Gairloch Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gairloch Mountain Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
21%
16153
8%
49560
4%
16108
25%
16108
10%
39190

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
8%
825
4%
2716
2%
821
11%
821
3%
2359
January16th to endNight
8%
872
5%
2876
1%
872
12%
872
4%
2469
February1st to 15thNight
12%
764
5%
2481
1%
761
16%
761
5%
2065
February16th to endNight
14%
683
7%
2124
1%
683
19%
683
7%
1713
March1st to 15thNight
18%
777
12%
2272
4%
777
25%
777
10%
1779
March16th to endNight
19%
751
11%
2207
5%
751
26%
751
11%
1714
April1st to 15thNight
20%
584
11%
1946
6%
584
27%
584
10%
1454
April16th to endNight
24%
557
15%
1740
8%
557
31%
557
15%
1237
May1st to 15thNight
28%
540
11%
1440
6%
540
31%
540
16%
1090
May16th to endNight
29%
561
9%
1496
3%
560
32%
560
15%
1142
June1st to 15thNight
21%
540
4%
1440
1%
540
23%
540
12%
1155
June16th to endNight
25%
540
6%
1440
2%
540
28%
540
16%
1122
July1st to 15thNight
39%
510
7%
1360
5%
510
40%
510
22%
980
July16th to endNight
34%
565
9%
1419
6%
532
36%
532
17%
1108
August1st to 15thNight
40%
539
10%
1498
7%
535
41%
535
18%
1118
August16th to endNight
44%
573
13%
1854
12%
573
47%
573
20%
1263
September1st to 15thNight
31%
540
13%
1800
9%
540
37%
540
17%
1233
September16th to endNight
29%
583
19%
1959
13%
583
38%
583
17%
1327
October1st to 15thNight
27%
720
12%
2160
6%
720
33%
720
15%
1567
October16th to endNight
17%
794
9%
2406
4%
794
22%
794
8%
1936
November1st to 15thNight
19%
805
7%
2554
3%
805
22%
805
9%
2061
November16th to endNight
15%
825
5%
2730
3%
825
18%
825
6%
2275
December1st to 15thNight
9%
825
3%
2730
0%
825
11%
825
3%
2403
December16th to endNight
7%
880
2%
2912
0%
880
10%
880
2%
2620

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
22%12%5%8%6%34345%21%
49963
Night
21%11%5%8%7%35%445%20%
49731
TransparencyDay
63%5%9%14%6%
49652
Night
62%5%10%14%5%
49560
SeeingDay
32%18%25%15%6%1
8462
Night
31%17%24%20%6%
16156

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
17%15%9%12%11%5%433311%
1552
16th to endDay
17%15%7%15%11%5%6%3349%
1700
February1st to 15thDay
17%13%6%14%11%6%5%34410%
1710
16th to endDay
14%16%8%11%8%3434418%
1634
March1st to 15thDay
16%15%7%8%10%46%33419%
2005
16th to endDay
17%16%8%11%7%2333321%
2369
April1st to 15thDay
23%15%47%5%2334423%
2333
16th to endDay
23%13%46%422345%27%
2331
May1st to 15thDay
27%11%36%5%23345%24%
2512
16th to endDay
23%11%46%5%345%47%22%
2618
June1st to 15thDay
28%11%36%6%24345%21%
2520
16th to endDay
28%9%36%42435%6%25%
2520
July1st to 15thDay
19%7%35%435%46%7%31%
2520
16th to endDay
25%9%36%5%2445%7%23%
2653
August1st to 15thDay
24%9%37%4345%6%6%24%
2448
16th to endDay
22%8%36%43445%8%28%
2348
September1st to 15thDay
25%8%36%4235%46%29%
2160
16th to endDay
21%8%36%334448%30%
1998
October1st to 15thDay
22%10%37%5%2435%8%25%
1800
16th to endDay
28%14%5%8%6%25%345%15%
1818
November1st to 15thDay
26%18%5%8%6%2423418%
1630
16th to endDay
21%22%7%9%5%34336%12%
1560
December1st to 15thDay
28%17%10%12%7%432336%
1560
16th to endDay
20%19%13%15%9%35%2234
1664
January1st to 15thNight
18%14%9%13%11%5%5%4348%
2716
16th to endNight
19%13%6%13%11%5%8%6%339%
2876
February1st to 15thNight
18%13%6%12%9%5%6%44414%
2480
16th to endNight
13%16%7%11%9%445%45%16%
2124
March1st to 15thNight
16%12%5%9%8%45%45%5%21%
2259
16th to endNight
18%13%6%9%7%34435%24%
2207
April1st to 15thNight
23%11%5%6%6%34446%23%
1946
16th to endNight
24%9%35%5%2343334%
1740
May1st to 15thNight
28%10%34423445%27%
1440
16th to endNight
21%9%36%6%45%5%5%7%24%
1494
June1st to 15thNight
26%10%46%6%445%45%22%
1440
16th to endNight
26%7%36%6%25%445%27%
1440
July1st to 15thNight
17%6%36%435%46%7%32%
1440
16th to endNight
23%7%47%5%246%6%7%24%
1515
August1st to 15thNight
21%6%35%6%245%5%6%30%
1509
16th to endNight
17%6%245%25%5%7%6%34%
1854
September1st to 15thNight
20%7%25%5%24448%34%
1800
16th to endNight
20%7%25%5%35%5%5%6%34%
1959
October1st to 15thNight
22%8%26%5%35%5%46%30%
2160
16th to endNight
27%11%47%5%45%45%5%19%
2406
November1st to 15thNight
23%14%48%6%35%5%45%17%
2554
16th to endNight
24%16%6%9%7%35%445%13%
2730
December1st to 15thNight
25%15%8%10%8%35%4448%
2730
16th to endNight
23%15%8%15%10%443335%
2912

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
75%5%8%7%2
1553
16th to endDay
78%46%8%2
1700
February1st to 15thDay
75%48%8%2
1713
16th to endDay
66%5%9%10%7%1
1634
March1st to 15thDay
67%47%12%7%
2015
16th to endDay
65%49%12%6%
2369
April1st to 15thDay
62%47%12%10%1
2333
16th to endDay
58%6%8%15%10%
2331
May1st to 15thDay
62%5%7%17%6%
2512
16th to endDay
60%6%8%17%6%
2622
June1st to 15thDay
64%5%10%13%5%
2520
16th to endDay
59%6%9%16%8%
2520
July1st to 15thDay
48%7%14%21%8%
2372
16th to endDay
59%6%11%15%5%
2486
August1st to 15thDay
57%8%10%17%5%
2434
16th to endDay
52%7%15%19%5%
2348
September1st to 15thDay
53%5%11%21%7%
2160
16th to endDay
51%6%12%20%9%
1998
October1st to 15thDay
57%5%11%17%8%
1800
16th to endDay
68%5%9%11%3
1818
November1st to 15thDay
69%5%8%14%2
1630
16th to endDay
73%5%10%7%3
1560
December1st to 15thDay
83%46%41
1560
16th to endDay
84%35%41
1664
January1st to 15thNight
76%5%8%7%2
2716
16th to endNight
73%6%8%8%3
2876
February1st to 15thNight
71%47%11%4
2481
16th to endNight
66%5%8%12%5%
2124
March1st to 15thNight
61%5%8%16%7%
2272
16th to endNight
61%48%15%8%1
2207
April1st to 15thNight
58%5%8%15%11%
1946
16th to endNight
53%49%17%13%1
1740
May1st to 15thNight
56%411%19%7%
1440
16th to endNight
56%6%11%18%7%
1496
June1st to 15thNight
63%410%15%4
1440
16th to endNight
57%6%9%15%10%
1440
July1st to 15thNight
47%7%16%19%8%
1360
16th to endNight
55%7%12%18%5%
1419
August1st to 15thNight
52%8%15%18%5%
1498
16th to endNight
45%8%16%23%5%
1854
September1st to 15thNight
47%7%11%24%9%
1800
16th to endNight
48%5%11%25%8%
1959
October1st to 15thNight
53%412%20%7%
2160
16th to endNight
64%5%9%16%4
2406
November1st to 15thNight
65%6%13%12%3
2554
16th to endNight
69%6%12%8%3
2730
December1st to 15thNight
76%6%9%6%1
2730
16th to endNight
81%47%41
2912

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
33%26%26%11%1
285
16th to endDay
32%24%27%12%1
304
February1st to 15thDay
33%23%27%13%1
281
16th to endDay
29%29%23%13%4
251
March1st to 15thDay
30%25%24%11%8%1
300
16th to endDay
30%26%25%11%31
352
April1st to 15thDay
34%27%20%12%4
330
16th to endDay
30%22%27%15%3
328
May1st to 15thDay
37%17%18%14%8%3
468
16th to endDay
31%16%26%17%5%1
519
June1st to 15thDay
38%14%24%15%5%
495
16th to endDay
32%11%29%16%7%2
495
July1st to 15thDay
24%9%27%25%11%2
475
16th to endDay
33%11%23%20%11%
514
August1st to 15thDay
29%8%25%21%12%1
421
16th to endDay
27%13%28%21%6%2
332
September1st to 15thDay
29%13%34%16%4
315
16th to endDay
27%17%27%16%8%2
285
October1st to 15thDay
25%15%29%15%9%4
270
16th to endDay
37%20%23%10%6%1
288
November1st to 15thDay
36%16%22%13%6%3
280
16th to endDay
36%23%22%11%4
285
December1st to 15thDay
47%18%21%9%2
285
16th to endDay
35%28%20%11%1
304
January1st to 15thNight
31%25%26%13%3
825
16th to endNight
34%26%22%12%3
872
February1st to 15thNight
30%23%26%16%3
764
16th to endNight
26%23%26%16%5%
683
March1st to 15thNight
27%20%27%18%5%
780
16th to endNight
28%22%23%18%5%1
751
April1st to 15thNight
31%18%21%25%3
584
16th to endNight
30%15%25%21%7%
557
May1st to 15thNight
34%11%21%19%11%1
540
16th to endNight
28%13%24%25%7%
561
June1st to 15thNight
36%9%25%22%5%
540
16th to endNight
28%10%30%23%6%
540
July1st to 15thNight
22%5%27%33%10%
510
16th to endNight
29%5%22%32%9%
565
August1st to 15thNight
25%6%19%32%15%
539
16th to endNight
22%6%21%34%14%
573
September1st to 15thNight
26%9%26%26%10%
540
16th to endNight
27%13%25%24%8%1
583
October1st to 15thNight
27%16%23%23%9%
720
16th to endNight
35%20%22%15%6%
794
November1st to 15thNight
34%17%22%20%5%1
805
16th to endNight
34%21%22%15%5%
825
December1st to 15thNight
41%22%20%10%4
825
16th to endNight
39%21%22%11%31
880
Page generated at 2018-04-24 11:03:00. Version ac04

Copyright 2018 A. Danko


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