Windsong Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windsong Observatory clear sky chart from 2005-11-06 to 2024-03-23.

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
24%
23260
18%
80755
7%
23166
37%
23166
18%
52345

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 10thNight
14%
753
24%
4331
5%
737
34%
737
12%
2266
January11th to 20thNight
13%
759
22%
4346
2%
740
30%
740
8%
2656
January21st to endNight
16%
832
12%
4861
6%
814
35%
814
8%
3441
February1st to 10thNight
15%
760
18%
2377
4%
760
32%
760
17%
1590
February11th to 20thNight
11%
743
19%
2220
3%
740
29%
740
15%
1481
February21st to endNight
14%
628
23%
1884
6%
628
34%
628
17%
1251
March1st to 10thNight
17%
760
21%
2280
7%
760
35%
760
18%
1507
March11th to 20thNight
15%
760
18%
2182
4%
760
30%
760
17%
1484
March21st to endNight
17%
801
21%
2075
5%
801
29%
801
19%
1435
April1st to 10thNight
18%
720
19%
1800
4%
720
27%
720
18%
1283
April11th to 20thNight
20%
711
17%
1775
3%
711
28%
711
21%
1251
April21st to endNight
16%
540
19%
1620
4%
540
28%
540
17%
1111
May1st to 10thNight
20%
540
12%
1620
5%
540
26%
540
14%
1167
May11th to 20thNight
18%
524
15%
1586
6%
524
26%
524
17%
1080
May21st to endNight
29%
389
11%
1551
9%
388
37%
388
16%
1016
June1st to 10thNight
29%
360
13%
1440
9%
360
40%
360
16%
936
June11th to 20thNight
28%
360
13%
1440
10%
360
39%
360
17%
939
June21st to endNight
36%
360
11%
1440
9%
360
45%
360
21%
872
July1st to 10thNight
40%
350
13%
1400
13%
350
48%
350
19%
866
July11th to 20thNight
43%
348
13%
1392
12%
348
50%
348
20%
863
July21st to endNight
41%
394
17%
1486
15%
372
48%
372
20%
908
August1st to 10thNight
39%
499
15%
1563
9%
497
44%
497
26%
986
August11th to 20thNight
44%
576
17%
1640
10%
576
47%
576
24%
1113
August21st to endNight
47%
792
21%
1980
10%
792
51%
792
34%
1284
September1st to 10thNight
38%
720
18%
1801
7%
720
44%
720
28%
1240
September11th to 20thNight
40%
720
24%
1980
12%
720
48%
720
31%
1239
September21st to endNight
35%
720
23%
1980
13%
720
45%
720
26%
1330
October1st to 10thNight
32%
720
18%
1980
9%
720
40%
720
22%
1350
October11th to 20thNight
31%
720
22%
2188
9%
720
45%
720
26%
1352
October21st to endNight
21%
792
16%
2574
5%
792
35%
792
17%
1756
November1st to 10thNight
29%
740
22%
2407
10%
740
44%
740
22%
1487
November11th to 20thNight
19%
760
24%
2470
8%
760
38%
760
20%
1541
November21st to endNight
21%
760
23%
2470
7%
760
40%
760
19%
1513
December1st to 10thNight
17%
760
20%
2607
6%
760
34%
760
16%
1702
December11th to 20thNight
18%
760
18%
3206
4%
759
34%
759
13%
1950
December21st to endNight
13%
829
14%
4803
3%
817
34%
817
9%
3099

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%7%35%5%3445%7%40%
78572
Night
17%8%35%5%3445%6%41%
81304
TransparencyDay
43%7%12%21%15%3
78277
Night
44%6%12%21%14%2
81133
SeeingDay
23%18%32%18%7%2
14202
Night
22%15%34%22%6%
23279

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 10thDay
14%8%35%5%3335%5%46%
2517
11th to 20thDay
17%8%36%5%3445%440%
2520
21st to endDay
22%12%36%5%24446%34%
2772
February1st to 10thDay
20%7%35%445%5%5%6%37%
1800
11th to 20thDay
14%7%35%6%345%47%42%
1848
21st to endDay
20%9%36%425%445%37%
1570
March1st to 10thDay
18%8%34435%46%7%39%
1897
11th to 20thDay
16%6%26%5%35%6%5%8%39%
1997
21st to endDay
18%9%26%5%23436%41%
2321
April1st to 10thDay
19%8%35%5%2445%7%38%
2160
11th to 20thDay
17%6%345%2446%8%41%
2134
21st to endDay
22%6%27%5%345%46%37%
2340
May1st to 10thDay
26%8%35%43445%6%32%
2340
11th to 20thDay
19%6%35%5%3445%7%40%
2322
21st to endDay
15%6%25%43445%7%44%
2725
June1st to 10thDay
19%6%36%6%36%46%9%33%
2520
11th to 20thDay
17%6%36%5%35%5%6%8%36%
2520
21st to endDay
16%6%35%5%45%5%6%10%35%
2520
July1st to 10thDay
13%5%25%6%5%5%5%6%8%40%
2520
11th to 20thDay
14%5%36%5%45%5%7%9%37%
2520
21st to endDay
12%5%36%6%35%6%6%9%38%
2744
August1st to 10thDay
10%7%36%6%46%6%6%9%37%
2345
11th to 20thDay
14%6%26%6%46%6%5%7%39%
2257
21st to endDay
13%5%35%5%35%5%6%8%42%
2376
September1st to 10thDay
15%5%35%435%5%5%6%45%
2158
11th to 20thDay
14%5%24433445%51%
1980
21st to endDay
19%5%25%33435%5%45%
1980
October1st to 10thDay
24%6%24423345%42%
1980
11th to 20thDay
16%425%424447%47%
1769
21st to endDay
20%6%35%4345%46%41%
1782
November1st to 10thDay
17%6%25%43434449%
1671
11th to 20thDay
19%6%1442345%6%45%
1710
21st to endDay
17%6%25%42445%6%44%
1710
December1st to 10thDay
18%7%35%5%35%5%5%5%39%
1569
11th to 20thDay
21%6%24434335%46%
1906
21st to endDay
21%10%36%5%34446%34%
2772
January1st to 10thNight
17%7%24323346%49%
4429
11th to 20thNight
16%11%46%5%33345%40%
4440
21st to endNight
23%12%46%5%34445%31%
4884
February1st to 10thNight
17%8%35%5%2445%6%40%
2377
11th to 20thNight
16%7%36%5%345%5%6%40%
2218
21st to endNight
18%9%25%5%24345%42%
1884
March1st to 10thNight
17%8%245%245%6%5%42%
2270
11th to 20thNight
14%10%35%6%3445%6%39%
2181
21st to endNight
17%9%36%434346%41%
2075
April1st to 10thNight
18%8%36%445%45%6%38%
1800
11th to 20thNight
18%6%246%345%5%5%39%
1775
21st to endNight
21%8%35%433445%39%
1620
May1st to 10thNight
23%9%45%4345%46%32%
1620
11th to 20thNight
18%6%36%6%345%5%7%36%
1585
21st to endNight
16%7%36%5%36%45%6%39%
1550
June1st to 10thNight
16%7%35%6%35%5%5%7%37%
1440
11th to 20thNight
19%7%35%5%35%5%5%7%37%
1440
21st to endNight
15%5%35%42447%10%41%
1440
July1st to 10thNight
13%6%36%5%36%46%9%40%
1440
11th to 20thNight
14%6%25%6%35%5%6%9%37%
1440
21st to endNight
12%6%35%5%46%6%5%9%41%
1574
August1st to 10thNight
8%6%26%6%35%7%7%8%42%
1573
11th to 20thNight
11%5%36%6%45%6%7%8%39%
1640
21st to endNight
14%6%2442446%7%48%
1980
September1st to 10thNight
13%6%26%6%45%5%5%6%43%
1801
11th to 20thNight
15%5%25%323446%51%
1980
21st to endNight
18%6%36%4245%5%5%44%
1980
October1st to 10thNight
22%7%24423445%42%
1980
11th to 20thNight
16%5%244345%5%7%46%
2188
21st to endNight
21%8%35%5%34435%39%
2574
November1st to 10thNight
14%5%25%5%34346%48%
2407
11th to 20thNight
18%7%25%424346%46%
2470
21st to endNight
17%6%244335%5%7%45%
2470
December1st to 10thNight
19%8%35%5%34445%40%
2607
11th to 20thNight
20%6%2442445%7%42%
3288
21st to endNight
20%12%36%5%3335%6%35%
4884

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 10thDay
40%5%9%30%14%2
2518
11th to 20thDay
46%7%9%24%12%2
2520
21st to endDay
51%7%8%22%10%2
2772
February1st to 10thDay
46%7%13%18%14%3
1800
11th to 20thDay
43%6%11%21%16%3
1857
21st to endDay
49%5%11%19%14%3
1570
March1st to 10thDay
43%6%13%20%14%4
1900
11th to 20thDay
41%7%11%23%14%4
1997
21st to endDay
46%5%9%17%17%6%
2321
April1st to 10thDay
46%5%11%19%16%3
2160
11th to 20thDay
41%6%11%21%18%3
2134
21st to endDay
47%6%9%18%16%4
2340
May1st to 10thDay
52%5%10%18%13%2
2340
11th to 20thDay
44%6%11%18%18%3
2326
21st to endDay
39%8%14%23%14%2
2725
June1st to 10thDay
46%8%13%21%11%1
2520
11th to 20thDay
45%8%12%19%15%2
2520
21st to endDay
44%8%15%20%13%1
2520
July1st to 10thDay
42%8%11%23%14%3
2450
11th to 20thDay
42%8%15%22%11%2
2445
21st to endDay
40%9%14%21%13%4
2591
August1st to 10thDay
40%10%16%21%12%1
2331
11th to 20thDay
42%9%14%21%13%1
2257
21st to endDay
38%8%12%22%18%2
2376
September1st to 10thDay
38%8%12%22%19%2
2158
11th to 20thDay
35%5%10%23%24%3
1980
21st to endDay
40%5%9%20%23%2
1980
October1st to 10thDay
46%5%9%21%15%4
1980
11th to 20thDay
36%7%11%27%18%1
1769
21st to endDay
44%6%13%19%15%4
1782
November1st to 10thDay
39%5%13%23%18%2
1671
11th to 20thDay
39%5%11%22%20%3
1710
21st to endDay
41%5%13%26%12%3
1710
December1st to 10thDay
45%7%13%16%17%2
1569
11th to 20thDay
43%5%13%17%17%5%
1906
21st to endDay
49%8%11%20%11%1
2772
January1st to 10thNight
38%412%30%12%3
4429
11th to 20thNight
47%6%11%22%11%3
4440
21st to endNight
56%6%9%16%11%2
4884
February1st to 10thNight
45%6%13%21%13%2
2377
11th to 20thNight
44%6%10%19%17%4
2220
21st to endNight
45%5%9%22%15%4
1884
March1st to 10thNight
43%6%10%23%15%4
2280
11th to 20thNight
45%6%12%17%17%4
2182
21st to endNight
45%5%9%17%18%6%
2075
April1st to 10thNight
47%5%10%19%15%3
1800
11th to 20thNight
45%6%9%19%18%3
1775
21st to endNight
47%6%10%18%14%5%
1620
May1st to 10thNight
52%6%11%15%12%3
1620
11th to 20thNight
45%8%13%18%13%4
1586
21st to endNight
46%8%14%18%12%1
1551
June1st to 10thNight
45%9%14%19%13%1
1440
11th to 20thNight
46%7%12%20%13%1
1440
21st to endNight
38%10%17%23%12%1
1440
July1st to 10thNight
39%10%13%23%14%1
1400
11th to 20thNight
41%8%17%24%9%1
1392
21st to endNight
38%10%14%24%12%2
1486
August1st to 10thNight
37%9%17%23%12%2
1563
11th to 20thNight
40%10%15%22%12%1
1640
21st to endNight
34%8%12%26%19%1
1980
September1st to 10thNight
41%7%12%22%17%2
1801
11th to 20thNight
34%7%9%21%26%2
1980
21st to endNight
42%6%8%21%20%3
1980
October1st to 10thNight
44%7%11%22%13%4
1980
11th to 20thNight
37%7%14%27%15%1
2188
21st to endNight
48%5%11%19%15%2
2574
November1st to 10thNight
37%7%11%22%19%4
2407
11th to 20thNight
42%410%22%19%3
2470
21st to endNight
39%5%13%27%14%2
2470
December1st to 10thNight
46%6%12%21%14%1
2607
11th to 20thNight
42%6%16%18%16%2
3288
21st to endNight
48%7%10%23%11%1
4884

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 10thDay
28%27%29%14%2
180
11th to 20thDay
29%28%32%7%4
180
21st to endDay
22%31%32%11%31
198
February1st to 10thDay
33%24%31%11%2
389
11th to 20thDay
28%33%29%8%1
456
21st to endDay
32%23%30%12%3
382
March1st to 10thDay
31%20%33%13%3
460
11th to 20thDay
28%25%32%11%3
460
21st to endDay
27%24%32%10%42
470
April1st to 10thDay
32%23%26%12%6%1
420
11th to 20thDay
26%25%31%14%31
412
21st to endDay
29%24%29%14%22
420
May1st to 10thDay
32%23%27%14%31
423
11th to 20thDay
22%17%43%14%5%
447
21st to endDay
19%16%34%23%6%2
485
June1st to 10thDay
21%14%35%20%8%1
450
11th to 20thDay
18%18%39%20%5%2
450
21st to endDay
16%16%35%23%8%2
450
July1st to 10thDay
16%9%34%25%14%2
445
11th to 20thDay
16%7%33%28%14%2
444
21st to endDay
13%9%40%27%10%1
488
August1st to 10thDay
10%12%33%32%11%2
446
11th to 20thDay
15%8%33%28%12%3
439
21st to endDay
12%11%33%26%12%5%
495
September1st to 10thDay
19%12%26%25%14%4
450
11th to 20thDay
19%13%28%23%10%7%
450
21st to endDay
22%13%31%21%8%4
450
October1st to 10thDay
29%12%26%19%9%5%
450
11th to 20thDay
18%18%34%18%10%2
405
21st to endDay
24%18%31%18%8%1
396
November1st to 10thDay
21%16%33%18%9%2
365
11th to 20thDay
28%22%28%16%5%
370
21st to endDay
25%20%32%16%6%1
370
December1st to 10thDay
23%33%29%11%4
229
11th to 20thDay
31%27%33%6%2
180
21st to endDay
24%29%32%9%33
198
January1st to 10thNight
23%20%38%16%3
760
11th to 20thNight
28%21%35%14%2
760
21st to endNight
21%23%35%18%3
836
February1st to 10thNight
24%19%38%18%1
760
11th to 20thNight
24%24%37%13%1
743
21st to endNight
27%21%34%15%3
628
March1st to 10thNight
25%20%34%17%3
760
11th to 20thNight
20%24%36%17%3
760
21st to endNight
25%20%35%15%4
801
April1st to 10thNight
24%22%33%18%3
720
11th to 20thNight
23%20%36%18%4
711
21st to endNight
25%19%38%16%3
540
May1st to 10thNight
31%14%31%19%3
540
11th to 20thNight
23%16%38%20%3
524
21st to endNight
18%9%39%29%5%
389
June1st to 10thNight
19%7%36%30%9%
360
11th to 20thNight
19%7%37%31%5%
360
21st to endNight
15%6%39%34%6%
360
July1st to 10thNight
15%5%33%38%9%
350
11th to 20thNight
16%331%39%11%1
348
21st to endNight
13%5%35%40%8%
394
August1st to 10thNight
11%5%36%40%8%
499
11th to 20thNight
14%6%29%40%11%
576
21st to endNight
15%6%26%38%14%2
792
September1st to 10thNight
16%5%34%34%11%1
720
11th to 20thNight
18%8%29%28%15%2
720
21st to endNight
22%8%29%28%11%2
720
October1st to 10thNight
27%10%27%24%11%2
720
11th to 20thNight
19%12%34%23%12%1
720
21st to endNight
26%16%33%18%7%
792
November1st to 10thNight
17%16%34%23%10%1
740
11th to 20thNight
24%18%35%17%6%
760
21st to endNight
22%21%32%20%41
760
December1st to 10thNight
26%18%34%18%4
760
11th to 20thNight
26%19%33%20%2
760
21st to endNight
26%20%35%17%2
836
Page generated at 2024-03-19 23:31:09. Version ac07

Copyright © 2024 Attilla Danko.


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