Grey Highland Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grey Highland Skies Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
22%
22970
12%
80122
6%
22866
30%
22866
13%
58924

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
8%
773
4%
4441
1%
753
13%
753
2%
3623
January11th to 20thNight
9%
758
3%
4154
2%
740
13%
740
2%
3654
January21st to endNight
13%
834
4%
4530
3%
814
18%
814
4%
3870
February1st to 10thNight
8%
760
7%
2470
2%
760
16%
760
6%
1973
February11th to 20thNight
9%
740
9%
2405
1%
740
19%
740
8%
1883
February21st to endNight
10%
611
10%
1911
1%
611
20%
611
9%
1455
March1st to 10thNight
12%
720
14%
1998
4%
720
21%
720
12%
1492
March11th to 20thNight
15%
720
18%
1980
6%
720
26%
720
15%
1438
March21st to endNight
21%
792
17%
2178
6%
792
30%
792
19%
1510
April1st to 10thNight
13%
720
14%
1860
2%
720
21%
720
15%
1387
April11th to 20thNight
25%
605
19%
1669
7%
605
32%
605
20%
1154
April21st to endNight
22%
540
15%
1620
6%
540
30%
540
16%
1149
May1st to 10thNight
31%
540
15%
1620
8%
540
37%
540
22%
1081
May11th to 20thNight
30%
397
21%
1459
14%
397
44%
397
21%
864
May21st to endNight
36%
388
17%
1551
11%
388
53%
388
27%
825
June1st to 10thNight
28%
360
14%
1440
10%
360
41%
360
19%
858
June11th to 20thNight
42%
360
18%
1273
16%
360
53%
360
25%
739
June21st to endNight
37%
360
16%
1260
13%
360
48%
360
25%
745
July1st to 10thNight
44%
350
19%
1225
17%
350
53%
350
35%
636
July11th to 20thNight
41%
348
18%
1350
18%
348
53%
348
29%
726
July21st to endNight
42%
591
17%
1672
10%
558
49%
558
32%
992
August1st to 10thNight
46%
537
18%
1600
12%
534
51%
534
35%
921
August11th to 20thNight
54%
534
23%
1598
14%
534
61%
534
34%
920
August21st to endNight
41%
634
20%
1822
9%
634
47%
634
29%
1133
September1st to 10thNight
43%
720
17%
1800
8%
720
46%
720
32%
1172
September11th to 20thNight
42%
720
25%
1946
13%
720
49%
720
34%
1164
September21st to endNight
37%
720
17%
1988
11%
720
42%
720
23%
1367
October1st to 10thNight
27%
720
16%
2160
11%
720
34%
720
19%
1511
October11th to 20thNight
19%
720
12%
2160
5%
720
27%
720
14%
1591
October21st to endNight
14%
792
11%
2380
5%
792
23%
792
10%
1878
November1st to 10thNight
17%
740
14%
2486
8%
740
26%
740
13%
1760
November11th to 20thNight
14%
760
11%
2660
6%
760
22%
760
9%
1991
November21st to endNight
13%
760
8%
2660
4%
760
19%
760
7%
2127
December1st to 10thNight
7%
760
5%
2660
1%
760
11%
760
4%
2221
December11th to 20thNight
6%
760
3%
3264
0%
759
10%
759
4%
2730
December21st to endNight
6%
826
2%
4872
0%
817
11%
817
1%
4384

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%12%5%9%7%45%5%5%7%28%
78798
Night
13%11%5%10%7%45%5%5%6%28%
80339
TransparencyDay
55%6%11%17%9%1
78508
Night
55%6%12%17%9%1
80164
SeeingDay
20%22%31%17%7%2
13926
Night
19%22%31%19%7%1
22991

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 10thDay
14%16%9%15%9%46%45%414%
2386
11th to 20thDay
10%18%10%20%12%7%5%5%446%
2790
21st to endDay
16%20%9%14%9%35%43412%
3124
February1st to 10thDay
11%15%7%13%14%5%6%5%35%14%
1710
11th to 20thDay
10%12%8%15%12%46%6%6%5%16%
1663
21st to endDay
15%16%7%10%8%5%6%5%4420%
1435
March1st to 10thDay
12%12%6%10%11%5%5%5%46%25%
1959
11th to 20thDay
11%13%7%10%7%35%5%45%29%
1980
21st to endDay
15%13%5%7%7%3445%5%31%
2178
April1st to 10thDay
15%14%6%9%7%44447%26%
2099
11th to 20thDay
16%12%46%4345%6%6%34%
2255
21st to endDay
20%11%47%5%3435%6%32%
2340
May1st to 10thDay
16%10%47%6%3445%7%34%
2340
11th to 20thDay
16%8%47%5%35%5%5%6%36%
2432
21st to endDay
13%6%26%5%35%5%6%8%41%
2725
June1st to 10thDay
15%6%36%5%36%6%6%9%36%
2520
11th to 20thDay
12%6%36%5%25%6%6%9%40%
2682
21st to endDay
14%6%26%5%45%5%6%8%38%
2700
July1st to 10thDay
10%5%25%5%36%5%6%9%43%
2700
11th to 20thDay
11%7%36%6%46%6%7%9%36%
2557
21st to endDay
10%7%36%6%5%6%6%6%10%34%
2547
August1st to 10thDay
10%5%36%7%45%7%6%9%37%
2327
11th to 20thDay
10%6%37%6%5%6%7%8%10%34%
2303
21st to endDay
14%6%46%6%45%6%6%9%35%
2516
September1st to 10thDay
16%8%36%5%45%5%5%7%36%
2160
11th to 20thDay
13%7%36%5%35%5%6%8%40%
2012
21st to endDay
15%8%47%7%445%6%7%32%
1972
October1st to 10thDay
18%10%48%6%35%45%6%30%
1800
11th to 20thDay
18%15%5%7%8%4446%6%22%
1800
21st to endDay
24%19%5%7%5%35%44418%
1972
November1st to 10thDay
13%17%5%9%7%345%5%6%26%
1592
11th to 20thDay
12%16%7%10%7%5%5%5%6%8%19%
1520
21st to endDay
15%17%8%13%8%37%6%5%5%13%
1520
December1st to 10thDay
13%20%10%18%9%45%4449%
1520
11th to 20thDay
16%17%8%14%9%46%45%5%13%
1906
21st to endDay
21%21%9%18%8%35%3337%
2756
January1st to 10thNight
15%14%9%15%9%45%5%5%7%13%
4445
11th to 20thNight
12%11%8%19%15%9%7%4437%
4154
21st to endNight
17%14%8%14%11%5%6%5%5%5%10%
4532
February1st to 10thNight
11%13%7%13%11%5%6%5%5%6%17%
2470
11th to 20thNight
10%11%7%15%9%5%7%5%6%6%20%
2403
21st to endNight
12%12%6%12%9%5%7%5%5%5%23%
1911
March1st to 10thNight
11%10%5%12%8%47%45%7%28%
1988
11th to 20thNight
11%12%7%9%7%35%445%34%
1979
21st to endNight
12%10%47%6%35%5%5%6%36%
2178
April1st to 10thNight
17%11%5%7%7%3445%7%30%
1860
11th to 20thNight
14%10%46%5%34447%38%
1669
21st to endNight
13%12%49%6%345%5%6%33%
1620
May1st to 10thNight
14%10%26%5%35%6%6%7%37%
1620
11th to 20thNight
15%5%345%25%5%5%7%45%
1458
21st to endNight
9%5%244245%6%8%51%
1550
June1st to 10thNight
14%6%26%445%46%9%40%
1440
11th to 20thNight
10%5%25%445%6%7%10%43%
1273
21st to endNight
11%6%26%5%4345%9%45%
1260
July1st to 10thNight
5%5%3442445%8%57%
1260
11th to 20thNight
8%5%245%35%46%8%50%
1395
21st to endNight
8%5%245%35%5%6%7%50%
1771
August1st to 10thNight
9%425%4345%6%9%50%
1611
11th to 20thNight
6%4145%346%6%9%50%
1598
21st to endNight
10%6%26%5%35%45%8%46%
1822
September1st to 10thNight
10%6%35%435%47%8%45%
1800
11th to 20thNight
12%5%2343446%7%50%
1946
21st to endNight
14%9%37%5%34447%38%
1988
October1st to 10thNight
17%8%36%6%45%45%8%35%
2160
11th to 20thNight
17%13%48%5%345%5%7%28%
2160
21st to endNight
19%14%5%8%7%445%5%6%21%
2380
November1st to 10thNight
14%13%47%7%46%5%5%6%29%
2486
11th to 20thNight
14%14%6%9%6%46%5%6%7%22%
2660
21st to endNight
15%15%7%11%7%46%5%5%7%17%
2660
December1st to 10thNight
16%15%9%15%8%46%5%5%6%12%
2660
11th to 20thNight
12%18%8%16%9%45%5%45%13%
3288
21st to endNight
21%19%10%18%7%444337%
4884

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
70%7%11%10%1
2387
11th to 20thDay
81%5%7%43
2790
21st to endDay
75%7%7%7%3
3124
February1st to 10thDay
72%5%8%11%31
1710
11th to 20thDay
67%5%10%12%5%1
1672
21st to endDay
66%5%9%13%6%1
1435
March1st to 10thDay
60%5%12%13%9%1
1962
11th to 20thDay
57%410%17%10%2
1980
21st to endDay
55%410%15%13%2
2178
April1st to 10thDay
58%5%9%17%10%1
2099
11th to 20thDay
48%6%9%21%15%1
2255
21st to endDay
53%5%11%18%11%2
2340
May1st to 10thDay
51%49%21%14%1
2340
11th to 20thDay
47%6%9%23%13%1
2436
21st to endDay
40%6%14%23%14%2
2725
June1st to 10thDay
43%7%12%21%15%1
2520
11th to 20thDay
39%7%12%25%16%1
2682
21st to endDay
42%7%13%24%13%1
2700
July1st to 10thDay
36%8%13%24%18%2
2626
11th to 20thDay
40%8%13%27%10%1
2479
21st to endDay
44%8%12%21%13%1
2405
August1st to 10thDay
40%9%16%23%12%1
2314
11th to 20thDay
42%9%16%23%10%
2303
21st to endDay
43%8%14%23%11%1
2516
September1st to 10thDay
46%6%13%23%10%2
2160
11th to 20thDay
41%7%13%27%12%
2012
21st to endDay
49%8%12%23%7%1
1972
October1st to 10thDay
52%7%11%17%12%1
1800
11th to 20thDay
62%6%11%14%6%1
1800
21st to endDay
68%411%10%6%
1972
November1st to 10thDay
59%5%11%17%7%
1592
11th to 20thDay
63%6%12%13%6%1
1520
21st to endDay
69%7%12%10%2
1520
December1st to 10thDay
76%5%10%8%2
1520
11th to 20thDay
73%8%8%10%2
1906
21st to endDay
81%6%6%6%1
2756
January1st to 10thNight
69%8%12%9%2
4445
11th to 20thNight
79%5%9%43
4154
21st to endNight
72%8%11%6%31
4532
February1st to 10thNight
66%5%12%13%3
2470
11th to 20thNight
63%5%12%14%5%
2405
21st to endNight
60%5%12%14%7%1
1911
March1st to 10thNight
56%5%12%17%9%1
1998
11th to 20thNight
52%5%10%19%11%2
1980
21st to endNight
48%411%20%14%3
2178
April1st to 10thNight
54%5%9%18%13%1
1860
11th to 20thNight
46%5%9%21%16%2
1669
21st to endNight
51%5%11%16%15%2
1620
May1st to 10thNight
44%6%11%21%16%2
1620
11th to 20thNight
39%5%10%26%17%3
1459
21st to endNight
30%7%17%27%16%4
1551
June1st to 10thNight
40%6%11%23%18%2
1440
11th to 20thNight
34%7%13%26%19%1
1273
21st to endNight
36%7%14%27%15%1
1260
July1st to 10thNight
26%6%12%28%23%3
1225
11th to 20thNight
31%6%16%31%15%1
1350
21st to endNight
32%7%15%29%15%2
1672
August1st to 10thNight
30%6%19%30%14%1
1600
11th to 20thNight
28%9%16%30%16%1
1598
21st to endNight
36%7%15%27%14%1
1822
September1st to 10thNight
34%8%15%29%13%2
1800
11th to 20thNight
31%6%15%32%16%1
1946
21st to endNight
45%6%13%26%10%
1988
October1st to 10thNight
47%7%11%20%14%1
2160
11th to 20thNight
54%7%14%18%7%
2160
21st to endNight
61%7%11%13%7%
2380
November1st to 10thNight
53%6%14%18%8%1
2486
11th to 20thNight
57%7%14%14%6%2
2660
21st to endNight
64%8%15%11%21
2660
December1st to 10thNight
71%6%13%8%2
2660
11th to 20thNight
71%7%11%10%2
3288
21st to endNight
81%6%6%6%1
4884

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
22%31%29%15%21
180
11th to 20thDay
22%36%29%10%2
258
21st to endDay
24%29%35%11%1
297
February1st to 10thDay
27%36%30%43
270
11th to 20thDay
23%37%36%41
270
21st to endDay
33%38%24%5%
210
March1st to 10thDay
24%30%31%11%3
402
11th to 20thDay
23%26%35%12%31
420
21st to endDay
30%24%30%13%3
462
April1st to 10thDay
25%26%34%10%4
420
11th to 20thDay
30%23%25%12%7%3
412
21st to endDay
27%24%30%13%42
420
May1st to 10thDay
22%26%28%18%6%1
423
11th to 20thDay
19%19%34%19%6%4
447
21st to endDay
18%16%31%22%10%4
485
June1st to 10thDay
16%19%33%23%7%1
450
11th to 20thDay
14%19%32%25%8%2
612
21st to endDay
17%17%37%20%7%3
630
July1st to 10thDay
13%12%32%29%12%3
621
11th to 20thDay
15%13%32%23%10%6%
482
21st to endDay
11%11%42%24%9%3
488
August1st to 10thDay
10%11%32%28%13%6%
446
11th to 20thDay
11%10%30%27%17%6%
439
21st to endDay
15%14%30%25%12%4
495
September1st to 10thDay
16%16%28%24%10%5%
450
11th to 20thDay
12%13%29%24%16%7%
450
21st to endDay
16%19%27%20%13%4
450
October1st to 10thDay
23%21%26%16%12%3
450
11th to 20thDay
23%30%31%12%3
450
21st to endDay
31%28%28%11%2
487
November1st to 10thDay
24%34%26%13%3
232
11th to 20thDay
25%29%33%9%31
180
21st to endDay
28%27%36%8%
180
December1st to 10thDay
24%38%30%8%
180
11th to 20thDay
27%34%29%8%21
180
21st to endDay
25%39%29%7%1
198
January1st to 10thNight
21%34%30%12%2
776
11th to 20thNight
25%29%30%14%21
760
21st to endNight
16%25%37%17%4
836
February1st to 10thNight
20%36%31%12%1
760
11th to 20thNight
20%30%34%13%2
743
21st to endNight
22%32%31%12%3
611
March1st to 10thNight
20%28%34%15%3
720
11th to 20thNight
21%28%33%14%4
720
21st to endNight
20%22%33%19%5%
792
April1st to 10thNight
24%24%35%16%2
720
11th to 20thNight
21%23%29%19%7%1
605
21st to endNight
21%21%31%19%8%
540
May1st to 10thNight
16%16%32%26%9%1
540
11th to 20thNight
18%12%34%26%10%
397
21st to endNight
11%15%33%30%11%
389
June1st to 10thNight
16%12%37%28%6%1
360
11th to 20thNight
13%12%28%35%12%
360
21st to endNight
14%11%33%28%13%1
360
July1st to 10thNight
9%7%34%32%18%
350
11th to 20thNight
8%11%35%28%16%1
348
21st to endNight
10%9%34%32%14%1
591
August1st to 10thNight
9%7%31%32%19%1
537
11th to 20thNight
7%8%25%36%22%2
534
21st to endNight
14%10%32%26%17%2
634
September1st to 10thNight
13%12%28%28%14%4
720
11th to 20thNight
13%11%30%27%15%4
720
21st to endNight
17%15%24%26%14%4
720
October1st to 10thNight
20%17%33%17%12%2
720
11th to 20thNight
26%23%29%16%6%1
720
21st to endNight
27%25%31%14%3
792
November1st to 10thNight
24%23%31%16%5%
740
11th to 20thNight
21%33%27%13%5%1
760
21st to endNight
25%29%30%14%2
760
December1st to 10thNight
25%30%32%9%3
760
11th to 20thNight
21%33%33%10%2
760
21st to endNight
28%33%27%12%1
836
Page generated at 2024-02-22 06:05:46. Version ac07

Copyright 2024 Attilla Danko


Grey Highland Skies Observatory Clear Sky Chart |Charts Home