D. S. Millas Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the D. S. Millas Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
47%
15580
23%
47148
15%
15537
55%
15537
28%
29134

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
24%
720
23%
2327
9%
716
41%
716
20%
1458
January16th to endNight
24%
768
25%
2457
10%
768
41%
768
21%
1545
February1st to 15thNight
27%
704
25%
2112
9%
701
43%
701
26%
1290
February16th to endNight
23%
631
24%
1893
8%
631
38%
631
24%
1177
March1st to 15thNight
30%
720
23%
2061
11%
720
40%
720
27%
1301
March16th to endNight
38%
768
21%
2112
11%
768
46%
768
30%
1327
April1st to 15thNight
40%
641
25%
1899
16%
641
51%
641
33%
1100
April16th to endNight
48%
540
25%
1695
16%
540
58%
540
32%
977
May1st to 15thNight
50%
540
20%
1620
11%
540
57%
540
28%
1020
May16th to endNight
61%
561
21%
1683
13%
561
66%
561
31%
1042
June1st to 15thNight
70%
540
16%
1620
14%
540
71%
540
29%
1023
June16th to endNight
74%
540
17%
1620
15%
540
75%
540
33%
985
July1st to 15thNight
68%
510
13%
1530
12%
510
68%
510
28%
999
July16th to endNight
73%
564
16%
1595
13%
531
75%
531
27%
1041
August1st to 15thNight
68%
539
18%
1627
18%
536
68%
536
27%
1059
August16th to endNight
64%
573
18%
1910
20%
573
65%
573
22%
1277
September1st to 15thNight
61%
708
19%
1968
18%
708
62%
708
28%
1322
September16th to endNight
60%
717
25%
1980
19%
717
65%
717
31%
1254
October1st to 15thNight
55%
684
32%
1892
25%
684
62%
684
38%
1103
October16th to endNight
50%
704
33%
2112
24%
704
63%
704
38%
1169
November1st to 15thNight
49%
700
31%
2259
25%
700
60%
700
36%
1205
November16th to endNight
38%
720
27%
2340
17%
720
52%
720
28%
1346
December1st to 15thNight
32%
720
23%
2340
12%
720
46%
720
24%
1442
December16th to endNight
29%
768
21%
2496
13%
768
40%
768
18%
1672

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
14%5%244345%6%7%41%
48043
Night
12%42442445%7%45%
47346
TransparencyDay
39%6%12%19%17%4
47744
Night
36%6%11%20%19%6%
47149
SeeingDay
15%6%18%23%22%13%
5458
Night
15%8%23%27%21%4
15582

By Month

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
18%7%24424245%43%
1611
16th to endDay
19%6%2342335%6%43%
1764
February1st to 15thDay
17%5%2432435%6%43%
1750
16th to endDay
19%5%24333346%43%
1580
March1st to 15thDay
18%42442435%7%42%
1899
16th to endDay
17%41443445%6%42%
2111
April1st to 15thDay
13%5%25%42445%6%44%
2058
16th to endDay
12%42342445%7%48%
2263
May1st to 15thDay
12%4245%25%448%44%
2331
16th to endDay
11%5%15%5%35%5%6%9%40%
2431
June1st to 15thDay
8%5%245%47%7%8%10%34%
2340
16th to endDay
6%3235%46%6%8%11%42%
2340
July1st to 15thDay
11%5%25%6%47%8%8%11%28%
2340
16th to endDay
8%436%6%48%7%8%10%30%
2465
August1st to 15thDay
10%4246%46%7%8%11%30%
2319
16th to endDay
14%6%26%7%46%7%6%10%26%
2292
September1st to 15thDay
13%5%25%6%345%6%7%38%
1980
16th to endDay
16%415%423446%45%
1980
October1st to 15thDay
12%41242333457%
1865
16th to endDay
12%42421223459%
1760
November1st to 15thDay
13%423313345%54%
1596
16th to endDay
15%424323445%48%
1620
December1st to 15thDay
19%7%1432345%5%41%
1620
16th to endDay
26%6%34323335%36%
1728
January1st to 15thNight
19%5%24324345%44%
2327
16th to endNight
17%6%34424345%43%
2457
February1st to 15thNight
15%5%24424336%48%
2103
16th to endNight
17%42442345%5%45%
1893
March1st to 15thNight
14%5%23424446%46%
2061
16th to endNight
12%5%24423348%47%
2112
April1st to 15thNight
12%42332445%6%51%
1899
16th to endNight
10%33432446%7%50%
1695
May1st to 15thNight
9%425%5%35%6%6%7%44%
1619
16th to endNight
7%5%23425%5%5%8%47%
1682
June1st to 15thNight
6%425%435%7%7%11%40%
1620
16th to endNight
43145%36%6%8%11%43%
1620
July1st to 15thNight
6%425%7%36%6%7%11%37%
1620
16th to endNight
5%325%5%37%8%8%12%36%
1703
August1st to 15thNight
7%5%25%5%346%8%12%38%
1638
16th to endNight
11%5%35%6%35%5%6%10%35%
1910
September1st to 15thNight
10%5%25%5%35%5%5%8%40%
1968
16th to endNight
13%413425%5%5%7%46%
1980
October1st to 15thNight
11%41332335%6%55%
1892
16th to endNight
11%413323235%59%
2112
November1st to 15thNight
12%323322246%57%
2259
16th to endNight
16%413323345%51%
2340
December1st to 15thNight
15%6%25%423346%44%
2340
16th to endNight
22%7%25%433347%36%
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
43%39%15%23%4
1612
16th to endDay
41%37%19%21%6%
1764
February1st to 15thDay
40%48%20%22%3
1752
16th to endDay
42%47%20%19%6%
1580
March1st to 15thDay
41%49%19%19%5%
1899
16th to endDay
41%5%12%21%16%3
2112
April1st to 15thDay
37%5%10%21%20%4
2058
16th to endDay
33%6%9%23%21%5%
2263
May1st to 15thDay
37%5%14%19%19%3
2331
16th to endDay
37%9%13%23%14%2
2435
June1st to 15thDay
37%11%20%22%6%1
2340
16th to endDay
31%10%16%26%13%2
2340
July1st to 15thDay
41%11%19%18%6%1
2201
16th to endDay
41%13%17%17%8%1
2310
August1st to 15thDay
42%11%16%19%8%1
2306
16th to endDay
49%9%14%15%9%
2292
September1st to 15thDay
42%8%14%16%15%2
1980
16th to endDay
39%5%11%19%20%4
1980
October1st to 15thDay
30%49%18%28%8%
1865
16th to endDay
29%26%18%30%11%
1760
November1st to 15thDay
31%36%16%32%9%
1596
16th to endDay
37%47%16%27%7%
1620
December1st to 15thDay
43%5%9%18%15%7%
1620
16th to endDay
50%38%16%14%5%
1728
January1st to 15thNight
42%37%18%22%5%
2327
16th to endNight
42%35%19%22%6%
2457
February1st to 15thNight
37%37%20%21%8%
2112
16th to endNight
39%37%20%22%5%
1893
March1st to 15thNight
38%5%10%19%19%8%
2061
16th to endNight
35%6%10%24%19%4
2112
April1st to 15thNight
32%410%23%23%6%
1899
16th to endNight
31%6%10%22%20%8%
1695
May1st to 15thNight
36%8%13%20%18%2
1620
16th to endNight
33%9%13%26%14%3
1684
June1st to 15thNight
33%10%20%24%9%1
1620
16th to endNight
29%10%17%24%15%2
1620
July1st to 15thNight
36%10%21%22%7%1
1530
16th to endNight
35%12%20%20%9%2
1595
August1st to 15thNight
36%10%16%23%11%1
1627
16th to endNight
41%10%18%17%12%1
1910
September1st to 15thNight
39%7%13%18%16%3
1968
16th to endNight
35%7%12%20%18%5%
1980
October1st to 15thNight
30%411%16%29%7%
1892
16th to endNight
29%35%18%31%12%
2112
November1st to 15thNight
29%35%17%30%13%
2259
16th to endNight
34%36%18%26%9%
2340
December1st to 15thNight
40%39%19%18%7%
2340
16th to endNight
48%38%15%18%5%
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
21%18%34%20%5%
90
16th to endDay
17%29%38%11%3
96
February1st to 15thDay
16%28%34%20%
90
16th to endDay
25%16%39%14%3
81
March1st to 15thDay
20%15%31%24%6%1
189
16th to endDay
18%9%32%24%12%2
288
April1st to 15thDay
15%11%31%20%17%4
270
16th to endDay
13%7%24%28%22%4
270
May1st to 15thDay
13%9%27%21%15%12%
288
16th to endDay
14%414%26%23%16%
331
June1st to 15thDay
10%111%20%30%25%
315
16th to endDay
10%10%26%23%27%
315
July1st to 15thDay
10%17%23%32%24%
305
16th to endDay
10%6%17%36%28%
326
August1st to 15thDay
15%11%18%29%23%
313
16th to endDay
16%19%23%29%20%
332
September1st to 15thDay
13%312%24%28%18%
315
16th to endDay
16%210%27%30%12%
314
October1st to 15thDay
15%324%28%19%9%
278
16th to endDay
14%6%15%27%29%6%
272
November1st to 15thDay
24%13%21%21%16%3
104
16th to endDay
15%11%30%24%15%3
90
December1st to 15thDay
28%14%28%21%6%
90
16th to endDay
32%16%32%15%21
96
January1st to 15thNight
23%17%29%23%6%
720
16th to endNight
21%16%35%23%3
768
February1st to 15thNight
18%16%34%27%3
704
16th to endNight
18%18%36%22%3
631
March1st to 15thNight
16%12%36%27%5%
720
16th to endNight
15%11%28%30%13%
768
April1st to 15thNight
13%11%31%27%15%
641
16th to endNight
12%5%28%33%19%1
540
May1st to 15thNight
11%426%30%23%3
540
16th to endNight
12%116%28%34%7%
563
June1st to 15thNight
8%113%32%33%11%
540
16th to endNight
5%9%35%37%11%
540
July1st to 15thNight
9%7%23%47%11%
510
16th to endNight
7%7%24%47%13%
564
August1st to 15thNight
10%19%25%42%10%
539
16th to endNight
13%9%25%40%9%
573
September1st to 15thNight
13%19%27%37%9%
708
16th to endNight
15%114%35%29%3
717
October1st to 15thNight
14%421%29%25%4
684
16th to endNight
12%6%25%29%22%3
704
November1st to 15thNight
13%8%26%28%21%2
700
16th to endNight
17%13%27%25%14%
720
December1st to 15thNight
18%11%30%27%10%
720
16th to endNight
25%12%28%26%6%
768
Page generated at 2017-10-07 14:07:55. Version ac04

Copyright 2017 A. Danko


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