Star
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star clear sky chart from 2005-11-05 to 2017-12-02.

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
51%
15662
24%
47856
18%
15616
58%
15616
30%
28891

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%
900
24%
2327
9%
895
42%
895
27%
1520
January16th to endNight
25%
901
25%
2437
9%
901
36%
901
25%
1624
February1st to 15thNight
31%
704
24%
2112
11%
701
41%
701
26%
1323
February16th to endNight
26%
631
24%
1893
10%
631
37%
631
24%
1195
March1st to 15thNight
32%
633
22%
2073
12%
633
42%
633
25%
1294
March16th to endNight
40%
576
23%
2034
17%
576
50%
576
29%
1151
April1st to 15thNight
37%
539
23%
1797
15%
539
49%
539
28%
1057
April16th to endNight
47%
540
25%
1800
21%
540
59%
540
35%
977
May1st to 15thNight
52%
539
21%
1800
16%
539
63%
539
33%
1011
May16th to endNight
66%
563
23%
1791
22%
561
71%
561
36%
1013
June1st to 15thNight
74%
540
17%
1488
16%
540
75%
540
35%
930
June16th to endNight
75%
540
21%
1450
19%
540
77%
540
36%
904
July1st to 15thNight
79%
510
16%
1530
18%
510
79%
510
33%
930
July16th to endNight
78%
564
15%
1669
18%
531
78%
531
29%
1036
August1st to 15thNight
82%
539
16%
1788
19%
536
82%
536
30%
1040
August16th to endNight
73%
573
19%
1910
22%
573
74%
573
24%
1249
September1st to 15thNight
72%
540
22%
1800
25%
540
73%
540
28%
1105
September16th to endNight
72%
681
29%
1944
26%
681
73%
681
38%
1147
October1st to 15thNight
64%
720
32%
2097
26%
720
67%
720
42%
1146
October16th to endNight
54%
768
35%
2304
28%
768
61%
768
39%
1270
November1st to 15thNight
54%
760
30%
2348
23%
760
62%
760
36%
1303
November16th to endNight
45%
780
31%
2535
24%
780
56%
780
34%
1386
December1st to 15thNight
38%
728
23%
2365
17%
728
46%
728
24%
1485
December16th to endNight
29%
893
18%
2564
11%
893
35%
893
20%
1795

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
11%5%25%5%35%5%5%7%40%
48558
Night
10%5%2442445%7%48%
48062
TransparencyDay
41%7%11%16%17%5%
48267
Night
34%6%12%18%19%8%
47858
SeeingDay
11%5%17%26%26%12%
5698
Night
13%6%22%29%22%4
15663

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
18%7%25%323435%43%
1611
16th to endDay
18%6%2432334445%
1784
February1st to 15thDay
16%8%3442334444%
1750
16th to endDay
16%6%35%5%2344444%
1580
March1st to 15thDay
17%6%25%424337%40%
1896
16th to endDay
11%6%26%5%35%5%5%6%41%
2187
April1st to 15thDay
11%5%25%5%35%45%6%43%
2151
16th to endDay
9%5%26%5%445%5%7%42%
2160
May1st to 15thDay
11%6%25%7%36%45%6%38%
2151
16th to endDay
8%5%26%6%46%6%6%8%39%
2319
June1st to 15thDay
7%426%7%5%7%7%8%9%33%
2469
16th to endDay
5%327%7%49%8%7%9%34%
2505
July1st to 15thDay
7%437%8%5%8%7%9%9%27%
2340
16th to endDay
9%5%37%8%5%8%7%9%9%26%
2383
August1st to 15thDay
6%5%26%8%48%7%7%9%33%
2160
16th to endDay
11%5%37%7%47%6%6%8%30%
2292
September1st to 15thDay
11%5%35%6%46%6%5%7%37%
2160
16th to endDay
10%5%15%434448%47%
2001
October1st to 15thDay
8%414424446%54%
1860
16th to endDay
10%413311335%59%
1920
November1st to 15thDay
9%414424446%53%
1839
16th to endDay
13%5%23323235%53%
1755
December1st to 15thDay
16%8%35%5%24445%40%
1632
16th to endDay
17%8%45%6%23246%37%
1653
January1st to 15thNight
14%7%24322345%48%
2327
16th to endNight
19%6%34323335%44%
2437
February1st to 15thNight
14%6%34422445%45%
2103
16th to endNight
17%5%2432325%5%46%
1893
March1st to 15thNight
16%6%23424446%44%
2073
16th to endNight
11%324423447%49%
2034
April1st to 15thNight
9%41443445%7%49%
1797
16th to endNight
7%42433435%9%51%
1800
May1st to 15thNight
7%41432446%10%49%
1799
16th to endNight
5%315%425%46%10%50%
1791
June1st to 15thNight
44245%35%6%6%11%44%
1488
16th to endNight
23235%35%7%7%11%45%
1450
July1st to 15thNight
43245%35%5%8%12%45%
1620
16th to endNight
43245%36%6%7%14%40%
1783
August1st to 15thNight
4314425%7%8%13%43%
1800
16th to endNight
8%425%5%46%47%10%40%
1910
September1st to 15thNight
7%4245%35%5%5%8%46%
1800
16th to endNight
6%4243245%6%8%51%
1944
October1st to 15thNight
7%224423346%58%
2097
16th to endNight
12%41331222461%
2304
November1st to 15thNight
10%41241435%6%55%
2348
16th to endNight
11%423323345%55%
2535
December1st to 15thNight
15%6%345%23346%43%
2365
16th to endNight
18%10%26%5%33335%37%
2564

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
43%4317%22%8%
1612
16th to endDay
42%3415%25%8%
1784
February1st to 15thDay
43%47%16%19%8%
1752
16th to endDay
41%5%6%17%20%7%
1580
March1st to 15thDay
46%38%16%19%5%
1896
16th to endDay
41%5%9%16%22%4
2189
April1st to 15thDay
38%5%9%19%19%6%
2151
16th to endDay
38%7%9%19%22%3
2160
May1st to 15thDay
43%7%12%14%17%5%
2151
16th to endDay
40%8%13%22%13%1
2323
June1st to 15thDay
43%10%13%20%10%1
2469
16th to endDay
42%11%15%16%11%1
2505
July1st to 15thDay
46%13%17%15%5%2
2201
16th to endDay
49%12%17%14%5%
2234
August1st to 15thDay
42%11%18%15%8%2
2148
16th to endDay
48%10%14%14%8%2
2292
September1st to 15thDay
43%10%13%15%12%5%
2160
16th to endDay
36%5%12%19%19%6%
2001
October1st to 15thDay
30%49%17%24%12%
1860
16th to endDay
27%35%12%35%15%
1920
November1st to 15thDay
32%5%7%15%30%8%
1839
16th to endDay
33%36%15%26%14%
1755
December1st to 15thDay
45%5%8%17%15%7%
1632
16th to endDay
49%37%18%16%4
1653
January1st to 15thNight
39%36%14%24%10%
2327
16th to endNight
42%45%15%23%8%
2437
February1st to 15thNight
39%47%17%20%10%
2112
16th to endNight
40%36%16%22%10%
1893
March1st to 15thNight
40%48%16%21%7%
2073
16th to endNight
33%5%12%20%22%5%
2034
April1st to 15thNight
33%6%10%21%19%8%
1797
16th to endNight
28%5%12%22%24%6%
1800
May1st to 15thNight
29%7%13%22%19%7%
1800
16th to endNight
28%7%16%25%19%2
1793
June1st to 15thNight
30%10%18%24%15%1
1488
16th to endNight
29%10%20%21%14%3
1450
July1st to 15thNight
28%11%25%22%8%3
1530
16th to endNight
29%14%25%21%7%1
1669
August1st to 15thNight
27%12%25%20%11%2
1788
16th to endNight
37%11%19%16%11%3
1910
September1st to 15thNight
33%9%16%19%14%6%
1800
16th to endNight
29%6%13%20%19%9%
1944
October1st to 15thNight
26%5%10%19%22%16%
2097
16th to endNight
29%2412%28%22%
2304
November1st to 15thNight
29%48%16%28%12%
2348
16th to endNight
30%37%16%23%17%
2535
December1st to 15thNight
41%410%18%19%6%
2365
16th to endNight
50%37%14%17%5%
2564

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
22%18%33%18%42
90
16th to endDay
15%30%40%9%31
96
February1st to 15thDay
14%22%43%15%4
90
16th to endDay
16%20%40%22%
81
March1st to 15thDay
27%20%40%11%1
90
16th to endDay
23%10%23%32%9%1
173
April1st to 15thDay
18%12%25%26%14%1
270
16th to endDay
12%8%26%32%18%1
270
May1st to 15thDay
13%8%24%27%19%6%
288
16th to endDay
10%322%28%23%11%
331
June1st to 15thDay
9%10%35%31%11%
444
16th to endDay
5%10%31%35%15%
495
July1st to 15thDay
5%6%30%40%16%
475
16th to endDay
9%419%41%24%
432
August1st to 15thDay
10%5%21%34%27%
313
16th to endDay
13%423%31%26%
332
September1st to 15thDay
9%210%17%35%24%
315
16th to endDay
10%18%24%41%14%
314
October1st to 15thDay
6%6%20%29%24%12%
195
16th to endDay
15%6%24%31%15%6%
144
November1st to 15thDay
13%6%34%31%11%2
135
16th to endDay
10%11%34%23%15%4
135
December1st to 15thDay
19%13%36%19%7%4
94
16th to endDay
19%19%30%18%11%
96
January1st to 15thNight
20%15%29%26%7%
900
16th to endNight
23%12%35%23%4
901
February1st to 15thNight
18%13%33%28%5%
704
16th to endNight
21%17%32%25%2
631
March1st to 15thNight
18%13%33%29%5%
633
16th to endNight
13%9%32%32%11%
576
April1st to 15thNight
11%10%37%26%12%
539
16th to endNight
9%7%32%35%15%
540
May1st to 15thNight
9%329%38%16%1
540
16th to endNight
6%119%38%28%5%
563
June1st to 15thNight
6%8%40%38%6%
540
16th to endNight
38%30%40%15%
540
July1st to 15thNight
4330%47%14%
510
16th to endNight
35%22%50%17%
564
August1st to 15thNight
4321%49%20%
539
16th to endNight
9%6%25%41%17%
573
September1st to 15thNight
10%25%24%47%10%
540
16th to endNight
8%9%37%38%5%
681
October1st to 15thNight
8%218%32%31%6%
720
16th to endNight
14%5%22%29%24%4
768
November1st to 15thNight
11%6%23%35%20%2
760
16th to endNight
14%7%28%29%18%1
780
December1st to 15thNight
18%9%28%31%12%
728
16th to endNight
23%11%30%26%7%
893
Page generated at 2017-12-03 10:16:48. Version ac04

Copyright 2017 A. Danko


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