Grayson Highlands
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grayson Highlands 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
37%
16291
17%
48788
11%
16251
44%
16251
19%
33285

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
18%
778
16%
2522
7%
776
30%
776
10%
1783
January16th to endNight
15%
832
16%
2704
6%
832
28%
832
12%
1884
February1st to 15thNight
15%
759
17%
2426
6%
757
28%
757
13%
1632
February16th to endNight
12%
631
17%
1893
5%
631
24%
631
10%
1388
March1st to 15thNight
20%
720
17%
1980
9%
720
27%
720
15%
1422
March16th to endNight
24%
768
13%
2112
7%
768
30%
768
16%
1554
April1st to 15thNight
28%
718
16%
1925
6%
718
37%
718
19%
1315
April16th to endNight
35%
582
17%
1662
8%
582
41%
582
20%
1147
May1st to 15thNight
33%
540
12%
1620
5%
540
39%
540
17%
1170
May16th to endNight
51%
561
12%
1684
9%
561
54%
561
21%
1155
June1st to 15thNight
60%
540
12%
1620
10%
540
62%
540
25%
1088
June16th to endNight
61%
540
15%
1620
12%
540
64%
540
27%
1060
July1st to 15thNight
59%
510
10%
1530
8%
510
60%
510
24%
1051
July16th to endNight
70%
564
12%
1595
10%
531
72%
531
28%
1030
August1st to 15thNight
63%
539
15%
1609
12%
536
64%
536
22%
1131
August16th to endNight
64%
632
18%
1778
15%
632
65%
632
25%
1225
September1st to 15thNight
56%
720
19%
1974
16%
720
57%
720
26%
1323
September16th to endNight
52%
717
21%
1980
17%
717
55%
717
26%
1347
October1st to 15thNight
46%
720
25%
2102
20%
720
53%
720
26%
1336
October16th to endNight
34%
768
28%
2304
17%
768
48%
768
25%
1414
November1st to 15thNight
41%
760
24%
2374
17%
760
51%
760
24%
1455
November16th to endNight
32%
780
24%
2535
16%
780
45%
780
20%
1571
December1st to 15thNight
25%
780
17%
2535
10%
780
35%
780
14%
1769
December16th to endNight
17%
832
16%
2704
6%
832
29%
832
9%
2035

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%8%47%6%35%5%5%6%31%
49278
Night
11%7%37%6%35%45%7%36%
48981
Cloud CoverDay
13%7%36%6%35%5%6%7%33%
49288
Night
11%6%35%5%35%5%6%8%39%
48985
TransparencyDay
48%9%11%16%12%2
48989
Night
41%10%12%18%13%2
48788
SeeingDay
20%15%21%20%14%8%
6038
Night
18%15%21%24%16%2
16296

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
14%8%49%7%35%5%45%29%
1746
16th to endDay
11%8%6%9%5%35%45%5%34%
1872
February1st to 15thDay
12%11%6%8%6%3435%5%32%
1736
16th to endDay
15%8%5%10%6%3435%7%31%
1580
March1st to 15thDay
15%8%46%5%24345%38%
1969
16th to endDay
17%9%47%6%24445%31%
2112
April1st to 15thDay
12%9%35%5%2445%6%39%
2021
16th to endDay
17%7%37%6%3445%6%33%
2309
May1st to 15thDay
16%8%48%7%45%5%5%6%26%
2331
16th to endDay
13%8%38%7%46%6%6%7%27%
2431
June1st to 15thDay
11%6%38%9%47%6%6%8%26%
2340
16th to endDay
8%7%47%8%5%6%6%6%7%30%
2340
July1st to 15thDay
13%9%38%7%5%7%6%6%8%21%
2340
16th to endDay
12%8%49%9%5%7%6%6%8%21%
2465
August1st to 15thDay
10%8%310%10%5%8%6%8%7%19%
2340
16th to endDay
11%8%48%7%46%6%7%9%24%
2411
September1st to 15thDay
14%9%48%7%36%45%6%29%
1983
16th to endDay
16%8%46%6%46%5%5%6%30%
1980
October1st to 15thDay
15%6%35%5%34445%42%
1857
16th to endDay
12%10%35%42333444%
1920
November1st to 15thDay
11%7%35%434446%42%
1813
16th to endDay
11%8%27%434446%41%
1755
December1st to 15thDay
13%11%46%6%35%45%5%33%
1755
16th to endDay
16%10%49%5%245%5%5%29%
1872
January1st to 15thNight
11%8%48%8%5%5%5%5%6%29%
2522
16th to endNight
13%8%38%7%45%5%5%431%
2704
February1st to 15thNight
11%9%5%7%6%35%35%5%34%
2424
16th to endNight
11%8%5%10%8%5%5%446%29%
1893
March1st to 15thNight
13%8%47%7%35%445%35%
1968
16th to endNight
11%8%48%7%35%5%5%7%31%
2112
April1st to 15thNight
10%8%37%5%35%46%6%38%
1925
16th to endNight
12%6%36%6%35%5%6%7%37%
1662
May1st to 15thNight
14%8%35%6%36%46%8%31%
1620
16th to endNight
7%7%36%6%35%6%7%10%34%
1682
June1st to 15thNight
6%435%7%26%7%7%12%36%
1620
16th to endNight
6%425%6%35%6%7%11%39%
1620
July1st to 15thNight
9%5%35%6%35%5%8%10%36%
1620
16th to endNight
5%425%6%45%6%9%12%36%
1703
August1st to 15thNight
8%6%26%6%48%6%6%9%34%
1620
16th to endNight
8%5%26%6%35%5%8%9%36%
1778
September1st to 15thNight
9%7%36%6%4445%7%40%
1974
16th to endNight
12%7%35%6%25%445%42%
1980
October1st to 15thNight
12%6%26%434346%44%
2102
16th to endNight
9%8%36%5%23345%46%
2304
November1st to 15thNight
12%6%25%42435%6%46%
2374
16th to endNight
11%7%37%5%3445%6%42%
2535
December1st to 15thNight
13%9%47%7%345%5%7%30%
2535
16th to endNight
15%9%5%10%7%45%45%6%26%
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%7%5%7%6%3446%8%32%
1746
16th to endDay
11%7%48%6%35%445%39%
1872
February1st to 15thDay
11%9%5%7%6%2445%5%36%
1736
16th to endDay
14%7%48%6%2346%7%34%
1580
March1st to 15thDay
15%7%35%43435%6%41%
1980
16th to endDay
17%9%36%6%3445%6%33%
2111
April1st to 15thDay
12%7%245%245%5%7%41%
2021
16th to endDay
17%6%35%6%345%5%7%34%
2309
May1st to 15thDay
17%6%36%7%46%5%6%7%28%
2331
16th to endDay
14%7%36%7%47%6%6%7%28%
2431
June1st to 15thDay
11%5%37%8%5%6%7%6%9%27%
2340
16th to endDay
10%6%36%7%46%6%8%8%31%
2340
July1st to 15thDay
14%6%37%6%48%7%7%9%23%
2340
16th to endDay
13%7%38%7%49%6%7%8%22%
2465
August1st to 15thDay
12%7%38%9%6%7%6%7%8%21%
2340
16th to endDay
12%7%37%7%47%6%7%10%26%
2411
September1st to 15thDay
16%7%46%7%35%5%5%7%30%
1983
16th to endDay
18%6%36%6%45%45%7%31%
1980
October1st to 15thDay
15%6%2442445%6%42%
1857
16th to endDay
13%5%26%434335%46%
1920
November1st to 15thDay
11%6%2443435%7%45%
1813
16th to endDay
12%5%35%5%2435%6%43%
1755
December1st to 15thDay
13%8%26%6%35%5%6%7%35%
1755
16th to endDay
14%9%47%6%345%5%6%32%
1872
January1st to 15thNight
11%6%36%7%445%6%8%33%
2522
16th to endNight
11%7%36%5%35%5%6%6%38%
2704
February1st to 15thNight
11%6%46%5%245%6%6%39%
2417
16th to endNight
10%5%37%7%45%5%7%7%33%
1893
March1st to 15thNight
12%6%36%6%345%5%6%38%
1980
16th to endNight
11%7%35%7%36%6%6%6%34%
2112
April1st to 15thNight
9%6%35%435%5%6%7%40%
1925
16th to endNight
13%5%25%5%346%5%8%39%
1662
May1st to 15thNight
14%6%35%5%35%5%6%8%35%
1619
16th to endNight
9%5%26%5%26%5%8%10%36%
1682
June1st to 15thNight
6%4245%36%7%7%12%38%
1620
16th to endNight
5%5%334445%8%11%42%
1620
July1st to 15thNight
9%4245%35%6%7%12%38%
1620
16th to endNight
5%325%437%6%9%13%39%
1703
August1st to 15thNight
12%5%25%6%36%6%6%7%38%
1620
16th to endNight
9%425%6%36%5%6%10%37%
1778
September1st to 15thNight
11%6%35%5%25%46%7%41%
1974
16th to endNight
15%6%25%42445%6%41%
1980
October1st to 15thNight
14%6%23434346%45%
2102
16th to endNight
10%5%26%423347%49%
2304
November1st to 15thNight
12%5%24423347%48%
2374
16th to endNight
10%6%36%42445%6%44%
2535
December1st to 15thNight
13%7%36%6%345%6%8%34%
2535
16th to endNight
14%9%47%6%35%5%6%6%30%
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
48%11%9%13%12%4
1747
16th to endDay
45%8%10%20%12%2
1872
February1st to 15thDay
48%9%9%16%14%2
1738
16th to endDay
47%9%12%15%12%2
1580
March1st to 15thDay
44%7%10%18%15%3
1980
16th to endDay
51%8%9%18%9%1
2112
April1st to 15thDay
41%7%12%22%12%4
2021
16th to endDay
48%7%9%16%13%3
2309
May1st to 15thDay
52%12%10%15%7%1
2331
16th to endDay
50%9%14%16%6%1
2435
June1st to 15thDay
50%14%12%15%7%
2340
16th to endDay
45%13%12%14%12%1
2340
July1st to 15thDay
52%14%12%10%9%
2201
16th to endDay
53%13%13%11%7%1
2310
August1st to 15thDay
56%12%11%12%6%
2327
16th to endDay
50%12%12%15%7%1
2411
September1st to 15thDay
51%7%10%15%11%2
1983
16th to endDay
51%6%9%15%14%1
1980
October1st to 15thDay
40%6%10%20%15%5%
1857
16th to endDay
39%6%7%22%19%5%
1920
November1st to 15thDay
38%6%9%14%23%7%
1813
16th to endDay
40%7%7%19%22%3
1755
December1st to 15thDay
45%10%10%16%14%3
1755
16th to endDay
52%7%11%13%12%2
1872
January1st to 15thNight
44%13%11%11%13%6%
2522
16th to endNight
44%11%11%15%13%2
2704
February1st to 15thNight
42%9%12%20%12%2
2426
16th to endNight
46%12%10%18%10%1
1893
March1st to 15thNight
45%10%10%18%12%2
1980
16th to endNight
46%11%11%18%10%1
2112
April1st to 15thNight
39%10%11%22%12%3
1925
16th to endNight
42%9%13%17%14%3
1662
May1st to 15thNight
44%13%14%18%9%
1620
16th to endNight
40%12%19%19%6%1
1684
June1st to 15thNight
35%14%20%20%8%
1620
16th to endNight
32%15%16%20%12%1
1620
July1st to 15thNight
36%15%16%17%11%1
1530
16th to endNight
30%15%22%21%8%1
1595
August1st to 15thNight
41%12%15%18%11%
1609
16th to endNight
38%12%15%23%9%1
1778
September1st to 15thNight
40%8%14%18%14%3
1974
16th to endNight
42%7%10%20%18%
1980
October1st to 15thNight
38%5%9%22%19%3
2102
16th to endNight
35%7%8%23%19%5%
2304
November1st to 15thNight
36%6%9%17%22%7%
2374
16th to endNight
37%7%8%20%21%4
2535
December1st to 15thNight
46%10%10%15%13%4
2535
16th to endNight
52%11%9%12%12%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
38%23%24%11%1
135
16th to endDay
30%31%24%13%
144
February1st to 15thDay
36%40%19%3
130
16th to endDay
37%33%22%42
81
March1st to 15thDay
27%24%22%18%6%
270
16th to endDay
23%26%23%19%5%1
288
April1st to 15thDay
24%19%23%20%10%1
270
16th to endDay
22%14%22%18%16%5%
270
May1st to 15thDay
22%23%25%13%7%7%
288
16th to endDay
18%12%22%18%12%15%
331
June1st to 15thDay
11%7%20%29%20%11%
315
16th to endDay
11%14%25%24%15%8%
315
July1st to 15thDay
16%11%22%20%15%13%
305
16th to endDay
10%418%27%22%16%
326
August1st to 15thDay
12%422%25%19%15%
313
16th to endDay
13%317%21%19%24%
332
September1st to 15thDay
16%6%13%20%27%15%
315
16th to endDay
19%6%15%23%21%13%
314
October1st to 15thDay
21%9%20%20%21%6%
315
16th to endDay
18%19%20%20%16%5%
336
November1st to 15thDay
23%12%21%23%12%4
231
16th to endDay
17%28%22%25%5%1
135
December1st to 15thDay
32%21%31%11%2
135
16th to endDay
36%22%32%6%1
144
January1st to 15thNight
27%26%23%18%4
780
16th to endNight
25%29%26%16%2
832
February1st to 15thNight
27%25%27%18%1
760
16th to endNight
23%35%25%13%1
631
March1st to 15thNight
24%23%26%20%4
720
16th to endNight
18%20%30%20%8%
768
April1st to 15thNight
21%22%24%24%7%
718
16th to endNight
16%17%24%28%11%1
582
May1st to 15thNight
17%13%28%25%12%2
540
16th to endNight
14%6%18%29%25%6%
563
June1st to 15thNight
8%5%16%33%31%4
540
16th to endNight
6%317%35%31%4
540
July1st to 15thNight
11%414%32%32%4
510
16th to endNight
4312%31%39%10%
564
August1st to 15thNight
12%111%33%35%5%
539
16th to endNight
12%110%29%39%6%
632
September1st to 15thNight
13%416%26%32%6%
720
16th to endNight
18%415%26%29%4
717
October1st to 15thNight
18%12%17%23%22%6%
720
16th to endNight
17%17%25%22%14%2
768
November1st to 15thNight
18%13%22%25%16%3
760
16th to endNight
22%19%21%23%12%
780
December1st to 15thNight
24%20%24%22%7%
780
16th to endNight
26%23%27%18%3
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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