Roanoke
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roanoke clear sky chart from 2005-11-05 to 2018-02-14.

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
46%
16409
22%
48996
14%
16372
55%
16372
27%
30823

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
29%
777
24%
2522
11%
776
46%
776
21%
1534
January16th to endNight
25%
832
23%
2704
10%
832
43%
832
22%
1672
February1st to 15thNight
26%
757
20%
2468
8%
757
41%
757
21%
1503
February16th to endNight
25%
631
25%
1877
10%
631
42%
631
24%
1176
March1st to 15thNight
35%
720
23%
1980
12%
720
45%
720
27%
1277
March16th to endNight
33%
768
19%
2112
11%
768
40%
768
26%
1398
April1st to 15thNight
35%
718
21%
1868
8%
718
43%
718
29%
1193
April16th to endNight
46%
654
22%
1734
9%
654
52%
654
30%
1137
May1st to 15thNight
46%
540
16%
1620
9%
540
52%
540
23%
1088
May16th to endNight
59%
561
16%
1684
12%
561
62%
561
28%
1099
June1st to 15thNight
69%
540
16%
1620
14%
540
71%
540
33%
1008
June16th to endNight
74%
540
18%
1620
16%
540
75%
540
35%
972
July1st to 15thNight
70%
510
12%
1530
11%
510
71%
510
27%
1005
July16th to endNight
75%
564
17%
1595
15%
531
77%
531
34%
990
August1st to 15thNight
68%
539
19%
1609
16%
536
69%
536
29%
1038
August16th to endNight
70%
681
20%
1827
15%
681
71%
681
31%
1200
September1st to 15thNight
67%
720
24%
1874
18%
720
68%
720
33%
1216
September16th to endNight
51%
717
20%
1980
18%
717
53%
717
25%
1341
October1st to 15thNight
53%
720
25%
2154
23%
720
58%
720
28%
1343
October16th to endNight
48%
768
32%
2304
23%
768
62%
768
34%
1311
November1st to 15thNight
48%
760
26%
2313
19%
760
58%
760
31%
1369
November16th to endNight
42%
780
27%
2577
19%
780
55%
780
29%
1453
December1st to 15thNight
32%
780
21%
2720
11%
780
46%
780
20%
1698
December16th to endNight
27%
832
22%
2704
10%
832
42%
832
18%
1802

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%35%5%6%7%40%
49056
Night
13%5%2442445%7%45%
49189
Cloud CoverDay
13%5%25%5%35%5%5%7%40%
49066
Night
13%5%2442445%7%45%
49193
TransparencyDay
40%7%12%21%15%3
48767
Night
37%6%11%23%17%3
48996
SeeingDay
18%7%19%23%20%10%
6094
Night
16%7%21%31%19%2
16417

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
13%5%25%43445%6%43%
1746
16th to endDay
13%7%245%25%445%44%
1872
February1st to 15thDay
12%6%26%436%5%5%6%40%
1695
16th to endDay
14%425%6%3446%8%38%
1592
March1st to 15thDay
13%424425%45%7%46%
1969
16th to endDay
17%6%25%5%34446%40%
2112
April1st to 15thDay
11%324424447%48%
2080
16th to endDay
16%5%245%2445%6%41%
2235
May1st to 15thDay
18%5%25%5%35%5%7%7%33%
2331
16th to endDay
11%4246%36%6%6%8%38%
2431
June1st to 15thDay
9%3145%36%6%8%10%38%
2340
16th to endDay
7%325%6%46%6%7%9%38%
2340
July1st to 15thDay
10%5%36%6%47%5%7%10%32%
2340
16th to endDay
7%427%7%47%7%8%10%31%
2465
August1st to 15thDay
13%5%25%6%46%7%7%9%31%
2340
16th to endDay
11%5%26%6%46%6%7%9%34%
2363
September1st to 15thDay
13%425%5%3446%7%43%
2083
16th to endDay
21%5%25%5%2435%6%36%
1980
October1st to 15thDay
17%413223336%49%
1805
16th to endDay
12%5%23423436%51%
1920
November1st to 15thDay
12%424414436%51%
1874
16th to endDay
14%324323446%49%
1708
December1st to 15thDay
13%325%4246%5%7%43%
1563
16th to endDay
18%6%25%425%347%38%
1872
January1st to 15thNight
13%5%24324446%47%
2522
16th to endNight
13%7%34424446%44%
2704
February1st to 15thNight
14%7%25%42335%6%44%
2466
16th to endNight
12%6%244345%5%6%44%
1877
March1st to 15thNight
14%42432445%7%45%
1968
16th to endNight
16%425%424447%43%
2112
April1st to 15thNight
13%5%2432445%6%46%
1868
16th to endNight
15%3144345%46%45%
1734
May1st to 15thNight
16%5%25%43445%7%40%
1620
16th to endNight
12%3145%26%6%5%9%41%
1682
June1st to 15thNight
8%3135%35%5%7%10%44%
1620
16th to endNight
6%313435%46%10%49%
1620
July1st to 15thNight
8%4145%36%6%6%10%42%
1620
16th to endNight
4425%5%36%6%7%12%42%
1703
August1st to 15thNight
13%314425%46%9%42%
1620
16th to endNight
9%3145%35%6%6%9%42%
1827
September1st to 15thNight
11%42443445%7%47%
1874
16th to endNight
18%5%25%5%2345%7%39%
1980
October1st to 15thNight
17%423423336%48%
2154
16th to endNight
12%413323345%55%
2304
November1st to 15thNight
14%42342334452%
2313
16th to endNight
13%423323436%52%
2577
December1st to 15thNight
14%6%35%5%3335%6%42%
2720
16th to endNight
15%6%26%5%345%5%7%36%
2704

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
13%5%25%4245%5%6%43%
1746
16th to endDay
12%7%34434445%43%
1872
February1st to 15thDay
12%6%26%5%35%5%46%40%
1695
16th to endDay
13%435%5%3446%8%39%
1592
March1st to 15thDay
13%423325%45%6%46%
1980
16th to endDay
17%6%245%24436%39%
2111
April1st to 15thDay
11%41442445%7%48%
2080
16th to endDay
16%425%42445%7%40%
2235
May1st to 15thDay
18%5%35%5%35%5%6%7%33%
2331
16th to endDay
11%425%6%36%5%7%9%37%
2431
June1st to 15thDay
9%3145%36%6%8%10%38%
2340
16th to endDay
8%425%5%46%7%7%9%38%
2340
July1st to 15thDay
11%5%26%7%46%6%7%9%31%
2340
16th to endDay
7%436%7%5%7%8%8%11%31%
2465
August1st to 15thDay
13%5%25%6%47%6%7%9%30%
2340
16th to endDay
11%5%25%7%46%6%6%10%33%
2363
September1st to 15thDay
13%425%6%3446%7%42%
2083
16th to endDay
21%6%245%2345%6%36%
1980
October1st to 15thDay
18%413323345%49%
1805
16th to endDay
12%5%23423435%51%
1920
November1st to 15thDay
12%414414346%51%
1874
16th to endDay
14%324423346%49%
1708
December1st to 15thDay
13%3244345%6%6%43%
1563
16th to endDay
18%7%25%424447%38%
1872
January1st to 15thNight
13%5%24423446%47%
2522
16th to endNight
13%7%24324447%43%
2704
February1st to 15thNight
14%6%25%42335%5%45%
2459
16th to endNight
11%5%25%5%245%5%6%44%
1877
March1st to 15thNight
14%5%2433445%7%45%
1980
16th to endNight
15%42443445%6%43%
2112
April1st to 15thNight
13%5%25%42435%6%46%
1868
16th to endNight
14%314435%45%6%45%
1734
May1st to 15thNight
16%5%25%5%3445%7%40%
1619
16th to endNight
12%3146%36%5%5%9%41%
1682
June1st to 15thNight
8%3145%3447%11%44%
1620
16th to endNight
6%322435%46%10%49%
1620
July1st to 15thNight
8%424436%6%6%10%41%
1620
16th to endNight
43245%36%6%8%11%42%
1703
August1st to 15thNight
12%4245%3446%9%42%
1620
16th to endNight
9%3245%45%5%5%9%42%
1827
September1st to 15thNight
11%43442445%7%47%
1874
16th to endNight
18%5%25%5%2435%7%40%
1980
October1st to 15thNight
17%414323346%48%
2154
16th to endNight
12%413323345%55%
2304
November1st to 15thNight
13%5%23423345%51%
2313
16th to endNight
13%423323446%52%
2577
December1st to 15thNight
14%6%35%434446%43%
2720
16th to endNight
15%6%26%5%345%5%7%37%
2704

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
39%6%11%21%17%3
1747
16th to endDay
41%48%25%15%3
1872
February1st to 15thDay
43%410%21%17%2
1697
16th to endDay
41%5%12%23%15%2
1592
March1st to 15thDay
37%5%11%24%17%4
1980
16th to endDay
45%5%9%22%13%3
2112
April1st to 15thDay
34%5%12%25%15%6%
2080
16th to endDay
41%6%10%20%15%6%
2235
May1st to 15thDay
46%8%14%17%10%2
2331
16th to endDay
40%8%15%23%10%1
2435
June1st to 15thDay
36%10%18%22%12%
2340
16th to endDay
37%10%16%17%14%2
2340
July1st to 15thDay
43%9%14%15%13%2
2201
16th to endDay
40%11%15%18%11%
2310
August1st to 15thDay
44%9%14%20%10%
2327
16th to endDay
42%10%15%18%10%1
2363
September1st to 15thDay
38%8%10%20%19%2
2083
16th to endDay
47%48%20%16%1
1980
October1st to 15thDay
36%5%9%26%17%4
1805
16th to endDay
35%38%27%20%4
1920
November1st to 15thDay
34%49%19%25%7%
1874
16th to endDay
35%39%25%23%2
1708
December1st to 15thDay
38%6%12%20%17%4
1563
16th to endDay
45%5%9%23%13%2
1872
January1st to 15thNight
37%6%10%19%19%7%
2522
16th to endNight
40%410%24%17%3
2704
February1st to 15thNight
39%410%23%18%3
2468
16th to endNight
38%411%26%16%2
1877
March1st to 15thNight
37%6%9%27%15%3
1980
16th to endNight
41%5%11%22%17%2
2112
April1st to 15thNight
37%311%23%17%5%
1868
16th to endNight
38%5%11%20%17%6%
1734
May1st to 15thNight
42%8%13%20%14%1
1620
16th to endNight
37%8%16%24%10%1
1684
June1st to 15thNight
32%9%18%24%14%1
1620
16th to endNight
28%10%16%22%18%3
1620
July1st to 15thNight
36%11%15%19%11%5%
1530
16th to endNight
31%9%19%24%14%1
1595
August1st to 15thNight
36%8%14%22%16%1
1609
16th to endNight
36%8%15%24%13%1
1827
September1st to 15thNight
35%7%12%20%18%4
1874
16th to endNight
43%6%10%19%18%1
1980
October1st to 15thNight
38%5%8%25%19%3
2154
16th to endNight
31%37%27%24%5%
2304
November1st to 15thNight
36%28%21%23%8%
2313
16th to endNight
34%38%25%23%4
2577
December1st to 15thNight
43%39%23%15%3
2720
16th to endNight
46%5%11%19%14%2
2704

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%22%30%19%31
135
16th to endDay
25%24%24%18%6%
144
February1st to 15thDay
22%24%40%10%3
130
16th to endDay
20%17%35%19%6%
131
March1st to 15thDay
19%16%24%28%10%
270
16th to endDay
21%11%27%27%10%1
288
April1st to 15thDay
17%13%21%28%17%2
270
16th to endDay
20%420%23%20%10%
270
May1st to 15thDay
23%12%28%16%11%7%
288
16th to endDay
16%319%22%23%15%
331
June1st to 15thDay
12%317%24%27%14%
315
16th to endDay
12%120%28%26%10%
315
July1st to 15thDay
17%13%28%28%11%
305
16th to endDay
10%9%26%32%20%
326
August1st to 15thDay
19%11%20%28%19%
313
16th to endDay
12%7%23%26%30%
332
September1st to 15thDay
16%212%17%29%21%
315
16th to endDay
25%19%21%25%15%
314
October1st to 15thDay
23%5%10%25%25%9%
315
16th to endDay
14%8%22%27%21%5%
336
November1st to 15thDay
18%6%20%29%21%2
292
16th to endDay
14%15%22%27%16%3
124
December1st to 15thDay
23%15%34%14%13%
91
16th to endDay
29%15%34%17%3
144
January1st to 15thNight
18%16%29%29%5%
780
16th to endNight
20%13%35%29%2
832
February1st to 15thNight
21%13%32%30%
760
16th to endNight
17%15%36%27%2
631
March1st to 15thNight
18%12%29%34%5%
720
16th to endNight
18%10%30%30%9%
768
April1st to 15thNight
17%14%28%28%10%
718
16th to endNight
17%6%23%33%17%1
654
May1st to 15thNight
19%423%36%14%2
540
16th to endNight
14%214%29%33%5%
563
June1st to 15thNight
8%113%35%39%2
540
16th to endNight
9%9%40%35%4
540
July1st to 15thNight
11%8%34%41%4
510
16th to endNight
6%7%30%46%8%
564
August1st to 15thNight
14%5%35%39%4
539
16th to endNight
10%6%29%45%7%
681
September1st to 15thNight
14%19%29%39%6%
720
16th to endNight
22%211%26%31%4
717
October1st to 15thNight
19%415%30%25%5%
720
16th to endNight
15%8%22%34%18%1
768
November1st to 15thNight
18%6%22%35%15%2
760
16th to endNight
17%11%23%32%14%
780
December1st to 15thNight
20%10%29%31%8%
780
16th to endNight
21%10%31%32%3
832
Page generated at 2018-02-15 10:58:47. Version ac04

Copyright 2018 A. Danko


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