Star Sherpa Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Sherpa Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
49%
15661
26%
47205
19%
15615
56%
15615
32%
27710

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
31%
899
27%
2327
10%
895
42%
895
28%
1497
January16th to endNight
28%
960
28%
2496
10%
960
39%
960
29%
1617
February1st to 15thNight
29%
880
24%
2287
8%
876
39%
876
31%
1457
February16th to endNight
24%
523
28%
1785
12%
523
40%
523
24%
1058
March1st to 15thNight
31%
540
26%
1980
15%
540
45%
540
22%
1166
March16th to endNight
32%
576
22%
2112
16%
576
42%
576
25%
1251
April1st to 15thNight
34%
539
25%
1859
16%
539
49%
539
30%
1034
April16th to endNight
39%
540
24%
1800
18%
540
52%
540
29%
1038
May1st to 15thNight
40%
540
22%
1722
15%
540
52%
540
27%
1066
May16th to endNight
53%
563
24%
1685
21%
561
59%
561
35%
995
June1st to 15thNight
77%
540
22%
1620
23%
540
80%
540
43%
876
June16th to endNight
75%
540
24%
1620
25%
540
78%
540
41%
887
July1st to 15thNight
77%
510
21%
1530
24%
510
79%
510
38%
884
July16th to endNight
84%
564
26%
1594
31%
531
85%
531
45%
853
August1st to 15thNight
84%
539
30%
1628
34%
536
85%
536
49%
821
August16th to endNight
73%
573
21%
1910
26%
573
74%
573
29%
1156
September1st to 15thNight
72%
540
24%
1840
27%
540
73%
540
34%
1029
September16th to endNight
75%
545
33%
1988
36%
545
77%
545
37%
1020
October1st to 15thNight
62%
720
31%
2160
24%
720
67%
720
42%
1159
October16th to endNight
53%
708
36%
2124
23%
708
64%
708
42%
1131
November1st to 15thNight
50%
700
29%
2100
21%
700
57%
700
37%
1173
November16th to endNight
38%
762
31%
2202
18%
762
49%
762
30%
1334
December1st to 15thNight
34%
900
24%
2340
12%
900
42%
900
29%
1540
December16th to endNight
31%
960
23%
2496
10%
960
40%
960
27%
1668

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
12%5%25%5%3445%7%44%
48210
Night
11%424323347%51%
47401
TransparencyDay
38%6%10%20%19%5%
47910
Night
32%5%9%21%21%8%
47206
SeeingDay
12%6%18%27%26%8%
5694
Night
13%7%24%30%20%2
15662

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
16%7%25%42233448%
1611
16th to endDay
20%6%1332333447%
1728
February1st to 15thDay
19%7%25%32432444%
1575
16th to endDay
20%5%24423245%43%
1696
March1st to 15thDay
22%6%25%323235%42%
1980
16th to endDay
15%6%36%5%2435%6%40%
2110
April1st to 15thDay
13%6%25%424446%46%
2088
16th to endDay
13%5%25%6%34446%43%
2160
May1st to 15thDay
13%6%37%5%36%5%46%37%
2226
16th to endDay
9%5%25%6%46%5%5%9%39%
2430
June1st to 15thDay
6%3145%47%7%7%8%41%
2340
16th to endDay
6%4245%46%7%7%10%40%
2340
July1st to 15thDay
8%326%7%5%7%6%7%10%34%
2340
16th to endDay
8%4245%46%7%7%10%38%
2466
August1st to 15thDay
5%2235%35%7%7%10%46%
2321
16th to endDay
10%5%26%6%47%6%6%9%34%
2292
September1st to 15thDay
10%5%15%5%3445%8%43%
2118
16th to endDay
8%2134345%5%7%52%
1959
October1st to 15thDay
11%423423336%53%
1800
16th to endDay
14%41221232460%
1769
November1st to 15thDay
10%5%335%34335%51%
1758
16th to endDay
16%6%2431323450%
1755
December1st to 15thDay
19%8%35%31323345%
1620
16th to endDay
18%7%35%5%23325%42%
1728
January1st to 15thNight
18%6%2332223351%
2327
16th to endNight
18%5%2331323449%
2496
February1st to 15thNight
16%5%23322335%50%
2278
16th to endNight
17%424323335%49%
1785
March1st to 15thNight
16%6%24323346%46%
1980
16th to endNight
12%6%35%423346%47%
2112
April1st to 15thNight
7%424424447%53%
1859
16th to endNight
10%5%24424446%50%
1800
May1st to 15thNight
10%5%24425%35%7%46%
1721
16th to endNight
6%424435%46%9%48%
1683
June1st to 15thNight
31143245%6%9%57%
1620
16th to endNight
4213325%46%9%55%
1620
July1st to 15thNight
5%315%426%5%7%12%46%
1620
16th to endNight
311342446%13%54%
1702
August1st to 15thNight
42232345%11%59%
1638
16th to endNight
7%4245%35%6%8%10%41%
1910
September1st to 15thNight
8%41442445%9%51%
1840
16th to endNight
6%2133235%5%7%57%
1988
October1st to 15thNight
8%313322345%59%
2160
16th to endNight
11%31222232462%
2124
November1st to 15thNight
9%414314336%56%
2100
16th to endNight
15%42441223452%
2202
December1st to 15thNight
15%6%35%423335%46%
2340
16th to endNight
17%7%34323345%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
42%25%18%23%7%
1612
16th to endDay
41%2419%24%6%
1728
February1st to 15thDay
44%35%18%19%7%
1576
16th to endDay
43%45%16%21%7%
1696
March1st to 15thDay
45%37%19%18%6%
1980
16th to endDay
44%5%7%17%22%2
2112
April1st to 15thDay
38%5%8%20%19%7%
2088
16th to endDay
42%5%8%19%19%4
2160
May1st to 15thDay
45%6%9%14%17%5%
2226
16th to endDay
39%9%13%21%13%1
2434
June1st to 15thDay
34%9%13%25%15%
2340
16th to endDay
35%9%14%20%18%1
2340
July1st to 15thDay
38%9%17%21%11%
2201
16th to endDay
36%10%18%22%11%
2311
August1st to 15thDay
29%8%15%28%15%1
2307
16th to endDay
42%10%14%19%11%2
2292
September1st to 15thDay
37%7%11%17%17%7%
2118
16th to endDay
27%7%12%22%21%8%
1959
October1st to 15thDay
31%5%7%19%21%14%
1800
16th to endDay
28%36%17%31%13%
1769
November1st to 15thDay
35%37%20%25%7%
1758
16th to endDay
38%35%14%28%8%
1755
December1st to 15thDay
45%26%19%18%6%
1620
16th to endDay
45%47%18%19%4
1728
January1st to 15thNight
39%25%15%27%9%
2327
16th to endNight
39%35%16%24%11%
2496
February1st to 15thNight
37%36%20%22%10%
2288
16th to endNight
38%45%20%20%10%
1785
March1st to 15thNight
39%48%18%19%9%
1980
16th to endNight
38%48%20%23%5%
2112
April1st to 15thNight
31%410%21%19%11%
1859
16th to endNight
34%5%9%22%21%7%
1800
May1st to 15thNight
36%7%8%19%17%9%
1722
16th to endNight
31%7%15%26%16%2
1685
June1st to 15thNight
22%8%12%31%22%2
1620
16th to endNight
24%7%14%24%25%4
1620
July1st to 15thNight
27%8%15%30%16%1
1530
16th to endNight
20%8%20%31%17%2
1594
August1st to 15thNight
19%6%15%35%20%3
1628
16th to endNight
33%9%16%21%15%3
1910
September1st to 15thNight
28%7%14%20%20%9%
1840
16th to endNight
25%6%9%20%25%12%
1988
October1st to 15thNight
26%48%21%22%17%
2160
16th to endNight
26%35%16%28%20%
2124
November1st to 15thNight
29%39%19%26%11%
2100
16th to endNight
37%2414%27%12%
2202
December1st to 15thNight
40%39%19%18%7%
2340
16th to endNight
42%38%18%20%6%
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
14%17%41%22%4
90
16th to endDay
23%26%30%12%7%
96
February1st to 15thDay
20%18%38%17%4
90
16th to endDay
24%17%41%13%2
81
March1st to 15thDay
31%20%33%12%3
90
16th to endDay
14%23%21%31%8%
96
April1st to 15thDay
16%14%35%21%10%
207
16th to endDay
24%10%27%21%13%2
270
May1st to 15thDay
15%12%33%25%9%3
363
16th to endDay
12%6%30%29%16%5%
517
June1st to 15thDay
7%111%36%35%7%
495
16th to endDay
7%214%32%31%12%
495
July1st to 15thDay
7%112%32%38%8%
475
16th to endDay
6%427%42%17%
515
August1st to 15thDay
6%329%43%16%
474
16th to endDay
18%5%20%37%17%
332
September1st to 15thDay
8%8%24%42%16%
273
16th to endDay
2345%32%14%
135
October1st to 15thDay
4222%42%17%10%
135
16th to endDay
23%321%25%22%5%
99
November1st to 15thDay
10%7%37%28%14%1
90
16th to endDay
26%15%35%11%8%2
90
December1st to 15thDay
25%10%41%12%7%3
90
16th to endDay
23%26%31%12%5%1
96
January1st to 15thNight
22%14%27%27%8%
900
16th to endNight
23%13%32%26%4
960
February1st to 15thNight
20%13%33%27%5%
880
16th to endNight
19%15%37%24%3
523
March1st to 15thNight
18%12%35%27%5%
540
16th to endNight
14%10%39%25%9%
576
April1st to 15thNight
9%14%38%25%10%
539
16th to endNight
11%9%36%29%12%1
540
May1st to 15thNight
13%7%34%31%11%2
540
16th to endNight
7%327%36%22%2
563
June1st to 15thNight
311%39%40%3
540
16th to endNight
411%36%37%9%
540
July1st to 15thNight
5%7%36%46%4
510
16th to endNight
3430%50%10%
564
August1st to 15thNight
5%433%43%12%
539
16th to endNight
10%333%44%7%
573
September1st to 15thNight
10%18%32%41%6%
540
16th to endNight
7%9%33%44%4
545
October1st to 15thNight
10%218%36%27%5%
720
16th to endNight
13%5%24%30%22%3
708
November1st to 15thNight
11%8%25%36%15%2
700
16th to endNight
18%11%29%25%14%
762
December1st to 15thNight
19%10%29%31%8%
900
16th to endNight
22%12%29%27%7%
960
Page generated at 2017-10-17 15:35:30. Version ac04

Copyright 2017 A. Danko


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