Galactic Stone Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Galactic Stone Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
59%
15895
20%
47030
16%
15853
64%
15853
30%
29559

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
45%
719
19%
2327
15%
716
52%
716
24%
1452
January16th to endNight
44%
768
23%
2397
17%
768
52%
768
28%
1484
February1st to 15thNight
45%
701
25%
2103
17%
698
54%
698
33%
1246
February16th to endNight
45%
631
24%
1863
14%
631
55%
631
32%
1125
March1st to 15thNight
47%
720
29%
1980
16%
720
58%
720
39%
1134
March16th to endNight
53%
768
27%
2112
19%
768
58%
768
39%
1234
April1st to 15thNight
55%
718
23%
1976
17%
718
60%
718
42%
1111
April16th to endNight
59%
702
26%
1863
18%
702
65%
702
41%
1093
May1st to 15thNight
75%
539
26%
1619
20%
539
78%
539
45%
866
May16th to endNight
76%
561
23%
1682
19%
561
78%
561
38%
997
June1st to 15thNight
71%
540
12%
1620
12%
540
72%
540
24%
1118
June16th to endNight
77%
540
9%
1620
8%
540
77%
540
23%
1149
July1st to 15thNight
76%
510
6%
1530
5%
510
76%
510
20%
1149
July16th to endNight
74%
564
6%
1595
6%
531
76%
531
20%
1168
August1st to 15thNight
77%
539
4%
1669
5%
536
77%
536
23%
1184
August16th to endNight
70%
690
9%
2027
10%
690
70%
690
20%
1463
September1st to 15thNight
63%
720
7%
1980
7%
720
63%
720
19%
1487
September16th to endNight
64%
693
15%
1914
15%
693
65%
693
22%
1365
October1st to 15thNight
67%
660
25%
1845
24%
660
70%
660
34%
1137
October16th to endNight
56%
704
28%
2112
25%
704
62%
704
33%
1250
November1st to 15thNight
59%
700
30%
2101
25%
700
67%
700
39%
1168
November16th to endNight
51%
720
29%
2259
22%
720
61%
720
34%
1303
December1st to 15thNight
51%
720
26%
2340
22%
720
59%
720
29%
1395
December16th to endNight
55%
768
23%
2496
23%
768
60%
768
29%
1481

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
8%5%26%6%46%6%6%8%37%
47873
Night
7%5%25%5%35%5%6%9%44%
47239
TransparencyDay
41%9%13%16%13%5%
47574
Night
34%8%16%19%14%5%
47042
SeeingDay
9%313%22%25%26%
5758
Night
9%318%32%26%9%
15902

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 15thDay
10%5%445%25%46%11%38%
1611
16th to endDay
9%5%345%3445%7%46%
1824
February1st to 15thDay
12%5%245%2345%7%46%
1750
16th to endDay
7%425%4245%5%6%50%
1610
March1st to 15thDay
5%314435%5%5%8%52%
1980
16th to endDay
8%425%5%25%45%7%48%
2111
April1st to 15thDay
6%3246%46%5%5%9%45%
1972
16th to endDay
5%315%5%35%5%6%8%48%
2101
May1st to 15thDay
5%315%5%3446%8%51%
2331
16th to endDay
6%325%7%5%7%7%6%8%36%
2431
June1st to 15thDay
12%6%36%7%5%8%7%7%11%23%
2340
16th to endDay
7%5%47%9%5%8%8%8%10%23%
2340
July1st to 15thDay
8%6%38%8%5%10%10%9%9%19%
2340
16th to endDay
7%7%49%8%6%9%9%8%9%19%
2465
August1st to 15thDay
7%6%28%10%7%9%9%9%9%20%
2276
16th to endDay
8%7%38%10%6%9%7%7%9%21%
2160
September1st to 15thDay
8%6%39%9%6%8%8%8%10%21%
1980
16th to endDay
9%7%49%9%46%7%7%9%23%
1905
October1st to 15thDay
6%6%25%7%5%5%7%6%7%38%
1783
16th to endDay
9%5%25%425%45%6%48%
1760
November1st to 15thDay
6%42443445%8%51%
1757
16th to endDay
8%4245%35%6%48%46%
1698
December1st to 15thDay
8%5%35%445%5%7%8%41%
1620
16th to endDay
7%425%5%35%6%6%8%46%
1728
January1st to 15thNight
9%6%45%5%25%46%8%41%
2327
16th to endNight
12%5%25%5%25%45%7%42%
2397
February1st to 15thNight
10%5%34323447%49%
2103
16th to endNight
7%6%36%5%23348%48%
1863
March1st to 15thNight
5%41443436%7%54%
1980
16th to endNight
6%424324447%54%
2112
April1st to 15thNight
5%3233235%5%10%53%
1976
16th to endNight
6%3144245%5%6%55%
1863
May1st to 15thNight
42133235%5%10%56%
1619
16th to endNight
42235%245%6%10%51%
1682
June1st to 15thNight
9%5%25%5%36%5%7%11%36%
1620
16th to endNight
5%425%6%47%7%9%13%33%
1620
July1st to 15thNight
5%425%5%47%7%10%14%30%
1620
16th to endNight
5%5%25%7%48%7%10%11%30%
1703
August1st to 15thNight
35%25%6%5%7%7%9%13%33%
1680
16th to endNight
7%5%37%6%46%7%9%12%31%
2027
September1st to 15thNight
7%5%36%8%47%7%8%12%28%
1980
16th to endNight
6%7%28%7%36%6%7%11%32%
1914
October1st to 15thNight
6%5%245%245%6%8%47%
1845
16th to endNight
8%6%25%42335%7%50%
2112
November1st to 15thNight
5%414335%45%7%54%
2101
16th to endNight
6%4245%345%5%7%49%
2259
December1st to 15thNight
9%5%25%43445%7%46%
2340
16th to endNight
6%5%25%5%345%7%8%44%
2496

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
37%7%10%20%18%5%
1612
16th to endDay
36%5%8%16%24%9%
1824
February1st to 15thDay
36%47%15%21%14%
1752
16th to endDay
32%6%11%16%22%11%
1610
March1st to 15thDay
28%5%11%24%21%8%
1980
16th to endDay
34%49%21%19%9%
2112
April1st to 15thDay
33%7%11%19%20%8%
1972
16th to endDay
32%6%10%20%23%7%
2101
May1st to 15thDay
29%7%12%23%19%8%
2331
16th to endDay
42%9%11%19%14%2
2435
June1st to 15thDay
50%11%16%16%3
2340
16th to endDay
51%13%20%11%3
2340
July1st to 15thDay
54%17%19%7%1
2201
16th to endDay
52%17%19%9%1
2310
August1st to 15thDay
51%16%24%6%
2263
16th to endDay
55%14%18%10%
2160
September1st to 15thDay
52%16%18%10%2
1980
16th to endDay
50%11%14%15%6%1
1905
October1st to 15thDay
40%9%9%15%15%9%
1783
16th to endDay
34%5%9%15%21%13%
1760
November1st to 15thDay
30%48%23%22%10%
1757
16th to endDay
34%6%9%18%18%12%
1698
December1st to 15thDay
38%7%11%20%15%6%
1620
16th to endDay
33%6%12%19%19%7%
1728
January1st to 15thNight
39%6%11%20%16%5%
2327
16th to endNight
39%410%17%19%8%
2397
February1st to 15thNight
34%48%17%22%13%
2112
16th to endNight
34%5%12%17%21%7%
1863
March1st to 15thNight
28%411%27%19%7%
1980
16th to endNight
28%5%12%26%19%8%
2112
April1st to 15thNight
24%7%16%23%21%6%
1976
16th to endNight
28%5%13%23%22%6%
1863
May1st to 15thNight
22%6%16%27%19%7%
1620
16th to endNight
26%9%19%23%18%2
1684
June1st to 15thNight
40%11%21%19%6%
1620
16th to endNight
39%15%24%16%4
1620
July1st to 15thNight
40%19%29%9%1
1530
16th to endNight
40%18%28%12%
1595
August1st to 15thNight
36%17%34%9%
1669
16th to endNight
41%16%25%14%1
2027
September1st to 15thNight
43%16%23%12%2
1980
16th to endNight
43%11%18%18%42
1914
October1st to 15thNight
32%8%12%19%18%7%
1845
16th to endNight
33%5%8%16%25%10%
2112
November1st to 15thNight
27%5%10%22%23%9%
2101
16th to endNight
32%5%10%21%17%12%
2259
December1st to 15thNight
36%5%11%24%16%5%
2340
16th to endNight
34%7%13%20%16%7%
2496

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
16%11%31%23%17%
90
16th to endDay
13%17%32%23%10%2
96
February1st to 15thDay
12%16%22%26%16%5%
90
16th to endDay
9%10%37%28%12%
111
March1st to 15thDay
6%7%34%33%15%2
270
16th to endDay
11%5%23%30%26%3
288
April1st to 15thDay
8%7%21%30%25%7%
270
16th to endDay
5%118%30%33%11%
270
May1st to 15thDay
6%315%27%29%18%
288
16th to endDay
7%17%19%30%33%
331
June1st to 15thDay
16%1413%25%38%
315
16th to endDay
6%413%23%52%
315
July1st to 15thDay
416%23%63%
305
16th to endDay
12%410%22%49%
326
August1st to 15thDay
8%310%22%54%
313
16th to endDay
12%310%24%46%
332
September1st to 15thDay
11%15%16%26%37%
315
16th to endDay
12%1315%34%32%
287
October1st to 15thDay
8%19%33%35%11%
255
16th to endDay
11%219%31%26%8%
272
November1st to 15thDay
9%116%33%30%8%
265
16th to endDay
7%227%36%20%4
168
December1st to 15thDay
6%5%40%34%13%
90
16th to endDay
5%6%18%44%21%3
96
January1st to 15thNight
12%6%27%37%15%
720
16th to endNight
15%6%28%36%12%
768
February1st to 15thNight
14%5%30%34%14%
704
16th to endNight
10%431%42%10%
631
March1st to 15thNight
6%5%35%40%11%
720
16th to endNight
8%5%27%41%15%
768
April1st to 15thNight
5%328%42%18%
718
16th to endNight
8%323%42%21%
702
May1st to 15thNight
5%112%44%31%3
540
16th to endNight
5%111%38%37%7%
563
June1st to 15thNight
10%16%23%42%15%
540
16th to endNight
6%215%41%32%
540
July1st to 15thNight
7%17%44%38%
510
16th to endNight
5%28%44%39%
564
August1st to 15thNight
5%27%46%38%
539
16th to endNight
9%15%17%37%28%
690
September1st to 15thNight
12%5%21%41%18%
720
16th to endNight
12%16%29%39%11%
693
October1st to 15thNight
8%14%41%30%4
660
16th to endNight
9%322%33%28%2
704
November1st to 15thNight
7%224%42%21%3
700
16th to endNight
8%329%40%16%1
720
December1st to 15thNight
11%328%37%18%
720
16th to endNight
8%5%23%40%20%1
768
Page generated at 2017-09-25 09:02:16. Version ac04

Copyright 2017 A. Danko


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