Dreamstead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dreamstead Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
50%
16087
24%
48484
16%
16045
58%
16045
30%
29466

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
29%
779
23%
2522
11%
776
44%
776
23%
1509
January16th to endNight
30%
788
26%
2509
14%
788
45%
788
25%
1554
February1st to 15thNight
31%
704
27%
2109
11%
701
47%
701
28%
1273
February16th to endNight
30%
631
26%
1893
12%
631
44%
631
27%
1153
March1st to 15thNight
35%
720
27%
2034
12%
720
48%
720
31%
1226
March16th to endNight
41%
768
23%
2112
11%
768
50%
768
32%
1274
April1st to 15thNight
44%
696
25%
1954
17%
696
51%
696
35%
1153
April16th to endNight
51%
540
30%
1695
20%
540
62%
540
38%
912
May1st to 15thNight
53%
539
24%
1620
15%
539
60%
539
35%
938
May16th to endNight
64%
561
21%
1682
15%
561
68%
561
35%
994
June1st to 15thNight
66%
540
16%
1620
13%
540
68%
540
29%
1037
June16th to endNight
72%
540
17%
1620
15%
540
73%
540
31%
1007
July1st to 15thNight
73%
510
11%
1530
9%
510
74%
510
26%
995
July16th to endNight
73%
564
14%
1595
14%
531
74%
531
27%
1071
August1st to 15thNight
72%
539
16%
1633
15%
536
73%
536
28%
1057
August16th to endNight
64%
591
17%
1928
19%
591
65%
591
21%
1300
September1st to 15thNight
66%
720
18%
1980
16%
720
67%
720
29%
1313
September16th to endNight
58%
717
22%
1980
17%
717
63%
717
29%
1298
October1st to 15thNight
55%
720
31%
1998
24%
720
62%
720
38%
1172
October16th to endNight
55%
768
36%
2304
28%
768
65%
768
39%
1239
November1st to 15thNight
55%
760
30%
2392
25%
760
64%
760
37%
1285
November16th to endNight
42%
780
28%
2535
20%
780
56%
780
30%
1428
December1st to 15thNight
38%
780
25%
2535
17%
780
51%
780
27%
1518
December16th to endNight
37%
832
23%
2704
16%
832
46%
832
21%
1760

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
11%5%25%5%35%5%5%8%42%
49030
Night
11%42442445%7%46%
48686
TransparencyDay
38%5%11%19%18%6%
48731
Night
36%5%11%19%20%8%
48489
SeeingDay
13%6%18%24%23%13%
5889
Night
12%7%21%30%22%4
16091

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
15%5%24424346%47%
1746
16th to endDay
14%5%25%43335%5%45%
1816
February1st to 15thDay
14%5%34424346%45%
1750
16th to endDay
14%5%2442325%7%46%
1580
March1st to 15thDay
14%425%423347%47%
1926
16th to endDay
14%4145%23446%47%
2111
April1st to 15thDay
10%425%32445%5%50%
2003
16th to endDay
8%314424448%53%
2264
May1st to 15thDay
9%325%425%45%8%48%
2331
16th to endDay
7%425%5%35%6%7%9%43%
2431
June1st to 15thDay
9%5%245%46%7%7%11%33%
2340
16th to endDay
5%325%6%46%6%6%11%40%
2340
July1st to 15thDay
7%5%36%7%5%8%8%7%10%29%
2340
16th to endDay
7%437%7%48%7%8%11%28%
2465
August1st to 15thDay
9%6%35%7%47%8%8%11%27%
2312
16th to endDay
12%6%36%6%46%7%6%8%29%
2260
September1st to 15thDay
12%425%6%25%6%8%9%37%
1980
16th to endDay
13%7%25%5%35%5%6%6%38%
1980
October1st to 15thDay
13%423323346%51%
1960
16th to endDay
10%31331234460%
1920
November1st to 15thDay
10%423323347%53%
1793
16th to endDay
12%425%423445%50%
1755
December1st to 15thDay
16%5%14324346%46%
1755
16th to endDay
20%8%35%5%23436%37%
1872
January1st to 15thNight
13%7%33423345%47%
2522
16th to endNight
17%5%25%32333447%
2509
February1st to 15thNight
15%425%323346%48%
2103
16th to endNight
13%5%234345%45%48%
1893
March1st to 15thNight
10%425%42435%6%50%
2034
16th to endNight
12%424323446%50%
2112
April1st to 15thNight
11%415%31345%7%50%
1954
16th to endNight
7%323425%45%7%54%
1695
May1st to 15thNight
6%424435%45%7%51%
1619
16th to endNight
5%425%5%25%7%6%9%45%
1682
June1st to 15thNight
8%426%5%45%6%7%12%36%
1620
16th to endNight
4426%6%46%6%7%11%40%
1620
July1st to 15thNight
6%3346%47%8%9%11%34%
1620
16th to endNight
6%425%6%47%8%8%13%32%
1703
August1st to 15thNight
7%3146%36%7%9%14%35%
1644
16th to endNight
11%5%26%6%45%7%7%12%31%
1928
September1st to 15thNight
10%5%25%6%36%5%7%9%38%
1980
16th to endNight
10%6%26%5%35%6%5%7%41%
1980
October1st to 15thNight
11%324323346%53%
1998
16th to endNight
9%413313445%58%
2304
November1st to 15thNight
10%423222346%56%
2392
16th to endNight
12%324423236%53%
2535
December1st to 15thNight
13%5%24423446%47%
2535
16th to endNight
18%6%25%43435%5%38%
2704

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%37%17%25%6%
1747
16th to endDay
40%25%17%23%10%
1816
February1st to 15thDay
40%25%18%23%8%
1752
16th to endDay
38%35%18%25%8%
1580
March1st to 15thDay
37%38%20%19%10%
1926
16th to endDay
38%311%17%23%6%
2112
April1st to 15thDay
35%39%20%21%9%
2003
16th to endDay
30%49%23%23%8%
2264
May1st to 15thDay
34%312%21%21%5%
2331
16th to endDay
35%5%14%26%15%2
2435
June1st to 15thDay
41%7%16%22%11%1
2340
16th to endDay
35%7%16%21%16%2
2340
July1st to 15thDay
42%9%20%17%5%2
2201
16th to endDay
43%10%18%19%6%1
2310
August1st to 15thDay
44%10%19%17%7%
2299
16th to endDay
48%8%15%15%10%1
2260
September1st to 15thDay
39%8%14%17%16%4
1980
16th to endDay
43%5%8%19%17%4
1980
October1st to 15thDay
33%39%21%23%9%
1960
16th to endDay
27%25%15%31%17%
1920
November1st to 15thDay
31%37%18%24%15%
1793
16th to endDay
36%37%15%25%12%
1755
December1st to 15thDay
39%311%17%19%9%
1755
16th to endDay
50%27%18%15%6%
1872
January1st to 15thNight
39%26%18%25%7%
2522
16th to endNight
41%2414%26%11%
2509
February1st to 15thNight
37%25%19%22%13%
2112
16th to endNight
37%35%18%22%12%
1893
March1st to 15thNight
34%38%20%22%10%
2034
16th to endNight
33%311%17%22%9%
2112
April1st to 15thNight
32%38%21%22%11%
1954
16th to endNight
28%310%23%22%11%
1695
May1st to 15thNight
31%5%13%20%23%7%
1620
16th to endNight
32%6%16%25%16%4
1684
June1st to 15thNight
38%7%18%24%11%
1620
16th to endNight
34%8%20%18%14%3
1620
July1st to 15thNight
36%11%24%20%6%1
1530
16th to endNight
37%10%21%19%8%1
1595
August1st to 15thNight
34%11%23%21%8%
1633
16th to endNight
42%9%18%16%11%1
1928
September1st to 15thNight
38%8%15%17%16%4
1980
16th to endNight
40%5%13%17%19%4
1980
October1st to 15thNight
31%38%21%22%11%
1998
16th to endNight
27%35%15%31%17%
2304
November1st to 15thNight
28%37%17%28%14%
2392
16th to endNight
34%26%16%24%14%
2535
December1st to 15thNight
37%39%18%22%8%
2535
16th to endNight
47%26%20%15%6%
2704

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
14%19%43%12%6%2
135
16th to endDay
13%27%36%11%10%
109
February1st to 15thDay
8%34%28%24%3
90
16th to endDay
17%8%54%17%2
81
March1st to 15thDay
13%14%31%25%12%1
216
16th to endDay
14%7%33%26%15%2
288
April1st to 15thDay
14%12%24%23%19%4
270
16th to endDay
10%5%23%30%23%7%
270
May1st to 15thDay
10%8%24%26%16%13%
288
16th to endDay
9%314%23%31%16%
331
June1st to 15thDay
13%17%26%24%26%
315
16th to endDay
7%19%26%26%28%
315
July1st to 15thDay
8%420%36%27%
305
16th to endDay
5%1322%36%30%
326
August1st to 15thDay
15%25%22%35%20%
313
16th to endDay
14%16%21%34%21%
332
September1st to 15thDay
15%211%22%30%17%
315
16th to endDay
17%210%30%26%13%
314
October1st to 15thDay
15%418%28%20%11%
315
16th to endDay
11%7%21%27%25%6%
336
November1st to 15thDay
17%6%24%28%20%2
211
16th to endDay
7%13%27%30%18%2
135
December1st to 15thDay
25%11%34%20%8%
135
16th to endDay
29%15%29%21%31
144
January1st to 15thNight
17%16%30%25%9%
780
16th to endNight
18%14%32%27%7%
788
February1st to 15thNight
17%13%31%29%7%
704
16th to endNight
15%13%35%30%4
631
March1st to 15thNight
12%14%33%30%9%
720
16th to endNight
14%12%27%29%15%
768
April1st to 15thNight
14%8%28%31%16%
696
16th to endNight
7%5%29%34%20%2
540
May1st to 15thNight
9%6%25%31%23%3
540
16th to endNight
7%116%37%30%6%
563
June1st to 15thNight
8%210%35%35%7%
540
16th to endNight
6%26%32%40%12%
540
July1st to 15thNight
8%15%29%39%16%
510
16th to endNight
8%1331%44%10%
564
August1st to 15thNight
9%1329%45%10%
539
16th to endNight
13%25%25%40%12%
591
September1st to 15thNight
12%17%27%40%10%
720
16th to endNight
14%210%35%32%4
717
October1st to 15thNight
13%321%32%23%5%
720
16th to endNight
10%7%21%31%26%2
768
November1st to 15thNight
11%6%20%36%22%2
760
16th to endNight
13%11%26%28%18%1
780
December1st to 15thNight
14%10%29%27%15%2
780
16th to endNight
21%10%24%33%9%
832
Page generated at 2018-01-21 12:19:28. Version ac04

Copyright 2018 A. Danko


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