Lake Dillon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Dillon Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
43%
15917
22%
46825
13%
15871
51%
15871
31%
27853

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
30%
897
20%
2503
10%
892
39%
892
23%
1621
January16th to endNight
30%
768
24%
2496
15%
768
43%
768
24%
1552
February1st to 15thNight
26%
701
15%
2278
7%
698
37%
698
20%
1497
February16th to endNight
24%
632
22%
1894
7%
632
39%
632
23%
1224
March1st to 15thNight
33%
720
22%
2073
9%
720
44%
720
30%
1228
March16th to endNight
32%
706
21%
2050
10%
706
42%
706
28%
1257
April1st to 15thNight
32%
539
19%
1798
10%
539
44%
539
26%
1044
April16th to endNight
34%
540
20%
1800
13%
540
45%
540
26%
1074
May1st to 15thNight
38%
540
17%
1608
9%
540
47%
540
28%
1008
May16th to endNight
47%
563
18%
1498
11%
561
54%
561
34%
883
June1st to 15thNight
55%
540
24%
1440
14%
540
62%
540
51%
737
June16th to endNight
68%
540
27%
1440
21%
540
73%
540
57%
720
July1st to 15thNight
74%
510
16%
1360
14%
510
76%
510
35%
837
July16th to endNight
74%
564
17%
1493
16%
531
76%
531
35%
881
August1st to 15thNight
69%
539
16%
1637
15%
536
71%
536
33%
950
August16th to endNight
72%
573
25%
1910
25%
573
75%
573
35%
1049
September1st to 15thNight
70%
530
28%
1766
26%
530
76%
530
37%
949
September16th to endNight
65%
522
30%
1776
25%
522
74%
522
42%
886
October1st to 15thNight
45%
660
26%
1980
16%
660
54%
660
37%
1093
October16th to endNight
47%
704
30%
2112
16%
704
57%
704
38%
1146
November1st to 15thNight
39%
869
28%
2269
12%
869
48%
869
38%
1314
November16th to endNight
37%
900
28%
2436
13%
900
46%
900
36%
1394
December1st to 15thNight
22%
900
16%
2520
5%
900
32%
900
24%
1639
December16th to endNight
26%
960
18%
2688
8%
960
35%
960
20%
1870

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
47%5%10%7%3445%6%40%
47844
Night
1438%7%3445%7%48%
47004
TransparencyDay
42%5%11%21%14%3
47525
Night
30%7%15%26%16%3
46825
SeeingDay
14%19%27%21%12%3
5806
Night
6%14%28%31%16%2
15920

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
35%15%9%37%35%7%39%
1447
16th to endDay
5%6%13%8%23346%44%
1728
February1st to 15thDay
5%7%18%9%44346%35%
1583
16th to endDay
37%16%10%5%4346%38%
1580
March1st to 15thDay
7%411%9%44346%43%
1887
16th to endDay
19%7%11%7%35%347%37%
2173
April1st to 15thDay
210%8%12%5%2445%6%37%
2150
16th to endDay
215%8%13%8%34346%29%
2160
May1st to 15thDay
5%14%6%10%7%35%5%45%30%
2338
16th to endDay
6%11%49%7%35%5%5%6%32%
2616
June1st to 15thDay
6%6%35%5%25%5%5%8%45%
2520
16th to endDay
33245%345%5%7%53%
2520
July1st to 15thDay
8%7%36%8%45%5%5%6%37%
2520
16th to endDay
9%7%47%8%47%6%6%7%31%
2570
August1st to 15thDay
12%7%48%7%36%45%7%31%
2313
16th to endDay
7%7%38%7%45%5%6%6%35%
2292
September1st to 15thDay
9%6%36%6%33335%47%
2113
16th to endDay
5%8%36%5%24436%50%
1849
October1st to 15thDay
48%5%7%5%24336%47%
1650
16th to endDay
38%48%423346%50%
1755
November1st to 15thDay
5%48%6%2335%7%51%
1583
16th to endDay
5%39%7%22245%55%
1521
December1st to 15thDay
5%5%14%10%6%4348%36%
1440
16th to endDay
5%6%14%12%5%5%35%6%34%
1536
January1st to 15thNight
2311%11%47%45%7%41%
2503
16th to endNight
4411%10%5%4335%46%
2496
February1st to 15thNight
3313%13%5%6%446%38%
2267
16th to endNight
25%13%11%45%447%40%
1894
March1st to 15thNight
338%7%4435%7%50%
2073
16th to endNight
16%6%8%6%23346%49%
2050
April1st to 15thNight
6%48%6%35%5%6%7%46%
1798
16th to endNight
110%48%6%2335%6%45%
1800
May1st to 15thNight
38%37%5%245%6%9%42%
1607
16th to endNight
36%245%25%5%6%9%48%
1497
June1st to 15thNight
221321435%9%62%
1440
16th to endNight
121322335%9%64%
1440
July1st to 15thNight
3333435%6%7%11%46%
1440
16th to endNight
42245%25%5%9%11%45%
1596
August1st to 15thNight
4425%4345%5%10%48%
1646
16th to endNight
5%4145%246%6%9%49%
1910
September1st to 15thNight
441442445%8%54%
1766
16th to endNight
23135%3345%6%60%
1776
October1st to 15thNight
26%25%41435%8%54%
1980
16th to endNight
17%27%323345%58%
2112
November1st to 15thNight
437%5%23445%58%
2269
16th to endNight
349%5%23338%54%
2436
December1st to 15thNight
4410%10%46%45%6%42%
2520
16th to endNight
35%11%12%6%5%449%36%
2688

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
38%9%19%20%9%2
1448
16th to endDay
38%6%15%23%12%3
1728
February1st to 15thDay
46%7%14%19%9%2
1583
16th to endDay
44%5%10%23%13%2
1580
March1st to 15thDay
40%412%26%14%1
1887
16th to endDay
44%6%10%25%10%2
2173
April1st to 15thDay
45%413%20%12%3
2150
16th to endDay
53%49%22%8%1
2160
May1st to 15thDay
52%5%10%21%9%
2338
16th to endDay
47%6%12%20%10%1
2620
June1st to 15thDay
34%412%20%20%7%
2520
16th to endDay
28%37%24%26%9%
2520
July1st to 15thDay
45%5%11%14%16%7%
2371
16th to endDay
48%7%15%15%9%3
2410
August1st to 15thDay
51%6%10%13%13%4
2298
16th to endDay
46%410%20%14%3
2292
September1st to 15thDay
39%38%18%21%8%
2113
16th to endDay
34%310%26%22%2
1849
October1st to 15thDay
36%5%8%25%21%3
1650
16th to endDay
33%310%29%19%3
1755
November1st to 15thDay
28%7%12%22%23%5%
1583
16th to endDay
29%413%31%15%5%
1521
December1st to 15thDay
42%7%14%24%9%
1440
16th to endDay
47%10%9%18%11%3
1536
January1st to 15thNight
30%14%17%22%12%2
2503
16th to endNight
34%10%12%23%14%4
2496
February1st to 15thNight
39%10%14%24%10%1
2278
16th to endNight
37%8%10%24%16%3
1894
March1st to 15thNight
29%7%14%31%13%2
2073
16th to endNight
34%6%15%31%10%2
2050
April1st to 15thNight
32%7%14%27%15%3
1798
16th to endNight
36%5%16%29%12%
1800
May1st to 15thNight
35%6%17%27%11%
1608
16th to endNight
29%5%19%29%12%2
1498
June1st to 15thNight
17%5%17%28%23%7%
1440
16th to endNight
16%413%26%26%12%
1440
July1st to 15thNight
28%10%17%18%16%7%
1360
16th to endNight
27%10%23%22%11%4
1493
August1st to 15thNight
31%7%20%20%15%5%
1637
16th to endNight
29%6%18%25%17%2
1910
September1st to 15thNight
27%6%14%21%22%7%
1766
16th to endNight
22%5%13%34%21%2
1776
October1st to 15thNight
25%6%13%29%20%4
1980
16th to endNight
25%5%13%31%21%2
2112
November1st to 15thNight
25%6%12%27%23%5%
2269
16th to endNight
27%412%31%19%4
2436
December1st to 15thNight
34%10%17%22%12%1
2520
16th to endNight
39%13%12%20%11%2
2688

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
17%16%24%23%11%6%
90
16th to endDay
7%32%32%25%21
96
February1st to 15thDay
24%25%27%20%2
90
16th to endDay
19%22%25%27%31
81
March1st to 15thDay
20%28%29%15%5%
177
16th to endDay
16%39%30%11%1
288
April1st to 15thDay
19%33%31%10%22
269
16th to endDay
24%37%26%7%3
270
May1st to 15thDay
17%21%31%20%8%1
378
16th to endDay
15%18%27%22%12%3
517
June1st to 15thDay
9%17%26%22%20%4
495
16th to endDay
6%12%28%26%20%5%
495
July1st to 15thDay
12%8%20%29%22%7%
475
16th to endDay
12%6%24%22%24%9%
429
August1st to 15thDay
19%12%25%29%10%4
315
16th to endDay
13%7%32%30%11%4
332
September1st to 15thDay
15%18%33%22%7%3
300
16th to endDay
10%10%38%18%14%7%
157
October1st to 15thDay
326%17%30%17%4
90
16th to endDay
17%17%26%23%11%3
96
November1st to 15thDay
7%22%20%24%20%5%
90
16th to endDay
22%23%35%17%1
90
December1st to 15thDay
16%36%30%12%4
90
16th to endDay
441%31%16%42
96
January1st to 15thNight
12%21%29%22%10%2
897
16th to endNight
7%19%35%28%8%1
768
February1st to 15thNight
7%20%40%24%7%
704
16th to endNight
8%21%37%27%4
632
March1st to 15thNight
5%18%35%28%10%
720
16th to endNight
6%19%38%28%6%
706
April1st to 15thNight
8%18%36%29%6%
539
16th to endNight
8%18%33%31%7%1
540
May1st to 15thNight
8%9%35%33%11%
540
16th to endNight
6%10%26%34%19%2
563
June1st to 15thNight
47%28%37%20%1
540
16th to endNight
2319%43%30%1
540
July1st to 15thNight
417%40%41%2
510
16th to endNight
5%1435%47%5%
564
August1st to 15thNight
6%18%42%38%2
539
16th to endNight
6%110%36%38%6%
573
September1st to 15thNight
5%212%50%25%5%
530
16th to endNight
35%19%37%28%5%
522
October1st to 15thNight
6%13%30%29%15%4
660
16th to endNight
6%13%27%33%14%3
704
November1st to 15thNight
7%18%30%31%11%1
869
16th to endNight
6%21%31%29%9%1
900
December1st to 15thNight
8%23%40%21%5%
900
16th to endNight
9%24%31%25%8%
960
Page generated at 2017-09-13 05:39:23. Version ac04

Copyright 2017 A. Danko


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