Windsong Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windsong Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
25%
15635
18%
49065
7%
15603
37%
15603
19%
32314

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
14%
780
19%
2716
5%
776
32%
776
15%
1738
January16th to endNight
13%
832
19%
2912
3%
832
34%
832
14%
1908
February1st to 15thNight
14%
764
17%
2357
4%
761
30%
761
16%
1608
February16th to endNight
14%
683
22%
2049
5%
683
33%
683
17%
1368
March1st to 15thNight
16%
764
16%
2288
5%
764
30%
764
16%
1576
March16th to endNight
18%
768
22%
2028
6%
768
31%
768
20%
1376
April1st to 15thNight
18%
718
17%
1796
4%
718
27%
718
19%
1293
April16th to endNight
20%
600
18%
1680
3%
600
30%
600
19%
1162
May1st to 15thNight
21%
540
15%
1620
6%
540
29%
540
16%
1128
May16th to endNight
23%
425
11%
1547
6%
424
30%
424
15%
1055
June1st to 15thNight
28%
360
11%
1440
7%
360
39%
360
14%
966
June16th to endNight
35%
360
11%
1440
11%
360
44%
360
21%
886
July1st to 15thNight
40%
340
11%
1360
12%
340
48%
340
21%
828
July16th to endNight
43%
376
14%
1418
13%
354
50%
354
19%
887
August1st to 15thNight
40%
513
16%
1584
10%
511
45%
511
26%
1007
August16th to endNight
50%
735
21%
1881
11%
735
53%
735
33%
1223
September1st to 15thNight
37%
720
18%
1861
8%
720
44%
720
29%
1247
September16th to endNight
43%
717
24%
1980
16%
717
49%
717
30%
1260
October1st to 15thNight
34%
720
22%
1999
10%
720
46%
720
25%
1307
October16th to endNight
24%
768
18%
2496
6%
768
39%
768
20%
1608
November1st to 15thNight
27%
760
19%
2472
9%
760
41%
760
21%
1601
November16th to endNight
23%
780
22%
2535
9%
780
40%
780
19%
1590
December1st to 15thNight
19%
780
17%
2694
5%
780
34%
780
15%
1773
December16th to endNight
13%
832
19%
2912
4%
832
32%
832
15%
1919

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
17%6%25%42445%6%39%
49564
Night
16%7%25%424446%41%
49235
Cloud CoverDay
18%6%24424447%39%
49574
Night
17%6%25%424446%40%
49240
TransparencyDay
43%6%11%20%15%2
49252
Night
43%5%11%20%15%2
49065
SeeingDay
22%16%31%19%8%2
6444
Night
21%14%34%22%6%
15635

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
15%6%35%32345%6%43%
1552
16th to endDay
16%6%245%23346%43%
1664
February1st to 15thDay
18%7%25%3345%5%6%36%
1831
16th to endDay
16%8%34425%446%40%
1710
March1st to 15thDay
21%7%25%324446%36%
1897
16th to endDay
17%7%25%423436%42%
2193
April1st to 15thDay
19%7%245%24446%38%
2152
16th to endDay
18%42443445%6%41%
2280
May1st to 15thDay
26%7%34423345%33%
2332
16th to endDay
17%5%2443445%7%39%
2576
June1st to 15thDay
24%6%25%424447%33%
2520
16th to endDay
14%5%35%435%5%6%9%35%
2520
July1st to 15thDay
13%5%25%6%46%46%8%36%
2520
16th to endDay
12%436%5%35%6%7%8%36%
2654
August1st to 15thDay
13%6%25%5%45%5%6%7%37%
2352
16th to endDay
11%5%25%435%5%5%8%42%
2319
September1st to 15thDay
13%5%25%434446%46%
2097
16th to endDay
16%5%24323345%49%
1980
October1st to 15thDay
20%5%24323335%44%
1959
16th to endDay
16%5%24423446%44%
1728
November1st to 15thDay
21%6%14423245%41%
1716
16th to endDay
16%42442346%6%44%
1755
December1st to 15thDay
18%6%25%324446%40%
1593
16th to endDay
21%7%25%334346%36%
1664
January1st to 15thNight
17%8%25%5%23345%42%
2716
16th to endNight
17%9%35%423445%40%
2912
February1st to 15thNight
16%8%35%5%245%45%38%
2356
16th to endNight
16%9%34424335%41%
2049
March1st to 15thNight
17%8%245%2446%5%37%
2275
16th to endNight
16%8%35%423335%43%
2028
April1st to 15thNight
16%8%35%44445%5%37%
1796
16th to endNight
20%6%25%423335%40%
1680
May1st to 15thNight
22%7%35%424446%36%
1620
16th to endNight
17%6%36%5%36%45%6%34%
1545
June1st to 15thNight
21%6%344245%46%35%
1440
16th to endNight
15%5%2442446%8%41%
1440
July1st to 15thNight
12%6%25%5%25%5%5%10%39%
1440
16th to endNight
11%5%25%5%37%5%6%8%37%
1514
August1st to 15thNight
9%426%6%25%5%6%7%42%
1594
16th to endNight
12%42433446%7%46%
1881
September1st to 15thNight
14%4145%35%5%46%43%
1861
16th to endNight
15%5%25%313445%49%
1980
October1st to 15thNight
18%6%24323445%45%
1999
16th to endNight
18%5%24424436%42%
2496
November1st to 15thNight
17%6%25%424236%44%
2472
16th to endNight
18%6%24323446%43%
2535
December1st to 15thNight
18%8%35%424445%39%
2694
16th to endNight
18%8%35%42335%6%37%
2912

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
15%7%3432335%5%43%
1552
16th to endDay
16%7%34423337%43%
1664
February1st to 15thDay
18%7%35%435%447%35%
1831
16th to endDay
16%8%35%325%346%40%
1710
March1st to 15thDay
21%8%23423347%35%
1907
16th to endDay
17%7%25%423436%42%
2193
April1st to 15thDay
20%6%25%423346%38%
2152
16th to endDay
19%5%23424446%42%
2280
May1st to 15thDay
26%7%35%323346%33%
2332
16th to endDay
17%5%24425%448%39%
2576
June1st to 15thDay
25%6%23424447%33%
2520
16th to endDay
15%5%245%35%5%5%9%36%
2520
July1st to 15thDay
13%5%25%6%45%6%6%8%35%
2520
16th to endDay
13%435%5%36%6%6%8%34%
2654
August1st to 15thDay
14%6%25%5%45%5%5%7%37%
2352
16th to endDay
12%5%25%5%345%5%7%43%
2319
September1st to 15thDay
14%424425%346%46%
2097
16th to endDay
17%5%23323345%49%
1980
October1st to 15thDay
21%5%23322336%44%
1959
16th to endDay
17%425%42335%5%44%
1728
November1st to 15thDay
22%6%14323335%42%
1716
16th to endDay
16%5%24323446%44%
1755
December1st to 15thDay
19%7%24414446%40%
1593
16th to endDay
21%8%24434435%36%
1664
January1st to 15thNight
17%7%35%5%23335%42%
2716
16th to endNight
18%9%35%33433440%
2912
February1st to 15thNight
16%8%26%42445%5%38%
2349
16th to endNight
17%8%25%5%23335%41%
2049
March1st to 15thNight
18%8%25%5%2345%6%37%
2288
16th to endNight
16%9%44423335%43%
2027
April1st to 15thNight
18%8%35%434345%37%
1796
16th to endNight
21%6%24424435%40%
1680
May1st to 15thNight
22%7%345%23446%35%
1620
16th to endNight
18%5%35%6%245%5%6%35%
1545
June1st to 15thNight
22%6%3442445%6%35%
1440
16th to endNight
15%425%425%6%5%8%40%
1440
July1st to 15thNight
12%5%24425%5%6%9%39%
1440
16th to endNight
11%435%5%37%5%6%10%35%
1514
August1st to 15thNight
9%5%26%6%35%46%8%42%
1594
16th to endNight
12%424325%5%5%7%46%
1881
September1st to 15thNight
14%4245%25%45%6%44%
1861
16th to endNight
16%5%24313345%48%
1980
October1st to 15thNight
18%6%25%313435%45%
1999
16th to endNight
18%5%24424346%42%
2496
November1st to 15thNight
17%6%25%414345%44%
2472
16th to endNight
18%5%25%323445%43%
2535
December1st to 15thNight
19%7%24424445%39%
2694
16th to endNight
18%9%3442335%6%37%
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
42%6%10%23%13%3
1553
16th to endDay
41%5%10%26%14%1
1664
February1st to 15thDay
46%5%13%18%13%2
1834
16th to endDay
45%411%21%14%3
1710
March1st to 15thDay
47%5%12%21%9%3
1907
16th to endDay
43%410%20%15%5%
2193
April1st to 15thDay
46%411%18%16%2
2152
16th to endDay
42%5%9%20%17%3
2280
May1st to 15thDay
52%49%16%13%2
2332
16th to endDay
43%7%13%20%12%2
2580
June1st to 15thDay
50%6%11%19%10%1
2520
16th to endDay
43%7%14%19%13%
2520
July1st to 15thDay
44%7%11%20%13%1
2371
16th to endDay
42%8%15%19%11%3
2487
August1st to 15thDay
44%7%14%19%13%
2338
16th to endDay
38%7%10%23%17%1
2319
September1st to 15thDay
38%6%12%20%20%2
2097
16th to endDay
37%47%21%26%2
1980
October1st to 15thDay
42%410%23%16%3
1959
16th to endDay
39%6%11%23%16%2
1728
November1st to 15thDay
44%5%12%20%15%1
1716
16th to endDay
39%5%12%24%15%2
1755
December1st to 15thDay
44%5%14%17%16%
1593
16th to endDay
48%7%12%17%12%1
1664
January1st to 15thNight
45%411%21%14%2
2716
16th to endNight
46%410%19%15%2
2912
February1st to 15thNight
46%6%12%19%12%2
2357
16th to endNight
45%410%19%16%2
2049
March1st to 15thNight
47%5%11%19%12%3
2288
16th to endNight
44%39%18%19%5%
2028
April1st to 15thNight
48%49%18%15%2
1796
16th to endNight
46%5%8%18%15%4
1680
May1st to 15thNight
49%5%11%16%13%3
1620
16th to endNight
48%8%14%17%8%2
1547
June1st to 15thNight
48%7%13%16%12%1
1440
16th to endNight
39%8%13%23%14%1
1440
July1st to 15thNight
39%8%13%24%14%
1360
16th to endNight
40%9%14%23%9%2
1418
August1st to 15thNight
37%8%14%22%14%2
1584
16th to endNight
34%7%12%26%17%
1881
September1st to 15thNight
39%6%11%22%18%1
1861
16th to endNight
38%47%21%26%2
1980
October1st to 15thNight
40%5%10%22%16%3
1999
16th to endNight
43%412%23%15%
2496
November1st to 15thNight
42%5%11%20%16%2
2472
16th to endNight
41%412%23%15%2
2535
December1st to 15thNight
46%5%13%20%12%
2694
16th to endNight
46%5%12%20%13%1
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
21%36%30%11%1
90
16th to endDay
26%23%40%9%
96
February1st to 15thDay
28%26%32%10%2
286
16th to endDay
21%29%31%14%2
291
March1st to 15thDay
30%18%33%12%3
312
16th to endDay
20%24%35%12%5%1
288
April1st to 15thDay
26%18%35%12%6%
270
16th to endDay
22%17%32%20%23
270
May1st to 15thDay
35%20%22%16%41
288
16th to endDay
20%12%39%19%6%
331
June1st to 15thDay
26%14%30%19%7%
315
16th to endDay
16%15%35%23%6%2
315
July1st to 15thDay
19%7%37%23%11%
305
16th to endDay
12%6%35%27%14%3
326
August1st to 15thDay
13%9%30%30%12%2
313
16th to endDay
12%6%30%27%16%6%
332
September1st to 15thDay
16%11%26%26%15%3
315
16th to endDay
22%6%28%18%12%11%
314
October1st to 15thDay
24%9%26%21%11%6%
315
16th to endDay
19%18%30%20%10%
288
November1st to 15thDay
27%13%30%17%9%2
280
16th to endDay
22%20%30%16%8%1
285
December1st to 15thDay
23%31%27%10%6%
123
16th to endDay
29%34%30%5%1
96
January1st to 15thNight
21%20%39%14%3
780
16th to endNight
24%20%36%16%1
832
February1st to 15thNight
21%19%39%17%1
764
16th to endNight
24%20%35%16%2
683
March1st to 15thNight
23%21%35%16%3
764
16th to endNight
22%21%33%17%4
768
April1st to 15thNight
22%20%35%17%3
718
16th to endNight
23%18%35%17%5%
600
May1st to 15thNight
28%14%31%21%3
540
16th to endNight
20%10%40%24%4
425
June1st to 15thNight
22%6%35%29%5%
360
16th to endNight
16%338%35%6%
360
July1st to 15thNight
13%337%35%10%
340
16th to endNight
11%234%40%10%
376
August1st to 15thNight
11%435%38%8%
513
16th to endNight
15%225%39%14%1
735
September1st to 15thNight
16%5%35%31%11%
720
16th to endNight
19%7%24%28%17%3
717
October1st to 15thNight
22%8%30%24%12%1
720
16th to endNight
22%16%33%18%8%
768
November1st to 15thNight
20%14%33%20%10%
760
16th to endNight
22%18%30%20%6%1
780
December1st to 15thNight
25%18%33%18%4
780
16th to endNight
25%20%36%15%1
832
Page generated at 2018-03-12 13:28:08. Version ac04

Copyright 2018 A. Danko


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