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Discovery Channel Telescope
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Discovery Channel Telescope clear sky chart from 2005-11-05 to 2017-03-26.

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
49%
15018
33%
45265
19%
14973
64%
14973
41%
22716

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
38%
720
30%
2327
17%
716
56%
716
32%
1202
January16th to endNight
35%
768
34%
2496
17%
768
57%
768
30%
1325
February1st to 15thNight
41%
704
31%
2226
18%
700
61%
700
38%
1093
February16th to endNight
33%
632
35%
1877
18%
632
55%
632
32%
995
March1st to 15thNight
39%
720
36%
1980
17%
720
57%
720
41%
1023
March16th to endNight
43%
748
35%
2057
15%
748
60%
748
46%
1039
April1st to 15thNight
32%
623
29%
1777
10%
623
49%
623
34%
927
April16th to endNight
40%
495
39%
1558
17%
495
62%
495
47%
666
May1st to 15thNight
44%
495
37%
1484
19%
494
60%
494
49%
670
May16th to endNight
45%
513
32%
1540
17%
513
58%
513
52%
674
June1st to 15thNight
47%
495
34%
1485
20%
495
58%
495
61%
635
June16th to endNight
66%
495
31%
1485
24%
495
71%
495
63%
635
July1st to 15thNight
72%
465
20%
1395
15%
465
75%
465
39%
779
July16th to endNight
72%
522
19%
1467
15%
489
74%
489
34%
862
August1st to 15thNight
74%
494
26%
1476
22%
491
75%
491
38%
812
August16th to endNight
79%
541
28%
1667
25%
541
81%
541
41%
896
September1st to 15thNight
73%
660
31%
1815
23%
660
78%
660
45%
1014
September16th to endNight
67%
656
41%
1815
26%
656
77%
656
60%
843
October1st to 15thNight
52%
660
38%
1911
22%
660
67%
660
50%
906
October16th to endNight
56%
704
40%
2112
24%
704
70%
704
50%
970
November1st to 15thNight
47%
700
36%
2139
19%
700
65%
700
45%
1014
November16th to endNight
43%
720
38%
2340
22%
720
63%
720
40%
1086
December1st to 15thNight
43%
720
32%
2340
19%
720
61%
720
32%
1227
December16th to endNight
33%
768
30%
2496
17%
768
50%
768
26%
1423

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
4423323446%58%
45707
Night
3413323346%63%
45461
TransparencyDay
26%36%18%29%16%
45402
Night
21%36%20%29%18%
45267
SeeingDay
12%19%30%26%9%2
4703
Night
6%14%24%28%20%4
15020

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
47%13313236%62%
1611
16th to endDay
6%8%13213336%57%
1728
February1st to 15thDay
29%34213347%57%
1634
16th to endDay
38%24423347%55%
1597
March1st to 15thDay
36%1231345%6%60%
1980
16th to endDay
45%12323337%62%
2053
April1st to 15thDay
3224323446%61%
1838
16th to endDay
341321234467%
2071
May1st to 15thDay
3312212346%65%
2136
16th to endDay
4312323345%65%
2221
June1st to 15thDay
11121223477%
2145
16th to endDay
111222334473%
2145
July1st to 15thDay
7%3246%46%6%8%7%43%
2145
16th to endDay
10%5%26%6%47%8%7%8%31%
2285
August1st to 15thDay
8%5%25%7%45%6%6%7%39%
2145
16th to endDay
6%5%25%5%45%5%6%8%42%
2179
September1st to 15thDay
7%5%25%6%45%5%46%46%
1815
16th to endDay
4212213335%69%
1815
October1st to 15thDay
3213313335%68%
1719
16th to endDay
3312212336%70%
1760
November1st to 15thDay
221231344467%
1717
16th to endDay
341221323468%
1620
December1st to 15thDay
5%8%23312347%56%
1620
16th to endDay
5%10%46%422345%50%
1728
January1st to 15thNight
36%14313445%60%
2327
16th to endNight
6%7%2432333458%
2496
February1st to 15thNight
26%23213345%64%
2215
16th to endNight
37%13313446%58%
1877
March1st to 15thNight
35%23212346%64%
1980
16th to endNight
321221335%6%67%
2057
April1st to 15thNight
242432335%6%61%
1777
16th to endNight
11121224474%
1558
May1st to 15thNight
2211213236%71%
1484
16th to endNight
21221333474%
1540
June1st to 15thNight
211111123477%
1485
16th to endNight
11221222378%
1485
July1st to 15thNight
3213445%5%8%9%49%
1485
16th to endNight
43246%46%7%9%10%39%
1575
August1st to 15thNight
42145%25%5%6%9%52%
1485
16th to endNight
2223435%5%7%10%51%
1667
September1st to 15thNight
3224425%36%6%58%
1815
16th to endNight
31111233475%
1815
October1st to 15thNight
3112213345%70%
1911
16th to endNight
221321224472%
2112
November1st to 15thNight
3212213345%67%
2139
16th to endNight
35%12222235%68%
2340
December1st to 15thNight
46%14223346%58%
2340
16th to endNight
6%8%36%424345%52%
2496

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
25%35%21%33%11%
1612
16th to endDay
27%26%19%32%11%
1728
February1st to 15thDay
27%26%24%21%17%
1634
16th to endDay
29%3422%28%11%
1597
March1st to 15thDay
23%3319%36%13%
1980
16th to endDay
23%2425%32%12%
2053
April1st to 15thDay
23%2322%34%13%
1838
16th to endDay
20%2418%38%15%
2071
May1st to 15thDay
19%2421%34%17%
2136
16th to endDay
21%2415%39%15%
2224
June1st to 15thDay
12%1210%32%39%
2145
16th to endDay
14%218%31%40%
2145
July1st to 15thDay
36%6%10%15%13%17%
2006
16th to endDay
44%7%17%16%12%1
2130
August1st to 15thDay
41%5%9%16%17%10%
2130
16th to endDay
37%5%13%17%19%6%
2179
September1st to 15thDay
37%48%15%19%14%
1815
16th to endDay
18%2116%37%22%
1815
October1st to 15thDay
20%3417%32%22%
1719
16th to endDay
17%2416%42%17%
1760
November1st to 15thDay
19%3423%31%17%
1717
16th to endDay
19%2419%33%20%
1620
December1st to 15thDay
27%38%25%24%10%
1620
16th to endDay
36%27%22%24%7%
1728
January1st to 15thNight
25%3421%31%12%
2327
16th to endNight
29%2418%31%13%
2496
February1st to 15thNight
22%27%22%23%20%
2226
16th to endNight
25%3424%28%14%
1877
March1st to 15thNight
21%2321%38%13%
1980
16th to endNight
18%26%25%33%13%
2057
April1st to 15thNight
24%25%20%33%14%
1777
16th to endNight
14%1323%37%18%
1558
May1st to 15thNight
15%25%25%30%20%
1485
16th to endNight
14%1418%42%18%
1541
June1st to 15thNight
12%119%31%44%
1485
16th to endNight
12%216%25%51%
1485
July1st to 15thNight
26%6%13%15%18%18%
1395
16th to endNight
31%7%20%23%13%3
1467
August1st to 15thNight
26%6%13%20%20%12%
1476
16th to endNight
24%6%16%22%21%8%
1667
September1st to 15thNight
24%5%12%20%21%15%
1815
16th to endNight
11%3318%37%25%
1815
October1st to 15thNight
15%3422%26%26%
1911
16th to endNight
16%25%13%37%24%
2112
November1st to 15thNight
19%25%23%32%16%
2139
16th to endNight
20%2317%32%23%
2340
December1st to 15thNight
27%46%21%26%13%
2340
16th to endNight
33%37%21%24%8%
2496

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%30%30%12%41
90
16th to endDay
16%28%25%19%8%2
96
February1st to 15thDay
10%29%34%12%12%2
149
16th to endDay
23%31%26%15%2
238
March1st to 15thDay
15%27%29%19%5%2
270
16th to endDay
15%23%33%19%43
267
April1st to 15thDay
20%30%32%10%5%1
209
16th to endDay
15%34%31%12%4
210
May1st to 15thDay
13%25%39%19%2
228
16th to endDay
9%24%33%23%7%1
266
June1st to 15thDay
5%23%43%20%7%
255
16th to endDay
18%37%42%8%1
255
July1st to 15thDay
8%8%35%38%9%
245
16th to endDay
12%421%41%16%4
271
August1st to 15thDay
10%320%46%15%3
255
16th to endDay
8%420%41%20%4
268
September1st to 15thDay
10%12%25%38%11%1
255
16th to endDay
10%10%29%34%10%3
255
October1st to 15thDay
6%26%31%23%8%3
159
16th to endDay
10%18%25%31%13%1
96
November1st to 15thDay
13%11%30%26%13%5%
90
16th to endDay
16%27%30%17%7%
90
December1st to 15thDay
8%21%35%18%13%2
90
16th to endDay
22%20%30%18%6%1
96
January1st to 15thNight
9%21%26%25%13%4
720
16th to endNight
10%21%27%25%13%2
768
February1st to 15thNight
7%18%28%30%12%2
704
16th to endNight
9%25%28%24%9%2
632
March1st to 15thNight
9%20%27%25%13%2
720
16th to endNight
6%18%30%28%14%2
748
April1st to 15thNight
8%25%27%25%10%1
623
16th to endNight
5%20%31%26%11%4
495
May1st to 15thNight
417%31%32%13%
495
16th to endNight
5%15%30%26%19%3
515
June1st to 15thNight
39%37%31%15%1
495
16th to endNight
1423%41%25%3
495
July1st to 15thNight
414%38%37%4
465
16th to endNight
427%31%43%10%
522
August1st to 15thNight
5%26%28%43%12%
494
16th to endNight
226%31%43%14%
541
September1st to 15thNight
3211%29%44%7%
660
16th to endNight
48%17%25%34%9%
656
October1st to 15thNight
414%25%31%19%4
660
16th to endNight
313%23%30%21%7%
704
November1st to 15thNight
5%15%28%28%16%6%
700
16th to endNight
9%18%25%24%16%5%
720
December1st to 15thNight
10%16%24%30%16%1
720
16th to endNight
11%20%28%25%10%2
768
Page generated at 2017-03-27 08:15:17. Version ac04

Copyright 2017 A. Danko


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