This page made possible by the sponsorship of: Dean Salman.

Deep Sky Remote Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Sky Remote Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
59%
15724
27%
46901
21%
15683
65%
15683
38%
26125

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
60%
716
29%
2327
28%
716
65%
716
40%
1193
January16th to endNight
53%
768
31%
2496
27%
768
61%
768
35%
1361
February1st to 15thNight
51%
703
25%
2288
20%
700
60%
700
35%
1235
February16th to endNight
46%
632
30%
1905
21%
632
56%
632
33%
1103
March1st to 15thNight
51%
720
30%
1980
19%
720
61%
720
40%
1132
March16th to endNight
51%
768
25%
2112
17%
768
57%
768
34%
1280
April1st to 15thNight
45%
563
23%
1822
15%
563
56%
563
29%
1047
April16th to endNight
45%
540
29%
1800
19%
540
59%
540
34%
950
May1st to 15thNight
53%
540
25%
1624
18%
539
60%
539
37%
890
May16th to endNight
54%
562
25%
1634
17%
561
60%
561
35%
925
June1st to 15thNight
67%
540
31%
1440
23%
540
72%
540
57%
722
June16th to endNight
76%
540
32%
1440
26%
540
80%
540
62%
710
July1st to 15thNight
70%
510
15%
1530
13%
510
72%
510
28%
943
July16th to endNight
74%
564
17%
1593
16%
531
75%
531
26%
1053
August1st to 15thNight
76%
539
19%
1611
19%
536
76%
536
32%
979
August16th to endNight
76%
573
26%
1876
26%
573
77%
573
35%
1044
September1st to 15thNight
70%
525
25%
1750
25%
525
74%
525
31%
1013
September16th to endNight
71%
648
36%
1834
27%
648
77%
648
53%
923
October1st to 15thNight
60%
660
32%
1980
22%
660
67%
660
46%
1032
October16th to endNight
64%
704
37%
2112
26%
704
73%
704
49%
1040
November1st to 15thNight
64%
700
34%
2100
26%
700
70%
700
45%
1069
November16th to endNight
56%
891
33%
2481
23%
891
64%
891
46%
1293
December1st to 15thNight
51%
900
22%
2520
16%
900
56%
900
35%
1501
December16th to endNight
46%
918
22%
2646
16%
918
51%
918
27%
1687

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
5%5%2442445%6%53%
47715
Night
5%5%23323346%57%
47096
TransparencyDay
29%6%10%19%23%11%
47410
Night
27%5%9%20%23%12%
46902
SeeingDay
10%12%27%32%14%3
5500
Night
8%6%20%34%25%4
15730

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
8%7%2221333459%
1611
16th to endDay
7%11%24322235%53%
1728
February1st to 15thDay
411%34423346%50%
1575
16th to endDay
7%11%245%33335%47%
1566
March1st to 15thDay
6%7%2432345%6%52%
1980
16th to endDay
5%6%35%4245%5%7%50%
2112
April1st to 15thDay
6%7%245%25%346%49%
2126
16th to endDay
5%5%1443445%7%53%
2160
May1st to 15thDay
5%5%25%335%5%5%7%49%
2325
16th to endDay
43134245%5%7%57%
2477
June1st to 15thDay
4313323236%65%
2520
16th to endDay
11221345%6%70%
2515
July1st to 15thDay
32145%46%6%9%9%45%
2340
16th to endDay
6%426%6%47%7%9%9%35%
2467
August1st to 15thDay
6%426%6%37%7%5%7%41%
2340
16th to endDay
33246%37%7%7%9%44%
2324
September1st to 15thDay
7%3146%35%5%6%6%48%
2097
16th to endDay
4213323335%64%
1794
October1st to 15thDay
9%213323346%58%
1650
16th to endDay
5%312312335%67%
1760
November1st to 15thDay
5%313313337%64%
1754
16th to endDay
46%1221233467%
1467
December1st to 15thDay
9%9%23423345%51%
1440
16th to endDay
9%11%45%323445%45%
1587
January1st to 15thNight
7%6%2321223463%
2327
16th to endNight
9%7%2331233459%
2496
February1st to 15thNight
48%34322345%58%
2277
16th to endNight
7%8%24413335%54%
1905
March1st to 15thNight
6%6%1332335%6%56%
1980
16th to endNight
6%7%2442345%6%52%
2112
April1st to 15thNight
9%5%23325%35%6%50%
1822
16th to endNight
6%423324335%58%
1800
May1st to 15thNight
5%42432345%7%55%
1624
16th to endNight
7%423413336%58%
1633
June1st to 15thNight
3112212336%70%
1440
16th to endNight
11123135%5%6%68%
1440
July1st to 15thNight
2225%7%47%7%8%8%43%
1620
16th to endNight
3325%7%37%7%9%11%35%
1701
August1st to 15thNight
33245%36%6%7%9%48%
1620
16th to endNight
3424435%6%7%10%48%
1876
September1st to 15thNight
4315%6%5%6%5%6%8%47%
1750
16th to endNight
432312325%70%
1834
October1st to 15thNight
5%312323346%62%
1980
16th to endNight
421331223469%
2112
November1st to 15thNight
5%413213346%63%
2100
16th to endNight
6%5%22212235%66%
2481
December1st to 15thNight
8%8%24312236%55%
2520
16th to endNight
9%12%34313345%48%
2646

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
29%415%32%17%1
1612
16th to endDay
34%411%24%21%4
1728
February1st to 15thDay
35%414%22%16%5%
1575
16th to endDay
39%38%20%26%2
1566
March1st to 15thDay
31%48%27%22%4
1980
16th to endDay
32%5%9%22%25%5%
2112
April1st to 15thDay
35%47%18%23%9%
2126
16th to endDay
28%5%8%22%25%8%
2160
May1st to 15thDay
30%6%10%19%26%7%
2325
16th to endDay
24%6%9%16%29%12%
2480
June1st to 15thDay
20%35%12%27%30%
2520
16th to endDay
12%36%12%25%39%
2515
July1st to 15thDay
29%9%14%12%14%19%
2201
16th to endDay
36%13%16%16%10%7%
2312
August1st to 15thDay
37%9%12%13%14%12%
2325
16th to endDay
31%8%13%18%19%9%
2324
September1st to 15thDay
33%8%10%14%19%14%
2097
16th to endDay
22%47%15%32%17%
1794
October1st to 15thDay
26%38%21%29%10%
1650
16th to endDay
20%5%6%21%37%8%
1760
November1st to 15thDay
21%39%23%33%8%
1754
16th to endDay
22%38%30%25%8%
1467
December1st to 15thDay
35%5%14%27%16%1
1440
16th to endDay
41%6%16%21%12%1
1587
January1st to 15thNight
26%311%31%23%3
2327
16th to endNight
31%37%28%23%5%
2496
February1st to 15thNight
29%313%24%20%7%
2288
16th to endNight
32%49%19%30%4
1905
March1st to 15thNight
29%36%29%24%5%
1980
16th to endNight
32%5%8%20%26%7%
2112
April1st to 15thNight
33%48%18%23%11%
1822
16th to endNight
28%36%21%28%12%
1800
May1st to 15thNight
27%5%10%18%29%9%
1625
16th to endNight
27%6%8%17%25%14%
1634
June1st to 15thNight
16%36%10%27%34%
1440
16th to endNight
13%47%11%21%41%
1440
July1st to 15thNight
31%12%11%12%10%20%
1530
16th to endNight
36%12%16%15%10%9%
1593
August1st to 15thNight
29%11%13%14%15%15%
1611
16th to endNight
27%7%13%18%20%11%
1876
September1st to 15thNight
32%7%11%14%17%17%
1750
16th to endNight
19%36%16%29%24%
1834
October1st to 15thNight
22%48%20%27%17%
1980
16th to endNight
18%45%19%39%11%
2112
November1st to 15thNight
23%38%21%31%12%
2100
16th to endNight
22%37%26%28%11%
2481
December1st to 15thNight
31%5%12%25%20%3
2520
16th to endNight
39%5%13%23%15%2
2646

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
41%8%21%20%7%1
90
16th to endDay
18%6%28%29%14%3
96
February1st to 15thDay
14%14%21%33%16%
90
16th to endDay
16%21%34%16%11%
123
March1st to 15thDay
13%22%30%25%7%
270
16th to endDay
11%30%35%15%6%
288
April1st to 15thDay
12%27%30%20%42
269
16th to endDay
18%26%34%15%3
270
May1st to 15thDay
13%18%38%22%6%1
288
16th to endDay
8%17%30%26%12%3
378
June1st to 15thDay
6%9%24%35%21%2
495
16th to endDay
2322%42%21%7%
490
July1st to 15thDay
5%218%47%21%3
305
16th to endDay
7%116%42%25%6%
327
August1st to 15thDay
8%217%47%20%3
315
16th to endDay
5%228%39%20%3
332
September1st to 15thDay
6%433%40%12%2
294
16th to endDay
8%7%29%32%15%6%
228
October1st to 15thDay
314%22%31%22%6%
90
16th to endDay
13%11%34%25%12%3
96
November1st to 15thDay
11%7%20%34%24%2
90
16th to endDay
24%16%31%22%5%
90
December1st to 15thDay
17%13%30%32%6%
90
16th to endDay
26%12%20%27%12%1
96
January1st to 15thNight
10%5%19%37%21%5%
720
16th to endNight
13%5%22%32%19%5%
768
February1st to 15thNight
9%6%27%36%16%2
704
16th to endNight
13%9%27%36%12%1
632
March1st to 15thNight
9%8%26%34%19%2
720
16th to endNight
10%10%23%34%20%1
768
April1st to 15thNight
12%13%24%34%12%1
563
16th to endNight
10%12%27%31%15%1
540
May1st to 15thNight
7%7%26%37%18%3
540
16th to endNight
9%9%22%29%23%4
563
June1st to 15thNight
45%20%35%32%2
540
16th to endNight
1116%37%36%5%
540
July1st to 15thNight
3111%34%42%6%
510
16th to endNight
46%34%44%9%
564
August1st to 15thNight
5%7%28%47%10%
539
16th to endNight
49%32%44%9%
573
September1st to 15thNight
5%113%38%35%6%
525
16th to endNight
6%215%28%35%10%
648
October1st to 15thNight
6%6%22%37%21%4
660
16th to endNight
5%5%19%34%28%6%
704
November1st to 15thNight
7%419%36%26%5%
700
16th to endNight
9%9%21%32%20%5%
891
December1st to 15thNight
13%7%23%36%16%2
900
16th to endNight
16%9%20%33%17%2
918
Page generated at 2017-09-11 17:35:20. Version ac04

Copyright 2017 A. Danko


Deep Sky Remote Observatory Clear Sky Chart | Charts Home