Charlottesville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charlottesville 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
45%
15272
21%
46579
14%
15235
53%
15235
27%
29320

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
30%
716
24%
2327
11%
716
46%
716
23%
1459
January16th to endNight
28%
768
23%
2496
11%
768
44%
768
24%
1541
February1st to 15thNight
29%
702
22%
2287
10%
701
45%
701
24%
1374
February16th to endNight
26%
631
26%
1910
11%
631
44%
631
25%
1187
March1st to 15thNight
32%
720
23%
1980
12%
720
42%
720
28%
1263
March16th to endNight
34%
768
20%
2112
11%
768
42%
768
25%
1408
April1st to 15thNight
33%
718
20%
1817
7%
718
41%
718
32%
1174
April16th to endNight
44%
714
21%
1794
10%
714
48%
714
33%
1174
May1st to 15thNight
44%
540
16%
1620
9%
540
49%
540
23%
1087
May16th to endNight
58%
471
16%
1593
13%
471
61%
471
24%
1011
June1st to 15thNight
68%
360
20%
1440
23%
360
71%
360
26%
824
June16th to endNight
63%
360
18%
1440
19%
360
68%
360
26%
848
July1st to 15thNight
64%
462
12%
1482
12%
462
65%
462
25%
958
July16th to endNight
75%
564
16%
1595
13%
531
77%
531
34%
939
August1st to 15thNight
70%
527
18%
1575
15%
524
71%
524
28%
1035
August16th to endNight
61%
662
16%
1712
11%
662
62%
662
26%
1200
September1st to 15thNight
65%
660
26%
1650
19%
660
66%
660
33%
1096
September16th to endNight
52%
657
18%
1839
17%
657
54%
657
25%
1262
October1st to 15thNight
51%
660
24%
1980
23%
660
57%
660
27%
1253
October16th to endNight
46%
704
29%
2112
21%
704
58%
704
35%
1217
November1st to 15thNight
44%
700
27%
2128
18%
700
55%
700
31%
1278
November16th to endNight
39%
720
22%
2502
15%
720
51%
720
26%
1458
December1st to 15thNight
35%
720
20%
2520
12%
720
46%
720
21%
1597
December16th to endNight
35%
768
22%
2668
14%
768
47%
768
22%
1677

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%245%35%5%5%7%42%
47372
Night
13%5%2443445%6%44%
46773
Cloud CoverDay
13%5%24435%5%5%7%42%
47382
Night
14%5%2442445%7%44%
46777
TransparencyDay
39%7%12%21%16%3
47083
Night
38%6%11%22%17%4
46580
SeeingDay
17%6%21%26%18%8%
5494
Night
16%6%25%33%16%1
15280

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
15%6%35%42345%5%43%
1611
16th to endDay
14%6%25%435%445%43%
1728
February1st to 15thDay
11%8%25%5%3445%6%43%
1575
16th to endDay
13%6%25%5%36%45%6%41%
1562
March1st to 15thDay
14%424334437%45%
1969
16th to endDay
15%7%35%5%34446%40%
2112
April1st to 15thDay
11%425%324447%50%
2131
16th to endDay
16%5%25%423346%43%
2175
May1st to 15thDay
16%6%245%25%5%5%7%37%
2331
16th to endDay
12%415%5%35%5%6%9%39%
2518
June1st to 15thDay
10%3145%35%6%7%9%43%
2520
16th to endDay
7%3245%47%6%6%10%42%
2520
July1st to 15thDay
10%425%6%47%5%6%9%35%
2385
16th to endDay
7%325%6%48%7%8%10%35%
2465
August1st to 15thDay
11%426%6%45%6%8%9%33%
2288
16th to endDay
12%425%6%46%7%6%8%35%
2127
September1st to 15thDay
9%425%5%35%5%6%6%45%
1980
16th to endDay
19%7%244345%5%6%35%
1788
October1st to 15thDay
18%414323337%47%
1650
16th to endDay
13%5%14314345%51%
1760
November1st to 15thDay
13%42432335%452%
1729
16th to endDay
16%31342445%5%48%
1455
December1st to 15thDay
15%5%33324447%46%
1440
16th to endDay
19%6%15%42434442%
1553
January1st to 15thNight
15%5%2432445%5%44%
2327
16th to endNight
14%6%24424445%45%
2496
February1st to 15thNight
14%5%2433445%5%46%
2285
16th to endNight
12%6%24425%35%6%46%
1910
March1st to 15thNight
16%413423446%47%
1968
16th to endNight
15%6%24434345%44%
2112
April1st to 15thNight
12%5%2443345%8%46%
1817
16th to endNight
15%42433435%7%46%
1794
May1st to 15thNight
18%5%24434448%39%
1620
16th to endNight
13%415%435%46%9%40%
1592
June1st to 15thNight
8%223435%5%7%10%45%
1440
16th to endNight
8%324425%6%6%9%45%
1440
July1st to 15thNight
10%5%25%4345%6%9%42%
1572
16th to endNight
4424426%6%8%12%43%
1703
August1st to 15thNight
8%5%25%6%346%7%8%39%
1586
16th to endNight
10%436%5%46%6%6%8%35%
1712
September1st to 15thNight
12%3145%35%46%6%47%
1650
16th to endNight
19%5%25%334347%40%
1839
October1st to 15thNight
18%414424345%45%
1980
16th to endNight
13%31332345%5%52%
2112
November1st to 15thNight
12%5%3432332452%
2128
16th to endNight
15%31442434449%
2502
December1st to 15thNight
15%7%2443444442%
2520
16th to endNight
16%5%145%2445%6%42%
2668

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
15%5%35%42345%5%43%
1611
16th to endDay
14%6%24434345%44%
1728
February1st to 15thDay
12%7%26%5%3345%5%43%
1575
16th to endDay
13%6%25%436%5%46%41%
1562
March1st to 15thDay
14%424344447%45%
1980
16th to endDay
15%7%35%434346%39%
2111
April1st to 15thDay
11%324414347%50%
2131
16th to endDay
16%425%42335%6%43%
2175
May1st to 15thDay
16%6%25%4345%5%8%36%
2331
16th to endDay
12%4245%35%5%6%9%39%
2518
June1st to 15thDay
10%314436%6%6%9%43%
2520
16th to endDay
7%3145%36%6%6%10%42%
2520
July1st to 15thDay
11%425%6%47%5%6%9%36%
2385
16th to endDay
6%325%6%47%8%8%11%35%
2465
August1st to 15thDay
11%5%25%6%46%6%8%9%33%
2288
16th to endDay
11%5%25%6%36%7%7%8%35%
2127
September1st to 15thDay
9%5%246%35%5%5%6%45%
1980
16th to endDay
19%7%245%245%5%7%34%
1788
October1st to 15thDay
18%5%14322346%47%
1650
16th to endDay
14%5%13414345%51%
1760
November1st to 15thDay
13%414324345%51%
1729
16th to endDay
17%31333435%5%48%
1455
December1st to 15thDay
16%5%2322435%7%45%
1440
16th to endDay
20%6%25%423445%42%
1553
January1st to 15thNight
15%5%3432435%6%44%
2327
16th to endNight
15%6%24324446%44%
2496
February1st to 15thNight
13%5%2442445%5%46%
2278
16th to endNight
12%6%25%42435%6%46%
1910
March1st to 15thNight
16%41342345%6%46%
1980
16th to endNight
16%5%245%24346%44%
2112
April1st to 15thNight
12%5%2432435%8%46%
1817
16th to endNight
14%5%14324348%45%
1794
May1st to 15thNight
18%5%24424448%39%
1619
16th to endNight
14%424435%5%6%8%41%
1592
June1st to 15thNight
8%3245%246%7%9%45%
1440
16th to endNight
8%324435%6%6%9%45%
1440
July1st to 15thNight
10%5%245%345%7%8%42%
1572
16th to endNight
5%324436%6%7%12%43%
1703
August1st to 15thNight
8%5%26%5%35%5%8%8%39%
1586
16th to endNight
10%436%6%46%6%7%8%35%
1712
September1st to 15thNight
11%3145%4446%6%47%
1650
16th to endNight
20%425%334347%40%
1839
October1st to 15thNight
17%5%24424345%45%
1980
16th to endNight
14%313323346%52%
2112
November1st to 15thNight
12%6%2432332452%
2128
16th to endNight
15%324424345%49%
2502
December1st to 15thNight
16%8%245%34445%42%
2520
16th to endNight
16%5%24434446%42%
2668

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%5%11%20%17%3
1612
16th to endDay
41%49%23%16%4
1728
February1st to 15thDay
41%49%22%17%3
1577
16th to endDay
41%5%10%21%17%3
1562
March1st to 15thDay
38%5%9%22%16%5%
1980
16th to endDay
45%5%10%18%15%4
2112
April1st to 15thDay
33%5%10%24%19%6%
2131
16th to endDay
40%5%11%17%18%6%
2175
May1st to 15thDay
43%8%13%18%13%1
2331
16th to endDay
39%8%14%24%12%
2522
June1st to 15thDay
35%9%16%23%14%1
2520
16th to endDay
34%10%16%21%15%2
2520
July1st to 15thDay
42%9%13%18%13%3
2246
16th to endDay
36%12%13%21%13%1
2310
August1st to 15thDay
43%9%13%20%12%1
2275
16th to endDay
42%9%15%19%10%1
2127
September1st to 15thDay
37%7%13%16%21%4
1980
16th to endDay
46%6%10%16%18%
1788
October1st to 15thDay
38%49%26%16%4
1650
16th to endDay
35%37%26%21%4
1760
November1st to 15thDay
34%49%20%24%6%
1729
16th to endDay
36%5%9%23%21%3
1455
December1st to 15thDay
38%5%11%23%15%5%
1440
16th to endDay
44%49%22%16%2
1553
January1st to 15thNight
40%410%18%19%6%
2327
16th to endNight
40%410%23%17%3
2496
February1st to 15thNight
37%49%24%19%4
2287
16th to endNight
38%49%23%20%3
1910
March1st to 15thNight
37%5%10%26%16%3
1980
16th to endNight
41%5%10%21%17%2
2112
April1st to 15thNight
36%5%11%20%20%5%
1817
16th to endNight
37%412%19%19%7%
1794
May1st to 15thNight
43%6%13%19%13%2
1620
16th to endNight
39%8%14%24%11%2
1594
June1st to 15thNight
31%10%14%26%14%2
1440
16th to endNight
33%9%15%20%17%3
1440
July1st to 15thNight
38%9%16%17%13%4
1482
16th to endNight
29%9%20%25%14%1
1595
August1st to 15thNight
37%10%13%21%15%1
1575
16th to endNight
42%8%12%22%11%1
1712
September1st to 15thNight
36%8%12%20%18%4
1650
16th to endNight
43%7%10%17%17%2
1839
October1st to 15thNight
41%39%23%17%3
1980
16th to endNight
32%38%26%23%5%
2112
November1st to 15thNight
36%36%19%24%9%
2128
16th to endNight
37%48%22%22%4
2502
December1st to 15thNight
44%49%20%17%3
2520
16th to endNight
42%5%12%21%15%3
2668

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
22%21%42%11%3
90
16th to endDay
30%20%32%12%4
96
February1st to 15thDay
21%28%35%13%1
90
16th to endDay
21%12%31%31%3
177
March1st to 15thDay
17%12%28%30%10%
270
16th to endDay
19%11%29%27%9%2
288
April1st to 15thDay
16%11%26%26%16%3
270
16th to endDay
21%326%23%17%7%
270
May1st to 15thDay
26%8%27%20%12%4
288
16th to endDay
20%225%21%21%9%
331
June1st to 15thDay
11%422%26%21%13%
315
16th to endDay
9%423%34%19%7%
315
July1st to 15thDay
17%118%29%26%7%
305
16th to endDay
7%10%34%30%15%
326
August1st to 15thDay
11%313%27%31%13%
297
16th to endDay
13%25%29%24%25%
268
September1st to 15thDay
11%210%18%29%26%
255
16th to endDay
30%316%18%19%11%
254
October1st to 15thDay
23%415%30%20%6%
255
16th to endDay
13%8%26%30%17%3
272
November1st to 15thDay
15%7%20%33%18%5%
260
16th to endDay
20%9%32%22%13%2
75
December1st to 15thDay
23%11%28%21%11%3
60
16th to endDay
32%11%31%19%4
67
January1st to 15thNight
18%12%33%30%5%
720
16th to endNight
18%10%37%29%2
768
February1st to 15thNight
18%10%37%32%1
704
16th to endNight
16%12%38%28%2
631
March1st to 15thNight
19%10%32%32%4
720
16th to endNight
18%9%33%30%7%
768
April1st to 15thNight
13%13%36%27%8%
718
16th to endNight
17%6%26%35%12%1
714
May1st to 15thNight
20%423%34%16%
540
16th to endNight
15%116%38%25%3
473
June1st to 15thNight
7%15%41%33%1
360
16th to endNight
8%116%45%26%
360
July1st to 15thNight
12%112%36%33%2
462
16th to endNight
6%9%36%40%6%
564
August1st to 15thNight
11%7%40%35%4
527
16th to endNight
13%29%33%36%4
662
September1st to 15thNight
12%212%32%34%4
660
16th to endNight
21%214%32%26%2
657
October1st to 15thNight
20%5%17%31%22%2
660
16th to endNight
15%6%28%34%15%
704
November1st to 15thNight
15%6%25%35%14%2
700
16th to endNight
18%8%29%30%12%1
720
December1st to 15thNight
20%7%31%31%9%
720
16th to endNight
19%7%30%38%4
768
Page generated at 2017-08-13 14:16:56. Version ac04

Copyright 2017 A. Danko


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