The Rose Dorothea Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Rose Dorothea Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
35%
14951
16%
46811
10%
14915
43%
14915
20%
32044

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
17%
720
14%
2506
5%
716
29%
716
12%
1812
January16th to endNight
13%
768
14%
2658
4%
768
26%
768
9%
1970
February1st to 15thNight
16%
704
12%
2192
3%
701
27%
701
12%
1634
February16th to endNight
20%
631
20%
1893
7%
631
36%
631
18%
1313
March1st to 15thNight
25%
720
14%
2123
8%
720
33%
720
18%
1517
March16th to endNight
27%
768
21%
2082
10%
768
37%
768
21%
1449
April1st to 15thNight
32%
718
18%
1796
6%
718
39%
718
25%
1285
April16th to endNight
39%
558
19%
1638
9%
558
44%
558
22%
1110
May1st to 15thNight
36%
540
15%
1620
8%
540
42%
540
21%
1142
May16th to endNight
44%
486
11%
1608
9%
485
48%
485
20%
1112
June1st to 15thNight
45%
360
11%
1440
15%
360
48%
360
15%
981
June16th to endNight
56%
360
12%
1440
17%
360
59%
360
23%
860
July1st to 15thNight
59%
340
12%
1360
17%
340
60%
340
22%
808
July16th to endNight
58%
403
15%
1443
19%
379
61%
379
22%
909
August1st to 15thNight
64%
539
16%
1608
13%
535
66%
535
29%
1006
August16th to endNight
65%
675
22%
1821
14%
675
67%
675
37%
1132
September1st to 15thNight
59%
720
20%
1896
14%
720
62%
720
35%
1208
September16th to endNight
56%
669
26%
1847
19%
669
61%
669
34%
1141
October1st to 15thNight
41%
660
21%
1850
13%
660
49%
660
25%
1241
October16th to endNight
30%
704
15%
2258
8%
704
40%
704
20%
1520
November1st to 15thNight
35%
700
15%
2277
11%
700
42%
700
18%
1568
November16th to endNight
29%
720
17%
2340
9%
720
39%
720
17%
1569
December1st to 15thNight
20%
720
14%
2427
5%
720
31%
720
13%
1754
December16th to endNight
14%
768
14%
2688
4%
768
26%
768
10%
2003

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
16%7%25%42445%7%39%
47980
Night
17%8%36%5%2445%6%34%
46985
Cloud CoverDay
17%7%35%424447%39%
47990
Night
17%8%36%5%2445%6%34%
46990
TransparencyDay
44%412%23%14%1
47672
Night
49%410%21%12%1
46811
SeeingDay
21%5%22%30%16%3
6020
Night
22%8%24%29%13%1
14951

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
17%10%47%42345%6%33%
1432
16th to endDay
18%10%46%6%3445%5%29%
1563
February1st to 15thDay
19%8%46%6%36%45%6%27%
1669
16th to endDay
14%8%37%5%3445%7%33%
1580
March1st to 15thDay
20%8%35%5%3345%7%30%
1826
16th to endDay
17%8%45%423345%40%
2139
April1st to 15thDay
18%7%24324346%42%
2152
16th to endDay
17%5%15%324447%44%
2320
May1st to 15thDay
23%8%35%324347%34%
2332
16th to endDay
15%6%25%424348%41%
2516
June1st to 15thDay
23%6%2431445%8%34%
2520
16th to endDay
13%5%24425%45%9%43%
2520
July1st to 15thDay
12%5%2442445%9%44%
2520
16th to endDay
12%414435%46%8%44%
2613
August1st to 15thDay
10%5%24435%45%8%45%
2340
16th to endDay
10%41432345%9%50%
2378
September1st to 15thDay
13%5%13324446%49%
2064
16th to endDay
13%5%23323347%48%
1838
October1st to 15thDay
19%6%24424336%43%
1779
16th to endDay
16%6%25%5%1336%7%41%
1612
November1st to 15thDay
24%7%33313346%37%
1581
16th to endDay
17%8%35%415%45%8%34%
1620
December1st to 15thDay
17%11%5%7%43345%7%28%
1530
16th to endDay
24%12%46%5%23245%26%
1536
January1st to 15thNight
18%10%5%9%5%34445%29%
2506
16th to endNight
20%11%37%7%3445%6%25%
2658
February1st to 15thNight
17%11%48%7%34446%26%
2191
16th to endNight
17%10%45%5%33446%34%
1893
March1st to 15thNight
19%9%35%6%2445%7%31%
2110
16th to endNight
17%8%35%42434438%
2082
April1st to 15thNight
18%9%35%42435%6%35%
1796
16th to endNight
19%7%345%34446%36%
1638
May1st to 15thNight
21%8%36%4235%46%32%
1620
16th to endNight
19%8%25%4345%5%8%31%
1606
June1st to 15thNight
23%6%34425%45%7%31%
1440
16th to endNight
16%6%24335%45%9%40%
1440
July1st to 15thNight
12%5%25%5%345%7%8%39%
1440
16th to endNight
13%5%25%6%35%5%6%9%35%
1541
August1st to 15thNight
7%5%25%5%36%6%8%8%40%
1620
16th to endNight
10%5%2442346%8%47%
1821
September1st to 15thNight
12%5%244345%46%47%
1896
16th to endNight
12%5%25%32345%6%49%
1847
October1st to 15thNight
20%6%23423445%40%
1850
16th to endNight
20%7%25%5%23446%36%
2258
November1st to 15thNight
20%7%35%5%25%445%35%
2277
16th to endNight
18%7%36%424348%34%
2340
December1st to 15thNight
20%9%5%7%43335%7%28%
2427
16th to endNight
21%12%47%5%2445%6%25%
2688

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%10%37%5%23447%32%
1432
16th to endDay
18%11%5%6%6%4335%6%28%
1563
February1st to 15thDay
19%8%5%7%7%36%35%7%26%
1669
16th to endDay
15%9%5%7%6%34347%33%
1580
March1st to 15thDay
21%7%26%5%335%5%6%30%
1836
16th to endDay
17%8%45%423345%39%
2139
April1st to 15thDay
18%7%24314346%42%
2152
16th to endDay
17%6%14323447%44%
2320
May1st to 15thDay
23%7%34423446%35%
2332
16th to endDay
15%6%24424348%41%
2516
June1st to 15thDay
23%6%243145%48%34%
2520
16th to endDay
13%5%244245%5%9%43%
2520
July1st to 15thDay
12%5%1442445%9%44%
2520
16th to endDay
12%4245%35%46%8%43%
2613
August1st to 15thDay
10%5%2443446%8%45%
2340
16th to endDay
10%5%1341345%8%49%
2378
September1st to 15thDay
13%413324346%49%
2064
16th to endDay
14%6%23423447%47%
1838
October1st to 15thDay
19%5%34324337%42%
1779
16th to endDay
16%6%35%42335%7%41%
1612
November1st to 15thDay
23%8%24323337%36%
1581
16th to endDay
18%7%36%4245%5%7%33%
1620
December1st to 15thDay
18%10%5%8%6%2336%7%27%
1530
16th to endDay
24%13%39%423335%25%
1536
January1st to 15thNight
19%10%5%9%5%33346%28%
2506
16th to endNight
19%12%48%7%3445%5%24%
2658
February1st to 15thNight
17%11%49%7%35%346%26%
2184
16th to endNight
16%10%46%6%32446%33%
1893
March1st to 15thNight
19%9%46%6%345%46%30%
2123
16th to endNight
17%9%36%424336%37%
2081
April1st to 15thNight
18%9%345%2435%5%35%
1796
16th to endNight
19%7%25%43445%5%36%
1638
May1st to 15thNight
21%8%36%4235%5%6%32%
1620
16th to endNight
19%8%25%335%46%7%31%
1606
June1st to 15thNight
23%7%35%425%45%6%31%
1440
16th to endNight
15%6%3432445%9%39%
1440
July1st to 15thNight
12%6%25%5%25%5%7%8%37%
1440
16th to endNight
13%5%35%6%35%5%7%8%35%
1541
August1st to 15thNight
8%5%245%36%6%7%8%41%
1620
16th to endNight
10%6%2342446%8%46%
1821
September1st to 15thNight
12%424434347%47%
1896
16th to endNight
11%6%2442345%5%48%
1847
October1st to 15thNight
19%7%24424345%40%
1850
16th to endNight
20%7%25%5%2345%5%36%
2258
November1st to 15thNight
20%7%25%6%33445%35%
2277
16th to endNight
18%7%36%5%3345%7%34%
2340
December1st to 15thNight
21%10%5%7%5%2335%6%27%
2427
16th to endNight
21%13%47%42445%6%24%
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
51%411%20%9%2
1433
16th to endDay
55%49%21%8%
1563
February1st to 15thDay
57%411%17%8%
1672
16th to endDay
50%312%20%11%1
1580
March1st to 15thDay
52%412%19%8%1
1836
16th to endDay
46%310%22%14%2
2139
April1st to 15thDay
42%39%22%18%2
2152
16th to endDay
39%410%25%17%2
2320
May1st to 15thDay
50%38%18%16%2
2332
16th to endDay
41%415%24%12%1
2520
June1st to 15thDay
47%413%21%11%
2520
16th to endDay
37%6%15%23%15%1
2520
July1st to 15thDay
35%6%14%26%15%1
2371
16th to endDay
35%6%16%25%12%2
2449
August1st to 15thDay
36%416%26%14%1
2327
16th to endDay
31%313%29%19%1
2378
September1st to 15thDay
34%411%24%23%1
2064
16th to endDay
35%48%28%20%2
1838
October1st to 15thDay
42%310%24%16%2
1779
16th to endDay
41%412%25%13%1
1612
November1st to 15thDay
49%311%21%12%1
1581
16th to endDay
47%6%12%22%10%
1620
December1st to 15thDay
55%314%15%10%
1530
16th to endDay
61%312%15%6%
1536
January1st to 15thNight
57%311%17%9%
2506
16th to endNight
59%48%18%8%
2658
February1st to 15thNight
59%310%18%7%
2192
16th to endNight
50%311%21%11%1
1893
March1st to 15thNight
53%311%18%11%1
2123
16th to endNight
49%28%18%17%3
2082
April1st to 15thNight
48%38%20%16%2
1796
16th to endNight
48%27%21%16%3
1638
May1st to 15thNight
51%39%17%14%2
1620
16th to endNight
50%414%18%9%2
1608
June1st to 15thNight
52%5%11%18%11%1
1440
16th to endNight
40%5%13%23%16%1
1440
July1st to 15thNight
40%5%13%26%13%
1360
16th to endNight
42%5%12%27%8%2
1443
August1st to 15thNight
37%6%14%25%15%1
1608
16th to endNight
34%414%27%18%1
1821
September1st to 15thNight
36%411%27%18%1
1896
16th to endNight
35%5%6%26%25%1
1847
October1st to 15thNight
45%39%23%15%2
1850
16th to endNight
48%312%21%13%
2258
November1st to 15thNight
50%410%19%12%2
2277
16th to endNight
49%212%22%10%2
2340
December1st to 15thNight
56%311%19%7%
2427
16th to endNight
59%5%10%16%8%
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
23%15%31%26%3
60
16th to endDay
29%13%30%26%
91
February1st to 15thDay
28%14%31%22%3
253
16th to endDay
13%15%37%27%4
239
March1st to 15thDay
25%12%34%22%4
270
16th to endDay
22%12%31%22%9%
288
April1st to 15thDay
23%7%30%30%7%
270
16th to endDay
24%425%31%11%3
270
May1st to 15thDay
31%225%25%10%5%
288
16th to endDay
18%218%36%22%1
331
June1st to 15thDay
24%218%32%20%2
315
16th to endDay
15%217%43%17%2
315
July1st to 15thDay
18%19%39%27%4
305
16th to endDay
13%19%39%30%6%
326
August1st to 15thDay
15%8%38%29%6%
313
16th to endDay
12%19%32%33%9%
332
September1st to 15thDay
17%117%31%25%6%
315
16th to endDay
20%115%26%23%12%
262
October1st to 15thDay
25%220%27%19%5%
248
16th to endDay
20%6%33%29%10%
240
November1st to 15thDay
27%5%22%29%11%3
235
16th to endDay
22%12%25%27%10%1
240
December1st to 15thDay
22%14%31%21%10%
150
16th to endDay
31%12%40%12%3
64
January1st to 15thNight
25%16%33%20%4
720
16th to endNight
27%19%30%17%3
768
February1st to 15thNight
24%15%34%22%2
704
16th to endNight
21%14%38%20%5%
631
March1st to 15thNight
24%11%32%24%6%
720
16th to endNight
22%12%28%26%10%1
768
April1st to 15thNight
23%5%31%32%6%
718
16th to endNight
23%5%23%32%13%1
558
May1st to 15thNight
26%124%31%13%3
540
16th to endNight
24%318%36%15%1
486
June1st to 15thNight
27%413%37%15%2
360
16th to endNight
18%211%43%21%1
360
July1st to 15thNight
14%210%45%25%1
340
16th to endNight
16%110%39%30%1
403
August1st to 15thNight
10%111%44%28%2
539
16th to endNight
13%19%37%31%5%
675
September1st to 15thNight
15%215%39%23%3
720
16th to endNight
15%214%32%27%7%
669
October1st to 15thNight
23%421%30%16%3
660
16th to endNight
24%9%28%25%10%
704
November1st to 15thNight
26%8%24%26%12%2
700
16th to endNight
22%15%25%25%10%1
720
December1st to 15thNight
25%14%31%22%5%
720
16th to endNight
30%14%34%17%2
768
Page generated at 2017-09-19 07:32:30. Version ac04

Copyright 2017 A. Danko


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