CAS DS-2
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CAS DS-2 clear sky chart from 2005-11-05 to 2018-11-30.

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
36%
16620
19%
51713
10%
16584
45%
16584
22%
33503

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
22%
779
18%
2716
7%
776
36%
776
17%
1752
January16th to endNight
21%
832
21%
2707
7%
832
39%
832
19%
1740
February1st to 15thNight
17%
764
16%
2482
5%
761
32%
761
16%
1646
February16th to endNight
18%
683
22%
2059
7%
683
37%
683
18%
1354
March1st to 15thNight
24%
780
21%
2230
9%
780
37%
780
20%
1491
March16th to endNight
24%
832
23%
2226
9%
832
36%
832
24%
1466
April1st to 15thNight
24%
778
16%
1946
4%
778
31%
778
23%
1345
April16th to endNight
33%
771
18%
1927
4%
771
40%
771
28%
1308
May1st to 15thNight
39%
523
17%
1693
10%
523
46%
523
20%
1134
May16th to endNight
45%
406
15%
1625
14%
406
51%
406
17%
1049
June1st to 15thNight
46%
390
16%
1560
14%
390
56%
390
20%
974
June16th to endNight
53%
390
15%
1560
19%
390
58%
390
24%
905
July1st to 15thNight
52%
370
14%
1480
18%
370
55%
370
20%
912
July16th to endNight
61%
475
14%
1608
14%
448
64%
448
25%
954
August1st to 15thNight
61%
578
17%
1718
14%
575
62%
575
28%
1103
August16th to endNight
60%
828
18%
2070
10%
828
61%
828
33%
1370
September1st to 15thNight
48%
780
23%
1950
12%
780
53%
780
31%
1302
September16th to endNight
54%
777
25%
2119
20%
777
58%
777
31%
1378
October1st to 15thNight
44%
780
19%
2340
15%
780
51%
780
25%
1516
October16th to endNight
35%
832
24%
2509
14%
832
48%
832
26%
1547
November1st to 15thNight
36%
820
21%
2667
12%
820
49%
820
23%
1665
November16th to endNight
30%
840
19%
2879
10%
840
42%
840
19%
1800
December1st to 15thNight
25%
780
14%
2730
6%
780
36%
780
13%
1877
December16th to endNight
23%
832
17%
2912
5%
832
38%
832
16%
1915

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
16%6%25%5%345%5%7%37%
52587
Night
16%5%2442445%7%41%
51889
Cloud CoverDay
16%5%25%5%35%45%7%38%
52597
Night
16%5%2442445%7%41%
51894
TransparencyDay
44%6%12%21%13%2
52281
Night
42%5%12%22%15%2
51713
SeeingDay
21%11%26%22%13%5%
7186
Night
20%10%27%28%12%1
16622

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
14%8%35%6%345%5%7%35%
1552
16th to endDay
15%8%36%6%34447%34%
1866
February1st to 15thDay
15%8%35%6%45%5%5%6%33%
1710
16th to endDay
16%7%36%6%34446%35%
1698
March1st to 15thDay
15%6%26%6%45%45%7%36%
2047
16th to endDay
19%6%25%5%33345%38%
2350
April1st to 15thDay
18%7%35%42445%7%36%
2332
16th to endDay
17%42443445%6%42%
2308
May1st to 15thDay
19%6%25%5%35%5%5%6%35%
2596
16th to endDay
19%5%25%5%35%5%5%7%34%
2842
June1st to 15thDay
14%5%25%5%36%6%5%8%35%
2730
16th to endDay
14%4245%35%5%6%9%38%
2730
July1st to 15thDay
10%5%25%6%46%6%6%9%35%
2730
16th to endDay
9%5%35%6%36%5%7%8%37%
2808
August1st to 15thDay
14%6%25%5%35%6%7%9%33%
2471
16th to endDay
14%4244335%6%8%42%
2484
September1st to 15thDay
19%415%42445%6%41%
2340
16th to endDay
16%6%2432345%5%43%
2168
October1st to 15thDay
20%5%2342435%8%40%
1950
16th to endDay
18%4234235%5%7%41%
2067
November1st to 15thDay
18%6%24423346%43%
1851
16th to endDay
19%4243235%5%6%42%
1733
December1st to 15thDay
18%6%26%6%2445%6%34%
1560
16th to endDay
18%6%45%5%345%5%7%33%
1664
January1st to 15thNight
17%6%245%4445%8%37%
2716
16th to endNight
15%8%25%5%2345%6%41%
2707
February1st to 15thNight
14%8%26%6%2445%6%37%
2480
16th to endNight
16%7%25%425%446%40%
2059
March1st to 15thNight
18%6%24424345%42%
2218
16th to endNight
16%6%235%23346%44%
2226
April1st to 15thNight
16%5%26%42446%7%38%
1946
16th to endNight
17%424324446%44%
1927
May1st to 15thNight
19%4344245%47%37%
1693
16th to endNight
17%5%246%345%46%39%
1623
June1st to 15thNight
17%5%25%42435%7%41%
1560
16th to endNight
11%425%5%235%5%10%43%
1560
July1st to 15thNight
10%435%5%35%5%7%8%40%
1560
16th to endNight
10%425%5%245%6%10%43%
1709
August1st to 15thNight
11%5%15%6%3446%7%43%
1729
16th to endNight
11%425%425%5%5%8%45%
2070
September1st to 15thNight
16%5%2333235%6%45%
1950
16th to endNight
15%4145%23347%45%
2119
October1st to 15thNight
20%5%23423347%42%
2340
16th to endNight
18%412323446%46%
2509
November1st to 15thNight
14%6%34324446%45%
2667
16th to endNight
17%5%245%2445%8%39%
2879
December1st to 15thNight
19%6%35%5%35%5%6%6%32%
2730
16th to endNight
17%7%25%5%2445%7%36%
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
14%7%45%6%3346%7%35%
1552
16th to endDay
15%8%36%6%35%446%35%
1866
February1st to 15thDay
16%7%36%6%35%5%5%6%33%
1710
16th to endDay
16%7%36%6%45%446%35%
1698
March1st to 15thDay
15%6%26%6%4445%7%36%
2058
16th to endDay
19%6%35%6%33345%38%
2349
April1st to 15thDay
18%7%35%43445%7%36%
2332
16th to endDay
17%42442445%5%43%
2308
May1st to 15thDay
19%6%25%6%35%5%5%6%35%
2596
16th to endDay
19%5%245%345%5%8%34%
2842
June1st to 15thDay
15%435%5%36%6%6%8%35%
2730
16th to endDay
13%4245%36%5%5%10%37%
2730
July1st to 15thDay
10%5%26%6%46%5%6%9%35%
2730
16th to endDay
9%5%26%6%46%5%6%7%38%
2808
August1st to 15thDay
15%5%15%5%45%6%7%8%34%
2471
16th to endDay
14%4244345%6%8%41%
2484
September1st to 15thDay
19%415%324446%41%
2340
16th to endDay
16%5%2432445%6%43%
2168
October1st to 15thDay
20%5%1342445%7%40%
1950
16th to endDay
17%5%1442345%7%42%
2067
November1st to 15thDay
18%6%23323346%43%
1851
16th to endDay
19%43333345%6%42%
1733
December1st to 15thDay
18%6%26%5%24447%35%
1560
16th to endDay
18%6%36%43445%7%33%
1664
January1st to 15thNight
16%6%25%5%4445%7%37%
2716
16th to endNight
14%8%25%424446%41%
2707
February1st to 15thNight
14%8%26%5%3445%6%37%
2473
16th to endNight
16%6%34425%447%40%
2059
March1st to 15thNight
17%5%245%24345%42%
2230
16th to endNight
17%6%235%23346%44%
2226
April1st to 15thNight
16%5%25%5%2446%7%38%
1946
16th to endNight
17%5%14423446%44%
1927
May1st to 15thNight
19%5%24425%45%7%37%
1693
16th to endNight
17%5%25%6%245%46%38%
1623
June1st to 15thNight
18%5%24424447%42%
1560
16th to endNight
11%5%15%43445%10%43%
1560
July1st to 15thNight
10%435%6%345%6%9%40%
1560
16th to endNight
10%4245%335%6%10%43%
1709
August1st to 15thNight
11%5%16%5%3446%7%43%
1729
16th to endNight
11%325%4245%5%8%45%
2070
September1st to 15thNight
17%5%2432335%6%46%
1950
16th to endNight
15%414423347%46%
2119
October1st to 15thNight
20%5%23423347%42%
2340
16th to endNight
18%423333346%46%
2509
November1st to 15thNight
15%6%24324346%45%
2667
16th to endNight
17%5%245%2445%8%40%
2879
December1st to 15thNight
19%5%35%436%5%6%6%32%
2730
16th to endNight
17%7%25%5%3445%7%36%
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
46%5%13%21%9%3
1553
16th to endDay
48%5%14%19%10%1
1866
February1st to 15thDay
48%6%11%20%10%1
1712
16th to endDay
49%313%23%8%1
1698
March1st to 15thDay
46%5%13%20%11%1
2058
16th to endDay
47%410%19%15%1
2350
April1st to 15thDay
46%5%10%20%12%4
2332
16th to endDay
40%5%9%20%18%5%
2308
May1st to 15thDay
48%6%9%18%14%2
2596
16th to endDay
46%8%12%18%12%1
2846
June1st to 15thDay
43%9%13%20%11%1
2730
16th to endDay
40%7%14%23%11%1
2730
July1st to 15thDay
43%7%11%19%15%2
2581
16th to endDay
41%8%12%22%13%2
2646
August1st to 15thDay
43%9%13%19%13%
2458
16th to endDay
38%6%11%22%18%2
2484
September1st to 15thDay
42%6%10%20%18%2
2340
16th to endDay
40%5%8%21%21%2
2168
October1st to 15thDay
43%5%12%21%15%1
1950
16th to endDay
40%5%11%25%15%1
2067
November1st to 15thDay
42%413%21%13%3
1851
16th to endDay
41%412%28%12%1
1733
December1st to 15thDay
48%6%15%19%8%
1560
16th to endDay
48%6%15%18%10%
1664
January1st to 15thNight
45%414%19%12%2
2716
16th to endNight
43%412%25%12%1
2707
February1st to 15thNight
46%414%21%11%1
2482
16th to endNight
43%410%23%15%2
2059
March1st to 15thNight
43%5%11%23%14%1
2230
16th to endNight
41%411%23%17%2
2226
April1st to 15thNight
43%5%13%20%15%2
1946
16th to endNight
40%6%9%20%19%4
1927
May1st to 15thNight
44%7%10%19%15%2
1693
16th to endNight
44%8%12%16%15%3
1625
June1st to 15thNight
40%8%11%22%15%
1560
16th to endNight
35%7%13%27%14%1
1560
July1st to 15thNight
40%8%12%19%15%2
1480
16th to endNight
34%9%17%21%14%2
1608
August1st to 15thNight
38%6%12%21%17%1
1718
16th to endNight
35%8%12%19%20%2
2070
September1st to 15thNight
39%5%10%22%19%2
1950
16th to endNight
38%5%7%22%23%2
2119
October1st to 15thNight
42%412%23%14%2
2340
16th to endNight
37%411%28%16%1
2509
November1st to 15thNight
40%5%12%23%13%4
2667
16th to endNight
42%412%24%13%1
2879
December1st to 15thNight
49%6%13%18%10%1
2730
16th to endNight
45%6%15%22%9%
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
33%21%26%13%5%
90
16th to endDay
24%17%37%17%3
143
February1st to 15thDay
26%28%34%8%
135
16th to endDay
22%16%37%21%1
279
March1st to 15thDay
20%21%31%22%3
330
16th to endDay
23%18%30%19%5%1
352
April1st to 15thDay
27%16%26%19%7%2
330
16th to endDay
21%13%30%19%9%5%
319
May1st to 15thDay
29%12%25%17%10%4
348
16th to endDay
26%7%22%23%14%5%
395
June1st to 15thDay
19%10%29%21%15%4
375
16th to endDay
17%7%32%25%12%3
375
July1st to 15thDay
13%324%26%23%7%
365
16th to endDay
11%427%28%20%7%
390
August1st to 15thDay
17%320%25%21%12%
358
16th to endDay
12%316%32%20%14%
396
September1st to 15thDay
22%8%17%18%22%11%
375
16th to endDay
23%413%25%19%12%
374
October1st to 15thDay
26%417%25%18%6%
375
16th to endDay
17%16%31%21%11%1
396
November1st to 15thDay
23%12%25%26%11%1
325
16th to endDay
19%20%33%21%5%
175
December1st to 15thDay
23%22%30%12%11%1
90
16th to endDay
29%20%35%13%1
96
January1st to 15thNight
21%15%35%23%4
780
16th to endNight
19%17%34%26%1
832
February1st to 15thNight
21%18%36%22%1
764
16th to endNight
23%18%35%19%3
683
March1st to 15thNight
22%17%32%24%3
780
16th to endNight
21%14%34%22%5%
832
April1st to 15thNight
20%17%33%23%4
778
16th to endNight
20%10%31%26%10%
771
May1st to 15thNight
22%7%25%33%10%
523
16th to endNight
19%420%35%17%1
407
June1st to 15thNight
19%5%22%33%19%
390
16th to endNight
13%223%45%14%1
390
July1st to 15thNight
13%122%38%21%1
370
16th to endNight
11%215%39%29%2
475
August1st to 15thNight
16%110%40%27%3
578
16th to endNight
14%214%35%31%2
828
September1st to 15thNight
18%421%31%22%2
780
16th to endNight
17%317%28%27%5%
777
October1st to 15thNight
23%6%19%27%18%3
780
16th to endNight
21%11%28%28%9%
832
November1st to 15thNight
19%10%29%28%11%1
820
16th to endNight
18%16%27%28%7%
840
December1st to 15thNight
25%12%30%24%6%
780
16th to endNight
23%14%33%26%2
832
Page generated at 2018-12-01 11:35:32. Version ac04

Copyright 2018 A. Danko


CAS DS-2 Clear Sky Chart |Charts Home