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 2017-08-12.

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
50%
15443
33%
46532
19%
15398
64%
15398
41%
23316

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
42%
768
35%
2112
15%
768
60%
768
45%
1072
April1st to 15thNight
33%
680
29%
1939
10%
680
50%
680
36%
995
April16th to endNight
40%
540
41%
1699
18%
540
63%
540
47%
716
May1st to 15thNight
44%
540
35%
1619
18%
539
59%
539
49%
732
May16th to endNight
45%
561
35%
1684
19%
561
59%
561
52%
732
June1st to 15thNight
48%
540
32%
1620
19%
540
59%
540
61%
692
June16th to endNight
66%
540
33%
1620
26%
540
71%
540
63%
690
July1st to 15thNight
72%
510
19%
1530
15%
510
75%
510
39%
850
July16th to endNight
72%
564
17%
1593
14%
531
73%
531
33%
947
August1st to 15thNight
74%
527
25%
1575
21%
524
75%
524
37%
873
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
4413323446%59%
47437
Night
3413323346%63%
46728
TransparencyDay
25%36%18%29%16%
47132
Night
21%36%19%29%18%
46534
SeeingDay
12%18%29%26%9%2
5249
Night
6%14%24%28%21%4
15445

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%
2112
April1st to 15thDay
3214323446%61%
2006
16th to endDay
3413212345%67%
2259
May1st to 15thDay
3312212346%65%
2331
16th to endDay
431232334466%
2429
June1st to 15thDay
11111223478%
2340
16th to endDay
111222334473%
2340
July1st to 15thDay
7%3246%46%5%8%7%44%
2340
16th to endDay
10%5%26%7%47%7%7%9%30%
2467
August1st to 15thDay
8%5%25%7%45%6%6%7%39%
2290
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%66%
2112
April1st to 15thNight
242432335%5%62%
1939
16th to endNight
11121224475%
1699
May1st to 15thNight
2111313236%71%
1619
16th to endNight
21121233475%
1684
June1st to 15thNight
21111123477%
1620
16th to endNight
11221222378%
1620
July1st to 15thNight
3313445%5%8%9%49%
1620
16th to endNight
5%325%6%46%7%9%10%39%
1701
August1st to 15thNight
32146%25%5%5%8%51%
1584
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%31%12%
2112
April1st to 15thDay
23%2322%34%12%
2006
16th to endDay
19%2419%39%15%
2259
May1st to 15thDay
18%2421%35%17%
2331
16th to endDay
20%2415%40%16%
2432
June1st to 15thDay
11%1211%33%39%
2340
16th to endDay
15%228%29%42%
2340
July1st to 15thDay
34%6%10%15%13%18%
2201
16th to endDay
45%8%18%15%11%1
2312
August1st to 15thDay
41%5%9%15%17%10%
2275
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
19%26%25%33%12%
2112
April1st to 15thNight
22%25%20%34%14%
1939
16th to endNight
13%2423%37%19%
1699
May1st to 15thNight
15%25%25%31%20%
1620
16th to endNight
13%1417%43%18%
1685
June1st to 15thNight
12%119%32%42%
1620
16th to endNight
12%216%24%52%
1620
July1st to 15thNight
26%6%14%15%17%19%
1530
16th to endNight
32%7%22%22%12%3
1593
August1st to 15thNight
27%6%13%20%20%12%
1575
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
16%23%33%18%43
288
April1st to 15thDay
17%28%33%11%6%2
269
16th to endDay
17%32%31%11%5%
270
May1st to 15thDay
12%27%36%18%31
288
16th to endDay
10%25%32%24%6%
330
June1st to 15thDay
421%42%20%8%1
315
16th to endDay
17%37%40%10%2
315
July1st to 15thDay
7%7%31%37%13%1
305
16th to endDay
12%319%40%17%6%
327
August1st to 15thDay
9%318%47%17%4
300
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%17%29%28%14%2
768
April1st to 15thNight
8%23%29%25%11%1
680
16th to endNight
5%22%30%25%12%3
540
May1st to 15thNight
416%32%32%14%
540
16th to endNight
5%15%28%26%19%3
563
June1st to 15thNight
39%36%31%17%1
540
16th to endNight
2422%41%26%3
540
July1st to 15thNight
313%40%36%4
510
16th to endNight
427%30%43%10%
564
August1st to 15thNight
5%16%28%45%12%
527
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 2017-08-13 11:16:18. Version ac04

Copyright 2017 A. Danko


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