CAS Remote Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CAS Remote Observing Site clear sky chart from 2005-11-05 to 2019-06-24.

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
60%
17985
33%
54026
24%
17945
69%
17945
46%
26856

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
53%
839
32%
2717
26%
836
65%
836
38%
1395
January16th to endNight
51%
896
33%
2912
26%
896
63%
896
37%
1499
February1st to 15thNight
54%
820
32%
2579
24%
820
66%
820
43%
1290
February16th to endNight
46%
736
33%
2207
26%
736
58%
736
36%
1219
March1st to 15thNight
49%
840
34%
2326
21%
840
62%
840
44%
1227
March16th to endNight
53%
896
33%
2464
18%
896
64%
896
48%
1277
April1st to 15thNight
42%
820
30%
2289
13%
820
56%
820
41%
1208
April16th to endNight
50%
624
39%
1900
21%
624
67%
624
52%
828
May1st to 15thNight
53%
630
36%
1889
23%
629
63%
629
53%
861
May16th to endNight
50%
657
32%
1972
20%
657
59%
657
52%
907
June1st to 15thNight
64%
630
34%
1890
27%
630
69%
630
64%
802
June16th to endNight
73%
609
32%
1827
27%
609
77%
609
69%
753
July1st to 15thNight
79%
555
21%
1665
18%
555
80%
555
41%
894
July16th to endNight
79%
612
17%
1737
14%
579
79%
579
30%
1065
August1st to 15thNight
81%
575
29%
1719
25%
572
81%
572
45%
884
August16th to endNight
82%
682
31%
1978
26%
682
82%
682
47%
1040
September1st to 15thNight
79%
780
30%
2145
25%
780
81%
780
48%
1187
September16th to endNight
72%
776
43%
2145
28%
776
82%
776
67%
953
October1st to 15thNight
59%
780
35%
2233
21%
780
71%
780
52%
1091
October16th to endNight
66%
832
41%
2496
30%
832
76%
832
56%
1135
November1st to 15thNight
60%
820
39%
2564
28%
820
73%
820
52%
1158
November16th to endNight
60%
840
37%
2730
32%
840
71%
840
50%
1222
December1st to 15thNight
58%
840
35%
2730
29%
840
69%
840
40%
1351
December16th to endNight
52%
896
30%
2912
25%
896
61%
896
33%
1610

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
4424423446%59%
54790
Night
2313323346%64%
54222
TransparencyDay
26%47%17%26%18%
54485
Night
20%37%18%29%19%
54028
SeeingDay
9%15%27%27%14%4
7743
Night
5%8%20%30%27%7%
17992

By Month

Percentage Cloud Cover SW (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
36%23423245%59%
1881
16th to endDay
46%14313345%60%
2016
February1st to 15thDay
38%24413246%58%
1942
16th to endDay
49%34423347%52%
1839
March1st to 15thDay
36%2222345%7%57%
2292
16th to endDay
35%1231335%6%61%
2464
April1st to 15thDay
34145%33446%59%
2317
16th to endDay
3412323336%65%
2661
May1st to 15thDay
4413323336%61%
2721
16th to endDay
4313314335%64%
2845
June1st to 15thDay
1111212235%75%
2730
16th to endDay
211221222474%
2641
July1st to 15thDay
6%426%6%46%5%6%6%43%
2535
16th to endDay
9%5%37%7%5%7%7%8%8%30%
2675
August1st to 15thDay
7%5%26%7%45%6%6%6%42%
2485
16th to endDay
7%326%6%45%5%6%5%45%
2572
September1st to 15thDay
5%315%6%45%6%46%50%
2145
16th to endDay
311342333469%
2145
October1st to 15thDay
421331333466%
2055
16th to endDay
322312335%69%
2080
November1st to 15thDay
2112212345%70%
1953
16th to endDay
35%12212235%68%
1890
December1st to 15thDay
46%14423346%59%
1890
16th to endDay
5%9%33324346%52%
2016
January1st to 15thNight
35%24423345%60%
2717
16th to endNight
47%23312345%59%
2912
February1st to 15thNight
27%1331235%6%62%
2568
16th to endNight
27%23324447%57%
2207
March1st to 15thNight
3413324347%62%
2326
16th to endNight
331231335%6%64%
2464
April1st to 15thNight
2313324445%63%
2289
16th to endNight
1211213336%72%
1900
May1st to 15thNight
112222336%71%
1889
16th to endNight
22221333471%
1972
June1st to 15thNight
1111112245%75%
1890
16th to endNight
1111222380%
1827
July1st to 15thNight
2313435%6%6%7%56%
1755
16th to endNight
2225%6%47%7%9%11%41%
1845
August1st to 15thNight
21134235%6%9%57%
1728
16th to endNight
2233245%7%9%56%
1978
September1st to 15thNight
32124245%5%6%61%
2145
16th to endNight
11121122381%
2145
October1st to 15thNight
321313335%70%
2233
16th to endNight
221212246%71%
2496
November1st to 15thNight
1212213336%69%
2564
16th to endNight
1412322335%69%
2730
December1st to 15thNight
36%22323346%62%
2730
16th to endNight
5%7%24423446%54%
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
28%25%19%31%13%
1882
16th to endDay
26%38%18%29%13%
2016
February1st to 15thDay
28%27%21%23%16%
1942
16th to endDay
32%37%18%26%11%
1839
March1st to 15thDay
25%37%19%31%11%
2292
16th to endDay
23%37%23%29%12%
2464
April1st to 15thDay
26%26%20%29%13%
2317
16th to endDay
21%25%19%33%16%
2661
May1st to 15thDay
23%37%19%30%15%
2721
16th to endDay
23%35%15%35%17%
2848
June1st to 15thDay
13%239%29%41%
2730
16th to endDay
15%126%26%46%
2641
July1st to 15thDay
36%7%9%11%13%21%
2396
16th to endDay
46%10%14%13%11%3
2520
August1st to 15thDay
38%7%10%13%17%13%
2470
16th to endDay
38%6%8%16%21%8%
2572
September1st to 15thDay
31%6%10%14%18%18%
2145
16th to endDay
18%25%15%32%25%
2145
October1st to 15thDay
22%3415%27%26%
2055
16th to endDay
17%35%15%37%20%
2080
November1st to 15thDay
16%26%24%30%19%
1953
16th to endDay
20%15%19%33%19%
1890
December1st to 15thDay
26%310%23%23%13%
1890
16th to endDay
33%38%22%23%8%
2016
January1st to 15thNight
26%35%20%29%14%
2717
16th to endNight
27%26%19%27%16%
2912
February1st to 15thNight
23%37%21%26%17%
2579
16th to endNight
28%45%20%27%13%
2207
March1st to 15thNight
23%37%19%35%11%
2326
16th to endNight
21%37%24%31%12%
2464
April1st to 15thNight
22%36%19%32%14%
2289
16th to endNight
13%25%21%36%19%
1900
May1st to 15thNight
14%37%22%33%18%
1890
16th to endNight
17%15%16%39%19%
1973
June1st to 15thNight
12%139%30%42%
1890
16th to endNight
10%136%23%55%
1827
July1st to 15thNight
21%9%13%12%17%25%
1665
16th to endNight
32%10%18%18%14%5%
1737
August1st to 15thNight
20%6%13%19%23%16%
1719
16th to endNight
21%6%12%22%25%11%
1978
September1st to 15thNight
21%6%11%17%23%18%
2145
16th to endNight
10%2315%35%32%
2145
October1st to 15thNight
17%37%18%26%27%
2233
16th to endNight
14%35%14%35%26%
2496
November1st to 15thNight
16%25%21%32%20%
2564
16th to endNight
17%26%19%31%23%
2730
December1st to 15thNight
23%38%23%25%15%
2730
16th to endNight
30%48%21%25%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
16%15%28%21%13%5%
180
16th to endDay
5%18%27%24%20%4
192
February1st to 15thDay
10%24%27%21%10%6%
277
16th to endDay
11%33%26%20%6%1
342
March1st to 15thDay
12%24%32%20%8%1
390
16th to endDay
10%23%34%22%8%1
416
April1st to 15thDay
10%27%33%14%10%3
389
16th to endDay
10%29%31%18%7%2
378
May1st to 15thDay
12%21%32%20%10%2
408
16th to endDay
11%21%34%22%8%1
458
June1st to 15thDay
316%35%29%9%4
435
16th to endDay
7%433%34%17%3
408
July1st to 15thDay
8%421%39%19%5%
365
16th to endDay
12%10%39%27%8%
391
August1st to 15thDay
10%117%43%19%7%
359
16th to endDay
11%118%35%23%9%
396
September1st to 15thDay
8%6%26%36%14%7%
375
16th to endDay
7%12%26%29%17%6%
375
October1st to 15thDay
10%21%33%18%12%2
285
16th to endDay
8%8%27%26%20%8%
192
November1st to 15thDay
318%26%23%24%3
180
16th to endDay
9%15%23%25%18%7%
180
December1st to 15thDay
6%15%21%32%22%2
180
16th to endDay
14%15%18%34%15%2
192
January1st to 15thNight
8%10%23%29%18%10%
840
16th to endNight
10%12%20%29%21%6%
896
February1st to 15thNight
6%11%24%32%20%5%
824
16th to endNight
7%15%28%30%15%2
736
March1st to 15thNight
7%14%25%29%18%4
840
16th to endNight
411%26%31%21%4
896
April1st to 15thNight
5%18%28%27%17%2
820
16th to endNight
315%27%30%19%3
624
May1st to 15thNight
211%29%31%22%2
630
16th to endNight
410%30%29%22%3
659
June1st to 15thNight
2424%39%24%3
630
16th to endNight
2219%35%35%4
609
July1st to 15thNight
46%32%47%8%
555
16th to endNight
3224%56%13%
612
August1st to 15thNight
31325%53%13%
575
16th to endNight
31424%49%16%
682
September1st to 15thNight
48%25%47%13%
780
16th to endNight
26%14%26%38%10%
776
October1st to 15thNight
48%23%31%25%6%
780
16th to endNight
27%19%29%27%12%
832
November1st to 15thNight
29%24%33%23%6%
820
16th to endNight
6%8%20%32%23%8%
840
December1st to 15thNight
8%11%18%32%25%4
840
16th to endNight
10%9%21%33%19%4
896
Page generated at 2019-06-24 17:41:30. Version ac04

Copyright 2019 A. Danko


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