1st to 10thNight
43%5%9%23%16%4
2660
11th to 20thNight
38%49%22%20%6%
3288
21st to endNight
39%7%13%24%15%2
4839

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
24%18%34%18%7%
270
11th to 20thDay
26%27%27%16%3
270
21st to endDay
25%21%33%18%31
297
February1st to 10thDay
23%21%38%15%4
270
11th to 20thDay
37%23%29%10%1
270
21st to endDay
28%18%30%21%3
377
March1st to 10thDay
22%17%31%22%6%1
460
11th to 20thDay
21%20%30%22%7%1
460
21st to endDay
22%15%30%25%7%1
490
April1st to 10thDay
22%17%28%22%10%1
420
11th to 20thDay
19%12%28%23%13%4
412
21st to endDay
25%10%30%22%12%2
420
May1st to 10thDay
19%14%31%22%11%3
423
11th to 20thDay
21%9%26%27%13%4
447
21st to endDay
19%423%26%22%7%
485
June1st to 10thDay
12%426%29%21%8%
450
11th to 20thDay
12%7%24%31%15%10%
450
21st to endDay
10%5%23%35%21%6%
450
July1st to 10thDay
11%318%27%31%11%
445
11th to 20thDay
7%314%35%29%13%
444
21st to endDay
11%316%35%25%10%
488
August1st to 10thDay
12%5%16%27%29%11%
446
11th to 20thDay
13%216%28%27%15%
439
21st to endDay
10%413%32%25%17%
495
September1st to 10thDay
14%5%14%26%23%18%
450
11th to 20thDay
13%417%27%30%10%
450
21st to endDay
27%8%17%27%16%5%
450
October1st to 10thDay
20%6%17%33%18%8%
450
11th to 20thDay
15%12%24%28%17%3
450
21st to endDay
17%11%31%28%10%3
495
November1st to 10thDay
17%10%25%31%13%4
455
11th to 20thDay
20%11%29%25%13%2
322
21st to endDay
17%13%33%26%9%2
180
December1st to 10thDay
20%15%34%22%7%2
180
11th to 20thDay
24%10%32%22%11%1
180
21st to endDay
26%12%34%20%7%2
211
January1st to 10thNight
18%11%38%29%4
760
11th to 20thNight
21%10%34%31%4
760
21st to endNight
17%10%40%29%3
836
February1st to 10thNight
17%10%38%33%3
760
11th to 20thNight
25%13%37%24%1
743
21st to endNight
20%13%38%27%3
628
March1st to 10thNight
16%13%37%30%4
760
11th to 20thNight
21%11%35%27%6%1
760
21st to endNight
18%12%35%30%6%
821
April1st to 10thNight
16%14%35%28%7%
720
11th to 20thNight
14%11%33%31%11%1
711
21st to endNight
18%7%29%37%9%
713
May1st to 10thNight
18%7%28%33%14%
540
11th to 20thNight
21%321%36%18%1
531
21st to endNight
17%115%39%25%3
452
June1st to 10thNight
10%115%45%27%1
360
11th to 20thNight
11%216%40%30%1
360
21st to endNight
10%217%49%21%2
360
July1st to 10thNight
13%212%33%35%6%
452
11th to 20thNight
6%210%36%42%5%
522
21st to endNight
9%211%41%33%4
591
August1st to 10thNight
13%27%41%34%4
537
11th to 20thNight
15%29%33%36%4
560
21st to endNight
12%411%37%32%4
792
September1st to 10thNight
16%212%32%31%6%
720
11th to 20thNight
13%413%35%31%4
720
21st to endNight
24%317%31%23%2
720
October1st to 10thNight
19%5%17%31%24%4
720
11th to 20thNight
18%7%23%35%17%1
720
21st to endNight
16%7%26%39%11%1
792
November1st to 10thNight
15%6%26%38%14%2
740
11th to 20thNight
17%8%30%35%11%
760
21st to endNight
15%7%31%36%10%1
760
December1st to 10thNight
20%8%35%30%7%1
760
11th to 20thNight
17%6%32%38%6%
760
21st to endNight
19%8%30%39%4
836
Page generated at 2024-03-24 23:37:02. Version ac07

Copyright © 2024 Attilla Danko.


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