Glens of Grandfather Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glens of Grandfather Mountain clear sky chart from 2005-11-06 to 2024-03-18.

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
39%
24365
18%
80025
11%
24260
47%
24260
19%
51738

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
20%
754
20%
4013
6%
737
37%
737
10%
2230
January11th to 20thNight
22%
758
25%
3947
8%
740
35%
740
9%
2259
January21st to endNight
19%
832
14%
4450
6%
814
38%
814
8%
2786
February1st to 10thNight
25%
760
20%
2456
10%
760
38%
760
18%
1556
February11th to 20thNight
13%
741
17%
2218
5%
739
25%
739
12%
1491
February21st to endNight
16%
628
18%
1884
6%
628
28%
628
15%
1289
March1st to 10thNight
24%
760
22%
2102
8%
760
36%
760
19%
1386
March11th to 20thNight
22%
752
16%
2068
6%
752
31%
752
17%
1449
March21st to endNight
25%
792
14%
2178
7%
792
31%
792
17%
1534
April1st to 10thNight
30%
720
17%
1980
7%
720
38%
720
22%
1276
April11th to 20thNight
33%
672
21%
1774
8%
672
42%
672
24%
1156
April21st to endNight
40%
540
22%
1620
12%
540
48%
540
23%
1039
May1st to 10thNight
35%
540
13%
1620
5%
540
41%
540
20%
1106
May11th to 20thNight
42%
531
12%
1593
7%
531
44%
531
18%
1125
May21st to endNight
53%
582
12%
1745
10%
582
54%
582
21%
1196
June1st to 10thNight
58%
540
13%
1620
11%
540
59%
540
22%
1124
June11th to 20thNight
58%
540
11%
1620
8%
540
61%
540
27%
1057
June21st to endNight
60%
540
14%
1620
11%
540
63%
540
25%
1072
July1st to 10thNight
64%
525
11%
1575
10%
525
65%
525
23%
1091
July11th to 20thNight
67%
522
10%
1566
9%
522
67%
522
22%
1077
July21st to endNight
68%
591
12%
1672
10%
558
70%
558
24%
1148
August1st to 10thNight
61%
537
11%
1600
9%
534
61%
534
22%
1125
August11th to 20thNight
61%
534
16%
1598
14%
534
62%
534
20%
1160
August21st to endNight
61%
672
15%
1891
13%
672
62%
672
25%
1306
September1st to 10thNight
57%
720
18%
1980
14%
720
58%
720
25%
1366
September11th to 20thNight
54%
720
18%
1980
15%
720
56%
720
23%
1386
September21st to endNight
48%
720
19%
1980
14%
720
53%
720
24%
1356
October1st to 10thNight
46%
720
21%
2052
17%
720
51%
720
25%
1345
October11th to 20thNight
39%
720
24%
2160
17%
720
50%
720
25%
1338
October21st to endNight
40%
792
28%
2376
20%
792
52%
792
28%
1397
November1st to 10thNight
45%
740
26%
2268
18%
740
56%
740
26%
1355
November11th to 20thNight
38%
760
25%
2470
16%
760
51%
760
25%
1429
November21st to endNight
37%
760
24%
2470
14%
760
50%
760
23%
1464
December1st to 10thNight
26%
760
19%
2470
9%
760
38%
760
15%
1658
December11th to 20thNight
27%
759
21%
2965
12%
759
41%
759
15%
1812
December21st to endNight
23%
831
11%
4444
8%
817
34%
817
8%
2794

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%6%36%6%45%5%6%8%37%
79047
Night
14%6%25%5%35%5%6%8%41%
80748
TransparencyDay
42%10%12%18%14%3
78770
Night
39%10%14%19%14%4
80544
SeeingDay
19%17%25%20%13%6%
14199
Night
17%16%22%25%17%3
24387

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
14%5%25%435%46%8%45%
2836
11th to 20thDay
13%7%35%5%4445%7%43%
2840
21st to endDay
20%7%25%5%3445%5%40%
3124
February1st to 10thDay
11%9%35%5%36%6%5%7%38%
1721
11th to 20thDay
16%10%35%5%3445%6%39%
1848
21st to endDay
17%6%36%6%445%5%8%37%
1570
March1st to 10thDay
13%6%25%5%35%5%5%7%45%
2076
11th to 20thDay
16%7%35%6%445%6%7%36%
2058
21st to endDay
18%7%36%7%35%45%7%35%
2178
April1st to 10thDay
11%5%25%5%45%5%6%8%43%
1980
11th to 20thDay
17%7%25%5%345%6%8%39%
2147
21st to endDay
15%5%36%6%35%5%46%40%
2340
May1st to 10thDay
14%6%26%6%45%5%7%8%36%
2340
11th to 20thDay
18%7%37%7%47%5%5%8%29%
2301
21st to endDay
15%7%36%6%46%6%7%10%31%
2531
June1st to 10thDay
13%6%36%8%5%7%6%6%8%31%
2340
11th to 20thDay
10%6%36%7%5%7%7%8%8%32%
2340
21st to endDay
9%6%37%7%5%7%7%8%10%30%
2340
July1st to 10thDay
11%6%38%8%5%8%7%9%9%26%
2340
11th to 20thDay
11%6%49%8%6%9%6%8%10%24%
2340
21st to endDay
10%7%48%10%6%8%7%7%9%25%
2547
August1st to 10thDay
14%7%37%8%5%7%7%9%9%23%
2327
11th to 20thDay
13%7%49%9%6%8%7%6%9%23%
2303
21st to endDay
15%6%37%6%5%6%6%8%9%29%
2440
September1st to 10thDay
14%7%38%6%36%6%6%8%32%
1980
11th to 20thDay
18%8%37%5%36%5%7%8%30%
1980
21st to endDay
20%6%25%7%45%6%6%7%34%
1980
October1st to 10thDay
18%5%25%42445%6%44%
1907
11th to 20thDay
13%6%24434446%49%
1800
21st to endDay
15%6%1442445%6%49%
1980
November1st to 10thDay
11%6%24323446%54%
1806
11th to 20thDay
12%4235%35%447%50%
1710
21st to endDay
14%5%35%434447%48%
1710
December1st to 10thDay
15%9%36%8%46%5%47%34%
1710
11th to 20thDay
13%5%25%42447%8%46%
2153
21st to endDay
18%6%245%36%5%5%7%39%
3124
January1st to 10thNight
13%6%25%5%45%6%6%7%43%
4109
11th to 20thNight
12%7%36%5%35%5%5%6%44%
4120
21st to endNight
19%7%345%35%446%40%
4532
February1st to 10thNight
12%6%26%5%35%6%7%8%41%
2456
11th to 20thNight
17%8%245%35%5%6%6%40%
2218
21st to endNight
13%7%36%7%35%5%7%8%37%
1884
March1st to 10thNight
12%6%26%6%35%5%6%5%45%
2102
11th to 20thNight
14%6%36%5%45%6%6%7%38%
2068
21st to endNight
15%7%35%5%36%45%8%38%
2178
April1st to 10thNight
11%5%26%435%5%6%9%44%
1980
11th to 20thNight
15%5%25%42445%8%45%
1774
21st to endNight
12%6%35%4345%6%8%44%
1620
May1st to 10thNight
13%6%26%6%45%5%7%8%38%
1620
11th to 20thNight
16%6%36%6%35%5%6%8%36%
1592
21st to endNight
14%6%36%5%345%6%10%37%
1744
June1st to 10thNight
11%5%36%5%36%6%8%11%36%
1620
11th to 20thNight
9%5%35%5%35%5%8%10%41%
1620
21st to endNight
7%435%7%35%6%9%12%38%
1620
July1st to 10thNight
11%6%345%36%7%7%11%37%
1620
11th to 20thNight
9%5%25%6%46%6%9%13%36%
1620
21st to endNight
6%435%7%47%9%8%13%35%
1771
August1st to 10thNight
13%6%26%5%36%6%7%11%36%
1611
11th to 20thNight
14%6%36%5%46%6%6%9%35%
1598
21st to endNight
12%6%35%5%36%6%7%9%38%
1891
September1st to 10thNight
13%7%27%5%35%5%5%7%41%
1980
11th to 20thNight
18%6%25%5%3445%7%38%
1980
21st to endNight
19%7%25%434346%43%
1980
October1st to 10thNight
18%6%24433446%45%
2052
11th to 20thNight
15%6%245%2335%6%49%
2160
21st to endNight
14%5%14334445%54%
2376
November1st to 10thNight
13%7%1442435%7%50%
2268
11th to 20thNight
14%42432445%7%50%
2470
21st to endNight
13%5%244335%6%7%47%
2470
December1st to 10thNight
16%7%36%5%46%5%5%7%37%
2470
11th to 20thNight
13%7%25%6%35%45%7%42%
3042
21st to endNight
20%8%35%5%35%5%6%7%34%
4532

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
33%8%13%22%20%5%
2837
11th to 20thDay
39%8%11%19%20%4
2840
21st to endDay
43%6%9%19%19%4
3124
February1st to 10thDay
42%10%12%17%15%4
1721
11th to 20thDay
44%9%10%17%16%4
1858
21st to endDay
44%10%12%15%14%6%
1570
March1st to 10thDay
37%8%11%21%18%6%
2076
11th to 20thDay
45%8%12%16%14%5%
2058
21st to endDay
48%8%12%19%11%2
2178
April1st to 10thDay
36%9%12%23%17%4
1980
11th to 20thDay
41%8%11%18%18%5%
2147
21st to endDay
41%11%13%21%12%2
2340
May1st to 10thDay
42%12%15%20%10%2
2340
11th to 20thDay
50%12%12%17%7%2
2305
21st to endDay
43%12%15%22%7%1
2531
June1st to 10thDay
47%12%15%17%8%1
2340
11th to 20thDay
44%14%14%15%12%1
2340
21st to endDay
43%13%15%17%11%1
2340
July1st to 10thDay
48%15%14%14%8%1
2275
11th to 20thDay
50%14%16%10%9%1
2271
21st to endDay
49%16%14%14%5%1
2405
August1st to 10thDay
50%16%14%14%5%
2314
11th to 20thDay
53%14%14%13%7%
2303
21st to endDay
46%12%16%17%6%3
2440
September1st to 10thDay
45%11%12%18%12%3
1980
11th to 20thDay
47%10%11%18%13%2
1980
21st to endDay
46%8%13%17%13%4
1980
October1st to 10thDay
40%7%10%19%20%5%
1907
11th to 20thDay
35%7%11%23%19%6%
1800
21st to endDay
34%7%9%25%18%7%
1980
November1st to 10thDay
31%7%10%19%27%7%
1806
11th to 20thDay
32%7%9%21%23%7%
1710
21st to endDay
35%6%10%22%22%5%
1710
December1st to 10thDay
49%7%10%17%14%4
1710
11th to 20thDay
33%8%12%20%21%6%
2150
21st to endDay
41%9%10%22%16%2
3124
January1st to 10thNight
34%11%14%22%13%7%
4109
11th to 20thNight
37%10%10%16%20%7%
4120
21st to endNight
45%7%10%16%16%7%
4532
February1st to 10thNight
37%10%13%20%17%3
2456
11th to 20thNight
43%8%12%18%15%5%
2219
21st to endNight
42%10%13%17%13%5%
1884
March1st to 10thNight
39%8%11%19%19%5%
2102
11th to 20thNight
42%11%13%20%11%3
2068
21st to endNight
43%11%13%20%11%2
2178
April1st to 10thNight
34%10%15%21%15%4
1980
11th to 20thNight
35%9%12%22%16%6%
1774
21st to endNight
36%10%15%23%15%1
1620
May1st to 10thNight
40%12%16%23%8%1
1620
11th to 20thNight
44%13%16%19%8%1
1593
21st to endNight
42%11%19%20%7%1
1745
June1st to 10thNight
39%14%17%20%8%1
1620
11th to 20thNight
34%13%23%21%8%1
1620
21st to endNight
33%16%19%19%10%3
1620
July1st to 10thNight
38%15%18%17%10%2
1575
11th to 20thNight
37%16%21%17%7%2
1566
21st to endNight
34%18%22%19%6%
1672
August1st to 10thNight
41%13%20%17%8%
1600
11th to 20thNight
42%15%16%17%8%1
1598
21st to endNight
40%12%18%20%8%1
1891
September1st to 10thNight
40%11%14%18%13%3
1980
11th to 20thNight
43%10%14%17%15%1
1980
21st to endNight
43%7%12%19%16%3
1980
October1st to 10thNight
37%9%11%18%21%3
2052
11th to 20thNight
36%7%11%23%18%5%
2160
21st to endNight
32%6%9%23%21%9%
2376
November1st to 10thNight
34%7%10%20%22%8%
2268
11th to 20thNight
32%7%10%20%22%8%
2470
21st to endNight
34%7%10%23%21%5%
2470
December1st to 10thNight
44%8%12%18%13%5%
2470
11th to 20thNight
37%10%13%15%20%5%
3044
21st to endNight
43%11%13%19%13%2
4532

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
33%35%24%7%1
270
11th to 20thDay
30%29%32%9%1
270
21st to endDay
28%36%27%7%1
297
February1st to 10thDay
22%34%33%10%1
270
11th to 20thDay
41%34%21%4
270
21st to endDay
36%34%25%4
225
March1st to 10thDay
24%28%28%15%5%
446
11th to 20thDay
24%34%25%13%31
449
21st to endDay
28%28%25%13%5%
462
April1st to 10thDay
22%26%27%17%7%1
420
11th to 20thDay
20%26%21%20%10%2
412
21st to endDay
22%19%28%14%12%4
420
May1st to 10thDay
17%23%34%13%9%5%
423
11th to 20thDay
21%11%27%22%11%7%
447
21st to endDay
19%8%23%23%16%11%
485
June1st to 10thDay
16%8%27%25%16%8%
450
11th to 20thDay
12%7%23%30%18%11%
450
21st to endDay
10%10%30%26%14%9%
450
July1st to 10thDay
10%421%27%25%14%
445
11th to 20thDay
9%5%17%33%24%13%
444
21st to endDay
10%418%32%22%14%
488
August1st to 10thDay
17%7%22%22%16%15%
446
11th to 20thDay
12%421%26%25%12%
439
21st to endDay
15%5%15%26%21%17%
495
September1st to 10thDay
14%416%28%26%13%
450
11th to 20thDay
16%8%15%23%28%10%
450
21st to endDay
22%10%23%25%16%4
450
October1st to 10thDay
23%11%18%22%19%6%
450
11th to 20thDay
17%19%25%20%16%3
450
21st to endDay
19%18%26%25%10%3
495
November1st to 10thDay
17%18%28%23%10%3
404
11th to 20thDay
20%28%30%18%31
270
21st to endDay
18%24%34%19%41
270
December1st to 10thDay
26%28%33%11%2
270
11th to 20thDay
22%23%38%13%3
270
21st to endDay
26%25%35%9%5%1
297
January1st to 10thNight
20%29%28%20%4
760
11th to 20thNight
21%27%27%21%4
760
21st to endNight
17%31%29%20%3
836
February1st to 10thNight
15%26%30%26%3
760
11th to 20thNight
25%32%26%16%1
743
21st to endNight
21%30%31%17%2
628
March1st to 10thNight
17%26%30%23%4
760
11th to 20thNight
22%21%30%18%8%
752
21st to endNight
20%21%29%22%8%
792
April1st to 10thNight
18%24%25%25%8%
720
11th to 20thNight
20%20%22%23%13%1
672
21st to endNight
16%16%23%32%13%1
540
May1st to 10thNight
16%14%30%25%14%1
540
11th to 20thNight
15%11%22%30%19%3
531
21st to endNight
17%6%14%27%28%7%
584
June1st to 10thNight
12%217%34%29%6%
540
11th to 20thNight
11%220%26%33%7%
540
21st to endNight
7%5%20%31%34%4
540
July1st to 10thNight
13%212%26%42%6%
525
11th to 20thNight
9%310%28%41%9%
522
21st to endNight
6%211%29%42%10%
591
August1st to 10thNight
15%210%26%39%7%
537
11th to 20thNight
14%411%29%35%7%
534
21st to endNight
14%310%26%38%9%
672
September1st to 10thNight
15%413%27%35%7%
720
11th to 20thNight
21%412%24%34%6%
720
21st to endNight
22%7%14%27%27%3
720
October1st to 10thNight
19%12%17%22%22%8%
720
11th to 20thNight
19%14%23%28%14%3
720
21st to endNight
17%16%22%31%11%3
792
November1st to 10thNight
17%14%19%32%14%3
740
11th to 20thNight
18%19%21%31%10%2
760
21st to endNight
17%19%24%28%11%1
760
December1st to 10thNight
21%23%25%25%7%
760
11th to 20thNight
18%22%25%27%6%1
760
21st to endNight
25%21%26%24%5%
836
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