Dreamy Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dreamy Skies Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
28%
15634
13%
46876
7%
15592
34%
15592
17%
33746

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
12%
900
6%
2506
2%
895
16%
895
7%
2119
January16th to endNight
15%
957
8%
2685
2%
957
20%
957
9%
2224
February1st to 15thNight
12%
701
9%
2271
3%
701
18%
701
8%
1787
February16th to endNight
19%
631
10%
1893
4%
631
25%
631
10%
1503
March1st to 15thNight
21%
720
15%
2101
6%
720
28%
720
17%
1500
March16th to endNight
27%
768
18%
2112
9%
768
34%
768
22%
1434
April1st to 15thNight
22%
548
14%
1769
7%
548
31%
548
16%
1237
April16th to endNight
32%
540
17%
1620
8%
540
39%
540
21%
1113
May1st to 15thNight
32%
540
13%
1620
7%
540
38%
540
22%
1113
May16th to endNight
36%
529
15%
1529
7%
528
46%
528
28%
975
June1st to 15thNight
39%
360
13%
1260
10%
360
46%
360
23%
779
June16th to endNight
46%
360
14%
1260
10%
360
52%
360
25%
774
July1st to 15thNight
56%
480
14%
1330
10%
480
60%
480
39%
779
July16th to endNight
53%
564
15%
1417
10%
531
55%
531
35%
891
August1st to 15thNight
55%
539
18%
1607
13%
536
62%
536
34%
935
August16th to endNight
53%
573
20%
1737
14%
573
58%
573
33%
1019
September1st to 15thNight
49%
639
19%
1899
14%
639
54%
639
31%
1152
September16th to endNight
45%
677
18%
1870
12%
677
49%
677
29%
1234
October1st to 15thNight
33%
660
17%
1892
10%
660
41%
660
22%
1307
October16th to endNight
20%
704
11%
2252
6%
704
27%
704
13%
1690
November1st to 15thNight
25%
700
15%
2276
11%
700
31%
700
15%
1627
November16th to endNight
17%
720
9%
2462
4%
720
24%
720
9%
1923
December1st to 15thNight
11%
864
5%
2664
1%
864
15%
864
8%
2216
December16th to endNight
11%
960
6%
2844
1%
960
15%
960
6%
2415

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%10%47%6%35%45%7%30%
47963
Night
14%10%47%6%3445%6%32%
47045
Cloud CoverDay
14%10%47%6%35%45%7%30%
47972
Night
14%10%47%6%35%45%6%32%
47050
TransparencyDay
52%6%12%18%9%1
47651
Night
51%6%13%18%9%
46876
SeeingDay
18%14%32%21%8%4
5954
Night
19%13%32%24%8%1
15638

By Month

Percentage Cloud Cover NE (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
16%16%6%12%7%45%45%5%15%
1432
16th to endDay
12%15%9%14%11%5%6%43413%
1539
February1st to 15thDay
12%16%6%12%11%35%5%3417%
1591
16th to endDay
11%17%6%11%10%445%4419%
1580
March1st to 15thDay
14%10%49%7%35%45%6%28%
1848
16th to endDay
15%11%47%5%3445%5%30%
2112
April1st to 15thDay
18%14%46%423445%31%
2187
16th to endDay
16%10%25%424446%36%
2340
May1st to 15thDay
18%7%36%5%345%5%7%32%
2331
16th to endDay
12%5%36%5%35%45%6%41%
2582
June1st to 15thDay
13%6%36%5%35%5%5%8%35%
2700
16th to endDay
13%6%35%6%35%5%6%8%35%
2700
July1st to 15thDay
10%5%25%6%36%5%6%8%39%
2546
16th to endDay
10%5%36%5%35%5%6%8%37%
2655
August1st to 15thDay
9%5%26%6%45%6%6%9%36%
2340
16th to endDay
13%6%36%5%3446%8%37%
2465
September1st to 15thDay
13%7%35%5%3435%7%40%
2049
16th to endDay
13%8%35%5%35%35%9%37%
1859
October1st to 15thDay
20%9%37%423346%32%
1738
16th to endDay
21%16%47%7%45%44419%
1617
November1st to 15thDay
14%13%47%5%4436%7%27%
1582
16th to endDay
18%17%6%10%8%35%43417%
1497
December1st to 15thDay
16%18%6%12%8%34346%16%
1296
16th to endDay
19%19%9%13%7%34335%9%
1377
January1st to 15thNight
18%14%5%11%8%46%44416%
2506
16th to endNight
12%12%7%11%10%46%5%5%6%16%
2685
February1st to 15thNight
11%14%6%11%8%5%5%45%5%20%
2269
16th to endNight
12%16%5%11%7%5%45%4422%
1893
March1st to 15thNight
13%10%5%7%5%34445%34%
2088
16th to endNight
14%9%36%333447%39%
2112
April1st to 15thNight
20%10%35%5%235%5%6%31%
1769
16th to endNight
15%9%25%5%2345%5%39%
1620
May1st to 15thNight
13%7%35%6%35%5%5%8%34%
1620
16th to endNight
12%5%245%2346%9%41%
1527
June1st to 15thNight
13%5%344245%7%6%42%
1260
16th to endNight
8%425%5%45%5%6%7%44%
1260
July1st to 15thNight
5%32442446%9%50%
1410
16th to endNight
6%424425%47%8%49%
1513
August1st to 15thNight
6%3244345%6%8%51%
1617
16th to endNight
10%4245%23348%50%
1737
September1st to 15thNight
12%5%34333347%49%
1899
16th to endNight
14%5%235%3445%7%43%
1870
October1st to 15thNight
17%8%26%5%23436%39%
1892
16th to endNight
21%12%36%6%34345%28%
2252
November1st to 15thNight
13%11%47%6%35%5%5%8%29%
2276
16th to endNight
17%16%5%7%5%44446%22%
2462
December1st to 15thNight
17%13%6%10%8%45%45%6%16%
2664
16th to endNight
19%16%8%11%7%35%44414%
2844

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
16%15%7%11%7%45%45%5%15%
1432
16th to endDay
12%14%9%13%11%5%5%43413%
1539
February1st to 15thDay
12%16%6%12%11%35%5%3417%
1591
16th to endDay
11%17%5%11%10%35%5%4419%
1580
March1st to 15thDay
14%10%5%9%7%3445%7%27%
1858
16th to endDay
15%12%47%5%3445%6%30%
2111
April1st to 15thDay
18%14%46%413345%31%
2187
16th to endDay
16%10%25%42345%6%36%
2340
May1st to 15thDay
17%7%37%5%345%5%7%32%
2331
16th to endDay
12%5%35%6%35%45%7%40%
2582
June1st to 15thDay
13%6%26%5%35%5%5%8%36%
2700
16th to endDay
12%6%35%6%35%6%6%8%35%
2700
July1st to 15thDay
10%5%25%6%45%6%6%8%38%
2546
16th to endDay
9%5%36%5%36%5%6%9%37%
2655
August1st to 15thDay
9%5%26%6%46%5%7%9%35%
2340
16th to endDay
13%6%36%5%4445%8%37%
2465
September1st to 15thDay
13%7%35%5%3435%7%40%
2049
16th to endDay
13%8%35%5%35%35%9%36%
1859
October1st to 15thDay
19%10%36%5%34346%32%
1738
16th to endDay
21%15%48%7%445%3419%
1617
November1st to 15thDay
14%12%5%8%5%3436%7%27%
1582
16th to endDay
18%17%5%10%8%35%44418%
1497
December1st to 15thDay
16%18%6%12%8%33446%16%
1296
16th to endDay
20%18%9%12%8%35%33410%
1377
January1st to 15thNight
18%14%5%11%8%46%44417%
2506
16th to endNight
13%12%7%11%10%46%6%5%6%16%
2685
February1st to 15thNight
11%14%7%10%9%45%45%5%20%
2262
16th to endNight
12%15%5%11%8%45%5%45%21%
1893
March1st to 15thNight
13%10%5%6%6%34445%34%
2101
16th to endNight
14%9%36%32435%6%39%
2112
April1st to 15thNight
19%9%35%5%235%5%7%31%
1769
16th to endNight
15%9%25%5%24446%38%
1620
May1st to 15thNight
13%7%35%6%35%5%5%7%35%
1619
16th to endNight
12%6%245%2436%9%41%
1527
June1st to 15thNight
13%5%24425%47%6%42%
1260
16th to endNight
7%5%15%5%35%5%6%7%44%
1260
July1st to 15thNight
5%32443446%9%50%
1410
16th to endNight
5%5%25%4245%6%9%49%
1513
August1st to 15thNight
6%3244345%5%7%52%
1617
16th to endNight
10%424433447%50%
1737
September1st to 15thNight
11%5%34424347%48%
1899
16th to endNight
14%6%2443445%7%43%
1870
October1st to 15thNight
16%8%26%5%23436%39%
1892
16th to endNight
20%11%46%6%24346%28%
2252
November1st to 15thNight
13%11%37%5%35%5%5%7%29%
2276
16th to endNight
17%15%5%8%5%35%446%21%
2462
December1st to 15thNight
17%14%5%10%7%46%5%5%6%16%
2664
16th to endNight
18%16%8%10%8%45%44414%
2844

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
69%6%10%10%3
1433
16th to endDay
75%5%7%8%2
1539
February1st to 15thDay
68%7%9%10%3
1593
16th to endDay
66%6%10%11%5%
1580
March1st to 15thDay
55%6%12%17%6%
1858
16th to endDay
53%6%11%17%8%1
2112
April1st to 15thDay
55%410%18%10%
2187
16th to endDay
47%5%15%14%15%2
2340
May1st to 15thDay
49%6%11%19%10%2
2331
16th to endDay
41%7%12%23%13%1
2586
June1st to 15thDay
44%7%13%21%12%1
2700
16th to endDay
43%9%14%20%11%1
2700
July1st to 15thDay
39%7%12%23%14%1
2397
16th to endDay
41%7%14%20%13%1
2488
August1st to 15thDay
40%8%13%22%12%1
2327
16th to endDay
43%7%12%22%12%1
2465
September1st to 15thDay
42%7%12%24%12%1
2049
16th to endDay
43%5%17%23%9%
1859
October1st to 15thDay
52%6%9%22%9%
1738
16th to endDay
65%7%12%10%3
1617
November1st to 15thDay
55%6%13%17%7%
1582
16th to endDay
70%411%9%2
1497
December1st to 15thDay
69%6%11%9%2
1296
16th to endDay
75%6%8%7%1
1377
January1st to 15thNight
69%6%8%10%4
2506
16th to endNight
65%8%12%10%2
2685
February1st to 15thNight
62%7%11%14%4
2271
16th to endNight
63%6%12%13%4
1893
March1st to 15thNight
50%5%12%20%9%
2101
16th to endNight
44%414%22%12%1
2112
April1st to 15thNight
51%5%10%19%11%1
1769
16th to endNight
46%6%10%19%14%2
1620
May1st to 15thNight
45%6%13%20%11%2
1620
16th to endNight
37%6%14%24%13%3
1529
June1st to 15thNight
38%7%13%22%16%
1260
16th to endNight
37%7%13%25%14%1
1260
July1st to 15thNight
29%6%15%29%19%1
1330
16th to endNight
31%8%16%27%14%
1417
August1st to 15thNight
28%8%17%29%14%
1607
16th to endNight
31%6%17%28%14%1
1737
September1st to 15thNight
34%6%13%30%14%1
1899
16th to endNight
39%7%15%29%8%
1870
October1st to 15thNight
46%5%11%24%11%
1892
16th to endNight
56%7%13%17%5%
2252
November1st to 15thNight
51%7%15%17%7%
2276
16th to endNight
62%6%14%11%3
2462
December1st to 15thNight
66%7%12%9%2
2664
16th to endNight
71%6%11%7%3
2844

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
23%17%50%6%2
90
16th to endDay
31%14%38%14%1
96
February1st to 15thDay
30%24%38%6%
90
16th to endDay
24%27%38%7%2
81
March1st to 15thDay
31%17%32%15%3
148
16th to endDay
27%11%31%20%7%1
288
April1st to 15thDay
26%15%30%17%9%
270
16th to endDay
24%15%33%13%9%3
270
May1st to 15thDay
22%18%30%16%8%3
288
16th to endDay
15%17%35%23%6%2
451
June1st to 15thDay
17%15%35%22%6%1
495
16th to endDay
14%14%37%23%7%3
495
July1st to 15thDay
10%12%33%28%10%4
475
16th to endDay
10%11%36%27%9%5%
515
August1st to 15thDay
9%6%30%28%13%12%
313
16th to endDay
18%8%25%22%17%8%
332
September1st to 15thDay
13%7%24%26%17%10%
315
16th to endDay
15%9%24%29%13%7%
270
October1st to 15thDay
25%14%30%17%9%1
255
16th to endDay
31%23%32%10%1
129
November1st to 15thDay
14%18%40%20%5%1
90
16th to endDay
28%23%36%5%41
69
December1st to 15thDay
33%31%28%311
60
16th to endDay
40%36%23%
69
January1st to 15thNight
25%21%32%17%3
900
16th to endNight
20%15%38%20%4
957
February1st to 15thNight
20%21%37%17%2
704
16th to endNight
25%17%30%22%4
631
March1st to 15thNight
20%18%33%20%5%
720
16th to endNight
22%13%33%24%5%1
768
April1st to 15thNight
23%15%34%20%4
548
16th to endNight
20%12%32%25%7%1
540
May1st to 15thNight
15%11%36%26%8%1
540
16th to endNight
16%9%31%30%11%
530
June1st to 15thNight
15%8%32%33%9%
360
16th to endNight
8%6%33%35%15%1
360
July1st to 15thNight
6%5%27%42%15%2
480
16th to endNight
8%230%37%18%1
564
August1st to 15thNight
7%226%37%23%2
539
16th to endNight
12%324%36%20%1
573
September1st to 15thNight
14%6%25%29%19%5%
639
16th to endNight
18%6%25%27%17%4
677
October1st to 15thNight
20%11%30%27%9%
660
16th to endNight
28%15%31%20%3
704
November1st to 15thNight
20%17%33%18%8%1
700
16th to endNight
25%17%34%18%3
720
December1st to 15thNight
25%19%37%14%2
864
16th to endNight
28%18%34%15%3
960
Page generated at 2017-09-21 07:18:22. Version ac04

Copyright 2017 A. Danko


Dreamy Skies Observatory Clear Sky Chart | Charts Home